R e v i e w s

Astronomy, astrophysics, and cosmology

Moscow University Physics Bulletin 2017. N 6.

We discuss the results of the cosmic ray energy spectrum and mass composition studies obtained with arrays for extensive air showers detecting. A survey of ground arrays performing such researches and a brief description of the primary particle characteristics recovery methods from experimental data are presented. Particular emphasis is given to the energy range of 10^16 – 10^18 eV where a transition from Galactic cosmic rays to extragalactic ones is expected. The complex of arrays created in the Tunka Valley for studies in this range is considered specially.

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Condensed matter physics

Moscow University Physics Bulletin 2017. N 6.

The charge accumulation in an insulating material under an electron beam bombardment exerts a significant influence to scanning electron microscopic imaging. This work investigates the charging formation process by a self-consistent Monte Carlo simulation of charge production and transportation based on a charge dynamics model. The charging effect in a semi-infinite SiO2 bulk and SiO2 trapezoidal lines on a SiO2 or Si substrate has been studied. We used two methods to calculate the spatial distributions of electric potential and electric field for two different systems respectively: the image charge method was used to deal with a semi-infinite bulk, and, random walk method to solve the Poisson equation for a complex geometric structure. The dynamic charging behavior depending on irradiation time has been investigated for SiO2. The simulated CD-SEM images of SiO2 trapezoidal lines with charging effect included were compared well with experimental results, showing the contrast change of SEM image along with scanning frames due to charging.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

Structural parameters, electronic, chemical bonding and optical properties of orthorhombic CsAlTiO4 are studied using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The equilibrium lattice constants, bulk modulus and electronic structure are obtained. To our knowledge, no data are available in literature of orthorhombic CsAlTiO4 with Pnma space group for comparison. Electronic and chemical bonding properties have been studied from the calculations of band structure, density of states and charge densities. The complex dielectric functions are calculated and we have explained the origins of spectral peaks.

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We have performed ab initio simulation of adsorption of atomic oxygen on a low defective surface (110) of titanium carbide, reconstructed with laser radiation. Relaxed atomic structures of the O/TixCy(110) surface with Ti- and C- vacancies, observed upon thermal impact have been studied based on the density functional theory. DFT calculations of their thermodynamic, electronic, and elastic properties have been carried out. We have established the bond length and adsorption energy for various reconstructions of the O/TixCy(110) surface atomic structure. We have examined the effects of the oxygen adatom upon the band and electron spectra of the O/TiC(110) surface in its various reconstructions. Effective charges of titanium and carbon atoms surrounding the oxygen adatom in various reconstructions have been identified. We have established charge transfer from titanium atom to oxygen and carbon atoms determined by the reconstruction of local atomic and electron structures, which correlate with atomic electronegativity values and chemisorption processes. Potential mechanisms for laser nanostructuring of titanium carbide surface have been suggested.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

The presented work is devoted to checking of the validity of results of high-performance modeling of SiO2 film growth. Modeling of high-energetic deposition process shows that refractive indices of deposited SiO2 films exceed the refractive index of fused silica substrate. This fact is entirely supported by the analysis of spectrophotometric data obtained for practical thin films deposited using respective deposition technique.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

The surface layers of single-crystal silicon Si(001) substrates subjected to plasma-immersion implantation by 2 and 5-keV helium ions to a dose of 5×1017 cm–2 have been stud-ied by high resolution X-ray reflectometry and transmission electron microscopy. It is shown that surface layer formed by helium ions has a multilayer structure composed of the upper sublayers of amorphized silicon, which are located under the sublayer with helium bubbles and sublayer with disturbed crystal structure. Electron density depth distribution, concentration and pore size distribution are defined. It is found that the average pore sizes of bubbles at implantation energies above constitute 4 and 8 nm, respectively.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

The phenomenological model of structural phase transitions in the double rubidium-dysprosium tungstate is proposed. The model is constructed by equivariant catastrophe theory methods. The temperature dependence of the heat capacity near the phase transitions at temperatures T1 = 9 K and T2 = 4,9 K was calculated. Comparison with experimental data shows satisfactory qualitative agreement. Under the proposed model the low-temperature phase transition can be interpreted as isomorphic.

