Waves-2018

R e g u l a r p a p e r s

Physics of nuclei and elementary particles

Moscow University Physics Bulletin 2018. N 6.

In the last years, spallation reactions have increasing in several works and research applications. They are applying as optimum neutron sources investigations or for energy production and nuclear-waste transmutation in accelerator-driven systems. In this paper, a series of Monte Carlo calculations using the MCNP-6 code performed to calculate, identify the behavior and number of proton-produced neutrons and photons.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

In this paper, we investigated a system, is composed of a natural Tungsten and Bismuth cylindrical targets. The target has been optimized to produce the maximum of neutrons yield with a diameter of 20 cm and varying height from 10 to 80 cm. The target is bombarded with a high-intensity accelerator by a 0.1 GeV to 3 GeV proton beam. The protons are assumed uniformly distributed across the beam of diameter 2 cm. In this work, we have used Monte Carlo method by using MCNP-6 code to simulate spallation neutron yield, neutron spectrum and distribution of the spallation neutrons coming out of the target in the target region. According to the results approving using several simulations for two targets Tungsten and Bismuth, the difference of spallation neutron yield increases by 8.92 % using a Bismuth target and for some Beam energy 3 GeV.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

The dynamics of the electron beam in a C--band linear accelerator, a bremsstrahlung source with a boundary energy switched between 2.5~MeV and 6~MeV, intended for stereotactic and three-dimensional conformal radiotherapy in a static and rotational mode is calculated.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

The evolution of single-particle characteristics of isotones with N = 28 approaching to the neutron drip-line is calculated within the dispersive optical model. According to the calculation, the particle-hole gap N = 28 sharply decreases with the neutron excess increase so that the 1f$_{7/2}$, 2p$_{3/2}$ and 2p$_{1/2}$ states practically degenerate at the neutron drip line and occupation probability of the states is close to 0.5. The degeneracy of these states is one of the reasons for the deformation of N = 28 isotones with neutron excess due to the Jahn-Teller effect.

Show AbstractBiophysics and medical physics

Moscow University Physics Bulletin 2018. N 6.

The objective of this study is to evaluate mathematically an empirical law governs the skin dose with photon beam energy and irradiation field size based on experiment data of dose distributions. The dose distributions were expressed on percentage depth dose (PDD). The measurements of PDDs were done as a function of irradiation field size with an uncertainty of 2% as recommended by IAEA protocols. The skin dose corresponds to PDD at depth of 0 mm for photon beam energy of 6 MV and 18 MV. For these both photon beam energies, the skin dose increased linearly with irradiation field size and the skin dose rate decreased in power law as a function of irradiation field size with mathematical error under to 10 %. This law allows us to predict the skin dose with irradiation field size for high radiotherapy quality and high protection of organ at risks.

Show AbstractTheoretical and mathematical physics

Moscow University Physics Bulletin 2018. N 6.

The problem of asymptotic stability of a stationary solution with an internal transition layer of the one-dimensional reaction-diffusion equation is considered. The main feature of this problem is the discontinuity (of the first kind) of the reactive syllable (source) at some interior point of the segment on which the problem is considered, as a result of which the solutions have large gradients near the interface. The conditions of existence, local uniqueness, and asymptotic stability of the solution with such an internal transition layer are obtained in the operation. For the proof we used the asymptotic method of differential inequalities.The obtained conditions for existence and stability should be taken into account when creating adequate models describing phenomena in media with discontinuous characteristics. The results of the work can be used to develop effective methods for the numerical solution of differential equations with discontinuous coefficients.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

The expression for the effective electric charge per unit length of dislocation were obtained. It is shown that the electric polarization charge arises when the electric field interacts only with the edge components of dislocations. An expression was obtained for the force acting on a dislocation in an electric field and it was shown that in experiments the determining role should be played by the projection of this force onto the dislocation slip plane.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

A mathematical model of an infinite waveguide of a constant rectangular cross-section with losses in the walls, described by Schukin-Leontovich boundary conditions, is proposed. To calculate the waveguide, Galerkin's incomplete method is applied. The basis consisting of standard ideal waveguide basis and extra functions that allow to exactly meet the boundary conditions is used. The eigen-modes of the waveguide in the terahertz range are calculated, the dispersion characteristics are plotted.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

A family of exact solutions of a quasilinear evolution equation, describing the process of reaction-diffusion in a medium with an infinite degree of degeneracy of two extreme roots of a source density function is found. Several terms of the formal asymptotic series are constructed, representing a solution of the initial-boundary value problem in a spatially homogeneous medium for the case of a Gaussian source density function in a neighborhood of the extreme roots. A justification is given for the correctness of the partial sum of the asymptotic series using the method of differential inequalities. It is shown that the forward region of the moving front of the contrast structure has an exponential character,the back region of the front is represented by a much more slowly decreasing function, which for the Gaussian source density function is expressed in terms of the power function of the logarithm of the coordinate.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

A model for describing the distribution of magnetization over the thickness of a film of a ferromagnetic semiconductor in an external constant electric field perpendicular to the film surface is considered. The formulas obtained make it possible to determine the dependence of this distribution on the values of the physical parameters of the film.

