Bulletin of the American Physical Society
2005 TSAPS/AAPT/SPS Joint Fall Meeting
Thursday–Saturday, October 20–22, 2005; Houston, TX
Session C4: Computational II |
Hide Abstracts |
Room: Shamrock B 261B |
Friday, October 21, 2005 3:00PM - 3:12PM |
C4.00001: Computing Energy Spectra for Simple Quantum Systems Using the Feynman-Kac Path Integral James M. Rejcek, Nail G. Fazleev, John L. Fry A method for calculating the first few energy eigenvalues for quantum systems using the Feynman-Kac path integral is presented. The exact analytical solution of the Feynman-Kac path integral for the finite square well is presented and compared with numerical simulations approximated by random walk simulations on a discrete grid. Using the Laplace transform of the Feynman-Kac path integral and knowing the form of the eigenvalue expansion of the integral, it is possible to calculate the first few energy eigenvalues within an estimated uncertainty. The method provides exact values in the limit of infinitesimal step size and infinite time for the ground state. [Preview Abstract] |
Friday, October 21, 2005 3:12PM - 3:24PM |
C4.00002: Self-Trapping at the Critical Point Terrence Reese, Bruce Miller Measurements of the properties of an excess low mass particle equilibrated in a fluid suggest that self-trapping occurs in a neighborhood of the liquid vapor critical point. Typical experiments performed to date include the mobility of the electron, and the annihilation rate of the positron and positronium. In particular, the enhanced annhilation rate for positron decay suggests that a ``microdroplet'' of the fluid nucleates around the particle while, in the case of positronium, there is a corresponding dimunition of the pick-off decay rate suggesting the nucleation of a droplet. In earlier work we used both mean field theory and the Feynman path integral to model both processes. Using recent, numerically exact, Lennard-Jones parameters for the host fluid, here we report on the first path integral studies of self-trapping at the critical point. In this preliminary study we investigate local structural changes in the fluid in the neighborhood of the quantum particle for a repulsive hard sphere particle-atom potential. By varying the hard sphere radius we are able to determine the conditions for maximum structural deformation. Using a crude estimator we can also approximate the pick --off decay rate for psoitronium. This permits a comparison with similar computations at neighboring temperatures and densities, and provides a rough idea of how the decay rate depends on the range of the repulsive Ps-atom interaction potential. [Preview Abstract] |
Friday, October 21, 2005 3:24PM - 3:36PM |
C4.00003: Short-Range Resonating Valence-Bond Theory and ``Hard Dimer'' Douglas Klein The structure of resonating valence-bond (RVB) wave-functions with singlet-spin-pairing limited to nearest neighbor sites is considered. It is noted that these basis states manifest a type of long-range spin-pairing order, from which it follows that in general extended systems the space so spanned is partitioned into different sectors, which in a very general context are non-interacting. So-called ``hard dimer'' models are defined on this RVB space, and some are solved exactly. Special attention is directed to the honeycomb lattice and subsets thereof, such as is of central interest in classical areas of (organic) chemistry. [Preview Abstract] |
Friday, October 21, 2005 3:36PM - 3:48PM |
C4.00004: Development of Antennas for Radially Polarized Terahertz Radiation Matthew Escarra, Jason Deibel, Kanglin Wang, Daniel Mittleman Recent advances in ultrafast optical techniques have created many new opportunities for sensing and imaging with terahertz radiation. However, much difficulty has been encountered when attempting to develop waveguiding techniques for terahertz pulses. An effective waveguide must exhibit both low loss and low dispersion over a broad frequency bandwidth. It has been demonstrated that a radial mode traveling down a cylindrical metal wire is a promising candidate. Unfortunately, typical Hertzian dipoles generate a linearly polarized field, which couples very poorly to the radially polarized guided mode. We describe a novel photoconductive terahertz antenna design with radial symmetry, which should permit significant improvement in coupling to cylindrical wire waveguides. Finite element simulations demonstrate that this antenna is capable of producing the desired radial mode. Simulations of the antenna coupling to the wire waveguide suggest that a coupling efficiency of greater than 50{\%} is achievable. Experimental analysis of the fabricated antenna supports these simulated results. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700