578 research outputs found

### The Wonder of Colors and the Principle of Ariadne

The Principle of Ariadne, formulated in 1988 ago by Walter Carnielli
and Carlos Di Prisco and later published in 1993, is an infinitary principle that is independent of the Axiom of Choice in ZF, although it can be consistently added to
the remaining ZF axioms. The present paper surveys, and motivates, the foundational importance of the Principle of Ariadne
and proposes the Ariadne Game, showing that the Principle of Ariadne,
corresponds precisely
to a winning strategy for the Ariadne Game. Some relations to other
alternative. set-theoretical principles
are also briefly discussed

### Skeletal myocyte types and vascularity in the Black Sicilian Pig.

The objective of this study was to verify the presence of giant fibres in the Black Sicilian pig skeletal
muscle and to evaluate the effect of sex on histochemical and morphometric characteristics of the
myocytes (myofibres) as well as vascularity of the muscle. Twenty Black Sicilian pigs (10 males, 10
females) from a farm in Sicily (Italy) were slaughtered at two years of age. Muscle tissues were
obtained from three muscles: psoas major, longissimus dorsi, and trapezius. Myofibres were stained
for myosin ATPase, succinic dehydrogenase, and α-amylase-PAS. For all fibre types, area and
perimeter were measured. Slow-twitch oxidative fibres, fast-twitch glycolytic fibres and fast-twitch
oxidative-glycolytic fibres were histochemically differentiated; an image-analyzing system was
used. The results showed no differences between males and females in percentage of the fibre types,
but there were significant differences between sexes in size of all the three fibre types. Psoas major
muscle had a high percentage of slow-twitch oxidative fibres and contained more capillaries per fibre
and per mm2 than trapezius and longissimus dorsi, in which fast-twitch glycolytic fibres dominated.
The cross-sectional area of all fibres types was larger in longissimus dorsi than in trapezius and psoas
major muscles; the giant fibres were absent in all the muscles studied. Fibre type composition may
contribute to the variation of meat quality

### Dynamics of Non-adiabatic Charged Cylindrical Gravitational Collapse

This paper is devoted to study the dynamics of gravitational collapse in the
Misner and Sharp formalism. We take non-viscous heat conducting charged
anisotropic fluid as a collapsing matter with cylindrical symmetry. The
dynamical equations are derived and coupled with the transport equation for
heat flux obtained from the M$\ddot{u}$ller-Israel-Stewart causal thermodynamic
theory. We discuss the role of anisotropy, electric charge and radial heat flux
over the dynamics of the collapse with the help of coupled equation.Comment: 15 pages, accepted for publication in Astrophys. Space Sc

### Thermal Conduction in Systems out of Hydrostatic Equilibrium

We analyse the effects of thermal conduction in a relativistic fluid, just
after its departure from hydrostatic equilibrium, on a time scale of the order
of thermal relaxation time. It is obtained that the resulting evolution will
critically depend on a parameter defined in terms of thermodynamic variables,
which is constrained by causality requirements.Comment: 16 pages, emTex (LaTex 2.09). To appear in Classical and Quantum
Gravit

### On the stability of the shear-free condition

The evolution equation for the shear is reobtained for a spherically
symmetric anisotropic, viscous dissipative fluid distribution, which allows us
to investigate conditions for the stability of the shear-free condition. The
specific case of geodesic fluids is considered in detail, showing that the
shear-free condition, in this particular case, may be unstable, the departure
from the shear-free condition being controlled by the expansion scalar and a
single scalar function defined in terms of the anisotropy of the pressure, the
shear viscosity and the Weyl tensor or, alternatively, in terms of the
anisotropy of the pressure, the dissipative variables and the energy density
inhomogeneity.Comment: 19 pages Latex. To appear in Gen. Rel. Gra

### Bianchi Type I Universes with Causal Bulk Viscous Cosmological Fluid

We consider the dynamics of a causal bulk viscous cosmological fluid filled
constantly decelerating Bianchi type I space-time. The matter component of the
Universe is assumed to satisfy a linear barotropic equation of state and the
state equation of the small temperature Boltzmann gas. The resulting
cosmological models satisfy the condition of smallness of the viscous stress.
The time evolution of the relaxation time, temperature, bulk viscosity
coefficient and comoving entropy of the dissipative fluid is also obtained.Comment: 11 pages, 5 figures, accepted for publication in International
Journal of Modern Physics

### Bulk Viscosity Effects on the Early Universe Stability

We present a discussion of the effects induced by the bulk viscosity on the
very early Universe stability. The matter filling the cosmological (isotropic
and homogeneous) background is described by a viscous fluid having an
ultrarelativistic equation of state and whose viscosity coefficient is related
to the energy density via a power-law of the form $\zeta=\zeta_0 \rho^\nu$. The
analytic expression of the density contrast (obtained for $\nu=1/2$) shows
that, for small values of the constant $\zeta_0$, its behavior is not
significantly different from the non-viscous one derived by E.M. Lifshitz. But
as soon as $\zeta_0$ overcomes a critical value, the growth of the density
contrast is suppressed forward in time by the viscosity and the stability of
the Universe is favored in the expanding picture. On the other hand, in such a
regime, the asymptotic approach to the initial singularity (taken at $t=0$) is
deeply modified by the apparency of significant viscosity in the primordial
thermal bath i.e. the isotropic and homogeneous Universe admits an unstable
collapsing picture. In our model this feature regards also scalar perturbations
while in the non-viscous case it appears only for tensor modes.Comment: 8 pages, no figur

### Dynamics of Charged Plane Symmetric Gravitational Collapse

In this paper, we study dynamics of the charged plane symmetric gravitational
collapse. For this purpose, we discuss non-adiabatic flow of a viscous fluid
and deduce the results for adiabatic case. The Einstein and Maxwell field
equations are formulated for general plane symmetric spacetime in the interior.
Junction conditions between the interior and exterior regions are derived. For
the non-adiabatic case, the exterior is taken as plane symmetric charged Vaidya
spacetime while for the adiabatic case, it is described by plane
Reissner-Nordstr$\ddot{o}$m spacetime. Using Misner and Sharp formalism, we
obtain dynamical equations to investigate the effects of different forces over
the rate of collapse. In non-adiabatic case, a dynamical equation is joined
with transport equation of heat flux. Finally, a relation between the Weyl
tensor and energy density is found.Comment: 21 pages, accepted for publication Gen. Relativ. Gra

### A causal model of radiating stellar collapse

We find a simple exact model of radiating stellar collapse, with a shear-free
and non-accelerating interior matched to a Vaidya exterior. The heat flux is
subject to causal thermodynamics, leading to self-consistent determination of
the temperature $T$. We solve for $T$ exactly when the mean collision time
$\tau_{c}$ is constant, and perturbatively in a more realistic case of variable
$\tau_{c}$. Causal thermodynamics predicts temperature behaviour that can
differ significantly from the predictions of non-causal theory. In particular,
the causal theory gives a higher central temperature and greater temperature
gradient.Comment: Latex [ioplppt style] 9 pages; to appear Class. Quantum Gra

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