Show AbstractRadiophysics, electronics, acoustics

Moscow University Physics Bulletin 2018. N 6.

The laser optoacoustic method which allows determining a volume concentration of polymer matrix and carbon filler in carbon fiber reinforced plastic (CFRP) composites is proposed and realized. Investigated samples were fabricated by vacuum infusion method. Volume concentration of epoxy resin matrix is measured for series of CFRP samples. It was shown that studied samples have areas with superfluity and deficiency of epoxy matrix. The developed method may be used for testing samples and for real composite constructions.

Show AbstractOptics and spectroscopy. Laser physics

Moscow University Physics Bulletin 2018. N 6.

In this paper, we estimate the strength of correlations between the layer thickness errors in the process of the optical coatings deposition with broadband optical monitoring. The strongest effect of thickness errors self-compensation is observed in case of high correlation between these errors. An estimate of self-compensation effect strength is suggested. Theoretical conclusions are confirmed by comparison to the results of practical coating deposition which exhibit the presence of strong self-compensation effect.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

The study of the interaction between humic substances (HS) and iron ions is of interest for investigating the migration pathways, the concentration of elements in natural waters, for HS practical use as a sorbent, as well as in solving environmental monitoring problems. Changes of spectral-luminescent properties and fluorescence kinetics of humic acids (HA) in water solution at addition of various concentration of ferric and ammonium chloride, and at change of solution pH were studied. Influence of HA and iron salts concentration, as well as solution pH on interaction of HA with Fe3+ are concluded.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

The simple analytical relations between the geometry of aperiodic thin-layer structures and the phase component of the reflection coefficient were deduced and investigated. The effective optical thickness of an aperiodic structure was introduced as a new parameter and then was analytically defined. The two-layer thin-layer model was proposed to describe wave properties of aperiodic thin layer structures with weak spatial heterogeneity of the refractive index. This model significantly simplifies the relations used to analyze wave properties of the concerned class of multilayer structures. Validity of the analytical results was proved by the corresponding numerical calculations.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

Attenuated total reflection (ATR) is often employed in the measurements of the FTIR spectra. Such a configuration is convenient for experiments with liquid samples, since pressing to the surface of the ATR crystal is not needed. Spectral changes that occur in the course of measurements with liquids are revealed. It is shown that significant variations in the concentrations of components may occur in the ATR-FTIR measurements of solutions. Redistribution of components of a solution in the vicinity of the ATR crystal may lead to inhomogeneity of the sample under study.

Show AbstractCondensed matter physics

Moscow University Physics Bulletin 2018. N 6.

BBound and free water are present in a wide variety of solids - single crystals, polymers, biopolymers, as well as in media with a hydrogen bond network as in water (2.7$\pm$0.1 Å in length). Some objects behave in the same way as two-component systems (open system) under external influences and demonstrate an abnormal change in properties at the same temperatures as free water. The paper presents the results of studies of temperature behavior of the permittivity, conductivity, and conductivity relaxation time of some hydrophilic polymers, crystallohydrates, and ferroelectrics. The analysis of the results showed that the temperature anomalies of the selected properties are observed in the vicinity of 20, 35, 65-75, and near 100°C, which are “special” temperatures for water: near these temperatures, the destruction of clusters of H2O molecules occurs, and at higher temperatures there is a transition of structural water into a free water. It is possible that the discrete nature of the diffuse temperature peaks of the properties is due to the presence of discrete energy levels of protons in the “matrix-water” system, which at stepwise heating (slow kinetics) leads to a rearrangement or destruction of the OH...O hydrogen bond network, as well as the over-population of the proton levels in the two-minimum potential, the release of deep traps, changes in the set of current carriers, their mobility, and the trajectories of transport in the bulk.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

Quasi one dimensional analytical model of electron transport through the system of scanning tunneling microscope needle, tetrapod nanocrystal CdTe/CdSe and substrate is developed. Using this model we investigate how the concentration of charge carriers in tetrapod, its zone structure, geometry and space orientation in relation to the substrate influence on volt-amperic characteristics. The main classes of current-voltage characteristics which can be measured in experiment are determined by numerical simulation. The classes of current-voltage characteristics determined in this way correspond to spatial orientation of tetrapods and their sizes. Based on the made classification of current-voltage characteristics from an array of previously measured characteristics we select those that correspond to transport electrons through the tetrapod from the needle of the scanning tunneling microscope to the substrate. By comparing the numerically calculated characteristics and the experimental characteristics of the described model, we determine parameters that give the best match.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

