Vol 23, No 3 (2022)
Section 1. Computer Science, Computer Engineering and Management
On the construction of stress discontinuity lines for a two-dimensional plastic region
Abstract
We consider the plasticity equations in the two-dimensional case and construct stress discontinuity lines in this paper. The construction of stress rupture lines has a fact: the rupture lines are located at the intersection point of lines of the same family (characteristics) and are directed along the angle bisector formed by these characteristics. To find these lines, we have constructed characteristics. Such a task is easier to solve in the case of plastic torsion, at that moment there is only one characteristic, and it is directed along the normal to the outer contour, and it is quite simple to find the sliding lines and their intersection points. Most of the works devoted to the construction of stress rupture lines solve the problem of plastic torsion for isotropic and anisotropic media. For problems of plane deformation of plastic material, this method is not sufficiently developed. This is the complexity of constructing sliding lines for such tasks and the presence of two families of sliding lines.
A homotopy of two known exact solutions is constructed: Prandtl and Nadai, that is, a continuous transformation of one solution into another in this article. We obtain the characteristics of the Prandtl solution at a=1. We obtain the characteristics of Nadai's solution at a=0. The characteristics of one family begin to intersect and stress discontinuity lines appear at a = 0,5. These lines are constructed in this work.
364-371
Construction of high-precision low-dimensional MgFE using local approximations and generating FE
Abstract
Composite structures (bodies), in particular, plates, beams, shells, are widely used in aviation and rocket and space technology. To analyze the stress state of elastic composite bodies (CB), the method of multigrid finite elements (MMFE) is effectively used, which is implemented on the basis of the Lagrange functional (in displacements). When constructing a multigrid finite element (MgFE), briefly a standard MgFE, using known procedures, a small base grid is used, which can be arbitrarily small, and large ones nested in a small one. The fine grid is generated by the partition of the MgFE, which takes into account its inhomogeneous, micro-inhomogeneous structure within the framework of the micro-passage. Large grids are used to reduce the dimension of the MgFE. The following is typical for a standard MgFE. Any large grid of a standard MgFE and corresponding approximations of displacements are determined on its entire area. This leads to an increase in the dimension of the standard MgFE with an increase in its order of accuracy, since in this case approximations of high-order displacements are determined on large grids. To reduce the error of solutions, high-precision MgFE are used, i. e., of a high order of accuracy, which have a large dimension. However, the use of high-precision MgFE is difficult, since they form discrete models of high-dimensional bodies.
In this paper, we propose a method of local approximations (MLA) for constructing high-current MgFE of small dimension (short - small-sized MgFE), which are used to calculate elastic homogeneous and CB by MgFE. Two types of small-sized MgFE are considered. Small-sized MgFE of the 1st type are designed on the basis of standard ones with the use of local approximations of displacements, which are determined on the subdomains of standard MgFE, of the 2nd type - with the use of finite element generators (FE). The brief essence of the construction of small-sized MgFE of the 1st type is as follows. According to the MLA, we define a smaller Н grid on the V0 area of the standard MgFE than its base one. The V0 region is represented by the boundary and inner regions. The boundary (inner) regions have a common boundary, which does not degenerate into a point (do not have a common boundary), with the V0 region. On the boundary (inner) regions, we define large grids that are embedded in a small Н grid and generate local approximations of small (high) order displacements. On the V0 region, using local approximations of the displacements of the boundary and inner regions, we construct the MgFE. Then, using the condensation method, we express the movements of the internal nodes of the MgFE through the movements of the nodes lying on its boundary, i.e. on the boundary of the V0 region. As a result, we obtain a high-precision Vp MgFE of small dimension, i.e. a small-sized MgFE of the 1st type, the dimension of which is equal to the dimension of the standard one. It is important to note that with an increase in the order of accuracy of the Vp MgFE, its dimension does not change, i.e. it does not increase, and therefore it is called a high-precision MgFE of small dimension, i.e. small-sized. The procedure for constructing small-sized MgFE of the 1st type is described in detail. As is known, the calculation of the static strength of structures is reduced to determining the maximum equivalent stresses for them, the determination of which with a small error for CB is an urgent problem.
