Bulletin of the American Physical Society
2006 Texas Section of the APS Joint Fall Meeting
Thursday–Saturday, October 5–7, 2006; Arlington, Texas
Session OT1: Other I |
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Chair: Ali Koymen, University of Texas at Arlington Room: UT Arlington, University Center Red River |
Friday, October 6, 2006 1:30PM - 1:42PM |
OT1.00001: Using the Feynman-Kac Path Integral Method in Finding Excited States of Helium. Nail G. Fazleev, James M. Rejcek, John L. Fry Group theory considerations and properties of a continuous path are used to define a failure tree procedure for finding eigenvalues of the Schrodinger equation using stochastic methods. The procedure is used to calculate the lowest excited state eigenvalues of eigenfunctions possessing anti-symmetric nodal regions in configuration space using the Feynman-Kac path integral method. Within this method the solution of the imaginary time Schrodinger equation is approximated by random walk simulations on a discrete grid constrained only by symmetry considerations of the Hamiltonian. The required symmetry constraints on random walk simulations are associated with a given irreducible representation and are found by identifying the eigenvalues for the irreducible representation corresponding to symmetric or antisymmetric eigenfunctions for each group operator. The method provides exact eigenvalues of excited states in the limit of infinitesimal step size and infinite time. The numerical method is applied to compute the eigenvalues of the lowest excited states of the helium atom that transform according to specific irreducible representations associated with explicitly determined symmetry groups. [Preview Abstract] |
Friday, October 6, 2006 1:42PM - 1:54PM |
OT1.00002: Chasing a polar catastrophe: \textit{ab-initio} theory of the LaAlO$_{3}$/SrTiO$_{3}$ interface Jaekwang Lee, A.A. Demkov A polar discontinuity at the abrupt oxide/oxide interface is one of several problems that need to be addressed before we can realize the promise of multiferroic oxide structures. To avoid the so-called polar catastrophe the interface undergrows roughening which renders the structure useless, unless the system finds a mechanism for compensating the interface charges. Recent experiments of Hwang and co-workers (\textit{Nature }\textbf{427}, 423-426 (2004) and \textit{Nature }\textbf{430}, 657-661 (2004)) suggest that in the case of perovskite oxides two quite different compensatory mechanisms are at play at the heterojunction. For the n-type LaAlO$_{3}$/SrTiO$_{3}$ interface it is purely electronic involving mixed valence Ti ions, while for the p-type it is an actual ionic reconstruction involving oxygen vacancies. We report a first-principles study of both interfaces within density functional theory. We consider the energetics and electronic structure of the interface, including the role of oxygen vacancies and band offsets. In addition we consider the interface stability with respect to inter diffusion of La and Sr across the interface. [Preview Abstract] |
Friday, October 6, 2006 1:54PM - 2:06PM |
OT1.00003: Energy and Properties of Fully Nonadiabatic Molecules Using Monte Carlo Methods Steve Alexander, R.L. Coldwell Recent advances in the area of Quantum Monte Carlo allow fully nonadiabatic wavefunctions to be computed for a number of chemically interesting molecules. These explicitly-correlated wavefunctions are compact, capture a high percentage of the correlation energy and automatically include all nonadiabatic corrections. They also eliminate the need to form potential energy surfaces. Instead, the vibrational and rotational energies of a molecule can be computed directly from the wavefunction. From these wavefunctions a variety of molecular properties can also be computed. We will present results for several simple molecules. [Preview Abstract] |
Friday, October 6, 2006 2:06PM - 2:18PM |
OT1.00004: A New Pion-Nucleon Partial Wave Analysis Michael Sadler, Shon Watson, Jugoslav Stahov Existing determinations of the masses, widths and decay modes of low-lying excited states of the nucleon, as compiled in the Review of Particle Physics, are determined from energy-independent partial wave analyses of pion-nucleon scattering data. For the N*(1440) and most other resonances under 2 GeV, the analyses cited are the Karlsruhe-Helsinki, Carnegie Mellon-Berkeley and Kent State analyses, the latter of which used the elastic amplitudes from the other two. The data included in these analyses were published before 1980. Other analyses, notably the recent ones from George Washington University and the Pittsburgh-Argonne group, are ``not used for averages, fits, limits, etc.'' Complete sets of measurements (differential cross sections, analyzing powers and spin rotation parameters) have been measured in the N*(1440) resonance region since 1980, culminating in the Crystal Ball program at BNL to measure all-neutral final states (charge exchange, multiple pi-zero final states, and inverse photoproduction). A new partial wave analysis of the Karlsruhe-Helsinki type has been started by Abilene Christian University, University of Tuzla, and Rudjer Boskovic Institute. The analysis is constrained by fixed-t and interior hyperbolic dispersion relations. Comparisons of the new analysis to modern experimental data and to previous analyses will be presented. [Preview Abstract] |
Friday, October 6, 2006 2:18PM - 2:30PM |
