Stability of the lateral surface of viscous fingers formed when a fluid is displaced from a Hele-Shaw cell

It is shown that instability develops on the lateral surface of viscous fingers formed when a fluid is displaced from a Hele-Shaw cell. This instability is caused by the inertia forces, whereas the viscous forces acting in the plane of the cell stabilize the surface.     

Thermoelectric figure of merit for semiconductor submicron layers

We show that in semiconductors of submicron dimensions, for certain relations between the electronic and phonon boundary conditions a heat flux may occur only through the electronic subsystem. Consequently, the thermoelectric figure of merit z does not involve the total thermal conductivity, but only its electronic component. In the ideal case of isothermal contacts, this leads to a sharp increase in z compared with massive semiconductors.Ya. A. Galan Ternopol' Pedagogical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 68–72, September, 1993.     

Displacement of a viscous fluid from an annular Hele–Shaw cell with a sink within the framework of the Brinkman model

The stability of the radial front of viscous fluid displacement from an annular Hele–Shaw cell with a sink of finite radius is analyzed. It is shown that in the absence of the surface tension and at a minimal manifestation of molecular diffusion the role of the stabilizing factor determining the displacement front structure can be played by small viscous forces in the cell plane. The viscous fingers formed in this case turn out to be wider than those in a rectangular cell.     

Thermodynamic study of adsorption of nickel complexes with Schiff bases from acetonitrile solutions on uncharged graphite surface

Adsorption of nickel N,N-ethylenebis(salicylideneimine) complex from acetonitrile solution on expanded natural graphite powder at 273–313 K is studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 10, 2004, pp. 1643–1646.Original Russian Text Copyright © 2004 by Afanasev, Aleksandrova, Akulova, Logvinov.     

Quasi-isentropic compressibility of deuterium and helium at pressures of 1500–5000 GPa

The quasi-isentropic compressibilities of deuterium and helium plasmas are measured in the pressure range 1500–5000 GPa at densities up to 8 g/cm³ using spherical experimental devices and an X-ray complex consisting of three betatrons and a multichannel optoelectronic system for taking X-ray images. The experimental results demonstrate the possibilities of high-energy-density experimental physics to reproduce the extreme states of substance typical of the Universe under laboratory conditions using the energy of traditional condensed explosives.     

Effect of small parameters on the structure of the front formed by unstable viscous-fluid displacement from a Hele-Shaw cell

The process of displacement of a viscous fluid from a Hele-Shaw cell consisting of two plates separated by a small gap is investigated. The front formed when the fluid is displaced from the cell by another, lower-viscosity fluid is unstable. The lower-viscosity fluid breaks through the layer of displaced fluid and forms channels called viscous fingers. As a result, a mixing zone occupied by both displaced and displacing fluids is formed. The structure of the unstable displacement front is investigated when the surface tension forces have no effect on the shape of the fingers. This situation is realized when a water-glycerin mixture is rapidly displaced from the cell by water. Equations taking the inertial and viscous forces acting in the plane of the plates into account are obtained by averaging the Navier-Stokes equations over the cell gap. Using the equations obtained the stability of a plane displacement front traveling in the direction of its normal and the stability of the lateral surfaces of the viscous fingers is investigated when the fluid velocities are parallel to the interface. From the solution for stability of the transverse displacement front it follows that the viscous forces acting in the plane of the plates determine the finger width (when there is no surface tension). Instability also develops in the flow on the longitudinal fluid interface. In this case the destabilizing factor is the inertial forces. Under the action of this instability the fingers, in their turn, lose stability and disintegrate into viscous bubbles.     

Nonlinear voltage-temperature characteristics of submicron semiconductor layers

Voltage-temperature characteristics (VTC) of current carriers in semiconductor layers that are substantially narrower than the bulk cooling length are constructed in the temperature approximation. The nature of the VTC nonlinearity is shown to crucially depend on the ratio of the bulk to the surface energy relaxation lengths of electrons. Because these lengths depend on the electron temperature, with changing external electric fields, the contributions of these surface and bulk scattering mechanisms to energy relaxation processes may vary, leading to visible changes of VTC.In conclusion, the author would like to express his gratitude to Yu. G. Gurevich for a fruitful discussion of the results of this work.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 85–90, October, 1991.