1,835 research outputs found
Measuring Nonequilibrium Temperature of Forced Oscillators
The meaning of temperature in nonequilibrium thermodynamics is considered by
using a forced harmonic oscillator in a heat bath, where we have two effective
temperatures for the position and the momentum, respectively. We invent a
concrete model of a thermometer to testify the validity of these different
temperatures from the operational point of view. It is found that the measured
temperature depends on a specific form of interaction between the system and a
thermometer, which means the zeroth law of thermodynamics cannot be immediately
extended to nonequilibrium cases.Comment: 8 page
Spatiotemporal Behavior of Void Collapse in Shocked Solids
Molecular dynamics simulations on a three dimensional defective Lennard-Jones
solid containing a void are performed in order to investigate detailed
properties of hot spot generation. In addition to the temperature, I monitor
the number of energetically colliding particles per unit volume which
characterizes the intensity of shock-enhanced chemistry. The quantity is found
to saturate for nanoscale voids and to be maximized after voids have completely
collapsed. It makes an apparent comparison to the temperature which requires
much larger void for the enhancement and becomes maximum during the early stage
of the collapse. It is also found that the average velocity and the temperature
of ejected molecules inside a cubic void are enhanced during the collapse
because of the focusing of momentum and energy towards the center line of a
void.Comment: 4 pages, 5 figures. A new figure and some references are adde
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
A Mathematical Analysis of the Intermediate Behaviour of the Energy Cascades of Quantum Turbulence
We propose a mathematical interpolation between several regimes of energy cascade in quantum turbulence in He II. On the basis of a physical interpretation of such mathematical expression we discuss in which conditions it is expected to appear an intermediate k(2) regime (equipartition regime) in the transition region between the hydrodynamic regime and the Kelvin wave regime (namely, between the k(-5/3) and k(-1) regions in coflow situations and between the k(-3) and k(-1) regions in counterflow situations). It is seen that if the energy rate transfer from the hydrodynamic region to the Kelvin wave region is sufficiently slow, such equipartition region will be present, but for higher values of such energy rate transfer it will disappear. For high rates of the energy rate transfer, the transition regime between the hydrodynamic and the Kelvin wave regimes will be monotonous, characterized by a negative exponent of k between -5/3 and -1 (or between -3 and -1), instead of the positive 2 exponent of the equipartition regime
Nonlinear Thermal Transport with Inertia in Thin Wires: Thermal Fronts and Steady States
In a series of papers we have obtained results for nonlinear heat transport when thin wires exchange heat non-linearly with the surroundings, with particular attention to propagating solitons. Here we obtain and discuss new results related to the propagation of nonlinear heat fronts and some conceptual aspects referring to the application of the second principle of thermodynamics to some nonlinear steady states related to non-propagating solitons
Alternative Vinen's equation and its extension to rotating counterflow superfluid turbulence
Two alternative Vinen's evolution equations for the vortex line density L in
counterflow superfluid turbulence, are physically admissible and lead to
analogous results in steady states. In Phys. Rev. B, 69, 094513 (2004) the most
used of them was generalized to counterflow superfluid turbulence in rotating
containers. Here, the analogous generalization for the alternative Vinen's
equation is proposed. Both generalized Vinen's equations are compared with the
experimental results, not only in steady-states but also in some unsteady
situations. From this analysis follows that the solutions of the alternative
Vinen's equation tend significantly faster to the corresponding final steady
state values than the solutions of the usual Vinen's equation, and that the
latter seems more suitable for the description of the experimental available
data.Comment: 16 pages, 6 figures. Submitted for publicatio
Knudsen Effect in a Nonequilibrium Gas
From the molecular dynamics simulation of a system of hard-core disks in
which an equilibrium cell is connected with a nonequilibrium cell, it is
confirmed that the pressure difference between two cells depends on the
direction of the heat flux. From the boundary layer analysis, the velocity
distribution function in the boundary layer is obtained. The agreement between
the theoretical result and the numerical result is fairly good.Comment: 4pages, 4figure
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
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