Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session C1: Poster Session I (2:00 pm - 5:00 pm) |
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Room: Exhibit CD |
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C1.00001: POLYMER AND SOFTER MATTER PHYSICS I |
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C1.00002: A New Supramolecular Route for Using Rod-Coil Block Copolymers in Photovoltaic Applications Raffaele Mezzenga, Nicolas Sary, Fanny Richard, Cyril Brochon, Nicolas Leclerc, Patrick Leveque, Jean Nicolas Audinot, Thomas Heiser, Georges Hadziioannou, Solenn Berson We propose a new supramolecular strategy to blend together rod-coil poly(3-hexylthiophene)-poly(4-vinylpyridine) (P3HTP4VP) block copolymers and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The P4VP and PCBM are mixed together by weak supramolecular interactions, and the resulting materials exhibit microphase separated morphologies of electron-donor and electron-acceptor rich domains. The microphase segregated P3HT-rod domains act as electron-donating species and the homogeneous P4VP block:PCBM blend acts as the electron-acceptor domain. We describe the photovoltaic performance of standard and inverted devices whose active layer is composed thereof and show the effect of finely engineering the interfacial properties of the active layer to obtain competitive photovoltaic performance with superior thermal stability. (1) N. Sary, F. Richard, C. Brochon, N. Leclerc, P. Leveque, JN Audinot, S. Berson, T. Heiser, G. Hadziioannou, R. Mezzenga, Adv. Mater. in Press (2010) [Preview Abstract] |
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C1.00003: Control of Rod-Rod Interactions in Poly(3-alkylthiophenes) Victor Ho, Bryan W. Boudouris, Rachel A. Segalman Poly(3-hexylthiophene) is a commonly used semiconducting polymer because of its relatively high charge transport ability, low band gap, and solution processiblity. Strong intermolecular interactions lead to the formation of nanofibers during crystallization, which prevents long-range microstructural ordering. We show rod-rod interactions, parameterized by the Maier-Saupe parameter, can be controlled by rational polythiophene side chain design. Effects of side chain passivation are evidenced by a depressed melting temperature and the presence of a liquid crystalline region. Additionally, the Maier-Saupe parameters are estimated for poly(3-dodecylthiophene) and poly(3-ethylhexylthiophene); the relative magnitudes of each are related to the interchain spacings obtained by x-ray diffraction experiments. The systematic tuning of the rod-rod interactions in polythiophenes allows for manipulation of the ratio of Maier-Saupe to the Flory-Huggins parameter, a crucial value in obtaining long-range order in rod-coil block copolymer morphologies. [Preview Abstract] |
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C1.00004: Mobility of self-localized defects in conjugated dendrimers Yongwoo Shin, Xi Lin In our previous study we have computed the intrinsic activation barrier for a topological soliton moving along a linear trans-polyacetylene chain. In this work we systematically investigate the adiabatic potential energy surfaces of self-localized defects, such as soliton, polaron, bipolaron, and exciton, at the dendrimer triple junctions using the Su-Schrieffer-Heeger (SSH) model Hamiltonian and ab initio calculations. All junction structures are found to be attractive energy basins for these self-localized defects. In particular, excitons can be trapped by a pair of closely positioned triple junctions with the hole and electron states both displaying separated charge density distributions. Under an external electric field, excitons can be split into spatially separated electrons and holes, localized at different junctions on the conjugated dendrimer. [Preview Abstract] |
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C1.00005: Electrical and structural changes during phase transitions in conducting polymer cubic phases Jinghang Wu, Wen-Shiue (Owen) Young, Thomas Epps, David Martin Bicontinuous cubic conducting polymer structures can be obtained by polymerization within an ordered surfactant mesophase. These materials are of interest for applications where both electronic and ionic mobilities are important such as in fuel cells, catalysts, and controlled drug delivery. This method provides a means for tailoring the morphology of polymers such as PEDOT (poly(3,4-ethylene dioxythiophene)) at the nanometer length scale. The thermal stability of cubic phases was studied as a function of EDOT monomer concentration in the non-polar phase up to 10 wt{\%}. The microstructure was examined by temperature dependent small angle x-ray scattering. The electronic transport properties were examined on the same samples using in-situ impedance spectroscopy. The morphology was also examined using low voltage electron microscopy (LVEM). [Preview Abstract] |
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C1.00006: Tuning intermolecular interactions in di-octyl substituted polyfluorene via hydrostatic pressure Keshab Paudel, Harrison Knoll, Meera Chandrasekhar, Suchi Guha Polyfluorenes (PFs), a class of poly para-phenylene based blue-emitting polymers, present intriguing structure-property relationships. The backbone conformations of dioctyl-substituted PF (PF8) depend on the torsion angle between monomers. We present photoluminescence (PL) and Raman studies of thin films, as-is bulk, and thermally annealed bulk samples of PF8 under hydrostatic pressure (0-6.5 GPa). The PL energies red-shift at different rates; their pressure coefficients elucidate the role of the backbone torsion angle. In the annealed sample the change in the torsion angle under pressure as the polymer evolves from a non-planar C$_{\alpha }$ conformer to a planar C$_{\beta }$ conformer causes a faster red-shift. Density-functional calculations of a fluorene oligomer corroborate this trend. Raman peaks harden with pressure; the intra-ring C-C stretch frequency at 1600 cm$^{-1}$ shifts at a rate of 7.2 cm$^{-1}$/GPa and exhibits asymmetric line shapes at higher pressures, characteristic of a strong electron-phonon interaction. [Preview Abstract] |
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C1.00007: Enhanced Photoemission in Alq3 Films due to Intermolecular Transitions Milhan Ajward, Xiaosheng Wang, Venkat Gangilenka, Hans Peter Wagner Thin aluminum quinoline (Alq3) organic films are frequently used as an efficient emissive layer in organic light emitting devices. However, the influence of crystalline order on the photoemission due to intermolecular transitions is still rather unexplored. In this work we systematically study the light emission by temperature dependent time-integrated and time-resolved photoluminescence (PL) in Alq3 films that are grown by organic molecular beam deposition. The crystalline order in the films is modified by (1) changing the Alq3 layer thickness, (2) varying the deposition rate, (3) using different substrates and (4) annealing. Depending on these conditions the layers show a more or less pronounced enhancement of the PL at $\sim $170 K which has been attributed to the formation of thermally activated self-trapped excitons. Due to the generation of these localized two-molecule exciton complexes the migration of excitons to non-radiative centers is reduced which leads to an increasing PL efficiency. This interpretation is supported by time-resolved PL measurements. [Preview Abstract] |
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C1.00008: Towards cost-effective, solution processed, encapsulant films for organic electronic devices -- controlling flow instabilities during film formation Jimmy Granstrom, Anshuman Roy, Griffin Rowell, Ji Sun Moon, Evan Jerkunica, Alan Heeger We present a general method for making thin and smooth films of a water-repelling perfluorinated polymer. These films function as encapsulation barrier layers against water and oxygen permeation. Based on a phenomenological analysis, we find that disturbances in flow due to the Rayleigh-Benard-Marangoni instability during drying of spin-cast perfluorinated polymer films cause high surface roughness and the formation of ``pinholes.'' Atomic Force Microscopy measurements show that this instability can increase the surface roughness by an order of magnitude. Casting films from solutions with higher polymer concentration and from solvents with higher viscosity suppress the instability and significantly reduce the roughness. Suppression of the instability results in improved barrier properties as indicated by the calcium thin film optical transmission test. [Preview Abstract] |
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C1.00009: The Microphase Separation of Conjugated Diblock Copolymers and their Application to Organic Photovoltaics Dian Chen, Serkan Yurt, Dhandapani Venkataraman, Thomas Russell Conjugated diblock copolymers with different block ratios (P3HT-b-PrT) were synthesized via GRIM polymerization. The PrT block is amorphous due to the substitution of the hexyl group in P3HT with an alkyl silane group, which drives the microphase separation of the polythiophenes-based block copolymer and the variation in the crystallinity between the two blocks. Thermal and solvent annealing were used to control the self-assembly of the BCPs and the orientation of the P3HT crystals, while the domain size was controlled by the block molecular weights. The BCPs were blended with n-type semiconductors, like phenyl-C61-butyric acid methyl ester (PCBM), which segregated to the amorphous domains by solvent and heat treatment. Such heterojunction structure could lead to high-performance organic photovoltaics. [Preview Abstract] |
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C1.00010: Thermoelectric Behavior of Carbon Nanotube-Filled Latex Composites Jaime Grunlan, Choongho Yu, Yeon Seok Kim, Dasarayong Kim Segregated-network carbon nanotube (CNT)-polymer composites were prepared and their thermoelectric properties were measured as a function of CNT concentration at room temperature. This study shows that electrical conductivity can be dramatically increased by creating a network of CNTs in the composite, while the thermal conductivity and thermopower remain relatively insensitive to the filler concentration. This behavior results from thermally disconnected, but electrically connected, junctions in the nanotube network, which makes it feasible to tune the properties in favor of a higher thermoelectric figure of merit. With a carbon nanotube concentration of 20 wt{\%}, these composites exhibit an electrical conductivity of 4940 S/m, thermal conductivity of 0.4 W/m\textbullet K and a thermoelectric figure of merit (\textit{ZT}) greater than 0.005 at room temperature. This study suggests that polymeric thermoelectrics are possible and provides the basis for further development of light-weight, low-cost and non-toxic polymer composites for thermoelectric applications in the future. [Preview Abstract] |
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C1.00011: Charge Transport in Organic Conjugated Polymers Used in Solar Cells - A Computational Study Yaping Li, Jolanta Lagowski Solar cells are one of the most important devices that can be used to solve the world energy and environmental needs. Recently, organic solar cells, because of their lightweight, low cost and processing flexibility, have attracted considerable attention in this field. To improve their efficiency, it is necessary to study their material properties. We investigate their charge transport characteristics using computational means. In particular we employ both the DFT and ZINDO theoretical approaches, to determine their transfer integrals, reorganization energies, transfer rates and mobilities. We find that polymers with large transfer integrals tend to have lower transfer rates if their reorganization energies are large. This suggests that in organic polymers, in addition to the transfer integral, the reorganization energy is also an important factor in determining charge transport rates. Trends in the transfer rates and mobilities for various organic polymers (in pristine and heterogeneous molecular environments) suitable for photovoltaic cell usage will be discussed. Our computational results will be compared with experimental values whenever possible. [Preview Abstract] |
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C1.00012: First-principles studies of Mg-doped LiFePO$_{4}$ for lithium ion batteries Siqi Shi, Hua Zhang, Wai-Ning Mei, Aifang Liu, Khoon-Cheng Lim We investigate the formation energy, crystal parameters and electronic properties of Mg-doped (Li site and Fe site) lithium iron orthophosphate (LiFePO$_{4})$ by using the first-principles calculations. We noticed that the Mg ions are much more easier to be doped on Fe site than Li site. Comparing with the pure LiFePO$_{4}$, we found the band gap of Mg-doped LiFePO$_{4}$ is a little narrower than that of the pure one, indicating that the enhancement of the electronic conductivity upon doping is likely. Furthermore, we discovered that Mg doped on the Fe site causes the bond length to change, which is consistent with our experimental data. The reduction of the Mg-O bond length favors the formation of Li$^{+}$ diffusion channels, hence improves the ionic dynamic properties of the olivine LiFePO$_{4}$. Mg-doped LiFePO$_{4}$ has bigger electricity peak area that the pure one, which is an indication of improved ionic diffusion. [Preview Abstract] |
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C1.00013: Morphological Effects on Proton Transport in Self-Assembled Anhydrous Polymers Scott Christensen, Yangbin Chen, Michael Thorn, Craig Versek, Ambata Poe, Mark Tuominen, S Thayumanavan, Ryan Hayward A critical component of fuel cell technology is efficient proton exchange membranes with the ability to selectively transport protons over micrometer length scales. For polymer membranes, the industry standard Nafion suffers from the need for humidification, preventing efficient operation above the boiling point of water. It would therefore be beneficial to use a solvent free membrane that allows for operation at high temperatures, thus increasing efficiency, lowering cost, and preventing catalyst poisoning. We describe the design and characterization of comb polymers containing amphoteric proton transfer functionalities that self-assemble into organized supramolecular structures. Comparison with analogous polymers lacking organization reveals that these self-assembled structures yield a two- to three-order of magnitude increase in proton conductivity, presumably due to the locally-increased concentration of proton-transport functionalities within the nano-phase separated domains. [Preview Abstract] |
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C1.00014: Off-normal deposition of PTFE thin films during 157-nm irradiation Sharon R. George, Stephen C. Langford, J. Thomas Dickinson Polytetrafluoroethylene (PTFE) is valued for its chemical stability, low surface energy, and insulating properties. The ablation of PTFE by F$_{2}$ excimer lasers (157 nm photons) involves photochemical scission of C-C bonds along the polymer chain. Depending on the fluence, the fragment masses can range from 50 to 2000 amu. Gaussian beam profiles allow for the production of spatially non-uniform distributions of fragment masses, with the lighter fragments concentrated in the center of the laser spot. The resulting trajectories for the light fragments can be strongly forward directed, while the heavy fragments are directed more to the side, well away from the surface normal. We present experimental evidence for these angular distributions, and numerically simulate this behavior with a simple, two-component hydrodynamic model. Under the conditions of our work, most of the ablated mass appears as heavier fragments and can be collected on substrates mounted to the sides or above and below the laser spot. This geometry may have advantages in some applications of pulsed laser deposition. [Preview Abstract] |
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C1.00015: Electronic and Transport Properties of Quasi-1D Wires of Biological Molecules Bj{\"o}rn Oetzel, Lars Matthes, Falk Tandetzky, Frank Ortmann, Friedhelm Bechstedt, Karsten Hannewald In the search for organic materials with good charge-transport properties, artificial stacks of biological molecules are considered attractive candidates [1,2]. In this spirit, we present ab-initio DFT calculations of the structural, electronic, and quantum-transport properties of quasi-1D wires based on guanine and eumelanin molecules [3]. Hereby, a special focus is put on the results for the electronic bandwidths and the consequences for potential applications. \\[4pt] [1] R. di Felice et al., Phys. Rev. B 65, 045104 (2001) \\[0pt] [2] P. Meredith et al., Pigment Cell Res. 19, 572 (2006) \\[0pt] [3] B. Oetzel et al. (unpublished) [Preview Abstract] |
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C1.00016: Slow and correlated fractal growth of organic material due to energetic cluster deposition Deeder Aurongzeb Growth mechanisms in organic thin-film deposition are crucial for tailoring growth morphologies and electronic properties. One problem with organic molecule is that they exhibit high sticking co-efficient and tends not to be planer with thickness like their inorganic counter part. We report surface correlation evolution in energetic cluster vapor deposited organic light emissive material tris (8-hydroxyquinoline) aluminum using phase modulated atomic force microscopy. For low thickness (5nm), photoluminescence measurement shows the emission peak is shifted by $\sim $0.4eV toward lower wavelength. [Preview Abstract] |
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C1.00017: Intermolecular band dispersion of quasi-single crystalline organic semiconductor monolayer measured by angle-resolved photoemission spectroscopy Manabu Ohtomo, Toshihiro Shimada, Tetsuya Hasegawa Band structure of organic semiconductors is important knowledge to improve the molecular design. Angle-Resolved Photoemission Spectroscopy (ARPES) studies using highly conductive single domain samples grown in-situ is the most direct technique. In this study, we developed a novel method to grow quasi-single crystalline monolayer on conductive substrate and electronic structure was investigated. As a template for orientation control, we used a step-bunched Si(111) substrate with dangling bond termination. In case of pentacene, it was confirmed that the crystal is quasi-single crystal with 2.2$^{\circ}$ rotated twins. The band dispersion was identical to that of thin-film phase. The effective mass and transfer integrals are evaluated using two-dimensional tight binding fit and compared with band calculations [1]. We also report the growth of 2,7-Dipheny[1]benzothieno[3,2-b]benzothiophene (DPh-BTBT) [2] on Bi-Si substrate and compare discuss its band structure. \\[4pt] [1] M.Ohtomo et al., APL \textbf{95}, 123308 (2009).\\[0pt] [2] K.Takimiya, JACS \textbf{128}, 3044 (2006). [Preview Abstract] |
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C1.00018: Morphological Studies of Bulk Heterojunction Organic Solar Cells Kristin Schmidt, James Rogers, Jeff Peet, Robert Coffin, Michael Dimitriou, Edward Kramer, Guillermo Bazan A new approach offers the potential of introducing structural control during device fabrication without the need of thermal annealing. It was shown that incorporating of small concentrations of solvent additives in the solutions of conjugated polymer and fullerene derivatives from which the bulk hetero junction (BHJ) films are cast leads to a modification of the blend morphology. Despite the excellent power conversion efficiency of these films, important questions regarding the BHJ domain morphology remain unanswered. To probe the internal structures we performed complementary grazing incidence small and wide angle scattering experiments (GISAXS and GIWAXS). In addition, we conducted NEXAFS experiments to determine the blend composition at the interfaces. The results indicate a pronounced effect of polymer chain architecture on the degree of chain ordering within the films. The ordering can be further improved by incorporation of solvent additives during the casting process. The morphological changes in the BHJ systems are well correlated with the device characteristics. [Preview Abstract] |
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C1.00019: Anisotropic Refractive Index Dispersion in Polycrystalline PTCDA Waveguides Milhan Ajward, Xiaosheng Wang, Venkat Gangilenka, John Markus, Hans Peter Wagner, Heidrun Schmitzer The dispersion of the inplane and normal refractive index in 3,5,9,10-perylentetracarboxylic dianhydride (PTCDA) waveguides has been determined using the m-line technique. TE and TM mode coupling at excitation wavelengths ranging from 633 to 910 nm has been accomplished by a Rutile prism. The PTCDA waveguides, which were grown by organic molecular beam deposition on Pyrex substrate, reveal a strong optical anisotropy between the inplane and normal refractive index values showing e.g. a birefringence of $\sim $0.8 at a wavelength of 633 nm. Our measurements demonstrate the high optical quality of our PTCDA waveguides as well as their potential for polarization dependent all-optical applications. In particular, the high compressibility of PTCDA waveguides along the soft crystallographic $a$-direction bears potential for pressure sensitive applications. [Preview Abstract] |
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C1.00020: Controlled Growth of Organic Semiconductor Films Using Electrospray Vapor-Liquid-Solid Deposition Daniel Shaw, Kevin Bufkin, Brad Johnson, David Patrick Interest in low molecular weight organic semiconductors (OS) for applications such as light-emitting diodes, photovoltaics, and other technologies stems in part from their prospects for enabling significantly reduced manufacturing costs compared to traditional inorganic semiconductors. However many of the best performing prototype devices produced so far have involved expensive or time-consuming fabrication methods, such as the use of single crystals or thin films deposited under high vacuum conditions. New methods are needed capable of rapidly and inexpensively producing high quality polycrystalline films, preferably involving near-ambient conditions. This poster will present studies of one such approach based on an electrospray vapor-liquid-solid growth technique. The method produces polycrystalline OS films deposited via atmospheric-pressure sublimation from a carrier gas (argon) which is partially ionized by a corona discharge. Vapor-phase molecules are then attracted to a charged substrate coated with a thin liquid solvent layer, in which they dissolve and grow as crystals, producing films with large grain sizes. This poster will describe the electrostatic and hydrodynamic features of the deposition mechanism, and the growth kinetics of the resulting polycrystalline films. [Preview Abstract] |
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C1.00021: Novel spectroscopic technique for exciton diffusion studies in organic semiconductors Vitaly Podzorov, Hikmet Najafov Organic semiconductors are very promising for future opto-electronics. One of the poorly explored issues in this area is the nature of electronic defects and their influence on performance of organic devices. Until recently defects have been mostly studied in polycrystalline and amorphous organic films, where disorder is typically very significant, leading to a complete domination over the intrinsic excitonic and polaronic properties. In this work, we present novel optical spectroscopic technique for characterization of impurities and defects relevant to exciton diffusion in highly ordered organic semiconductors with relatively small density of defects that allows observation of intrinsic properties and their evolution with disorder. [Preview Abstract] |
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C1.00022: Influence of metal-organic interfaces on charge carrier dynamics Andrew Platt, Whitney Shepherd, Thomas Hathaway, Garrett Banton, John Anthony, Oksana Ostroverkhova The interfaces of organic materials with metals play an important role in the function of various organic devices such as organic light-emitting diodes, thin-film transistors, and solar cells. In particular, it is important to understand what effect the interface has on charge injection and on the photoexcited charge carrier dynamics. We examine the influence of metal-organic interfaces between functionalized anthradithiophene (ADT) derivatives and Au or Al on charge carrier dynamics at various time-scales after excitation. While transient photocurrents observed on picosecond time-scales were similar in devices with Au and Al electrodes, continuous wave photoresponse, as well as dark currents, were significantly higher in Au devices. We also employ single molecule fluorescence spectroscopy to study charge transfer dynamics at the nanoscale. In particular, carrier transfer to the electrode (Au or Al) changes a ``blinking'' behavior of the ADT single molecules. By analyzing the ``on'' and ``off'' time statistics, forward and back electron transfer rates between Au or Al and single molecules of ADT are estimated. [Preview Abstract] |
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C1.00023: Oxygen-related defect in PPV Marilia Caldas, Alice Ruini, Arrigo Calzolari Pristine poly-para-phenylene vinylene (PPV) films are structured as crystalline grains immersed in amorphous regions. Inside the grain we must look at three-dimensional (3D) properties, while on-chain processes possibly dominate in the amorphous regions. Defect and impurities due to environmental contamination are usually present and the role of defects can be distinct in one-dimensional (1D) systems compared to its 3D counterparts. We investigated simple defects in PPV that can be introduced by exposure to water, the impact the electron transport properties of 1D chains [1], and on the electronic structure of the crystalline regions. We start from classical molecular dynamics, and proceed to ab initio Density Functional Theory calculations both for single chains and bulk systems through large-supercell defect simulations. For he special case of the C=O keto-defect we find a state with unexpected electron-hole separation, which suggests that the experimentally detected photoluminescence bleaching and photoconductivity enhancement could be due to exciton dissociation caused by the spatial characteristics of the defect. [1] L. Zoppi et al, Phys. Rev. B 78, 165204 (2008). We acknowledge support from CNR, Italy. MJC acknowledges support from FAPESP and CNPq, Brazil. [Preview Abstract] |
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C1.00024: Constitutive modelling of binary blends of monodisperse polymers Daniel Read, Sathish Sukumaran, Kamakshi Jagannathan We present a tube-model theory to describe the non-linear rheology of entangled blends of long and short monodisperse polymers. For each test chain it is conceptually important to distinguish a ``thin tube" (including entanglements with all other chains) and a ``fat tube" (including entanglements with the slowly-moving long chains only). We have developed both a detailed version of the theory, including correlations along, and between, both the thin and fat tubes, allowing for different constraint-release rates on each, and also a simplified ``4 tensor" constitutive model. We compare both with experimental rheometric data, noting in particular the variation of effective stretch relaxation time of long chains with dilution in short chains. We also use the simplified model to simulate the flow of a blend in complex geometries, again comparing against experimental data. [Preview Abstract] |
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C1.00025: The Size of the Dynamic Bead in Polymers Alexander Agapov, Alexei Sokolov Neutron spectroscopy is, currently, one of the most powerful tool to probe the polymer dynamics in space and time. Employing the Neutron Spin-Echo (NSE) technique it is now possible to investigate the relaxation processes from picosecond to nearly microsecond time regime, i.e. from local beta-relaxation to large-scale motions such as Rouse dynamics and reptation. We have analyzed the available neutron scattering literature data on Rouse dynamics for six different polymers. The performed analysis provided the direct estimate of the characteristic dynamic bead size. We show that the traditionally defined Kuhn segment length, fails to describe consistently the chain dynamics and statistics in these six polymers. Understanding the contradiction between the traditional Kuhn segment and experimentally obtained dynamic bead size still remains a challenge. [Preview Abstract] |
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C1.00026: Polymer dynamics at the solid-liquid interface Changqian Yu, Subhalakshmi Kumar, Janet S. Wong, Sung Chul Bae, Steve Granick Novel experimental platforms of few-molecule fluorescence spectroscopy, especially FCS (fluorescence correlation spectroscopy) and FRET (F\"{o}rster resonance energy transfer) are used to study how polymers diffuse in the adsorbed state. ~We quantify how the translational diffusion coefficient depends on chain length, surface coverage and surface heterogeneity. ~Experiments in progress, using FRET, seek to quantify how the end-to-end distance in the adsorbed state compares to its value in free solution. [Preview Abstract] |
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C1.00027: ABSTRACT WITHDRAWN |
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C1.00028: Dynamic characterization of jets of polymer solutions Darrell Reneker Polymer jets that are accessible for detailed observation are created by electrospinning and by mechanical extension of a polymer solution. Laser Doppler experiments measure the velocity in the axial direction of the jet, and at the same time, the diameter of the jet. The tensile stress along a jet is measured by observation of the widening of a short lateral displacement pulse as the pulse moves along the jet. Observation of the colors produced by subtractive interference of particular wavelengths from a beam of white light provide a dynamic measurement of jet diameter in the range from around 1 micron to 15 microns. Microscopic observation of the birefringence of a jet between crossed polarizers provides information about the molecular relaxation time as a function of concentration. Observations of moving glints of reflected light accent the development of curvature in the jets, which is particularly useful for electrospinning jets. Stereographic videography shows the shape of the flow modified Taylor cone. Such observations of jets provide new information about the behavior, in extensional flow, of polymer molecules in solutions of changing concentration. [Preview Abstract] |
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C1.00029: New conduction mechanism in doped trans-polyacetylene through soliton-bipolaron transition Andre Botelho, Minghai Li, Xi Lin By considering the independent movement of a soliton and an anti-soliton in a periodic boundary condition, a new mechanism arises for soliton motion. First, the soliton (anti-soliton) moves while the anti-soliton (soliton) remains pinned by the ion. The soliton and anti-soliton then form a locally stable bipolaron. From this local minimum, the bipolaron can dissociate into its original soliton/anti-soliton pair, with one remaining pinned and the other moving towards an empty ion site. This mechanism has lower energy than when considering the motion of a single soliton in a periodic boundary condition. Energies were calculated using an SSH model with an added Coulombic interaction between each CH site and positive ions in a regular lattice. The model was treated in the Hartree Fock approximation and transition points calculated through the nudged elastic band (NEB) method. [Preview Abstract] |
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C1.00030: Blends of Diblock Copolymers with Attempt to Achieve Triblock Morphologies Eric Anderson, Vikram Daga, James Watkins, Sam Gido Morphological behavior of hydrogen-bonded self-assembled structures of blends of two diblock copolymers Poly(styrene-$b$-ethylene oxide) and poly(butadiene-$b-$acrylic acid) were studied by small angle x-ray scattering and transmission electron microscopy with a goal to obtain morphologies equivalent to triblock copolymers. Depending on the ratio of the block copolymers and the solvent casting condition, macrophase or microphase separation was observed. Commercially available triblock Pluronic{\textregistered} surfactants poly((ethylene oxide)$_{x}$-b-(propylene oxide)$_{y}$-b-(ethylene oxide)$_{x})$ were also blended with diblock copolymers including poly(butadiene-b-acrylic acid) to obtain unique morphologies. [Preview Abstract] |
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C1.00031: Hierachically Ordered Structures Enabled by Evaporative Self-Assembly of Confined Comb Block Copolymer Myunghwan Byun, Ned B. Bowden, Zhiqun Lin We demonstrate the controlled evaporative self-assembly of an asymmetric comb block copolymer toluene solution in a wedge-on-flat geometry for generating the microscopic gradient surface patterns of comb bclock copolymer. These periodic hierarchically ordered structures (i.e., straight lines and punch-hole like mesh) are dictated by the height of the upper wedge lens that determines the height of capillary bridge. Upon subsequent solvent vapor treatment, morphological changes via the interplay of surface tension-driven destabilization at the micrometer scale and solvent vapor-induced microphase separation of comb block copolymer at nanometer scale are observed. As such, this facile approach offers a new platform for patterning the block copolymer thin film with various domain structures in a simple, robust, and cost-effective manner. [Preview Abstract] |
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C1.00032: Guided Organization of $\lambda $-DNAs into Microring-Arrays from Liquid Capillary Microbridges Myunghwan Byun, Suck Won Hong, Jin-Woo Cho, Zhiqun Lin Well-ordered, mesoscale $\lambda$-DNA ring-arrays have been successfully produced via controlled evaporative self-assembly with capillary actions in liquid capillary microbridges. The dimension of the $\lambda$-DNA microrings can be readily tuned by the choice of the PDMS molds. This approach opens a new avenue to utilize evaporative self-assembly as an alternative to conventional lithographic techniques for generating biomolecular patterned arrays in a simple, precise, and cost-effective manner. Using this facile and robust route, a great variety of biomaterials can easily and precisely organized into well-ordered ring arrays, which may have potential applications in functional scaffolds for cell and tissue growth, biosensors, etc. [Preview Abstract] |
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C1.00033: Controlled evaporative self-assembly of hierarchically structured regioregular conjugated polymers Myunghwan Byun, Robyn L. Laskowski, Ming He, Feng Qiu, Malika Jeffries-El, Zhiqun Lin A toluene solution of the semiconducting conjugated polymer regioregular poly (3-hexylthiophene) (rr-P3HT) was confined in a sphere-on-flat geometry, forming an axially symmetric, capillary-held microfluid, from which the consecutive ``stick--slip'' motion of the contact line of the solution via solvent evaporation was effectively regulated. As a result, hierarchical ``snake-skin'' like structures of high regularity were obtained where each microscopic ellipsoid within the ``snake-skin'' was composed of bundles of rr-P3HT nanofibers. This facile, one-step deposition technique based on controlled evaporative self-assembly opens up a new avenue for organizing semicrystalline conjugated polymers into two-dimensional ordered patterns in a simple, cost-effective, and controllable manner. [Preview Abstract] |
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C1.00034: Effect of Electric Field Strength on Diffusion of Ionic Drugs from Polyacrylamide Hydrogels Anuvat Sirivat, Sumonman Niamlang The apparent diffusion coefficients, Dapp, and the release mechanisms of ionic-drugs from drug-loaded polyacrylamide hydrogels, drug-loaded PAAM, were investigated for the effects of various drug sizes (Lactic acid, 3.11 {\AA}; Sulfanilamide,3.47 {\AA}; Ampicillin, 5.14 {\AA}), matrix pore sizes, and electric filed strengths. The Dapp of the drugs from the drug-loaded PAAM increases with decreasing drug size, increasing matrix pore size or applied electric field strength. The increase in Dapp can be attributed to the combination of the iontophoresis and the electroporation of the matrix pore. The Dapp of drug from the drug-loaded PAAM apparently obey the scaling behavior: Dapp/Do=(drug size/pore size)m with the scaling exponent m equal to 0.73 and 0.50 at the electric fields of 0 and 0.1 V, respectively. [Preview Abstract] |
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C1.00035: Electrical Conductivity Response of Poly (phenylene vinylene) / Zeolite Composites Exposed to Ethanol vapour Intira Yimlamai, Anuvat Sirivat Conducting polymers such as poly (p-phenylene vinylene) (PPV) can serve as the active material in organic vapor sensor because PPV possesses good optical and electrical properties. PPV can be synthesized by a relative simple technique and doped with sulfuric acid to improve its electrical properties. The composites of 10{\%} (v/v) doped PPV and ZSM-5 zeolites (Si/Al = 23, 50, 80, 280) were prepared by dry mixing to be used as an ethanol vapor sensor. The four-point probe technique was used to evaluate the effects of doping molar ratio and Si/Al ratio when the sensing materials were exposed to ethanol vapor. When exposed to ethanol vapor, the electrical conductivity response of the doped PPV and ZSM-5 zeolites increased with increasing mole of sulfuric acid but decreased as the ratio Si/Al increased. Although the doped PPV showed positive response when exposed to ethanol vapor but the composites of 10{\%} (v/v) PPV/ ZSM-5 zeolites showed negative electrical conductivity responses, similar to those of the undoped PPV and ZSM-5 zeolites. The difference in the interaction between ethanol molecules and the sensing materials on the electrical conductivity responses were investigated by the FT-IR measurements. [Preview Abstract] |
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C1.00036: Dielectrophoresis Force and Deflection of Dielectric Elastomers and Blends under AC field Ruksapong Kunanuraksapong, Anuvat Sirivat The effects of frequency and amplitude of AC electric field on the deflection distance and the dielectrophoresis force of the of acrylic elastomers (AR71), styrene copolymers (SAR and SBR), and blends with poly(p-phenylene) (AR71:PPP and SAR:PPP) were investigated. The dielectrophoresis forces of the dielectric elastomers and blends were measured by a vertical cantilever under various frequencies (0.3-60 Hz) and at the amplitudes of 200, 300, 500, 600 and 800 Vpp/mm. In addition, the effect of thickness of specimens and the particle concentration on the dielectrophoresis force were studied. Poly(p-phenylene) particles were added into AR71 and SAR with particle concentrations of 5, 10, 15 and 20 vol{\%}. The forces were calculated from the non-linear deflection theory of the cantilever. The dielectrophoresis forces and deflection distances of the dielectric elastomers and blends generally increase with increasing amplitude but slightly decrease with increasing frequency, and they dramatically drop at the cut-off frequency. The cutoff frequencies are 12.0, 1.5 and 1.5 Hz for AR71, SAR, and SBR, at E = 800 Vpp/mm, respectively. [Preview Abstract] |
