David Jou
Universitat Autònoma de Barcelona, Departament de Fisica, Faculty Member
The paper deals with the meaning of non-equilibrium temperatures in nanosystems with an internal variable, describing defects inside them, and implications on heat transport. In equilibrium all definitions of temperature lead to the same... more
The paper deals with the meaning of non-equilibrium temperatures in nanosystems with an internal variable, describing defects inside them, and implications on heat transport. In equilibrium all definitions of temperature lead to the same value, but in nonequi-librium steady states they lead to different values, giving information on different degrees of freedom. We discuss the caloric and entropic non-equilibrium temperatures and the relations among them, in defective nanosystems (crystals with dislocations or porous channels, carbon nanotubes in a solid matrix and so on), crossed by an external energy flux. Here, we present a model for nanocrystals with dislocation defects submitted to an external energy flux. The dislocations may have a strong influence on the effective thermal conductivity, and their own dynamics may be coupled in relevant way to the heat flux dynamics. In the linear case the constitutive relations, the rate equations for the internal variable and the heat flux are worked out and a generalized telegraphic heat equation is derived in the anisotropic and isotropic case, describing the thermal disturbances with finite velocity.
ABSTRACT
Research Interests:
Research Interests:
ABSTRACT
Research Interests:
The objective of this paper is twofold: first, to examine how the concepts of extended irreversible thermodynamics are related to the notion of accompanying equilibrium state introduced by Kestin; second, to compare the behavior of both... more
The objective of this paper is twofold: first, to examine how the concepts of extended irreversible thermodynamics are related to the notion of accompanying equilibrium state introduced by Kestin; second, to compare the behavior of both the classical local equilibrium entropy and that used in extended irreversible thermodynamics. Whereas the former does not show a monotonie increase, the latter exhibits a steady increase during the heat transfer process; therefore it is more suitable than the former one to cope with the approach to equilibrium in the presence of thermal waves.
Research Interests:
Research Interests:
ABSTRACT
Research Interests:
A new, simple and physically transparent derivation of thermodynamics and hydrodynamics of radiating fluids is presented. The hydrodynamics is then extended to strongly inhomogeneous radiating fluids. The presence of inhomogeneities gives... more
A new, simple and physically transparent derivation of thermodynamics and hydrodynamics of radiating fluids is presented. The hydrodynamics is then extended to strongly inhomogeneous radiating fluids. The presence of inhomogeneities gives rise, among other changes, to new stresses (the stresses that are added to the classical Eddington stresses). The physical basis of the analysis is the requirement that solutions to the governing equations agree with results of the experimental observations that constitute the empirical basis of equilibrium thermodynamics.
Research Interests:
ABSTRACT
Research Interests:
Physical objects with energy $u_w(l) \sim l^{-3w}$ with $l$ a characteristic length and $w$ a numerical constant ($-1 \leq w \leq 1$), lead to an equation of state $p=w\rho$, with $p$ the pressure and $\rho$ the energy density. Special... more
Physical objects with energy $u_w(l) \sim l^{-3w}$ with $l$ a characteristic length and $w$ a numerical constant ($-1 \leq w \leq 1$), lead to an equation of state $p=w\rho$, with $p$ the pressure and $\rho$ the energy density. Special objects with this property are, for instance, photons ($u = hc/l$, with $l$ the wavelength) with $w = 1/3$, and some models of cosmic string loops ($u = (c^4/aG)l$, with $l$ the length of the loop and $a$ a numerical constant), with $w = -1/3$, and maybe other kinds of objects as, for instance, hypothetical cosmic membranes with lateral size $l$ and energy proportional to the area, i.e. to $l^2$, for which $w = -2/3$, or the yet unknown constituents of dark energy, with $w = -1$. Here, we discuss the general features of the spectral energy distribution of these systems and the corresponding generalization of Wien's law, which has the form $Tl_{mp}^{3w}=constant$, being $l_{mp}$ the most probable size of the mentioned objects.
Research Interests:
Research Interests:
ABSTRACT
ABSTRACT