Comparative study of evolution of structured flows at boundary of the regime change “diffusion — concentration convection” in isothermal multicomponent mixing in gases by techniques of visual and numerical analysis

During isothermal multicomponent diffusion process, the number of effects appear that are not observed visually when mixed in binary mixtures. These include occurrence of convective instability with subsequent formation of structured flows. The feature of this type of mixing is that convection is realized under conditions of decrease in density of mixture with height. Flow visualization method allows to fix information about distribution of medium parameters by dynamics of structures in convective flows. Application of computer processing methods, as well as techniques of identifying images of thermophysical fields, allows to obtain quantitative information about convective flows. For an isothermal ternary gas mixture heliumargonnitrogen, shadow images of structural formations formed in convective flows due to the instability of mechanical equilibrium are represented in this work. To carry out digital analysis of experimental shadow images, a simplified virtual model of the lower chamber of the diffusion cell was created. Based on digital analysis of visual images, quantitative characteristics related to estimation of the size of convective formations, period of their formation, and linear velocity of convection cells when moving through diffusion channel are presented. It has been established that the growing convective disturbances arising in the system cause a change in the characteristic scale of convective cells. The analysis of shadow images also showed that a vortex is formed in convective flows, which consists mainly of a component with the highest molecular weight. Comparison of visual images of experimental fields with simulation flows is implemented, on the basis of which composition of mixture components in convective structures is estimated. It is shown that the obtained value of the concentration of the heavy component in the vortex filament can be taken as the minimum

Quantum Diffusion and Eigenfunction Delocalization in a Random Band Matrix Model

We consider Hermitian and symmetric random band matrices $H$ in $d \geq 1$ dimensions. The matrix elements $H_{xy}$, indexed by $x,y \in \Lambda \subset \Z^d$, are independent, uniformly distributed random variables if \abs{x-y} is less than the band width $W$, and zero otherwise. We prove that the time evolution of a quantum particle subject to the Hamiltonian $H$ is diffusive on time scales $t\ll W^{d/3}$. We also show that the localization length of an arbitrarily large majority of the eigenvectors is larger than a factor $W^{d/6}$ times the band width. All results are uniform in the size \abs{\Lambda} of the matrix.Comment: Minor corrections, Sections 4 and 11 update

RESEARCH OF THE FEATURES OF PHASE FORMATION OF COATINGS OF THE Al-Ti-Ni-Mo SYSTEM, OBTAINED BY PLASMA SPRAYING METHOD

In this work, we studied the microstructures of coating samples of the Al-Ti-Ni-Mo system, and also carried out an x-ray phase analysis to determine the phases of the components of the system. The alloy was obtained by aluminothermic reduction of oxides in a resistance furnace

The influence of gluconate bath parameters on the rate of electrodeposition and mechanical properties of Co–W coatings

The given study overview the results obtained for Co–W alloys electrodeposited from gluconate bath. Namely, the influence of different parameters (the concentration of the bath components, pH, temperature, cathodic current density, volume current density, hydrodynamic conditions, insoluble and soluble anodes) on the rate of electrodeposition and microhardness of the coatings has been investigated. The given research determine the conditions ensuring high deposition rate, microhardness and bath efficiency. It was shown, that the deposition rate, tungsten content and microhardness reach the maximum values at pH 6.5, regardless on the concentration of bath components. Also, it was detected the macroscopic size effect of microhardness, which is linked to the fact that for a fixed cathodic current density microhardness depends on volume current density. In addition, different anodes (Pt, graphite, W and Co–W) were investigated to reveal the anode influence on reaching the maximum values of the current efficiency and microhardness