East European Journal of Physics 2021-06-07T21:35:40+00:00 Serhii Hirnyk Open Journal Systems <p>EEJP is an international peer-reviewed Journal devoted to experimental and theoretical research on the nuclear physics, cosmic rays and particles, high-energy physics, solid state physics, plasma physics and controlled thermonuclear fusion, physics of charged particle beams, plasma electronics, radiation materials science, physics of thin films, condensed matter physics, functional materials and coatings, technical thermophysics and industrial power,&nbsp;medical physics and physical technologies in an interdisciplinary context.</p> <p>EEJP registered by the order of Ministry of Education and Science of Ukraine <strong>No. 1643 of 28.12.2019</strong>, and included in the list of scientific professional Editions of Ukraine (<strong>category “A”, specialty: 104, 105</strong>), in which results of dissertations for obtaining Ph.D. and Dr. Sci. degrees in physical and mathematical sciences can be published.</p> <p>The Journal is a part of the <strong>Web of Science Core Collection (ESCI)&nbsp;</strong>scientometric platform and indexed by&nbsp;<strong>SCOPUS</strong>.</p> <p>&nbsp;</p> Polyadic Hopf Algebras and Quantum Groups 2021-06-07T21:35:40+00:00 Steven Duplij <p>This article continues the study of concrete algebra-like structures in our polyadic approach, where the arities of all&nbsp;operations are initially taken as arbitrary, but the relations between them, the arity shapes, are to be found from some&nbsp;natural conditions (“arity freedom principle”). In this way, generalized associative algebras, coassociative coalgebras,&nbsp;bialgebras and Hopf algebras are defined and investigated. They have many unusual features in comparison with the&nbsp;binary case. For instance, both the algebra and its underlying field can be zeroless and nonunital, the existence of the unit&nbsp;and counit is not obligatory, and the dimension of the algebra is not arbitrary, but “quantized”. The polyadic convolution&nbsp;product and bialgebra can be defined, and when the algebra and coalgebra have unequal arities, the polyadic version of&nbsp;the antipode, the querantipode, has different properties. As a possible application to quantum group theory, we introduce&nbsp;the polyadic version of braidings, almost co-commutativity,&nbsp; quasitriangularity and the equations for the R-matrix (which&nbsp;can be treated as a polyadic analog of the Yang-Baxter equation). We propose another concept of deformation which is&nbsp;governed not by the twist map, but by the medial map, where only the latter is unique in the polyadic case. We present&nbsp;the corresponding braidings, almost co-mediality and M-matrix, for which the compatibility equations are found.</p> 2021-04-28T00:00:00+00:00 Copyright (c) 2021 Steven Duplij Vortex Dynamo in an Obliquely Rotating Stratified Nanofluid by Small-Scale Non-Helical Forces 2021-06-01T11:33:11+00:00 Michael I. Kopp Anatoly V. Tur Volodymyr V. Yanovsky <p>In this work, a large-scale instability of the hydrodynamic -effect in an obliquely rotating stratified nanofluid taking into account the effects of Brownian diffusion and particle flux under the influence of a temperature gradient (thermophoresis)&nbsp; is obtained. The instability is caused by the action of an external small-scale non-spiral force, which excites small-scale velocity oscillations with zero helicity and a low Reynolds number. Nonlinear equations for large-scale motions are obtained using the method of multiscale asymptotic expansions by a small parameter (Reynolds number). A linear large-scale instability of hydrodynamic -effect is investigated depending on the parameters of rotation , temperature stratification , and concentration of nanoparticles . A new effect of the generation of large-scale vortex structures in nanofluid at &nbsp;is associated with an increase in the concentration of nanoparticles is obtained. The maximum instability increment&nbsp; is reached&nbsp; at inclination angles &nbsp;for the Prandtl numbers&nbsp; , and for the Prandtl numbers &nbsp;&nbsp;at&nbsp; inclination angles&nbsp; &nbsp;. It has been found that the frequency changing of the parametric impact will make it possible to control and track the generation of large-scale vortex structures. It is shown that circularly polarized Beltrami vortices appear in nanofluid as the result of new large-scale instability development. In this paper, the saturation regime of large-scale instability in an obliquely rotating stratified nanofluid with an external small-scale non-spiral force is investigated. In the stationary regime was obtained a dynamic system of equations for large-scale perturbations of the velocity field. Numerical solutions of this system of equations are obtained, which show the existence of localized vortex structures in the form of nonlinear Beltrami waves and kinks. The velocity&nbsp; profile of kink tends to be constant at large Z values.