Bulletin of the American Physical Society
2006 Ohio Section of the APS Fall Meeting
Friday–Saturday, October 13–14, 2006; Orrville, Ohio
Session P: Poster Session |
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Chair: Zach Vierheller, The University of Akron Room: Wayne College Boyer Gymnasium, 4:00pm-5:30pm |
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P.00001: Infrared and magneto-optical studies of novel condensed matter systems Lee Kohlman, Sasa Dordevic We will present the results of our recent infrared and magneto-optical measurements on high temperature supercondutors La$_{2-x}$Sr$_x$CuO$_4$, heavy fermion metal YbFe$_4$Sb$_{12}$ and half-metallic ferromagnet Mn$_5$Ge$_3$. The results demonstrate the power of spectroscopic techniques, which allow one to study materials in extreme experimental conditions, such as temperature as low as 4.2 K and magnetic field as high as 33 Tesla. The results reveal failure of free-electron model for these novel condensed matter systems and importance of electron-electron correlations. [Preview Abstract] |
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P.00002: Optical properties of tips for apertureless near-field microscopy Nam-Heui Lee, Ryan Hartschuh, Disha Mehtani, Alexander Kisliuk, Mark Foster, Alexei Sokolov, Igor Tsukerman Apertureless near-field optical microscopy techniques provide unique chemical characterization with nanoscale resolution, overcoming the diffraction limit of light via surface plasmon resonance generation on a metal tip. The surface plasmon resonance depends on the type of metal used for the tip, morphology of the metal surface, and cone angle of the tip. The proximity of the incident wavelength to the resonance wavelength for the tip is another important factor, and this has been studied for gold- and silver-coated tips. Electric field enhancement is maximized when the plasmons resonate at the probing wavelength. Thus, identifying the resonance frequency of the tip apex is crucial and challenging to effective near-field optics. A dark-field scattering spectroscopy used with a side-illumination nano-Raman spectrometer has been exploited to experimentally determine the optical properties of various tips. The dependence of the optical resonance on the metal deposited is shown for silver- and gold-coated tungsten tips and silicon nitride tips. The enhancement of the Raman signal for silicon with gold-coated silicon nitride tips is $\sim $ 3 times stronger for a wavelength of 647 nm than for a wavelength of 514.5 nm. The former wavelength is closer to the plasmon resonance observed for this tip at $\sim $680 nm. [Preview Abstract] |
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P.00003: The effect of variation in conformational size in pom-pom polymer on bulk and surface thermodynamics Sewoo Yang, Namheui Lee, Roderic P. Quirk, Mark D. Foster, Boualem Hammouda, Sushil Satija We have investigated the effect on bulk and surface thermodynamics of changing the size of the linear portion between junctions of a pom-pom polymer in blends of linear and branched polystyrene (PS). A series of pom-pom PS synthesized using anionic polymerization had well-defined structures and narrow molecular weight distributions. Small Angle Neutron Scattering (SANS) measurements of bulk blend samples revealed that varying the linear portion of the pom-pom branched polymer altered the effective interaction parameter. In addition, the purely entropic contribution to the interaction parameters was estimated by extrapolating data measured in blends with linear PS-$r$-deuterated PS linear copolymers having different degrees of deuterium labeling Neutron Reflectometry (NR), and Surface Enhanced Raman Spectroscopy (SERS) measurements show that varying the length of the central linear portion of the pom-pom polymer also affects the surface segregation. [Preview Abstract] |
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P.00004: HPC-Microgels: New Look at Structure and Dynamics John McKenna, Kiril Streletzky, Rami Mohieddine Issues remain unresolved in targeted chemotherapy including: an inability to effectively target cancerous tissue, the loss of low molecular weight medicines to the RES system, the high cytotoxicity of currently used drug carriers, and the inability to control the release of medicines upon arrival to the target. Hydroxy-propyl cellulose(HPC) microgels may be able to surmount these obstacles. HPC is a high molecular weight polymer with low cytotoxicity and a critical temperature around 41C. We cross-linked HPC polymer chains to produce microgel nanoparticles and studied their structure and dynamics using Dynamic Light Scattering spectroscopy. The complex nature of the fluid and large size distribution of the particles renders typical characterization algorithm CONTIN ineffective and inconsistent. Instead, the particles spectra have been fit to a sum of stretched exponentials. Each term offers three parameters for analysis and represents a single mode. The results of this analysis show that the microgels undergo a multi to uni-modal transition around 41C. The CONTIN size distribution analysis shows similar results, but these come with much less consistency and resolution. During the phase transition it is found that the microgel particles actually shrink. This property might be particularly useful for controlled drug delivery and release. [Preview Abstract] |
