Voronezh State University

About: Voronezh State University is a education organization based out in Voronezh, Russia. It is known for research contribution in the topics: Silicon & Boundary value problem. The organization has 5166 authors who have published 6097 publications receiving 31680 citations. The organization is also known as: VSU & Voronezh University.

Solid-phase interaction in the hydroxyapatite/titanium heterostructures upon high-temperature annealing in air and argon

Abstract: Samples of 100- and 500-nm-thick hydroxyapatite films on titanium were investigated using scanning electron microscopy, electron probe X-ray microanalysis, and X-ray powder diffraction. The films were prepared by high-frequency magnetron sputtering of a target in an argon atmosphere (1 × 10−1 Pa) at a magnetron power density of 40–70 W/cm2. These conditions provided growth of films at a rate as high as 0.7 nm/s. It was demonstrated that the hydroxyapatite film annealed in argon is characterized by deep pores that have diameters ranging from 0.3 to 8.0 µm and are uniformly distributed throughout the film surface. The electron probe X-ray microanalysis confirmed the presence of all elements (Ti, O, Ca, P) under investigation, except for hydrogen, in the samples of the films. For biologically compatible hydroxyapatite, the optimum ratio Ca : P ≃ 1.5–1.7 was achieved in the hydroxyapatite/titanium system with a 500-nm-thick hydroxyapatite layer upon annealing in argon at a temperature of 1050°C for 30 min. It was established that the hydroxyapatite/titanium system contains intermediate phases, including calcium titanate CaTiO3, which proved the interaction of hydroxyapatite with titanium.

Spectrogram and localization of a sound source in shallow water

Abstract: The paper describes an approach to detecting a sound source and estimating the radial velocity and distance from the receiver, based on repeat Fourier transformation of the interference pattern formed during motion. The obtained spectrogram contains localized domains of the spectral density of single modes. We estimate the localization domain and spectral density distribution and discuss the resolution of moving sound sources. We present the results of a field experiment and consider the interference immunity of the approach for localizing a source using a single receiver.

Hysteretic Nonlinearity in Inverted Pendulum Problem

Abstract: This work is dedicated to the problem of inverted pendulum under hysteretic nonlinearity in the form of backlash in the suspension point. We present the results for various motion of the suspension point, namely, the vertical and horizontal motions. We consider the mathematical model of inverted pendulum with vertically oscillating suspension and in the frame of presented model the explicit stability criteria for the linearized equations of motion are found. Dependencies between initial conditions and driven parameters, that provide periodic oscillations of the pendulum, are obtained. In the next step we consider the mathematical model of inverted pendulum under state feedback control (horizontal motion of suspension). Analytic results for the stability criteria as well as for the solution of linearized equation are observed and analyzed. The theorems that determine stabilization of the considered system are formulated and discussed together with the question on the optimal control. We also investigate the elastic inverted pendulum with backlash in the suspension point (horizontal motion). The problem of stabilization together with an optimization problem for such a system is considered. Algorithm (based on the bionic model) which provides the effective procedure for finding of optimal parameters is presented and applied to considered system. Phase portraits and dynamics of the Lyapunov function are also presented and discussed.

Electrical and structural properties of LiNbO3 films, grown by RF magnetron sputtering

Abstract: Nanocrystalline films of LiNbO3 on substrates (001)Si and (001)Si–SiO2 were synthesized by the method of RF magnetron sputtering. The elemental composition, structure of the LiNbO3 films, and also—electrical properties of heterostructures (001)Si–LiNbO3 and (001)Si–SiO2–LiNbO3 were studied. The dielectric constant of the LiNbO3 films calculated from the capacitance at the accumulation region was about 28. The resistivity was 1·109 ohm cm for films on (100)Si and 1.6·1011 ohm cm for films on (001)Si–SiO2. It has been determined that transmission of the current in the studied structures during direct biases is defined by hopping conduction, and, during reverse biases—by the Poole–Frenkel effect.