East European Journal of Physics https://periodicals.karazin.ua/eejp <p>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><strong>East European Journal of Physics</strong> <strong>has been selected for coverage in Clarivate Analytics products and services.&nbsp;Beginning with 2017 it will be indexed and abstracted in: "Emerging Sources Citation Index"(ESCI).</strong></p> en-US <p>Authors who publish with this journal agree to the following terms:<br><br></p> <ol type="a"> <ul> <li class="show">Authors retain copyright and grant the journal right of first publication with the work simultaneously licensed under a&nbsp;<a href="http://creativecommons.org/licenses/by/4.0/" target="_new">Creative Commons Attribution License</a>&nbsp;that allows others to share the work with an acknowledgement of the work's authorship and initial publication in this journal.</li> </ul> </ol> <ol type="a"> <ul> <li class="show">Authors are able to enter into separate, additional contractual arrangements for the non-exclusive distribution of the journal's published version of the work (e.g., post it to an institutional repository or publish it in a book), with an acknowledgement of its initial publication in this journal.</li> </ul> </ol> <ol type="a"> <ul> <li class="show">Authors are permitted and encouraged to post their work online (e.g., in institutional repositories or on their website) prior to and during the submission process, as it can lead to productive exchanges, as well as earlier and greater citation of published work (See&nbsp;<a href="http://opcit.eprints.org/oacitation-biblio.html" target="_new">The Effect of Open Access</a>).</li> </ul> </ol> serhii.hirnyk@karazin.ua (Serhii Hirnyk) serhii.hirnyk@karazin.ua (Serhii Hirnyk) Tue, 30 Jul 2019 12:52:51 +0300 OJS 3.1.1.4 http://blogs.law.harvard.edu/tech/rss 60 Algebraization in Stability Problem for Stationary Waves of the Klein-Gordon Equation https://periodicals.karazin.ua/eejp/article/view/13477 <p>Nonlinear traveling waves of the Klein-Gordon equation with cubic nonlinearity are considered. These waves are described by the nonlinear ordinary differential equation of the second order having the energy integral. Linearized equation for variation obtained for such waves is transformed to the ordinary one using separation of variables. Then so-called algebraization by Ince is used. Namely, a new independent variable associated with the solution under consideration is introduced to the equation in variations. Integral of energy for the stationary waves is used in this transformation. An advantage of this approach is that an analysis of the stability problem does no need to use the specific form of the solution under consideration. As a result of the algebraization, the equation in variations with variable in time coefficients is transformed to equation with singular points. Indices of the singularities are found. Necessary conditions of the waves stability are obtained. Solutions of the variational equation, corresponding to boundaries of the stability/instability regions in the system parameter space, are constructed in power series by the new independent variable. Infinite recurrent systems of linear homogeneous algebraic equations to determine coefficients of the series can be written. Non-trivial solutions of these systems can be obtained if their determinants are equal to zero. These determinants are calculated up to the fifth order inclusively, then relations connecting the system parameters and corresponding to boundaries of the stability/ instability regions in the system parameter place are obtained. Namely, the relation between parameters of anharmonicity and energy of the waves are constructed. Analytical results are illustrated by numerical simulation by using the Runge-Kutta procedure for some chosen parameters of the system. A correspondence of the numerical and analytical results is observed.</p> Nataliia Goloskubova, Yuri Mikhlin ##submission.copyrightStatement## https://periodicals.karazin.ua/eejp/article/view/13477 Mon, 29 Jul 2019 00:00:00 +0300 Research of the Syngle Crystal and Multilayer Composite Detectors Response Under Irradiation by Fast Neutrons https://periodicals.karazin.ua/eejp/article/view/13478 <p>The object of this work was to study the response of the detectors based on the oxide scintillators under irradiation by a flux of fast neutrons from <sup>239</sup>Pu-Be source by counting photomultiplier tube pulses.