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C1.00037: Novel Electroactive-paper Gel Preparations via 1-butyl-3-methylimidazolium chloride (BMIMCl) Solvent Wissawin Kunchornsup, Anuvat Sirivat Papers used in the field of electro-responsive applications are known as Electroactive-papers (EAPaps), consisting primarily of a cellulose. 1-butyl-3-methylimidazolium chloride (BMIMCl) is an interesting ionic liquid that acts as an effective cellulose solvent for EAPap due to its high solubility without chain derivatization, less chain degradation, and stability in electro-responsive applications. In our work, physical and chemical cellulose gels were fabricated and studied for the effects of varying crosslinking ratio (CR) and aging time (tag), with glutaraldehyde (GA) acting as the crosslinking agent. The crosslinking reaction conversion could be increased by increasing the CR and tag; the reaction products are ketone linkages and by-product water molecules. A difference in optical properties could be observed and related to the differing amounts of ketone linkages, as confirmed by FTIR-ATR, and the degradation temperature (Td). Our paper-gels showed potential characteristics towards electro-responsive applications: less preparation time ($<$ 14 hours) and stable gel properties. [Preview Abstract] |
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C1.00038: ABC Triblock Copolymer Vesicles with Mesh-like Morphology Wei Zhao, Thomas Russell, Gregory Grason Polymer vesicles can be made from poly(isoprene-b-styrene-b-2-vinylpyridene) (PI-b-PS-b-P2VP) triblock copolymer under the confinement of anodic aluminum oxide (AAO) membrane. It was found that these vesicles have well-defined, nanoscopic size and a microphase-separated hydrophobic core, comprised of PS and PI blocks. Vesicle formation was tracked using both transmission and scanning electron microscopy. A mesh-like morphology formed in the core at a well-defined composition of three blocks. Confinement played an important role in generating these vesicles with such an unusual morphology. [Preview Abstract] |
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C1.00039: Confinement Effects of Polyvinylidene Fluoride-Co- Trifluoroethylene Nanorods Kathleen McEnnis, Jodie Lutkenhaus, Thomas Russell Polyvinylidene fluoride-co-trifluoroethylene (PVdF-TrFE) readily crystallizes into the ferroelectric $\beta $ crystal phase and the crystallization and properties of PVdF-TrFE are affected by confinement. PVdF-TrFE nanorods were made by wetting and filling anodized aluminum oxide (AAO) templates that ranged in pore diameter from 15nm to 200nm. Modulated differential scanning calorimetry (MDSC) and X-ray diffraction (XRD) were used to analyze the effect of confinement on the transitions and structure. The ferroelectric and piezoelectric behavior of confined PVdF-TrFE nanorods was investigated using a high voltage displacement measuring fixture and results were compared to the bulk film. Crystallization within confined PVdF-TrFE nanorods was increasingly suppressed in smaller diameter pores, while the ferroelectric-paraelectric Curie transition remained invariant. [Preview Abstract] |
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C1.00040: Self diffusion studies of P3HT:PCBM blends using Dynamic Secondary Ion Mass Spectrometry (DSIMS) Louis Perez, Michael Brady, Neil Treat, Craig Hawker, Michael Chabinyc, Guillermo Bazan, Edward Kramer The mechanism by which conjugated polymer-fullerene blends form interpenetrating networks necessary for charge separation and collection in bulk heterojunction (BHJ) solar cells remains uncertain. Recent evidence from an experimental phase diagram of P3HT and PCBM suggests that phase separation occurs due to the crystallization of the two components rather than from immiscibility in the liquid state. Diffusion studies of P3HT/PCBM can reveal the molecular mobility in such blends both before and after crystal formation. To determine the tracer diffusion constant of P3HT, a deuterium labeled d-P3HT, has been synthesized and has been used as a tracer macromolecule for depth profiling studies. Dynamic secondary ion mass spectrometry (DSIMS) has been employed to determine concentration versus depth profiles after annealing for different times at various temperatures. Initial results indicate that d-P3HT diffuses much more slowly into a spun cast P3HT film than does deuterium labeled PCBM, a result expected from the relative sizes of the molecules. [Preview Abstract] |
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C1.00041: Order and phase behavior of diblock copolymers and nano-particles mixture in confinement : A Molecular Dynamics study Lenin S. Shagolsem, Jens-Uwe Sommer Diblock copolymers(DBC) and nano-particles(NP) composite show new structures apart from that of a pure DBC. Interesting effects are observed when such composite are in confined geometries. For example, morphology changes, inhomogeneous NP distribution and its effect on the formation of ordered structures. We study, via MD simulation, a coarse grained model of cylinder forming DBC and NP composite confined between walls (which can be neutral or selective) with a particular focus towards an understanding of its order and phase behavior in this restricted environment. In particular, we investigate the effect of temperature on the NP enrichment near the walls also orientation of cylinders for different wall separation. Further, we study how the variation of NP volume fraction affects segregation and morphology. [Preview Abstract] |
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C1.00042: Temperature Tailored Dispersion of Carbon Nanotubes in Water Krishna Etika, Florian Jochum, Patrick Theato, Jaime Grunlan Despite their immense potential, the ability to control the dispersion and microstructure of carbon nanotubes remains a hurdle for their widespread use. Stimuli-responsive polymers show conformation changes with applied external stimulus (pH, temperature, light etc.). Temperature responsive polymers based on poly(N-cyclopropylacrylamide) [p-PNCPA], with varying amounts of pyrene functionality, were used to disperse carbon nanotubes in water. Cryo-TEM micrographs show that SWNTs stabilized using p-PNCPA exists in an exfoliated and bundled state below and above the lower critical solution temperature (LCST) of the polymer, respectively. Viscosity measurements on SWNT/p-PNCPA aqueous suspensions show a shear thinning and nearly Newtonian behavior at temperatures below and above LCST of the polymer, respectively. Studies performed on the SWNT/p-PNCPA composites suggests that microstructure of SWNTs in the suspensions is preserved in the solid composite, as evidenced by SEM imaging and electrical conductivity measurements. [Preview Abstract] |
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C1.00043: Vertical alignment of nanorods in thin film polymer nanocomposites Miguel A. Modestino, Jeffrey J. Urban, Rachel A. Segalman Controlling orientation of anisotropic nanocrystals in conjugated polymer nanocomposites can lead to hybrid materials with new or improved properties for optoelectronic applications. Here, we demonstrate that careful control of rod-rod interactions and solvent evaporation rates can yield polymer composites containing arrays of vertically aligned CdSe nanorods over large areas ($>$1 cm$^{2})$. Grazing incidence x-ray scattering together with transmission electron microscopy (TEM) results show the presence of hexagonally packed arrays of nanorods uniaxially oriented in thin films polymer composites and cross-sectional TEM shows a strong segregation of the arrays toward the surfaces of the films. Also, we demonstrate how systems with different polymer-rod and substrate-rod interactions exhibit equivalent behavior, while varying the rod-rod interactions has a significant impact in the self-assembly of the nanocrystals. The use of aligned nanorods in photovoltaic devices, polarized light emitting diodes and solar-to-fuel devices also will be discussed. [Preview Abstract] |
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C1.00044: Directed assembly of nanoparticles for hybrid photovoltaic Vivian Chuang, Alexander Mastroianni, Kari Thokelsson, Wanli Ma, Paul Alivisatos, Ting Xu Nanoparticles have unique optical and electronic properties. Be able to control the hierarchical assembly of nanoparticles in thin films may lead to devices for energy harvest and storage. Recently it was shown that nanoparticles can be assembled with high precision using block copolymer-based supramolecules.1 Here we present detailed studies on nanoparticle assembly in thin films. Effects of varies parameters including: small molecular loading, supramolecular morphology, film thickness, nanoparticle loading, interfacial interaction and solvent annealing condition on the macroscopic alignment of nanoparticle assembly as well as inter-particle ordering within the copolymer microdomain have been systematic investigated. We show that nanoparticle assembly can be readily aligned either parallel or perpendicular to the substrate. In addition, inter-particle distances can be tailored. A Schottky barrier type solar cell has been fabricated to correlate the structure and device performance and cell efficiency. 1. Zhao, Y.; Thorkelsson, K.; Mastroianni, A. J.; Schilling, T.; Luther, J. M.; Rancatore, B. J.; Matsunaga, K.; Jinnai, H.; Wu, Y.; Poulsen, D.; Frechet, J. M. J.; Paul Alivisatos, A.; Xu, T. Nat Mater 2009, advance online publication. [Preview Abstract] |
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C1.00045: Wide Angle X-ray Scattering Studies of C$_{60}$ Miscibility with Polymers Katie Campbell, David Bucknall, Yonathan Thio, Bilge Gurun C$_{60 }$and other fullerenes have been shown to have limited solubility in common organic solvents and to form charge-transfer complexes with a variety of small molecules. Among factors that promote solubility and charge-transfer complex formation are aromaticity, electron donating capability, atoms much larger than carbon such as chlorine. However, studies of C$_{60}$ miscibility with polymers have been limited. We previously showed that C$_{60}$ has a miscibility limit of $\sim $1wt{\%} with polystyrene via wide angle x-ray scattering (WAXS) and molecular dynamics simulations. We have studied a series of polymers with structural features shown to be important in small molecule/C$_{60}$ interactions using WAXS: poly(para-phenylene ethynylene), poly(4-vinylpyridine), poly(vinylpyrrolidone), poly(4-chlorostyrene), poly(9-vinylphenanthrene), and poly(2-vinylnaphthalene). In each case, the point of C$_{60}$ aggregation, observable by WAXS, was taken as the miscibility limit for a given polymer system. The miscibility of C$_{60}$ in these polymers was correlated with the factors mentioned above and compared with the miscibility in solvents with analogous structures as the repeat units. [Preview Abstract] |
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C1.00046: Investigation of polymer single crystals templated by surface-modified carbon nanotubes Eric D. Laird, Bing Li, Wenda Wang, Christopher Y. Li Carbon nanotubes (CNT) decorated with periodic polymer lamellae were introduced in 2005 and were termed ``nano-hybrid shish kebabs'' (NHSK). Growth of these polymer single crystals was observed to be sensitive to the chemistry of the CNT sidewall. In order to gain insight into CNT-assisted polymer crystal nucleation and growth, several model systems were investigated. Polyethylene (PE) and Nylon-6,6 were crystallized on CNT as described in previous work, using tubes with a range of surface modifications. Thermal analysis and microscopy study have shown that the crystallization behavior of polymers can be tailored by adjustment of the surface chemistry of CNTs. Model systems that developed into NHSK were deposited into films (e.g. NHSK paper). Contact angle measurements on these films helped to demonstrate that both the surface roughness and chemistry of the NHSK paper can be tuned by controlled NHSK growth. Superhydrophobic films have been successfully achieved. [Preview Abstract] |
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C1.00047: Optical properties of composite functionalized carbon nanotubes and Au nanorods thin films Deokjin Yu, James Wicksted Optoelectronic properties of hybrid layer-by-layer (LbL) structures of Au nanorods and functionalized single-walled carbon nanotubes (SWNT) might be utilized in future solar cells and optoelectronic sensor devices. The SWNTs were functionalized with poly (sodium 4-styrenesulfonate) (PSS) by in situ polymerization. The Au nanorods were prepared with wet-chemical methods. Sequential LbL deposition of poly (diallyldimethyl ammonium chloride) (PDDA) and PSS-SWNTs on glass substrate were carried out to obtain the polyelectrolyte multilayer films. Au nanorods were then polymer coated on the multilayer films. Optical properties of these composite films were studied using Raman scattering and UV-VIS-IR absorption spectroscopy. [Preview Abstract] |
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C1.00048: Effects of gold nanoparticles on the electro-optical properties of a polymer dispersed liquid crystal A. Hinojosa, C. Shive, Suresh Sharma We have studied the electro-optical properties of a polymer-dispersed liquid crystal (PDLC) as functions of relative concentrations of gold nanoparticles. PDLC samples were synthesized between indium-tin-oxide (ITO) coated glass slides, separated by SiO$_{2}$ spacers, by using liquid crystal E44, a monofunctional acrylic oligomer (CN135), and a tetrafunctional crosslinker (SR295). A UV photoinitiator (SR1124) was used to facilitate the curing of the monomer exposed to UV radiation from a Hg spectral lamp. A He-Ne laser was used to measure optical transmission through the PDLC as a function of applied \textit{ac} electric field (1 kHz). The PDLC without gold nanoparticles shows the expected behavior; transmission through the PDLC increases from a minimum (opaque) to a maximum (transparent) with increasing electric field. The electro-optical behavior of the PDLC is altered significantly (e. g., relatively low switching field) upon addition of relatively low concentrations of gold nanoparticles into the starting PDLC syrup. We present electro-optical data as functions of gold nanoparticle concentration and discuss possible mechanism to understand our results. [Preview Abstract] |
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C1.00049: Structural Properties of Hybrid Nanoparticle/Polymer Composites for Solar Energy Devices Elaine Chan, Bryan McCulloch, Rachel Segalman, Alexander Hexemer Hybrid nanoparticle/polymer composites are promising materials for solar energy applications, because the structural properties of these materials can be manipulated at the relevant nanometer length scales to improve device performance. X-ray scattering measurements coupled with modeling and computer simulation present a powerful framework for characterizing the self-assembled morphologies of these nanostructured materials at the appropriate length scales. We examine herein nanoscale structure and ordering in candidate hybrid nanoparticle/polymer photovoltaics using modeling and simulation. Simulations based closely on X-ray scattering data of these nanocomposite films are performed to probe the underlying structure in these materials. The resulting structural models and aspects of the simulations will be discussed. [Preview Abstract] |
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C1.00050: Carbon Black Haloing of Clay and Its Influence on Electrical and Mechanical Properties of Epoxy Composites Krishna Etika, Michael Cox, Jaime Grunlan Studies of acetone-based suspensions suggest a synergistic stabilization of clay by carbon black (CB) that involves a haloing effect (i.e., CB surrounding clay). This unique microstructure influences the electrical and mechanical properties of epoxy composites that contain both particles. With the addition of 0.5 wt{\%} clay, electrical conductivity increases by an order of magnitude for CB-filled epoxy (relative to composites containing no clay), but no significant improvement is observed in storage modulus. Composites containing equal concentrations of CB and clay show reduced electrical conductivity, but significant improvement in storage modulus (relative to composites containing equal amount (wt{\%}) of either CB or clay alone). Both electrical conductivity and storage modulus improve in composites containing a 1:2 clay:CB (wt/wt) ratio. This synergy between CB and clay is a useful tool for simultaneously improving the electrical and mechanical properties of solution processed composites. Similar synergy has also been observed with carbon nanotubes and clay, which has resulted in a dramatic reduction in percolation threshold. [Preview Abstract] |
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C1.00051: Tailored Nanoparticles for Enhancing Polymer Adhesion Gregory Su, Katherine Best, Thangamani Ranganathan, Todd Emrick, Alfred Crosby Nanoparticles have been widely reported to affect the physical properties of bulk polymer materials. ~Here, we report the ability of tailored inorganic nanoparticles to enhance interfacial properties, specifically the self-adhesion of a polymer melt. ~Gold nanoparticles tailored with low-molecular weight (MW$\sim $1500 g/mol) polystyrene ligands are introduced to the surface of a polystyrene film (MW$\sim $278 kg/mol) with low polydispersity. ~A second polystyrene film is brought into contact with the nanoparticle-decorated surface and subsequently annealed. ~ The resulting interfaces were characterized with the double cantilever beam (DCB) method to determine the strain energy release rate, G$_{c}$, of the welded interface as a function of nanoparticle surface coverage. ~The interfacial strength (G$_{c})$ increases with nanoparticle area fraction until a maximum G$_{c}$ is achieved at an optimal value of 0.07{\%}. ~The value of G$_{c}$ approximately increased by 100{\%} relative to a sample without nanoparticles. ~This enhancement of interfacial adhesion reveals the potential for~utilizing nanoparticles to improve mechanical properties of polymer interfaces in general. [Preview Abstract] |
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C1.00052: The Assembly of Nanorods in Comb Polymer Supramolecules Alexander Mastroianni, Kari Thorkelsson, Joseph Luther, Paul Alivisatos, Ting Xu Inorganic nanoparticles exhibit a wide range of size-dependent properties and present great promise in technological applications. Fully harnessing this potential requires developing bottom-up strategies to assemble nanoparticles over multiple length scales simultaneously. Nanoparticles have been co-assembled with block copolymers (BCPs). Often this approach requires delicate balance between particle-polymer interactions and entropic penalty associated with polymer chain deformation upon particle incorporation. Recently, we showed that a coil-comb supramolecule formed by non- covalent attachment of small molecule amphiphiles to one block of a BCP can be used to direct nanoparticle assemblies with high precision. The alkyl tail of the small molecules chosen interacts favorably with the native alkyl ligands of a wide variety of inorganic nanoparticles and eliminates the need for particle surface modification. Upon attaching small molecule to one BCP block, the polymer chain stiffens, providing entropic driving force to further direct nanoparticle organization within BCP microdomains. Here, the co-assembly of these supramolecules with nanorods was systematically investigated as a function of small molecule loading, supramolecular morphology, nanorod diameter, and aspect ratio. The presented fundamental studies pave a path toward nanorod-based device fabrication. [Preview Abstract] |
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C1.00053: Shape-induced phase transformation in nanoparticle assemblies Yugang Zhang, Fang Lu, Daniel van der Lelie, Oleg Gang The role of interparticle interactions in a behavior of condensed phases of spherical objects is remaining in a focal point of diverse studies of micro- and nanoscale colloid systems. At the same time, recent advances in a fabrication of well-defined nanoscale materials allow for an exploration of geometrical effects in systems containing objects with non-spherical shapes. Herein, we report a phase evolution of 3D assemblies of ligand coated cube-like palladium nanoparticles. We observed a continuous phase transformation of particles assemblies from a simple cubic phase to a face-centered cubic rich phase with an increase of capping ligand thickness. The details of structural evolution were revealed using small angle x-ray scattering and electron microscopy methods. The observed phase transformation is attributed to an evolution of particle's shape from cube to quasi-sphere geometry, which was effectively regulated by amount of a ligand adsorbed on a particle surface. [Preview Abstract] |
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C1.00054: Multi-stimuli responsive block copolymers and gels in ionic liquids Takeshi Ueki, Masayoshi Watanabe Ionic liquids (ILs) are room temperature molten salts and have attracted much attention because of their unique properties. The characteristics of ILs (non-volatility, non-flammability, chemical stability, high ionic conductivity) can contribute to high performance energy-conversion materials. On the other hand, some polymers greatly change their solubility in ILs in response to external stimuli such as temperature and light. We have found that poly($N$-isopropylacrylamide) (PNIPAm) and poly(benzyl methacrylate) (PBnMA) show upper critical solution temperature (UCST)-type phase behavior and lower critical solution temperature (LCST)-type phase behavior in an ILs, respectively. Most recently, we also discovered that certain polymers change their solubility induced by photo stimuli. In this study, we describe hierarchical self-assembly of multi block copolymer in IL. The ABC-triblock copolymer consists of PBnMA as A with a high LCST (105 $^{\circ}$C) segment, IL-compatible PMMA as B, and PPheEtMA as C with a low LCST (42 $^{\circ}$C) segment; the copolymer exhibits doubly thermo-sensitive self-assembly in IL to form an ion-gel. PBnMA and PPheEtMA (A and C) blocks are expected to aggregate at different $T_{c}$s. [Preview Abstract] |
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C1.00055: Kinetics and physical properties of photolatent base catalyzed thiol-epoxy resins Christopher Comer, Olivia McNair, Charles Hoyle, Daniel Savin Typical epoxy resin systems based on multifunctional epoxides and multifunctional amines yield polymeric materials with unrivaled chemical resistance, toughness, and adhesion. Unfortunately amine cured epoxy resins must be mixed immediately prior to application because reactivity of the amine and epoxy is too high. Thiol-epoxy resins offer a less reactive alternative to these traditional epoxy resins and are catalyzed by the addition of a tertiary amine, such as DBN. In this study a combination of a diepoxide with multifunctional thiols based on mercaptoacetate (MA) and mercaptopropionate (MP) were polymerized using a photolatent base catalyst or DBN. The reactivity of the MA and MP based thiols were characterized using Real-time FT-IR. Mechanical and thermal properties of the resins were characterized using DMA, DSC, MTS, pencil hardness, and impact resistance. Thiol-cured epoxy systems have uniform network structures, as indicated by sharp tan $\delta$ peaks and distinct glass transition region shown by DMA and DSC respectively. [Preview Abstract] |
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C1.00056: Surface-Initiated ARGET ATRP and Characterization of Thermoplastic Elastomer Montomorillonite Composites Jeffrey Easley, Amanda Beck, Christopher Ellison Polymer nanocomposites, with enhanced properties as compared to their bulk polymer counterparts, are becoming more prominent in advanced material applications. Here we report the synthesis of poly(n-butyl acrylate-b-styrene) (PBA-b-PS) from the surface of functionalized montmorillonite clay via activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP). The ARGET mechanism allows for a substantial reduction in the amount of transition metal catalyst required. It also exhibits potential for eventual scale-up and the industrial adoption of ATRP as a versatile method for producing polymers with well-defined compositions and functionalities. The composite materials resemble traditional thermoplastic elastomer triblock copolymers, with the clay platelets dividing the central, rubbery PBA block. We used SAXS, NMR, and TEM to characterize the composition and structure of the composites. The resulting material properties were measured by tensile testing, dynamic mechanical analysis, and TGA. We anticipate the composites to have exceptional barrier properties due to the high degree of clay dispersion, which may lead to applications as recyclable packaging materials. [Preview Abstract] |
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C1.00057: Impact of Non-Covalent Interactions on the Miscibility of Fullerenes in Polymers Say Lee Teh, Dias Linton, Mark Dadmun Our recent studies have demonstrated that the incorporation of electron donor-acceptor (EDA) interactions in single-walled carbon nanotubes (SWNT) polymer nanocomposites dramatically improves the dispersion of the SWNT in the polymer matrix. These results indicate that the polymer connectivity and curvature of the nanoparticle play a crucial role in the realization of this improvement. As such, the importance of nanoparticle shape and curvature on the formation of the non- covalent interaction becomes an interesting question. To examine this problem, we have used UV- Vis spectroscopy and x- ray diffraction to quantify the miscibility limit of C60 fullerene with the incorporation of electron donor-acceptor interactions between the polymer and fullerene. The results indicate a distinct difference in the ability of EDA interactions to improve the dispersion of fullerenes relative to their impact on SWNT. [Preview Abstract] |
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C1.00058: Dynamic Mechanical Analysis of Hydroxyapatite Nanoparticle /Gelatin Porous Scaffolds H. Ghossein, I. Dranca, S. Vyazovkin, A. V. Stanishevsky Porous nanoceramic/polymer scaffolds were fabricated by a freeze-drying process from synthetic nanosized hydroxyapatite / gelatin (nanoHA/Gel) mixtures with nanoHA loading varied from 0 to 50 {\%} by weight. The scaffolds had interconnected porosity up to 90{\%}, pore diameter in the range of 20 -- 300 micron, and pore wall thickness in the range of 3 -- 10 micron. Depending on the nanoHA/Gel mixture preparation routine, the HA nanoparticles either distribute uniformly within the matrix, or form aggregates on the surface of the pore walls. Dynamic mechanical analysis (DMA) of nanoHA/Gel scaffolds revealed the bending and tensile moduli up to 500 MPa and 800 MPa, respectively, when nanoHA loading was around 30{\%} by weight. These moduli increase by a factor of 1.6 after the cross-linking of polymer. NanoHA loading above 50 {\%} by weight results in both moduli above 2 GPa, but the cross-linking reduces them significantly. It has been further shown that the uniform dispersion of nanoHA within the polymer matrix improves the mechanical properties of the scaffolds. [Preview Abstract] |
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C1.00059: Thiol-ene/methacrylate systems for mechanical damping Olivia McNair, Askim Senyurt, Huanyu Wei, Trent Gould, Scott Piland, Charles Hoyle, Daniel Savin Ternary thiol-ene-methacrylate (TEMA) networks as materials for mechanical energy damping are unique to the sports world. Using a photoinitiation process, TEMA systems are formed via an initial thiol-ene step-growth mechanism along with traditional radical polymerization of acrylate and ene monomers. Final networks have two-part morphologies: acrylate homopolymer sectors imbedded in a multi-component mesh. Several (TEMA) systems have been synthesized and analyzed via thermal and mechanical probing. Initial studies on these ternary systems have shown excellent properties compared to traditional ethylene vinyl alcohol (EVA) copolymers. For example, PEMA networks exhibit glass transition temperatures 33 K higher than EVA, resulting in improved damping at room temperature. This research will help develop relationships between tan delta, glass transition and their effects on mechanical energy damping for ternary (TEMA) systems. [Preview Abstract] |
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C1.00060: Finite size effects in nanocomposite thin films, fibers, and mats L.I. Clarke, D.R. Stevens, E.W. Skau, L.N. Downen, T.J. Hoffman Composites consist of particles embedded within a supporting matrix. The matrix properties are enhanced by formation of a network of particles which spans the material and imparts some quality of the particle to the composite, even at relatively low doping levels. Such percolation processes have been extensively studied, with a particular focus on the role of particle size and shape on network formation. However, with modern fabrication techniques, composites can now be formed where the sample size is similar to that of the particle. In this case, finite size effects may become experimentally important. We present experimental and 3-D continuum Monte Carlo simulation studies of finite size effects in nanofibers (individually or in random mats) and thin films. We find that when any dimension of the sample is less than 10-20 times the largest dimension of the particle, finite-size effects may occur. This result is particularly important when the particle has a large aspect ratio (e.g., carbon nanotubes) and thus a long length, comparable with sample size. [Preview Abstract] |
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C1.00061: 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 nanoparticle fillers 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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C1.00062: Guided Assemblies of Ferritin Nanocages: Highly Ordered Arrays of Monodisperse Nanoscopic Elements Yunxia Hu, Dian Chen, Soojin Park, Todd Emrick, Thomas Russell Protein nanocages, like horse spleen ferritin (HSF, 12 nm in diameter) with magnetic cores (8 nm in diameter), have the distinct advantage over synthetic nanoparticles of being truly monodisperse in size and shape. Provided planar, ordered arrays of nanocages can be achieved, these attributes can be used to generate two-dimensional arrays of nanoscopic elements, in which~each element is exactly the same size and shape, and the areal density and lateral packing can be manipulated by the charge on the nanocage surface. This strategy is shown to be viable, providing a unique pathway to overcome some of the current technological limitations in generating addressable media. [Preview Abstract] |
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C1.00063: Flame Retardant Polyelectrolyte-Nanoclay Layer-by-Layer Assemblies on Cotton Galina Sukhonosova, Yu-Chin Li, Jaime Grunlan Thin composite films of branched polyethylenimine (BPEI) and Laponite clay platelets were prepared using layer-by-layer assembly. Film thickness was tailored by altering the pH of the aqueous mixtures used to deposit theses films, resulting in growth that ranged from 0.5 to 5 nm per bilayer. In all films, the clay platelets are uniformly deposited and look analogous to a cobblestone path in atomic force microscopy (AFM) surface images. These thin coatings were deposited onto cotton fabric and the fabric has significantly more char left after burning than the uncoated fabric. Thermogravimetric analysis (TGA) results reveal that fabric coated with 10-bilayers of BPEI-Laponite produces up to 6 wt{\%} char at 500\r{ }C, which is almost an order of magnitude greater than untreated fabric. This study demonstrates that polymer-clay assemblies could improve the thermal stability of cotton and may be useful for fire safety applications. [Preview Abstract] |
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C1.00064: Highly Transparent and Conductive Carbon Nanotube Thin Film Assemblies Daniel Gamboa, Yong Tae Park, Aaron Ham, Jaime Grunlan Layer-by-layer (LbL) assembly was used to generate transparent, highly conductive thin films containing carbon nanotubes. Purified single-walled carbon nanotubes (SWNT), stabilized with negatively-charged deoxycholate, were alternately deposited with poly(diallyldimethylammonium chloride) [PDDA] from water onto a PET substrate. These assemblies exhibit visible light transmission $>$ 70{\%} (measured at 700 nm) and electrical conductivity of $\sim $ 100 S/cm ($\sim $ 50 nm thick with a sheet resistance of $\sim $ 2 k$\Omega $/sq) after 20-bilayers of deposition. After heating for just two minutes at 350$^{o}$C (on a glass substrate), transparency is increased and conductivity approaches 400 S/cm. With just two bilayers of SWNT/PDDA, these films have an electrical conductivity of 30 S/cm (12 nm thick with a sheet resistance of 70 k$\Omega $/sq) and transmission greater than 95{\%} at 700nm. This study demonstrates the ability of the LbL technique to produce highly transparent and conductive nanotube-based thin films. These types of films are potentially useful for anti-static films with few bilayers or transparent electrodes with tens of bilayers. Flexible displays, smart windows and solar cells could all benefit from this technology platform. [Preview Abstract] |
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C1.00065: Influence of Clay Platelet Spacing on Oxygen Permeability of Thin Film Assemblies Morgan Priolo, Daniel Gamboa, Jaime Grunlan Thin films of anionic natural montmorrilonite clay and various polyelectrolytes have been produced by alternately dipping a plastic substrate into dilute aqueous mixtures containing each ingredient in an effort to show the influence of clay platelet spacing on thin film permeability. After polymer-clay layers have been sequentially deposited, the resulting transparent films exhibit a brick wall nanostructure comprised of completely exfoliated clay bricks in polymeric mortar. This brick wall forms an extremely tortuous path for a molecule to traverse, creating channels perpendicular to the concentration gradient that increase the molecule's diffusion length and delay its transmission. To a first approximation, greater clay spacing (i.e., reduced clay concentration) produces greater oxygen barrier. Oxygen transmission rates below 0.005 cm$^{3}$/m$^{2}\cdot $day have been achieved for films with only eight clay layers (total thickness of only 200 nm). With optical transparencies greater than 86{\%} and the ability to be microwaved, these thin film composites are good candidates for flexible electronics packaging and foil replacement for food. [Preview Abstract] |
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C1.00066: Electrical Treeing Induced Vascular Networks for Fluid Transport Kristopher Behler, Eric Wetzel Electrical treeing (ET) is a stepwise dielectric breakdown process in which partial discharges in a dielectric material generate a branched hollow network of tubules between the electrode and the ground. Overtime, exposure of dielectric materials to global electric fields which are lower than the dielectric strength results in electrical trees (ETs). This dielectric breakdown is exploited to induce a controlled growth of ETs in epoxies to demonstrate a fabrication technique of synthetic vascular systems in engineering materials. Both AC, $\pm $20 kV at 100 Hz sine wave, and DC, up to -60 kV, voltages were used to grow ET in planar and volumetric systems. AC treeing induces a more bush-like highly branched structure, whereas DC treeing results in a more tree-like structure possessing mostly low ordered branches. In addition to voltage, the geometric arrangement of the electrode and ground, and the use of electrode surface treatments with multi-walled carbon nanotubes (MWCNTs) were investigated. Applications for vascular networks were demonstrated by filling the ETs with dyed liquids. [Preview Abstract] |
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C1.00067: Magnetic Field Alignment of Block-Copolymer / Nanoparticle Composites Matthew R. Hammond, Herve Dietsch, Olivier Pravaz, Peter Schurtenberger In composites of spindle-type magnetic nanoparticles dispersed in a cylinder-forming block copolymer (BCP), the nanorods can effectively template the orientation of nearby BCP cylinders. Specifically, the preferred cylinder alignment is predominantly parallel to the long axis of a neighboring particle. By application of a uniaxial magnetic field during composite casting from solution, the particles can be partially aligned, imparting an overall alignment to the final composite. At present, the alignment that has been achieved is only very modest, yet the method appears to be general, and future improvements should be forthcoming. [Preview Abstract] |
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C1.00068: Small-molecule-directed nanoparticle assembly towards stimuli-responsive nanocomposites Kari Thorkelsson, Yue Zhao, Alexander Mastroianni, Thomas Schilling, Joseph Luther, Benjamin Rancatore, Kazuyuki Matsunaga, Hiroshi Jinnai, Yue Wu, Daniel Poulsen, Jean Fr\'echet, Paul Alivisatos, Ting Xu The precise control of spatial organization in nanoparticle assemblies would enable one to take advantage of the various optical, electrical, and magnetic properties found in inorganic nanoparticles, but such control is difficult, and remains an impediment in the ``bottom-up'' production of functional materials. Most current methods are either highly dependent on the materials used, or not precise enough to use in the fabrication of functional materials. We show how this challenge has been overcome using a diblock copolymer-based supramolecule. 3-pentadecylphenol was hydrogen bonded to the poly(4-vinylpyridine) block of a polystyrene-block-poly(4-vinylpyridine) diblock copolymer. The alkyl moiety of the small molecules interacts favorably with the alkyl ligands used on a number of nanoparticles, and also forces the poly(4-vinylpyridine) block into a comb conformation. This restricts the location of the nanoparticles and forces them into a well-organized array. This strategy has been successful in assembling nanoparticles without special considerations for the actual core material or shape. A variety of small molecules could also be used. [Preview Abstract] |
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C1.00069: Phase Behavior and Magnetic Alignment of Hydrogen Bonded Side Chain Liquid Crystalline Block Copolymers Manesh Gopinadhan, Pawel Majewski , Evan Beach, Paul Anastas, Chinedum Osuji Hydrogen bonding between a poly(styrene-b-acrylic acid) backbone and an imidazole terminated biphenyl mesogen results in the formation of a side-group liquid crystalline block copolymer (LC BCP).We use a combination of FTIR, X-ray scattering and DSC to characterize the phase behavior of the PAA-LC system, which is largely dominated by the sub-stoichiometric saturation of the binding capacity of the chain. In the melt, the self assembled materials exhibited composition and temperature dependent smectic LC phases along with characteristic birefringence and multiple thermal transitions associated with LC polymers. The diblock copolymers (LC BCP) microphase separated into lamellar microdomains with homeotropic anchoring at the IMDS. Alignment of a hierarchically ordered lamellar BCP was performed using a 5 T magnetic field at elevated temperature in the melt state and characterized by SAXS. The system exhibits a tilted smectic structure, which on alignment by the field displays scattering patterns akin to those observed in bookshelf or chevron-type structures. These results demonstrate that simple non-covalent interactions can be used to generate LC order and thus provide a convenient handle for subsequent alignment of BCP structures by magnetic fields. [Preview Abstract] |
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C1.00070: Holey polymer films templated by growth and self-assembly of water drops over evaporating polymer solutions Vivek Sharma, Mohan Srinivasarao Water drops that nucleate and grow over evaporating polymer solutions exhibit non-coalescence and pack like hard spheres. In this study, we elucidate how the growth and self-organization of a population of close packed drops occur in response to the heat and mass fluxes involved in water condensation and evaporation of organic solvent. We examine the role of solvent and polymer in controlling the kinetics of growth and assembly of droplets, which eventually evaporate away, producing a polymer film with ordered array of pores. We describe a rich array of experimental observations and theoretical considerations about water droplet growth, noncoalescence and assembly that have not been reported in the published literature so far. Most importantly, we provide insights into how the porous, microstructure is generated and how the size of pore can be controlled. [Preview Abstract] |