</p> 2021-04-28T00:00:00+00:00 Copyright (c) 2021 Michael I. Kopp, Anatoly V. Tur, Volodymyr V. Yanovsky Energy Activation Spectrum of Low-Temperature Acoustic Relaxation in High-Purity Iron Single Crystal. Solution of the Inverse Problem of Mechanical Spectroscopy by the Tikhonov Regularization Method 2021-06-01T11:33:09+00:00 Yuri A. Semerenko <p>When studying the temperature dependences of the acoustic absorption and the modulus of elasticity, absorption peaks are often observed, which correspond to the characteristic step on the temperature dependence of the modulus of elasticity. Such features are called relaxation resonances. It is believed that the occurrence of such relaxation resonances is due to the presence in the structure of the material of elementary microscopic relaxors that interact with the studied vibrational mode of mechanical vibrations of the sample. In a sufficiently perfect material, such a process is characterized by a relaxation time <em>τ</em>, and in a real defective material by a relaxation time spectrum <em>P(τ)</em>. Most often such relaxation processes have a thermally activated character and the relaxation time <em>τ(T)</em> is determined by the Arrhenius ratio <em>τ(T)=τ<sub>0</sub>exp(U<sub>0</sub>/kT)</em>, and the characteristics of the process will be &nbsp;<em>U<sub>0&nbsp;</sub></em>- activation energy, <em>τ<sub>0</sub></em>&nbsp;- period of attempts, Δ<sub>0</sub> - characteristic elementary contribution of a single relaxator to the dynamic response of the material and their spectra. In the low temperatures region the statistical distribution of parameters <em>τ<sub>0</sub></em>&nbsp;and Δ<sub>0</sub>&nbsp;can be neglected with exponential accuracy, and the relaxation contribution to the temperature dependences of absorption and the dynamic elasticity modulus of the material will be determined only by the activation energy spectrum&nbsp;<em>P(U)</em> of microscopic relaxors. The main task of mechanical spectroscopy in the analysis of such relaxation resonances is to determine <em>U<sub>0</sub></em>, <em>τ<sub>0</sub></em>, Δ<sub>0</sub>&nbsp;and <em>P(U)</em>. It is shown, that the problem of recovering of spectral function <em>P(U)</em>&nbsp;of acoustic relaxation of a real crystal can be reduced to the solving of the Fredholm integral equation of the first kind with an approximately known right part and concerns to a class of ill-posed problems. The method based on Tikhonov regularizing algorithm for recovering <em>P(U)</em>&nbsp;from experimental temperature dependences of absorption or elasticity module is offered. It is established, that acoustic relaxation in high-purity iron single crystal in the temperature range 5-100&nbsp;K is characterized by two-modes spectral function <em>P(U)</em>&nbsp;with maxima at 0.037&nbsp;eV and 0.015&nbsp;eV, which correspond to the <em>a</em>-peak and&nbsp;its&nbsp;<em>a</em><em>'</em> satellite.</p> 2021-04-28T00:00:00+00:00 Copyright (c) 2021 Yuri A. Semerenko Polarization Effects in the Reaction d+eˉ → d+eˉ 2021-06-01T11:33:06+00:00 Gennadiy I. Gakh Mykhailo I. Konchatnyi Nikolay P. Merenkov Andrij G. Gakh Egle Tomasi-Gustafsson <p>The differential cross section and polarization observables for the elastic reaction induced by deuteron scattering off electrons at rest, &nbsp;are calculated in the one-photon-exchange approximation. The following polarization observables were calculated: 1- the analyzing powers (asymmetries) due to the tensor polarization of the deuteron beam, 2 - the spin correlation coefficients caused by the arbitrarily polarized electron target and the vector polarized deuteron beam, 3 - the coefficients of the polarization transfer from the arbitrarily polarized target electron to the recoil electrons. The differential cross section and polarization observables have been expressed in terms of the deuteron electromagnetic form factors: &nbsp;(charge monopole), &nbsp;(magnetic dipole) and &nbsp;(charge quadrupole). Numerical estimations are given for the analyzing powers (asymmetries) due to the tensor polarization of the deuteron beam. They are calculated as functions of the deuteron beam energy for some values of the scattering angle (the angle between the deuteron beam and the recoil electron momenta). For the numerical calculation we use the existing phenomenological parametrization of the deuteron electromagnetic form factors. It turns out that the analyzing powers (asymmetries) are increasing with the growth of the deuteron beam energy and they have appreciable sensitivity to the value of the scattering angle. The specific interest of this reaction is to investigate the possibility to use this reaction for the measurement of the polarization of the high energy deuteron beams.