Diffusion Stability of Mechanical Equilibrium in Compressible Isothermal Gases
— This paper is presented stability condition of mechanical equilibrium for diffusion of compressible isothermal gases in a cylindrical domain. Two general cases of the divergent stable motions were considered when density depended on the conditions 0  u div  and 0  u div . Stability criterion of mechanical equilibrium for the compressible gas mixture is proposed by defining continuous dependence of the velocity vector for the compressible flows in the Navier-Stokes problem from initial date. Using the parametrix method of theory nonlinear partial differential equations were obtained the velocity components for the transient compressible flows. Introduced stability condition for isothermal gases was predicted in the principal form by the energy conservation law and based on the transport equation for an appropriate convergent-divergent turbulent gas motion.
DIFFUSION IN ISOTHERMAL TERNARY GAS MIXTURES
It is experimentally shown that if there are more than two components in the gas mixture, the system becomes instable even when the density of mixture is lower in upper part than in the bottom. The transition from the diffusion to the convective mixing is possible by the certain values of the pressure, the temperature, the viscosity and geometrical characteristics of the vessel. Some threecomponent gas mixtures are characterized by the atypical concentrational distribution of the system components during the convection, which is caused by the difference of diffusion coefficients. The existence of structural formations at this process was shown by Tepler's shadow method. The linear analyses of stability can explain reasons of this «paradox of stability». The were found the following novel effects in isothermal three-component gas mixtures with steady stratification of density of the gas mixture: there are observed the curves ) ( p i α with two maximums on a number of mixtures at variation of the channel diameter; there are registered some transitions from diffusion to convection and back at measurement of composition of mixture not only at the first stage of mixing, but also on the subsequent ones. The theoretical results are compared with experimental findings of stability border in three-component gas systems.
Selective etching of InP in NaF solution
Abstract The crossing porous structure of InP has been obtained by electrochemical etching in NaF solutions. The behavior of the periodic oscillation occurs at different potential ranges for the different concentrations of solutions, and it will disappear with the concentration of the solution decreased. The scanning electron microscope (SEM) image shows that the pores have two directions on the surface and are perpendicular to each other. The two directions are assigned to [0 1 1] and [ 0 1 ¯ 1 ], respectively. The SEM image of the cross-section also shows that the two directions are assigned to [1 1 1]B and [ 1 1 ¯ 1 ¯ ]B. Both are due to the selective etching of F− ions. The crossing porous structure of InP is a very promising feature for the three-dimensional structure of III–V compound semiconductors for photonic band gap materials.