Bulletin of the American Physical Society
Joint Fall 2010 Meeting of the Texas Sections of the APS, AAPT, Zone 13 of SPS and the National Society of Hispanic Physicists
Volume 55, Number 11
Thursday–Saturday, October 21–23, 2010; San Antonio, Texas
Session SM4: Computational and General II |
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Chair: Liao Chen, University of Texas at San Antonio Room: University Center I Pecan Room, 2nd floor |
Saturday, October 23, 2010 10:00AM - 10:12AM |
SM4.00001: Simulating rigid body motion in incompressible two phase flow for applications in energy harvesting Curtis Lee, Jessica Sanders, John Dolbow, Peter Mucha, Tod Laursen Computational treatment of floating solids, in the presence of free surfaces and/or breaking waves, poses several modeling challenges. A motivating example where these systems are of interest is found in offshore wave energy harvesting systems, where a floating structure converts mechanical oscillations to electrical energy. In this work, we take the first steps in developing a robust computational strategy for treating rigid bodies with possible internal dynamics, such that they may be fully coupled to a fluid environment with free surfaces and arbitrarily large fluid motion. Our technique solves Lagrangian type rigid body equations coupled with the Eulerian formulation of the Navier Stokes equations for an immersed solid. This technique represents a subtle departure from standard methods, which solve the equations of motion completely on the Eulerian grid, and therefore facilitates the integration of internal components. To demonstrate this ability, simple rotational and translational components have been implemented with promising results. [Preview Abstract] |
Saturday, October 23, 2010 10:12AM - 10:24AM |
SM4.00002: Numerical Simulation of Optical Propagation through Atmospheric Turbulence Pushpa Raj Pudasaini, Michael Vera, Madhab Pokheral We studied the propagation of optical waves through atmospheric turbulence. The extended random media is modeled by a set of two dimensional thin Gaussian phase screens with the phase power spectral densities appropriate to the natural medium being modeled. We use the spectrum developed by Kolmogorov for the variation of index of refraction. Rather than treat these perturbations throughout the atmosphere, their effect for a portion of the propagation is usually addressed using a phase screen. This modeling method alters the phase of the optical wave at a discrete series of locations, in a way that corresponds to the cumulative impact of the fluctuations. Usually in the interest of the computational efficiency, simulation of the optical travel proceeds by using a position space representation of the wave function at the screen location, then using the Fourier methods to propagate between screens in the wave vector space representation. We used Crank-Nicolson method for simulating the propagation between the screens. We studied the inner scale effect on the irradiance variance for the different strength parameters. Our simulation results bear the strong resemblance to laser propagation experiment over kilometer length path in the atmosphere. [Preview Abstract] |
Saturday, October 23, 2010 10:24AM - 10:36AM |
SM4.00003: Accelerating Convergence of Generalized Hypergeometric Functions Joshua Willis The class of generalized hypergeometric functions $_pF_q$ is very broad, encompassing most of the special functions of physics. They can be defined by a power series that, for $_{q+1}F_q$, converges when $|z| < 1$. But in many cases of interest, particularly at the branch point $z = 1$, this power series converges too slowly to be computationally useful. Series acceleration techniques can often transform a slowly convergent series into a computationally feasible algorithm, but for complex parameters the generalized hypergeometric function resists most acceleration techniques. In this talk we show how we can accelerate such series, using remainder estimates in terms of inverse power series that can be calculated to any desired asymptotic order. For many cases, this may provide an effective technique to evaluate such functions, particularly near the branch point where direct integration of the differential equation fails. [Preview Abstract] |
Saturday, October 23, 2010 10:36AM - 10:48AM |
SM4.00004: Further Studies of Hydrogenic Quantum Systems Using the Feynman-Kac Path Integral Method J.M. Rejcek, N.G. Fazleev The Feynman-Kac path integral method is applied to atomic hydrogen quantum system for the purpose of evaluating eigenvalues. These are computed by random walk simulations on a discrete grid. The study includes rescaling and the use of symmetry that allows higher order eigenstates to be computed. The method provides exact values in the limit of infinitesimal step size and infinite time for the lowest eigenstates. [Preview Abstract] |