</p> 2021-04-28T00:00:00+00:00 Copyright (c) 2021 Gennadiy I. Gakh, Mykhailo I. Konchatnyi, Nikolay P. Merenkov, Andrij G. Gak, Egle Tomasi-Gustafsson Mode-Converting Corrugations for Cavities of Second-Harmonic Gyrotrons with Improved Performance 2021-06-01T11:33:13+00:00 Tetiana Tkachova Vitalii Shcherbinin Viktor Tkachenko <p>Mode-converting longitudinal corrugations are used as a means of improving the selectivity properties of cavities for second-harmonic gyrotrons. As an example, 100-kW 0.3-THz second-harmonic gyrotron is considered. For the operating second-harmonic mode and most dangerous first-harmonic competing modes, the eigenvalues, ohmic losses and beam-wave coupling coefficients are investigated with respect to dimensions of a corrugated cavity. The most optimal parameters are found for a gyrotron cavity with mode-converting corrugations, which ensure the widest range of a single mode operation for the 0.3-THz second-harmonic gyrotron. It is shown that, in this range, the gyrotron output power can be increased up to 180 kW. It is found that output mode purity of the 0.3-THz second-harmonic gyrotron falls off due to mode-converting corrugations, which induce undesirable coupling of the operating mode with neighboring Bloch harmonics in the output section of the gyrotron cavity.</p> 2021-04-10T00:00:00+00:00 Copyright (c) 2021 Tetiana Tkachova, Vitalii Shcherbinin, Viktor Tkachenko Semiclassic Models of the Dissipative Regime of Instability and Superradiation of a Quantum Radiator System 2021-06-01T11:33:04+00:00 Volodymyr V. Kuklin Valentin T. Lazurik Eugen V. Poklonskiy <p>The paper discusses the similarity between dissipative generation and superradiance regimes for systems of excited quantum emitters placed in an open cavity. In the case of the existence of a resonator field due to reflections from the ends of the system, a dissipative generation regime is usually realized. In this case, the decrement of oscillations in the waveguide in the absence of radiators turns out to be greater than the increment of the arising instability of the system of radiators placed in the resonator. When describing this mode, the influence of the emitters on each other and the sum of their own fields is neglected. The resonator field forces the oscillators to emit or absorb quanta synchronously with it, depending on the local value of the population inversion. Lasing takes on a weakly oscillatory character due to an asynchronous change in the population inversion of the system of emitting dipoles (nutations), which have a ground and excited energy levels. To describe the process, the equations of the semiclassical theory based on the use of the density matrix are quite sufficient. In the case when there is no resonator or waveguide field, taking into account the eigenfields of the oscillators becomes essential. To simulate the superradiance process, large emitting particles are used, to describe which one should use the equations for the density matrix. It is shown that the interaction of quantum emitters in this case is due to electromagnetic fields under conditions when the overlap of their wave functions is insignificant. Equations are obtained that allow considering the process of interaction of emitters. When the emitters interact, an integral field is formed in the resonator, an increase in the intensity of which leads to synchronization of the emitters. It is shown that the characteristic times of the development of the process, as well as the attainable amplitudes of the excited fields for dissipative regimes of generation and regimes of superradiance of emitters filling an open resonator, are comparable.</p> 2021-04-28T00:00:00+00:00 Copyright (c) 2021 Volodymyr V. Kuklin, Valentin T. Lazurik, Eugen V. Poklonskiy Microstructure and Hardening Behavior of Argon-Ion Irradiated Steels 18Cr10NiTi and 18Cr10NiTi-ODS 2021-06-01T11:33:02+00:00 Igor Kolodiy Oleksandr Kalchenko Sergiy Karpov Victor Voyevodin Mikhail Tikhonovsky Oleksii Velikodnyi Galyna Tolmachova Ruslan Vasilenko Galyna Tolstolutska <p>Microstructure and nanohardness evolution in 18Cr10NiTi and 18Cr10NiTi-ODS steels after exposure to argon ion irradiation has been studied by combination of nanoindentation tests, XRD analysis, TEM and SEM observation. ODS-modified alloy was produced on the basis of conventional 18Cr10NiTi austenitic steel by mechanical alloying of steel powder with Y(Zr)-nanooxides followed by mechanical-thermal treatment. XRD analysis has showed no significant changes in the structure of 18Cr10NiTi steel after irradiation at room and elevated temperatures (873 K) and in ODS-steel after irradiation at 873 K, whereas the evidences