Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session R1: Poster Session III: 1:00 pm - 4:00 pm
Sponsoring Units: APSRoom: Morial Convention Center Exhibit Hall A
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R1.00001: POLYMERIC AND ORGANIC MATERIALS II |
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R1.00002: Ultrafast dephasing processes in $\beta $-carotene homologues Masazumi Fujiwara, Kensei Yamauchi, Mitsuru Sugisaki, Hideki Hashimoto, Richard Cogdell Carotenoid is an important pigment in a bacterial light-harvesting system together with bacteriochlorophyll (BChl). In the photosynthetic system, these two kinds of pigments cooperate to efficiently capture the solar energy and to transfer that energy to the reaction center within a few picoseconds. In this study, transient grating signals in $\beta$-carotene homologues using sub-20 fs excitation pulses were measured in order to investigate the dependence of the coherence dynamics on the $\pi$-conjugation length of these carotenoids. The $\pi$-conjugation length is a decisive factor in determining the efficiency of energy transfer to BChls. Therefore, it is important to study how the conjugation length affects the coherence dynamics. The results show that the population-induced dephasing is a major factor in the total dephasing process in the longer-chain carotenoids. On the other hand, pure dephasing time, which indicates the strength of the system-bath interactions, does not depend on the conjugation length. It is also concluded that the central C=C stretching mode is the major channel for energy dissipation to the environment regardless of the conjugation length. [Preview Abstract] |
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R1.00003: Characterization of Bioderived Polyhydroxyalkanoates by Size Exclusion Chromatography Ioan Negulescu, Rafael Cueto, Kelly Rusch, Teresa Gutierrez-Wing, Benjamin Stevens The plant derived polyesters, better known as polyhydroxyalkanoates, PHAs, are renewable and sustainable: [-O-CH(CH3)-(CH2)x-CO-]n. If x = 0 PHA is Poly(lactic acid), PLA; if x = 1 or 2 it is Poly(hydroxy butyrate), PHB, or Poly(hydroxy valerate), PHV. SEC and light scattering have been used before for determination of the absolute molecular mass of PLA dissolved in CHCl3 (Malmgren et al., J. Thermal Anal. Calorim., 2006, 83, 35-40). To our best knowledge there is no publication on the determination of the absolute MW of other PHAs. The bioderived polymers analyzed in this work were four catalog PHA samples: PHB Fluka 81329, PHB Natural Aldrich 363502, 95PHB/5PHV Aldrich 403105, and 92PHB/8PHV Aldrich 403113. SEC/LS instrumentation used: three Phenogel (1K-10000K) columns + a guard column, an Agilent pump and Wyatt Heleos MALS, QUELS (DLS), ViscoStar and rEX DRI detectors, all in series. The experimental dn/dc of PHB in CHCl3 (0.0336 ml/g at 658nm) allowed the determination of absolute MW of all PHA samples: PHB Fluka Mw 345,100 Mn 218,400; PHB Aldrich Mw 335,700 Mn 185,000; 92PHB/8PHV Mw 144,700 Mn 91,970; 95PHB/5PHV Mw 253,000 Mn 193,800. [Preview Abstract] |
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R1.00004: Assembly of functionalized dicomponent nanorods at liquid-liquid and -air interfaces Bokyung Kim, Soojin Park, Dian Chen, Thomas McCarthy, Thomas Russell Nanoporous templates are used to fabricate nanorods which have attracted significant interest for the fabrication of functional materials with interesting optical, electrical and magnetic properties due to their shape. We investigated a method for preparing well-ordered Anodized Aluminum Oxide (AAO) template using block copolymer micelles to transfer block copolymer patterns to the surface of aluminum as a mask during RIE. Electrochemical deposition was used to deposit Au blocks and poly(pyrrole) blocks into AAO templates to prepare dicomponent nanorods. Varying the diameter and length of them can be easily controlled by the hole diameter of AAO templates and the electroplating time. By taking advantage of the different properties and functions of the individual components for offering additional degrees of freedom in self-assembly, their distinct surface chemistry was prepared. At liquid-liquid and --air interfaces, functionalized nanorods were distinctly self-assembled to adjust the interfacial interactions and stabilize two phases. [Preview Abstract] |
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R1.00005: Fabrication of Highly Ordered Silicon Oxide Dots and Stripes from Block Copolymer Thin Films Bokyung Kim, Soojin Park, Jiayu Wang, Thomas Russell A general route to fabricate highly ordered arrays of nanoscopic inorganic oxide dots and stripes from block copolymer thin films is described. Poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) thin films with cylindrical microdomains oriented normal and parallel to the surface were used as templates for the fabrication of nanoscopic silicon oxide. A thin PDMS layer was spin-coated onto the nanopatterned film, followed by thermal annealing. The PDMS diffused into the pores by capillary action. PDMS was transformed to silicon oxide by oxygen plasma treatment, while PS-b-P4VP was completely degraded, resulting in ordered arrays of silicon oxide. [Preview Abstract] |
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R1.00006: Oscillatory jet flow in electrospinning of polymer nanofibers Sureeporn Tripatanasuwan, Darrell Reneker The flow of polymer solution into an electrospinning jet can be controlled by the pressure applied to the fluid, and the flow out can be controlled by the electrical potential of the fluid. When the average flow rate of solution carried away by the jet was smaller than the rate at which the liquid was forced through the orifice into the jet, the solution flow rate and the electrical current both oscillated in time. The amount of fluid near the orifice grew larger and caused the flow out of that region to increase, and the amount of fluid near the orifice decreased. Then the cycle repeated. The oscillatory phenomena were demonstrated using a jet of polyethylene oxide in water (Molecular weight, 400k, concentration about 5{\%}) flowing through a tube with a diameter of 0.7 mm. The pressure was 500 to 2500 Pascals, and the applied potential was around 5 kV. The frequency of oscillation (about 0.5 Hertz) was affected by the resistivity of the polymer solution (around 4500 ohm-meters). [Preview Abstract] |
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R1.00007: Interaction Chromatography of Random Copolymers with Tunable Monomer Sequence Distributions Chang Y. Ryu, Junwon Han, Byung Ho Jeon, James J. Semler, Young K. Jhon, Jan Genzer We demonstrate that high performance liquid chromatography (HPLC) in the interaction chromatography (IC) mode is capable of distinguishing among various comonomer sequences in random copolymers (RCPs). A series of poly(styrene-co-4-bromostyrene) (PBr$_{x}$S), where x is the mole fraction of 4-BrS, RCPs have been prepared by brominating parent monodisperse polystyrene (PS). The distribution of S and 4-BrS segments in PBr$_{x}$S was adjusted by varying the solvent quality for PS before the bromination reaction. We utilize both normal and reversed phase IC techniques to demonstrate that the adsorption-based retention of PBr$_{x}$S RCPs is affected not only by their chemical composition, but also by the comonomer distribution in the RCP. Both IC techniques are mutually complementary; they provide information on the interplay between the macromolecular collapse and segment blockiness affected by the adsorption-based retention times in HPLC. [Preview Abstract] |
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R1.00008: Polymorphism Control of Poly(vinylidene fluoride) Jianfen Zheng, Aihua He, Junxing Li, Charles C. Han Poly(vinylidene fluoride) (PVDF) is well-known for its polymorphism, and can exhibit five different polymorphs depending on its processing conditions. The $\alpha $-phase is the most common and stable polymorph and the $\beta $-phase is the most important one due to its piezoelectric and pyroelectric properties. Polymorphism control of PVDF has been realized through electrospinning. PVDF fibrous membranes with fiber diameter in the range of 100 nm to several micrometers were produced by electrospinning and the crystal phase of electrospun PVDF fibers can be adjusted at the same time. Through the control of electrospinning parameters such as the solvent and electrospinning temperature, PVDF fibrous membranes containing mainly $\alpha $- or $\beta $- or $\gamma $-phase could be fabricated successfully. [Preview Abstract] |
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R1.00009: Role of Crystallinity in CNT Dispersion and Electrical Conductivity of SWCNT-Thermoplastic Nanocomposites Ade Kismarahardja, James Brooks, Keesu Jeon, Rufina Alamo Using a homopolymer iPP and a series of propylene-ethylene random copolymers with a content of ethylene from 7 to 21 mol{\%} as matrixes, SWCNT nanocomposites have been prepared in a range of CNT concentration from 0.15 to 1 wt{\%}. The poly(propylenes) have crystallinities ranging from 70 to 10 {\%}, and serve to test the role of CNTs acting as nucleants to preserve the uniform dispersion of CNTs after sonication in solution. Growth of the semicrystalline structure from the nanotubes is a barrier to prevent CNT clustering. Less crystallizable polymers lead to composites with poorer dispersion and lower electrical conductivity. At SWCNT concentrations of 0.15wt{\%}, SEM images of nanocomposites with the highest crystallinity matrix indicate de-bundled and uniformly dispersed nanotubes, while CNT aggregates remain in the lowest crystallinity nanocomposites. Electrical conductivity in the former is relatively high, while the latter are insulators. Also discussed is CNT dispersion from analysis of Raman spectra and polymorphism of the nanocomposites in reference to the unblended matrix. [Preview Abstract] |
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R1.00010: Self-Assembling Semicrystalline Polymer into Highly Ordered, Microscopic Concentric Rings by Evaporation Myunghwan Byun, Suck Won Hong, Lei Zhu, Zhiqun Lin A drop of semicrystalline polymer, poly(ethylene oxide) (PEO) solution was placed in a restricted geometry consisting of a sphere on a flat substrate (i.e., sphere-on flat geometry). Upon solvent evaporation from the sphere-on-flat geometry, microscopic concentric rings of PEO with appropriate high molecular weight were produced via controlled, repetitive pinning (``stick'') and depinning (``slip'') cycles of the contact line. The evaporation-induced concentric rings of PEO exhibited a fibrillar-like surface morphology. Subsequent isothermal crystallization of rings at 40 \r{ }C and 58 \r{ }C led to the formation of multilayer of flat-on lamellae (i.e., spiral morphology). In between adjacent spirals, depletion zones were developed during crystallization, as revealed by AFM measurements. The present highly ordered, concentric PEO rings may serve as a platform to study cell adhesion and motility, neuron guidance, cell mechanotransduction, and other biological processes. [Preview Abstract] |
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R1.00011: Drying-mediated Formation of ``Coffee Rings'' of Regioregular Conjugated Polymers Myunghwan Byun, Suck Won Hong, Zhiqun Lin A drop of semicrystalline conjugated polymer, regioregular poly(3-hexylthiophene) (\textit{rr} P3HT) toluene solution was allowed to evaporate from a confined geometry consisting of either a spherical lens or a cylindrical lens on a Si substrate (i.e., sphere-on-Si or cylinder-on-Si geometry). As toluene evaporated, mesoscale concentric ``coffee rings'' and fingerings of P3HT were formed as a result of controlled, repetitive ``stick'' and ``slip'' motions of the contact line. By tuning the interfacial interaction between P3HT and the Si substrate, different surface morphologies were obtained as revealed by AFM measurements. The P3HT patterns formed on native silicon oxide surface exhibited nearly amorphous morphology, while nanorod-like structures were emerged on either HMDS treated or HF treated Si substrate. [Preview Abstract] |
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R1.00012: New insight into surface melting in ultrathin polymer films: a combined surface x-ray scattering study Tadanori Koga, Y. Wang, M. Rafailovich, J. Sokolov, A. Tikhonov, D. Schultz, M. Lee, X. Li, J. Wang The crystallization of ultrathin polymer films on solid substrates has been studied for decades due to its importance in determining interfacial properties of coatings. Numerous groups have demonstrated that the rate of crystallization, crystal orientation, and density of nucleation points can be very different from bulk. We previously observed that, by using the shear modulation force microscopy (SMFM) measurements, the surface melting temperature (T$_{s})$ of polyethylene (PE) thin films decreased by 40\r{ }C relative to the bulk melting temperature (T$_{m})$ when the thickness was close to the lamellar domain spacing ($\sim $15 nm). This large depression can't be explained by the classical Thomson-Gibbs equation. In order to delve deeper into the mechanism of the surface melting, we integrated a variety of in-situ surface-sensitive scattering techniques, i.e., grazing-incidence x-ray diffraction (GID), grazing-incidence small-angle x-ray scattering (GISAXS), and diffuse scattering. We will present the detailed x-ray results and shed new light on the mechanism. [Preview Abstract] |
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R1.00013: The Equilibrium Amorphous Fraction of Polymer Crystals Buckley Crist Knowledge about disordered surfaces is important to the understanding of both melting and crystallization of polymer crystals. The concept of a surface roughening transition is well documented in atomic crystals; at sufficiently high temperatures, the entropic effects of a rough surface overcome the enthalpic penalty associated with atomic scale asperities. Similar effects operate when chain-like molecules crystallize. We concentrate fist on the basal surface perpendicular, or nearly perpendicular, to the molecular axes in extended chain crystals. In one case the positions of the chains are ideal, but liquid-like conformational defects are permitted near the surfaces. In the second case we add axial positional disorder to individual chains. Both models predict temperature-dependent equilibrium non-crystalline surface zones, the size of which depends on assumptions about surface defect free energy. This study is concludes with some comments about the equilibrium non-crystalline component of folded chain crystals. [Preview Abstract] |
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R1.00014: Asymmetrical Functionalization of Nanoparticles Mediated by Polymer Single Crystals Bing Li, Christopher Li Considerable attention has been paid to nanoparticle (NP) research because of their fascinating properties and potential applications in nanotechnology and biotechnology. Asymmetrically functionalizing NP is of particular interest because it could directly lead to controlled patterning of NPs into complex structures for a variety of applications. Herein we report using 2-dimensional thiol-terminated poly(ethylene oxide) (HS-PEO) lamellar single crystals to immobilize gold NPs (AuNPs). Furthermore, this unique technique also enables asymmetric functionalization of AuNPs. Free-standing bilayer AuNP/PEO films were obtained. Dissolving PEO single crystals led to free asymmetrically functionalized AuNPs and AuNP complexes. The degree of functionalization (number of polymer chains per particle) can be readily controlled by tuning the molecular weight. The low molecular weight PEO undergoes integral folding, which leads to the high areal density of thiol groups and thus the higher degree of functionalization, and vice versa. We anticipate that this methodology could be applied to other metal or semiconductor NPs. [Preview Abstract] |
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R1.00015: Periodic Modification of Nanofibers by Polymer Crystallization Bingbing Wang, Christopher Li Electrospinning polymer nanofibers are one of the most useful 1D nanometer-scaled materials that have numerous potential applications in the fields of filter applications, and templates for tissue engineering. Herein we show that polymer nanofibers can also be used as 1D nucleation agents to induce polymer crystallization. Poly(ethylene oxide) was electrospun into nanofibers which was used to induce PEO crystallization in solution. Shish kebab morphology was observed with the nanofiber as the shish and the PEO lamellar crystals as the kebabs. This unique morphology was named as nano fiber shish kebabs (NFSKs). We demonstrated that the structural parameters of the NSFK such as the fiber diameter, periods, the kebab size etc. could be readily controlled by the electrospinning and crystallization conditions. This NSFK also renders 3D features to the otherwise 1D nanofibers. It also serves as a vehicle for incorporating a variety of functional groups to the nanofiber systems, which, in turn, leads to numerous biomedical as well as electronic applications. [Preview Abstract] |
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R1.00016: Shear-induced orientation of poly(vinylidene fluoride-co-trifluoroethylene) thin films Heejoon Jung, Jiyoun Chang, Cheolmin Park Control of molecular and micro structures of crystalline polymers, in particular in organic electronics, has been widely studied because of the significant influence of the electrical performance of polymers by the controlled structures. Shear technique has been known as one of the most effective methods for manipulating micro structure of many different polymers. The application of the shear method to polymer films is, however, very difficult of the thickness of less than 200nm. In order to utilize the shear method for thin polymer film, we designed a new shear apparatus. We have demonstrated global ordering of semi-crystalline P(VDF-TrFE), well known crystalline polymer for in non-volatile ferroelectric polymer memory, using simple static shear in large area of a few centimeter squares. The orientation, systematically examined as a function of shearing temperature, rate and film thickness, was elucidated by Atomic force Microscope and Field-Emission Scanning Electron Microscope and related to the ferroelectric polarization of a metal/ferroelectric/metal capacitor. In addition, the globally ordered thin film P(VDF-TrFE) crystal was characterized by Grazing Incident Wide Angle X-rays. [Preview Abstract] |
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R1.00017: Surface Orientation in Injection-Molded Thermotropic Liquid Crystalline Copolyester (TLCP) Plaques Robert Bubeck, Jun Fang, Wesley Burghardt, Susan Burgard, Katherine Robertson, Daniel Fischer Attenuated total reflection Fourier transform infra-red (ATR-FTIR), C K edge near edge X-ray adsorption fine structure (NEXAFS) spectroscopies, and 2-D WAXS in transmission were used to characterize surface orientation in thermotropic liquid crystalline copolyester (TLCP) injection-molded plaques to varying depths into the samples. Injection-molded TLCPs have bimodal orientation states due to contributions from ``skin'' and ``core'' regions resulting from extensional and shear flow, respectively, in the mold. The NEXAFS is sensitive to the orientation of the molecular \textit{pi} orbital of backbone phenyl groups of the top 2 nm of a surface. ATR-FTIR obtained using a Herrick Seagull{\texttrademark} variable angle reflectance accessory is sensitive for dichroic ratios to a depth of 5 microns. Orientation parameters derived from the 1502/cm absorption band for equivalent positions are often typically about 5 to 10 percent less by ATR-FTIR than by NEXAFS. The orientational states are being correlated with physical properties of injection-molded TLCP samples. [Preview Abstract] |
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R1.00018: Synthesis and Self-Assembly of Amphiphilic Protoporphyrin-Based Oligomers Jianjun Miao, Lei Zhu An amphiphilic discotic molecule based on asymmetric protoporphyrin has been synthesized by attaching two triethylene glycol monomethyl ether (TEG) chains to the two vinyl groups in protoporphyrin via bromination and etherification, followed by attaching two octadecylamine (ODA) chains to the two carboxylic acid groups in protoporphyrin via amidization. The purity of the sample was verified by 1H NMR, size-exclusion chromatography, and mass spectroscopy. Self-assembly in the solid state was studied by differential scanning calorimetry and X-ray diffraction (XRD). A broad melting peak was observed at ca. 100 degC, and a weak ordering was observed by XRD. Self-assembly in selective solvents was studied by dynamic light scattering and transmission electron microscopy. Large vesicles of 120 nm with a narrow distribution were observed. [Preview Abstract] |
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R1.00019: Nanomechanical Measurements on Ultra-thin Poly(n-butyl methacrylate) Films. Shanhong Xu, Gregory McKenna The mechanical properties of ultra-thin poly (n-butyl methacrylate) (PBMA) films were investigated by the novel bubble inflation technique developed in our lab. Creep experiments were performed at temperatures above the glass transition temperature (Tg) of bulk PBMA. The deflection of the film is large enough to neglect the bending stiffness of the film. Surface effects were observed to play a much more important role in the inflation of the PBMA film, than had been observed for poly(vinyl acetate) (PVAc) and polystyrene (PS) previously investigated in our labs. Estimates of the surface energy contribution to film mechanical resistance for our measurements on PBMA are approximated 50{\%} while those for PVAc and PS were between 8 and 31{\%} depending on the details of the testing conditions including pressure and film thickness. [Preview Abstract] |
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R1.00020: ``Phase'' Behavior of Aqueous Solutions of Poly($N$-isopropylacrylamide) Tomoaki Kawaguchi, Kunihiko Kobayashi, Masashi Osa, Takenao Yoshizaki A series of linear poly($N$-isopropylacrylamide)(PNIPAM) samples were prepared by living anionic polymerization. The cloud-point curves for their aqueous solutions were determined by monitoring the transmittance of light through the solutions. The transmittance decreased monotonically with increasing temperature below the cloud point, as expected, but unexpectedly, it remained at a constant value if heating was stopped at a temperature. It means that the decrease in transmittance with increasing temperature does not necessarily correspond to the phase separation, i.e., the cloud-point curve for an aqueous solution of PNIPAM is not always identical with the coexistence curve. [Preview Abstract] |
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R1.00021: Effect of Intermolecular Hydrogen Bonding on the Dynamics of Poly (2-vinylpyridine) Mixtures Containing Low Molecular Weight Phenolic Compounds Pornpen Atorngitjawat, Robert Klein, Amanda McDermott, Paul Painter, James Runt The dynamics of poly(2-vinylpyridine) (P2VPy) mixed with a series of low molecular weight phenolic molecules (containing one to six hydroxyl groups) were investigated using broadband dielectric spectroscopy. For all mixtures, FTIR spectroscopy indicates significant intermolecular H-bonding. All mixtures were single phase except for that containing 10 mol{\%} hexahydroxybenzophenone, which formed a H-bonded complex with P2VPy. Intermolecular hydrogen bonding resulted in significant suppression of the P2VPy local relaxation in the glassy state. The segmental relaxations for mixtures containing 30 and 50{\%} polyhydroxy compounds where broadened, indicating dynamic heterogeneity, whereas all P2VPy - ethylphenol mixtures exhibited dynamic homogeneity. Changes in relaxation strength of the segmental process are considered in light of calculated dipole moments for all species under investigation. [Preview Abstract] |
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R1.00022: Small Angle Neutron Scattering of poly (ethylene oxide) ethyl alcohol / water mixtures Sang Hak Shin, Robert Briber, Boualem Hammouda, Derek Ho PEO solutions have interesting and complex features which arise from the interplay of the hydrophilic and hydrophobic sites on the chain (the oxygen atom and alkyl group respectively). PEO in ethanol forms an opaque gel-like mixture with a partial crystalline structure as confirmed by wide angle X-ray scattering. Addition of a small amount of water disrupts the gel: PEO in ethanol with 4 vol {\%} water becomes a transparent solution. We confirmed the crystalline structure of PEO in ethanol and investigated the PEO chain conformation in mixed ethyl alcohol / water solutions using small angle neutron scattering (SANS). We also measured the phase behavior and spinodal temperature of PEO solutions in these mixed solvents with SANS. The phase behavior changes from an upper critical solution temperature (UCST) to a lower critical solution temperature (LCST) as the fraction of water is increased. The thermodynamic behavior changes from an UCST to LCST between 5$\sim $9{\%} volume fraction water. PEO solutions which have more than 4$\sim $10 vol {\%} water behave as an athermal polymer solution. The proposed origin of this unusual phase behavior comes from the formation of hydration layer around the PEO chain. [Preview Abstract] |
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R1.00023: Multiscale Computer Simulation of Failure in Aerogels Brian Good Aerogels have been of interest to the aerospace community primarily for their thermal properties, notably their low thermal conductivities. While such gels are typically fragile, recent advances in the application of conformal polymer layers to these gels has made them potentially useful as lightweight structural materials as well. We have performed computer simulations of aerogel thermal conductivity and tensile and compressive failure, with results that are in qualitative, and sometimes quantitative, agreement with experiment. However, recent experiments in our laboratory suggest that gels having similar densities may exhibit substantially different properties. In this work, we extend our original diffusion limited cluster aggregation (DLCA) model for gel structure to incorporate additional variation in DLCA simulation parameters, with the aim of producing DLCA clusters of similar densities that nevertheless have different fractal dimension and secondary particle coordination. We perform particle statics of gel failure on these clusters, and consider the effects of differing DLCA simulation conditions, and the resultant differences in fractal dimension and coordination, on gel strength and failure mode. [Preview Abstract] |
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R1.00024: Active substrates through controlled creasing of surface-attached hydrogels Jungwook Kim, Ryan Hayward A hydrogel film confined to a rigid substrate may undergo a mechanical instability to form sharp creases on its surface when placed under compressive stress. We will describe how this instability can be harnessed to generate substrates with surface chemical patterns that can be dynamically hidden and displayed. We employ lithographically micro-patterned underlying substrates as a route to spatially control the formation of creases. Using surface-bound hydrogels composed of poly(N-isopropylacrylamide), we prepare temperature-responsive dynamic substrates, whose surface reversibly fold and flatten as temperature is changed. Finally, deposition of polyelectrolytes on the hydrogel surface is exploited as a way to selectively pattern the surface chemistry of the gel. We focus on the use of poly(ethylene glycol) grafted polyelectrolytes with and without the integrin-binding peptide (RGD) as a route to dynamically control cell-substrate interactions. [Preview Abstract] |
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R1.00025: Designing Surface Instabilities as Responsive Materials Edwin Chan, Jeffrey Karp, Robert Langer Materials with surface properties that respond to external stimuli have potential applications as sensory devices, therapeutic materials and ``smart'' adhesive coatings. An example of a responsive material is a topographic surface whose pattern length-scale changes drastically in response to a stimulus. A potential approach to creating such a material is to take advantage of the morphological phase transition observed in elastic instability such as surface wrinkles. In this contribution, we present a general strategy to developing a responsive surface that takes advantage of this morphological transition in a poly(ethylene glycol) based elastomer. The responsiveness of this material is designed by the reversible transition between two distinct pattern length-scales; a small length-scale pattern of a microlens array that responds to an osmotic stress and leads to morphological phase transition to a large length-scale wrinkling pattern. Both these pattern length-scales are material's-defined since the microlens array forms naturally as a result of the residual stress that develops during polymerization, while the surface wrinkles forms due to the buckling stress that develops due to the applied osmotic pressure. Finally, we show that this phase transition occurs reversibly and demonstrate potential application of the material as an alternative design of a self-cleaning surface. [Preview Abstract] |
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R1.00026: Correlation properties of dipole systems Yuri Popov, Philip Taylor We study theoretically the effects of electrostatic dipole- dipole interactions in ionomers, and the correlation properties of dipoles attached to either low-molecular-weight fluid or polymer chains. In particular, we study orientation-orientation correlations in systems of physical (extended) dipoles with relatively weak dipole moments. Correlation corrections to the free energy in such dipole systems are different from those in systems of point charges described by the Debye theory. The underlying physics, however, is similar: nearby dipoles rearrange around a given dipole in order to compensate for changes in its dipole moment and thus provide electrostatic screening. We develop both a simple Poisson-Boltzmann-like theory for such screening and a field-theoretic approach, which provides a natural language for describing such phenomena in a polymer context. New correlation lengths are obtained. [Preview Abstract] |
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R1.00027: Micromechanics of Yielding for Ethylene / Methacrylic Acid Ionomers. Robert Scogna, Richard Register Partially neutralizing an ethylene/methacrylic acid copolymer (E/MAA) with either sodium or zinc leads to an increase in the yield stress, by an amount which increases with the level of neutralization. This is a direct consequence of increasing nanoscale heterogeneity: the formation of ion-poor and ion-rich domains within the amorphous phase of the ionomer. This segregation is evident by dynamic mechanical testing, which reveals that, upon neutralization, the $\beta $ relaxation peak of an unneutralized E/MAA copolymer splits into two parts which represent the relaxations in ion-poor and ion-rich regions. Though both sodium and zinc cations are capable of producing this segregation, the critical degree of neutralization required to produce the split relaxation is higher for zinc. The ion-poor relaxation occurs near the T$_{g}$ of low-density polyethylene while the temperature of the ion-rich relaxation increases monotonically with the degree of neutralization. Thus, increasingly higher temperatures or lower strain rates are needed to fully relax the ion-rich domains as the neutralization level is increased, resulting in the higher measured yield stress. [Preview Abstract] |
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R1.00028: Ion Conduction and Polymer Dynamics of Poly(2-vinylpyridine) - Lithium Perchlorate Mixtures Pornpen Atorngitjawat, James Runt Ion conduction and polymer dynamics of single phase mixtures of poly(2-vinylpyridine) (P2VPy) with 0.1 to 10 mol{\%} lithium perchlorate (LiClO$_{4})$ were investigated using broadband dielectric spectroscopy. Interpretation of the relaxation behavior was assisted by findings from wide-angle and small-angle X-ray scattering experiments, and other techniques. Five dielectric relaxations were observed: a local $\beta $ process in the glassy state, a segmental relaxation, a slow segmental process, an ion-mode relaxation, and electrode polarization. The local P2VPy relaxation was strongly suppressed with increasing LiClO$_{4}$ content arising from the formation of transient crosslinks, which lead to a subsequent decrease in the number of free pyridine groups, and/or a reduction in the local free volume in the presence of LiClO$_{4}$. Ion conduction at low LiClO$_{4}$ concentrations ($<$ 10 mol{\%}) is governed by the diffusion of anions through the matrix, which is strongly coupled with the segmental relaxation. At relatively high LiClO$_{4}$ concentration (10 mol{\%}), partial decoupling between ion motion and the segmental relaxation was observed, leading to increased conductivity. [Preview Abstract] |
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R1.00029: Surface Structure of Ionic Liquids Determined by X-ray reflectivity and Sum-Frequency Generation Spectroscopy Doseok Kim, Yoonnam Jeon, Jaeho Sung, Wei Bu, David Vaknin, Yukio Ouchi X-ray reflectivity and surface sum-frequency generation spectroscopy were used to study the surface of [BMIM][X] ionic liquids (BMIM = 1-butyl-3-methylimidazolium, X = BF$_{4}$, PF$_{6,}$ and I). Sum-frequency signal strength from the terminal methyl groups of the cation at the surface indicates the topmost surface of these ionic liquids are occupied by polar-oriented hydrophobic butyl chains having $\sim $1/3 of the alkyl chain density of fully-packed hexadecanol Langmuir monolayer. X-ray reflectivity data could be fitted well by the assuming the first layer with low electron density followed by the electron-rich second layer on top of bulk ionic liquid. Detailed analysis of the reflectivity data in conjunction with the sum-frequency findings strongly suggests the molecules forming the top-most layer are on average oriented with their butyl chains (loosely packed) towards the gas/liquid interface while the core/anions (densely-packed) are in contact with the bulk liquid. [Preview Abstract] |
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R1.00030: Surface Energy Effects on Polyelectrolyte Adsorption Ryan J. Murphy, Vivek M. Prabhu, Denis Pristinski, Eric K. Lin Fluid-based directed assembly of functional nanoparticles is a promising approach to rapid fabrication of future devices. Current approaches of precise placement of these nanoscale building blocks onto pre-defined positions formed by lithography are of current interest. These methods allow for designer surfaces containing feature sizes both chemical and topological on the nanometer length scale. However, little is known about the kinetics of self assembly of charged macromolecular building blocks. Here, we investigate the adsorption kinetics of cationic polyelectrolytes as a function of surface energy, prepared by combinatorial methods. Ellipsometry and quartz crystal microbalance are used to understand the equilibrium and dynamic behavior. Constructing the adsorption phase diagram is a crucial first step towards developing a process mechanism for the directed assembly of nanoscale building blocks with polymers and nanoparticles as model systems. [Preview Abstract] |
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R1.00031: Generating surface energy gradients for block copolymer thin film studies Julie Lawson, Thomas Epps The development of block copolymer materials for future nanotechnologies requires an understanding of how surface energetics affect block copolymer thin film phase behavior. Surface energy gradients allow for combinatorial studies of these effects. In this work, surface energy gradients were created by vapor deposition of functionalized chlorosilanes on UVO-cleaned silicon substrates in a chamber under dynamic vacuum. The diffusion profiles of the chlorosilanes were controlled by the placement of the chlorosilane reservoirs in the chamber relative to the vacuum outlet and the substrate, allowing the profile of the surface energy gradient on the substrate to be tuned. X-ray photoelectron spectroscopy (XPS) was used to examine the results of the vapor deposition process. Additionally, thin films of a poly(styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymer with a bulk cylindrical morphology were flow coated onto the gradient substrates, and the resulting phase behavior was characterized with atomic force microscopy (AFM). [Preview Abstract] |
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R1.00032: Helix self-assembly through the coiling of cylindrical micelles. Sheng Zhong, Honggang Cui, Zhiyun Chen, Karen Wooley, Darrin Pochan Both single and double helical superstructures with the length of several micrometers have been created through solution self-assembly of cylindrical micelles for the first time. Helical micelles which occur as a racemic mixture were formed from the co-assembly of poly(acrylic acid)-\textit{block}-poly(methyl acrylate)-\textit{block}-polystyrene triblock copolymers with triethylenetetramine or diethylenetriamine. Kinetic study reveals that the helix cylinders evolve from the stacking of intermediate micelle domains. The helix pitch could be efficiently adjusted by adjusting the amount and type of multiamine added. For example, the pitch distance would increase nearly 20{\%} by increasing the relative molar amount of triethylenetetramine by 50{\%} or substituting the tetraamine triethylenetetramine by the triamine diethylenetriamine. The helical structure exhibits unprecedented regularity for a nanostructure self-assembled from solution, which is proposed to be the result of long range electrostatic interactions coupled with uniaxial tension along the cylinder. [Preview Abstract] |
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R1.00033: Self-assembled Patterns of Block Copolymer/Homopolymer Blends Dong Sik Park, Erol Sancaktar The addition of homopolymer (A) into an asymmetric triblock copolymer (ABA) increases the periodic orientation normal to substrate, enabling a directed self-assembly of the block copolymers into arrays of highly oriented, high-aspect-ratio cylindrical nanostructure over large areas. The application of the physical properties of block copolymers provides substantial benefits in the nanotechnologies including nanostructured membranes, nanotemplates for nanoparticle synthesis, photonic crystals, and high-density information storage media. [Preview Abstract] |
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R1.00034: UV-convergent One-loop Theory of Homogeneous Diblock Copolymer Melts Jian Qin, Piotr Grzywacz, David Morse A renormalized one-loop theory is used to analyze collective and single chain correlations in the disordered phase of diblock copolymer melts. For chains with intermediate lengths ($\bar{N} \sim 1000$), the deviation of the scattering intensity from predictions of the random phase approximation is found to be significant even far away from the mean field MST. The decrease in the wavenumber $q^\star$ at which the scattering intensity is the maximum is shown to be a result of inter-molecular correlations, which leads to wavenumber dependent apparent $\chi$ parameter, and to be unrelated to fluctuation-induced changes in single-chain correlations. The relationship to the Fredrickson-Helfand-Barrat theory is discussed. [Preview Abstract] |
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R1.00035: Thin film effects on the morphology of diblock and triblock copolymers Karen Sohn, Ken Kojio, Robert Coffin, Brian Berry, Guillermo Bazan, Edward Kramer, Michael Sprung, Jin Wang Surface effects in block copolymer thin films cause variations in the morphology from what is expressed in the bulk. The SEBS and SEB systems being studied have a composition such that both spherical and cylindrical morphologies are present in the bulk, depending on the annealing temperature. The bulk order-order transition from cylinders to spheres occurs at 140$^{\circ}$C, but in thin films the morphology is more dependent on film thickness and substrate characteristics than the annealing temperature. The morphology of thin films was studied on silicon oxide and polystyrene brushes using SFM and GISAXS. The polystyrene blocks of the SEBS and SEB were deuterated and then studied with d-SIMS in order to determine which block wets the interface with the substrate. For samples annealed at 180$^{\circ}$C, SFM shows a cylindrical morphology on SiO$_{2}$ substrates in the SEB, but a spherical morphology on the PS brush. GISAXS is used to determine whether the morphology is spheres or perpendicular cylinders. The SEBS shows a spherical morphology by SFM on both substrates. [Preview Abstract] |
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R1.00036: A Comparative Study of Microphase Separation of Polyurethane Multiblock Copolymers with Different Soft Segment Chemistries. Rebeca Hernandez, Taeyi Choi, Jadwiga Weksler, Ajay Padsalgikar, Lichong Xu, Christopher Siedlecki, James Runt We focus in this study on three series of chemically well-defined polyurethanes (PUs) with the same hard segments (MDI-BDO) but different soft segment chemistries of interest in biomedical applications: 1000 g/mol aliphatic polycarbonate, polytetramethylenoxide and a mixed macrodiol of polydimethylsiloxane (PDMS) and polyhexamethylenoxide. Using quantitative small-angle X-ray scattering we demonstrate that the degree of hard/soft segment demixing varies greatly between the materials. For example, the PDMS-based copolymers exhibit a three phase, core-shell morphology, while the other copolymers exhibit a typical two phase structure. Additional analysis was conducted with a number of experimental probes including FTIR to assess inter- and intracomponent hydrogen bonding, and tapping mode AFM to characterize the nanoscale morphology. [Preview Abstract] |
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R1.00037: Hierarchical Self-Assembly of Block Copolymers for Lithography-Free Nanopatterning. Sang Ouk Kim, Bong Hoon Kim, Sang Chul Jeon Development of a truly macroscopic scale nanopatterning process applying self-assembling materials has proved limited success. Hierarchical self-assembly is an alternative approach, which may produce complex architectures accommodating diverse functionalities. The mutually interacting multi-scale orderings of a hierarchical assembly may provide an opportunity to control over the diverse length scales simultaneously. We present lithography-free, truly macroscopic scale nanopatterning process utilizing hierarchical self-assembly of block copolymers. A micropatterned block copolymer film was self-organized from an evaporating block copolymer solution over an arbitrarily large area. The thickness modulation of the patterned film directed the spontaneous alignment of nanoscale morphology, producing a marvelous hierarchical morphology comprising microscale and nanoscale orderings. This facile and robust nanopatterning process employing the two levels of spontaneous orderings represents a versatile pathway to control nanoscale morphology by manipulating microscale architecture. Reference: B. H. Kim, et al. Adv. Mater. in press. [Preview Abstract] |
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R1.00038: Block Copolymer Micelle Shuttles with Controllable Transfer Temperature between Ionic Liquids and Aqueous Solutions Zhifeng Bai, Yiyong He, Timothy Lodge Micelle shuttle is the term we used in our recent report that amphiphilic poly((1,2-butadiene)-\textit{block}-ethylene oxide) (PB-PEO) block copolymer micelles (including spheres, cylinders, and vesicles) transfer, reversibly and with preservation of micelle structures, from an aqueous phase at room temperature to a hydrophobic ionic liquid at high temperature. We further found that the micelle shuttle could be realized in other ionic liquids, indicating its generality. The driving force for the transfer mainly originates from the deteriorating solvent quality of water for the PEO corona block at high temperature. The transfer temperature could be effectively tuned by adding ionic or non-ionic additives to the aqueous phase. Such an uncommon yet simple round-trip delivery system is of specific interest in quantitatively transporting solvophobic reagents, products, or byproducts between an ionic liquid reaction medium and an aqueous introduction or purification phase. [Preview Abstract] |
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R1.00039: Sphere-Forming and Cylinder-Forming Block Copolymer Thin Films Aligned Under Oscillatory Shear Andrew Marencic, Ranulfo Allen, Richard Register, Paul Chaikin Large-amplitude oscillatory shear has been shown to orient bulk block copolymers of spherical, cylindrical, or lamellar morphologies; however, no such experiments have been described for block copolymer thin films. Using oscillatory shear to orient microdomains would be advantageous in the creation of complex patterns especially in constrained geometries where simple shear is not possible. Here we demonstrate the ability to orient sphere-forming (trilayer) and cylinder-forming (monolayer) block copolymer thin films using oscillatory shear. The shearing field was applied to the film through a viscous fluid using a parallel-plate rheometer, allowing for continuous range of strain and shear rate. Real-space images were taken using atomic-force microscopy. As expected, a minimum strain within the film is required to induce ordering. We also observed that a larger stress is required to orient these thin films using oscillatory shear when compared to simple shear experiments. We also investigated how the ordering evolves with the number of cycles of shear applied to the film. [Preview Abstract] |
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R1.00040: Hydrogenated ROMP Block Copolymers as Thermoplastic Elastomers John Bishop, Richard Register Thermoplastic elastomers (TPEs) are typically symmetric ABA triblock copolymers made up of a ``soft'' rubbery midblock (B) and ``hard'' endblocks (A) that are usually glassy. We have used living ring-opening metathesis polymerization (ROMP) and subsequent hydrogenation to synthesize TPEs with glassy and semicrystalline ``hard'' blocks. The hydrogenated ROMP polymers we use include hydrogenated polynorbornene (hPN), a highly crystalline polymer with Tm = 143C; hydrogenated polyhexylnorbornene (hPHN), a rubbery amorphous polymer with Tg = -22C; and hydrogenated polymethyltetracyclododecene (hPMTD), a glassy polymer with Tg = 163C. The mechanical properties of our amorphous hPMTD-hPHN-hPMTD TPEs, where microphase separation is driven by interblock repulsion, are comparable to commercially-available TPEs (also amorphous) at room temperature. In analogous hPN-hPHN-hPN triblocks, where the endblocks are crystalline instead of glassy, microphase separation is driven by crystallization from a homogeneous melt, resulting in materials that are much easier to process, and with superior solvent resistance. However, the hPN endblocks show plastic deformation at moderate strains, yielding tensile strengths for the semicrystalline TPEs below those of their amorphous counterparts. [Preview Abstract] |
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R1.00041: Composition Distributions and Effective Concentration of Miscible Polymer Blends Probed by MD Simulation Wenjuan Liu, Ralph Colby, Dmitry Bedrov Using molecular dynamics we simulate the effects of thermally-driven concentration fluctuations and chain connectivity on segmental dynamics of miscible weakly interacting polymer blends. These naturally lead to local variations in glass transition temperature and hence, a distribution of segmental relaxation times. The self-concentration and pure component limits naturally truncate the Gaussian distribution of compositions surrounding a given segment. The most-probable composition differs considerably from the mean-field estimation of Lodge and McLeish for blend compositions that differ from 50/50, when we consider chain connectivity effects for all chains in the control volume. [Preview Abstract] |
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R1.00042: Phase diagram of a binary liquid crystal mixture involving induced mesophase transitions Tsang-Min Huang, Thein Kyu, Shila Garg, Kathy McReary Phase transition temperature versus composition phase diagram of a binary nematic mixture (MBBA/5CB) has been established based on polarized optical microscopy and differential scanning calorimetry. The observed phase diagram is of an azeotrope type with a unique induced smectic phase, which is not present in neat constituents. This induced mesophase reveals a mosaic texture reminiscent of a smectic-B or a higher order smectic phase. At extreme compositions, the coexistence of nematic and solid crystal phases can be identified. Wide-angle x-ray diffraction was employed to determine the ordered mesophase structures. A theoretical model is being developed in the context of Flory-Huggins theory for liquid-liquid demixing in conjunction with a modified Maier-Saupe-McMillan theory to elucidate the interplay among nematics, higher order smectics, and eutectic crystals. [Preview Abstract] |