&nbsp; In the process of the research the counting efficiency of the detectors was measured in units of (pulse×s<sup>-1</sup>×cm<sup>-2</sup>)/(neutron×s<sup>-1</sup>×cm<sup>-2</sup>) for single-crystal and multilayer composite detectors ZWO (ZnWO<sub>4</sub>), CWO (CdWO<sub>4</sub>), BGO (Bi4Ge3O12, composite). The measured response for ZWO detector was ~ 64 pulse/neutron, for CWO&nbsp;~&nbsp;36&nbsp;pulse/neutron, for BGO ~&nbsp;0.44 pulse/neutron. The detectors response was registered by a fast preamplifier with the operation speed of up to 500 MHz, based on high-speed operational amplifiers with voltage feedback. The statistical error of measurement for the neutron registration efficiency by the broadband channel made 7% for the detectors with the effective thickness of ~ 40-50 mm, which is due to the spherical geometry of the experiment. The formation of the detector response is affected by the following parameters of neutron reactions: cross section of inelastic and resonant scattering of scintillator nuclei, density of composite nuclei levels, resonance region width, lifetimes of long-lived states and their number. The measured values of the counting efficiency of fast neutrons registration are accounted for the fact that the inelastic scattering reaction for some nuclei is the starting point that triggers the cascade process of the nuclear states discharge. The registration of the cascade of the discharge gamma-quanta, ranging from nanoseconds to a few microseconds, causes an increase in the detector counting efficiency and, as a consequence, an increase in the detector sensitivity to neutron detection. The observed increase in the counting efficiency of secondary gamma quanta is realized when the neutrons are slowed down in the detectors having sufficiently noticeable thickness and appropriate isotopic composition.</p> Volodymyr Ryzhikov, Gennadiy Onyshchenko, Ivan Yakymenko, Sergei Naydenov, Alexandr Opolonin, Sergei Makhota ##submission.copyrightStatement## http://creativecommons.org/licenses/by/4.0 https://periodicals.karazin.ua/eejp/article/view/13478 Mon, 29 Jul 2019 00:00:00 +0300 Novel Phosphonium Dye TDV1 as a Potential Fluorescent Probe to Monitor DNA Interactions with Lysozyme Amyloid Fibrils https://periodicals.karazin.ua/eejp/article/view/13481 <p>The applicability of the novel cationic phosphonium dye TDV1 to monitor the complexation between DNA and pathologically aggregated proteins, amyloid fibrils, was tested using the optical spectroscopy and molecular docking techniques. TDV1 has been found to be highly emissive in buffer solution and is characterized by one well-defined fluorescence peak attributed to the dye monomers. The association of the dye with the double stranded DNA was followed by the enhancement of monomer fluorescence coupled with a bathochromic shift of the emission maximum. The addition of fibrillar lysozyme (LzF) to TDV1-DNA mixture led to the further enhancement of fluorescence intensity of the monomeric dye form coupled with a hypsochromic shift of the emission maximum and an appearance of a second long-wavelength peak. An assumption has been made that the fluorescence enhancement augmenting with increasing the protein concentration in the TDV1/DNA system is produced by the interaction of the free TDV1 monomers with lysozyme fibrils as well as by the LzF-induced conformational alterations of DNA. The long-wavelength peak emerging in the presence of LzF is presumably a consequence of the J-aggregate formation upon the TDV1 association with lysozyme fibrils. The molecular docking studies showed that TDV1 monomers are incorporated into the fibril grooves associating with 7 β-strands in such a way that the dye long axis is parallel to the fibril axis. The most energetically favorable position of TDV1 is the S60-W62/G54-L56 groove in the lysozyme fibril core. In contrast, the TDV1 dimers seem to associate with the more hydrophilic side of the model β-sheet. Cumulatively, the results from the absorption and fluorescence measurements, together with the molecular docking analysis are consistent with the minor groove mode of the TDV1 binding to dsDNA. The electrostatic interactions seem to play a predominant role in the TDV1 complexation with the double stranded DNA, while the hydrophobic interactions and steric hindrances are supposed to be influential in the association of TDV1 with fibrillar lysozyme.