Table of contents

The International Conference PhysicA.SPb was held 19-23 October 2020 in Saint-Petersburg, Russia. The Conference continues the tradition of Saint-Petersburg Seminars on Physics and Astronomy originating from mid-90s. Since then PhysicA.SPb maintains both scientific and educational quality of contributions delivered to the audience. This is the main feature of the Conference that makes it possible to combine the whole spectrum of modern Physics and Astronomy within one event.

PhysicA.SPb/2020 has brought together over 400 academics from many universities and research institutes across whole Russia as well as from UK, Japan, South Africa, China, Armenia, Belarus, Azerbaijan, Netherlands and France. Oral and poster presentations were combined into well-defined sections among which one should name Astronomy and Astrophysics, Optics and spectroscopy, Physics of ferroics, Nanostructured and thin-film materials, Mathematical physics and numerical methods, Devices and materials for the THz and microwave ranges, Biophysics, Optoelectronic devices, Surface phenomena, Physics and technology of energy conversion, Plasma physics, hydrodynamics and aerodynamics, Nuclear and elementary particle physics, Impurities and defects in solids, and Physics of quantum structures.

This issue of the Journal of Physics: Conference Series presents the extended contributions from participants of PhysicA.SPb/2020 that were peer-reviewed by expert referees through processes administered by the Presiders of the Organising and Program Committees to the best professional and scientific standards. This was made possible by the efforts of the Sectional and Technical Editors of this Issue: Prof. Petr Arseev (Lebedev Physical Institute), Prof. Alexander Ivanchik (Ioffe Institute), Prof. Polina Ryabochkina (Ogarev Mordova State University), Prof. Yuri Kusraev (Ioffe Institute), Dr. Sergey Nekrasov (Ioffe Institute), Dr. Nikolay Bert (Ioffe Institute), Dr. Nikita Gordeev (Ioffe Institute), Dr. Alexey Popov (Ioffe Institute), Dr. Prokhor Alekseev (Ioffe Institute), Dr. Mikhail Dunaevskii (Ioffe Institute), Dr. Kirill Zaytsev (Prokhorov General Physics Institute), Dr. Alexandra Kalashnikova (Ioffe Institute), Dr. Evgenia Cherotchenko (Ioffe Institute) and Prof. Dmitry Khokhlov (Moscow State University).

The Conference is supported by the Russian Foundation for Basic Research (grant no. 20-02-22042).

The Editors: Nikita S. Averkiev, Sergey A. Poniaev and Grigorii S. Sokolovskii

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

• Type of peer review: Single-blind

Single-anonymous: authors' identities are known to the reviewers, reviewers' identities are hidden from authors

Double-anonymous: author and reviewer identities are hidden to each other

Triple-blind: author and reviewer identities are hidden to each other, and from the Editor(s)

Open: author and reviewer identities are known to each other

• Describe criteria used by Reviewers when accepting/declining papers. Was there the opportunity to resubmit articles after revisions?

The main criteria used by Reviewers when accepting/declining papers were the novelty of the research, its technical merit, scientific value and originality. Additionally, submissions were ranked basing on content, length, and language. In most of cases, the authors had the opportunity to resubmit articles after revisions.

• Conference submission management system: https://physicaspb2020.iopconferenceseries.rivervalleytechnologies.com/

• Number of submissions received: 328

• Number of submissions sent for review: 273

• Number of submissions accepted: 254

• Acceptance Rate (Number of Submissions Accepted / Number of Submissions Received X 100): 77.4%

• Average number of reviews per paper: 1

• Total number of reviewers involved: 391

• Any additional info on review process (ie plagiarism check system): All submissions were checked for plagiarism with Antiplagiat (#1 plagiarism detection system in Russia) https://www.antiplagiat.ru/

• Contact person for queries: Prof Grigorii Sokolovskii gs@mail.ioffe.ru

The radiation transport problem in the plane–parallel medium with the large velocity gradient is considered. The Sobolev approximation is used. The effects of continuum absorption and line overlap are taken into account. The photon loss probability functions are calculated and tabulated. Two calculations are performed – for the Gaussian spectral line profile and for the rectangular profile. It is shown that at particular choice of the rectangular profile width the results of the calculations are very close. The evaluated photon loss probability functions may be used in the calculations of energy level populations of OH molecule in the interstellar gas flows.

The observations of the pulsar wind nebulae (PWNe) indicate the presence of efficient acceleration of positrons and electrons in these sources. The Fermi acceleration in the colliding shock flows can explain the observed hard synchrotron emission spectra of PWNe with bow shocks (BSPWNe). This may result in their maximal luminosities in the far ultraviolet range (FUV; 1250 — 2000 Å, ∼ 6 — 10 eV) due to the synchrotron emission of pairs rather than due to the thermal emission of the shocked interstellar matter. Fine spectroscopic observations of sufficiently bright sources with Hubble Space Telescope could be applied to distinguish between these two scenarios. In this paper we simulate BSPWNe flows structure with the relativistic magnetohydrodynamic code PLUTO, consider particle transport and their synchrotron emission for a number of BSPWNe. We calculate the synchrotron FUV luminosities of these BSPWNe and discuss the prospective of their observation in FUV. We also consider possible contribution of PSR J1741-2054 to the positron excess detected by AMS-02 and PAMELA.

We present a preliminary analysis of spectral evolution of 35 long bright gamma-ray bursts (GRBs) detected by Konus-Wind instrument. From the temporal and spectral analyses of the sample, we investigate the evolution of parameters of the smoothly joined broken power-law spectral model (the Band "GRB" function), in particular, we analyse hardness-intensity correlation within a burst. We show that the bulk of bursts exhibit E_p ∝ F^γ relation with the slope γ ∼ 0.3−0.5, where E_p is the vF_v spectrum peak energy and F is the energy flux; while a number of events have the smooth initial phase with strong spectral evolution with γ ≳ 1. Finally, we discuss derived the Band function parameters and their evolution pattern in the framework of GRB emission models.

An analysis of the isotopic composition of nuclei in galactic cosmic rays (GCR) in the orbital experiment of the PAMELA collaboration allows us to study the problems of the origin and propagation of cosmic rays in the Galaxy. Due to the high statistical and methodological accuracy, the data of the PAMELA magnetic spectrometer provided significant progress in studying the isotopic composition of light nuclei from H to Be in the GCR in the energy region of ∼ 0.1-1 GeV / nucleon and for the first time made it possible to estimate the contribution of local sources from close ones to the GCR (∼ 100 pc) of recent (∼ 10⁶ yrs) supernova explosions. To date, the isotopic composition of carbon nuclei in the GCR has been measured only for the ¹³C / ¹²C ratio in the energy region ∼ 0.05-0.13 GeV / nucleon in the VOYAGER 1.2 space experiment and the upper limit for the ¹⁴C / ¹²C ratio was estimated in the ACE / CRIS experiment for energies 0.12-0.43 MeV / nucleon. In this work, using PAMELA flight data 2006-2014, on the rigidity of the detected nuclei and their speed (time-of-flight analysis and ionization losses in the multilayer calorimeter of the device), an attempt was made to determine the isotopic composition of carbon nuclei in the energy region of ∼ 0.1-1 GeV / nucleon. The half-life of ¹⁴C nuclei is 5730 years and can be detected in the case of a supernova explosion in the last ∼ 5 10⁴ years at a distance of ∼ 100 200 pc. The results of isotope analysis of carbon nuclei in GCR (spectra ¹²C, ¹³C, ¹⁴C and ¹⁴C / ¹²C - ratio depending on the rigidity and energy of the nuclei) in comparison with the existing measurement data will be presented.

The entrainment matrix is an important parameter of superfluid hydrodynamics and is extensively used to model, e.g., neutron-star oscillations and glitches. Here we present a detailed step-by-step algorithm to calculate this matrix for a series of modern BSk energy-density functionals. Using it, both the entrainment matrix and equation of state can be determined self-consistently, within the same microscopic approach.

The data on the content of cosmogenic isotopes ¹⁴C and ¹⁰Be in the Earth's atmosphere at a time interval of 15000-5000 BC were analyzed. On Earth at this time there was a transition from the ice age to the Holocene. The reconstruction of Wolf numbers based on radiocarbon data is presented, which describes solar activity and takes into account changes in the Earth's climate during the period under consideration. The increase in global temperature during the transition to the Holocene was accompanied by a sequence of warming (for example, Meiendorf warming) and cooling. The obtained reconstruction of Wolf numbers indicates that at separate time intervals: 13600-13000, 9300-9000, 8300-8000 BC the Sun was in a state of deep minima of activity. We also note the activity minima at ≈ 10700 and 7500 BC. The periods of extremely high activity of the Sun were also distinguished, so at maxima ≈ 12350 and 6715 BC. Values of Wolf numbers could exceed 200. The duration of the first of these periods was several hundred years, and at that time Meiendorf warming took place on Earth (≈12500-11850 BC). The question arises: are these events related?

Eleven proxy records of Northern Fennoscandia and North Atlantic climate variability were analyzed. Correlation of climatic records with (a) a quasi 11-year solar cycle of Schwabe, (b) a quasi 22-year solar cycle of Heil, (c) a quasi 20-year planetary-tidal cycle, related to wobbling of the Sun around the baricenter of the solar system, has been studied. A weak but stable and statistically significant correlation between the climatic proxies of Northern Fennoscandia and a double solar cycle was found to be present through the AD 1700–2000. No evidence of a connection between climatic records and both solar Schwabe cycle and quasi 20-year astronomic cycle were found. Possible physical mechanisms behind the revealed effect are discussed.

The work is devoted to the study of the characteristics of the PING-M hard x-ray polarimeter using its physical model (PING-P FM). The PING-M instrument is developed jointly by the Moscow Engineering Physical Iinstitute and the Ioffe Institute for the mission "Interhelioprobe". The operation of the device is based on Compton scattering. The degree and direction of linear polarization are determined by measuring the asymmetry of the scattered radiation field. The device uses active scatterers that register the Compton recoil electron. A useful event is the case when two impulses in the detector-scatterer and in the detector-receiver of scattered radiation coincide. The physical model represents the detector part of the polarimeter. It contains three scatterers and six receivers of scattered radiation – a total of 18 pairs of detectors oriented at different azimuthal angles. As a result of the experiments, the dependences of counting rates in pairs of detectors on the positional angle of the polarization plane of the incident radiation were measured. The modulation depth of this dependence determines the sensitivity of the device to the polarization degree. The sensitivity of the device is estimated.

We study the cosmic rays (CR) positrons propagation from the near Earth Geminga pulsar wind nebula on the basis of a analytical model of the two-zone spherically symmetric particle diffusion from a central source. We calculate the near Earth spectral distribution of positrons originating from the pulsar. The obtained spectra are compared with the results of another authors considering the problem of the positron excess revealed by PAMELA and AMS-02 experiments.

The data on the concentration of ions in the core of the Greenland Ice Sheet Project 2 (GISP2) were analysed to find the cause of storm activity in the north-west Atlantic during the Holocene. It was shown that there is cyclical transfer of ionic components with a period of ∼ 2700 years due to changes in storm activity. As a possible cause of storm changes, secular variations in the position of the geomagnetic pole over the past several thousand years have been considered. In particular, the periodicity of fluctuations in the longitude of the north geomagnetic pole was compared with the frequency of intensification of storm activity. It has been demonstrated that the spectra of these variations are similar, from which it is concluded that secular variations in the magnetic field are the basis of the processes that determine the variability of storm activity and climate in the north-west Atlantic during the Holocene.

In January 2005, a series of powerful Solar Proton Events (SPEs) associated with an increase of flare activity on the Sun was observed. Increases of solar proton fluxes with energies 165-500 MeV allowing particles to reach stratospheric altitudes (∼30 km and below) were registered during the events starting on 15, 16 and 17 January. The strongest event, with particle energies exceeding 500 MeV, took place on 20 January and was accompanied by an increase of the neutron monitor counting rate (Ground Level Enhancement). The events under study resulted in a considerable increase of stratospheric ionization. In this work an impact of these events on intensity of the stratospheric polar vortex playing an important part in the mechanism of solar-atmospheric links is studied. A noticeable intensification of the vortex (increase of western wind velocity) was revealed at all the stratospheric levels in the course of the SPE series under study. It was shown that auroral activity (precipitations of auroral electrons generating bremsstrahlung X-rays) is also a possible factor of the vortex intensification. The obtained results provide evidence that ionization changes associated with powerful SPEs and auroral activity may influence the state of the stratospheric polar vortex on the day-to-day time scale. A possible cause of the vortex intensification seems to be temperature variations associated with changes of chemical composition of the polar stratosphere due to ionisation changes.

The data obtained by the BAT γ-ray telescope on board the SWIFT satellite in the energy range of 15-350 keV with a time resolution of 64 ms were used to study the temporal structure of the γ-ray burst GRB 190114C emission by means a modified spectral analysis technique. The analysis revealed quasi-periodic fluctuations with main periods of 3.84 s and 2.24 s. Both oscillations start simultaneously, continue throughout of the burst, and are equally modulated. Based on this evidence, it can be argued that all three episodes of the burst were controlled by one "central engine".

Evolution of the cosmic microwave background (CMB) temperature with redshift ${T}_{\text{CMB}}={T}_{\text{CMB}}^{0}\times (1+z)$ is predicted by the standard ΛCDM cosmological model and has been confirmed by measurements of the Sunyaev-Zel'dovich effect in Plank data (at z ≤ 1) and excitation of CO rotational levels in quasar spectra (at 1.7 ≤ z ≤ 2.7). Excitation of the fine-structure levels of neutral carbon (C_I) is also sensitive to the temperature of the CMB radiation. However collisions and UV pumping lead to a significant degeneracy of the fitting parameters, since poor data on physical conditions. We found that a joint fit to excitation of low H₂ rotational and CI fine-structure levels can break this degeneracy and provide a tighter constraints on the T_CMB. We present estimates of the T_CMB derived from excitation of C_I fine-structure levels in the Milky Way clouds and high redshift absorption systems.

A one-dimensional quasi-linear beam relaxation leads to the formation of a plateau-like electron distribution function. Of greatest practical interest is the case when the initial velocity of the beam v₀ greatly exceeds the thermal velocity of the plasma electrons V_T, and the initial velocity spread in the beam ∼Δv₀ is small compared with v₀. These conditions are usually met for solar flares. The article deals with the features of the energy spectra and polarization of hard x-ray radiation (HXR) in the energy range of 20 -150 keV generated by electrons with a plateau-like electron distribution function. Calculations in the framework of a thick target take into account not only the energy losses of electrons interacting with plasma particles, but also changes in their angular distribution. It is shown that the break down energy of the electron spectrum leads to changes in HXR spectra, as well as the degree of linear polarization. There is a characteristic softening of the spectrum near the break-down energy. HXR polarization increases with quanta energy and can reach tens of percent.

The article describes a method for absolute calibration of the photon detection efficiency of the OnSemi/SensL MicroFJ-60035 silicon photomultiplier by the Newport Power/Energy Meter 841-PE with the 883-UV photodiode sensor head, and the PicoQuant PLS-270 fast diode source of 277 nm ultraviolet emission. The dependences of the power of the detected emission and the number of ultraviolet photons on the distance to the source were obtained. The photon detection efficiency of the silicon photomultiplier was measured to be approximately 8% compared to the 9.6% level claimed by the manufacturer. It was also shown that, within the experimental setup, absorption of the 277 nm emission at paths in the air shorter than 1 m is not significant, and the angular distribution of the emission source is homogeneous. The obtained three-dimensional calibration surface of the dependence of the irradiance on the distance to the detector and the source intensity will be employed for development of a novel camera of the TAIGA-IACT telescope array.

