## Determining the bound energies of dissolved hydrogen on a basis of the multichannel diffusion model in a solid

Published in category «Condensed matter physics»

The hypothesis for a multichannel character of the hydrogen diffusion in solids has been substantiated in the article. Based on this hypothesis, a mathematical model of hydrogen diffusion in the crystalline lattice was constructed. The model provided determining the dissolved hydrogen binding energies using an extraction curve. The curve was measured by industrial vacuum-extraction procedure with mass-spectrometric detection of hydrogen streams. The article presents various experimental data that support the validity of the multichannel model and discusses the advantages and disadvantages of the proposed approach in comparison with the well-known method of thermal desorption spectra (TDS) that is recognized as the classical way of experimental determination of the dissolved hydrogen binding energy in solids.

## Numerical simulation of liquid metal turbulent heat transfer from an inline tube bundle in cross-flow

Published in category «Simulation of physical processes»

Results of numerical simulation of turbulent flow field and heat transfer of liquid metal in cross-flow over inline tube bundles consisting of smooth round tubes are presented. Computations have been performed with the CFD-code ANSYS Fluent on the base of two-dimensional unsteady RANS formulation using the SST turbulence model by Menter and assuming constant physical properties of a fluid with the Prandtl number equal to 0.023. The Reynolds number was ranged from 26200 to 52400. Instantaneous and time-averaged velocity and temperature fields obtained for bundles of different intertube spacing at variation of the bundle width (number of tube rows in the spanwise direction) were analyzed. Integral characteristics of heat transfer were compared with experimental data.

## Weakly swirling flow in a model of blood vessel with stenosis : numerical and experimental study

Published in category «Simulation of physical processes»

Investigation of weakly swirling flow in a model of blood vessel with asymmetrical stenosis has been performed using both experimental flow measurement techniques (ultrasound Doppler) and computational fluid dynamics methods. A special attention was paid to getting data for the length of reverse-flow zone occurring past the stenosis. It was established that the laminar steady-state flow model was acceptable for numerical analysis of flow past the given geometry stenosis at the Reynolds number values less than 300. At higher values of this parameter, application of the semi-empirical k-ω SST turbulence model was preferable. It was shown that flow swirl was able to lead to an increase of the reverse-flow zone.

## Theoretical base of the approach to the representation of aggregate information on the cross sections of the scattering processes

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

In the present paper, the approach to the representation of aggregate information on the cross sections of elementary processes is described and its justification within mathematical statistics is given. It is caused by necessity of integrated account of the results obtained by different works at different times, in different groups, based on experimental and theoretical studies in various energy ranges. The main attention is paid to the process of electron-atom scattering. As an example of the proposed approach application, the aggregate result on thus obtained integral cross sections of electron impact excitation of the transitions in the hydrogen atom is presented.

## Rough estimates and binomial approximations for the crocco equation in the boundary problems

Published in category «Mathematical physics»

In order to solve the Crocco boundary problems known as the typical one and the uniform one, binomials (as approximants of exact solutions) and integral identities have been used. The extent of the closeness of the exact solution to its approximation was estimated using the ϕ(0) value. The solution of the typical Crocco boundary problem was proved to have a logarithmic singularity of the derivative at ϕ = 0. The Crocco equation was found to provide both necessary and sufficient conditions for the minimum of a positive distribution being vortex in dϕ/dh. The uniform Crocco boundary problem was demonstrated to be equivalent to the two typical Crocco boundary problems with a common critical point.

## The criterion for the optimal sampling of copper thermistor to measure in the atmosphere under normal conditions

Published in category «Experimental technique and devices»

In this paper a new parameter is suggested as a criterion for selecting the optimal value of the copper thermal resistance in temperature measurements in the atmosphere under normal conditions. The proposed parameter is directly proportional to the sensitivity of thermal resistance and inversely proportional to the product of ‘dead’ resistance and ‘dead’ temperature (the product of errors of temperature and resistance when their determination). It has been shown through the example of 4 samples that this criterion is convenient. For one of the thermal resistance this parameter is higher in the investigated range of temperatures.