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R1.00043: Dynamic Heterogeneity in Interacting Miscible Polymer Blends Ashish Gaikwad, Timothy Lodge Dynamic heterogeneity leading to time-temperature superposition (tTS) failure has been widely reported in non-interacting/weakly interacting miscible polymer blends. However, coupling of the component dynamic response in blends, even with a huge dynamic asymmetry in the pure components, is possible with H-bonding interactions. This study is focused on finding the minimum level of interaction necessary for thermo-rheological simplicity in blends. Blends of styrene-\textit{co}-vinylphenol (PSVPh) and poly(vinyl methyl ether) (PVME) were chosen. Incorporation of styrene provides an effective way to modulate H-bonding interactions in the system. Linear viscoelastic data indicate that tTS fails for PS/PVME blends, whereas data obtained for different PVPh/PVME blends showed that tTS was obeyed a over wide temperature range. For PSVPh/PVME blends with low PSVPh content, tTS was successful. This suggests that the presence of alternating styrene and vinyl phenol units was insufficient for dynamic response decoupling. Further studies are in progress, with varying vinyl phenol content in PSVPh, to explore the influence of H-bonding on dynamic heterogeneity and blend dynamics. [Preview Abstract] |
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R1.00044: Induced Mesophase in Mixtures of Photopolymerizable Hyperbranched Polyester and Liquid Crystal Mesogen Namil Kim, Thein Kyu, Mami Nosaka, Hiroto Kudo, Tadatomi Nishikubo Phase behavior of a mixture of eutectic liquid crystals (E7) and hyperbranched polyester (HBPEAc-COOH) has been investigated using polarized optical microscopy and differential scanning calorimetry. The observed phase diagram is an upper azeotrope, exhibiting the coexistence of nematic + isotropic phase in the vicinity of 90$\sim $110$^{\circ}$C above the clearing temperature of neat E7 (60$^{\circ}$C). With decreasing temperature a focal-conic fan shaped texture develops in the composition range of 70$\sim $90 wt{\%} of E7, suggestive of induced smectic S$_{m}$-A phase in the mixture containing no known smectic phase in their neat forms. Wide angle x-ray diffraction (WAXD) technique revealed the existence of higher order mesophase(s). The phenomenon of induced mesophase in the hyperbranched polyester/E7 system will be discussed. [Preview Abstract] |
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R1.00045: Interfacial slip in polymer blends with nanoparticles Joseph Ortiz, Eihab Jaber, Dilip Gersappe The interfacial region in polymer blends has been identified as a low viscosity region in which considerable slip can occur when the blend is subjected to shear forces. Here, we use Molecular Dynamics simulations to establish the role that added nanofiller particles play in modifying the interfacial rheology. By choosing conditions under which the fillers are localized either in the two phases, or at the interface we can look at the interplay between the strengthening capability of nanoparticles, and the change in the interfacial slip behavior. We examine particle size, attraction between the particle and the polymer component and the amount of filler in the material. Our studies are performed both above and below the point at which the filler particles form a transient network in the blend. [Preview Abstract] |
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R1.00046: X-ray characterization of hybrid PEO-clay nanocomposite films Eduard A. Stefanescu, Ioan I. Negulescu, William H. Daly The objective of the present contribution is to understand how clays with different chemistry, sizes and surface areas interact with each-other and affect the structure and characteristics of polymer based nanocomposite multilayered films. In order to search for new synergistic properties and/or improve the properties of nanocomposite films already known, here we study polymer nanocomposites that have Laponite as well as Montmorillonite incorporated in various ratios. Although the polymer-clay solutions that are used to fabricate the nanocomposite films are completely exfoliated, XRD measurements confirm that all our dried multilayered films are highly structured. The X-ray reflections predominantly correspond to the PEO intercalated clay suggesting the presence of polymer- clay stacks in the system. We observed that the gradual replacement of Montmorillonite with equivalent amounts of Laponite in the nanocomposite films leads to an increase in the integrated and maximum intensities of the XRD intercalation peaks. The differences in the intensity of XRD peaks are attributed to variations in the size and aspect ratio of the two clays present in the films. [Preview Abstract] |
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R1.00047: Interfacial and random field effects in polymers filled with nanoparticles Fouad Aliev, Vladimir Dolidze, Ivan Joel Lopez We report on the influence of filling of poly(n-alkyl methacrylates) with nanoparticles on glass transition and relaxation processes in as investigated by dielectric spectroscopy and DSC. In order to estimate the role of interfacial effects at nanoparticle-polymer interface we used two types of Aerosil particles: with hydrophilic and hydrophobic surfaces. The agglomeration even of 2-3 volume percent of Aerosil particles in polymer forms a 3D-network dividing the polymer into random domains with liner size of several hundred nm, depending on the concentration of filling particles. The result of the filling of polymer is at least two fold: random field effects imposed by network and very developed area of the particles surface imposes interfacial effect on polymers. The relaxation times of $\alpha $-relaxation process (sensitive to glass transition) in both filled polymers are faster than those of bulk polymers measured at the same temperatures. This might be interpreted as reduction of glass transition temperature in filled polymers. Semiquantitatively this reduction is in accordance with the Vogel-Fulcher data analysis of the temperature dependencies of $\alpha $-processes relaxation times and with results of DSC experiments. We assign observed influences of nanoparticles on polymer to interfacial effects. The influence of random field is less important in glass forming systems due to their internal random structure. [Preview Abstract] |
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R1.00048: Polymer nanocomposite (PNC) T$_{g}$ from the perspective of percolation theory Jamie Kropka, Peter Green, Venkat Ganesan A number of researchers have speculated on the connections between the liquid to glass transition and percolation concepts. Most recently, the film thickness dependence of T$_{g} $ exhibited by polymers has been quantified in terms of the change in percolation threshold when transitioning from a 3D to 2D system. Here, we extend these concepts to develop a model for the behavior of PNC T$_{g}$. The placement of impurities (nanoparticles) in a lattice (polymer matrix) changes the percolation threshold of the system, which we claim can be related to a change in T$_{g}$. Specific treatments of the impurities can result in either increases or decreases in T$_{g} $ relative to the pure system, and the magnitude of the changes in T$_{g}$ are related to the size and shape of the lattice impurities. We discuss the details of our results for such effects and compare them to experimental observations reported for PNCs. [Preview Abstract] |
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R1.00049: Effect of shear on the rheological and electrical properties of epoxy/MWCNTs dispersions Sameer S. Rahatekar, K. K. Koziol, Alan H. Windle, Erik K. Hobbie, Jeffery W. Gilman We report the rheological, electrical and associated microstructural properties of multiwall carbon nanotubes (MWCNTs) suspended in an epoxy resin under shear. Above a critical concentration, we find a network of MWCNT aggregates with enhanced conductivity and viscosity. High shear results in MWCNT dispersion, with shear thinning and low electrical conductivity. The influence of MWCNT concentration and length on the scaling behavior of the elastic shear modulus is studied, and the role of individual MWCNT bending on the elastic shear modulus is discussed. We find significant differences in the scaling of the elastic shear modulus for different MWCNT lengths. Finally, we carry out small angle neutron scattering (SANS) in an attempt to establish a quantitative relationship between MWCNT microstructure and the corresponding rheological and electrical properties. [Preview Abstract] |
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R1.00050: The amount of immobilized polymer in PMMA SiO$_{2}$ nanocomposites determined from calorimetric data Christoph Schick, Albert Sargsyan, Andreas Wurm, Sevan Davtyan, Anahit Tonoyan The existence of an immobilized fraction in PMMA SiO$_{2}$ nanocomposites was shown on the basis of heat capacity measurements at the glass transition of the polymer. The results were verified by enthalpy relaxation experiments below the glass transition. The immobilized layer is about 2~nm thick at low filler content if agglomeration is not dominant. The thickness of the layer is similar to that found in semicrystalline polymers and independent from the shape of the nanoparticles. Nanocomposites therefore offer a unique opportunity to study the devitrification of the immobilized fraction (RAF) without interference of melting of crystals as in semicrystalline polymers. It was found that no devitrification occurs before degradation of the polymer. No gradual increase of heat capacity or a broadening of the glass transition was found. The cooperatively rearranging regions (CRR) are either immobilized or mobile. No intermediate states are found. Sargsyan A, Tonoyan A, Davtyan S, Schick C. European Polymer Journal 2007:43:3113-3127. [Preview Abstract] |
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R1.00051: ABSTRACT WITHDRAWN |
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R1.00052: ``Cooperative'' Secondary Relaxation Induced High Room-Temperature Dielectric Constant in Supramolecular Diblock Copolymer Assembly Wei Chen, Jia-Yu Wang, Thomas Russell The development of high-dielectric-constant polymers as active materials in high-performance devices is one of challenges in polymer-based electric system like flexible high-energy-density capacitors and organic thin-film transistors. Here, we incorporated homochiral (1S)-(+)-10-camphorsulfonic acid (CSA) and non-linear optical Disperse Yellow 7 (DY7) into poly(2-vinylpyridine)-block-poly(methyl methacrylate) (P2VP-b-PMMA) copolymers via both ionic interactions and hydrogen bonding, forming a supramolecular assembly with cylindrical nanostructures. In contrast to the P2VP homopolymer assembly with a dielectric constant less than 10 at room temperature, supramolecular diblock copolymer assembly exhibits a temperature- and frequency-independent dielectric constant close to 50 at frequencies lower than 100 Hz. This is comparable with that of ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (PVDF-TrFE-CFE) terpolymer (40$\sim $60) and larger than those of PVDF ($\sim $10) and PVDF-TrFE ($<$20). Such a high room-temperature dielectric constant arises from the cooperative secondary relaxation between two blocks which increases the relaxation amplitude of CSA and DY7, both of which have large dipole moments. [Preview Abstract] |
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R1.00053: Electric Field Enhanced Diffusion of Salicylic Acid through Polyacrylamide Hydrogels Sumonman Niamlang, Anuvat Sirivat The release mechanisms and the diffusion coefficients of salicylic acid -loaded polyacrylamide hydrogels were investigated experimentally by using a modified Franz-diffusion cell at 37 $^{\circ}$C to determine the effects of crosslinking ratio and electric field strength. A significant amount of salicylic acid is released within 48 hours from the hydrogels of various crosslinking ratios, with and without electric field. The release characteristic follows the Q vs. t$^{1/2}$ linear relationship. Diffusion coefficient initially increases with increasing electric field strength and reaches the maximum value at electric field strength of 0.1 V; beyond that it decreases with electric field strength and becomes saturated at electric field strength of 5 V. The diffusion coefficient increases at low electric field strength (less 0.1 V) as a result of the electrophoresis of the salicylic acid, the expansion of pore size, and the induced pathway in pigskin. For electric field strength higher than 0.1 V, the decrease in the diffusion coefficient is due to the reduction of the polyacrylamide pore size. The diffusion coefficient obeys the scaling behavior D/D$_{o}$=(drug size/pore size)$^{m}$, with the scaling exponent m equal to 0.93 and 0.42 at electric fields of 0 and 0.1 V, respectively. [Preview Abstract] |
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R1.00054: Induced Interaction of NH4NO3 With Poly(p-phenylene vinylene) by means of Zeolite Y Jirarat Kamonsawas, Anuvat Sirivat Conducting polymers are unique among the sensing materials known to us at present. They have many advantages over conventional metal sensors. Poly(p-phenylenevinylene) (PPV) can serve as the active material in sensor devices because PPV possesses good optical and electrical properties, and it can be synthesized by a relatively simple technique. Zeolite is chosen as inorganic filler to be introduced into the conductive polymer matrix in order to increase electrical sensitivity toward ammonium nitrate vapour. The objective of our work is to investigate the effects of Si/Al ratio and cation type on the gas electrical conductivity sensitivity towards ammonium nitrate and corresponding interactions. [Preview Abstract] |
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R1.00055: Styrene-Isoprene-Styrene Triblock Copolymer (SIS)/Polydiphenylamine Blends for Actuator Application Kraipop Thongsak, Anuvat Sirivat Styrene-Isoprene-Styrene triblock copolymer (SIS) is a dielectric material exhibiting many properties similar to polyisoprene elastomer, which has been widely studied for eletroactive applications. In our work, SIS films were prepared via film casting at various polystyrene (PS) contents (19 wt {\%}, 29 wt {\%}, and 44 wt {\%}), yielding three different morphology films as characterized by an optical microscope, SEM, and TEM. Polydiphenylamine (PDPA), a conductive polymer, was synthesized by the oxidative polymerization and doped with HCl. For electroactive applications, electrorheological properties of pure SIS films and SIS/PDPA blends under stretching at a fixed temperature of 25$^{\circ}$C were measured to determine the effects of morphology (spherical, cylindrical, and lamella morphology), particle concentration, and doping level on the electrorheological properties measured: the storage and the loss modulii (G' and G''), the storage modulus responses ($\Delta $G$\prime $2kV/mm), and the storage modulus sensitivities ($\Delta $G$\prime $2kV/mm/G'0), under applied electric field strength varying from 0 to 2 kV/mm. [Preview Abstract] |
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R1.00056: The effects of monomer sequence distribution and isotopic substitution on solution phase behavior of random copolymers Young Kuk Jhon, Ramanan Krishnamoorti, Jan Genzer We report on the effect of chemical composition, co-monomer distribution and H/D isotopic substitution on the phase behavior in copolymers of poly(styrene-co-4-bromostyrene) (PBr$_{x}$S), where x denotes the mole fraction of 4-bromostyrene (4-BrS), in cyclohexane. By adjusting the solvent quality during bromination of parent polystyrene, either random or random blocky PBr$_{x}$S, (r-PBr$_{x}$S or b-PBr$_{x}$S, respectively), were synthesized. We studied the temperature dependence of phase behavior of PBr$_{x}$S with various x in cyclohexane as a function of the polymer concentration using light scattering. Our results reveal that for a given 4-BrS content, the cloud points of b-PBr$_{x}$S solutions are consistently higher and broader than those observed in r-PBr$_{x}$S solutions. The transition temperature has also been found to depend on the isotope substitutions of H or D in either the polymer or the solvent. Small angle neutron scattering measurements indicate significant differences in the temperature dependence of the thermodynamic behavior for the random and blocky samples and the nature of the fluctuations upon approaching the phase boundaries. [Preview Abstract] |
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R1.00057: The Antimicrobial Activity of Porphyrin Attached Polymers Lesley Thompson We are interested in testing the antimicrobial activity of a porphyrin that is attached to a polymer. The porphyrin (5-(4-carboxyphenyl)-10,15,20-tris-(4-pryridyl)) was synthesized from methyl 4-formyl benzoate, 4-pyridinecarboxaldehyde, and pyrrole and attached to a copolymer of polystyrene/poly(vinyl benzyl chloride), which was synthesized by free radical polymerization. The antimicrobial activity of the polymer-attached porphyrin was then determined for gram-negative E. Coli grown to 0.80 OD. In this procedure, glass slides were coated with polymer-attached porphyrin via dip-coating, and the E. Coli bacteria were plated in Luria Broth media. The plates were subsequently exposed to light overnight before they were incubated as porphyrins act as photo-sensitizers when irradiated with light. The polymer-attached porphyrin did exhibit antimicrobial activity and parameters that affect its efficiency will be discussed. [Preview Abstract] |
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R1.00058: Mesoscale Patterns Formed by Evaporation of a Polymer Solution in the Proximity of a Sphere on a Smooth Substrate: Molecular Weight and Curvature Effects Suck Won Hong, Jianfeng Xia, Myunghwan Byun, Qingze Zou, Zhiqun Lin A drop of polymer solution was constrained in a sphere-on-flat geometry, resulting in a liquid capillary bridge. As solvent evaporated, intriguing surface patterns of polymer formed, which were strongly dependent on the molecular weight (MW) of polymer. Dotted arrays were formed at low MW; concentric rings were produced at intermediate MW; concentric rings, rings with fingers, and punch-hole-like structures, however, were yielded at high MW. Rings with fingers as well as punch-hole-like structures were manifestations of simultaneous occurrence of the ``stick-slip'' motion of the contact line and the fingering instabilities of rings. In addition, the curvature of the sphere in the sphere-on-flat geometry was found to affect the pattern formation. A decrease in the curvature of the sphere led to an earlier onset of the formation of punch-hole-like structures when high-MW polymer was employed as the nonvolatile solute. [Preview Abstract] |
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R1.00059: Thermal-reversible, size-selective desorption of nanoparticles from polymer brushes Richard Vaia, Steve Diamanti, Shafi Arifuzzaman, Jan Genzer The ability to reversibly modulate surface energy and chemistry will provide new opportunities for future separation and sensing technologies. Post-polymerization functionalization of covalently-tethered polymer brushes affords a robust platform technology for these goals. Using standard succinimide-based coupling, hydroxyl pendants of poly(2-hydroxyethyl methacrylate) (PHEMA) brushes were conjugated to oligo-peptides, alkanes, fluoroalkanes, and oligo(ethylene glycol) (OEG) through an alpha-terminus primary amine. Coupling of these different chemical moieties allows tailoring of the surface energy ($\theta _{H2O}\sim $40--110$^{o})$, that combined with PHEMA grafting density and molecular weight (MW), leads to tunable adsorption of analytes. OEG-modified PHEMA brushes exhibit thermal-reversible desorption of analytes that is size-selective. For example, Au NPs of larger size are liberated from the brushes at shorter heating times; hence mixtures of Au NPs of different sizes can be sequentially released by controlling substrate heating. The impact of electrolyte content, Au NP surface chemistry, coupling efficiency and OEG MW is discussed to elucidate the detailed molecular mechanisms dominating the size and temperature-dependent OEG-Au NP binding efficiency. [Preview Abstract] |
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R1.00060: SANS from CO$_{2}$-saturated coals at conditions relevant to subsurface sequestration Yuri Melnichenko, Andrzej Radlinski, Gang Cheng, Maria Mastalerz, George Wignall Carbon dioxide (CO$_{2})$ is the greenhouse gas which makes the largest contribution to global warming and roughly one third of the United States' CO$_{2}$ emissions are generated by fuel-burning power plants. Capture and storage of CO$_{2}$ in underground geologic structures may significantly reduce CO$_{2}$ emissions to the atmosphere. Sequestration of CO$_{2}$ in unmineable deep coal seams is particularly attractive as many coal-burning power plants are located near sites potentially suitable for geological storage. It is widely assumed that CO$_{2}$ can be captured and retained in coals by virtue of several of mechanisms, such as fluid trapping of an ``immobile phase'' inside the pore space, adsorption to the pore surface and chemical bonding inside the organic coal matrix in the vicinity of pore walls. We report the results of the first small-angle neutron scattering (SANS) studies of several coals saturated with CO$_{2}$ at temperatures and pressures similar to those found in deep coal seams which are likely to be used for industrial-scale underground storage of CO$_{2}$. We found that the porous coal matrix may work to create absorbed fluid phase with the physical density much exceeding the density of the bulk fluid at the same thermodynamic conditions. Fluid densification is different in different coals which may explain the observed differences in sorption capacity and migration rates. [Preview Abstract] |
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R1.00061: Selective excitation of excitonic transitions in PTCDA crystals and thin films V.R. Gangilenka, A. DeSilva, Lyubov V. Titova, L.M. Smith, H.P. Wagner, R. Scholz We study various exciton transitions in PTCDA crystals and in thin films at low temperatures ($\sim $5 K) by photoluminescence excitation spectroscopy (PLE) using DCM and RG6 dyes. The investigated PTCDA crystals are grown by sublimation and thin films are deposited on Si substrate by organic molecular beam deposition (OMBD) at high vacuum. The PLE excitation energy ranging from 1.878 to 2.172 eV enables the selective excitation of Frenkel excitons and of charge transfer transitions between PTCDA molecules in the same unit cell (CT1) as well as between stacked molecules along the growth direction (CT2). The observed excitation energy dependence of the emission bands supports the assignment of the different recombination channels obtained from time resolved PL measurements [1]. [1] A. Yu. Kobitski, R. Scholz, I Vragovic, H. P. Wagner, and D. R. T. Zahn, Phys. Rev. B \textbf{66}, 153204 (2002). [Preview Abstract] |
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R1.00062: Variable-Density Micelle Arrays in Block Copolymer Thin Films John Papalia, Douglas Adamson, Richard Register, Paul Chaikin Thin films of sphere-forming block copolymers are attractive templates for surface patterning and nanofabrication, offering control over both the sphere (micelle) diameter and their average spacing (areal density). Within a given film, these quantities are statistically uniform: that is, there has not previously been a way to vary the number density of spheres across the film. By contrast, films having a thickness gradient are straightforward to prepare; however, regions of the film whose thickness is not commensurate with an integral number of layers of spheres will spontaneously form micron-scale islands or holes (terraces) of commensurate thickness, and a uniform areal density. By blending the block copolymer with matrix homopolymer, this terrace formation can be suppressed, so that creating a gradient in film thickness will also produce a gradient in micelle density. We employ a polystyrene-polyisoprene diblock copolymer with block molecular weights of PS/PI 68/12 kg/mol, blended with PS homopolymer of varying molecular weights, in gradient films spanning thicknesses from 0-3 layers of spheres. At 50{\%} PS homopolymer, terraces are still observed for homopolymer molecular weights in the ``wet brush'' region (9-50 kg/mol), but are completely suppressed when the homopolymer is excluded from the micelle coronae (110 kg/mol). [Preview Abstract] |
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R1.00063: ABSTRACT WITHDRAWN |
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R1.00064: Nanohole Structure in Polystyrene-\textit{block}-poly(methyl methacrylate) Thin Film Wonchul Joo, Seung Yun Yang, Jin Kon Kim, Hiroshi Jinnai Cylindrical nanoporous structures were prepared by using the mixture of polystyrene-\textit{block}-poly(methyl methacrylate) copolymer and PMMA homopolymer, and they were analyzed by using transmission electron microtomography and X-ray reflectivity. Two methods were employed for nanoporous structures: (1) whole PMMA phase was removed by UV irradiation and (2) only PMMA homopolymer was removed with selective solvent. We found that the nanoporous structure in the film prepared by method (1) exhibited cylindrical shape through the entire the film thickness. On the other hand, when the nanoporous film was prepared with the selective solvent, nanoporous structures exhibited a funnel-shape that the diameter of nanopores located near the top of the film is larger than that located near the bottom of the film. [Preview Abstract] |
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R1.00065: Thickness Dependence of Fluorescence Dynamics in Thin and Ultrathin Polystyrene Films Yohei Tateishi, Yohei Okada, Keiji Tanaka, Toshihiko Nagamura Fluorescence dynamics such as lifetime and rotational relaxation time for 6-(N-(7-nitrobenz-2-oxa-1,3- diazol-4-yl)amino) hexanoic acid (NBD) in polystyrene (PS) solid was examined as a function of film thickness, t. Both times decreased with decreasing thickness once the film became thinner than a critical value, to. Interestingly, in the case of ultrathin films, both times were insensitive to the film thickness. In addition, fluorescence intensity per unit thickness also decreased with decreasing thickness at t $<$ to, meaning that the fluorescence quantum yield was dependent on the thickness at t $<$ to. These results could be explained in terms of a simple three-layer model composed of surface, bulk and interfacial layers. [Preview Abstract] |
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R1.00066: Interfacial Characterization of Poly(methyl methacrylate) with Non-solvents Yoshihisa Fujii, Hironori Atarashi, Masahiro Hino, Keiji Tanaka, Toshihiko Nagamura Density profiles of a perdeuterated poly(methyl methacrylate) (dPMMA) film in water, hexane and methanol, which are `non-solvents' for dPMMA, were studied by neutron reflectivity (NR). The interfaces of dPMMA with the liquids were diffuse in comparison with the pristine interface with air; the interfacial width with water was thicker than that with hexane. Interestingly, in water, the dPMMA film was composed of a swollen layer and the interior region, which also contained water, in addition to the diffused layer. The interface of dPMMA with hexane was sharper than that with water. Although there were slight indications of a swollen layer for the dPMMA in hexane, the solvent molecules did not penetrate significantly into the film. On the other hand, in methanol, the whole region of the dPMMA film was strikingly swollen. The modulus of dPMMA in the vicinity of the interfaces with liquids was also examined on the basis of force-distance curves measured by atomic force microscopy. The modulus decreased closer to the outermost region of the film. The extent to which the modulus decreased in the interfacial region was consistent with the amount of liquid sorbed into the film. [Preview Abstract] |
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R1.00067: Two photon absorption in PTCDA films using the z-scan technique A.M. Ajward, V.R. Gangilenka, H. Schmitzer, H.P. Wagner The two-photon absorption coefficient of a polycrystalline PTCDA (perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride) thin film was measured at 880 nm using the z-scan technique. The 2 $\mu $m thick PTCDA film was grown by organic molecular beam deposition (OMBD) on Pyrex. For the z-scan measurements $\sim $1 ps pulses were focused onto the thin film using a microscope objective lens (100x) of numerical aperture 0.55 and a beam waist of 1 $\mu $m. The films have been moved by a translation stage with a travel range of 100 $\mu $m and with a step size of 0.5 $\mu $m. The two-photon absorption coefficient of PTCDA obtained from a fit with open aperture measurements at different intensities results to $\sim $100 cm GW$^{-1}$. The z-scan measurements demonstrate that crystalline PTCDA films possess strong nonlinear optical properties that might be utilized for optical applications. [Preview Abstract] |
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R1.00068: Photochemical Branching/Crosslinking of Preformed Polymers Using bis-Benzophenone Nicholas Carbone, Mary Dickson, Jeffrey Koberstein We show that bis-benzophenone (bis-BP) is an effective method to photochemically crosslink essentially any reformed polymer system that contains abstractable hydrogen atoms. When bis-BP is mixed into a polymer and exposed to UV radiation, it abstracts~hydrogen atoms from any chains in proximity, thereby initiating a cascade of free radical reactions that include several mechanisms that can lead to covalent polymer crosslinking. Herein we study the early stages of branching reactions that precede gelation by following molecular weight changes in~bis-BP modified polystyrene (PS) by Gel Permeation Chromatography. Quantitative molecular~weight changes in PS:bis-BP thin films are studied as a function of irradiation~ time, PS:bis-BP molar ratio, and film height.~ AFM studies are employed qualitatively to investigate the relationship between molecular weight~and the degree of dewetting of thin PS films deposited on silicon wafers. [Preview Abstract] |
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R1.00069: Toward a mininum criteria of multi dimensional instanton formation for condensed matter systems? Andrew Beckwith We present near the end of this document a promising research direction as to how to generalize a technique initially applied to density wave current calculations to questions of instanton formation in multi dimensional condensed matter systems. Initially we review prior calculations done through a numerical simulation that the massive Schwinger model used to formulate solutions to CDW transport in itself is insufficient for transport of soliton-antisoliton (S-S') pairs through a pinning gap model of CDW transport. Using the Peierls condensation energy permits formation of CDW S-S' pairs in wave functionals. This leads us to conclude that if there is a small spacing between soliton-antisoliton (S-S') charge centers, and an approximate fit between a tilted washboard potential and the system we are modeling, that instantons are pertinent to current/transport problems. This requires a very large `self energy' final value of interaction energy as calculated between positive and negative charged components of soliton-antisoliton (S-S') pairs with Gaussian wave functionals as modeled for multi dimensional systems along the lines of Lu's generalization given below. The links to a saddle point treatment of this instanton formation are make explicit by a comment as to a cosmology variant of instanton formation in multi dimensions we think is, with slight modifications appropriate for condensed matter systems. [Preview Abstract] |
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R1.00070: The Anomalous Translocation Dynamics of Long-Chain Molecules Srabanti Chaudhury, Binny J. Cherayil Models of translocation based on simple Brownian diffusion mechanisms generally fail to account satisfactorily for anomalies in measured and simulated values of the average time of passage of long chain molecules through narrow pores. In an effort to rationalize these anomalies, we formulate an alternative model in which the time evolution of the number of monomers on one side of the pore is governed by the stochastic dynamics of a particle moving in a linear potential under the action of thermal fluctuations with long-ranged temporal correlations. We use this model in the limits of strong and weak diffusive bias to derive closed form expressions for the mean first passage time for pore crossing and the mean square displacement of a monomeric segment. These expressions, unlike those obtained from fractional Fokker-Planck formulations of the problem, are well-defined everywhere, and are also consistent with available numerical data. [Preview Abstract] |
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R1.00071: Electric Field and Electron-Electron Interactions Effects on Bipolaron Transport in Polythiophene Yaping Li, Jolanta Lagowski Polythiophene is one of the most widely used organic conjugated polymer. Its charge transport mechanism has been a subject of many intensive studies. We employ the extended Su-Schriefer-Heeger's theoretical model (SSH), including electric field and electron-electron interactions, to study bipolaron transport in polythiophene. This model involves the solution of coupled equations, consisting of the time-dependent Schrodinger equation and the classical motion equation for the lattice displacement, which are solved numerically in a self-consistent way. The time-dependent unrestricted Hartree--Fock approximation is also used. The parameters employed in the computations are determined by requiring good agreement with theoretical and experiment values for band gap and bond lengths. We find that a bipolaron does not distort in a weak electric field, however, a strong electric field can dissolve it, transforming localized charges into free charges. Electron- electron interactions do not significantly affect the nature of bipolaron transport in polythiophene. [Preview Abstract] |
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R1.00072: Theoretical studies of the structures and optical properties of the dimers of the fluorene and carbazole derivatives. Jolanta Lagowski, Zhijun Gong The intrinsic properties of the ground and excited states of fluorene, carbazole, fluorene-vinylene and fluorene-acetylene dimers and fluorene-carbazole unit are studied. The ground state optimized structures and energies are obtained using the molecular orbital theory and the density functional theory (DFT). The ground state potential energy curves of the dimers are also obtained. All molecules are nonplanar in their electronic ground states. The character and energy of the first 20 singlet-singlet electronic transitions are investigated by applying the time-dependent DFT approximations to the correspondingly optimized ground state geometries. The lowest singlet state is studied with the configuration interaction (singles) approach (CIS). CIS results suggest geometry relaxation in the first singlet excited state. [Preview Abstract] |
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R1.00073: Orientational Relaxation in Simulated Polymer Melts Taylor Dotson, John McCoy, Joanne Budzien, Douglas Adolf, Keenan Dotson, Julieanne Heffernan The orientational relaxation of simple polymer chains was studied using second Legendre polynomial autocorrelation functions. Such functions are commonly fit with a Kohlrausch-Williams-Watts (KWW) stretched exponential form. The value of the stretching parameter, $\beta $, and the degree that it changes as the glass transition is approached are both of physical interest. In the current project, a novel approach to determining the value and variation of $\beta $ from molecular dynamics simulations is implemented. The methodology is found to produce KWW fits of high accuracy. Moreover, the stretching parameter, $\beta $, is found to collapse to a single-valued function of the decay timescale $\tau $ regardless of thermodynamic path. Connections are drawn to experimental results and theoretical implications of the research are discussed. [Preview Abstract] |
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R1.00074: Molecular Dynamics Simulations of Nanoimprinting Process Jan-Michael Carrillo, Andrey Dobrynin Using coarse-grained molecular dynamics simulations we have studied Nanoimprinting Process. The simulations were performed as follows: 1) the master image was created by pressing a substrate with an attached hemisphere, representing the master, into a thin polymeric film. 2) In order to preserve the shape of the master image in the polymeric film, the polymers were cross-linked at different cross-linking densities. 3) The original hemispherical master was replicated by pressing the mold into monomeric liquid. The quality of the molding process was evaluated by comparing the shapes of the original hemisphere and the molded one. We have established how the differences between the original and replica depend on the size of the master, the fraction of the cross-links, the network shear modulus and the master mold-monomer liquid affinity, which is controlled by the parameters of the Lennard-Jones potential. [Preview Abstract] |
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R1.00075: Probing the segmental mobility and energy of the active zones of a protein chain (aspartic acid protease) by a coarse-grained bond-fluctuation Monte Carlo simulation Ras Pandey, Barry Farmer A protein chain such as aspartic acid protease is described by a specific sequence of 99 residues each with its own specific characteristics. In a coarse-grained description, the backbone of a protein chain is described by nodes tethered together by peptide bonds where each node (the amino acid group) is characterized by molecular weight and hydrophobicity. A well-developed and somewhat mature computational modeling tool for the polymer chain such as the bond-fluctuation model is used to study such a specific protein chain with its constitutive amino groups and their sequence. The relative magnitude of hydrophobicity is used to develop appropriate interaction potentials for these amino acid groups in explicit solvent. The Metropolis algorithm is used to move each node and solvent constituent. Local energy and mobility of each amino group are analyzed along with global energy, mobility, and conformation of the protein chain. Effect of the solvent interaction and its concentration on these quantities will be presented. [Preview Abstract] |
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R1.00076: Brownian dynamics simulations of tethered polymers on curved surfaces Margaret Linak, Martin Kenward, Kevin D. Dorfman Surface tethered polymers are an important component in many physical systems, including coating applications, microfluidic devices, drug delivery vehicles and molecular targets in DNA microarrays. The recent renewed interest in low-density tethered polymers (i.e., below the characteristic surface density of a polymer brush) is partially attributed to their applicability in the latter circumstances. We present a study of an isolated polymer chain tethered to a curved, impenetrable surface, where the radius of curvature is varied from highly convex, through flat, to highly concave. Utilizing Brownian dynamics simulations, we examine the equilibrium properties of the polymer as a function of its stiffness and molecular size, as well as, the degree (and sign) of the surface curvature. Our results for curved surfaces have potential implications in a number of microfluidic and biological systems. [Preview Abstract] |
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R1.00077: Phase Behavior of Polystyrene-block-poly(2-vinylpyridine) coordinated by Metal Chloride Dong Hyun Lee, Wonchul Joo, Jin Kon Kim, June Huh, Du Yeol Ryu The morphology and order-to-disorder transition (ODT) of asymmetric polystyrene-block-poly(2-vinylpyridine) copolymers (PS-P2VP) varying chain length of P2VP coordinated with CdCl$_{2}$ were investigated by rheometry, synchrotron small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). D-spacing of PS-P2VP coordinated with tiny amount of CdCl$_{2}$ increased greatly. With increasing amount of CdCl$_{2}$, spherical microdomains were changed to hexagonally-packed cylinders. This is due to intra-chain coordination between CdCl$_{2}$ and pyridine ring. [Preview Abstract] |
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R1.00078: Vibrational Spectroscopy of Polymers at High Pressures Erik Emmons, K.C. Chiartkunchand, Richard Kraus, Jeffrey Thompson, Aaron Covington Vibrational spectroscopy of polymers at high-pressures ($>$1 GPa) is an interesting but relatively unexplored field. Early studies by Bridgman in the 1940s revealed a crystalline phase transition in only one polymeric material, poly (tetrafluoroethylene), at high pressures. Since that time, however, there have been relatively few studies of high-pressure polymorphism in polymers, with the exception of experiments on polyethylene. Hence, there is still not a clear picture of how common structural phase transitions are at high pressure in polymeric materials, in contrast to the situation for small organic molecules. The results of high-pressure vibrational spectroscopic studies of semi-crystalline polymeric materials such as $\alpha$- and $\beta$-poly (vinylidene fluoride) will be presented. [Preview Abstract] |
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R1.00079: ABSTRACT WITHDRAWN |
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R1.00080: Evolution of multicompartment micelles to mixed corona micelles Chun Liu, Zhibo Li, Marc Hillmyer, Timothy Lodge Multicompartment micelles, self-assembled nanoscopic aggregates with subdivided solvophobic cores, have received great interest recently. This novel type of micelle was first realized by the micellization of triptych triblock copolymers---u-EOF (E: polyethylethylene; O: polyethylene oxide; F: polyperfluoropropylene oxide) in aqueous solutions. u-EOF micelles with the cores consisting of E and F blocks underwent a gradual transition from nanostructured vesicles to segmented worms, and finally to multicompartment ``hamburgers'' as the ratio of the hydrophilic O block to the hydrophobic E/F block increased. Herein, we report on the further manipulation of their structures via the introduction of a second solvent---tetrahydrofuran (THF), which is selective for both E and O blocks. As THF content increases, the micelles evolve from multicompartment micelles to mixed corona micelles with corresponding morphological changes, as evidenced in cryogenic transmission electron microscopy and dynamic light scattering. [Preview Abstract] |
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R1.00081: Control of microdomain orientations in block copolymer thin films with chemically-patterned substrate Mikihito Takenaka, Satoshi Akasaka, Yasuhiko Tada, Tomohiro Inoue, Hiroshi Yoshida, Hirokazu Hasegawa We demonstrate defect-free and well-aligned self-assembly of cylindrical microdomains in block copolymer thin films on chemically-patterned substrates in arbitrarily large areas. Poly(styrene-b-methyl methacrylate) (PS-PMMA) with weight average molecular weight and weight fraction of PS being 6.7x10$^{3}$ and 0.69, respectively, was spin coated on chemically nano-patterned substrate and annealed to undergo microphase separation. The chemically patterned substrate was prepared by patterning polystyrene grafted silicon wafer by conventional electron beam lithography, to form hexagonally arranged circular areas having higher affinity to cylindrical microdomain forming blocks. The epitaxially-grown cylinder structures were well aligned with defect-free hexagonal lattice, although the chemically-patterned substrate have some defects in its pattern. This result suggests that self-assembly of PS-PMMA can clean-up and interpolate the defects of patterned substrate while patterned substrate can align the orientation of block copolymer domain structures. [Preview Abstract] |
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R1.00082: Control of the processing window for block copolymer nanostructures by the addition of a homopolymer Junhan Cho, Du Yeol Ryu, Kwang Hyun Song, Sang Bo Na, Youngmin Kim Processing window for block copolymer nanostructures is often limited by a material at hand and effective intermonomer interactions. Taking polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) as a model system, which is one of the most widely used passive electronic materials, we investigated how to control the processing window for generating nanostructures from PS-b-PMMA by the addition of PS homopolymer. The ordering transition points were measured for the neat copolymer and its mixtures by optical and radiation scattering methods. A molecular model based on a random-phase approximation theory was then used to elicit the effective interactions between constituent blocks and to predict the measured ordering transition temperatures for the design and fabrication of nanostructures from the copolymer system at desired processing condition. [Preview Abstract] |
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R1.00083: Order-to-disorder Transition on PS-b-PI Copolymer Thin Film Changhak Shin, Hyungju Ahn, Du Yeol Ryu, Kwang-Woo Kim The microphase separation transition in thin film system has been studied for diblock copolymers poly (styrene-b-isoprene) [PS-PI]. It has been broadly known that the microphase- separated or ordered state for block copolymers possesses a lower average density than the disordered state due to the dominant entropic contribution to the free energy. In this study, we used ellipsometry to probe transition temperatures in block copolymer thin films because it makes use of the change in polarization induced upon the reflection light from a covered substrate and allows the calculation of the thickness of the film. The phase behavior is compared based on the volumetric change on transition. [Preview Abstract] |
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R1.00084: Surface Neutrality for PS-b-PMMA Copolymer Thin Film Sujin Ham, Eunhye Kim, Changhak Shin, Du Yeol Ryu, Craig Hawker, Thomas Russell Many attempts were made to control over the microdomain orientations of block copolymers in the thin films such as application of strong electric field, solvent annealing and chemical modification of the substrate surface because a variety of nanoscale periodic patterns of the block copolymers offers the potential use as nanolithographic templates, data storage, electronics and membranes. From this study, we suggest the experimental surface conditions for neutrality based on PS/PMMA. Lamellar or cylinder-forming PS-b-PMMA copolymers were used to investigate the thickness dependence of the perpendicular orientation of the microdomains by varying the chemical compositions (PS/PMMA) of underlying random copolymer brushes. The brush surfaces modified by the random copolymers were obtained by thermal annealing due to simple chemical reaction. From the thickness windows for the perpendicular orientation in PS-b-PMMA thin films, the real neutral surface could be observed. [Preview Abstract] |
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R1.00085: Optical Absorption and Emission of Fully Conjugated Heterocyclic Aromatic Rigid-rod Polymers Containing Sulfonated Pendants Shih Jung Bai, Shen-Rong Han Fully conjugated poly[(1,7-dihydrobenzo[1,2-d:4,5-d']\textit{di}imidazole-2,6-diyl)-2-(2-sulfo)-$p$-phenylene] (sPBI) has a \textit{para}-catenated rod-like backbone, which was synthesized and fabricated for \textit{mono}-layer polymer light-emitting diode (PLED) showing a threshold voltage of 4.5 V and a green light (530 nm) emission. Its SO$_{3}$H moiety attached to the $p$-phenyl ring improved electron \textit{de}localization along the backbone resulted in a \textit{red shift} of absorption spectrum. sPBI was further derivatized for rigid-rod polyelectrolyte sPBI-PS(Li$^{+})$ by attaching propanesulfonated pendants to the heterocyclic moiety of intractable sPBI for water solubility. This fully conjugated polyelectrolyte sPBI-PS(Li$^{+})$ was fabricated for light-emitting electrochemical cells (PLECs) with a dopant of LiCF$_{3}$SO$_{3}$ or LiN(CF$_{3}$SO$_{2})_{2}$ for effects of propanesulfonated pendants and lithium dopants on lunimescent emission and on room-temperature conductivity. sPBI-PS(Li$^{+})$ PLECs doped with 0.41 and 1.01 wt.{\%} of LiN(CF$_{3}$SO$_{2})_{2}$ showed higher green light (514 nm) electroluminescence emission intensity with a threshold voltage of 3.0 V and -4.6 V, respectively. Emission intensity of the sPBI-PS(Li$^{+})$ PLEC did not raise upon increasing the conductivity of the luminescent layer. [Preview Abstract] |