Calculations show that small-sized MgFE of the 1st type generate maximum equivalent stresses in CB, the errors of which are 25÷50 smaller than the errors of analogous stresses obtained using standard ones, on the basis of which small-sized, i.e. small-sized MgFE of the 1st type are more effective than standard ones. The use of small-sized MgFE of the 1st type in MMFE calculations makes it possible to determine the maximum equivalent stresses with a small error for large CB partitions.
The construction of small-sized MgFE of the 2nd type is shown, which are designed on the basis of standard high-precision MgFE with the use of generating FE. A small-sized MgFE of the 2nd type has the same order of accuracy as the standard one, but its dimension is smaller than the dimension of the standard one. The advantage of small-sized MgFE of the 2nd type is that they give rise to discrete CB models of smaller dimension than standard ones.
372-390
Search for broadband signals ground-based radio navigation system
Abstract
In the present paper, a method of temporary search for broadband of frequency manipulationwith minimal shift keying (MSK) signals of ground-based radio navigation systems (RNS) is considered. The method is based on a multi-alternative optimal signal detection (the signal may belong to one of the orthogonal signals) using the evaluation-correlation principle of processing (ECPP) under conditions of a priori uncertainty.
The problem of representing broadband MSK signal as a signal with double discrete frequency-phase modulation (FPM) was solved. The law of phase manipulation in the form of a binary sequence of elements bl of a length code Ltэ (in the “Sprut” RNS, L = 16383, tэ = 2,5, mcs is the duration of the signal element) is defined through the law of frequency manipulation in the form of a binary sequence of elements dl of a known length L code. The representation of the signal in the form FPM allows, during correlation processing, to replace the correlation integral on the interval [0, Ltэ] by L the sum of correlation integrals on the intervals [0, tэ] or by L the sum of element-by-element correlations.
The calculation of element-by-element correlations allows the use of a matrix apparatus for the ECPP of the analyzed signal. With the technical implementation of the “search” procedure, there is no need to form 2L pairs of reference quadrature signals with the length L of the modulating code, and instead of that a pair of element-by-element correlations is memorized and over time tэ, according to a code element dlk, cyclically shifted by k-1 elements, frequency manipulation and a code element bkl, cyclically shifted by k-1 elements, phase manipulation, block-by-block accumulation L of quadrature correlations is performed.
The use of upper-left and lower-right triangular matrices with binary elements bkl makes it possible to search for broadband MSK signal with additional phase manipulation of a discrete information message.
The structure of the optimal algorithm of parallel search for ECPP of the broadband MSK signal with the use of a matrix apparatus, which allows to implement the optimal algorithm “of search” during the duration Ltэ of the signal in real time.
391-408
Estimation of the number of aperiodic words
Abstract
In 1902 W. Burnside raised the issue of local finiteness of groups, all elements of which are of finite order. The first negative answer was obtained in 1968 in the article by by P.S. Novikov and S.I. Adian. Finiteness of the free Burnside group of period n was established for n = 2, n = 3 (W. Burnside), n = 4 (W. Burnside, I. N. Sanov), n = 6 (M. Hall). The proof of infinity of this group for odd n ≥ 4381 was given in the article by P. S. Novikov and S. I. Adian (1967), and for odd n ≥ 665 in the book by S. I. Adian (1975). In relation with these results we consider the set of m-aperiodic words. Word is called l-aperiodic if there are no non-empty subwords of the form Yl in it. In the monograph by S. I. Adian (1975) it was showen the proof of S. E. Arshon (1937) of the fact that in the two-letters alphabet there is an infinite set of arbitrarily long 3-aperiodic words. In the book by A. Yu. Olshansky (1989) the theorem on the infinity of the set of 6-aperiodic words was proved, and a lower bound function for the number of words of a given length was obtained. Our aim is to get an estimate for the function f(n) of the number of -m - aperiodic words of the length in the two-letters alphabet. The results can be applied when encoding information in space communications.
