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Friction stir welding of butt joints in aluminum alloys is considered. Experiments show that, with disruption of the welding temperature and time, defects localized at the boundary of the weld seam are observed: specifically, gaps due to the differential deformation of the seam and the matrix.

The problem of determining the total and generalized aerodynamic forces for an airplane wing during vibrations in a compressible flow with allowance for the real frequencies of its natural vibrations is considered. The need to develop operational numerical methods for solving the problem, which is reduced to a Neumann-type boundary problem for a scalar Helmholtz equation, is substantiated. The results of numerical calculations of the wing of the Yak-130 aircraft are presented.

An adequacy of mathematical modelling of the technical object dynamics is always a challenge, and a user can make up his mind about the modelling package using simple test schemes. The article presents the schemes that are quite common from the point of view of an inexperienced user, but have specifics in mathematical modelling. The features of the schemes are that therein failures of equilibrium equations (such as the first Kirchhoff law) and continuity (such as the second Kirchhoff law) can occur. These features can lead to incorrect results when using the OpenModelica package, while the domestic PA9 and PRADIS packages used in modelling these schemes give the correct result. The article presents two simple schemes, the simulation result of which can be a priori estimated, and provides simulation results for three packages - OpenModelica, PA9, and PRADIS.

Mathematical modeling is offered for describing the effect of variable incidence between the body axis and the high enthalpy air flow on conjugated heat and mass transfer in a heat shield material at the thermochemical decomposition of the shield. Results of numerical simulation were obtained for spatial supersonic flow near a body with pitch variations. The effect of body oscillation with the rates 0–100 deg/s on heat and mass characteristics was studied.

Friction stir welding of butt joints of aluminum alloys is considered. It is experimentally determined, that when temperature and time parameters are violated, defects in the form of discontinuities are localized at the boundary of the weld and the base metal, due to incompatibility of deformations of the weld metal and the adjacent base material. Keywords friction welding with stirring, aluminum alloy, mode parameters, structure, defects, strength. feofanov.fan1@yandex.ru

On the analysis basis of trends in the development of aluminum alloy plasma welding it is shown that in most cases for critical structures there is used welding with a non-consumable electrode on reversed polarity with adding wire material. A welding method with a hollow anode to increase non-consumable tungsten electrode durability is described. It is shown that to increase quality of welded joints in aluminum-lithium alloys the application of plasma-forming gas programmable pulse feed has promising outlooks. In this case side by side with the decrease of such defects as pores and oxide films the obtaining of more fine-grained structure in metal seams is marked.

A high-speed aircraft, capable of maneuvering when moving in dense layers of the atmosphere, is subjected to high dynamic and thermal loads, which can lead to destruction of its shape and changes i...

A modern large-sized aircraft dynamic properties analysis, determined by the specificity of its layout scheme, demonstrates that the engines on under the wing elastic pylons lightly damped oscillations cause a number of undesirable phenomena, including intense accumulation of fatigue damage of the pylon-to-the-wing attachment, in fact in the area of engine installation in the pylon and the wing. The results of theoretical and experimental research show that with some engine attachment to the pylon structural modification it becomes possible to use the engines inertial and gyroscopic properties to absorb these oscillations. In this case, the motor tones damping coefficients increase by an order of magnitude or even more, so the gyroscopic coupling of elastic vibration tones is realized. With the rational choice of the additional parameters of elastic and dissipative bonds in the engine attachments it is possible to affect the aircraft wing and engines aero elastic vibrations effectively, which has a significant effect on the aircraft elements structural capabilities. A mathematical model of aero elasticity (MMAE) with respect to the kinetic moment of the engine rotors and specially designed units for attaching the engines to the pylons was developed in order to study the influence and the selection of rational elastic-dissipative parameters of the pylons-under-the-wing aircraft engine mounts. The method of predetermined basic forms is used for the aircraft with running engines on the pylons MMAE synthesis. The given forms are considered as the aircraft basic structure forms natural vibrations in the void. This work treats the engine nacelle and the rotor as absolutely rigid bodies, the elasticity of the rotor to the nacelle attachment is neglected. The pylon is modeled by an elastic beam, and the elastic and dissipative properties of the pylon-to-the-wing and the engine-to-the-pylon attachments are correspondingly by elastic-dissipative bonds. Schematic diagrams of the engine to the pylon attachments are proposed. The results of the study devoted to the influence of the proposed attachment points modifications on the load and integral strength characteristics of the main structural elements of the engine – pylon – wing dynamic system on the example of an An-124 aircraft are presented. The practical implementation of the proposed solutions aimed to reduce the level of fatigue damage to structural elements of the aircraft feasibility is proved.