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C1.00071: Collapse of an HIV-1 protease (1DIFA-dimer) in an effective solvent medium by a Monte Carlo simulation Ras Pandey, Barry Farmer HIV-1 protease (1DIFA) consists of two polypeptide chains, each monomer with 99 residues where two aspartic acid residues (Asp$^{25})$ form the active catalytic site. The conformation and dynamics of the protein chain (with 198 residues) are investigated on a cubic lattice where empty sites represent effective solvent. Specificities of residues are captured via an interaction matrix (residue-residue, residue-solvent) of the Lennard-Jones potential. We examine global properties such as the variation of the root mean square displacement and radius of gyration with the time steps for a range of solvent interaction strength. Local quantities include energy and mobility profiles of residues to understand the active segments (useful in proteolysis). The hydrophobic residues possess higher energy and lower mobility while the electrostatic and polar residues are more mobile despite their lower interaction energy. We find that the radius of gyration of the protein collapses (globular structure) in a narrow range of solvent interaction strength. [Preview Abstract] |
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C1.00072: Anti-Brownian ELectrokinetic (ABEL) Trapping of Single High Density Lipoprotein (HDL) Particles Samuel Bockenhauer, Alexandre Furstenberg, Quan Wang, Brian DeVree, Xiao Jie Yao, Michael Bokoch, Brian Kobilka, Roger Sunahara, W. E. Moerner The ABEL trap is a novel device for trapping single biomolecules in solution for extended observation. The trap estimates the position of a fluorescently-labeled object as small as $\sim $10 nm in solution and then applies a feedback electrokinetic drift every 20 us to trap the object by canceling its Brownian motion. We use the ABEL trap to study HDL particles at the single-copy level. HDL particles, essential in regulation of ``good'' cholesterol in humans, comprise a small ($\sim $10 nm) lipid bilayer disc bounded by a belt of apolipoproteins. By engineering HDL particles with single fluorescent donor/acceptor probes and varying lipid compositions, we are working to study lipid diffusion on small length scales. We also use HDL particles as hosts for single transmembrane receptors, which should enable study of receptor conformational dynamics on long timescales. [Preview Abstract] |
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C1.00073: Non-affine deformation in semi-flexible polymer gels Anindita Basu, Wen Qi, Xiaoming Mao, Tom Lubensky, Paul Janmey, Arjun Yodh Compared to flexible polymer gels, semi-flexible filamentous biopolymer networks generally have larger elastic moduli, marked strain-stiffening behavior, and a pronounced negative normal stress when deformed under shear. Theoretical models based on either entropic stretching or enthalpic bending of polymer segments can capture these unusual behaviors to some extent but differ in their predictions about whether the deformation of these materials is affine. We test the validity of this affine assumption by embedding fluorescent tracer beads of different sizes within different bio-polymer gels and quantifying their displacements under shear deformation using confocal microscopy. Gels studied include fibrin and collagen gels. Fiber concentration and pH of the gels are systematically varied to understand the effect of network mesh-size, filament thickness and persistence length on non-affinity. The gels are studied under a wide range of applied strain, well into the strain-stiffening regimes. [Preview Abstract] |
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C1.00074: Low-Frequency Changes in Rigor Crossbridge State -- A Reflection of Correlated Motion? Caroline Ritz-Gold The structure of muscle fibers in the state of rigor takes the form of a hierarchic, interconnected filament network. In this network, individual rigor crossbridges are strongly bound to actin and exist in two different conformational states. We have used EPR spectroscopy of spin-labeled fiber bundles to monitor changes in these conformational states as a function of time. These changes appeared in the time-series data as spontaneous, irregular fluctuations taking place on many time scales -- with a period ranging from minutes to hours. When fibers were treated with the substrate analog MgPPi, the time series exhibited a slowly-decaying large-amplitude response transient. The power spectra of both types of time-series data took a 1/f-like form with a mean slope of --1.3. This kind of 1/f-like behavior has been taken to reflect complexity and long-range correlations in many types of real-world system. We conclude that the low-frequency changes we have observed in crossbridge state may reflect the presence of long-range correlated motion taking place within the rigor-state filament network. [Preview Abstract] |
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C1.00075: Rheological Properties of N-(isopropylacrylamide)-Clay based Nanocomposite gels Divya Bhatnagar, Jack Lombardi, Miriam Rafailovich Polymer -Clay nanocomposite gels (NC gels) consisting of N-(Isopropylacrylamide) (NIPA) and exfoliated inorganic clay (hectorite) were investigated in terms of their rheological properties. Depending on the clay concentration (Cclay), NC gels exhibit unique changes in their mechanical strength. To investigate their mechanical properties NC1-NC25 gels were subjected to oscillatory shear rheometry and Oscialltory stress, frequency and temperature sweep was conducted to evaluate the respective G's with varying shear stress, frequency and temperature. The results from stress sweep indicated the clear dependence of G' on Cclay. G' increased with an increase in clay content making NC25 the stiffest and NC1 the softest. Frequency sweep also suggested the formation of a stable polymer-clay platelet system. Results from temperature sweep suggested the stability of the polymer-clay network over a range of temperatures where a slight drop was seen in G' for gels NC1-NC8. From NC10-NC25, temperature had no effect on their respective G's. Glucose was added into the NC3 and NC5 polymer-clay system and Oscillatory stress and frequency sweep were conducted. The glycated NC3 gel collapsed when the glucose concentration was increased to 0.5-1\%(w/v) although glycated NC5 did not register much noticeable results. [Preview Abstract] |
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C1.00076: Hybrid Gels from Self-Assembling Peptide Networks Sameer Sathaye, Nikhil Sharma, Radhika Nagarkar, Joel Schneider, Darrin Pochan Hybrid Gels constitute a novel class of polymeric materials developed with an aim of combining and/or enhancing the diverse and complementary properties of their individual constituent networks. Self-assembling peptide hydrogels formed from aqueous solutions of beta-hairpin forming peptides have been extensively reported. These hydrogels are interesting candidates as part components of hybrid gels due to their ability to retain their inherent physical properties in the presence of other hydrogel networks and other added functionality (e.g. an inorganic coating of the gel fibrillar nanostructure). Synergistic interactions of these peptidic networks with other added polymer co-networks with a range of tunable synthetic characteristics and properties have been explored by various characterization techniques such as Dynamic Mechanical Analysis (DMA), Transmission Electron Microscopy (TEM) and Small Angle Neutron Scattering (SANS).~ The ease of producing co-networks between a wide array of target polymer networks and beta-hairpin peptides as the fundamental, core network will be discussed [Preview Abstract] |
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C1.00077: New Insights on the Structure of a Periciliary Layer of Lungs Liheng Cai, Brian Button, Richard Boucher, Michael Rubinstein The human airway surface layer (ASL) consists of two parts: an upper mucus layer in contact with air and a lower periciliary layer (PCL) protecting epithelial cells from mucus and pathogens it contains. We study the polymer size and concentration dependence of penetration depth of fractionated labeled dextran from solutions into PCL. We find that dextran with molecule size smaller than 20 nm can penetrate into PCL from dilute solutions. The penetration depth of dextran into PCL increases with decreasing molecular size below 20 nm. Semidilute solutions of high molecular weight dextran with molecule size larger than 50 nm can penetrate into PCL as long as the solution correlation length is smaller than 20 nm. The penetration depth dependence on correlation length for semidilute solutions is similar to penetration depth dependence on dextran size for the case of dilute solutions. The coincidence of the two penetration depth dependence suggests the existence of a brush-like protective barrier inside PCL with mesh size decreasing from top to bottom of this layer. [Preview Abstract] |
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C1.00078: Phosphate mediated self-organizing scaffolds in bio-organic antimicrobial peptide (KSL) -- a coarse-grained MC simulation Barry Farmer, Glenn Johnson, Donald Eby, Ras Pandey A coarse-grained model was used to predict the self-organization of a cationic oligopeptide, KSL (sequence, KKVVFKVKFK) in phosphate buffer. Monte Carlo simulations consisted of a range of peptides concentrations ($C_{KSL}$\textit{= 0.01- 0.07}) and a fixed phosphate concentration ($C_{w} =0.1)$. Specificity of the interaction between each residue and the phosphate solvent are considered via an interaction matrix for the well-depth of the LJ potential. The stochastic motion of the oligopeptides is described using Metropolis algorithm and the end-state equilibrium is the self-assembly of peptides into the scaffold aggregates via non-covalent bonding. We examine the energy and mobility profiles of each peptide residue, their characteristic surrounding within the range of interaction, radial distribution function, radius of gyration and global dynamics of the peptides. We find that the density of the aggregate decays exponentially from its central core if strong phosphate interaction is considered. The radius of gyration for the peptide scaffold structure decreases systematically on increasing the phosphate interaction. [Preview Abstract] |
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C1.00079: Binding of peptides (CR3-1, S2) to clay substrate and their intercalation in clay galleries by a coarse-grained Monte Carlo simulation Lawrence Drummy, Sharon Jones, Barry Farmer, Richard Vaia, Rajesh Naik, Hendrik Heinz, Ras Pandey Monte Carlo simulations are performed to study binding of peptides (CR3-1: \textit{Trp-Pro-Ser-Ser-Tyr-Leu-Ser-Pro-Lle-Pro-Tyr-Ser} and S2: \textit{His-Gly-Lle-Asn-Thr-Thr-Lys-Pro-Phe-Lys-ser-Val}) to a clay substrate and a stack of mobile platelets on a cubic lattice. A bond-fluctuation description is used to model both clay platelet and the peptide chains. Specificity of each residue is incorporated via an interaction matrix for the residue--residue and residue-clay interactions guided by an all-atom MD simulations and their hydrophobicity. We examine the mobility of each residue, the energy, and their density profiles, and correlation profiling the proximity to the substrate or a stack of mobile platelets. The exfoliation and dispersion of the platelets are analyzed as a function of peptide concentration. The interstitial spacing between the platelets, i.e., the average height of the gallery is found to increase due to binding of S2 and its intercalation, consistent with the laboratory observations. [Preview Abstract] |
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C1.00080: Polymer-Peptide Nanoparticles: Synthesis and Characterization He Dong, Jessica Y. Shu, Ting Xu Conjugation of synthetic polymers to peptides offers an efficient way to produce novel supramolecular structures. Herein, we report an attempt to prepare synthetic micellar nanoparticles using amphiphilic peptide-polymer conjugates as molecular building blocks. Spherical nanoparticles were formed upon dissolution of peptides in PBS buffer through the segregation of hydrophobic and hydrophilic segments. Both molecular and nano- structures were thoroughly investigated by a variety of biophysical techniques, including circular dichroism (CD), dynamic light scattering (DLS), size exclusion chromatography (SEC), transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The results demonstrate that structural properties of these biohybrid materials depend on both the geometry of the hydrophobic domain and the size of synthetic polymers. Given the diversity of functional peptide sequences, hydrophilic polymers and hydrophobic moieties, these materials would be expected to self-assemble into various types of nanostructures to cover a wide range of biological applications. [Preview Abstract] |
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C1.00081: Tuning Lattice Spacing in DNA-Mediated Assembly of Nanoparticle Superlattices Dmytro Nykypanchuk, Oleg Gang, Mathew Maye, Alexei Tkachenko DNA encoding of nanoparticles allows for assembly of well-defined superlattices in which the particle relative positions are defined by recognition interactions and DNA length. DNA connectivity in such superlattices provides for structure responsiveness and tunability via application of various stimuli. Here we discuss (i) the effect of changing electrostatic interactions between DNAs and (ii) application of osmotic pressure to tune the structure of the DNA/nanoparticles superlattices. Using these two approaches a lattice parameter can be tuned within tens of nanometers while preserving the long range order and integrity of assembled structures. The observed structure variations, probed by Small Angle X-ray Scattering, are in a reasonable agreement with estimations which account for changes of excluded volume and DNA persistent length under the applied stimuli. [Preview Abstract] |
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C1.00082: FLUIDS AND SOFT MATTER I |
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C1.00083: Evidence of a dynamical length scale in a 2D glassy colloid Lisa Dixon, David Grier We use holographic video microscopy to study the dynamics of glassy bidisperse colloidal monolayers within circular regions defined by holographic optical traps. Establishing a pinned boundary condition affects the free particles' diffusion by an amount that depends on distance from the boundary. Both the effective diffusion coefficient and the diffusivity exponent are suppressed by pinning at the boundary, and the degree of suppression diminishes as the boundary's radius increases. These observations suggest the presence of a length scale over which dynamical information is transmitted through the glassy system. [Preview Abstract] |
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C1.00084: Thickness dependent metal insulator transition in diamond-like-carbon films of different thickness Soma Mukherjee, B.K. Chaudhuri, C.C. Chou, H.D. Yang, H. Sakata, M. Wakaki Transport properties of amorphous diamond-like-carbon (DLC) films of different thickness (90 and 600nm) prepared by plasma-beam ion-injection deposition (PBIID) method have been studied. The 90nm thick film (DLC1) shows metallic behavior above 200K and a metal- insulator transition occurs below this temperature. The metallic resistivity can be fitted with the relation $\rho =\rho _{0}^{\prime }$(sp$^{2})$T$^{\beta }$ (with $\beta \quad \sim $1). The much thicker film DLC2 (600nm thick) is, however, a semiconductor over the temperature range 80-300K showing large increase of resistivity below 150K. The scanning electron and micrographs and Raman spectroscopic studies show the presence of nanometer size diamond-like crystals embedded in the amorphous matrix. Comparatively larger number of such nanodiamonds and larger sp$^{3}$/sp$^{2}$ ratio observed from XPS study can be attributed to the higher resistivity ($\sim $10$^{10}$ ohm cm) of DLC2 than that of DLC1($\sim $10$^{4}$ ohm cm). Low temperature semiconducting behavior of the thinner film is explained by Mott variable range hopping (VRH) model while the resistivity of the thicker film is found to follows Mott small polaron hopping (SPH) model in the high temperature range. Thickness dependence of DLC film conductivity has also been discussed. [Preview Abstract] |
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C1.00085: Sublimation of two dimensional wet granular matter under swirling motion Kai Huang, Ingo Rehberg The dynamical behaviors of two dimensional wet granular matter under swirling motion is studied by experiments. Different from dry granular matter, the cohesion induced by capillary bridges formed between particles tends to keep the wet granular clusters rigid against swirling motion. However, the rigid clusters are not stable: random sublimation and deposition transitions are observed. The transition dynamics and morphological changes of rigid clusters are studied by particle tracking techniques. The mechanism driving the transitions will also be discussed. [Preview Abstract] |
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C1.00086: Stress propagation in isotropic packs with anisotropic boundaries Nathan Krapf, Thomas Witten Stresses in marginally jammed, anisotropic packs built up from a solid floor propagate along oblique rays toward the floor \footnote{ D. A. Head, A. V. Tkachenko, and T. A. Witten. Eur. Phys. J. E 6, 99-105 (2001))}. This clear anisotropic propagation must result from anisotropic packing and/or anisotropic boundary conditions. Here we numerically isolate the effect of anisotropic boundaries by using an explicitly isotropic periodic pack in a marginally jammed, isostatic state. We then remove the periodicity in one direction and anchor the beads along one edge to a substrate. This preserves the isostatic condition while rendering the boundary anisotropic. However, we find hyperstatic modes along one edge of the pack and hypostatic modes at the other. We show that these extra modes decay rapidly away from the boundaries. Remarkably the hypostatic modes cause the pack to be unstable under any force applied to a single bead. This instability can be remedied by applying a suitable cluster of forces to adjacent beads, allowing a clear measurement of the bulk response. We discuss the resulting stress response. [Preview Abstract] |
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C1.00087: Self-organized Criticality or not in Spherical Bead Piles Larry Markley, Mary Mills, D.T. Jacobs This experiment examined a conical bead pile and the distribution of avalanche sizes when using uniform 3mm zirconium spheres ("beads") and then dropping beads from different heights on central vs. random locations on the pile. The bead pile is built by pouring beads onto a circular base where the bottom layer of beads had been glued randomly. Beads are then individually dropped from a fixed height after which the pile is massed. This process is repeated for thousands of bead drops. By measuring the number of avalanches of a given size that occurred, the resulting distribution could be compared to a power law description as predicted by self-organized criticality. We found that the probability, P(s), for avalanches of size s depends very strongly on how the beads are dropped onto the pile. If beads are individually dropped on the pile's apex from a low drop height, then P(s) is a simple power law in s. At higher drop heights still falling on the apex of the pile, an energy dissipation function is the best descriptor. However, for drops that occur pseudo-randomly over the entire surface of the pile, the falling beads undergo ballistic reflections and ejections rather than settling on the pile to produce avalanches. We acknowledge support from NSF-REU DMR 0649112. [Preview Abstract] |
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C1.00088: Percolation transition in spherical granular material Heather Moore, Lorenzo Dumancas, Tyler Rhoades, Mark Zimmerman, D.T. Jacobs Two properties of percolation were studied by measuring the resistance to the flow of electricity through a system of conducting and insulating spheres. The percolation threshold was measured on two system sizes by varying the volume fraction of conducting spheres in the mixture of 1 mm diameter silver coated and uncoated glass spheres and found to be 0.180$\pm $0.006 by volume of conducting spheres. This value is consistent with other experimental observations in a variety of 3D systems. Near the percolation threshold, the conductance exhibited a power-law relation with respect to the difference of the composition from the threshold composition. We acknowledge support from the Howard Hughes Medical Institute through its undergraduate science education program and to the College of Wooster. [Preview Abstract] |
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C1.00089: Self-phase modulation in azo-dye-doped liquid crystals Hui-Chi Lin, Chia-Wei Chu, Ming-Shian Li, Andy Ying-Guey Fuh We investigate the photo-induced reorientation in azo-dye doped liquid crystal (ADDLC) films by observing the diffraction patterns due to self-phase modulation. The experimental results show that the change of refraction index ($\Delta $n) of the ADDLC sample increases with the intensity of green light (I$_{G})$ to a maximum $\Delta $n = 0.09 at I$_{G}$ = 0.7 W/cm$^{2}$ , then decreases to zero at I$_{G}$ = 1.1 W/cm$^{2}$, and increases again with I$_{G}$ to a saturated$\Delta $n = 0.0376 at I$_{G}$ = 1.8 W/cm$^{2}$. The mechanism is mainly due to the competition between the negative and positive torques resulted from trans$\to $cis and cis$\to $trans isomerizations of azo dyes, respectively. The reorientation effect in the ADDLC sample illuminated by the biphotonic lasers (green and red lasers) is also studied by observing the self-phase modulation diffraction pattern. The experimental results indicate that the biphotonic lasers can used to modulate the change of refractive index of the sample. The reason is due to the fact that the red light can enhance the positive torque resulted from cis$\to $trans isomerization, and then change the direction of reorientation of LCs. [Preview Abstract] |
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C1.00090: Effect of Polymer on Response Time in an Electroclinic Elastomer Frank Bentrem, Christopher Spillman, Amit Kapur, Stanislas Tsoi, Jawad Naciri, Banahalli Ratna The molecular switching time of an electroclinic liquid crystal elastomer is examined in response to increasing electric field as a function of temperature and cross-linking density. There is an initial increase in the characteristic molecular switching time that reaches a maximum value at intermediate field strengths. Further increasing the field strength decreases the elastomer switching time in an expected manner. We analyze the electro-optic response observed in the material at the molecular scale and identify three predominant time regimes. These three regimes offer insight into the response of both the tethered liquid crystal mesogens and the effect of polymer backbone. The results provide fundamental insight into the nature of the elastomer response to an electric field, where the resistive restoring force of the polymer backbone in the elastomer is countered by the forces exerted by the realignment of the permanent electric dipole of the electroclinic mesogens. [Preview Abstract] |
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C1.00091: Investigation of Dielectric Properties of Liquid Crystals near Phase Transitions Michael Kordell, Tracy Lawson, Chandra Prayaga, Laszlo Ujj Precise capacitance measurement has been performed near the phase transitions of scientifically important liquid crystals such as 8-CB. The details of the measurements to get high precision data on dielectric constant and its temperature dependence will be presented. The results show significant changes of the dielectric properties of the liquid crystal near the smectic-to-nematic and nematic-to-liquid phase transitions attributed to structural changes of the relevant phases. In order to measure the details of the functional dependence near the phase transition, the temperature was varied with milliKelvin precision. The data was obtained using a self-assembled RC circuit with phase sensitive lock-in amplifier detection. Calibration of the device was made by measuring known standard capacitances. In order to get high accuracy the measurement was completely computer controlled. The Method applied here will contribute to the better understanding of thermodynamic behavior of liquid crystals and can be routinely used to characterize novel materials showing phase transitions. [Preview Abstract] |
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C1.00092: Formation of Large Chiral Domains in the B4 Phase by Nucleation and Chirality-Preserving Growth of Helical Filaments D. Chen, M.A. Glaser, J.E. Maclennan, N.A. Clark, E. Korblova, D.M. Walba The growth of helical filaments in the B4 phase is investigated in mixtures of a bent-core mesogen (NOBOW) and a calamitic mesogen (8CB). Due to freezing point depression, the B4 phase forms directly from isotropic phase in the mixtures. This enables us to show, for the first time, that the left- and right- chiral domains are composed of left- and right- handed helical filaments respectively. The formation of a chiral domain can be described as a nucleation and growth process, starting from a nucleus of arbitrary chirality. Starting from such a nucleus, the local chirality is maintained by chirality-preserving growth of helical filaments. The formation of large chiral domains in the mixture is due to the low density of nucleation sites. A tree branching model of the B4 helical filament growth has been proposed which accounts for the observed local homochirality of the helical filaments and the local phase coherence between the helical filaments. [Preview Abstract] |
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C1.00093: Effects of carbon nanotubes on liquid crystal order parameter and Freedericksz transition in electro-optic cells Georgi Georgiev, Erin Gombos, Michael McIntyre, Michael Mattera, Peter Gati, Yaniel Cabrera, Peggy Cebe We studied the effects of multiwalled carbon nanotubes (MWCTs) at low concentrations (0.01 wt {\%}) on the Freedericksz transition of a 4-Cyano-4'-pentylbipenyl (5CB) liquid crystal using transmission ellipsometry. In addition, we calibrated the altitudinal angle of CNTs as a function of the electric field and directed the azimuthal angle which gave us complete control of the 3D orientation of the CNTs. Our results show that in the presence of CNTs the voltage and width for the Freedericksz transition are reduced by a factor of 1.8 as compared to the control electro-optic cell without CNTs. The shift in transition voltage correlates with increase in order parameter of the electro-optic cell as measured by our polarized UV/Vis absorption spectroscopy results. Research supported by: Assumption College Faculty Development Grant, funding for students' stipends, instrumentation and supplies, the NSF Polymers Program of the DME, grant (DMR-0602473) and NASA grant (NAG8-1167). [Preview Abstract] |
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C1.00094: Effect of carbon nanotubes on the crystallization and ordering behavior of liquid crystals Georgi Georgiev, Erin Gombos, Michael McIntyre, Robert Judith, Peggy Cebe We used carbon nanotubes (CNTs) to affect the crystallization behavior of smectic, cholesteric and nematic liquid crystals and of their blends at different compositions. Using polarized microscopy and microscopic transmission ellipsometry we observed significant change in the crystal structure and orientation. The carbon nanotubes served as nucleation centers for crystal growth. Differential Scanning Calorimetry results showed large shifts in the phase transition temperatures. This is due to the effect of the CNTs on the crystallization kinetics. Research supported by: Assumption College Faculty Development Grant, funding for students' stipends, instrumentation and supplies, the NSF Polymers Program of the DMR, grant (DMR-0602473) and NASA grant (NAG8-1167). [Preview Abstract] |
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C1.00095: Environmentally Responsive Cholesteric Materials Petr Shibaev, Cristina Schlesier, Robert Uhrlass, Igor Yaminsky The majority of thermotropic cholesteric liquid crystals are hydrophobic and therefore not suitable for sensing environmental agents present in aqueous media. At the same time thermotropic liquid crystals (including thermotropic monomers) are easily manageable and can form almost ideal highly birefringent planar structures at appropriate temperatures. Thus, it is highly desirable to find new ways in order to modify the properties of thermotropic liquid crystals and make them more hydrophilic in a way that allows to retain their other properties. Two different ways of increasing hydrophilicity are suggested. The first one is a design of novel hydrophilic thermotropic mixtures containing derivatives of benzoic acids and/or cyclohexanoic acids as well as pyridine derivatives The second one is a modification of thermotropic liquid crystal properties by addition of hydrophilic nanoparticles. Both approaches result in highly hydrophilic materials suitable for environmental sensing. The properties of the materials are discussed. Cholesteric sensors sensitive to changes in pH are designed and studied. Higher pH results in a shift of the selective reflection band towards longer wavelength and pronounced color changes. The surface of the sensor analyzed by AFM also changes, which reveals the mechanism of the response. The semiquantitative model of response is suggested and discussed. [Preview Abstract] |
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C1.00096: Electron Fluid Dynamical Equations for Breakdown Waves Moving into an Ionized Medium Mostafa Hemmati, Vrege Amirkhanian For investigation of breakdown waves propagating into an ionized medium, we use a set of one-dimensional, steady state, three component fluid equations. Our set of equations consists of the equation of conservation of mass, momentum, and energy, coupled with the Poisson's equation. We are considering waves for which the electric filed force on electrons is in the opposite direction of the propagation of the wave. Also, the electron gas partial pressure is considered to be much larger than that of the other species; therefore, it provides the driving force for the propagation of the wave. For breakdown waves propagating into an ionized medium, the fluid equations and also the boundary conditions at the wave front have to be modified to account for the current in front of the wave. For breakdown waves propagating into an ionized medium, we will present the modified set of fluid equations, the proper set of boundary conditions, and also the wave profile for electric field, electron velocity, electron temperature, electron number density and ionization rate within the dynamical transition region of the wave. [Preview Abstract] |
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C1.00097: Surface effects on nanoscale Poiseuille flows under large driving force Chong Liu, Zhigang Li The advances in nanotechnology make the miniaturization of fluidic devices possible. The reduction in the dimension of fluidic devices from micro- to nanoscale requires a deep understanding of the static and dynamic properties of nanoscale flows. In this work, we examine the effects of fluid-wall interaction on the fluid flux of nanoscale Poiseuille flows under large external driving force. The mass flux of liquid Ar and He confined by two parallel planar walls are measured by molecular dynamics simulations. For liquid Ar, a bimodal behavior in the flux is observed as the effective surface effect is varied. However, the bimodal behavior for Ar is not observed for He. At weak fluid-wall interactions, the flux of He is independent of fluid-wall binding energy, while it decreases monotonously with increasing fluid-wall binding energy when the fluid-wall interaction is strong. [Preview Abstract] |
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C1.00098: Critical particle size where the Stokes-Einstein relation breaks down Zhigang Li The validity of the Stokes-Einstein (SE) relation for particle diffusion in the nano and molecular scales has attracted much interest, but the results in the literature are controversial. In this work, it is shown that there exists a critical particle size where the SE relation breaks down by comparing particle transport in the macro- and molecular scales. Using molecular dynamics simulations, we study the critical size and find that the van der Waals force plays an important role in particle diffusion as the particle size approaches molecular scale. Due to the limitations of computing facilities, we could not find exactly where the critical particle size is, but the simulation results qualitatively predict that this critical size is of a few nanometers. [Preview Abstract] |
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C1.00099: \textit{Ab initio} molecular dynamics simulations of the static, dynamic and electronic properties of liquid Bi Jaime Souto, M.M.G. Alemany, L.J. Gallego, L.E. Gonzalez, D.J. Gonzalez We perform a comprehensive study of the static, dynamic and electronic properties of liquid Bi near melting by means of 124-atom \textit{ab initio} molecular dynamics simulations based on PARSEC, a real-space implementation of pseudopotentials constructed within the density-functional theory. The predicted results are in good agreement with available experimental data, thus confirming the adequacy of this technique to achieve a reliable description of a non-simple liquid metal such as liquid Bi, whose static structure has reminiscences of the rhombohedral structure of the crystal. Our results for the intermediate scattering function, density of states and electrical conductivity also show markedly differences to those of simple liquid metals. [Preview Abstract] |
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C1.00100: Fluid and ionized gas dynamics in a nanosecond discharge Manish Jugroot Understanding ionized gases and plasmas in small spaces are highly interesting as the complexity of micro-technology systems increases. A self-consistent model of plasma and neutral gas dynamics is applied to nanosecond short-gap microplasmas. Fluid equations of the fully self-consistent model are described with emphasis on the close coupling among the plasma, the fluid and the electric field. The microplasmas are studied from an initial cloud and the momentum and energy transfer are investigated. Gas heating and depletion initiation are observed, highlighting the close interaction between the fluid and the ionized gas in governing the evolution of the nanosecond microplasmas. [Preview Abstract] |
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C1.00101: Lattice gas methods on curved surfaces Dan Cianci, Zachary Needell, Peter Love We present a hydrodynamic lattice gas model for two-dimensional flows on curved surfaces with dynamical geometry. This model is the extension to two dimensions of a dynamical geometry lattice gas model studied in one-dimension. We expand upon a variation of the two-dimensional flat space model created and studied by Frisch, Hasslacher and Pomeau in 1986. Rules for dynamic geometry are constructed using the Pachner moves, which change the triangulation of our manifold but not the topology. Prior work defined the model and showed that the number of triangles lattice grows with time as, closely matching the mean field prediction. We present preliminary results of a Chapman-Enskog analysis generalized to treat the case of a lattice gas flowing on a curved two-dimensional surface. [Preview Abstract] |
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C1.00102: Numerical Simulation of a Brownian Elastic Filament in Random Stokes Flow Steven Elliott, Karim Figueroa, Yuan-Nan Young The dynamics of elastic filaments in Stokes flow has significant effects on its ability to be transported (Young and Shelley, PRL, 99, 058303, 2007). Motivated by these results, in this work we numerically investigate the dynamics of an elastic filament in a random Stokes flow. By employing the numerical algorithm designed by Tonberg and Shelley (JCP, 196, 8, 2004), our area of focus is primarily concerned with dynamics of the filament in a random cellular flow. We compute the critical value of ? (the ratio of the strength of the flow compared to the rigidity of the filament) where the dynamics of the filament change in terms of its susceptibility to buckling instability. We also calculate the effective diffusivity of the filament in various random Stokes flows. Furthermore, thermal fluctuations are incorporated into the slender-body equations of motion, and their effects on filament transport in Stokes flows are quantified. Finally, preliminary work on the hydrodynamic interaction effects on filament transport will be presented. [Preview Abstract] |
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C1.00103: Influence of molecular-scale roughness on the surface spreading of an aqueous nanodrop Alenka Luzar, C.D. Daub, J. Wang, S. Kudesia, D. Bratko We study the spreading of an aqueous nanodrop on a smooth surface decorated by sub-nanoscale asperities at varied surface coverage and with different distribution patterns. Using molecular dynamics simulations, we consider two substrate materials, a hydrophilic and a hydrophobic one. Interestingly, the introduction of surface asperities gives rise to a sharp increase in the apparent contact angle on {\it both} types of surfaces. The superhydrophobic state with the maximal contact angle of 180 degrees is reached when the asperity coverage on a hydrophobic substrate is below 25\%, suggesting that superhydrophobicity can also be achieved by nanoscale roughness of a macroscopically smooth material. We further examine the effect of surface roughness on droplet mobility on the substrate. The apparent diffusion constant shows a dramatic slowdown of the nanodroplet translation even for asperity coverage in the range of 1\% for hydrophilic surface, while droplets on corrugated hydrophobic surfaces retain the ability to flow around the asperities. In contrast, for smooth surfaces we find that the drop mobility on the hydrophilic surface exceeds that on the hydrophobic one. [Preview Abstract] |
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C1.00104: ARTIFICIALLY STRUCTURED MATERIALS |
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C1.00105: Electronic Properties of Strained Si [111] Nanowires Paul Logan, Xihong Peng First principles density-functional theory was used to calculate the effects of strain on the electronic properties of Si nanowires along the [111] direction for wires up to 2.5 nm in diameter. Our results show that the Si [111] nanowires can have direct or indirect band gaps depending on the amount of strain applied to the wires. The exact strain required for the transition from indirect to direct gap was thoroughly investigated in nanowires with different diameters. The larger the nanowire, the larger expansive strain is required to produce a direct band gap. In addition, our calculations reveal a strong dependence of both the gap and effective masses of electrons and holes on the applied strain. We discussed our results in terms of bonding/antibonding and orientation of the electron orbitals near the conduction and valence band edges. [Preview Abstract] |