409-416
Conservation laws and solutions of the first boundary value problem for equations of two-dimensional elasticity theory
Abstract
If a system of differential equations admits a group of continuous transformations, then the system can be represented as a set of two systems of differential equations, it is known. As a rule, these systems have a smaller order than the original system. The first system is automorphic, characterized by the fact that all its solutions are obtained from a single solution using transformations of this group. The second system is permissive, its solutions, under the action of the group, pass into themselves. The resolving system carries basic information about the source system. Automorphic and resolving systems, two-dimensional stationary elasticity equations are studied in this work. They are systems of first-order differential equations. Infinite series of conservation laws for a resolving system of equations and an automorphic system are constructed for the first time in this work. Since the two-dimensional system of elasticity equations is linear, there are infinitely many such laws. In this paper, an infinite series of linear conservation laws with respect to the first derivatives is constructed. It was these laws that made it possible to solve the first boundary value problem for the equations of elasticity theory in the two-dimensional case. These solutions are constructed in the form of quadratures, these quadratures are calculated along the contour of the studied area.
417-422
Section 2. Aviation and Space Technology
The choice of the energy parameters of an oxygen-hydrogen propellant expander cycle rocket engine
Abstract
In liquid-propellant rocket engines (LRE), made according to an expander cycle scheme, the turbine of the turbopump unit is driven by heated fuel in the cooling path of the combustion chamber (CC). The absence of a gas generator greatly increases the reliability of the rocket engine and provides a number of advantages compared to other engine schemes.
At the moment, the existing oxygen-hydrogen liquid-propellant rocket engines by expander cycle scheme do not suit modern tactical and technical requirements for the level of thrust and pressure in the CC of the engine. Therefore, it is necessary to study ways to increase the energy parameters of a liquid-propellant rocket engine and identify promising engine schemes.
This article proposes schematic solutions for an oxygen-hydrogen gasless LRE, analyzes the influence of various factors on the specific parameters of the engine, as well as recommendations for designing expander cycle LRE.
A mathematical model for calculating the main energy and geometric parameters of the engine has been developed. Prospective pneumohydraulic schemes of an oxygen-hydrogen liquid-propellant expander cyсle rocket engine are proposed, depending on the tactical and technical requirements.
424-436
Local heat transfer parameters in the areas of the developing temperature boundary layer in the cavities of gas turbines local heat transfer parameters in the areas of the developing temperature boundary layer in the cavities of gas turbines
Abstract
In this work, an analytical determination of the local heat transfer coefficient in the planes of rotation of gas turbines is carried out using an affine-like model for the distribution of temperature and dynamic spatial boundary layers with a convective component (at Pr < 1). The method of analytical study used in the work led to results close to the experimental values.
The problem of determining the thickness of the energy loss is solved using the integral relation of the energy equation of the temperature spatial boundary layer, which makes it possible to integrate the necessary curvature over the surface. The law of heat transfer of the turbulent boundary layer for the rotational motion of the flow and motion according to the law of “solid body” is expressed.
Equations are obtained for determining the local heat transfer coefficient by the Stanton criterion for various external flow laws for a power-law velocity distribution in the boundary layer according to the affine-like model of the temperature boundary layer.
Heat transfer coefficients correlate with sufficient accuracy with experimental data and dependencies published by other authors: J. M. Owen, L. A. Dorfman, I. V. Shevchuk. The deviation of the results obtained from the dependence of the model with a convective component and with affinity-like profiles do not have statistically significant differences. The obtained results of the study and their comparison with the results of other authors showed that they are suitable for engineering calculations and analysis of the impact of local heat transfer coefficients on high-temperature units of a turbopump unit.
437-450
Design of the fastening assembly of the guys on the power spokes reflector
Abstract
Currently, global communication systems are developing towards mastering high frequency bands for organizing high-speed information transmission channels, which requires large-sized antenna systems with reflectors up to 50 meters. Most of the technical solutions used for assembling large-sized reflectors are based on technological volumetric templates that geometrically completely imitate the necessary reflective surface of the reflector. The mass of such templates increases in cubic dependence on the increase in the diameter of the reflector, which is why it becomes more and more laborious to use them when assembling large-sized antennas due to the increase in the dimensions and weight of the templates.
The purpose of the study is to design the attachment point for guy wires on the power spoke of the reflector for a "templateless" assembly. The spoke is a composite isogrid structure on which brackets are fixed for attaching power units. The fastening unit is an assembly unit consisting of a bracket and clips and allows you to precisely adjust the necessary pull tension force to fix the cord in the working position without the use of one-piece fastening methods.