A mathematical model of the process of unsteady heat transfer of a thermionic heat-protection system in convective heating has been formulated and investigated. The effects of evaporation (emission) of electrons from the surface of the emitter on the drop in the temperature of a composite thermionic heat-protection shell have been demonstrated. The effects of some types of heat-transfer agents in a composite shell on the heat-transfer regimes in a body have been investigated. Qualitative agreement of the computation results with the existing data has been achieved.

Photovoltaic and photoconductive properties of styrene–nonyl-methacrylate copolymer and poly(N-epoxypropylcarbazole) film composites doped with the tetranuclear metal complex Cu4L4(OCH3)4 (L– = N,N′-dibenzyl-N″-trichloroacetyltriamidophosphate) and a sensitizer, i.e., an organic compound with intramolecular charge transfer, were investigated. It was found that these composites had hole-type photoconductivity in the visible spectral range. The internal photoelectric effect was determined by the photogeneration of charge carriers from the metal complex and sensitizer. The kinetics of formation and relaxation of photogenerated charge carriers were studied using ESR. It was concluded that metal-complex molecules in the polymer composite increased the efficiency of photogeneration of nonequilibrium charge carriers and affected the composite photovoltaic properties.

—The microhardness, the structure of the maraging steel (MAS) 03N18K3M3T, and its susceptibility to delayed fracture (DF) after various regimes of treatment, including surface irradiation with argon ions Ar+ with an energy of 40 keV have been studied in this work. It has been shown that the most significant improvement in the properties (maximum hardness and minimum strength decrease upon DF) is reached if using irradiation at the final stage of steel treatment. The efficiency of this treatment regime is seen in the change of the mechanism of the crack propagation: from the brittle intergranular mechanism after steel aging for 3 h at 400°C (remaining the same in the case of ion irradiation before aging) to the quasi-cleavage mechanism during the irradiation after aging. It has been noted that in the latter case the microstructure of the investigated steel becomes more homogeneous over the entire volume of the sample as compared to the steel after the preliminary irradiation.

A mathematical model of the process of unsteady conjugate heat transfer of a thermionic thermal protection system during supersonic air flow around a spherically-blunted cone is investigated Estimates of the effect of evaporation (emission) of electrons from the emitter surface on lowering the temperature of the composite shell of the thermoelectronic thermal protection are made. The influence of different angles of attack on heat transfer modes in the system of multielement thermionic thermal protection has been studied Qualitative agreement of calculated results with the known data has been found.

Dynamics of charged fullerene in a surface layer of fullerite is studied under the influence of neutral or charged particles of the gas phase surrounding the fullerite material. The translational displacements of the nodes of the crystal lattice structure are determined by the equations of motion of the centers of mass of fullerenes. Central fullerene, which is described as a discrete set of sixty carbon atoms, plays a special role in the presented mathematical model. Angular oscillations and rotations of the central fullerene are described by the dynamic Euler equations. All other fullerenes have a centrally symmetric field of the potential of interaction with the surrounding atoms and molecules. In this regard, we use the hybrid discrete–continuous mathematical model with four potentials that describe the interactions between the surrounding fullerenes, smoothed fullerene and an atom, a pair of atoms, and electric charges. The results of a numerical study of influence of the Coulomb interaction on the rotational and translational motion of the C60 fullerene are presented.