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R1.00086: Non-linear V-I Characters of LSMO/PAn/Co/Al Organic Spin-Valve Z.L. Liu, H.G Cheng, Z.H. Qin, J. Chen, X.J. Wang The present paper used the magnetron sputtering and Sol-Gel method to prepare the organic spin-valves composed of La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO)/ polyaniline (PAN)/Co/Al. We Adopted the four probe to study the MR of the spin valve and observed the non-linear V-I characters. The TMR effect in the organic spin valve was also studied. [Preview Abstract] |
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R1.00087: Electroluminescence of Conjugated Rigid-rod Polymer Tuned by Emission Layer Thickness Shih Jung Bai, Hua-Wei Tseng, Jen-Wei Huang \textit{Bi}layered light emitting diodes were fabricated with fully conjugated rigid-rod polymer poly-$p$-phenylenebenzobisoxazole (PBO) on top of hole conducting poly(3,4-ethylene-dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) using indium-tin-oxide on glass as the substrate and also the electron injecting cathode. The hole injecting anode was Al vacuum evaporated onto the PBO layer. Electroluminescence emission was obtained showing a \textit{blue} shift in emission $\lambda _{max.}$ together with a lowered threshold voltage for the \textit{bi}layered polymer diodes having a smaller PBO layer thickness. When the PBO thickness changing from 90 nm to 27 nm with a constant PEDOT:PSS layer thickness of 54 nm, the $\Delta \lambda _{max.}$ and the $\Delta $V$_{threshold}$ were 70 nm and 3.5 V, respectively. [Preview Abstract] |
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R1.00088: Growth Kinetics of Au Nanoparticles: Mean Field Modeling and SAXS. Hilmar Koerner, Michael Tambasco, Robert MacCuspie, Richard Vaia, Sanat Kumar Gold (Au) nanoparticles (NPs) are a mainstay of current nanoscience and technology. With such a diversity of applications, developing a better understanding of the impact of macromolecular additives on single-phase fabrication routes, and ultimately on the resultant interfacial composition and structure (size, shape and dispersity), is critical to optimize performance and lower production cost. In-situ small-angle x-ray scattering (SAXS) is uniquely situated to directly monitor the morphological evolution of Au NPs from single phase reduction of Au(I) by tert-butylamine-borane. Deconvolution of the in-situ SAXS profiles provides direct information on the evolution of NP size, polydispersity and relative number density, as well as the on-set of clustering and superstructure formation. The size-time profiles agree with mean-field calculations elucidating the role of ligands, their length and structure on the nucleation and growth kinetics as well as thermodynamic and structural characteristics of the Au NPs. In general, the combined approach provides new insights on the impact of additives on the various stages of NP formation and the ability to quantify particle-pair potentials and ascertain impact on assembly -- de-assembly process of NP superstructures. [Preview Abstract] |
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R1.00089: Effect of Ligand Molecular Weight and Nanoparticle Core Size on Polymer-Coated Gold Nanoparticle Location in Block Copolymers Joshua Petrie, Bumjoon Kim, Glenn Fredrickson, Ed Kramer Gold nanoparticles modified by short chain polymer thiols [Au-PS] can be designed to strongly localize in either domain of a polystyrene-b-poly(2-vinylpyridine) [PS-PVP] block copolymer or at the interface. The P2VP block has a stronger attractive interaction with bare gold than the PS block. Thus, when the areal chain density $\Sigma $ of end-attached PS chains falls below a critical areal chain density $\Sigma c$ the Au-PS nanoparticles adsorb to the PS-b-P2VP interface. The effect of the polymer ligand molecular weight on the $\Sigma c$has been shown to scale as $\Sigma c\sim $ ((R+Rg)/(R*Rg))\^{}2, where R is the curvature of the Au nanoparticle core radius. To test this scaling relation for $\Sigma c$ further we are synthesizing gold nanoparticles with different core radii and will present preliminary results on $\Sigma c$as a function of R. [Preview Abstract] |
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R1.00090: Patterning of Nano-Objects on PS-$b$-PMMA Thin Films by Selective Swelling Kookheon Char, Jeong Gon Son, Paul F. Nealey, Huiman Kang Nano-objects have recently received great attention due to their unique photonic, electronic, and magnetic properties. However, in order to take full advantage of these properties of nano-objects, massively parallel assembly or integration of nano-objects is required. Block copolymers are well known to spontaneously form a wide range of nanostructures and block copolymer thin films can easily allow nano-scale patterns. In this presentation, we would like to introduce a new approach to realize nano-object patterning on perpendicularly oriented polystyrene-block-poly(methyl methacrylate) thin films. Our main idea is based on the properties of block copolymer thin films that simultaneously form the topographical and chemical patterns. We employed the annealing with selective solvents to realize topographical patterns of block copolymer thin films, from which we realized nano-object patterns either in the grooves of the patterns or on the top of the patterns. We verified the structures and mechanisms for the nano-object patterns on block copolymer thin films using Atomic Force Microscopy, Field-Emission Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy. [Preview Abstract] |
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R1.00091: Target site search strategy of gene regulatory proteins Andrew Spakowitz, Mario Diaz de la Rosa Gene expression is orchestrated by a host of regulatory proteins that coordinate the transcription of DNA to RNA. Regulatory proteins function by locating specific binding sequences of DNA and binding to these sequences to form the transcription initiation complex. In many instances, these regulatory proteins only have several hundred copies that must efficiently locate target sequences on the genome-length DNA strand. The non-specific binding of regulatory proteins to random sequences of DNA is believed to permit the protein to slide along the DNA in a stochastic manner. Periodically, a thermal kick or an interaction with another bound protein will disengage the regulatory protein from the DNA surface, leading to three-dimensional diffusion. Eventually, the protein will reattach to the DNA at some new location that is dictated by both the diffusivity of the protein and the DNA configuration. Cycling through these random events constitutes a search strategy for the target site. We build a reaction-diffusion theory of this search process in order to predict the optimal strategy for target site localization. The statistical behavior of the DNA strand acts as a necessary input into the theory, and we consider several governing behaviors for the DNA strand. We explore the impact of DNA configuration on target site localization in order to predict how protein expression will vary under different experimental conditions. [Preview Abstract] |
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R1.00092: Conformational Dynamics and Interactions of a DNA Aptamer Observed by Single Molecule Spectroscopy James Taylor, Qusai Darugar, Ajish Potty, Richard Willson, Christy Landes Single molecule fluorescence resonance energy transfer (FRET) and fluorescence correlation spectroscopy (FCS) are used to study the interactions and structural dynamics of a DNA aptamer. Studies are performed both in the the presence of and in the absence of the aptamer's binding target, the dimeric form of vascular endothelial growth factor (VEGF) protein. FRET and FCS experiments are conducted to determine the characteristics of conformational fluctuations by the ``anti-VEGF'' aptamer (aV) under the two protein conditions, as well as under differing counterionic conditions. It is shown that aV in the absence of VEGF has conformational fluctuations on a relatively fast time scale (single milliseconds to tens of milliseconds), and that these fluctuations are largely counterion dependent, being especially sensitive to Mg$^{2+}$ concentration. While these fluctuations also occur in the presence of VEGF, results show that the dynamics occur on a slower time scale (hundreds of milliseconds to single seconds), indicating that there is indeed an interaction between the aV aptamer and its binding target, VEGF. [Preview Abstract] |
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R1.00093: Scaling Exponents for Polymer Translocation through a Nanopore Kaifu Luo, Tapio Ala-Nissila, Pawel Pomorski, Mikko Karttunen, See-Chen Ying, Aniket Bhattacharya We present results of extensive computer simulations and scaling theory for computing the relevant scaling exponents associated with polymer translocation through a nanopore [1]. We present results for the scaling of the average translocation time and the fluctuation in the reaction coordinate for the case of spontaneous and field-driven translocation in 2D and 3D. The models used include: (i) the fluctuating bond model with single-segment Monte Carlo moves, (ii) Langevin dynamics, and (iii) GROMACS MD simulations using the bead-spring model for flexible polymers without an explicit solvent. We contrast our results to the recently presented alternate theories for polymer translocation [2,3]. \\ \noindent{\footnotesize{ 1. K. Luo {\em et al.}, J. Chem. Phys. {\bf 124}, 034714 (2006); {\bf 124}, 114704 (2006); {\bf 126}, 145101 (2007); Phys. Rev. Lett. {\bf 99}, 148102 (2007); I. Huopaniemi {\em et al.}, J. Chem. Phys. {\bf 125}, 124901 (2006); Phys. Rev. E {\bf 75}, 061912 (2007); K. Luo {\em et al.}, e-print arXiv:0709.4615.\\ 2. J. K. Wolterink {\em et al.}, Phys. Rev. Lett. {\bf 96}, 208301 (2006); D. Panja {\em et al.}, J. Phys.: Condens. Matter {\bf 19}, 432202 (2007).\\ 3. J. L. A. Dubbeldam {\em et al.}, Europhys. Lett. {\bf 79}, 18002 (2007); Phys. Rev. E {\bf 76}, 010801 (2007).}} [Preview Abstract] |
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R1.00094: Stretch-Induced density fluctuations in glassy polymers Mikihito Takenaka, Shotaro Nishitsuji, Shimizu Hirofumi, Shin'ya Yoshioka Glass materials are hard but fragile. The fragileness of glass strongly depends on its processing and the heterogeneity developed during the processing in glass materials may be important in its destruction under deformation. However, the mechanism how the heterogeneity develops into cavitation or cracking is not well understood. Here we show that the stretch induced the violation of the incompressibility by the coupling between the stretch and density fluctuations due to the strong density dependence of viscosity in glassy polymer. We demonstrate that the small-angle X-ray scattering intensity of a glassy polymer increases with stretch and exhibits so-called butterfly pattern. This butterfly pattern agrees with that calculated with the Navier-Stokes equation including the density dependence of viscosity proposed by Furukawa and Tanaka [Nature, 443, 434 (2006)]. Moreover, the shear-thinning behavior agrees with the simulation results with the Navier-Stokes equation. Our results explored that the origin of the cavitation of glassy polymer is the violation of the incompressibility by the coupling between the stretch and density fluctuations. [Preview Abstract] |
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R1.00095: Functionalized polymeric nanotubes Cecile Malardier-Jugroot New nanomaterials already play a key role in several emerging technologies such as nanomotors, nanoelectronics and drug delivery. The increased interest in nanotechnology comes from the fact that nanoscale materials have new physical and chemical properties compared to the bulk. Among the methods used to fabricate new nanomaterials, the most successful in producing precise structure, is the bottom-up method which builds the desired products from the atomic or molecular scale by self-assembly. We will present a new self-assembly process of amphiphilic alternating copolymers into nanotubes combining a computational (molecular modeling) and experimental (small angle neutron scattering, atomic force microscopy) characterization. The nanoarchitechture, predicted by numerical methods and characterized experimentally, has an internal diameter of about 28 {\AA} and an external diameter of about 41 {\AA}. In addition, the combined characterization of the nanotube revealed that the interior of the tube is hydrophobic while the exterior is hydrophilic. The self-assembly will be illustrated by the association of poly(styrene-alt-maleic anhydride) and the effect of the functionalization of the polymer chain on the forces stabilizing the nanotubes (hydrogen bonds, $\pi -\pi $ interactions) will be presented. [Preview Abstract] |
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R1.00096: A New Design of Coiled-Coil Helix Bundle Peptide-Polymer Conjugates Jessica Shu, Cen Tan, William DeGrado, Ting Xu Coiled-coil helix bundles, a common tertiary motif found in many natural proteins, underpins many structural and catalytic functions of natural proteins. \textit{De novo }design has shown that the interior of the helix bundle can be tailored to perform well-defined functions, while the exterior dictates the environment in which it is situated. By attaching synthetic polymers to helix bundle-forming peptides, producing peptide-polymer conjugates, the polymer will mediate the interactions between the helix bundle and its environment, enable the macroscopic self-assembly of the bundles, and potentially, allow them to function in non-biological environments. We report a novel design of peptide-polymer conjugates, where upon attachment of polymer to the exterior of the helix bundle stabilizes the peptide secondary and tertiary structures and preserves the built-in function of the bundle. This new design strategy should be applicable to other coiled-coil peptides and shows great promise as an avenue toward peptide-based biomolecular functional materials. [Preview Abstract] |
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R1.00097: Effects of molecular weight and entanglement on the dispersion of a layer of platelets in a polymer chain matrix Barry Farmer, Ras Pandey A stack of thin sheets (a model for clay platelets) is initially placed in a matrix of polymer chains. How the dynamic polymer chain matrix (purely entropic constraints) affects the dispersion of sheets is the subject of this computer simulation study. A stack of four sheets constitutes the layer with a small initial inter-layer distance on a discrete lattice. A fraction of the lattice sites are randomly occupied by the polymer chains. Both sheets and chains are modeled by the bond-fluctuation mechanism. Coarse-grained chains and platelets interact and execute their stochastic motion via Metropolis algorithm. Dispersion of the sheets is examined by varying the molecular weight of the polymer chains which form the dynamic network, including entanglements. The relaxation time for dispersion increases on increasing the molecular weight. Exfoliation almost ceases in a matrix with chains beyond a certain length. [Preview Abstract] |
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R1.00098: Numerical Self-Consistent Field Theory of Flat and Curved Polymer Thin Films Tanya L. Chantawansri, Carlos J. Garcia-Cervera, Hector D. Ceniceros, Glenn H. Fredrickson Using self-consistent field theory, we explore the numerical methods and boundary conditions involved in modeling the self-assembly of inhomogeneous polymer thin films deposited on flat and curved substrates. The model is simulated using a fourth-order accurate spectral collocation method first used by Cochran et al. [Macromolecules 2006, 39, 2449-2451] to model bulk polymeric systems, but where we apply finite difference approximations and non-periodic boundary conditions for the film in the direction normal to the substrate. Boundary conditions are employed to model experimentally relevant substrate conditions such as a ``neutral'' or attractive bounding surface. For a neutral surface where the substrate has no preferential attraction to either polymer segment, it is appropriate to utilize Neumann boundary conditions, while a surface with a preferential attraction can be modeled using Robins or mixed boundary conditions. [Preview Abstract] |
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R1.00099: Topologically constrained polymer collapse Alexander Grosberg, Thomas Vettorel, Kurt Kremer Linear polymer chains in an equilibrium melt are strongly entangled, and coils strongly overlap. Similarly, collapsed (globular) single chain is strongly self-entangled in equilibrium. It is a fundamental question of polymer physics - what happens if the formation of these entanglements or self-entanglements is either completely prohibited or strongly slowed down (like in a melt of unconcatenated rings, in a gel, etc). We address this question by massive Monte Carlo simulation based on the use of non-local moves which dramatically speed up relaxation while strictly preserving the topology. The effects of topologically supported separation of chains, or parts of the same chain, have far reaching applications ranging from gel collapse, to interphase chromosome territories, to statistics of knots in proteins. [Preview Abstract] |
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R1.00100: Target Finding Time for Microtubules Interacting with Catastrophe-Suppressing Drugs Mitra Shojania Feizabadi Target finding time for microtubules interacting with catastrophe-suppressing drugs is investigated in this study. In the steady state of microtubules interacting with catastrophe-suppressing drugs, two types of microtubules exist, one with drug tips and the second without drug tips. This work shows that microtubules in the first group are slower in finding a target than are those in the second group. This result is consistent with experimental findings. [Preview Abstract] |
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R1.00101: Stability of Fddd structure in diblock copolymer Myung Im Kim, Satoshi Akasaka, Tsutomu Wakada, Mikihito Takenaka, Hirokazu Hasegawa Recently we reported a new bicontinuous microdomain morphology with the symmetry of Fddd space group found in a polystyrene-\textit{block}-polyisoprene (PS-PI) diblock copolymer with M$_{n}$ = 2.64 x 10$^{4 }$g/mol and f$_{PI }$= 0.638 (\textit{Macromolecules} 2007, 40, 4399). The SAXS profile observed for this polymer coincided with that of the Fddd structure reported for PI-PS-PEO triblock terpolymers (\textit{Macromolecules} 2002, 35, 7007). To examine the reproducibility and stability of the Fddd structure in PS-PI diblock copolymers, we synthesized four different PS-PI diblock copolymers (S1-S4) with slightly different compositions and molecular weights from that previously reported. We investigated the microdomain structures of S1-S4 as a function of temperature in situ by SAXS and for the quenched samples by TEM. All four samples exhibited the Fddd structure in different temperature ranges and order-order transitions (lamella-Fddd-gyroid or Fddd-gyroid) as well. Although the temperature ranges of the Fddd structure are narrow, prolonged annealing in the temperature range did not alter the morphology suggesting the thermal stability of the Fddd structure. Thus, we could confirm the reproducibility of the Fddd structure, which is stable in the temperature range between lamellar and gyroid morphologies. [Preview Abstract] |
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R1.00102: APPLICATIONS |
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R1.00103: Using radar waves to image subsurface heterogeneities: a case study from Randolph College, VA Tatiana Toteva, Reeju Pokharel, Archana Datta A 2D ground penetrating radar survey at 250 MHz central frequency was conducted on Randolph College's campus, in Lynchburg, VA. The experimental setup consisted of three radar profile lines, each with length of 70 -- 100 m. The goals of the project were to image subsurface heterogeneities, and define depth to bedrock. Conventional seismic refraction conducted earlier at the side revealed irregular topography of the subsurface and high degree of uncertainty in the arrival times of the elastic waves. Radar surveys have the potential to provide much higher resolution images. We observed a number of point reflectors and multiple layering of the subsurface soil. [Preview Abstract] |
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R1.00104: Integrated Detector for Ballistic Electron Emission Luminescence Biqin Huang, Jing Xu, Ian Appelbaum Ballistic electron emission luminescence (BEEL) uses injected hot electrons to induce interband transitions and light emission in semiconductor collectors. Local hot electron injection and rastering from a scanning tunneling probe can therefore potentially provide a means to image buried luminescent layers. However, a sensitive photon detector is required to compensate for low external efficiency. We have directly integrated a Si photodetector to a GaAs/AlGaAs BEEL structure by UHV thin-film metal wafer bonding. This room-temperature technique overcomes index mismatch and numerical aperture problems associated with far-field detection. We expect this method will make BEEL microscopy generally applicable to the study of buried luminescent layers in light emitting devices based on arbitrary material systems. THis work is funded by US DOE. [Preview Abstract] |
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R1.00105: Reduced Contact Resistance in Quantum Cascade Lasers Matthew Escarra, Scott Howard, Anthony Hoffman, Claire Gmachl Quantum cascade (QC) lasers have shown tremendous potential as powerful and compact mid-infrared light sources. However, improvement in the high-efficiency operation of these devices must be made for their transfer to real-world utilization. The internal, current, voltage, and optical efficiencies all must be maximized. In particular, high voltage efficiency requires minimizing the voltage defect in the quantum design and parasitic voltage dropped elsewhere in the device. The majority of this parasitic voltage lies in the metal-semiconductor contact junctions. To study this contact resistance, we designed and fabricated a QC laser structure without the active lasing region. Rapid thermal annealing (RTA) on this ``empty'' structure shows a 35.2{\%} reduction in contact resistance at room temperature, which would correspond with a 7{\%} improvement in laser wall-plug efficiency. Different annealing conditions were tested in order to optimize this reduction. Varying contact metallization and top growth also holds the potential for further reduction in contact resistance and improvement in QC laser efficiency. [Preview Abstract] |
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R1.00106: Quantum-Dot Photodetectors: High Sensitivity due to Controllable Kinetics Andrei Sergeev, Li-Hsin Chien, Nizami Vagidov, Vladimir Mitin Comparing to the quantum wells, the quantum-dot structures provide more opportunities to control electron kinetics and to optimize operating regimes of quantum-dot photodetectors. At room temperatures, the photoelectron capture in quantum-dot structures is determined by the electron diffusion in the potential of intentionally or unintentionally charged quantum dots1. Therefore, the capture time can be drastically increased by a proper choice of geometry of the quantum-dot structure and modulation doping. Suppression of capture processes provides longer lifetimes of photoelectrons, thus increasing the photoconductive gain and responsivity. Here we exploit a model of the QD detectors operating at room temperatures and study electron diffusion in the self-consistent field of potential barriers surrounding quantum dots. Using the Monte-Carlo method and analytical evaluations, we investigate photoelectron capture and transit processes as functions of the quantum dot positions, sensor geometry, and external electric field applied. Finally, we calculate the photoconductive gain and discuss the optimal structures and regimes. [1] A. Sergeev, V. Mitin, and M. Stroscio, Physica B 316-317, 369 (2002). [Preview Abstract] |
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R1.00107: Cascaded Emission Regions in 2.4 $\mu$m GaInAsSb Light Emitting Diode's for Improved Current Efficiency John Prineas, Jeff Yager, Jonathon Olesberg, Chuanshun Cao, Madhu Reddy, Chris Coretsopoulos Infrared optoelectronics play an important role in sensing of molecules through characteristic vibrational resonances that occur at those wavelengths. For molecules in aqueous and at room temperature, where optical transistions tend to be broad, the broadband emission of light emitting diodes (LEDs) are well suited for obtaining molecular absorption spectra. The 2-2.6 $\mu$m range is an advantageous range for sensing of glucose. Voltages available in batteries and control electronics are limited to much higher voltages than those required to turn on an infrared LED, and moreover have limited current supply. Here, we demonstrate room temperature operature of 5-stage cascaded emission regions in 2-2.6 $\mu$m GaInAsSb LEDs. We report three times higher turn on voltage, and nine times improved current efficiency compared to a single stage device. [Preview Abstract] |
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R1.00108: Surface charge effects on the plasmonic band gap of metallodielectric gratings Ian Foti-Landis, Paul White, Jennifer Steele Surface plasmon resonances of both metal nanoparticles and metal surfaces are highly sensitive to changes in their dielectric environment. The changes in surface plasmon resonance due to target molecules binding to the metal have been found to be caused by both a local change in dielectric environment as well as changes in the surface chemistry of the metal. The majority of investigations of these competing effects have primarily been limited to the localized surface plasmon resonances of metal nanoparticles. Here, the effects of surface chemistry on surface plasmons will be investigated using metallodielectric gratings. This periodic geometry supports traveling surface plasmon waves that show a plasmonic band gap in the dispersion relationship when two counterpropagating waves are simultaneously excited. The band gap energy changes in response to chemical functionalzation, giving unique information on how the surface chemistry affects the surface plasmon resonance. This work focuses on the effect of charged species as a function of pH. [Preview Abstract] |
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R1.00109: Electric field controlled left-handed-materials lens S.V. Bely, R.V. Petrov, M.I. Bichurin, A.V. Filippov, G. Srinivasan Microwave lenses are useful for scanning and multi-beam antennas of radar systems, telemetries, and radio-astronomy of the cm and mm-wave bands. The development of electric and/or magnetic field controlled lenses using magnetoelectric material would facilitate improvement if the antenna technologies. We designed such lenses consisting of metal resonators on dielectric substrates with the control elements made of yttrium iron garnet and PZT. The control is based on the variation of magnetic permeability of the ferrite via the electric potential applied to piezoelectric. It results in change in the parameters of transmitted microwave--beam and focal length of the lens. The lens works in cm-wave band. The gain factor of the lens is 6 dB. Theoretical estimates and optimization of the lens parameters were also carried out. [Preview Abstract] |
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R1.00110: Design,fabrication and FEM simulation of a novel Optical-MEMS sensor Vaibhav Mathur, Jin Li, William Goodhue Optical waveguides are used in a variety of telecommunications systems to route, add or drop optical signals from the network. Here a combination cantilever/waveguide structure is proposed as the core element of either a vibration/shock sensor or light modulator. An AlGaAs layered dielectric waveguide is fabricated on GaAs substrates and undercut to form a suspended beam. The suspended AlGaAs waveguide is micro-cleaved to produce cantilever segments of equal or unequal lengths, corresponding to either the same or different fundamental frequencies resonance (as the natural frequency is a function of length).The sample is vibrated using a piezo driver. If the vibration frequency supplied to the chip is near one of the resonances the waveguide becomes periodically misaligned as the cantilever displacement amplitude builds up causing a periodic loss in signal at the output end of the guide. In this work cantilever/waveguide structures are fabricated and a detailed FEM(Finite element method) analysis of the device carried out. Also wave propagation and subsequent optical misalignment simulation is carried out on the FEM based COMSOL Multiphysics Package. [Preview Abstract] |
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R1.00111: Automation of analysis of electronic microscope images Gagik Shmavonyan Many-sided analysis of multiple images of electronic microscope is a hard and time-consuming process. Besides, the analyses become more actual in the case of distorted, not high quality images of electronic microscopes, i.e. images of scanning tunneling microscope. To increase the accuracy and velocity of analyses a method is suggested, which allows analyzing the surface of semiconductor crystal. The method allows to get information on the position of the atoms of the 1$^{st}$, 2$^{nd}$ and 3$^{rd}$ crystallographic planes, analyze surface defects and dislocations, differentiate two and more materials on the surface, determine surface reconstruction or atomic structure, etc. [Preview Abstract] |
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R1.00112: A 100 MHz antenna based on magnetoelectric composite materials A.S. Tatarenko, R. Petrov, G. Srinivasan, M.I. Bichurin Results on miniaturization of a 100 MHz-antenna based on magnetoelectric composites are presented. A composite with large and equal permittivity and permeability is sought for the task. In such composites both miniaturization and impedance match to free-space are possible. A sample of nickel zinc ferrite and bismuth strontium titanate prepared by the conventional ceramic processing is used. The dipole antenna operating at 100 MHz consists of a composite substrate 220 mm in diameter and 8.5 mm in width and a Cu-strip 6.5 mm in diameter. Antenna characteristics are measured with a vector network analyzer. Scattering parameter data indicates resonance at 98 MHz and an antenna miniaturization factor of 7-10, in agreement with theoretical estimates. [Preview Abstract] |
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R1.00113: Magnetoelectric Composites for 1.3 GHz Antennas R.V. Petrov, A.S. Tatarenko, G. Srinivasan, M.I. Bichurin A microstrip miniaturized antenna based on magnetoelectric composite has been designed and characterized. Theoretical estimates of antenna properties are given. To miniaturize UHF antennas, one needs slow-wave topologies and magneto-electric (ME) materials with equal and high permeability and permittivity. Nickel Zinc Ferrites (Ni$_{1-x}$Zn$_{x}$Fe$_{2}$O$_{4}$, x=0-0.5, NZFO) are potential candidates for use as the magnetic phase in the composite since they have high permeability, in the range 4-50, and low magnetic loss tangent. The dielectric phase use is bismuth strontium titanates (Sr$_{1-1.5x}$Bi$_{x}$TiO$_{3}$, 0.04$<$x$<$0.25, BST) that have high permittvity and low dielectric loss tangent. A sample with nickel zinc ferrite and 2{\%}~BST is used. A microstrip dipole element of 47 mm in length and 2 mm in width is placed on a composite substrate with dimensions 65 x 40 x 2.2 mm$^{3}$. The other side of the substrate has a metal ground plane. Measurements of transfer scattering parameter S$_{21}$ are made. A miniaturization factor of 5-10 is achieved. The miniaturization methodology discussed here is useful for mobile communication platforms, radar systems, and remote-controlled ground based systems. [Preview Abstract] |
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R1.00114: A magnetoelectric composite based microwave phase shifter M.I. Bichurin, V.M. Petrov, G. Srinivasan Magnetoelectric (ME) properties of ferrite-ferroelectric composites arise from their response to elastic and electromagnetic force fields. The unique combination of magnetic, electrical, and ME interactions opens up the possibility of electric field tunable ferromagnetic resonance (FMR) based devices [1]. Here we discuss an ME phase shifter operating in the FMR region at 9.3 GHz. A slot line on a yttrium iron garnet film bonded to lead zirconate titanate (PZT) provides a basis for the phase shifter. The circularly polarized microwave magnetic field of the slot line interacts with the ferrite and causes variation of phase velocity with the controlling magnetic and electric fields. Electrical tuning is realized with the application of a control voltage due to PZT. The estimated phase shift per unit length and unit voltage is to 20 deg/cm kV for a PZT thickness of 0.5 mm. 1 S. Shastry and G. Srinivasan, M.I. Bichurin, V.M. Petrov, A.S. Tatarenko. \textit{Phys. Rev. B}, 70 064416 (2004). - supported by grants from the Office of Naval Research and the Russian Foundation for Basic Research. [Preview Abstract] |
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R1.00115: Development of a Capacitive Measurement Apparatus for Steel Alloy Magnetostriction Christopher L. Milby, Joseph L. Wiewel, Matthew W. Beckner, Mark S. Boley In our laboratory we have developed steel alloy torque transducers that operate via a magnetoelastic principle, converting applied stress to an external magnetic field signal subsequent to appropriate magnetic pre-conditioning. We have found that linearity, repeatability, and sensitivity of these transducers is highly dependent on the nickel and chromium content of these alloys which is directly linked to the extent that these materials enhance or degrade the ``engineering magnetostriction coefficient'' of the alloy; therefore its measurement is fundamental to the application of these alloys. In our present apparatus, we applied a large current to produce a saturating axial magnetic field in the sample, which was physically connected to change the capacitance between two large adjustable plates, then related this change to a capacitance bridge voltage to ascertain a sample dimensional change on the order of ppm. Values agreeing with previously measured coefficients were found for pure nickel, while values in qualitative agreement with the magnetoelastic sensitivity of several steel alloys applied in magnetic torque sensing technology were also found, confirming that our apparatus can predict the optimal materials for magnetic torque sensing. [Preview Abstract] |
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R1.00116: Determining Optimal Austenitizing and Tempering Temperatures and Quenching Media for a Steel Torque Transducer Joseph L. Wiewel, Christopher L. Milby, Matthew W. Beckner, Mark S. Boley In our laboratory we have developed a series of high-stress steel alloy magnetoelastic torque transducers that convert applied stress to an external magnetic field signal. We have found that linearity, repeatability, and sensitivity of these transducers is highly dependent on the heat treatment to which the steel is subjected, which is severely limited by the minimum hardness coefficients that will be required in the actual technological application such as in a power delivery shaft. In our study, we focused on cases where Rockwell hardness coefficients in the forties or low fifties are expected, using a steel alloy with low nickel and chromium content. Austenitizing temperatures varied from 775 to 870 Celsius, while tempering temperatures varied from 205 to 540 Celsius, all in a helium atmosphere. The quenching medium following the austenitizing and tempering processes varied between oil and water. The study showed that a tempering temperature around 425 Celsius resulted in the best linearity and re-zeroing capabilities (repeatability) of the transducers, also corresponding to the least hysteresis. Additionally, water quench reduced sensitivity as compared to oil quench at the same temperature. [Preview Abstract] |
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R1.00117: Liquid Supramolecular NanoStamping (LiSuNS) Arum Amy Yu, Francesco Stellacci The development of high resolution bio-devices has generated a demand for the development of novel printing techniques able to minimize fabrication time and labor. Supramolecular NanoStamping (SuNS) is a stamping method that can copy single-stranded DNA features in a sequence specific way in only three steps: a master containing single stranded DNA features is immersed in a solution of complementary DNA (cDNA) molecules modified with a chemical group at the end (Hybridization). Another substrate is placed onto the hybridized master so that a chemical bond can form between cDNA and the secondary substrate (Contact). The two substrates are then separated by heating or mechanical force and a copy composed of cDNA is left on the secondary substrate (Dehybridization). However, like all other contact printing techniques, SuNS' efficiency highly depends on the roughness of the substrates used. Here, we present an extension of SuNS, Liquid Supramolecular NanoStamping (LiSuNS). LiSuNS eliminates the need of contact between two solid substrates by introducing a liquid prepolymer that is cured after contact. Using LiSuNS, we achieved large coverage $>$10cm\^{}2. Moreover, because LiSuNS prints 3-D physical information as well as 1-D chemical information (i.e DNA sequences), it can be used to generate a complete DNA-based bio-device with 3-D physical shape (e.g. channels) and chemically modified patterns. [Preview Abstract] |
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R1.00118: The Application of Supramolecular Nanostamping (SuNS) to the Replication of DNA Nanoarrays Ozge Akbulut, J. Jin-Mi, Ryan D. Bennett, Ying Hu, Hee-Tae Jung, Robert E. Cohen, Anne M. Mayes, Francesco Stellacci The present spot size for DNA microarrays is on the order of micrometers. However, there is a need for smaller arrays to allow the detection of smaller volumes of analytes. Although, SPM-based techniques are capable of fabricating nanoscale bio-arrays, such fabrication methods are serial in nature and consequently slow and expensive. A recently introduced method, Supramolecular Nanostamping (SuNS) can overcome this problem by replicating DNA microarrays. In SuNS, a master (i.e. a DNA microarray made of DNA features immobilized onto a surface) is hybridized with its complementary DNA molecules terminated with `sticky' end groups. A secondary surface is then placed onto the hybridized master to allow for bond formation with the `sticky ends' of the complementary DNA. Afterwards, the master and the secondary surface are separated using heat or mechanical forces effectively achieving a replica of the original DNA array. Here, we demonstrate the application of SuNS to DNA nanoarrays proving that SuNS can reproduce DNA arrays with features as small as 14 $\pm $ 2 nm spaced 77 $\pm $ 10 nm. Moreover, we show that hybridization of these nanoarrays can be detected using AFM in a simple and scaleable way that does not require labeling of the DNA strands. [Preview Abstract] |
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R1.00119: Compact Four-Wavelength Quantum Cascade Laser Source for Multi-Wavelength Spectroscopic Systems Fatima Toor, Scott Howard, Claire Gmachl Quantum cascade laser (QCL) technology in the mid-infrared wavelength range has great potential for applications in environmental trace gas sensing. QCL-based spectroscopic techniques have been developed by several research groups [1]. However, more research work is needed to make QCL-based spectroscopic techniques more sensitive while being compact and field deployable. Here we propose a QCL source that can emit four wavelengths of light at ambient temperature and can be mounted on a single chip. The four QCL wavelengths are $\lambda $ = 7$\mu $m, 9$\mu $m, 11$\mu $m and 13$\mu$m essentially covering the second atmospheric transmission window. The four-wavelength QCL source is designed using a heterogeneous cascade design with two wavelengths each combined in one waveguide. For each two wavelength device, the number of active region and injector stages for the two QCLs are optimized such that each wavelength has equal laser threshold current density. This work was supported in part by MIRTHE (NSF-ERC). [1] Kosterev A., Tittel F. K., ``Chemical sensors based on quantum cascade lasers.'' ~\textit{IEEE JQE Special Issue on QC Lasers}, 38 (2002): 582-591 [Preview Abstract] |
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R1.00120: Effect of optical feedback on high frequency current-driven polarization switching of vertical-cavity surface-emitting lasers Wang-Chuang Kuo, Chuan-Pi Hsu, Da-Long Cheng, Wei Chang, Tsu-Chiang Yen In vertical-cavity surface-emitting lasers (VCSELs) which exhibit polarization switches (PS) in L-I curves, the current-driven polarization switch (CDPS) has been studied extensively, and a cutoff frequency of 90 kHz constrained by the bandwidth of thermal response was reported. In this research, the CDPS with high frequency current modulation and optical feedback were experimentally and theoretically investigated. The experimental results reveal that, with the assistance of polarization-selective optical feedback of about -15 dB, the cutoff frequency of the CDPS could be raised to 50 MHz. A set of rate equations was employed to simulate the enhancement of CDPS and to address the interaction of optical feedback with the PS. These results will help to extend the application of CDPS to even higher frequency. [Preview Abstract] |
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R1.00121: A simple method for determining the wavelength drift of vertical-cavity surface-emitting lasers Da-Long Cheng, Tsu-Chiang Yen Wavelength drift versus current characteristic is one of the important laser characteristics in vertical-cavity surface-emitting lasers (VCSELs). This investigation presents a simple method for determining the wavelength drift with current change. The extremely simple setup merely consists of a neutral-density filter (ND Filter), a photo detectors and a voltage meter. The ND filter is like a Fabry-Perot etalon when the incident angle of the laser approximates to zero. Therefore, the regular oscillations can be observed in the light versus bias current characteristic ($L-I$ curve) of VCSELs. Experimental result shows that the wavelength drift per milliampere of the VCSEL is 0.78 nm/mA. [Preview Abstract] |
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R1.00122: Direct-Write, Deep UV Pattern Definition in PMMA Andrew Spisak, Brian Burke, Keith Williams In this poster presentation, we discuss opportunities for direct-write UV photolithography through metallized apertures defined by focused ion beam on SPM cantilevers. This process offers subwavelength ($<$200nm) feature sizes without the need to generate a mask, and the writing process can take place in fully ambient conditions. In our preliminary work, we have patterned polymethyl methacrylate (PMMA) resist by exposing it with the fifth harmonic (213 nm) of an Nd:YAG source through metallized contact apertures in contact with resist. Interference patterns with both near- and far-field origins were observed. We present a straightforward model for interference effects generated in our process, and discuss our ability to tune these effects and generate subwavelength patterns. [Preview Abstract] |
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R1.00123: Controlling the Random Telegraph Signal in Carbon Nanotube FETs Kenneth Evans, Jack Chan, Keith Williams Random Telegraph Signal (RTS) is quite readily observed in nanotube-channel field effect transistors (NTFETs), even at temperatures approaching 300 K. RTS arises from the population and depopulation of energy levels associated with charge traps along the channel. In this poster presentation, we will discuss the interpretation of RTS spectra as a `molecular barcode' of states associated with specific surface dopants (adsorbates), and we will describe our work to chemically modify the channel in order to control the surface scattering. [Preview Abstract] |
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R1.00124: Synchrotron based measurements of the photoelectron spectrum of CdTe nanoparticles A. Naqvi, S. L. Hulbert, W. Chen, A. H. Weiss A nanoparticle solution of CdTe of size 585 nm was deposited on silicon substrates of approximately 1cm$^{ }$ x 1 cm after etching the substrate with HF. The nanoparticles were exposed to soft x-rays of varying energy under ultra high vacuum, $\sim $10$^{-10 }$torr using beam line U16B at the National Synchrotron Light Source (NSLS) at Brookhaven National Lab. We performed Auger electron spectroscopy measurements on the nanoparticles and identified the peaks through spectroscopic analysis and monitored the damage of the nanoparticles by observing their fluorescence by gradually increasing the photon energy. The nanoparticles were observed to exhibit a time dependent damage response. Future studies aimed at exploring the potential use of nanoparticles as radiation sensitizing agents for cancer treatment are proposed. [Preview Abstract] |
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R1.00125: First principles study of hydrogen storage in non-transition metal decorated graphitic materials Gyubong Kim, Noejung Park, Seung-Hoon Jhi Hydrogen has been considered an ideal material that can replace fossil-based fuels as its byproduct is simply water without emitting green house gases. Recently, transition metal (TM)- dispersed porous materials have been suggested as plausible candidates for hydrogen storages that possess optimal hydrogen binding characteristics. A serious problem in this approach is that TM atoms tend to aggregate instead of being atomistically dispersed, which results in the deterioration of hydrogen uptake. Here we study the hydrogen adsorption on non-transition metal (NTM) atoms dispersed on graphene using ab initio methods. We observe that the clustering energy of NTM atoms is much smaller than that of TM atoms, which indicates that NTM can be almost free of clustering on graphene. We also study hydrogen adsorption on those NTM atoms to find comparable storage capacity to that in TM dispersed graphene. [Preview Abstract] |
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R1.00126: Theoretical study of the structural, mechanical, and electronic properties in hydrides Ryoji Sahara, Bun Tsuchiya, Hiroshi Mizuseki, Shinji Nagata, Tatsuo Shikama, Yoshiyuki Kawazoe Although an understanding of the mechanical behavior such as elastic properties and hardness of hydrides is important for their applications, theoretical studies have received little attention and only recently some progress has been made. In the present study, first-principles calculations have been performed on hydrides of Ti, Zr, and Hf. The elastic properties are estimated as a function of hydrogen concentration. Equilibrium lattice constants and the bulk moduli are estimated using Murnaghan EOS. While, the elastic constants, shear moduli, and Young's moduli are estimated introducing the strain tensor. The origin of these properties is explained in terms of the changes in the bonding characters as well as cohesive energy. A semi-empirical relationship between the bulk modulus/shear modulus and the Vickers hardness is introduced to predict hardness of these materials from the present first-principles calculation results. [Preview Abstract] |
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R1.00127: The crystal structure of $^{7}$Li$_{2}$ND Masami Tsubota, Magnus H. Sorby, Satoshi Hino, Takayuki Ichikawa, Bjorn C. Hauback, Yoshitsugu Kojima Recently much attention has been given to reversible hydrogen storage materials possessing high gravimetric capacity. Lithium amide/imide systems are promising candidates. Chen \textit{et al.}[1] found that a mixture of lithium amide and lithium hydride can reversibly store hydrogen up to 6.5 mass{\%} forming lithium imide (Li$_{2}$NH). Among them, the crystal structure of Li$_{2}$NH is still controversial. Balogh \textit{et al.}[2] have reported a cubic structure model. However, this model differs significantly from theoretical structure models. In this work, the crystal structure of the isotopically substituted $^{7}$Li$_{2}$ND has been investigated by powder neutron and synchrotron X-ray diffraction experiments. In our data some peaks, which should be a single peak for cubic symmetry, were obviously split indicating a lower symmetry than cubic for lithium imide. The structure of $^{7}$Li$_{2}$ND will be described. [1] P. Chen \textit{et al}., J. Phys. Chem. B \textbf{107} (2003) 10967. [2] M.P. Balogh \textit{et al.}, J. Alloys Compd. \textbf{420} (2006) 326. [Preview Abstract] |