The analytical approach and finite element analysis were adopted as research methods. Using an analytical calculation, the maximum tensile force of the guys in the designed unit was determined, thereby setting the maximum load for its operation. The coefficient of friction between the cord and the clamp in each individual case is determined experimentally. After simplifying the design and construction scheme of the bracket, the analytical calculation was carried out for a three-dimensional rod frame.
To confirm the results of the calculation, a finite element model of the bracket was built and its static analysis was carried out. For the developed model of the bracket, the maximum stresses were determined and their comparative analysis was carried out with the results obtained analytically.
The results of the design of the bracing attachment point. With the help of solid modeling, the mass and overall characteristics of the braces fastening unit are determined. The limiting ranges of tension forces and the materials used in the knot, as well as its strength characteristics, were determined.
Conclusion. This node can be used in the "templateless" method of assembling a reflector for a wide range of large antennas, it has high manufacturability and versatility.
451-460
Approximation of beam support coefficient values at vibrations and buckling
Abstract
The problem of calculating the first natural frequency of vibration and the first critical force for a beam with elastic supports is considered. An analytical review of the literature on solving such problems showed that in the theory of vibrations and the theory of stability of beams, consideration of the support conditions is based on the use of support coefficients, the values of which were obtained after solving the corresponding differential equation. The reviewed literature contains only a limited set of values of these coefficients, mainly for ideal supports of simple types: hinges, fixed, etc. Consideration of the stiffness of supports can only be found in individual editions and only for a limited number of values. In this work, the calculation of the support coefficients depending on the stiffness of the beam supports for the first natural frequency of vibrations and the first critical force is made. The obtained values were divided into three zones and approximated within each zone by quadratic functions. The use of quadratic approximation made it possible to obtain simple analytical dependencies suitable for engineering applied calculations, and the division of stiffness into zones provided an acceptable error of the obtained values. Also, quadratic dependencies made it possible to solve inverse problems for determining the stiffness of supports for a given value of the first natural frequency of vibrations or the first critical force. A detailed study of the error of the obtained approximating functions over the entire considered range of stiffness was carried out, which showed that the error in determining the coefficient of supports during fluctuations is not more than 2 %, and in case of loss of stability – 6 %. The error depends on the combination of stiffness of the supports, and can increase if the stiffnesses differ by more than an order of magnitude. The high sensitivity of the solution of the inverse problem to the input data was also established, which is the result of the high nonlinearity of the dependence of the coefficients of the supports on the stiffness. The obtained results can be used in engineering calculations of the first natural frequency of vibrations and the first critical force of a beam with elastic supports.
461-474
Method for calculating the thermodynamic characteristics of a vortex ejector with known geometric dimensions
Abstract
Based on the previously compiled physical and mathematical model of the vortex ejector workflow, its solution was made. The solution of this model made it possible to compile two calculation methods: a method for calculating the optimal geometry of a vortex ejector for given thermodynamic characteristics and a method for calculating the thermodynamic characteristics of a vortex ejector with known geometric dimensions [1; 2].
Vortex ejectors are used in many areas of aerospace engineering. The compiled development of a method for calculating the thermodynamic characteristics of a vortex ejector with known geometric dimensions will make it possible to use vortex ejectors more widely in the aerospace industry. The calculation method is based on the concepts of tangential stresses arising in a viscous medium when two flows moving at different speeds interact.
The mechanism of kinetic energy transfer from a high-energy gas to a low-energy one is shown.
475-485
The concept of an educational and scientific experiment for conducting on-orbit testing of any types of photovoltaic cell
Abstract
The article proposes the concept of an experiment for conducting flight testing of various samples of photovoltaic converters. The purpose of the experiment is to study the behavior of new types of solar cells in outer space.
The research will be carried out by testing samples on board the spacecraft. The experiment will be carried out by a device that collects data on the electrical properties of solar cells. The information received will be presented in the form of a voltage characteristic. During the experiment, its dependence on external parameters will also be studied. In particular, the correlation of the current-voltage characteristic from the values of temperature and illumination of solar cells will be investigated. Based on the data obtained, the efficiency of photovoltaic converters will be determined. Their degradation as a result of exposure to cosmic ionizing radiation will also be studied. The authors are tasked with designing and developing an experimental installation that will be a payload module of a small CubeSat-class spacecraft.
