73,631 research outputs found
Demixing can occur in binary hard-sphere mixtures with negative non-additivity
A binary fluid mixture of non-additive hard spheres characterized by a size
ratio and a non-additivity parameter
is considered in infinitely many
dimensions. From the equation of state in the second virial approximation
(which is exact in the limit ) a demixing transition with a
critical consolute point at a packing fraction scaling as
is found, even for slightly negative non-additivity, if
. Arguments concerning the stability of the
demixing with respect to freezing are provided.Comment: 4 pages, 2 figures; title changed; final paragraph added; to be
published in PRE as a Rapid Communicatio
Computer simulation of uniformly heated granular fluids
Direct Monte Carlo simulations of the Enskog-Boltzmann equation for a
spatially uniform system of smooth inelastic spheres are performed. In order to
reach a steady state, the particles are assumed to be under the action of an
external driving force which does work to compensate for the collisional loss
of energy. Three different types of external driving are considered: (a) a
stochastic force, (b) a deterministic force proportional to the particle
velocity and (c) a deterministic force parallel to the particle velocity but
constant in magnitude. The Enskog-Boltzmann equation in case (b) is fully
equivalent to that of the homogeneous cooling state (where the thermal velocity
monotonically decreases with time) when expressed in terms of the particle
velocity relative to the thermal velocity. Comparison of the simulation results
for the fourth cumulant and the high energy tail with theoretical predictions
derived in cases (a) and (b) [T. P. C. van Noije and M. H. Ernst, Gran. Matt.
1, 57 (1998)] shows a good agreement. In contrast to these two cases, the
deviation from the Maxwell-Boltzmann distribution is not well represented by
Sonine polynomials in case (c), even for low dissipation. In addition, the high
energy tail exhibits an underpopulation effect in this case.Comment: 18 pages (LaTex), 10 figures (eps); to be published in Granular
Matte
DSMC evaluation of the Navier-Stokes shear viscosity of a granular fluid
A method based on the simple shear flow modified by the introduction of a
deterministic non-conservative force and a stochastic process is proposed to
measure the Navier-Stokes shear viscosity in a granular fluid described by the
Enskog equation. The method is implemented in DSMC simulations for a wide range
of values of dissipation and density. It is observed that, after a certain
transient period, the system reaches a hydrodynamic stage which tends to the
Navier-Stokes regime for long times. The results are compared with theoretical
predictions obtained from the Chapman-Enskog method in the leading Sonine
approximation, showing quite a good agreement, even for strong dissipation.Comment: 6 pages, 4 figures; to appear in Rarefied Gas Dynamics: 24th
International Symposium (AIP Conference Proceedings
Spatial Coherence Resonance near Pattern-Forming Instabilities
The analogue of temporal coherence resonance for spatial degrees of freedom
is reported. Specifically, we show that spatiotemporal noise is able to
optimally extract an intrinsic spatial scale in nonlinear media close to (but
before) a pattern-forming instability. This effect is observed in a model of
pattern-forming chemical reaction and in the Swift-Hohenberg model of fluid
convection. In the latter case, the phenomenon is described analytically via an
approximate approach.Comment: 4 pages, 4 figure
Controlled localization of interacting bosons in a disordered optical lattice
We show that tunneling and localization properties of interacting ultracold
atoms in an optical lattice can be controlled by adiabatically turning on a
fast oscillatory force even in the presence of disorder. Our calculations are
based on the exact solution of the time-dependent Schroedinger equation, using
the Floquet formalism. Implications of our findings for larger systems and the
possibility of controlling the phase diagram of disordered-interacting bosonic
systems are discussed.Comment: 7 pages 7 fig
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