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The thermoelectric properties of heavily doped p-type PbTe are studied theoretically in the temperature interval of 300 to 900\,K. The calculations are based on the three-band model of PbTe electron energy spectrum, which takes into account transport of the electrons and light holes in $L$-extrema and of the heavy-holes in $\Sigma$-extremum. On the base of the Boltzmann kinetic equation the full set of the relevant kinetic characteristics is calculated including the electrical and thermal conductivities, the Seebeck coefficient and the thermoelectric figure-of-merit $ZT$. All calculated thermoelectric quantities agree well with the available experimental data over the whole temperature interval of 300 to 900\,K. We were able to reproduce the significant increase of the figure-of-merit up to $ZT \approx 1.2$ that was experimentally observed recently in heavily doped p-PbTe.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

The thermoelectric properties of heavily doped p-type PbTe are studied theoretically in the temperature interval of 300 to 900\,K. The calculations are based on the three-band model of PbTe electron energy spectrum that takes into account the transport of electrons and light holes in L-extrema and of the heavy holes in $\Sigma$-extrema. The thermoelectric characteristics appear to be very sensitive to the heavy hole band parameters. The best fit with experiment was obtained at $m_{hh}=5m_0$ and $E_{g \Sigma} = 0.5$\,e$\!$V when all calculated thermoelectric quantities agree very well with the available experimental data over the whole interval of 300 to 900\,K. We were able to reproduce the significant increase of the figure-of-merit up to $ZT \approx 1.2$ that was experimentally observed recently in heavily p-doped PbTe. Our results show that $ZT$ maximum corresponds to the temperature wherein the light hole and heavy hole band edges coincide so that a prominent density-of-states singularity is formed in the valence band.

Show AbstractPhysics of nuclei and elementary particles

Moscow University Physics Bulletin 2017. N 6.

The effect of different fuel ratio f3 (the ratio between the 3He and D densities) on D-3He fusion reaction in spherical tokamak has been considered. By solving the zero dimensional particle and power equations numerically the temporal evolution plasma parameters such as the fusion power, synchrotron power and radiation power for different fuel ratios are calculated and compared to each others.

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Motivated by the extra-dimensional propagation idea, we consider, in a general way, an effective higher-dimensional model for neutrinos where the shape of the compactified extra dimensions determines the observed neutrino masses in ordinary four-dimensional spacetime.

Show AbstractEngineering physics

Moscow University Physics Bulletin 2017. N 6.

The objective of this analysis is to present the validation study of the latest release of the reactor physics lattice transport code DRAGON5 by TRX and BAPL critical experiments of light water reactors for neutrons calculations of Moroccan 2 MW TRIGA MARK-II research reactor. This study is accomplished through the analysis of integral parameters of five light water reactor critical experiments TRX-1, TRX-2, BAPL-UO2-1, BAPL-UO2-2 and BAPL-UO2-3 based on the Open-source Draglibs nuclear data libraries ENDF/B-VII.1 and JEFF-3.1.2. These experiments are being considered as standard benchmarks lattices for testing and validating the reactor physics lattice transport code DRAGON5 as well as nuclear data libraries. The integral parameters - and - of the said lattices are calculated using the reactor physics lattice transport code DRAGON5 at a room temperature and compared to measured values as well as the Monte Carlo values based on the Chinese evaluated nuclear data library CENDL-3.0. It was found that the results calculated show good agreement with the experiment and the MCNP results. Therefore, this study reflects the validation, the adequacy and the accuracy of the reactor physics lattice transport code DRAGON5 based on the Open-source Draglibs nuclear data libraries ENDF/B-VII.0.1 and JEFF 3.1.2 evaluation with SHEM-295 group-structure and can also be important to execute neutronic analysis of thermal reactor such as the Moroccan 2 MW TRIGA MARK-II research reactor at CENM, achieved initial criticality on May 2, 2007.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

We report on a fabrication method of extremely small metallic nanostructures which uses commercially available polystyrene with low molecular weight as a negative resist for electron-beam lithography. The samples were covered with polystyrene by physical vapor deposition. The method allows to form structures with a high ($5\div10\,\text{нм}$) spatial resolution and a high yield on non-uniform arbitrary shaped surfaces. The technological processes for forming the line or dots arrays, electrodes with nanogaps and radially located electrodes were developed. The processes parameters are presented in this work. The possibility of the nanostructures fabrication on a cantilever tip apex of the scanning probe microscope was also demonstrated.