Supramolecular interaction of carbon nanotori in a columnar phase is described using the methods of classical molecular dynamics. The collective behavior and dynamic properties of toroidal molecules arising under the action of the van der Waals forces are studied. The conditions under which columnar structures based on molecular tori become unstable and rearrange into another structure are investigated. The reasons for the appearance of two types of directed rotational motion from the chaotic motion of molecules are discussed.

The optical emission spectra of pure metals Fe, Zr, Ta and W are measured during their irradiation with Ar+, Kr+ and Xe+ ions (5, 10, 15 and 20 keV). It is found out that the energy and ion type in this energy range do not appreciably affect the thermal emission spectral profile of these targets and hence do not influence the thermal spike temperature formed in the zones of passing dense cascades of atomic displacements. It is shown that a constant temperature regime of the thermal peaks (T = const) is fulfilled in the case where the average radius R of the cascade region is proportional to the square root of the incident ion energy$$ \left(R\sim \sqrt{E}\right) $$, and the major part of the thermal energy is released at the cascade periphery of a fixed length. As a result, the energy per atom of the medium, released in this region, does not vary with the ion energy and cascade radius. It is also shown that the thermal spike temperature for all ion types essentially depends on the target material.

The article presents a study on the implantation of silver titanium alloy VT6. It has been shown that ion implantation contributes to the creation of compressive stresses in the surface layer of the target, which makes it possible to increase the endurance indices of the processed alloy under alternating loads. Ultrasonic processing leads to the formation of a nanostructured layer on the surface of a VT6 alloy target. As a result of ultrasonic impact treatment, the structure of the surface layer undergoes significant changes.

The properties and structure of the joints of the layered composite material based on aluminum alloys 1570— 1915—1570, made by resistance spot welding, automatic argon arc welding and friction stir welding are presented. The spot, lap and butt joints are made. The strength of the joints made by automatic argon arc welding with the AMg63 fi lling wire was 333...377 MPa at 180° bend angle. The butt joints obtained by the friction stir welding have strength factor of 0.90...0.92 from the strength of the base metal.

In this paper, the results of empirical studies by Nobel Prize laureates in Economic Sciences 2019 Michael Kremer, Abhijit Banerjee and Esther Duflo are discussed. Field experiments in education and healthcare systems as well as in the financial and technological areas made it possible to evaluate differently the effectiveness of traditional instruments of economic and social policy in poor countries, offering new, better practices and reforms aimed at poverty alleviation. In addition to the relevance of the findings in politics, the experiments by the laureates provided development economics with powerful analytical and methodological tools, forming the foundation for future academic investigations in this branch of economics.

Basic defects arising during the friction stir welding (FSW) of aluminum alloy butt-joints are systemized. There are revealed basic reasons of such defects arising such as faulty fusions, a flash, a metal overheating on the right side of a seam. A range of optimum correlations expressing a length of linear displacement of a tool along a joint during its one revolution (feed for one revolution) is defined, in which a qualitative formation of aluminum alloy seams is ensured. A possibility of defect correction by means of the repeated FSW pass is shown.

The development of hard-to-recover reserves is now becoming a prerequisite for a successful oil business. Nevertheless, there is still no consensus on what reserves should be classified in this category and what benefits should be received by oil industry workers during their development. At the same time, it is the improvement of the tax system that can spur the development of new technologies for the extraction of “complex” oil and ensure the profitability of its production.

The accelerated Ar+ ion irradiation at a fluence of 1.2 × 1015 cm–2 for 4 seconds formed 6.2% austenite in a cold-worked Fe–6.29 at % Mn alloy with a structure of α ferrite. The related ion beam heating of a foil 25 μm thick is 299 ± 5°C, according to temperature monitoring. The content of manganese calculated from Mossbauer spectroscopy data in α and γ phases after irradiation is 5.5 and 17.1 at %, respectively. Grounds for the activation of low-temperature atomic mobility in the alloy are discussed in this paper. The mobility was shown to not be caused by the formation of radiation defects and radiation-enhanced diffusion. Nanoscale dynamic effects, resulting in the possible viscous flow of material at the front of post-cascade shock waves propagating in a undamped mode, play a vital role.

