St Petersburg Polytechnic University Journal-Physics and Mathematics最新文献

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

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 was 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.

The role of the STIM2→nSOCE signaling pathway was investigated in a model of Alzheimer's disease (AD) 5FAD mice that express amyloid and presenilin toxicity simultaneously. It was observed that expression of STIM2 protein was downregulated in the hippocampus of adult 5FAD mice at the age 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 mice lowered the amount of amyloid plaques in the cortex of 5FAD mice by three times. The observed data confirms the scientific hypothesis that activation of STIM2-dependent store-operated calcium entry can have a therapeutic effect for treatment in AD.

A novel electron spectrometer has been designed to study low-voltage field-induced emission of nanostructures such as nanoporous carbon, nanotubes, nanodiamond and other carbon structures. The estimated high resolving power of the device is mainly achieved by using an original energy analyzer of high energy dispersion and by retarding the electron beam by the factor of tens and hundreds in terms of energy. The analyzer pass energy governs the absolute energy resolution ΔЕ of the spectrometer; 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 thermoemitter as the test object. The study then proved that the recorded spectra reflected physical phenomena taking place on the emitter surface.

This paper is dedicated to finite-element modeling (FEM) of elastic waves caused 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.

The conventional model of the processes occurring in the course of a p–n-junction's partial avalanche breakdown has been analyzed in this paper. Microplasma noise spectra of industrially produced LEDs were compared with those predicted by the model. It was established that the data obtained experimentally on reverse-biased LEDs could not be described in terms of this model. The degree to which the fractal properties were pronounced was shown to be variable by changing the reverse voltage. The 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.

The steady axi-symmetric 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 non-linear ordinary differential equations. The resulting intricate non-linear boundary value problem is solved numerically by the fourth-order Runge Kutta method with shooting iteration technique. The analytical solutions are presented for a special case. The effects of various physical parameters on velocity and temperature profiles are discussed through graphs. The values of skin friction coefficient and the Nusselt number are tabulated and examined. It is found that the thermal boundary layer thickness increases with the increase of velocity slip, magnetic field, surface convection parameter and curvature parameter and decreases with Prandtl number.

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.

A new hydrophysical measuring complex has been developed on the basis of a laser instrument for measuring hydrospheric pressure variations. The complex was previously engineered and experimentally verified. This equipment allows to investigate the amplitude-phase variations of hydrospheric 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 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 of the data obtained and new spheres of application.