Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session J2: Prize Session (DCP, DCOMP, GSNP) |
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Sponsoring Units: DCP DCOMP GSNP Chair: Daniel Neumark, University of California, Berkeley Room: Colorado Convention Center Four Seasons 4 |
Tuesday, March 6, 2007 11:15AM - 11:51AM |
J2.00001: Frontiers of Surface Science. Structure, Bonding and Dynamics on the Nanoscale at High Pressures and at the Buried (solid-liquid and solid-solid) Interfaces Invited Speaker: Model surfaces from single crystals to monodispersed nanoparticles are investigated at high pressures and at liquid interfaces by sum frequency generation (SFG) vibrational spectroscopy and high pressure scanning tunneling microscopy. The phenomena discovered by surface studies at low pressures in the past, adsorbate-induced restructuring, the chemical activity of surface defects, surface mobility of adsorbates and coadsorption-induced ordering are detected at high pressures as well. Newly discovered surface phenomena include the low melting point of nanoparticles, the coadsorption of water and hydrogen at polymer and metal surfaces, respectively, and hot electron flow during exothermic processes across oxide-metal interfaces (nanodiodes). Applications of surface science expanded into nanosciences, catalysis, tribology, polymers, biointerfaces, microelectronics, energy conversion and environmental chemistry will be discussed. [Preview Abstract] |
Tuesday, March 6, 2007 11:51AM - 12:27PM |
J2.00002: Aneesur Rahman Prize Talk Invited Speaker: During the past decade there has been a unique synergy between theory, experiment and simulation in Soft Matter Physics. In colloid science, computer simulations that started out as studies of highly simplified model systems, have acquired direct experimental relevance because experimental realizations of these simple models can now be synthesized. Whilst many numerical predictions concerning the phase behavior of colloidal systems have been vindicated by experiments, the jury is still out on others. In my talk I will discuss some of the recent technical developments, new findings and open questions in computational soft-matter science. [Preview Abstract] |
Tuesday, March 6, 2007 12:27PM - 1:03PM |
J2.00003: Conformation-specific spectroscopy and dynamics in the complexity gap Invited Speaker: Studies of the spectroscopy and conformational isomerization dynamics of flexible molecules typically fall into one of two size regimes: (i) small-molecule studies in which the molecule possesses two minima and a single barrier (e.g., \textit{cis-trans} isomerization about a double bond) or (ii) large macromolecules for which it is impossible to describe the potential energy surface in exhaustive detail (e.g., protein folding). Between them is a `complexity gap' of considerable proportions. This talk will describe our group's contributions to studies of molecules that are in that complexity gap in the sense that they have potential energy surfaces containing tens to hundreds of minima, and many times that number of transition states. By employing double resonance laser spectroscopy of isolated molecules cooled in a supersonic expansion, it is possible to obtain the ultraviolet and infrared spectral signatures of the individual conformational isomers of these molecules free from interference from others present in the sample. This foundation of spectroscopic data also serves as the basis for conformation-specific studies of the dynamics of conformational isomerization. In these studies, either infrared excitation or stimulated emission pumping (SEP) is used to excite a single conformation with a well-defined internal energy, thereby initiating conformational isomerization. By re-cooling the products prior to interrogation downstream, the energy thresholds for isomerization between individual X$\to $Y reactant-product pairs can be determined. Several examples from our recent work will be given to illustrate the kinds of insight that can be drawn from these studies regarding the conformational preferences, spectral signatures, barrier heights and relative energies of minima, fractional abundances, isomerization pathways, and internal energy flow accompanying isomerization. [Preview Abstract] |
Tuesday, March 6, 2007 1:03PM - 1:39PM |
J2.00004: Nicholson Medal - Award Talk Invited Speaker: |
Tuesday, March 6, 2007 1:39PM - 2:15PM |
J2.00005: Nicholas Metropolis Award Talk: Quasi-static Modeling of Plasma and Laser Wakefield Acceleration Invited Speaker: Plasma wakefields driven by intense ultrashort charged particle or laser beams can sustain acceleration gradients three orders of magnitude larger than conventional RF accelerators. These wakefields are promising for accelerating charged particles in short distances for applications such as an energy booster of a linear collider and as a ultra-compact accelerator. In the Plasma Wakefield Accelerator (PWFA) or Laser Wakefield Accelerator (LWFA), the space charge force of an electron beam or the ponderomotive force of a laser beam expels plasma electrons away from its path, forming a bubble-like structure where the longitudinal electric field inside of it provides accelerating and the transverse Lorentz force provides focusing forces on electrons. Recently, quasi-monoenergetic beams from self-trapped plasma electrons in wakefields driven by intense laser beamd have been observed in experiments in many laboratories around the world, and a PWFA experiment performed at Stanford Linear Accelerator Center (SLAC) successfully demonstrated that the energy of particles at the tail of the driving electron can be doubled from $\sim$40 GeV to $\sim$80 GeV in just 80 cms. However, to fully understand these experiments requires a particle-based computer model because the interaction between the plasma and the driver is highly nonlinear. We have developed a highly efficient, fully parallelized, fully relativistic, three dimensional particle-in-cell code, QuickPIC, for simulating plasma wakefield acceleration. The model is based on what is called the quasi-static or frozen field approximation, which assumes that the driver does not evolve during the time it takes for it to pass a plasma particle and reduces a fully three-dimensional electromagnetic field calculation and particle push into a two-dimensional electrostatic field solve and particle push. This algorithm reduces the computational time by at least 2 to 3 orders of magnitude. Comparison with a fully explicit PIC model (OSIRIS) shows excellent agreement for problems of interest. QuickPIC simulations of the SLAC PWFA experiment have revealed important physics and achieved good agreement with experiment measurement. Theoretical analysis of the stability of acceleration can now be guided and verified by QuickPIC simulations. [Preview Abstract] |
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