of domains refinement and microstrain appearance were revealed after irradiation of 18Cr10NiTi-ODS steel at room temperature (RT). Layer-by-layer TEM analysis was performed to investigate the microstructure of alloys along the damage profile. The higher displacement per atom (dpa) and Ar concentration clearly lead to increased cavities size and their number density in both steels. The swelling was estimated to be almost half for 18Cr10NiT-ODS (4.8%) compared to 18Cr10NiTi (9.4%) indicating improved swelling resistance of ODS-steel. The role of oxide/matrix interface as a sink for radiation-induced point defects and inert gas atoms is discussed. The fine dispersed oxide particles are considered as effective factor in suppressing of cavity coarsening and limiting defect clusters to small size. The hardness behavior was investigated in both non-irradiated and irradiated specimens and compared to those at RT and elevated temperature of irradiation. The hardness increase of unirradiated ODS-steel is associated mainly with grain refinement and yttrium oxides particles addition. The hardening of 18Cr10NiTi-ODS after Ar ion irradiation at RT was found to be much lower than 18Cr10NiTi. Black dots and dislocation loops are observed for both steels in the near-surface area; however, the main hardening effect is caused by the cavities. Oxide dispersion strengthened steel was found to be less susceptible to radiation hardening/embrittlement compared with a conventional austenitic steel.</p> 2021-04-28T00:00:00+00:00 Copyright (c) 2021 Igor Kolodiy, Oleksandr Kalchenko, Sergiy Karpov, Victor Voyevodin, Mikhail Tikhonovsky, Oleksii Velikodnyi, Galyna Tolmachova, Ruslan Vasilenko, Galyna Tolstolutska Effect of Ti, Al, Si on the Structure and Mechanical Properties of Boron-Rich Fe–B–C Alloys 2021-06-01T11:33:15+00:00 Elena V. Sukhova <p>The effects of substitution of Fe in the boron-rich Fe–B–C alloys, containing 10.0–14.0&nbsp;% B; 0.1–1.2 % C; Fe – the remainder, 5.0 % Ti, Al, or Si (in wt. %) have been studied with optical microscopy, X-ray diffractometry, scanning electron microscopy, energy dispersive spectroscopy. Mechanical properties, such as microhardness and fracture toughness, have been measured by Vickers indenter. The microstructure of the master Fe–B–C alloys cooled at 10 and 10<sup>3</sup> K/s consists of primary dendrites of Fe(B,C) solid solution and Fe<sub>2</sub>(B,C) crystals. It has been found that titanium has the lowest solubility in the constituent phases of the Fe–B–C alloys, with preferential solubility observed in the Fe(B,C) dendrites, where Ti occupies Fe positions. This element has been shown to be mainly present in secondary phases identified as TiC precipitates at the Fe<sub>2</sub>(B,C) boundaries. Titanium slightly enhances microhardness and lowers fracture toughness of the boron-rich Fe–B–C alloys due to substitutional strengthening of Fe(B,C) dendrites and precipitation of the secondary phases. The level of the content of Al or Si in the Fe(B,C) and Fe<sub>2</sub>(B,C) solid solutions and quantity of the secondary phases observed in the structure suggest that more Al or Si are left in the constituent phases as compared with Ti. These elements mainly enter the crystal lattice of Fe<sub>2</sub>(B,C) phase replacing iron atoms and form at their boundaries AlB<sub>12</sub>C and SiC compounds respectively. The additions of Al and Si to the boron-rich Fe–B–C alloys help to modify their fragility: while they slightly decrease microhardness values, addition of these elements improves the fracture toughness of the constituent phases. Increase in a cooling rate from 10 to 10<sup>3</sup> K/s does not bring about any noticeable changes in the solubility behavior of the investigated alloying elements. The rapid cooling gives rise to microhardness and fracture toughness of the phase constituents which average sizes significantly decrease. The effects of the alloying elements on the structure and mechanical properties of the investigated boron-rich Fe–B–C alloys have been explained considering differences in the atomic radii and electronic structure of the solute Ti, Al, or Si atoms.