Resonance Compression of Acoustic Beams in Crystals

The resonant excitation of an intense elastic wave through nonspecular reflection of a special pump wave in a crystal is described. Geometric criteria are found under which mode conversion, when the incident and reflected beams belong to different acoustic branches, coexists with total internal reflection of an acoustic beam. In this case, the entire energy of an incident pump wave is spent on the excitation of a narrow intense reflected beam close in structure to an eigenmode. A consistent choice of orientations of the sagittal plane and crystal surface that excludes the reflection of a parasitic wave of leakage is found. The resonance parameters have been found for a medium with an arbitrary anisotropy. General relations are concretized for monoclinic, orthorhombic, trigonal, tetragonal, cubic, and hexagonal systems. Estimates and illustrations are given for a series of such crystals. The intensity of the reflected beam increases with its narrowing, but its diffraction divergence also increases with this narrowing. Nevertheless, the intensity of the beam can be increased by a factor of 5–10 at sufficiently high frequencies while keeping its divergence at an acceptable level. Amplification by two orders of magnitude can be achieved by compressing the beam in two dimensions through its double reflection

Variations of cosmic rays according to the data of interplanetary probes Zond-3 and Venus-2

Cosmic ray intensity variation measured by Zond 3 and Venus 2 interplanetary probe

Capture of particles of dust by convective flow

Interaction of particles of dust with vortex convective flows is under theoretical consideration. It is assumed that the volume fraction of solid phase is small, variations of density due to nonuniform distribution of particles and those caused by temperature nonisothermality of medium are comparable. Equations for the description of thermal buoyancy convection of a dusty medium are developed in the framework of the generalized Boussinesq approximation taking into account finite velocity of particle sedimentation. The capture of a cloud of dust particles by a vortex convective flow is considered, general criterion for the formation of such a cloud is obtained. The peculiarities of a steady state in the form of a dust cloud and backward influence of the solid phase on the carrier flow are studied in detail for a vertical layer heated from the sidewalls. It is shown that in the case, when this backward influence is essential, a hysteresis behavior is possible. The stability analysis of the steady state is performed. It turns out that there is a narrow range of governing parameters, in which such a steady state is stable.Comment: 14 pages, 10 figures, published in Physics of Fluid

The Nature of Thermopower in Bipolar Semiconductors

The thermoemf in bipolar semiconductors is calculated. It is shown that it is necessary to take into account the nonequilibrium distribution of electron and hole concentrations (Fermi quasilevels of the electrons and holes). We find that electron and hole electric conductivities of contacts of semiconductor samples with connecting wires make a substantial contribution to thermoemf.Comment: 17 pages, RevTeX 3.0 macro packag

Mathematical model of stacked one-sided arrangement of the burners

Paper is aimed at computer simulation of the turbulent methane-air combustion in upgraded U-shaped boiler unit. To reduce the temperature in the flame and hence NOx release every burner output was reduced, but the number of the burners was increased. The subject of studying: complex of characteristics with space-time fields in the upgraded steam boiler E-370 with natural circulation. The flare structure, temperature and concentrations were determined computationally

