Bulletin of the American Physical Society
2005 72nd Annual Meeting of the Southeastern Section of the APS
Thursday–Saturday, November 10–12, 2005; Gainesville, FL
Session CC: Theoretical Physics II |
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Chair: Alan Dorsey, University of Florida Room: Hilton Azalea |
Thursday, November 10, 2005 10:45AM - 10:57AM |
CC.00001: Simulating Underwater Leader Growth Lee Culver, Gary Hunter, James Espinosa Dielectric breakdown in water is always preceded by the growth of leaders. The structure and growth of these leaders have been previously simulated with fractals; however, present mathematical models are rife with undesired parameters. We eliminate many of these parameters with a physical model that describes a leader as a protonic mobility wave. Graphical-simulation results will be presented and compared with photographic data. [Preview Abstract] |
Thursday, November 10, 2005 10:57AM - 11:09AM |
CC.00002: A Nonlinear Oscillator With Velocity Dependent Frequency 'Kale Oyedeji, Ronald E. Mickens We study the mathematical properties of a harmonic type oscillator in which the square of the angular frequency is an even, quadratic function of the velocity. After calculating the first integral of this system, phase-space and symmetry arguments are used to prove that all solutions are periodic. From the first-integral, a closed form, integral representation is obtained for the period of the oscillations; but, this formula does not allow for the explicit determination of the period as a function of the initial amplitude. (The initial conditions are taken to be x(0) = A and dx(0)/dt = 0.) However, the application of the mean-value theorem to the integral, along with information on the small amplitude behaviors of the frequency gives a theoretical, closed form expression for the dependence of the frequency on A. We compare this theoretical expression to ``data'' gotten from the numerical integration of the differential equations. [Preview Abstract] |
Thursday, November 10, 2005 11:09AM - 11:21AM |
CC.00003: New Method for Calculating The Electron Impact Ionization of Ions Bidhan Saha, Arun K. Basak, M.A. Uddin The electron impact single ionization of ionic targets ( 1 $\le $ Z $\le $ 92) is reported using a recently proposed method [1]. It is based on the simplified version of the improved-binary-encounter-dipole (siBED) model [2]. Including the both the ionic and the relativistic corrections (RQIBED model) [3] we have recently investigated the ionization of He-like[4] and Be-like systems [5] with considerable success. However, the presence of adjustable parameters make it dependent on available experimental results We have applied a new techniques to avoid this and show explicitly how to evaluate cross sections for filled as well as unfilled s-orbital targets. Details will be presented at the conference. [1] M. A. Uddin, A. K. F. Haque, a. K. Basak, K. R. Karim and B. C. Saha, Phys Rev A (2005) in press [2] W. M. Huo, Phys. Rev. A 64, 042719 (2001). [3]M. A. Uddin, M. A. K. F. Haque, A. K. Basak and B. C. Saha, Phys. Rev. A 70, 032706 (2004). [4] M. A. Uddin, A. K. F. Haque, M. S. Mahbub, K. R. Karim, A. K. Basak, B. C. Saha, Int. J. Mass Spect. 244, 76 (2005). [Preview Abstract] |
Thursday, November 10, 2005 11:21AM - 11:33AM |
CC.00004: Charge Correlations in Spectral Line Shapes Jeffrey Wrighton, James Dufty Spectral line broadening theory is reformulated to examine the validity of standard approximations for the correlations among the plasma perturbers (electrons and ions) and with a charged radiator. Using conditions for quasi-static ions, the broadening operator (width and shift operator) is calculated to second order in the interaction of the plasma perturbers with the bound electrons of the radiator. All other charge correlations are included without approximation, including plasma coupling to the total net charge on the radiator. A semi-classical representation of these results provides the necessary physical quantities required for recently proposed methods of molecular dynamics simulation in plasma spectroscopy. The effects of correlations on the microfield distribution, shift operator, and electron broadening are discussed briefly. [Preview Abstract] |
Thursday, November 10, 2005 11:33AM - 11:45AM |