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R1.00128: Hydrogen Accumulation inside Single-Walled Carbon Nanotubes Encapsulated in a Pd Matrix A. Lipson, C. H. Castano Giraldo, B. F. Lyakhov, E. I. Saunin, A. Yu. Tsivadze Palladium metal possesses the unique property of dissociating molecular hydrogen into an atomic form while simultaneously exhibiting high H-diffusivity, while single-walled carbon nanotubes (SWCNTs) have been actively explored during the last decade as an effective hydrogen storage medium. We report a study of hydrogen storage in which electrochemical hydrogen loading of this material provides reproducibly high net capacity of SWCNT (reduced to hydrogen content in the Pd matrix). The synergetic effect has been achieved by encapsulating Single-Walled Carbon Nanotubes in thin Pd layers on a Pd substrate creates resulting from the combination of the Pd and the SWCNTs properties with regards to hydrogen. [Preview Abstract] |
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R1.00129: Multimetal plasmonic nanomaterials for solar energy harvesting Ramki Kalyanaraman, Justin Trice, Radhakrishna Sureshkumar, Hernando Garcia Efficient broadband solar absorbing coatings could significantly enhance the performance of Si solar cells. Here, we present the design of novel SiO$_{2}$-based nanomaterial coatings based on multimetal plasmonic absorption. By implementing an efficient homogenization procedure based on the tight lower bounds of the Bergman-Milton formulation {[}Garcia et al. Phys. Rev. B, 75, 045439 (2007)], we have predicted the absorption coefficient of a quaternary nanocomposite consisting of Cu, Ag, and Au nanospheres embedded in a SiO$_{2}$ host matrix. A simulated annealing algorithm was used to predict nanocomposite properties (particle size and volume fractions) which result in a broadband absorption (350 - 800 nm) that matches the shape of the solar emission. These results show that novel optical materials can be made from multimetal-dielectric nanocomposites. [Preview Abstract] |
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R1.00130: ABSTRACT WITHDRAWN |
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R1.00131: Relation between Packing Density and Thermal Transitions of Alkyl Chains on Layered Silicate and Metal Surfaces Hendrik Heinz, Richard A. Vaia, Barry L. Farmer Characterization through experiment and simulation shows that the orientation of the alkyl layers and reversible phase transitions on heating are a function of the cross-sectional area of the alkyl chains in relation to the available surface area per alkyl chain (packing density). On even surfaces, a packing density less than 0.2 leads to nearly parallel orientation of the alkyl chains on the surface, conformational disorder, and no reversible melting transitions. A packing density between 0.2 and 0.75 leads to intermediate inclination angles, semi-crystalline order, and reversible melting transitions on heating. A packing density above 0.75 results in nearly vertical, lattice-like alignment of the surfactants on the surface and no reversible melting transitions. The same principle applies to curved surfaces, taking into account a local radius of curvature and a distance dependent packing density on the surface. The chain length (minimum C10) and interface chemistry have little impact on this behavior but determine chemical functionality and transition temperatures. [Preview Abstract] |
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R1.00132: Characterization of iPP/CNT PCN through Transmission Ellipsometry Georgi Georgiev, Yaniel Cabrera, Mark Cronin, Christopher Rocheleau, Brian Feinberg, Peggy Cebe Microscopic Transmission Ellipsometry is a fast and efficient technique for studying anisotropic organization in polymers. Polymer Carbon Nanotube Composites (PCNs) are the largest commercial application of carbon nanotubes (CNT) in nanotechnology. Isotactic Polypropylene (iPP) is one of the best model systems to study in this field because iPP/CNT PCNs can form alpha, beta, and gamma crystallographic phases under a variety of crystallization conditions: nonisothermal and isothermal melt crystallization, shear, stress, fiber extrusion, etc. The morphological structure and the orientation of the crystals can also be finely controlled under those conditions. We complement Microscopic Transmission Ellipsometry studies with other techniques: Differential Scanning Calorimetry, X-ray scattering and dielectric spectroscopy. [Preview Abstract] |
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R1.00133: Effects of Molecule-Electrode Binding on Molecular Junctions Peter Doak, Jon Malen, Kanhayalal Baheti, Arun Majumdar, Rachel Segalman, Don Tilley Measurements of the Seebeck coefficient or thermopower of metal-molecule-metal junctions offer additional insight into single molecule transport. By applying a temperature bias across a junction created via an Au-Au STM break junction a thermoelectric voltage can be measured which is related to the transmission function through a derivative. Previously dithiol molecules have been studied by this method. Here, the effects of altering the binding to the electrodes will be demonstrated. When the binding group is altered to cyano or amine functionalities, the thermopower is greatly affected suggesting markedly different behavior in response to tuning of molecular energy levels. This indicates important changes in the junction transmission functions near the chemical potential of the contacts. For example, we show that measurements of dinitrile molecules cannot be interpreted as simple shifts of a single Lorentzian transmission peak across the contact chemical potential. Additionally these measurements show that the binding groups can have considerably more influence on junction behavior than other forms of molecular functionalization and provide a useful means to interrogate theories of junction transport. [Preview Abstract] |
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R1.00134: Controlled one dimensional poly (3-hexythiophene) nano fiber for high performance organic field effect transistor Sung Won Lee, Unyong Jeong We demonstrate here how to fabricate cylinder shape, one dimensional organic field effect transistor for high performance field effect transistor device. To reduce the size and increase component density in circuit we used electro-spinning as a fabrication method. Coaxial nozzle was used for cylindrical semiconductor and gate insulator defines. Regio-regular Poly (3-hexythiophene) and poly vinyl phenol was used as semiconductor and gate insulator respectively. Electrical performance is not reported here because of environmental instability. However, we expect good electrical performance will be shown shortly because this device form cylindrical conduction channel compare to thin film type field effect transistor. Here we propose electro-spinning is an easy one step process to fabricate one dimensional polymer field effect transistor. [Preview Abstract] |
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R1.00135: Low-temperature characterization of organic conducting thin films Gregory Topasna, Daniela Topasna Conducting polymer thin films were investigated at low temperatures. We present results for such a spin coated film made of poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) which was tested for temperatures below 20 \r{ }C. The film was probed over several cycles of cooling then heating. For each cycle the results showed a similar temperature dependent resistance. Such polymer thin films have potential applications as flexible temperature sensors. [Preview Abstract] |
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R1.00136: Electronic properties of adjoined TiO2 nanocrystals O. Diwald, M.J. Elser, N. Siedl, J. Bernardi The discussion of particle attachment effects is indispensable for deeper insights into electronic conduction across grain boundaries and thus essential to photovoltaics. We investigated the condensation of isolated TiO$_{2}$-nanocrystals [1] induced via the application of a simple hydration-dehydration cycle. The resulting particle network shows a mesoporous structure as well as significant changes in the optical absorption properties as investigated by UV-diffuse reflectance spectroscopy. In addition, polarizable conduction band electrons are only observed in the network which consists of adjoined TiO$_{2}$-nanocrystals [2]. Since photo-assisted tunneling between localized states in the oxide particle network represents an important conduction mechanism in dye-sensitised solar cells, UV induced charge separation processes were studied on nanocrystal aggregates using EPR and IR spectroscopy. Corresponding results will be discussed in the light of associated structural data. [1] Berger et al. Chem. Phys. Chem. 2005 6 2104-2112 [2] Elser et al. J. Phys. Chem. B 2006, 110, 7605 [Preview Abstract] |
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R1.00137: Photooxidation of Acetone and Butanone on Rutile TiO$_{2}$ (110) Daniel P. Wilson, David Sporleder, Michael G. White Interest in the photooxidation of organic compounds on heterogeneous surfaces such as TiO$_{2}$ has increased in recent years. Here, acetone and butanone, two common organic ketones, are studied under UHV conditions to determine what fragmentation occurs during photooxidation and to gain insight as to the predictability of desorbing species. The data was collected using a pump-probe time-of-flight (TOF) method. Excitation occurs via exposure to 3.7 eV photons followed by ionization with 13.05 eV photons. Preheating the surface to $\sim $200K facilitated the formation of an organic-diolate species needed for photoactivity. During butanone photooxidation, different desorption mechanisms between mass 30 and masses 27-29 are evident. Background thermal results and preliminary translational energy distributions are calculated for acetone and some butanone fragments and are presented here. [Preview Abstract] |
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R1.00138: Ultrafast Carrier Dynamics in Water-Splitting Photocatalysts Elizabeth Carroll, Owen Compton, Michael Sarahan, Frank Osterloh, Delmar Larsen Semiconductors that photocatalytically split water into hydrogen and oxygen using solar energy represent promising renewable energy technologies. Charge carrier dynamics on sub-nanosecond timescales dictate the overall efficiency of charge separation, and consequently, photocatalytic activity of these materials. Using transient absorption spectroscopy, we investigated photoexcited carrier trapping, recombination, and interfacial charge transfer dynamics in water-splitting niobate nanosheets. Ca$_{2}$Nb$_{3}$O$_{10}$ generated H$_{2}$ from water with 0.22{\%} quantum yield, but no O$_{2}$ was formed. Carriers relaxed with second-order kinetics on a sub-nanosecond time scale that depended on the nanosheet size. Methanol was used as a sacrificial donor to separate electron and hole dynamics and identify absorption spectra for the trapped carriers. In aqueous methanol, hole scavenging was observed within 100 ps in direct competition with electron-hole recombination. The nanosheets were also functionalized with metal and semiconductor nanoparticles to form novel photocatalyst nanostructures. Colloidal IrO$_{2}$ was attached to Ca$_{2}$Nb$_{3}$O$_{10}$ to sensitize the catalyst for visible light absorption. Interfacial electron transfer stabilized the charge separation in IrO$_{2}$, and O$_{2}$ was generated. [Preview Abstract] |
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R1.00139: Applications of Physics to Measuring and Improving the Performance of Buildings in Hot, Humid, Hurricane-Prone Climates Norman Witriol, Myron Katz, Christophor Faust, Jinson Erinjeri In this presentation we will present topics showing how physics can be applied to measuring and improving the performance (energy efficiency and durability of the structure, health, safety, and comfort of the occupants) of buildings in hot, humid, hurricane-prone climates representative of the climate in New Orleans and the Gulf Coast. [Preview Abstract] |
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R1.00140: Modeling of Magnetic Field Assisted Assembly Rene Rivero, Shanmugamurthy Fnu, Gaurav Devrani, Vijay Kasisomayajula, Michael Booty, Anthony Fiory, Nuggehalli Ravindra A simplified model of the magnetic field assisted assembly process is presented and developed. Objects are moved by magnetic forces into an assembled pattern such as into an array of recesses. All the forces involved in the assembly process are considered in the model. An example in which an object comes in contact with the recess and settles into it in order to initiate the modeling process is illustrated. Experimental techniques for the assembly process with an optimal control system with feedback is described. The results of the study are analyzed in relation to applications in fabricating heterogeneous systems. [Preview Abstract] |
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R1.00141: Probing molecules in integrated silicon-molecule-metal junctions by inelastic tunneling spectroscopy. Wenyong Wang, Adina Scott, Nadine Gergel-Hackett, Christina Hacker, David Janes, Curt Richter A hybrid technology where molecular devices are integrated with traditional semiconductor microelectronics is a promising approach for future electronic applications. Key challenges in this area include developing devices in which the molecular integrity is preserved and identifying in-situ characterization techniques to probe the molecules within the completed devices. In this study, we present the first experimental report of inelastic electron tunneling spectroscopy of integrated metal-molecule-silicon devices with molecules assembled directly to silicon contacts. The results provide direct experimental confirmation that the chemical integrity of the monolayer is preserved and that the molecules play a direct role in electronic conduction through the devices. Spectra obtained under varying measurement conditions show differences related to the silicon electrode, which can provide valuable information about the physics influencing carrier transport in these molecule/Si hybrid devices. [Preview Abstract] |
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R1.00142: Watching electrons tunnel Simon Moser To get insight to time resolved inner atomic or molecular processes, laser pulses of few femtoseconds or even attoseconds are needed. These short light pulse techniques ask for broad frequency spectra, control of dispersion and control of phase. Hence, linear optics fails and nonlinear optics in high electromagnetic fields is needed to satisfy the amount of control that is needed. One recent application of attosecond laser pulses is time resolved visualization of tunnel ionization in atoms applied to high electromagnetic fields. Here, Ne atom electrons are excited by an extreme ultraviolet attosecond laser pulse. After a while, a few cycles nearly infrared femtosecond laser pulse is applied to the atom causing tunnel ionization. The ion yield distribution can be measured as function of the delay time between excitation and ionization and so deliver insight to the time resolved mechanisms. [Preview Abstract] |
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R1.00143: Application of the double and triple parabolic quantum well in a laser Martin Molinar, German Campoy Using a structure of two and three consecutive parabolic potentials (harmonic oscillator), enclosed in an infinite rectangular well, we solve the Schroedinger's equation and get the eigenvalues for the Hamiltonian. Trying with a few periods of the structure, we can see the rise of subbands. This system can be used for the development of a semiconductor laser diode built with the deposition of semiconductors on a substrate. We calculate the energy differences between neighboring states and they are then compared with those values found in the literature for similar systems. The emission frequency, the gain and the efficiency of the periodic structure are calculated, for different widths of the parabolic wells and this let us to explore the possibility of use parabolic potentials instead rectangular wells for build a semiconductor laser diode. [Preview Abstract] |
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R1.00144: ATOMIC, MOLECULAR & OPTICAL (AMO) PHYSICS |
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R1.00145: Making BEC for study Quantum physics by modulating the Magnetic potential Jinah Park, Dahyun Yum, Wonho Jhe The achievement of Bose Einstein Condensation (BEC) has opened a new chapter in atomic physics. With BEC in dilute atomic gases, quantum physics, solid state physics modeling and many physical phenomena, which has been hard to treat, could be studied beyond the research on BEC itself. In this sense, BEC in ultracold weakly interacting gases has been a very important meaning in recent years. Until now, many experimental results related with thermal atoms in the modulating potential have been carried out. It is no doubt that it is very interesting subject to study quantum mechanical phenomena in various potential configurations. We have been experimenting with the neutral rubidium 87 atoms for making BEC. Our experimental setup to obtain BEC is consisted of double Magneto-Optical Trap (MOT) system, Time Orbiting Potential (TOP) magnetic trap and evaporative cooling technique using rf-knife edge which is typical BEC setup. Here our experimental results are reported. [Preview Abstract] |
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R1.00146: Superconducting atom chips: recent results and prospects Adrian Lupascu, Cedric Roux, Andreas Emmert, Thomas Nirrengarten, Gilles Nogues, Michel Brune, Jean-Michel Raimond, Serge Haroche Atom chips offer a very interesting set of tools for the magnetic trapping and manipulation of neutral atoms close to surfaces and on-chip optoelectronic devices. In our experiments we investigate atom chips built using superconducting wires in a cryogenic environment. We have recently produced the first Bose-Einstein condensate using this setup. We observe the onset of the Bose-Einstein condensation for 1 x 10$^{4}$ atoms at a temperature of 100 nK. This result opens the way for studies of ultra-cold atoms interacting with superconducting structures. We also envision to excite the dense atomic cloud towards long lived Rydberg states. Making use of the phenomenon of dipole blockade could lead to the deterministic production of a single atom in a Rydberg state. [Preview Abstract] |
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R1.00147: Nonlinear Phenomena in Bose-Einstein condensates Lincoln D. Carr We present a medley of results from the last three years on nonlinear phenomena in BECs [1]. These include exact dynamics of multi-component condensates in optical lattices [2], vortices and ring solitons [3], macroscopic quantum tunneling [4], nonlinear band theory [5], and a pulsed atomic soliton laser [6]. 1. {\it Emergent Nonlinear Phenomena in Bose-Einstein Condensates: Theory and Experiment}, ed. P. G. Kevrekidis, D. J. Frantzeskakis, and R. Carretero-Gonzalez (Springer-Verlag, to appear, 2008) -- see L. D. Carr and Joachim Brand, e-print arXiv:0705.1139 (2007); Joachim Brand, L. D. Carr, B. P. Anderson, e-print arXiv:0705.1341 (2007). 2. R. Mark Bradley, James E. Bernard, and L. D. Carr, e-print arXiv:0711.1896 (2007). 3. G. Herring, L. D. Carr, R. Carretero-Gonzalez, P. G. Kevrekidis, D. J. Frantzeskakis, e-print arXiv:0709.2193 (2007); L. D. Carr and C. W. Clark, Phys. Rev. A v. 74, p.043613 (2006); L. D. Carr and C. W. Clark, Phys. Rev. Lett. v. 97, p.010403 (2006). 4. L. D. Carr, M. J. Holland, and B. A. Malomed, J. Phys. B: At. Mol. Opt. Phys., v.38, p.3217 (2005) 5. B. T. Seaman, L. D. Carr, and M. J. Holland, Phys. Rev. A, v. 71, p.033622 (2005). 6. L. D. Carr and J. Brand, Phys. Rev. A, v.70, p.033607 (2004); L. D. Carr and J. Brand, Phys. Rev. Lett., v.92, p.040401 (2004). [Preview Abstract] |
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R1.00148: Bose-Einstein condensation in low dimensional layered structures Patricia Salas, M.A. Solis Bose-Einstein condensation critical temperature, among other thermodynamic properties are reported for an ideal boson gas inside layered structures created by trapping potential of the Kronig-Penney type. We start with a big box where we introduce the Kronig-Penney potential in three directions to get a honey comb of cubes of side {\it a} size and walls of variable penetrability $(P=mV_{0} ab/\hbar ^{2})$, with bosons instead of bees. We are able to reduce the dimensions of the cubes to simulate bosons inside quantum dots. The critical temperature, starting from that of an ideal boson gas inside the big box, decreases as the small cube wall impenetrability increases arriving to a tiny but different from zero when the penetrability is zero $(P\longrightarrow \infty )$. \ We also calculate the internal energy and the specific heat, and compare them to the ones obtained for the case of the same Kronig-Penney potential in one direction (simulating layers), and two directions (nanotubes). [Preview Abstract] |
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R1.00149: Spin Nematics and Quantum Fluctuation-Controlled Coherent Spin Dynamics of Hyperfine Spin F=2 Cold Atoms Jun Liang Song, Gordon Semenoff, Fei Zhou We show that quantum fluctuations lift the accidental continuous degeneracy that was found in the mean field analysis of spin nematic states of hyperfine spin F=2 $^{87}$Rb. Two distinct spin nematic states with higher symmetries are selected out depending on scattering lengths: a uniaxial spin nematic and a biaxial spin nematic. Recently we also study coherent spin dynamics mainly driven by quantum fluctuations. Unlike the usual mean-field driven dynamics, quantum fluctuation-controlled spin dynamics are sensible to the variation of fluctuations and the potential induced by quantum fluctuations can be tuned by four or five orders of magnitude in optical lattices. These dynamics have unique dependence on quadratic Zeeman fields and potential depth in optical lattices. We find that although these dynamics are difficult to observe in traps, it is possible to observe them in optical lattices; particularly they can survive in F=2 $^{87}$Rb condensates with a relatively short life time. [Preview Abstract] |
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R1.00150: Bose-Einstein Condensates of Cesium Atoms in an Optical Lattice Chen-Lung Hung, Xibo Zhang, Nathan Gemelke, Cheng Chin The realization of the Mott-insulator to superfluid phase transition with neutral atoms in an optical lattice provides a rare opportunity to test many-body physics with accuracy. We report progress on an experimental and quantitative comparison of the superfluid to Mott-insulator phase boundary with results from the Bose-Hubbard model, using Bose-condensed cesium atoms confined to a thin layer of an optical lattice potential. Feshbach resonances with cesium atoms enable us to scan the on-site interaction over a wide range without modifying the tunneling rate and the overall trapping potential; chemical potential can be adjusted by loading a varied mean atomic density into the lattice. We describe the physical apparatus constructed for this investigation, including novel construction designed to achieve precise and agile control of the magnetic field used in tuning interactions, adiabatic loading and manipulation of the lattice potential, and tight two-dimensional confinement applied to negate the effect of gravity without sacrifice in system homogeneity. [Preview Abstract] |
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R1.00151: Development of an apparatus for simultaneous trapping of $^{6}$Li-$^{87}$Rb mixtures Qun Wei, Michael Brown-Hayes, Woo-Joong Kim, Carlo Presilla, Roberto Onofrio Ultracold dilute atomic gases are providing a new window into quantum physics, with particular regard to the first-principle study of various superfluid phenomena. It is critical, in order to open this window, to reach deeper Fermi degeneracy, and this requires, for Fermi-Bose mixtures, to optimize the heat capacity matching between the Fermi and the Bose gases. After discussing a thermodynamical model showing that heat capacity matching is improved by using species selective traps, we discuss the status of an apparatus in which we trap fermionic $^{6}$Li and bosonic $^{87}$Rb in a magneto-optical trap. [Preview Abstract] |
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R1.00152: Casimir forces in sphere-plane and cylindrical-plane geometries Qun Wei, Woo-Joong Kim, Michael Brown-Hayes, Diego Dalvit, Hayden Brownell, Roberto Onofrio We report on the status of an experiment aimed at measuring the Casimir force in cylinder-plane geometry. In order to characterize the apparatus, we have first performed small distance electrostatic calibrations in the sphere-plane geometry free from parallelism issues. This has allowed us to better identify various general issues on the measurement of the Casimir force, such as the distance dependence of the residual (contact) potential, and the delicate assessment of the absolute distance. Recent electrostatic calibrations in the cylinder-plane geometry after an upgrade of the parallelization system will be also reported. [Preview Abstract] |
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R1.00153: Universal Dependence in Ultra-Cold Fermi Gases Shizhong Zhang Over the last few years, there have been considerable efforts in understanding the physics of BEC-BCS crossover in ultra-cold fermi gases. Despite the fact that the problem can be easily formulated, it has not been amendable to analytic solutions. Various approximations have been used to address the problem especially around unitarity. Here we present some general considerations on the problem, relying on the fact that the system is dilute and thus the interaction effects comes only from two-body encounters. These enables us to express certain physical quantities(total energy, interaction energy, rf-spectrospcopy shift and closed channel fractions) in terms of one univeral function, depending only on temperature and interaction strength. The result obtained should be valid throughout the crossover and thus we expect it to have testable consequences in the future experiments. [Preview Abstract] |
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R1.00154: Ultra-cold atom experiment and strongly interacting Fermi system Li Yan Recent progresses in low temperature atomic experiment, especially the magnetic tunable inner-atom interaction via Feshbach resonance, give people a way to approach the study of low temperature and strongly interacting fermion system. In the strong interaction limit, i.e. the unitary limit range, system experiences BCS-BEC crossover, with universal thermodynamic properties. This kind of universality not only simplifies the theoretical research on strongly interacting fermion system but also help people to prove the uniqueness of strongly interacting system in ultra-cold atom experiment. [Preview Abstract] |
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R1.00155: Emergent vortex dynamics in two-dimensional neutral superfluids Cheng-Ching Wang, Rembert Duine, MacDonald Allan We derive an effective action for the vortex translational zero modes of a superfluid by integrating out environmental modes which include phase and density fluctuations of the condensate. When the quantum dynamics of the fluctuations are treated as frozen with negligible Berry phases in adiabatic limit, we confirm the occurrence of vortex Magnus force and adiabatic vortex mass due to compressibility of the superfluids in agreement with earlier studies. In addition, we also show the results beyond adiabatic limit in which the quantum dissipative action can be derived and solved analytically. We show that the adiabatic approximation is only valid in large system with small coherence length $R \gg \xi$. Furthermore, we also build a numerical model based on discrete Gross-Pitaevskii equation to show the renormalization and broadening of the vortex cyclotron resonance peaks. It is demonstrated that well-defined cyclotron peaks in spectral functions can be sustained only when the condition $R \gg \xi$ is satisfied. With the mapping between discrete Gross-Pitaevskii equation and bosonic single-band Hubbard model, we propose that the adiabatic vortex dynamics can be realized by tuning the ratio between tunneling energy $J$ and on-site interaction energy $U$ such that $UN_{a} \gg J$ in cold atom systems with optical lattices, in which $N_{a}$ is the total number of bosonic atoms. [Preview Abstract] |
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R1.00156: Violation of classical inequalities and EPR correlations in a two-mode three-level atomic system Eyob Sete We investigate violation of Cauchy-Schwarz and Bell inequalities in two-mode three-level cascade system with injected atomic coherence in the framework of quantum theory of multiwave mixing. We show that Cauchy-Schwarz inequality is strongly violated when there is strong entanglement in the system. It also appears that Bell inequality is violated in region where there is weak entanglement while well preserved where there is strong entanglement in the system. We thus note that there are states which are entangled but do not violate Bell inequality. We also show that this system can be used to prepare states that exhibits EPR correlations. [Preview Abstract] |
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R1.00157: Fiber optic laser delivery system for planar ion traps Elizabeth George, David Leibrandt, Isaac Chuang The use of trapped ions for quantum computation requires precise focusing and alignment of lasers for cooling the ions and performing logic gates. On-trap fiber optics would eliminate the need for alignment of lasers to the traps and allow scaling of surface-electrode ion traps on large chips to smaller sizes. We have developed a design for implementing on-trap fiber optics with an integrated beam focusing lens using microfabrication techniques. The design uses SU-8 photoresist structures to align the fiber and focusing lens to the trap. We present details of the design and the results of preliminary testing. [Preview Abstract] |
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R1.00158: In-Situ Optical Heterodyne in time Resolved Coherent Anti-Stokes Raman Scattering Yehiam Prior, Andrey Shalit, Yuri Paskover We show both theoretically and experimentally that pure vibrational modes cannot be observed in the power spectrum of time resolved degenerate Coherent Anti-Stokes Raman Scattering (CARS), unless the optical signal is linearized by an optical heterodyne detection scheme. A new heterodyne detection method is introduced, where the local oscillator is not provided externally, but is produced \textit{in-situ} by the addition of small amounts of highly anisotropic molecules to the measured sample. The rotational anisotropy of the added molecules gives rise to a slowly evolving signal, which in turn serve as the local oscillator in heterodyned time resolved CARS. We have shown that the strength of the local oscillator can be controlled by amount of material added, in our experiments CS$_{2 }$added to the measured chloroform or bromoform liquids. Small change of total anisotropy of the sample is expressed as dramatic changes in the intensity of the peaks corresponding to the fundamental vibrational frequencies. This method can be utilized for distinguishing of the fundamental frequencies from beats appearing in the signal due to quadratic (intensity) detection of the nonlinear signal. [Preview Abstract] |
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R1.00159: Cold antihydrogen production in the ATRAP2 apparatus Jonathan Wrubel, G. Gabrielse, P. Larochelle, D. Le Sage, B. Levitt, W.S. Kolthammer, R. McConnell, P. Richerme, A. Speck, M.C. George, D. Grzonka, W. Oelert, T. Sefzick, Z. Zhang, A. Carew, D. Comeau, E.A. Hessels, C.H. Storry, M. Weel, J. Walz We have developed a new ATRAP2 experimental platform, which has succeeded in producing thousands of anthydrogen (\={H}) atoms in a combined Penning-Ioffe trap. The Penning trap provides confinement for charged particles and the quadrupole Ioffe trap provides a neutral atom trap for \={H} atoms. Up to 78,000 antiprotons (\={p}) are trapped and cooled to 7K in a 1T bias field with every ejection from CERN’s Antiproton Decelerator. At the same time $5\times 10^6$ positrons ($e^+$) are loaded. Several shots are stacked and adiabatically transferred into neighboring electrodes in the center of the quadrupole Ioffe trap. Fine control in the Penning trap is provided by 37 individually rf and dc biased gold-plated copper cylinders. The Ioffe trap is ramped to full field and the \={p} are coaxed to interact with the $e^+$. As the \={p} are cooled by the $e^+$, \={H} atoms are formed that may be trapped by the Ioffe trap. The apparatus includes MnF$_2$ windows in the Ioffe trap to transmit Lyman-$\alpha$ radiation into the production space, which is needed for future laser cooling and precision spectroscopy of \={H}. [Preview Abstract] |
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R1.00160: Density Matrix Descriptions for Pump-Probe Optical Phenomena in Moving Atomic Systems Verne Jacobs Reduced density matrix descriptions are developed for pump-probe optical phenomena in moving many-electron atomic systems, taking into account atomic collisions and external magnetic fields. Time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations are developed in a unified manner. In a semiclassical perturbative treatment of the electromagnetic interaction, compact Liouville-space operator expressions are derived for the linear and the general (n'th order) non-linear electromagnetic-response tensors. These expressions are valid for coherent atomic excitations and for the full tetradic-matrix form of the collision operator in the Markov approximation. [Preview Abstract] |
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R1.00161: \textit{Ab initio} studies on molecules and clusters in external electrostatic fields Rajeev Pathak Influence of a uniform static external electric field on some aliphatic and aromatic molecular species is studied within the density functional theory (DFT) employing the 6-311++G(2d,2p) basis-set with B3LYP exchange-correlation prescription. The electric field perturbs the molecular geometry; alters the dipole moments and engenders a molecular vibrational Stark effect. For polar molecules, significant frequency shifts are observed for field orientations both parallel and antiparallel to their permanent dipole moments; where HOMO-LUMO gaps alter significantly. Time dependent DFT analysis reveals that an increase in the applied field strength increases the excitation energies amongst frontier MOs with a concomitant decrease in oscillator strengths. Structural evolution of water clusters, (H$_{2}$O)$_{n}$, n=6-8 is studied within DFT: the intermolecular hydrogen bonds stretch, and eventually break at some threshold values, triggering a conformational transformation, with configurations appearing as local minima on the cluster's potential energy landscape, with abrupt increase in the electric dipole moments and `opening up' of three dimensional morphologies of water. [Preview Abstract] |
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R1.00162: Analysis of the nuclear motion in a HeNe* transient molecule Cristian Bahrim, Joseph Hunt Based on a model potential for describing the interaction between He and Ne$^{\ast}$ atoms during a collision [1] we predict a series of vibrational states within several electronic adiabatic potential wells of the HeNe$^{\ast }$ system for internuclear distances R $<$ 6 a$_{0}$. The identification of vibrational states suggests the formation of a HeNe$^{\ast }$ temporary molecule. In our study two theoretical approaches are employed: (1) the \textit{harmonic approximation} is based on the assumption that during a collision (which is considered as being one period of vibration) the nuclear motion is harmonic, and (2) the \textit{anharmonic approximation} which uses the best fit of the electronic adiabatic potential wells with a Morse anharmonic function, as is typically done for stable molecules [2]. A set of vibrational-electronic transitions which can be measured using IR spectroscopy is proposed. The relative population of Ne$^{\ast }$ atoms after collisions and successful IR photo-absorption is predicted for experimental testing of the dominant character of the nuclear motion: whether is harmonic or anharmonic. The existence of a HeNe* transient molecule could have a positive impact on improving the performance of He-Ne lasers. [1] Bahrim C, Kucal H and Masnou-Seeuws F 1997 \textit{Phys. Rev. A} \textbf{56} 1305. [2] Bahrim C and Hunt J 2006 \textit{J. Phys. B }\textbf{39} 4683. [Preview Abstract] |
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R1.00163: Compton Profiles of Atoms and Ions Khondkar Karim We present momentum-space properties of several atoms and ions including He, Be, B, C, N, O, and Ne atoms, and the respective ions in many possible ionization stages. The calculations have been done using Hartree-Fock atomic model. The Compton profile data presented here could be used to obtain doubly differential cross section of electron production in ion-atom collision from electron-ion cross sections. The plots of electron distribution in momentum space reveal interesting features that are not apparent in electron's radial probability distribution in coordinate space. [Preview Abstract] |
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R1.00164: Fully Differential Cross Sections in Two-Photon Double Ionization of Helium Daniel Horner, Thomas Rescigno, C. William McCurdy We present total, single differential, and triple differential cross sections for two-photon double ionization of helium above and below the threshold for sequential ionization (54.4 eV). Sequential double ionization exhibits characteristic behavior seen in the total and differential cross sections. Evidence of this behavior also arises below the threshold through ``virtual sequential ionization.'' Using the method of exterior complex scaling, we compute numerically converged wave functions describing two unbound electrons on a large, but finite volume. From these wave functions, using formally exact integral methods, we extract ionization amplitudes, from which we compute the observable cross sections. [Preview Abstract] |
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R1.00165: Adsorbates effects in H$^{- }$ - Na/Cu(111) collisions Bogdana Bahrim, Song Yu The (111) faces of Cu, Ag and Au present a band gap that extends just below the vacuum level at the $\overline \Gamma \quad {\rm g}$point [1]. The effect is to forbid electrons with energies in a certain range to be transferred into the metal along the surface normal. Thus, the presence of a band gap should dramatically influence various experiments in ion-surface collisions involving electron capture or loss. In recent years, this topic received a great interest [2 -- 4]. Adsorbates deposition makes the electron dynamics at such surfaces to be even more complex. We analyze some interesting adsorbates effects: (1) projectile energy levels and widths are strongly perturbed when this approaches close to an adsorbate atom; (2) scattering by adsorbates may be used to laterally confine surface state electrons; (3) adsorbates may enhance the band gap effect; (4) adsorbates tend to couple the surface states to the bulk states. Results for the H$^{-}$ projectile interacting with a Na/Cu(111) surface are reported. [1] E.V. Chulkov, V.M. Silkin and P.M. Echenique 1999 \textit{Surf. Sci. }\textbf{437, }330. [2] A.G. Borisov, A.K. Kazansky and J.P. Gauyacq 1999 \textit{Phys. Rev. B. }\textbf{59}, 10935. [3] H.S. Chakraborty, T. Niederhausen and U. Thumm 2004 \textit{Phys. Rev. A.} \textbf{70}, 052903. [4] B. Bahrim, B. Makarenko and J.W. Rabalais 2005 \textit{Surface Sci.} \textbf{594}, 62. [Preview Abstract] |
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R1.00166: Spectroscopic and Magnetic Susceptibility Analyses of the $^{7}F_{J}$ and $^{5}$D$_{4}$ Multiplet Manifolds of Tb$^{3+}$(4f$^{8})$ in TbAlO$_{3}$ Kelly Nash, John Gruber, Dhiraj Sardar, Uygun Valiev, Abdulla Uzokov, Gary Burdick Detailed analyses of temperature-dependent spectroscopic and magnetic susceptibility data are reported for the crystal-field split energy levels of the $^{7}$F$_{J}$ and $^{5}$D$_{4}$ of Tb$^{3+}$ TbAlO$_{3}$. The spectroscopic data include absorption spectra obtained between 480 and 2940 nm from 8 to 300 K. High resolution fluorescence spectra are reported, representing transitions from $^{5}$D$_{4}$ to$^{ 7}$F$_{6,5,4}$, at a sample temperature of 85 K. Using crystal-field modeling techniques recently adapted for low symmetry systems, we have assigned all 58 experimental Stark levels within the $^{7}$F$_{J}$ and $^{5}$D$_{4}$ manifolds, with a fitting standard deviation of 4.5 cm$^{-1}$ (3.8 cm$^{-1}$ rms error). Furthermore, the theoretical Stark levels and calculated wavefunctions were used to determine the temperature dependence of the magnetic susceptibility along the $c$-axis of the TbAlO$_{3}$ crystal. Agreement is obtained between the calculated susceptibility and temperature-dependent magnetic data reported earlier. The susceptibility calculation also confirms the predicted ordering of states within the $^{7}$F$_{6}$ multiplet manifold. [Preview Abstract] |
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R1.00167: Ultracold Cesium Feshbach Molecules Michael Mark, Steven Knoop, Francesca Ferlaino, Martin Berninger, Harald Sch{\"o}bel, Hanns-Christoph N{\"a}gerl, Rudolf Grimm We present our recent work on ultracold Cesium Feshbach molecules in an optical dipole trap. We have implemented a new crossed-beam laser trap, which traps atoms and molecules simultaneously. By scanning one laser beam the ellipticity can be dynamically tuned for an optimal trap configuration. We routinely prepare ultracold mixed atomic and molecular or pure molecular samples at temperatures down to 30 nK [1]. We selectively populate Feshbach molecules in various $s$-, $d$-, $g$- and even $l$-wave states [2]. We have experimentally demonstrated that the $l$-wave dimers can be stable against spontaneous decay on the timescale of one second well above the dissociation threshold [3]. We have recently implemented the technique of resonantly modulated magnetic field spectroscopy [4]. Transitions between the atomic continuum and dimer states, and vice versa, as well as dimer-dimer transitions can be driven. Our main motivation is to apply this technique to search for trimer and tetramer states, whose presence has been indicated by resonances in collisional loss measurements.\newline [1] F. Ferlaino et al., in preparation; [2] M. Mark et al, Phys. Rev. A 76, 042514 (2007); [3] S. Knoop et al., arXiv:0710.4052; [4] T. M. Hanna et al., Phys. Rev. A 75, 013606 (2007) [Preview Abstract] |
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R1.00168: Helium Spectra in Atonic Mechanics Alfred Phillips, Jr. In our model of the helium atom, we postulate that the angular momentum of each electron divided by $\hbar $ equals an integer, $n$, plus a fraction$,\Delta n$. By minimizing the energy the energy of the helium atom, we find that the $\Delta n$ values are a function of the total angular momenta, $J$, irrespective of the integer, $n$. We thus obtain a set of $\Delta n$ values for the singlet and triplet states of helium. The $\Delta n$ values are related to fractals. In our model, we made adjustments to the electron mass so that the calculated energy values agree with the seventeen values for the singlet \textit{1s-ns} configurations listed in NIST Atomic Spectra Database Levels Data. The adjustments to the electron mass were usually very close to unity except for the ground state for which the adjustment was $\sim $5{\%}. (Adjustments like these suggest that we may be able to study three-body effects with spectral accuracy.) By doing this, we had good agreement with all of the NIST spectral values for helium (191 lines of He I, and 243 lines of He II). This conceptually and mathematically simple procedure can be used for other atoms. [Preview Abstract] |
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R1.00169: The Adiabatic-to-Diabatic Mixing Angle for the Inelastic Collision B($^{2}$P$_{1/2})$ + H$_{2}(j, n) \quad \leftrightarrow $ B($^{2}$P$_{3/2})$ + H$_{2}(j$', $n$') David Weeks, Matthew Garvin The Born-Oppenheimer approximation breaks down when two adiabatic potential energy surfaces become sufficiently close. Under these conditions, the nuclear dynamics are governed by a set of coupled diabatic surfaces. Derivative coupling matrix elements can be used to compute the transformation from the adiabatic to the diabatic potential energy surfaces. A line integral along various contours through the vector field defined by the derivative coupling matrix elements is used to compute the adiabatic-to-diabatic mixing angle. In particular, we investigate the path independence of this coupling angle for the inelastic collision B($^{2}$P$_{1/2})$ + H$_{2}(j) \quad \leftrightarrow $ B($^{2}$P$_{3/2})$ + H$_{2}(j$') collision (1). (1) D.E. Weeks, T.A. Niday, and S.H. Yang, J. Chem. Phys, 125, 164301 (2006). [Preview Abstract] |
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R1.00170: Vibrational and Spin as well as Linear Kinetic Energies Should Be Included in Pair Production and Annhiliation Energy Relations Stewart Brekke By including the vibrational and spin Kinetic Energies in Pair Production and Annihilation Formulas a closer reconciliation between theory and experimental results can result. The creating photon may create particle vibration and spin as well as mass and linear motion. In pair production: $hf = 2m_{0}c^2 + 1/2m_{0}v^2_- +1/2m_{0}v^2_+ 1/2I\omega^2_{r_-} + 1/2I\omega^2_{r_+} (n +1/2)\hbar\omega_{v_-} + (n +1/2)\hbar_{v_+}$. In pair annihilation at least two photons must be produced which get their energy from the linear, vibrational and spin kinetic energies as well as the mass-energy conversion. $hf_1 + hf_2 +.... = 2m_{0}c^2 + 1/2m_{0_-}v^2 + 1/2m_{0_+}v^2 + 1/2 I\omega^2_{r_-} + 1/2I\omega^2_{r_+} + (n + 1/2)\hbar\omega_{v_-} + (n +1/2)\hbar\omega_{v_+}$. [Preview Abstract] |
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R1.00171: Compton Effect Energy Formulas Should Include Vibrational and Spin as well as Linear Kinetic Energies Stewart Brekke In Compton scattering the incident photon affects not only the linear, but also the vibrational and spin kinetic energies after impact. $hc/\lambda_1 + m_{0}c^2 + 1/2m_{0}v^2 + 1/2I\omega^2_{r_1} + (n+1/2)\hbar_{v_1} = hc/\lambda_2 +m_{0}c^2 + 1/2mv_2^2 +1/2I\omega_{2_r}+ (n +1/2)\hbar\omega_{2_v}$. If the incident photon produces a relativistic speed, the equation should be $hc/\lambda_1 + m_{0}c^2 +1/2m_{0}v_1^2 + 1/2I\omega^2_{r_1} + (n +1/2)\hbar\omega_{v_1} = hc/\lambda_2 + mc^2 +mv^2_2 + 1/2I\omega^2_v + (n +1/2)\hbar\omega_{v_2}$. By including the other kinetic energies a closer reconciliation between theory and experiment will occur. [Preview Abstract] |
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R1.00172: Feedback-controlled radiation pressure cooling Yehiam Prior, Mark Vilensky, Ilya Sh. Averbukh We propose a new approach to laser cooling of micromechanical devices, which is based on the phenomenon of optical bistability. These devices are modeled as a Fabry-Perot resonator with one fixed and one oscillating mirror. The bistability may be induced by an external feedback loop. When excited by an external laser, the cavity field has two co-existing stable steady-states depending on the position of the moving mirror. If the latter moves slow enough, the field in the cavity adjusts itself adiabatically to the mirror's instantaneous position. The mirror experiences radiation pressure corresponding to the intensity value. A sharp transition between two values of the radiation pressure force happens twice per every period of the mirror oscillation at non-equivalent positions (hysteresis effect), which leads to a non-zero net energy loss. The cooling mechanism resembles Sisyphus cooling in which the cavity mode performs sudden transitions between two stable states. We provide a dynamical stability analysis of the coupled moving mirror -- cavity field system, and find the parameters for efficient cooling. Direct numerical simulations show that a bistable cavity provides much more efficient cooling compared to the regular one. [Preview Abstract] |
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R1.00173: Effect of Disorder on a Bose-Einstein Condensate with Tunable Interactions D. Dries, Yong P. Chen, J. Hitchcock, M. Junker, T. A. Corcovilos, C. Welford, R. G. Hulet We have investigated the effect of a disordered optical potential on the transport and phase coherence of a Bose-Einstein condensate (BEC) of $^7$Li. We observe damping of BEC dipole oscillations even when the disorder strength, $V_D$, is small, while for large $V_D$, transport is completely inhibited. Time-of-flight images show that the BEC gradually loses phase coherence for $V_D > \mu/2$, with coherence completely lost when $V_D=\mu$, where $\mu$ is the chemical potential of the BEC. We interpret this loss of coherence as resulting from fragmentation of the BEC as seen from \textit{in-situ} measurements of the density distribution. While these experiments were performed with a BEC healing length, $\xi$, that is small in comparison to the disorder length scale, we are currently attempting to observe the Anderson localization predicted to occur for large $\xi$. Using a magnetically-tuned Feshbach resonance, the \textit{s}-wave scattering length, $a_s$, is reduced to near zero where $\xi$ becomes very large. Results of applying the disorder potential to this nearly non-interacting condensate, with $a_s$ much less than the Bohr radius, will be reported. [Preview Abstract] |