The electron microscopic and diffraction analysis presented in the article showed that the structure of the surface layer of the titanium alloy OT4 after implantation at an accelerating voltage of 30 kV from the cathode Cu-Pb-Bi has a different hierarchical character. As a result of investigations of each of the levels, it was determined experimentally that the deformation mechanism under the action of internal stresses, as well as diffusion-relaxation reactions, are the main reasons for their formation, leading to the appearance of structural features in the surface layer of the OT4 alloy. In this case, penetration of alloying components to a depth of 10-25 nm is observed.

A mathematical model of the process of unsteady heat transfer of a thermionic thermal protection system during convective heating is presented. The effect of the evaporation (emission) of electrons from the surface of the emitter on a decrease in its temperature is studied. It is shown that the some coolants in the composite shell affects the heat-transfer modes of active thermal protection. The calculation results qualitatively agree with the known data.

The influence of high-speed particle fluxes on changes in the structure and properties of materials has been widely studied currently. The effect exerted by particles moving at very high speeds can have both negative (in spacecrafts) and positive character (dynamic processing of tool steels). Therefore a task for studying an effect of high-speed particle flows on structure change in tool steels and improving their performance properties has been set in the paper. The study has used an explosive method for creation of a high-speed flow of SiC + Ni and Al2O3 particles. Samples after dynamic alloying have been subjected to diffusion nitriding. Microstructure of specimens made of X12M, R18, R6M5K5steel has been studied using optical and electron metallography. Wear resistance of the samples has been also tested on a friction machine. Theoretical and experimental results on a complex effect of high-speed microparticle flows and nitriding on a structure and properties of tool steels have been obtained during the research. It has been established that dynamic alloying by particles leads to formation of a specific structure in a composite material reinforced with channels. Central fiber (channel) zone with powder particles residues is surrounded by areas of amorphous state which is succeeded by a zone with a nanocrystalline fragmented cellular structure. Then we observe a zone with a microcrystalline structure that transits to a zone with crystalline structure which is characteristic for a matrix material of structural steel. The obtained data can expand and complement some ideas about mechanisms for dynamic loading of solids and condensed matter, plastic deformation, physical mechanics of structurally inhomogeneous media at different levels, a number of effects arising from collision and ultra-deep penetration of microparticles into metals. It has been shown that wear resistance of high-speed steel subjected to dynamic alloying in the quenched state is increased by 1.2 times in comparison with wear resistance of steel alloyed in the annealing state.

Experimental fuel rods were tested in the PV-2 loop facility of the MIR reactor under conditions close to operation of full-size fuel rods in a PWR core. In the tests, the external condition of the cladding of the experimental fuel rods and structural elements of FA was evaluated visually; the thickness of the oxide film on the outer surface of the cladding of some fuel rods was measured. At the completion of the tests, all fuel rods remained tight, and no defects were found on the surface of the cladding and structural elements of FA. The thickness of the oxide film on the surface of the fuel rods made from the alloy E-110 (ultrapure), E-125 did not exceed 10 μm with average fuel burnup 32 MW·days/kg.

