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Abstract: In this paper, the spectral properties of the triangular lattice of grana are investigated. By the finite difference time domain method, the transmittance spectra of the structure are calculated and the components of the scattering matrix are determined, which makes it possible to determine the effective parameters of the structure. As a result, it was shown that a two-dimensional lattice of grana can be represented as a homogeneous film with a thickness equal to the height of the grana. It is shown that the positions of the resonances before and after the homogenization of the structure coincide, which makes this method attractive for estimated calculations of the structure. PubDate: 2022-02-01
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Abstract: In this paper, temperature distribution in the diffusion flame during combustion of isopropanol or isopropanol with addition of boron nanoparticles in the amount of 0.5 wt % in oxygen was studied experimentally by using coherent anti-Stokes Raman scattering (CARS) spectroscopy. The addition of boron was found to result in an increase in temperature in the flame front by 150 K. PubDate: 2022-02-01
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Abstract: This paper presents the results of experimental measurements of the elastic moduli of structural materials using a technique with laser sources of ultrasonic pulses. This method allows measurements to be carried out locally (lateral resolution from 1 mm, object thickness from 2 mm) and promptly (measurement time of less than 1 s) and with one-sided access to the controlled object. PubDate: 2022-02-01
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Abstract: A computational–theoretical model is developed for a nonequilibrium flow around a blunt wedge of finite dimensions by a hypersonic airflow at an angle of attack taking into account ionization. The results of mathematical modeling of the gas-dynamic and kinetics processes of chemical transformations, dissociation, and ionization, as well as the nonequilibrium excitation of vibrational degrees of freedom of diatomic molecules in the regions of compression and rarefaction of the flow and in the regions of separated flow and near wake at the velocity corresponding to the Mach number M = 16, are presented. PubDate: 2022-02-01
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Abstract: In this work, by using the wave equations proposed by the authors for the vector of the vibrational velocity of particles and the well-known equation for acoustic pressure in an inhomogeneous stationary medium, the influence of the parameters of the medium on the vector-phase properties of the acoustic field is investigated. For the first time, analytical equations are found for the phases and moduli of the vectors of the complex intensity and acoustic energy flux density (acoustic intensity vector), vibrational velocity, pressure, and energy density, which establish a relation between them and both the medium density and the speed of sound. The proposed approach allows an analytical analysis of the influence of the density of and speed of sound in an inhomogeneous medium on the parameters of the acoustic field. In turn this approach opens possibilities of solving the reciprocal problem on finding the spatial distribution of the density and the speed of sound of a medium on the basis of measured values of the acoustic pressure and the vibrational velocity. PubDate: 2022-02-01
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Abstract: The flows in a combustion chamber shaped as an annular gap between plates with multiheaded rotating detonation of the propane–air mixture entering the chamber in the direction of the symmetry axis from the reservoir with the stagnation parameters specified are investigated numerically. The conditions for the formation of a preset number of waves in the multiheaded detonation wave are determined; they are associated with the dimensions of the combustion chamber and the parameters of the initiators. The values of the highest number of waves for the specified dimensions of the combustion chamber are obtained. It is found that the existence of the highest critical value of the number of waves in the multiheaded detonation is associated with blocking the feed of the combustible mixture. It is found that the mutual angles between the waves that make up the multiheaded detonation are gradually aligned with an uneven arrangement of initiators. For the calculations carried out on the Lomonosov supercomputer of Moscow State University, an original computer complex based on the modified Godunov method and one-stage reaction kinetics is used. PubDate: 2022-01-01
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Abstract: In a strongly correlated ZrB12 (zirconium dodecaboride) metal with an electronic phase separation (dynamic charge stripes), an analysis of the Fermi surface topology is carried out and a map of the open/closed trajectories of charge carriers is constructed. We propose an explanation for the suppression of the charge transport anisotropy in ZrB12 comparing the obtained theoretical results with experimental magnetoresistance data at liquid helium temperatures in a magnetic field up to 80 kOe. PubDate: 2022-01-01
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Abstract: The evolution of the shape of a sequence of cavities accompanying the coalescence a freely falling drop with a liquid at rest is traced by the method of high-speed video recording. The flow is visualized by the dark field method in the side view (the line of sight lies on the free surface), as well as in the LED-based backlight. In the first case, LED sources were installed on top and on the side of the transparent cuvette; in the second case, a spotlight located behind the cuvette was added to the LED sources. For the first time, the high-resolution experimental technique allows registering the bottom oscillations of the secondary cavities and visualizing the groups of gas bubbles, including frozen-in ones, which reproduce the initial shape of the rapidly filling second cavity, which is formed during splash coalescence. The next shallow cavity is formed after the splash top is submerged. The last cavity is formed by a returning drop previously ejected from the top of the splash. An increase in the rate of the collapsing cavity depth is associated with the conversion of the available potential surface energy (APSE) with a decrease in the area of the free surface of the fluid. PubDate: 2022-01-01
