Bulletin of the American Physical Society
2010 Annual Meeting of the California-Nevada Section of the APS
Volume 55, Number 12
Friday–Saturday, October 29–30, 2010; Pasadena, California
Session D4: Atomic and Molecular Physics II |
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Chair: John Price, California State University, Dominguez Hills Room: Building 47, Downs Laboratory of Physics, Classroom 107 |
Friday, October 29, 2010 4:00PM - 4:12PM |
D4.00001: Efficient multipole expansion techniques for modeling the electrostatic field of large distributions of charge Apostol Gramada, Philip Bourne Despite being very useful as a conceptual tool, the multipole expansions have rather limited use in the {\em practical} numerical modeling of the electrostatic fields. What prevents their application to many practical problems are the slow convergence and/or inapplicability of these expansions at short distances from the distribution of charge, and the dependence of these convergence properties on the expansion center. These limitations are severely restrictive, for example, when modeling the electrostatic field of large biomolecules in the immediate vicinity of their surface. We present two techniques -- the rankwise distributed multipole analysis (RWDMA)\footnote{A. Gramada and P.E. Bourne, Phys. Rev. E 78, 066601 (2008)} and a partitioning algorithm\footnote{A. Gramada and P.E. Bourne, (submitted)} -- techniques that, together, overcome the above limitations, and illustrate them with applications to the coarse-grained modeling of the field of large biological molecules. [Preview Abstract] |
Friday, October 29, 2010 4:12PM - 4:24PM |
D4.00002: Multipole Excitation of Fullerene C$_{60}$ Molecules in a Semi-Classical Model Krishna Lamichhane, Matthias Brack, Peter Winkler The local current approximation (LCA) is introduced and derived from a general variational principle. This approach serves as a semiclassical description of strongly collective excitations in finite fermions systems. Here it is first applied to study the coupling of surface and volume dipole oscillations in the fullerene C60 molecules. The spectrum obtained for the coupling of the pure translational mode with compressional volume modes in the semiclassical LCA shows the close agreement with the experimentally observed spectra. Applying the same approach to the photoionization cross section of C60, we discuss the results of higher multipole resonances of fullerene molecules. The comparison to data obtained from electron scattering experiments reveals the adequacy of the semi-classical approach as well as the collective nature of several high angular momentum resonances. Similar to the results of the dipole case, the coupling of surface and volume Plasmon modes in C60 molecules is seen to shift both peaks slightly towards lower energies. [Preview Abstract] |
Friday, October 29, 2010 4:24PM - 4:36PM |
D4.00003: Atomic Physics Measurements in Support of X-ray Astronomy Peter Beiersdorfer, G.V. Brown, R.E. Kelley, C.A. Kilbourne, M. Leutenegger, F.S. Porter, M. Obst, J.K. Lepson, P. Desai, M.F. Gu X-ray astronomy has been a voracious consumer of atomic data, especially after the launch of the Chandra and XMM-Newton X-ray Observatories, which have produced very high-resolution grating spectra of point sources. One of the important issues has been to understand the physics underlying the Fe L-shell spectra, and the Fe XVII spectrum in particular. A lot of progress has been made, including measurements of the electron-impact and resonance excitation cross sections, which now provides a rather clear picture of the production mechanism of the Fe XVII spectrum. Recent measurements of the radiative rates provide additional information on the deexcitation channels, while investigations of dielectronic satellite transitions provide a measure of the electron temperature. Many questions, however, still remain. Work at LLNL was performed under the auspices of DOE under contract DE-AC53-07NA27344 and supported by NASA's APRA program under contracts NNH07AF81I and NNG06WF08I. Part of this work was supported by Chandra Cycle 10 Award AR9-0002X. [Preview Abstract] |
Friday, October 29, 2010 4:36PM - 4:48PM |
D4.00004: Atomic and Condensed Matter Spectroscopy with an Optical Frequency Comb Keith Penney, Derek Kimball, Erik Helgren, Jason Singley, Tony Masiello, Khoa Nguyen Optical frequency combs are innovative tools created only in the last decade which have made possible many advances in spectroscopy and have enabled ultra-precise atomic clocks based on optical transitions. An optical frequency comb is based on a femtosecond pulsed laser; the Fourier transform of the train of femtosecond pulses is a ``comb'' of equally-spaced frequencies spanning from visible to infrared. We discuss how the new optical frequency comb at California State University -- East Bay will be used for direct spectroscopy of atoms to measure hyperfine structure and search for heretofore undiscovered energy levels in rare earth atoms. We also discuss application of the femtosecond laser for characterization of the optical properties of bulk materials. [Preview Abstract] |
Friday, October 29, 2010 4:48PM - 5:00PM |
D4.00005: Emergence of semifluxons in long 0-$\pi$-0 Josephson junctions as a topological state change Michael Grupp, Reinhold Walser, Wolfgang Schleich We present a generic, analytical model of the emergence of semifluxons in long 0-$\pi$-0 Josephson junctions and demonstrate its implementation in the context of ultracold matter waves using optical junctions. Semifluxons are well-known topological states at the interface of superconductors (1), related to ordinary quantized magnetic flux or vortices in superfluid systems. They appear in particular when there is a spatially varying tunnel rate in the Josephson junction. This interesting subject has stimulated previous work to implement analogous states in ultracold quantum gases (2). \\[4pt] (1) E. Goldobin, et al., Phys. Rev. Lett., 92, 057005 (2004)\\[0pt] (2) R. Walser, et al., NJP, 10, 045020 (2008) [Preview Abstract] |
Friday, October 29, 2010 5:00PM - 5:12PM |
D4.00006: How the geometry of phase space influences chaotic ionization Korana Burke, Kevin Mitchell A Rydberg electron exposed to periodic alternating electric field pulses exhibits chaotic behavior. The ionization fraction drastically changes depending on the size and separation of positive and negative pulses. The ionization fraction as a function of the pulse strength shows a step-function-like behavior which disappears at longer kicking periods. Using the geometric tools from nonlinear dynamics we explain this and the rest of the features of the dependence of the ionization fraction on kicking parameters. [Preview Abstract] |
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