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C1.00106: Magnetic behavior of misaligned cut-wire pairs in an extended unit cell V. T. T. Thuy, N. T. Tung, V. D. Lam, J. Y. Rhee, S. J. Lee, J. W. Park, Y. P. Lee Many recent works have demonstrated that the interactions between constituent elements in metamaterials can lead to intriguing phenomena that do not exist in the conventional structures with uncoupled elements. Therefore, this issue has attracted a considerable interest in the perspectives of new physical properties and novel applications. It is well known that cut-wire pair (CWP) has been widely recognized as a magnetic resonator providing the negative permeability for metamaterials. In this study, we found that there exists the strong effect of the interaction between closest elements on the resonance behavior of CWP structure. Based on that understanding, we investigated the influence of interaction on the magnetic response of the CWP structure with an extended unit cell, which consists of four identical CWPs. We systematically arranged their relative positions in the cell, i.e., intentionally misaligned two of the four CWPs. The results show that the misalignments of CWP in the extended cell can lead to multiple magnetic resonances, which are not observed in the conventional structure. Therefore, this study suggests an additional degree of freedom to control the magnetic response of CWP metamaterials. [Preview Abstract] |
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C1.00107: Tunability of electric response in a polarization-independent fishnet metamaterial N.T. Tung, J.W. Park, S.J. Lee, J.Y. Rhee, Y.P. Lee The first realization of the negative refraction in a metamaterial medium by Smith in 2000 [1], has significantly changed our understanding of the EM wavematter interaction. Recently, a three-dimensional optical negative refraction using fishnet structure has been reported by J. Valentine \textit{et al. }[2], which might offer the opportunity to explore a large variety of optical phenomena associated with negative-refractive index, as well as applications in the fields of scaling down of photonics and superlens imaging. In our effort to tune the electric response of the metamaterial independently from the magnetic one, we used a polarization-independent fishnet structure operating at microwave frequency and investigated their optical property changes by varying the thickness of dielectric spacer. It has been found that the overlapping frequency region of double-negative permittivity and permeability can be indeed controlled and, thereby, the negative-refraction range by changing the dielectric spacer thickness. This thickness effect is also shown more prominently in the THz-frequency regime. \\[4pt] [1] D. R. Smith \textit{et. al.}, \textit{Phys. Rev. Lett.} \textbf{84}, 4184 (2000). \\[0pt] [2] J. Valentine \textit{et. al.}, \textit{Nature} \textbf{455}, 376 (2008). [Preview Abstract] |
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C1.00108: Nanoscale Electron-Beam-Induced Deposition from Bulk Liquid Precursors Eugenii U. Donev, J. Todd Hastings We present a novel technique for direct-write patterning of nanostructures: LP-EBID, liquid-precursor electron-beam-induced deposition. We have deposited metal nanostructures from bulk aqueous solutions of platinum (Pt) and gold (Au) precursors. While traditional EBID processes using gas-phase precursors produce highly contaminated metal deposits (e.g., only 25--40 at.\% Pt content), we show that LP-EBID yields high-purity deposits ($\sim$90 at.\% Pt) at rates more than ten times higher than those of gas-phase EBID. We have also investigated how the lateral size of Pt nanoparticles varies with charge dose, and how the already deposited particles are affected by the subsequent deposition of their neighbors (i.e., proximity effects). Furthermore, we demonstrate that LP-EBID can produce dense arrays (60 nm pitch) of Pt nanodots and nanowires (25 nm diameter or width), which compare favorably with the typical resolution of resist-based e-beam lithography. [Preview Abstract] |
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C1.00109: Dynamics of Electron Relaxation in PbSe Quantum Dot Films Jesse Engel, Matt Sheldon, Wanli Ma, Paul Alivisatos Films of colloidally synthesized quantum dots exhibit an energy landscape disordered in both onsite energies and structural periodicity. Hopping models have proven very effective in describing the steady state conduction of these films, however much is still unknown about their dynamics. Electron localization leads to poor screening, permitting long range coulomb interaction, which can lead to ``glassy behavior'' such as long relaxation times and memory effects. Here, we present results on the time evolution of the resistance of thin films PbSe quantum dot transistors. We observe distinctive power law decays on the order of thousands of seconds, which vary with voltage and temperature. Transient peak heights and power law decay exponents are found to increase for higher applied fields, with peak heights reaching an order of magnitude higher than the steady state at electric field values of 100kV/cm. The decay transients for increasing fields are also found to turn into growth transients (exponent $>$ 0) for decreasing fields, leading to pinched hysteresis loops in I-V characteristics for sweep rates greater than 0.01V/s. We correlate nonlinear features in the transient decay of film resistance and its equilibrium values to the dynamics of relaxation in the coulomb glass. [Preview Abstract] |
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C1.00110: Fano resonance in a system of coupled quantum point contacts Lev Murokh, Pavel Ivanushkin, Jonathan Bird We examine theoretically the modification to the conductance of a quantum point contact (QPC) placed between two reservoirs, due to its coupling to a localized state. We derive a coupled set of equations of motion for the electron operators in the QPC, reservoirs, and the localized state and obtain an expression for the current through the QPC. This expression has clear Fano resonant form but, in the contrast to the standard case, both the resonant width \textit{$\Gamma $} and the Fano parameter $q$ are not constants but depend on the electron energies in the QPC and reservoirs. The total conductance is obtained after integrating over these energies. We study the dependencies of the QPC conductance on the temperature, source-drain voltage, the number of QPC subband involved in transport, and the strength of the QPC-localized state coupling. We compare our results with experimental data previously obtained by our group [1,2] in a system of \textit{two} coupled QPCs when one of them is near pinch-off. Our research clearly supports the idea of localized state formation in QPCs. References [1] Y. Yoon \textit{et al}., Phys. Rev. Lett. \textbf{99}, 136805 (2007). [2] Y. Yoon \textit{et al}., Phys. Rev. B \textbf{79}, 121304(R)~(2009). [Preview Abstract] |
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C1.00111: Density of states and scattering matrix in quasi-one-dimensional systems Vassilios Vargiamidis, Vassilios Fessatidis We analyze the relation between the density of states obtained from the energy derivative of the Friedel phase (or the scattering matrix) and that obtained from the Green's function of quasi-one-dimensional systems with a double delta-function scattering potential. In the case of repulsive scatterers, we show that the local Friedel sum rule is valid when a correction term is included. In the case of attractive scatterers, we show that the local Friedel sum rule is valid provided that the integrated local density of states is specially treated to include the full contribution of the quasibound state. We also show that in a Fano resonance the peak position of the density of states is generally different from the peak position of the transmission probability. However, when the resonance line shape is close to a Breit-Wigner type, those peak positions coincide. [Preview Abstract] |
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C1.00112: Double quantum dots in carbon nanotubes Javier von Stecher, Bernhard Wunsch, Mikahil Lukin , Eugene Demler, Ana Maria Rey We study the behavior of few-electrons confined in a double-well quantum dot in semiconducting carbon nanotubes. These carbon nanostructures exhibit richer physics than GaAs ones due to the additional valley degree of freedom. We calculate and characterize the low energy eigenstates in the presence of a magnetic field and double-well detuning. Spin-orbit coupling lifts the spin and valley degeneracy and, in the presence of exchange interactions, leads, at small detunings and weak magnetic fields, to a spin-valley antisymmetric two-electron ground state which is not a pure spin-singlet state. At large detuning, the strong Coulomb interactions accessible in carbon nanotubes can substantially modify the non-interacting eigenstates via higher orbital-level mixing. The latter manifest in current transport experiments by the disappearance of the Pauli blockade. [Preview Abstract] |
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C1.00113: Worm Algorithm Study of the 1D Electron Gas Abhijit C. Mehta, Shailesh Chandrasekharan, Harold U. Baranger We develop a new Path Integral Monte Carlo (PIMC) algorithm, based on the ideas of the worm algorithm, to study the behavior of electrons confined to quantum wires and rings at finite temperature. This algorithm should allow efficient measurement of spin and charge fluctuations for Coulomb-interacting fermions in both the liquid and Wigner crystal regimes. In a ring geometry, the algorithm should also be able to sample electron windings. In our first study we focus on the physics of spin-charge separation and spin-incoherence in the 1D electron gas in a harmonically confined quantum wire. Preliminary results show the emergence of an anti-ferromagnetic spin chain with an exponentially suppressed spin exchange coupling. [Preview Abstract] |
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C1.00114: Luminescence of colloidal CdSe/ZnS nanoparticles as a probe of solvent state Andrey Antipov, Andrei Sergeev, Vladimir Mitin, Mark Swihart, Alexandr Verevkin We demonstrate the sensitivity of colloidal CdSe/ZnS nanoparticles (NPs) photoluminescence (PL) intensity and wavelength to the solvent state. Several dramatic changes in PL are observed near solvent phase transitions, such as pronounced changes in PL peak energy and PL line width. For instance, a shift in the PL peak energy of up to $\sim $25 meV is observed for particles dispersed in water near the freezing point T=273 K. We attribute this anomalous temperature dependence of the PL to kinetic and thermal effects in nanoparticles as well as in the solvent. In the last case, the photoluminescence probe allows one to track even small changes in the solvent state. [Preview Abstract] |
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C1.00115: Quantum Dots-in-a-Well Infrared Photodetectors-Electronic Structure and Optical Properties Hakan Pettersson, Linda Hoglund, Fredrik Karlsson, Per-Olof Holtz, Qin Wang, Susanne Almqvist, Carl Asplund, Hedda Malm, Erik Petrini, Mats-Erik Pistol, Jan Andersson Quantum dots-in-a-well (DWELL) infrared photodetectors is a new class of nanophotonic devices with the potential of significantly increasing the performance and reducing the cost of infrared detectors. Here we present a comprehensive study of DWELL photodetector structures using a variety of optical techniques (PL, PLE, and PC). Complementary tunnel capacitance measurements support the electronic structure obtained from the optical measurements. A detailed energy level scheme based on the experimental findings is presented and compared to theoretical modeling. The presented work show the importance of combining different electrical and optical techniques to obtain a consistent model of complicated quantum structures which is crucial for the development of future nanophotonic devices. [Preview Abstract] |
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C1.00116: Two-dimensional Chiral Imprinting Petr Shibaev, Cristina Schlesier, Robert Uhrlass, Benjamin Crooker, Igor Yaminsky Chirality is commonly defined for three dimensional objects and manifests itself, for instance, in optical activity of chiral molecules and polarization of microwaves reflected from three dimensional structures. Here we report two dimensional chiral structures created on the flat transparent substrate by simple nanoimprinting technique. The geometry of the printed structures with a thickness not exceeding a few nanometers represents a repetitive pattern of chiral triangles. These structures display optical activity by rotating a plane of polarization and changing ellipticity of the refracted light beam (with the wavelengths of 532nm and 630nm). The peculiarities of the changes in polarization are discussed in terms of the geometry of the triangles and dielectric properties of the deposited material. The model explaining the behavior of the imprinted lattice is suggested. [Preview Abstract] |
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C1.00117: Photon-phonon coupling in acousto-optical microcavities Martin Maldovan, Edwin Thomas Periodic materials have unique physical properties due to their singular interaction with waves. Photonic crystals can control the propagation of light and can be engineered to guide optical beams or confine and trap light resonantly. Analogously, phononic crystals can manage the propagation of mechanical waves and can be used for acoustic filtering or localization of sound. In this paper, we present a new class of physical system that combines photonic and phononic properties. We show how photons and phonons can be localized in the same area at the same time, providing new means for an enhanced interaction between them. We calculate the strength of optical and mechanical interactions considering different structural morphologies and materials for the proposed photonic-phononic crystals. This research helps to develop physical mechanisms for light-induced generation of coherent mechanical excitations in photonic crystals, photon-phonon mediated effects that can result in optical cooling, and the simultaneous management of optical and mechanical waves on a photonic-phononic microchip. [Preview Abstract] |
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C1.00118: Photonic Band Gap Enhanced Energy Transfer in Eu$^{3+}$ Doped TbPO$_{4 }$ Inverse Opal Ji Zhou, Zhenwen Yang Photoluminescence (PL) of Eu$^{3+}$ doped TbPO$_{4}$(TbPO$_{4}$: Eu) inverse opal photonic crystals was investigated. The results showed that the energy transfer from the donor Tb$^{3+}$ to the acceptor Eu$^{3+ }$can be enhanced effectively by the photonic bandgaps in the photonic crystals. When the fluorescence emission wavelength of the donor Tb$^{3+}$ overlapped the photonic band gap, the fluorescence intensity of the donor was suppressed, while the fluorescence intensity of the acceptor Eu$^{3+ }$was obviously enhanced. This enhancement can be attributed to the inhibition of radiative emission of donor in the inverse opal photonic crystals. [Preview Abstract] |
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C1.00119: Photoluminescence Efficiency of Self Assembled Ge Dots David J. Lockwood, Nelson L. Rowell, Isabelle Berbezier, Guillaume Amiard, Antoine Ronda, David Grosso For self assembled Ge dots, the predicted nonlinear increase in the photoluminescence (PL) efficiency with decreasing dot diameter has been evaluated using the dot size distribution observed from atomic force microscopy and transmission electron microscopy. The dots were formed by thermal annealing of an amorphous Ge layer deposited by molecular beam epitaxy on a thin insulating layer of either TiO$_{2}$/SiO$_{2}$ or just SiO$_{2}$ [1] on Si(001). For the present range of particle sizes (2.5 to 60 nm), the dot PL appeared primarily as a wide near-infrared band near 800 meV. The peak energy of the PL band reflects the average dot size and its shape depends on the dot size distribution. Using theoretical calculations for the band gap energy, the PL energy spectrum was transformed into the PL variation with dot size. The present results show how, conversely, dot size distributions can be obtained from PL data. \\[4pt] [1] N.L. Rowell, et al., J. Electrochem. Soc. 156, H913 (2009). [Preview Abstract] |
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C1.00120: Plasmon-enhanced absorption in a metal nanoparticles and photosynthetic molecules hybrid system Zhiyuan Fan, Alexander Govorov Photosystem I from cyanobacteria is one of nature's most efficient light harvesting complexes, converting light energy into electronic energy with a quantum yield of 100{\%} and an energy yield about 58{\%}. It is very attractive to the nanotechnology community because of its nanoscale dimensions and excellent optoelectronic properties. This protein has~ the potential to be utilized in devices such as solar cells, electric switches, photo-detectors, etc. However, there is one limiting factor for potential applications of a single monolayer of these photosynthetic proteins. One monolayer absorbs less than 1{\%} of sunlight's energy, despite their excellent optoelectronic properties. Recently, experiments [1] have been conducted to enhance light absorption with the assistance of metal nanoparticles as artificial antenna for the photosystem I. Here, we present a theoretical description of the strong plasmon-assisted interactions between the metal nanoparticles and the optical dipoles of the reaction centers observed in the experiments. The resonance and off-resonance plasmon effects enhance the electromagnetic fields around the photosystem-I molecules and, in this way, lead to enhanced absorption. \\[4pt] [1] ~I. Carmeli, I. Lieberman, L. Kraversky, Zhiyuan Fan,~ A. O. Govorov, G. Markovich, and S. Richter, submitted. [Preview Abstract] |
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C1.00121: Plasmonic electromagnetically-induced transparency without symmetry breaking Xingri Jin, Yuehui Lu, Haiyu Zheng, YoungPak Lee, JooYull Rhee, WonHo Jang Electromagnetically-induced transparency (EIT) [1] results from the quantum interference between two pathways connecting the upper level with the lower levels, which leads to the probability for the atoms in the upper level to vanish. Its plasmonic analogue can be achieved by coupling of bright and dark plasmonic modes [2] based on the magnetic-plasmon resonance (MPR) [3]. To activate the dark plasmonic mode, a broken symmetry is generally resorted to, as reported in Ref. 2. Nevertheless, according to the picture of plasmonic EIT mediated by MPR, it is shown that the plasmonic analogue of EIT can be achieved even in the symmetric structures based on the second-order MPR [4]. This provides not only a supplement for the existing concept, but also a profound insight into the plasmonic coherent interference in the near-field zone. \\[4pt] [1] M. Fleischhauer, A. Imamoglu, and J. P. Marangos, Rev. Mod. Phys. \textbf{77}, 633 (2005). [2] S. Zhang, D. A. Genov, Y. Wang, M. Liu, and X. Zhang, prl \textbf{101}, 047401 (2008). [3] Y. Lu, H. Xu, N. T. Tung, J. Y. Rhee, W. H. Jang, B. S. Ham, and Y. P. Lee, {\tt arXiv:0906.4029v4}. [4] X. Jin, Y. Lu, H. Zheng, Y. P. Lee, J. Y. Rhee, and W. H. Jang, {\tt arXiv:0911.2062v1}. [Preview Abstract] |
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C1.00122: Scalar Wave Propagation Through a Nano-hole N.J.M. Horing, D. Miessein, J.D. Mancini In this work, an integral equation is formulated which describes scalar wave transmission through a nano-hole on a plasmonic sheet in terms of the Green's function for the associated Helmholtz problem. Taking the radius of the nano-hole to be the smallest length parameter of the system, we obtain an exact solution of the integral equation for the Green's function analytically and in closed form. The Green's function is then applied to the analysis of wave transmission through the nano-hole. [Preview Abstract] |
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C1.00123: Light Scattering and the electromagnetic near-field from a nanosphere near to the surface of a semi-infinite medium Luis Ramirez-Rodriguez, Raul Garcia-Llamas Light Scattering and the near field of a linearly polarized monochromatic electromagnetic wave produced by a nanosphere of radius R located in vacuum to a distance D near to the surface of a semi-infinite homogeneous medium is studied theoretically. The space is divided in three regions: I) in the sphere, II) out of the sphere in vacuum III) out of the sphere in the homogenous medium. Using a multipolar expansion and the boundary conditions the Maxwell's equations are solved. As a consequence of the presence of the surface an image mirror of the sphere is considered, then a shift phase produced for this image sphere is assumed, therefore these fields should be written in another reference system, hence the addition theorem for vector spherical wave functions is used. [Preview Abstract] |
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C1.00124: Detection of qubit-oscillator entanglement in nanomechanical systems Thomas Schmidt, Kjetil Borkje, Bjoern Trauzettel, Christoph Bruder In recent years, various proposals have been made on how to create entanglement between a quantum oscillator and a qubit. We propose a nanoelectromechanical device which would allow the detection of such entanglement by coupling the oscillator and the qubit to a quantum point contact. We demonstrate that measurements of the current and the symmetrized current noise of the quantum point contact reveal information about a bipartite expectation value matrix of the oscillator-qubit system. This matrix allows the evaluation of a specific entanglement witness. This proposal is a step towards the detection of entanglement between a discrete and a continuous variable in nanomechanical systems. [Preview Abstract] |
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C1.00125: Fabrication of Nanoscale Devices by Electromigration Swatilekha Saha, Guoguang Qian, K.M Lewis Currently, transport properties through nanostructures are of considerable importance due to the increased demand for nanometer sized electronic devices. One of the main challenges is to create electrodes with nanometer sized separation, where nanoparticles or molecules can be incorporated. Electromigration has proved to be a consistent method for creating gaps of such dimension. Here, we have fabricated gold (Au) nanowires of thickness 25-50 nm and length 200 nm by e-beam lithography. Then Au nanoparticles or Fe porphyrin molecules is deposited on the wires and a gap of size $<$10 nm is formed by electromigration. This results in confinement of the Au nanoparticles or porphyrin molecules in the gap. When Au nanoparticles are used, it is found that the resistance of the sample decreases by a factor of 10 and the I-V behavior is ohmic. By functionalizing the Au nanoparticles, the sample can then be used as a chemical sensor operable at room temperature. Experiments will be proposed to study transport through Fe porphyrin molecule at 4K to observe Coulomb blockade, which has applications as switches in molecular electronic devices. [Preview Abstract] |
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C1.00126: Calculations of Electron Transport through Radicals Manuel Smeu, Gino DiLabio Organic radicals are of interest in molecular electronics because a singly occupied molecular orbital (SOMO) would have a higher energy than its doubly occupied analog, suggesting they might make better conductors. The unpaired electron present in a radical leads to degeneracy splitting in other energy levels and such molecules may act as spin filters. Our study employs first principles transport calculations that are performed using a combination of density functional theory and a non-equilibrium Green's function technique. The conductance of 1,4-benzenediamine (BDA) molecules bridging two Au electrodes was modeled. These molecules were substituted in the 2-position with: -CH3, -NH2, and -OH; as well as with their radical analogs: -CH2, -NH, and -O, all of which have $\pi $-type SOMOs. The conductance of a radical with a $\sigma $-type SOMO was also calculated from a BDA molecule with the H atom in the 2-position removed. Comparing the transmission spectra for these species will yield insight into the nature of electron transport through radicals vs. transport through their reduced form as well as the nature of transport through $\pi $- and $\sigma $-type molecular orbitals. [Preview Abstract] |
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C1.00127: In-situ XRD Investigations of the Solid--state Synthesis of Doped Thermoelectric Cobalt Oxides Haiyan Chen, Jianming Bai, Trevor Tyson Thermoelectric materials are important in converting waste heat into electricity or electrical power directly into cooling or heating. Calcium cobalt oxide has been shown to posses large figure of merit and is considered an excellent candidate for high temperature thermoelectric applications. Doping with other metal oxides is one way to improve thermoelectric properties of this family of materials. To understand the synthesis of these materials, we have carried out time resolved in-situ XRD study of the solid state reactions involved in the production of calcium cobalt oxide and doped calcium cobalt oxide from metal carbonate and metal oxides. In this presentation, observed phase transitions, intermediates, and phase evolutions will be reported and discussed. These results will be helpful in the understanding of reaction mechanisms and can provide insights into the doping mechanism involved in the improvement of the thermoelectric characteristics of calcium cobalt oxides. This work is supported by DOE Grant DE-FG02-07ER46402 and NSF Instrumentation grant DMR MRI-0722730. [Preview Abstract] |
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C1.00128: Effect of doping on the electronic structure and transport properties of half-Heusler compounds Mal-Soon Lee, S.D. Mahanti, Nathan J. Takas, Paramathesh Maji, Ferdinand P. Poudeu Narrow-band-gap half-Heusler semiconductors are promising candidates for high-temperature thermoelectrics due to large power factor $S^2\,\sigma $, $S$ is Seebeck coefficient and $\sigma $ is the electrical conductivity. $S^2\,\sigma $ is usually maximized by changing the carrier concentration through doping. We have carried out transport measurements in $Hf_{0.5} Zr_{0.5} Co_x Ir_{1-x} Sb_{0.99} Sn_{0.01} $ for different $x$ and temperatures ($T)$. The nominal hole concentration $n=1.78\times 10^{20}/cm^3$. Measured $S$values ($\mu V/K)$ are in the range 14-122 at 300 K and 90-216 at 750 K. The systems we have chosen to calculate $S$ are (Hf,Zr)(Co,Ir)Sb. We have used \textit{ab intio} band structure, Boltzmann transport equation (assuming constant relaxation time) and the rigid band approximation (RBA). We find values in the range 121-257 at 300 K and 262-390 at 750 K. To understand the origin of these differences, we have examined the validity of RBA. We observe that isovalent impurities do not change the band structure significantly, whereas charged impurities change the host band structure. Transport properties are also influenced by the change in the band structure. [Preview Abstract] |
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C1.00129: Giant Thermo-Power Enhancement in Multilayered Superlattices A.M. Bratkovsky, A.S. Alexandrov We have developed a theory of polaron crossover from 3D to 2D and applied it to superlattices with heavily doped layers, like Nb:STO. In the crossover region the polaron energy spectrum is quantized into subbands with their subband binding energy and polaron mass essentially depending on the size of the confinement layer, when the thickness of the layer is comparable or less than the Fr\"ohlich polaron radius. We have shown that this condition is satisfied in Nb:SrTiO$_3 $/SrTiO$_3$ superlattices and proposed a detailed explanation of the giant thermopower enhancement observed in these structures [1,2]. The theory predicts a giant confinement enhancement of the figure of merit in those polaronic MQWs where the scattering of polarons is dominated by impurities.\\[4pt] [1]~H. Ohta, S. Kim, Y. Mune, T. Mizoguchi, K. Nomura, S. Ohta, T. Nomura, Y. Nakanishi, Y. Ikuhara, M. Hirano, H. Hosono, and K. Koumoto, Nature Mat. 6, 129 (2007).\\[0pt] [2] W. S. Choi, H. Ohta, S. J. Moon, Y. S. Lee, and T. W. Noh, arXiv:0906.5391. [Preview Abstract] |
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C1.00130: Electron Dominated Thermal Transport in (Hf,Zr)N-(Sc,Y)N Superlattices Joseph Feser, Mona Zebarjadi, Jeremy Schroeder, Robert Wortman, Dongyan Xu, Ali Shakouri, Arun Majumdar, Timothy Sands Alloyed metal-semiconductor superlattices composed of (Hf,Zr)N-(Sc,Y)N have been studied as candidate thermoelectric materials because of their potential to simultaneously reduce the lattice thermal conductivity using interface scattering and enhance the thermoelectric power factor using energy-dependent electron filtering. Temperature-dependent thermal conductivity measurements on thin films have been performed using the 3-Omega method between 30K - 800K for various alloy compositions and superlattice spacings in order to provide insight into the phonon and electron transport processes. The results indicate a strong electronic component where the temperature dependence of thermal conductivity is consistent with thermionic emission. We demonstrate that by controlling alloy composition, the barrier height of the resulting Schottky barrier can be controlled. Boltzmann Transport modeling is used to estimate the effective barrier heights. [Preview Abstract] |
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C1.00131: Magnetocaloric properties of Co/Cr superlattices Tathagata Mukherjee, Ralph Skomski, David Sellmyer, Christian Binek Nanostructured materials aiming on refrigeration applications are experimentally realized by molecular beam epitaxial (MBE) growth of Co/Cr superlattices using mean-field theoretical concepts as guiding principles.\footnote{T. Mukherjee, S. Sahoo, R. Skomski, D. J. Sellmyer, and Ch. Binek, Phys. Rev. B \textbf{79}, 144406-1-9 (2009).} Magnetocaloric properties are deduced from measurements of the temperature and field dependence of the magnetization of our samples. More generally, the potential of artificial antiferromagnets for near room-temperature refrigeration is explored. The effects of intra-plane and inter-plane exchange interactions on the magnetic phase diagram in Ising-type model systems are revisited in mean-field considerations with special emphasis on tailoring magnetocaloric properties. The experimental results are discussed in light of our theoretical findings, and extrapolations for future improved nanostructures are provided. Financial support by NRI, and NSF through EPSCoR, Career DMR-0547887, and MRSEC. [Preview Abstract] |
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C1.00132: Effect of field sweep rate on magnetization dynamics of exchange-coupled nanocomposite magnets Chuanbing Rong, J. Ping Liu It has been found that magnetization dynamics of a nanocomposite magnet is different from that of single-phase magnets. Open recoil loops are considered as a characteristic for nanocomposite magnets. Recently, it is revealed that openness of recoil loops of nanocomposite magnets is strongly dependent on sweep rate of applied magnetic fields, while similar dependence for single-phase nanocrystalline magnets is not observed [1]. In this work, we studied the sweep-rate dependence of Henkel plots and first order reversal curves (FORC), reversible magnetization in the FePt/Fe$_{3}$Pt nanocomposite magnets. was found that the positive peaks of Henkel plots, representing the strength of exchange coupling interactions, decreases with decreasing sweep rate. The reversible magnetization also decreases with decreasing sweep rate, especially in the nanocomposite magnets. More interestingly, it was found that the FORC with fast sweep rate shows a completely single-phase magnetic behavior, while a slight two-phase behavior with slow sweep rate. These phenomenacan be explained by the unstable magnetizations in the exchange-hardened magnetic soft phase. [1] C.B. Rong, Y. Liu, J. P. Liu, Appl. Phys. Lett., 93, 042508 (2008). [Preview Abstract] |
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C1.00133: ABSTRACT WITHDRAWN |
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C1.00134: PHYSICS EDUCATION |
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C1.00135: Theories of Causality Robert Jones There are a wide range of views on causality. To some (e.g. Karl Popper) causality is superfluous. Bertrand Russell said ``In advanced science the word cause never occurs. Causality is a relic of a bygone age.'' At the other extreme Rafael Sorkin and L. Bombelli suggest that space and time do not exist but are only an approximation to a reality that is simply a discrete ordered set, a ``causal set.'' For them causality IS reality. Others, like Judea Pearl and Nancy Cartwright are seaking to build a complex fundamental theory of causality (Causality, Cambridge Univ. Press, 2000) Or perhaps a theory of causality is simply the theory of functions. This is more or less my take on causality. [Preview Abstract] |
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C1.00136: Home-made experiment of Dye-sensitized TiO$_{2}$ Nanocrystalline Solar Cells and its education evaluation M.F. Tai, M.C. Shieh, T.W. Chen Dyes extracted from some natural fruits including anthocyanins absorb sunlight and effectively activate electrons of anthocyanins. Thus these activated electrons are conducted between TiO$_{2}$ nanocrystals and form electric potential and current between two electrodes. The dyes can be gotten from the natural fruits, such as blackberries, raspberry, pomegranate seeds and bing cherries. This principle permits making a dye sensitized TiO$_{2}$ nanocrystallines solar cell (DSSC). All required materials and tools for fabricating a home- made DSSC are easy to obtain around home. The procedures are perfect hands-on experiment as well as demonstration in K-12 schools or home settings. We have designed several protocols for fabricating DSSC and have successfully demonstrated in more than 100 activities with different level students. K-12 Students were able to build their own working DSSC's within 2-3 hours sessions and learned about alternative energy sources. These experiments can inspire students and general public about the modern technology in daily life. Low cost (low than US \$3 in Taiwan)and safety are also ensured in our DSSC experiments. [Preview Abstract] |
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C1.00137: Establishing a Physics mentoring Program for a Philadelphia Middle School J.T. Mlack, A. Wilson, W. Harris, A. White, S.S. Mehta, V. Ramdass Our SPS chapter has established a regular physics mentoring program at Independence Charter Middle School located in Philadelphia, PA. Members visit the school on a bi-weekly basis and perform 1-2 hour, inquiry-based~lecture demonstrations of physics phenomena that integrate with the science lessons of middle school students. At the end of the school year, a capstone activity in the form of a Rube Goldberg competition among the middle school students was held on the Drexel campus with Drexel faculty and graduate students participating as judges. [Preview Abstract] |
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C1.00138: Rolling vs. Sliding: The inclusion of non-conservative work in the classic comparison Alex Chediak, Terry Buehler, Benjamin Lee, Daniel Donaldson A semester-long mechanics course typically covers moment of inertia, angular velocity, and rolling. A classic comparison is made between rolling without slipping and sliding without friction. In either case, no non-conservation work is performed---all the gravitational potential energy that the rolling or sliding object possesses at the top of the incline plane is converted into kinetic energy. In the case of the sliding object, the kinetic energy term is simply $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $mv$^{2}$. In the case of the rolling object, the kinetic energy term is $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $mv$^{2}$ + $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 2$} $I$\omega ^{2}$. The friction here is \textit{static} not \textit{kinetic, }so it does no mechanical work. Since the sliding object has no angular velocity, its linear velocity is greater than that of the rolling object, and it reaches the bottom of the track faster. But if a rolling and sliding object, each of the same material, were to race down an incline plane, which would win? The answer depends on the \textit{effective coefficient of friction, }C$.$ If $C > \mu_s$, which will occur at angles approaching 90$^{\circ}$, the rolling object slips. And if $C < \mu_k$, the rolling object has a greater linear acceleration and wins the race to the bottom. Experimental results to verify a theoretical model (including the dependency on incline angle) will also be presented. [Preview Abstract] |
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C1.00139: Conceptual chains and its application to study solving problems in physics Carlos Enrique Lopez Campos This work reports a theoretical model developed with the aim to explain the mental mechanisms of knowledge building during the problem-solving process in physics using a hybrid approach of assimilation- formation of concepts. The model has been termed \textit{conceptual chains} and represents graphic diagrams of conceptual dependency, which have yielded information about the background knowledge required during the learning process, as well as about the formation of diverse structures that correspond to distinct forms of networking concepts. Additionally, the conceptual constructs of the model have been classified according to five types of knowledge. Evidence was found about the influence of these structures, as well as of the distinct types of knowledge about the degree of difficulty of the problems. [Preview Abstract] |
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C1.00140: Teaching Students About the Process of Science: Using Google to Collect and Analyze Student Lab Measurements Kristen Larson, Jim Stewart The process of science necessarily includes critical analysis of uncertainty in repeated measurements. We demonstrate how the measurements that students make can be collected and analyzed in real time with Google Docs. Showing students how their measurements compare to the rest of the class provides a valuable opportunity to teach about uncertainty and the process of science. Student work can be compiled by the instructor after the fact, but Google makes it easy for students to submit their measurements via a web form and instantly see how their measurements fit with the rest of the class. Analysis, including histograms, fits, and virtually anything that can be done with a spreadsheet, is updated automatically and available to students. We show how the tools can be readily customized and implemented seamlessly with two examples from large undergraduate classes: measurement of the acceleration due to gravity in introductory physics lab, and measurement of the Hubble constant in introductory astronomy. [Preview Abstract] |
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C1.00141: Three Dimensional Periodic Table of the Elements `Elementouch' Yoshiteru Maeno A three-dimensional periodic table of the elements `Elementouch', useful in a wide variety of occasions of science education, is introduced. The element names are continuously arranged on three circular surfaces representing the electron orbits of an atom. In this way, the properties of each element in its typical ionic state can be seen more clearly than in the widely-used long period table, introduced in 1905 by Alfred Werner. The Elementouch can be readily made using the patterns downloaded from the following URL: http://www.ss.scphys.kyoto-u.ac.jp/elementouch/index-e.html . [Preview Abstract] |
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C1.00142: STATISTICAL AND NONLINEAR PHYSICS |
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C1.00143: Scaling in a Model of Material Damage with Healing Joseph Gran, James Holliday, John Rundle, Don Turcotte, William Klein A variety of studies have modeled the physics of material deformation and damage as examples of generalized phase transitions, involving either critical phenomena or spinodal nucleation. Here we study a model for frictional sliding with interactions $R\gg1$ and recurrent damage that is parameterized by a process of damage and partial healing during sliding. We define a mapping to a percolation transition, and show that the scaling exponents are, within measurement error, the same as for mean field percolation and spinodal nucleation. Several time dependent healing processes are investigated including instaneous healing. We also investigate the resulting interevent temporal spacing and the frequency of aftershocks and compare our results with experiments and Omori's law. [Preview Abstract] |