This paper aims at the creation of a selenocentric catalogue of lunar objects' positions (SCLOP) and development of a theoretical simulation model of orbital referencing of lunar objects taken by space lunar satellite to the selenocentric coordinate system defined by SCLOP. The data produced by the modern space lunar missions serve as the basis for multi-parameter and highly accurate digital simulation model. The results obtained in the work are important and relevant for the development of navigation technologies on creation and orienting of coordinate systems and the study of celestial bodies' figures. To solve the problems stated in this work, the following new results are produced: a) reliability of coordinate data in modern systems of coordinate and time support for lunar objects is investigated by the robust analysis; b) a method and a software complex for transforming selenographic coordinates (TSC) are developed; c) the software package is tested for work with navigation data and determining planetary parameters; d) a method of adaptive regression modeling (ARM) for transforming coordinate systems and assessing structures and parameters of the selenocentric system (SS) is created; e) an algorithm of multi-parameter identification of SS based on ARM-approach is developed to carry out works on expansion and estimation of the reference selenocentric system; f) a global dynamic selenocentric system is constructed on the basis of optical observations taken at "Clementine", "LRO", and "Apollo" missions; g) as a result, a simulation digital model of orbital referencing of lunar objects optical observations, taken by star sensors of lunar satellite and on-board laser interferometer, to the selenocentric coordinate system is developed.

The neutron stars crust and white dwarfs consist of a degenerate relativistic electron gas and atomic nuclei arranged into a crystal lattice. The type of lattice that ions form may depend on many parameters, for example, on the external magnetic field, temperature (T), and ion number density (n). In this paper, we consider the effect of electron background polarization on the type of lattice at T = 0. Two approximations are used to describe this background. If it is described by the Thomas-Fermi model, the influence of polarization is determined only by the parameter κ_TFa, where κ_TF is the Thomas-Fermi wave number, a = (4πn/3)^−1/3 is the radius of the ion sphere and at κ_TFa ⋦ 1 the bcc lattice has the lowest energy. On the other hand, if we use the random-phase approximation for the electron dielectric function, the energy of the static lattice will be a function of κ_TF and the relativistic electron parameter x_r. In this case, the bcc lattice possesses the lowest energy at κ_TFa < 0.28 and any x_r, while at higher κ_TFa the formation of other lattice in consideration (fcc and hcp) is possible.

This work considers the analysis of libration dynamics of the planets' moons. To study such processes, it is necessary to use methods for investigating complex systems, as an influence from neighboring celestial bodies on spin-orbital motion of a moon should be taken into account. This fully applies to the Moon's rotation about its axis. The construction of modern theories of the physical libration of the Moon (PhLM) is based on gravimetric, seismic, satellite observations, and lunar laser ranging, which in its turn has allowed to increase the accuracy by several orders of magnitude compared to the PhLM theories of the end of the 20th century. To satisfy the modern requirements for accuracy of the physical libration theory, it is necessary to apply a precise ephemeris of the Moon's motion. In this paper, the DE421 modern numerical ephemeris is analyzed. The features of its construction and practical application are studied. The accurate values of ephemeris parameters are produced and an algorithm for determining the Moon's center of mass coordinates and establishing the angles of physical libration on the basis of DE421 is developed. As a result, a comparative analysis of the physical libration angles with the values produced by the analytic theory of physical libration is conducted. The calculations are made over a time period of 800 years. The comparative analysis shows that significant differences in the ephemerides of 15 and 80 arc seconds in longitude and latitude respectively are caused by the planets' gravity field, and those impacts should be considered when working with the analytic ephemeris.

In this paper, the work on investigating fractal structures on Venus was performed on the basis of observations taken by the "Magellan" spacecraft (NASA). The uncertainties in some data produced by "Magellan" were filled by the information that had been collected before – in "Venera 15", "Venera 16", and "Pioneer" missions. During the implementation of the work a digital map of Venus' surface was built, and its spatial model was created. It is worth noting that the choice of basic level surface on Venus is defined by a certain value of potential or a point on its surface through which the geoid passes. The model of Venus' physical surface was created use the harmonic expansion into spherical functions of altimetry data the "Magellan" mission. In the present paper, for determining and analyzing fractal dimensions the Minkowski mathematical algorithm, which is a simplified option of Hausdorff-Besicovitch dimension and provides high reliability and accuracy, was used. As a result, fractal correlations of Venus' geoid anomalies in both longitude and latitude as well as the mean value of fractal dimensions were calculated. The following values of mean fractal dimension for Venus surface are obtained: in latitude – D_β = 1.003; in longitude – D_λ = 0.98. Based on these values, we may conclude that the topographic model of Venus' physical surface is close to spherical figure. The comparison between the obtained Venus fractal parameters with the ones of the Earth shows the good agreement.

A connection between solar activity and decadal Length of day variations is investigated. Statistical comparison of Length of day with various geomagnetic and Solar activity indices has been done for the last 140 years. A jump in Length of day (LOD) is found at the moment of the geomagnetic storm, the largest one for the last few decades, that happened in late October 2003, the so called Halloween storm. This change in rotational velocity of the Earth can not be explained by any known atmospheric or oceanic influences. Moreover, such jump in LOD is an unique one for the few recent years. It is supposed that this jump can be caused by transfer of angular momentum between Solar wind and the solid Earth. A possible mechanism of such a transfer is proposed.

The influence of positronium photoionization rate on the heating of PSR J0250+5854 polar cap is considered. It is assumed that the polar cap is heated only by reverse positrons accelerated in pulsar diode. It is supposed that pulsar diode is located near the star surface (polar cap model) and operates in the steady state space charge-limited flow regime. The influence of a small-scale magnetic field on the electric field inside the pulsar diode is taken into account. The reverse positron current is calculated in the framework of two models: rapid and gradually screening. To calculate the production rate of electron-positron pairs we take into account only the curvature radiation of primary electrons and its absorption in magnetic field. It is assumed that some fraction of electron-positron pairs may be created in bound state that can later be photoionized by thermal photons from star surface.

The effect of weakly supersonic flow on two-tori pulsar wind nebula is considered. It is shown that the flow going past the nebula does not destroy its two-tori structure, but, on the contrary, contributes to its stability. Under the effect of the flow, the windward and the leeward polar outflows in the nebula operate at drastically different conditions. In the result, two opposite jets of the nebula which form within these polar outflows may differ in their dynamics and appearance. Our work bears implications for the Vela pulsar wind nebula, which interacts with a supersonic flow of Mach number ∼ 1.3 produced by the reverse shock of its parent supernova.

We study the effects of diffusion on damping of oscillations in the neutron star cores. This dissipation mechanism is usually ignored in the literature. As we show, the effect of diffusion is always smaller than viscous dissipation if the normal (nonsuperfluid and nonsuperconducting) matter of neutron stars is considered. However, we argue that for superconducting stars the role of diffusion may increase.

In this work, using multi-parameter harmonic analysis and expansion of altimetry into spherical functions, models of the Moon's physical surface (digital lunar selenocentric map - DLSM) are built, and a comparison of similarity of chosen local areas of the complex lunar structure is performed. The constructed DLSM have radius-vectors of the surface points in accordance with the space measurements taken. As result, the averaged fractal dimension of the selenocentric surfaces profiles models was found to 1.345. The similarity and difference parameters were determined by the author's method using fractal similarity coefficients. The analysis of macrosurfaces based on multi-parameter and fractal methods for the selenocentric models built in this work has not been conducted before.

Neutron star crust consists of highly neutron excess nuclei, which are inaccessible for laboratory experiments. In the deepest region of the crust (so-called inner crust, located after the neutron drip) atomic nuclei are immersed into the sea of degenerate unbound neutrons. Study of the crust structure and equation of state in such conditions relies on the theoretical nuclear mass models. In particular, it is convenient to use the compressible liquid drop model, which contains the surface tension term. A thermodynamically consistent description must take into account adsorption of neutrons on the nucleus surface (neutron skin) and dependence of surface tension on matter properties in two-phase equilibrium. We calculate the surface tension of nuclear matter by the extended Thomas-Fermi approach. For this aim, we parametrize the number density profile of the two-phase system by Fermi-Dirac type functions, totally containing 5 parameters, and minimize the thermodynamic potential Ω to obtain equilibrium configuration. We use Skyrme-type nuclear interactions SLy4 and BSk24, fulfilling experimental data of atomic nuclei, observational constraints on the maximal neutron star mass and theoretical calculations of high-density nuclear matter. The results are presented as a function of neutron chemical potential, which is useful for compressible liquid drop models in the inner crust of a neutron star.

The Tunka-Grande and TAIGA-Muon arrays are the part of a single experimental complex, which also includes the Tunka-133 and TAIGA-HiSCORE (High Sensitivity COsmic Rays and gamma Explorer) wide-angle Cherenkov arrays, TAIGA-IACT array (Imaging Atmospheric Cherenkov Telescope) and Tunka-Rex radio antennas array (Tunka Radio Extension). This complex is located in the Tunka Valley (Buryatia Republic, Russia), 50 km from Lake Baikal. It is aimed at investigating the energy spectrum and mass composition of charged cosmic rays in the energy range 100 TeV - 1000 PeV, searching for diffuse gamma rays above 100 TeV and studying local sources of gamma rays with energies above 30 TeV.

This report outlines 3 key points. The first is a description of the Tunka-Grande and TAIGA-Muon scintillation arrays. The second part presents preliminary results of the search for diffuse gamma rays with energies above 50 PeV according to the Tunka-Grande data. The third part is devoted to the prospects of the search for diffuse gamma rays with energies above 100 TeV using the TAIGA-Muon array.

Relativistic plasma outflows are observed in gamma-ray burst sources, jets of active galactic nuclei, pulsar wind nebulae and supernovae explosions. Magnetohydrodynamical (MHD) shock waves inevitably result from interactions of such relativistic outflows with the ambient interstellar matter. The widely used single-fluid MHD description of relativistic shock waves is the main tool to study the global structure of such objects. However, to justify the validity of the global MHD models and to interpret the observed emission spectra of space objects with relativistic shocks, a kinetic description of electrons, positrons, and ions at microscales is needed. We model a plane relativistic shock propagating transverse to a regular magnetic field in the electron-ion plasmas with imposed turbulent fluctuations in the shock upstream. Namely we study the effect of the micro-scale plasma processes on macroscopic parameters of the mildly-relativistic shocks as the adiabatic index of the relativistic fluid in the shock downstream. The adiabatic index is a macroscopic parameter of the single-fluid MHD models commonly used for shock modeling at much longer hydrodynamical scales and it is especially important for the MHD modeling of the mildly-relativistic shocks.

One of the most important features of the Universe in studies of evolution of the early Universe is conservation of entropy of particles being in thermal contact with each other in comoving volume. Destruction of any particles (for example, annihilation of electrons and positrons) or thermalization processes lead to transfer or sharing of entropy. In this paper hypothetical process of occurrence of thermal contact between photons and axions in the early Universe is considered to examine the effect of the process on yields of D,⁴He and ⁷Li in Primordial Nucleosynthesis. It is found that change in photon entropy caused by thermalization of photons and axions lead to stronger overlapping between the intervals of acceptable values of η for ⁴He and ⁷Li. At the same time interval of acceptable values of η for D/H is shifted in opposite direction relatively to ⁴He.

This work is dedicated to the modern and relevant problem of predicting the Earth's pole motion. Using regression modelling, we form a complex model, consisting of a set of optimal mathematical structures each describing the dependence of its step's remnant on time. The comparison between the results produced in this paper with other works on the study of North pole dynamics has shown that the models obtained using adaptive regression modelling (ARM) approach allows predicting the Y-coordinate more accurately while conserving the accuracy of the X-coordinate. Our results confirm the promise of using the so called adaptive dynamic regressions developed currently for describing the Earth's pole position's dynamics. The ARM-approach compared to the classic methods for analyzing time series has a number of advantages: 1) an expansion of the concept of a mathematical model's structure describing a certain dynamics could be performed; 2) the oscillations' harmonics stable in time are isolated; 3) the accuracy of predicting changes over a certain time period increases several times, which has an important practical value.

The recent discoveries in multi-messenger astronomy allow us to study the Universe in a new way. The Advanced LIGO and Advanced Virgo gravitational-wave (GW) detectors have opened the possibility for regular detection of transients from compact binary merger events. The Konus-Wind (KW) spectrometer continuously observes the whole sky and enables searches for transient events over various timescales from milliseconds to hours. It provides a unique opportunity to study high energy transients, in particular, gamma-ray counterparts to gravitational wave detections. In this paper, we present the methodology and results of the search for gamma-ray counterparts to 56 GW events in KW data. While no counterpart candidate was found in our search, we report upper limits on soft gamma-ray emission from these events, including several events not observed by other wide-field high-energy instruments such as Fermi-GBM, INTEGRAL-SPI-ACS and Swift-BAT. We finally discuss the potential of KW to detect bursts as weak as GRB 170817A.

We present constraints on physical conditions in diffuse HD/H2-bearing molecular clouds using measured HD/H₂ column density ratio. We used recently published formalism that describes how this ratio changes with ultraviolet field intensity, number density and cosmic ray ionization rate. Out of them the most important parameter is the cosmic ray ionization rate, as it determines the chemistry in neutral medium and is still poorly constrained in ISM. Using the result of absorption line analysis in our Galaxy and in several high-redshift systems we found that value of cosmic ray ionization rate is ${1.3}_{-0.5}^{+1.3}\times {10}^{-17}{\text{s}}^{-1}$ in our Galaxy and is few × 10⁻¹⁸ s⁻¹ in DLAs at high redshifts.

In this work, connections between UBV (PSC UBV) photometric systems for various laws of interstellar extinction are calculated on the basis of digital database on astrophysical observations of Engelhardt astronomical observatory (EAO) and using the specialized software package for analyzing brightness characteristics. The following results are obtained: 1) when using various laws of interstellar extinction, the value of difference in the position of reaction curves is proportional to the difference between UBV dependencies and color indices; 2) the positions of reaction curves and connection curves between UBV and color indices are influenced by spectral characteristics of the filters used in observations; 3) the same applies to the transformation of stellar magnitudes from one standard system to another, as response curves as a rule significantly differ; 4) another conclusion is that for any separate model of interstellar extinction the differences in color between photometric systems do not depend on spectral and luminosity classes.

In this work, the projective geometry method was used for analyzing star clusters. When carrying out the calculation procedures, it was considered that non-linear distortion factors had been removed from the measured stars' coordinates. Determination of stars' proper motions is of great practical importance, as the inertial coordinate system relies on catalogues of star positions, and it is necessary to be aware of the stellar reference marks' time shift. In the practical part of the work, the breadboard simulation of the use of the proposed method for determining stars' proper motions is performed. At the same time, it is supposed that at 90"/mm breadboard image scale the absolute values of proper motions do not exceed 0.050" over a period of 50 years. As result, determined that the standard deviation of the calculated proper motions μ_α, μ_β from their true value is 0.0065 arcseconds for the first model (when the proper motions of the reference "stars" are negligible and equal to 0) and 0.0072 arcseconds or the second model (when the reference stars do have real proper motions). These values indicate the high accuracy of the used method.

We present a spectroscopic analysis of seven Extremely Strong Damped Lyα systems at redshifts z = 2–3, obtained with the intermediate-resolution spectrograph X-shooter on the Very Large Telescope. For all systems we estimated column densities of the neutral atomic hydrogen H_I, metal abundances and dust depletion. We firmly detected molecular hydrogen H₂ in two systems in our sample; for the remaining systems we set a conservative upper limits on the H₂ column densities. The properties of the obtained systems are in consistency with the sample of the Extremely Strong Damped Ly_α systems available in the literature.

Total electron content (TEC) is one of the most important parameters of the Earth's ionosphere. This parameter determines the degree of ionization and the dispersion properties of the ionosphere. Now the most affordable way to determine ionospheric parameters is the use of radio signals from the global navigation satellite systems GLONASS, GPS, GALILEO and BDS. TEC is now being routinely monitored by global GNSS networks almost everywhere on Earth except geomagnetic poles. The observations of TEC at the Vostok antarctic station were carried out jointly by Saint Petersburg State University and Arctic and Antarctic Research Institute. Observations were started in 2016 and continued to this day with small interruptions. In this work we have processed the GNSS observations with RTKLIB and GeNeSiS software packages. As a result of this processing we have estimated the TEC from code and phase observables. The resulting TEC time series were analysed and compared to the global TEC map. A reasonable accordance with previous results has been reached. However, our results are specific to the South Geomagnetic Pole and reflect ionospheric behaviour near it. It can be seen that TEC changes more abruptly near the Geomagnetic Pole than elsewhere. These results may potentially augment our knowledge about ionosphere structure and evolution near the geomagnetic poles.

