97,091 research outputs found
Local Physical Coodinates from Symplectic Projector Method
The basic arguments underlying the symplectic projector method are presented.
By this method, local free coordinates on the constrait surface can be obtained
for a broader class of constrained systems. Some interesting examples are
analyzed.Comment: 8 page
Dynamical instabilities in density-dependent hadronic relativistic models
Unstable modes in asymmetric nuclear matter (ANM) at subsaturation densities
are studied in the framework of relativistic mean-field density-dependent
hadron models. The size of the instabilities that drive the system are
calculated and a comparison with results obtained within the non-linear Walecka
model is presented. The distillation and anti-distillation effects are
discussed.Comment: 8 pages, 8 Postscript figures. Submitted for publication in Phys.
Rev.
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
Comment on "Theory and computer simulation for the equation of state of additive hard-disk fluid mixtures"
A flaw in the comparison between two different theoretical equations of state
for a binary mixture of additive hard disks and Monte Carlo results, as
recently reported in C. Barrio and J. R. Solana, Phys. Rev. E 63, 011201
(2001), is pointed out. It is found that both proposals, which require the
equation of state of the single component system as input, lead to comparable
accuracy but the one advocated by us [A. Santos, S. B. Yuste, and M. L\'{o}pez
de Haro, Mol. Phys. 96, 1 (1999)] is simpler and complies with the exact limit
in which the small disks are point particles.Comment: 4 pages, including 1 figur
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