East European Journal of Physics

5-10

Authors: Nataliia S. Goloskubova, Yuri V. Mikhlin

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.

19-26

Authors: Olga Zhytniakivska, Uliana Tarabara, Kateryna Vus, Valeriya Trusova, Galyna Gorbenko, N. Gadjev, Todor Deligeorgiev

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.

33-38

Authors: Mykhailo M. Solovan, Taras T. Kovaliuk, Pavlo D. Maryanchuk

The paper presents the results of studies of the effect of silicon surface treatment on the electrical and photoelectric properties of nanostructured MoOx/n-Si heterojunctions. The nanostructured heterojunctions MoOx/n-Si, were prepared by deposition of thin films of molybdenum oxide (n-type conductivity) by reactive magnetron sputtering in the universal vacuum system Leybold Heraeus L560 on the nanostructured silicon substrates (n-type conductivity), which were made by chemical etching with the assistance of silver nanoparticles. Dark and light volt-ampere (I – V) characteristics of the heterojunctions under study were measured, the value of the potential barrier height, the values of the serial Rs and the shunt Rsh 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 Rs and shunt Rsh 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 MoOx/n-Si was carried out at illumination by white light with intensity Popt = 80 mW/сm2. It was established that the heterostructure No.5 MoOx/n-Si with grown nanowires and etched silver nanoparticles has a maximum open-circuit voltage Voc = 0.17 V, short-circuit current density Isc = 10 mA/cm2. The possibilities of using the obtained heterostructures as photodiodes were analyzed.

46-51

Authors: Natalia Yu. Filonenko, Alexander I. Babachenko, Ganna A. Kononenko

In the paper we obtained the expression of cementite free energy and determined the solubility of manganese and silicon in Fe3C cementite depending on the temperature. Investigation was carried out for alloys with carbon content of 0.55-0.60 % (wt.), silicon content of 0.95-1.0 % (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 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 % (wt.), silicon of 0.97 % (wt.) and manganese of 0.85 % (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 % of the volume. In the alloys we revealed the highly dispersed inclusions of Fe2.7Mn0.3C, Fe0.25Mn1.4C0.6 and Fe9SiC0.4 carbides, whose volume ratio was up to 1.5 %, 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 % (atoms). Manganese can replace up to 12 % of iron atoms, and silicon can replace up to 4.5 % of iron atoms, depending on temperature. The calculated data obtained in this paper are in good agreement with those found experimentally by other authors.

58-63

Authors: Viktoriia V. Lisovska, Tetiana V. Malykhina, Valentina O. Shpagina, Ruslan M. Timchenko

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 239PuBe neutron source. The model of the source of fast neutrons has been developed. 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. 109 neutrons were used as primary particles emitted isotropically, and we used our simulation results of 239PuBe neutron source to describe the initial energy spectrum. The created model of 239PuBe neutron source can be used for the investigation of scintillation detectors Bi4Ge3O12, CdWO4, Gd2SiO5 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 239PuBe neutron source, using Bi4Ge3O12 or CdWO4 scintillators is more preferable. Results of the virtual nuclear physical experiments satisfy the published experimental data.

69-74

Authors: Vasyl I. Maslov, Denys S. Bondar, Iryna P. Levchuk, Sofiia A. Nikonova, Ivan M. Onishchenko

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=2b, 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 Ez0. Other bunches are in zero longitudinal electrical wakefield Ez=0. Between bunches of this sequence longitudinal electrical wakefield and radial force are not zero Ez0, Fr0. The focusing radial force in regions, occupied by bunches, is constant along each bunch Fr=const. Between bunches the radial force is inhomogeneous Frconst. All positron bunches of sequence are focused identically and uniformly.

113-116

Authors: Alla Tanshina

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.