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Abstract: In the present study ZnO nanocrystals embedded in a SiO2 matrix were successfully produced by means of radio frequency magnetron sputtering deposition using ZnO and SiO2 targets. Multilayer structures consisting of ZnO/SiO2 bilayers were deposited on Si substrate wafers either in vacuum or in an oxygen-rich ambience. Subsequently, the structures were heat-treated at different temperatures and in different atmospheres. This procedure resulted in spherical ZnO nanocrystals with a narrow size distribution as determined by transmission electron microscopy. Photoluminescence (PL) properties of the ZnO nanocrystals were studied by means of steady-state luminescence spectroscopy with excitation in the blue-UV spectral range. The PL properties of the samples were observed to depend strongly on the ZnO nanocrystal size. A broad PL band in the visible spectral range is observed and is tentatively ascribed to defects on or in the vicinity of the nanocrystal surfaces. Sharp characteristic PL lines in the UV range were detected in relatively large ZnO nanocrystals. These lines are tentatively attributed to bound exciton and donor–acceptor pair recombinations, and they are similar to the corresponding lines observed in bulk ZnO. The role of surface defects for the PL properties of nanocrystalline ZnO is discussed. [Copyright &y& Elsevier]

The general principles of widely used constructions of industrial electric-drive systems based on doubly fed induction machines without using external sensors of electromagnetic variables and mechanical motion coordinates according to the frequency converter are considered. Examples for implementation and the results of experimental studies are given. [ABSTRACT FROM AUTHOR]

The possibility of control of interconnected mechanical and thermal processes in nonlinear perturbed dynamic systems is considered both for irregular motions and parametric temperature perturbations. The conditions on system parameters and temperature control providing the stability of stationary points are obtained. It is shown that the choice of the parameters of thermal and mechanical subsystems and the introduction of the mechanical control subsystem proportional to the temperature gradient between its elements into the feedback can provide both regularization of oscillations and control of oscillations at parametric temperature perturbations. Computer calculations were performed, quantitative estimates which prove the qualitative analysis of constructed mathematical models were obtained. [ABSTRACT FROM AUTHOR]

The mathematical model describing the nonstationary heat processes occurring in three-dimensional (3D) plates under electron-beam or laser welding by movable heat sources has been developed. On the base of a modified method of elementary balances, software permitting to automatically solve the tasks of calculation, analysis, and visualization of 3D nonstationary temperature fields under arbitrary laws of heat source motion and to consider different types of heat exchange processes and nonlinear temperature dependences of thermal performances has been developed. It is shown that it is possible to control the plate temperature field during welding via selecting the law of heat source motion. Numerical experiments have been carried out. The results are compared with results obtained with the help of other computation methods and such a comparison verifies that the suggested mathematical model and algorithms operate properly. [ABSTRACT FROM AUTHOR]

Interrelated mathematical models of nonstationary thermal processes, the thermoelastic mode of deformation, and durability of a temperature probe are constructed. The probe is used in space technologies and operates under temperature shock conditions. Algorithms and appropriate software are developed. They allow problems of computation and analysis of nonstationary temperature fields of the probe and its thermoelastic mode of deformation to be solved automatically during the design phase. Also, the durability of the probe in the case of sudden temperature differences can be estimated. Computer experiments are carried out; they confirm the efficiency of the mathematical, algorithmic, and software support. Quantitative estimations are obtained, and recommendations for ensuring the efficient functioning of the probe are developed. [ABSTRACT FROM AUTHOR]

Classical problems of the development of algorithms for estimation of nonmeasurable state coordinates for the systems of a general-purpose industrial asynchronous electric drives with vector control are discussed. Modern problems related to the synthesis of algorithms for preliminary and online identification of the essentially varying parameters of an induction motor are considered. A variant of the realization of these algorithms in a class of adaptive systems with the specifying model and the complete state observer is analyzed in detail. [ABSTRACT FROM AUTHOR]

Geminal alkylammonium surfactants containing a hexamethylene spacer show a specific behavior, namely, a catalytic effect at low concentrations of the detergent in the system. The critical micellization concentrations of these surfactants are by an order of magnitude lower than those of the related surfactants with one hydrophobic fragment. The effect exerted on the hydrolysis of carboxylic acid esters by micellar structural rearrangements induced by addition of a supporting electrolyte is determined. [ABSTRACT FROM AUTHOR]