Based on the results of the work, the appearance of the flight testing experiment was developed, the requirements for the payload module were determined and a project for its creation was proposed. At this stage, the circuit design and software implementation of the module itself are under development. In the course of the work, the main requirements that this module provides to the main systems of the spacecraft were also formulated.
To carry out the mission of the experiment, it is planned to integrate the payload module on the platform of the ReshUCube-2 form factor 3U. This satellite will be equipped with equipment enabling technological experiments.
486-497
Method for processing the results of cavitation tests of TNA pumps in order to obtain an approximating function
Abstract
When designing rocket engines, the problem of providing the specified basic design parameters is solved. In connection with the increase in requirements for products of rocket and space technology, the requirements for ensuring the energy efficiency of all its constituent elements are also increasing. As a rule, the task of increasing the energy characteristics of a rocket engine is carried out by increasing the pressure in the combustion chamber and the rotational speed of the turbopump shaft. An increase in the rotational speed of the shaft of a turbopump unit requires the provision of a cavitation-free operation of the pump with the absence of cavitation breakdown.
This problem can be solved in various ways: by constructive improvement of the pump or by increasing the pressure parameter at the pump inlet. However, too much increase in inlet pressure is not possible, as this will increase the thickness of the walls of the rocket's fuel tanks and a corresponding increase in the mass of the entire rocket. Turning on the screw, although it does not guarantee cavitation-free operation at any inlet pressure, is the most preferred method.
The geometry of the bore part of both the screw prepump and the pump blades is designed to ensure non-cavitational operation. When designing, at the stage of experimental testing of pump modes, it is possible to use the methods of computational fluid dynamics (Computational Fluid Dynamics, CFD). These methods are used in various areas of general engineering and have proven themselves well. However, the rocket motor pump has a high pressure drop with relatively small dimensions. The question arises of adapting CFD methods to modeling cavitation tests.
This work is aimed at deriving a function approximating the THA pump test data set with a view to its further adaptation for CFD methods.
498-507
Methodological principles for the formation of a number of unified space communication satellite platforms
Abstract
This article formulates the topical problem of formalizing the methodological principles of the search for a compromise between repeatability and modification (novelty) of the properties of new models of space technology – communication satellites. The main methodological principles of continuity of development are the unification of products and their component parts, means of technological equipment and technological processes, which makes it possible to reduce their diversity and nomenclature. The order of the nomenclature of the articles and their component parts is achieved by the development of parametric and type-size series with rationally chosen intervals between the adjacent members of the series according to a complex criterion, a link to the target product performance with the cost of creating the product. The work developed a project model and defined criteria for selecting the size type of a universal space platform. In designing a new spacecraft on the basis of a unified space platform, there is a need to refine it to meet the resource requirements of the new payload (mass and energy consumption). The article sets out the methodological principles for assessing the range of effective applications of the universal space platform for the two most extreme cases of resource requirements (by mass and energy consumption) of the payload: the resources of the platform are excessive or insufficient. Methodological principles have been developed for the formation of a number of unified space platforms. Using the methodological principles for the formation of a series of unified space platforms, the effectiveness ranges of USP were evaluated and the completeness of a number of geostationary communication satellites of the development of “ISS” was assessed.
508-519
Modeling and verification of working process parameters in gas generators for pressurizing fuel tanks of liquid propellant rocket propulsion systems
Abstract
The main requirements for LRE gas generators are high stability of operation ease of workflow management, as well as high efficiency of the generator gas. A particularly difficult task is to ensure the sustainability of the workflow. In addition to the probability of transverse vibrations in the in-chamber volume, due to the presence of additional volumes of various configurations and lengths attached to the reaction chamber, acoustic vibrations of complex longitudinal modes may occur. Most of the existing methods of testing a gas generator are criterion-empirical in nature and are based on the processing of experimental results, which does not always provide the required accuracy of calculating dynamic and thermal characteristics. The need for experimental and theoretical refinement of the calculation methods of thermodynamic processes of gas generators is an urgent task that will significantly reduce the material and time costs for preliminary design, testing and fine-tuning of modern models of engines and power plants of aircraft. Therefore, the calculation and analysis of the LRE gas generator is an important stage in the design and development of modern engine designs. Using the finite element method of the SOLID WORKS software package, a model of a two-zone gas generator for supercharging fuel tanks of the LRE was built. A study was conducted on modeling the workflow in a gas generator, visualization of thermodynamic processes in the product was built, numerical characteristics were obtained. The method of autonomous bench (firing) tests of gas generators of fuel tank boost, the method of verification of numerical methods is considered.
