The aim of this work was to study the process of reactive ion-beam sputtering of gallium arsenide using optical emission analysis of plasma in the target region to determine the optimal conditions for the formation of intrinsic GaAs oxides. The ion source was a plasmatron based on an anode layer accelerator (UAS), which generated a stream of accelerated argon and oxygen ions with an energy of 400–1200 eV. The target was made from tellurium doped gallium arsenide. Intense GaI lines (2874.2 Å, 2943.6 Å, 4033.0 Å and 4172.1 Å), atomic argon ArI, argon ions, and also FeI lines were detected in the spectrum upon sputtering of GaAs by Ar+ ions. The appearance of iron lines can be explained by the sputtering of the pole tips of the magnetic system of the ion source. An increase in the accelerating voltage from 1 to 3 kV leads to an increase in the intensity of the peaks of atomic gallium GaI (4172.1 Å) by 2.38 times, the GaI line (4033.0 Å) by 3.25 times, the GaI line (2943.6 Å) 3.4 times, GaI lines (2874.2 Å) 5 times. It was found that an increase in the partial pressure of oxygen leads to a sharp decrease in the peaks of GaI (4033.0 Å) and GaI (4172.1 Å) due to the chemical interaction of gallium and oxygen. Sputtering in pure oxygen reduces the intensity of these peaks by 8 and 5 times, respectively. The intensities of the peaks of atomic gallium GaI (2874.2 Å) and GaI (2943.6 Å) decreased in 2 and 1.78 times, respectively. In the presence of a positive potential on the target, the intensity of all lines of atomic gallium monotonically decreases with increasing potential. In the emission spectrum, lines of atomic oxygen OI (7774.2 Å) and molecular positive ions O⁺₂ (6418.7 Å, 6026.4 Å, 5631.9 Å and 5295.7 Å) were detected. In the presence of a positive potential on the target, a monotonic decrease in the intensity of the above oxygen lines was observed. This indicates an intensification of chemical interaction of oxygen with target elements and, accordingly, a decrease in the free active oxygen particles.

In this paper, two different receiver structures to multiuser detection that are appropriate for the code-division multiple-access systems with antenna arrays in fading channels are investigated and compared. We analyze and compare the performance of the two different multiuser detection structures for uplink or downlink channels. The number of elements of receiving antenna array may be limited in the downlink channel due to the small size of receivers. We assume a synchronous system, but it can be easily extended to an asynchronous system. The first approach is based on the distributed decorrelator where the signal decorrelation is performed by each receiving antenna element independently and decorrelated outputs are combined according to the maximum ratio. The second approach is the central decorrelator where the signal decorrelation is performed once collectively on the outputs from all elements of receiving antenna array. Both decorrelators provide the same performance in the additive white Gaussian noise channels. The distributed decorrelator provides the better performance in flat fading channels. We employ the decorrelator to demonstrate our results. The results discussed in the present paper can be extended to other configurations such as the blind adaptive space-time multiuser detection.

The purpose of the work, the results of which are presented within the framework of the article, was to develop algorithms for calculating the damage to a solid or a system of solids based on the Monte Carlo method and the analytical boundary element method. The analytical boundary element method was used to calculate and analyze the stress-strain state of a solid under the distributed surface load. Based on indicators of the stress state, the algorithms for numerically assessing the dangerous volume and integral damage using the Monte Carlo methods, have been developed. Based on the pattern of distribution of stress fields, the technique of determining the area for randomly generating integration nodes is described. General recommendations have been developed for determining the boundaries of a subdomain containing a dangerous volume. Based on the features of the Monte Carlo methods, a numerical assessment of the indicators of damage of continuous media for a different number of integration nodes was carried out. Methods and algorithms were used to calculate the dangerous volume and integral damage in the plane and spatial cases for the two most common laws of the distribution of surface forces in the contact mechanics of solids: in case of contact interaction of two non-conformal bodies (Hertz problem) and when a non deformable rigid stamp is pressed into elastic half-plane or half-space. The scientific novelty of the work is to combine analytical and numerical approaches for the quantitative assessment of damage indicators of the power system. As a result the quantitative indicators of the dangerous volume (in the flat case - the dangerous area) and the integral damage of the half-plane and half-space related to the value of the applied load are obtained.