Methods of determining molecular oxygen in liquid hydrocarbon fuels are comparatively evaluated. The proposed gas-chromatographic method is based on use of a cryogenic capillary trap for preliminary separation of gaseous contaminants of oxygen, argon, and nitrogen from gasoline vapors, separation of these contaminants into oxygen together with argon and nitrogen in the analytical column of the chromatograph, measurement of the total volume fraction of oxygen and argon with a thermal-conductivity detector, and calculation of the volume fraction of oxygen with introduction of a correction that accounts for the fraction of argon in the overall total with oxygen. [ABSTRACT FROM AUTHOR]

An integral statistical procedure of determination of the attitude motion of a satellite using the data of onboard measurements of angular velocity vectors and the strength of the Earth’s magnetic field (EMF) is suggested. The procedure uses only the equations of kinematics of a solid body and is applicable to determining both controlled and uncontrollable motions of a satellite at any external mechanical moments acting upon it. When applying this procedure, the data of measurements of both types, accumulated during a certain interval of time, are processed jointly. The data of measuring the angular velocity are smoothed by discrete Fourier series, and these series are substituted into kinematical Poisson equations for elements of the matrix of transition from a satellite-fixed coordinate system to the orbital coordinate system. The equations thus obtained represent a kinematical model of the satellite motion. The solution to these equations (which approximate the actual motion of a satellite) is found from the condition of the best (in the sense of the least squares method) fit of the data of measuring the EMF strength vector to its calculated values. The results of testing the suggested procedure using the data of measurements of the angular velocity vectors onboard the Foton-12 satellite and measurements of EMF strengths are presented. [ABSTRACT FROM AUTHOR]

Abstract: Luminescence and excitation spectra as well as their temperature dependence were investigated for nominally pure yttrium trifluoride powders using synchrotron radiation. Broad emission bands in VUV-visible spectral range were observed under excitation above 11eV in YF3 at 10K. At least three emission bands were distinguished peaking at 5.6eV (220nm), 4.5eV (280nm) and 3.1eV (400nm). It was shown that the emission bands at 5.6eV (220) and 4.5eV (280nm) are intrinsic but the long wavelength emission at 3.1eV (400nm) is of extrinsic nature. The excitation spectra for the two intrinsic luminescence bands have their individual features, but in both cases a sharp peak at the fundamental absorption edge is observed. This fact as well as a large Stokes shift of intrinsic luminescence (more than 5eV) and a large width of the emission bands (near 1eV) allows us to assign the 4.5eV (280nm) and 5.6eV (220nm) emission to the radiative decay of self-trapped excitons in YF3. The strong influence of temperature on the intrinsic luminescence, observed at temperatures above 120K, are used to evaluate the activation energy of thermal quenching. [Copyright &y& Elsevier]

The transient absorption due to electron polaron states in LiNbO 3 , KNbO 3 , SrTiO 3 -Nb and glasses containing alkali niobates has been studied. The electron polarons are suggested to be Nb 4+ ions in various oxygen environments in all these crystals. It is shown that the position of the absorption band depends on Nb environment. The recharging of niobium states is suggested to be responsible for a fraction of the transient absorption in the phosphate glasses. The disordered structure of these glasses can account for wide absorption bands. [ABSTRACT FROM AUTHOR]

Theoretical foundations have been developed and a mathematical model of dynamic heat‐ and mass‐exchange processes in a glassmaking furnace has been constructed, which makes it possible to calculate and visualize nonstationary temperature fields in the furnace volume and nonstationary fields of velocities of convective glass‐mass flow in the molten bath. Test calculations for a specific structure of a glassmaking furnace which have shown the effectiveness of the model constructed have been performed. [ABSTRACT FROM AUTHOR]

The transient optical absorption and kinetics of absorption decay is studied in undoped, Fe doped, and Cu doped LiNbO3 crystals irradiated by pulsed electron beam. The 1.6 eV band of electron polaron trapped at antisite niobium was observed in all crystal samples. The nature of centers responsible for transient absorption is discussed. Electron polarons are shown to be less stable in LiNbO3:Fe compared with LiNbO3:Cu and undoped LiNbO3. It is suggested that a major part of electrons and holes created by irradiation are trapped in the vicinity of dopants. [Copyright &y& Elsevier]