520-530
Section 3. Technological Processes and Materials
Studying the factor of ice of icing field loss from fresh water in the millimeter range
Abstract
In this work, the attenuation of microwave radiation in an artificially formed icing field on the ice cover of a freshwater lake was measured in the millimeter range. The measurements were made using microwave radiometry at frequencies of 22, 34, 90, and 125 GHz with a cyclic change in the ambient temperature in the range from –19 to –31 °C. A special technique was used, which makes it possible to determine the attenuation of microwave radiation in it from the increments of radio brightness temperature between ice cover and without icing field. In the proposed method, the loss factor was found under the condition that attenuation in ice is determined by electromagnetic losses in the medium. The measurements were carried out on the ice cover of a fresh lake with a water salinity of about 100 mg/l. As a result of the study, it was found that the formation of radiation by ice is strongly influenced by scattering on inhomogeneities of the medium. This conclusion was made from a comparison of the calculations of the expected ice loss factor of icing field and the data obtained from measurements by the method used. The greatest difference in the loss factor (several tens of times) was found at frequencies of 90 and 125 GHz. It has been suggested that radiation scattering occurs on crystalline hydrates of salts and can be caused by increased electrical conductivity of thin water films on the surface of crystals. This feature can arise, as was recently established, during the formation of ice 0 crystals in the medium. This ice is formed from deeply supercooled water at temperatures below –23 °C. The observed effect is of interest for the development of radar measurements of fresh natural ice at low temperatures and low concentrations in salts (about 100 mg/kg). Such ice can form from slightly salty water with a salt content of up to several grams per liter or when water with a salinity of ~ 100 mg/l freezes in a confined space. The results obtained are of interest for microwave aerospace determination of areas of the ice cover with its structural disturbances, through which the water of the reservoir can penetrate to the ice surface with subsequent freezing. At the same time, radars can be effective at icing field temperatures below –20 °C, when liquid inclusions almost completely freeze out. For the temperature range above the eutectic point, where liquid inclusions appear, passive radiometric measurements can be effective.
532-541
Development of a human-machine interface for cascade control mills in obtaining nepheline ore charge
Abstract
Aluminum and alloys based on it are the main materials for space engineering, both in the production of vehicle parts, and in the organization of power supply and electronics. The raw material for producing aluminum is alumina.
Alumina production is a multi-stage process that includes the processing of raw materials in various ways: mechanically, thermally, chemically. Mechanical processing of raw materials is the first stage of production, it includes a crushing department and a batch preparation department. The preparation of the charge from nepheline ore for further stages of production takes place in mills with the addition of limestone and recycled solution. The ratio of the components entering the mills directly affects the composition of the charge and the quality of the final product. At the same time, the required quality of the charge is not always ensured, since the costs of the components are set by a person based on the results of a rare chemical analysis performed by the laboratory with a delay.
The aim of the work is to improve the control of the mill when receiving a mixture of nepheline ore. A virtual mill control program and a mnemonic diagram were developed in the TIA Portal software environment using the S7-1500 microprocessor controller. A system for automatic control of the lime and alkaline modules of the raw charge has been developed.
The control program is built on the basis of calculating the moisture content of the charge, as well as the alkaline and limestone modules, depending on the composition of the ore, limestone, as well as the feed rates of circulating water, ore and limestone to the mill. The mnemonic diagram includes an indication of important process parameters, trends in input and output characteristics, and tools for setting control actions.
