Numerical simulation of the crystallization front inversion in oxide single crystals grown from melt using the Czochralski method

The process of pulling a Czochralski grown oxide single crystal out from melt has been numerically simulated for the first time from the moment of seeding until attaining a stationary growth regime. It is established that the phase boundary inversion at the lateral (shouldering) growth stage is a rather complicated process accompanied by intense oscillations of the crystallization rate. Diagrams illustrating variations of the crystal shape during this process are presented.     

Piezoresistive and posistor effects in polymer-semiconductor and polymer-ferropiezoceramic composites

In this study, piezoresistive and posistor effects in polymer-semiconductor and polymer-ferropiezoceramic composites have been investigated. The results show that composites based on crystallizable polymers, such as PVDF, HDPE, and PP dispersed by semiconductors and ferropiezoelectric fillers have piezoresistive and posistor properties, respectively. At low pressure, charge carriers tunneling through the located thin polymer among filler particles into the barrier define the conductivity of the composite. When pressure value is increased from 0 to 1 MPa, the thickness of the interlayer decreases and tunnel conductivity descends exponentially depending on barrier height. The piezoresistor sensitivity of a composite based on PVDF-70 vol % + Si-30 vol % is higher than a composite based on HDPE-70 vol % + Ge-30 vol %. Furthermore, the posistor properties of polymer composites dispersed by ferropiezoceramic are determined as the maximum resistance that varies significantly with temperature. Posistor effect in composites based on polymer + ferropiezoceramic is associated with the height of the barrier layer, which changes according to properties of filler, polymer, and dielectric permittivity of two-phase composites. The highest specific resistance related to HDPE-70 vol % + BaTiO₃-30 vol % composite was observed at ~403 K.     

Electrical properties of electrodeposited CdTe thin films

The electrical properties of electrodeposited CdTe thin films have been studied. The temperature-dependent electrical conductivity data obtained have been used to determine the conductivity type and semiconductor parameters (E _g, B, and α) of the films.     

Heat engineering calculation of a parabolo-cylindrical solar concentrator with tubular reactor for crude oil preparation for refining in the oil fields

A technique is proposed for the heat engineering calculation of a parabolo-cylindrical concentrator with tubular solar reactor, and the expressions are presented to calculate, for the specified flux density of the direct solar radiation in the particular region located at latitude 42 N (Baku and other Azerbaijan regions), the temperature of the solar reactor surface and the fluid.     

Mathematical model of two-step vibroexciter with low mechanical frequency

A mathematical model of two-step vibroexciter with low mechanical frequency is presented. The mathematical model makes it possible to determine the vibrator’s parameters using an electromechanical analogy and the model accuracy is sufficient for practical application.     

Current transport and formation of energy structures in narrow Au/n-GaAs Schottky diodes

The current transport and formations of potential barrier height in narrow Au/n-GaAs Schottky diodes (SD) with a contact surface in length of 200 μm, width of 1 and 4 μm have been investigated.It was determined that features of current transport are in good agreements with the thermionic emission theory in the forward bias as like high-quality conventional (flat) SD. Features of current transport in the reverse bias also is well described by thermionic emission theory, but it has specific features unlike I–V characteristics flat SD.Forward bias of narrow SD current–voltage (I–U) characteristics are represented by straight lines in semi-logarithmic scale in a wide range, nearly nine order of current up to 0.7 V with near unit ideality factor. In the beginning of the reverse voltage, the current practically was extremely low, by increasing in voltage the current jump in steps approximately for 3–4 order in voltage of 3–4 V, then current increases linear for 3–5 order in semi-logarithmic scale by increasing in voltage up to nearly 7 V.Numerical values of parameters such as the saturation currents, the operating barrier height, ideality factor, dimensionless factor are obtained. The correlations between ideality factor and dimensionless factor were meaningful.The energy diagrams of narrow SD have been drawn in absence and presence of forward and reverse voltage. It is found that electronic processes in narrow SD are well described by energy model of real narrow metal–semiconductor contacts. The additional electric field arising in near contact area of the semiconductor because of creating contact potential difference between contact surface and to it adjoining free surfaces of the metal and semiconductor.     

Sorbents based on diatomite from shemakha deposit for cleaning used compressor oils

Treatment of diatomite from the Shemakha deposit with aqueous hydrochloric acid and sodium hydroxide solutions yielded its modified forms studied in the process of regeneration of used (waste) compressor oil KM-40. It is shown that in cleaning capacity, the modified forms of diatomite are superior to natural diatomite. It is proved that acid and base centers occurring on the surface of the original and modified forms of diatomite are active in the used compressor oil cleaning process.     

Relationships between complexes of thermophysical properties and compressibilities of fluids

Based on experimental data for water and toluene, relationships between complexes of thermophysical quantities at a given temperature and pressure and between them and compressibility complexes are established.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 1, pp. 91–96, July, 1977.