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Chikova Tamara S., Bashmakov Victor I.

Reversible plasticity of metallic single crystals at the stage of their residual twinning.

Published in category «Condensed matter physics»

The work studies regularities of the formation of wedge-shaped twins under growing concentrated load in single crystals of bismuth, zinc and bismuth-antimony alloy. It was established that the twinning, detwinning and stopping of the twin deformation near the stress concentrator can take place simultaneously with the load growth. Reversibility of plastic deformation during twinning in metals at the stage of residual twinning development were discovered. Various manifestations of spontaneous detwinning of wedge-shaped twins which emerge at stress concentrators when indenting Bi, Zn, Bi-Sb single crystals with increasing load are quantitatively studied. Depending on the value and the sign, local fields of elastic stress can encourage or discourage twinning, or cause detwinning.

Views: 888 Comments: 0

Kapralova Victoria M., Ilinskiy Alexander V., Castro Arata Rene Alejandro, Nabiullina Lilia A., Shadrin Evgeniy B.

An effect of optical radiation on charge and magnetic states of the iron ions in the sillenites.

Published in category «Condensed matter physics»

The silico-sillenite single crystals with various concentration of impurity iron ions have been studied. An effect of light on the charge state of iron ions has been found involving the transition of Fe3+ to Fe2+. The transition was recorded by means of ESR signal intensity measurement. The parameters of the ESR absorption lines were obtained and analyzed. The nature of chemical bonds between iron ions and surrounding ligands was shown to be changed by the laser-induced recharge. A consistent model for optical recharge process and magnetic properties modification of iron impurity centers in the silico-sillenite single crystals has been suggested.

Views: 887 Comments: 0

Ganesh N. Vishnu, Ganga B., Hakeem Abdul A.K., Saranya Sarani, Kalaivanan Raja

Hydromagnetic axisymmetric slip flow along a vertical stretching cylinder with a convective boundary condition.

Published in category «Simulation of physical processes»

Steady axisymmetric laminar boundary-layer slip flow of a viscous incompressible fluid and heat transfer towards a vertical stretching cylinder in the presence of a uniform magnetic field is investigated. It is assumed that the left surface of the cylinder is heated by a hot convective flow. Using a similarity transformation, the governing system of partial differential equations is first transformed into a system of coupled nonlinear ordinary differential equations. The resulting intricate nonlinear boundary value problem is solved numerically by the fourth-order Runge – Kutta method with the shooting iteration technique. The analytical solutions are presented for a special case. The effects of various physical parameters on the velocity and temperature profiles are discussed through graphs. The values of the skin friction coefficient and the Nusselt number are tabulated and examined. It is found that the thermal boundary layer thickness increases with an increase in the velocity slip, the magnetic field, the surface convection parameter and the curvature parameter and decreases with the Prandtl number.

Views: 814 Comments: 0

Gataulin Yakov A., Zaytsev Dmitry K., Smirnov Evgeny M., Yuhnev Andrey D.

Numerical study of spatial-temporal evolution of the secondary flow in the models of a common carotid artery.

Published in category «Simulation of physical processes»

Numerical study of the secondary flow in the two geometrically different models of a common carotid artery has been carried out. One of the models (Model 1) is characterized by a statistically averaged curvature, and the second one (Model 2) is attributed to the maximal curvature of the artery. It was shown that the most intensive swirl occurred at the phase of flow rate decreasing, the maximum values of the swirl parameters were observed at the interface of the cervical and thoracic segments of the artery. This interface is the place where the Dean vortices are transformed into a single vortex forming a swirling flow. The swirl intensity averaged over the systole and characterized by the ratio of the maximal values of the axial and circumferential velocities was evaluated as 0.20 for Model 1 and 0.25 for Model 2. Generally, it was in accordance with the data of clinical measurements.

Views: 792 Comments: 0

Makhov Ivan S., Panevin Vadim Yu., Vinnichenko Maxim Ya., Sofronov Anton N., Firsov Dmitry A., Vorobjev Leonid E.

Impurity assisted terahertz luminescence in quantum well nanostructures under interband photoexсitation.

Published in category «Atom physics and physics of clusters and nanostructures»

The results of experimental study of the impurity-assisted photoluminescence in far- (terahertz) and near-infrared spectral ranges in n-GaAs/AlGaAs quantum well structures with different well widths under interband photoexcitation of electron-hole pairs have been presented. In the far-infrared photoluminescence spectra the optical electron transitions between the first electron subband and donor ground state as well as between excited and ground donor states were revealed. Observation of these optical electron transitions became possible because of the depopulation of the donor ground state in the quantum well due to the non-equilibrium charge carrier radiative transitions from the donor ground state to the first heavy hole subband. The opportunity to tune the terahertz radiation wavelength in structures with doped quantum wells by changing the quantum well width was demonstrated experimentally.