## Digital system of fluorescence visualization for antibacterial photodynamic therapy in dentistry

Published in category «Experimental technique and devices»

In the present work the novel compact system for visualization of the spatial intensity distribution of the photosensitizer fluorescence for the antibacterial photodynamic therapy in dentistry is suggested. The compact intraoral system includes visible imaging camera and violet laser diode. The wavelength of the laser radiation is matched to the short-wavelength absorption peak of the photoditazin, so the effective excitation of its fluorescence is ensured. The built-in spectral-selective optical filter allows the camera to detect only the spatial distribution of the fluorescence intensity while the excitation radiation is blocked. Intraoral fluorescent images obtained with the suggested system can be used for diagnosis of residual amount of pathogens.

## The trajectory analysis algorithm for electrostatic fields providing an angle focusing of given order in the plane of symmetry

Published in category «Physical electronics»

A class of focusing electrostatic fields built as inverse corpuscular optics problem solution has been investigated. An effective algorithm to make trajectory analysis of these fields was suggested and tested. The algorithm was based on the special parametric form of potentials representation. The main complexity of the problem is to treat the result of inverse form of potential representation, where coordinates are functions of the potential and the flux, but it is impossible to give the potential by an explicit function of coordinates. To solve the equations of motion in a direct form, it is necessary to find (numerically) coordinates at every integration step. It reduces the precision and increases the time of the calculations. We suggested using a parametric form of the potential and the relationship between coordinates. Direct equations of motion can be replaced with differential equations for parameters, which can be solved without any difficulty. The results obtained can be applied to designing of new energy-analyzing devices with enhanced capabilities.

## Modeling of the plasticity of microstructured and nanostructured materials

Published in category «Physical materials technology»

A new approach to modeling of the plasticity of materials with nanostructure and ultrafine one has been proposed. Its main advantage is the minimum number of physical parameters in use. In the context of the proposed model, we calculated the volumetric density of the energy of surface tension of the material grains. This energy is a significant part of the internal energy during deformation. The size dependence of the melting temperature of nanoparticles was compared with experimental data. We obtained size dependence of the yield point on its basis. Yield point was interpreted as the result of changes of grains surface energy during the deformation. The obtained yield point dependence on the grain size was related to the Hall-Petch law, and this resulted in confirmation of the hypothesis on the crucial role of surface tension forces in the initial stage of plastic deformation of ultrafine materials.

## Elementary results on the dosimetric properties of SrSO4:Eu2+ phosphor

Published in category «Physical materials technology»

A polycrystalline sample of SrSO4: Eu2+ phosphor has been successfully synthesized using the co-precipitation method and studied for its luminescence properties. The phosphor showed rather high optical stimulated luminescence (OSL) sensitivity which was about 75% of that for the commercially available α-Al2O3: C phosphor (TLD-500). The continuous wave (CW)-OSL curve exhibited three components having photoionization cross-sections of 1.78۰10–17, 7.70۰10–17 and 17.69۰10–17 cm2 respectively. The thermal luminescence (TL) sensitivity was about 100 times higher than that for TLD-500. The kinetic parameters for TL curve such as activation energy and frequency factor were calculated using peak shape treatment. OSL components were determined from CW and linear modulated (LM)-OSL data. The minimum detectable dose was found to be 11.6 mGy with 3σ of background. Also reusability studies showed that it was possible to reuse the phosphor for 10 cycles without change in the OSL output. In the TL mode the dose-response was nearly linear in the range of measurement (20 – 400 mGy), and fading was 40% in 72 h. Photoluminescence spectra of SrSO4: Eu2+ exhibited emission in the near-UV region at 254, 315, and 323 nm when excited with an UV source.