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Abstract: The first results of direct expedition measurements of atmospheric absorption of electromagnetic waves in the sub-terahertz frequency range of 0.1–1 THz, carried out in order to select an optimal site from the point of view of the microwave astroclimate for development of an observatory that can become an element of the radio interferometer of the Suffa observatory and, in the future, enter into collaboration with the Event horizon telescope (EHT), are presented in brief. The EHT, presenting an image of the shadow of a black hole, today consists of a dozen antennas located around the globe, and at present has no elements in its network in northern Eurasia. The studies performed may be useful not only for radio astronomy problems, but also for space communications, radar of the Moon, asteroids, and the detection of space debris objects. The first results of direct measurements of propagation of subterahertz waves at the selected sites confirmed the initial hypothesis of the expedition. This hypothesis was formulated on the basis of an analysis of meteorological data, as well as satellite data on atmospheric absorption in other ranges: optics and low-frequency radio bands. It was assumed that the work in the subterahertz frequency range in the eastern part of the northern Caucasus is more promising than in the western Caucasus. The western part is more attractive because today there are a number of observatories already operating, and the installation of one more antenna would have been much easier in terms of the necessary infrastructure and required highly qualified personnel. The hypothesis of the predominance of the eastern part was convincingly confirmed in the completed research by comparing the absorption in the 2- and 3-mm bands from the previously surveyed areas of the Western Caucasus (Terskol peak, Pastukhov mountain, KMO, BTA, RATAN-600 sites, etc.) with those studied during the expedition in 2021 for the Eastern sites on the Mayak (Gunib), Stolovaya, and Shalbuzdag mountains. Even measurements at the highest peak not only in the Western Caucasus, but also in Europe, at Mount Elbrus, carried out as part of this expedition, gave results worse than those in Dagestan and North Ossetia, confirming the futility of further search for a place for an effective subterahertz instrument in the eastern part of the North Caucasus. PubDate: 2022-01-01
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Abstract: A multiple (from 20 to 3 kV) decrease in the ignition threshold of commercial flash lamps for solid-state lasers under HF pumping at a megahertz frequency has been detected. It has been found that, upon water cooling of the lamp, the cathode glow is developed during HF pumping on both electrodes, in contrast to the pulsed ignition for the capacitance discharge, since both electrodes alternately act as the anode and cathode. At the stage of ignition development, the Faraday dark space is observed in the middle part of the lamp and its size decreases with the increasing HF pumping voltage until the lamp is ignited by a solitary streamer between the electrodes. It has been established that the main factors that determine a decrease in the full lamp ignition threshold are the high-frequency field amplitude and the coolant impedance, as well as the ignition range. The HF ignition of the lamp with a discharging gap of up to 60 cm (an ignition threshold of ~5 kV) has shown the universality of the developed ignition mode. PubDate: 2022-01-01
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Abstract: A compressible laminar boundary layer on a permeable plate with uniform injection is studied numerically for the gas Prandtl numbers Pr = 0.1…1.0. Regimes in which the injected-gas temperature is lower than that of the adiabatic impermeable wall are considered. For a number of stagnation temperatures, the existence of a minimum in the temperature of the permeable wall is confirmed, the value of the minimum being lower than the injected-gas temperature. The critical temperature of the adiabatic permeable wall is introduced for the case when the lowest temperature is displaced closer to the critical injection section with a decrease in the injected-gas temperature and then finally coincides with it. The dependence of the criterion previously obtained on the Prandtl and Mach numbers and the stagnation temperature is specified, which makes it possible to estimate the temperature range of the injected gas at which the lowest temperature of the permeable wall is possible. PubDate: 2022-01-01
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Abstract: The phenomenon of double periodicity of the mechanical properties of a thin ice field in a rigid pool is studied. A modal analysis of the experimental data was carried out, that makes it possible to identify two main periods in the spatial distribution of the reaction of ice to cross-cutting penetration. A new mathematical model for evolution of the properties of an ice field is developed. It is based on the ability of the viscoelastic mechanical system to emit perturbations with a certain spatial length and to accumulate them over time, which theoretically explains the effects observed in the experiment. PubDate: 2022-01-01
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Abstract: The results of analytical modeling of a system of helical vortices detached from the ends of the rotating blades of an NEJ rotor (proposed by N.E. Joukowsky) are presented. An analytical solution for determining the decreasing flow velocity on the blade, induced by the vortex wake, is constructed. For the first time, the wake vortex system was simulated using a model with a uniform vorticity distribution in the core of each tip vortex detached from the NEJ rotor blades. The solution was obtained by extending the Dyson method, which was previously used only for a separate helical vortex, to a multivortex system of blade vortices. This result can be used to construct theoretical and numerical models to assess the optimal performance of rotors and predict the occurrence of erosion and icing on their blades. The results of this work are of interest for a fundamental understanding and description of the behavior of flows with a system of helical vortices in rotor aerodynamics and other studies, where multivortex helical structures arise in swirling flows, e.g., in tornado cores, in vortex devices and cyclonic separators, in combustion chambers, etc. PubDate: 2021-12-01