</p> 2021-04-10T00:00:00+00:00 Copyright (c) 2021 Elena V. Sukhova A Variational Technique for Thermodynamics of Liquid K(1-x)Rbx Alloys 2021-06-01T11:32:54+00:00 Rajesh C. Malan Aditya M. Vora <p>Liquid&nbsp;<em>K_(1-x) Rb_x</em> binary alloys with various thermodynamical proportions of participating elements are investigated. The properties of thermodynamic interest are included in the study. The internal energy <em>(Fint)</em>, Helmholtz free enrgy<em> (F<sub>H</sub>)&nbsp;</em>and the entropy <em>(S)</em>&nbsp;have been calculated in a concentration range from&nbsp;<em>X=0.0</em> to&nbsp;<em>X=1.0</em> increasing in a step of 0.1 in the present work. Apart from the internal energy <em>(Fint)</em>, various contributions to this energy are also calculated and separately depicted in the present article. A variational approach has been adopted for the present calculation. A single potential with a set of two parameters is used for the calculation of all properties of the alloys. Static Hartree local field function (H) is used to consider screening effect. Various local field correction functions are used to take into account the exchange and correlation effect. Comparison with experimental data at some concentration shows the good agreement with the presently obtained data. With the help of current results, the applied model potential found very suitable with individual parameters for thermodynamical study. As the present results provide the data even where minimum availability of the experimental findings, it can serve as a data base for the future calculation which deals with thermodynamics of the liquid alloys. Present results allow one to get proportion based tuned properties of the&nbsp;<em>K_(1-x) Rb_x</em> for different requirements.</p> <p><sub><em></em></sub></p> 2021-04-29T00:00:00+00:00 Copyright (c) 2021 Rajesh C. Malan, Aditya M. Vora Investigation on Electrical Properties of Solid Polymer Sheets (HDPE AND LDPE) at Audio Frequency Range 2021-06-01T11:32:51+00:00 Sarat K. Dash Hari S. Mohanty Biswajit Dalai <p>Two different groups of solid polymer sheets: low density polyethylene (LDPE) sample of thickness 0.006&nbsp;cm and 0.007&nbsp;cm along with high density polyethylene (HDPE) sample of the thickness of 0.009&nbsp;cm, 0.010&nbsp;cm were taken in this work. The measurement of electrical properties such as dielectric constant, <em>ε'</em>&nbsp;and dielectric loss, <em>ε''</em>&nbsp;for LDPE and HDPE polymer sheets have been measured using a dielectric cell. The dielectric cell has been fabricated which consists of two circular parallel plates of pure stainless steel each of 5 cm diameter and 2 mm thickness. An impedance bridge (GRA 650A) was used for measurement of capacitance, <em>C</em>, and dissipation factor, <em>D </em>in the audio frequency (AF) range, 100&nbsp;Hz to 10 kHz. Different samples were loaded in between the two plates of the cell and the capacitance as well as the dissipation factor were estimated from the dial readings of the bridge. Effect of frequency variation on <em>ε'</em>, <em>ε''</em>, relaxation time, <em>τ</em>&nbsp;, dissipation factor, tan<em>δ</em> and ac conductivity, <em>σ</em>&nbsp;were also discussed at audio frequency range. The complex permittivity, <em>ε</em><em>*</em>, related to free dipole oscillating in an alternating field and loss tangent, tan<em>δ</em>&nbsp;were calculated. The frequency-dependent conductivity, dielectric behavior, and electrical modulus, both real (<em>M'</em>) and imaginary (<em>M"</em>) parts of LDPE and HDPE have been studied in this work. The values of the real part of the electrical modulus (<em>M'</em>) did not equal to zero at low frequencies and it is expected that the electrode polarization may develop in both sheets. These findings reveal an increased coupling among the local dipolar motions in a short-range order localized motion. The analysis of real (<em>ε'</em>) and imaginary (<em>ε''</em>) parts of dielectric permittivity and that electrical modulus real (<em>M'</em>) and imaginary (<em>M"</em>) parts signify poly dispersive nature of relaxation time as observed in Cole-Cole plots.</p> 2021-04-29T00:00:00+00:00 Copyright (c) 2021 Sarat K. Dash, Hari S. Mohanty, Biswajit Dalai Numerical Modeling and Analysis of HTM-Free Heterojunction Solar Cell Using SCAPS-1D 2021-06-01T11:32:49+00:00 Danladi Eli Alhassan Shuaibu Muhammad Sani Ahmad Jamila Tasiu <p>In this research paper, a HTM-free perovskite solar cell (PSC) structure with Titanium (TiO<sub>2</sub>), methyl ammonium lead triiodide (CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>) and platinum (pt) as electron transport material (ETM), photon harvester and metal back contact is proposed. Solar Cell Capacitance Simulator (SCAPS-1D) program was used to implement the model and simulation. Effect of parameters such as thickness of ETM, thickness of absorber, doping concentration of ETM &amp; absorber and electron affinity (EA) of ETM were investigated systematically. From the obtained results, it was found that the parameters affect the performance of the solar cell. When the thickness of ETM was varied from 0.02 to 0.10&nbsp;μm. The results show that photovoltaic parameters decrease with the thickness increase. When the thickness of the absorber was varied from 0.1 to 1.0 μm, the optimized value was found at thickness of 0.4&nbsp;. When the doping concentration of absorber and EMT were varied from 10<sup>10</sup>–10<sup>17 </sup>cm<sup>-3</sup> and from 10<sup>15</sup>–10<sup>20 </sup>cm<sup>-3</sup>, the highest values of PCEs were obtained at 10<sup>16</sup> cm<sup>-3</sup> and 10<sup>20 </sup>cm<sup>-3</sup> for Absorber and ETM. Also when the EA was varied in the range of 3.7 eV to 4.5 eV, the optimized value was at 3.7 eV. Upon optimization of the above mentioned parameters, power conversion efficiency (PCE) was found to be 25.75&nbsp;%, short circuit current density (J<sub>sc</sub>) 23.25 mAcm<sup>-2</sup>, open circuit voltage (V<sub>oc</sub>) 1.24 V and fill factor (FF) 89.50 %.