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P.00005: Surface Imaging of HIP 106231 via Light Curve Inversion Rachael Roettenbacher, Robert Harmon The star HIP 106231 (LO Pegasi) was observed with the intention of mapping its starspots. Starspots, similar to sunspots on the Sun, are dark areas on the surface of a star caused by intense magnetic fields. CCD images of HIP 106231 and the surrounding star field were obtained using an 8-inch Meade Schmidt-Cassegrain Telescope in conjunction with a Santa Barbara Instruments Group ST-8E CCD Camera and CFW8 filter wheel. Aperture photometry was used to create light curves (i.e. plots of brightness vs. time) for the B, V, R and I photometric filters. The light curves were analyzed via Light Curve Inversion, which is a technique that produces an image of the starspots based on the variations in the star's brightness they produce as they rotate into and out of view of Earth. We present a map which indicates the presence of a mid-latitude spot or projection from a polar spot. [Preview Abstract] |
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P.00006: Magnetic properties of electrodeposited Co$_{0.45}$Fe$_{0.55}$ nanowire arrays Petru Fodor, Georgi Tsoi, Lowell Wenger The structural and magnetic properties of an array of micron-long Co$_{0.45}$Fe$_{0.55}$ alloy nanowires with diameters ranging from 12 to 52 nm electrodeposited in porous anodic alumina templates have been studied using X-ray diffractometry, scanning electron microscopy, and magnetization measurements. The nanowires are found to crystallize in a body-centered-cubic (bcc) structure along the (110) axis for all diameters studied. The magnetization curves indicate a highly anisotropic behavior with the easy axis along the nanowire axis and a coercivity of 3500 Oe at room temperature. Results from the magnetization hysteresis and magnetic relaxation measurements suggest that the magnetization reversal takes place through localized nucleation in volumes smaller than the physical volume of the nanowires. The localization of the nucleation combined with the cooperative effects arising from magnetostatic interactions between the nanowires, limits the coercivity of the nanowire arrays. [Preview Abstract] |
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P.00007: Advancements in tip preparation methods for scanning nanoRaman spectroscopy. Scott Hamilton, Andrey Malkovskiy, Nam-Heui Lee, Ryan Hartschuh, Alexei Sokolov, Mark Foster Tip enhanced Raman spectroscopy uses the enhanced electric field around a metallized probe to enhance the Raman signal from a very small scattering volume in proximity to the tip, yielding sub-diffraction limit spectroscopic resolution.~ Reproducible production of metallized tips that yield high field enhancement is a vital component of this technology. Moving beyond simple thermal evaporation coated tips, tips with more complicated features are being investigated.~ This includes tips decorated with metal nanoparticles of different sizes and shapes, tips with laterally patterned metal layers, and tips composed of layers of metal separated by thin dielectric films.~ To probe the electric fields of potential structures, nanoRaman scans are performed on patterned surfaces covered with thin analyte films with the goal of finding areas of greatest enhancement with high resolution. [Preview Abstract] |
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P.00008: ZnO nanostructures growth at low temperature from Zn powder and Zn Acetate Monica Morales, B.B. Claflin, Wally Rice, G.C. Farlow, D.C. Look In this work we report the synthesis of various types of ZnO nanostructures under two different approaches: Vapor Phase Transport process (VPT) using Zinc acetate as the source material, and simple thermal evaporation of Zinc powder (99.9{\%}). Each process has specific growth parameters. ZnO nanostructures were synthesized on silicon and sapphire wafers at temperatures ranging from 360\r{ }C to 500\r{ }C. Comparison of Atomic Force Microscope (AFM) images and of Scanning Electron Microscope (SEM) images show that the precise control of the gas flow (O$_{2}$/Ar mixture), as well as the growth time, are key in the formation, size and shape of the nanostructures. Low Temperature Photoluminescence measurements indicate that the depositions are of very good quality. [Preview Abstract] |