In this work, the physical parameters of near-Earth objects (NEO), i.e. small celestial bodies crossing the Earth's orbit, are investigated. First of all, the study of NEO, whose number exceeds 15 thousand, is important in terms of asteroid threats. NEO are mainly stony and iron, but also could be comet nuclei that had lost the icy component under the influence of solar radiation. As a result of analyzing 14800 near-Earth asteroids from the Apollo group, in this work near-Earth objects closely genetically related to the existing meteor showers are determined. 2002LV and 2001MG1 asteroids are the closest to the Kappa-Cygnids by orbital elements. 2014RS17, 2006BF56, 2001YB5 asteroids are the closest to the Delta-Cancrids by orbital elements. 2008VL14, 2006UF17, 2010VF, 2000DO1, 2010CF55, 2010TN55, 2007EJ88, 481482 2007CA19 asteroids are the closest to the Virginids by orbital elements. The D-criterion method was used in the analysis.

Detection of ms-spikes and quasi-periodic subsecond pulsations in the solar flare hard X-rays (HXR) provides useful information about the processes of electron acceleration and transport along the flare magnetic loops. To search for HXR pulsations, we processed the data of BATSE/CGRO spectrometer of high temporal resolution 0.016 s and 0.064 s. BATSE energy range is about 20 keV – 1 MeV. For the powerful solar flare SOL1998:08:19T21:39:21 the FFT and wavelet analysis show the presence of HXR pulsations of ∼ 0.16 – 0.25 s. BATSE data was analyzed for six energy channels 28.8 – 33.1 keV, 37.1 – 41.8 keV, 46.6 – 55.8 keV, 55.8 – 64.6 keV, 64.6 – 74.0 keV, and 74.0 – 99.1 keV. HXR-spikes were detected. The spike shape is practically triangular with FWHM about 100 ms. Simulations of kinetic models of electron transport with short pulses showed that when the duration of an individual spike is longer than ∼ 80 ms, the smearing of pulses practically does not occur. Injection pulses shorter than 30 – 60 ms are not preserved even with a strongly anisotropic distribution of accelerated electrons and a small gradient of the magnetic field. In the isotropic case at the looptop, the decay phase of the X-ray spikes becomes longer compared to the rising phase which is not true for the anisotropic case. The pulse smearing effect is stronger for the softer energy spectra of accelerated electrons.

The paper describes a new developed method of sample gasification using yeast oxidation of monosaccharides in plant tissue for ¹³C/¹²C isotope ratio mass spectrometric analysis. Variations in the carbon isotopic composition of the leaf surface have been shown; the δ¹³C value for chlorophytum varies from -37 ‰ to -32 ‰ from the tip of the leaf to its base. It has been shown first that the spectral composition of radiation affects the ratio of carbon isotopes in plant leaves: the predominance of blue component in the spectrum results in accumulation of heavy ¹³C isotope up to δ¹³C = -25 ‰.

We have investigated the molecular composition of the tooth enamel microregions in the normal and initial stages of the development of fluorosis by means of the IR and Raman spectroscopy. It has been shown that in the pathology of fluorosis, tooth mineralization takes place with the formation of calcium fluoroapaptite. It was found that an increased fluorine content causes a change in the characteristic profile of the bands and a redistribution of the intensity of the components of the υ₁ PO₄ and υ₃ CO₃ groups of the infrared and υ₄ PO₄ Raman spectra. The resulting IR and Raman spectra can be utilized as standards in the development of a new diagnostic approach of the early forms of the disease.

The study of molecular composition of the biomimetic composites on the basis of nanocrystalline carbonate-substituted (C-HAP) and polar amino acids of L-lysine hydrochloride and L-arginine hydrochloride was performed in the work. Results of the study show that the change in acidity of the medium (pH≥11.2, ≥7.55 и ≤5) occurs under transformation of the conformational environment of L-lysine hydrochloride molecules with the formation of L-lysine structure as while increase of pH level as in the presence of C-HAP nanocrystals. At the same time composites basing on L-arginine keep their amorphous structure in the presence of synthesized C-HAP in the different media. The detected differences in the molecular environment of hydrochloride forms of amino acids during the interaction with nanocrystalline C-HAP prove to be significant for the development of technology of the integration between biocomposites and hard dental tissues.

The paper presents the results of a numerical study of the flow in a symmetric model of a healthy popliteal venous valve with different leaflet elasticity. The focus is on the analysis of the stagnant area under the valve leaflet. The stagnant area under the valve leaflet, as well as behind the valve, is of great practical interest to phlebologists in terms of the possibility of blood clots. The flow in the constructed simplified model of the venous valve gave good qualitative agreement with the clinical ultrasound data for a leaflet with Young modulus of 1.2 MPa.

Recently, a number of models of polymerase chain reaction (PCR) have been proposed. In such models, the kinetics of a reaction product and a fluorescence reporter used are usually identified. An intercalation dye is one of the two ways for "real time" detection of reaction product accumulation. In this work a PCR model is proposed, with using of intercalation dye to obtain a PCR curve. The concentration of bound intercalation dye was calculated at the end of each PCR cycle. This calculation is based on an equilibrium equation for intercalation dye binding with DNA. An analysis of simulation results demonstrates a significant difference between the accumulation kinetics of the reaction product and the fluorescent signal of the bound intercalation dye.

In this paper a device that provides the nucleic acids extraction and loading into a microfluidic chip for subsequent analysis by amplification methods was performed. The device is made by soft lithography from Silastic T4. The mechanical properties of the material (Young's modulus) and the contact angle after Ar plasma treatment were studied. The strength of the connection of the device elements was evaluated. The device usability was checked by nucleic acids extraction from E.coli samples and using model solutions of the GAPDH gene cDNA.

The paper presents the results of spectral-fluorescence and diffuse-optical studies of biological tissues when exposed to a low-temperature atmospheric pressure plasma in a mixture of air with argon with an exposure of up to 10 minutes. Potential fluorophores were identified and the coefficients of optical absorption and transport scattering of biological tissues were determined. The analysis conducted allows to conclude that plasma probing leads to significant inhibition of cellular respiration and the development of coagulation effects in biological tissues.

The conception "organ-on-a-chip" is a simulation of a living organism functional unit using a microfluidic device and additional technologies. Such technology can clarify some process in human body, reactions on drugs and help to create the new way of treatment without animal models. Calcific aortic stenosis is characterized as long developing disease that is more often observed among the elderly people. "Organ-on-a-chip" via microfluidic technology can simulate some process of this disease such as the calcium salts deposition in shorter time than it happens in living human body. Moreover it can explain the nature of disease. In this work we investigated the deposition of calcium salts in vessels by imitating the processes in the microfluidic chip and mathematical modelling.

Using UV absorption spectroscopy and circular dichroism, we studied the interaction of DNA-cisplatin complexes with nonhistone chromosomal proteins HMGB1 and HMGB2. It was shown that the presence of platinum ions affected the ability of HMGB2 to form large supramolecular complexes with DNA. The role of C-terminal domain of the HMGB1/2 proteins is discussed.

The effect of sodium hypochlorite (NaClO) on nucleic acids (NAs) was investigated depending on the concentration of the NaClO. We have performed detailed analysis of the FTIR and UV spectra of the NAs incubated with NaClO. It was found that both the destruction of the secondary structure of DNA (denaturation) and the chemical modification of nitrogenous bases occur.

Expansion microscopy (ExM) is a powerful tool which allows to visualize intracellular structures with increased resolution due to physical widening of the sample. ExM resolution is comparable to that of some super-resolution microscopy techniques, but it does not require the use of complex and expensive optical equipment, thereby providing improvement in resolution even if relatively simple microscopes are used. In this work we successfully utilized ExM to visualize structures formed by FtsZ protein and DNA in Escherichia coli cells. The results of the work demonstrate that structures formed by both FtsZ and DNA are highly sensitive to the sample preparation procedure which should be optimized in each case of the ExM use.

The dependence of the yield of M. tuberculosis DNA from model solutions under the influence of megahertz ultrasound in the range from 1.2 to 3.0 W/cm² on magnetic particles was studied. The dependences of the DNA yield upon sounding for 1, 5, and 10 minutes are obtained. Under ultrasound exposure, the maximum yield is 98%, which is 39% higher than the DNA yield in the absence of a similar effect. It was shown that the efficiency of DNA extraction on magnetic particles using ultrasound is not linearly dependent on the intensity of scoring. The result of the electrophoresis of the sample after ultrasonic treatment of different intensities in megahertz for 1, 5 and 10 minutes is also shown.

This work is devoted to experimental methods for producing calcium-phosphorus compounds, including calcium hydroxyapatite, using microwave radiation. Two types of synthesis were used: template method and chemical precipitation. During synthesis, the heating time and power were changed. The obtained samples were studied using scanning electron microscopy, X-ray diffraction analysis, and the BET (Brunauer-Emmett-Teller) sorption method.

Mechanical deformations of neuronal membrane occur when exposed to an electrical pulse. A one-dimensional mathematical model of such deformations of a cylindrical cell is proposed, based on the fluid dynamics equations and the Lippmann equation connecting electric effects with the membrane strength. The model qualitatively reproduces experimentally observed effects of cell membrane mechanical deformations evoked by both an action potential moving along axon and an electric pulse injected through electrode.

In paper, using the Memory Functions Formalism, we carry out a comparative analyzing the induced neuromagnetic responses of the cerebral cortex of healthy people to the two visual flickering stimuli. At the first stage, based on the correlation coefficient, we determined the regions whose interaction (on average for the group) for different stimuli differs most strongly. Next, we analyze the phase portraits of dynamic orthogonal variables and the memory function power spectra. We have found the differences in dynamic, spectral and stochastic characteristics of the magnetoencephalogram signals of the cerebral cortex under the influence of the considered stimuli. The findings provide an opportunity for a deeper understanding of the processes of the spread of excitation in the cerebral cortex with visual stimuli.

The main component of connective tissue and human organs — collagen protein is widely used in tissue engineering, regenerative medicine and cosmetology. The new methods search for assessing the structural and qualitative characteristics of collagen is currently an urgent area. This research is devoted to analyze by FTIR spectroscopy the various structural forms of collagen during the transition from molecular to fibrillar form and also collagen fibrils destruction.

It was shown that during the formation of fibrils in the IR spectra, a peak arise with a wavenumber of 1083 cm⁻¹. The magnitude of this peak can be used to judge the degree of fibrillation of molecular collagen in vitro. It was shown that the addition of a hydrogen peroxide solution with concentrations of 0.6, 1.5, and 3% in the initial solution with fibrillar collagen leads to the destruction of fibrils, which manifests itself in a noticeable fading of the peak with a wavenumber of 1083 cm⁻¹.

Results of experimental studies on Si-W coatings fabrication by magnetron co-sputtering from two sources for electrodynamic structures in millimeter and submillimeter range of electromagnetic waves are presented. Control over sheet resistivity of the resulting coatings by varying the power of a magnetron with a tungsten target is demonstrated. Dependence of complex permittivity of Si-W coatings upon dielectric substrates on chemical composition in the frequency range of 50-70 GHz is studied.

Radiation-conductive heat transfer in a semi-transparent medium has been studied. Two methods for measuring thermal conductivity components are described. Thermal resistance of a remote reflecting surface, the thickness of radiation-conductive relaxation, the depth of penetration of thermal radiation, as well as radiant and conductive components of thermal conductivity of foamed polyethylene were measured using an aluminum foil radiation screen. The dependences of the total thermal conductivity of simple and aluminum-metalized polyester bulk non-woven canvases on the thickness to which it is compressed were measured. Radiant and conductive components of the thermal conductivity of non-woven material are calculated. It is shown how metal nanocoating of fibers reduces radiant thermal conductivity of the material.

This article presents the results of a theoretical study of a field emission cell with a vertically oriented emitter. The field emission cell was formed based on a combination of etched methods with a Ga⁺ focused ion beam and local ion-stimulated tungsten deposition. The influence of the geometric parameters of the field emission cell on the electric field strength at the emitter top is estimated. It was found that a decrease in the rounding-off radius of the emitter top from 150 to 5 nm leads to an increase in the electric field strength by more than an order of magnitude from 1.28 × 10⁶ to 16 × 10⁶ V/cm. A decrease in the diameter of the field emission cell from 2.5 μm to 900 nm contributes to an increase in the electric field strength by 33.6 % from 3.04 × 10⁶ to 4.58 × 10⁶ V/cm.

The expediency of using the radar method for detecting radiation contamination at long distances is substantiated in this article. The design of a radar for the detecting of small radioactive formations in the air at the long distances is developed. The dependence of the reflection coefficient of microwave radiation on the wavelength for determining the level of radioactive radiation is established. The investigation results of radioactive contamination in the atmosphere are presented.

Simultaneous generation of pulses of high-frequency Super-Radiance and low-frequency Coherent Spontaneous Radiation from an ultra-relativistic electron bunch moving in a waveguide placed in a spatially periodic and / or uniform longitudinal magnetic field is studied. The low-frequency radiation can weaken expansion of the bunch and decrease a velocity spread. This significantly improves electron micro-bunching and increases energy of high-frequency pulses. Such effect makes possible fairly efficient high-frequency cyclotron radiation of the bunch near an autoresonance regime, when the wave phase velocity is very close to speed of light.

The concept of an electron maser based on the excitation of the single supermode formed by a fixed set of transverse eigenmodes is proposed. A possible approach to form a high-Q supermode inside a simple cavity is the use of the Talbot effect, namely, periodic reproduction of the transverse structure of a multimode wave field in an oversized waveguide.

The work is devoted to exploration of arrays of vertical aligned silicon nanowires (SiNWs) obtained by cryogenic dry etching in ICP mode with height of 4.5-5.5 μm and aspect ratio of 7. It was shown that geometry of nanowires has crucial influence on rate of wet etching in KOH since it is higher for 3D objects than for planar wafer, and the diameter should be the same along the nanowire for controlled wet etching. Wet etching in 4% KOH solution during 30 s allowed to save array of uniformity vertical aligned SiNWs with height of 4 μm and diameter of 500 nm. Such treatment reduced concentration of defects detected by deep-level transient spectroscopy, particularly, it drops as minimum in two times for deep level with £0=0.68-0.74 eV placed near to surface of wafer.

The effect of sulphur surface passivation on the optical and electronic properties of InP was investigated. In the work, the approach of simultaneous measurement of the dynamics of the absorbed current and cathodoluminescence under continuous electron beam irradiation is used. This approach allows us to study the trapping of charge by traps and their influence on the luminescent properties. It was shown that hole traps are observed in the samples; moreover, the localization of a positive charge leads to an increase in the luminescence intensity. Passivation was found to significantly reduce the number of hole traps.

We demonstrate the experimental measurements of the turn-on delay in InAs-and InP-based quantum cascade lasers operating under pulsed electrical pumping with non-zero rise time. We report the unexpected delay time dependence on the pumping current density, that does not agree with available theoretical predictions. Performed numerical simulation of the model based on rate equations is only in qualitative, but not quantitative, agreement with our observations.

Composite single crystal structures based on iron borate FeBO₃, namely diamagnetically diluted iron-gallium Fe_1-xGa_xBO₃ and iron-aluminium Fe_1-xAl_xBO₃ borates with low x-values, as well as doped GaBO₃:Ni single crystals with Ni 0.1-0.01 mass %, have been synthesized using modified flux growth technique. Two technological modes that allowed improving the quality of the samples have been developed: crystallization in (1) open and (2) closed crucibles. Thin magnetic film of iron borate on a diamagnetic gallium borate substrate have been synthesized by liquid-phase epitaxy route.

In this study we related structural properties of GaN grown on ceramic substrate and studied with transmission electron microscopy with the results of photo-and cathodoluminescence investigations. We found that stacking faults in the basal plane were responsible for both strong room temperature visible emission and exciton-related ultraviolet luminescence at cryogenic temperature.

