Volume 38, Issue 2

Abstract. The Green–Naghdi theory of heat conduction enjoys great research interest because it is developed in a very general way and because it is capable of accounting for thermal pulse transmission in a very general manner. In this paper, that theory is revisited, and some questions it leaves open are pointed out.

Abstract. Cystic fibrosis (CF) is a chronic progressive pulmonary disorder caused by mutations in the CFTR (cystic fibrosis transmembrane conductance regulator) gene. A CF lung is generally characterized by obstructed airflow to an extent that leads to destruction of airway wall support structure. Airway resistance, resulting from both laminar and turbulent flow, is an important mechanical factor contributing to flow of air into and out of the airways. There are numerous research studies focusing on airflow in the respiratory system that assumed flow to be only laminar and steady. The goal of this research is to describe the air flow mathematically by considering the resistance from both laminar and turbulent airflow throughout the entire respiratory tract. Furthermore, we implement a model that includes airway clogging in CF lungs and recalculate the rate of air flow given these obstructions.

Abstract. According to standard thermophysical theories, cross effects are mostly present in multicomponent systems. In this paper we show that for relativistic fluids an electric field generates a heat flux even in the single-component case. In the non-relativistic limit the effect vanishes and Fourier's law is recovered. This result is novel and may have applications in the transport properties of very hot plasmas.

Abstract. Phonon transport in dielectric film depends on phonon polarization and their frequencies. This requires the solution of frequency-dependent Boltzmann equations for energy transport in dielectric films. In the present study, a frequency-dependent solution of the Boltzmann equation is obtained for a two-dimensional silicon film, and variation of equivalent equilibrium temperature in the film is presented. The influence of film width on phonon transport in the film is examined. The comparison of equivalent equilibrium temperature obtained from the frequency-dependent and -independent solutions is also presented. It is found that ballistic phonons suppress equivalent equilibrium temperature increase in the film. Two-dimensional phonon transport reduces to one-dimensional transport in film as the film width increases to more than twice of the film thickness.

Abstract. An analysis of entropy production and its evolution in the frequency domain upon application of electromagnetic fields to ferrimagnetic material has been investigated. The spectral entropy of NiZn ferrites doped with different amounts of Yttrium has been studied by numerical simulation. Under the application of an oscillating electromagnetic field, the system is out of equilibrium as there is entropy production due to the dielectric and magnetic polarization. A system subjected to electromagnetic fields and at constant temperature T has been considered. For the numerical simulation of the behavior of the entropy production due to magnetic relaxation, experimental data have been correlated to a recently published causality model. For the entropy production due to dielectric relaxation, experimental data have been used. Entropy production related to magnetic response could be associated with two mechanisms: domain wall motion and spin rotation. Entropy production related to dielectric processes could be associated with the delay of the different components of the polarizability as a function of the frequency of the applied field and the correlation with the transport charge mechanism in the material. At the frequency range under study, the entropy production due to dielectric relaxation is negligible. Thus entropy spectra could be a suitable tool for the analysis of the ferrimagnetic materials.

Abstract. A hydrodynamic model describing the superfluid phase transition of He close to the λ-line is presented. In the work, which generalizes a phase field model of λ-transition previously formulated by the same authors, the independent fields are the density, the temperature, the velocity, the heat flux, and a scalar function f , linked to the modulus of the wave-function ψ, solution of the Ginzburg–Landau equation. In this framework, the heat flux is given by a modified Maxwell–Cattaneo equation. The restrictions on the constitutive quantities are obtained from the entropy principle, using the Liu method of Lagrange multipliers. A maximum theorem is proved that allows the model to satisfy the second law of thermodynamics.