Geodesic Deviation in Kaluza-Klein Theories

We study in detail the equations of the geodesic deviation in multidimensional theories of Kaluza-Klein type. We show that their 4-dimensional space-time projections are identical with the equations obtained by direct variation of the usual geodesic equation in the presence of the Lorentz force, provided that the fifth component of the deviation vector satisfies an extra constraint derived here.Comment: 5 pages, Revtex, 1 figure. To appear in Phys. Rev. D (Brief Report

Explicit Solution of the Time Evolution of the Wigner Function

Previously, an explicit solution for the time evolution of the Wigner function was presented in terms of auxiliary phase space coordinates which obey simple equations that are analogous with, but not identical to, the classical equations of motion. They can be solved easily and their solutions can be utilized to construct the time evolution of the Wigner function. In this paper, the usefulness of this explicit solution is demonstrated by solving a numerical example in which the Wigner function has strong spatial and temporal variations as well as regions with negative values. It is found that the explicit solution gives a correct description of the time evolution of the Wigner function. We examine next the pseudoparticle approximation which uses classical trajectories to evolve the Wigner function. We find that the pseudoparticle approximation reproduces the general features of the time evolution, but there are deviations. We show how these deviations can be systematically reduced by including higher-order correction terms in powers of $\hbar^2$.Comment: 16 pages, in LaTex, invited talk presented at the Wigner Centennial Conference, Pecs, Hungary, July 8-12, 2002, to be published in the Journal of Optics B: Quantum and Classical Optics, June 200

Mean Field Dynamics in Non-Abelian Plasmas from Classical Transport Theory

Based on classical transport theory, we present a general set of covariant equations describing the dynamics of mean fields and their statistical fluctuations in a non-Abelian plasma in or out-of-equilibrium. A procedure to obtain the collision integrals for the Boltzmann equation from the microscopic theory is described. As an application, we study a hot non-Abelian plasma close to equilibrium, where the fluctuations are integrated out explicitly. For soft fields, and at logarithmic accuracy, we obtain B\"odeker's effective theory.Comment: 4 pages, revtex, no figures. Typo removed, a reference updated, version as to appear in Phys. Rev. Let

Disks around the Young Stars TW Hya and HD 100546 Imaged at 3.4 Millimeters with the Australia Telescope Compact Array

We present observations of the young stars TW Hya and HD 100546 made with the Australia Telescope Compact Array at 89 GHz with $\sim2''$ resolution and $\sim3$ mJy continuum sensitivity. Compact thermal dust continuum emission is detected from disks surrounding both stars. HD 100546 also shows hints of extended emission, presumably a residual protostellar envelope, which is also visible in scattered light at optical wavelengths. For TW Hya, HCO$^+$ J=1--0 line emission from the circumstellar disk is detected and spatially resolved. The observed size and intensity are in good agreement with model calculations based on an irradiated disk with substantial depletions derived previously from single dish observations of higher-J HCO$^+$ transitions.Comment: 19 pages including 6 figures; accepted for publication in Ap

Kinetic Equation for Gluons in the Background Gauge of QCD

We derive the quantum kinetic equation for a pure gluon plasma, applying the background field and closed-time-path method. The derivation is more general and transparent than earlier works. A term in the equation is found which, as in the classical case, corresponds to the color charge precession for partons moving in the gauge field.Comment: RevTex 4, 4 pages, no figure, PRL accepted versio

Inhomogeneous magnetism induced in a superconductor at superconductor-ferromagnet interface

We study a magnetic proximity effect at superconductor (S) - ferromagnet (F) interface. It is shown that due to an exchange of electrons between the F and S metals ferromagnetic correlations extend into the superconductor, being dependent on interface parameters. We show that ferromagnetic exchange field pair breaking effect leads to a formation of subgap bands in the S layer local density of states, that accommodate only one spin-polarized quasiparticles. Equilibrium magnetization leakage into the S layer as function of SF interface quality and a value of ferromagnetic interaction have also been calculated. We show that a damped-oscillatory behavior versus distance from SF interface is a distinguished feature of the exchange-induced magnetization of the S layer.Comment: 10 pages, 7 Postscript figure

Brief Overview of Bioinformatics Activities in Singapore

10.1371/journal.pcbi.1000508PLoS Computational Biology5

Nucleon-Nucleon Interaction: A Typical/Concise Review

Nearly a recent century of work is divided to Nucleon-Nucleon (NN) interaction issue. We review some overall perspectives of NN interaction with a brief discussion about deuteron, general structure and symmetries of NN Lagrangian as well as equations of motion and solutions. Meanwhile, the main NN interaction models, as frameworks to build NN potentials, are reviewed concisely. We try to include and study almost all well-known potentials in a similar way, discuss more on various commonly used plain forms for two-nucleon interaction with an emphasis on the phenomenological and meson-exchange potentials as well as the constituent-quark potentials and new ones based on chiral effective field theory and working in coordinate-space mostly. The potentials are constructed in a way that fit NN scattering data, phase shifts, and are also compared in this way usually. An extra goal of this study is to start comparing various potentials forms in a unified manner. So, we also comment on the advantages and disadvantages of the models and potentials partly with reference to some relevant works and probable future studies.Comment: 85 pages, 5 figures, than the previous v3 edition, minor changes, and typos fixe

Infrared Dark Clouds in the Small Magellanic Cloud?

We have applied the unsharp-masking technique to the 24 $\mu$m image of the Small Magellanic Cloud (SMC), obtained with the Spitzer Space Telescope, to search for high-extinction regions. This technique has been used to locate very dense and cold interstellar clouds in the Galaxy, particularly infrared dark clouds (IRDCs). Fifty five candidate regions of high-extinction, namely high-contrast regions (HCRs), have been identified from the generated decremental contrast image of the SMC. Most HCRs are located in the southern bar region and mainly distributed in the outskirts of CO clouds, but most likely contain a significant amount of H2. HCRs have a peak-contrast at 24 $\mu$m of 2 - 2.5 % and a size of 8 - 14 pc. This corresponds to the size of typical and large Galactic IRDCs, but Galactic IRDCs are 2 - 3 times darker at 24 $\mu$m than our HCRs. To constrain the physical properties of the HCRs, we have performed NH3, N2H+, HNC, HCO+, and HCN observations toward one of the HCRs, HCR LIRS36-EAST, using the Australia Telescope Compact Array and the Mopra single-dish radio telescope. We did not detect any molecular line emission, however, our upper limits to the column densities of molecular species suggest that HCRs are most likely moderately dense with n ~ 10^{3} cm-3. This volume density is in agreement with predictions for the cool atomic phase in low metallicity environments. We suggest that HCRs may be tracing clouds at the transition from atomic to molecule-dominated medium, and could be a powerful way to study early stages of gas condensation in low metallicity galaxies. Alternatively, if made up of dense molecular clumps < 0.5 pc in size, HCRs could be counterparts of Galactic IRDCs, and/or regions with highly unusual abundance of very small dust grains.Comment: accepted for publication in the Astronomical Journa