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R1.00174: Electron Impact K-Shell Ionization of Atoms $(2\le Z\le 92)$ M.A.R. Patoary, M. Alfaz Uddin, A.K.F. Haque, A.K. Basak, B.C. Saha The electron impact ionization phenomena have fundamental importance ranging from plasma to astro-physics. Reliable K-shell ionization cross sections (KSICS) are needed for various quantitative analyses. Even the first order quantal calculations are rather both lengthy and not too easy to implement for various modeling calculations. We propose a \textit{parameter free} model based on the widely used binary encounter approximation (BEA) [1,2] by incorporating both the ionic and relativistic corrections and have tested to evaluate KSICS with considerable success as compared to experimental results even up to E=1 GeV. \newline [1] M. Gryziniski, Phys. Rev. A. \textbf{138}, 336 (1965). [2] L. Vriens, Proc. Phys. Soc (London) \textbf{89}, 13, (1966). [Preview Abstract] |
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R1.00175: ARTIFICIALLY STRUCTURED MATERIALS |
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R1.00176: Fabrication of metamaterials in THz region using ink jet system and characterization using THz-TDS Yew Li Hor , Hee Lim, John Federici This article demonstrates the use of new fabrication techniques to fabricate metamaterials in THz range via a material deposition system. The patterns of these metamaterials follow the conventional designs which are single ring-SRR and double-Dots with varying conductivities. Highly conductive nano particle Ag and Pedot/PSS polymer inks are used as structural medium. The fabricated metamaterials of effective lattice sizes of 50 to 80 micron are then characterized using THz-TDS with 0.1 to 3 THz range in transmission mode. The detail steps of fabrication and THz-TDS experimental setup are elaborated. The absorption spectra of different thicknesses and different background substrate of these metamaterials are presented and discussed. Additional, the theoretical modeling of the fabricated samples are shown and compared with the experimental result. [Preview Abstract] |
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R1.00177: Drift Instability of a 2D Magnetoplasma in a Periodic Potential M. Tahir, K. Sabeeh, V. Fessatidis, N.J.M. Horing We examine the drift instability of a magnetized 2D electron plasma in a weak periodic potential, taking account of a steady current. In this, we treat a strong magnetic field inducing Landau quantization, and analyze both the inter- and intra-Landau band plasmon spectra within the framework of the random phase approximation, determining the occurrence of magnetoplasmon instability as a function of drift speed. [Preview Abstract] |
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R1.00178: A study of Diamond like Carbon films deposited by PECVD using DC and pulsed DC power supply Rajeev Gupta, D. K. Rai, Debjit Dutta, S. K. Ram, Satyendra Kumar Diamond like carbon (DLC) films were deposited on different substrates using acetylene and hydrogen gases by DC and pulsed DC glow discharge PECVD technique. Substrates surfaces were pre-treated with hydrogen plasma prior to deposition. High deposition rates and uniform thin film were obtained using pulsed DC PECVD technique. The bulk and surface properties of these films were investigated using Raman spectroscopy, optical transmission and atomic force microscopy techniques. Spectroscopic ellipsometry was used to determine optical band gap, refractive index and thickness of DLC films. Fourier transform infrared spectroscopy was used to find the hydrogen content, absorption coefficient and sp$^{3}$/sp$^{2}$ ratio in our films. Calculation of secondary electron emission coefficient ($\gamma$) is done by plotting Paschen curves. A comparative study of qualitative aspects of DLC films deposited by DC and pulsed DC using Raman spectroscopy will be presented. [Preview Abstract] |
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R1.00179: Stability and structure of free-standing III-V nanorods: An \textit{ab initio} investigation Roman Leitsmann, Friedhelm Bechstedt The interest in anisotropic needlelike crystals has been recently stimulated by the potential need as building blocks for nanoscale electronic and photonic devices. Due to their considerable potential for optoelectronics or high-speed electronics nanorods (NRs) consisting of III-V semiconductors are of particular interest. In most cases the growth direction of III-V semiconductor NRs is parallel to the [111] axis of the bulk zinc-blende (\textit{zb}) structure. However, the crystal structure of the NRs may change noticable, depending on growth conditions and growth method. In particular, changes of the crystal symmetry from the cubic to the hexagonal (wurtzite - $w)$ stacking of the cation-anion bilayers have been observed in many cases. We report ab initio investigations of hexagon-shaped III-V semiconductor NRs with varying crystal structure, varying surface passivation, and varying diameter [1]. Their stability is dominated by the free surface energies of the corresponding facets. We observe a phase transition between local \textit{zb} and $w$ geometry of the rods versus the preparation conditions of the surfaces [1] J. Appl. Phys. \textbf{102}, 063528 (2007) [Preview Abstract] |
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R1.00180: Bloch oscillation and Stark localization in graded lattices Kin Wah Yu, K. Yakubo, J. J. Xiao In this work, we report Bloch oscillation (BO) in graded elastic [1] and plasmonic [2] lattices. This is an unusual kind of oscillatory motion due to the band structure of graded lattices and is analogous to electronic BO in semiconductor superlattices. The study is related to the recently identified localized excitations called gradons which is peculiar to graded lattices [1,2]. We will use semiclassical theory to establish the conditions for BO and study the dynamics of BO in these systems. Moreover, we will confirm semiclassical solution by time-domain simulations of the propagation of wave packets. Results of these two methods will be compared. In this way, we can understand the origin of gradon localization more clearly. Results of the present research also offer great potential applications for controlling wave propagation by means of graded materials.\newline [1] J. J. Xiao, K. Yakubo, K. W. Yu, Phys. Rev. B {\bf 73}, 054201 (2006); 224201 (2006). \newline [2] J. J. Xiao, K. Yakubo, K. W. Yu, Appl. Phys. Lett. {\bf 88}, 241111 (2006); {\bf 89}, 221503 (2006). [Preview Abstract] |
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R1.00181: Modeling the self-assembly of nanoparticle and nanorod superlattices Alexey Titov, Petr Kral Coloidal semiconductor PbSe/CdSE nanoparticles (NP) of the sizes of 3-10 nm can self-assemble in fcc, hcp and single-hexagonal (sh) superlattices [1]. We model the Coulombic, van der Waals and steric interactions between these NPs to understand the exact conditions under which they can self-assemble in these lattice structures. Our simulations show that non-local dipoles of the NPs and their screening by the conducting substrate are both crucial for the sh lattice formation. We model analogously the self-assembly of semiconducting CdSe nanorods (NRs), realized also in the presence of electric fields [2], and the binary semiconducting-metallic nanoparticle superlattices [3]. \newline [1] D. Talapin, E. Shevchenko, C. B. Murray, A. Titov and P. Kr\'al, Nano Letters 7, 1213 (2007). \newline [2] A. Titov and P. Kr\'al, submitted. \newline [3] E. V. Shevchenko, D. V. Talapin, N. A. Kotov, S. O'Brien, C. B. Murray, Nature 439, 55-59 (2006). [Preview Abstract] |
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R1.00182: Experimental Study of Electrical Properties of ZnO Nanowire Random Networks for Gas Sensing and Electronic Devices Daqing Zhang, Sirisha Chava, Chris Berven, Anirbaan Mukherjee, Vanvilai Katkanant ZnO nanostructures are an attractive material for electronic and optical applications due to their many unique properties. Our research focuses on studying mats of ZnO nanowires as an electronic material with particular interest in their interaction with various gases. The ZnO nanowires were synthesized on sapphire substrates using a tube furnace at atmospheric pressure. Two-terminal current-voltage (I-V) measurements were used to examine the electrical conductivity of the ZnO nanowire mat as a function of temperature and exposure to various gases. Temperature-dependant measurements were performed in vacuum using a continuous flow cryostat over $\sim $150 K to $\sim $ 300 K. Gas exposure experiments were conducted in a custom-built environmental chamber which was filled with various testing gases (Ar, CO, CO$_{2}$, H$_{2})$ at 3psig or under vacuum. We observed reversible changes in the I-V characteristics as a function of gas exposure. For CO, the currents increased by a factor of about four. In addition, changes in the I-V behavior were found to be reversible after evacuation. Possible mechanisms for the gas-specific responses of the ZnO nanowire mat will be discussed. [Preview Abstract] |
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R1.00183: CdSe, CdTe and core-shell CdSe-CdTe nanowires: A density functional study. R. Ramprasad, Tom Sadowski Semiconductor nanowires (NWs) are attractive in photovoltaic applications due to their ability to support a large number of electron-hole pairs (excitons) and the possibility of enhanced transport of dissociated charge carriers. To facilitate transport along the long axis of the nanowires, efficient charge separation of the exciton is desired. There is evidence suggesting that at a Type II band offset between two semiconductors enables charge separation more easily than in single component systems. The focus of this study is to provide an understanding of the tendency for electron-hole separation in core-shell CdSe-CdTe NWs, which contain a radial Type II band offset. In particular, first principles computational methods have been applied to infinitely long CdSe-CdTe heterostructure NWs in the wurtzite crystal structure over a range of core and shell sizes. The interfacial energy of the nanorods, the band gaps, and the location of the electron and hole states are assessed as a function of the number of CdSe pairs, and core and shell radii. The overlap of the electron and hole wavefunctions, determined to quantify the extent of electron-hole separation, is differentiated with that for single-component CdSe and CdTe nanowires. [Preview Abstract] |
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R1.00184: Fano effect in quantum wires with a uniform transverse electric field V. Vargiamidis, V. Fessatidis We investigate the effect of an external uniform transverse electric field on the Fano resonance in electronic transport of a quantum wire with a finite range impurity. We employ the Feshbach coupled-channel theory for calculating the transmission probability. The attractive impurity is P\"{o}schl-Teller along the propagation direction but is an arbitrary function of the lateral coordinate. For this type of impurity analytical solution to the scattering problem is possible. The Fano line shape resulting from the interference of direct transmission and transmission via a quasibound state created in the impurity, is shown to be strongly affected by the strength of the electric field. In particular, we show that as the strength of the electric field increases the resonance width continuously decreases and finally shrinks to zero. Consequently, the Fano line shape collapses. The vanishing of the resonance width indicates the transformation of the quasibound state into a true bound state in the continuum. Depending on the strength of the impurity, the collapse of the Fano line shape can even occur in the regime of weak electric field. This interesting collapsing behavior of the Fano resonance has also been shown to occur in purely one-dimensional systems (i.e., in 1D mesoscopic open rings). We also examine the pole structure of the transmission amplitude, in the complex energy plane, as a function of the electric field strength. [Preview Abstract] |
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R1.00185: Dynamics of an Electron in a Saddle Potential Subject to Crossed Electric and Magnetic Fields K. Sabeeh, A. Yar, V. Fessatidis, N.J.M. Horing, M.L. Glasser We analyze the role of an electric field in the scattering/tunneling of an incident plane electron wave through a quantum point contact in a magnetic field. In this, the point contact is modeled as a saddle potential. We employ the Bogoliubov transformation and guiding center coordinates following the techniques of H.~A.~Fertig and B.~I.~Halperin (Phys.~Rev.~B \textbf{36}, 7969 (1987)), but we expand the analysis to include the effects of the applied electric field here and examine the temporal development of the incident plane electron wave rather than that of a bath eigenfunction. [Preview Abstract] |
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R1.00186: Magneto-optics of single Rashba spintronic quantum dots subjected to a perpendicular magnetic field Manvir Kushwaha We report on the theoretical investigation of the effect of the Rashba-type spin-orbit interaction (SOI) on the Fock-Darwin energy spectrum in the parabolically confined quantum dots in the presence of a perpendicular [to the original two-dimensional electron gas (2DEG)] magnetic field. The study is based on the exact analytical results obtained without any approximation and numerical simulation. We observe that the SOI modifies drastically the optical, thermodynamic, as well as magneto-optical properties of the (narrow-gap InAs) quantum dots. We discuss the dependence of the Fock-Darwin spectrum, Fermi energy, optical transitions, and magnetization on all the important parameters involved in the theory such as, for example, the orbital quantum number, the magnetic field, the confinement potential, and the Rashba parameter that characterizes the strength of the SOI. The illustrative examples include the results both with and without the SOI, for the sake of comparison. One of the most important observation is that the Rashba SOI causes the band mixing and band shifting in the quantum dots and the Fock-Darwin energy spectrum becomes richer but complex. This complexity seems to arise due to an intricate interplay between the SOI and the Zeeman energy. [Preview Abstract] |
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R1.00187: Left-handed materials: detailed experimental parametric studies of the fishnet structure V.D. Lam, J.B. Kim, J.W. Park, N.T. Tung, S.J. Lee, Y.P. Lee Recently, a new area of research, called left-handed materials (LHMs), has attracted considerable interests due to their unusual physical properties and novel applications. The first experimental evidence for the existence of LH behavior was proposed by Smith \textit{et al}., using the split-ring resonator combined with the continuous wire. Several different designs, utilizing this idea for the LHM, have been reported. Zhou \textit{et al.} investigated the LHM based on the H-shaped wires, which exhibits a negative refraction index in the microwave range. Dolling \textit{et al.} introduced a modification with rectangular structures (the so-called fishnet structure) and demonstrated the LH characteristics at a wavelength of 780 nm while S. Zhang \textit{et al.} employed an array of elliptical apertures, showing the LH behavior in the near-infrared regime. The main purpose of these modified structures is to find out the optimized structure that can be easily fabricated and experimentally characterized, especially, LHM working at optical frequencies. In this report, we present the experimental results of the parametric study on the fishnet structure, which are also compared with the previous theoretical studies. These structures were designed, fabricated, and measured in the microwave frequency regime. [Preview Abstract] |
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R1.00188: Nonlinear Fano effect in semiconductor quantum dots: Detecting weak interactions Alexander Govorov The Fano interference effect appears when a discrete state of an atom or quantum dot couples with a continuum of states. In self-assembled quantum dots, the coupling may come from the tunnelling or Auger processes [1,2,3]. This study develops a theory of Fano effect in self-organized quantum dots under the condition of strong optical pumping. Our theory shows that the Fano effect becomes greatly enhanced in the nonlinear regime. In the linear regime, if the dot-continuum interaction is very weak, the optical detection of Fano effect is impossible because of the Heisenberg principle. In other words, in the linear regime, a finite lifetime of an exciton creates an energy uncertainty and the Fano interference effect becomes invisible. However, in the nonlinear regime, the natural radiative broadening does not play the main role and even a very weak dot-continuum interaction becomes apparent. This nonlinear method can be used to detect very weak interactions between a two-level system (or qu-bit) and a continuum of states of any nature. The nonlinear Fano effect in InGaAs quantum dots has been observed in the recent experiments performed in Munich and Edinburgh [3]. This study was performed in collaboration with: W. Zhang, M. Kroner, K. Karrai, and R. J. Warburton. [1] A.O. Govorov, R. J. Warburton, and K. Karrai, Phys. Rev. B RC, 67, 241307 (2003). [2] K. Karrai et al., Nature 427, 135 (2004). [3] M. Kroner et al., submitted to Nature. [Preview Abstract] |
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R1.00189: Optically Injected Charge and Spin Density Patterns in Quantum Wells John Sipe, Rashad Abrarov, Eugene Sherman We investigate the charge and spin dynamics following optical injection of currents in quantum wells taking into account momentum relaxation, electron-hole drag and the long-range Coulomb forces. Our numerical approach uses expansion of the investigated quantities in the Hermite-Gaussian basis. We find that on time scale of the order of one picosecond the carrier and current densities demonstrate complex patterns even when the effects of the spatially nonuniform forces are expected to be weak. This behavior can lead to a difference between results on the dynamics of carriers traced by different experiments; the charge displacements seen in the THz radiation and optical pump-probe experiments can be sufficiently different. The resulting spin density patterns arising due to the spin-dependent electron-hole skew scattering are calculated and analyzed in terms of the spin-orbit coupling, Coulomb forces, and the carrier momentum relaxation effects. [Preview Abstract] |
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R1.00190: Computational Study on the Magneto-optical Effects from Gyrotropic Gratings. Min Hyung Cho, Yue Hui Lu, Y. P. Lee, Joo Yull Rhee Maxwell's equations with non-diagonal complex dielectric tensor are numerically studied for the calculation of Magneto-optical(MO) effects from one-dimensional lossy gyrotropic or magnetic gratings. Owing to the periodicity of the structure, the dielectric tensor is expanded out in Fourier series and the electric and the magnetic vectors are written in terms of Bloch wave. Then, Maxwell's equations are simplified as a system of ordinary differential equations, and the solutions can be simply written in terms of exponential function with the eignevalue of system times the initial value. Finally, by considering the multiple reflection in the grating structure with Airy-like internal reflection series, the reflection and the transmission matrices are obtained and used to calculate the MO effect. The Kerr rotations of the 0th and the 1st diffracted orders are calculated as a function of various parameters. The calculated results agree excellently with the experimental data for permalloy gratings. This method can also be used for many interesting applications and easily extended to two-dimensional gratings. [Preview Abstract] |
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R1.00191: Giant Photonic Band Gaps in one dimensional Photonic heterostructures Jesus Manzanares-Martinez, Raul Archuleta-Garcia In this work we show that it is possible to design Giant Photonic Band Gaps in Heterostructures via the the determination of the group velocity. A photonic Heterostructure is composed by the union of two or more distinct photonic crystals.We present the calculation of the Heterostructure band structure implementing the supercell technique in the Wave Plane Method. We show that even if the Heterostructure present a very complicated Photonic Band structure, it is possible to discriminate the regions of low (high) transmission obtaining the group velocity. We verify the very existence of the forbidden (allowed) regions with the theoretical calculations of the light transmision. [Preview Abstract] |
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R1.00192: Two-dimensional photonic crystal heterostructure with Omnidirectional band gap Raul Archuleta-Garcia, Damian Moctezuma-Enriquez, Jesus Manzanares-Martinez We present the numerical determination of Giant Omnidirectional (3D) photonic band gaps calculated for a two dimensional heterostructure, which are composed by the union two photonic crystals. The Photonic Band Structure is calculated via the implementation of the supercell technique on the the Plane-Wave Method. We have optimized the structure in order to obtain the biggest band gap. [Preview Abstract] |
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R1.00193: Synthesis and study of composite silver-polymer metamaterials M. Mayy, G. Zhu, Yu Barnakov, M. Noginov We have designed, synthesized and characterized a range of non-magnetic metamaterials with continuously tunable dielectric constant. Powders of 30 nm silver nanoparticles were suspended in Tetrahydrofuran solution of Polymethylmethacrylate and exposed to Q-switched laser radiation in order to separate nanoparticles and/or reduce the degree of aggregation. The films of Ag-PMMA composites with different concentrations of silver nanoparticles $N$ were deposited onto glass substrates and characterized in optical transmission and reflection experiments. Using known formula for reflectivity and transmissivity in three-layered structures, we extracted from the experimental data the spectra of real \textit{$\varepsilon $}$_{eff}$'\textit{($\lambda )$} and imaginary \textit{$\varepsilon $}$_{eff}$\textit{''($\lambda )$} parts of the effective dielectric constants. The experimental maximal value of \textit{$\varepsilon $}$_{eff}$' exhibited monotonous growth and reached \textit{$\varepsilon $'}=12.8 at $\lambda $=2.4 $\mu $m at the maximal concentration of Ag nanoparticles studied. The demonstrated value of \textit{$\varepsilon $}$_{eff}$' exceeds that in Si and appears to be the highest in 1.5-2.5 $\mu $m spectral range. The demonstrated easy-to-synthesize nanocomposite adds to the tool box of photonic metamaterials with extreme values of \textit{$\varepsilon $}. [Preview Abstract] |
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R1.00194: Magnetic dipole systems for probing optical magnetism N. Noginova, G. Zhu, M. Mavy, M.A. Noginov, I.V. Bondarev Recent advances in plasmonic-based metamaterials show that magnetic component of the optical field can be strongly modified by properties and geometry of metallic nanostructures, leading to such interesting effects as negative magnetic permeability and magnetic resonance in optical range. To probe such effects experimentally, systems containing rare-earth ions having magnetic dipole-related transitions can be used as spectroscopic tools. We report development, first experimental results and theoretical consideration of such systems based on Eu$^{3+}$ ions. [Preview Abstract] |
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R1.00195: Artificial Molecules Patanjali Kambhampati, Samuel Sewall, Ryan Cooney, D.M. Sagar Confinement of carriers in quantum dots results in hydrogenic like states for the exciton. Thus a single excitation in a quantum dot bears resemblance to a hydrogen atom; these materials are often referred to as `artificial atoms'. A pair of excitons will form a four body biexciton, akin to a hydrogenic molecule. Quantum confinement increases the binding energy of the ground state of the biexciton. Quantum confinement should also produce bound states for the excited states of the biexciton. Thus the excitonic `hydrogen molecule' should have an eigenstate spectrum in the vein of molecular orbitals. The eigenstate spectrum of the biexciton has remained elusive due to the ultrafast timescale of relaxation processes in quantum dots which mask observation of the excited states. Here, we show the first, direct observation of excited states of the biexciton, completing the analogy of excitons in quantum dots to atomic and molecular systems. [Preview Abstract] |
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R1.00196: Hollow Quantum Dot Shells: Optical Response Function Analysis Jared Maxson, Slava V. Rotkin We consider the response of finite two-dimensional lattice shells of coupled quantum dots, approximated as dipoles, to an applied external electric field. We assume that the lattice constant is much smaller than the wavelength of applied electric field, to provide a coherent excitation. Using the matrix Green's function and Coupled Dipole Hamiltonian, the response function is derived and analyzed numerically. Treating the dipole coupling as a parameter, the response function of an entirely decoupled lattice is calculated, from which the coherence effects are identified in the fully coupled case. The effect of hollowness is considered, in which optical resonator effects are determined, resulting from the matching of the radius of the cylindrical shell to the light wavelength. The response function is decomposed into partial response functions due to individual modes, in which the polarization dependence is determined by altering the orientation of the incident field. [Preview Abstract] |
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R1.00197: Wave Transmission Through a Nano-hole Desire Miessein, N.J.M. Horing We have examined the integral equation for scalar wave transmission through a nano-hole modeled as a single point, employing a formal procedure for an exact solution, which is found to involve a divergent integral. Analyzing two distinct cutoff procedures we find them to be in agreement for small nano-holes ($\sim $ 50nm). Furthermore, similar results are obtained using first approximations in the Neumann series and in the Fredholm series solutions for the original integral equation for small nano-holes. [Preview Abstract] |
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R1.00198: Nanostructured Silicon Optical Waveguides Prabhakar Bandaru, David Yang, Jung Park, Shayan Mookherjea Nanophotonic ``void'' or ``slotted'' waveguides, with features smaller than the wavelength of light, could be helpful in tailoring the phase difference between the transmitted TE (transverse electric) and TM (transverse magnetic) waves, as well as mode-shaping of the field by near-field interactions of highly-confined modes. Such artificially-induced birefringence can be utilized for chip-scale optical delay lines and compact waveguide-based polarization switches incorporating phase retardation. Using electron-beam lithography and dry etching, we have fabricated and demonstrated multi-slot waveguides in silicon-on-insulator chips, with slot width 100 nm and slot-to-slot spacing of 150 nm. We have measured the group index in both the TE and TM polarizations, and the experimental values agree closely with computational simulations using a fully-vectorial finite-difference mode-solver. We observe an engineered birefringence (refractive index difference between TE and TM waves) of $\sim $ 1.4 over an 80 nm waveguiding bandwidth (1530-1610 nm). [Preview Abstract] |
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R1.00199: F\"{o}rster Resonance Energy Transfer between Nanoparticles and Nanowires. Pedro L. Hernandez-Martinez, Alexander O. Govorov We develop a theoretical model to describe F\"{o}rster resonance energy transfer (FRET) between semiconductor nanoparticles (NPs) and nanowires (NWs). We obtain an analytical equation in the dipole limit and a numerical solution for the general case. We find that, for FRET between NPs and NW, the transfer time is proportional to 1/d\^{}5, where $d$ is the distance between NP and NW. The calculated transfer time between CdTe NPs and NWs is 16.9 ns. This number agrees well with the experimental value, 16 ns [1]. We also found good agreement with the experimental data [1] for other NP-NW distances. For a NW material, we explore a semiconductor (CdTe) and metals (Au and Ag) [2]. In a NP-NW bio-conjugate, excitons flow from NPs to a NW and then become collected in a NW. When voltage is applied across a NW, this system is expected to demonstrate enhanced photo-current and photo-voltage responses. The enhancement effect comes from energy channeling from NPs to a NW due to FRET. This system can be used in optoelectronic devices and energy conversion systems. [1] J. Lee, A. O. Govorov, and N. A. Kotov, Nano Letters 5, 2063-2069 (2005). [2] J. Lee, P. Hernandez, J. Lee, A. O. Govorov, and N. A. Kotov, \textbf{Nature Materials}, 6, 291 -- 295 (2007).. [Preview Abstract] |
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R1.00200: Nanometer sized electrodes fabricated by electromigration of Au and Pd nanowires Alexandru Vlad, S\'ebastien Faniel, Beno\^it Hackens, Vincent Bayot, Sorin Melinte Electromigration-driven metallic nanowire failure is presented. Here, Au and Pd nanowires patterned by electron-beam lithography were electrically stressed up to their breaking point. Feedback control and simple voltage sweep techniques have been successfully used to form nanometer-sized gaps. We observe a material- and geometry-dependent behavior. The Au nanowires showed a Joule-induced reversible resistance increase with the applied voltage up to the breaking point. In contrast, Pd nanowires presented an anomalous resistance decrease close to their failure point. This was associated to the melting and agglomeration of metallic grains within the electrically stressed nanowires. The SEM images acquired at intermediate stages of electromigration agree with the electrical data findings. The influence of the nanowire geometry upon the morphology of fabricated nanoelectrodes is considered. Beside the morphological characterization of our break junctions, we also measured their current-voltage characteristics. We observed single electron tunneling effects, probably due to the presence of metallic clusters formed close to the nanoelectrodes during the electromigration. Our results are consistent with recent findings on Coulomb blockade phenomena in electromigrated gold break junctions. [Preview Abstract] |
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R1.00201: Molecular spin clusters for quantum computation Marco Affronte Molecular spin clusters are prototypical systems exhibiting coherent dynamics of the electronic spin. The pattern of the lowest lying spin states is well defined and controlled at the synthetic level. The chemical bottom up approach used for the synthesis of molecules also allows to reduce intrinsic sources of decoherence and to build links between clusters, thus creating entanglement of spin states. Molecular spin clusters can be deposited at surfaces, thus forming scalable networks. Different molecules and ligands may be combined to exploit different functionalities, the latter being defined at molecular level. These facts provide extraordinary motivation to attempt the implementation of molecular quantum processors that, in turns, are test bench for novel quantum algorithms. Recent achievements obtained on antiferromagnetic molecular rings will be presented. [Preview Abstract] |
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R1.00202: Quantum Computing using Rotational Modes of Dimers Kenji Mishima, Koichi Yamashita In this paper, we numerically constructed general-purpose phase-correct global quantum gates by using \textit{inter}molecular rotational modes of two polar molecules coupled by dipole-dipole interaction to encode two qubits and implement the Deutsch-Jozsa algorithm. The calculations were based on the multi-target optimal control theory (MTOCT). The molecular systems we examined were NaCl-NaBr, NaCl-NaCl, and NaBr-NaBr dimer systems. The rotational states in the ground vibrational state of the ground electronic state of these pairs were taken as two qubits. When implementing the Deutsch-Jozsa algorithm by combining these elementary gates, we obtained a maximum probability 97.95 {\%} for NaBr-NaBr system with the interval $R$=5.0 nm in the repulsive configuration, which is the best performance of the two-state Deutsch-Jozsa algorithm compared with \textit{intra}molecular vibrational-vibrational, vibrational-rotational, and electronic-vibrational qubits reported so far. [Preview Abstract] |
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R1.00203: Thermal conductivity of Si nanocrystals Shang-Fen Ren, Wei Cheng Thermal conductivities of spherical Si nanocrystals (NCs) are investigated with three different models: a macroscopic approximation, a semi-microscopic model that calculates the heat capacity of NCs with a microscopic Valance-Force-Field Model (VFFM), and a full microscopic description of phonon thermal conduction that calculate both heat capacity and phonon group velocity by the VFFM. The results are compared, and the advantages and limitations of each of these models are discussed. It is shown that for spherical Si NCs, the macroscopic approximation is quite good for NCs with a diameter larger than 1.33 nm. For smaller NCs, the VFFM predicts that the thermal conductivity increases quickly when the size decreases, opposite to the macroscopic approximation, and VFFM also predicts that the minimum of thermal conductivity for spherical Si NCs occurs at a diameter of 1.33 nm, the limit at which the macroscopic approximation applies. [Preview Abstract] |
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R1.00204: Thermoelectricity in Ca$_{3}$Co$_{4}$O$_{9}$: An Atomic Structure Perspective T. Tyson, Z. Chen, J. Tu, Q. Li The temperature dependent local structure about the Co sites in the misfit system referred to as Ca$_{3}$Co$_{4}$O$_{9}$ was examined by x-ray absorption spectroscopy. Density Functional calculations utilizing a large cell were used to obtain the optimized atomic structure. The detailed atomic structure about the Co sites was determined from the XAFS measurements. The complementary density functional computations of the structure and atomic forces provide a new 3D model of the structure and point to a unique configuration which may be the origin of the high thermoelectricity in this material. [Preview Abstract] |
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R1.00205: Maximizing thermoelectric figure-of-merit at high temperature in p-type Bi-Sb-Te system. Bo Yu, Yi Ma, Jian Yang, Bed Poudel, Yucheng Lan, Dezhi Wang, Zhifeng Ren, Qing Hao, Gang Chen Bismuth telluride alloys and their derivatives are the most important thermoelectric materials used in refrigeration devices around room temperature. Using mechanical alloying and hot press, we have achieved 100{\%} dense nano-structured p-type Bi$_{x}$Sb$_{2-x}$Te$_{3}$ samples. We demonstrated here that the enhanced dimensionless figure-of-merit (ZT) are due to enhanced phonon-scattering, and the ZT peak could be easily shifted to higher temperature by varying the composition and processing conditions. [Preview Abstract] |
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R1.00206: Thermoelectric Properties Studies on n-type Bi$_{2}$Te$_{3-x}$Se$_{x}$ Jian Yang, Xiao Yan, Yi Ma, Bed Poudel, Yucheng Lan, D.Z. Wang, Z.F. Ren, Q. Hao, G. Chen Bi$_{2}$Te$_{3-x}$Se$_{x}$ is a classic room temperature n-type thermoelectric material. In spite of the long history of research, its ZT is still below 1. By directly making nano sized particles using mechanical alloy from element, then pressing the nanoparticles into 100{\%} dense bulk sample with nano-structures by hot press, we expect to decrease the thermal conductivity by the increased grain boundary scattering of phonons so to improve the ZT above 1. The ratio of Te/Se was varied systematically to investigate its effect on thermal conductivity. [Preview Abstract] |
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R1.00207: Thermionic cooling on barium strontium thin film surface Feng Jin, Guogang Qian, Scott Little Strong thermionic emission was observed from low-work-function barium strontium oxide thin films. Such strong thermionic emission resulted a large cooling effect on the emitting surface. Temperature drops as high as 90 \r{ }C C was obtained. Barium strontium oxide [(BaSr)O] thin films approximately 1 $\mu $m in thickness were deposited on tungsten substrates using RF magnetron sputter deposition. Thermionic emission from the thin film was characterized and the work function of the thin film was measured using Richardson line method. The temperature drop or cooling of the thin film surface at different emission current was measured using a high precision optical pyrometer. [Preview Abstract] |
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R1.00208: Mn linear chains deposited on CuN/Cu(001): environment effects on the Mn-Mn interactions Maria Andrea Barral, Ana Maria Llois, Ruben Weht, Gustavo Lozano Scanning tunneling microscopy (STM) was used recently to study the interaction among manganese atoms deposited on thin insulating copper nitride islands grown on Cu(001). The value of the exchange interaction J among manganese atoms for different atomic arrangements was obtained, showing that it strongly depends on the Mn deposition sites. In this contribution we present the result of ab initio calculations for different arrangements of infinite Mn chains on CuN/Cu(001) to understand the influence of the environment on the Mn-Mn exchange interactions. [Preview Abstract] |
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R1.00209: Photopatterning in phase separating reactive ternary systems Pratyush Dayal, Olga Kuksenok, Anna Balazs We investigate a ternary ABC phase separating system in which components A and B undergo reversible photochemical inter-conversion reaction while component C remains non-reactive. We focus on systems with unequal forward and backward reaction rates. It has been well known that in such binary systems the competition between phase separation and chemical reaction results in hexagonal patterns contrary to lamellar structures for equal reaction rates. Since the chemical reaction favors miscibility a phase diagram is established to determine the phase boundary of such systems. We demonstrate that by confining chemical reaction to designated places using masks more complicated structures could be formed in the binary AB systems. We elucidate the scenarios in which the third non-reactive C component results in the displacement of AB domains from the reaction sites in favor of C. This migration is driven by difference in the free energies between the reaction sites and the masked regions. A rich variety of complex super-lattice patterns can be formed by changing the processing variables such as initial concentration, distance between the masks and rates of forward and backward reaction. [Preview Abstract] |
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R1.00210: Self assembled silicon nanowire Schottky junction assisted by collagen Didier Stievenard, Billel Sahli, Yannick Coffinier, Rabah Boukherroub, Oleg Melnyk We present results on self assembled silicon nanowire Schottky junction assisted by collagen fibrous. The collagen is the principle protein of connective human tissues. It presents the double interest to be a low cost biological material with the possibility to be combed as the DNA molecule. First, the collagen was combed on OTS modified surface with gold electrodes. Second, silicon nanowires were grown on silicon substrate by CVD of silane gas (SiH4) at high temperature (500\r{ }C) using a vapor-liquid-solid (VLS) process and gold particles as catalysts. In order to increase electrostatic interaction between the collagen and the nanowires, these latters were chemically modified by mercaptopropylmethoxysilane (MPTS), then chemically oxidized. Therefore, the nanowires were transferred from their substrate into water and a drop of it deposited on the surface. Nanowires are only bound to collagen and in particular, in electrode gaps. The formation of spontaneous Schotkty junction is demonstrated by current-voltage characteristics. [Preview Abstract] |
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R1.00211: COMPUTATIONAL METHODS: DYNAMICS, TRANSPORT, AND PLASMA |
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R1.00212: Merging for Complex Particle Kinetic modeling of multiple plasma beams (inter-penetrating flows) Alexander Lipatov We suggest a merging procedure for the Complex Particle Kinetic (CPK) model in case of inter-penetrating flow (multiple plasma beams). Each CPK macro-particle includes a Maxwellian distribution in velocity and Gaussian distribution in space with internal dynamics (see [Hewett, 2003], for details). It is assumed that an arbitrary distribution of real particles can be represented by such a superposition in phase space (moving--finite----element approach) at least as well as could be done with the standard particle in cell (PIC)/Monte Carlo (MC) delta functions and their associated ``shape factors". The CPK method allows us to provide a global simulation of the complex plasma objects on the Hall-MHD (fluid) scale (aggressive merging) with automatic incorporation of the kinetic/particle description of the particle-wave processes (aggressive fragmentation) where it is necessary. The CPK approximation works well for ions, electrons, dust grains and neutral components. This code was tested in the simulations for the study of the interaction of the plasma flow with comets and Io's atmosphere. In this report we examine the standard (PIC) and the CPK methods in the case of the particle acceleration by shock surfing. The plasma dynamics is described by a standard (particle-ion-- fluid- electron) hybrid model. While a particle-mesh method is well enough verified approach, the CPK model seems to be a good approach in case of multiscale simulation which includes multiple subdomains with various particle/fluid plasma behavior. [Preview Abstract] |
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R1.00213: Non-Local Thermodynamic Equilibrium Modeling of Tungsten Plasma Matthew Foster, J. Abdallah Jr., J. Colgan Controlled fusion tokamaks such as ITER present challenging theoretical plasma modeling issues. Since the divertor region of ITER will be coated with tungsten, accurate collisional-radiative (CR) models are required to understand the high radiative power losses associated with tungsten. The energy loss due to radiative processes for high-Z ions can be critical in understanding the ionization balance of the plasma. We present non-local thermodynamic equilibrium (non-LTE) calculations for a tungsten plasma using the Los Alamos National Laboratory suite of atomic codes. We examine the radiated power losses and ion balance distributions for a variety of electron temperatures ranging from 2 keV to 30 keV and densities associated with conditions found in ITER. [Preview Abstract] |
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R1.00214: Merging for Complex Particle Kinetic modeling of multiple plasma beams (inter-penetrating flows) Merging for Complex Particle Kinetic modeling of multiple plasma beams (inter-penetrating flows) Alexander Lipatov We suggest a merging procedure for the Complex Particle Kinetic (CPK) model in case of inter-penetrating flow (multiple plasma beams). Each CPK macro-particle includes a Maxwellian distribution in velocity and Gaussian distribution in space with internal dynamics (see [Hewett, 2003], for details). It is assumed that an arbitrary distribution of real particles can be represented by such a superposition in phase space (moving--finite----element approach). The CPK method allows us to provide a global simulation of the complex plasma objects on the Hall-MHD (fluid) scale (aggressive merging) with automatic incorporation of the kinetic/particle description of the particle-wave processes (aggressive fragmentation) where it is necessary. The CPK approximation works well for ions, electrons, dust grains and neutral components. This code was tested in the simulations for the study of the interaction of the plasma flow with comets and Io's atmosphere. In this report we examine the standard (PIC) and the CPK methods in the case of the particle acceleration by shock surfing. [Preview Abstract] |
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R1.00215: Boiling Dynamics with Diffuse Interface Methods Teemu Laurila, Mika Saukkonen, Tapio Ala-Nissila, Juha Ruokolainen We study the dynamics of fluid systems composed of two phases of a sigle component, such as a mixture of water and water vapour. Diffuse interface methods (Anderson et al., Ann. Rev. Fluid Mech., 98) can be used to desribe the system without explicitly keeping track of interfaces. An implementation of standard fluid dynamics on a FEM platform (ELMER) is converted to the diffuse interface method. Using the Van der Waals equation of state and proper boundary conditions, we obtain a consistent description of a liquid/gas system in coexistence (closed system) or undergoing a transition (open system). However, we find that this description requires the use of interface widths in the range of those of real systems. This leads to a dead-end with numerics, since it is numerically unfeasible to solve a system large enough to contain a supercritical domain. Our proposed solution inlvolves fitting the two-phase bulk free energy to obtain the stable state densities and the surface tension according to experimental or approximated values. Furthermore, an addition to the boundary condition is needed to account for three-phase contact line motion. We aim to apply the resulting model to two-phase phenomena in microfluidics (Zwaan et al. , PRL 07), and boiling in particular (Nikolayev, PRL, 06). [Preview Abstract] |
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R1.00216: Response Dynamics of an over damped driven linear chain of coupled fractional oscillators B.N. Narahari Achar, John W. Hanneken The dissipative motion of an elastic chain in a random potential provides an interesting model relevant to several phenomena in Condensed Matter Physics. A useful alternative approach is one in which the dissipative term is expressed as a fractional derivative. A generalized model, a linear chain of coupled fractional oscillators is presented here. The generalization is carried out operationally by starting with the integral equation of motion of driven, over damped, linear chain of harmonic oscillators (in which the inertial term is absent) and replacing the regular integral by a fractional integral according to the methods of fractional calculus. The solution is obtained by Laplace transforms. In the continuum limit the fractional diffusion- wave equation is obtained. The solution and numerical application are discussed. [Preview Abstract] |
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R1.00217: Distribution of Zeros of the Mittag-Leffler Function John W. Hanneken, David M. Vaught, B.N. Narahari Achar The Mittag-Leffler function, which is a generalization of the exponential function, occurs naturally in the solution of physical problems involving fractional differential equations. The zeros of the Mittag-Leffler functions play a significant role in the dynamics solutions. Complete and correct information about the distribution of zeros has not yet been available. A systematic analysis of the zeros of E$_{\alpha ,\alpha }$(z) has been carried out and an iteration formula for the number of zeros for arbitrary alpha has been obtained. [Preview Abstract] |
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R1.00218: BIOLOGICAL PHYSICS |