Saturday, October 23, 2010 10:48AM - 11:00AM |
SM4.00005: Computational Study of a Random Surface Model Matthew Drake, Jonathan Machta, Youjin Deng, Douglas Abraham, Charles Newman We present results of Monte Carlo simulations of the equilibrium random surface model proposed in [1]. The model includes both the Volmer-Weber and Stranski-Krastanow growth regimes. In one limit, the model reduces to the two-dimensional Ising model in the height representation. We find that the critical temperature is reduced when the Ising model constraint of a single height steps is relaxed. The critical properties of the model are explored using a variant of the worm algorithm. \\[4pt] [1] C. Newman and D. B. Abraham, Equilibrium Stranski-Krastanow and Volmer-Weber models, Europhys. Lett., 86, 16002 (2009). [Preview Abstract] |
Saturday, October 23, 2010 11:00AM - 11:12AM |
SM4.00006: New Trigger Logic for the STAR Forward Meson Spectrometer John Calvin Martinez The Forward Meson Spectrometer (FMS) is an electromagnetic calorimeter in the STAR Experiment at RHIC that covers the pseudorapidity region 2.5 $<$ eta $<$ 4 and full azimuth. One of the goals of the FMS is to separate two possible causes of large, previously observed proton transverse single-spin asymmetries, the Sivers effect and the Collins effect. To meet this goal, it will be valuable for the FMS to trigger more efficiently on eta mesons and jet-like events than it does at present. In order to increase the trigger efficiency for non-localized events, like jets and eta decays, a new trigger algorithm has been developed that includes a system of eight overlapping jet-patches, each covering an approximate area of 1.5 x 1.5 in azimuth-pseudorapidity space. The new trigger logic and the expected rates for 200 and 500 GeV pp collisions will be presented. [Preview Abstract] |
Saturday, October 23, 2010 11:12AM - 11:24AM |
SM4.00007: A Newtonian Description of the Linear Stark Effect James Woodyard, James Espinosa After the discovery of the magnetic effect on spectral lines by Zeeman, it was only natural that physicists should look for a similar effect when an electric field was applied. A nonlinear model of the hydrogen atom developed by Woldemar Voigt was investigated and predicted a second order effect that would require huge electric fields in the ten of millions of volts per centimeter. Fortunately, Johannes Stark ignored this ominous prediction by a leading theoretician and discovered a linear electric effect that would quickly be named after himself. Soon after Bohr introduced his quantum theory of the Hydrogen Atom, Schwarzschild and Epstein independently utilized Sommerfeld's extension of Bohr's theory to arrive at an empirically correct formula. We will show how our classical theory of the hydrogen atom can account for the linear Stark effect. [Preview Abstract] |
Saturday, October 23, 2010 11:24AM - 11:36AM |
SM4.00008: Wide-Angle Spectral Split-Step Method for 2D or 3D Beam Propagation Clifton Clark, Robert Thomas We develop a method for non-paraxial beam propagation that obtains a speed improvement over the Finite-Difference Split-Step method (FDSSNP) recently reported by Sharma \emph{et al.}. The method works in the eigen-basis of the Laplace operator ($\nabla_T^2$), and in general requires half as many operations to propagate one step forward so that a 2X speedup can be realized. However, the new formulation allows the Fast Fourier Transform (FFT) algorithm to be used, which allows an even greater speedup. The method does not require a numerical matrix inversion, diagonalization, or series evaluation. The diffraction operator is not approximated, and in the absence of refractive index fluctuations the method reduces to an exact solution of the Helmholtz equation. [Preview Abstract] |
Saturday, October 23, 2010 11:36AM - 11:48AM |
SM4.00009: Compact Accelerator Driven Thorium Cycle Subcritical Reactor Akhdiyor Sattarov, Peter McIntyre Thorium cycle subcritical reactor driven by 800MeV protons delivered by flux coupled superconducting stack of cyclotrons can operate as a sealed unit for up to 7 years and is stable against melt-down. Small, low power units with minimum security and small crew of operators are perfect candidates for powering remote small towns. The reactor can eat long-lived waste coming from conventional nuclear power plants and can be used as sealed waste processing unit powering at the same time remote, low power demanding objects. [Preview Abstract] |
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