136,205 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.
Sonine approximation for collisional moments of granular gases of inelastic rough spheres
We consider a dilute granular gas of hard spheres colliding inelastically
with coefficients of normal and tangential restitution and ,
respectively. The basic quantities characterizing the distribution function
of linear () and angular
() velocities are the second-degree moments defining the
translational () and rotational () temperatures. The
deviation of from the Maxwellian distribution parameterized by
and can be measured by the cumulants associated
with the fourth-degree velocity moments. The main objective of this paper is
the evaluation of the collisional rates of change of these second- and
fourth-degree moments by means of a Sonine approximation. The results are
subsequently applied to the computation of the temperature ratio
and the cumulants of two paradigmatic states: the
homogeneous cooling state and the homogeneous steady state driven by a
white-noise stochastic thermostat. It is found in both cases that the
Maxwellian approximation for the temperature ratio does not deviate much from
the Sonine prediction. On the other hand, non-Maxwellian properties measured by
the cumulants cannot be ignored, especially in the homogeneous cooling state
for medium and small roughness. In that state, moreover, the cumulant directly
related to the translational velocity differs in the quasi-smooth limit
from that of pure smooth spheres (). This singular
behavior is directly related to the unsteady character of the homogeneous
cooling state and thus it is absent in the stochastic thermostat case.Comment: 14 pages, 8 figures; v2: some parts rewritten, new references added;
published in a special topic decicated to Carlo Cercignan
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