9,366 research outputs found
Multiphase smoothed-particle hydrodynamics
We adapt the smoothed-particle hydrodynamics (SPH) technique to allow a multiphase fluid in which SPH particles of widely differing density may be freely intermixed. Applications include modelling of galaxy formation and cooling flows
Fundamental relation between longitudinal and transverse conductivities in the quantum Hall system
We investigate the relation between the diagonal () and
off-diagonal () components of the conductivity tensor in the
quantum Hall system. We calculate the conductivity components for a short-range
impurity potential using the linear response theory, employing an approximation
that simply replaces the self-energy by a constant value
with the scattering time. The approximation is equivalent to assuming
that the broadening of a Landau level due to disorder is represented by a
Lorentzian with the width . Analytic formulas are
obtained for both and within the framework of this
simple approximation at low temperatures. By examining the leading terms in
and , we find a proportional relation between
and . The relation, after
slight modification to account for the long-range nature of the impurity
potential, is shown to be in quantitative agreement with experimental results
obtained in the GaAs/AlGaAs two-dimensional electron system at the low
magnetic-field regime where spin splitting is negligibly small.Comment: 21 pages, 8 figures, accepted for publication in J. Phys.: Condens.
Matte
Bogoliubov excitation spectrum of an elongated condensate from quasi-one-dimensional to three-dimensional transition
The quasiparticle excitation spectra of a Bose gas trapped in a highly
anisotropic trap is studied with respect to varying total number of particles
by numerically solving the effective one-dimensional (1D) Gross-Pitaevskii (GP)
equation proposed recently by Mateo \textit{et al.}. We obtain the static
properties and Bogoliubov spectra of the system in the high energy domain. This
method is computationally efficient and highly accurate for a condensate system
undergoing a 1D to three-dimensional (3D) cigar-shaped transition, as is shown
through a comparison our results with both those calculated by the 3D-GP
equation and analytical results obtained in limiting cases. We identify the
applicable parameter space for the effective 1D-GP equation and find that this
equation fails to describe a system with large number of atoms. We also
identify that the description of the transition from 1D Bose-Einstein
condensate (BEC) to 3D cigar-shaped BEC using this equation is not smooth,
which highlights the fact that for a finite value of the junction
between the 1D and 3D crossover is not perfect.Comment: 17 pages, 6 figure
Tables of two-sided tolerance factors for normal distributions
Tables of two-sided tolerance factors for normal distribution
Approximate Canonical Quantization for Cosmological Models
In cosmology minisuperspace models are described by nonlinear
time-reparametrization invariant systems with a finite number of degrees of
freedom. Often these models are not explicitly integrable and cannot be
quantized exactly. Having this in mind, we present a scheme for the
(approximate) quantization of perturbed, nonintegrable, time-reparametrization
invariant systems that uses (approximate) gauge invariant quantities. We apply
the scheme to a couple of simple quantum cosmological models.Comment: 16 pages, Latex, accepted for publication in Int. Jou. Mod. Phys.
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