Show AbstractBiophysics and medical physics

Moscow University Physics Bulletin 2017. N 6.

Monte Carlo model for photon beam output from Varian Clinac 2100 linear accelerator was validated by comparison of calculated PDD and dose profiles to measurements. Monte Carlo calculation method is considered to be the most accurate method for dose calculation in radiotherapy physics. The objective of this study is to build a Monte Carlo geometry of Varian Clinac 2100 linear accelerator as realistically as possible and then to investigate the removing of flattening filter impact on dosimetry. Monte Carlo codes used in this work were BEAMnrc code to simulate photons beam and DOSXYZnrc code to examinate absorbed dose in water phantom. PDDs and beam profiles were calculated for 6×6 cm2 and 10×10 cm2 field sizes. Good agreement was found between calculated PDD and beam profile compared to measurements. Gamma index acceptance rate was more than 98% of both distribution comparisons PDDs and dose profiles and our results were more developed and accurate. Varian Clinac 2100 linear accelerator was accurately modeled using Mote Carlo codes: BEAMnrc, DOSXYZnrc and BEAMDP codes package. Varian Clinac 2100 with removing flattening filer could increase the dose by a gain was approximately 80% for 6×6 cm2 field size and it was approximately 110% for 10×10 cm2 at the build-up dose region but for all depth in water phantom, the dose of without FF configuration of linac was increased by more than 40% of dose of with FF configuration of linac. Monte Carlo model for photon beam output from Varian Clinac 2100 linear accelerator was validated by comparison of calculated PDD and dose profiles to measurements. Monte Carlo calculation method is considered to be the most accurate method for dose calculation in radiotherapy physics. The objective of this study is to build a Monte Carlo geometry of Varian Clinac 2100 linear accelerator as realistically as possible and then to investigate the removing of flattening filter impact on dosimetry. Monte Carlo codes used in this work were BEAMnrc code to simulate photons beam and DOSXYZnrc code to examinate absorbed dose in water phantom. PDDs and beam profiles were calculated for 6×6 cm2 and 10×10 cm2 field sizes. Good agreement was found between calculated PDD and beam profile compared to measurements. Gamma index acceptance rate was more than 98% of both distribution comparisons PDDs and dose profiles and our results were more developed and accurate. Varian Clinac 2100 linear accelerator was accurately modeled using Mote Carlo codes: BEAMnrc, DOSXYZnrc and BEAMDP codes package. Varian Clinac 2100 with removing flattening filer could increase the dose by a gain was approximately 80% for 6×6 cm2 field size and it was approximately 110% for 10×10 cm2 at the build-up dose region but for all depth in water phantom, the dose of without FF configuration of linac was increased by more than 40% of dose of with FF configuration of linac.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

The flattening filter (FF) volume reduction increases the clinical photons for deep tumor treatment increasing. The beam softening determination is essential for flattening filter improvement in geometry shape and materials. Determination and understanding the photon beam properties using material and geometry of a beam modifier is very important for dosimetry improvement in radiotherapy department and also for patient life quality development. This Monte Carlo study aims to investigate the relative attenuation and associated beam softening due to flattening filter volume reduction. The FF volume was reduced by 10 %, 20% and 30% of the initial volume data provided by the manufacturer. The relative attenuation and beam softening coefficients increased with FF volume reduction more near the beam central axis than the beam edge. We have illustrated that relative photon beam softening coefficient v was more stable than the coefficient u as a function of off-axis distance and with FF volume reduction. For increasing the photon fluence and dose delivered inside the phantom volume as mentioned in IAEA protocols, the FF volume should be reduced more near the FF top region than the FF edge region. Our work can be a basic investigation that will be used in improvement for the future linac configuration in terms of photon beam softening for material, geometry, and volume that were used in beam modifiers as a flattening filter.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

