48,374 research outputs found

    Multipole polarizability of a graded spherical particle

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    We have studied the multipole polarizability of a graded spherical particle in a nonuniform electric field, in which the conductivity can vary radially inside the particle. The main objective of this work is to access the effects of multipole interactions at small interparticle separations, which can be important in non-dilute suspensions of functionally graded materials. The nonuniform electric field arises either from that applied on the particle or from the local field of all other particles. We developed a differential effective multipole moment approximation (DEMMA) to compute the multipole moment of a graded spherical particle in a nonuniform external field. Moreover, we compare the DEMMA results with the exact results of the power-law graded profile and the agreement is excellent. The extension to anisotropic DEMMA will be studied in an Appendix.Comment: LaTeX format, 2 eps figures, submitted for publication

    A Cosmological Model with Dark Spinor Source

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    In this paper, we discuss the system of Friedman-Robertson-Walker metric coupling with massive nonlinear dark spinors in detail, where the thermodynamic movement of spinors is also taken into account. The results show that, the nonlinear potential of the spinor field can provide a tiny negative pressure, which resists the Universe to become singular. The solution is oscillating in time and closed in space, which approximately takes the following form g_{\mu\nu}=\bar R^2(1-\delta\cos t)^2\diag(1,-1,-\sin^2r ,-\sin^2r \sin^2\theta), with Rˉ=(1∼2)×1012\bar R= (1\sim 2)\times 10^{12} light year, and δ=0.96∼0.99\delta=0.96\sim 0.99. The present time is about t∼18∘t\sim 18^\circ.Comment: 13 pages, no figure, to appear in IJMP

    Stability of Discrete Solitons in the Presence of Parametric Driving

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    In this brief report, we consider parametrically driven bright solitons in the vicinity of the anti-continuum limit. We illustrate the mechanism through which these solitons become unstable due to the collision of the phase mode with the continuous spectrum, or eigenvelues bifurcating thereof. We show how this mechanism typically leads to complete destruction of the bright solitary wave.Comment: 4 pages, 4 figure

    Large-Scale Monte Carlo Study of a Realistic Lattice Model for Ga_(1-x)Mn_xAs

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    The properties of Mn-doped GaAs are studied at several doping levels and hole compensations, using a real-space Hamiltonian on an fcc lattice that reproduces the valence bands of undoped GaAs. Large-scale Monte Carlo (MC) simulations on a Cray XT3 supercomputer, using up to a thousand nodes, were needed to make this effort possible. Our analysis considers both the spin-orbit interaction and the random distribution of the Mn ions. The hopping amplitudes are functions of the GaAs Luttinger parameters. At the coupling J~1.2eV deduced from photoemission experiments, the MC Curie temperature and the shape of the magnetization curves are in agreement with experimental results for annealed samples. Although there are sizable differences with mean-field predictions, the system is found to be closer to a hole-fluid regime than to localized carriers
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