</p> Olga Zhytniakivska, Uliana Tarabara, Kateryna Vus, Valeriya Trusova, Galyna Gorbenko, Nikolai Gadjev, Todor Deligeorgiev ##submission.copyrightStatement## https://periodicals.karazin.ua/eejp/article/view/13481 Mon, 29 Jul 2019 00:00:00 +0300 Study of Advanced Nanoscale ZrN/CrN Multilayer Coatings https://periodicals.karazin.ua/eejp/article/view/13483 <p>The scientific interest in the investigation of nitride composites as protecting materials in tool and machining industries intensively increases. The good oxidation resistance of CrN single-layer films and high melting point, good chemical and thermal resistance of ZrN compound are motive factors for designing of multilayer composites composed of these metal nitrides. The suggested advantages of ZrN/CrN multilayer coatings as structural materials are the high-temperature resistance, high density and extreme hardness compared to the metal-nitride systems. Experimental ZrN/CrN multilayer coatings were deposited on AISI 321 steel substrates by using a cathodic arc evaporation device equipped with two high-purity metal Cr and Zr targets. Structural, chemical and morphological characteristics together with mechanical properties of multilayer composites were analyzed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and Vickers hardness tester. SEM analysis revealed an increase of roughness and concentration of the droplets on the surface of the coatings when negative bias potential decreased to -70&nbsp;V. The results of data obtained from the X-ray analysis showed (200) and (111) plane for ZrN and Cr<sub>2</sub>N phases as the most intense. The peak positions of ZrN were shifted towards lower diffraction angles comparing with bulk values and indicated a decrease of the inter-planar distance and formation of compressive stresses. The calculated lattice strain values in the ZrN were higher than those of the CrN, indicated a greater presence of dislocations and defects in the lattice of ZrN. The averaged crystallite sizes in ZrN and CrN layers were 11-14 and 7-12 nm, respectively. The maximum value of the Vickers microhardness was found to be 6600HV0.01 that is 2.1 and 1.8 times greater than the corresponding values of binary CrN and ZrN coatings.</p> Olga Maksakova, Alexander Pogrebnjak, Vyacheslav Beresnev, Vyacheslav Stolbovoy, Sónia Simoẽs, Dosym Yerbolatuly ##submission.copyrightStatement## https://periodicals.karazin.ua/eejp/article/view/13483 Mon, 29 Jul 2019 00:00:00 +0300 Effect of Silicon Surface Treatment on the Electrical and Photoelectric Properties of Nanostructured MoOx/n-Si Heterojunctions https://periodicals.karazin.ua/eejp/article/view/13484 <p>The paper presents the results of studies of the effect of silicon surface treatment on the electrical and photoelectric properties of nanostructured MoO<sub>x</sub>/<em>n</em>-Si heterojunctions. The nanostructured heterojunctions MoO<sub>x</sub>/<em>n</em>-Si, were prepared by deposition of thin films of molybdenum oxide (<em>n</em>-type conductivity) by reactive magnetron sputtering in the universal vacuum system Leybold Heraeus L560 on the nanostructured silicon substrates (<em>n</em>-type conductivity), which were made by chemical etching with the assistance of silver nanoparticles. Dark and light volt-ampere (<em>I</em> – <em>V</em>) characteristics of the heterojunctions under study were measured, the value of the potential barrier height, the values of the serial <em>R</em><sub>s</sub> and the shunt <em>R</em><sub>sh</sub> resistance at room temperature were determined. It was established that the silicon surface treatment does not affect the potential barrier height, but significantly affects the values of serial <em>R</em><sub>s</sub> and shunt <em>R</em><sub>sh</sub> resistance. The electrical and photoelectric properties of the obtained structures were investigated, the dominant mechanisms of current transfer through the heterostructures under forward bias are well described in the framework of emission-recombination and tunneling models with the presence of interface states. The main mechanism for the charge carrier transport through heterojunctions with the reverse bias is the Frenkel–Pool emission. Investigation of photoelectric properties of heterojunctions MoO<sub>x</sub>/<em>n</em>-Si was carried out at illumination by white light with intensity<em> P</em><sub>opt</sub> = 80 mW/сm<sup>2</sup>. It was established that the heterostructure No.5 MoO<sub>x</sub>/<em>n</em>-Si with grown nanowires and etched silver nanoparticles has a maximum open-circuit voltage <em>V</em><sub>oc</sub>&nbsp;=&nbsp;0.17 V, short-circuit current density <em>I</em><sub>sc</sub> = 10 mA/cm<sup>2</sup>. The possibilities of using the obtained heterostructures as photodiodes were analyzed.