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C1.00144: DEFINITION of (so MIScalled) ``Complexity" As UTTER-SIMPLICITY!!!(sMciUS!!!) VERSUS DEVIATIONS FROM( sMciUS!!!): ``COMPLICATEDNESS" DEFINITION(S) and MEASURE(S)!!! F. Young, E. Siegel (so MIScalled) ``complexity''(sMc) associated BOTH SCALE- INVARIANCE Symmetry-RESTORING(S-I S-R) [vs. S-I S-B!!!], AND X (w)~P(w )~1/w$^{(1.000...)}$ ``pink''/Zipf/Archimedes-HYPERBOLICITY INEVITABILITY CONNECTION is by simple-calculus SISR's logarithm- function derivative: (d/dw)ln(w)=1/w=1/w$^{(1.000...)}$, hence: (d/dw) [SISR](w)=1/w=1/w$^{(1.000...)}$=(via Noether-theorem relating continuous-(SISR)-symmetries to conservation-laws)=(d/dw)[4-DIV (J(INTER-SCALE)=0](w)=1/w =1/w$^{(1.000...)}$. Hence sMc is information inter-scale conservation [as Anderson-Mandell, Fractals of Brain; Fractals of Mind(1994)-experimental- psychology!!!], i.e. sMciUS!!!, VERSUS ``COMPLICATEDNESS", is sMcciUS!!!: EITHER: PLUS (Additive: Murphy's-law absence) OR TIMES (Multiplicative: Murphy's-law dominance) various disparate system-specificity ``COMPLICATIONS". ``COMPLICATEDNESS" MEASURES: DEVIATIONS FROM sMciUS!!!: EITHER [S-I S-B] MINUS [S- I S-R] AND/OR [``red"/Pareto X(w)~P(w)~1/w$^{(\#=/=1.000...)}$] MINUS [X(w)~P(w)~1/w$^{(1.000...)}$ ``pink"/Zipf/Archimedes-HYPERBOLICITY INEVITABILITY] = [1/w$^{(\#=/=1.000...)}$] MINUS [1/w$^{(1.000...)}$]; almost but not exactly a fractals Hurst-exponent-like [\# - 1.000...]!!! [Preview Abstract] |
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C1.00145: (so: called/BNL/DoE-hyped) ``Self-Organized-Criticality"(SOC) is Merely Newton's(1687) Law of Motion F = ma REdiscovery: LONG PRE-``Bak"!!! P.R.E. Bak, E. Siegel ``Bak''/BNL/DoE ``self-organized-criticality''(SOC) usual BNL/DoE media-hype P.R spin-doctoring ``show-biz'' ``Bush-waaa-...-aaah!!!'' is manifestly-demonstrated in two distinct ways to be nothing but Newton's Law of Motion F = ma REdiscovery!!! PHYSICS: (1687) cross-multiplied F = ma rewritten as 1/m = a/F = OUTPUT/INPUT = EFFECT/CAUSE = inverse-mass mechanical-susceptibility = $\chi $(``$\omega $''); $\chi $ (``$\omega $'') $\sim $(fluctuation-dissipation theorem-equivalence /proportionality)$\sim $ P(``$\omega $'') ``noise'' power-spectrum; E $\sim $ $\omega $ ; and E $\sim $(or any/all media with upper-limiting-speeds)$\sim $ m. Thus: $\omega \quad \sim $ E $\sim $ m; inversion yields: 1/$\omega $ $\sim $ 1/E $\sim $ 1/m $\sim $ a/F = $\chi $(``$\omega $'') $\sim $ P(``$\omega $''); hence: F = ma dual/inverse-integral-transform is ``'SOC'''s'' P($\omega ) \quad \sim $ 1/$\omega $!!! ; ``PURE"-MATHEMATICS: F = ma double-integral time-series s(t) = [vot + (1/2) at$^{(2)}$] inverse/dual-integral-(Fourier, Laplace)-transform formally defines power-spectrum: P($\omega )=\Xi$ s(t) e$^{[-(i OR no i)wt]}$ dt = $\Xi $[vot + (1/2) at$^{2}$] e$^{[-(i OR no i)wt]}$ dt = vo $\Xi $ t e$^{[-(i OR no i)wt]}$ dt + (1/2) $\Xi $ [a =/= a(t)] e$^{[-(i OR no i)wt]}$ dt = vo (d/d$\omega ) \quad \delta (\omega )$ +(1/2) [a $\ne $ a(t)] (d/d$\omega )^{(2)}$ $\delta (\omega )$ = vo/$\omega $(0) +(1/2) [a $\ne $ a(t)] / $\omega $\^{}(1.000...): if a = 0, then P($\omega) \quad \sim $ 1/$\omega $(0), versus if a $\ne $ a(t) $\ne $0, then P($\omega ) \quad \sim $ 1/$\omega \quad \sim $ 1/$\omega^{(1.000...)}$; same exact conclusion as from physics: SOC $<$=(reexpresses)=$>$ F = ma!!!: SOC Rediscovery of F=ma: LONG PRE-``Bak''!!! [Preview Abstract] |
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C1.00146: Coupled Optical Parity-Time Symmetric Non-Linear Dimers Hamidreza Ramezani, Tsampikos Kottos We investigate the dynamics of coupled optical non-linear dimers with Parity-Time (PT) symmetry, induced by judiciously tailored gain/loss processes. We show that this system admits stationary solutions for non- linearity strength smaller than a critical value which depends on the gain/loss parameter. Then we examine the beam dynamics for such type of systems. We find that the interplay of non-linearity and PT-symmetry, results in a controlled unidirectional beam propagation. Applications of our results in optics as much as in the framework of atomic Bose-Einstein condensates are discussed. [Preview Abstract] |
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C1.00147: Dynamical Mechanism of Scaling Behaviors in Multifractal Structure Kyungsik Kim, Jae Won Jung, Soo Yong Kim The pattern of stone distribution in the game of Go (Baduk, Weiqi, or Igo) can be treated in the mathematical and physical languages of multifractals. The concepts of fractals and multifractals have relevance to many fields of science and even arts. A significant and fascinating feature of this approach is that it provides a proper interpretation for the pattern of the two-colored (black and white) stones in terms of the numerical values of the generalized dimension and the scaling exponent. For our case, these statistical quantities can be estimated numerically from the black, white, and mixed stones, assuming the excluded edge effect that the cell form of the Go game has the self-similar structure. The result from the multifractal structure allows us to find a definite and reliable fractal dimension, and it precisely verifies that the fractal dimension becomes larger, as the cell of grids increases. We also find the strength of multifractal structures from the difference in the scaling exponents in the black, white, and mixed stones. [Preview Abstract] |
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C1.00148: Multifractal Structures in the temperature and the humidity Kyungsik Kim, Cheol-Hwan You, Dong-In Lee The multifractal structure of the temperature and the humidity is investigated in eight cities of Korea. For our cases, we estimate the generalized Hurst exponent, the Renyi exponent, and the singularity spectrum for tick data of the temperature and the humidity. In particular, we discuss the recent findings that suggest the scaling exponents characterizing the multifractality. After analyzing the multifractality, we compare the multifractal property of eight different cities and discuss the different behavior of each city. [Preview Abstract] |
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C1.00149: Unusual phase diagram of the generalized contact process with two absorbing states Man Young Lee, Thomas Vojta We investigate the generalized contact process with two absorbing states in one and two dimensions by means of large-scale Monte-Carlo simulations. In addition to the conventional active and inactive phases we find a region of the phase diagram where the simple contact process is inactive, but an \emph{infinitesimal} activation rate at the boundary between different inactive domains causes the system to be in the active phase. In this region, the steady state density depends on the boundary activation rate via a stretched exponential. We also study in detail the phase transition between the active and inactive phases focusing on the universality of the critical behavior. [Preview Abstract] |
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C1.00150: Thermodynamic length, Fisher information, and dissipation David Sivak, Gavin Crooks We explore thermodynamic length, defined as the root-mean squared fluctuations of the variables conjugate to the control parameters, as a non-equilibrium framework for understanding physical limits on the efficiency of non-equilibrium processes. Thermodynamic length equips thermodynamic state space with a Riemannian metric, and minimum thermodynamic length paths minimize the dissipation for slow, but finite time, transformations. Our reformulation of thermodynamic length analysis provides access to a non-equilibrium quantity (dissipation) through equilibrium properties (relaxation time and Fisher information). We derive analytic expressions for Fisher information (related to the derivative of thermodynamic length) in one-dimensional bistable energy landscapes, and find that it can vary by several orders of magnitude across a given landscape. Through simulation, we find that thermodynamic length analysis accurately predicts the instantaneous dissipation of far-from-equilibrium processes across the entire energy landscape. Finally, we derive the thermodynamic length framework as a special case of linear response theory. [Preview Abstract] |
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C1.00151: Cooperation/Competition Property Heterogeneity Xiu-Lian Xu, Chun-Hua Fu, Da-Ren He We show that the heterogeneity index, which was proposed by Hu and Wang (Physica A 2008 387 3769), can be used to describe the disparity of the cooperation sharing or competition gain distributions that is very important for the cooperation/competition system dynamic understanding. An analytical relation between the distribution parameters and the heterogeneity index is derived, which is in a good agreement with the empirical results. Our theoretical and empirical analyses also show that the relation between the distribution parameters can be analytically derived from so-called Zhang-Chang model (Physica A 2006 360 599 and 2007 383 687). This strongly recommends a possibility to create a general dynamic cooperation/competition model based on Zhang-Chang model. [Preview Abstract] |
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C1.00152: Relationship between uniqueness and competition ability Ai-Fen Liu, Xiu-Lian Xu, Da-Ren He In our previous paper (Feng A X, Xu X L, He D R 2009 Chin. Phys. Lett. 26 058901) we proposed quantitative definitions of uniqueness and competition ability. Their trivial linear relationship was analytically discussed. In this letter, we present analytical discussion on the more interesting anomalous cases. The analytical result shows that, instead of the trivial linear relationship, the relationship between uniqueness and competition ability obeys a power law. The competition between Beijing restaurants is taken as an example. The empirical investigation results show a strong support to the analytical conclusion. [Preview Abstract] |
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C1.00153: Property relationships of the physical infrastructure and the traffic flow networks Ta Zhou, Sheng-Rong Zou, Da-Ren He We studied both empirically and analytically the correlation between the degrees or the clustering coefficients, respectively, of the networks in the physical infrastructure and the traffic flow layers in three Chinese transportation systems. The systems are bus transportation systems in Beijing and Hangzhou, and the railway system in the mainland. It is found that the correlation between the degrees obey a linear function; while the correlation between the clustering coefficients obey a power law. A possible dynamic explanation on the rules is presented. [Preview Abstract] |
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C1.00154: Network-Physics (NP) BEC DIGITAL(\#)-VULNERABILITY; ``Q-Computing"=Simple-Arithmetic;Modular-Congruences=SignalXNoise PRODUCTS=Clock-model;BEC-Factorization;RANDOM-\# Definition;P=/=NP TRIVIAL Proof!!! E.I. Pi, E. Siegel Siegel[AMS Natl.Mtg.(2002)-Abs.973-60-124] digits logarithmic- law inversion to ONLY BEQS BEC:Quanta/Bosons=\#: EMP-like SEVERE VULNERABILITY of ONLY \#-networks(VS.ANALOG INvulnerability) via Barabasi NP(VS.dynamics[Not.AMS(5/2009)] critique);(so called)``quantum-computing''(QC) = simple-arithmetic (sansdivision);algorithmiccomplexities:INtractibility/UNdecidabi lity/INefficiency/NONcomputability/HARDNESS(so MIScalled) ``noise''-induced-phase-transition(NIT)ACCELERATION:Cook-Levin theorem Reducibility = RG fixed-points; \#-Randomness DEFINITION via WHAT? Query(VS. Goldreich[Not.AMS(2002)] How? mea culpa)= ONLY MBCS hot-plasma v \#-clumping NON-random BEC; Modular-Arithmetic Congruences = Signal x Noise PRODUCTS = clock-model; NON-Shor[Physica A,341,586(04)]BEC logarithmic-law inversion factorization: Watkins \#-theory U statistical- physics); P=/=NP C-S TRIVIAL Proof: Euclid!!! [(So Miscalled) computational-complexity J-O obviation(3 millennia AGO geometry: NO:CC,``CS'';``Feet of Clay!!!'']; Query WHAT?:Definition: (so MIScalled)``complexity''=UTTER-SIMPLICITY!! v COMPLICATEDNESS MEASURE(S). [Preview Abstract] |
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C1.00155: The price of anarchy in basketball Brian Skinner Optimizing the performance of a basketball offense may be viewed as a network problem, wherein each play represents a ``pathway'' through which the ball and players may move from origin (the in-bounds pass) to goal (the basket). Effective field goal percentages from the resulting shot attempts can be used to characterize the efficiency of each pathway. Inspired by recent discussions of the ``price of anarchy'' in traffic networks, this paper makes a formal analogy between a basketball offense and a simplified traffic network. The analysis suggests that there may be a significant difference between taking the highest-percentage shot each time down the court and playing the most efficient possible game. There may also be an analogue of Braess's Paradox in basketball, such that removing a key player from a team can result in the improvement of the team's offensive efficiency. [Preview Abstract] |
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C1.00156: Fractal Weyl law in an open, chaotic Hamiltonian system Jordan Ramilowski, David Farrelly The original Weyl law states that the number of quantum bound states, up to some energy E, scales as $\hbar^{-d}$, where $d$ is the (integer) dimension of the system. Recently, several open quantum maps have been found to obey a {\it fractal} version of this law, i.e., the number of quasibound states (resonances) scales as $\hbar^{-d}$, but with $d$ a non-integer. The fractal dimension can be traced to the localization of the resonances on a fractal classical phase-space object - the repeller: the repeller is the intersection of two fractal sets of classical trajectories which remains trapped in the infinite past and the infinite future. Here fractal Weyl law behavior is demonstrated numerically in an open {\it Hamiltonian} system -- rather than in a map. The system, a rotating version of the Henon-Heiles problem, supports a large number of above-barrier resonances. Fractal Weyl behavior is found to hold far from the classical limit and, as in maps, the complex resonance wave functions are localized on a classical repeller whose structure is elucidated. Implications of these findings for physical problems of current interest are discussed - e.g., for the chaotic ionization of the hydrogen atom by a circularly polarized microwave field. [Preview Abstract] |
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C1.00157: Chaos and Order in the /. Body Problem Amanda Logue, John F. Lindner, Jacob Lynn, Frank W. King We study the classical dynamics of a line body or slash (/) and a point body or dot (.) interacting gravitationally. For this /. body problem, we show that the force and torque on the slash integrate exactly, greatly facilitating analysis. The diverse dynamics include a stable synchronous orbit, generic chaotic orbits, sequences of unstable periodic orbits, spin stabilized orbits, and spin-orbit coupling that can unbind the slash and dot. Applications include the dynamics of asteroid-moonlet pairs and asteroid rotation and escape rates. This work was supported in part by NSF DMR-0649112. [Preview Abstract] |
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C1.00158: Two-dimensional, one-way coupled arrays Katsuo Maxted, John F. Lindner, Barbara J. Breen A damped, two-way coupled array of bistable oscillators quickly dissipates all excitations. However, the corresponding one-way coupled array can topologically force solitary waves to propagate indefinitely. Experimentalists have realized one-way coupling in one-dimensional arrays by powering the coupling with falling water. The corresponding one-way motion is an extreme example of wave propagation in anisotropic media like light in calcite. Here, we generalize this phenomenon to higher dimensions in computer simulations. This work was supported in part by NSF DMR-0649112. [Preview Abstract] |
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C1.00159: Escape from the 3 Body Problem Margaret Raabe, John F. Lindner Computing the minimum speed for a projectile to escape a solar system consisting only of a ``star'' and a ``planet'' is nontrivial and was controversial until just recently, when it was analyzed in the context of the \textit{restricted} 3 body problem: if most of the system's mass is in the star, the projectile should be shot slightly outward of the planet's motion, but if most of the system's mass is in the planet, the projectile should be shot toward the star for a gravity assist. Here, we analyze the escape problem in the context of the \textit{full} 3 body problem, allowing the projectile to perturb the star and the planet, using cluster computing techniques. This work was supported in part by NSF DMR-0649112. [Preview Abstract] |
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C1.00160: Characterization of Non-Linear Pendulums through Frequency Bifurcation Vy Tran, Richard Atherton, Eric Brost, Jillian Schleicher, Ann Ziegler, Martin Johnston, Jeff Jalkio The bifurcation of a sinusoidally-driven pendulum was studied by sweeping through a range of driving frequencies. At each step, the dynamics were characterized by calculating the periodicity, principle Lyapunov exponent, system parameters, and the fractal dimensionality of the Poincare sections. The system was then modified by placing a magnet under the pendulum which opposed a magnet attached to the end of the pendulum. This dipole-dipole interaction split the original single-well potential into a double-well potential. The bifurcation was repeated for the perturbed wells and the characterization parameters were calculated and compared with the unperturbed system. The results from both pendulums were compared with simulated systems created using an ODE solver. [Preview Abstract] |
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C1.00161: Chaotic Phase Space of a Hydrogen Atom in Crossed Electric and Magnetic Fields Korana Burke, Kevin Mitchell The motion of the electron of a hydrogen atom placed in crossed external electric and magnetic fields exhibits chaotic behavior. By an appropriate choice of surface of section, we show that the ionization process is governed by the geometry of a homoclinic tangle, and its associated phase space turnstile. This geometry can be used to make predictions about the ionization rate of this system. [Preview Abstract] |
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C1.00162: The Emergence of Robustness in Finite Random Discrete Networks Natali Gulbahce, Christof Teuscher Biological networks are often able to restructure themselves for the efficient and robust execution of a specific task. It has been shown that random Boolean networks possess a ''connectivity of stability,'' [1] where the damage spreading is invariant of the system size $N$. Here we study the emergence of robustness in such networks by defining robustness as an evolutionary goal and using optimization tools from physics and computer science. We numerically study damage spreading and robustness in finite random discrete networks that undergo change over time in order to investigate how an evolutionary process such complex systems both robust and near-optimal over time. Our results suggest that resource and performance constraints are sufficient for networks to evolve toward a critical connectivity. [1] T. Rohlf, N. Gulbahce, and C. Teuscher. Damage Spreading and Criticality in Finite Random Dynamical Networks. Physical Review Letters, 99, 248701, 2007. [Preview Abstract] |
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C1.00163: Nanodroplet Activated and Guided Folding of Graphene Nanostructures Petr Kral, Niladri Patra, Boyang Wang We demonstrate by molecular dynamics simulations that water nanodroplets can activate and guide the folding of planar graphene nanostructures [1]. Once the nanodroplets are deposited at selected spots on the planar nanostructure, they can act as catalytic elements that initiate conformational changes and help to overcome deformation barriers associated with them. Nanodroplets can induce rapid bending, folding, sliding, rolling and zipping of the planar nanostructures, which can lead to the assembly of nanoscale sandwiches, capsules, knots and rings.\\[4pt] [1] Patra, N.; Wang, B.; Kral, P. Nano Letters, 2009, in press [Preview Abstract] |
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C1.00164: The Mechanical Properties of Graphene Oxide and Graphene Nanoribbons Probed by Single-Molecule Manipulation Sitara Wijeratne, Ching-Hwa Kiang, Wei Lu, Amanda Higginbotham, James M. Tour The discovery of free standing graphene has attracted significant attention because of its band structure and its relevance to quantum electrodynamics in solid state systems. Graphene oxide nanoribbons (GONR), produced by lengthwise oxidative cutting of multiwalled carbon nanotubes (MWCNTs), have similar electronic structure to graphene oxide produced by chemical exfoliation from graphite. We use the atomic force microscopy (AFM) to pull single graphene oxide nanoribbons and their reduction products, graphene nanoribbons, in solution to study their mechanical properties. We found that the elasticity of the nanoribbons can be explained by the worm-like chain (WLC) model, which is used to explain the biopolymer behavior. [Preview Abstract] |
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C1.00165: Beyond the Death of Linear Response: 1/f- noise Resonance Gerardo Aquino, Mauro Bologna, Paolo Grigolini, Bruce West Non-ergodic renewal processes have recently been shown by several authors to be insensitive to periodic perturbations, thereby apparently sanctioning the death of linear response, a building block of nonequilibrium statistical physics. We show that it is possible to go beyond the ``death of linear response" and establish a permanent correlation between an external stimulus and the response of a complex network generating non-ergodic renewal processes, by taking as stimulus a similar non-ergodic process. We propose a theory for the transport of information through non-ergodic systems that explains why 1/f-noise is an efficient stimulus for complex systems. The ideal condition of 1/f-noise corresponds in fact to a singularity that is expected to be relevant in several experimental conditions of physical and biological interest. [Preview Abstract] |
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C1.00166: Langevin Description of Anomalous Diffusion Processes in the Presence of External Potentials Stephan Eule, Rudolf Friedrich The role of external forces in systems exhibiting anomalous diffusion is discussed within the framework of Langevin equations. Since there exist different possibilities to include the effect of an external field the concept of {\it biasing} and {\it decoupled} external fields is introduced. This leads to two different forms of time-fractional Fokker-Planck equations. Complementary to the recently established Langevin equations for anomalous diffusion in a time-dependent external force-field by Magdziarz et al. the Langevin formulation of anomalous diffusion in a decoupled time-dependent force-field is derived. Thereby the mathematical concept of subordination is applied. [Preview Abstract] |
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C1.00167: SEMICONDUCTORS |
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C1.00168: Magneto-Transport Study of Undoped and Fe-doped AlGaN/GaN Ying-Chieh Wang, Ikai Lo, Ming-Hong Gau, Thomas Aggerstam, Sebastian Lourdudoss The beating pattern of Shubnikov-de Haas oscillations for six samples of AlGaN/GaN heterostructures due to the spin-splitting of 2DEG have been observed. Two series of samples grown by metal-organic vapor phase epitaxy (MOVPE) were used in the study. One is undoped Al$_{x}$Ga$_{1-x}$N/GaN with different x values (x= 0.17, 0.29, 0.33), and the other is Fe-doped Al$_{x}$Ga$_{1-x}$N/GaN with the x values of 0.18, 0.19 and 0.21. The Shubnikov-de Haas measurements were performed at T = 0.3K for the magnetic field from 0.25 to 12 Tesla. The persistent photoconductivity (PPC) effect was used to vary the carrier concentration of the samples. The largest spin-splitting energy was observed on the sample of Fe-doped Al$_{0.21}$Ga$_{0.79}$N/GaN to be 5.96meV. After extended illuminated time, the carrier concentration of Fe-doped AlGaN/GaN increased at least 23{\%}; meanwhile the undoped AlGaN/GaN just produced 10.7{\%} increment at most. We found that the Fe-doped AlGaN/GaN exhibited higher PPC effect than the undoped samples. [Preview Abstract] |
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C1.00169: Magnetic Molecules on GaN: A Low Temperature STM Investigation Kendal Clark, D. Acharya, V. Iancu, E. Lu, A. Smith, S.-W. Hla Spin electron interactions involving magnetic molecules on semiconductor surfaces are of great interest for the development of molecular spintronic devices. Here, we studied structural and electronic properties of TBrPP-Co molecules deposited on a freshly grown nitrogen polar GaN (0001(bar)) surface using a scanning tunneling microscopy and spectroscopy at 4.6 K under ultra-high-vacuum conditions. On GaN (0001(bar)), the molecules bind to the surface via two molecular conformations: saddle and planar. STM images show self-assembled clusters of molecules on GaN (0001(bar)) surface. Within the self-assembled molecular clusters, the molecules are aligned either parallel or 90 degree rotated to each other. Scanning tunneling spectroscopy clearly reveals the HOMO and LUMO gap of the molecule within the bandgap of the GaN semiconductor. Molecular charge transfer is taking place within the system, shown by the shifting of the HOMO level of the molecule 0.4eV towards the valence band of the semiconductor. This work leads the way for future work of spin active molecules on semiconductor surfaces.. [Preview Abstract] |
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C1.00170: Investigation of the thickness of titanium dioxide by x-ray photoelectron spectroscopy A. Chourasia About 100 A of elemental titanium were deposited on silicon substrates using the e-beam technique. The films were exposed to a partial pressure of oxygen at 5 x 10$^{-7}$ Torr. The substrate temperature was maintained at 600$^{\circ}$C and the time of exposure was varied between 30 min and 3 hours. The oxidation of titanium as a function of the exposure time has been studied using the x-ray photoelectron spectroscopy technique. The magnesium x-radiation (energy = 1253.6 eV) has been used for this purpose. The titanium 2p and oxygen 1s regions have been investigated. The spectral data have been recorded at 45$^{\circ}$ take-off angle. The spectral data have been analyzed to estimate the thickness of the titanium dioxide formed on the substrate as a function of the exposure time. [Preview Abstract] |
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C1.00171: Synthesis and characterization of ruthenium dioxide nanorods Suman Neupane, Latha Kumari, Gary Kaganas, Wenzhi Li We report the synthesis of ruthenium dioxide (RuO$_{2})$ nanorods by chemical vapor deposition. The growth and morphology of the RuO$_{2}$ nanorods are determined by the flow rate and pressure of the oxygen gas. An oxygen flow rate of 600 sccm at atmospheric pressure (760 Torr) inside the reaction chamber results in high density pinetree-like nanorods, whereas oxygen flow rate of 300 sccm at pressure of 1 torr is favorable for the formation of club-shaped RuO$_{2}$ nanorod array. X-ray diffraction and high resolution transmission electron microscopy have indicated that the RuO$_{2}$ nanorods are of orthorhombic phase with rutile crystal structure. [Preview Abstract] |
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C1.00172: Electrical and Structural Characterization of Pulsed Laser Deposited High-k Dielectric Thin Films on Si and Ge Michelle Jamer, M. Alper Sahiner The thin film growth conditions are correlated with the local structure and the electrical properties in Hf$_{x}$Zr$_{1-x}$O$_{2 }$(x=0.25-0.90) high-k dielectric thin films on Si and Ge substrates. We used pulsed laser deposition (PLD) technique in preparation of the thin films. Thin film growth parameters such as partial oxygen pressure, substrate temperature, laser frequency were systematically varied and the response of the local structure and electrical properties of the resulting high-k dielectric thin films were monitored. The local structural information acquired from extended x-ray absorption spectroscopy (EXAFS) was correlated with the thin film growth conditions. EXAFS experiments were conducted at the National Synchrotron Light Source of Brookhaven National Laboratory. The competing crystal phases of oxides of Hf and Zr were identified and the intricate relation between the stabilized phase and the parameters as: the substrate temperature; Hf to Zr ratio; and the partial oxygen pressure were revealed. The capacitance versus voltage and capacitance versus frequency measurements were performed. EXAFS modeling and fitting will be presented and structure growth and capacitance response correlations will be presented. [Preview Abstract] |
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C1.00173: The emission of ion bursts from single crystal ZnO during 248-nm irradiation Demetrious Wilson, Enamul Khan, Steve Langford, Tom Dickinson Exposing chemical-vapor-transport grown, single crystal ZnO to 300 mJ/cm$^{2}$ pulses of 248-nm radiation (KrF excimer) produces occasional bursts of ion emission. This fluence is well below the threshold for optical breakdown near 500 mJ/cm$^{2}$, which we identify by the presence of 473-nm emission due to the 5s$^{2 3}$S$_{1}$ to 4s$^{1}$4p$^{1 3}$P$_{1}$ transition of excited neutral zinc. The principal ion was identified as Zn$^{+}$ by quadrupole mass spectroscopy. These ions are often accompanied by electrons to form a tenuous plasma. The bursts are not correlated with pulse-to-pulse fluctuations in laser intensity. We attribute these bursts to the accumulation of laser-produced defects during prolonged irradiation. When the defect density reaches a critical value, a burst is observed. [Preview Abstract] |
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C1.00174: Energy Transfer from an Electron-Hole Plasma layer to a Quantum Well in Semiconductor Structures S.K. Lyo We investigate the energy transfer mechanism and rates from an electron-hole plasma in a quasi-two-dimensional (2D) quantum well to an empty quantum well separated by a wide barrier. The rates are compared and contrasted with the 2D-2D transfer rates of classical excitons. The temperature dependence of the 2D-2D transfer rate of excitons is found to be strikingly different from that of electron-hole plasmas in general. The dependences of the rates on the carrier density, the center-to-center distance between the quantum wells, and the temperature are studied. [Preview Abstract] |
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C1.00175: Electric-pulse-induced resistive switching in Cr-doped Ti2O3 thin films Zhongwen Xing, Naijuan Wu, Alex Ignatiev The electrical-pulse-induced resistive switching effect is studied in (Ti0.85Cr0.15)2O3 (TCO) films grown on Ir-Si substrates by pulsed laser deposition. Such a TCO device exhibits bipolar switching behavior with an EPIR ratio as large as about 1000{\%} and threshold voltages smaller than 2V. The resistive switching characteristics may be understood by resistance changes of a Schottky junction composed of a metal and an n-type semiconductor, and its nonvolatility is attributed to the movement of oxygen vacancies near the interface. [Preview Abstract] |
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C1.00176: Magnetotransport properties and weak localisation in thin n-GaAs films A.M. Gilbertson, L.F. Cohen, A.K.M. Newaz, S.A. Solin A number of applications require nanoscale devices that retain diffusive transport for application e.g. devices based on the geometrical enhancement of classical properties for high resolution magnetic and electric field sensing [2,3], and the non-ballistic spin transistor. We recently reported on the properties of a 90nm thick GaAs film suitable for such high resolution sensing applications [4]. A dimensional crossover with respect to both WL and electron-electron interactions was observed in the temperature dependence of the conductivity and phase coherence length, respectively [4,5]. We extend this work by studying a further three GaAs films (70 nm, 110 nm and 200 nm) with equal doping density to the original 90nm film. It is demonstrated that proximity of the layer to the surface makes the film thickness an important parameter in determining the transport properties at high and low temperatures. \newline[2] S.A.Solin et al., APL 80, 4012 (2002). \newline[3] Y.Wang et al., APL 92, 262106 (2008). \newline[4] A.M.Gilbertson et al. APL 95, 012113 (2009). \newline[5] D.J.Newson et al.,Phil. Mag. B 52, 437 (1985). [Preview Abstract] |
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C1.00177: Experimental studies of Landau quantization in GaAs two-dimensional electron systems at low magnetic fields D.R. Hang, C.F. Huang, K.A. Cheng, Shih-Fang Chen The effects of Landau quantization are very important in two- dimensional electron systems (2DESs). Based on such quantization, it is well-established how to explain the quantum Hall effect by considering the localization effects under a high perpendicular magnetic field. On the other hand, the localization strength is reduced with decreasing the magnetic field. In this way, the semiclassical Shubnikov-de Haas (SdH) formula can become valid. To further understand the magnetic- field-induced crossover from the quantum Hall liquid to semiclassical transport, we performed the transport measurements on GaAs 2DESs at low magnetic fields. Semiclassical oscillations following SdH formula were observed under the formation of the localization-induced mobility gap. Our measurements revealed the difference between the bulk and edge transports in the low-field quantum Hall effect. From our study, the semiclassical-conducting and localized electrons can coexist in the 2DESs at low magnetic fields. [Preview Abstract] |
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C1.00178: Correlation-hole induced scillatory pfaffian states in even-denominator fractional quantum Hall effects Yuan-Ming Lu, Yue Yu, Ziqiang Wang A theory is developed for the paired even-denominator fractional quantum Hall states in the lowest Landau level. We show that electrons bind to quantized vortices to form composite fermions, interacting through an exact instantaneous interaction that favors chiral p-wave pairing. There are two canonically dual pairing gap functions related by the bosonic Laughlin wavefunction (Jastraw factor) due to the correlation holes. Remarkably,we find a new ground state lower in energy than the Moore-Read pfaffian for intermediate Coulomb interactions: a pfaffian with an oscillatory pairing function. We explore the unusual features and experimental implications of such a state. Connections to recent experiments are also discussed. [Preview Abstract] |
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C1.00179: Quantization of the Poynting vector in a magnetic field Keshav Shrivastava The flux quantization of the magnetic vector of the electromagnetic wave leads to the quantization of the Poynting vector. The electron-hole radiative interaction in a lattice leads to the formation of an electron-photon pair so that the electron moves along with the photon. The photon single-particle energy is flux quantized so that the flux quanta get attached to the electron. We find that e$^{2}$/hc$^{2}$ is also a fundamental constant just as h/e$^{2}$ is. Both the constants are in the dimensions of resistivity. [1] K. N. Shrivastava, AIP Conf. Proc.1017,47-56(2008); 1017, 422-428(2008); 1136, 469-473(2009); 1150, 59-67(2009); 1169, 48-54(2009). [Preview Abstract] |
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C1.00180: Critical Tunneling Currents in Quantum Hall Superfluids: Pseudospin-Transfer Torque Theory Jung-Jung Su, Allan H. MacDonald At total filling factor $\nu=1$ quantum Hall bilayers can have an ordered ground state with spontaneous interlayer phase coherence. The ordered state is signaled experimentally by dramatically enhanced interlayer tunnel conductances at low bias voltages; at larger bias voltages the inter-layer currents are similar to those of the disordered state. We associate this change in behavior with a Josephson-like critical current beyond which static inter-layer phase differences cannot be maintained, and examine the dependence of this critical current on sample geometry and on the phase stiffness and phase order parameters that characterize the system at long wavelengths. Our analysis is based in part on analogies between coherent bilayer behavior and spin-transfer torque physics in metallic ferromagnets. [Preview Abstract] |
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C1.00181: A Density Functional Theory Calculation Of The Oxygen Vibration Mode Frequencies In CdTe Wei Cheng, Lei Liu, Peter Yu, Z.X. Ma, Sam Mao The vibrational frequencies of oxygen impurity in CdTe have been calculated for a variety of oxygen environments using first-principle density functional theory. The local mode of an isolated oxygen atom substituting for Te is found to have a frequency of 331.86 cm$^{-1}$ as compared with the experimental value of 349.8 cm$^{-1}$. Two high frequency modes (at around 1104 cm$^{-1})$ have previously been identified with the vibrational modes of a complex consisting of a substitutional oxygen and a neighboring Cd vacancy. We found that the frequencies of such oxygen-complexes are far too low to explain the experimental results. In stead we found that the frequency of an oxygen molecule or dimmer located inside a Cd vacancy is in good agreement with experiment. [Preview Abstract] |
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C1.00182: First-principles Study of Hydrogen depassivation of Mg acceptor by Be in GaN Qiming Zhang, Xiao Wang, Chihsiang Wang The process of hydrogen depassivation of the acceptor by can convert the as-grown high-resistivity -doped into a - conducting material. A first-principles study on the process will be presented. The formation energies of various complex of impurities and point defects have been calculated and compared. The diffusion barriers of the hydrogen atom in the doped GaN have been obtained by the Nudge-Elastic-Band method. The results explain successfully the experimental observation that the hole concentration has been significantly enhanced in a Be-implanted Mg-doped GaN. [Preview Abstract] |
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C1.00183: Investigation of Threading Dislocations in Undoped and Doped AlN Epilayers by TEM B. Cai, M.L. Nakarmi Aluminum nitride (AlN) has emerged as a promising deep ultraviolet material for the development of deep ultraviolet optoelectronic devices such as light emitting diodes and photodetectors in the spectral range down to 200 nm. The characterization of threading dislocations and techniques to reduce the threading dislocations are crucial to improve the material quality and the performance of the devices. We report on the investigation of threading dislocations of AlN epilayers grown on sapphire substrates using transmission electron microscopy (TEM). Bright and dark field images of cross section and plan view images were taken to investigate the propagation and annihilation of threading dislocations. We found that the edge type threading dislocations dominate the total dislocation density. The threading dislocations are greatly reduced by inserting an intermediate layer. Microanalysis of doped AlN epilayers grown on AlN/sapphire templates is also performed. Comparative TEM analysis of the microstructures in connection to the generation and annihilation of threading dislocations due to the different dopants will also be presented. [Preview Abstract] |
