Influence of the structure of a porous medium on the residual gas saturation in the case of capillary displacement by a liquid

A model of a porous medium consisting of randomly branching conical pores is used to investigate the quasistatic displacement of gas by a wetting liquid without application of an external pressure. Allowance is made for the circumstance that in the capillary process all the pores have at least one-sided permeability for the liquid phase. An expression is obtained that relates the residual gas saturation to the parameters which characterize the structure of the pores and the wetting properties of the system. Two new characteristics of the pore space are introduced — the branching parameter and the opening angle of the pores — and the influence of these parameters on the residual saturation is investigated. It is shown that for individual classes of natural media the residual gas saturation depends only on the porosity and the contact angle of wetting.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 128–133, September–October, 1981.     

Negative filament tension in the Luo-Rudy model of cardiac tissue

Scroll waves are vortices that occur in three-dimensional excitable media. Scroll waves have been observed in a variety of systems including cardiac tissue, where they are associated with cardiac arrhythmias. The disorganization of scroll waves into chaotic behavior is thought to be the mechanism of ventricular fibrillation, which lethality is widely known. One of the possible mechanisms of scroll wave instability is negative filament tension, which was studied theoretically using low-dimensional models of excitable medium. In this article we perform a numerical study of negative filament tension using the Luo-Rudy phase 1 model, which is widely used in cardiac electrophysiology. We show that this instability exists in this model, study its manifestation and discuss its relation to cardiac arrhythmogenesis.     

The impact of instability appearance on the quadratic law for flow through porous media

In the present paper, we attempt to explain the macroscopic flow law evolution in porous media according to the Reynolds number. A crenellated channel, considered as an element of such a medium, is used to perform numerical simulations in stationary and non-stationary cases. In the case of non-stationary laminar flows, we point out flow instabilities occurring in the channel at high Reynolds numbers and we focus on their influence on the macroscopic law. We qualitatively prove that they generate an additional quadratic contribution to Forchheimer’s law. We use two methods to study this contribution: first, a periodic disturbance, for which the instabilities appearing at the beginning of disturbance become regular oscillations; then a pulse disturbance of the entry velocity field which enables us to link the additional quadratic contribution to the existence of an accumulation of fluid at low velocity in the channel.     

Temperature behavior of conductivity in a La2CuO4 + δ single crystal upon the paramagnetic-antiferromagnetic transition

The temperature dependence of the resistance of a La₂CuO_{4 + δ} (δ ≈ 0.05) single crystal with the Neel temperature T _N ≈ 205 K was investigated in order to establish the correlation between the transport and magnetic properties of the crystal. The R(T) dependence near T _N reveals a kink related to the enhancement of sample’s conductivity upon the transition from the antiferromagnetic to paramagnetic state. With an increase in temperature far above T _N, the transition from the dielectric (dR/dT < 0) to metal (dR/dT > 0) occurs. The observed behavior of resistance is attributed to delocalization of carriers above T _N.     

Millimeter-wave spectrum of Ne–CO: new measurements

The b-type rotational transitions of the van der Waals complex, Ne–CO have been measured using the intracavity OROTRON jet spectrometer in the frequency range of 80–115 GHz. The high sensitivity of this technique enabled us to detect all three Ne isotopic modifications of the complex, ²⁰Ne–CO, ²²Ne–CO, and ²¹Ne–CO in natural abundance. The observed and assigned transitions belong to the Q-branch of the K = 1–0 subband and include also R (0) and P (2) lines. The newly obtained data were analysed together with previously observed millimeter-wave b-type and microwave a-type rotational transitions.     

Prolongation of two phases in the model of fluid displacement through a capillaryProlongement de deux phases dans le modèle du déplacement d'un fluide dans un capillaire

The problem of a piston-like displacement of a fluid by another in a capillary is examined. It is suggested that each fluid is prolonged into the domain occupied by the other fluid. This enables the replacement of the two-phase flow problem by a transient single-phase flow problem, with discontinuity in velocity and pressure on a film interface. The problems related to the triple point are solved by introducing a limit fluid near the pore wall. The demonstration of the Washburn equation contributes to the physical justification of our model. To cite this article: Y. Lucas et al., C. R. Mecanique 334 (2006).     

Two Types of Transient Phenomena and Full Relaxation Macroscale Model for Single Phase Flow through Double Porosity Media

Darcy's flow of a weakly compressible fluid through double porosity media is studied in the framework of the homogenization theory. In previous papers, various classes of single-phase flow have been detected with various determination of the effective permeability tensor for each class. In this paper, the full model including transient phenomena is developed, where the macroscale momentum balance equation represents a modification of Darcy's law with a nonequilibrium term. The effective permeability tensor appears to be nonstationary and is changing during the system evolution in time. Three relaxation times characterize the transient transformations of each component of the macroscale flow velocity.This effect is superposed with the second relaxation phenomenon caused by the exchange flow between dense blocks and the highly conductive matrix. The relaxation times for the effective permeability and for the exchange flow are shown to have different orders.All relaxation parameters are explicitly determined through solutions of cell problems.