</p> Mykhailo Solovan, Taras Kovaliuk, Pavlo Maryanchuk ##submission.copyrightStatement## https://periodicals.karazin.ua/eejp/article/view/13484 Mon, 29 Jul 2019 00:00:00 +0300 Regularities of Changes in Kearns Texture Coefficient at Cold Rolling of Zr-2.5%Nb Alloy https://periodicals.karazin.ua/eejp/article/view/13488 <p>-ray studies of the changes in characteristics of crystallographic texture with cold deformation of Zr‑2.5%Nb alloy plates by longitudinal and cross rolling up to 56% at the speed of&nbsp; 5…10&nbsp;sec<sup>-1</sup> were carried out. The original plates were made from longitudinal fragments and rings cut from Æ15.0´1.5&nbsp;mm² tube, and were then annealed at 580&nbsp;°C. Texture of the plates was studied by the method of inverse pole figures with calculation of the Kearns texture coefficient along the normal to the plate plane. Dependences of the texture coefficient on degrees of deformation of the plates are built. A discrepancy was found between texture coefficient values measured on different sides of the plates, which is associated with the straightening of the original tube fragments and invariance of “<em>c</em>”-axes distribution after subsequent annealing of the initial plates. By introducing corrections to the degree of deformation calculated from the parameters of the cross section of the original tube, such discrepancies were eliminated for the data on cross-rolling of the material. As a result, for both deformation schemes, two stages of changes in the texture coefficient with alloy deformation were revealed: the initial stage of its growth and the subsequent stage of minor changes. Both stages are mainly linear and have the boundary value of the texture coefficient equal to 0.65...0.68. To study the structural mechanisms of changes in the texture of the alloy, an original technique of comparative analysis of changes in the texture coefficient of the material and in the distribution of crystallographic orientations is applied. It is established that at the initial stage of changes in the texture coefficient with deformation in both schemes, the rotation of the crystallographic “<em>c</em>” axes of the material occurs abruptly, and it does at angles of more than 60°. This confirms the essential role of twinning in the texture changes of the alloy. In particular, we have shown that the initial stage is significantly dominated by the {102}á011ñ system of tensile twins. Connection of twinning with differences in texture changes at the longitudinal and cross rolling of the alloy is discussed.</p> Viktor Grytsyna, Dmitry Malykhin, Tetiana Yurkova, Kostiantyn Kovtun, Tetiana Chernyayeva, Gennadiy Kovtun, Vira Kornyeyeva, Olena Slabospitskaya, Irina Tantsura, Viktor Voyevodin ##submission.copyrightStatement## https://periodicals.karazin.ua/eejp/article/view/13488 Mon, 29 Jul 2019 00:00:00 +0300 Investigation of Silicon and Manganese Solubility in Cementite of Iron-Based Alloys https://periodicals.karazin.ua/eejp/article/view/13485 <p>In the paper we obtained the expression of cementite free energy and determined the solubility of manganese and silicon in Fe<sub>3</sub>C cementite depending on the temperature. Investigation was carried out for alloys with carbon content of 0.55-0.60&nbsp;% (wt.), silicon content of 0.95-1.0&nbsp;% (wt.), manganese content of 0.8-0.9% (wt.), the rest was iron. The smelting of Fe-Mn-Si-C system alloys was carried out in the alundum crucible furnace in argon atmosphere. The cooling rate of alloys after casting was 10&nbsp;K/s. Microstructure analysis along with X-ray diffraction analysis was used to determine the structural state of the alloys. In addition, the physical characteristics of the alloys studied in this paper were determined, such as alloy chemical dependence of ultimate strength, extension and contraction ratio, impact toughness and hardness. The results obtained in this paper showed that the iron-based alloy with the content of carbon of 0.57&nbsp;% (wt.), silicon of 0.97&nbsp;% (wt.) and manganese of 0.85&nbsp;% (wt.)) had the superior microstructure and physical properties. The microstructure of alloys studied in the paper is represented by pearlite, which makes up to 95&nbsp;% of the volume. In the alloys we revealed the highly dispersed inclusions of Fe<sub>2.7</sub>Mn<sub>0.3</sub>C, Fe<sub>0.25</sub>Mn<sub>1.4</sub>C<sub>0.6</sub> and Fe<sub>9</sub>SiC<sub>0.4</sub> carbides, whose volume ratio was up to 1.5&nbsp;%, the rest was ferrite. As it is known, the structural constituent of pearlite is cementite. The cementite has a significant effect on the physical properties of alloys. Application of quasi-chemical method enables to calculate the free energy of silicon and manganese doped with cementite and to determine the temperature dependence of silicon and manganese content in cementite. It is ascertained that there is a slight increase of carbon content in cementite (up to 28.79&nbsp;% (atoms). Manganese can replace up to 12&nbsp;% of iron atoms, and silicon can replace up to 4.5&nbsp;% of iron atoms, depending on temperature. The calculated data obtained in this paper are in good agreement with those found experimentally by other authors.