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P.00009: The Rayleigh Hypothesis and Scattering at Photonic Crystal Surfaces Prabasaj Paul, Kyaw Nyein, Robert Choudury We examine the Rayleigh hypothesis in the context of scattering of light off photonic crystal interfaces. First, the hypothesis -- which was initially suggested for scattering of waves off rough surfaces between homogeneous media -- is rephrased to apply to photonic crystal interfaces. Next, an exact and explicit functional form is presented that maps a class of plane photonic crystal surfaces to periodic rough surfaces in free space, so that known criteria for the validity of the Rayleigh hypothesis for scattering at rough surfaces can be applied directly to scattering at the photonic crystal surfaces. We present numerical results for scattering amplitudes at a photonic crystal surface using both an exact method (based on a surface integral formulation) and an approximate method (based on the Rayleigh hypothesis). The results are consistent with the analytical criteria for the range of validity of the approximate method. [Preview Abstract] |
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P.00010: Analysis of the Mars Global Surveyor Radio Occultation Data Katherine Yeager The Mars Global Surveyor which was launched on November 7, 1996 was designed to orbit Mars over a two year period and collect data on the surface morphology, topography, composition, gravity, atmospheric dynamics, and magnetic field. This data will be used to investigate the surface processes, geology, distribution of material, internal properties, evolution of the magnetic field, and the weather and climate of Mars. The instruments on the nadir equipment deck consist of a camera, thermal emission spectrometer, laser altimeter, and a radio transmission relay. The main instrument that we were interested in was the radio transmission relay. My research consisted of the analysis of the Electron Density Profiles for the Martian ionosphere in the seven occultation seasons that range from December 1998 to June 2005 that were obtained from the MGS radio science experiment. The main data that I collected consisted of the values for the F1 peak and the E peak for each profile. The F1 peaks are photo ionization by EUV photons and the E peaks are from the absorption of x-ray photons. I also calculated the F10.7 values for each day that I observed in the occultation seasons. I have also been analyzing the dependence of the peak values on solar zenith angle and the F10.7 value. From the data obtained a model for each occultation season was generated and then compared to the Chapman function for further analysis. [Preview Abstract] |
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P.00011: Comparative Analysis of the Tour Jete and Aerial with Detailed Analysis of Aerial Takeoff Mechanics Mimi Pierson, Kim Coplin Whether internally as muscle tension or from external sources, forces are necessary for all motion. This research focused on athletic rotations where conditions of flight are established during takeoff. By studying reaction forces that produce torques, moments of inertia, and linear and angular differences between distinct rotations around different principle axes of the body (tour jete in ballet - longitudinal axis; aerial in gymnastics - anteroposterior axis), and by looking at the values of angular momentum in the specific mechanics of aerial takeoff, we can gain insight into possible causes of injury, flaws in technique and limitations of athletes. Results showed significant differences in the horizontal and vertical components of takeoff between the tour jete and the aerial, and a realization that torque was produced in different biomechanical planes. Both rotations showed braking forces before takeoff to counteract forward momentum and increase vertical lift, but the angle of applied force varied, and the horizontal components of velocity and force and vertical velocity as well as moment of inertia throughout flight were consistently greater for the aerial. Breakdown of aerial takeoff highlighted the relative importance of the takeoff phases, showing that completion depends fundamentally upon the rotation of the rear foot and torso twisting during takeoff rather than the last foot in contact with the ground. [Preview Abstract] |
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P.00012: Enhanced Macroscopic Quantum Tunneling of a Damped Metastable System Coupled to a Nanomechanical Resonator Brian Siller, Brad Trees Recent work in the field of quantum computing has focused to a large extent on viable qubit candidates. One such candidate is an underdamped, current-biased Josephson junction, called a phase cubit, coupled to a nanomechanical resonator. At a bias current just below the critical current of the junction, the system is metastable, and tunneling out of a local minimum in the washboard potential describing the junction could become a concern with regard to controlling the operation of a qubit. We report on calculations of the tunneling rate of such a Josephson system coupled to a nanomechanical resonator. We have looked at both strongly damped and weakly damped junctions, modeling the damping of the junction by the harmonic-oscillator bath method made popular by Caldeira and Leggett. We were interested to see if a resonance between the junction and the resonator, when one of the resonator's natural frequencies matches the plasma frequency of the junction, would result in an enhancement of the tunneling rate. We report on our findings of the tunneling rate in these systems. [Preview Abstract] |
