Linear Homogenization in the Analysis of Cellular Structures Produced by Additive Technology

Russian Engineering Research - Linear homogenization is applied to cellular structures produced by selective laser melting (SLM). Samples of different materials with cells of different...     

Study of the processes of steam-hydrogen mixture generation in a reactor for hydrothermal aluminum oxidation for power units

This work is devoted to the study of the processes of generation of steam-hydrogen gaseous mixtures formed in the hydrothermal oxidation of aluminum and its further utilization in power units. One of the main objects of this study is a reactor that generates steam-hydrogen mixtures, and the main problem is the continuous mode of its operation. Analytical calculations of thermodynamic parameters that are characteristic of the continuous hydrothermal oxidation of aluminum are reported together with the results of the experimental study of this mode. A combination of theoretical and experimental studies made it possible to determine the composition of aluminum-water suspensions and the range of thermodynamic parameters that are optimal for the continuous reactor of steam-hydrogen mixture generation.     

Pressure crystallization of a polymeric sphere

A calculation scheme is proposed to determine external pressure during frontal crystallization of a polymeric sphere in an effort to compensate internal stresses. An analytical dependence which relates an external pressure with the crystallization front coordinate specified by temperature conditions is obtained.Institute of Industrial Chemistry, Ural Division of the Russian Academy of Sciences, Perm'. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 63, No. 4, pp. 481–485, October, 1992.     

Heat-insulating aerogel composites for a hydrothermal reactor

The SiO₂–TiO₂ aerogel composites used in the heat insulation of a hydrothermal reactor and the method of their fabrication using a liquid glass technology are analyzed. The process of fabrication of the composite material includes the following stages: the ion exchange of sodium liquid glass with the formation of silica hydrosol; the concentration of hydrosol; the formation of hydrogel and its maturing; the formation of alcogel of an SiO₂–TiO₂ composite material; surface modification; subcritical drying of alcogel with the formation of SiO₂–TiO₂ composite ambigel; and its heat treatment, granulation, and classification. The influence of infrared absorber (titanium dioxide) and the temperature of heat treatment of an SiO₂–TiO₂ aerogel composite material on its structural and thermal characteristics is studied.     

Electrical and gas-sensitive properties of a resistive thin-film sensor based on tin dioxide

A simple model of a resistive thin-film sensor is used to derive an analytic expression that describes the dependences of the response to the effect of reducing gas on temperature, partial gas pressure, the concentration of donor impurity in the SnO₂ film, and the duration of the exposure to gas. An analysis of experimental data showed that the processes of adsorption and desorption of H₂ molecules at T < 510 K are mainly controlled by adsorption centers occupied by oxygen in the form of O ₂ ^? , while the centers with O^? control these processes at T > 563 K. At T ≥ 510 K, the methane molecules interact with the centers occupied by O^?. The desorption-activation energies are determined in a wide temperature range using the data on the time dependences of the response. This energy equals 0.36 eV for hydrogen at T < 510 K. At T > 563 K for hydrogen and T > 510 K for methane, the desorption-activation energy is equal to 1.3 eV. The adsorption-activation energy is equal to 2.5 eV for methane.     

Polarization dependence of EXAFS and XANES spectra of superconducting films on the basis of Y-Ba-Cu-O

Superconducting films of Y-Ba-Cu-O have been studied by EXAFS and XANES spectroscopy. Films of thickness 1000 Å obtained by laser sputtering onto sapphire substrates hadT _c of about 90 K, ΔT _c of about 2 K and the \(\bar c\) axis orientation normal to the substrate surface. The EXAFS and XANES spectra were measured in the region of Y and CuK edges at different orientations of the sample with respect to the polarization vectorē. The spectra were measured in the surface-sensitive total electron yield detection mode. The observed differences between the spectra are discussed and compared with theoretical calculations.     

A Method of Cumulative Sums in the Problem of Detection of Traffic Changes in Computer Networks

The problem of tastest finding the moments when the exponential parameter of the Pareto distribution is changed is solved by applying the method of cumulative sums. Analytical expressions for basic characteristics of the method—the average time of delay of the determination of the change-point and the average time between two incorrect determinations—are derived. An algorithm of detection of variations in the traffic in a computer network is developed.