Increasing dose for improved radiotherapy efficiency is essential for linear accelerator development and also for flattening filter geometry and material enhancement. Determination and understanding the photon beam properties using material and geometry of a beam modifier is very important in radiotherapy department and also for high patient life quality. This Monte Carlo study aims to improve the FF in a linac for increasing the photon number at the entrance of treatment volume tumor and the dose delivered inside the treatment volume as recommended by the IAEA protocols. The aim of this study was to check out the possibility to reduce the flattening filter volume for improving the clinical photons at phantom surface. We have studied photon attenuation coefficients and beam softening coefficients with FF volume reduction. The FF volume was reduced by 10%, 20% and 30% of initial FF volume. The photon fluence increased with FF volume reduction near the beam central axis than the beam edge and the beam softening coefficients remained apparently invariable with FF volume reduction as a function of off-axis distance. Our work can be a basic study that will be used in research and improvement for future linac configuration in terms of photon attenuation and beam softening for a material, geometry and volume that were used for finding out good flattening and good softening to produce an optimal delivered dose as recommended by IAEA.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

It is of great interest to estimate absorbed doses in organs before radiation therapy, especially in nuclear medicine field. In this regard, the internal dose distribution is required. According to the MIRD formalism, Specific Absorbed Fraction (SAF) is an essential parameter for internal dosimetry. In the present work, SAF values for the voxelized phantom (Golem) of the GSF-National Research Center for Environment and Health were calculated using Geant4/GATE with Standard packages and compared with GSF Monte Carlo reference data. Photon irradiations of 30 keV, 100 keV and 1 MeV energy were simulated in eleven different sources and target organs: liver, kidneys, lungs, brain, pancreas, spleen, colon, Red bone marrow (RBM), stomach, thyroid and adrenals. The SAF for self-absorption and for cross-irradiation to other organs were calculated and compared with literature. The results agree with published data, with an average relative difference less than 3%, for the self-absorption of 100 keV and 1 MeV photon energies. The agreement of Geant4/GATE and GSF code might depend on the distance between target and source, the target mass and the photons energy. Generally, the present results indicate that GATE might be used with gamma emitters for internal dosimetry in regard to our prospective works.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

The paper describes the principles of visualization and analysis of thermal fields generated by different physiological processes around the facial area and in the environment. By means of infrared thermography with high spatial and temporal resolution, the dynamics of these fields is studied and their possible application for quantitative evaluation of psychophysical parameters is analyzed. The software module has been developed and tested for combining infrared and visible camera images. A technique is proposed for complex recording and analysis of central and peripheral nervous activity using a thermal camera that captures three types of time-varying temperature fields around the facial area: exhaled gas flows, cutaneous blood circulation, sweat gland activity.

Show AbstractTheoretical and mathematical physics

Moscow University Physics Bulletin 2017. N 6.

In this paper the 2D model of the mantle with a floating continent is considered. On the example of this problem the possibility of using the apparatus of R-functions for solving boundary value problems with non-standard geometry was shown.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

The non-linear action of the electric dipole field on the propagation of electromagnetic waves within the eikonal approximation of parameterized post-Maxwellian vacuum electrodynamics is investigated. The angles of the nonlinear eletrodynamics curvature of rays along which the electromagnetic impulses propagate and the time difference of normal waves propagation from the electromagnetic radiation source to the receiver are calculated.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

We study a solution with an internal transition layer of a one-dimensional boundary value problem for the stationary reaction-advection-diffusion differential equation that arises in mathematical modeling of transport phenomena in the surface layer of the atmosphere in case of non-uniform vegetation in the assumption of space isotropy along one of the horizontal axes and the neutral atmospheric stratification. The parameters of a boundary value problem having a stable stationary solution with internal transition layer localized near the different vegetation border are provided. The existence of such solution and its local Lyapunov stability and uniqueness were proved. The results can be used for developing multidimensional substance transfer models in case of spatial heterogeneity.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

It is shown that in a continuous medium with screw dislocations oriented predominantly along one axis, the rotation velocity of the polarization plane of an electromagnetic wave is much greater if it propagates in the direction perpendicular to this axis than in the collinear one. For a given dislocation density tensor, the conditions under which the rotation velocity of the polarization plane of the electromagnetic wave reaches its maximum are found.

Show AbstractRadiophysics, electronics, acoustics

Moscow University Physics Bulletin 2017. N 6.