Views: 828 Comments: 0

Vinnichenko Maxim Ya., Makhov Ivan S., Selivanov Anatoliy V., Sorokina Anastasiya M., Vorobjev Leonid E., Firsov Dmitry A., Shterengas Leonid M., Belenky Gregory L.

Auger-recombination effect on the nonequilibrium charge carriers concentration in InGaAsSb /AlGaAsSb quantum wells.

Published in category «Atom physics and physics of clusters and nanostructures»

The interband photoluminescence spectra of InGaAsSb/AlGaAsSb quantum wells with different well widths have been experimentally studied. The dependence of the concentration of the charge carriers participating in the radiative recombination on the pumping intensity level was calculated. Results of theoretical calculations appeared to be in good agreement with the experimental relationship between the photoluminescence intensity at spectral maxima and the pumping intensity. The resonant Auger recombination involved two holes and one electron and caused a significant decrease in the charge carrier concentration was detected in one of the samples. Recommendations were made to increase the operating efficiency of semiconductor injection lasers at wavelengths of about 3 μm for suppressing the parasitic nonradiative Auger recombination.

Views: 995 Comments: 0

Yakovenko Sergey V., Budrin Sergey S., Dolgikh Stanislav G., Chupin Vladimir A., Shvets Vyacheslav A.

Hydrophysical laser-interference complex.

Published in category «Experimental technique and devices»

A new hydrophysical measuring complex has been developed on the basis of the laser measuring instrument of hydrosphere pressure variations. The latter was previously engineered and experimentally approbated. The use of this equipment allows solving problems on investigation of the amplitude-phase variations of hydrosphere vibrations and waves in the low-frequency range. All performance data of the complex was considerably improved by virtue of the operating experience obtained previously. Radically new opportunities of the created equipment were provided since the apparatus was rigged with new sensors for accompanying measurements and a container, which allowed working independently. The new hydrophysical measuring complex is easier to operate and maintain, ensures higher quality data obtained and new spheres of its application.

Views: 745 Comments: 0

Shashkina Antonina S., Krivosheykin Anatoliy V., Skvortsov Nicolay N., Vorotkov Mikhail V.

Fractal properties of the led avalanche breakdown.

Published in category «Physical electronics»

The conventional model of processes occurring in the course of p–n-junction’s partial avalanche breakdown has been analyzed in this paper. Microplasma noise spectra of industrially produced LE Ds were compared with those predicted by the model. The data obtained experimentally on the reverse-biased LEDs were established not to be described in terms of this model. The degree of pronouncedness of fractal properties was shown to be variable by changing the reverse voltage. Discovered fractal properties of microplasma noise can serve as the basis for further studies which are bound to explain the breakdown characteristics of real LEDs and to correct the conventional model of p–n-junction’s avalanche breakdown.

Views: 750 Comments: 0

Bondarenko Vyacheslav B., Davydov Sergey N., Gabdullin Pavel G., Gnuchev Nikolay M., Maslevtsov Andrey V., Arkhipov Anton A.

Electron spectrometer for studying field-induced emission from nanostructured objects.

Published in category «Physical electronics»

A novel electron spectrometer has been designed to study low-voltage field-induced emission of nanostructures such as nanoporous carbon, nanotubes, nanodia-mond and other carbon structures. The estimated high resolving power of the device is mainly achieved by using an original energy analyser of high energy dispersion and by retarding the electron beam by the factor of tens and hundreds in terms of energy. The analyser pass energy governs the absolute energy resolution ΔЕ of the spectrome-ter; ΔЕ value varies approximately in the range of 10 meV < ΔЕ < 300 meV. There are three different working modes adapted for emission of widely variable current. The minimal emission current at which energy analysis is still possible is approximately 0.1 nA. The spectrometer working modes were tested experimentally using a ther-moemitter as the test object. The study then proved that the recorded spectra reflected physical phenomena taking place on the emitter surface.

Views: 857 Comments: 0

Ivankov Alexey A., Kutuzov Anton V., Krivoruchko Lyudmila A.

The additive model of usdg records: attractor dimensions of determinated addends.