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C1.00184: Defects in ZnO Nanoparticles Samuel Teklemichael, Matthew McCluskey Zinc oxide (ZnO) has a paramount potential for opto-electronic applications. In this work, we study defect properties of ZnO nanoparticles, grown by a solid-state pyrolytic reaction method, using IR spectroscopy. A series of IR spectral lines have been observed at liquid-helium temperatures with an acceptor hole binding energy of $\sim $ 0.4eV. Deuterium-grown samples reveal no isotopic shift for the lines, indicating they are electronic and not vibrational. Furthermore, electron paramagnetic resonance (EPR) showed lines at g = 1.96 and g = 2.003. The former is assigned as shallow donors, whereas the latter may be attributed to holes on oxygen atoms which surround zinc vacancies. [Preview Abstract] |
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C1.00185: DFT-based Theoretical Calculation of Nb- and W-doped Anatase TiO$_{2}$ Takahiro Suenaga, Hideyuki Kamisaka, Hisao Nakamura, Koichi Yamashita The structure and electronic states in the Nb-doped TiO$_{2}$ (TNO) and W-doped TiO$_{2 }$(TWO) in anatase phase were investigated from the first-principle using DFT-based band structure method. In addition to the cases where the dopant substituting a Ti atom, cells containing a dopant (M$_{Ti}$; M = Nb, W) and an oxygen vacancy (V$_{O})$ were calculated in order to clarify the role of the oxygen vacancy in the system. Furthermore, cells containing two dopants and an oxygen vacancy (2M$_{Ti}$--V$_{O})$, and cells with a dopant and two oxygen vacancies (M$_{Ti}$--2V$_{O})$ were calculated. Energetically stable structures were found among the sampled 2W$_{Ti}$--V$_{O}$ and W$_{Ti}$--2V$_{O}$ cells, while the corresponding structures in TNO did not show any significant energy stabilization. Impurity states were found in the stable 2W$_{Ti}$--V$_{O}$ and W$_{Ti}$--2V$_{O}$ structures, and an approach of the two W$_{Ti}$ atoms was observed in the former. The present results rationalize the lower electronic conductivity of TWO than that of TNO, and suggest possible formation of complex structures consisting of the W$_{Ti}$ dopants and the oxygen vacancies. [Preview Abstract] |
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C1.00186: The role of quantum confinement in $p$-type semiconductor InP nanocrystals Luis Tortajada, M.M.G. Alemany, Murilo L. Tiago, L.J. Gallego, James R. Chelikowsky We characterize the impurity state responsible for current flow in Zn-doped InP nanocrystals through first-principles calculations based on a real-space implementation of density-functional theory and pseudopotentials. We found the activation energy of the acceptor state to range from 0.03 eV in the bulk to 2.5 eV in smaller nanocrystals as a result of quantum confinement. The maximum value for nanocrystals is an order of magnitude larger than the maximum value found for InP nanowires (0.2 eV). Our results show that reducing the dimensionality in $p$-type InP materials strongly inhibits the capability of the materials to generate free carriers. [Preview Abstract] |
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C1.00187: Doping of BN Honeycomb structure: First-Principles Study Can Ataca, Ethem Akturk, Salim Ciraci Using first-principles density functional theory calculations, we have investigated the structural, electronic and magnetic properties of monolayer boron-nitride (BN) honeycomb structure which is functionalized by adatom adsorption and by substituting B and N atoms with foreign atom. We considered low and high density coverage of foreign atoms. Generally most of 3d transition metal atoms, some of group 4A, 5A, and 6A elements are bound with significant binding energy and modify the electronic structure of bare BN monolayer resulting in metallic, even half-metallic state. In low coverage case, the bands form by adsorbed atom are flat and charge is mostly localized on the adatom. The band structure of parent BN is not affected except localized states in the band gap. [Preview Abstract] |
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C1.00188: Hydrogen-Related Defects in Strontium Titanate Marianne Tarun, Matthew McCluskey Due to the presence of hydrogen in most as-grown crystals and their influence on the structural and electronic properties useful for device applications, efforts have been made to study hydrogen as an impurity in important compounds such as strontium titanate (SrTiO$_{3})$. Hydrogen forms a strong bond with oxygen, providing a powerful driving force for its incorporation in SrTiO$_3$. The resulting O-H bond gives rise to defects in SrTiO$_3$. Local vibrational modes (LVMs) of these O-H complexes are identified using IR absorption spectroscopy. Two O-H modes at 3355 and 3384 cm$^{-1}$ wavenumbers are observed after hydrogenation at 800$^{\circ}$C in sealed ampoules filled with H$_{2}$ gas. Isotope substitution experiments reveal that the defect consists of 2 H atoms. The thermal stability of the defect is determined through a series of isochronal annealing experiments. The observed LVMs are tentatively ascribed to a defect consisting of a Sr vacancy and 2 H atoms, each of which is bound to an O atom. This model explains the observed temperature dependent behavior of the frequency of the LVMs. [Preview Abstract] |
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C1.00189: Characterization investigation and evaluation of ESD robustness of high power light-emitting diodes Shih-Chun Yang, Pang Lin, Han-Kuei Fu, Chien-Ping Wang, Tzung-Te Chen, An-Tse Lee, Sheng-Bang Huang, Mu-Tao Chu This paper reports on the ability of high power light-emitting diodes (LED) to endure electrostatic discharge (ESD). The en-durance of ESD is a part of reliability of LED, especially in the horizontal structure of the insulating property of the sapphire substrate. Under the test of reverse-bias stress, the endurance of ESD is stronger as the leakage current of LED is smaller. Al-though many companies adopt the vertical structure which the substrate is conductive as their products, modification of the electrical properties of LED is an important subject in reliability engineering. [Preview Abstract] |
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C1.00190: Spin manipulation in a pulse-pumped double quantum dot with spin-orbit coupling Denis Khomitsky, Evgenii Sherman Dynamical processes in semiconductor quantum dots are of great interest due to the variety of physical phenomena and possible applications. When the spin-orbit coupling (SOC) is present, even simple systems such as single-electron quantum dots show a rich dynamics in the coupled charge and spin channels. This coupling is in the core of the proposal for a new technique to manipulate the spins in quantum dots by electric field [1,2]. We consider the full dynamics of an electron in a one-dimensional double quantum dot with SOC pumped by an external electric field. Here the tunneling between single quantum dots plays the crucial role in the low-energy states, and both the electron states and the tunneling are spin-dependent. The interplay of the irregular dynamics for spin and charge degrees of freedom is important for the entire system, demonstrating the abilities of a coherent spin manipulation. [1] E. I. Rashba and Al. L. Efros , Phys. Rev. Lett. \textbf{91}, 126405 (2003) [2] K.C. Nowack et al., Science \textbf{318}, 1430 (2007) [Preview Abstract] |
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C1.00191: Intrinsic disorder corrections to the anomalous Hall effect Alexey A. Kovalev, Yaroslav Tserkovnyak In the presence of delta-correlated Gaussian disorder, the Anomalous Hall effect acquires corrections due to side-jump and skew scattering processes. These corrections have no dependence on the strength of disorder resembling the intrinsic anomalous Hall effect. We formulate a general procedure for calculating such corrections in general non-interacting multiple-band systems. [Preview Abstract] |
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C1.00192: Coherent oscillations and giant edge magnetoresistance in singly connected topological insulators Rui-lin Chu A topological insulator has a pair of extended states at the edge in the bulk insulating regime. We study a geometry in which such edge states will manifest themselves in a qualitative manner through periodic oscillations in the magnetoconductance of a singly connected sample coupled to leads through narrow point contacts. Detailed calculations identify the parameters for which these oscillations are expected to be the strongest, and also show their robustness to disorder. Such oscillations can be used as a spectroscopic tool of the edge states. A large change in the device resistance at small B, termed giant edge magnetoresistance, can have potential for application. [Preview Abstract] |
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C1.00193: Magnetic and electronic properties of Mn acceptors in the (110) GaAs surface and subsurface layers P.M. Koenraad, J.K. Garleff, M. Bozkurt, A.P. Wijnheijmer, P. Struder, B. Bryant, N.J. Curson, C.F. Hirjibehedin, M.E. Flatt\'e Scanning tunneling spectroscopy and topography measurements were performed on Mn doped GaAs at low temperature and in high magnetic fields. Mn acceptors in the (110) surface and subsurface layers of gallium arsenide were identified and analyzed. The Mn induced spectroscopic features appearing in the bandgap region of GaAs were analyzed as a function of the depth of the Mn acceptor below the surface and showed a clear depth dependence. By accurately modeling the tip induced band bending the binding energy of a hole to a Mn acceptor could be determined and an increase of this binding energy was observed when the Mn acceptor approaches the surface. This result agrees with a recently reported enhanced binding energy, as observed by STM, for an electron bound to a Si donor that is close to a (110) GaAs surface and a theoretical predicted binding energy enhancement for Mn acceptors close to the (110) GaAs surface. The topographic features of Mn acceptors appearing at different depths below the surface were analyzed in magnetic fields up to 6 T perpendicular to the surface and up to 1 T in the plane of the of the surface. No change of the contrast was observed. [Preview Abstract] |
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C1.00194: Electron spin-polarization by means of Zeeman and Aharonov-Bohm effects in a double quantum dot ring Eric Hedin, Abigail Perkins, Yong Joe A mesoscale Aharonov-Bohm (AB) ring with a quantum dot (QD) embedded in each arm is studied with a tight-binding model for unique transmission properties arising from a combination of AB effects and Zeeman splitting of the QD energy levels. Theoretical analysis of this system has shown that resonance sharpening of the AB oscillation peaks occurs in a balanced ring near resonance, giving sensitive flux-dependence transmission [1]. Combining this effect with Zeeman splitting allows sensitive control of the spin-polarized output of the device. Weighted spin polarization results as a function of electron energy, perpendicular magnetic flux, parallel magnetic field, and QD coupling and energy levels are presented. In cases with perpendicular flux, the AB-oscillations exhibit non-periodicity, due to a flux-dependent shift in the QD energy levels via the Zeeman effect. \\[4pt] [1] E. R. Hedin, Y. S. Joe, and A. M Satanin, Jnl. of Computational Electronics, \textbf{7}, 280 (2008). [Preview Abstract] |
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C1.00195: Quasiparticle interference on the Surface of the topological Insulator Bi$_{2}$Te$_{3}$ Wei-Cheng Lee, Congjun Wu, Daniel P. Arovas, Shou-Cheng Zhang The quasiparticle interference of the spectroscopic imaging scanning tunneling microscopy has been investigated for the surface states of the large gap topological insulator Bi$_{2}$Te$_{3}$ through the T-matrix formalism. Both the scalar potential scattering and the spin-orbit scattering on the warped hexagonal isoenergy contour are considered. While backscatterings are forbidden by time-reversal symmetry, other scatterings are allowed and exhibit strong dependence on the spin configurations of the eigenfunctions at k points over the isoenergy contour. The characteristic scattering wavevectors found in our analysis agree well with recent experiment results. Ref: W.-C. Lee, C. Wu, D. P. Arovas, and S.-C. Zhang, arXiv:0910.1668 [Preview Abstract] |
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C1.00196: Ab-Initio Study of Magnetic Properties of Mn-doped MgSiN Jeffrey Rufinus The current interest in the field of semiconductor spintronics is mostly focused on transition metal-doped binary materials. Recently, however, the explorations of transition metal-dopd ternary semiconductors have gained attention, duel to experimental confirmations of possible high Curie temperature in chalcopyrite compounds. A density functional theory study was performed on Mn-doped ternary material MgSiN$_2$. Our results show Mn-doped MgSiN$_2$ to be antiferromagnetic for Mn$_{Mg}$ (Mn substitutes Mg site) and ferromagnetic for Mn$_{Si}$ (Mn substitutes Si site). [Preview Abstract] |
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C1.00197: Simulating manipulation of a single electron in quantum wells Lilia Meza-Montes, A. Rodriguez-Moreno, D. Hernandez-de-la-Luz The search of quantum-dot based qubits has led to recent experiments which allow the coherent manipulation of a single electron spin in quantum dots. In order to address this kind of experiments theoretically, we determine the time evolution of the movement of a single electron, described by a Gaussian packet, through a quantum well whose barrier heights depend on time. The entrance of the packet is obtained by lowering the left barrier, the trapping into the well by returning it to its original height, and finally the leaving is caused when the right barrier disappears. The time-dependent Schroedinger equation is solved within a finite-difference scheme. [Preview Abstract] |
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C1.00198: STM-based Interface Studies of Cobalt on Epitaxial Graphene on SiC(0001)-6H Andreas Sandin, Alex M. Pronschinske, Daniel B. Dougherty, J.E. (Jack) Rowe For the Co-graphene interface we found new surface-potential-derived interface states shifted differently on single monolayer and on bilayer graphene. Our graphene growth method is based on the high temperature annealing applied to bulk 6H-SiC(0001)-Si in a UHV Omicron/AFM/STM/ multi-probe system at NC State in the Physics Department. For undoped epitaxial graphene on SiC the intrinsic carrier doping is n-doped due to its interaction with the growth buffer layer of the SiC substrate, and its Dirac point lies $\sim $ 0.4 eV below the Fermi level. Gold overlayers have the effect of moving the Fermi level back down into the valence band so that the Dirac point moves into the unoccupied part of the local density of states.$^{2 }$Our results imply a doping charge increase for Cobalt on graphene which is opposite to that found for gold. 2. Gierz, I.; Riedl, C.; Starke, U.; Ast, C. R.; Kern, K., Atomic Hole Doping of Graphene. \textit{Nano Lett. }\textbf{2008,} $8$ (12), 4603-4607. [Preview Abstract] |
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C1.00199: Optical Signatures of Topological Insulators Ming-Che Chang, Min-Fong Yang The axion coupling in topological insulators couples electric polarization with magnetic field, and magnetization with electric field. As a result, the usual laws of electromagnetic wave propagation are modified. We report on the Fresnel formula for the reflection of electromagnetic wave at the interface of materials with different axion couplings. The Brewster angle and the Goos-H\"{a}nchen effect are also studied. We find that, because of the axion coupling, in order to realize the Brewster-angle condition, the incident polarization should be rotated away from the plane of incidence. The maximum angle of rotation is $\pi/4$ when both materials have nearly the same refraction indices. This offers a convenient way to determine the axion angle by optical measurement. [Preview Abstract] |
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C1.00200: Surface Fermi level and surface state density in GaAsSb surface intrinsic-$n^{+}$ structures by photoreflectance spectroscopy Kuang-I Lin, Jung-Tse Tsai, Ming-Hsun Lee, Pei-Chin Chiu, Shu-Han Chen, Jen-Inn Chyi, Jenn-Shyong Hwang The III-V ternary semiconductor GaAsSb has recently attracted considerable attention as the base layer of the high speed heterojunction bipolar transistors (HBT). Performance optimization of the HBT requires a precise determination of the surface state density and the surface Fermi level position of the GaAsSb alloy, but few such determinations have been reported. In this work, photoreflectance is employed to investigate the Fermi level pinning and the surface state density of a GaAs$_{0.65}$Sb$_{0.35}$ surface intrinsic-$n^{+}$ (SIN$^{+})$ structure based on the thermionic emission theory and the current-transport theory by the dependence of surface barrier height on the pump beam intensity. The surface state density is estimated as approximately 1.91 x 10$^{13}$ cm$^{-2}$, and the Fermi level is located 0.63 eV below the conduction band edge at the surface. The high surface state density leads the surface Fermi level to be strongly pinned within the bandgap demonstrated by sequential etching of the intrinsic layer. [Preview Abstract] |
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C1.00201: Autoionization resonance states of two-electron atomic systems with finite spherical confinement Yew Kam Ho, Sumana Chakraborty We investigate the lowest-lying $S$-wave resonant states of two-electron atoms confined by spherical quantum dots under the framework of the stabilization method. Extensive Hylleraas type wave functions taking into account of the correlation effects between all the charged particles are used in the present investigation. A finite oscillator potential is used to represent the spherical quantum dot confinement potential. We have obtained resonance energies and widths for the quantum confined two-electron atoms with different depths and various ranges of the quantum dot potentials. Oscillation in the resonance width as the dot size changes is observed, a result of quantum dot size effect similar to the phenomenon of the electric-field effect on hydrogenic impurity in a spherical quantum dot [1]. \\[4pt] [1] S. Sahoo, Y. K. Ho, Phys. Rev. B \textbf{69,} 165323 (2004); S. Sahoo, Y.C. Lin, Y. K. Ho, Physica E \textbf{40,} 3107 (2008) [Preview Abstract] |
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C1.00202: Nano-wire in a Magnetic Field N.J.M. Horing, J.D. Mancini We analyze the energy spectrum and propagation of electrons in a quantum wire on a $2D$ host medium in a normal magnetic field. Here, the Hamiltonian term representing the quantum (nano) wire has the form of a one-dimensional Dirac delta function. We derive the associated Schr\"{o}dinger quantum-wire Green's function in closed form. The energy spectrum is then determined by examination of the frequency poles of the Green's function, with Landau-quantization-like splintering of levels. [Preview Abstract] |
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C1.00203: Quantum Magnetic Field Effects on the Spectrum of a Double Dot System N.J.M. Horing, J.D. Mancini This work is concerned with electron states and propagation in a two-dimensional quantum double-dot system embedded in a two-dimensional host sheet subject to Landau quantization. In particular, the dynamical Green's function and energy spectrum are evaluated with the two dots represented by Dirac delta function potentials. The integral equation for the double-dot Schr\"{o}dinger Green's function is solved in closed form in terms of the infinite sheet Green's function for two-dimensional electrons subject to Landau quantization with no quantum dots. The dispersion relation for the double dot sub-band energies is obtained by analyzing the (frequency) poles of the Green's function. The proliferation of energy levels due to Landau quantization is examined in detail. [Preview Abstract] |
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C1.00204: Collective properties of excitons in the presence of a two-dimensional electron gas Oleg Berman, Godfrey Gumbs, Patrick Folkes We have studied the collective properties of two-dimensional (2D) excitons in a quantum well (QW) which contains 2D excitons and a two-dimensional electron gas (2DEG). We also analyzed the excitations for a system of 2D dipole excitons with spatially separated electrons and holes in coupled quantum wells (CQW) when one of the wells contains a 2DEG. Calculations of the superfluid density and the Kosterlitz-Thouless (K-T) phase transition temperature for the 2DEG-exciton system in a QW have shown that the K-T transition temperature increases with increasing exciton density and that it might be possible to have fast long range transport of excitons. The superfluid density and K-T transition temperature for dipole excitons in CQW in the presence of a 2DEG increase with increasing inter-well separation. [Preview Abstract] |
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C1.00205: Enhanced Electroluminescence and efficiency droop behavior of direct current aged InGaN-based light-emitting diodes Tzung-Te Chen, Han-Kuei Fu, Chien-Ping Wang, Shih-Chun Yang, An-Tse Lee, Sheng-Bang Huang, Mu-Tao Chu, Han-Yu Shih, Yang-Fang Chen The enhancement of electroluminescence from the various direct current aged InGaN-based light-emitting diodes (LEDs) is presented. It is found that the light output intensity of the aged LED shows an enhancement of about 150{\%} at low driving current density compared with that of the original LEDs. The efficiency increases and the peak-efficiency-current shifts toward lower magnitude of the aged LEDs with increasing the stressing time. Since the EL enhancement issue is inherently an efficiency problem, the physics origin of the efficiency droop behaviors and the increased EL intensity could be highly related. [Preview Abstract] |
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C1.00206: The influence of crystallographic orientation on the optical properties of wurtzite InGaN/GaN quantum wells Stanislav Khatsevich, Daniel Rich, Ofer Moshe We have examined the effects of crystal orientation on the properties of excitonic emission from wurtzite InGaN/GaN quantum wells (QWs) with piezoelectric polarization using exciton binding and transition energy calculations. We show numerical results for the band gaps, effective heavy-hole masses, piezoelectric polarizations and fields, exciton wavefunctions, exciton binding and transition energies and radiative lifetimes of excitonic emission as a function of the QW crystallographic growth planes. Band-edge and effective-mass parameters for a continuum of GaN crystallographic orientations, on which InGaN/GaN QWs are grown, were obtained from In-composition- and strain-dependent \textbf{\textit{k$\cdot $p}} calculation for InGaN, using the \textbf{6$\times $6} \textbf{\textit{k$\cdot $p}} Hamiltonian in appropriate {\{}\textit{hkil}{\}} representations. We have performed calculations for a continuum of technologically relevant QW growth planes {\{}$h-h$0$l${\}} oriented at various angles relative to the (0001) $c$-plane. The decrease of the electric field in the InGaN/GaN QW growth direction leads to an increased exciton transition energy and oscillator strength, which results in an increase of the exciton binding energy and decrease of the excitonic radiative lifetime. These results indicate that InGaN/GaN QW materials grown on{\{}$h-h$0$l${\}}-oriented planes in a wide variety of angles can be used for optimized operation of optoelectronic devices. [Preview Abstract] |
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C1.00207: Low-energy magnetoabsorption spectra of graphite Jei Wang, Min Fa Lin The low-energy magnetoabsorption spectra of bulk graphite are investigated by the Peierls-coupling tight-binding method. According to the depicted wave functions, the Landau levels are divided into two groups when the fingerprints of the wave functions are under consideration. These Landau levels lead to some band-edge states along $K-H$ direction. The main contribution to absorption peaks originates from the states in the vicinity of the $H$ and $K$ points. The absorption frequencies of Landau peaks exhibit the $\sqrt B $ dependence at the $H$ point while those of states at $K$ point show $B$ dependence. The square-root divergent peaks due to the additional $k_z $-dependent energy dispersion are much different from the case of few-layer graphene. We derive regular frequency-dependent absorption rates and composite field-dependent frequencies in this work. The relationship between the magneto-optical properties and electronic structures are explored. The selection rules can be reasonably explained by the characteristics of the wave functions. [Preview Abstract] |
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C1.00208: First-principles study of GaAs nanowires Seymur Cahangirov, Salim Ciraci We present a systematic study of the atomic and electronic structure of GaAs nanowires using first-principles pseudopotential calculations. We consider six different types of nanowires with different diameters all grown along [111] direction and reveal interesting trends between cohesive energy and nanowire type with varying diameters. Generally, the average cohesive energy of nanowires with wurtzite stacking is higher than those with zinc blende stacking for small diameters. We found that most of the bare nanowires considered here are semiconducting and continue to be semiconducting upon the passivation of surface dangling bonds with hydrogen atom. However, the surface states associated with the surface atoms having two dangling bonds in zinc blende stacking occur in the band gap and can decrease the band gap to change the nanowire from semiconducting to metallic state. These nanowires become semiconducting upon hydrogen passivation. Even if the band gap of some nanowires decreases with increasing diameter and hence reveals the quantum confinement effect, generally the band gap variation is rather complex and depends on the type and geometry, diameter, type of relaxation and also whether the dangling bonds of surface atoms are saturated with hydrogen. [Preview Abstract] |
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C1.00209: Confinement of electrons in size modulated silicon nanowires Seymur Cahangirov, Salim Ciraci Based on first-principles calculations we showed that superlattices of periodically repeated junctions of hydrogen saturated silicon nanowire segments having different lengths and diameters form multiple quantum well structures. The band gap of the superlattice is modulated in real space as its diameter does and results in a band gap in momentum space which is different from constituent nanowires. Specific electronic states can be confined in either narrow or wide regions of superlattice. The type of the band lineup and hence the offsets of valence and conduction bands depend on the orientation of the superlattice as well as on the diameters of the constituent segments. Effects of the SiH vacancy and substitutional impurities on the electronic and magnetic properties have been investigated by carrying out spin-polarized calculations. Substitutional impurities with localized states near band edges can make modulation doping possible. Stability of the superlattice structure was examined by ab initio molecular dynamics calculations at high temperatures. [Preview Abstract] |
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C1.00210: Electroluminescence and Photoluminescence of Microcavity Exciton-Polaritons Na Young Kim, Wolfgang Nitsche, Lianda Yan, Sven Hoefling, Alfred Forchel, Yoshihisa Yamamoto Microcavity exciton-polariotns, half-light and half-matter quasi-paritlces, have been studied extensively for about last two decades because the inherent nature as a mixture of cavity photons and quantum well excitons provides a unique testbed to explore fundamental nature of physics. Recently, there have been increasing efforts to build photonic devices using microcavity exciton-polaritons. An essential step toward practical devices is to establish efficient electrical pumping scheme. Here we compare optical properties of GaAs-based microcavity exciotn-polartions in terms of electrical versus optical pumping schemes, and we address a promising design of a microcavity wafer to improve electrical pumping efficiency. [Preview Abstract] |
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C1.00211: Suppression of quadrupole polariton generation due to large $\chi^{(3)}$ effect in Cu$_2$O Shahin Mani, Joon Jang, John Ketterson Cuprous oxide (Cu$_2$O) is a dipole-forbidden semiconductor exhibiting a vanishing second-order nonlinear susceptibility and a large third-order nonlinear response.$^1$ We employ resonant two-photon excitation to create quadrupole polaritons in this semiconductor aiming at the Bose-Einstein condensation of polaritons. Generally, to observe this quantum phase transition, high optical excitations at low temperature is essential. Using a Z-scan setup, we explore the resonant two- photon generation of polaritons in Cu$_2$O at 2K. Our results suggest that the third-harmonic generation of the incident light severely limits the polariton density at high excitation levels. Based on the measured nonlinear optical parameters, the experimentally achievable polariton density is estimated. \newline \newline [1] S. Mani, J. I. Jang, and J. B. Ketterson, Opt. Lett. {\bf 34}, 2817 (2009). [Preview Abstract] |
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C1.00212: Solution-based \textit{in-situ} synthesis and fabrication of ultrasensitive CdSe photoconductors Nelson Coates, Liang Li, Daniel Moses Solution-based semiconductor device fabrication offers the advantages of low cost, large area coverage, control of morphology, and simplified doping. Here, we present a novel solution-based \textit{in-situ} synthesis and film fabrication method demonstrated for CdSe films, where both the quantum dot (QD) synthesis and bulk film formation occurs simultaneously on a substrate in ambient atmosphere. The films fabricated using this method exhibit high photoconductive gain while retaining a relatively high signal bandwidth. We will present the synthetic route, as well as our studies of steady-state and transient photoconductivity that elucidate the mechanisms underlying the photoconductive gain and the role of carrier density on the carrier transport [Preview Abstract] |
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C1.00213: METALS |
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C1.00214: \textit{Ab-initio} calculations on the energetics of vacancies in $\alpha $-Fe under strain field Eric Sanchez, Sergio Orozco, Zhengzheng Chen, Nicholas Kioussis \textit{Ab-initio} calculations have been carried out to investigate the energetics of vacancies in $\alpha $-Fe under external deformation. We found that volumetric compression has a significant effect on the energetics of vacancies. The formation energy of mono-vacancy decreases with increasing compression monotonically. The $<$111$>$ di-vacancies experience a binding-repelling transition when volumetric compression exceeds 13.2{\%}. On the other hand, uniaxial deformation has weaker influence on the formation and binding energies. However, this type of deformation distinguishes $<$001$>$ di-vacancies: those which are parallel to the strain have larger (smaller) binding energies than those perpendicular ones under compression (expansion). Our results indicate that external strain field is a key factor to modulate the concentration of vacancy and/or vacancy clusters in $\alpha $-Fe. [Preview Abstract] |
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C1.00215: Synthesis of nanoporous platinum thin films by dealloying copper from Cu$_{80}$Pt$_{20}$ Aditya Abburi, Brandon Fosso, Eric Colegrove, W.J. Yeh Nanoporous structures with high active surface areas are critical for a variety of applications. We demonstrate the synthesis of nanoporous platinum thin films by dealloying. Dealloying is a corrosion process in which one or more elements are selectively removed from an alloy leading to a 3-dimensional porous structure of the more noble element. Cu$_{80}$Pt$_{20}$ films ($\sim $100--250~nm thick) are formed by cosputtering and dealloyed in aqueous H$_{2}$SO$_{4}$ solutions to selectively remove copper while allowing self-assembly of platinum into a nanoporous structure. The platinum nanoporous layers have a pore size of 20--100~nm, a surface area enhancement $>$20 times. Applications for these structures range from high surface area electrodes for biomedical sensors to use as skeletal structures for fundamental studies (e.g. low temperature heat exchangers or sensitivity of surface diffusivity to chemical environment). In this work we will review our current method of synthesis of the alloy thin film and include our most recent results demonstrating porosity in Pt. [Preview Abstract] |
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C1.00216: Fabrication of all-metal strained bimorphs by controlling the stress in titanium-tungsten sputtered thin films Yehya Senousy, Cindy Harnett The strain architecture technique has been used recently to fabricate out-of-plane micro and nanostructures. Applications of such structures include actuators and microcoils for antenna applications. These free standing structures have been fabricated using bilayer films with strain mismatch. Materials used for the bilayer films included GaAS/InGaAs, Si/SiGe and oxide/metal layers. In this paper, we introduce a new fabrication method for these out-of-plane microcoils. The method depends on obtaining a bilayer film by controlling the stress in titanium-tungsten (TiW, 10 wt.{\%} Ti) thin films deposited under two different conditions. The stress control is achieved by varying the pressure of the argon gas during sputtering. The stress of the majority of metal films sputtered is tensile including TiW. As the pressure of the argon gas decreases, an increase in ``atomic peening'' increases the compressive stress in the TiW film. This characteristic of TiW allows the use of different substrates, like silicon, glass, GaAs and plastics, to obtain free standing and out-of-plane structures. [Preview Abstract] |
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C1.00217: Growth instabilities at oblique incidence deposition; a detailed comparison between experiment and simulation Bene Poelsema, Frits Rabbering, Herbert Wormeester We report on a combined experimental and simulational study of super Poisson roughening at grazing incidence deposition of Cu on Cu(001). The experimental results have been obtained using high resolution electron diffraction. The Ehrlich-Schwoebel barrier and details of the long range attractive interaction potential, used in the simulation were obtained by comparison of calculations with experimental data. Using these data we obtain distinct similarities between simulation and experiments at temperatures and polar angles of incidence ranging from, respectively, 230-270 K and 40-85$^{\circ}$. The formation of quite well ordered ripple patterns, oriented perpendicular to the plane of incidence, at initial coverages is followed by a rotation of the ripple patterns by 90$^{\circ}$ towards parallel to the incident plane for thicker films. Accurate incorporation of both interlayer mass transport and steering are key to this result. [Preview Abstract] |
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C1.00218: A necessary and sufficient condition for non-zero longitudinal magnetoresistance Hridis Pal, Dmitrii Maslov While conventional wisdom predicts zero longitudinal magnetoresistance (LM) in any material owing to the fact that the Lorentz force on a charge carrier acts perpendicular to the applied magnetic field and hence should not affect its motion in the direction of the field, numerous experiments show otherwise. We find that the origin of non-zero LM, in the simplest model, can be attributed to the Fermi surface topology. It is shown that, as a minimal requirement for non-zero LM, presence of anisotropy in the spectrum is essential, although not all types of anisotropy can give rise to the non-zero value, thus requiring anisotropy to be present in a special way. We derive a necessary and sufficient condition for the spectrum to show non-zero LM and discuss its implications. [Preview Abstract] |
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C1.00219: Growth structure and superconductivity of Bi$_{1.7}$Bi$_{0.3}$Sr$_{2}$Ca$_{2}$Cu$_{3}$O$_{10+\delta }$ ceramics synthesized from glass-crystal precursors processed in solar type ovens J.V. Acrivos, D.D. Gulamova, J.G. Chigvinadze, D. Loy The growth structure as well as the superconductivity of Bi/Pb2223 alloys is reported. Periodic lattice distortions (PLD) along the ab plane diagonal, direction of superconducting transport at the transition temperature, $T_{c}$=107K are found to dominate the growth. Trransport induced by the PLD may be responsible for the sharp T$_{c}$ transitions, and the bursts of frequency and Abrikosov oscillations observed above the transition temperature up to 150K. Chemical synthesis in a heliostat oven was followed by fast quenching of the melt and annealing at 840-850K, XRD near the Cu K-edge, and T$_{c}$ measured by axial-torsional vibrations in transverse magnetic fields. T$_{c}$ and phaase purity obtained by green solid state chemistry, in a solar spectrum, will be discussed. [Preview Abstract] |
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C1.00220: Calculation for the Work Function of Metal Cluster Chin-Sheng Wu We use the density functional theory to calculate the electronic structure of small metallic clusters. The charge difference between the electron density of Friedel oscillation and positive background builds up the barrier-work function, which confines the electron gas inside clusters. The exchange correlation potential is also taken into account. The calculations for various metallic densities are performed. [Preview Abstract] |
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C1.00221: Electronic, structural, and thermodynamic properties of mixed actinide dioxides (U, Pu, Am) O$_{2}$ from hybrid density functional theory Li Ma, Asok K. Ray As a continuation of our studies of pure actinide metals using hybrid density functional theory,\footnote{R. Atta-Fynn and A. K. Ray, Europhysics Letters, \textbf{85}, 27008-p1- p6 (2009); Chemical Physics Letters, \textbf{482}, 223-227 (2009).} we present here a systematic study of the electronic and geometric structure properties of mixed actinide dioxides, U$_{0.5}$Pu$_{0.5}$O$_{2}$, U$_{0.5}$Am$_{0.5}$O$_{2}$, Pu$_{0.5}$Am$_{0.5}$ O$_{2}$ and U$_{0.8}$Pu$_{0.2}$O$_{2}$. The fraction of exact Hartree-Fock exchange used was 40{\%}. To investigate the effect of spin-orbit coupling on the ground state electronic and geometric structure properties, computations have been carried out at two theoretical levels, one at the scalar-relativistic level with no spin-orbit coupling and one at the fully relativistic level with spin-orbit coupling. Thermodynamic properties have been calculated by a coupling of first-principles calculation and lattice dynamics. [Preview Abstract] |
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C1.00222: A Hybrid DFT Description of the Ground State Properties of Americium-I Raymond Atta-Fynn, Asok Ray Americium-I (Am-I) is a strongly correlated metal which has been determined experimentally to be a non-magnetic, double HCP crystal with well-localized 5$f$ electrons. However, theoretical descriptions of Am-I based on density functional theory (DFT) yield the correct structural properties but the wrong magnetic ground state and a very poorly described 5$f$ electron spectra. In this work, we will show that hybrid DFT, which replaces a fraction (40{\%} to be exact) of approximate DFT exchange with exact Hartree-Fock (HF) exchange, yields structural, magnetic, and electronic properties of Am-I which are in excellent agreement with experimental data. The primary reason why DFT fails to describe Am-I, namely the overestimation of the exchange interaction leading to a spin-polarized ground state, and how this failure is corrected by hybrid DFT, will be discussed. [Preview Abstract] |