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Abstract: With the use of high-speed video filming, the effect of the appearance of droplets with near-zero velocities in gas–droplet flows past bodies was discovered for the first time. The formation of levitating droplets occurred as a result of the coalescence of droplets falling and reflected from the model. It has been suggested that the main mechanism for the appearance of drops with near-zero velocities is momentum exchange as a result of the collision of droplets with opposite directions and values of velocity close in magnitude. The effect of an increase in the size of large levitating drops due to the coalescence of falling droplets with them due to multiple collisions has been detected. PubDate: 2021-12-01
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Abstract: To conduct research on mechanical periodic effects on a person, it is proposed to use a new type of device—hydrodynamic oscillators (wave hydromassagers), which are capable of creating three-dimensional (in particular, spiral) waves in hydrodynamic flows with amplitudes and frequencies of speeds and pressures of a wide spectrum, including vacuum zones on the treated surface. The data obtained can be used in the design of hydromassage devices for physiotherapy. PubDate: 2021-12-01
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Abstract: Rutherford’s formula for the scattering of charged α-particles in a Coulomb field can easily be generalized to the case of gravitational scattering. One of the types of gravitational scattering in the Solar System is gravity assist maneuvers. In this paper, an effective gravitational scattering cross section is introduced by analogy, and the generalized Rutherford formula for gravitational scattering is presented for performing gravity assists. It is shown that, with its use, it is possible to increase significantly the efficiency of the recurrent procedure for the search for ballistic scenarios of interplanetary flights. PubDate: 2021-12-01
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Abstract: The problem of motion of two bodies (planets) with comparable masses around a massive сentral body (star) is considered in proposition that planet masses are significantly less than the mass of the сentral body. It is assumed that the movement of the planets occurs in the same plane and orbits are close to circular. The motion of the planets is constructed directly in polar coordinates using the method of undefined frequencies proposed by the author, which is a modification of the method of successive approximations. The first approximation is obtained, which is the sum of uniform circular motion and small quasi-periodic terms for each planet. The latter are the sum of periodic components whose periods are equal to the periods of circular motions of both bodies, as well as their sums and differences. Herewith the periods of circular motions change in comparison with what Kepler’s third law gives: the period of the inner planet increases, and the outer one decreases. The second feature of the constructed approximate solution is the absence of secular perturbations. PubDate: 2021-12-01
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Abstract: Exact solutions of the classical problem of a plane unsteady potential flow of an ideal incompressible fluid with a free boundary are presented. The fluid occupies a semi-infinite strip bounded from above by the free surface and from the sides by two solid vertical walls approaching each other with a constant velocity. Solutions are obtained for a situation where the capillary and gravity forces are absent, and the fluid motion is entirely determined by the motion of the walls. Singularities inevitably arise in the solutions of the equations of motion in a finite time: this time is limited from above by the moment of collision of the walls. Examples of exact solutions corresponding to the formation of bubbles, cusps, and droplets are considered. PubDate: 2021-12-01
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Abstract: The radial dynamics of a single-walled carbon nanotube under dynamic compression is considered in a linear formulation. The equation based on the Kirchoff hypotheses for the bending deformation of a thin-walled cylindrical shell (circular ring) is applied. The effective parameter found by the comparison of eigenfrequencies within the framework of molecular dynamics and elastic shell theory is engaged. The applied external pressure is varied step by step and further remains constant within the time period considered. The vibratory motion and exponential deflection growth regimes are studied depending on the ratio of this pressure to the critical static pressure. These parameters can also be expressed through the number of carbon atoms composing a circular ring. PubDate: 2021-12-01
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Abstract: From August to October 2019, the aerosol backscattering and deformation of the Earth’s crust were monitored in the tunnels of the Baksan Neutrino Observatory above the Elbrus volcano chamber. An omnidirectional modulation of the seasonal crust compression with a multiple excess of the average rate (~4 μm/day) and with a change in the sign of decrease in the lidar-signal scattering on aerosols to anomalous growth in the “hot” tunnel is found. It is established that the modulation is induced by the rapid cooling of the external atmosphere. The delays of the accelerated compression of the strainmeter arm (up to 14 μm/day) and the beginning of growth of the backscattering lidar signal relative to the beginning of the temperature decrease (~2 and ~7 days, respectively) are measured. The mechanism of the phenomena discovered is discussed. PubDate: 2021-11-01
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