Thermo-e.m.f. of hot current carriers is experimentally investigated in non-doped n-InSe crystals with a dark specific resistance of 2·10³≤ρ_D0≤9·10⁶Ω·cm at 77 K and doped with erbium with 10⁻⁵≤N_Er≤10⁻¹at.%. It was found that its absolute value (|U_T|), in addition to $\hat{E}$ and T₀, also depends on ρ_D0 and N. In the non-doped samples with ρ_D0≤1·10⁴Ω·cm and doped with N_Er>10⁻² at.%, the dependence $|{U}_{T}|(\hat{E})$ consists of successive sections: $|{U}_{T}|\sim {\hat{E}}^{2},}\quad|{U}_{T}|\sim \hat{E}$ and $|{U}_{T}|\sim {\hat{E}}^{0.5}$. In non-doped with ρ_D0≥ 5·10⁴ Ω·cm and alloyed with 10⁻⁵≤N_Er≤ 10⁻² at.% samples at T₀ < 250 K and low-heating $\hat{E}$ dependence $|{U}_{T}|(\hat{E})$ obeys the law $|{U}_{T}|\sim {\hat{E}}^{\kappa }$ with 2<κ≤5. The value of k monotonously depends on N_Er and reaches its maximum value at N_Er=5·10⁻⁴ at.%. At T₀ >250 K, in all the samples studied, as well as in non-doped low-resistance and doped with N_Er>10⁻² at.% samples for all T₀, the dependence $|{U}_{T}|(\hat{E})$ follows the theory of thermo-e.m.f. of hot current carriers in spatially homogeneous crystalline semiconductors. To explain the results in non-doped high-resistance and doped with 10⁻⁵≤N_Et≤10⁻² at.% samples at T₀<250 K, the influence of random macroscopic defects must also be taken into account. A qualitative explanation of the results is proposed.

The gas aerial cooler apparatus (ACA) were characterized. These ACA serves for cooling the service gas. The analysis of engineering documentation was carried out in order to establish the range of amenable to control parameters of the engineering status, to carry out the recognition of failures (if ever) and damages that could led to a failure. The applied method of acoustic emission (AE) yielded total and direct information on the defect growth (hazard rate) in materials of operational facilities. The AE control might be used as a determinative procedure for the selection of criteria needed for assessing the status of diverse structures as well as for release to continued operation the production facilities (with providing a necessary level of safety during the enterprise operation) because the AE control enables to detect a fault at early stage of its growth. By applying the AE method for elaboration of a control of specific objectives, complicated problems related to generation of elastic waves from growing cracks and their transformation during propagation up to sensors were successively resolved.

The work extends the study of the ionization properties of phosphorus atoms as trapping/emission centres in the electric field of silicon p-n junctions operating at low temperatures. The goal is describing the ionization of phosphorus atoms by a single effective parameter, the ionization energy of phosphorus energy levels E_ion. An approach to the study is based on manipulating the space charge concentration N_eff in a nonirradiated silicon p⁺/n/n⁺ structure via filling phosphorus donors with electrons supplied by a laser pulse. Extracting the N_eff from the experimental current pulse response shapes recorded at variable temperature and pulse repetition rate allowed building Arrhenius plot for evaluating E_ion in the electric field. This value is shown to be 6.4±1.1 meV that is paradoxically low, being about 7 times less than the referred data.

We provide the exact solution of the dispersion equation for a waveguided semiconductor structure with a photonic crystal core that provides the efficient second harmonic generation in the visible range. The comparison of the results with an approximate solution shows good agreement.

The waveguide structure of a semiconductor quantum-cascade laser is presented, which provides compensation of material dispersion of the refractive index. This structure can be used to generate radiation with a frequency of 1.4 THz due to nonlinear light conversion.

Results of an epitaxial growth of 3C-SiC epilayers on hexagonal 6H-SiC, 4H-SiC substrates are described. The study of the obtained epitaxial layers grown on 6H substrates was made by photoluminescence and optical microscopy. Also, an image analysis of the interface of 3C-SiC epitaxial layers with 6H, 4H, and 15R substrates obtained by Transmission Electron Microscopy (TEM) are presented. Difference between the layers on the Si and C faces are discussed.

The investigation is focused on the defects in silicon p⁺-n-n ⁺ detectors irradiated with the 53.4 MeV ⁴⁰Ar ions, which generate a nonuniform defect distribution including a heavily damaged region inside the Bragg peak. The dependences of the bulk generation current and of the capacitance on bias voltage and the spectra of radiation-induced defects demonstrate new features: a step in the current rise, a region with a practically constant capacitance, and abnormal dependence of the peak amplitudes of vacancy-related defects on fluence. The changes of the DLTS spectra are assigned to the influence of silicon properties inside the Bragg peak region acting as a highly compensated insulating layer.

X-ray diffraction and high-precision scanning electron microscopy methods were used to study the long-term evolution of the defect structure of diffusion filter-membranes Pd-Y. Analysis of X-ray diffraction data and microelectronic photographs showed that the recovery of the dislocation structure in the membranes was not uniform. Differences in the processes of hydrogen conservation in the structure of membranes are determined reversible hydrogen doping. Preservation by alloy of superstructural ordered regions was detected.

Radiation hardness of different types of GaN based epitaxial structures which can be used as elements of electronic devices is studied by Hall effect,CV and IV measurements, as well as photoluminescence and Raman scattering. It is shown that proton irradiation leads to formation of deep acceptor states reducing conductivity of high electron mobility transistors (HEMTs) and Si-doped layers and is accompanied by a redistribution of the defect-related lines in the photoluminescence spectra. Our results demonstrate that proton irradiation increases conductivity for GaN:C, while decreases it for GaN:Fe and GaN:(Fe+C) layers.

Many properties of condensed matter systems can be described by means of pair correlation functions that makes them an important structural characteristic. The shortest-graph interpolation method allows us to calculate pair correlation functions of classical crystals with pairwise interactions between particles. However, there is still no just so simple and practical approach to predict correlation functions in crystals with many-body interactions that are ubiquitous in nature. In this work, a simple modification of the interpolation method is suggested allowing to describe pair correlations bcc Fe lattice, considered as a classical crystal with many-body interactions of embedded atom model type. It is shown that the radial distribution function of the crystal can be calculated with high accuracy if mean square displacements are known. The obtained results would be useful in various fields of condensed matter physics, materials science, and crystallography.

The paper is devoted to the analytical solution of the problem for 1D hemodynamical equations with periodic boundary conditions. The method of the solution is based on the asymptotic expansions on the small parameter and Fourier method. The attention is focused only on the first-order terms in the expansion. The solution, obtained for the particular case of initial conditions, is used for the comparison of rheological models of blood. It is demonstrated that the strongest damping takes place for the Power Law non-Newtonian model.

Solitons are essentially nonlinear and stable objects in various environments. In this work, the molecular dynamics method is used to study the propagation of solitary waves in a discrete medium in the form of an A₃B stoichiometry crystal and their interaction with nanopores. The model under consideration was a Pt ₃Al crystal, the atoms of which interacted through the potential obtained by the immersed atom method. Such waves can propagate to hundreds of nanometers across the crystal. We have studied the passage of waves through a cell containing nanopores of various diameters. The mechanisms of energy dissipation in the process under consideration are shown. The distance after the obstacle at which the wave front is restored is estimated. The energy characteristics of a solitary wave after interaction with a topological defect in the form of a cylindrical nanopore are calculated. The results obtained can be useful both from a fundamental point of view in studying the properties of solitons, and from practical for non-destructive testing methods.

We study the problem of construction of explicit isometric embeddings of (pseudo)-Riemannian manifolds. We discuss the method, which is based on the idea that the exterior symmetry of the embedded surface and the interior symmetry of its metric must be the same. In case of high enough symmetry of the metric such method allows transforming the expression for induced metric, which is the one to be solved in order to construct an embedding, into a system of ODEs. It turns out that this method can be generalized to allow the surface to have lower symmetry as long as the above simplification occurs. This generalization can be used in the construction of embeddings for metrics, whose symmetry group is hard to analyze, and the construction of the isometrically deformed (bent) surface. We give some examples of the application of this method. In particular, we construct the embedding of spatially-flat Friedmann model and isometric bendings of a sphere, 3-sphere, and squashed AdS universe, which is related to the Godel universe.

The paper deals with the features of modeling physical processes during the propagation of ultrasonic waves in metallic media. A mathematical model for the propagation of shear vertical (SV) ultrasonic waves generated by a single element of a 32-element electromagnetic acoustic phased array has been developed. The calculation of the acoustic field of the 32-element SV electromagnetic acoustic transducer (EMAT) phased array was made. The total displacements for models with defects and without them were calculated. A computer simulation of the process of reflection of the ultrasonic beam from a defect was made. The developed model allows one to study the influence of shape, size, location of defects in the plate as well as the plate geometric parameters on the formation of the reflected signal.

At article of the main factors rendering of influence on the reliability of material control results by ultrasonic thickness gauge are determined. The necessity of the use of automatic calibration of ultrasonic thickness gauge for reduction of measurement error is justified. The neural network for the realization of automatic device calibration is developed. The received experimental results are presented.

The possibility of stepwise formation of the active laser medium on a plasma of multicharged ions is shown based on the numerical simulation results. Practically, such compression can be carried out with a high-voltage generator, storage and forming lines. It is presented that at conditions I_m ≥ 200kA in stepwise pumping mode, it is possible to obtain Xe-plasma parameters with an electron temperature Te>400 eV and a concentration Ne>10²⁰ cm⁻³. Such plasma is a good medium for amplification of spontaneous radiation at several transitions in the spectral region λ≈10 nm in a Xe-plasma of Ni-like ions: it can provide a gain at the transitions g+~ ∼ 1-2 cm⁻¹.

The article is devoted to the study of the lateral surface shape of a vertical liquid bridge of small volume between two arbitrary convex solid surfaces in the axisymmetric case. A variational statement of the original problem is given. The solution is found by the iteration method under the assumption that the Bond number is small. An algorithm for the iterative process is proposed, taking into account the action of gravity. It was found that the maximum number of different profiles of the lateral surface of the liquid bridge corresponding to one selected set of parameters is four. As an example, the problem of the lateral surface shape between a sphere and a plane has been solved.

The work is devoted to the construction of explicit embeddings for the metrics of the black holes, formed by nonsingular matter distribution. One of the possible examples of such type of solutions is regular black holes. Using the existing classification of minimal symmetric embeddings of the Schwarzschild metric as a base, we construct embeddings for regular black holes with de Sitter interior. Another simple example is black hole, formed by collapsing homogeneous spherically symmetric cloud of dustlike matter. We discuss embeddings for two variants of such black holes -the one with the eternally existing horizon, when dust ball never leaves the interior of the horizon, and another variant with the dynamically forming horizon.

The Dzyaloshinskii-Moriya interaction constant for iron-gallium borate Fe_xGa1-_xBO3 single crystals has been calculated on the basis of considering antisymmetric exchange in a pair of nearest-neighbouring magnetic ions. Both numerical and analytical calculations predict a square-law dependence of the Dzyaloshinskii-Moriya constant on the contents of magnetic ions, x, in the crystals.

The paper considers the experimentally observed instability of capillary shaping during the growth of thick-walled sapphire tubes by the Stepanov method. The explanation of this phenomenon is based on the theoretical model of radiative-conductive heat transfer in a crystal. An algorithm is developed for the asymptotic expansion of the problem based on the presence of two small parameters. It is shown that the spatial density of the radiation is inhomogeneous along the cross section of the tube and is maximum near its inner walls. This leads to their overheating and the meniscus separation from the inner edges of the shaper.

In this paper we study a one-dimensional spatially-continuous reaction-diffusion system, related to patterning of Drosophila's retina. We search for conditions of stability or diffusion-driven (Turing) instability of a homogeneous prepattern steady state.

The height function of the six-vertex model with the domain-wall boundary conditons in the free fermion point is computed by the Monte Carlo algorithm. The numerical results are in good agreement with the analytical expression for the limit shape height function. This paper is a "warm up" for the forthcoming one, where the two-point correlation function for the height function is calculated.

We present a systematic review of the basic properties of regular black holes (RBH) and self-gravitating solitons replacing naked singularities including electrically charged RBHs and electromagnetic spinning solitons, predicted by analysis of regular solutions to dynamical equations with metrics of the Kerr-Schild class governing their behavior. We briefly outline observational cases which display and verify their fundamental generic features which are the de Sitter vacuum interiors and relation of their masses to spacetime symmetry breaking.

Variable cross-section rods are used in many parts and mechanisms. For example, conical rods are widely used in percussion mechanisms. The strength of such parts directly depends on the natural frequencies of vibrations. Oscillations and vibration are also used in diagnostics, for example in acoustic diagnostics of defects. The paper presents a method that allows numerically finding a variable cross section of an elastic rod from the natural frequencies of longitudinal vibrations. It is assumed that the cross-sectional area varies along the axis and is described by an exponential function of a polynomial of degree n. The boundary condition on the left end is hard, on the right-elastic. It is shown that to determine n unknown coefficients of the cross section function, n natural frequencies are required.

The self-organized criticality (SOC) phenomena for dynamical systems with spatial degrees of freedom is commonly observed in application to different aspects of natural sciences. In our study we also consider our sandpile model as such a system. Since the first mention in 1987, a sandpile model, which is a common example of spatiotemporal evolution, became widely applied for avalanche-like processes. With a simple computer simulation we show that an avalanche as a result of natural system evolution has a fractal border structure, and approves SOC phenomena of a sandpile model. We also demonstrate Gutenberg-Richter dependence for avalanche process in a sandpile model.

The surface topography, local current distribution and piezoresponse signal in porous ferroelectric PZT films are studied using conductive atomic force microscopy (c-AFM) and piezoforce microscopy (PFM). The PZT films were formed from solutions with the addition of 0–20 wt% polyvinylpyrrolidon (PVP) as a porogen with the molecular weight of 360000. Applying c-AFM, the topography images and distribution maps of the local current of the same surface area are obtained, which made it possible to compare the profiles of the topography and current signals. It is shown that in PZT films prepared without PVP addition, the local currents flow inside the grains forming the columnar structure with nonconductive grain-boundaries. At PVP content of 1-3 wt%, separate current peaks are observed on the analyzed profiles, but starting from 6 wt% PVP and higher, the local current flowing in the pore regions exceeds the current recorded in the grain area.

The results of studying the dielectric constant σ' and the third harmonic coefficient γ_3ω of a new organic ferroelectric diisopropylammonium bromide (C₆H₁₆NBr, DIPAB), embedded in porous glasses with an average pore size of 100 nm are presented. Diffusion and shifting of the phase transition to low temperatures by 5 K were detected in comparison with bulk DIPAB. A decrease in the phase transition temperature in nanocomposites with DIPAB nanoparticles is qualitatively consistent with theoretical models of the size effects on the structural phase transition.

The Cahn-Hillard equation, previously obtained to describe the decomposition of metal solid solutions, is adapted to analyze the spinodal decomposition of A²B⁶ semiconductor solid solutions. The obtained differential equation is used to describe the spinodal decomposition of the Zn_xCd_1-xTe solid solution, which is synthesized under conditions close to the boundaries of absolutely unstable regions on the state diagram of the system. A quantitative description of the composition modulation effect that appears in the material when its growth under the indicated conditions is given.

Computer simulations of the spinodal decomposition of the Zn_xCd_1-xTe solid solution showed that micro oscillations of the material composition are connected by the resonance phenomenon between the excess mixing energy and the energy of elastic strains arising in the inclusions of the new phase coherently conjugated with the lattice of the initial crystal. It is shown that such resonance phenomena are most intense when the conditions for the material synthesis are chosen in the immediate vicinity of the spinodal curves in the phase state diagram of the system.

The kinetics of the first-order solid-state structural transition in monodisperse n-alkanes samples of odd tricosane C₂₃H₄₈ and even tetracosane C₂₄H₅₀ was studied by FTIR spectroscopy. The initial nuclei location of the new phase was revealed. The process of crystal structure rearrangement is initiated in the interlayers between neighboring lamellar for odd tricosane, while the nanonuclei in even tetracosane arise in the crystalline lamellas cores. Thus, the influence of the number evenness of carbon atoms in the n-alkanes chains on the first-order structural phase transition has been proved.

The task about the conductivity of a thin conductive layer in a longitudinal alternative electric field is solved. The relationship between layer thickness and charge carrier mean free path is arbitrary. The Soffer model is used as boundary conditions for Boltzmann equation. The isoenergy surface of a semiconductor is an ellipsoid of revolution. Analytical expressions are obtained for conductivity tensor components as functions of layer thickness, isoenergy surface anisotropy parameter, electric field frequency, surface roughness parameters, and chemical potential. The limiting cases of a degenerate and non-degenerate electron gas are considered. The dependences of conductivity tensor components on the above parameters are analyzed. The results obtained for cases of a degenerate and non-degenerate electron gas are compared. A comparative analysis of results is made with calculations in the view of diffuse-mirror boundary conditions and with known experimental data.