Changing the user interface always entails risks of decreasing application ergonomics and user churn. The purpose of this work is to find methods for changing the user interface without the need to use and increase the number of active users. Using Alpha/Beta testing and analysis of application metrics, it is possible to include design in each iteration and remotely manage the application configuration, which improves the user interface of the application. The way to integrate the UI modification and adaptation phase into an iterative software development model is proposed in this article. The successful user interface improvement experiments that have improved application metrics are described. In this work, the problem was highlighted, lack of information and control over user purchases, which negatively affected the number of purchases. A hypothesis is put forward that the user must have an effective visualization and control tool in the application. As a result of the experiment, the hypothesis was confirmed by an increase in the number of purchases and user activity. There was also a data security issue in the application, which put users at risk of data loss. An experiment was conducted to change the default value of user settings, which led to an increase of the positive metrics for using the data reservation functionality. The problem of polling users is also considered, which is an important component in the process of improving the ergonomics of an application. The method of remote user polling was used, which allowed to receive quick feedback from users and quickly respond to requests from users. The result of the work is the confirmation of the hypothesis of changes in the user interface in the cycles of the iterative development model, the positive dynamics of application metrics, as well as the satisfaction of users with the changes.

Application of the technology of consecutive construction of the functionally expanding model range of structural system prototypes is an advanced conceptual development direction of intellectual systems construction methods. The guiding principle of intellectual system construction under the suggested technology is that a highly sophisticated system is worked out and adjusted by stages with the use of the structural increment and functional complexity parallel-sequential scheme. At every construction step it is implemented in the form of a hardware and software complex – the structural prototype with a certain set of allocated components and performed functions. The structural prototype is understood as a certain version of its construction in the form of a logical or physical model, which includes a predetermined set of information, technical and software tools, performs system functions, makes it possible to evaluate the achieved parameter levels, as well as ensures further system build-up and development. Verbal-heuristic and graphic-heuristic models, which reflect the set of original requirements and the intelligent system structure, are used as mandatory prototypes of primary levels. The mandatory prototype of subsequent levels of the system technology includes a material model of the system nucleus, which combines hardware and software components, where joint functioning delivers the required set of integrative systematic properties. Sequential step-by-step choice of all the more complex prototypes with simultaneous enrichment of the composition of applied tools and performed system functions forms the expanded model range of the system. In the practice of systems development it is limited with a certain upper level prototype, which meets preset technical requirements to the system. Step-by- step development and adjustment of models, which are highly complicated prototypes, with the use of the parallel-sequential scheme of their structural enrichment and functional complication, is the effective technological trend of co-engineering.

The issues related to the features of operation and modes setting of a high-voltage switching power source based on a sequential autonomous resonant inverter with reverse diodes used to excite an atmospheric pressure barrier type discharge are discussed in the article. It is indicated that the characteristic features of the autonomous resonant inverters operation are the occurrence of damped voltage fluctuations in the LC circuit of the inverter, as well as the dependence of the output alternating voltage on the ratio of the inverter operating frequency (thyristor switching frequency) to the natural resonant frequency of the LC circuit. Depending on this ratio, the inverter can operate in discontinuous, boundary and continuous current mode. The amplitude and shape of the inverter output voltage were controlled using a 1:1000 voltage divider with a C1-65A oscilloscope. The shape of the gate trigger pulses was obtained using a C1-167 oscilloscope. It is established that when the gate trigger pulses are asymmetrical relative to each other due to the operation features of the step-up transformers, the value of the alternating high-voltage at the inverter output is insufficient to excite the atmospheric pressure barrier type discharge. In the case of the gate trigger pulses symmetry, the output voltage of the inverter stage reaches the values required for the breakdown of the dielectric medium. Oscillograms of the inverter output voltage while adjusting its operating frequency are obtained. It is shown that the amplitude value of the voltage at the gas-discharge load increases as the operating frequency of the inverter increases. For the gate trigger pulses frequency of 250 Hz the value of the inverter output voltage amplitude was 3.4 kV, for 460 Hz – 4.0 kV, and for 550 Hz – 4.2 kV.

