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Introduction. A large number of building materials is used for construction of buildings and structures, the reinforced concrete is being one of them. It has the leading position when choosing the material for construction of buildings and structures. However, like any other material, the reinforced concrete has its disadvantages: apart from considerable weight of the reinforced concrete structures, the impossibility to cover with them the large spans can also be referred to disadvantages, as the increase of structures’ spans impairs the economic efficiency of using the reinforced concrete. To handle this, engineers have developed the technology of steel reinforcement prestressing. Thanks to prestressed reinforcement, it has become possible to increase the spans and reduce the cross section of the reinforced concrete structures. This scientific paper investigates the technology of steel reinforcement post-tensioning.Materials and Methods. The materials for the research were obtained from the available scientific editions, articles, journals and Internet blogs. The documents’ content analysis method was used to write the article. In the course of the research, it is planned to find the information about the post-tensioning technology. The object of the study is the steel wire-rope post-tensioning.Results. Thanks to the research, the data on the history of origin of the reinforcement prestressing technology was obtained and the advantages and disadvantages of post-tensioning were analysed.Discussion and Conclusions. After the research, the data on the technology of steel reinforcement post-tensioning was obtained, the application of the technology in Russia in the construction of industrial and civil facilities was considered. This technology allows increasing the spans and reducing the cross section of the reinforced concrete structures.

The results of a theoretical study of a high power W-band extended interaction klystron with a hollow electron beam are presented. Numerical studies were carried out using the PARS computer code, taking into account the thermal spread of electron velocities at the cathode. As a result of the research and optimization of the parameters, the design of the electron-optical system and the interaction system of the 6-cavity klystron was developed, which provides a record output power of 8.6 kW for a given frequency with a gain of 56 dB, an electronic efficiency of 32 $$\%$$ and a full efficiency of 26 $$\%$$ . Using the developed two-stage depressed collector with a recovery efficiency of 54 $$\%$$ in dynamic mode, it is possible to provide the full efficiency of the device at the level of 40 $$\%$$ . The results of numerical calculations of the dynamics of electrons and their interaction with electromagnetic fields from the cathode to the collector in the quasi-three-dimensional approximation are presented.

Results are presented from a theoretical study on optimizing the parameters of an electron gun of a powerful multicavity extended interaction klystron at a frequency of 95 GHz, ensuring the formation of a dense annular electron beam and its transport through interaction region with a current transmission coefficient of 99%, with taking into account of the thermal spread of electron velocities at the cathode.

Conditions for ensuring the equilibrium stationary state of high-density solid electron beams, transported in cylindrical drift tubes and focused by uniform magnetic field, are investigated. Calculation results are compared to data obtained using the quasi-three-dimensional Arsenal-MSU computer code and analytical formulas proposed by other authors.

A multi-frequency terahertz radiation source based on quantum-cascade lasers is described. The prospects of its application for the study of atmospheric phenomena and the creation of lidars and remote sensing equipment are discussed. The influence of radiation attenuation in the atmosphere for three frequency ranges was studied using the proposed terahertz source. Estimates of the influence of the laser spectral line width on terahertz radiation attenuation coefficient measurements in the atmosphere were obtained.

The conditions for ensuring the equilibrium steady-state of a high-density hollow electron beam transported in cylindrical drift tubes and focused by a uniform magnetic field are investigated. The results of numerical calculations of the currents limited due to the longitudinal deceleration of electrons by the space charge and the violation of equilibrium transverse magnetic focusing conditions when transporting beams of different configurations in klystron-type devices are presented. The limitations of the working length of the device associated with the excitation of diocotron instability are estimated. The calculation results were compared with the data obtained by the quasi-3D Arsenal—MSU computer code and by the approximate analytical formulas of other authors.

The conditions providing the equilibrium stationary state of high-density solid and annular electron beams, transported in cylindrical drift tubes and focused by a homogeneous magnetic field, have been investigated. An efficient numerical model is proposed to determine the distributions of the electrostatic potential, charge density, and electron velocities in the stationary state of these beams, with allowance for the space-charge forces. The results of the numerical calculations for the limiting currents, determined by the longitudinal deceleration (caused by space-charge forces) and conditions for equilibrium transverse magnetic focusing for transported beams of different configurations on the length of a klystrontype vacuum electronic device, are presented. The limitations on the device working length, related to the excitation of diocotron instability, are estimated. The calculation results are compared with the data obtained using the quasi-three-dimensional program “Arsenal-MSU” and analytical formulas suggested by other researchers.

We present the results of a comparative theoretical analysis of the electron beam bunching in a single-stage klystron amplifier using analytical models, a one-dimensional disk program, and a two-dimensional program. Data on the influence of various one-dimensional and two-dimensional nonlinear effects on the efficiency of electron beam bunching at different values of the space charge parameter and the modulation amplitude are presented. The limits of applicability of analytical and one-dimensional numerical models for electron beam bunching analysis in high-power klystron amplifiers are found.

We demonstrate the possibility of using a multi-frequency terahertz source to identify substances basing on the analysis of relative amplitudes of the terahertz waves scattered by the object. The results of studying experimentally the scattering of quasi-monochromatic radiation generated by a two-frequency terahertz quantum-cascade laser by the surface of the samples containing inclusions of absorbing substances are presented. It is shown that the spectral features of absorption of these substances within the terahertz frequency range manifest themselves in variations of the amplitudes of the waves at frequencies of 3.0 and 3.7 THz, which are scattered by the samples under consideration.

In this letter we propose an approach to obtain directive radiation from wire lasers with subwavelength transverse dimensions and length much larger than the radiation wavelength (wire lasers) based on spatial filtering of their radiation using a combination of a spherical lens and a diaphragm. Theoretical modeling based on the antenna model for wire lasers shows that a directive beam with the uniform phase front can be formed when the diaphragm separates the maximum of the image field of the laser created by the lens. We demonstrate spatial filtering of wire laser radiation experimentally using a terahertz quantum cascade laser.

Variations in the regimes of heat/mass exchange between the water and air are studied in laboratory conditions using a quick-response thermocouple. Characteristic vertical temperature profiles are given, the interconnections between temperature gradients in laminar water and air layers are shown, and the dependence of heat/mass exchange regimes on the difference of water and air temperatures is considered.

Using instrumental investigations at the Black Sea shore, new data on the change in the heat-mass exchange under upwelling are obtained for the first time; the interrelation between the regimes of heat-mass exchange with a difference in air and water temperatures near the interface is established. The increased values of total heat flow at the shore as compared with the same flows in the open sea are recorded.

The calculations show that the absorption of the direct solar radiation in the surface 1-metre layer of the oceandepending on the transparence of the water can result in he change of the heat-and-mass exchange in it. Two new regimes of the heat and mass exchange are described, found experimentally in situ with the help of micro-thermoprobe. Data on the intensity of heat-and-mass exchange of the ocean and atmosphere are given. Formation of climate and weather on the Earth is basically determined by heat and massexchange between the ocean and the atmosphere which occurs by mean of processes of water evaporation, effective long-wave radiation and contact heat transfer. Being the initial cause ofglobal circulation of atmospheric and water masses on the Earth these processes themselves take place on the very surface of the ocean in a layer of 40 1um thin.Radiation characteristics of the ocean and the atmosphere are different and due to radiationexchange between the Sun, the Earth and Space are in thermal disbalance —