A model of convergence of cylindrical shock waves in a gas with a uniform density has been considered. The partial differential equations of this model have been reduced to ordinary differential equations, from which the law of convergence of such shock waves and the de-pendence α = f(γ, eff) of their self-similarity index α on the heat capacity ratio in front of the shock wave (γ) and behind the shock wave front(eff) of the gas have been found. This depend-ence for cylindrical shock waves has been shown to agree with the experimental data within the measurement error

Show AbstractOptics and spectroscopy. Laser physics

Moscow University Physics Bulletin 2017. N 6.

The radiation pattern and near-field polarization of a spheroidal metallic nanoparticle located above a silicon substrate are studied in the case of interaction of the system with a linearly and circularly polarized field. It is shown that, in comparison with the symmetric directivity diagram of a spheroidal particle in a free space, the directivity pattern of the particle near the silicon substrate becomes strongly asymmetric and forward scattering predominates. The change in the polarization of the near field of a nanoparticle in the presence of a substrate for different values of the wavelengths near the plasmon resonance is studied. Polarization of the near field is described by means of generalized Stokes parameters, which make it possible to visualize the results visually.

Show AbstractAstronomy, astrophysics, and cosmology

Moscow University Physics Bulletin 2017. N 6.

During solar eclipse July 22, 1990 a sharp increase of thermal neutrons flux directed from the Earth surface was detected in Pamir region. In the following years such events were observed during the New and Full Moons, when the Lunar and Solar tides are combined and the amplitude of the total tide is especially high. At the same time, tidal forces can play the role of trigger for the release of deep-earth seismic energy. Therefore, the authors tried to find correlation between the time of earthquakes and New and Full Moons, which could provide a basis for a new type of seismic activity predictors. The correlation was found for the region of Pacific seismic ring and adjacent areas with latitude from 40oN to 10oS. The present paper describes the results of the measurements of thermal neutrons directed from the Earth’s surface from August 1 till August 14, 1994. The experiment was carried out in the region of Western Pamir at Moskvina clearing at the altitude of 4200 m above sea level in the day-time. Due to the quiet heliophysical, geophysical and weather conditions during this period the intensity of the secondary cosmic rays should be almost constant. Nevertheless, there are some days when we observed twice and more variation of thermal neutrons counting rate. The present paper shows that the observed increases of the neutrons intensity are produced by the Lunar and Solar tides. The obtained results confirm the role of the tidal forces in thermal neutrons flux generation near the Earth’s surface. Astronomical Almanac (1994) of the Russian Academy of Sciences was used in the present study.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

In this study a risk of single event upsets from cosmic particles for computer memory with error correction onboard spacecraft is modeled. A brief description of existing mechanisms of the detection and correction of errors in memory is given. Formulas for calculating the probability of occurring of >1, 2 and so on errors in at least one memory block are presented. Values of the probability of uncorrectable errors for the concrete conditions of spacecraft flight are computed for certain microchips.

Show AbstractPhysics of Earth, atmosphere, and hydrosphere

Moscow University Physics Bulletin 2017. N 6.

Numerical simulation of the ocean free gravity waves generation by passage of low-frequency surface seismic waves across the bottom is described in this paper. The dynamics of bottom movement was reconstructed based on real GPS data, recorded during disastrous Tohoku earthquake 11.03.2011. Numerical simulation results show that horizontal movements of underwater slopes play the key role in the free gravity waves generation.

Show AbstractMoscow University Physics Bulletin 2017. N 6.

In the work we carried out a statistical analysis of the velocity distribution TEC changes for different sets of stations. For the full study, we used data of 2010 and 2014 y.y. from about 400 IGS network stations located in the high (200 sites), medium (over 100) and equatorial (over 100 stations respectively) latitudes. The data were obtained in various geo- heliophysical conditions, phases of the solar 24-cycle activity - minimum and practical peak of the solar cycle. The aim of the analysis is the experimental determination of the threshold values of the TEC slips, that are associated with the “tails” of the investigated distributions for a given physically adequate level of significance. It was found that the threshold value at which the measured TEC values can be considered as statistical noise, depending on the latitude of the observation region. The maximum threshold is for the Arctic region, and the minimum - to the medium latitudes stations.

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Optics and spectroscopy. Laser physics

Moscow University Physics Bulletin 2017. N 6.

Calculations have been carried out according to which the measurements carried out according to the scheme proposed in the commented paper do not differ from each other before and after the collapse of the quantum state vector.

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