&nbsp; The optimized result shows an improvement of ~1.95 times in PCE, ~1.06 times in J<sub>sc</sub>, ~1.44 times in V<sub>oc</sub> and ~1.28 times in FF as compared to the initial device with the following parameters, PCE=13.22 %, J<sub>sc</sub>=21.96 mAcm<sup>−2</sup>, V<sub>oc</sub>=0.86 V and FF=69.94 %.</p> 2021-04-30T00:00:00+00:00 Copyright (c) 2021 Danladi Eli, Alhassan Shuaibu, Muhammad Sani Ahmad, Jamila Tasiu Modeling and Simulation of Lead-Free Perovskite Solar Cell Using SCAPS-1D 2021-06-01T11:32:48+00:00 Omeiza Abdulmalik Muhammed Danladi Eli Peter Henry Boduku Jamila Tasiu Muhammad Sani Ahmad Nuhu Usman <p>In this work, the effect of some parameters on tin-based perovskite (<em>CH<sub>3</sub>NH<sub>3</sub>SnI<sub>3</sub></em>) solar cell were studied through device simulation with respect to adjusting the doping concentration of the perovskite absorption layer, its thickness and the electron affinities of the electron transport medium and hole transport medium, as well as the defect density of the perovskite absorption layer and hole mobility of hole transport material (HTM). A device simulator; the one-dimensional Solar Cells Capacitance Simulator (SCAPS‑1D) program was used for simulating the tin-based perovskite solar cells. The current-voltage (J-V) characteristic curve obtained by simulating the device without optimization shows output cell parameters which include; open circuit voltage (<em>V<sub>oc</sub></em>)&nbsp;=&nbsp;0.64V, short circuit current density (<em>I<sub>sc</sub></em>) = 28.50mA/, fill factor (FF) = 61.10%, and power conversion efficiency (PCE)&nbsp;=&nbsp;11.30% under AM1.5 simulated sunlight of 100mW/cm<sup>2</sup> at 300K. After optimization, values of the doping concentration, defect density, electron affinity of electron transport material and hole transport material were determined to be: 1.0x10<sup>16</sup>cm<sup>-3</sup>,&nbsp;1.0x10<sup>15</sup>cm<sup>-3</sup>, 3.7 eV and 2.3 eV respectively. Appreciable values of solar cell parameters were obtained with&nbsp;&nbsp;<em>J<sub>sc</sub></em>&nbsp;of 31.38&nbsp;mA/cm<sup>2</sup>, <em>V<sub>oc</sub></em>&nbsp;of 0.84 V, FF of 76.94% and PCE of 20.35%. when compared with the initial device without optimization, it shows improvement of ~1.10 times in <em>J<sub>sc</sub></em>, ~1.80 times in PCE, ~1.31 times in Voc and ~1.26 time in FF. The results show that the lead-free&nbsp;<em>CH<sub>3</sub>NH<sub>3</sub>SnI<sub>3&nbsp;</sub></em> perovskite solar cell which is environmentally friendly is a potential solar cell with high theoretical efficiency of 20.35%.</p> 2021-04-30T00:00:00+00:00 Copyright (c) 2021 Omeiza Abdulmalik Muhammed, Danladi Eli, Peter Henry Boduku, Jamila Tasiu, Muhammad Sani Ahmad, Nuhu Usman Influence of Electron Injection on the Characteristics of a Hollow Cathode Glow Discharge 2021-06-01T11:32:47+00:00 Stanislav V. Pogorelov Volodymyr A. Timaniuk Nikolay G. Kokodii Ihor V. Krasovskyi <p>The article presents the results of experimental studies of a glow discharge with a hollow cathode in helium and argon gases using an auxiliary discharge as an electron emitter. The authors proposed to make the electrode common for both discharges in the form of a cylindrical metal mesh. The advantage of this design is explained as follows. The connection between the discharges is carried out through holes in the grid with a geometric transparency of 0.2, which makes it possible not only to smoothly control the glow discharge current, but also to enhance the discharge current. Plasma is known to be one of the most efficient electron emitters; however, its use as a cathode in devices with a glow discharge at low gas pressures is complicated by the fact that a grid with small holes is required to separate the electron flow from the plasma, and it is impractical to use such a system in view of low mechanical strength of the grid Since the hollow cathode works effectively at low gas pressures, the release of an electron flux from the plasma of some auxiliary discharge is possible with much larger holes in the grid separating the plasma and the hollow cathode cavity. In this case, the grid can be made such that it can withstand sufficiently high thermal loads and can operate