Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session B21: Society of Physics Students |
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Sponsoring Units: SPS Chair: Gary White, Society of Physics Students/AIP-Education Room: Colorado Convention Center 106 |
Monday, March 5, 2007 11:15AM - 11:27AM |
B21.00001: Electronic Structure Calculations of Si, SiC, Si$_{3}$N$_{4}$ and SiO$_{2}$ Ryan Jacob, A.R. Chourasia The band structure of Si, SiC, Si$_{3}$N$_{4}$ and SiO$_{2}$ have been studied using a DFT computational approach implemented in CRYSTAL98. The Becke exchange has been employed. Two types of correlations have been explored: Perdew, Wang, and Lee, Yang, Parr. The atomic basis sets with a polarization function have been optimized for each configuration in these materials. The density of states in the valence and conduction bands has been computed in each case. The projected density of states of the constituents has also been computed. The band gap and the dielectric constant have been calculated for these materials. These values have been compared with the available experimental data. The correlation between the electronic polarizability and the Auger parameter determined previously from x-ray photoelectron spectroscopy will be presented. [Preview Abstract] |
Monday, March 5, 2007 11:27AM - 11:39AM |
B21.00002: Electronic energy transfer in the layered single crystal Sm[Ag$_{.5}$Au$_{.5}$(CN)$_{2}$]$_{3}$ Stefan Oehrlein, Christie Larochelle The aim of this study is to examine the energy transfer between [Ag$_{.5}$Au$_{.5}$(CN)$_{2}$]$_{3}$ donors and the Sm$^{3+}$ acceptors with which they have been doped. The single crystals of [Ag$_{.5}$Au$_{.5}$(CN)$_{2}$]$_{3}$ have been doped with varying concentrations of Samarium. Energy transfer was characterized using steady-state excitation and emission spectra, lifetime measurements and time-resolved spectra. Data was obtained as a function of temperature between 77 K and room temperature. Strong luminescence is seen at all temperatures in the mixed-metal system, a contrast from the luminescence displayed in the pure gold and silver dicyanide donors. [Preview Abstract] |
Monday, March 5, 2007 11:39AM - 11:51AM |
B21.00003: Anomalous elastic response of diamond single crystals to shock compression Keith McLaughlin, Mikhail Ladanov, Ivan Oleynik, Sergey Zybin, Mark Elert, C.T. White We have performed large-scale molecular-dynamics simulations of shock-wave propagation in single-crystal diamond and observed an anomalous elastic response of the material in the intermediate range of shock-wave intensities between the elastic-plastic split shock-wave regime and the graphitization regime of shock compression. The anomalous elastic response is characterized by the absence of plastic deformations in highly uniaxially compressed material. The unusual materials response in shock-compressed diamond is attributed to unique and complex constitutive relationships: both shear and longitudinal stresses are non-monotonic functions of compression. This example clearly demonstrates the necessity of generalization of the notion of the Hugoniot elastic limit (HEL) to include critical shear stresses in a criterion of materials yielding upon shock compression. [Preview Abstract] |
Monday, March 5, 2007 11:51AM - 12:03PM |
B21.00004: Magnetic Properties of Manganese(III) in Cluster-based Coordination Polymers. Kevin J. Little, D.M. Pajerowski, M.W. Meisel, D.R. Talham, H. Zhou, A. Lachgar Magnetization studies, using a SQUID magnetometer operating down to 2~K and up to 7 T, were performed on one-, two-, and three-dimensional coordination polymers built with [Mn($L$)]$^+$ complexes and [Nb$_6$Cl$_{12}$(CN)$_6$]$^{4-}$ clusters. All three structures exhibited paramagnetic properties and no signs of long-range ordering down to 2 K. The magnetic properties are dominated by the Mn(III) ions, $S = 2$ and $g \approx 2$, per formula unit, and deviations between the samples at low temperatures are associated with the different anisotropic Mn(III) environments of each material. [Preview Abstract] |
Monday, March 5, 2007 12:03PM - 12:27PM |
