40,756 research outputs found
Simple equation of state for hard disks on the hyperbolic plane
A simple equation of state for hard disks on the hyperbolic plane is
proposed. It yields the exact second virial coefficient and contains a pole at
the highest possible packing. A comparison with another very recent theoretical
proposal and simulation data is presented.Comment: 3 pages, 1 figur
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
On the radial distribution function of a hard-sphere fluid
Two related approaches, one fairly recent [A. Trokhymchuk et al., J. Chem.
Phys. 123, 024501 (2005)] and the other one introduced fifteen years ago [S. B.
Yuste and A. Santos, Phys. Rev. A 43, 5418 (1991)], for the derivation of
analytical forms of the radial distribution function of a fluid of hard spheres
are compared. While they share similar starting philosophy, the first one
involves the determination of eleven parameters while the second is a simple
extension of the solution of the Percus-Yevick equation. It is found that the
{second} approach has a better global accuracy and the further asset of
counting already with a successful generalization to mixtures of hard spheres
and other related systems.Comment: 3 pages, 1 figure; v2: slightly shortened, figure changed, to be
published in JC
Cosmographic constraints on a class of Palatini f(R) gravity
Modified gravity, known as gravity, has presently been applied to
Cosmology as a realistic alternative to dark energy. For this kind of gravity
the expansion of the Universe may accelerate while containing only baryonic and
cold dark matter. The aim of the present investigation is to place cosmographic
constraints on the class of theories of the form within
the Palatini approach. Although extensively discussed in recent literature and
confronted with several observational data sets, cosmological tests are indeed
inconclusive about the true signal of in this class of theories. This is
particularly important to define which kind of corrections (infra-red or
high-energy) to general relativity this class of theory indeed represent. We
shed some light on this question by examining the evolution of the deceleration
parameter for these theories. We find that for a large range of
, models based on gravity in the Palatini
approach can only have positive values for , placing thus a broad
restriction on this class of gravity.Comment: 4 pages, 2 figures, Latex, Submitte
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