Josep Enric Llebot

A thermodynamic approach to heat and electric conduction in solids

Heat and electric conduction in a rigid solid is investigated in the framework of extended irreversible thermodynamics. This allows us to apply directly the original procedure of Onsager to the analysis of the reciprocal relations. A non-local constitutive equation for the heat flux previously obtained is compared with microscopic equations used for the analysis of second sound in solids. A hydrodynamical analogy of this equation leads to the possibility of a turbulent phonon flow under some specific physical conditions.

Extremal climatic states simulated by a 2-dimensional model Part I: Sensitivity of the model and present state

The criterion, based on the thermodynamics theory, that the climatic system tends to extremizesome function has suggested several studies. In particular, special attention has been devotedto the possibility that the climate reaches an extremal rate of planetary entropy production.Due to both radiative and material effects contribute to total planetary entropy production, climatic simulations obtained at the extremal rates of total, radiative or material entropy productionappear to be of interest in order to elucidate which of the three extremal assumptionsbehaves more similar to current data. In the present paper, these results have been obtainedby applying a 2-dimensional (2-Dim) horizontal energy balance box-model, with a few independentvariables (surface temperature, cloud-cover and material heat fluxes). In addition, climaticsimulations for current conditions by assuming a fixed cloud-cover have been obtained. Finally, sensitivity analyses for both variable and fixed cloud models have been carried out.

Electric current fluctuations in extended irreversible thermodynamics

Starting from the generalised Gibbs equation of extended irreversible thermodynamics, a thermodynamic potential which offers a suitable description of the electric current fluctuations in an isotropic rigid conductor is derived.

On the admissible values of the heat flux in hyperbolic heat transport

Abstract The thermodynamic stability restrictions on the maximum value of the heat flux in nonequilibrium steady states are compared with the restrictions which must be satisfied by the initial values of the heat flux in order to guarantee the positive character of the absolute temperature along the evolution towards equilibrium in hyperbolic heat transport.

Temperature and measurement: comparison between two models of nonequilibrium radiation

We generalize a previous proposal of an experiment (J. Fort, D. Jou, J.E. Llebot, Physica A 248 (1998) 97) that, on the basis of predicted corrections to the Planck spectral law, may allow to determine experimentally what quantity is measured by a thermometer in steady-state nonequilibrium systems composed of matter and radiation. We include the photon number flux as an additional constraint. According to the model presented, the differences between the spectra predicted from two possible temperature definitions are higher than previously thought. In contrast to some previous papers, our model does not consider a specific matter content for the system.

Bacterial flagellar rotation as a nonequilibrium phase transition

We propose a model for a mechanism leading to a threshold in the protonmotive force for the rotation of the motor of bacterial flagella. Such a model is based on a finite relaxation time of some intermediate molecular configurations, which leads to a nonlinear motor torque for small values of angular velocity.

On the fast and the slow components of thermal fluctuations

In the framework of extended irreversible thermodynamics, we propose a unified description of the fluctuations of both the temperature and the heat flux. Their two-time correlations are obtained in equilibrium. When applied to non-equilibrium steady states, the formalism suggests some modifications in the usual fluctuation-dissipation expressions, gives a non-vanishing correlation between quantities of different time reversal symmetry, and provides a simple example of the breaking of the validity of the Onsager relations.

Extremal climatic states simulated by a 2-dimensional model Part II: Different climatic scenarios

Different climatic simulations have been obtained by using a 2-Dim horizontal energy balancemodel (EBM), which has been constrained to satisfy several extremal principles on dissipationand convection. Moreover, 2 different versions of the model with fixed and variable cloud-coverhave been used. The assumption of an extremal type of behaviour for the climatic system canacquire additional support depending on the similarities found with measured data for pastconditions as well as with usual projections for possible future scenarios.

MEASURABLE TEMPERATURES IN NONEQUILIBRIUM RADIATIVE SYSTEMS

Information theory yields different predictions for the radiation intensity of nonequilibrium radiative systems, depending on what quantity one identifies with the temperature. A possible experiment is proposed that may, in principle, be used in order to determine whether the generalized temperature of extended irreversible thermodynamics is the measurable temperature in nonequilibrium radiative systems or not.

Information-theoretical derivation of an extended thermodynamical description of radiative systems

A radiative equation of the Cattaneo–Vernotte type is derived from information theory and the radiative transfer equation. The equation thus derived is a radiative analog of the equation that is used for the description of hyperbolic heat conduction. It is shown, without recourse to any phenomenological assumption, that radiative transfer may be included in a natural way in the framework of extended irreversible thermodynamics (EIT).