Vol 72, No 6 (2017)

We discuss the results of cosmic-ray energy spectrum and mass composition studies obtained with arrays for extensive air-shower detection. An overview of ground arrays that perform such research and a brief description of methods of the primary particle characteristics recovery from experimental data are presented. A particular emphasis is given to the energy range of 10¹⁶–10¹⁸ eV, where a transition from galactic to extragalactic cosmic rays is expected. The array complex constructed in the Tunka Valley for the studies in this range is specifically considered.

In this paper, the process of convection in the Earth’s mantle in the presence of a floating continent is considered. The model is a two-dimensional rectangular region of viscous thermally conducting fluid that obeys the equations of hydrodynamics. The method of Rvachev R-functions is used for the description of the problem geometry and the boundary conditions.

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 the case of non-uniform vegetation on the assumption of space isotropy along one of the horizontal axes and neutral atmospheric stratification. The parameters of the model at which a boundary value problem has a stable stationary solution with an internal transition layer localized near the boundary between different vegetation types are provided. The existence of such a solution and its local Lyapunov stability and uniqueness are proven. The results can be used for developing multidimensional substance transfer models in the case of a spatial heterogeneity.

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.

A model of the convergence of cylindrical shock waves (SWs) 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 dependence α = f(γ, 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 (γ_eff) of the gas have been found. This dependence for cylindrical shock waves has been shown to agree with the experimental data within the measurement error.

We studied the radiation-directivity pattern and the near-field polarization of a spheroidal metallic nanoparticle located over a silicon substrate by interaction with a linearly and circularly polarized field. It is shown that the directivity pattern of the spheroidal particle near the silicon substrate becomes strongly asymmetric and forward scattering is predominant compared with the symmetric diagram of a particle in free space. The change of the near-field polarization of the nanoparticle in presence of the substrate is studied for different wavelengths in the vicinity of the plasmonic resonance. The near-field polarization is described using the generalized Stokes parameters, which allow pictorial visualization of results.

An ab initio simulation of the adsorption of atomic oxygen on the low-defect titanium carbide (110) surface reconstructed by laser radiation was performed. The relaxed atomic structures of the (110) surface of the O/Ti_xC_y system with Ti and C vacancies observed during the thermal treatment were studied in terms of the density functional theory. DFT calculations of their structural, thermodynamic, and electronic properties were performed. The bond lengths and adsorption energies were determined for various reconstructions of the atomic structure of the O/Ti_xC_y(110) surface. The effects of the oxygen adatom on the band and electronic spectra of the O/Ti_xC_y(110) surface were studied. The effective charges on the titanium and carbon atoms surrounding the oxygen atom in various reconstructions were determined. The charge transfer from titanium to oxygen and carbon atoms was found, which is determined by the reconstruction of the local atomic and electronic structures and correlates with chemisorption processes. The potential mechanisms of laser nanostructuring of the titanium carbide surface were suggested.

The surface layers of single-crystal silicon Si(001) substrates subjected to plasma-immersion implantation with 2- and 5-keV helium ions to a dose of 5 × 10¹⁷ cm^–2 were probed via grazing incidence small-angle X-ray scattering and transmission electron microscopy. A surface layer formed by helium ions was found to possess a multilayer structure, wherein the upper layer is amorphous silicon, being on top of a sublayer with helium bubbles and a sublayer with a disturbed crystal structure. The in-depth electron density distribution, as well as the concentration and pore-size distribution, were established. The average pore sizes of bubbles at the above implantation energies are 4 nm and 8 nm, respectively.

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.

The thermoelectric properties of heavily doped p-type PbTe have been theoretically studied in the temperature range from 300 to 900 K. The calculations are based on a three-band model of the PbTe electron energy spectrum taking into account the transport of electrons and light holes in the L-extrema and heavy holes in the Σ-extrema. The thermoelectric quantities turned out to be very sensitive to the parameters of the heavy-hole band. The best agreement with the experiment is reached at m_hh = 5m₀ and E_gΣ = 0.5 eV, where all calculated thermoelectric quantities agree well with the available experimental data within the entire interval from 300 to 900 K. The calculation confirms a significant increase of the value of the thermoelectric figure-of-merit to ZT = 1.2 that has been recently observed experimentally in heavily doped p-PbTe samples. The maximum of ZT corresponds to the temperature at which the band edges of light and heavy holes coincide in energy so that the steepest singularity in the density of states in the valence band is formed.

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

The flattening filter (FF) volume reduction increases the clinical photons for deep tumor treatment. The beam softening determination is crucial for flattening filter improvement in geometry 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 offaxis 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.

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, 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.

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.

A numerical experiment for reproducing the generation of free gravity waves in the ocean by low-frequency surface seismic waves passing across the bottom is described. The dynamics of the bottom movement is reconstructed based on the real GPS data recorded during the disastrous Tohoku earthquake of March 11, 2011. Results of the numerical simulation show that horizontal movements of underwater slopes play a key role in the generation of free gravity waves.

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 (5–10 nm) spatial resolution and a high yield on non-uniform arbitrary shaped surfaces. The technological processes for forming line or dot arrays, electrodes with nanogaps, and radially located electrodes were developed. The process parameters are presented in this work. The possibility of fabrication of nanostructures on a cantilever tip apex of the scanning probe microscope was also demonstrated.

We present the calculations which show that the measurements performed according to the scheme proposed in the commented paper do not differ from each other before and after the collapse of the state vector.