А model of absorption of electromagnetic energy of radiofrequency range by biological tissues is described in the article. The problems of modeling the interaction of microwave radiation and biological tissues represented as multilayer structures are considered. Patch-antenna models for six sub-bands overlapping the 500–3500 MHz range are developed. The model of biological tissue was developed on the basis of MRI imaging, which allows for modeling under near real-life conditions. Based on the developed models of transceivers and biotissue, models have been created that allow to analyze the absorption of electromagnetic energy in the near- and far fields of the transmitter. From the results of modelling in the near field we can see that there are certain absorption maxima at frequencies of 750, 938, 1250 and 1357 MHz. Based on the results of the far field modeling it can be noted that in the range of 750 to 1000 MHz there is no absorption peak at 938 MHz. Also, as a result of the simulation, a decrease in the magnitude of absorption starting from 750 MHz was registered. Absorption peak absence is also observed in the area of 1357 MHz frequency. In the range of 2.5–3 GHz both in the near and far fields practically linear decrease of absorption value is observed. When analyzing the influence of structures' sizes on electromagnetic energy absorption in biological tissues, it was found that the nature of change in absorption value is a nonlinear value. In the range of 0.5–2 GHz both increase and decrease of absorption at thickening or thinning of layers is observed. It should also be noted that when the size of each layer increases by 10 %, the peak of absorption in the area of 1156 MHz frequency is observed. For the 2–3.5 GHz range there are no significant changes in the chart shape when the layer thickness changes.

The aim of this work is to select a synthesis method for a broadband matching circuit that provides maximum power transfer from a signal source to a load in the presence of a changing load impedance of a radio engineering device. To achieve this goal, an analysis of the main directions of designing broadband matching circuits (analytical, numerical, graphic-analytical synthesis methods) was carried out. Based on the results of a comparison of synthesis methods, their features (advantages and disadvantages) were indicated. The analysis of methods of synthesis of broadband matching circuits was carried out. For the analysis, the generalized Darlington method, the method of real frequencies, the structural-parametric synthesis method based on the T-matrix apparatus, and the graphic-analytical method based on the Volpert-Smith diagram were chosen). Using these synthesis methods, broadband matching circuits were obtained for various types of loads. Comparison of the results obtained was carried out according to several indicators: the level of the power transfer coefficient in the operating frequency range, the sensitivity of the power transfer coefficient to the change in the ratings of the elements of the matching circuit and the load impedance, provided that the number of elements of the matching circuit is no more than six. Based on the comparison and analysis, it was found that the most preferable synthesis method for solving the problem posed is the method of real frequencies. Its advantage is the use of a combination approach (iterative determination of the parameters of the resistance function with an analytical representation of the transfer function). Matching circuits obtained using this synthesis method provided the highest level of power transmission coefficient, as well as the lowest sensitivity value in a given frequency band for the considered types of loads.

The research results of multisensors based on optical fiber, the principle of which is to change the conditions of propagation of optical radiation in the optical fiber in the places where macro-bends are formed at the points of impact, are presented in the paper. The formation of macro-bends leads to an additional attenuation of the power of optical radiation propagating through the optical fiber. A single-mode optical fiber was used with the parameters, which are supported by numerous manufacturers and comply with the recommendations of ITU-T G.655. The measurements were carried out for four wavelengths of optical radiation (1310, 1490, 1550, 1625 nm), corresponding to the transparency windows of the optical loss spectrum of the optical fiber. Using optical reflectometry methods, it was determined that the amount of attenuation of optical radiation of each macro-bend formed at the point of action of the multisensor does not depend on the number of simultaneously formed macro-bends and also does not depend on the location of the point of action along the length of the multisensor. The dependences of the attenuation of the optical radiation power introduced by the macro-bends of the optical fiber on the radius, length, or angle of the macro-bends formed at the multisensory impact points are determined experimentally. The obtained dependences also allow one to determine the optimal parameters of the formed macro-bends of the multisensor to obtain the maximum range of attenuation change for each value of the wavelength. The values of the minimum distance between the impact points, the maximum number of impact points and the optimal values of the radius and angle of the optical fiber macro-bend at the impact points are determined. The results obtained provide opportunities to continue the development of multisensors that allow us to receive information about parameters from several impact points, that are located on a single optical fiber, simultaneously.