The energy gap was revealed in the Dirac cone of the BiSbTeSe2 topological insulator after the submonolayer deposition of a ferromagnetic metal. As a ferromagnet, cobalt and manganese were used. Such way of the energy gap opening is novel in comparison to the bulk ferromagnetic doping of topological insulators.

In this work, various regimes of local anodic oxidation (LAO) of MoSe2 were studied. Here we show that there is a certain set of oxidation parameters that results in the anisotropic oxidation of MoSe2. In this mode, LAO leads to the formation of oxidized triangles. The triangles have the same orientation on the surface of the flakes, which indicates that MoSe2 is oxidized mainly along the crystallographic directions of the zigzag edges. These results can be useful for determining crystallographic directions of zigzag/armchair edges and the degree of single-crystallinity of MoSe2 flakes.

An array of CuO nanowhiskers have been fabricated by heating of copper coatings formed on stainless steel mesh substrate in air. Cross-sections of the nanowhiskers were studied by transmission electron microscopy. It was established that whiskers consist of two or more grains with incoherent boundaries. The mechanism of the formation of incoherent boundary is revealed. An important role of the incoherent boundaries in the formation of the nanowhiskers is discussed.

A computer modelling of magnetization behavior in ultrathin ferromagnetic films, divided by antiferromagnetic film is carried out. The exchange integral value is different for each ferromagnetic films. One of the films is magnetohard, the second one is magnetosoft. The situation where magnetosoft film has the exchange integral value twice smaller than the value of magnetohard film is investigated. Heisenberg model is used. Calculations are made using Metropolis algorithm. The phase transition temperature is obtained for all three films. The magnetic field was applied along the film plane. The simulation showed that magnetizations of ferromagnetic films first become perpendicular to the direction the staggered magnetization vector in the antiferromagnetic film. With a higher magnetic field value, the magnetization vectors of the ferromagnetic films become mutually perpendicular. Thus, in these multi-layer systems, it is possible to control the orientation of the substances spins, which is an important property for implementing spintronics devices.

The results of studies of semipolar GaN(10-12) layers synthesized on a nano-patterned Si(100) substrate are presented. It is shown that in the method metalorganic vapor phase epitaxy, the use of a nanorelief consisting of V-shape groove with inclined faces close to the Si(111) plane can lead to the formation of regions of cubic gallium nitride in the nano-groove. Model of the origin of the cubic phase are based on the formation of AlN nuclei in (0001) and (10-10) nano-groove and the conjugation of the AlN(10-10) and c-GaN planes by the "magic mismatch" mechanism.

The aim of this work is to calculation and fabrication silicon membranes for acoustic sensors with operating ranges of resonant frequencies from 10 kHz to 100 MHz and pressures from 0.1 to 10³ kPa. In this paper, analytical dependences of pressure and resonance frequency on geometrical parameters of membranes are presented. The ranges of the thickness (30-50 μm) and the length of the edge membranes (0.2-1.0 mm) were defined. Experimental studies of the etching of the silicon wafer with a solution of 30% KOH were carried out and the etching rate was found to be 1.2-1.8 μm/min. Anisotropic wet etching was used to form square-shaped silicon membranes with a thickness of 30-50 μm and an edge length of 0.2 to 1.0 mm with resonant frequencies in the range of 0.7 to 30 MHz. The obtained results can be used in the development of acoustic sensors based on of monocrystalline silicon.

The structures Au/GaAs(001) with gold nanoclusters are created by annealing of Au films deposited onto GaAs surface. The samples are diagnosed stepwise by scanning probe microscopy. Using reflectance anisotropy spectroscopy, Au clusters are established to possess plasmons with the in-surface anisotropy. The measured anisotropy spectrum consists of a resonant feature near the energy of 2 eV typical of local plasmons of Au clusters. The results are explained theoretically, and the new spectral feature is assigned to anisotropic plasmons of Au nanoclusters located on GaAs surface.

The thermodynamic parameters of a long chain molecular crystals (LCMCs) set are analyzed. We revealed the dependence of LCMC's melting points with a different chain length on the habitus of the first-order phase transition's elementary volume. It was shown that LCMCs with the same chemical structure of the "core" (normal alkanes {CH₃(CH₂)_nCH₃}, normal alkanols {CH₃(CH₂)_nCOH}, diols {COH(CH₂)_nCOH}, carboxylic {CH₃(CH₂)nCOOH} and dicarboxylic {COOH(CH₂)_nCOOH} acids) lose their individual thermodynamic properties and approach the properties of polymethylene with an increase in the number of –CH₂– groups.

It has been experimentally established, that reversible electro-plastic effect, which is similar to the well-known case in crystalline metals, is observed on the σ(ε) diagrams for ribbon metallic glasses (MG). It has been established that passing of the impulse electrical current through the loaded specimen of MG leads to the larger fall of the mechanical stress than furnace heating at the same temperature. A linear relation between the fall of mechanical stress and temperature, depending on alloy composition, is observed. Growth of the duration of a current impulse at constant current density increases heating of the specimens with the larger reversible fall of the mechanical stress. Value of the reversible fall of mechanical stress, obtained with the impulses of electrical current in amorphous alloy, is caused not only by thermal expansion but also other reversible processes that are the result of the impact on amorphous alloys (for example, structural relaxation, that is reversible on the initial stage).

Current-voltage and capacitance-voltage characteristics of polyvinyl alcohol (PVA) films with the inclusion of multi-walled carbon nanotubes (MWCNT) deposited on silicon and ITO substrates were experimentally studied. It is shown that such structures demonstrate rectifying properties and their current-voltage characteristics are nonlinear. With direct bias, the structures have a positive temperature coefficient of resistance (TCR). With a reverse bias, the sign of TCR changes from negative to positive. A qualitative analysis of the results based on the tunneling mechanism of current transfer is presented.

Intercalation of graphene formed on silicon carbide surface with iron, cobalt and silicon has been used to form the graphene/silicides/SiC interfaces. The experiments were carried out in situ in ultrahigh vacuum conditions. The elemental composition and chemical state of the sample surfaces, as well as their atomic structure, were controlled by high-energy-resolution photoelectron spectroscopy and low-energy electron diffraction. The nominal thicknesses of the deposited iron, cobalt and silicon layers varied in the range of 2-20 Å, and the temperature of the sample annealing was changed from room temperature to 600°C. It is shown, that the intercalation of graphene/Fe/SiC with Si leads to the formation of Fe-Si solid solution layer covered with surface silicide Fe₃Si, while intercalation of graphene/Co/SiC with Si results in the formation of a Co-Si solid solution and CoSi silicide covered with Co₃Si surface phase. The obtained silicide layers are reliably protected by graphene, making it compatible for nanoscale applications at ambient conditions.

We propose a new method to obtain the three-dimensional quantum-sized object arrays with reduced surface density. These arrays are formed by elastic transformation of the InGaPAs layer grown on the GaAs surface. We present the results on influence of the InGaP layer thickness, the substrate temperature, and exposure time in the arsenic flow on the optical and structural properties of the formed three-dimensional islands.

Heterostructures with embedded layers of single InAs and In_0.8Ga_0.2 As quantum dots (QDs) in a GaAs matrix have been obtained by metalorganic vapor-phase epitaxy. The photoluminescence spectra of these QDs have been measured in a wide temperature range and the analysis of the photoluminescence peaks behavior has been carried out. As a result, it have been found that the In_0.8Ga_0.2 As QDs has better size uniformity and contains a smaller number of defective islands in comparison with InAs QDs.

Vertical carbon nanowalls have been fabricated by RF magnetron sputtering of a graphite target in an argon plasma without hydrogen presence. The effect of deposition parameters such as substrate temperature, argon pressure, deposition time and RF power on the morphology and the structure of carbon nanowalls was investigated by using Raman spectroscopy and atomic force microscopy. The argon ion bombardment of the substrate is crucial for the nucleation and growth of carbon nanowalls. A specific range of RF power and argon pressure values was established at which nanowalls formation is possible. The height of nanowalls produced at minimal RF power increases non-monotonically with the deposition time. It turned out that the nanowalls growth rate has an extremum, after reaching which the growth rate of the thickness of nanowalls increases.

We have shown the possibility of Ga(In)AsP on GaAs (100) nanowire growth in a quasi-closed volume from the vapour phase witn the use of Sn catalyst. We have investigated the dynamics of nanowire formation depending on the growth time at constant V/III ratio given by the process temperature. It is shown that growth of free-standing nanowires is realized through the vapor-liquid-solid mechanism. Based on the Raman scattering data sequential growth of two phases have been shown. Phosphorous concentration in free-stamding nanowires was estimated to be high.

The method of metal-assisted chemical etching for obtaining silicon nanowires, which consists of two stages, was studied. The conditions and modes for producing layers at both stages of the implemented technology are established, which include (1) chemical deposition of an array of self-organizing Ag nanoparticles on a Si substrate as a catalyst mask and (2) chemical etching of SiNWs to various depths from 110 to 1200 nm. The optical properties and morphology of a metal-catalyst (Ag) film were studied depending on the deposition time and solution concentration. Spectral ellipsometry was used to characterize the samples at all stages of MACE. Using the measured ellipsometric angles, the dielectric functions were determined, as well as the thicknesses and parameters of the fractions of composite layers in a multilayer model by approximating the effective Maxwell Garnett and Bruggeman medium for two-component layers. Samples with Ag nanoparticles with different morphologies were studied using reflection spectrophotometry in the wavelength range from 200 to 600 nm. The results showed that composite Ag-Si structures are promising for obtaining plasmon effects in both the visible and IR spectral regions.

The surface features of oxide layers (< 100nm) grown on single-crystal n-InP (100) samples in acid electrolyte on initial stage were investigated by atomic force and lateral force microscopy. The time of electrochemical oxidation of samples was the variable parameter. There is difference found in the oxide layer phase structure grown in the electrolyte during different time. The initially formed (17 s) islands (a nucleated oxide phase) were divided, then coalescence appeared (26 s), and the occurrence of a second phase was detected. With an increase in the time (40 s) of oxidation, the surface morphology becomes more uniform.

The effect of the composition and temperature of the subphase on the effective dipole moment of the Langmuir monolayers of a liquid crystal 4-n-octyl-4'-cyanobiphenyl on the surface of pure water and an aqueous solution containing copper nanoparticles was studied. It is shown that the presence of nanoparticles in the subphase leads to increase of the area occupied by the monolayer in the condensed state, increase of the collapse pressure, and reduce of the surface potential at the end of monolayer compression. The effective dipole moments of liquid crystal molecules were calculated for monolayers formed under various conditions.

The publication describes the study of durability in tensile creep of VT1-0 commercial titanium in its two states-coarse-grained and ultrafine-grained. It is shown that the best temperature for log-term testing is 350°C. At this temperature, the ultrafine-grained titanium structure remains stable both during free annealing and durability testing. The obtained data enable retrieving the difference in fracture initiation energies for titanium in its coarse-grained and ultrafine-grained states.

The homologous series of thermoplastic polyetherimide based on resorcinol dianhydride R (1,3-bis-(3,3',4,4'-dicarboxyphenoxy)benzene) and tetranuclear diamine BAPB (4,4'-bis(4"-aminophenoxy) biphenyl) (R-BAPB) were synthesized in powder form. Fibers were obtained by melt spinning of this polyimide. It was analyzed, how changes in the molecular weight of polyimide can affect the ability to form fibers through the melt. The influence of the degree of orientation high-temperature drawing on the thermal mechanical properties and the change in the morphology of the polymer was studied. An increase in draw ration (DR) from 1 to 4 led to a substantial increase in tensile strength and Young's modulus of polyimide fibers.

In the process of this work, an oligoimide FT-BAPB-R-BAPB-FT was synthesized, the particles of which consist of numerous lamellas having a semi-crystalline structure. On the DSC thermogram of oligoimide powder, two endo peaks were observed at 281.1°C and 306.4°C. A unique WAXS experiment was performed in-situ by heating the reactor oligoimid powder in a heat chamber. There was no significant difference in the X-ray profiles when the sample was heated. It should be noted that the transformation of the crystalline cell does not occur until the sample melts. It was revealed that the degree of crystallinity decreases during heating. We believe that the low-temperature endopeak is associated with the melting of small crystallites and amorphization of the sample. However, a significant increase in crystal size was found to be a result of recrystallization. Thus, the high-temperature endopic corresponds to the melting of larger crystallites.

In this work, the two-stage process for producing polyimide fiber from polyamic acid (PAA) by wet spinning was used. Polyimide fibers were obtained by thermal and chemical imidization. The effect of the imidization method (chemical and thermal) on morphology, chemical structure, thermal stability and mechanical properties of polyimide fibers was investigated. A number of research methods were used in the work, such as Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calometry (DSC), thermogravimetric analysis (TGA) and determination of strength characteristics.

The optical reflection spectra of PbSe films and PbSe films coated with a layer of linear chain carbon were studied by IR Fourier spectroscopy in the wavelength range of 1-16 μm. In all IR spectra of the samples, two minima were observed, related to plasma fluctuations of free charge carriers and related to the PbSe and PbSeO₃ phases. It was found that the PbSe film coated with a layer of linear chain carbon is less oxidized. This conclusion is confirmed by the results of x-ray structural studies of the samples. The results showed a decrease in the percentage of oxygen-containing phase PbSeO₃ by 2-4 times.

Meso-aryl-substituted porphyrin monolayers were obtained by the Langmuir method depending on the aliquots applied to the water surface and the composition of the subphase. Regardless of the composition of the subphase (pure water or a solution with copper nanoparticles stabilized by surfactant) porphyrin compression isotherms showed the formation of monolayers until a film collapse state is reached. The presence in the subphase volume of copper nanoparticles stabilized by a surfactant (sodium dodecyl sulfate) contributed to the formation of a more stable porphyrin monolayer. A significant difference in the values of the surface potential at the end of porphyrin monolayer compression depending on the composition of the subphase is established. This fact is very promising in the context of creating film heterostructures with improved operational properties.

The technique for determination of strain and elemental composition distribution across the graded layer in heterostructures by means of selected area electron diffraction in transmission electron microscope (TEM) is proposed. The approach accounts for the modification in the residual elastic strain due to sample thinning during TEM specimen preparation. The technique is approved using In_0,7Ga_0,3As/In_xAl_1-xAs/GaAs(001) and Al_0,75Ga_0,25N/AlN/Al₂O₃ heterostructures, and the results are in a good agreement with those obtained by alternative ways.

The synthesis of III-nitride binary compounds on commercial standard (001) silicon wafers by vapour-phase epitaxy is one of the promising directions for III-nitride technology development. However, the difference between crystal symmetry of Si(001) and wurzite (0001) surface structures is challenge that hinders the development. A use of silicon substrates with nano-patterned surface is one of the solutions to the problem. In this paper we present a transmission electron microscopy study of polar and semipolar GaN layers grown by halide vapour-phase epitaxy and metalorganic vapour-phase epitaxy on nano-patterned silicon (001) substrate. Crystallographic orientation relationships between the silicon substrate and GaN layers is identified. For GaN layers grown by metalorganic vapour-phase epitaxy an effect of SiC buffer layer synthesized by original growth method on their microstructure and surface morphology is under consideration.

In this work, the hydrogen diffusion through an amorphous Fe₉₂Si₆B₂ alloy membrane has been investigated. It has been established that the hydrogen diffusion decreases with the growth of the acidity of the environment at the constant ionic force of solution. The probable mechanisms of the blocking of hydrogen flow through the membrane have been discussed. An insignificant variation of the mechanical characteristics (ultimate tensile strength, microhardness, Young's modulus) of Fe₉₂Si₆B₂ amorphous alloy has been detected.

The influence of the anodization current density to the morphology and composition of the surface of porous silicon before and after its impregnation with an antibiotic was investigated using atomic force microscopy and IR spectroscopy. Layers of porous silicon were obtained by electrochemical etching; variable technological parameters of anodizing were the current density and the type of conductivity of the silicon plate. The results obtained are discussed in terms of their use in targeted drug delivery.

