Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session U10: Computational Physics |
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Sponsoring Units: DCOMP Chair: Jerome Delhommelle, University of South Carolina Room: Hyatt Regency Jacksonville Riverfront City Terrace 6 |
Monday, April 16, 2007 3:30PM - 3:42PM |
U10.00001: Insights into the Molecular Mechanism underlying Polymorph Selection Jerome Delhommelle, Caroline Desgranges We use molecular simulations to study polymorph selection during the crystallization of charge-stabilized colloidal suspension. By modifying the conditions of crystallization, we invert the stability of two polymorphs and induce the formation of crystallites whose structure is predominantly that of the stable polymorph. However, our simulations reveal that kinetics play a major role not only during the nucleation step but also in the growth mechanism. The growth of post-critical crystallites of the stable polymorph proceeds through a complex mechanism involving the cross-nucleation of a third metastable polymorph followed by the conversion of this third polymorph into the stable structure. [Preview Abstract] |
Monday, April 16, 2007 3:42PM - 3:54PM |
U10.00002: Quantum Modeling in Simulation of Turbulent Flows Yosef Tirat-Gefen Major atmospheric events can be modeled by turbulent flows. We provide a brief introduction to the mathematical fundamentals of turbulence and fluid dynamics, and discuss the possible use of modeling techniques borrowed from quantum mechanics. This work deals with an isotropic homogeneous flow, which allows us to study the turbulence phenomena in a more simplified way. We represent the Navier-Stokes equations modeling fluctuations for such a type of flow by applying the Fourier transform to each term, leading to space-time representation of the flow. We trace a parallel of such representation to ones found in quantum systems. We revisit the gas lattice automata model introduced in 1973 by Hardy, de Pazzis and Pomeau, and investigate how to implement it in highly parallel fine-grain machines, such as state-of-the-art supercomputers supporting reconfigurable processors and the future quantum computers. Unlike the probabilistic partial differential equation (PPDE) models used in traditional turbulent flow theory, there is no need of complex calculations or integrations as the flow is modeled as an assembly of cells and particles. [Preview Abstract] |
Monday, April 16, 2007 3:54PM - 4:06PM |
U10.00003: Numerical Calculation of Nonlinear Seismic Pulse Propagation in a Hysteretic Elastic Material Dan Kosik The stress-strain relation for materials such as soil and sand exhibit hysteretic elastic behavior and are modeled using the Preisach-Mayergoyz method for a numerical calculation of a propagating seismic pulse. The source pulse is taken to be the result of pressure applied to the inner surface of a cylindrical cavity in order to simulate a two dimensional dynamite source. The nonlinear differential equation of motion that is solved includes traditional nonlinear elasticity terms appropriate to materials with atomic elasticity and the dominant anelastic terms appropriate to consolidated materials that exhibit hysteretic elastic behavior. For parameters characteristic of sand at the Earth's surface, a comparison of nonlinear to linear seismic pulse propagation gives a nonlinear pulse with a much larger amplitude and slower propagation speed than a corresponding linear pulse. These results have important implications for the detailed behavior of strong seismic waves moving in soft sediments, their dominant frequencies, amplitudes, and methods by which they may be attenuated will depend on getting the detailed pulse structure right. [Preview Abstract] |
Monday, April 16, 2007 4:06PM - 4:18PM |
U10.00004: Chaos Control of 4-D Chaotic Systems using Recursive Backstepping Nonlinear Controller John Laoye, Uchechukwu Vincent, Semiu Kareem This paper examines chaos control of two four dimensional chaotic systems namely: the Lorenz-Stenflo (LS) system that models low-frequency short-wavelength gravity waves and a new four-dimensional chaotic system (Qi systems), containing three cross products. The control analysis is based on recursive backstepping design technique and it is shown to be effective for the 4-D systems considered. Numerical simulations are also presented. PACS: 05.45.Pq; 05.45.Gg; 05.45.Ac Keywords: Chaos control; Lorenz-Stenflo System; Qi System; Backstepping design [Preview Abstract] |
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