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P.00013: Applications of Terahertz Spectroscopy to the Analysis of DNA Christopher Lemon, Joe Knab, Yunfen He, Andrea Markelz, Janet Morrow Terahertz spectroscopy is a unique analytical method that investigates collective, low-energy vibrational modes of molecules. This technique is especially useful for the characterization of biological molecules, which have a large number of normal modes in the far infrared region. However, terahertz spectroscopy as applied to biological molecules is in its infancy. Proteins have been largely studied, but DNA has not been extensively explored. Only a few solid-state studies have been conducted on the nitrogenous bases and deoxyribonucleosides. In order to be more biologically relevant, a series of experiments on deoxribonucleotides has been performed in the solution state. The mononucleotides were studied in both pellet and solution forms in order to draw comparisons between the two states. These observations are similar to those obtained from a series of ab initio calculations. Since this technique can be applied to detect binding events, the well-characterized biotin and avidin system was studied. Spectra of biotin, avidin, and the complex were obtained. Based on absorbance and refractive index changes, it can be concluded that binding of biotin and avidin has occurred to form the complex. As a result, terahertz spectroscopy is a viable tool for detecting binding events. [Preview Abstract] |
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P.00014: Long-time Correlations in Electromyography Signals Ulrich Zurcher, Rachel Maynard We have previously reported that the mean-square displacement calculated from electromyography time series of low back muscles exhibit a plateau-like behavior for intermediate times [$50 \, \mbox{ms} < t < 0.5 \, \mbox{s}$], so that $\left< [x_ {t} - x_{0} ]^{2} \right> \sim t^{0}$. This behavior is unexpected, and indicates the presence of long-time correlations in the signal. For fractal Brownian motion, the Hurst exponent calculated from the mean-square displacement and the exponent from the spectral density $P ( f) \sim 1/f^{\alpha}$, $\alpha = 2 H + 1$. For the EMG time series $y^{0}_{i} = x_{i}$, we have generated iterated time series, $y_{i}^{n+1} = [y_{2 i }^{n} + y_{2i+1}]/2$, and have calculated the corresponding time correlation functions, $C^{n} ( t) = \left< x_{i+ t}^{n} x_{i}^{n}\right>/\left<(x_{i}^{n})^{2} \right>$. We find that the correlation functions converge to a simple limit, $C(0) = 1$, $C(1) = -0.5$ and $C(n) =0 $ for $n \geq 2$. This limit is consistent with the plateau behavior of the mean- square displacement. We discuss the connection between the behavior of the iterated correlation functions and the properties of the spectrum. [Preview Abstract] |
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P.00015: Synthesis and characterization of CdS nanoparticles Ivan Dolog, Robert Mallik, Anthony Mozynski, Greg Zartman Previous work by our group has characterized the conduction mechanisms for ultra thin CdS films modified by self assembled monolayers of adamantane based compounds. In the current work we have synthesized CdS nanoparticles using an aqueous precipitation method developed by G. A. Martinez-Castanon.~ Raman, Inelastic Electron Tunneling and Reflection Absorption Infrared spectra are presented. These data are used to determine the composition of the sythesized substance. The Raman spectrum shows asymmetric broadening of CdS peaks. It is known that Raman scattering is dependent on particle size and information from this broadening is anticipated to a determination of CdS nanoparticle size. Work is also underway to determine the size of the nanoparticles by modeling nanoparticles as single crystalline semiconductors spheres. Future work is planned to study the adsorption of self assembled monolayers on the CdS nanoparticles and their effect on photovoltaic properties. [Preview Abstract] |