А combined method for forming a cryptographic key is proposed in the article. The proposed combined formation consists of two stages: the formation of partially coinciding binary sequences using synchronized artificial neural networks and the elimination of mismatched bits by open comparison of the parities of bit pairs. In this paper, possible vulnerabilities of the basic method of forming a cryptographic key using synchronized artificial neural networks are considered, their danger is assessed, and a correction of the method is proposed to ensure the required confidentiality of the generated shared secret. At the first stage, a deferred brute-force attack is considered. To neutralize this attack, it is proposed to use the convolution function of the results of several independent synchronizations. As a convolution function, the bitwise addition modulo 2 of the vectors of the weights of the networks is used. Due to the correction of the first stage of the basic algorithm, the amount of deferred search exponentially increases, and frequency analysis of binary sequences also becomes ineffective. At the second stage, an attack based on the knowledge of pair parities is considered, taking into account the proposed method for correcting the first stage. The analysis of the influence of network parameters on the process of eliminating the bit mismatch at the second stage is carried out. Statistical modeling of this analysis has been performed. The results obtained showed that the cryptanalyst could not uniquely distinguish the values of the remaining bits. The proposed combined method makes it possible to increase the confidentiality of the generated shared secret and significantly reduce the number of information exchanges in comparison with the Neural key generation technology.

When assembling electronic complexes for medical purposes, it is important to install highly reliable semiconductor devices in electronic equipment. Experimental studies and the example of high-power bipolar transistors in this work show how you can select copies of an increased level of reliability for their subsequent installation in critical electronic devices. To select highly reliable samples, individual forecasting was used according to informative parameters measured for a particular sample at the initial moment in time. Experimental studies (training experiment) included measuring at the initial moment of time for each sample of transistors of electrical parameters, which may contain information on reliability, and then conducting accelerated tests of transistors for reliability for a time corresponding to normal operating conditions specified in the technical documentation. The training experiment is performed once and used to obtain a predictive rule, which is applied to other similar samples that did not participate in the training experiment. To obtain a predictive rule, the method of majority logic was used. Prediction is performed in the form of assigning a specific sample to the class of highly reliable samples for a given future operating time. To perform prediction, the values of the informative parameters are measured at the initial moment of time for a particular sample of interest, they are converted into binary numbers (zero or one) using the threshold values found from the results of the training experiment, and the decision on the correspondence of the sample to the class of highly reliable transistors is made by a set of binary numbers. To classify a sample as a highly reliable one, it is sufficient that the number of ones exceeds the number of zeros in the resulting set of binary numbers.

Stricter requirements for the quality and reliability of manufactured products, as well as the need to increase the service life of machines, mechanisms and various devices, the operation of which is associated with the use of liquid or gas-air media, is the reason for the emergence of new and improvement of traditional methods for obtaining filter materials with higher performance characteristics. A method for a comprehensive analysis of the properties of regenerated filter materials for fine air purification is proposed. The overwhelming majority of filters, after their service life is exhausted, cannot be regenerated, since this, as a rule, is associated with high energy costs. At the same time, the development of methods for such regeneration is quite relevant from the point of view of resource conservation. In this regard, the purpose of this work is to use a number of physical research methods for the purpose of a comprehensive analysis of polymeric fibrous filter materials for air purification that have undergone regeneration. Filtration materials obtained by the «melt-blowing» method from polymer granules by processing the granulate in an extruder, aerodynamic spraying of the melt and the formation of a fibrous-porous layer on a forming mandrel were selected for research. The main filtration characteristics of the original and regenerated filter materials (breakthrough coefficient, aerodynamic drag),as well as the electrophysical properties of the primary and secondary filter materials, the presence of a spontaneous electret charge have been investigated. The main stages of regeneration and evaluation of physicochemical, mechanical and operational properties of fibrous-porous materials that have undergone secondary thermo-aerodynamic processing in comparison with the original ones are described. It is shown that the studied materials retain their basic properties, while the structure of the fibers changes and the electret effect is enhanced.