Samples of Fe-B alloys were prepared by quenching the melt using a rotating copper disk and certified with X-Ray analysis. It is established that some of the alloys have an amorphous structure. In the amorphous ribbons of the Fe-B system, gyromagnetic effects are observed, replacing each other as the temperature of the sample changes. The observed features are interpreted using magnetometric studies.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

Thermoelectric properties of p-PbTe were studied theoretically within the acceptor doping interval of 5х10$^{19}$ – 4x10$^{20}$ cm$^{−3}$ and in the temperature range of 300–900 K. A three band model of the electron energy spectrum was used in the calculations that included not only the light electrons and holes in L-points of Brillouin zone but also the heavy holes in its 6-points. The heavy 6-band plays an important role in the thermoelectric figure-of-merit enhancement of this material at high acceptor doping. The calculated thermoelectric quantities are sensitive to the doping level. The figure-of-merit increases with the doping level, and the maximum achieved ZT value was 1.3 at 900 K. This maximum is observed close to the temperature at which energies of the light and heavy hole extrema coincide, and the Fermi level is not far from it.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

The effect of spherical SiO$_2$ nanoparticles of 20 to 80 nm in diameter embedded into the PEDOT: PSS buffer layer of organic solar cells (OSC) based on star-shaped oligomers on their efficiency was studied experimentally in detail. Measurements and analysis of the current-voltage characteristics of the samples, their absorption spectra and study of the morphology of the surface of the buffer layer with embedded nanoparticles were carried out. It is shown an increase in the OSE efficiency for the case of embedded into the PEDOT:PSS layer SiO2 nanoparticles with a diameter of 20 and 50 nm, which slightly depends on the concentration of the nanoparticles in the buffer layer.

Show AbstractAstronomy, astrophysics, and cosmology

Moscow University Physics Bulletin 2018. N 6.

In this paper a task of the operative monitoring of radiation conditions in the near-Earth space is considered, as a part of a project of the system of small satellites “Universat-SOKRAT” which is being developed in Moscow State University. A scientific approach to the realization of this task is determined. A choice of the satellite orbits and spatial orientation and the configuration of energetic charged particle detectors is validated taking into account other tasks performed by the projected satellite system.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

The purpose of this paper is to consider the cosmological models which contain two scalar fields. One field is an inflaton, the other is the source of the observed accelerated expansion of the universe at the present time. For the model, which is considered in this work, the corresponding chiral cosmological model was found and the metric of internal field's space is defined.

Show AbstractPhysics of Earth, atmosphere, and hydrosphere

Moscow University Physics Bulletin 2018. N 6.

The numerical simulation method is used to study particular features of the dynamics of weak tsunami waves caused by deep-focus Okhotsk Sea earthquake on May 24, 2013. It is established that a vast area of co-seismic deformations in combination with small depths of the Okhotsk Sea and high latitudes created favorable conditions for the manifestation of the Earth rotation effects in the dynamics of the 2013 Okhotsk Sea tsunami. By comparing the results of calculations performed with and without Coriolis force, it is shown that the rotation of the Earth has a significant effect on the wave field, changing the waveforms and the distribution of maximum amplitudes.

Show AbstractMoscow University Physics Bulletin 2018. N 6.

The objective of the present paper is to perform laboratory and direct numerical modeling of turbulent wind over water surface under stable stratification conditions. Laboratory and numerical experiments are performed under the same bulk Reynolds (Re) and Richardson (Ri) numbers which allow a direct comparison between the measurements and calculations. The wind flow with the air-water temperature difference of up to 20K and relatively low wind speed (up to 3 m/s) are obtained within lab experiment in a Wind-Wave flume on the basis of a Large Thermostratified Tank at IAP RAS. It allows to realize a sufficiently strong stable stratification with bulk Ri up to 0.04. The air velocity is retrieved by employing both contact (Pitot-tube) and PIV methods, and the air temperature profile is measured simultaneously by a set of contact probes. The same bulk Ri and Re are prescribed in direct numerical simulation where turbulent Couette flow is considered as a model of the near water constant-stress atmospheric boundary layer. The mean velocity and temperature profiles obtained in our laboratory and numerical experiments agree well and also are well predicted by the Monin-Obukhov similarity theory. The results show that sufficiently strong stratification, although allowing a statistically stationary turbulent regime, leads to a drastic reduction of both turbulent momentum and heat fluxes. Under this regime, the flow turbulent Reynolds number (based on the Obukhov length scale and friction velocity) is found to be in agreement with known criteria characterizing stationary strongly stratified turbulence.

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