Published in category «Biophysics and medical physics»

The paper presents the algorithm and the mathematical support to estimate the correlation dimensions of attractors manifested themselves in the most powerful harmonics of spectra retrieved during Doppler sonography assessment of human cerebral circulation. The objective of the present study was to estimate the correlation dimensions for power spectral densities of the most powerful harmonics. The results of real clinical data analysis are given. The estimates of the correlation dimensions were formed for the different examined body’s states: in the rest and under test for hypocapnia. The significant relation was found between those estimates of the correlation dimensions and psychoemotional state of volunteer.

Views: 805 Comments: 0

Bezrukova Alexandra G., Vlasova Olga L.

Mixtures of 3D disperse systems with nano- and microparticles: optical characterization.

Published in category «Biophysics and medical physics»

The multiparameter analysis of simultaneous optical data for systems of nano- and /or microparticles (3D disperse systems, dispersions, colloids, ensembles) by presentation of system characteristics as N-dimensional vectors of optical parameters (ND-vectors) can help to elucidate changes in the state of the particles in systems. In this paper, the application of ND-vector approach is shown on the examples of dispersion mixtures: mixture of influenza virus particles with albumin proteins (as a model of dispersions at the process of vaccine production); mixture of Coli bacillus and clay dispersions (as natural water model). This approach can serve as the on-line control platform for the management of technological processes with mixtures.

Views: 810 Comments: 0

Smirnova Natalia V., Petrova Natalia O., Lebedeva Inna O., Popryadukhin Pavel V., Dobrovolskaya Irina P., Yudin Vladimir E.

Tissue reconstruction of skin failues and soft-tissue injuries using regenerative medicine methods.

Published in category «Biophysics and medical physics»

The electrospinning technique has been used to manufacture the composite material based on nanofibers made of aliphatic copolyamide and composite nanofibers made of chitosan and chitin nanofibrils. Experimental in vivo studies of the material worked out as wound covering were carried out to treat the vast and multilayered wound on the rat’s back. After 28 days and nights of observation the complete epithelialization of the wound surface was established to occur in the experimental rat group. Histological analysis of scar tissue showed the presence of small minority of capillaries and a low amount of infiltrate cells. The survival of animals was 100 %. At the same time, in the control group of animals, the lethality was observed in 11 % of cases, and suppurative complications were observed in 100 % of cases. To increase the rate of tissue regeneration, and to reduce the infection probability the thrombocyte gel prepared from the peripheral blood of the patients was used. The curative effect was proved to increase when applied simultaneously the wound coatings and autologous blood product separation – thrombocyte gel and platelet-rich plasma.

Views: 792 Comments: 0

Chernyuk Daria P., Vlasova Olga L., Bezprozvanny Ilya B., Popugaeva Еlena А.

Hyperexpression of STIM2 protein lowers the amount of abeta plaques in the brain of alzheimer’s disease mouse model.

Published in category «Biophysics and medical physics»

The role of STIM2 - nSOCE signaling pathway was investigated in model of Alzheimer’s disease (AD), 5×FAD mice, that express amyloid and presenilin toxicity simultaneously. It was observed that expression of STIM2 protein was downregulated in the hippocampus of adult 5×FAD mice at the ages of 4 and 6 months. It was shown that expression of PSD95 protein was downregulated together with STIM2 protein. It was established that hyperexpression of STIM2 protein in the hippocampus of adult mouse was able to lower the amount of amyloid plaques in the cortex of 5×FAD mice by three times. The observed data confirms scientific hypothesis that activation of STIM2-dependent store-operated calcium entry can have therapeutic effect for treatment in AD.

Views: 746 Comments: 0

Pivkov Andrey V., Lobachev Aleksandr M., Polyanskiy Vladimir A., Modestov Victor S.

Numerical simulation of ultrasonic waves in the isotropic elastic layer with the piezoelectric actuator.

Published in category «Mechanics»

This paper is devoted to the finite-element modeling (FEM ) of elastic waves сaused by the work of a piezoactuator. For this purpose, a mathematical model of the ‘elastic layer – piezoelectric element’ system has been developed. In the terms of the model, the simultaneous solution of the piezoelectricity and the solid-mechanics equations was employed. This model allowed us to describe the propagation process of high-frequency mechanical vibrations, caused by the application of the probing electrical pulse to the electrodes of the piezoelectric element (the vibrations occur in the elastic layer) and to reproduce the potential difference arising in the reception of the reflected wave. The influence of t-parameters of the FEM and numerical integration scheme on the calculation results was investigated. The essential sensitivity of the reflected-wave’s delay-time to the integrating time-step was found.

Views: 841 Comments: 0