Growing of Tubes with a Small Inner Diameter from the Melt by the Stepanov Method

A mathematical model is suggested for describing the growth of a crystal tube with a small inner diameter from the melt by the modified Stepanov method with the tube being affected by temperature pulses. The behavior of the inner and outer radii of the tube as a function of the amplitude and duration of temperature jumps is studied.     

Anisotropy in the strength of cellulosic fibres

Conclusions It is proposed to use the equation of a lemniscate, or the Cassini curve, to determine the destructive stress at break for cellulose films in any direction. Thereupon, to determine , it is necessary to know the destructive stress along two basic directions (₀ and ₉₀).To obtain cellulosic films which are isotropic in plane, a necessary and sufficient condition is ₀=₉₀.Translated from Khimicheskie Volokna, No. 6, pp. 34–35, November–December, 1987.     

Specific features of wake flow behind a two-dimensional body with a cavity on its rear edge

We present experimental results on the effect exerted by the width of a cavity made at the rear edge of a two-dimensional model on the magnitude of the bottom pressure, the Strouhal number, and the turbulent characteristics of a wake.Academic Scientific Complex A. V. Luikov Heat and Mass Transfer Institute of the Academy of Sciences of Belarus, Minsk. Institute of Hydrodynamics, Max Planck Society, Göttingen, Germany. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 66, No. 3, pp. 259–262, March, 1994.     

Thermoelastic stresses in ribbons and tubes grown from the melt by the Stepanov method

Ribbons and tubes grown from the melt by the Stepanov technique have a wide range of technical applications. Sapphire ribbons are used as substrates in microelectronics and sapphire tubes are used as gas-discharge balloons in laser engineering, fine chemical technology and high-vacuum equipment. Practice has shown that misorientation angles of small-angle boundaries in sapphire crystals should not exceed several degrees because an increase in the misorientation angles between blocks drastically lowers the strength and worsens the dielectric properties of these crystals. One of the main mechanisms of formation of the block structure of melt-grown crystals, including shaped sapphire crystals, is dislocation polygonization that begins when the dislocation density exceeds a certain critical value. In turn, dislocations are formed under deformations due to thermal stresses. Calculations of thermal fields in crystals and the corresponding thermoelastic stress fields can be used as an input to improve and optimize the growth process. The dependence of thermoelastic stresses in ribbons and tubes on the technological parameters has been calculated.Nomenclature ₁ Thermal diffusivity of the melt - ₂ Thermal diffusivity of the crystal - k ₁ Thermal conductivity of the melt - k ₂ Thermal conductivity of the crystal - V ₁ Velocity vector of the melt - V ₂ Velocity vector of the growing crystal - V ₀ Crystal pulling rate - H _f Latent heat of fusion - ₁ Density of the melt - ₂ Density of the crystal - in Interface normal vector - Crystal-melt interface normal vector - t Interface tangential vector - s Sided crystal-melt tangential vector - T _m Melting temperature - T _e Ambient temperature - T ₁ ⁰ Temperature at the bottom of the meniscus - T ₂ ⁰ Crystal temperature at the top of the meniscus - Normal vector at lateral surfaces of the crystal and meniscus - Stefan-Boltzmann constant - ₁ Emissivity of the meniscus lateral surface - ₂ Emissivity of the crystal lateral surface - g Acceleration due to gravity - _LG Melt-gas surface tension - a Die half dimension - ₀ Angle of growth - _t Thermal expansion coefficient - h ₁ Heat transfer coefficient of the melt - h ₂ Heat transfer coefficient of the crystal - C s Heat capacity - E Young's modulus - Poisson's coefficient - Melt kinematic viscosity - P Pressure in the melt     

Adaptive control system for car parking

In the paper, the first results of the work on the development and implementation of an adaptive control system for car parking are presented. The proposed approach to construction of a car control system differs from the commonly accepted approach [1–3] and is based on the autonomous adaptive control method [4] developed by the research team headed by A.A. Zhdanov. In the framework of this method, car control and training and retraining of the control system are implemented in one process with satisfaction of all necessary conditions and constraints. This allows the control system to adjust to parameters of a particular car and to automatically readjust if these parameters vary in the course of the car usage. In the paper, a program modeling car parking based on the principles developed in this study is described. Examples of parking a car for some particular cases of mutual location of obstacles and the desired slot in the parking place are presented.     