</p> Natalia Filonenko, Alexander Babachenko, Ganna Kononenko ##submission.copyrightStatement## https://periodicals.karazin.ua/eejp/article/view/13485 Mon, 29 Jul 2019 00:00:00 +0300 Solubility of Boron and Carbon in Ferrite of the Fe-B-C System Alloys https://periodicals.karazin.ua/eejp/article/view/13486 <p>Investigation was carried out for Fe-B-C alloys with carbon content of 0.0001–0.01&nbsp;% (wt.) and boron content of 0.0001–0.01&nbsp;% (wt.), the rest is iron. To determine the structural state of alloys we use the microstructure analysis, X-ray microanalysis and X-ray structure analysis. The level of microstraines, dislocation density and the coercive force of ferrite is determined, and it is shown that structure imperfection grows with boron content increase in the alloy. The obtained results enable to suggest that boron atoms in a solid solution of α-iron occupy substitutional-interstitial positions depending on boron content. In the paper it is shown experimentally, that at room temperature solubility limit of boron and carbon in the ferrite is 0.00012&nbsp;% (wt.) and 0.006 % (wt.). When boron and carbon content increases further, the following phases are formed: Fe<sub>2</sub>B, Fe<sub>3</sub>(CB) and Fe<sub>23</sub>(CB)<sub>6</sub>. In this paper by means of quasi-chemical method we obtain for the first time temperature dependence of the free energy for α-iron solid solution, as well as solubility limit of carbon and boron. Maximum mass fraction of carbon may be up to 0.016&nbsp;% (wt.), and maximum boron mass fraction – up to 0.00025&nbsp;% (wt.). At room temperature the boron solubility limit in ferrite is 0.0001&nbsp;% (wt.), and carbon one is 0.004 % (wt.). The calculated numerical values of the solubility of boron and carbon in ferrite of the Fe-B-C system alloys are less than that of the experimental results. This can be explained by the fact that boron atoms interact more actively with structure imperfections than carbon atoms. At high temperatures the solubility of carbon and boron in given phase increases.</p> Natalia Filonenko ##submission.copyrightStatement## https://periodicals.karazin.ua/eejp/article/view/13486 Mon, 29 Jul 2019 00:00:00 +0300 GEANT4 Modeling Of Energy Spectrum Of Fast Neutrons Source For The Development Of Research Technique Of Heavy Scintillators https://periodicals.karazin.ua/eejp/article/view/13487 <p>The proposed work demonstrates the results of creating and investigating the mathematical model of the source of fast neutrons. Computer modeling of the energy spectrum of fast neutrons was carried out for <sup>239</sup>PuBe neutron source. The model of the source of fast neutrons has been developed.&nbsp; Neutrons in this model have an energy spectrum from 100 keV to 11 MeV with 100 keV step. Simulation is performed by the Monte-Carlo method. The model carrier is a computer program developed in the C++ programming language in the Linux operating system environment, using the Geant4 toolkit. All necessary classes describing low-energy models were used for the simulation of the passage of neutrons through materials of detectors. Those take into account the elastic scattering, inelastic scattering, radiative capture and fission. We consider these processes because models of processes implemented in our software will be also used for other problems of neutrons transport, for example, for passing neutrons through various substances, and for conducting virtual laboratory works. The PhysicsList class of our program contains classes G4NeutronHPElastic, G4NeutronHPElasticData, G4NeutronHPInelastic, G4NeutronHPInelasticData, G4NeutronHPCapture, G4NeutronHPCaptureData, etc. based on the NeutronHP model for neutron interactions at low energy, as well as the neutron data library G4NDL4.5. Diagrams containing energy spectra of a source of fast neutrons modeled in two ways are presented in the paper. The analysis of the obtained energy spectra is carried out. Virtual nuclear physics experiments are carried out with the aim of testing the elaborated neutron-matter interaction model. The processes occurring in scintillator substances during the passage of fast neutrons through them, have been studied. 