671 research outputs found
Nonequilibrium Temperature and Thermometry in Heat-Conducting Phi-4 Models
We analyze temperature and thermometry for simple nonequilibrium
heat-conducting models. We show in detail, for both two- and three-dimensional
systems, that the ideal gas thermometer corresponds to the concept of a local
instantaneous mechanical kinetic temperature. For the Phi-4 models investigated
here the mechanical temperature closely approximates the local thermodynamic
equilibrium temperature. There is a significant difference between kinetic
temperature and the nonlocal configurational temperature. Neither obeys the
predictions of extended irreversible thermodynamics. Overall, we find that
kinetic temperature, as modeled and imposed by the Nos\'e-Hoover thermostats
developed in 1984, provides the simplest means for simulating, analyzing, and
understanding nonequilibrium heat flows.Comment: 20 pages with six figures, revised following review at Physical
Review
Diffuse-interface model for rapid phase transformations in nonequilibrium systems
A thermodynamic approach to rapid phase transformations within a diffuse
interface in a binary system is developed. Assuming an extended set of
independent thermodynamic variables formed by the union of the classic set of
slow variables and the space of fast variables, we introduce finiteness of the
heat and solute diffusive propagation at the finite speed of the interface
advancing. To describe the transformation within the diffuse interface, we use
the phase-field model which allows us to follow the steep but smooth change of
phases within the width of diffuse interface. The governing equations of the
phase-field model are derived for the hyperbolic model, model with memory, and
for a model of nonlinear evolution of transformation within the
diffuse-interface. The consistency of the model is proved by the condition of
positive entropy production and by the outcomes of the fluctuation-dissipation
theorem. A comparison with the existing sharp-interface and diffuse-interface
versions of the model is given.Comment: 15 pages, regular article submitted to Physical Review
The dynamics of dissipative multi-fluid neutron star cores
We present a Newtonian multi-fluid formalism for superfluid neutron star
cores, focussing on the additional dissipative terms that arise when one takes
into account the individual dynamical degrees of freedom associated with the
coupled "fluids". The problem is of direct astrophysical interest as the nature
of the dissipative terms can have significant impact on the damping of the
various oscillation modes of the star and the associated gravitational-wave
signatures. A particularly interesting application concerns the
gravitational-wave driven instability of f- and r-modes. We apply the developed
formalism to two specific three-fluid systems: (i) a hyperon core in which both
Lambda and Sigma^- hyperons are present, and (ii) a core of deconfined quarks
in the colour-flavour-locked phase in which a population of neutral K^0 kaons
is present. The formalism is, however, general and can be applied to other
problems in neutron-star dynamics (such as the effect of thermal excitations
close to the superfluid transition temperature) as well as laboratory
multi-fluid systems.Comment: RevTex, no figure
Ideal gas sources for the Lemaitre-Tolman-Bondi metrics
New exact solutions emerge by replacing the dust source of the
Lem\^aitre-Tolman-Bondi metrics with a viscous fluid satisfying the monatomic
gas equation of state. The solutions have a consistent thermodynamical
interpretation. The most general transport equation of Extended Irreversible
Thermodynamics is satisfied, with phenomenological coefficients bearing a close
resemblance to those characterizing a non relativistic Maxwell-Bolzmann gas.Comment: 7 pages, Plain TeX with IOP macros, important corrections to previous
version, 3 figures (to appear in Classical and Quantum Gravity, June 1998
Phenomenological approach to the critical dynamics of the QCD phase transition revisited
The phenomenological dynamics of the QCD critical phenomena is revisited.
Recently, Son and Stephanov claimed that the dynamical universality class of
the QCD phase transition belongs to model H. In their discussion, they employed
a time-dependent Ginzburg-Landau equation for the net baryon number density,
which is a conserved quantity. We derive the Langevin equation for the net
baryon number density, i.e., the Cahn-Hilliard equation. Furthermore, they
discussed the mode coupling induced through the {\it irreversible} current.
Here, we show the {\it reversible} coupling can play a dominant role for
describing the QCD critical dynamics and that the dynamical universality class
does not necessarily belong to model H.Comment: 13 pages, the Curie principle is discussed in S.2, to appear in
J.Phys.
Nonequilibrium corrections in the pressure tensor due to an energy flux
The physical interpretation of the nonequilibrium corrections in the pressure
tensor for radiation submitted to an energy flux obtained in some previous
works is revisited. Such pressure tensor is shown to describe a moving
equilibrium system but not a real nonequilibrium situation.Comment: 4 pages, REVTeX, Brief Report to appear in PRE Dec 9
Information theory in the study of anisotropic radiation
Information theory is used to perform a thermodynamic study of non
equilibrium anisotropic radiation. We limit our analysis to a second-order
truncation of the moments, obtaining a distribution function which leads to a
natural closure of the hierarchy of radiative transfer equations in the
so-called variable Eddington factor scheme. Some Eddington factors appearing in
the literature can be recovered as particular cases of our two-parameter
Eddington factor. We focus our attention in the study of the thermodynamic
properties of such systems and relate it to recent nonequilibrium thermodynamic
theories. Finally we comment the possibility of introducing a nonequilibrium
chemical potential for photons.Comment: 1 eps figure upon request by e-mail, to appear in Journal of Physics
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
Hyperbolic subdiffusive impedance
We use the hyperbolic subdiffusion equation with fractional time derivatives
(the generalized Cattaneo equation) to study the transport process of
electrolytes in media where subdiffusion occurs. In this model the flux is
delayed in a non-zero time with respect to the concentration gradient. In
particular, we obtain the formula of electrochemical subdiffusive impedance of
a spatially limited sample in the limit of large and of small pulsation of the
electric field. The boundary condition at the external wall of the sample are
taken in the general form as a linear combination of subdiffusive flux and
concentration of the transported particles. We also discuss the influence of
the equation parameters (the subdiffusion parameter and the delay time) on the
Nyquist impedance plots.Comment: 10 pages, 5 figure
Why hyperbolic theories of dissipation cannot be ignored: Comments on a paper by Kostadt and Liu
Contrary to what is asserted in a recent paper by Kostadt and Liu ("Causality
and stability of the relativistic diffusion equation"), experiments can tell
apart (and in fact do) hyperbolic theories from parabolic theories of
dissipation. It is stressed that the existence of a non--negligible relaxation
time does not imply for the system to be out of the hydrodynamic regime.Comment: 8 pages Latex, to appear in Phys.Rev.
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