This work is aimed at finding and developing new ways to improve and optimize the characteristics of transparent conductive electrodes based on SWCNT by forming a texture in a continuous layer by combination of lithography and oxygen plasma treatment. A theoretical and an experimental justification for choosing thickness of a textured pattern, together with the experimental results of optical and electrophysical measurements were presented. The resistance of the textured electrode was 187.5 Ohm/sq, which is 17.5% lower than resistance of the electrode made from a continuous SWCNT layer with a same transparency of 95%. An analytical calculation showed that the use of extremely absorbing SWCNT films for texturing allows to obtain ∼ 54% gain in the resistance of a textured electrode compared to a continuous SWCNT's layer.

The work is devoted to the study on the influence of various factors on the microporous structure parameters of the zeolite compositions being formed. To study the parameters of the microporous structure, sorption analysis methods were used. Zeolites of the BETA type and compositions based on them were chosen as objects under study. It was found that the formation of zeolite compositions is greatly influenced by the nature of the binder (matrix) and peptizer, which determine the proportion of micropores in the zeolite composition. It is shown that in the study of the textural characteristics of zeolite compositions, preliminary sample preparation (heat treatment to remove the moisture adsorbed by them) is necessary.

Transparent glass-ceramics of the zinc aluminum silicate system nucleated by TiO₂ and doped with FeO were developed by melt-quenching at 1580 °C with subsequent secondary heat-treatments at 720 – 1050 °C. The glass-ceramics based on nanosized gahnite crystals were characterized by X-ray diffraction, Raman and optical spectroscopy. The glass-ceramics exhibit a broad (1.5-2.5 μm) absorption due to the ⁵E → ⁵T₂ (⁵D) transition of Fe²⁺ ions in T_d sites in gahnite crystals. They are promising as saturable absorbers of the short-wave IR lasers.

The technique of obtaining Ag/Por-Si composite material with homogeneously distributed silver nanoparticles over the surface of porous silicon by one cycle of electrochemical treatment of single-crystalline silicon. The effect is achieved by using an electrolyte to produce porous silicon with a special composition containing silver ions. During the electrochemical anode treatment of single-crystalline silicon in Ag-containing electrolyte a layer of porous silicon and silver islets are formed on the sample surface simultaneously. It is shown that the controlling the conditions of electrochemical processing provide an opportunity to form homogeneously distributed on the surface silver nanoparticles with a narrow-size distribution.

The aim of the work is to investigate different approaches for the growth of planar gallium phosphide layers on silicon by molecular beam epitaxy. Atomic force microscopy and reflection high energy electron diffraction were used to study surface morphology and estimate the film domain structure. Developed growth technique with the use of a low-temperature AlGaP/GaP seeding layer allowed us to achieve atomically flat pseudomorphic single-phase GaP on Si(001).

In this work, a sensor layer based on zinc oxide nanowires was synthesized by low-temperature hydrothermal method. The gas sensitivity of sample to isopropyl alcohol vapor was studied both during heating and under ultraviolet radiation. It was shown that depending on the presence of moisture on the surface of zinc oxide nanowires, isopropyl alcohol vapor can act as a reducing or oxidizing gas upon activation of gas sensitivity by ultraviolet irradiation. It was shown that there is an optimal intensity of irradiation, which determines the maximum response of sample. The gas sensitivity under moist air conditions demonstrates the possibility of practical application of adsorption resistive gas sensors with light-activation at room temperature.

A comparative study of bipolar resistive switching in thin films of titanium dioxide, fabricated by different techniques, was carried out by analysis of current-voltage characteristics (I-V). For this purpose metal-insulator-metal (MIM) structures were formed with 60-nm-thick titanium dioxide layer deposited by atomic layer deposition (ALD) or RF magnetron sputtering. Based on the analysis of resistance switching characteristics, it was found that the deposition technique of titanium dioxide thin films influences the reproducibility of high-resistance state (HRS) at cycling measurements, the on-resistance (low resistance state)/off-resistance (HRS) ratio, the average values of SET [switching the resistance from a HRS to a low resistance state (LRS)] and RESET [switching the resistance from LRS to HRS] voltages and the number of resistive switching cycles. The results of study of the thin film topography performed by atomic force microscopy (AFM) suggest that the difference in resistive switching parameters could be caused by structural properties of titanium dioxide layers deposited by different techniques.

Graphene is considered as a promising candidate for manufacturing of sensors due to its extreme sensitivity to molecule absorption. In this work, we show the connection between the electrical and optical properties of epitaxial graphene chips grown on 4H-SiC and intended for the production of protein-based sensors. Using of a complex of techniques, including Raman spectroscopy, atomic force microscopy, Kelvin probe microscopy, study of I-V characteristics and low-frequency noise, it is shown that the character of frequency dependence of the spectral density of voltage fluctuations and its value at a frequency of 1 Hz can be used for classification and selection of graphene chips for their application as sensors. Classification of the graphene chips will allow more efficient development of graphene-based biosensors.

Quasi-two-dimensional GaTe layers were grown by molecular beam epitaxy on GaAs (001) substrates at T_s = 450–520°C. The effect of the growth temperature on the GaTe surface morphology has been studied by scanning electron microscopy. It is shown that GaTe layer grown at high T_s = 520°C exhibits pronounced surface relief anisotropy. This sample demonstrates also near band-edge photoluminescence (PL) at T = 11K with the peak energy of ∼1.72 eV, which can be associated with the emission of excitons bound at the acceptor. The nature of 1.45 eV and 1.57 eV peaks appearing in the PL spectra is also discussed in detail.

It has been shown that in multilayer graphene/polystyrene composite, the static magnetization curve looks the same as in a type-II superconductor. The electron spin resonance in the same composite was studied as a function on temperature and magnetic field. The observed g-factor of 2.003 was independent of temperature and was in the range (g = 2.0022-2.0035) characteristic of a free carbon electron. This behavior of the g-factor excludes the appearance of an internal magnetic field in the composite.

The possibility of synthesizing semiconductor films of copper oxide and films of copper oxide with linear chain carbon, which have good sensitivity to methanol and ethanol vapors, is shown in the work by a thermoresistive method. The proposed gas sensitivity mechanism describing the increase in resistance in methanol and ethanol vapors shows good agreement with the obtained experimental results.

Methods of X-ray diffraction (XRD), Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy were applied to POLEMA W sample after He plasma irradiation. The W reflections of the plasma treated sample exhibit an evident asymmetry characterized by a negative asymmetry parameter. Using the Williamson-Hall Plot technique the XRD reflection asymmetry has been successfully quantitatively described in frame of a model with two W phases with slightly different unit cell parameters and essentially different crystallite size and microstrain values.

The paper presents the results of the microstructure and morphology study of two-dimensional Ge QD arrays in a Si/Al2O3 matrix formed by annealing multilayer periodic structures with Ge nanolayers in a Si/Al2O3 matrix. The distinctive features of samples in the series are the location and thickness of the Si barrier layers between Ge and aluminium oxide matrix. X-ray reflectometry and diffractometry and transmission electron microscopy studies have shown that large Al₆Ge₅ crystallites are formed and the multilayer structure is destroyed after annealing of the multilayer sample Al₂O₃/Ge without Si. It was found that the presence of Si barrier layers in multilayer Al₂O₃/Si/Ge structures reduces the interdiffusion of Al and Ge, but Ge_1-xSi_x nanocrystallites are formed as a result of Si and Ge interdiffusion. Thus, the introduction of Si barrier layer into the Al₂O₃/Ge structure allowed obtaining of two-dimensional arrays of Ge_1-xSi_x nanocrystallites with the penetration of Si up to 0.64.

The peculiarities of prism coupling elements input and output of narrow-band radiation into ion diffusion waveguide are researched. Gradient waveguide with a thickness of 1.67 μm was formed by ion exchange in K8 glass. The output signal intensity dependence on the input and output angles of incidence radiation was measured by developed automatic hardware-software system based on synchronous detection method to improve the signal-to-noise ratio. It was shown the maximum of output signal is reached at equal input and output angles.

A method and unit for dynamic control of conversion characteristics of spectrometric paths of multichannel charged particle registration systems based on specialized microchip with a large degree of integration similar to IDE1140 in structure is proposed. The conversion characteristics are controlled during operation of the device by auto-adjusting the offset and gain of the scaling amplifier. The proposed method allows to use the entire dynamic range of the analog-to-digital converter and adjust the temperature drift for each channel at the hardware level during operation of the device.

The short-lived resonances have proved to be very useful in the study of heavy-ion collisions at SPS, RHIC, and the LHC. Properties of these particles measured in dominant hadronic decay channels carry a wealth of information about the hadron chemistry and reaction dynamics. Resonances containing one or two strange quarks contribute to the study of the strangeness enhancement phenomenon predicted as a signature of the phase transition to quark-gluon plasma in heavy-ion collisions. Resonance integrated and differential yields are sensitive to the hadron re-scattering and regeneration in the hadronic phase. The resonance production has only scarcely been studied in heavy-ion collisions at NICA energies. These proceedings are devoted to the review of the expected properties of the resonances and their sensitivity to different stages of Au+Au collisions at $\sqrt{{}^{{s}_{NN}}}$= 11 GeV. Results of feasibility studies for reconstruction of ρ(770)⁰, K^*(892)⁰, ϕ(1020) and Λ(1520) resonances in the MPD experimental setup as a function of collision energy and centrality are presented.

Studying the properties and evolution of the QGP is one of the main goals in modern heavy ion physics. Due to strange quark content K*⁰ meson is a good probe for the study of QGP formed in heavy-ion collisions. K^*0-meson production was previously measured by PHENIX in symmetric Cu+Cu collisions at $\sqrt{{}^{{s}_{NN}}}$ = 200 GeV and U+U collisions at$\sqrt{{}^{{s}_{NN}}}$ = 200 GeV. K^*0-meson production in asymmetric Cu+Au collisions at $\sqrt{{}^{{s}_{NN}}}$ = 200 GeV and U+U collisions at$\sqrt{{}^{{s}_{NN}}}$ = 200 GeV and spherically asymmetric uranium nuclei at $\sqrt{{}^{{s}_{NN}}}$ = 200 GeV and U+U collisions at$\sqrt{{}^{{s}_{NN}}}$ = 192 GeV was performed for continuation the study of the QGP properties. This report presents invariant transverse momentum spectra and nuclear modification factors of K^*0-mesons which were measured in Cu+Au collisions at the energy of $\sqrt{{}^{{s}_{NN}}}$ = 200 GeV and U+U collisions at$\sqrt{{}^{{s}_{NN}}}$ = 200 GeV and U+U collisions at the energy of $\sqrt{{}^{{s}_{NN}}}$ = 200 GeV and U+U collisions at$\sqrt{{}^{{s}_{NN}}}$ = 192 GeV. In results, K^*0-mesons yields are less suppressed than the yields of non-strange mesons, which might indicate that additional particle production mechanisms are involved in the K^*0-meson production. The production of the K^*0-mesons in Cu+Cu, Cu+Au, and U+U collisions scales with N_part and seems to depend on nuclear overlap size, but not on its geometry.

Quark gluon plasma (QGP) is one of the most discussable objects in modern particle physics. One of the ways to study QGP is to measure production of different particles in various relativistic ion collisions. Nuclear modification factors (R_ab) for protons were previously measured in symmetric Au+Au collisions at $\sqrt{{}^{{s}_{NN}}}$ = 200 GeV and U+U collisions at$\sqrt{{}^{{s}_{NN}}}$= 200 GeV. Asymmetric Cu+Au system in comparison with Au+Au results allows to study the influence of collision geometry on proton production. This report presents invariant transverse momentum (p_T) spectra, R_ab values of protons obtained in Cu+Au collisions at the energy of $\sqrt{{}^{{s}_{NN}}}$ = 200 GeV and U+U collisions at$\sqrt{{}^{{s}_{NN}}}$ = 200 GeV and the results of comparative analysis of proton (three valence quarks) and φ, π⁰-mesons (quark antiquark pairs) production as a function of quark content and collision geometry (Cu+Au and Au+Au).

Using the method of Raman spectroscopy the study of bone tissue of rats has been made in this work after hyperthermia and injection of allogenic hydroxyapatite. It has been established that the process of thermal treatment of bone material up to 70°C for 15 minutes allows preserving organic components of biomaterials

Spectra and time dependencies of fractoluminescence (FL) signals of silicon (Si) and quartz (SiO₂) crystals are obtained when diamond crystals are scratched on their surfaces. Signals are generated when barriers preventing dislocation movement along sliding planes are broken. Simultaneously, the Si and SiO₂ crystals break down into nanocrystals (nc). The band 1.62 eV and 2.14 eV corresponds in FL spectra of Si and SiO₂ nc accordingly. After the crystals are broken, powders are formed. The size of Si and SiO₂ nc in powders was determined by photoluminescence (PL) and Raman spectroscopy.

The Raman spectra of dental tissues with periapical periodontitis have been analyzed. Chemometric analysis of the Raman spectra of hard dental tissues of healthy patients and the patients with periapical periodontitis has been carried out. The main spectral features of dental tissues with periapical periodontitis have been identified, which will further allow developing new methods of early detection of periapical periodontitis.

The present research focuses on modeling and analyzing a PPLN-transducer as a logical element, taking into account the heterogeneity in dispersion of group velocities along its length, and aims at the creation of a gradient PPLN. Within the framework of the research, a model has been built and logical elements AND, OR, XOR have been simulated on the example of periodically poled waveguide structure of lithium niobate with gradient composition.

The necessity of method developing for losses compensation in the fiber optic communication lines after irradiation is substantiated. The reasons of appearance of radiation color centers in the optical fiber, which are the main sources of losses in irradiated fiber, are considered. The different methods of the governance of color centers relaxation rate after γ-radiation influence to the optical fiber are researched A method of the relaxation processes rate increasing of color centers is developed. It's using allows to compensate the negative influence of γ-radiation on the fiber optic communication line of the during data transmission. The received experimental results are presented.

Collisions of alkali atoms in the ground state are accompanied by the exchange of electron polarization between the colliding atoms, which lead to the polarization transfer between particles. As a result of this process, the electronic orientation is transferred from the spin oriented atoms to unpolarized atoms, along with the polarization transfer, the magnetic resonance frequency shifts of polarized atoms occur too. In this work the magnetic resonance frequency shifts of arising from spin exchange collisions in a mixture of alkali potassium and rubidium atoms at the optical orientation of atoms are calculated. The situation when optical pumping by resonant polarized radiation is carried out only for atoms of the one kind is considered. The spin exchange process between alkali atoms was described in the formalism of the complex cross section for spin exchange process. The real and imaginary parts of the complex cross section were calculated using the interaction potentials of alkali atom dimers. The calculation of the frequency shifts is carried out on the basis of data on the interaction potentials for the following pairs of alkali atoms K-K, K-Rb and Rb-Rb. Maxwell averaging of the cross sections over the velocities was done and the temperature dependences of the magnetic resonance frequency shifts for K and Rb atoms were plotted.

Heat treatment conditions effect on the characteristics of the Z₃-exciton resonant luminescence of CuCl nanocrystals in potassium-aluminaborate glass is studied. The observed patterns of luminescence buildup are explained by the participation of thermal effects in recombination processes. The size effect in the resonance emission of Z₃-excitons at 80 K is confirmed. The inverse dependence of the defectiveness of CuCl crystals in glass on the luminescence buildup rate of Z₃-excitons is established.

In this work, the stability of short-wavelength spatial modes in quarter-disk cavities was studied. It was found that in such resonators, short-wave modes (with wavelengths λ smaller than the radius R of the quarter-disk λ<<R) in space form figures similar to folded twice m-polygons. The m-order of allowed stable modes decreases rapidly with an increase in the δ/R parameter of deviation from the ideal quarter-disk shape. Unlike half-disk resonators, quarter-disk resonators with δ/R>0.1 lack total internal reflection modes.

XPS and NEXAFS spectroscopy were used to study calcium copper titanates (CCTO) solid solutions doped with iron and nickel atoms. The CCTO compound spectra analysis shows that titanium atoms have +4 charge state, and copper and calcium atoms – +2, and their valency does not change when doped with iron and nickel atoms at the concentration of the latter up to 6 atomic percent. In this case, doping atoms are mainly embedded into the positions of titanium atoms and have Fe ³⁺ and Ni ^2,5+ charge states.