CC.00005: Some Comments on Regularized Classical Coulomb Potentials Wayne Bomstad, Aparna Baskaran, John Klauder, James Dufty A classical statistical mechanics for electron -- proton charge neutral systems does not exist, due to the singular attractive Coulomb interaction at short distances. This problem is removed in quantum theory due to diffraction effects. A classical theory is restored using regularized Coulomb interactions incorporating these effects which are finite at short distances. Regularized Coulomb interactions can be constructed by an exact mapping of the quantum pair distribution function onto the corresponding classical function. Approximate evaluations of this mapping by variational and perturbation methods are critiqued, with suggestions for improvement. [Preview Abstract] |
Thursday, November 10, 2005 11:45AM - 11:57AM |
CC.00006: Radial oscillation of a gas bubble in a fluid as a problem in canonical perturbation theory James Stephens The oscillation of a gas bubble is in a fluid is of interest in many areas of physics and technology. Lord Rayleigh treated the pressure developed in the collapse of cavitation bubbles and developed an expression for the collapse period. Minnaert developed a harmonic oscillator approximation to bubble oscillation in his study of the sound produced by running water. Oscillating bubbles are important to oceanographers studying the sound spectrum produced by water waves, geophysicists employing air guns as acoustic probes, mechanical engineers concerned with erosion of turbine blades, and military engineers concerned with the acoustic signatures developed by the propeller screws of ships and submarines. For the oceanographer, Minnaert's approximation is useful, for the latter two examples, Lord Rayleigh's analysis is appropriate. On the one hand, a bubble can be treated as a harmonic oscillator in the small amplitude regime, whereas even in the relatively moderate pressure regime characteristic of air guns the oscillation is strongly nonlinear and amplitude dependent. Is it possible to develop an analytic approximation that affords insight into the behavior of a bubble beyond the harmonic approximation of Minnaert? In this spirit, the free radial oscillation of a gas bubble in a fluid is treated as a problem in canonical perturbation theory. Several orders of the expansion are determined in order to explore the dependence of the oscillation frequency with bubble amplitude. The expansion to second order is inverted to express the time dependence of the oscillation. [Preview Abstract] |
Thursday, November 10, 2005 11:57AM - 12:09PM |
CC.00007: Green -Kubo Expression for the shear viscosity of a dense granular fluid. Aparna Baskaran, James Dufty A system of smooth inelastic hard spheres is considered as a microscopic model for a granular fluid. The standard method of linear response used to obtain exact expressions for hydrodynamic transport coefficients for normal fluids is generalized for this inherently nonequilibrium system. This method is then used to obtain Helfand and Green -- Kubo forms for the shear viscosity of this granular fluid. This expression has the important property that there are no apriori limitations on density or the degree of inelasticity on its domain of validity. Several differences from the corresponding result for normal fluids with continuous potentials and that for elastic hard spheres are noted. Then, some approximate analytical evaluations of this expression are presented and used to make some observations on the mechanisms of momentum transport processes in this fluid. [Preview Abstract] |
Thursday, November 10, 2005 12:09PM - 12:21PM |
CC.00008: Application of Microchannel Plate System for Mass Spectrometry Measurements Misganaw Getaneh, Ken Grabowski, David Knies, Catalina Cetina, Graham Hubler, Scott Tumey A microchannel plate (MCP) detector module with active area of 10 x 2 cm$^{2}$ is used as a position detector for mass spectrometry. The MCP detects electrons scattered by an MeV ion beam as it goes through a thin Carbon foil which is placed at a 45$^{\circ}$ angle with respect to the beam. The scattered electrons' transverse motion is restricted by application of uniform electric and magnetic fields parallel to the axis of the MCP. The charge that is amplified by the MCP is deposited on a double-delay line anode. Differential timing and charge partitioning are used to determine the horizontal and vertical positions of the ion. [Preview Abstract] |
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