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C1.00223: Color prediction of transition metal nitrides by ab-initio methods Jinwoong Kim, Seung-Hoon Jhi, Do Seok Han, Seung Gyun Ahn Transition metal nitrides have been used as decorative coating materials because of their high hardness and lustrous color. While the electronic structure of these materials is relatively well understood, their color and its variation by defects are still considered as a topic in the area of empirical approach. Here we present a procedure for color-prediction from first principles. Both the intraband and the interband transitions are considered to determine the optical properties and the color. The dielectric function and the reflectivity of the compounds are calculated and then used to obtain the RGB color codes. It is found that calculating the screened plasma frequency and the metal d band correctly is critical to reproduce the color observed in experiment. The effects of interstitial defects are also discussed. [Preview Abstract] |
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C1.00224: The half-metallicity of the Co$_{2}$FeSi full Heusler alloy in bulk, clean surface and interfaces with Si ; first-principles investigation Miyoung Kim, Hanjo Lim, Jaeil Lee We report the \textit{ab-initio} calculational results on the half-metallicity of Co$_{2}$FeSi full Heusler alloys in bulk, (001) surfaces and interface with Si. Employing the +U corrections within the FLAPW[1] method, we investigate the effect of correlation interaction on half-metallicity and magnetic properties. For bulk, the +U approach reproduces experimental values of the minority spin band gap and total spin magnetic moment. The (001) surfaces and interfaces with Si are calculated to be metallic by both LDA and GGA due to the surface and interface states developed at E$_{F}$. Upon +U correction, the Co-terminated clean surface recovers half-metallicity with a reduced band gap (0.40 eV) from the bulk value while the rest of the systems are still metallic, which can be explained by the correlation and hybridization effects. [1] E. Wimmer, H. Krakauer, M. Weinert, and A. J. Freeman, PRB \textbf{24}, 864 (1981). [Preview Abstract] |
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C1.00225: First-principles Calculations of Ideal Tensile and Shear Strengths for Gum-Metal Approximants Naoyuki Nagasako, Michal Jahnatek, Ryoji Asahi, J\"urgen Hafner A newly developed bcc-type Ti-23Nb-0.7Ta-2Zr-O (mol{\%}) alloy named Gum-Metal showed unusual properties including ultralow elastic modulus, ultrahigh strength, super-elastic-like behavior, and super-plastic-like behavior, in particular, accompanied by dislocation-free plastic deformation. [1]. As proposed in first-principles calculations, one of the requirements for the Gum-Metal is dramatic softening of the elastic shear modulus C'=(C11-C12)/2 $\sim $ 0, which happens at a valence electron concentration around 4.24. We also study ideal tensile and shear strengths for Gum-Metal approximants to understand microscopic origin of such unique mechanical properties. The most stable Gum-metal approximant among all the possible 1820 atomic configurations of Ti12Nb4 has been determined, and showed good agreement with the experimental elastic constants of Gum-Metal.\\[4pt] [1] T. Saito et al., Science 300, 464 (2003). [Preview Abstract] |
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C1.00226: Crack propagation in a gold crystal with and without the presence of an interface Majid Karimi, Carl LeBlond, Ted Kaplan The Embedded Atom Method (EAM) is used to study crack propagation in Au crystals and at an AuNi interface.~ The interface is constructed with an appropriate number of dislocations introduced to compensate for the lattice mismatch between Au and Ni crystals.~ Once the the stability of the interface is established, a starter crack is introduced and its properties are determined and compared with those of pure Au and Ni crystals.~ The massively parallel molecular dynamics code (lammps) is used for these studies. [Preview Abstract] |
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C1.00227: Phase-field modeling of coupled dynamics of dislocation and hydrogen density fields in BCC iron based on first principles calculation Hideki Mori, Hajime Kimizuka, Shigenobu Ogata We construct a numerical model of the coupled evolution of hydrogen-concentration and defect fields in iron based on a phase-field (PF) microelasticity theory, with coupling of the long-range elastic interactions and short-range chemical interactions that control hydrogen and dislocation motion. To obtain the physical parameters included in the PF free-energy functional, the interaction energy between a hydrogen atom and dislocation core, the hydrogen-concentration dependence of misfit energy and eigenstrains are quantitatively determined using density-functional-theory (DFT) calculations. Based on these data, we investigate a time evolution of the hydrogen-dislocation interactions under applied external stress. For atomic interaction between hydrogen and dislocation core, it is observed that hydrogen concentration distribution is affected by the motion of dislocation. [Preview Abstract] |
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C1.00228: QUANTUM FLUIDS AND SOLIDS |
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C1.00229: Path-integral Monte Carlo Study on Weakly-Coupled $^4$He Superfluids Yongkyung Kwon, K. Birgitta Whaley We have performed path-integral Monte Carlo calculations to analyze the dynamics of flow between two weakly-coupled $^4$He superfluids, employing a system of $^4$He atoms inside a tube whose diameter and length are an order of a few nanometers. The two $^4$He superfluids separated by a wall in the middle of the tube are connected to each other through an array of apertures created in the wall. For the case of a single aperture it is found that the local suppression of superfluidity near the wall is greatly dependent on the size of the aperture hole. The superfluid fraction computed through the local decomposition of the winding number estimator is reduced to about 30\% at $T=0.6 $ K near the aperture hole with the diameter of 4~\AA~while it is hardly suppressed at all when the diameter of the hole is as large as 8~\AA. For the case of an array of apertures, we investigate the effects of aperture-aperture coupling on the local superfluidity by varying the inter-aperture distance. The velocity-velocity correlation function is computed to analyze the correlation among the superflows through the different apertures. These results are discussed in relation with the synchronous phase slippages observed in recent experiments of Packard {\it et~al.} for an array of apertures connecting two reservoirs of superfluid $^4$He. [Preview Abstract] |
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C1.00230: Solid helium nanometer inclusions in LiNbO$_{3}$ Avishai Ofan, Lihua Zhang, Ophir Gaathon, Sasha Bakhru, Hassaram Bakhru, David Welch, Yimei Zhu, Richard M. Osgood Jr. He implantation is a reoccurring technique in a variety of fabrication strategies for microelectronic and optical devices. Because of its extremely low solubility in crystals, impurity He atoms are known to nucleate and accumulate as bubbles in metals which can result in the build up of extremely high pressures near the crystal's theoretical shear strength. It is of interest to extend the understanding of the atomic-scale He inclusions in complex oxides, which offer a wide variation in mechanical and unusual ionic and dielectric properties. We show, using high-resolution-TEM of He-implanted LiNbO$_{3}$, that He inclusions in LiNbO$_{3}$ hold extremely high pressure, and are probably at solid phase. In addition, the energetically favored shape of the inclusions is spherical and not oblate as predicted by elastic theory. When annealed, the spherical He bubbles migrate and accumulate into a nonoblate thick bubble due to preferred pyramid-twinning-system orientation. [Preview Abstract] |
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C1.00231: A RF Preamplifier Design For Low Temperature NMR Experiments. Sung Su Kim, Chao Huan, Larry Phelps, Jian-Sheng Xia, Neil Sullivan, Donald Candela It was reported by several research groups that the recently discovered possible supersolid state of solid ${ }^4$He has strong correlations with the presence of ${ }^3$He impurities and other defects. These observations aroused new interest in the NMR study of solid ${ }^4$He doped with ${ }^3$He. However, the extremely low concentration of ${ }^3$He (less than 100 ppm) and the long nuclear spin lattice relaxation times in the interested regime lead to a challenging task to achieve detectable NMR signals. We present a new design for a low temperature preamplifier working with a crossed-coil NMR probe. This preamplifier reduces the noise temperature to 1 K at a sample temperature as low as 250 mK when it is thermally anchored to the mixing chamber of a dilution refrigerator. With an adapted design, we are able to cool down the sample to about 10 mK and keep the noise temperature well below 4 K. [Preview Abstract] |
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C1.00232: PHYSICS OF BEAMS |
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C1.00233: ABSTRACT WITHDRAWN |
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C1.00234: A New Look at Cross Sections Richard Kriske The author presents a new view on the calculations of cross- sections for the interaction of particles, in particle the increase of cross section that can be achieved by slowing particles down. [Preview Abstract] |
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C1.00235: HIGH PRESSURE PHYSICS |
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C1.00236: Formation of New Carbon Structure under Quasi-Hydrostatic High Pressure Minseob Kim, Jing-Yin Chen, Choong-Shik Yoo The crystal structure of single wall carbon nanotubes (SWNT) has been studied using synchrotron x-ray diffraction to 15 GPa as well as, of the recovered samples, using transmission electron microscope (TEM) at the ambient pressure. While the majority of SWNT remains unchanged upon the pressure cycling, the recovered samples also exhibit new carbon species about $\sim $2-3 {\%} in forms of amorphous carbon bundles with various sizes of carbon onions. The structure of the recovered species varies depending on the pressure-transmitting medium, from highly crystalline in N$_{2}$ and He to highly disordered in Ne. In this paper, we will discuss the crystal structure of several pressure-treated SWNT samples as observed in x-ray diffraction and in relations with the TEM images. [Preview Abstract] |
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C1.00237: Pressure-induced amorphization and polyamorphism in TiO$_{2}$-B nanoribbons Quanjun Li The phase transitions of TiO$_{2}$-B nanoribbons were investigated with synchrotron X-ray diffraction and the Raman spectroscopy. Our results have shown PIA occurred in TiO$_{2}$-B nanoribbons upon compression, resulting in a high density amorphous (HDA) form related to the baddeleyite structure. Upon decompression, the HDA form transforms to a low density amorphous (LDA) form while the samples still maintain their pristine nanoribbon shape. HRTEM image reveals that the LDA phase has an $\alpha $-PbO$_{2}$ structure with short range order. We propose a homogeneous nucleation mechanism to explain the PIA for the TiO$_{2}$-B nanoribbons. Our study demonstrates that PIA and polyamorphism occurred in the one-dimensional (1D) TiO$_{2}$ nanomaterials for the first time and provides a new method for preparing 1D amorphous nanomaterials from crystalline nanomaterials. [Preview Abstract] |
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C1.00238: Constitutive Description of Large Elastic Deformations in Diamond and Silicon Crystals from First-Principles M. Salvetti, S. Duchenne, D.M. Parks, N. Marzari Within a continuum approach, the prediction of the mechanical response of single crystals at large elastic deformations relies on the accurate description of the strain energy density function \textit{$\Psi $}. The coupling of hydrostatic and deviatoric terms at high compressions is of particular interest for applications, and the effect is generally not taken into account by current models available in the literature [1,2]. We present a general approach that leads to the construction of strain energy density functions of cubic single crystals based on data obtained from density functional theory (DFT) calculations. We connect the deformation-induced energy changes and Cauchy stress calculated from DFT calculations to the Lagrangian description frequently adopted within the continuum theory of hyperelasticity [3]. In particular, we adopt a coordinate--free invariant formulation [4] that intrinsically preserves the properties of the cubic symmetry group. We present results on diamond and silicon single crystals, and highlight both similarities and striking differences. [1] R.G.Veprek \textit{et. al}, \textit{Mater. Sci. Eng. A} \textbf{4248}, 366-378 (2007) [2] B.P Gearing, L. Anand, \textit{Int. J. Solids Struct.} \textbf{41}, 827-845 (2004) [3] A.N. Norris, \textit{J. Mech. Mater. Struct.} \textbf{3}, No.2, 243-260 (2008) [4] J.P. Boehler, \textit{Z. Angew. Math. Mech}. \textbf{59}, 157-167 (1979) [Preview Abstract] |
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C1.00239: Crystal Structure and Lattice Dynamics of Fe-Si Alloys under High Pressure Yi Zhang, Ravhi Kumar, Zackari Fisk, Yuming Xiao, Michael Hu, Paul Chow, Andrew Cornelius, Changfeng Chen The crystal structure and lattice dynamics of Fe-Si alloys under high pressures up to 115 GPa are studied by first- principles density functional theory (DFT) calculations. Our results agree well with the X-ray diffraction and nuclear inelastic x-ray scattering experiment. The calculated thermodynamic properties and sound velocities give new insights to the studies of Earth's core. [Preview Abstract] |
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C1.00240: BIOLOGICAL PHYSICS |
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C1.00241: Spindle Checkpoint Regulated by Non-Equilibrium Collective Spindle-Chromosome Interaction; Relationship to Single DNA Molecule Force-Extension Formula Leif Matsson The spindle checkpoint, which blocks segregation until all sister chromatid pairs have been stably connected to the two spindle poles, is perhaps the biggest mystery of the cell cycle. The main reason seems to be that the spatial correlations imposed by microtubules between kinetochores and nonlinear dependence on the increasing number of such kinetochores, have been disregarded in earlier studies. From these missing parts a non-equilibrium collective spindle-chromosome interaction is obtained for budding yeast (\textit{Saccharomyces cereviciae}) (\textit{J. Phys. Cond. Matter} \textbf{21} (2009) 502101). The interaction, based on a non-equilibrium statistical mechanics, senses and counts the stably attached kinetochores and senses the threshold for segregation. It blocks segregation until all sister chromatids pairs are bi-oriented, regulates tension such that segregation is synchronized, explaining how the cell might decide to segregate replicated chromosomes. It also predicts kinetochore oscillations at a frequency which agrees well with observation. Finally, a relationship between this interaction and the force-extension formula of a single DNA molecule is obtained. [Preview Abstract] |
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C1.00242: ABSTRACT WITHDRAWN |
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C1.00243: Nucleation Dynamics of Particles with Directional Interactions Toni Perez, Amit Chakrabarti, James D. Gunton Protein aggregation is a subject of many studies both experimentally and theoretically since many diseases are related to undesirable protein condensation. Proteins can be modeled as globular particles with highly directional interactions. A simple model that describes this kind of protein consist of patchy particles whose interactions depend on the orientation of the patches on the surface of each particle [1]. Recently the phase diagram of a six-patch model has been reported showing the existence of different ordered phases [2]. In this work, we discuss the dynamics of the nucleation and growth process of the six-patch model using Brownian dynamics simulations. In particular we study the kinetics of the process by which chains form and ultimately collapse to spherical droplets.\\[4pt] [1] N. Kern and D. Frenkel, J. Chem. Phys. 118, 9882 (2003)\\[0pt] [2] H. Liu, S. K. Kumar and J. F. Douglas, Phys. Rev. Let. 103, 018101 (2009) [Preview Abstract] |
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C1.00244: The symmetries of interacting helices of charge Jonathan Landy, Joseph Rudnick Many important biological molecules are helical in shape. In vivo, these molecules are often highly charged and thus strongly repel. In certain instances, however, they are found to be packed at high density. This results in systems with a high degree of coupling between lattice packing structure and internal molecular symmetry. We present various results of a symmetry based analysis of the pair interaction. In particular, we provide a new perspective on a previously obtained result by Kornyshev and Leikin [1]: the pair interaction is a nowhere continuous function of the angle between charges on a single helix. 1. A.A. Kornyshev and S. Leikin, Biophys. J. 75 (1998). [Preview Abstract] |
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C1.00245: Mimicking the folding pathway to improve homology-free protein structure prediction Karl Freed, Joe DeBartolo, Andres Colubri, Abhishek Jha, James Fitzgerald, Tobin Sosnick Since demonstrating that a protein's sequence encodes its structure, the prediction of structure from sequence remains an outstanding problem that impacts numerous scientific disciplines including many genome projects. By iteratively fixing secondary structure assignments of residues during Monte Carlo simulations of folding, our coarse grained model without information concerning homology or explicit side chains outperforms current homology-based secondary structure prediction methods for many proteins. The computationally rapid algorithm using only single residue (phi, psi) dihedral angle moves also generates tertiary structures of comparable accuracy to existing all-atom methods for many small proteins, particularly ones with low homology. Hence, given appropriate search strategies and scoring functions, reduced representations can be used for accurately predicting secondary structure as well as providing three-dimensional structures, thereby increasing the size of proteins approachable by homology-free methods and the accuracy of template methods whose accuracy depends on the quality of the input secondary structure. Inclusion of information from evolutionarily related sequences enhances the statistics and the accuracy of the predictions. [Preview Abstract] |
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C1.00246: Multi-field C-13 NMR Relaxation Study of the Tripeptide Glycine-Proline-Glycine-NH$_{2}$ John Shibata, Mary Forrester T$_{1}$ and T$_{2}$ C-13 NMR relaxation measurements were performed on the tripeptide Gly-Pro-Gly-NH$_{2}$ on 300 MHz, 500 MHz, and 800 MHz NMR instruments (1). T$_{1}$ and T$_{2}$ data at different field strengths were analyzed to reveal the internal dynamics of this tripeptide. The results are compared to the classification scheme of rigidity by Anishetty, et al. (2). The dynamics of the tripeptide at different carbons in the molecule probe the site-specificity of the motions. We compare the dynamics revealed at the glycines with the dynamics in the proline ring. These motions are also being studied by molecular dynamics using the molecular modeling program Tinker (3). (1) Measurements at 500 MHz and 800 MHz were performed at the Alabama High Field NMR Center, University of Alabama at Huntsville, Huntsville, AL. (2) Anishetty, S., Pennathur, G., Anishetty, R. BMC Structural Biology \textbf{2}:9 (2002). http://www.biomedcentral.com/1472-6807/2/9. (3) Dudek, M. J., Ramnarayan, K., Ponder, J. W. J. Comput. Chem. 19, 548 (1996). http://dasher.wustl.edu/tinker. [Preview Abstract] |
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C1.00247: Insights into the Opening and Closing Dynamics of Biotin Carboxylase Brian Novak, Dorel Moldovan, Grover Waldrop, Marcio de Queiroz Biotin carboxylase (BC) is a homodimer which catalyzes biotin carboxylation. A reaction is thought to occur in one monomer at a time (half-sites reactivity). BC can also function as a monomer. Evidence has shown that the B domain moves with hinge motion of 45\r{ } between an unliganded form and one with bound ATP, suggesting that some of the energy from ATP hydrolysis might be harnessed to do useful work. The free energy along a closure angle for the B domain was calculated using MD simulations for a monomer and dimer with and without one bound ATP. We found that the monomer favors a closed state with or without ATP with mean times for opening much smaller than the reaction time, and the most stable structure for the dimer without ATP was with both monomers open. For the dimer with ATP, opening the B domain without ATP caused the other B domain to open, but hysteresis was observed when closing it, preventing an accurate calculation. The data suggest that the most stable state has both sides closed, supporting the idea of half-sites reactivity. [Preview Abstract] |
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C1.00248: ABSTRACT WITHDRAWN |
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C1.00249: Thermal and Chemical Denaturation of Staphyloccocal Nuclease: A Dynamic Light Scattering Study William Oliver III, Wesley Stites, Elaine Christman, Amee Salois, Lauren Clark, Nathan Tobey Thermal and chemical denaturation data are presented from dynamic light scattering (DLS) experiments in which both wild-type and a quadruple mutant form of the small globular protein staphylococcal nuclease (SN) were studied. Previous studies on this particular mutant, known as mutant 62, indicate it has a smaller solvent- accessible surface area, and hence, more compact denatured state than wild-type SN. We performed DLS experiments at temperatures from $23^{\circ}$C--$55^{\circ}$C for dilute solutions of SN in buffer for GuHCl concentrations from 0--2 M. Diffusivities were measured and protein sizes were calculated. A dramatic increase in protein size occurs at temperatures ranging from $44.4^{\circ}$C -- $53.0^{\circ}$C as the GuHCl concentration was increased. Protein size is also dependent on GuHCl concentration at temperatures below this dramatic denaturation event. These and other results will be presented as well as their implications for the existence of intermediate states and models for denaturation in this system. [Preview Abstract] |
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C1.00250: An efficient variational method to study the denaturation of DNA induced by superhelical stress Daniel Jost, Ralf Everaers Many fundamental biological processes, like transcription or replication, need the opening of the double-stranded DNA. One common way to control the local denaturation is to impose superhelical stress to the DNA using protein machineries. To describe superhelical effect for circular molecules, Benham introduced a model where the standard thermodynamic description of base-pairing is coupled with torsional stress energetics. Here, we introduce an efficient mean-field approximation of the Benham model. Our self-consistent solution is confident and computationally-fast, compared to the full treatment of the model. In particular, our formulation allows to compute the probability of bubble formation for given length and position along the sequence. Evolution of this probability as a function of the superhelical stress could inform us on the ability for organisms to control the strength of superhelicity acting on their genomes. [Preview Abstract] |
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C1.00251: Microstructural Phase Changes of DPPC-Ergosterol Supported Membranes Stressed by Ethanol Juan Vanegas, David Block, Roland Faller, Marjorie Longo Microstructure of DPPC-Ergosterol supported lipid bilayers (SLBs) stressed by ethanol is examined at the nanoscopic level using atomic force microscopy (AFM). Alcohols such as ethanol are known to cause changes in the phase behavior of phospholipids as well as inducing the formation of an interdigitated phase of reduced thickness, where the hydrophobic tails of the top and bottom lipids intercalate causing an increase in the area per lipid as well as the solvent exposed surface of the headgroups. SLBs composed of 75-100 mole {\%} 1,2-Dipalmitoyl-sn-Glycero-3-Phosphocholine (DPPC) and 0-25 mole {\%} ergosterol were deposited on mica through the vesicle deposition method. In order to observe the ethanol-induced phase changes that can be observed in free bilayers, the vesicles must be prepared in buffer solution containing ethanol. The presence of salt is required to reduce the effect of the strong interaction between the bilayers and the support, which in the absence of ethanol and salt induces the formation of a tilted phase similar to the interdigitated phase in DPPC bilayers deposited above the melting temperature. As previously observer by other groups, ethanol-induced changes in SLBs often require heating above the transition temperature after addition of ethanol, or sample preparation in the presence of the alcohol. The later method was used as it produces more consistent results and the observations agree well with the previously reported phase diagram of DPPC-Ergosterol with ethanol. [Preview Abstract] |
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C1.00252: Rapid Formation of Supported Lipid Bilayers on Unfavorable Surfaces under AC-Electric Fields Benxin Jing, Y. Elaine Zhu Lipid vesicles and supported bilayers have been studied as model systems to understand the structures, transport and biological function of cell membranes. In this work, we investigate the AC-electric field induced instability and supported bilayer formation of lipid vesicles on unfavorable solid surfaces by fluorescence microscopy. We have designed a microchannel fluid cell with embedded asymmetric electrode surfaces to apply non-uniform AC-electric fields across lipid vesicle thin films and control the formation of supported lipid bilayers of mixed egg PC/1,2-dioleoyl-3-trimethylammonium-propane(DOTAP) on solid substrates. In the absence of applied AC-fields, we observe no formation of supported lipid bilayers of egg PC/DOTAP on a quartz surface coated with a monolayer of 11-Mercaptoundecanoic acid. In contrast, we observe the rapid spreading of egg PC/DOTAP lipids from the edge of the gold electrode to the thiol-treated quartz surface to form lipid bilayers of varied morphology under applied AC-fields of varied frequency from 1-100 kHz. A strong dependence of AC-field frequency and strength on the lipid spreading velocity and resulting morphology of lipid bilayers is quantified. The mechanism involving AC- induced counterion redistribution and lipid segregation is also experimentally explored. [Preview Abstract] |
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C1.00253: Electrophoretic Mobility of Sarcoplasmic Reticulum Vesicles is determined by Amino Acids of A+P+N Domains of Ca$^{2+}$-ATPase Laura Satterfield, Robert Word, Jonathan Abramson, Pavel Smejtek It was found that the electrophoretic mobility of sarcoplasmic reticulum (SR) vesicles originates from ionizable amino acids of cytoplasmic domains of the Ca$^{2+}$-ATPase, the Ca$^{2+}$ pump of SR. The mobility was measured at pH 4.0, 4.7, 5.0, 6.0, 7.5, and 9.0 in the region of ionic strength from 0.05 to 0.2 M. Mobility data were supplemented by studies of SR vesicles by photoelectron microscopy. The mobility data were analyzed using Helmholtz-Smoluchowski model. The charge of the SR vesicles is dominated by the charge of the Ca$^{2+}$-ATPase. The charge is due to ionized amino acids obtained from the amino acid sequence of Ca$^{2+}$ pump, pKa and pH. It was shown that a linear relationship exists between the mobility and the total charge on three cytoplasmic domains of Ca$^{2+}$ pump: A, P, and N. The relationship between mobility, $\mu $, and the charge of A, P, N domains of the Ca$^{2+}$ pump, Q, is $\mu =\alpha +\beta $*Q where $\beta $ = 0.033 $\pm $ 0.002 mu/e and $\alpha $ = 0.11 $\pm $ 0.02 mu. The mobility unit, mu = 1x10$^{-8}$ m$^{2}$-V$^{-1}$-s$^{-1}$. [Preview Abstract] |
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C1.00254: Self-assembly of Amphiphilic Nanotubes and Lipids into Synthetic Vehicles: Computer Simulation Study Meenakshi Dutt, Olga Kuksenok, Steven Little, Anna C. Balazs Via Dissipative Particle Dynamics (DPD) approach, we study the self-assembly of amphiphilic nanotubes and lipids immersed into a hydrophilic solvent. Each nanotube encompasses an ABA triblock architecture, with a hydrophobic stalk and two hydrophilic ends. Individual lipids are composed of a hydrophilic head group and two hydrophobic tails. We show that an energetically unfavorable interaction between the solvent and the hydrophobic segments of the nanotube and the lipids drive them to self-assemble so as to shield the hydrophobic entities from the hydrophilic solvent. The equilibrium self-assembled structures formed depend upon the concentrations of the lipids and nanotubes, the hydrophobic fraction of the nanotube, the degree of hydrophobic mismatch between the nanotube and the bilayer, and the presence of hydrophilic end-tethers. We isolate the conditions that promote the formation of specific equilibrium self-assembled structures. The simulations are supported by free energy calculations for the amphiphilic nanotube-lipid-solvent system. Ultimately, these self-assembled structures of nanotube-lipid systems can be used for making hybrid control release vehicles. [Preview Abstract] |
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C1.00255: Characterization of Self-Forming Liposomes Zephyr McCormick, Rajan Bista, Aaron Covington We are currently using Raman spectroscopy to investigate thermodynamic phase transitions of self-forming liposomes, trademarked QuSomes {\texttrademark}. A Renishaw InVia Raman microscope system is used to acquire Raman spectra using a low-power argon ion laser (514.5 nm). A temperature-controlled sample holder is used to vary the temperature between -4 and 110\r{ }C. Spectral indications of phase transitions are seen. Techniques to examine mechanical properties of liposome formation, as well as size distribution and separation, are being developed. Preliminary data will be presented. [Preview Abstract] |
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C1.00256: Interruptions between the triple helix peptides can promote the formation of amyloid-like fibrils Avanish Parmar, Eileen Hwang, Barbara Brodsky It has been reported that collagen can initiate or accelerate the formation of amyloid fibrils. Non-fibrillar collagen types have sites where the repeating (Gly-Xaa-Yaa)n sequences are interrupted by non- Gly-Xaa-Yaa sequences, and we are investigating the hypothesis that some of these interruptions can promote amyloid formation. Our experimental data show that model peptides containing an 8 or 9 residue interruption sequence between (Gly-Pro-Hyp)n domains have a strong propensity for self association to form fibrous structures. A peptide containing only the 9-residue interruption sequence forms amyloid like fibrils with anti-parallel $\beta $ sheet. Computational analysis predicts that 33 out of 374 naturally occurring human non-fibrillar collagen sequences within or between triple-helical sequences have significant cross-$\beta $ aggregation potential, including the 8 and 9 residue sequences studied in peptides. Further studies are in progress to investigate whether a triple-helix peptide promotes amyloidogenesis and whether amyloid interferes with collagen fibrillogenesis. [Preview Abstract] |
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C1.00257: A simple electrostatic model applicable to biomolecular recognition T. P. Doerr, Yi-Kuo Yu An exact solution is presented for a model consisting of a layer of high dielectric constant material ({\em e.g.}, water) of varying thickness separating two regions of low dielectric constant material ({\em e.g.}, DNA, RNA, protein) in each of which is embedded a point charge. While the presence of the screening layer always lowers the energy for indentical charges compared to the case of an infinite medium of low dielectric constant, the presence of a sufficiently thick screening layer also lowers the energy compared to the case of an infinite medium of {\em high} dielectric constant. The behavior of the energy leads to a substantially increased repulsive force. For charges of opposite sign, the screening layer always lowers the energy compared to the case of an infinite medium of either high or low dielectric constant. The attractive force in this case is weaker than in an infinite medium of low dielectric constant material but stronger than in an infinite medium of high dielectric constant material. The presence of this behavior, which we name asymmetric screening, in the simple system presented here confirms the generality of the behavior that was established in a more complicated system of an arbitrary number of charged dielectric spheres in an infinite solvent. [Preview Abstract] |
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C1.00258: Studies of Amyloidogenic Peptide Dynamics by Dielectric Relaxation Spectroscopy Fioleda Prifti, Donald Barry, Izabela Stroe Recent theoretical studies\footnote{F. Despa et al., J. Biol. Phys. (2008) 34, 577} show that amyloidogenic peptides associate to form oligomers through long-range hydrophobic attractions. When peptides aggregate in larger composites, their hydrophobic patches are buried inside the newly formed amyloidogenic assembly. This gradually changes their interactions with the surrounding water molecules. The various amyloidogenic structures can then be differentiated based on the partition of the interface water and the dielectric signal of water. Here, we present dielectric relaxation spectroscopy measurements of amyloidogenic (human IAPP and A$\beta $ (1-42)) and non-amyloidogenic (rat IAPP and A$\beta $ (1-42) scrambled) peptides over a frequency range of 10$^{-3}$ to 10$^{7}$ Hz, at different concentrations (5-100 $\mu $M), and over a large incubation time interval (0-220 h). In comparing the dielectric response of the amyloidogenic and non-amyloidogenic peptides, we find that it varies from peptide to peptide. Our experimental results also reveal a shift in the dielectric response as a function of time and concentration for each peptide. We attribute these variations in the dielectric signal to structural changes that affect the surrounding and cage water associated with the amyloid aggregates. Our results are in agreement with theoretical predictions. [Preview Abstract] |
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C1.00259: Spatial organization and segregation of two self-avoiding polymers in a closed cylindrical pore Youngkyun Jung, Bae-Yeun Ha We present some results on the spatial organization and segregation of two self-avoiding polymers trapped inside a closed cylindrical pore, obtained using molecular dynamics simulations. Closed cylindrical confinement is shown to play a unique role in influencing chain miscibility and segregation dynamics. Our diagram for chain miscibility shows that under strong confinement chains segregate better, if they are shorter and the con?ning space is more asymmetric; when applied to bacterial chromosomes, it implies that chromosome miscibility depends on how they are structured inside the cell. Finally, longitudinal con?nement is also shown to have nontrivial effects on segregation dynamics; it can signi?cantly slow down segregation despite a shorter distance for each chain to travel to partially segregate. [Preview Abstract] |
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C1.00260: \textit{In vivo} fluorescence fiber-optic microscopy of superfast Ca$^{2+}$ transients in syrinx muscles Anal\'{I}a Dall'As\'en, Jorge M\'endez, Franz Goller Optical techniques in conjunction with fluorescent markers have revolutionized the investigation of dynamical cellular processes, such as studies of calcium ion (Ca$^{2+})$ dynamics in muscles. Recently, it was shown that songbirds have superfast syringeal muscles, which can modulate song acoustics up to 250~Hz. Such rapid contraction cycles most likely require very rapid Ca$^{2+}$ kinetics. We developed a technique to measure Ca$^{2+}$ transients in syringeal muscles of anesthetized birds with a custom-built endoscope. The fluorescence measurements were carried out before and after applying a calcium indicator dye and while muscles were stimulated electrically. The results show fast ($\sim $50-ms FWHM) and superfast~($\sim $7-ms FWHM) Ca$^{2+}$ transients. The strongest signals were observed 30-40 minutes after applying the dye. This study confirms that rapid Ca$^{2+}$ transients in syringeal muscles facilitate superfast contraction kinetics and demonstrates the feasibility of this optical technique as a biosensor for detecting fluorescence signals of muscular calcium activity on a ms timescale of living animals. [Preview Abstract] |
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C1.00261: A Simple System for Long-Term 3D Tracking of Quantum Dot Probes in Live Cells Brian Long, Tania Vu The intracellular signaling of G-protein coupled receptors is governed in part by their location and transport on the cell surface and within the cytosol. Bright and relatively photostable fluorescent nanocrystal quantum dot (QD) probes are well-suited for investigation of the spatial dynamics of membrane receptor proteins, including their membrane diffusion, internalization, and intracellular transport. A major obstacle to obtaining long-term information on receptor dynamics with microscopy is that QD probes can only be tracked for as long as they remain within the depth of field of the microscope. We have implemented a simple and flexible 3D tracking system that requires only an epifluorescence microscope, computer control of a piezo-driven stage and an EMCCD camera. We demonstrate 100-200 nm z-position accuracy over a 10 micron depth for 10s of minutes, with temporal resolution of 7.2s per (x,y,z) coordinate. These capabilities allow measurement of QD probe positions for durations relevant to the long-term signaling dynamics of membrane receptors. We will present the application of this system to measuring the spatial dynamics of QD-membrane receptor probes for long durations in live cells. [Preview Abstract] |
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C1.00262: Regulatory Biophysics From Sequence Data Anand Murugan, Justin B. Kinney, Curtis G. Callan Jr., Edward C. Cox We demonstrate a new technique for probing the function of a regulatory sequence, using ultra-high-throughput sequencing to generate large data sets of the activity of mutant sequences. An information theoretic data analysis technique is then used to model the activity, avoiding assumptions about noise in the experiment. We apply this technique to the well studied \emph{lac} promoter in \emph{E coli.} and characterize the specificities of the DNA binding proteins in physical units and infer their \emph{in vivo} interaction energy. [Preview Abstract] |
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C1.00263: Receptor clustering: delicate balance between beneficial signal amplification and detrimental noise amplification. Gerardo Aquino, Robert Endres The bacterial chemotaxis pathway allows cells to sense minute changes in chemical concentration, implying highly accurate sensing. This accuracy is believed to arise from signal amplification by receptor clusters, formed predominantly at the bacterial cell poles. However, receptor clustering should also have detrimental affects on the accuracy of sensing. First, random fluctuations in chemical concentration are amplified in addition to the signal. Second, due to the proximity of receptors in clusters, previously bound (and sensed) ligand molecules are likely to rebind the same or a nearby receptor, increasing the measurement uncertainty. Here, we investigate both the beneficial and detrimental effects of receptor clustering on the accuracy of sensing. Our preliminary findings suggest an optimal complex size, amplifying signals but avoiding saturation by noise. Our findings may help explain the recently proposed receptor cooperativity of 10-20 receptors based on in vivo FRET data. [Preview Abstract] |