B21.00005: Thickness dependent properties of CMR Manganite thin films on lattice mismatched substrates: Distinguishing Strain and Interface Effects Anthony Davidson III, Rajeswari Kolagani, Ellisaveta Bacharova, Grace Yong, Vera Smolyaninova, David Schaefer, Rajeh Mundle Epitaxial thin films of CMR manganite materials have been known to show thickness dependent electrical and magnetic properties on lattice mismatched substrates. Below a critical thickness, insulator-metal transition is suppressed. These effects have been largely attributed to the role of bi-axial lattice mismatch strain. Our recent results of epitaxial thin films of La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ (LCMO) on two substrates with varying degrees of compressive lattice mismatch indicate that, in addition to the effect of lattice mismatch strain, the thickness dependence of the properties are influenced by other factors possibly related to the nature of the film substrate interface and defects such as twin boundaries. We have compared the properties of LCMO films on (100) oriented LaAlO$_{3}$ and (001) oriented NdCaAlO$_{4 }$both of which induce compressive bi-axial strain. Interestingly, the suppression of the insulator-metal transition is less in films on NCAO which has a larger lattice mismatch. We will present results correlating the electrical and magneto transport properties with the structure and morphology of the films. [Preview Abstract] |
Monday, March 5, 2007 12:27PM - 12:51PM |
B21.00006: Aspects of melting in thin molecular films adsorbed onto a graphite substrate using molecular dynamics simulations Cary Pint This work is conducted in order to study the behavior of very thin (nearly 2-D) films of molecules adsorbed onto a graphite substrate when the film is exposed to temperatures near the temperature-induced melting point. Simulations of both the linear normal alkanes (C$_{n}$H$_{2n+2})$ and perflourinated alkanes (C$_{n}$F$_{2n+2})$ of different chain lengths indicate that the nature of the melting transition in thin films composed of these molecules are dependent upon features of the molecules themselves, such as their chain length and flexibility. This is due to thermal fluctuations that dominate the behavior of the film prior to the melting point which seem to depend on these molecular features, as well as on aspects of the film- such as the adsorbed solid phase. A picture of melting in (quasi) 2-D films based on ``allowed'' thermal fluctuations is presented, and is expected to be generalizable to more complex films of molecules on a variety of different solid substrates. [Preview Abstract] |
Monday, March 5, 2007 12:51PM - 1:03PM |
B21.00007: First-principles molecular reactive dynamics of energetic materials Aaron Landerville, Ivan Oleynik, Carter White The understanding of initiation chemistry of shock-compressed energetic materials on the atomic scale is of fundamental importance for developing a predictive theory of initiation of detonation. We have performed first-principles density-functional modeling of reactive molecular collisions of PETN and RDX molecules aimed at elucidating the first chemical events that trigger the chemistry behind the shock wave front. We will discuss fundamental mechanisms responsible for the transformation of mechanical energy from the shock wave into molecular degrees of freedom that result in excitation of a reaction mode and eventual bond breaking. We will also discuss the stereochemistry of initial reaction events, unimolecular, bi-molecular or multi-molecular nature of initial reactive events and the relationship of the simulated reactive collisions with a non-equilibrium shock wave environment. [Preview Abstract] |
Monday, March 5, 2007 1:03PM - 1:15PM |
B21.00008: Determining the Time Evolution of Bose-Einstein Condensate Merideth Frey Bose-Einstein condensates (BEC) offer a macroscopic way to analyze the quantum mechanical world. In order to measure most properties of these condensates, the cooled atomic gas must be released from its potential trap and allowed to expand. Oftentimes an analytic solution for the time-evolution of the BEC wavefunction after release from the trap cannot be found and a numerical solution is needed. By applying a recent numerical method for solving the Gross-Pitaevskii equation, the time-evolution for BEC after release from potential traps of various geometries can be found. For this project, spherically and cylindrically symmetric traps are analyzed. When applicable, the numerical results are compared with analytical solutions to evaluate the error in the method. Numerical solutions will also be found for potential trap geometries that produce interesting interference effects due to the quantum behavior of Bose-Einstein condensates. [Preview Abstract] |
