591 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
PROGETTAZIONE DI PARATIE FILTRANTI A SOSTEGNO DI PENDII INSTABILI
Nella nota, facendo riferimento al caso delle paratie filtranti, sono analizzate tre classi di metodi progettuali
semplificati (metodi allo Stato Limite Ultimo, Metodi Ibridi e Metodi negli Spostamenti), con l’intento di fornire
uno strumento utile al progettista per dimensionare la struttura e per valutare l’efficacia dell’intervento
Frame dragging and super-energy
We show that the vorticity appearing in stationary vacuum spacetimes is
always related to the existence of a flow of super-energy on the plane
orthogonal to the vorticity vector. This result, toghether with the previously
established link between vorticity and super--energy in radiative (Bondi-Sachs)
spacetimes strength further the case for this latter quantity as the cause of
frame dragging.Comment: 12 pages Latex. To appear in Phys.Rev. D. Typos correcte
Dynamics of viscous dissipative gravitational collapse: A full causal approach
The Misner and Sharp approach to the study of gravitational collapse is
extended to the viscous dissipative case in, both, the streaming out and the
diffusion approximations. The dynamical equation is then coupled to causal
transport equations for the heat flux, the shear and the bulk viscosity, in the
context of Israel--Stewart theory, without excluding the thermodynamics
viscous/heat coupling coefficients. The result is compared with previous works
where these later coefficients were neglected and viscosity variables were not
assumed to satisfy causal transport equations. Prospective applications of this
result to some astrophysical scenarios are discussed.Comment: 22 pages Latex. To appear in Int. J. Mod. Phys. D. Typos correcte
On Scaling Solutions with a Dissipative Fluid
We study the asymptotic behaviour of scaling solutions with a dissipative
fluid and we show that, contrary to recent claims, the existence of stable
accelerating attractor solution which solves the `energy' coincidence problem
depends crucially on the chosen equations of state for the thermodynamical
variables. We discuss two types of equations of state, one which contradicts
this claim, and one which supports it.Comment: 8 pages and 5 figures; to appear in Class. Quantum Gra
Polymer models of chromatin organization
This is an invited commentary on the research field concerning the modelling of chromosome organization in the cell nucleus of eukaryotes
Perioperative myocardial infarction in elderly patients with hip fracture. Is there a role for early coronary angiography?
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
Some analytical models of radiating collapsing spheres
We present some analytical solutions to the Einstein equations, describing
radiating collapsing spheres in the diffusion approximation. Solutions allow
for modeling physical reasonable situations. The temperature is calculated for
each solution, using a hyperbolic transport equation, which permits to exhibit
the influence of relaxational effects on the dynamics of the system.Comment: 17 pages Late
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
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