13,494 research outputs found
Shear-free and homology conditions for self-gravitating dissipative fluids
The shear free condition is studied for dissipative relativistic
self-gravitating fluids in the quasi-static approximation. It is shown that, in
the Newtonian limit, such condition implies the linear homology law for the
velocity of a fluid element, only if homology conditions are further imposed on
the temperature and the emission rate. It is also shown that the shear-free
plus the homogeneous expansion rate conditions are equivalent (in the Newtonian
limit) to the homology conditions. Deviations from homology and their
prospective applications to some astrophysical scenarios are discussed, and a
model is worked out.Comment: 13 pages Latex. To apppear in Month.Not.Roy.Astr.Soc. Corrected typo
Cylindrical Collapse and Gravitational Waves
We study the matching conditions for a collapsing anisotropic cylindrical
perfect fluid, and we show that its radial pressure is non zero on the surface
of the cylinder and proportional to the time dependent part of the field
produced by the collapsing fluid. This result resembles the one that arises for
the radiation - though non-gravitational - in the spherically symmetric
collapsing dissipative fluid, in the diffusion approximation.Comment: Some comments and a new reference added. To appear in Class. Quantum.
Gra
On the gravitomagnetic effects in cylindrically symmetric spacetimes
Using gyroscopes we generalize results, obtained for the gravitomagnetic
clock effect in the particular case when the exterior spacetime is produced by
a rotating dust cylinder, to the case when the vacuum spacetime is described by
the general cylindrically symmetric Lewis spacetime. Results are contrasted
with those obtained for the Kerr spacetime.Comment: 11 pages Latex, to appear in J.Math.Phy
Collapsing Spheres Satisfying An "Euclidean Condition"
We study the general properties of fluid spheres satisfying the heuristic
assumption that their areas and proper radius are equal (the Euclidean
condition). Dissipative and non-dissipative models are considered. In the
latter case, all models are necessarily geodesic and a subclass of the
Lemaitre-Tolman-Bondi solution is obtained. In the dissipative case solutions
are non-geodesic and are characterized by the fact that all non-gravitational
forces acting on any fluid element produces a radial three-acceleration
independent on its inertial mass.Comment: 1o pages, Latex. Title changed and text shortened to fit the version
to appear in Gen.Rel.Grav
The Levi-Civita spacetime as a limiting case of the Gamma spacetime
It is shown that the Levi-Civita metric can be obtained from a family of the
Weyl metric, the Gamma metric, by taking the limit when the length of its
Newtonian image source tends to infinity. In this process a relationship
appears between two fundamental parameters of both metrics.Comment: LaTeX2e 17 page
On the compressibility equation of state for multicomponent adhesive hard sphere fluids
The compressibility equation of state for a multicomponent fluid of particles
interacting via an infinitely narrow and deep potential, is considered within
the mean spherical approximation (MSA). It is shown that for a class of models
leading to a particular form of the Baxter functions containing
density-independent stickiness coefficient, the compressibility EOS does not
exist, unlike the one-component case. The reason for this is that a direct
integration of the compressibility at fixed composition, cannot be carried out
due to the lack of a reciprocity relation on the second order partial
derivatives of the pressure with respect to two different densities. This is,
in turn, related to the inadequacy of the MSA. A way out to this drawback is
presented in a particular example, leading to a consistent compressibility
pressure, and a possible generalization of this result is discussed.Comment: 13 pages, no figures, accepted for publication Molec. Physics (2002
Static cylindrical symmetry and conformal flatness
We present the whole set of equations with regularity and matching conditions
required for the description of physically meaningful static cylindrically
symmmetric distributions of matter, smoothly matched to Levi-Civita vacuum
spacetime. It is shown that the conformally flat solution with equal principal
stresses represents an incompressible fluid. It is also proved that any
conformally flat cylindrically symmetric static source cannot be matched
through Darmois conditions to the Levi-Civita spacetime. Further evidence is
given that when the Newtonian mass per unit length reaches 1/2 the spacetime
has plane symmetry.Comment: 13 pages, Late
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