Monday, March 5, 2007 1:15PM - 1:27PM |
B21.00009: Regulating the Tumor Cell Population Dynamics by Controlling the Proliferation Rate Sarah Hirschbeck, Mitra Shojania Feizabadi The two-compartment model of cancer cell population dynamics introduces two subpopulations for a tumor (proliferating and quiescent). In precious theoretical models, the interaction of tumor cells with chemotherapeutic drugs is expressed as an additional term which reduces the size of subpopulations because of the killing effect of the drug with different killing rates. We develop a simple mathematical model for a more realistic interaction of anti-cancer drugs with tumor cells. The key assumption used in developing this model is that the anti-cancer drug not only kills the subpopulations but also decreases the proliferating rate of the proliferating subpopulation during the course of therapy. Finally, we present the numerical result for the evolution of the subpopulations based on this model. [Preview Abstract] |
Monday, March 5, 2007 1:27PM - 1:39PM |
B21.00010: ABSTRACT WITHDRAWN |
Monday, March 5, 2007 1:39PM - 1:51PM |
B21.00011: Coherent Population Exchange between BCS Atom Pairs and Ground Molecular BEC Atom Pairs Andrew Robertson, Hong Ling Two fermionic atoms of opposite spins (represented by the hyperfine Zeeman sublevels)~can be combined either into a molecule highly localized in real space or into a Bardeen-Cooper-Schrieffer (BCS) pair highly correlated in momentum space.~ In an attractive fermionic system with atoms of opposite spins, we show that the simultaneous presence of a Feshbach resonance and an optical laser coupling can lead to a coherent superposition between the ground molecular state and the~BEC state.~By optically perturbing the system, we demonstrate numerically stable~coherent atom-molecule oscillations. [Preview Abstract] |
Monday, March 5, 2007 1:51PM - 2:03PM |
B21.00012: Cr$^{3+}$ optical probes of structural transformation in porous alumina M.L. Lombardi, J.K. Krebs High surface area aluminum oxide is useful as a catalytic support for gas conversion devices. Upon heat treatment at temperatures in the range of 700 to 1200$^{ o}$C, the high surface area structures undergo a series of transformations terminating in a dense ceramic composed of particles with the corundum structure. These structural transformations occur as the porosity of the material decreases, thus reducing the catalytic surface area. Among the various porous aluminum oxide structures, theta alumina is the highest temperature form that maintains porosity. Lanthanum impurities have been shown to increase the conversion temperature for the theta to corundum transition by preventing boundary creep. We report on an optical technique to observe the structural transition by monitoring the spectrum of trivalent chromium impurities. Since the energies of the d electrons of the chromium impurities shift with the local environment of the ion, optical spectra of the impurities provide sensitive probes for the local structure of the host alumina. We monitor the local structure as a function of heat treatment for various lanthanide concentrations. The temperature of the theta to corundum transition is unaffected by lanthanum addition at concentrations below 0.2 molar percent and increases significantly at higher concentrations. [Preview Abstract] |
Monday, March 5, 2007 2:03PM - 2:15PM |
B21.00013: Raman Spectroscopy of Carbon Nanotubes Richard Bergstrom Jr., Ernst Knoesel Raman spectroscopy is an optical technique used to analyze vibrational modes in materials. Raman is used in carbon nanotubes for the study of phonon modes which produce the vibrations. There are two principle bands of phonons in carbon nanotubes, the G-mode and the Breathing mode. Through the examination of the Breathing mode phonons we can determine the nanotube type and size. By studying the relationship between the two phonon modes we would like to gain insight into the conductivity and the heat transfer between nanotubes. [Preview Abstract] |
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