The possible formation of a solid phase in the lead coolant in the BREST-OD-300 reactor, a problem common for reactors of such type, is numerically investigated. For modeling unsteady processes in the steam generator operating with a liquid-metal coolant under the conditions involving the occurrence of crystallization–melting phenomena, a procedure that makes it possible to take into account the process ambiguity depending on the state of the heat-transfer contact surface oxide layer was used. Accidents caused by a rupture of the main steam header and by failure of the regenerative feedwater heating system are considered. The influence of certain reactor parameters on the solid phase formation dynamics in such accidents is estimated. If loss of tightness occurs in the main steam header with simultaneous loss of power supply to the reactor and failure of the steam generators’ shutoff and control valves and also in the case of regenerative feedwater heating system failure with retaining the supply of feedwater to the steam generators, the solid phase fully blocks the flow section in all four loops of the primary coolant circuit. Depending on the state of the heat-transfer contact surface oxide layer, the flow sections of the steam generators themselves or those of the steam generator cavities in the concrete shell can be blocked. The main factor causing the lead coolant to become solidified in the case of steam header rupture is a sufficiently large amount of feedwater in the secondary coolant circuit pipelines and heat-transfer equipment at high pressure. At the same time, in an accident involving failure of the regenerative feedwater heating system, this volume is not of key importance for the solid phase formation dynamics in the lead coolant. The study results can be used in elaborating the designs of lead cooled reactors.

Aim: to study the distribution of HLA-antigens in married couples with failed conception and/or carrying of pregnancy, and to assess the occurrence rate and the presence of common alleles of the main histocompatibility complex in couples with infertility and miscarriages. Materials and methods. We conducted HLA-typing of 198 married couples with aggravated obstetric history. The main inclusion criteria were conception failures and unsuccessful outcomes of previous pregnancies. The HLA-class I antigen typing was carried out using a standard micro-lymphocyte-toxic test («Gisans», Russia); for the class II HLA-antigens, real-time polymerase chain reaction («DNA-Technology», Russia) was used. Based on the obstetric and gynecological history, the patients were divided into 2 subgroups: 1st – those with infertility and 2nd– with recurrent miscarriages. The comparison group included 101 married couples with no aggravated obstetric history, no infectious, no endocrine or anatomical abnormalities, and having 2 or more children. The occurrence rates of classes I and II HLA-antigens in women and men from the examined groups were compared with those in healthy individuals living in the same area. Results. In the examined couples with recurrent miscarriages, the HLA-A11 antigen occurred significantly more often in men, and HLA-В35 antigen – less often in women. In women of the infertile couples, HLA-A19 antigen was detected more often than in couples with children. In women with infertility, the HLA-DRB1*08 and HLA-DQA1*0401 alleles were less common than in women without fertility disorders. In the examined couples with infertility and recurrent miscarriages, statistically significant predominance of 3 genes common to the HLA class II system was found. In couples with normal fertility functions, the absence of homologous alleles of the HLA class II system in their genotypes was typical. Conclusion. HLA typing allows for predicting the risk of infertility and reproductive failure.

On the basis of the extensive base of experimental research results there are defined standard stress-strain properties of welded butt-joints of aluminum alloys thermally non-hardened with Al-Mg system. It is shown that during friction welding with stir there is a formation of a gradient structure with ultra-fine grain in the stir area. It is defined that at the heart of the mechanism of a joint formation are placed phenomena of plastic deformation of a displacement and turn of structural elements. There is defined a range of optimum proportions expressing a length of a tool linear displacement along a joint during one its turn in which a qualitative formation of thin sheet joints of the Al-Mg system.

The article studies the reproductive potential and features of the functioning of the “rooted” regional economy using the example of the multiethnic North Caucasus territory. The article presents and conceptually interprets the results of a representative economic-sociological study on traditional economic forms and practices of the North Caucasus population (household farms, personal subsidiary plots, family farms, individual enterprise, self-employment). The economic assets of these forms and practices, their reproductive potential and their contributions to the region’s economy are estimated. The article reveals their key role in the economic structure of the rooted sector of the region’s economy.