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R1.00219: Procedure to Measure Effect of Excess Body Mass on Musculoskeleture: I. Foundation Saami J. Shaibani Increasing levels of obesity are having an increasingly adverse impact on individual and societal health. While much effort is directed to the harmful consequences of excess body mass on the cardiovascular system, there is relatively little research on how obesity compromises the response of the musculoskeletal system across the complete range of body types. This shortfall is addressed here by a comprehensive physics-based approach to produce a wide spectrum of representative adults, who are carefully chosen to cover both sexes, a full spread of percentiles for stature, and multiple weight levels. The latter encompass healthy, overweight and obese conditions defined by the standard parameter, body mass index (BMI). The distribution of body mass is computed for female and male subjects at all height percentiles and values of BMI to generate a detailed description of a diverse population. This cohort can then be examined for more advanced aspects of musculoskeleture, an important precursor for which is included here by calculating the extent of excess body mass at each body part as a function of BMI. [Preview Abstract] |
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R1.00220: How Phospholipid Diffusion Depends on the Presence of Alpha-Hemolysin Pores and Adsorbed DNA Mo Jiang, Bo Wang, Sung Chul Bae, Steve Granick Building on our recent finding that the adsorption of a flexible macromolecule to a supported phospholipid bilayer produces spots of different lipid heterogeneity even in bilayers comprised of one single type of phospholipid, investigations are now reported regarding DNA and also a pore-forming protein, bacterial streptolysin. The larger question is to understand how macromolecules of bio-significance with specific macroscopic geometric structures affect phospholipid mobility. [Preview Abstract] |
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R1.00221: Molecular dynamics simulations of DNA-polycation complexes Jesse Ziebarth, Yongmei Wang A necessary step in the preparation of DNA for use in gene therapy is the packaging of DNA with a vector that can condense DNA and provide protection from degrading enzymes. Because of the immunoresponses caused by viral vectors, there has been interest in developing synthetic gene therapy vectors, with polycations emerging as promising candidates. Molecular dynamics simulations of the DNA duplex CGCGAATTCGCG in the presence of 20 monomer long sequences of the polycations, poly-L-lysine (PLL) and polyethyleneimine (PEI), with explicit counterions and TIP3P water, are performed to provide insight into the structure and formation of DNA polyplexes. After an initial separation of approximately 50 {\AA}, the DNA and polycation come together and form a stable complex within 10 ns. The DNA does not undergo any major structural changes upon complexation and remains in the B-form. In the formed complex, the charged amine groups of the polycation mainly interact with DNA phosphate groups, and rarely occupy electronegative sites in either the major or minor grooves. Differences between complexation with PEI and PLL will be discussed. [Preview Abstract] |
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R1.00222: A Mathematical Model for Calculating the Effect of Toroidal Geometry on the Measured Magnetic Field Brenda Skoczelas, Ranjith Wijesinghe A mathematical model to calculate the measured magnetic field from a stimulated nerve has been presented in the past. Traditionally, electrodes have been used to measure these propagating action signals in nerves, but a less invasive technique is to use toroids. However, up until now, when using a toroidal transformer to record the nerve action currents, the thickness of the toroid has yet to be considered in the model and how it may affect the propagating compound action potential. In this presentation, we will discuss the development of a new model, to which the thickness of the toroid is taken into account. These dimensions are important because the toroid represents an inhomogeneity in the extracellular medium that redistributes the extracellular current. In the past, toroids with very small diameters have been used and as they may not disrupt the action current. With a better understanding of the toroidal effects, we may be able to increase the accuracy and dependency of such measured magnetic signals. The final goal will be to compare our theoretical model to experimentally gathered data. [Preview Abstract] |
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R1.00223: Co-existence of silent and oscillatory regimes of a single neuron's activity Tatiana Malaschenko, Andrey Shilnikov, Gennady Cymbalyu Bursting, tonic spiking, sub-threshold oscillations and silence are basic robust regimes of activity of a single neuron. A model of a leech heart interneuron demonstrates three different types of co-existence: (1) silence and bursting, (2) silence and tonic spiking, and (3) silence and sub-threshold oscillations. We show that these types of co-existence can be explicated by the unstable sub-threshold oscillations (USTO) separating silence and an oscillatory regime and setting the threshold between them. The range of parameters, where the co-existence is observed, is determined by the critical values at which the USTO appear and disappear. More precisely, the USTO occur through the sub-critical Andronov-Hopf bifurcation, where the rest state loses stability. Then, the USTO disappear on the homoclinic bifurcation near which the oscillatory regime disappears as a regime. The bifurcation values are calculated and shown to match the empirical transition values found in numerical experiments in Cymbalyuk et al., 2002. [Preview Abstract] |
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R1.00224: Biophysically realistic minimal model of dopamine neuron Sorinel Oprisan We proposed and studied a new biophysically relevant computational model of dopaminergic neurons. Midbrain dopamine neurons are involved in motivation and the control of movement, and have been implicated in various pathologies such as Parkinson's disease, schizophrenia, and drug abuse. The model we developed is a single-compartment Hodgkin-Huxley (HH)-type parallel conductance membrane model. The model captures the essential mechanisms underlying the slow oscillatory potentials and plateau potential oscillations. The main currents involved are: 1) a voltage-dependent fast calcium current, 2) a small conductance potassium current that is modulated by the cytosolic concentration of calcium, and 3) a slow voltage-activated potassium current. We developed multidimensional bifurcation diagrams and extracted the effective domains of sustained oscillations. The model includes a calcium balance due to the fundamental importance of calcium influx as proved by simultaneous electrophysiological and calcium imaging procedure. Although there are significant evidences to suggest a partially electrogenic calcium pump, all previous models considered only elecrtogenic pumps. We investigated the effect of the electrogenic calcium pump on the bifurcation diagram of the model and compared our findings against the experimental results. [Preview Abstract] |
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R1.00225: An Analytical Study of the Interplay between Geometrical and Energetic Effects in Protein Folding Yoko Suzuki, Jeff Noel, Jose Onuchic We introduce a Gaussian filament with a C${}_{\alpha}$ structure-based (G\={o}) potential as a new theoretical scheme based on a Hamiltonian approach. This model takes into account geometrical information in a realistic fashion without the need of phenomenological descriptions. In order to make this model more appropriate for comparison with protein folding simulations and experiments, we introduce a many-body interaction into the potential term to enhance cooperativity. We apply our new analytical model to a $\beta$-hairpin type peptide and compare our results with a molecular dynamics simulation of a structure-based model. those comparisons successfully give the quantification of the interplay between geometrical and energetic effects. [Preview Abstract] |
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R1.00226: Single-Point Mutations and Protein Structure Deviations Roy Campbell The V4 proteins, LmcA and LmcB, in the social amoeba Dictyostelium are believed to play an important role in the growth to development transition of the organism. Whether or not a normal transition occurs depends on whether one or the other or both of the proteins is expressed. The proteins only differ by one non-conserved residue. In order to understand the possible differences in protein structure and function we performed an ab initio structure calculation for each protein using the Monte Carlo fragment insertion method implemented by Rosetta. The predicted structures were found to be dramatically different. This result inspired a comprehensive survey of all the Protein Data Bank structures related by a single-point mutation. The distribution of mutations with respect to the resulting rms deviation in atomic coordinates was found to have a simple exponential behavior. [Preview Abstract] |
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R1.00227: Crystallographic and solution studies of fluorescence photocycle of GFP Georgi Georgiev, Jasper van Thor, J. Timothy Sage Phototransformation in GFP is a competing process to the excited state proton transfer (ESPT) ionizing the chromophore, and decarboxylating Glu222. The fluorescence photocycle itself is an ESPT from chromophore to Glu222, ionizing chromophore and neutralizing Glu222. Cryotrapped reaction intermediates of the phototransformed GFP electrostatically mimic intermediates in the fluorescence photocycle. Illumination at 100K leads to appearance of both a visible absorption band at 497nm, indicating an ionized chromophore in a non-equilibrium environment, and of multiple IR bands due to photogenerated carbon dioxide, confirming the decarboxylation of Glu222. Polarized IR measurements on single crystals, measurements on mutant GFP, and solvent exchange measurements allow us to identify IR difference signals due to Gln69, Cys70, and weakly hydrogen-bonded internal water molecules. [Preview Abstract] |
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R1.00228: Cooperative Macromolecular Disassembly via the Heat Shock Chaperone Hsc70 Jason Puchalla, Kelly Krantz, Robert Austin, Hays Rye Many essential cellular functions depend on the assembly and disassembly of macromolecular complexes. A general class of protein known as molecular chaperones regulates several of these processes. How can complex protein structure be quickly and efficiently disassembled by the action of a small number of these proteins? One such example is that of clathrin: a ubiquitous coat protein that stabilizes vesicular trafficking by forming a scaffold onto the membrane surface. This scaffold must be removed before the vesicle can deliver its cargo. We report on the cooperative disassembly of yeast-derived GFP-labeled clathrin baskets via its interaction with Hsc70. We exploit the highest signal-to-noise light bursts from single fluorescent baskets transiting a confocal excitation spot to recursively determine the brightness and size distribution of the baskets during the uncoating process. This minimal uncoating system demonstrates the ability of a surprisingly simple protein system to facilitate rapid structural changes through cooperative action. [Preview Abstract] |
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R1.00229: Linking Inverse Square Law with Quantum Mechanical Probabilities Shantilal Goradia ({\copyright}2007 by S Goradia) I modify the Newtonian inverse square law with a postulate that the probability of interaction between two elementary particles varies inversely as the statistical number of Planck lengths separating them. For two nucleons a million Planck lengths apart, the probability of an interaction is a trillionth (almost never), seemingly contradicting gravity. Likewise, statistical expression of the size of the universe implicitly addresses the issue of dark energy by linking fine-structure constant \textit{$\alpha $} = 1/137 with the cosmological constant \textit{$\lambda $} = 1/$R^{2}$ (abstract submitted 11/11/07 for APS APR2008 meeting). Since light travels one Planck length per Planck time, the radius $R$ of the spherical shape of the universe is 10$^{60}$ Planck lengths, linking the cosmological constant \textit{$\lambda $ = }1/10$^{120}$ (see equation 14 in Einstein's 1917 paper) with $\alpha $ by the relationship 1/\textit{$\alpha $} $\approx $ \textit{ln}$\surd $(1/ \textit{$\lambda $}). Intuitive answers to the questions raised suggest that the elementary particles interact via Planck scale mouths $^{(1),}$ with higher probabilities at smaller distances. This intuition may be supported by genetics, explaining issues such DNA -- nucleosome interaction $^{(2) (3)}$. [1] http://www.arxiv.org/pdf/physics/0210040 [v. 3] [2] www.gravityresearchinstitute.org [3] Segal E. \textit{et al}$,$ A genomic code for nucleosome positioning.\textit{ Nature} 442, pp. 772-778, 2006. [Preview Abstract] |
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R1.00230: Fullerenes Can Induce Toxic Physical Changes of DNA Fabian Czerwinski, Lene B. Oddershede Fullerenes are fascinating symmetric carbon nanostructures. Nowadays, they are widely used because of their characteristic physical and chemical properties. Until now research has mainly been focused on commercial applications of fullerenes. Only a few investigations have addressed the potential biological hazards, one of which is that fullerenes are believed to alter the elastic properties of DNA upon binding. In our experiments we use optical tweezers with sub-piconewton and nanometer resolution to probe the structural changes and the potential damages which fullerenes might induce on single DNA molecules. Therefore, force-extension relations can be obtained under physiological conditions while varying the concentration of different types of fullerenes. It has theoretically been predicted [1], that certain fullerenes can function as a minor-groove binder to double-stranded DNA, thus altering its elastic properties significantly. Fullerenes are capable of causing severe damage inside living organisms by forming DNA regions which are not accessible for proper enzymatic functions. A further goal of the study is to establish fullerenes as a tool for a more detailed investigation of DNA-protein interactions, such as the trafficing of polymerases or the packing by procaryotic proteins. [1] Zhao X, Striolo A, and Cummings PT: C$_{60}$ Binds to and Deforms Nucleotides. BiophysJ (89):3856-62, 2005. [Preview Abstract] |
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R1.00231: A study of the stability of the DNA double helix in complexes of DNA with the bipyridyl-(ethylenediamine)platinum(II) molecular ion. Attila Szabo, Scott Lee The DNA double helix is usually stabilized by the formation of a complex with a ligand. However, the exact nature of the complex can destabilize the double helix, as is well known in complexes of DNA with diaminedichloroplatinum(II). We report the results of our study of the complex of DNA with bipyridyl-(ethylenediamine)platinum(II), abbreviated [(bipy)Pt(en)]$^{2+}$, via ultraviolet melting experiments. We find that the DNA double helix is stabilized by the formation of the complex: the temperature of the onset of melting of the DNA double helix increases with increasing amounts of [(bipy)Pt(en)]$^{2+}$. The onset temperature is increased by about 14 $^{o}$C for a ligand content of one [(bipy)Pt(en)]$^{2+}$ for every three DNA base pairs. [Preview Abstract] |
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R1.00232: From frontier states to an inter-nucleotide potential for DNA: a density functional theory based study Maria Fyta, Efthimios Kaxiras We present results from accurate density functional theory based simulations of individual DNA bases and representative base-pairs in various relative configurations, as they are likely to appear in the equilibrium and stretched forms of DNA. Specifically, we extract the salient features of electronic structure of these molecules and reveal that the frontier states in the base pairs are related to only one component of the pair. For all combinations of bases and base pairs studied here, the nature of these states was not affected by separation of the bases or base pairs along different directions or rotation along the helical axis. From the same calculations we were able to parametrize and construct an optimized intermolecular potential for DNA nucleotides, that accounts for hydrogen bonding, stacking interactions and the contribution from the sugar backbone. These calculations serve to set the stage for more extensive coarse grain calculations of DNA related biophysical phenomena. [Preview Abstract] |
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R1.00233: Drug-Membrane Interactions Studied by Vibrational Sum-Frequency Spectroscopy Lauren Wolf, Kimberly Briggman The activity of a number of drugs depends directly on their interaction with cell membranes and, thus, an understanding of drug-membrane interactions is necessary for improving their pharmacological performance. Drug molecules can interact with membranes by directly binding to membrane-bound proteins or by intercalating into the lipid matrix itself, altering membrane properties such as fluidity, thickness, internal pressure, and phase transition temperature. Here, we focus on the effects of local anesthetics incorporated into the lipid matrix, studying the structural changes induced in supported lipid bilayers by vibrational sum-frequency spectroscopy (VSFS). We find that in addition to depressing the phase transition temperature of the lipid bilayers, most anesthetics also sharpen the gel to liquid- crystalline transition, suggesting an increase in membrane constituent cooperativity. This behavior contrasts the effects of cholesterol on lipid bilayers, which increases membrane rigidity and broadens the phase transition. The structure of the membrane-intercalated anesthetics themselves will also be discussed. This work demonstrates the potential of using supported lipid bilayers and surface-sensitive techniques for future pharmacological studies. [Preview Abstract] |
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R1.00234: Structure of Functional \textit{Staphylococcus aureus }$\alpha $-Hemolysin Channels in Tethered Bilayer Lipid Membranes. Frank Heinrich, Gintaras Valincius, Duncan J. McGillivray, Joseph W.F. Robertson, Ilja Ignatjev, John J. Kasianowicz, Mathias Loesche We demonstrate the functional reconstitution of the \textit{Staphylococcus aureus }$\alpha $-hemolysin channel in membranes tethered to gold. Electrical impedance spectroscopy measurements show that the pores have essentially the same properties as those formed in free-standing bilayer lipid membranes. Neutron reflectometry (NR) provides high-resolution structural information on the interaction between the channel and the disordered membrane, and validates predictions based on the channel x-ray crystal structure. NR also shows that the proximity of the solid interface does not affect the molecular architecture of the protein-membrane complex. The results suggest that this technique could be used to elucidate molecular details about the association of other proteins with membranes. It also may provide structural information on domain organization and stimuli-responsive reorganization for transmembrane proteins in membrane mimics. [Preview Abstract] |
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R1.00235: Molecular Dynamics Simulated Annealing Study of Gramicidin A in Water and the Hydrophobic Environment Takaharu Mori, Yuko Okamoto Gramicidin A is a hydrophobic 15-residue peptide with alternating {\scriptsize D}- and {\scriptsize L}-amino acids, and it forms various conformations depending on its environment. For example, gramicidin A adopts a random coil or helical conformations, such as $\beta^{4.4}$-helix, $\beta^{6.3}$-helix, and double-stranded helix in organic solvents. To investigate the structural and dynamical properties of gramicidin A in water and the hydrophobic environment, we performed molecular dynamics simulated annealing simulations with implicit solvent based on a generalized Born model. From the simulations, it was found that gramicidin A has a strong tendency to form a random-coil structure in water, while in the hydrophobic environment it becomes compact and can fold into right- and left-handed conformations of $\beta$-helix structures. We discuss the folding mechanism of the $\beta$-helix conformation of gramicidin A. [Preview Abstract] |
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R1.00236: Photo- and bio-physical characterization of novel blue and near-infrared lipophilic fluorophores for neuronal tracing Jeff Tonniges, Maria Hansen, Bernd Fritzsch, Brian Gray, Michael Nichols Lipophilic fluorescent dyes have been used to trace neuronal connections because of their ability to diffuse laterally between nerve cell membranes. Given the large number of connections that a typical neuron makes with its neighbors, a diffusion-matched set of spectrally distinct dyes is desirable. Previously, a trio of dyes was developed with well-separated green, red and far red fluorescence emission that permitted triple labeling [1]. To extend this set to five, we have been characterizing the properties of novel blue and near-infrared candidates. By combining two-photon and confocal microscopy all of these candidates can be imaged using a single Ti:S laser. Here we present measurements of the absolute two-photon excitation spectra along with single- and two-photon fluorescence recovery after photobleaching measurements of the diffusion coefficient in spinal cord samples. [1] H. Jensen-Smith et al., Immunol. Invest., in press, 2007. [Preview Abstract] |
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R1.00237: Coupled Translational and Rotational Fluctuations of Tethered Beads Andrew Spakowitz, Shafigh Mehraeen Single-molecule manipulation plays an important role in determining the physical mechanisms responsible for biological function. Establishing a robust method of predicting the fluctuating behavior of a tethered bead provides insight into how to maximize the signal-to-noise ratio to improve experimental resolution. We theoretically address the behavior of single-molecule experimental apparatuses. Our theory is amenable to addressing a variety of different bead-tether systems, thus providing a basis for comparing and contrasting these different experimental setups and for adapting the theory to the specific experimental system of interest. Fluctuations in both the location and orientation of the bead are incorporated in the theory; we explore their coupled effect on the observed behavior in single-molecule systems. The physical behavior of the tether molecule is described using the wormlike chain model. Making use of our exact solutions for wormlike chain model statistics, our current treatment achieves exact precision for the polymer behavior, apart from the approximations that are inherent to the wormlike chain model. We find that the impact of rotational fluctuations on the bead motion is largest when the radius of the bead is comparable to the length of the chain tether. We explore the impact that chain length and bead radius have on the resolution of single-molecule experiments and how to maximize the signal-to-noise ratio. [Preview Abstract] |
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R1.00238: Formation of highly ordered self assembled monolayers of alkanethiol molecules on thermally annealed gold films. Young-Kyu Hong, Hyunung Yu, Tae Geol Lee, Noah Lee, Jae Ho Bahng, Nam Woong Song, Won Chegal, Hyun Kyong Shon, Ja-Yong Koo We controlled the ordering between alkanethiol molecules in self-assembled monolayers (SAMs) formed on a Au surface by modifying surface topography of Au films. The ordering between molecules was evaluated using Fourier Transform infrared (FTIR) spectroscopy. A thermal annealing in hydrogen environment removed the nm-scale protrusions from the surface of as deposited Au film resulting in an increase in grain size and a decrease in roughness. This process allowed the alignment of Au atoms in the (111) direction. Together with the aligned Au surface, Au nanoparticles were also prepared as a rough surface with tiny grain size of $\sim $ 10 nm. The symmetric and asymmetric CH$_{2}$ vibrations in the FTIR spectra showed a larger blueshift from the SAMs on an flatter Au surface. Binding specificity of molecules was examined by Secondary Ion Mass Spectroscopy (SIMS) using a Au pattern formed on a SiO$_{2}$/Si wafer. The molecular signal matched with the Au pattern and the ratio of the signals on Au to SiO$_{2}$ was larger than 1000, indicating that the level of non-specific binding was negligible. This method of improving and controlling the ordering between molecules in the SAMs can be applied to sub $\mu $m patterns on a SiO$_{2}$/Si wafer. [Preview Abstract] |
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R1.00239: Detecting Low Levels of Cytochalasin B in 3T3 Fibroblast Cells by Analysis of Electrical Noise Obtained from Cellular Micromotion Douglas Lovelady, David Rabson, Chun-Min Lo We performed several micromotion experiments using the electric cell-substrate impedance sensing (ECIS) apparatus on a confluent layer of 3T3 fibroblast cells exposed to differing, low-level amounts of the toxin cytochalasin B. We previously developed a technique to distinguish cancerous from non-cancerous cultures.\footnote{\frenchspacing D.C. Lovelady {\it et alia}, {\it Phys. Rev. E} {\bf 76}, 041908 (2007)} Our goal here is to see if the same technique can be used to distinguish toxin levels in a single cell type. The noise of the time series extracted from these experiments is characterized by the power spectrum, Hurst exponent, DFA (detrended fluctuation analysis) exponent, first zero and first $1/e$ crossing of the autocorrelation function. These measures describe the long- and short-term correlations in the signal, which tell us something about the average behavior of these cells in culture. A change in the behavior of these cells is clearly revealed by an examination of these measures. A principal-component analysis shows a separation of the different toxin levels in the multidimensional space. To our knowledge, this is the most sensitive technique for detecting such a low level of cytochalasin B in 3T3 fibroblast cells. [Preview Abstract] |
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R1.00240: Trapping Single Molecules With a Solid State Nanopore Marc Gershow, David Hoogerheide, Eric Brandin, Jene Golovchenko We demonstrate a single molecule trap based on a solid state nanopore. A single molecule of DNA is driven through a nanopore by an applied eletric field. The passage of the molecule through the nanopore is detected by a decrease in the ionic current through the pore. After the molecule has passed through the pore, we reverse the applied field to recapture the molecule and drive it through the pore again. Upon detection of this second passage, we again reverse the applied field, leading to a third passage through the pore, and so on. Thus the molecule is continually confined by a $\frac{1}{r}$ potential maintained by active feedback. Upon each passage through the pore, the state of the molecule is electronically interrogated via the measured current blockage. Molecules can be trapped, detected, and analyzed in free solution without any labels or chemical modifications. Repeated electronic interrogation of a single molecule provides a means for greatly enhancing the accuracy with which each molecule can be characterized by a nanopore and allows measurement over time of dynamical properties such as the molecule's conformation and chemical state. [Preview Abstract] |
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R1.00241: Subcellular modification of tissue by near-field laser ablation M. E. Reeves, J. A. Hoffmann, Jasper Nijdam, Benjamin Gamari We report on the development of a near-field approach to MALDI (Matrix-assisted laser desorption and Ionization). In this technique analytes embedded in an energy absorbing matrix are ablated from the surface of a sample. In the infrared region, the matrix can be water by exciting the 3-micron vibrational mode of the water molecule. 3-micron wavelength lasers are available with sufficient power to ablate materials of interest, particularly biological samples, however, in most cases the spot size is fairly large, about 40 microns or more, due to the primitive optics available for this wavelength of light. In our laboratory, we have demonstrated near-field focusing of a 3-micron laser to a sub-wavelength spot size with energy sufficient to ablate material from the sample surface. We will review our findings and describe demonstrations of tissue modification by this approach at length scales smaller than a single cell. This approach has the potential to allow the identification and mapping of proteins expressed in intact cells and tissues, which is of great interest as protein expression connects genomic information with the functioning of an organism. [Preview Abstract] |
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R1.00242: Fluorescence spectroscopy investigation and molecular docking simulation of the interaction of $\beta $-lactoglobulin A (BLGA) with meso-tetrakis(4-sulfonatophenyl) porphyrin (TSPP) Ivan Silva, Lorenzo Brancaleon, Sam Sansone The interaction of TSPP and $\beta $-lactoglobulin A (BLGA) was studied as a function of pH (6.0-9.0). TSPP is a dye that is currently in clinical trials for its application in photodynamic therapy of cancer, and BLGA is a well known globular protein. Binding to the protein affects the photophysics of the dye, hence its potential in clinical applications. Data from TSPP fluorescence experiments were analyzed and modeled by computational methods. Protein-dye interaction was studied using fluorescence spectroscopy to record the spectral shift (from 643nm to 649nm) to quantify bound and free dye with use of Gaussian curve fitting. TSPP-induced quenching of protein fluorescence determined the binding constant and the number of binding sites through S-V and double-log plots. Fluorescence lifetime characterized the effects of the binding and the location of the binding site through FRET. Unlike the binding of protoporphyrin IX, pH dependence of the TSPP binding to BLG is not modulated by the pH conformational change of the protein. Molecular simulation of the docking of TSPP monomers to BLGA dimers were done using the Arguslab software. Simulations reveal that the interaction is driven by the four negative charges on TSPP which keep it on the surface of the protein. [Preview Abstract] |
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R1.00243: The Peyrard-Bishop-Dauxois Model of DNA Dynamics Boian Alexandrov, Alan Bishop, Anny Usheva, Kim Rasmussen This presentation details aspects of the rapid development of the connection between the dynamics of double strand DNA, and experimental findings that has occurred in the recent years. We will approach this topic by demonstrating the Peyrard-Bishop-Dauxois model's ability to provide useful insight on several experimental observations. Specifically, we will discuss the melting behavior of various DNA sequences, and mechanical unzipping through dynamic force spectroscopy. Focusing on viral transcription initiation we will further show how the connection between DNA dynamics and DNA's biological functionality is becoming increasingly strong. Finally, we will describe a probable connection between DNA dynamics and the ability of repair proteins to recognize UV-radiation damages. [Preview Abstract] |
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R1.00244: Design of new inhibitors for H5N1 avian influenza using a molecular dynamics simulation Jin Woo Park, Won Ho Jo Recently, there has been a growing interest in the treatment of H5N1 avian influenza. One of the most widely used antiviral agents is oseltamivir. However, it has been reported that oseltamivir is not as effective against the neuraminidase subtype N1 as it is against subtypes N2 and N9. In our research we addressed this problem by designing new inhibitors and these altered inhibitor's binding affinities were calculated. In this study, we introduced chemical groups to the existing oseltamivir, so to fit into the newly discovered cavity in the subtype N1. When the binding strengths of the oseltamivir and the newly designed inhibitors for N1 were calculated to examine the drug efficiency through a molecular dynamics simulation, then compared with each other, it was found that one of the designed molecules exhibited a strong binding affinity, with more than twice the binding strength than that of oseltamivir. Since the aforementioned designed inhibitor appears to have the possibility for oral activity according to the criteria of human oral bioavailability, we propose that the inhibitor is a promising antiviral drug for H5N1 avian influenza. [Preview Abstract] |
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R1.00245: Phenotypic variability of growing cellular populations Ting Lu, Tongye Shen, Matthew Bennett, Peter Wolynes, Jeff Hasty The dynamics and diversity of proliferating cellular populations are governed by the interplay between the growth and death rates among the various phenotypes within a colony. In addition, epigenetic multistability can cause cells to spontaneously switch from one phenotype to another. By examining a generalized form of the relative variance of populations and classifying it into intracolony and cross-colony contributions, we study the origins and consequences of cellular population variability. We find that the variability can depend highly on the initial conditions and the constraints placed on the population by the growth environment. We construct a two-phenotype model system and examine, analytically and numerically, its time-dependent variability in both unbounded and population-limited growth environments. We find that in unbounded growth environments the overall variability is strictly governed by the initial conditions. In contrast, when the overall population is limited by the environment, the system eventually relaxes to a unique fixed point regardless of the initial conditions. However, the transient decay to the fixed point depends highly on initial conditions, and the time scale over which the variability decays can be very long, depending on the intrinsic time scales of the system. [Preview Abstract] |
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R1.00246: Biomolecular Network Simulator: Software for Stochastic Simulations of Biomolecular Reaction Networks on Supercomputers Yaroslav Chushak, Brent Foy, John Frazier At the functional level, all biological processes in cells can be represented as a series of biochemical reactions that are stochastic in nature. We have developed a software package called Biomolecular Network Simulator (BNS) that uses a stochastic approach to model and simulate complex biomolecular reaction networks. Two simulation algorithms - the exact Gillespie stochastic simulation algorithm and the approximate adaptive tau-leaping algorithm - are implemented for generating Monte Carlo trajectories that describe the evolution of a system of biochemical reactions. The software uses a combination of MATLAB and C-coded functions and is parallelized with the Message Passing Interface (MPI) library to run on multiprocessor architectures. We will present a brief description of the Biomolecular Network Simulator software along with some examples. [Preview Abstract] |
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R1.00247: Determining behaviors of biological networks with dynamic logic method. SuPing Lyu Dynamic logic method was used to study dynamic behaviors of some network motifs. This method combines logic operations and kinetic parameters of biological interactions (response or delay times). The analysis is simple because it is pure symbolic operation without numerical calculation. We proved in general that if networks are cycles with an odd number of suppression interactions, the cycles will oscillate. Delay times are necessary for oscillatory networks. If delay times are zero, the systems stay at stable states. If there are an even number of suppression interactions, the cycles have two stable states. Signal travel in chain-like networks was also studied. The depths of travel depend on the pulse width of signals and the filters of chains. Same signals with different pulse widths can have different biological responses (one stimulation to multiple responses). When pulsive signal travel in cycles, they can remain to be pulses, die, or become flat (all active) depending on the filters of cycles. The coupled cycles have complicated behaviors that are determined by their intrinsic structures and filters. Interestingly, chaotic behaviors were very rarely observed from analysis. [Preview Abstract] |
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R1.00248: Active Dynamics of Microtubule Bundles Assaf Zemel, Alex Mogilner Microtubule bundles play a central role in a variety of dynamical processes in cells such as cell division, neural growth and blood platelet formation. These processes are driven by the activity of molecular motors that exert sliding forces on the microtubules. In such bundles, motor proteins may crosslink two or more filaments, forming discrete clusters of microtubules whose dynamics is governed by a balance of the motor-generated forces. The connectivity of these microtubule-motor complexes is an essential property of the bundle and dictates its dynamics. We present a systematic computational study of these microtubule bundles based on force-balance computer simulations as well as a simplified analytical theory. This allows us to calculate the characteristic times of microtubule sorting and spreading, as well as the effective diffusion constants and drift coefficients as a function of the microtubule density and the polarity fraction of the microtubules. Application of our theory in the study of blood platelet formation is presented. [Preview Abstract] |
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R1.00249: Preliminary comparative studies of \textit{Thermus aquaticus} resilience to thermal and microwave heat input Konrad Kabza, Karen George, Stella von Meer, Armin Kargol \textit{Thermus aquaticus} was grown using existing ATCC protocol. Bacteria were cultured in large batches and each batch partitioned into usable 250 mL aliquots. These samples were then tested using identical parallel experiments, one heated with a traditional thermal heat source, while the other was irradiated with a 2.45 GHz conventional microwave oven. Relative growth of the \textit{Thermus aquaticus} was measured using UV visible spectroscopy at 400 nm. Multiple runs of the same experiments were averaged and the growth data for two modes of energization plotted. A unique low microwave exposure apparatus with a flow-through cell will be described and the entire experimental setup discussed. [Preview Abstract] |
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R1.00250: Electroshock weapons can be lethal! Marjorie Lundquist {\it Electroshock weapons} (EWs)$-$stun guns, tasers, riot shields$-$are electroconductive devices designed to {\it safely} incapacitate healthy men neuromuscularly, so they are called {\it nonlethal} or {\it less-lethal}. EW firms seeking large {\it nonmilitary} markets targeted law enforcement and corrections personnel, who began using EWs in prisons/jails and on public patrol in 1980 in the USA. This shifted the EW-shocked population from healthy soldiers to a heterogeneous mix of both sexes, ages 6-92, in a wide variety of health conditions! An EW operates by disrupting normal physiological processes, producing transient effects in healthy people. But if a person's health is sufficiently compromised, the margin of safety can be lost, resulting in death or permanent health problems. 325 people have died after EW shock since 1980. Did the EW {\it cause} these deaths? Evidence indicates that EWs {\bf do} play a causal role in most such deaths. EWs can be lethal for people in diabetic shock$^1$ (hypoglycemia), which may be why Robert Dziekanski$-$a Polish immigrant to Canada$-$died so quickly after he was tasered at Vancouver Airport: not having eaten for over 10 hours, he likely was severely hypoglycemic. The EW death rate in North America is 30 times higher than need be, because EW users have {\bf not} been properly trained to use EWs on a {\bf heterogeneous} population {\bf safely!} \\ $^1$J. Clinical Engineering {\bf 30}(3):111(2005). [Preview Abstract] |
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R1.00251: Analytic Thermodynamic Calculations for an Immobilized Molecule under Poisson-Boltzmann Interactions using a Spheroidal Geometry Joaquin Ambia-Garrido, Montgomery Pettitt The change in some thermodynamic quantities such as Gibbs' free energy, entropy and enthalpy of the binding of a particle tethered to a surface or particle are analytically calculated. These particles are considered ellipsoids and submerged in a liquid. The ionic strength of the media allows the linearized version of the Poisson-Boltzmann equation (from the theory of the double layer interaction) to properly describe the interactions between an ion penetrable spheroid and a hard plate. We believe that this is an adequate model for a DNA chip and the predicted electrostatic effects suggest the feasibility of electronic control and detection of DNA hybridization and design of chips underline avoiding the DNA folding problem. [Preview Abstract] |
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R1.00252: ABSTRACT WITHDRAWN |
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R1.00253: Kinesin motor protein as an electrostatic ratchet machine George Tsironis, Aleix Ciudad, Jose Maria Sancho Kinesin and related motor proteins utilize ATP fuel to propel themselves along the external surface of microtubules in a processive and directional fashion. We show that the observed step-like motion is possible through time varying charge distributions furnished by the ATP hydrolysis circle while the static charge configuration on the microtuble provides the guide for motion. Thus, while the chemical hydrolysis energy induces appropriate local conformational changes, the motor translational energy is fundamentally electrostatic. Numerical simulations of the mechanical equations of motion show that processivity and directionality are direct consequences of the ATP-dependent electrostatic interaction between the different charge distributions of kinesin and microtubule. Treating proterins as continuous dielectric media and using a Green's function formalism we find analytical expressions for the electrostatic energy in the vicinity of the protein surfaces. We calculate the Bjerrum length in the interior of the protein and analyze its dependence on the charge proximity to the protein interface. We apply these results to kinesin and estimate the pure electrostatic ATP-ADP interaction to be larger than 2k T. [Preview Abstract] |
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R1.00254: Efficiency optimization of the Buttiker-Landauer Heat Engine Ronald Benjamin, Ryoichi Kawai We study the energetic efficiency of a Brownian heat engine driven by spatially inhomogeneous temperature in presence of periodic potential, via Molecular Dynamics (MD) simulation as well as by numerically solving the inertial Langevin equation. We explore various potential shapes and different locations of the temperature boundary to identify the parameter regime in which the efficiency can be optimized. However the irreversible heat flow from the hot to the cold reservoir due to the particle's kinetic energy severely limits the efficiency and is not very sensitive to variations of the parameters. We also investigated the heat engine when it works with maximum power and found that the efficiency is much lower than that of the corresponding endoreversible engine. [Preview Abstract] |
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R1.00255: The anomalous polarization property in laser diode Tzu Fang Hsu, Yen Chun Lin, Yung Hsun Chen We have experimentally found some anomalous polarization property in laser diode (LD). As laser beam was merely passing through a polarizer, the polarization curve acted as normal cosine function which obeyed the behavior of linear polarization, fitting the property of LD. However, the polarization curve that linear polarized beam reflected by a glass plate became the shape, W, which is much more different to the curve of linear polarized light. By experimentally demonstrated, it is found that this anomalous curve was revealed as the linear polarized laser beam experienced the condition of second reflection, so that the curve of reflecting by mirror was normal cosine function and by prism was also the W shape. [Preview Abstract] |
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R1.00256: Anomalous diffusion and passage time distributions of microscopic particles through biological layers M. Gregory Forest, Christel Hohenegger, Scott McKinley, Lingxing Yao The field of passive microrheology was launched by Mason and Weitz in 1997, and has subsequently advanced in a variety of experimental and theoretical directions. The original aim is to infer viscoelastic properties from mean-squared displacement statistics of Brownian particles (beads) dispersed in the material. Extensions to bead-bead correlations have been advanced to screen local particle-material chemical potentials. The experimental measurements are equally, if not more so, ideal for characterizing the anomalous diffusive transport properties of soft matter, which are fundamental to pathogen or drug carrier diffusion through biological layers. Direct and inverse modeling and simulation tools will be presented, together with an evaluation of how well mean squared displacement serves as a proxy for passage time distributions. [Preview Abstract] |
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R1.00257: Test of the noise-induced nonequilibrium kinetic focusing of voltage-gated ion channels Armin Kargol, Konrad Kabza, Stella von Meer It has been postulated [1] that voltage-gated ion channels can be focused into specific conformational states by application of fluctuating voltages, such as dichotomous noise. We conducted an experimental test on Shaker K+ channels. We applied the dichotomous noise, reproducing the conditions in [1] as close as physiologically feasible. We also varied the frequency and the amplitude of the dichotomous noise within a certain range. We observed that in some cases, for intermediate noise frequencies (1-2 kHz) and large amplitudes, the probability for intermediate states in the Markov model of the ion channel gating kinetics can be significantly increased above the maximal value for any static voltages. However, so far the scale of the focusing effect observed experimentally is smaller than the numerical simulations predict. \newline [1]. M.M.Millonas, D.R.Chialvo, Phys.Rev.Lett. 76, 550 (1996) [Preview Abstract] |
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R1.00258: Wavelet-based protocols for ion channel electrophysiology Armin Kargol Ion channel gating kinetics is usually represented as a discrete Markov model whose input is the applied membrane voltage and the output is the ionic current. A current paradigm in experimental ion channel electrophysiology is to subject the channels to static voltages, which results in equilibrium or near-equilibrium conditions. We implement a new type of rapidly fluctuating voltage inputs that drive ion channels into nonequilibrium distributions. We discuss an algorithm for generating time-varying voltage inputs as a composition of wavelets, which allows optimization of spectral and temporal properties of voltage inputs for specific purposes, such as model selection. The outputs of channel Markov models for the Shaker K$^{+}$ channels are compared to the experimental data (whole cell ionic currents) recorded from these channels. [Preview Abstract] |
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R1.00259: On the estimation of spectral density of X-ray sources using attenuation measurements Claudia Huerta, Luis Vazquez, Marian Manciu, Teodor Vulcan, Felicia Manciu, Robert Waggener The high energy X-rays typically used in Medical Physics (100s kV -20 MeV ) have such short wavelengths, that creating a diffraction grating is impossible. Because the absorption coefficient depends on the wavelength, one can use transmission data through filters of various thicknesses to obtain information about the spectral density of the X-ray source. Neglecting non-linear processes, there is a linear dependence of the transmission data on the spectral distribution. Unfortunately, the corresponding underdetermined system is ill-conditioned, and traditional methods used to solve inverse problems (such as Singular Valued Decomposition) typically fails, even for very small levels of noise affecting the attenuation data (much lower than is typically obtained in an experiment). We will present a very robust algorithm for detecting the bremsstrahlung spectrum, which seek for a smooth function that minimizes the distance to the experimental transmission data. We will show that the algorithm works very well even for very noisy attenuation data, even when no prior knowledge of spectral distribution is available. [Preview Abstract] |