in typical discharge modes with a hollow cathode. The injection of electrons into the cathode cavity of the glow discharge changes the radial distribution of the glow intensity, the width of the cathode dark space, and other parameters of the plasma in the cathode cavity. The influence of electrons penetrating from the auxiliary discharge into the cathode cavity of the main discharge becomes significant when the current of these electrons is comparable to or exceeds the current of electrons leaving the grid cathode surface as a result of γ-processes. In parallel with the measurement of the optical and electrical characteristics of the hollow cathode glow discharge plasma, measurements of the electron concentration were carried out by the microwave sounding method. The entire current of the auxiliary discharge penetrates into the cavity of the main discharge; however, after acceleration in the cathode dark space, the electrons penetrating from the auxiliary discharge ionize gas atoms and noticeably increase the current of the main discharge. Additional ions formed due to the ionization of the gas by the injected electrons knock out new electrons from the cathode surface, which makes it possible to increase the discharge current.</p> 2021-04-30T00:00:00+00:00 Copyright (c) 2021 Stanislav V. Pogorelov, Volodymyr A. Timaniuk, Nikolay G. Kokodii, Ihor V. Krasovskyi Propagation Analysis of Pu Radionuclides as a Result of Fire Incidents in the Exclusion Zone of the Chernobyl NPP in April 2020 2021-06-01T11:32:46+00:00 Maryna F. Коzhevnikova Volodymyr V. Levenets <p>In consequence of nuclear accidents that have occurred in various parts of the world, radioactive contamination of the environment is observed. The risks of spreading pollution can increase during floods, fires and some natural disasters. The lack of effective measures that aimed at eliminating possible sources of fire in the meadow zone and forest lands in the Chernobyl exclusion zone (ChEZ) leads to a high risk of fire emergence. The temporal and spatial distribution of fires shows that they occur throughout the ChEZ, including in the most contaminated areas. The risk of fires increases with climate change and measures to prevent them should be considered in emergency programs. ChEZ area is contaminated with long-lived radionuclides such as <sup>137</sup>Cs, <sup>90</sup>Sr, Pu isotopes (<sup>238</sup>Pu, <sup>239 + 240</sup>Pu, <sup>241</sup>Pu) and <sup>241</sup>Am. As a result of forest fires radionuclides contained in wood and underlying surface are carried out into the atmosphere along with smoke. Diseases arising under the influence of ionizing radiation from Pu and <sup>241</sup>Am isotopes pose a serious problem for human health. To assess of the spatial distribution of Pu isotopes and <sup>241</sup>Am we used data on forest fires that occurred in the Chernobyl zone in April 2020. To evaluatе the dynamics of the release of radioactive substances into the atmosphere during fire incidents on the ChEZ territory, the following software products were used: NASA WorldView, HYSPLIT program. The HYSPLIT program allows to reconstruct the trajectories of radionuclide propagation in the atmosphere using meteorological data and to obtain a reliable picture of the distribution of radionuclides in the study area. The maps of the volumetric activity of Pu isotopes in the air and the fallout on the soil as a result of fires were obtained. It was found that the radioactivity due to the presence of this element in the air and during the fallout of radioactive particles on the soil is low (it reaches 1.0E-7...0.1 Bq/m<sup>3</sup> in the air, 1.0E-6...1 Bq/m<sup>2</sup> on the soil). The analysis of the propagation of Pu isotopes as a result of the movement of air masses in the places of fires in the exclusion zone of the Chernobyl nuclear power plant and the associated dangers for the population and the environment has been carried out.</p> 2021-04-30T00:00:00+00:00 Copyright (c) 2021 Maryna F. Коzhevnikova, Volodymyr V. Levenets Molecular Dynamics Study of Insulin Mutants 2021-06-01T11:32:44+00:00 Olga Zhytniakivska Uliana Tarabara Valeriya Trusova Kateryna Vus Galyna Gorbenko <p>Human insulin, a small protein hormone consisting of A-chain (21 residues) and B-chain (30 residues) linked by three disulfide bonds, is crucial for controlling the hyperglycemia in type I diabetes. In the present work molecular dynamics simulation (MD) with human insulin and its mutants was used to assess the influence of 10 point mutations (His<sup>A8</sup>, Val<sup>A10</sup>, Asp<sup>B10</sup>, Gln<sup>B17</sup>, Ala<sup>B17</sup>, Gln<sup>B18</sup>, Asp<sup>B25</sup>, Thr<sup>B26</sup>, Glu<sup>B27</sup>, Asp<sup>B28</sup>), 6 double mutations (Glu<sup>A13</sup>+Glu<sup>B10</sup>, Ser<sup>A13</sup>+Glu<sup>B27</sup>, Glu<sup>B1</sup>+Glu<sup>B27</sup>, Ser<sup>B2</sup>+Asp<sup>B10</sup>, Asp<sup>B9</sup>+Glu<sup>B27</sup>, Glu<sup>B16</sup>+Glu<sup>B27</sup>) and one triple mutation (Glu<sup>A15</sup>+Asp<sup>A18</sup>+Asp<sup>B3</sup>) in the protein sequence on the structure and dynamics of human insulin. A series of thermal unfolding MD simulations with wild type (WT) human insulin and its mutants was performed at 400 K with GROMACS software (version 5.1) using the CHARMM36m force field. The MD results have been analyzed in terms of the parameters characterizing both the global and local protein structure, such as the backbone root mean-square deviation, gyration radius, solvent accessible surface area, the root mean-square fluctuations and the secondary structure content. The MD simulation data showed that depending on time evolution of integral characteristics, the examined mutants can be tentatively divided into three groups: 1) the mutants His<sup>A8</sup>, Val<sup>A10</sup>, Ala<sup>B17</sup>, Asp<sup>B25</sup>, Thr<sup>B26</sup>, Glu<sup>B27</sup>, Glu<sup>A13</sup>+Glu<sup>B10</sup>, Glu<sup>B1</sup>+Glu<sup>B27</sup> and Glu<sup>B16</sup>+Glu<sup>B27</sup>, which exert stabilizing effect on the protein structure in comparison with wild type insulin; 2) the mutants Gln<sup>B17</sup>, Asp<sup>B10</sup>, Ser<sup>B2</sup>+Asp<sup>B10</sup> and Glu<sup>A15</sup>+Asp<sup>A18</sup>+Asp<sup>B3</sup> that did not significantly affect the dynamical properties of human insulin with a minimal stabilizing impact; 3) the mutants Asp<sup>B28</sup>, Asp<sup>B9</sup>+Glu<sup>B27</sup> and Ser<sup>A13</sup>+Glu<sup>B27</sup>, Gln<sup>B18</sup>, destabilizing the protein structure. Analysis of the secondary structure content provided evidence for the influence of Asp<sup>B28</sup>, Asp<sup>B9</sup>+Glu<sup>B27</sup> and Ser<sup>A13</sup>+Glu<sup>B27</sup>, Gln<sup>B18</sup> on the insulin unfolding. Our MD results indicate that the replacement of superficial nonpolar residues in the insulin structure by hydrophilic ones gives rise to the increase in protein stability in comparison with the wild type protein.</p> 2021-04-30T00:00:00+00:00 Copyright (c) 2021 Olga Zhytniakivska, Uliana Tarabara, Valeriya Trusova, Kateryna Vus, Galyna Gorbenko Modeling of Molecular Mechanisms of Radiation Adaptive Response Formation 2021-06-01T11:32:42+00:00 Maryna A. Bondarenko Olga V. Zaytseva Valerija М. Trusova <p>The phenomenon of adaptive response is expressed in the increase of resistance of a biological object to high doses of mutagens under the conditions of previous exposure to these (or other) mutagens in low doses. Low doses of mutagen activate a number of protective mechanisms in a living object, which are called hormetic. Thus, the adaptive response and hormesis are links in the same chain. Radiation hormesis refers to the generally positive effect of low doses of low LET radiation on biological objects. The phenomenology of radiation-induced adaptive response and radiation hormesis for biological objects of different levels of organization is considered; the review of existing theories describing the dose-effect relationship has been reviewed. The hypothesis proposing one of the mechanisms of formation of radiation adaptive response of cells taking into account the conformational structure of chromatin has been submitted. The analysis of modern concepts of the phenomenon of hormesis on the basis of modeling of molecular mechanisms of formation of hormetic reactions to low-dose low LET radiation has been carried out. The parameters that can be used for quantitative and graphical evaluation of the phenomenon of hormesis was considered, and a formula for calculating the coefficient of radiation-induced adaptive response has been proposed. A review of mathematical models describing the radiation relative risk of gene mutations and neoplastic transformations at low-dose irradiation of cohorts has been performed. The following conclusions have been made: radiation hormesis and adaptive response are generally recognized as real and reproducible biological phenomena, which should be considered as very important phenomena of evolutionarily formed biological protection of living organisms from ionizing radiation. The hormesis model of dose-response relationship makes much more accurate predictions of a living object's response to radiation (or other stressors) in the low-dose range than the linear threshold (LNT) model does. The LNT model can adequately describe reactions only in the region of high doses of radiation, and, therefore, extrapolation modeling of biological object’s reactions from the zone of high doses to low doses is not correct.</p> 2021-04-30T00:00:00+00:00 Copyright (c) 2021 Maryna А. Bondarenko, Olga V. Zaytseva, Valerija М. Trusova