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David Jou

Publications and source records attributed to David Jou.

18 recordsLinked to original sources
arXiv2024

Internal tensorial variables and a heat transport equation with inertial, thermal viscosity and vorticity terms

Phonon hydrodynamics describes the motions of heat carriers (phonons) at sub-continuum scales: diffusive, ballistic, viscous, and vortical. In a previous paper, these behaviours were investigated within the framework of non-equilibrium thermodynamics with internal variables at the macroscopic scale, deriving generalizations of the Guyer-Krumhansl equation. In particular, a generalized heat conduction equation, containing not only the Fourier, Maxwell-Vernotte-Cattaneo, and Guyer-Krumhansl contributions, but also a term describing phonon vortices, was obtained. In this paper, we provide new insight and clarifications into the same model for rigid heat-conducting media. Then, we a posteriori identify two non-local macroscopic internal variables, $Q^s$ and $Q^a$ (the symmetric part and the antisymmetric part of a second order tensor $Q$) with the symmetric (changed in sign) and antisymmetric gradients of the heat flux, $-(\nabla J(q))^s$ and $(\nabla J(q))^{a}$. Also an identification of these two tensorial internal variables is obtained by an asymptotic approach. This generalizes the heat equation with additional terms containing the time derivative of the heat flux describing the viscous and vortical motions of phonons. These terms may describe the transfer from ordered rotational motion of phonon vortices to rotational microscopic motions of diatomic particles constituting complex polar crystals, in analogy to the hydrodynamics of classical micropolar fluids. Therefore, this paper fits into the currently explored area of phonon vorticity and its interactions with the heat flux itself.

cond-mat.mes-hall↗
arXiv2022

Multiscale heat transport with inertia and thermal vortices

In this paper, we present a Hamiltonian and thermodynamic theory of heat transport on various levels of description. Transport of heat is formulated within kinetic theory of polarized phonons, kinetic theory of unpolarized phonons, hydrodynamics of polarized phonons, and hydrodynamics of unpolarized phonons. These various levels of description are linked by Poisson reductions, where no linearizations are made. Consequently, we obtain a new phonon hydrodynamics that contains convective terms dependent on vorticity of the heat flux, which are missing in the standard theories of phonon hydrodynamics. Moreover, the equations are hyperbolic and Galilean invariant, unlike current theories for beyond-Fourier heat transport. The vorticity-dependent terms violate the alignment of the heat flux with the temperature gradient even in the stationary state, which is expressed by a Fourier-Crocco equation. The new terms also cause that temperature plays in heat transport a similar role as pressure in aerodynamics.

cond-mat.mes-hall↗
arXiv2019

When theories and experiments meet: rarefied gases as a benchmark of non-equilibrium thermodynamic models

The role of thermodynamics in deriving constitutive equations is unique, and various approaches have been developed in the last decades. In the present paper, the frameworks of Extended Irreversible Thermodynamics (EIT) and Non-Equilibrium Thermodynamics with Internal Variables (NET-IV) are discussed and compared to each other on the basis of a particular problem of rarefied gases. In this comparison, both theoretical and experimental aspects are taken into account. Eventually, an experiment by Meyer and Sessler covering a wide range of pressures and frequencies is investigated. Here, concentrating on the scaling properties and the density dependence of parameters, the change of speed of sound in terms of frequency and pressure is recovered using NET-IV, and this fitting is compared to the results of Lebon and Cloot using EIT.

physics.flu-dyn↗
arXiv2017

Hamiltonian and Godunov Structures of the Grad Hierarchy

The time evolution governed by the Boltzmann kinetic equation is compatible with mechanics and thermodynamics. The former compatibility is mathematically expressed in the Hamiltonian and Godunov structures, the latter in the structure of gradient dynamics guaranteeing the growth of entropy and consequently the approach to equilibrium. We carry all three structures to the Grad reformulation of the Boltzmann equation (to the Grad hierarchy). First, we recognize the structures in the infinite Grad hierarchy and then in several examples of finite hierarchies representing extended hydrodynamic equations. In the context of Grad's hierarchies we also investigate relations between Hamiltonian and Godunov structures.

cond-mat.stat-mech↗
arXiv2014

Transition to ballistic regime for heat transport in helium II

The size-dependent and flux-dependent effective thermal conductivity of narrow capillaries filled with superfluid helium is analyzed from a thermodynamic continuum perspective. The classical Landau evaluation of the effective thermal conductivity of quiescent superfluid, or the Gorter-Mellinck regime of turbulent superfluids, are extended to describe the transition to ballistic regime in narrow channels wherein the radius $R$ is comparable to (or smaller than) the phonon mean-free path $\ell$ in superfluid helium. To do so we start from an extended equation for the heat flux incorporating non-local terms, and take into consideration a heat slip flow along the walls of the tube. This leads from an effective thermal conductivity proportional to $R^2$ (Landau regime) to another one proportional to $R\ell$ (ballistic regime). We consider two kinds of flows: along cylindrical pipes and along two infinite parallel plates.