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R1.00260: The Detection of Protein via ZnO Resonant Raman Scattering Signal Guiye Shan, Guoliang Yang, Shuang Wang, Yichun Liu Detecting protein with high sensitivity and specificity is essential for disease diagnostics, drug screening and other application. Semiconductor nanoparticles show better properties than organic dye molecules when used as markers for optical measurements. We used ZnO nanoparticles as markers for detecting protein in resonant Raman scattering measurements. The highly sensitive detection of proteins was achieved by an antibody-based sandwich assay. A probe for the target protein was constructed by binding the ZnO/Au nanoparticles to a primary antibody by eletrostatic interaction between Au and the antibody. A secondary antibody, which could be specifically recognized by target protein, was attached to a solid surface. The ZnO/Au-antibody probe could specifically recognize and bind to the complex of the target protein and secondary antibody. Our measurements using the resonant Raman scattering signal of ZnO nanoparticles showed good selectivity and sensitivity for the target protein. [Preview Abstract] |
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R1.00261: Influence of dissolved gasses on hydrophobic interaction at different length-scales Alenka Luzar, D. Bratko Despite widespread experimental evidence of the influence of dissolved gases on hydrophobic interaction, the mechanism of observed effects are still unknown. We present direct calculations of the hydrophobic force between model hydrophobic surfaces in the presence and absence of dissolved gases, and varying surface separation up to 4 nm. We monitor gas adsorption at molecular resolution inaccessible to experiments. We find insignificant gas adsorption, confined to the first molecular layer, and no dependence of the width of the perturbed water layer on the amount and type of dissolved gas. The results offer a molecular-level interpretation for the lack of influence of dissolved gas on the short-range hydrophobic force, a finding that is consistently reported in experiments that show a dramatic gas effect at long-range, but minimal at short-range or in determining the adhesion force or interfacial energy. Finally, a coarse-grained approach is discussed to deal with apparent non-equilibrium effects at longer-range and implications to biological systems and nanoscience. [Preview Abstract] |
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R1.00262: Imaging Applications of the Geant4 Simulation Toolkit Joseph Perl Geant4 is a toolkit for the simulation of the passage of particles through matter. While Geant4 was originally developed for High Energy Physics (HEP), applications now include Nuclear, Space and Medical Physics. Medical applications of Geant4 in North America and throughout the world have been increasing rapidly due to the overall growth of Monte Carlo use in Medical Physics and the unique qualities of Geant4 as an all-particle code able to handle complex geometry, motion and fields with the flexibility of modern programming and an open and free source code. Many developers of imaging technology use Geant4 by way of GATE, the Geant4 Application for Emission Tomography, which wraps around Geant4 to simplify use and add imaging features, while other imaging developers use Geant4 directly. This talk will provide an overview of these applications, with a focus on how Geant4's unique qualities, such as its support for moving geometries and electric and magnetic fields, are applied to medical imaging. [Preview Abstract] |
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R1.00263: Sequence effects on the translocation of heteropolymers through a small channel Michel G. Gauthier, Gary W. Slater Using a recently developed Monte Carlo algorithm and an exact numerical method, we calculate the translocation probability and the average translocation time for charged heterogeneous polymers driven through a nanopore by an external electric field. The heteropolymer chains are composed of two types of monomers (A and B) which differ only in terms of their electric charge. We present an exhaustive study of chains composed of 8 monomers by calculating the average translocation time associated with the 256 possible arrangements for various ratios of the monomer charges ($\lambda_{A} / \lambda_{B}$) and electric field intensities, $E$. We find that each sequence leads to a unique value of the translocation probability and time. We also show that the distribution of translocation times is strongly dependent on the three parameters $\lambda_{A}$, $\lambda_{B}$ and $E$. Finally, we present results that highlight the effect of having repetitive patterns by studying the translocation times of various block copolymer structures for a very long chain composed of $N=2^{18}$ monomers (with the same number of A and B monomers). [Preview Abstract] |
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R1.00264: INSULATORS AND DIELECTRICS |
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R1.00265: The new single crystals with alpha-quartz structure obtained by hydrothermal method Miclau Marinela, Bucur Raul, Poienar Maria, Vlazan Paulina, Grozescu Ioan, Muscutariu Ioan, Miclau Nicolae Interest of Si1-xGexO2 single crystal with alpha-quartz structure is connected to improvement of electromechanical coefficients and rise of alpha -- beta phase transition of quartz one. Growth of alpha - Si1-xGexO2 single crystal was realized by a hydrothermal method of temperature gradient in autoclaves, made from Cr--Ni alloys. Nutrient material was prepared from synthetic quartz and placed in the bottom of autoclaves. There was loaded GeO2 powder additive in proportions to quartz nutrient. Single crystals were investigated by electron microprobe analysis, X-ray diffraction and atomic force microscopy. The most important result, which was obtained during the investigations, is an experimental proof of growth of Si1-xGexO2 solid solutions single crystals (with quartz structure) under the hydrothermal conditions. The present results thus open the possibility to tune the piezoelectric properties of these materials by varying the chemical composition. [Preview Abstract] |
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R1.00266: Anomalous relaxation of damped graded elastic lattices M.J. Zheng, J.J. Xiao, K. Yakubo, K.W. Yu We study the relaxation of harmonic vibrational excitations of damped graded lattices with a mass gradient. In the previous work, no damping was considered [1]. In this work, we re-examine the vibrational modes in a rigorous quasi-normal mode approach. It is shown that both the damping positions and boundary conditions can affect the relaxation spectrum. Moreover, there exists a dip at the gradon transition frequency for one- dimensional (1D) graded chains with damping at two ends or on all the sites. In two-dimensional (2D) orthogonally graded squared lattices (OGSL), there exist a dip and a peak at the two boundary frequencies of soft-hard gradon region. Moreover, the dip and peak structures in the relaxation spectrum can be explained by the anomalous gradon wavefunctions.\newline [1] J. J. Xiao, K. Yakubo, K. W. Yu, Phys. Rev. B {\bf 73}, 054201 (2006); 224201 (2006). [Preview Abstract] |
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R1.00267: Density of States of Silicon, Silicon Dioxide, Silicon Nitride and Silicon Carbide Hong Dong, A.R. Chourasia, S.D. Deshpande The density of states of Si, SiC, Si$_{3}$N$_{4}$ and SiO$_{2}$ have been studied using a DFT computational approach implemented in CRYSTAL06. This code employs linear combinations of Gaussian type functions to represent single particle wave functions. The Becke exchange and Lee, Yang and Parr correlation have been employed. The atomic basis sets with a polarization function have been optimized for each configuration in these materials. The unit cell parameters have also been optimized. The density of states in the valence and conduction bands have been computed in each case. The projected density of states of the constituents has also been computed. The band gap has been calculated for these materials. These values are compared with the available experimental data. The correlation between the electronic polarizability and the Auger parameter determined previously from x-ray photoelectron spectroscopy will be presented. [Preview Abstract] |
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R1.00268: Spectral representation theory of graded composite materials K.L. Chan, C.M. Kwok, K.W. Yu In graded composite materials, the physical properties can vary continuously in space and it may give different physical phenomena when compared with homogeneous materials. The Bergman-Milton spectral representation is a rigorous mathematical formalism to express the effective dielectric constant of nongraded composite materials [1]. In this study, we consider a material (rather than microsture [2]) graded composites, and generalize the Bergman-Milton spectral representation to extract the spectral density function for the effective dielectric constant of this graded composite material in the frequency domain [3]. Analytic and numerical solution will be presented for graded films and graded spheres. \newline \newline [1]\textbf{ D. J. Bergman,} \textit{Phys. Rev. B }\textbf{\textit{14}}\textit{, 4304 (1976).} \newline [2] \textbf{J. P. Huang, K. W. Yu, G. Q. Gu,} \textbf{M.} \textbf{Karttunen, }\textit{Phys. Rev. E }\textbf{\textit{67}}\textit{, 051405 (2003).} \newline [3] \textbf{L. Gao, J. P. Huang, K.W. Yu,} \textit{Eur. Phys. J. B }\textbf{\textit{36}}\textit{, 475 (2003).} [Preview Abstract] |
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R1.00269: Optical Trapping Forces from Electric Fields Inside Dielectric Materials Douglas Bonessi, Keith Bonin, Thad Walker We developed a method for computing forces from internal electric fields. The internal fields are found using discrete dipole approximation (DDA) and finite difference time domain (FDTD) approaches and the results are compared. We are interested in the results from an optical trapping viewpoint, though other simulations are used for benchmarks. This method can handle arbitrary input beams and particle sizes and shapes. We hope to report on similar calculations to calculate optical torques on birefringent particles in the Mie size regime. [Preview Abstract] |
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R1.00270: DFT Ab initio Calculation of Vibrational Frequencies in AsSe glass Keshav Shrivastava, Hasan Kassim, Ahmad Nazrul Rosli By using DFT double zeta wave functions, we calculated the structure, bond length (picometer, pm), frequencies(intensities)[degeneracy] for various clusters of arsenic selenide. Our results are as follows. (i) AsSe(diatomic) bond length 216pm, 244.0(1/cm). (ii) As$_{2}$Se(linear) bond length 228.5 pm, frequencies 27.6(1.9) and 387.6(4.3). (iii) As$_{2}$Se(triangular) As-Se 243.4 pm, As-As 223.3 pm, frequencies 237.3(2.4) and 332.4(0.05)(1/cm). (iv) As$_{3}$Se (triangular) bond length 238.4 pm, frequencies 107.5 and 296(weak)(1/cm). (v) As$_{4}$Se (square) bond length 250.2 pm, 58.5(0.04), 241.3(5.9)(1/cm). (vi) AsSe$_{3}$ (triangular), bond length 231.2 pm, 75.9(0.003), 103.5(1.26)[2], 350.9(33.2)[2]. From this study we identify that linear As-Se-As for which the calculated frequency is 27.6(1/cm) is in agreement with the data of Nemanich, Phys. Rev. B 16, 1655(1977), J. C. Phillips et al Phys. Rev B 21, 5724(1980). We have successfully calculated several vibrational frequencies accurately which agree with the Raman data. \begin{enumerate} \item V. R. Devi et al J. Non-Cryst. Solids 351, 489(2005);353,111(2007) \end{enumerate} [Preview Abstract] |
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R1.00271: Raman spectroscopy of multiferroic trigonal boracite Co$_3$B$_7$O$_{13}$Cl Milko Iliev, Viktor Hadjiev, Maria-Eugenia Mendoza, Jordi Pascual Raman microscopy was applied to study the polarized Raman scattering from untwinned domains of Co$_3$B$_7$O$_{13}$Cl (Co-Cl) in the trigonal, $R3c$, ferroelectric phase. The symmetry ($A_1$ or $E$) and mode polarization (LO or TO) for all observed Raman lines were determined from comparison of the spectra measured in several scattering configurations. It was found that as a rule the TO-LO splitting is small or negligible. A group of $A_1$ modes, characterized by a quasi-one-component Raman tensor, was tentatively assigned to stretching vibrations of Cl, O, or B along the trigonal axis, which in this material is parallel to the ferroelectric polarization direction. [Preview Abstract] |
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R1.00272: Infrared spectroscopy of Dysprosium doped KPb$_{2}$Br$_{5}$ and KPb$_{2}$Cl$_{5}$. Peter Amedzake, Ei Brown, Uwe Hommerich, Sudhir Trivedi, John Zavada The infrared optical properties of rare earth doped crystals with narrow phonon spectrum ($<$ 300 cm$^{-1})$ remains of current interest for applications in IR solid-state gain media. The maximum phonon energies of KPb$_{2}$Cl$_{5}$ and KPb$_{2}$Br$_{5}$ are only $\sim $200 cm$^{-1}$ and $\sim $150 cm$^{-1}$, which reduce non-radiative decay through multi-phonon relaxations. In this work, we present spectroscopic results of Dy: KPb$_{2}$Cl$_{5}$ and Dy: KPb$_{2}$Br$_{5}$ for possible applications in mid-infrared gain media. The investigated materials were grown by horizontal and vertical Bridgman technique. Dy: KPb$_{2}$Cl$_{5}$ and Dy: KPb$_{2}$Br$_{5}$ exhibited characteristic Dy$^{3+}$ absorption bands in the visible and infrared regions. Optical excitation at $\sim $800 nm resulted in the observation of a broad 4-5 $\mu $m mid-IR emission ($^{6}$H$_{11/2}$ $\to \quad ^{6}$H$_{13/2})$ at room temperature. The mid-IR emission lifetime was measured to be $\sim $5.5 ms for Dy: KPb$_{2}$Cl$_{5}$ and $\sim $3.8 ms for Dy: KPb$_{2}$Br$_{5}$, respectively. Based on temperature dependent lifetime studies and Judd-Ofelt calculations, the emission quantum efficiencies for the 4-5 $\mu $m bands were estimated to be near unity. More details on the IR optical properties of Dy: KPb$_{2}$Cl$_{5}$ and Dy: KPb$_{2}$Br$_{5 }$will be presented at the conference. [Preview Abstract] |
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R1.00273: Mid-infrared Emission and Energy Transfer Properties of Sensitized Rare Earth Ions in KPb$_{2}$Cl$_{5}$ Althea Bluiett, Erica Pinkney, Ei Brown, Uwe Hommerich, Sudhir Trivedi, John Zavada Mid-infrared emission (4-5 $\mu $m) originating from the first excited state of Pr$^{3+}$ and from the first excited state of Nd$^{3+}$ were generated by means of Yb$^{3+}$ and Tm$^{3+}$ sensitization, respectively. The mechanisms involved in sensitizing Pr$^{3+}$ and Nd$^{3+ }$ions were determined by studying the decay kinetics of the $^{2}$F$_{5/2}\to ^{2}$F$_{7/2}$ transition of Yb$^{3+}$ and the $^{3}$F$_{4}\to ^{3}$H$_{6}$ transition of Tm$^{3+}$ under 970 nm and 1750 nm laser excitation, respectively. It was observed that the emission lifetime of the $^{2}$F$_{5/2}\to ^{2}$F$_{7/2}$ transition and the $^{3}$F$_{4}\to ^{3}$H$_{6}$ transition were reduced considerably in the presence of the activator ions Pr$^{3+}$ and Nd$^{3+}$, respectively. Strong 4-5 $\mu $m emission from Pr$^{3+}$ and Nd$^{3+ }$were observed in Yb, Pr: KPb$_{2}$Cl$_{5 }$and Tm, Nd:KPb$_{2}$Cl$_{5}$, respectively. These findings indicate that significant energy transfer was transpired. Concentration dependent studies will be conducted to ascertain the dopant concentrations for efficient MIR emission. [Preview Abstract] |
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R1.00274: Rectifying Current-Voltage Characteristics of BiFeO$_{3}$/Nb-doped SrTiO$_{3}$ Heterojunction Hao Yang, H.M. Luo, H. Wang, D.M. Feldmann, Q.X. Jia Epitaxial c-axis oriented BiFeO$_{3}$ (BFO) thin films were deposited on (001) Nb-doped SrTiO$_{3}$ (Nb-STO) substrates by pulsed laser deposition. Introducing Bi vacancies causes the BFO thin film to evolve to a $p$-type semiconductor and form a $p-n$ heterojunction with $n$-type semiconductor Nb-STO. The current density vs voltage ($J-V)$ and capacitance vs voltage ($C-V)$ characteristics of the heterojunction were investigated. A typical rectifying$ J-V$ effect was observed with a large rectifying ratio of 5$\times $10$^{4}$. Reverse $C-V$ characteristics exhibit a linear 1/$C^{2}$ vs $V$ plot, from which a built-in potential of 0.6 V is deduced. The results show a potential application of BFO/Nb-STO heterojunction for oxide electronics. [Preview Abstract] |
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R1.00275: Wet-chemistry synthesis and dielectric properties of pure and Rb and V doped Cs$_{2}$Nb$_{4}$O$_{11}$ Jianjun Liu, Robert Smith, Wai-Ning Mei Cs$_{2}$Nb$_{4}$O$_{11 }$(CNO) is an antiferroelectric compound whose single crystal structure and antiferroelectric properties have been recently reported [1]. It has a space group of Pnna and a phase transition temperature at 165 $^{o}$C. In this study we synthesized CNO powdered samples, both pure and doped with rubidium and vanadium, by using a wet-chemistry method. Dielectric measurements showed that the phase transition temperature shifted with the doping. We analyzed the mechanism of this antiferroelectric phase transition based on the observed results. [1] Robert W. Smith, Chunhua Hu, Jianjun Liu, Wai-Ning Mei, Kuan-Jiuh Lin, J. Solid State Chem. 180 (2007) 1193-1197. [Preview Abstract] |
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R1.00276: Effect of Pressure on the Atomic and Electronic Structure of Hexagonal YMnO$_{3}$. Zhiqiang Chen, Trevor Tyson, Sungbaek Kim, Sang-Wook Cheong The multiferroic hexagonal system YMnO$_{3}$ is known to possess a significant polarization at room temperature. To understand the mechanism behind the polarization, we conducted high pressure x-ray diffraction measurements for pressures between ambient and 20 GPa. The powder diffraction data were refined to obtain the atomic level structure as a function of pressure. The pressure dependence of resistivity at room temperature (for pressures up to $\sim $6 GPa) was determined. Complementary density functional calculations were conducted to correlate the changes in electronic structure and polarization with the observed changes in atomic structure with pressure. [Preview Abstract] |
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R1.00277: Acoustic and Optical Properties of Er$^{3+}$- doped LiNbO$_{3}$ Alem Teklu, Narayanan Kuthirummal, Daniel Morrall, Jay Dandrea Elastic constants of pure and Er$^{3+}$doped lithium niobate (LiNbO$_{3})$ single crystals have been determined using resonant ultrasound spectroscopy (RUS). When comparing the elastic constants for pure and doped LiNbO$_{3}$ crystals, the bulk modulus was found to increase by 5.2{\%} after doping. Also the elastic constants were compared. C$_{11}$ decreased by 4{\%}, C$_{12}$ increased by 18{\%} and C$_{44}$ increased by 16.6{\%}. The surface-doping explains the decrease in elastic constant in only one direction. The presence of Er$^{3+}$ ions on the surface of LINbO$_{3}$ has been monitored using photoacoustic spectroscopy. The photoacoustic spectrum revealed very weak absorptions corresponding to $_{4}$F$^{7/2}$, $_{4}$F$^{9/2 }$and $_{2}$H$^{11/2}$ levels of Erbium, indicating the presence of Erbium. [Preview Abstract] |
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R1.00278: Dielectric response in potassium tantalite/potassium niobate multilayers M. E. Reeves, Shuogang Huang, Jennifer Sigman, David Norton, Hans Christen We report measurements of the dielectric response of thin-film multilayers of potassium tantalite/potassium niobate. The measurements were made by evanescent-probe microscopy, a technique that is quite sensitive to material placed in the near-field proximity of the sample probe. The measurements were performed at a frequency of 1.7 GHz with the electric field polarized perpendicular to the plane of the film. Our results show that there are two distinct phase transitions. The first coincides with a structural transition in the material and indicates the onset of coupling between the potassium niobate layers. The transition moves to higher temperature as the spacing between the layers in increased. A second lower temperature transition indicates the onset of anti-ferroelectric ordering in the sample. The temperature of this transition is nearly independent of layer thickness and is not connected with a structural transition. The mechanism for the transitions will be discussed and data measured on asymmetric multilayers will be presented. [Preview Abstract] |
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R1.00279: Anomalous size dependence of inverse participation ratio of localized eigenfunctions in graded elastic lattices M.J. Zheng, M. Goda, K. Yakubo, K.W. Yu Recently, we studied harmonic vibrational excitations in graded elastic lattices [1]. It is found that the eigenfunctions exhibit a transition from extended phonon states to localized gradon states when the frequency is increased beyond a critical frequency called the gradon transition frequency. At the same time, the inverse participation ratio (IPR) can exhibit a rapid increase at gradon transition. This unusual behavior prompts us to study the size dependence of the IPR of gradon wave function. A quantum analogue is established for the hump structure at the gradon front, via the fact that the probability of a quantum particle is inversely proportional to its velocity. In this way, the envelope function can be determined analytically, and matches the gradon wave function quite well. We find that the size ($N$) dependence can be captured by the relation: $N$IPR = $C_1\log(N) + C_2$, where $C_1$ and $C_2$ are constants. The interpretation is important in the understanding of a wide variety of properties of graded systems.\newline [1] J. J. Xiao, K. Yakubo, K. W. Yu, Phys. Rev. B, {\bf 73}, 054201 (2006); 224201 (2006). [Preview Abstract] |
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R1.00280: SUPPLEMENTARY ABSTRACTS |
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R1.00281: Physics and Operational Research: measure of uncertainty via Nonlinear Programming Yasser A. Davizon-Castillo Physics and Operational Research presents an interdisciplinary interaction in problems such as Quantum Mechanics, Classical Mechanics and Statistical Mechanics. The nonlinear nature of the physical phenomena in a single well and double well quantum systems is resolved via Nonlinear Programming (NLP) techniques (Kuhn-Tucker conditions, Dynamic Programming) subject to Heisenberg Uncertainty Principle and an extended equality uncertainty relation to exploit the NLP Lagrangian method. This review addresses problems in Kinematics and Thermal Physics developing uncertainty relations for each case of study, under a novel way to quantify uncertainty. [Preview Abstract] |
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R1.00282: Physics of Large Scale Production Systems under Uncertainty Yasser A. Davizon-Castillo Large Scale Production Systems (LSPS) are analyzed from the physics perspective based on the measure of uncertainty. A novel approach to quantify uncertainty is presented using Little's law and Uncertainty Inequalities in Throughput and Work in Process. The extended version of an Uncertainty equality relation is used to measure the levels of uncertainty in the LSPS in a Nonlinear Programming context. Conservation of Energy Principle is used to determine the measure of uncertainty overall the system. The main contribution is the analogy from the physical phenomena to a LSPS arena using the Conservation of Energy Principle. [Preview Abstract] |
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R1.00283: A High-resolution Rapidly-updated Meteorological Data Analysis System for Aviation Applications Chi Shing Lau, Ming Chung Chu, Jones Tsz-Kai Wan, Ping Wah Li We present our work on the recent development of a high spatial- and temporal-resolution meteorological data analysis system for the identification and monitoring of mesoscale to microscale weather phenomena over the Hong Kong International Airport (HKIA) and its vicinity. The system can be updated minutely with a horizontal resolution of 150 m. The system is adapted from the Local Analysis and Prediction System (LAPS) from NOAA. Apart from conventional data such as automatic weather stations, wind profilers and satellite observations, automatic aircraft reports (AMDAR), LIDARs and Terminal Doppler Weather Radar (TDWR) data are ingested into the system. The LIDAR and TDWR data are complimentary to each other so that wind field can be identified in both clear and convective weather. Ingesting the above data into the system helps generate a comprehensive 3-dimensional structure of the atmosphere over the airport and nearby airspace. The analysis system would also be useful for nowcasting aviation-related weather after integrating with numerical weather prediction models. Several cases such as land-sea breeze, gust front and tropical cyclone are discussed. Our results could bring significant insights into aircraft safety and air traffic efficiency to the flights operating at other airports over the world. [Preview Abstract] |
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R1.00284: Simulating a charged spherical pendulum in time-varying electric and magnetic fields Mark Wellons, Frank King, Todd McAlpine We simulate and analyze the dynamics of a charged spherical pendulum in time-varying electric and magnetic fields. The time-varying electric field is directed perpendicular to the gravitational field and serves as a driving force for the pendulum. The time-varying magnetic field is directed parallel to the gravitational field and serves to deflect the motion of the pendulum. We analyze the dynamics of the system to determine the conditions for which chaotic behavior is observed. We also include viscosity to look for strange attractors. The equations of motion are integrated using Objective C and the graphical user interface, including the three dimensional graphical representation of the system, is developed using Cocoa. [Preview Abstract] |
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R1.00285: POST-DEADLINE ABSTRACTS |
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R1.00286: Electrode-side impedance nonlinearity in polycarbazole bioelectrodes quantifiable by a quaternion formalism M. Ovadia, D.H. Zavitz, Y.P. Kayinamura, J.F. Rubinson Nonlinear response to sinusoidal electrification is a phenomenon rarely observed for conductive interfaces. We report nonlinear response as an electrode phenomenon in a conjugated polymer electrode polycarbazole. While other semiconductors manifest an impedance quantifiable in the complex field ($e.g.$ Warburg where complex Z = Z$_{W\infty }$ and resistive with Z = Z$_{Hl}$ [Hl-Halbleiter]) the polycarbazole manifests no definable impedance due to essential nonlinearity. There is no description available for this form of pseudoconductivity. We introduce a quaternion formalism Z$_{\subset T}$=a+bi+cj+dk [where a,b,c,d are real and i$^{2}$=j$^{2}$=k$^{2}$=-1 and jk=i] that successfully describes all conductivity (c=d=0) and pseudoconductivity presently known as a normed ring, and reduces to the complex field for conductivity. In this formalism, the normalized impedance of a capacitor is Z=i, the experimentally determined polycarbazole pseudoimpedance Z$_{\subset T}$=k, that of a resistance is Z=1 and that of the Z$_{W\infty }=\surd $i=i$^{\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} }$. The non-Abelian character of Z$_{\subset T}$ implies that the Onsager relation fails for some interfaces. Remarkably, certain Kramers-Kronig relations (Hilbert transformation in not only the complex but also the [j,k] plane) still hold for certain experimental setups. Computation of the energy integral $\smallint $\textbf{D}$^{.}$\textbf{E}dt reveals that charge transport is lossless, similar to conduction in an ordinary capacitance. [Preview Abstract] |
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R1.00287: Static And Dynamic Studies In Nonyloxycyanobiphenyl (9ocb) Confined To Anopore Membranes Sergio Diez Berart, Miguel Angel Perez Jubindo, David O. Lopez, M. Rosario de la Fuente, Josep Salud We analyze and compare the static and dynamic properties of alkoxycyanobiphenyl (9OCB). This compound exhibits an I-N-SmA phase sequence. After confining into Anopore structures several phenomena can be seen: Both phase transitions change in their nature, C$_{p}$ peaks becoming lower, broader and shifted down in temperatures. A possible first-to-second order transition could be determined for the N-SmA. There developes a surface induced nematic layer that becomes larger when temperature decreases. Molecular dynamics out from the nematic layer is quite similar to that of the bulk. [Preview Abstract] |
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R1.00288: ABSTRACT WITHDRAWN |
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R1.00289: Electric Polarization and ME effect in layered iron oxide Sumio Ishihara, Makoto Naka, Jyoji Nasu Rare-earth iron oxides $R$Fe$_2$O$_4$. ($R$: rare-earth elements) is an exotic dielectric material with charge-order driven electric polarization and magnetoelectric effect caused by spin-charge coupling. The crystal structure consists of paired Fe-O triangular lattices and $R$-O block ones alternately stacked. Since a nominal valence of Fe ion is 2.5+, an equal amount of Fe$^{2+}$ and Fe$^{3+}$ coexists in the paired triangular lattices. In the electron diffraction experiments, Bragg reflections at $(h/3\ h/3\ 3m+1/2)$ appear below 320K($\equiv T_{\rm CO}$) in LuFe$_2$O$_4$. This observation indicates a valence order of Fe ion, i.e. a charge order of the Fe $3d$ electrons. Around $T_{\rm CO}$, a spontaneous electric polarization and dielectric anomalies turn up. Moreover, around the ferrimagnetic spin ordering temperature $(T_{\rm SO}=$250K), the gigantic ME effects are recently discovered. We present a theory of a dielectric magnet $R$Fe$_2$O$_4$ as a electronic ferroelectric and multiferroic material [1]. We address the following issues: (i) origin of the electric polarization and the FE transition, (ii) mechanism of the coupling between electric polarization and magnetization. Present study shows that the novel dielectric properties in this material arises from interplay among the geometrical frustration and the multi-degrees of freedom of electron. \par \noindent [1] A. Nagano, M. Naka, J. Nasu, \& S. Ishihara, Phys. Rev. Lett. {\bf 99}, 217202 (2007). [Preview Abstract] |
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R1.00290: Fermi surface and local density of states of ordered and disordered stripes. Mats Granath For a doped antiferromagnet with short-range spin stripe correlations and long-range charge stripe order the manifestation of charge order changes abruptly as a function of momentum along the Fermi surface. The disorder averaged local density of states is isotropic when integrated only over states which contribute to the ``nodal'' spectral weight whereas it displays long range charge stripe order when integrated only over states which contribute to the ``antinodal'' spectral weight. An effectively two dimensional nodal liquid can thus coexist with static charge stripes provided there is no static spin order. For commensurate spin and charge stripe ordered systems the Fermi surface consists of a nodal hole pocket and an open ``stripe band'' section. Due to the stripe order the relation between hole density and size of a pocket will be reduced compared to a paramagnet by a factor of two for even charge period and four for odd charge period and we find an estimated upper limit on the area fraction of a hole pocket of 1.6\% for charge period four and 4\% for charge period five. We also discuss why electron pockets are not expected for a stripe ordered system and show that the open Fermi surface section may be electron like with a negative Hall coefficient. [Preview Abstract] |
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R1.00291: Modification of amorphous carbon film surfaces by thermal grafting of alkenes monolayer Hussein Sabbah, Souraya Ababou-Girard, Francine Solal, Christian Godet, Bruno Fabre, Maryline Guilloux-Viry, Andre Perrin, Stephanie Deputier The integration of molecules and semiconductors opens new possibilities for large area devices in the fields of biochemical sensors, molecular electronics.This work aims at improving the control of the surface of amorphous carbon thin films, in order to optimize molecular grafting processes and investigate the electronic properties of molecular assemblies. Robust devices are expected from this covalent grafting, through strong C-C interface bonds. A quantitative comparison of thermally assisted gas phase and liquid phase processes using linear alkenes has been performed using X-ray photoelectron spectroscopy (XPS). In order to understand the grafting mechanisms and the a-C surface reactivity towards alkenes at different temperatures (160 - 300 \r{ }C), surface coverage values are compared using a-C films, with different average C sp$^{3}$ / sp$^{2}$ hybridization, residual oxygen contamination, surface densities and surface energies, as obtained from XPS, grazing angle X-ray reflectivity and contact angle measurements. [Preview Abstract] |
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R1.00292: Calculated Zhang-Rice Singlet Dispersion in Mott-Insulators Xiangang Wan, Quan Yin, Sergey Savrasov Using a combination of local density functional theory and cluster exact diagonalization based dynamical mean field theory (LDA+DMFT), we calculated many body electronic structures of several Mott-insulating oxides including undoped prototype high Tc materials. The dispersions of the lowest occupied electronic states are associated with the Zhang-Rice singlets (ZRS) in cuprates, and with doublets, triplets, quartets and quintets in more general cases. The spectral weight of ZRS band decreases as it approaches the BZ center, as observed by many recent ARPES experiments. Our results are in good agreement with experiments [Preview Abstract] |
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R1.00293: Exploration of Strongly Coupled Plasma Dynamics and Equilibrium Using the Particle-in-Cell Methodology D.V. Rose, D.R. Welch, T.C. Genoni, T.A. Mehlhorn, R.B. Campbell Particle-based numerical simulations are required to study the dynamics and evolution of inhomogeneous nonequilibrium multispecies strongly coupled plasmas. Molecular dynamics (MD) and particle-in-cell (PIC) techniques and been compared previously [K. Y. Sanbonmatsu, et al., J. Phys. IV (France) 10, Pr5-259 (2000)], with the PIC methodology demonstrating the capability of improved accuracy over the MD simulations at high resolution. However, the PIC simulations were significantly slower, limiting their utility. Here we explore several schemes to improve the computational speed of such calculations including non-iterative, implicit EM field solvers and subgrid models. The simulations are compared directly with the results of Sanbonmatsu, et al., and a new theoretical analysis of the hypernetted chain model where all inter-species correlations are retained [V. Schwarz, et al., Contrib. Plasma Phys. 47, 324 (2007)]. [Preview Abstract] |
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R1.00294: Ionic salt-bridge dependence of dimerization of the GCN4 Leucine zipper Yanxin Liu, Prem Chapagain, Bernard Gerstman The role that ionic interactions, or salt-bridges, play in protein folding and dimerization is still controversial. We perform computational simulations on the GCN4 leucine zipper to investigate the effect of ionic interactions. A three dimensional lattice model incorporating a Monte Carlo Metropolis Algorithm is employed to simulate the dimeriztion process. Our results show that stronger ionic interactions result in more stable dimers, in agreement with experiments. Our simulations also show that increasing the strength of the ionic interactions does not lead to a monotonic increase in the speed of the dimerization process. We find an optimal intermediate ionic interaction strength at which the dimer is stable and the dimerization process proceeds at the maximum rate. We present quantitative results of dimerization rates, heat capacity, and free energy landscapes as a function of the ionic strength for the GCN4 leucine zipper. [Preview Abstract] |
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R1.00295: Entanglement of Uniformly Accelerating Schr\"{o}dinger, Dirac, and Scalar Particles Wai Lim Ku, Ming Chung Chu We study how the entanglement of an entangled pair of particles in two different modes is affected when one or both of the pair is uniformly accelerated, while the detector remains in an inertial frame. We find that the entanglement is unchanged if all degrees of freedom are considered. However, particle pairs are produced when a relativistic particle is accelerated, and more bipartite systems emerge. We identify the particle and antiparticle excitations in the asymptotic regions where there is no acceleration, which corresponds to detection by inertial detectors. We calculate the entanglements between particles/antiparticles in the two modes, and we find that the distribution of entanglements into the different bipartite systems varies as the acceleration. In particular, the entanglement of a pair of accelerating fermions is transferred preferentially to the produced antiparticles when the acceleration is large, and the entanglement transfer is complete when the acceleration approaches infinity. However, no such entanglement transfer to the antiparticles is observed for scalar particles. [Preview Abstract] |
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R1.00296: Experimental observation of solitons propagating in a hydro-mechanical array of one-way coupled oscillators Kelly M. Patton, James Gallagher, John F. Lindner Arrays of two-way coupled oscillators are familiar and have been extensively studied. However, arrays of one-way coupled oscillators have been studied only in the last five years, mainly computationally and theoretically. One-way coupling seems impossible, because it appears to violate Newton's third law (and energy conservation). However, we have constructed arrays of one-way coupled oscillators by enabling each oscillator to modify an external force that does work on a neighboring oscillator. We observe solitons propagating in our arrays and compare their behavior with computer simulations and theory. [Preview Abstract] |
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R1.00297: Cyclotron radiation and emission in graphene Takahiro Morimoto, Yasuhiro Hatsugai, Hideo Aoki While the physics of ``Massless Dirac" particles in graphene has been kicked off by the observation of an anomalous quantum Hall effect, interests begin to extend optical properties, which includes recent spectroscopy studies on unevenly spaced Landau levels $\propto \sqrt{N}$ in magnetic fields. Here we point out that the graphene Landau levels should have an interesting implication on the Landau-level laser proposed decades ago [H. Aoki, Appl. Phys. Lett. {\bf 48}, 559 (1986)]. Having this in mind we have calculated the optical conductivity for graphene in magnetic fields,% with the linear-response theory, including the effect of disorder to show the following: (i) The unevenly spaced Landau levels do give rise to an interesting situation, where the $N=0$ Landau level stands alone for an appropriate level of disorder. This should help in realizing the population inversion (across $N=0$ and $N\geq1$ here) necessary for lasing. (ii) The optical conductivity, which reflects the unevenly spaced Landau levels, has some peaks that {\it increase} with temperature. (iii) As for the relaxation processes, which are examined with an extention of the treatment for ordinary quantum Hall systems, graphene's peculiar cyclotron energy $\propto \sqrt{B}$ along with its 2D nature favor the cyclotron emission over other relaxation processes. [Preview Abstract] |
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R1.00298: ABSTRACT WITHDRAWN |
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R1.00299: Structural Phase Transitions induced by Compressive and Tensile Strains in Ordered Sc$_{0.5}$Ga$_{0.5}$N and Sc$_{0.5}$In$_{0.5}$N Alloys. Ahmad Alsaad, Ahmad Ahmad Local-density approximation calculations (LDA) within density functional theory (DFT), Berry phase approach within modern theory of polarization and phonon calculations within the density functional perturbation theory are performed to predict the existence of breaking-symmetry structural phase transitions in ordered Sc$_{0.5}$Ga$_{0.5}$N and Sc$_{0.5}$In$_{0.5}$N alloys. It has been demonstrated that the existence of strain-induced structural phase transition leads to optimized optical, electronic, acoustic, and piezoelectric properties of ordered Sc$_{0.5}$Ga$_{0.5}$N and Sc$_{0.5}$In$_{0.5}$N. In particular, It has been shown that ordered Sc$_{0.5}$Ga$_{0.5}$N and Sc$_{0.5}$In$_{0.5}$N alloys at fixed Ga, In and Sc compositions exhibit tremendous piezoelectric response (i.e., the e$_{33}$ piezoelectric coefficient adopts a huge value as large as 8.3 C/m$^{2})$ as a function of the in-plane compressive and tensile strains. In addition, several optical, electric, acoustic anomalies will be shown and discussed. We also reveal the reason behind, and consequences of, these unusual properties associated with the biaxial strain-induced structural phase transitions. [Preview Abstract] |
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R1.00300: Characterizing soliton behavior in noise-mediated one-way coupled oscillators Christine E. Weidert, Barbara J. Breen, John F. Lindner While arrays of coupled bistable oscillators have been extensively studied, the unique behavior of such arrays under one-way coupling has been studied only in the last few years. Using numerical simulations run on a high-speed parallel computing cluster and theoretical arguments, we show that the speed of solitons propagating in these arrays is proportional to the coupling strength. In addition, we refine and improve a metric, the complexity, that quantifies the intricacy of the spatiotemporal behavior of the array as a function of coupling and noise. [Preview Abstract] |
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R1.00301: Wetting-like phase transitions in a surface-enhanced type-I superconductor Vladimir Kozhevnikov, Margriet Vab Bael, Pratap Sahoo, Kristiaan Temst, Chris Van Haesendonck, Andre Vantomme, Joseph Indekeu Superconductivity in single crystal Sn samples with surface enhanced order parameter was studied experimentally. Controllable surface enhancement was achieved by mechanical polishing or by ion irradiation. A first-order surface superconductivity transition was found in parallel magnetic fields close to the bulk critical field Hc(T) and for temperatures above 0.8Tc up till a surface critical temperature Tcs higher than Tc, where Tc is the bulk critical temperature. The resulting phase diagram agrees with that predicted for interface delocalization or wetting transitions in type-I superconductors, based on the Ginzburg--Landau theory. [Preview Abstract] |
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R1.00302: Viscoelastic Relaxation of Molten Phosphorus Pentoxide David Sidebottom, Jessica Changstrom We report the first ever dynamic light scattering study of the viscoelastic relaxation in anhydrous liquid P$_{2}$O$_{5}$. Properties of the time decay of the dynamic structure factor, including the average structural relaxation time and the stretching exponent, were obtained for temperatures from 850 \r{ }C to near the glass transition (T$_{g}$ = 419 \r{ }C) using photon correlation spectroscopy. Analysis indicates that P$_{2}$O$_{5}$ is a strong glassforming liquid but one which exhibits an abnormally non-exponential relaxation near T$_{g}$. The viscoelastic behavior of P$_{2}$O$_{5}$ is compared with that of its metaphosphate counterpart to demonstrate how changes in bond connectivity influence both fragility and levels of dynamic heterogeneity. [Preview Abstract] |
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R1.00303: Structural distortions in the spin-gap regime of the quantum antiferromagnet SrCu2(BO3)2 Carlo Vecchini, Laurent Chapon, Hiroshi Kageyama, Othon Adamopoulos, Alexandros Lappas Since the so-called pseudo spin-gap was suggested to be relevant for the appearance of high-Tc superconductivity, a number of studies have been made on low-dimensional quantum spin systems with a singlet ground state. SrCu2(BO3)2 is an example of a 2D frustrated magnet in which a rectangular network of spin-1/2 Cu dimers displays a spin-gap (T$<$20K). Spin anisotropies are needed to describe accurately the dynamics of this 2D orthogonal dimer model. Accurate knowledge of the lattice symmetry is necessary to rationalize the ground state properties. This is the first detailed crystallographic study within the gap region. Our powder neutron diffraction reveals distortions of the tetragonal structure that uncover an intimate spin-lattice coupling. The interdimer Cu-O-Cu angles increase abruptly by 0.4 deg, consistent with strengthening of the superexchange interaction. This is accompanied by a sharp reduction of the static buckling within the CuO2 planes and a contraction of the interlayer distances. We discuss the role of the structural deformations and the symmetry rules imposed for the development of the Dzyaloshinsky-Moriya exchange. [Preview Abstract] |
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R1.00304: Hypervelocity Impact on Interfaces: A Molecular-Dynamics Simulations Study Martina E. Bachlechner, Eli T. Owens, Robert H. Leonard, Bronwyn C. Cockburn Silicon/silicon nitride interfaces are found in micro electronics and solar cells. In either application the mechanical integrity of the interface is of great importance. Molecular-dynamics simulations are performed to study the failure of interface materials under the influence of hypervelocity impact. Silicon nitride plates impacting on silicon/silicon nitride interface targets of different thicknesses result in structural phase transformation and delamination at the interface. Detailed analyses of atomic velocities, bond lengths, and bond angles are used to qualitatively examine the respective failure mechanisms. [Preview Abstract] |
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R1.00305: Nanoscale X-ray Diffraction Microscopy at the Nanoprobe Beamline Martin Holt, Robert Winarski, Jorg Maser The near-term completion of the Nanoprobe Beamline at the Advanced Photon Source as part of the Center for Nanoscale Materials Project will provide a dedicated facility for hard X-ray microscopy at a landmark 30nm spatial resolution. Integrating a high-flux synchrotron X-ray beamline with an advanced optomechanical experimental platform at an energy range of 3-30keV will make possible nanoscale studies of functional and biological materials with a high degree of precision and efficiency. The unique capabilities of hard X-ray microscopy techniques such as large penetration depths, experimental sensitivity to elemental composition, crystallographic phase, and strain when applied at this length scale offer unique opportunities for many fields of sciences. The challenges and scientific impact of extending X-ray microscopy techniques such as scanning probe X-ray fluorescence, scanning probe microdiffraction, spectroscopy, tomography, and full-field imaging to the nanoscale will be discussed. [Preview Abstract] |
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R1.00306: Hard X-ray Nanoprobe Development at Argonne National Laboratory Robert Winarski, Martin Holt, Jorg Maser, Volker Rose, Deming Shu, Brian Stephenson The Hard X-ray Nanoprobe beamline will explore nanoscale objects at a spatial resolution of 30 nanometers, using x-ray fluorescence spectroscopy, transmission imaging, diffraction, and scattering. X-ray fluorescence measurements will provide element-specific imaging of individual nanoparticles inside of samples. Transmission imaging will allow three dimensional mappings of thick specimens and devices. X-ray diffraction and scattering capabilities will examine strain states and ordering in nanoscale systems. The beamline is designed for two modes of operation: a scanning probe mode, where the spatially coherent fraction of the x-ray beam is focused by high-resolution x-ray optics onto a small area of a sample, and a full-field transmission mode, where the full, partially coherent x-ray beam is used to illuminate a sample for transmission imaging at high resolution. [Preview Abstract] |