The excitation function and angular distributions of elastic α-particle scattering on28Si have been measured in the laboratory energy range 6-28 MeV using a backscattering technique on a thick target, yielding a continuous energy distribution. More than 200 narrow states are observed, with widths in the range ∼ 30-100 keV at excitation energies E* = 13-32 MeV. Angular distributions at backward angles were measured, and angular momentum values of more than 83 states have been deduced. The analysis gives spin-parities Jπ, α-partial widths Γα and reduced widths of the narrow high-lying resonant states in32S. The experimentally observed states display both the negative- and the positive-parity rotational-like sequences with seemingly no parity splitting, a finding which is at variance with most potential-model predictions. The deduced effective moment of inertia indicates a more extended structure than the ground-state configuration. The observed strength of each ℓ-value is analyzed in terms of an underlying split doorway state of Lorentzian form, which yields an interpretation as fragmented rotational α +28Si states. [ABSTRACT FROM AUTHOR]

Time-resolved luminescence and absorption of ZnWO 4 and ZnWO 4 :Fe have been studied. The fast decaying luminescence at ∼1.7 eV is attributed to either Fe 2+ or a Fe 3+ related center. The two observed stages in luminescence decay kinetics under ionising radiation are suggested to be due to two types of self-trapped excitons. [ABSTRACT FROM AUTHOR]

The theoretical base was developed and the mathematical model of dynamic thermal processes in a compartment of public transport was constructed. The software which is realized the constructed mathematical model was developed. The mathematical model provides for the possibility of taking into account the most possible environmental conditions which can have place in the actual operating conditions of a transport even the angle of illumination - the current temperature of the external environment, the presence of solar radiation taking into account the angle of sun’s illumination, and the temperature of the roadway. The software allows calculation and visualization non –stationary temperature fields in the public transport’s compartments using the example of a trolley bus. For a specific trolley bus design, a series of experiments to calculate the comfortable temperature for passengers were conducted, These experiments are showed the performance of the constructed model and allowed to formulate a specific proposal for improving the thermoregulation system of the trolleybus’ passenger compartment.

In the case of the reaction of triphenylcyanurate and phenyl glycidyl ether, we showed that the oxirane rings may react at high temperature with the cyanurate rings to form isocyanurate fragments, which, in turn, react with excess epoxide to form oxazolidone rings. [ABSTRACT FROM AUTHOR]

Results are reported on the effects of various heat-treatment modes on the strength, plasticity, and short-time cracking resistance characteristics (K) for the torsion in 45KhN2MFA-Sh steel. The cyclic cracking resistances have been compared for test temperatures of 20 and 200°C for 45KhN2MFA-Sh and 50Kh3N2M2FA-Sh steels following various modes of heat treatment. The microfractographic aspects of cracking resistance in these high-tensile steels are considered. [ABSTRACT FROM AUTHOR]

The structure of the dimethylbenzylamine (DMBA)-phenylglyc idyl ether (PGE)-phenol complex was studied by IR andH NMR spectroscopy under various conditions of its formation. The active catalyst in the cyclotrimerization of isocyanates is a complex of composition DMBA : PGE : PhOH = 1 : 1 : 2, in which the oxygen atom of the zwitter-ion PhCHNMeCHCH(O)CHOPh that forms after opening, of the epoxide cycle is bound to two phenol molecules by a very strong hydrogen bonds. In this complex, the oxygen atom of both the zwitter-ion and the phenolate anion can be catalytic centers. Two schemes of the cyclotrimerization of isocyanate in the presence of the aforementioned catalytic system are suggested, depending on whether the catalytic complex has time to form or not. [ABSTRACT FROM AUTHOR]

The rate of cyclotrimerization of phenyl isocyanate in chlorobenzene at 120 °C in the presence of the tertiary amine-α-oxide-proton donor (PD) ternary catalytic system has been studied using a dual calorimeter and a series of phenols with various acidities as the PD. In the presence of weakly acidic phenols, complexes of quaternary ammonium type bases are formed in the ternary catalytic systems. Acidic phenols afford salt complexes with the transfer or a proton from phenol to the tertiary amine in a quantitative yield, while the α-oxide present remains unaffected. The structures of the complexes were studied by IR and by IR andH NMR spectroscopy. [ABSTRACT FROM AUTHOR]