О повышении информативности теста тонометрии

The effect of the tonometer contact surface shape on the accuracy of measuring the true and tonometric pressures is analyzed. Possible modifications of the tonometry method, which can not only make the intraocular pressure measurement more accurate but also enable us to estimate parameters characterizing the elastic properties of the corneal and scleral eye segments, Ec and Es, are discussed. The tonometers with flat (Maklakov's method) and convex (convex-tonometry) contact surfaces are taken as examples. It is shown that the pressure measurement accuracy can be increased substantially with increase in the accuracy of the tonometer contact area radius measurement and if the individual Ec and Es values are attained from independent measurements. Possible measurement modification methods which make it possible to estimate together the individual values of the intraocular pressure and the parameters Ec and Es that separately characterize the elastic properties of the cornea and the scleral segment. The tonometry modification consists in measuring within each examination the intraocular pressure by the standard method using successively both tonometers considered, of two different weights each (four measurements). The complication of the measurement procedure is justified not only by the possibility to increase the intraocular pressure measurement accuracy but also by the possibility to simultaneously estimate the individual elastic characteristics of the cornea and the scleral segment, which may be important for diagnostics and therapeutic efficacy control.На основе численного решения механической задачи о тонометрии проанализированы влияние формы поверхности контакта тонометра на точность измерения истинного и тонометрического давлений. Обсуждаются возможные модификации метода тонометрии, позволяющие не только повысить точность измерения внутриглазного давления (ВГД), но и оценить индивидуальные значения параметров, характеризующих упругие свойства роговичного Ec и склерального Es сегментов глаза. Для примера выбраны тонометры с плоской (метод Маклакова) и выпуклой (конвекс-тонометрия) контактной поверхностями. Показано, что точность измерения давлений может быть существенно повышена, если повысить точность измерения радиуса пятна контакта тонометра с роговицей, а также, если из независимых измерений будут известны индивидуальные значения Ec и Es. Описаны возможные способы модификации измерений, позволяющие совместно оценить индивидуальные значения ВГД и параметров Ec и Es, раздельно характеризующих упругие свойства роговицы и склерального сегмента. Модификация тонометрии состоит в том, что в каждом исследовании необходимо стандартным методом измерить тонометрическое давление последовательно двумя рассматриваемыми тонометрами двух различных весов (четыре измерения). Усложнение процедуры измерения оправдывается не только возможностью повышения точности измерения внутриглазных давлений, но и возможностью одновременной оценки индивидуальных характеристик упругости роговицы и склерального сегмента, которые могут иметь самостоятельное значение при диагностике заболеваний и для контроля результатов применения лекарственных препаратов

Dark matter and structure formation a review

This paper provides a review of the variants of dark matter which are thought to be fundamental components of the universe and their role in origin and evolution of structures and some new original results concerning improvements to the spherical collapse model. In particular, I show how the spherical collapse model is modified when we take into account dynamical friction and tidal torques

Post-vaccination immunity phenotypes upon usage of EpiVacCorona vaccine in the persons who suffered COVID-19

The dominance of reliably immunized population is a fundamental factor in prevention of COVID-19 pandemia, with immune prophylaxis taking a dominant position. Due to lack of clear data on the intensity of specific immunity after a new coronavirus infection, consolidation of immunological memory by vaccination becomes the urgent task, in order to exclude the risk of re-involvement of previously ill patients into the epidemic process. Meanwhile, many questions related to vaccination of COVID-19 survivors do not get distinct answers. To study the features of immune response, using a vaccine based on SARS-CoV-2 peptide antigens (EpiVacCorona), we monitored 81 participants. The inclusion criteria were data confirming COVID-19 in the anamnesis (medical documentation), low levels or absence of antibodies to the SARS-CoV-2 nucleocapsid protein, and negative PCR tests for SARS-CoV-2. When assessing the data of post-vaccinal immunity checked 21 days after 1st dose of the vaccine, the patients were divided into 2 groups: those who did not respond, and those who developed the immune response. In order to identify possible reasons for different phenotypic patterns of humoral response to vaccination, a comparative analysis of B lymphocyte indexes was carried out in these groups. Absolute counts, subpopulation composition and activation potential of peripheral blood B lymphocytes were determined by flow cytofluorometry using appropriate labeled monoclonal antibodies purchased from Beсkman Coulter. Comparative analysis of B lymphocyte indexes on the day of first vaccination showed that the persons who did not respond to the vaccine had smaller counts of circulating B cells, i.e., both percentage and absolute cell numbers, than in comparison group, as well as changed ratio of B1-to-B2 subpopulations. After administration of the first vaccine dose (by day +21), in alternative variant of the antibody response to V1, the differences in the parameters of B cells were presented as a smaller percentage and absolute numbers of regulatory B lymphocytes in non-responding participants. Moreover, the contents of minor B cell subpopulations were decreased in the non-responding group than in the comparison group, thus affecting the values of the B1:B2 ratio. In general, the presented data demonstrate that the absence of secondary immune response to antigens of the SARS-CoV-2 peptide vaccine could be is associated with altered differentiation of B1 and B2 subpopulations, B regulatory lymphocytes, B memory cells