10<sup>9</sup> neutrons were used as primary particles emitted isotropically, and we used our simulation results of <sup>239</sup>PuBe neutron source to describe the initial energy spectrum. The created model of <sup>239</sup>PuBe neutron source can be used for the investigation of scintillation detectors Bi<sub>4</sub>Ge<sub>3</sub>O<sub>12</sub>, CdWO<sub>4</sub>, Gd<sub>2</sub>SiO<sub>5 </sub>and others, as well as studying their characteristics. Processes in heavy oxide scintillators substance during the registration of fast neutrons can be studied using the developed model. It is shown that for registration of the flow of neutrons from <sup>239</sup>PuBe neutron&nbsp; source, using Bi<sub>4</sub>Ge<sub>3</sub>O<sub>12</sub> or CdWO<sub>4</sub> scintillators is more preferable. Results of the virtual nuclear physical experiments satisfy the published experimental data.</p> Viktoriia Lisovska, Tetiana Malykhina, Valentina Shpagina, Ruslan Timchenko ##submission.copyrightStatement## https://periodicals.karazin.ua/eejp/article/view/13487 Mon, 29 Jul 2019 00:00:00 +0300 Improvement of Properties of Self-Injected and Accelerated Electron Bunch by Laser Pulse in Plasma, Using Pulse Precursor https://periodicals.karazin.ua/eejp/article/view/13505 <p>The accelerating gradients in conventional linear accelerators are currently limited to ~100&nbsp;MV/m. Plasma-based accelerators have the ability to sustain accelerating gradients which are several orders of magnitude greater than that obtained in conventional accelerators. Due to the rapid development of laser technology the laser-plasma-based accelerators are of great interest now. Over the past decade, successful experiments on laser wakefield acceleration of electrons in the plasma have confirmed the relevance of this acceleration. Evidently, the large accelerating gradients in the laser plasma accelerators allow to reduce the size and to cut the cost of accelerators. Another important advantage of the laser-plasma accelerators is that they can produce short electron bunches with high energy. The formation of electron bunches with small energy spread was demonstrated at intense laser–plasma interactions. Electron self-injection in the wake-bubble, generated by an intense laser pulse in underdense plasma, has been studied. With newly available compact laser technology one can produce 100 PW-class laser pulses with a single-cycle duration on the femtosecond timescale. With a fs intense laser one can produce a coherent X-ray pulse. Prof. T.&nbsp;Tajima suggested utilizing these coherent X-rays to drive the acceleration of particles. When such X-rays are injected into a crystal they interact with a metallic-density electron plasma and ideally suit for laser wakefield acceleration. In numerical simulation of authors, performed according to idea of Prof. T.Tajima, on wakefield excitation by a X-ray laser pulse in a metallic-density electron plasma the accelerating gradient of several TV/m has been obtained. It is important to form bunch with small energy spread and small size. The purpose of this paper is to show by the numerical simulation that some precursor-laser-pulse, moved before the main laser pulse, controls properties of the self-injected electron bunch and provides at certain conditions small energy spread and small size of self-injected and accelerated electron bunch.</p> Vasyl Maslov, Denys Bondar, Iryna Levchuk, Ivan Onishchenko ##submission.copyrightStatement## https://periodicals.karazin.ua/eejp/article/view/13505 Tue, 30 Jul 2019 00:00:00 +0300 Uniform Focusing of Sequence of Relativistic Positron Bunches in Plasma https://periodicals.karazin.ua/eejp/article/view/13506 <p>Plasma-based accelerators sustain accelerating gradients which are several orders greater than obtained in conventional accelerators. Focusing of electron and positron beams by wakefield, excited in plasma, in electron-positron collider is very important. The focusing mechanism in the plasma, in which all electron bunches of a sequence are focused identically, has been proposed by authors earlier. The mechanism of focusing of a sequence of relativistic positron bunches in plasma, in which all positron bunches of sequence are focused identically and uniformly, has been investigated in this paper by numerical simulation by 2.5D code LCODE. Mechanism of this identical and uniform focusing involves the use of wave-length λ, which coinciding with double longitudinal dimension of bunches λ=2D<sub>b</sub>, the first bunch current is in two times smaller than the current of the following bunches of sequence and the distance between bunches equals to one and a half