OT1.00005: Changes in Routes to Chaos with Increasing Number of Degrees of Freedom Zdzislaw Musielak There are at least five basic routes to chaos discovered in low-dimensional dynamical systems. To investigate routes to chaos in higher-dimensional systems, generalized Lorenz models and coupled Duffing oscillators were considered. The generalized Lorenz models with dimensions ranging from four to nine were constructed by taking into account higher-order modes in doubled Fourier expansions of a stream function and temperature variations. Degrees of freedom were added to the original Duffing system by coupling two, three, four, five and six non-linear oscillators together. The obtained results show that routes to chaos in these systems significantly change when the number of degrees of freedom is increased. Physical implications of these result will be discussed. [Preview Abstract] |
Friday, October 6, 2006 2:30PM - 2:42PM |
OT1.00006: Probabilistic aspects of isoscaling Jorge Munoz, Jorge Lopez, Claudio Dorso, Carlos Hernandez The problem of isoscaling, found in nuclear reactions, was studied using simple probabilistic arguments. Sampling two reservoirs containing different number of ”neutrons” but the same number of ”protons”, produced isoscaling. The parameters alpha and beta extracted from these results were found to depend on the number of protons and neutrons in each reservoir. These results show that mere sampling is a major contributor to isoscaling phenomena in nuclear reactions. [Preview Abstract] |
Friday, October 6, 2006 2:42PM - 2:54PM |
OT1.00007: What should be our approach to understanding the universe? Hui-Yiing Chang Besides understanding the concepts of physics and learning to apply them to different contexts, it is most crucial that students examine the basis of their beliefs in these theories. It becomes necessary, then, to expand our conception considerably beyond the scope of the physics textbook. This process is possibly effectuated by gaining a representative understanding of the liberal arts through study of several areas, and self-expression of one's convictions. Respecting of differences is important, as well as the expectation that proposing of new ideas is often accompanied by conflict and disequilibrium within individuals and the community. In this session, we will discuss the approaches of significant ancient scientists and philosophers to understanding the universe, and trace the development to modern conventionally accepted theories. A higher goal of physics education is to produce ``reforming physicists'' that unravel the truth for the betterment of society. [Preview Abstract] |
Friday, October 6, 2006 2:54PM - 3:06PM |
OT1.00008: Interaural Coherence and Localization Eric Pepin In a study of the relationship between interaural coherence and localization ability, two experiments were performed. Both made use of a 1/3 octave band of low frequency sound and a 1/3 octave band of high frequency sound. Stimuli with coherences ranging from 0.2 to 0.8 were created in three recording environments using a KEMAR and digitally altered to eliminate interaural level differences (ILD). The environments had short, medium, and long reverberation times. The coherences were measured and were accurate to one significant figure. Experiment 1 had two goals: to determine the relationship between interaural coherence and the ability to localize using interaural time differences (ITD) and to determine if localization ability was dependent only on coherence. The relationship between coherence and localization was tested in a headphone lateralization experiment in which psychometric functions were generated. The functions revealed a linear relationship, with the ability to localize high coherence sounds breaking down quickly at small ITD. Within standard error, ITD localization appeared to be dependent only on coherence. In Experiment 2, a 3-down 1-up staircase method was employed to determine how opposing ILDs affected ITD localization. When the task could be completed, the threshold values were linearly related, however, the ability broke down at large ILDs. Both experiments provide a linear description of interaural coherence and localization, with thresholds being sharp deviations from these trends. [Preview Abstract] |
Friday, October 6, 2006 3:06PM - 3:18PM |
OT1.00009: Is Quantum Mechanics Nonlocal? James Espinosa The formalism of Quantum Mechanics can be used to predict eigenvalues and probabilities. So, whether this formalism requires the quantum world to be local or non local should be expressible in probabilistic terms and without the introduction of, so-called, hidden variables. Local or not should be expressible within the theory itself. This would mean that Bell's inequality is in fact empty of physical implications for the quantum theory. We put forth a necessary condition for the quantum theory of the decay of two-spin bound states to be local and find that this condition is satisfied by these systems. [Preview Abstract] |
Friday, October 6, 2006 3:18PM - 3:30PM |
OT1.00010: Angular Momentum in de Broglie-Bohm Quantum Theory Donald H. Kobe The time rate of change of angular momentum of a many-particle system in an electromagnetic field in the de Broglie-Bohm formulation of quantum mechanics is equal to the classical torque plus a quantum torque due to the quantum force. When an average is taken with respect to the probability density the average of the quantum torque is zero. The average of the time derivative of the angular momentum is equal to the time derivative of the average angular momentum. The average of the equation is thus the same as the classical form. The resulting equation agrees with Ehrenfest's theorem for the quantum angular momentum operator. [Preview Abstract] |
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