We present a theoretical and numerical investigation of effect of a weak coherent holding radiation on transverse field structures in a wide-aperture laser with fast saturable absorption. In the absence of the coherent driving, the laser is able to support various types of "free" bright solitons. We show that even weak driving can control their topology making the scheme promising for topologically protected information processing.

The formation of two-dimensional bright spatial solitons by in-phase laser beams with a wavelength of 532 nm propagating in the bulk of photorefractive lithium niobate crystal under the reversal of the sign of the nonlinear optical response of the material with the contribution of the pyroelectric effect has been experimentally demonstrated. It is shown that varying the distance between the beams at the input face of the crystal leads to the interaction of pyroelectric solitons, which allows the formation of non-rectilinear propagation paths of light beams.

This study is devoted to a new section in the field of singular optics-to beams carrying a fractional topological charge. A feature of this type of beams is structural instability, and with the slightest external perturbation, these beams form arrays of optical vortices. These vortices can be connected and, as it were, form an integral picture, or disintegrate due to the fact that during the propagation each of the vortices receives an additional phase incursion. These studies were based on a theoretical calculation and experimental study of the vector structure of beams transporting optical vortices with a fractional topological charge and the proof of the process of forming asymmetric TE (transversely electrical) and TM (transverse magnetic) modes in free space, and the study of the features of their "thin" vector structures in free space.

The optical reflectance and transmittance spectra of a periodic InGaN semiconductor heterostructure with 100 quantum wells are studied at room temperature. Numerical modeling with a single set of parameters gave a quantitatively accurate fit of the experimental reflection and transmission spectra in a wide wavelength range. The radiative decay parameter is determined to be 0.25 meV and the nonradiative decay parameter is 40 meV.

In this work, the powder and ceramic samples of gadolinium tantalum niobate (Gd(Nb_xTa_1-x)O₄) grown by the liquid-phase method were studied. Phase homogeneity and composition were determined by x-ray diffraction analysis and electron probe microanalysis. Luminescent properties were studied by local cathodoluminescence technique. All samples obtained a high phase homogeneity. It was found that the dependence of the monoclinic lattice parameters on the niobium content in the niobium-tantalum pair has monotonic character. The solid solutions were formed at synthesis temperatures from 1180 to 1400°C. The sample of pure gadolinium niobate (GdNbO₄) showed the maximal cathodoluminescence intensity.

Structural and dynamic properties of short-period GaN/AlN superlattices with the thicknesses of the constituent layers varying from two to several monolayers, grown using the method of submonolayer digital molecular beam epitaxy, are experimentally and theoretically studied. It is established that in the grown samples there are two types of periodicity. One type is formed by periodic sequence of GaN and AlN layers in the superlattice, and the second one is related with periodic interruptions in the growth of superlattice for the evaporation of excess Ga metal. The dependences of the positions and intensities of the lines in the Raman spectra on the period of the superlattice are determined, and microscopic nature of optical phonon modes is established. The doublet structure of the E(TO) lines localized in the GaN and AlN layers of superlattice, genetically related to the E₂(high) and E1 phonon branches of the bulk crystal, is first discovered and explained. A strong dependence of the polar modes localized in the AlN layer on the thickness of layer forming the superlattice is revealed. The results of complex studies will improve the accuracy of quantitative estimation of important parameters of superlattice structures and can be used to optimize growth parameters for the fabrication of structurally perfect short-period GaN/AlN superlattices.

Transparent glass-ceramics of magnesium aluminum silicate system based on nanosized MgAl2O4 spinel crystals nucleated by TiO₂ and doped with Fe₂O₃ were developed. Their structure and spectroscopic properties were studied. The glass-ceramics are important as reference samples in development of saturable absorbers in the short-wave infrared spectral range (2-3 μm).

This study is devoted to the investigation of the optical properties and composition of GaPN/GaP nanowire heterostructure. Nanowire arrays were grown on Si substrate (111) by the plasma-assisted molecular beam epitaxy. Polydimethylsiloxane membrane encapsulation was used to obtain the free-standing NW arrays. The morphology of GaPN/GaP NW was investigated with scanning electron microscopy. The optical properties of the GaPN nanowire arrays were determined at the He temperature (5K) with photoluminescence spectroscopy. Analysis of photoluminescence response allowed us to conclude that the incorporation of nitrogen atoms during the growth occurs both in the nanowires and in the parasitic islands with different content. Direct bandgap-like behaviour of the GaPN/GaP nanowires demonstrates the potential of nanowire-polymer matrix practical application in future optoelectronic devices.

The results of experimental and theoretical studies of phonon modes in short-period GaN/AlN superlattices grown by PA MBE on the (0001) Al₂O₃ substrate are reported. In the framework of Density Functional Theory and Elastic Continuum Model the lattice dynamics properties are studied of (GaN)_m(AlN)_n SLs (m+n≤24), where n and m are the number of monolayers. Good agreement between experiment and theory is found, which made it possible to establish unambiguously a relationship between the features observed in the Raman spectra and the microscopic nature of the acoustic phonon modes. The obtained results open new possibilities for analyzing the structural properties of GaN/AlN SLs by Raman spectroscopy.

We study bound states in the continuum related supercavity modes in finite lattices of silicon rods. Two low-frequency symmetry-protected modes are examined. We find that Q factor has almost cubic dependence on the rod number and 50 rods are enough for Q exceeds 10⁴. We discuss possible applications of these supercavity modes based on their electromagnetic field pattern. The structure surrounded by liquid media keeps its functionality by substitution silicon rods with rods made of Ge-Sb-Te.

We theoretically examine the quantum vortices creating through barrier-suppression ionization of two dimensional hydrogen atom by ultrashort laser pulse. We show that for the considered case of ionization, the excited discrete atomic states do not impact on the vortex formation, and the problem can be considered in the single-level atom approximation.

We propose a convenient method for generating optical traps based on a spatially structured beam. The proposed method of optical trap shaping utilizes interference of few Gaussian beams which waists, inclination angles and beam number are chosen for controllable trapping of micron-sized particles in three-dimensional space. In addition to implementing non-contact trapping, optical visualization in all planes was performed with digital holographic microscopy. This method contributes to the accurate localization of the studied specimens inside the cuvette over whole volume.

We investigated the high-order mode structure of a weakly guiding twisted anisotropic optical fibre. An analytical solution of the vector wave equation for this case is presented. We obtained analytical expressions for the higher-order modes with an azimuthal number ℓ = 2 and their propagation constants of such a fibre, considering the mutual effect of linear anisotropy of fibre's material, twisting, including torsional mechanical stress, and spin-orbital interaction. We showed that optical vortex beams with topological charge ±2 are the modes of the fibres considered.

In this work, SiO₂ sol-gel glass doped with Eu³⁺ was investigated its structural and luminescence properties. It was shown that a area containing crystallites of cristobalite with a size of about 45 nm is formed on the glass surface. The Eu³⁺ spectrum in surface area was obtained. It was demonstrated that the main part of the sample is X-ray amorphous; however, the Eu³⁺ spectrum in it demonstrates the presence of short-range order.

The article presents a phase sensitive amplifier based on cascaded second harmonic generation and difference frequency generation in a waveguide in the gradient periodically poled lithium niobate. The influence of the composition gradient in periodically poled lithium niobate on phase and spectral dependence of amplification factor is described. The increase of 35% is shown in spectral range of the gradient amplifier in comparison with the gradientless one in the range of 1.55 μm. The dependence of amplification factor of the optical signal from the propagation direction in the waveguide channel in gradient PPLN is also presented.

A method for measuring of the defects density distribution profile over the area of the LED chip is presented. Using the blue commercial LEDs as an example, it is shown that the emission power decreases when LEDs testing under the increased density pulsed current for 190 h. The decrease of the LEDs emission power is accompanied by a change in the defects density distribution profile. It was determined that during the degradation process a non-uniform increase in the defects density occurs in various regions of the heterostructure: in regions with a higher defect density, the increment in the density of defects is larger.

In this paper we investigate in details the scenario of a transition to chaos in the spin-wave optoelectronic oscillator. The feature of the investigated circuit is the presence of two nonlinearities with different nature – modulation instability of spin waves and nonlinearity of the transmission characteristic of the electro-optical modulator. The influence of a position of the modulator bias point on the scenario of chaos development is experimentally investigated.

The static characteristics of 1.5 μm wafer-fused VCSEL with the thin n⁺⁺-InGaAs/p⁺⁺-InGaAs/p⁺⁺-InAlGaAs tunnel junction (TJ) were investigated. The devices with the 8 μm diameter of the buried tunnel junction (BTJ) demonstrate effective single-mode lasing. A rapid increase in the threshold current, accompanied by an abrupt change in the output optical power is observed for devices with BTJ-diameter less than 7 μm. The observed behavior can be explained by increasing in the overlap of the optical mode with the unpumped (passive) part of the active region, which leads to the additional optical absorption. On the one hand, since the high-order transverse modes have the higher optical losses due to larger overlap with the unpumped part of the active region, then lasing via fundamental mode is more preferable even at large size of BTJ region. On the other hand, the reduction of effective index step between the BTJ region and the regions outside BTJ (caused by using small TJ etching depth) and the lateral smoothing of the difference in the height of the surface relief after TJ regrowth results in the significant drop of the transverse optical confinement factor and rise of absorption. Moreover, the absorption effect can be also strongly enhanced by increasing the heatsink temperature due to decreasing in the gain-to-cavity detuning.

Optical and electrical characteristics of asymmetrical InAs/InAsSb/InAsSbP LED heterostructures with the InSb content in the active layer of 0.15 and 0.16 were studied in the temperature range 4.2 -300 K. At T < 150 K, radiative transitions involving donor-acceptor states in the InAs substrate were observed in electroluminescence spectra, and the presence of these states also showed up in the peculiarities of current-voltage characteristics. A strong effect of the quality of the InAsSb/InAsSbP heterointerface on the characteristics of the heterostructures was observed.

In this article the temperature dependences of selective contacts based on MoO_x were studied. The p-Si/MoO_x/Al structure was fabricated. Current-voltage and capacitance-voltage characteristics in the temperature range from 80 to 300K were measured. Band diagram was also calculated to reveal potential barriers location and its influence on charge carrier transport.

The temperature dependences of the diffusion and recombination saturation currents and the energy gap have been obtained for a GaAs photoelectric converters. Saturation currents by IV characteristic analysis, and the energy gap by electroluminescence peak position have been determined. It has been shown that the relationship between saturation currents and energy band gap is characterized by the only parameter J_z (current invariant). At the temperature range of 100 -420 K this parameter does not depend on the temperature.

Microwave photonics is implemented in many applications, including the area of inertial navigation systems based on high-precision fiber-optic gyroscopes. Microwave photonic technologies allow increasing the fiber-optic gyroscope accuracy. This paper investigates and evaluates the effect of ultra high frequency modulation of laser radiation on the closed-loop fiber-optic gyroscope output signal. Research results show that ultra high frequency modulation makes it possible to broaden spectrum width due to redistribution to modulation harmonics of the laser radiation. This approach allows to reduce the standard deviation of the laser-driven fiber-optic gyroscope output signal more than 2.5 times compared to using a laser-driven fiber-optic gyroscope without modulation. In order to achieve the noise level of a laser-driven fiber-optic gyroscope the same as the noise level of a fiber-optic gyroscope with a broadband source, it is necessary to use a broadband noise source with a constant power spectral density and higher output power. This study is useful for understanding how application of microwave photonic technologies can impact on the fiber-optic gyroscope output signal. The obtained results can be used for researchers in this area of study and can facilitate the rapid development of this field.

Due to the development of high technologies, there is a need to use computer systems to support the increasingly complex types of human activities. It provides high accuracy and speed of various research and medical examinations. Taking into account the daily workload of doctors in the Intensive Care Unit, remote medical diagnostics systems are being implemented in many referral hospitals to predict the course of diseases. Decision-making is the result of processing certain information, the medical history patients based on the use of accumulated knowledge. Therefore, it can be concluded that automatic and visual control systems make the diagnosis process more accurate and easier. The aim of the work is to develop an optoelectronic system for visual monitoring and data transmission for patients in a coma by Li-Fi technology.

The contribution of several mechanisms to the external quantum efficiency (EQE) droop in blue InGaN/GaN LEDs occur at different current densities j and voltages in MQWs situated inside and outside of a depletion region around p-n junction. It is clarified that an increase in EQE droop at 300-400 K (j < 10 A/cm²) is due to non-radiative losses related to an enhancement in trap-assisted tunneling. It is also associated with a growth in the concentration of delocalized carriers. The main source of the EQE droop under direct current and at pulse mode when j > 30 A/cm² is non-equilibrium filling of lateral regions of different size within MQWs placed outside of depletion region by delocalized carriers activated by injection when voltage exceed a threshold value (U > Uth). This leads to a decrease in localized potential and to the blue shift of EQE maximum over wavelengths followed by the EQE droop.

The work presents a method allowing calculating the input admittance of an acousto-optic modulator with XY-cut lithium niobate substrate for a specific interdigital transducer structure is presented. The method does not require complex numerical computations and is sufficiently accurate. The method is based on the information about the pole of a Green's function for a given piezocrystal. A method of measuring parameters and finding the types of the excited acoustic waves based on joint time-frequency analysis using modern vector network analyzers is also presented. Good correlation between theoretical and experimental investigation is demonstrated.

We demonstrate the possibility of using vertical-cavity surface emitting lasers with intracavity contacts and a rhomboidal oxide current aperture for creating compact optically pumped ¹³³Cs atomic magnetometer operating in non-zero magnetic fields, which is promising to use in magnetoencephalographic systems. The magnetic resonance parameters were studied in a two-beam MX optically pumped magnetic field sensor scheme based on the effect of the magnetic resonance line narrowing at high laser pumping and high concentrations of alkali-metal atoms. The ultimate sensitivity of OPM was estimated by the ratio of the magnetic resonance steepness to the probe light shot noise level. It is shown that a magnetic sensor based on the vertical-cavity surface emitting lasers and a compact (0.125 cm³ volume) Cs vapor cell can achieve a shot noise-limited sensitivity better than 15 fT in 1 Hz bandwidth. Developed intracavity contacted VCSELs suitable for use in compact atomic magnetometers for magnetoencephalographic systems.

Numerical simulations of power characteristics and emission spectra of LED structures with the active layer made of InAsSb with InSb molar fraction 0, 0.06 and 0.15 were performed. A satisfactory agreement between the modelled and experimentally recorded electroluminescence spectra was achieved for all the structures studied. The results of the modelling of the power characteristics showed very good design of the heterostructures in respect to carrier concentrations in their layers. Still, the results of the simulations predict that in theory the power of the studied LEDs can be enhanced by almost an order of magnitude.

We present an experimental study of the optical gain of edge-emitting lasers based on a new type of quantum-sized InGaAs active medium grown on GaAs substrates, which we refer to as quantum-well-dots (QWDs). It is shown that the single layer QWD active region provide at least 33 cm⁻¹ optical gain at 1030 nm comparable to the values typical for InGaAs quantum wells (QWs), and the width of the gain spectra characteristic for InAs quantum dots (QDs). Thus, QWD active region combines the advantages of both QW and QD heterostructures and has a great potential for improving characteristics of various semiconductor devices.

The heterostructure design for 1.55 μm range VCSELs is proposed and realized. The wafer fusion technique was used to form the final heterostructure. The growth of AlGaAs/GaAs distributed Bragg reflectors (DBRs) on GaAs substrate and the optical cavity with an active region on InP substrate as well as a tunnel junction (TJ) regrowth was performed by molecular beam epitaxy (MBE). A key feature of the proposed design is the use of n⁺⁺-InGaAs/p⁺⁺-InGaAs/p⁺⁺-InAlGaAs TJ, which allows, due to the effective removal of oxide from the InGaAs surface, to use MBE for re-growth of the TJ surface relief. Despite of the presence in heterostructure a narrow-gap InGaAs layers, a noticeable increase in internal optical loss in lasers can be avoided due to the short-wavelength shift of the edge of interband light absorption in ⁺⁺-InGaAs layers (Burshtein-Moss effect). Fabricated VCSELs demonstrate single-mode operation with a threshold current less than 2 mA and a slope efficiency of ~ 0.46 W/A, which are comparable with characteristics of VCSELs with n⁺⁺/p⁺⁺-InAlGaAs TJ with a similar level of mirror losses.