of wavelength 1.5λ. We numerically simulate the self-consistent radial dynamics of lengthy positron bunches in homogeneous plasma. In simulation we use the hydrodynamic description of plasma. In other words the plasma is considered to be cold electron liquid, and positron bunches are aggregate of macroparticles. Positron bunches are considered to be homogeneous cylinders in the longitudinal direction. Positrons in bunches are distributed in radial direction according to Gaussian distribution. It is shown that in this case only first bunch is in the finite longitudinal electrical wakefield E<sub>z</sub>¹0. Other bunches are in zero longitudinal electrical wakefield E<sub>z</sub>=0. Between bunches of this sequence longitudinal electrical wakefield and radial force are not zero E<sub>z</sub>¹0, F<sub>r</sub>¹0. The focusing radial force in regions, occupied by bunches, is constant along each bunch F<sub>r</sub>=const. Between bunches the radial force is inhomogeneous F<sub>r</sub>¹const. All positron bunches of sequence are focused identically and uniformly.</p> Vasyl Maslov, Denys Bondar, Iryna Levchuk, Sofiia Nikonova, Ivan Onishchenko ##submission.copyrightStatement## https://periodicals.karazin.ua/eejp/article/view/13506 Tue, 30 Jul 2019 00:00:00 +0300 Formalization of Cognition Process as an Additional Component Responsible for Development of Theoretical Physics https://periodicals.karazin.ua/eejp/article/view/13507 <p>Theoretical physics has attained stage when new methodological approaches should be taken into considerations.&nbsp;In particular they should introduce larger discipline in theoretical speculations. In this paper one introduces concept of cognition manifold as methodological framework for development of&nbsp;description of reality by theoretical physics with the aid of theoretical speculations. One assumes that this is a way for constructing fundamental and universal physical theories. The cognition manifold is&nbsp;composed of basis which represents models of our space as a medium and bres representing models&nbsp;of processes in corresponding space. Models are based on accessible experimental results and also on&nbsp;new assumptions and hypotheses obtained by theoretical speculations. In order to maintain dyscipline&nbsp;in these speculations one considers status of assumptions and theories spanned on cognition manifold&nbsp;as a function defined on elements of fibres. One accentuates importance of selforganizing reasoning as&nbsp;more appropriate for recognition of reality in comparison with precise pure mathematical proof. One&nbsp;considers also proof with respect to reality. This paper is considered as an attempt to formalization&nbsp;of cognition process what is manifested by three main components: cognition manifold, status of assumptions&nbsp;and theories and concept of selforganizing reasoning.</p> Jaroslaw Kaczmarek ##submission.copyrightStatement## http://creativecommons.org/licenses/by/4.0 https://periodicals.karazin.ua/eejp/article/view/13507 Tue, 30 Jul 2019 00:00:00 +0300 A.I. Akhiezer Institute of Theoretical Physics https://periodicals.karazin.ua/eejp/article/view/13508 <p>Development Strategy of the Institute of Theoretical Physics Akhiezer (hereinafter - ITF) has also passed the test of time: the institute has managed to keep up-to-date scientific directions and the continuity of the leading scientific schools of the UFTI - KIPT. Of course, there were problems. But a serious international ITF rating helped him to resist in the difficult post-Soviet era, and in modern times. The focus of today's ITF is the development of current and advanced frontiers of modern physical science. But most importantly, all the research departments of the ITF have in their staff talented (and very initiative) young scientists, despite the fact that the past years have not very much favored the influx of young people into science. Moreover, their creative achievements were marked by scientific awards of both domestic and international level. The truth that is professed in the ITF: the main thing is not only to accumulate knowledge and experience, but also to pass them on to a worthy change. The fact that the relations in the team are humanly built friendly and democratically helps very well. And it is already obvious: the ITF has withstood the competition in the post-Soviet space and has accumulated a solid scientific potential. Today, the scientific ideology of the ITF is its traditions.</p> Alla Tanshyna ##submission.copyrightStatement## https://periodicals.karazin.ua/eejp/article/view/13508 Tue, 30 Jul 2019 00:00:00 +0300