cond-mat.supr-con↗
arXiv2013

Effective thermal conductivity of helium II: from Landau to Gorter-Mellink regimes

The size-dependent and flux-dependent effective thermal conductivity of narrow channels filled with He II is analyzed. The classical Landau evaluation of the effective thermal conductivity of quiescent He II is extended to describe the transition to fully turbulent regime, where the heat flux is proportional to the cubic root of the temperature gradient (Gorter-Mellink regime). To do so we use an expression for the quantum vortex line density $L$ in terms of the heat flux considering the influence of the walls. From it, and taking into account the friction force of normal component against the vortices, we compute the effective thermal conductivity.

cond-mat.other↗
arXiv2013

Spectral energy distribution and generalized Wien's law for photons, cosmic string loops and related physical objects

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 $p=wρ$, with $p$ the pressure and $ρ$ 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.

gr-qc↗
arXiv2013

A duality-invariant Einstein-Planck relation and its consequences on micro black holes

We discuss the consequences of a duality-invariant Einstein-Planck relation on the equation of state of micro black holes. The results are analogous to those obtained from the "world crystal" model, but with some significative differences, as for instance a limiting vanishing value for temperature for very small black holes. The model leads to a total evaporation of micro black holes but with the final stage being very slow.

gr-qc↗
arXiv2010

Hydrodynamic equations of anisotropic, polarized and inhomogeneous superfluid vortex tangles

We include the effects of anisotropy and polarization in the hydrodynamics of inhomogeneous vortex tangles, thus generalizing the well known Hall-Vinen-Bekarevich-Khalatnikov equations, which do not take them in consideration. These effects contribute to the mutual friction force ${\bf F}_{ns}$ between normal and superfluid components and to the vortex tension force $ρ_s{\bf T}$. These equations are complemented by an evolution equation for the vortex line density $L$, which takes into account these contributions. These equations are expected to be more suitable than the usual ones for rotating counterflows, or turbulence behind a cylinder, or turbulence produced by a grid of parallel thin cylinders towed across a superfluid, because in these situations polarization is expected to play a relevant role.

cond-mat.other↗
arXiv2010

A mathematical model of counterflow superfluid turbulence describing heat waves and vortex-density waves

The interaction between vortex density waves and high-frequency second sound in counterflow superfluid turbulence is examined, incorporating diffusive and elastic contributions of the vortex tangle. The analysis is based on a set of evolution equations for the energy density, the heat flux, the vortex line density, and the vortex flux, the latter being considered here as an independent variable, in contrast to previous works. The latter feature is crucial in the transition from diffusive to propagative behavior of vortex density perturbations, which is necessary to interpret the details of high-frequency second sound.

cond-mat.other↗
arXiv2010

Vortex density waves and high-frequency second sound in superfluid turbulence hydrodynamics

In this paper we show that a recent hydrodynamical model of superfluid turbulence describes vortex density waves and their effects on the speed of high-frequency second sound. In this frequency regime, the vortex dynamics is not purely diffusive, as for low frequencies, but exhibits ondulatory features, whose influence on the second sound is here explored.

cond-mat.other↗
arXiv2010

Vortex length, vortex energy and fractal dimension of superfluid turbulence at very low temperature

By assuming a self-similar structure for Kelvin waves along vortex loops with successive smaller scale features, we model the fractal dimension of a superfluid vortex tangle in the zero temperature limit. Our model assumes that at each step the total energy of the vortices is conserved, but the total length can change. We obtain a relation between the fractal dimension and the exponent describing how the vortex energy per unit length changes with the length scale. This relation does not depend on the specific model, and shows that if smaller length scales make a decreasing relative contribution to the energy per unit length of vortex lines, the fractal dimension will be higher than unity. Finally, for the sake of more concrete illustration, we relate the fractal dimension of the tangle to the scaling exponents of amplitude and wavelength of a cascade of Kelvin waves.

cond-mat.other↗
arXiv2008

Vortex dynamics in rotating counterflow and plane Couette and Poiseuille turbulence in superfluid Helium

An equation previously proposed to describe the evolution of vortex line density in rotating counterflow turbulent tangles in superfluid helium is generalized to incorporate nonvanishing barycentric velocity and velocity gradients. Our generalization is compared with an analogous approach proposed by Lipniacki, and with experimental results by Swanson et al. in rotating counterflow, and it is used to evaluate the vortex density in plane Couette and Poiseuille flows of superfluid helium.

cond-mat.other↗
arXiv2007

Phenomenological description of the vortex density in rotating BEC superfluids

We propose a phenomenological equation for the vortex line density in rotating Bose-Einstein condensates as a function of the angular speed. This equation provides a simple description of the gross features of the increase in vortex number from the appearance of the first vortex to the theoretical rigid-body result for high vortex density, and allows one to compare with analogous situations in superfluid helium, after the suitable changes in the relevant parameters are made.

cond-mat.other↗
arXiv2007

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.

cond-mat.other↗
arXiv2004

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.

cond-mat.mtrl-sci↗
arXiv2002

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.

cond-mat.stat-mech↗