## Optical and thermal properties of PTh-co-PANI-Ti random copolymer composite for photovoltaic application

Published in category «Physical materials technology»

In thе present work, a polythiophene (PTh)-co-polyaniline (PANI)-titaniun (Ti) copolymer has been synthesized as a novel copolymeric composite material for photovoltaic (PV) application. The focus of the study was to evaluate optical and thermal properties of the PTh-co-PANI-Ti copolymer containing different types of monomers. The optical conductivity was determined from the UV-VIS spectra that were used to calculate the extinction coefficients. The structure and morphology of composite was analyzed through field emission-electron microscopy (FESEM). The PTh-co-PANI-Ti copolymer composite exhibited significant photovoltaic (PV) response to light intensity. J-V analysis showed an increase in conversion efficiency from 0.21 to 1.5 of PTh-co-PANi-Ti with illumination light intensity. PV properties demonstrated that the PTh-co-PANI-Ti exhibited the highest power conversion efficiency ɳ = 1.5, with a short circuit current Isc = 0.72 mA, an open circuit voltage Voc = 0.9 V and a fill factor FF = 0.51. Thermo-gravimetric (TG) and differential thermal (DTA) analyses were carried out for the thermal stability of the PTh-co-PANI-Ti copolymer composite. The results obtained from the characterization of PTh-co-PANI-Ti showed that many properties of PV action are present in as-synthesized material.

## Advances in hydrotropic solutions: an updated review

Published in category «Physical materials technology»

Approximately a century ago, in 1916, the term ‘hydrotropy’ was coined by the scientist Carl A. Neuberg to address anionic organic salts which considerably augmented the aqueous solubility of poorly soluble solutes. Currently hydrotropic solutions possess high industrial demand due to their unique features, such as easy availability, good recovery, absence of fire hazards, high separation factors without any solutes emulsification problem and eco-friendly nature. The present review takes the readers through a concise overview, geometrical features of hydrotropic agents, hypothetical mechanisms and their different advances towards drug delivery. Moreover, this review would provide an insight into the future perspectives concerned with drug delivery and hydrotropism.

## The sensitivity of the adaptive algorithm with a posteriori error control to marking criteria

Published in category «Mathematics»

The aim of this work is to compare different marking strategies, their influence on the work of adaptive algorithms with a posteriori error control for plane elasticity problems. The error control was performed using functional error majorant. Implemented adaptive algorithms were based on the functional error majorant with no symmetry limitation on free tensor, computed using the zero-order Raviart-Thomas approximations on triangular meshes. The four most commonly used element marking criteria were used in adaptation. Numerical results for several plane strain problems have been presented, including the case of different materials and geometry. A comprehensive analysis of obtained results was given.

## Spectral and angular radiation characteristics of a charged particle in the plane monochromatic electromagnetic wave

Published in category «Radiophysics»

Relying upon the solution of the relativistic equation of a charged particle motion that was obtained by A.A. Rukhadze et al., the spectral and angular characteristics of ultra-relativistic intensive radiation of a relativistic charged particle have been studied, the particle being linearly accelerated by a superpower laser pulse. The case where the particle propagates in vacuum without brake light was examined. The interaction of the charged particle with the large-amplitude ultra-short laser pulse was analyzed in details using the relativistic consideration. Formulae for the average radiated power of the relativistic charged particle, depending on the initial conditions, the electromagnetic-wave amplitude, intensity and polarization were obtained. For the case where the laser pulse can be represented by a monochromatic plane wave, analytical expressions for the radiation characteristics were put forward and the phase-angular distributions of relativistic radiated power and intensity were found. The Fourier transform of the electric-intensity radiation field of the charged particle and the particle’s spectral density radiation in the field of a plane monochromatic wave for different types of polarization (linear and circular ones) were determined.

## The motion of a charged particle in the field of a frequency-modulated electromagnetic wave and in the constant magnetic field

Published in category «Radiophysics»

In this article the problem on the motion of a charged particle in the field of frequency-modulated electromagnetic wave and in the external uniform static magnetic field has been analyzed; the exact solutionsof the corresponding equations have been presented. This problem is of great importance to study the interaction of high-intensity laser pulses with solid targets and to develop practically multifrequency lasers and the laser-modulation emission technology. The formulae for the mean kinetic energy of a relativistic charged particle as a function of initial conditions, electromagnetic wave amplitude, wave intensity and its polarization parameter were obtained. The different cases of initial conditions of a charged particle motion and of a wave polarization were investigated. The obtained results can be put to use when studying the hightemperature plasma formed on the surface of the target and when searching for new modes of laser-plasma interaction.