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P.00016: Study of PSAs based on Acrylic Block Copolymers by Scanning Probe Microscopy Carlos A. Barrios, Mark D. Foster Techniques developed from scanning probe microscopy (SPM) allow the observation of surfaces on a highly local level and in a way in which bulk dissipative mechanisms play a much less prominent role. Unfortunately, sticky surfaces are difficult to characterize due to strong interactions with the probe. Deposition of hydrophobic coatings on SPM tips is used in this work to study adhesive surfaces. The primary goal of this work is to study the short time aging of model PSAs, particularly under humid conditions for a blend of acrylic triblock copolymer and homopolymer having similar molecular weights. Well-defined polymers were synthesized by ATRP. Hydrophobic modification of tips using chlorosilanes allowed the resolution of pull-off forces on mildly adhesive surfaces. Force-penetration curves of acrylic block copolymer-homopolymer blends showed a transition point in which the slope of the loading region changes to almost twice its original value and a constant force region just before debonding. Such behavior may be related to a superficial phase separation between the two components of the blend and a fibrillation process, respectively. Current work focuses on the quantification and analysis of these differences. [Preview Abstract] |
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P.00017: Lifetime Measurements and Deformation in $^{79}$Sr Y.K. Ryu, R.A. Kaye, S.R. Arora, S.L. Tabor, T. Baldwin, D.B. Campbell, C. Chandler, M.W. Cooper, C.R. Hoffman, J. Pavan, M. Wiedeking, J. D\"oring, Y. Sun, S.M. Gerbick, O. Grubor-Urosevic, L.A. Riley High-spin states in $^{79}$Sr were produced following the $^{54}$Fe($^{28}$Si, $2pn$) fusion-evaporation reaction using a beam energy of 90 MeV at the Florida State University (FSU) Tandem-Linac facility, and the resulting de-exciting $\gamma$ rays were detected with the FSU Ge array of 10 Compton-suppressed detectors. The $^{54}$Fe target was thick enough so that all of the synthesized nuclei could stop completely in the target, resulting in Doppler-shifted $\gamma$-ray line shapes that could be analyzed using the Doppler-shift attenuation method. In all, 23 lifetimes were measured in three separate band structures using this method, and then used to infer transition quadrupole moments ($Q_t$) and quadrupole deformations ($\beta_2$) using the rotational model. The results show good qualitative agreement with the predictions of both cranked Woods-Saxon (CWS) and projected shell model (PSM) calculations. The band based on a $d_{5/2}$ single-particle orbit, verified in this study through $\gamma - \gamma$ coincidences, intensity measurements, and directional correlation of oriented nuclei (DCO) ratios, was found to have the largest average deformation ($\beta _{2,{\rm ave}} = 0.41$) among the three bands, in agreement with the CWS and PSM predictions. [Preview Abstract] |
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P.00018: Compositional Models of Hematite-Rich Spherules (Blueberries) at Meridiani Planum, Mars and Constraints on Their Formation A. Schneider, D Mittlefehldt The Mars Exploration Rover Opportunity discovered hematite-rich spherules (``blueberries'') believed to be diagenetic concretions formed in the bedrock in stagnant or slow-moving groundwater. These spherules likely precipitated from solution, but their origins are poorly understood. Three formation mechanisms are possible: inclusive, replacive and displacive. The first would result in a distinct spherule composition compared to the other two. We propose that chemical clues may help to constrain the nature of blueberry formation. We used Alpha Particle X-ray Spectrometer data for undisturbed soils that were blueberry-free and with visible blueberries at the surface in Microscopic Imager images. We made plots of the elements versus iron for the spherule-rich soils and compared them to a mixing line representative of a pure hematite end member spherule (called ``the zero model''). This modeled the replacive formation mechanism, in which pure hematite would replace all of the original material. If the spherules grew inclusively, chemical data should reflect a compositional component of the rock grains included during formation. Four models were developed to test for possible compositions of a rock component. These models could not easily explain the APXS data and thus demonstrate that the most plausible rock compositions are not components of blueberries. [Preview Abstract] |
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P.00019: Instability of Electric Field Induced Pattern Formation in Thin Liquid Films Emily Tian Modern lithographic technologies rely on creating patterns in thin films. Among the methods of achieving particular morphologies is the application of electric fields. In this talk, the morphology of the interface of a thin liquid film confined between two electrodes separated by an air gap is investigated by means of a weakly nonlinear stability analysis. In the long-wavelength limit, an interface evolution equation is derived which incorporates the effects of electrical stress and surface tension. The thickness ratio of the air gap to the liquid crucially determines pattern formation, which here consists of liquid columns and holes. [Preview Abstract] |
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