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C1.00264: Systems Biology of Clostridium Acetobutylicum: Sugar Metabolism and TNT Reduction Margaret Hurley, Christian Sund, Matthew Servinsky Rapid advancements in biotechnology are expected to impact multiple areas of interest to the Army, including decontamination, degradation of toxic chemicals and biofuels. This project is a joint experimental/computational effort to map out the metabolic pathways in Clostridium acetobutylicum, and use this information to develop a systems biology model of this system. This organism has been chosen specifically due to the fact that it has potential application to both biofuel production and nitroaromatic degradation. It is hoped that a systems biology model may provide key information to enhance both of these processes. Details will be presented of a first-generation model of central carbon metabolism in C. Acet., developed upon gene expression data accumulated from bacteria grown on different carbohydrate sources. Additional work will discuss the effect of TNT exposure and potential relevant enhancements of the model. [Preview Abstract] |
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C1.00265: Origin and Spatial Distribution of Forces in Motile Cells Josef A. Kas, Claudia Brunner, Michael Goegler, Allen Ehrlicher, Daniel Koch, Thomas Fuhs, Charles Wolgemuth A fundamental step in cell migration is the advancement of the cell's leading edge. It is generally accepted that this motion is driven by actin polymerization against the plasma membrane but this has not been directly measured. Our SFM measurements together with drugs that stimulate or inhibit actin polymerization or myosin contractility create a map of the magnitude, direction, and origin of the dynamic intracellular forces. We resolve that the force generating mechanism at the leading edge is indeed actin polymerization, and we directly measured the force associated with the retrograde flow within the lamella, critically demonstrating that the protrusion forces are decoupled from the cell body and are generated exclusively at the leading edge. Actin-mediated myosin contractility is primarily responsible for cell body and substrate force generation. These quantitative and polymer specific measurements presented here offer essential insight into the movement of cells, which is an important prerequisite for cancer metastasis and nerve regeneration. [Preview Abstract] |
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C1.00266: System dynamics of non-diffusively coupled oscillators Lauren Lazarus, Joseph Tranquillo Many physical systems are composed of multiple oscillators which when coupled tend to synchronize. In many systems, coupling is assumed to be bidirectional and diffusive, which in phase space acts to strongly attract limit cycles to one another. Our simulations explore the impact of other forms of coupling, such as synaptic, phase and transient coupling which also occur in physical systems and can have a profound impact on system dynamics. For example, when we transformed two unit oscillator into Cartesian coordinates and coupled only one state variable, the limit cycles collapsed to equilibrium points. We have also found bifurcation routes to and from limit cycles when the FitzHugh-Nagumo and Hindmarsh-Rose neuron models were coupled via unidirectional synapses which do not occur when the cells are coupled diffusively. The underlying reason for these differences is that non-diffusive coupling may be alternately attractive and repulsive at various phases of the limit cycles. These results suggest that the type of coupling can be just as important in determining system behavior as the dynamics of the individual oscillators. [Preview Abstract] |
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C1.00267: Single-molecule tracking of DNA and actin Kejia Chen, Stephen Anthony, Bo Wang, James Kuo, Steve Granick Our newly-developed particle-tracking methods enable us to track not only center-of-mass position, as is classical to do, but also internal degrees of freedom. This is illustrated in studies of how actin filaments diffuse through entangled actin networks and also how lambda-DNA diffuses through entangled actin network. In both cases, we track configurational rearrangements of the moving objects, in movies consisting of time series with thousands of sequential images. The algorithm developed is generic enough to be applied to other systems with irregular-shaped objects. [Preview Abstract] |
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C1.00268: Effect of c-Met Inhibitor on HGF-induced Ovarian Carcinoma Cell Migration Chun-Min Lo, Jun-Chih Lo, Kay-Pong Yip The dysregulation of hepatocyte growth factor (HGF) and its receptor, c-Met, in cell migration contributes to tumor invasion and metastasis in numerous cancers including ovarian cancer. Specific inhibitors against HGF/c-Met signaling like SU11274, therefore, may have important therapeutic potential for the treatment of cancers. Here, we applied electric cell-substrate impedance sensing (ECIS) and traction force microscopy to evaluate the effect of SU11274 on HGF-treated SKOV-3 ovarian cancer cells. Our results showed that, compared with control cells, HGF-treated cell monolayer displayed lower junctional resistance between cells, larger cell-substrate separation, and higher cell micromotion. In addition, individual HGF-treated SKOV-3 cells demonstrated weaker traction forces on the collagen-coated polyacrylamide substrate than did control cells. These changes lead to faster directional movement of HGF-treated cells, as demonstrated with wound healing assay. Treatment of SKOV-3 cells with SU11274 indicated significant inhibition of HGF stimulation on all assays tested. [Preview Abstract] |
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C1.00269: A Mathematical Analysis of of Second Messenger Compartmentalization in Neurons Wen Chen, Herbert Levine, Wouter-Jan Rappel Recent experiments in hippocampal neurons have demonstrated the existence of compartments with elevated levels of second messenger molecules. This compartmentalization is believed to be necessary to ensure signaling specificity. Here we use analytical and numerical techniques to investigate the diffusion of a second messenger in the soma and the dendrite of a neuron. We obtain analytical solutions for the diffusion field and examine the limit in which the width of the dendrite is much smaller than the radius of the soma. We find that both the degradation rate and the width of the dendrite play a critical role in determining the concentration within the two compartments. [Preview Abstract] |
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C1.00270: ABSTRACT WITHDRAWN |
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C1.00271: How electroshock weapons kill! Marjorie Lundquist Growing numbers of law enforcement officers now carry an electroshock weapon (ESW). Over 500 U.S. deaths have followed ESW use in the past 26 years; over 450 of these deaths followed use of an electromuscular disruptor in the past 9 years. Most training courses teach that ESWs are safe; that they can kill only by the direct effect of electric current on the heart; and that a death following use of an ESW always has some {\it other} cause. {\bf All these teachings are false!} The last was disproved by Lundquist.$^1$ Williams$^2$ ruled out direct electrical effects as a cause of almost all the 213 deaths he studied, leaving disruption of normal physiological processes as the only alternative explanation. Careful study of all such deaths identifies 4 different ways that death has or could have been brought about by the ESW: kidney failure following rhabdomyolysis [rare]; cardiac arrest from hyperkalemia following rhabdomyolysis [undocumented]; lactic acid-induced ventricular fibrillation [conclusive proof impossible]; and [most common] anoxia from so much lactic acid in the circulating blood that it acts as an oxygen scavenger, continuously depleting the blood of oxygen until most of the lactate has been metabolized. $^1$M. Lundquist, {\bf BAPS 54}(1) K1.270(2009). $^2$Howard E. Williams, {\bf Taser Electronic Control Devices and Sudden In-Custody Death}, 2008. [Preview Abstract] |
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C1.00272: Non-neutral theory of biodiversity: Bose-Einstein condensation in ecosystems Ginestra Bianconi, Luca Ferretti, Silvio Franz We present a non-neutral stochastic model for the dynamics taking place in a meta- community ecosystems in presence of migration. The model provides a framework for describing the emergence of multiple ecological scenarios and behaves in two extreme limits either as the unified neutral theory of biodiversity or as the Bak-Sneppen model. Interestingly, the model shows a condensation phase transition where one species becomes the dominant one, the diversity in the ecosystems is strongly reduced and the ecosystem is non-stationary. This phase transition can be mapped to a Bose- Einsetin condensation and extend the principle of competitive exclusion to open ecosystems. These framework might be relevant for the study of the impact of invasive species in native ecologies. [Preview Abstract] |
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C1.00273: Noise can speed up solitary waves in population genetics Oskar Hallatschek While the deterministic behavior of solitary waves is well-understood, their noisy counterparts are still somewhat enigmatic. The current consensus is that number fluctuations due to discreteness substantially reduce the velocity of a traveling solitary wave. Here, we show that the very same fluctuations can sometimes increase the wave speed. In fact, we describe a new class of solitary waves whose velocity goes to zero as the noise vanishes (i.e., in the deterministic limit). The fluctuations due to discreteness drive these waves, and give them a finite velocity. We calculate the wave velocity analytically as a function of noise strength, and compare with simulations. The presented class of solitary waves naturally occurs in the context of genetics. They describe, for instance, the spread of a mutation that increases the dispersal rates or the carrying capacity. We discuss the biological implications of our results. [Preview Abstract] |
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C1.00274: The effects of temperature and magnetic flux on electron transport through a four-channel DNA model Sunhee Lee, Eric Hedin, Yong Joe The temperature dependence of the conductivity of lambda phage DNA has been measured by Tran \textit{et al} [1] experimentally, where the conductivity displayed strong (weak) temperature dependence above (below) a threshold temperature. In order to understand the temperature effects of electron transport theoretically, we study a two-dimensional and four-channel DNA model using a tight-binding (TB) Hamiltonian. The thermal effects within a TB model are incorporated into the hopping integral and the relative twist angle from its equilibrium value between base-pairs. Since these thermal structural fluctuations localize the electronic wave functions in DNA, we examine a temperature-dependent localization length, a temperature-driven transmission, and current-voltage characteristics in this system. In addition, we incorporate magnetic field effects into the analysis of the transmission through DNA in order to modulate the quantum interference between the electron paths that comprise the 4-channel structure. [1] P. Tran, B. Alavi, and G. Gruner, PRL \textbf{85}, 1564 (2000). [Preview Abstract] |
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C1.00275: Behavior of Amphiphilic Helix-Bundle based Peptide-Polymer Conjugates in Solution and at the Air-Water Interface Jessica Shu, He Dong, Yu-Ja Huang, Ting Xu Amphiphilic peptide-polymer conjugates are a desirable class of materials because they combine the precise chemical structure and functionality of biomolecules, the stability and processibility of synthetic polymers, and the ability to self-assemble into interesting hierarchical nanostructures in solution. As one of the most important motifs underlying many of the functionalities found in natural proteins, coiled-coil helix bundles present unique opportunities to generate functional materials with structures and functionalities similar to those seen in nature. Here, we present fundamental studies, both in solution and at the air-water interface, of amphiphilic helix-bundle based conjugates, where an alkane tail is appended to the N-termini of 3- and 4-helix bundle-forming peptides, and PEG chains are coupled to the exterior of the bundle. Liquid surface reflectivity of Langmuir monolayers indicates that PEG changes the 2D packing behavior of the conjugates, and preliminary DLS and SAXS indicate that they form spherical micelles with diameters in the range of 10 nanometers. Fundamental understanding of the structures that these novel materials form and the interactions that guide their assembly are necessary for controlling multi-length scale assembly in multi-component systems, and may also lead to very unique function biomolecular materials. [Preview Abstract] |
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C1.00276: Modification of solid state nanopore characteristics through chemical etching Edward Graef, Changbae Hyun, Mourad Benamara, Jiali Li Solid state nanopores have been shown to detect the passage of single biomolecule translocations by monitoring the changes in current passing through the nanopore under an applied voltage. One of the key issues is the resolution limitations due to the thickness of the nanopore. This research is centered on the monitoring and modification of the thickness and diameter of the nanopore itself for increased resolution of detecting biomolecules. Through the use of wet etching with phosphoric acid, the thickness as well as the diameter of the nanopore can be modified to change the resolution for single biomolecule detection. Using HRTEM and STEM EELS techniques we have shown that chemical modification has been successful in changing both the diameter and thickness of solid state nanopores. [Preview Abstract] |
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C1.00277: ABSTRACT WITHDRAWN |
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C1.00278: Limits of Gradient Sensing and Information Transmission in Eukaryotic Cells Bo Hu, Wen Chen, Herbert Levine, Wouter-Jan Rappel Eukaryotic cells are able to direct their movements by sensing chemical gradients. The accuracy of such chemotactic response relies on the ability of cells to infer gradients from a heterogenous distribution of ligand-bound receptors on the membrane. Here, we use two different approaches, the maximum likelihood estimate (MLE) method and the partition function calculation, to explore the physical limits of eukaryotic gradient sensing. We further characterize the chemotaxing cell as a Markovian information processing system, and analytically derive the upper bounds on the cell capacity of information transmission. Our results suggest that both external and internal fluctuations are important limiting factors to chemotactic efficiency. [Preview Abstract] |
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C1.00279: Investigation of stochastic noise in the response of the external phosphate sensor in E. coli Chetan Sood, Yi-Ju Hsieh, Micha Adler, Alex Groisman, Barry Wanner, Ken Ritchie In E. coli, phosphate starvation activates a two-component regulatory system consisting of the transmembrane sensor protein PhoR and the cytoplasmic regulator protein PhoB. Near the activation threshold ($\sim $4 $\mu $M extra-cellular phosphate concentration) we expect significant variation across a population in the phenotypic response, which includes the formation of additional PhoR. To characterize this variation, we grew E. coli in a microfluidic chemostat and monitored production of a PhoR/yellow fluorescent protein (Venus) fusion in response to external phosphate concentration. The scale ($\sim $100 $\mu $m) and architecture of the growth chambers allowed for stable control of the extra-cellular environment and long-time maintenance of isolated, identical populations of cells. We will present the results of measurements of the phenotype variation due to the PhoR/PhoB sensor switch in populations of identical cells and compare these results to simulations of the expected stochastic noise in the response of this regulatory system. We will discuss the implications of these results on the fidelity of the phosphate sensor switch. [Preview Abstract] |
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C1.00280: Nonlinear Interaction of the Beat-Photon Beams with the Brain Neurocenters: Laser Neurophysics V. Alexander Stefan I propose a novel mechanism for laser-brain interaction: Nonlinear interaction of ultrashort pulses of beat-photon, ($\omega _{1}$-- $\omega _{2})$, or double-photon, ($\omega _{1}+\omega _{2})$, \footnote{Maria Goeppert-Mayer, \textbf{\"{U}ber Elementarakte mit zwei Quantenspr\"{u}ngen}, \textit{Ann Phys} \textbf{9}, 273, 95. (1931). } beams with the corrupted brain neurocenters, causing a particular neurological disease. The open-scull cerebral tissue can be irradiated with the beat-photon pulses in the range of several 100s fs, with the laser irradiances in the range of a few mW/cm$^{2}$, repetition rate of a few 100s Hz, and in the frequency range of 700-1300nm generated in the beat-wave driven free electron laser.\footnote{V. Alexander Stefan, \textbf{The Interaction of Photon Beams with the DNA Molecules: Genomic Medical Physics.} American Physical Society, 2009 \textbf{APS March Meeting}, March 16-20, 2009, abstract {\#}K1.276; V. Stefan, B. I. Cohen, and C. Joshi, \textbf{Nonlinear Mixing of Electromagnetic Waves in Plasmas }\textit{Science} 27 January 1989:Vol. 243. no. 4890, pp. 494 -- 500 (January 1989).} This method may prove to be an effective mechanism in the treatment of neurological diseases: Parkinson's, Lou Gehrig's, and others. [Preview Abstract] |
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C1.00281: Magnetic Tunneling Junction based Sensors for Bio-detection Applications L.R. Shah, N. Bhargava, S. Kim, J. Kolodzey, K. Cheng, S. Sun, R. Stearret, X. Kou, E.R. Nowak, J.Q. Xiao Magnetic tunneling junctions are capable of sensing very weak magnetic fields at room temperature. It is a suitable device to detect a biomolecule which is tagged with magnetic nanoparticles. We have designed and developed Al2O3- and MgO- based MTJ sensors using microfabrication techniques. The study reveals that in the case of Al2O3-based sensors the shape anisotropy in the free magnetic electrode results in a linear and hysteresis free magnetoresistance (MR) curve. Moreover, Al2O3 based sensor have 28{\%} TMR and sensitivity of up to 0.4 {\%}/Oe over a magnetic field range of $\pm $ 40 Oe. In the case of MgO-based sensors, there are two possible methods to achieve a linear and hysteresis free MR response. One can increase the aspect ratio in free magnetic electrode, alternatively, one can use superparamagnetic free layer. MgO-based sensor has about 90{\%} TMR and sensitivity of 1.1 {\%}/Oe over the field range of $\pm $ 40 Oe. [Preview Abstract] |
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C1.00282: ENERGY RESEARCH AND APPLICATIONS |
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C1.00283: Mass, Energy, Space And Time Systemic Theory---MEST Dayong Cao Things have their physical system of the mass,energy, space and time of themselves-MEST. The time is from the frequency, the spac is from the amplitude. Also they have different space-time and MEST of themselves, but all of them have the balance system of MEST. In the solar system, the mass-energy is center and the space-time is around. So sun absorb the absorptive wave, and absorb the mass-energy; and radiate the light, and radiate the space-time. The light give the planets the repulsion energy; the absorptive wave give the planets the gravitational potential energy. And there is the balance energy equation of planet (with a Round revolution orbit), $ \frac{1}{2}mv^2+m'c^2=-mgr=-G\frac{Mm}{r}$. $\Delta \frac{1}{2}mv^2=\Delta m'c^2,{\begin{array}{*{20}c} \hfill \\ \end{array} }\frac{1}{2}mv^2=-\frac{1}{2}mgr\to \frac{1}{2}mv^2=m'c^2\to mv^2=-mgr\to ma=-mg$ Among it, ``$m'c^2$'' is the energy of space-time of planet, ``$\frac{1}{2}mv^2$'' is the kinetic energy of planet, ``$G\frac{mM}{r}$'' is potential energy of planet. The equation: ``$m'c^2$'' show that the planets have the wave of itself, and the wave give the planets the repulsion energy. So it do not fall from the heaven. In atomic system, there is the balance energy equation of electron (with a Round revolution orbit), $\frac{1}{2}m_e v_e ^2+m_e 'c^2=-\frac{1}{4\pi \varepsilon _0 }\frac{q_1 q_2 }{r_e }$. $\Delta \frac{1}{2}m_e v_e ^2=\Delta m_e 'c^2,{\begin{array}{*{20}c} \hfill \\ \end{array} }\frac{1}{2}m_e v_e ^2=\frac{1}{4\pi \varepsilon _0 }\frac{q_1 q_2 }{r_e }\to \frac{1}{2}m_e v_e ^2=m_e 'c^2\to m_e v_e ^2=\frac{1}{4\pi \varepsilon _0 }\frac{q_1 q_2 }{r_e }$ Among it, ``$m_e 'c^2$'' is the energy of space-time of electron, ``$\frac{1}{2}m_e v_e ^2$'' is the kinetic energy of electron, ``$\frac{1}{4\pi \varepsilon _0 }\frac{q_1 q_2 }{r_e }$'' is electric potential energy. [Preview Abstract] |
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C1.00284: Blowpipe Mineralogy for Physics/Environment: Highest-Possible-Tc SC Quest; BOTH PERMANENT FOREVER Carb-IDES SOLID-State Sequestration AND Drought(s)-Elimination Kurt Segler, W. Williams, E. Siegel Detailed are old blowpipe[Kraus,Hunt,Ramsdell, Mineralogy (1936)] new applications:charcoal-block reduction of borates to yield (``N-NW'' of MgB2) Overhauser-[PR 35,1,411(1987); Intl.J.Mod.Phys.1,2 \& 4,927(1987)]-``land'' predicted high-EST- POSSIBLE Tc SC $\sim$ ``LiD2''; very-early: Siegel[Phys.Stat.Sol.(a) 11,45(1972);Semiconductors \& Insulators 5: 39,47,62(1979)] carb- IDES SOLID-state phase-TRANSITIONED CHEMICALLY-REDOX"-REACTED STABLE PERMANENT LONG-term STRATEGY, NOT ``CO2" BUT NON-gas Carbon-``ELEMENT"-sequestration: PROFITABLE MARKETABLE SALEABLE VALUABLE USEFUL ``Grab and Sell" TRUMPS ``cap and trade"!!!; Mott alloying/vertical metal-insulator transitions in ``borax-(GLASS)- beads"; and very-early Siegel [3rd Intl.Conf.Alt.Energy,Hemi- sphere/Springer(1980)-vol.5/p.459] ``FLYING-WATER" ``Hindenberg- effect"(H2-UP;H2O-DOWN) via H2-maximal-Archimedes-buoyancy ``chemical-rain-in-piplines", only via Siegel GMR enabled diffusive-magnetoresistance(DMR)enabled Siegel proprietary ``magnetic-H-valve": Renewables-H2-H2O purposely flexible versatile agile scaleable retrofitable integrated operating- system for PERMANENT drought(s)-elimination FOREVER!!! [Preview Abstract] |
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C1.00285: FRAUD/SABOTAGE Killing Nuclear-Reactors Need Modeling!!!: "Super"alloys GENERIC ENDEMIC Wigner's-Disease/.../IN-stability: Ethics? SHMETHICS!!! Aziz Asphahani, Sidney Siegel, Edward Siegel Carbides solid-state chemistry domination of old/new nuclear- reactors/spent-fuel-casks/refineries/jet/missile/rocket-engines in austenitic/FCC Ni/Fe-based(so miscalled)``super"alloys(182/82; Hastelloy-X,600,304/304L-SSs,...,690!!!) GENERIC ENDEMIC EXTANT detrimental(synonyms): Wigner's-diseas(WD)[J.Appl.Phys.17,857 (1946)]/Ostwald-ripening/spinodal-decomposition/overageing- embrittlement/thermal-leading-to-mechanical(TLTM)-INstability: Mayo[Google:``If Leaks Could Kill"; at flickr.com search on ``Giant-Magnotoresistance"; find: Siegel[J.Mag.Mag.Mtls.7,312 (1978)]$<<<$``Fert"-"Gruenberg"(1988/89)2007-physics Nobel/Wolf/ Japan-prizes]necessitating NRC-inspections of 40+25 = 65 Westin- ``KLouse PWRs(12/2006)]-Lai[Met.Trans.AIME,9A,827(1978)]-Sabol- Stickler[Phys.Stat.Sol.(1970)]-Ashpahani[Intl.Conf. H in Metals, Paris(1977]-Russell[Prog.Mtls.Sci.(1983)]-Pollard[last UCS rept. (9/1995)]-Lofaro[BNL/DOE/NRC Repts.]-Pringle[Nuclear-Power:From Physics to Politics(1979)]-Hoffman[animatedsoftware.com], what DOE/NRC MISlabels as ``butt-welds" ``stress-corrosion cracking" endpoint's ROOT-CAUSE ULTIMATE-ORIGIN is WD overageing-embritt- lement caused brittle-fracture cracking from early/ongoing AEC/ DOE-n"u"tional-la"v"atories sabotage!!! [Preview Abstract] |
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C1.00286: Mass, Energy, Space And Time Systemic Theory ---MEST --- photoelectric conversion equation Dayong Cao Things have their physical system of the mass,energy, space and time of themselves-MEST. The time is from the frequency, the spac is from the amplitude. Also they have different space-time and MEST of themselves, but all of them have the balance system of MEST. Also thing can leave off its old balance system, it will go into a new balance system. In atomic system, there is the balance energy equation of electron (with a Round revolution orbit), \[ \frac{1}{2}m_e v_e ^2+m_e 'c^2=-\frac{1}{4\pi \varepsilon _0 }\frac{q_1 q_2 }{r_e }. \] Among it, ``$m_e 'c^2$'' is the energy of space-time of electron, ``$\frac{1}{2}m_e v_e ^2$'' is the kinetic energy of electron, ``$\frac{1}{4\pi \varepsilon _0 }\frac{q_1 q_2 }{r_e }$'' is electric potential energy So when the light go into the metal, there is the photoelectric effect and the electron go out the atom, it get the new balance energy equation. \[ \frac{1}{2}m_p v_p ^2+m_p 'c^2=h\nu -\Delta E, \] Among it, ``$m_p 'c^2$'' is the energy of space-time of photoelectron, ``$\frac{1}{2}m_p v_p ^2$'' is the kinetic energy of photoelectron, ``$h\nu $'' is the energy of the light, ``$\Delta E$'' is the electron need some energy to run out of the atom. [Preview Abstract] |
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C1.00287: Time resolved in-situ crystalline structure evaluation of methane clathrate using X-ray diffraction Narayan C. Das, Paul Rumbach, Paul E. Sokol, Humberto Carvajal-Ortiz, Lisa M. Pratt Methane clathrate or methane hydrate is seen as potential source of greenhouse gas as alternative clean energy as well as possible agents of global climate change, their study continues to be a very active topic of research for the future economy. A current challenge in gas hydrate involves the evaluation of hydrate crystal and pore structure that are revealing guides to the physics and chemistry of hydrate growth as well as to the effect of environmental conditions or handling procedures. This work examines time resolved in-situ crystalline structure development of methane hydrate at different pressure and temperature in control water-methane systems by X-ray diffraction technique. We have developed high pressure cell in conjugation with X-ray diffraction instruments allowing in situ and real-time examination of structure and growth of methane clathrate. [Preview Abstract] |
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C1.00288: FLYING-WATER Renewables-H2-H2O TERRAFORMING: PERMANENT Drought(s)-Elimination FOREVER!!! M. Lyons, E. Siegel ``Water water everywhere; ne'er a drop to drink''[Coleridg(1798)]; now:``Hydrogen hydrogen everywhere;STILL ne'er a drop to drink'': ONLY H2 can be ``FLYING-WATER''/``chemical-rain-in-pipelines''/ ``Hindenberg-effect (H2-UP;H2O-DOWN): atomic-weights ratio: {O/H2O}=[16]/[18]$\sim$90\%; O already in air uphill; NO H2O pumping need! In water-starved glacial-melting world, rescue ONLY by Siegel[3rd Intl.Conf.Alt.Energy,Hemisphere/Springer(1980)- vol.5/ p.459]Renewables-H2-H2O purposely flexible versatile agile customizable scaleable retrofitable integrated operating- system. Rosenfeld[Sci.315,1396(3/9/2007)]-Biello[Sci.Am.(3/9/ 2007)]crucial geomorphology which ONLY maximal-buoyancy light- est-element H2 can exploit, to again make ``Mountains into Fount- ains": Siegel ``terra-forming''(and ocean-rebasificaton!!!) long pre-``Holdren''-``Ciccerine" ``geo-enginering'', only via Siegel proprietary magnetic-hydrogen-valve permits H2 flow in already in-ground dense BCC/ferritic-steels pipelines-network (NO new infrastructure) counters Tromp[Sci.300,1740(03)]global-pandemics (cancers/blindness/famine)dire-warning about H2-(ALONE)economy CATASTROPHIC H2 ozone-layer destruction sobering cavat to dangerous H2-automotion-economy panacea hype! [Preview Abstract] |
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C1.00289: Integrated Multilayer Nanogenerator Fabricated Using Paired Nanotip-to-Nanowire Brushes Yaguang Wei, Sheng Xu, Rusen Yang, Zhonglin Wang We present a new approach to a nanogenerator (NG) that is composed of integrated, paired nanobrushes made of pyramid-shaped metal coated on nanotip (NTP) arrays and hexagonal-prism-shaped ZnO nanowire (NW) arrays, which were synthesized using a chemical approach at $<$100 \r{ }C on the two surfaces of a common substrate, respectively. With one piece of such a structure stacked in close proximity over another to form a layer-by-layer matched brush architecture, direct current is generated by exciting the architecture using ultrasonic waves. A four-layer integrated NG is demonstrated to generate an output power density of 0.11 \textit{$\mu $}W/cm2 at 62 mV. The layer-by-layer assembly provides a feasible technology for building three dimensional NGs for applications where force or pressure variations are available. [Preview Abstract] |
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C1.00290: FRAUD/SABOTAGE Killing Nuclear-Reactors!!! ``Super"alloys GENERIC ENDEMIC Wigner's-Disease IN-stability!!! Aziz Asphahani, Sidney Siegel, Edward Siegel Siegel [[J.Mag.Mag.Mtls.7,312(78); PSS(a)11,45(72); Semis.\& Insuls.5(79)] (at: ORNL, ANS, Westin``KL"ouse, PSEG, IAEA, ABB) warning of old/new nuclear-reactors/spent-fuel-casks/refineries/ jet/missile/rocket-engines austenitic/FCC Ni/Fe-based (so MIS- called)``super"alloys(182/82;Hastelloy-X; 600;304/304L-SSs; 690 !!!) GENERIC ENDEMIC EXTANT detrimental(synonyms): Wigner's- diseas(WD)[J.Appl.Phys.17,857(46)]; Ostwald-ripening; spinodal- decomposition; overageing-embrittlement; thermomechanical- INstability: Mayo[Google: ``If Leaks Could Kill"; at flickr.com search on ``Giant-Magnotoresistance"; find: [Siegel$<<<$``Fert"(88) 2007-Nobel/Wolf/Japan-prizes]necessitating NRC inspections on 40+25=65 Westin``KL"ouse PWRs(12/06)]; Lai[Met.Trans.AIME,9A,827 (78)]-Sabol-Stickler[PSS(70)]; Ashpahani[Intl.Conf. H in Metals (77)]; Russell[Prog. Mtls.Sci.(83)]; Pollard[last UCS rept. (9/95)]; Lofaro[BNL/DOE/NRC Repts.]; Pringle[Nuclear-Power:From Physics to Politics(79)]; Hoffman[animatedsoftware.com],...what DOE/NRC MISlabels as ``butt-welds" ``stress-corrosion cracking" endpoint's ROOT-CAUSE ULTIMATE-ORIGIN is WD overageing-embrit- tlement caused brittle-fracture cracking from early/ongoing AEC/DOE-n``u''tional-la``v''atories sabotage!!! [Preview Abstract] |
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C1.00291: Surface Tension Mediated Conversion of Light into Work Peter Soler, David Okawa, Stefan Pastine, Alex Zettl, Jean Frechet We have found that optothermally generated surface tension gradients can be used to produce and control the motion of composites on liquids. A floating object will move when surrounded by an asymmetric surface tension gradient due to an imbalance in the forces it is exposed to. We utilize the absorptive properties of carbon nanotube/polydimethylsiloxane composites to convert light energy into thermal surface tension gradients. Spatially defined irradiation produces localized surface tensions gradients and controlled linear motion. This can be extended to produce controlled motion under blanket irradiation by carefully defining the placement of the absorbing material. This also dictates the location of the optothermal surface tension gradients and can be used to produce linear or rotational motion. Controlled motion under either laser irradiation or focused sunlight is presented, with forces in the range of 1-20 $\mu $N. Millimeter size rotors have been shown to produce rotational motion up to 100 rpm. Current research focuses on the investigation of design parameters that control forces and efficiencies. [Preview Abstract] |
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C1.00292: Structure and oxygen storage/release capacities of Dy$_{1-x}$Y$_{x}$MnO$_{3+\delta }$ (0 $\le $ x $\le $ 1) S. Remsen, B. Dabrowski, O. Chmaissem, S. Kolesnik, J. Mais Synthesis, oxygen storage/release capacities (OSC), oxygen absorption/desorption rates, and structural properties of Dy$_{1-x}$Y$_{x}$MnO$_{3+\delta }$ (0 $\le $ x $\le $ 1) have been studied by x-ray and neutron powder diffraction, dilatometry, and thermogravimetric analysis. These materials have been found to have excellent reversible OSC at low-temperatures of 200 - 375\r{ }C and various oxygen partial-pressures, making them potential candidates for oxygen sorbents in novel gas separation methods such as thermal swing absorption and thermal-automatic recovery processes. The OSC of the Dy$_{1-x}$Y$_{x}$MnO$_{3+\delta }$ system relies on the difference in oxygen content of a reversible phase transitions between hexagonal P63cm ($\delta $ = 0) and a previously unreported stable phases of this system (0 $<$ $\delta \quad <\quad 0.5)$ and pyrochlore Fd3m [$\delta $ = 0.50, Subramanian \textit{et al.} J. Solid State Chem. \textbf{72,} 24 (1988)]. [Preview Abstract] |
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C1.00293: On the recuperation and production of electricity from scattered sources of energy Simon Berkovich Massive production of electricity from renewable sources encounters a number of complications. Thus, among the various ways of transforming solar radiation into electricity would be to heat compressed air as directly as possible for expansion. Employing a regular steam cycle is complicated and incurs high-maintenance costs. Stabilizing a delicate influx of energy from solar, winds, and wave sources is resolved similarly to computer processing with component of different productivities, namely with buffering and pipelining. Actually, the pipelining scheme for heating the air is somehow used to make the heating process more thermodynamically efficient. However, because of timing misbalance it may contribute to the temporal variations of the main working cycle. All these temporal variations problems can be handled by ``buffering'' scheme, in the way similar to processing of intensive information flows with relatively slow computers. Most effective embodiment of this scheme would be generating electricity from the surf waves as they do not suffer from intermittent interruptions. This can be done for storing and recuperation enhancement of energy by using liquid nitrogen. [Preview Abstract] |
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C1.00294: Structural, optical and electrochemical properties of SnO$_{2-x}$ thin films Rohan Bandekar, M.B. Sahana, Sudakar Chandran, Ratna Naik, Vaman M. Naik Tin dioxide is considered to be one of the promising anode materials for Li-ion battery because it has high energy density ($\sim $780 mAhg$^{-1})$. We synthesized SnO$_{2-x}$ thin films by a facile cost effective method of metalorganic decomposition technique using Tin 2 ethylhexanoate as the precursor. Ten layers of precursor solution are spin coated on stainless steel substrates and processed at 500 $^{circ}$C for two minutes after each coating. The resulting films were annealed at various ambient such as air, hydrogen (10{\%} in Ar) and high vacuum (10$^{-6}$ torr) at different temperatures from 500$^{circ}$C to 700$^{circ}$C. The structure and composition of these films were analyzed by Raman spectroscopy, x-ray diffraction, scanning and transmission electron microscopy, and X-ray photoelectron spectroscopy to study the effect of synthesis condition on crystallinity, microstructure, and chemical composition. We also prepared thin films on ITO coated glass/quartz substrates under identical conditions for optical analysis. The structure and electrochemical property correlations of these films processed under different ambient will be presented. [Preview Abstract] |
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C1.00295: Fundamental limits of energy dissipation in computation Graham Boechler, Jean Whitney, Craig Lent, Alexei Orlov, Greg Snider The limiting factor for microprocessor development in recent years has been heat generation, which has led to a debate regarding the limits of energy dissipation required for computation. Landauer argued that energy is unavoidably lost only when data is erased---the so-called Landauer Principle. Quasi-adiabatic computation is a proposed solution which relies on recycling the energy used during computation. This has been challenged recently by the assertion that recovering the energy is impossible due to a fundamental minimum energy of kTln(2) that must be lost during the charging and discharging of an RC circuit. We experimentally measured the power dissipated in an RC circuit in the time and frequency domains. In both cases, we measure an energy dissipation less than kTln(2) in the resistor while many times kT is delivered to the capacitor. Our experiments demonstrate that there is no fundamental lower limit to the energy that must be dissipated in charging and discharging a capacitor, even for energy losses well below kT. This therefore provides experimental support for the Landauer Principle: there is no fundamental lower limit for energy dissipation required for computation. [Preview Abstract] |
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C1.00296: Improving E85-Engine Performance and Efficiency K. Huang, R. Tao E85 is an important alternative fuel with 85{\%} ethanol and 15{\%} gasoline. However, it is widely reported that E85 vehicles have difficulties to start in winter. There are also complains about the E85 engine performance. Here we report that with proper application of electrorheology, we can solve these issues and improve the engine performance. E85 vehicles all have port injected engines. The fuel is injected into cylinders as droplets. Before the ignition, the fuel evaporates. Because E85 is more viscous than gasoline, the injected E85 droplet size is not small. Especially, in the winter the cold weather makes the viscosity even higher, leading the E85 droplets even bigger. Since evaporation starts from the droplet surfaces, large droplets are difficult to be evaporated before the ignition comes. When there is no enough fuel vapor, the engine cannot start. To solve this problem, we introduce a small device just before the fuel injection, which produces a strong electric field to reduce the fuel viscosity, leading to much smaller fuel droplets in atomization. The evaporation is much faster and the engine is easier to start. After the engine is started, the warm metal surfaces help evaporate the fuel and the engine operates fairly well. As the small fuel droplets produced by our device make the combustion fast and timely, engine efficiency and performance are also improved. [Preview Abstract] |
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C1.00297: Bidirectional Single-Electron Counting and the Fluctuation Theorem Yasuhiro Utsumi, Dimitri Golubev, Michael Marthaler, Keiji Saito, Toshimasa Fujisawa, Gerd Schoen We investigate the direction-resolved full counting statistics of single-electron tunneling through a double quantum dot system and compare with predictions of the fluctuation theorem (FT) for Markovian stochastic processes. Experimental data obtained for GaAs/GaAlAs heterostructures appear to violate the FT. After analyzing various potential sources for the discrepancy we conclude that the nonequilibrium shot noise of the quantum point contact electrometer, which is used to study the transport, induces strong dot-level fluctuations which significantly influence the tunneling statistics. Taking these modifications into account we find consistency with the FT once we introduce the ``effective temperature.'' Y. Utsumi, D. S. Golubev, M. Marthaler, K. Saito, T. Fujisawa, Gerd Schoen, arXiv:0908.0229 [Preview Abstract] |
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