Ensuring the tightness and integrity of the filtration and capacitance properties of hy-drocar-bon bearing productive horizons is determined by the volume and depth of pen-etration into their structure of the pore space of dispersion and dispersed phases, the technological heterogeneous systems used, their physical and mechanical properties, the insulating properties of the forming groove, the innovative solutions (technologies, tech-nical means). Based on the results of the general-ization of theoretical, experimental, field research, recommendations are given on the formulations (compositions) of technolog-ical colloidal and hardening systems to solve the problem (raising the maintenance-free period of effective well work) in the construction of wells in fields with complex geological and technological conditions for their development and development.Methods are proposed for designing a well design that takes into account the joint per-ception of excess loads by the system casing cement stone; formulations of washing biopolymer salts compositions and oil-filled materials for a wide range of thermobaric condi-tions for the occurrence of oil and gas reservoirs; the design of downhole hydrosensitivity generators on a grouting mortar pumped through them. The proposed investment solu-tions with positive results are tested during the construction of wells.

State-of-the-art development of HF radio communication systems follows the idea of significant spreading the bandwidth of variable ionospheric radio channels. In this case, the topical scientific and technical problem is to overcome the negative effect of the frequency intramode dispersion of the medium. For these purpose, we tackled the problem of increasing the efficiency of the channel adaptive SDR-equalizer operating under the various geophysical conditions of the mid-latitude radio propagation path Cyprus-to-Yoshkar-Ola. The following operation modes of the SDR-equalizer were considered: periodic channel testing; estimating the SDR-equalizer parameters and training the SDR-equalizer. For experimental implementation of the testing mode, we developed a physical model of a communication HF signal with a wideband fast frequency hopping. There were experimentally determined: the minimum required bandwidth of the partial subchannel; the number of subchannels to correct for dispersion in 1 MHz channels. In addition to this, there are presented data on the influence of diurnal variations of the ionosphere on the SDR-equalizer parameters.

In this paper, the effect of deformation of a fullerite crystal on the dynamic properties of a rotating C60 molecule located in the center of a selected fragment is analyzed. The spherical potential of pair interaction is used to determine the dynamic characteristics of surrounding molecules. The angular oscillations and rotation of the central C60 molecule are described using the dynamic Euler equations. The effect of the direction of deformation of a fragment of a fullerite crystal on the precessional displacement of a rotating fullerene molecule is investigated depending on the direction and magnitude of the initial angular velocity.

The article provides insight into the technical implementation and characteristics of a multi-beam surveillance radar designed to work as part of the small-sized unmanned aerial vehicle traffic control complex in a “smart city”. In the article, it is pointed out that the advantages of this type of radar are a long range, resistance to weather conditions, quick changeover of the frame in a wide scanning area. The proposed technical concept is the one of the radar, which provides detecting drones at a range of up to 10 km. The description includes the design of the receiving phased array antenna and the structure of the receiving channel. The requirements for the dynamic range of the receiver are well justified, and the need to use automatic gain time control to expand the scan area in the range is clearly illustrated. The required parameters and characteristics of the equipment mainly correspond to the existing models of survey radars and the models being developed and are quite achievable with a modern technical base. The article presents characteristics of a multi-beam radar experimental sample and the results of its tests at observing drones. The tests have proven the predicted characteristics, and demonstrated the ability to effectively suppress reflections from the ground, as well as gave credence to the calculated detection range parameters and the strong immunity of the radar to bad weather conditions. The materials provided in the article are supported with the radar images received in course of the experiments.

The precessional motion of a fullerene molecule during deformation of a section of a fullerite crystal was studied. The dynamic characteristics of the C60 fullerene molecule inside the crystal fragment were determined using the apparatus of classical mechanics using the model of atom-atomic interactions, the dynamic Euler equations, and the equation of the dynamics of translational motion. For numerical implementation, the Runge-Kutta method of the fourth order of accuracy is used. As a result of the performed numerical experiments, the effect of the rotation frequency of the fullerene molecule and the direction of deformation of the fullerite fragment on the ability of the C60 molecule to withstand the external forces was studied.