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R1.00307: Low temperature growth of boron nitride nanotubes Chee Huei Lee, Ming Xie, Jiesheng Wang, Yoke Khin Yap Boron nitride nanotubes (BNNTs) are promising nanostuctures that will complement the applications of carbon nanotubes in various emerging areas. However, the synthesis of BNNTs is still challenging and required high growth temperatures (1500\r{ }C to 3000\r{ }C). Here we will discuss about two approaches for low temperature growth of BNNTs. First, we have reported on the growth of \textit{pure} BNNTs at 600\r{ }C by a plasma-enhanced pulsed-laser deposition (PE-PLD) technique [1]. These BNNTs were grown vertically-aligned on substrates. Latest result on the effect of catalyst, growth temperatures, ambient gas pressures, substrate bias voltages and the growth mechanism will be discussed in the meeting. Secondly, effective growth of BNNTs is recently achieved by conventional thermal chemical vapor deposition (CVD). Our new CVD approach leads to effective growth of long and clean BNNTs at 1200 \r{ }C. SEM, TEM, EELS, Raman, FTIR, and UV absorption data indicate that these BNNTs are having high structural ordered and a energy band gap $>$ 5.6 eV. [1]. J. Wang et. al, Nano Lett. 5, 2528 (2005). [Preview Abstract] |
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R1.00308: Non-affine deformations in biological gels Qi Wen, Anindita Basu, Jessamine Winer, Arjun Yodh, Paul Janmey Compared to flexible polymer gels, filamentous biopolymer networks generally have larger elastic moduli, a striking increase in elastic modulus with increasing strain, and a pronounced negative normal stress when deformed under simple shear. Different theoretical models based on either entropic elasticity of semiflexible filaments or enthalpic bending and stretching of rods can under some conditions account for all three of these unusual features. An essential difference between theories that relate microscopic structural parameters such as persistence length and mesh size of biopolymer gels to their macroscopic rheology are predictions about whether deformation of these materials is affine. We test the validity of this affine assumption by embedding micron-sized fluorescent beads within the networks and quantifying their displacements under shear deformation. Measures of non-affine deformation are small for networks of thin relatively flexible filaments and get smaller as strain increases. The small non-affine measures are consistent with the entropic model for non-linear elasticity of semiflexible polymer networks. However, as filament stiffness and mesh size increases the deformations become more non-affine, these results are possible more consistent with enthalpic bending and stretching models. [Preview Abstract] |
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R1.00309: Interference in the Mott Insulator State of Distinguishable Particles Lin Tian, Fumitaka Fujiwara, Tim Byrnes, Yoshihisa Yamamoto Particle statistics plays a crucial role in strongly interacting quantum many-body systems. Here, we study the Hubbard model for distinguishable particles at unit filling. We show that when on-site repulsive interaction dominates over tunneling, the ground state is a Mott insulator state with higher order coherence between the particles. This result can be experimentally confirmed by the recovery of the interference pattern in the density correlation functions and is robust against non- uniformity of the interaction and tunneling parameters. We also show that this state is a maximally entangled state, in contrast to its bosonic counterpart. L. Tian, F. Fujiwara, T. Byrnes, and Y. Yamamoto, preprint, arXiv/0705.2023. [Preview Abstract] |
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R1.00310: Spin-state polarons as a precursor to ferromagnetism and metallicity in hole-doped LaCoO$_3$ A. Podlesnyak, M. Russina, E. Pomjakushina, K. Conder, D. Khomskii Lightly doped cobaltites La$_{1-x}$Sr$_x$CoO$_3$ exhibit magnetic properties at low temperatures, in strong contrast to the diamagnetic LaCoO$_3$. We undertook an inelastic neutron scattering study with the goal to identify the energy spectrum and magnetic state of cobalt ions in the doped system with $x=0.002$. In distinguish to the parent compound, where no excitations have been found for $T<30$~K, an inelastic peak at $\Delta E \sim 0.75$~meV was observed in La$_{0.998}$Sr$_{0.002}$CoO$_3$ at $T=1.5$~K. The intensity of this excitation is much higher than what is expected from an estimated concentration of doped holes. Furthermore, strong Zeeman splitting of the inelastic peak corresponds to an unusually high effective magnetic moment $\sim 15 \mu_B$. Neighboring low-spin (LS) Co$^{4+}$ and intermediate-spin Co$^{3+}$ ions can share an $e_g$ electron by swapping configuration. The $t_{2g}$ electrons, in their turn, couple ferromagnetically. Therefore, we propose that the holes introduced in the LS state of LaCoO$_3$ are extended over the neighboring Co sites forming spin-state polarons and transforming the involved Co$^{3+}$ ions to the higher spin state. Grows of spin-state polarons with hole doping finally results in a metallic ferromagnetic state for $x > 0.3$. [Preview Abstract] |
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R1.00311: Metal-insulator transition in graphene oxide Geunsik Lee, Kyeongjae Cho Using the first-principles density-functional theory method, we show that metallic graphene undergoes a metal-insulator transition upon adsorption of oxygen, and that the fully oxidized metastable graphene has a large energy gap of 3.27 eV. Graphene oxide (GO) shows the transition at the coverage of 1/3 - 1/2 monolayer of epoxide group. Each O atom saturates two $\pi $ orbitals, and the GO band structure is determined by the connectivity of metallic channels of $\pi $ orbitals. Although such directional conduction is verified for most of GOs that we considered, we have found that longer range interaction between $\pi $ orbitals also plays an important role in the electronic structure of GOs. We apply our results to the implication on electrical conductions in dry and wet GO samples. [Preview Abstract] |
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R1.00312: Tight-binding Calculation of Electronic Properties of Oligophenyl and Oligoacene Chains Adam Hinkle, Antonio C. Cancio, Mahfuza Khatun Within recent years, allotrophic structures of carbon have been produced in the forms of tubes and ribbons which offer the promise of extraordinary electronic and thermal properties. Here we present analyses of oligophenyl and oligoacene systems-- -infinite, one-dimensional chains of benzene rings linked along the armchair and zigzag directions. These one-dimensional structures, which are amenable to calculation by analytical means, exhibit features very similar to carbon nanotubes and nanoribbons. Using a tight-binding Hamiltonian we analytically determine the energy bands of these systems. From these results we calculate the density of states and wavefunction symmetries for each structure. We also discuss the effect doping has on the energy as well as examine the transport properties. [Preview Abstract] |
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R1.00313: Investigation of colloidal interactions in nanoparticle suspensions with a single optical trap Joseph Junio, Eric Blanton, H. Daniel Ou-Yang Colloidal interaction parameters such as virial coefficients or bulk modulus are traditionally measured by scattering methods. However, experimental difficulties often limit the range of applications of these methods to idealized systems. Multiple optical tweezers have also been used to study interparticle forces, but this has been limited to micron size individual particles at infinite dilution. We propose a new approach to investigate many body interactions of sub-micron colloidal particles in native suspensions with a single optical trap. Using a blinking optical trap and confocal detection of optical signals, this approach can be used to measure many body interactions in suspensions of colloidal particles in the range of tens to hundreds nanometers in size. Theoretical calculation and preliminary experimental data will be presented at the talk. [Preview Abstract] |
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R1.00314: 3-D structure and dynamics of microtubule self-organization Jing Wang, H. Daniel Ou-Yang Laser scanning confocal microscopy was used to study the dynamics of 3D assemblies spontaneously formed in microtubule (MT) solutions. Microtubule solutions prepared by mixing and incubating tubulin in the presence of GTP and Oregon Green conjugated taxol in PM buffer were placed in long, sub-millimeter thin glass cells by the capillary action. Within 24 hours, starting with a uniform distribution, microtubules were found to be gradually separated into a few large ``buckled'' bundles along the long direction, and in the middle plane, of the sample cell. A well-defined wavelength of the buckling sinusoids was around 510 $\mu $m. The cross section of these round bundles was approximately 40 $\mu $m in diameter and the lengths were several centimeters. Detailed analysis of the 3-D image within the bundles revealed that each bundle seemed to consist of loosely packed MTs. It appeared that MTs were phase separated resulting from attractive interactions between charged MT fibers. The ``buckling'' behavior could be the result of geometrical constraints of the repulsive cell walls and the repulsive interaction between bundles. Detailed 3-D observations of the dynamic evolution of MT assembly could provide insight to the mechanisms of cellular MT organization and phase separation of charged colloidal rods. [Preview Abstract] |
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R1.00315: Genetic Engineering of Optical Properties of Biomaterials Paul Gourley, Robert Naviaux, Michael Yaffe Baker's yeast cells are easily cultured and can be manipulated genetically to produce large numbers of bioparticles (cells and mitochondria) with controllable size and optical properties. We have recently employed nanolaser spectroscopy to study the refractive index of individual cells and isolated mitochondria from two mutant strains. Results show that biomolecular changes induced by mutation can produce bioparticles with radical changes in refractive index. Wild-type mitochondria exhibit a distribution with a well-defined mean and small variance. In striking contrast, mitochondria from one mutant strain produced a histogram that is highly collapsed with a ten-fold decrease in the mean and standard deviation. In a second mutant strain we observed an opposite effect with the mean nearly unchanged but the variance increased nearly a thousand-fold. Both histograms could be self-consistently modeled with a single, log-normal distribution. The strains were further examined by 2-dimensional gel electrophoresis to measure changes in protein composition. All of these data show that genetic manipulation of cells represents a new approach to engineering optical properties of bioparticles. [Preview Abstract] |
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R1.00316: Ambient-pressure thermodynamic measurements on UGe$_{2}$ F. Hardy, C. Meingast, H. von Loehneysen, J. Flouquet, A. Huxley, J. Lashley, R.A. Fisher, N.E. Phillips The pairing interaction leading to the formation of the Cooper pairs remains unidentified in the ferromagnetic superconductor UGe$_{2}$. Nevertheless, there is strong experimental evidence that superconductivity is not mediated by the magnetic fluctuations that drive T$_{Curie}$ (p) to zero; it rather appears closely related to another phase boundary T$_{x}$ (p) that occurs at lower pressure. Theoretical works suggested that this additional phase boundary could arise either from a coupling between SDW and CDW orderings or from a peak in the electronic density of states. Although the existence of this anomaly is experimentally incontestable between 0.6 and 1.2 GPa, the situation at ambient pressure remains ambiguous. We discuss the aforementioned scenarios in the light of recent high-resolution thermal expansion and calorimetric measurements realized under high magnetic fields at ambient pressure. [Preview Abstract] |
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R1.00317: Ressonance Raman Excitation Energy Map and High Resolution Transmission Electron Microscopy of hundreds of (n,m) Single Wall Carbon Nanotubes Ado Jorio, Pedro B.C. Pesce, Paulo T. Araujo, Stephen K. Doorn, Pasha Nikolaev In this work we measure the Raman spectra of a single wall carbon nanotube (SWNT) sample with a wide diameter distribution - 1nm to 6nm - with closely spaced laser lines over the 1.26eV to 2.71eV energy range and did a thorough analysis of the observed features. The most intense peaks are assigned to the scattering of light by a single RBM phonon in ressonance with the well-known excitonic $E_{ii}$ transitions. Comparison of the Raman map with the diameter distribution of the sample, obtained from high resolution transmission electron microscopy (HRTEM) measurements of 395 different nanotubes allows us to determine the diameter dependence of the RBM cross section. Furthermore, a number of weaker features are identified with different mechanisms, such as the RBM overtone and cross polarized transitions. [Preview Abstract] |
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R1.00318: Ripples in epitaxial graphene Francois Varchon, Pierre Mallet, Jean-Yves Veuillen, Laurence Magaud On the basis of extensive ab initio calculation supported by scanning tunneling experiments, we have elucidated the complex morphology of the graphene/SiC (0001) interface [1]. We demonstrate that a carbon buffer layer is always present at the interface. It is a key characteristic of the system because this buffer layer electronicaly decouples the graphene layer from the substrate [2]. It has a mosaic structure that is reminiscent of a graphene honeycomb lattice distorted by the formation of strong covalent bonds with the substrate. The substrate-induced nanostructuration extends up to the ontop graphene layer where it generates an incommensurate modulation of the honeycomb lattice. The possible opening of a gap induced by the substrate [3] in the epitaxial graphene electronic structure will also be discussed. [1] F.Varchon et al. cond-mat/0712.3394, (submitted to PRB) [2] F.Varchon et al. Phys. Rev. Lett. 99, 126805 (2007) [3] S.Y.Zhou et al. Nature Mat. 6, 771 (2007) [Preview Abstract] |
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R1.00319: Phase transition via intermediate state and control of piezoelectric parameters in lead-zirconate-titanate based solid solutions V. Sobolev, V. Ishchuk, N. Spiridonov Presentation contains results of experimental investigation of the influence of external electric field on the stability of phases in antiferroelectric substances with a small difference in the free energies of the ferroelectric and antiferroelectric states. The composition-electric-field phase diagrams with intermediate states of coexisting domains of the ferroelectric and antiferroelectric phases are obtained for lanthanum-modified lead-zirconate-titanate solid solutions. This intermediate state appears in the process of inducing of the ferroelectric state by an external electric field in antiferroelectric solid solutions. Peculiarities of the intermediate state caused by interphase interactions between coexisting ferroelectric and antiferroelectric domains are revealed. Analysis of the dependences of piezoelectric material parameters on external electric field at the phase transition via an intermediate state has been performed. It is demonstrated that within the interval of existence of the intermediate state the piezoelectric material parameters can be effectively controlled by an applied electric field. [Preview Abstract] |
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R1.00320: Entangled Photon Quantum Key Distribution: Theory and Experiment Israel Owens Secure communications face growing challenges due to technological advances such as the anticipated arrival of quantum computers. Quantum key distribution offers a new method for the distribution of cryptographic key material that is secure against these challenges. I will describe a method of quantum key distribution that is based on using entangled photon pairs (EQKD). In particular, I will discuss and emphasize the key theoretical and experimental components of EQKD and the details of recent test-bed data results. [Preview Abstract] |
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R1.00321: Zero dimensional area law in a gapless fermion system Gregory Levine, David Miller The entanglement entropy of a gapless fermion subsystem coupled to a gapless bulk by a ``weak link'' is considered. It is demonstrated numerically that each independent weak link contributes an entropy proportional to $\ln{L}$, where $L$ is linear dimension of the subsystem. [Preview Abstract] |
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R1.00322: E=2mc$^2$ Kwadwo Dompreh The Albert Einstein mass-energy equation $E=mc^2$ which is used primarily in the estimation of the amount of energy in fission reaction can be can be modified to give an equation which is used calculate the amount of energy in a fusion reaction. This theory is deduced using the Gedenken experiment used in special relativity and a computer simulation using the Matrix laboratory. The energy harnessed is non -- radioactive and can be used to power our homes, industries and even our automobiles. When the equation is applied to cosmological bodies such as the Suns, Starts and others gives a better understanding of their origin. [Preview Abstract] |
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R1.00323: Density Functional Theory Study of Polyanilines and Polypyrroles Monica Bastola, Sudip Neupane, Pedro Derosa From the moment polymers were found to be able to conduct electricity, upon appropriate doping, a number of technological applications have been implemented and a large number of other applications are envisioned. There is however still a lack of deep understanding of the correlation between the properties at the molecular level and the corresponding properties at the macroscopic level. Bridging the gap, the development of a multiscale model able to connect the two words, is certainly a task that must be accomplished. One step towards that aim consists on the development of strategies that allow to infer from molecular properties macroscopic properties what requires sufficiently accurate and computationally inexpensive models able to study the evolution of molecular properties into macroscopic properties. This work presents a density functional study of polyanilines and polypyrroles, geometry, HOMO-LUMO gap energy, charge distribution and the molecular orbital structures are calculated as function of polymer size and structure. For the polypyrroles the relation between these properties and the oligomer size will be presented. For the polyanilines, the fully reduced leucoemeraldine based, the half oxidized emeraldine based and the fully oxidized pernigraniline are studied and compared. [Preview Abstract] |
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R1.00324: Ion Size Effect on Glow Peak Temperature in Dielectric Binary Mixed Crystals Doped With Divalent Europium Ricardo Rodriguez-Mijangos, Raul Perez-Salas Thermoluminiscence measurements at room temperature of ``beta'' irradiated divalent Europium doped binary mixed alkali halides with RbCl and KBr components at several concentrations x in molar fraction are carried out. The experiments have been carried out to identify the effect of composition in thermoluminiscense glow peaks. A typical glow peak has been distinguished for each composition. A linear dependence of its temperature on the composition x has been found. This is principally associated with the radii size change of halogen ions. Comparison with results in mixed KCl:KBr. KBr:RbBr and KCl:RbCl support that assertion. [Preview Abstract] |
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R1.00325: Consistent Hybrid Simulation of MD and CFD Shugo Yasuda, Ryoichi Yamamoto The idea of multi-scale hybrid simulation is expected to be very useful for overcoming several difficult problems remain unsolved in frontiers of computational science in general. A striking example is the case of hydrodynamics of complex fluids or soft matters, for most of which no reliable constitutive relation is known explicitly. Our strategy to overcome this problem is very straightforward. We are developing a multi-scale hybrid method which combines computational fluid dynamics (CFD) as a fluid solver and molecular dynamics (MD) as a direct generator of constitutive relations in a consistent way. The numerical algorithm is rather simple. We perform usual lattice-mesh based simulations for CFD level, but each lattice is associated with a small MD cell which generates a ``local stress'' according to a ``local flow field'' given from CFD instead of using any constitutive functions at CFD level. Some algorithms to smooth out noses arising from MD simulations in a consistent way are being developed. Comparisons of the numerical results obtained by our hybrid-simulations and those by normal CFDs with a Newtonian constitutive relation are made in order to show the validity of our hybrid simulation method. [Preview Abstract] |
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R1.00326: Manipulation of the vibration of cold ground-state Cesium molecules Matthieu Viteau, Amodsen Chotia, Maria Allegrini, Daniel Comparat, Pierre Pillet Creating in an efficient way, a large and dense sample of ultracold molecules in their fundamental ground state, i.e. with neither vibration nor rotation, is an important step toward the realization in further experiments. Among them, cold collisions, controlled chemistry, or accurate spectroscopic measurement. One further motivation is the possibility to go towards the realization of a Bose-Einstein molecular condensate. But all existing experiments of cold molecules (Feshbach resonance, photoassocation) formed molecules in high vibrational state, mostly close to the dissociation limit. We want to explore different schemes to create or transfer cold molecules (Cs$_{2})$ to the electronical and vibrational fundamental state ($^{1}\Sigma _{g}^{+}$ v=0). We have studied the photoassociation of cold atoms in a high vibrational level ($^{1}\Sigma _{g}^{+}$ or $^{3}\Sigma _{u}^{+})$ follow by an optical pumping scheme. We use a shaped femtosecond laser to realize the optical repumping step in order to excite the molecules to a potential which have good decay to lower vibrational levels. [Preview Abstract] |
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R1.00327: Thermodynamically stable noncomposite vortices in mesoscopic two-gap superconductors Liviu Chibotaru, Vu Hung Dao Two-gap (or two-band) superconductors such as recently discovered MgB$_{2}$ show new qualitative effects with respect to conventional ones. For example the fractionalization of the magnetic flux associated to individual vortices is predicted in massive two-gap superconductors. It can either result from the inequality of the winding numbers of the vortices in the two condensates ($L_1 \neq L_2$) having a common vortex core (composite vortices), or the vortex cores in each of the two bands can be spatially separated (noncomposite or deconfined vortices). In both cases they never correspond to the ground state, i.e. are thermodynamically unstable. Thus only the usual Abrikosov vortices are experimentally observed in massive two-gap superconductors. Within the two-gap Ginzburg-Landau theory we have found the existence of thermodynamically stable noncomposite vortices in mesoscopic superconductors in a large domain of the $T - H$ phase diagram. The appearance of these vortex phases is caused by a non-negligible effect of the boundary of the sample on the superconducting order parameter and represents therefore a genuine mesoscopic effect. For low values of interband Josephson coupling vortex patterns with $L_1 \neq L_2$ can arise in addition to the phases with $L_1 =L_2$. The calculations show that noncomposite vortices could be observed in thin mesoscopic samples of MgB$_{2}$. [Preview Abstract] |
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R1.00328: Destruction of global coherence in long superconducting nanocylinders Vu Hung Dao, Liviu Chibotaru Recent realizations of the Little-Parks experiment on long hollow cylinders with nanoscale diameter have shown the destruction of superconductivity at zero temperature around half quanta of applied magnetic flux. In addition the observed resistive transition unexpectedly broadens when departing from zero magnetic field. A quantum phase transition near half flux quanta has been argued to explain this anomalous behavior. However this theory does not explain the step-like features observed in the temperature variations of the resistance. We show here that the puzzling behavior of the resistance results from an alternation of normal and superconducting sections along the tube. First within the Ginzburg-Landau theory we have found that the transition is of second order if the studied cylinders are homogeneous, which precludes the existence of nonhomogeneous phases. From this we conclude that the phase separation must be triggered by the tube inhomogeneities. Within a minimal model where cylinder properties vary along its axis, our BCS calculations of the superconducting state are in a good agreement with experimental data, in particular, the multistep transitions are naturally explained. A small discrepancy near half flux quanta may be ascribed to the charge imbalance induced by the normal electron flow. [Preview Abstract] |
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R1.00329: Long Time Tail of the Velocity Autocorrelation Function in a Two-Dimensional Moderately Dense Hard Disk Fluid Masaharu Isobe Alder and Wainwright discovered the slow power decay $\sim t^{- d/2}$ ($d$:dimension) of the velocity autocorrelation function in moderately dense hard sphere fluids using the event-driven molecular dynamics simulations. In the two-dimensional case, the diffusion coefficient derived using the time correlation expression in linear response theory shows logarithmic divergence, which is called the ``2D long- time-tail problem''. We revisited this problem to perform a large-scale, long-time simulation with one million hard disks using a modern efficient algorithm and found that the decay of the long tail in moderately dense fluids is slightly faster than the power decay ($\sim 1/t$). We also compared our numerical data with the prediction of the self-consistent mode-coupling theory in the long time limit ($\sim 1/(t\sqrt{\ln{t}})$). [Preview Abstract] |
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R1.00330: First and second order coherence of exciton-polariton condensates G. Roumpos, C.W. Lai, A. Forchel, Y. Yamamoto The microcavity exciton-polariton system offers the possibility to study condensed matter physics with optical techniques. In particular, condensation of microcavity exciton-polaritons in momentum space, as well as spontaneous buildup of spatial and temporal coherence, were recently demonstrated. We investigate the first and second order coherence of exciton-polariton condensates both in coordinate and in momentum space. We measured the spatial coherence length of up to 20 $\mu m$, while $g^{(2)}(t=0)$ was measured to be close to 2 for appropriate near- and far-field filtering. This experiment provides insights into the phase and intensity fluctuations induced by polariton interactions. [Preview Abstract] |
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R1.00331: Effect of terminal functional group of self-assembled monolayers formed on gold surface on the adsorption of Amyroid fibrils by AFM Kohei Uosaki, Masaya Tsukamoto, Kazuyasu Sakaguchi, Yuya Asanomi Amyroid fibril, which is known to cause BSE and Alzheimer disease, is a solid and stable fiber of several tens of nm wide and several $\mu $ m long and has a potential to be used as nano-materials because functional molecules and metal and semiconductor nano-particles can be attached. However, it is not yet possible to align the Amyroid fibrils on a solid surface as programmed. In this study, interaction between Amyroid $\beta $ (A$\beta )$ fibrils and self-assembled monolayers (SAMs) with various functional groups constructed on a gold surface was investigated by in situ AFM. Amyroid $\beta $10-35 (A$\beta $10-35) peptide was synthesized and the peptide was incubated at 37 deg. for more than a week to obtain the fibril. SAMs of alkylthiols with methyl, OH, COOH, NH2, and SO3 groups were formed on Au(111) surface and AFM images were obtained by MAC mode in a solution containing the fibrils. It was clarified that electrostatic and hydrophobic interactions play important roles in adsorption behavior of the fibrils. [Preview Abstract] |
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R1.00332: Effect of nickel doping on the magneto-transport properties of Sm$_{0.55}$Sr$_{0.45}$MnO$_{3}$ manganites Maher Abdelhadi We studied the effects of nickel (Ni) doping on the magneto-transport properties of Sm$_{0.55}$Sr$_{0.45}$MnO$_{3}$ manganites near the metal-insulator transition. Various concentrations of Ni-doped Sm$_{0.55}$Sr$_{0.45}$MnO$_{3}$ samples up to 5{\%} were prepared (Ni was partially substituted at the Mn-site). The temperature dependence of resistivity and magnetoresistance were measured as a function of Ni concentrations. We observed a nonlinear reduction of the metal-insulator transition temperature (MIT) and a decrease in the width of the peaks in the temperature dependence of resistivity with increasing concentration of Ni. The peaks become sharper at high Ni concentration. The resistivity peaks at various magnetic fields collapses on themselves at the high temperature ends above the MIT. [Preview Abstract] |
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R1.00333: Biomimetic nucleation of calcium carbonate layers at the air-water interface Kyungil Kim The interaction between calcium carbonate crystals and chitosan at the air-water interface was investigated. Chitosan was selected as an organic, pseudo-structural component of calcium carbonate biominerals in the subphase in the presence of octadecyl sulfate Langmuir monolayers. Calcite crystallization was studied using X-ray diffraction and optical microscope techniques; in-situ grazing incidence x-ray diffraction was performed at synchrotron sources. Calcite crystallization under octadecyl sulfate monolayers shows a superlattice structure. This chitosan system also results in ACC(amorphous calcium carbonate) formation in the early stage of crystallization. [Preview Abstract] |
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R1.00334: 1H-NMR Study of Silica-Poly(epsilon-carbobenzyloxy-L-lysine) Composite Particles as Function of Temperature Erick Soto, Jerome Koch, Dale Treleaven, Paul Russo Nearly monodisperse silica-poly(epsilon-carbobenzyloxy-L-lysine) composite particles were synthesized. The hydrodynamic radius of the composite particles and silica core was 200 and 100 nm respectively. Separately, poly(epsilon-carbobenzyloxy-L-lysine) was synthesized having a molecular mass of 200 kDa and a polydispersity of about 1.08. 1H-NMR spectra of the untethered polypeptide dissolved in deuterated m-cresol was collected at different temperatures ranging from 15 to 40 $^{o}$C. The sharp change in the chemical shift of several protons at around 27 $^{o}$C suggests a coil-helix conformation transition. Similarly, 1H-NMR spectra of the composite particles exhibits a more subtle change in chemical shifts in the explored temperature range suggesting a conformation transition of the tethered polypeptide. [Preview Abstract] |
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R1.00335: An improved algorithm for the functional renormalization group and its application to two-dimensional Hubbard model Hirokazu Takashima, Ryotaro Arita, Kazuhiko Kuroki, Hideo Aoki Among the methods that treat strongly correlated electron systems, the functional renormalization group (fRG) method has desirable a feature that it can take account of the shape of the Fermi surface with an unbiased inclusion of diagrams up to the one-loop level. Specifically, the temperature-flow functional renormalization group (T-flow fRG), proposed by Honerkamp and Salmhofer[1], can be a powerful method. We adopted the equal interval patch discretization in the Cartesian coordinates, for which we have constructed a fast and stable algorithm. This method becomes especially powerful at lower T. We also propose a way to include the Matsubara frequency in the four-point coupling and the self-energy. With the present algorithm we discuss spin, charge, and pairing susceptibilities and the spectral function at low T for the two-dimensional Hubbard model, including the effect of t' and t''. [1] C. Honerkamp and M. Salmhofer, Phys. Rev. B \textbf{64}, 184516 (2001). [Preview Abstract] |
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R1.00336: Dynamic nuclear polarization in biased quantum wires using spin-orbit coupling Vikram Tripathi, Anson C. H. Cheung, Nigel R. Cooper We propose a new method for dynamic nuclear polarisation in a quasi one-dimensional quantum wire utilising the spin-orbit interaction, the hyperfine interaction, and a finite source-drain potential difference. In contrast with current methods, our scheme does not rely on external magnetic or optical sources which makes local control much more feasible. Using this method, a significant polarisation of a few per cent is possible in currently available InAs wires which may be detected by conductance measurements. This may prove useful for nuclear magnetic resonance studies in nanoscale systems as well as in spin-based devices where external magnetic and optical sources will not be suitable. [Preview Abstract] |
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R1.00337: Storage capacity and retrieval time of small-world neural networks Hiraku Oshima, Takashi Odagaki To understand the influence of structure on the function of neural networks, we study the storage capacity and the retrieval time of Hopfield-type neural networks for four network structures: regular, small world, random networks generated by the Watts-Strogatz (WS) model, and the same network as the neural network of the nematode Caenorhabditis elegans. Using computer simulations, we find that (1) as the randomness of network is increased, its storage capacity is enhanced; (2) the retrieval time of WS networks does not depend on the network structure, but the retrieval time of C. elegans's neural network is longer than that of WS networks; (3) the storage capacity of the C. elegans network is smaller than that of networks generated by the WS model, though the neural network of C. elegans is considered to be a small-world network. Reference : H. Oshima and T. Odagaki, Phys. Rev. E \textbf{76}, 036114 (2007). [Preview Abstract] |
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R1.00338: Current-Induced Magnetic Domain Wall Motion at Low Current Density via Perpendicular Anisotropy Soon-Wook Jung, Woojin Kim, Taek-Dong Lee, Kyung-Jin Lee, Hyun-Woo Lee The current-induced motion of magnetic domain walls carries great potentials for applications such as nano-scaled logic and memory devices. To achieve this goal, a large reduction in the threshold current density $J_{c}$ for the domain wall motion is highly desired. Here we show that by introducing and properly exploiting the perpendicular magnetic anisotropy, $J_{c}$ can be reduced by one or even two orders of magnitude in experimentally accessible parameter regimes. Using the collective coordinate approach, we analyzed the physical origin of the reduction. The analytic result was also tested by micromagnetic simulations of the LLG equation with spin transfer torque terms. The resulting $J_{c}$ is insensitive to domain wall pinning forces and also to the non-adiabaticity, both of which are hard to control in experiments. [Preview Abstract] |
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R1.00339: Probing Micromechanical Properties of Biological Cells by Oscillatory Optical Tweezers Angela Zaorski, Ming-Tzo Wei, Huseyin C. Yalcin, Jing Wang, Samir N. Ghadiali, Arthur Chiou, H. Daniel Ou-Yang We used oscillatory optical tweezers to probe the micromechanical properties of cultured alveolar epithelial cells in vitro. The frequency-dependent viscoelasticity of these cells was measured by optical trapping and forced oscillation of either a submicron endogenous intracellular organelle (intra-cellular) or a 1.5$\mu $m silica bead attached to the cytoskeleton through trans-membrane integrin receptors (extra-cellular). Both the storage modulus and the magnitude of the complex shear modulus followed weak power-law dependence with frequency. These data are comparable to data obtained by other measurement techniques. The exponents of power-law dependence of the data from the intra- and extra- cellular measurements are similar, whereas, the differences in the magnitudes of the moluli from the two measurements are statistically significant. [Preview Abstract] |
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R1.00340: Molecular magnetic coupling at atomic scale Jinfeng Jia, Yingshuang Fu, Shuaihua Ji, Xi Chen, Xucun Ma, Qikun Xue Understanding and manipulating magnetic interactions between molecules is not only meaningful to molecular magnetism, but also expected to have profound impact on the development of molecular spintronics and quantum computation. Tunneling spectroscopy of CoPc multilayer prepared on nanometer-sized Pb islands on Si(111) were measured with a subkelvin temperature scanning tunneling microscope. We observed magnetic excitations of coupled molecular spins via inelastic electron tunneling spectroscopy, and determined the coupling strength between CoPc adjacent layers with Heisenberg model. We further demonstrate the coupling between molecules, and coupling of single-molecule spin with metallic host can both be manipulated by changing their stacking sequence via molecular manipulation. [Preview Abstract] |
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R1.00341: Model of the magnetostriction of planar domain walls in ferromagnets and antiferromagnets Mikhail Indenbom, Jian-Jun Li Recently we have shown that all details of magnetisation of magnetic thin films and multilayers deposited onto thin substrates can be revealed by simultneous measurements of the substrate flexion and torsion. This technique is complimentary to the ordinary vector magnetometer being capable to resolve the signal from a ferromagnetic (F) layer with the magnetisation negligible compared to one of the other layers or even from an antiferromagnetic (AF) layer and to study, for example, the formation of planar domain walls in a spring-magnet F/F bilayer or an exchange-bias F/AF bilayer. In the current presentation we are using a 1D model of the planar domain wall in order to demonstrate a variety of magnetostrictive signals wich can be obtained in such systems. For clarity we neglect the thickness, magnetic anisotropy and magnetostriction of the control F-layer (an ideal permalloy). We have calculated how spin rotation induced in this layer by the applied magnetic field penetrates into the magnetostrictive AF or F layer and forms the planar domain wall. [Preview Abstract] |
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R1.00342: Heat Transport in Epoxy Networks: A Molecular Dynamics Study Vikas Varshney, Soumya Patnaik, Barry Farmer, Ajit Roy In this poster, thermal behavior of a crosslinked epoxy network along with its un-crosslinked counterpart is presented using atomistic molecular dynamics simulations. The simulations were performed on EPON-862 and curing agent-W (DETDA), used as a model system using consistent valence force field (CVFF). The thermal transport is discussed in terms of its thermal conductivity, as calculated using both equilibrium as well as non-equilibrium molecular dynamics approaches, based on Green-Kubo and Fourier law formalisms, respectively. The results are found to be in good agreement with respect to experimental findings. Different energetic contributions of heat flux towards thermal conductivity and their possible coupling in terms of kinetic energy, van der Waals and electrostatic interactions are also discussed. In addition, the broad distribution of low frequency vibrational modes from power spectrum of velocity autocorrelation function suggests their disordered and amorphous nature. The poster also presents heat movement across a crosslinked slab using thermal relaxation simulations and estimates the thermal diffusivity, thermal relaxation time and mean free path for epoxy networks. [Preview Abstract] |
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R1.00343: Electron Spin Resonance Force Microscopy of Spin Probes Eric W. Moore, SangGap Lee, Steven A. Hickman, Seppe Kuehn, John A. Marohn Nitroxide spin labels, such as 4-amino TEMPO can be used to as environmental, conformal and structural probes in biological and polymer systems. We report on our efforts to detect electron spin resonance of 4-amino TEMPO in a polymer matrix using the magnetic resonance force microscope as a proof of concept for future experiments on spin labeled proteins. Our microscope operates at high vacuum and low temperature, using a custom fabricated single crystal silicon cantilever in the magnet-on-cantilever geometry. The applied field is provided by a microstripline resonator at 18 GHz. [Preview Abstract] |
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R1.00344: Electrical Transpot in Ultra Long Bundles of Carbon Nanotube Amelia Church, Rakesh Shah, Xianfeng Zhang, Saikat Talapatra We will present electrical transport measurements performed on bundles of millimeter long multi walled carbon nanotubes (MWNT). These MWNTs were grown using air assisted floating catalyst chemical vapor depostion method. The temperature dependence of resistance of these MWNT bundles as a function of bundle length will be presented. The variation in the electrical transport properties as a function of MWNT lengths as seen from the current-voltage measurements will also be discussed. [Preview Abstract] |
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R1.00345: Benzene confinement in single-walled carbon nanotubes: inelastic and quasielastic neutron scattering N.R. de Souza, A.I. Kolesnikov, N. Verdal, A.P. Moravsky We characterize experimentally the dynamical properties of benzene confined in single-walled carbon nanotubes (SWNT) of diameter 14 {\AA}. The presence of benzene inside the nanotubes is demonstrated by measuring the small-angle neutron scattering intensities from a properly prepared C$_{6}$D$_{6}$ benzene -- SWNT sample. The incoherent inelastic neutron scattering spectra from C$_{6}$H$_{6}$ benzene in the nanotubes and in the bulk crystal are measured at 4 K, up to an energy transfer of 130 meV. The effective vibrational density of states reveals a significant redistribution of all intermolecular modes for the confined benzene, whereas the intramolecular modes are nearly unaffected. Incoherent quasielastic neutron scattering spectra from C$_{6}$H$_{6}$ benzene in the nanotubes were also collected from 9 K to room temperature, at an energy-transfer resolution of approx. 80$\mu $eV. The orientational and translational diffusive dynamics of confined benzene are discussed on the basis of these data. [Preview Abstract] |
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R1.00346: Patterned nanoring magnetic tunnel junctions and current-induced magnetization switching Z.C. Wen, H.X. Wei, Y.N. Han, X.F. Han Patterned nanoring (NR) magnetic-tunnel-junctions (MTJs) with outer diameters between 100 and 400nm and narrow ring widths between 25 and 30nm were successfully fabricated. The NR structure consists of CoFeB electrodes and Al-oxide barrier. The tunnelling magnetoresistance (TMR) ratio of the patterned NR-MTJs is in the range of 20\%-50\% observed at room temperature with $RA$ lower than $50\Omega \mu$m$^2$. These NR- MTJs allow current-induced magnetization switching with a low switching current density of around $9\times 10^6 A /cm^2$. Due to the small stray field and high TMR ratio, NR-MTJs offer superior prospects for very high density magnetic random access memory (MRAM), recording medium and other spintronics devices. [Preview Abstract] |
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R1.00347: Spin waves in 2D classical XY-model Snehadri Ota, Smita Ota The description of phase transition in the microcanonical formalism has gained growing interest in recent years for the calculation of thermostatic properties of physical systems and microcanonical entropy.$^{1}$ We have carried out micro-canonical Monte Carlo simulations of the 2D XY-model using periodic boundary conditions.$^{2,3}$ In case of microcanonical Monte Carlo simulation some thermodynamic-like relations apply that allow definition of variable by averaging, specifically, the temperature. The energy distributions of the spins have been obtained for the the Kosterlitz-Thouless situation.$^{4}$ In this case, the energy distribution of vortices show features that is due to spin waves, which agrees with the spin wave theory which predicts that E$_{sw}$=-2+T/2. References: [1] H.Behringer and M.Pleimling, Phys.Rev.E \textbf{74} (2006) 11108 [2] M.Creutz, Phys.Rev.Lett. \textbf{50} (1983) 1411 [3] S Ota and S B Ota, Phys.Lett.A \textbf{367} (2007) 35 [4] J B Kogut, Rev.Mod.Phys. 51 (1979) 659 [Preview Abstract] |
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R1.00348: First-order transition in 2D classical XY-model Snehadri Ota, Smita Ota We have carried out micro-canonical Monte Carlo simulations of the extended 2D XY-model in 30$\times $30 lattice using periodic boundary conditions.$^{1-4}$ The energy distributions of the spins have been obtained for the value of the parameter q=55.$^{3,4}$ The energy distribution of the spins in the lattice shows features that can be associated with spin wave and vortex excitations.$^{5}$ The results agree with the first-order transition observed in canonical Monte Carlo simulations, due to vortex nucleation.$^{3}$ References: [1] M.Creutz, Phys.Rev.Lett. \textbf{50} (1983) 1411 [2] S Ota and S B Ota, Phys.Lett.A \textbf{367} (2007) 35 [3] E.Domany, M.Schick, R.H.Swendsen, Phys.Rev.Lett. \textbf{52} (1984) 1535 [4] J.E.van Himbergen, Phys.Rev.Lett. \textbf{53} (1984) 5; Phys.Rev.B \textbf{29} (1984) 6387 [5] J B Kogut, Rev.Mod.Phys. \textbf{51} (1979) 659 [Preview Abstract] |
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R1.00349: Fabrication and characterization of InAs/AlGaSb HEMTs with high-k gate insulators Toshihiko Maemoto, Kenji Fujiwara, Tatsuya Inoue, Naoki Amano, Masatoshi Koyama, Shigehiko Sasa, Masataka Inoue We report on the fabrication and characterization of InAs/AlGaSb high electron mobility transistors (HEMTs) with high-k gate insulators (Al$_{2}$O$_{3}$ and HfO$_{2})$. InAs/AlGaSb quantum well structures were grown by molecular beam epitaxy on a semi-insulating GaAs substrate [1]. From Hall measurements at room temperature, the as-grown wafer showed an electron mobility of 20,000-25,000 cm$^{2}$/Vs and a sheet carrier density of 1.0-2.0x10$^{12}$ cm$^{-2}$. InAs/AlGaSb HEMTs have demonstrated a maximum extrinsic transconductance of 181mS/mm at room temperature. The gate leakage current has been markedly decreased by using thin high-k gate insulators. A typical gate current density of less than 1 nA/mm at room temperature was achieved by inserting the high-k gate insulator. We also found that the leakage current density was smaller than for other experimental results on InAs HEMTs with a Shottky gate [2]. In addition, we evaluated the electron motility and drift velocity by increasing the electronic field between the sources and the drain. [1] T. Maemoto \textit{et al.}, Journal of Physics: Conference Series 38, 112 (2006). [2] J. Bergman\textit{ et al.}, 61th Device Research Conference, June 23-25 (2003). [Preview Abstract] |
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R1.00350: Phonon Transport in Carbon Nanotubes G. Pennington, S.J. Kilpatrick, A.E. Wickenden An understanding of phonon transport in carbon nanotubes (CNTs) is important considering potential electronic and thermal management applications. Weak intrinsic phonon scattering in these quasi-one-dimensional materials allows unique properties including high thermal conductivity. Thus CNTs may provide novel thermal management solutions critical for many emerging electronics technologies, including the development of high-power, high-temperature transistors/lasers and the continued scaling down of feature sizes in high-performance microelectronics. Carbon nanotubes are also expected to exhibit relatively large optical phonon decay times. It is widely believed that non-equilibrium phonons lead to conductance degradation, negative differential conductance, and enhanced thermal breakdown of suspended CNTs.[1] Furthermore, absorption of hot optical phonons by conducting carriers would significantly alter device characteristics in the low-field ballistic limit. Thermal properties are also affected as the slow decay of hot optical phonons is expected to lead to reduced thermal diffusivity, and the development of inhomogeneous heating within a nanotube. In this talk, we discuss simulations of CNT phonon transport based on Monte Carlo solution of the phonon Boltzmann transport equation. [1] E. Pop, D. Mann, J. Cao, Q. Wang, K. Goodson, and H. Dai, ``Negative Differential Conductance and Hot Phonons in Suspended Nanotube Molecular Wires,'' Phys. Rev. Lett., vol. 95, pp. 155505-8, October 2005. [Preview Abstract] |
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