A combination of advanced concepts is applied for designing micro-cavity structures aimed for single-photon sources with high photon-extraction efficiency in the telecom O-band at ~1.3 μm. The device design consists of a broad stop-band bottom distributed Bragg reflector (DBR), a top DBR formed in a dielectric micropillar with additional circular Bragg grating and a central dielectric passive cavity. This combination of photonic elements is compatible with electric carrier injection and provides overall photon-extraction efficiency of ~83% as shown by 3D finite-difference time-domain simulations.

Narrow gap heterostructures consisting of two double heterostructures (N-InAsSbP/n-InAs/P-InAsSbP and P-InAsSbP/n-InAs_0.9Sb_0.1/N-InAsSbP) grown sequentially onto a n+-InAs substrate and further processed into a two-color photodiode with individual sensing operation at 3.3 and 4 have been studied. Presented and discussed are the photodiode construction details, I-V characteristics as well as sensitivity and detectivity spectra measured at room temperature.

Photoelectric properties of MIS tunnel diodes produced on high-resistive p-type silicon wafers with thin aluminium nitride AlN insulator layer and Pd or Al metal gate electrodes were investigated. It was found that synthesized AlN films possess a fixed positive charge, which leads to the creation of near-surface inversion layer in silicon substrate. The ratio of the photocurrent to the dark current K = Iph / Idark (on / off ratio) was found to depend on the gate electrode material, illumination intensity and the applied reverse bias. For studied MIS structures K ratio varied from 10 ⁴ to 10 ⁵ and was two orders of magnitude higher than that for the control MS structure without the insulator layer. High on / off ratio of such MIS structures with AlN tunnelling insulator promotes their application as an effective photodetectors in optoelectronics.

A study of the mechanism of uptake and conversion of microwave energy into heat energy is presented. The term "SHF – trigger", which activates at the atomic, electronic, and molecular scales, is introduced for the mechanism of micro cracking, destruction, and crashing of quartz-containing rocks. It has been found that the uptake and conversion of microwave energy into heat energy begins there were some criteria of the sample instability in energy consummation are satisfied. This mechanism of the energy conversion with the heating effect differs from other modes of heating by its efficiency; accordingly, a special criterion is required. The loss tangent of a dielectric, such as mineral or heterogeneous rock, could serve as a measured parameter. This parameter is attributed to slowly establishing modes of relaxation, which manifest themselves in the presence of polar molecules, complicated anion radicals, chemically bounded water, solid/liquid interfaces, borders of dielectrics and conductors. In addition, a new mechanism of conversion of microwave energy into heat energy in points of contact between water-saturated pores in model specimens was suggested.

The experimental data on the thermovoltaic effect in bulk samples of samarium sulfide (SmS) are considered in this work in accordance with the represented kinetic model. The kinetic laws of the elementary process of samarium ions ionization have been studied, expressions are obtained for both the dynamics of the ionization process and the process statics in the context of the law of mass action in bulk samples of samarium sulfide. Such a description of the thermovoltaic effect made it possible to obtain the current-voltage characteristics of the samples at a constant temperature. All basic parameters were obtained for the thermovoltaic generator being developed: short circuit current and open circuit voltage; the internal resistance of the generator as well as the maximum power dissipation at the found load resistance was determined by calculation.

Thermal processes in SmS/Sm_1-xGd_xS heterostructures are investigated. It is noted that cooling is observed on the Sm_1-xGd_xS side when these heterostructures are heated. Cooling value is less than that of previously observed in SmS, but the stability is higher. It is shown that the main factor influencing the cooling effect is the collective casting of electrons into the conduction band from impurity levels. There are two multidirectional electron flows as a result of this fact - due to the thermovoltaic effect and due to the Seebeck effect.

Current-voltage and capacitance-voltage characteristics of tunnel diode structures with GaAs-n++/i-GaAs/i-Al_0,2Ga_0,8As/Al_0,2Ga_0,8As-p++ active region and i-layer thicknesses of 7.5 nm and 10 nm and epitaxial growth temperature of 450 °C and 500 °C have been studied. The tunnel diode structures grown by the molecular beam epitaxy technique are intended for application as connecting elements in multijunction photovoltaic converters of high-power monochromatic optical radiation. According to the results obtained, the peak tunnel current density of up to 200 A/cm² is achieved. Forward current-voltage and capacitance-voltage characteristics of tunnel p-i-n diode structures were measured at room temperature. The capacitance-voltage characteristics of the tunnel diodes being tested were obtained experimentally with the frequency dependence of S-parameters simulated within 10-1000 MHz at bias voltages of 0.4–1 V.

The process of generating an acoustic signal during laser heating of metals and dielectrics is analyzed in the framework of the theory of thermoelasticity. A comparison of the experimental optoacoustic signal and the theoretical distribution of mechanical stresses for plates with a hole of aluminum alloy and silicon nitride is performed. It was found that the standard theory of thermoelasticity can qualitatively describe the dependence of the optoacoustic signal on the stress near the hole in the silicon nitride plate, but is not enough to correctly describe the dependence of the signal on the stress near the hole in the metal plate. It is noted that in order to achieve agreement between the obtained experimental and theoretical results for metals, in addition to the thermal effect of laser radiation on the lattice, it is necessary to take into account the additional effect of the electron system.

Here we introduce the research studies of perovskite solar cells with multistructured photoelectrodes based on very wide bandgap nanocrystalline materials. A series of solar cells with the device architecture FTO/c-TiO₂/ZrO₂(HfO₂)/CH₃NH₃PbI₃/Spiro-MeO-TAD/Au was fabricated and characterized. The results obtained demonstrate a successful possibility of PV application of the nanostructured oxide materials with bandgap values exceeding 5 eV. We propose a mechanism, which describes charge carrier transport at the interface of perovskite/multistructured photoelectrode.

The features of the formation of a SiO₂ hard mask using dry etching and nanosphere lithography are considered in the paper. A series of experiments was carried out using a variation of plasma etching parameters such as ICP and RF power, pressure as well as a substrate temperature. As a result, optimal parameters were found to obtain both good selectivity and high etching rate.

Quantum objects in the host material of photovoltaic converters can expand the spectral sensitivity to the long-wavelength spectral region. Samples with InAs quantum dots and thin layers in the host GaAs material were studied theoretically with the assumption of high-power laser subband irradiation input. Threshold factors have been established that affect the possibility of radiation heating. For noticeable increase in the temperature of the base material the necessary illumination values were estimated.

Hybrid organic-inorganic perovskite solar cells (PSCs) have attracted significant interest owing to their high power conversion efficiency (PCE) and low cost. Moreover, PSCs demonstrate high performance under low light illumination without significant reduction in PCE. However, photovoltaic properties of PSCs under low light conditions are rarely reported. Here, the potential of planar PSCs for efficient performance under low illuminance conditions was investigated. Planar perovskite solar cells with FTO/c-TiO₂/c-SnO₂/CH₃NH₃PbI₃/Spiro-MeOTAD/Au architecture were studied under variable illumination intensities in the range of 10 – 1000 W/m². Significant enhancement in PCE up to 18.4% was observed for planar PSCs under low light conditions (<100 W/m²), as compared to the 16% PCE value obtained under AM1.5 illumination. This was attributed to the decreased charge accumulation at the ETL/perovskite interface and increased charge collection efficiency under low light illumination. PSCs performance was additionally studied under artificial LED lighting (5500K, 1000 lux) and the PCE values exceeding 24% were obtained. The results of this work verify excellent low-light performance of planar PSCs and provide the possibility for their application as power sources for various low-power wireless devices (sensors, detectors, Internet of Things devices, etc.).

The results of studying the In_xGa_1−xAs laser power converters with the indium percentage of 18% and of 23% are presented. In the mode of 1064 nm laser radiation conversion the photovoltaic parameters dynamics with raising temperature is discussed.

Nanosphere lithography is well suited for quick and easy formation of ordered structures on the entire silicon wafer. After coating of close packed mask of spheres, they must be reduced in diameter. In various studies, the main method used for spheres diameter reducing is dry etching using capacitively coupled plasma (CCP) mode. In this paper, we present the possibility of spheres etching using inductively coupled plasma (ICP) mode, comparing the results obtained with CCP mode. A strong degradation of the spheres morphology was demonstrated at CCP mode, while the degradation effect was not sufficient using ICP mode. However, the effect of spheres migration over the silicon surface during ICP etching was observed. A preliminary thermal annealing of spheres allows one to avoid this effect. Finally, a technology of reducing the spheres size with minimal degradation and preserving the original spherical geometry was developed.

We study experimentally the influence of the laser-induced temperature gradient on the parameters of propagating magnetostatic surface waves in thin film of the ferromagnetic metallic alloy Galfenol Fe_0.81Ga_0.19. The material has a pronounced magnetocrystalline anisotropy and exhibits the long-distance propagation of magnetostatic surface waves excited with femtosecond laser pulses. The excitation pulse heats up the sample locally, what leads to the spatial-temporal change of magnetization and anisotropy parameters of the film, and thus excites the magnetostatic surface waves. We show experimentally that the spectrum of the excited waves narrows as they propagate in such a gradient medium. By changing the orientation of external magnetic field with respect to anisotropy axes of the sample, we control whether the low- or high-frequency part of the spin waves spectrum is suppressed.

This paper presents the results of a study of the structural and dielectric properties of barium-strontium titanate (Ba_0.5Sr_0.5TiO₃) with a high concentration of doped manganese ions. It was found that upon the addition of manganese ions, the phase transition point shifts toward lower temperatures. A graph of the dependence of the ceramic lattice parameters on the concentration of manganese ions is presented. It is shown that with an increase in the sintering temperature of ceramics, the dielectric constant of the samples increases.

Recently, much attention has been paid to the development of new microminiature solid-state cooling devices and heat energy converters based on the electrocaloric effect. But researchers pay little attention to aspects of the electrocaloric effect associated with its time and frequency characteristics. These phenomena must be taken into account when developing highly efficient thermodynamic cycles for solid-state cooling devices. In this work, we conducted an experimental study of the dependence of the electrocaloric response of a ferroelectric sample on the period and duty cycle of the control signal was studied. It was demonstrated, that value of electrocaloric response in studied ceramics may vary by more then 15% depending on period and duty cycle of electric pulses.

In this work, nanocrystalline yttrium orthochromite (YCrO₃) was synthesized via the solution combustion method using metal nitrates and glycine. The resulting powder was used for sintering YCrO₃ porous ceramics. The SEM, EDX, PXRD and TMA were used to examine structural and morphological features of both the preceramic powder and the sintered ceramics. The electroconductivity of the obtained porous ceramics was investigated in the temperature range from 25 to 1200 °C. YCrO₃ bulk conductivity was found to depend on the microstructure and the pore volume fraction: at temperatures below 400 °C the electrical conductivity was higher than the values for high-density ceramics, while for temperatures above 800 °C the electrical conductivity of the resulting material approaches the values of high-density ceramics (σ_dc = 1.97·10⁻² S/cm at 1000 °C).

Recent numerical results for ionization of quantum dots by periodic electric field during the electric dipole spin resonance are compared with known analytical approaches. It is found that in finite-length quantum wires the numerical ionization rate is slower than the analytical one, especially for low driving field when the confinement potential strongly affects the dynamics. Still, the analytically predicted ionization times are in satisfactory correspondence with mean energy threshold times when the energy crosses the border between localized and continuum states.

The spin-dependent electron transport in two coupled quantum rings with Rashba spin-orbit interaction and magnetic flux was studied by using quantum graph approach. We show the dependence of spin-polarization on system parameters such as the Rashba coupling constant, the radius of the rings, the angles between the leads and the attachment point of the rings. The spin-polarization can be controlled and changed from -1 to +1 by using a magnetic flux. Also it was shown that this model is a limiting case of double Rashba quantum ring when the length of the middle lead between rings vanishes.

The current-voltage characteristic of a superlattice based on the semi-Dirac crystals has been studied. The case of the absence of a gap between valence and conduction mini-band has been considered. Such a superlattice has been shown to be characterized by both semi-metal and narrow-band semiconductor electrical properties. From the one hand there is the point in the Brillouin zone close to which the depletion of the states occurs without gap opening. From the other hand there is the portion of negative differential conductivity in the current-voltage characteristic. The dependences of longitudinal conductivity and maximum of the current-voltage characteristic on the Fermi energy have been investigated.

The dynamical theory of X-ray diffraction is developed to the case when the incident and reflected X-ray beams are spatially bounded. X-ray diffraction in complicated lateral periodic structures is considered. Effects, due to periodic regular elastic deformations of a crystal lattice on an angular distribution of the scattered intensity, are investigated. Using the found solutions, numerical simulations of reciprocal space maps for crystals with periodically distributed elastic strains were performed. It was established, that for crystals modulated by a surface acoustic wave, diffraction orders consist of the main reflection vertical band and a pair of inclined bands, induced by spatially bounded X-ray beams. In the case of diffraction in crystals with the surface grating, one observes additional satellites along inclined bands caused by the spatial modulation of incident X-ray wave. Results of X-ray diffraction on a crystal modulated by a surface acoustic wave and on a crystal with a metal surface grating are presented.

Self-organized quantum dots (QD) InP/GaInP₂ are natural electronic molecules (EM). They are promising objects for the study of the physics of strongly correlated electronic systems and the creation of quantum logic elements. In this work, we used micro-photoluminescence technique to study the effect of molecular oxygen on emission properties of these QDs and possible reducing their surface density.

The article presents a brief generalization of our recent experiments confirming that "irreversibility field" in Nb-Ti superconducting tapes is determined by the inhomogeneity of superconducting properties. It is shown that the effect is a direct consequence of the so-called δl-pinning, i.e. pinning caused by local reduction of the electrons mean free path. Based on the understanding of the irreversibility field nature, an assessment of the individual pinning force is performed. Good agreement is obtained with the estimations performed in the framework of the Larkin-Ovchinnikov pinning model (LO), which is valid for magnetic field less than the irreversibility field. The competing model is considered which is also valid for field range below the irreversibility field - the anisotropic pinning model (APM). The comparison of the fundamental length scales introduced in the LO and APM models is given.

Gaussian impurity bands in GaN responsible for intracenter optical absorption and photoluminescence, give rise to defect-assisted carrier tunneling (hopping) through the barriers in the pn nanostructures with InGaN/GaN quantum wells (QWs). The tunneling injection of majority cariers into the QW results in the current humps and in rapid increase in the radiative recombination efficiency at low enough forward bias. As the bias increases, the carrier confinement in the QW weakens, leading to tunneling injection of minority cariers into the barriers, which results in the emission efficiency saturation and droop.

In this paper, we theoretically analyze the recombination and spin dynamics of excitons in an inhomogeneous ensemble of colloidal nanocrystals, which consists of several subensembles with different lifetimes and degrees of circular polarization of exciton photoluminescence (DCP). Each subensemble is described within a three-level model of interacting exciton states, including two excited states and a ground state. Various ratios of parameters, leading to a nontrivial time-dependent DCP and a difference in the integral and equilibrium DCP characteristics, are considered. It is shown that the presence of subensembles with different polarizations and lifetimes results in nonmonotonic dependence and a change in the sign of the DCP in magnetic field and as a function of time can occur. The theoretical model was implemented to describe the time dependences of the DCP in ensembles of colloidal CdSe nanoplatelets synthesized in the air and argon atmosphere.

Using the relaxation time approximation, an analytical expression was obtained for the direct current density arising in a two-dimensional superlattice when, in addition to two elliptically polarized waves, a constant field acts on the sample along one of the directions.

The effect of the Fe doping profile of the GaN buffer layer in the heterostructures for high-electron mobility transistors was studied experimentally and by computer simulation. The exponential Fe tail extending to the nominally undoped layers may greatly affect the properties of the structure. Reducing the distance between the channel and the Fe-doped buffer to less than 1 μm results in a decrease in the density and mobility of the two-dimensional electron gas. It also leads to the higher off-state avalanche breakdown voltage and reduced leakage current. A good agreement between simulation and experimental data is obtained when taking into account a Fe segregation effect, while an abrupt doping profile lead to significant discrepancies between them