542-550
Development of control principles for the desalination unit for closed life support systems for space purposes
Abstract
The development of the Solar system by humans implies the creation of long-term habitable bases on a number of cosmic bodies: the Moon, Mars, etc. Maintaining an environment favorable for the crew on such bases is possible thanks to life support systems (LSS), in which a closed mass transfer of products and waste between the crew, the unit of higher plants and other links is implemented. Closure increases the reliability and autonomy of the system, and reduces the cost of its supply.Controlling such mass transfer appears to be a difficult technical task requiring many man-hours, which is a valuable resource in the implementation of manned space missions. In the general case, this problem is solved by means of automation, however, it is necessary to take into account the specifics of the processes that support mass transfer, since this will allow finding ways to simplify the hardware and logical components, increase their versatility and reliability.
This article presents an analysis of the technological processes of the experimental unit for the separation of NaCl from solutions of mineralized human metabolites and proposes a simple control algorithm that can be used for all processes of the unit without fundamental changes. Without the development of a NaCl transformation cycle, it becomes almost impossible to create a long-term functioning biological and technical life support system – the optimal LSS option for alien bases.In such systems, mass transfer occurs between the crew and the link of higher plants and there is a danger of NaCl accumulation in irrigation solutions and subsequent poisoning of the plant link. Therefore, the problem of controlling the NaCl transformation cycle in mass transfer processes of a high degree of closure is relevant, and the universal principles of automated control can be used not only in space, but also in terrestrial applications: in closed agrotechnical cycles and scientific and educational stands.
551-560
Magnetic properties and electric polarization at heterogeneous substitution in bismuth pyrostannate Bi2 (Sn0,9Ме0,1)2O7, Ме = Cr3+, Fe3+
Abstract
Bismuth pyrostannate Bi2Sn2O7 is a diamagnet and belongs to the structural type of the A2B2O7 pyrochlore class. In this class of compounds, in the presence of magnetic ions, very interesting magnetic properties appear. Chromium- and iron-substituted bismuth pyrostannates Bi2(Sn0.9Me0.1)2O7, Me = Cr, and Fe were synthesized by solid-phase synthesis. X-ray diffraction analysis showed that the samples correspond to the Pc monoclinic cell of the Bi2Sn2O7 α-phase at room temperature. The magnetic properties up to 1100 K in magnetic fields up to 0.86 T and the electric polarization at frequencies of 10, 3, and 1 mHz in the temperature range 80–550 K have been studied. The effect of heterogeneous substitution by Cr3+ and Fe3+ ions on the magnetic properties and electric polarization of bismuth pyrostannate is investigated. An analysis of the experimental data revealed the dependence of the magnetic properties on the degree of filling of the electron shells of chromium and iron ions. The Bi2(Sn0.9Cr0.1)2O7 compound exhibits ferromagnetic properties, while Bi2(Sn0.9Fe0.1)2O7 exhibits antiferromagnetic properties. In chromium-substituted bismuth pyrostannate during the α→β transition, the paramagnetic Curie temperature increases by a factor of 3. The temperature dependence of the inverse magnetic susceptibility is characterized by hysteresis in the temperature range of 400–900 K. The reverse magnetic susceptibility of Bi2(Sn0.9Fe0.1)2O7 in the entire temperature range is satisfactorily described by the Curie-Weiss law. Studies of the magnetic properties have established that the Fe3+ ions are in a high-spin state. The polarization hysteresis in Bi2(Sn0.9Cr0.1)2O7 is found, which shifts along the polarization axis and depends on temperature. Bi2(Sn1-xFex)2O7, x=0.1 is characterized by a linear field dependence. With an increase in the concentration of iron ions, a hysteresis arises in the field dependence of the electric polarization. The hysteresis of polarization in Bi2(Sn0.9Cr0.1)2O7 which depends on temperature was found. The nonlinear field dependence of the polarization in Bi2(Sn0.8Fe0.2)2O7 can be explained by the interaction of the dipole and migration polarizations and the presence of oxygen vacancies. For the Bi2(Sn0.9Cr0.1)2O7 compound, a transition to the dipole glass state was found. In the β-phase of Bi2(Sn0.8Fe0.2)2O7 above T = 400 K, no polarization hysteresis is observed and the electron-relaxation polarization predominates. The mechanism of the occurrence of electronic polarization is explained with the appearance of anionic vacancies upon heterogeneous substitution of tin ions.
561-571