Study of the thermodiffusion constant of an Ar-Kr mixture at low temperatures

Reasons for divergence between theoretical and experimental values of the thermodiffusion constant of an Ar-Kr mixture at temperatures below 273K are studied.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 1, pp. 83–90, July, 1979.     

Laminar Flow Past a Circular Cylinder under the Effect of Nonstationary Jet Efflux to the Near‐Wake Region

Changes in a laminar flow past a circular cylinder under the effect of jets blowing out to its rare region have been studied numerically. Jet efflux was caused by a return flow of a part of the incoming flow in the inner channels of the cylinder due to the pressure difference between its front and end stagnation points. The channels connected the inlet window formed in the zone of the front stagnation point with two outlet windows on the backside surface of the cylinder. The influence of the coordinates of the jets issuing through the outlet windows and dimensions of the inlet and outlet windows on variation of the drag and lift coefficient and distribution of the coefficients of pressure and friction on the cylinder surface has been considered. It is shown that under the effect of blowing out the cylinder drag decreased by 4% and the amplitude of buoyancy force oscillations decreased by 40%.     

Producing a compact long-lived plasma formation

A method of producing compact long-lived plasma formations (plasmoids) is described. The method is based on the effect of capture of a high-current relativistic electron beam under conditions of significant overcompensation of space charge of the beam by positive background ions. Requirements are formulated which are placed on the parameters of a plasma-beam system for the realization of this method, and numerical estimates are given of the overall electric charge and energy content of the electron component of a plasmoid. The dynamics of forming a plasmoid are investigated experimentally.Translated from Teplofizika Vysokikh Temperatur, Vol. 42, No. 6, 2004, pp. 843–849.Original Russian Text Copyright © 2004 by B. V. Alekhin, A. E. Dubinov, V. S. Zhdanov, V. G Kornilov, K. E. Mikheev, V. D. Selemir, N. V. Stepanov, V. I. Chelpanov, and O. A. Shamro.     

Determination of forms of element occurrence in samples of vanadium slag and slime

Complex research of technogenic raw material samples is carried out. Using the methods of X-ray diffraction and X-ray fluorescence analysis, the chemical and phase compositions of roasted vanadium slag and slime are established. The compounds of the base elements are extracted sequentially according to a three-stage scheme recommended by the European Commission. Their low mobility is recorded. Vanadium and manganese compounds possess higher mobility in the slag than in the slime. Iron and chromium form solid oxides and silicates that are disintegrated only under the action of HNO₃. The methods of microwave plasma atomic emission spectrometry (MP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) are used to determine the gross contents of V, Mn, Fe, Cr, Zn, Ni, Ba, Sr, Rb, Y, Ga, Ge, Mo, La, and Ce in the samples of slag and slime. It is shown that the total concentration of V, Mn, and Cr considerably exceeds the values of the maximum allowable concentrations (MAC) of these elements established for soils, objects with a sample base that is no less complex. Possible leaching of the forms of elements from solid samples of vanadium slime and slag with 0.1 M Na₂CO₃ solution and the mobile phase for reversed-phase high performance liquid chromatography (RP HPLC) is studied. Mostly, vanadium compounds are extracted under these conditions. Manganese compounds are extracted by 1–10%. An inconsistency is found between the time of retention during the chromatographic separation of V and Fe forms in the model mixtures and solutions obtained after the samples of vanadium slag and slime have been chemically treated.