The work is devoted to the study of gyroscopic phenomena in the interaction of a rotating fullerene molecule and a xenon atom incident on it. The methods of classical molecular physics are used: intermolecular potentials, Newton's equations for describing the motion of particles, and the Runge–Kutta numerical method of high order of accuracy. A mathematical model is constructed and implemented for the rotation frequencies of fullerene up to 1014 Hz and the speed of the incident xenon atom of the order of 103 m s−1. For such parameters of the problem, the de Broglie wavelength of the incident atom and the fullerene molecule become smaller than the diameter of the carbon atomic nucleus. This made it possible to apply the Newtonian approach without involving quantum mechanics. The aim of this work is the consistent application of the apparatus of classical mechanics to reveal the effect of the precession of rotating fullerene inside fullerite. © 2020 Wiley-VCH GmbH

A mathematical model of a thermionic thermal protection system has been developed to study the characteristics of heat and mass transfer in a spatial, high-enthalpy air flow around a body. The effect of electron evaporation (emission) from the emitter surface on the decrease in the temperature of the composite shell of thermionic thermal protection is estimated. The effect of different angles of attack on the heat-transfer regimes in the system of multielement thermionic thermal protection is studied. Qualitative agreement of the calculation results with the known data has been obtained.

The influence of oscillations of a conic body with a nose blunted over a sphere on the conjugate heat and mass transfer in its heat-resistant coating in the case where the material of the conical part of the body is subjected to thermomechanical failure as a result of the fl ow of a high-enthalpy gas over it was investigated. Results of a numerical investigation of the three-dimensional supersonic fl ow over such a body executing an oscillatory motion in the pitch plane are presented.

In this article, we conduct research on the effect of corrosion tests on the hydrogen diffusion process in gas steel in electrochemical permeability tests. This tests show that a long corrosion test time reduces the hydrogen diffusion coefficient by an order of magnitude, indicating the formation of aging defects in the steel. During operation, the diffusion coefficient decreases by two orders of magnitude, which also indicates the formation of a large number of defects in the steel. Consequently, based on the change in the diffusion coefficient in the material, it is possible to assess the degree of material failure.

Studies address to the propagation of wideband wave packets over the ionospheric HF radio channel. We tackled the problem of deconvolution of a wideband HF signal with frequency hopping spread spectrum, corrupted by the frequency dispersion due to the propagation over the channel with a 1 MHz bandwidth from the single-mode propagation range. We assumed that errors in dispersion correction can occur during signal processing. That errors are caused by the noise variations in the channel. Errors cause losses in the data transfer rate. A method of training adaptive dispersion corrector with the use of the data on sounding a wideband channel is presented. Corrector implements the deconvolution function. Based on the experimental data gathered on the radio propagation path Cyprus-to-Yoshkar-Ola, we obtained the dependence of the signal-to-noise ratio on the error value in a wideband channel of 1 MHz bandwidth with a fading depth of up to 20 dB. Considering losses due to the inverse filtering, we estimated the ultimate data transfer rates of HF modems and gain in the covertness of the wideband HF communication system.

Paper presents the findings of experimental research into the single-mode propagation of HF radio waves over long-haul paths by analyzing frequency range where single-mode propagation exists. The influence of various geophysical factors on single-mode propagation range was thoroughly studied. The analysis of the possibilities of the operation of narrowband (3 kHz) and wideband (1 MHz) communication systems in that frequency range is presented.

Research focused on the problem of developing digital adaptive equalizer in the frequency band of wideband HF communication to overcome the negative effect of nonlinear phase dispersion. Developed methods, algorithms and software are supported by the SDR technology and were implemented with the use of the USRP N210 platform. They use state-of-the-art approaches in digital signal processing, including those elaborated by the authors. Verification of methods, algorithms, and software for adaptive equalization was carried out in full-scale experiments on LFMCW sounding over the Cyprus-to-yoshkar-Ola propagation path of length of 2600 km. Besides, the specific objective of the research was studying equalization efficiency in megahertz-bandwidth channels the single-mode (1F mode) propagation band.