Summaries of the Issue
PHOTONICS AND OPTOINFORMATIСS
We address the problem of high-accuracy estimation of the Fried parameter r0 by comparing two approaches based on estimation of statistical properties of intensity-based wavefront measurements with parameter-fitting to the theoretically predicted values. In the first approach, the phase of the aberration-degraded field is restored from the measurements to obtain the statistical estimate for the structure function. Due to the iterative nature of the most phase retrieval methods, this approach requires significant computational time and thus cannot provide results in real time. In the second approach, the structure function of the sub-aperture wavefront slopes is directly calculated and related to the turbulence parameters in real time. We describe the equations used to obtain the estimate of the Fried parameter by both methods and check their accuracy with numerical simulations.
Subject of Research. We present the results of analytical research and experimental implementation of quantum key distribution protocol based on multi-mode weak coherent states with untrusted detection node. Such states are based on interference of phase-coded sidebands in case, where legitimate users are sending these states to the untrusted detection node that could be controlled by an eavesdropper. Method. The method of initial states generation is applied. Their propagation via fiber-optic lines and interference result is shown. A classical approximation is used for description. The experiment is carried out with the power measurement system connected on detection node side. We present the experimental scheme and show that in the classical regime the interference pattern is obtained at the fiber-optic 2x2 beam splitter with 50:50 ratio depending on the phase difference of the radiofrequency modulating signals (4.8 GHz) applied to LiNbO3 phase modulators, which modulate an optical carrier (1550 nm) in the blocks of legitimate users. Main Results. Experimental results are in accordance with analytical ones. Harmonical dependence of the optical power at the sidebands is obtained as an interference result. In this case, visibility of interference pattern is up to 97.4% and is good enough. Thus, application of these results in terms of quantum optics and experimentation in quantum single-photon regime might be a subject of future research. Practical Relevance. Practical application of research results lies in the development of quantum key distribution protocols and optical schemes with special attention to eavesdropping of quantum states and attacking the detection nodes. Application of the proposed multi-mode coherent states enables the legitimate users to extract information, while an eavesdropper does not obtain any information about encoded bits due to ambiguity of detection events.
Subject of Research. The paper presents the results of the laser diode module optical system alignment, which includes three steps: the laser diode radiation collimation, the laser beams multiplexing from three sources and the radiation input into the optical fiber. The laser diode module optical system with a fiber output is realized as a stepped configuration of sources position with a height shift of laser diodes relative to each other by 1.6 mm. Semiconductor laser diodes with Fabry-Perot resonator and peak generation wavelength of 1020 nm are used as radiation sources. The core diameter of the output multimode quartz optical fiber is equal to 400 μm and the numerical aperture is NA 0.22. Method. The method of spatial multiplexing for laser beams from three laser diodes in a continuous-wave mode was implemented. The residual divergence and deviations control of the optical axes in each channel were carried out by measuring the laser beam profiles in two sections with the beam profile meter displaced strictly along the laser beams propagation axis by 100 mm. The radiation input efficiency into the optical fiber was determined by measuring the radiation power before entering the laser beam and at the output from the optical fiber. Main Results. The maximum output power of the laser diode module prototype is 19.65 W. The loss reduction is achieved owing to the application of anti-reflective coatings on the lenses and a highly reflective coating on the mirrors, taking into account the spectral composition of the radiation and the angle of incidence of the laser beams. Practical Relevance. The implemented assembly method can be used to manufacture higher output power laser diode modules, including more than three laser diodes without reduction in effectiveness. The developed micro-optical component positioning test bench allows for high-precision alignment of lenses and mirrors, and optical fiber coupling of optoelectronic devices.
The effect of additives in sodium germanate glass on the up-conversion luminescence of an erbium ion was studied. Samples of glasses were prepared by high-temperature synthesis in corundum crucible. Synthesis temperature was 1250 °С. Synthesized glass had a composition of 58,95GeO2–27,79Na2O–8,67Yb2O3–4,34LaO–0,25Er2O3 mol% with additives of 5 mol% of the following oxides: Al2O3, Nb2O5, SiO2, BaO, TiO2, PbO, P2O5, MgO. Up-conversion luminescence spectra were recorded in the wavelength range from 450 to 700 nm when excited by a semiconductor laser at 975 nm. Three bands were identified on the luminescence spectra corresponding to radiative transitions of the erbium ion 2H11/2→4I15/2 with maximum of about 520 nm; 4S3/2→4I15/2 with maximum of 550 nm and 4F9/2→4I15/2 with maximum of 670 nm. The luminescent properties of the glass with additives were compared to those of the initial glass. The effect of additives on the relative intensity redistribution of upconversion luminescence was shown. Compared to the red luminescence band (4F9/2→4I15/2), the green band (2H11/2→4I15/2) intensity is a maximum for glass with the addition of phosphorus oxide; glass with the addition of lead oxide has the minimum intensity. The obtained dependence of the relative intensities of the up-conversion luminescence bands on the glass composition can find practical application in the development of optical luminescent sensors, as well as up-converters for solar cells.
Subject of Research. The paper presents results of the experimental study on the dependence of the noise floor level of a fiber-optic interferometric sensor array on the gain factor of operational amplifiers located on the signal processing board and connected in series into a single cascade. Method. The fiber-optic interferometric sensor array is based on Michelson interferometers, arrayed with time division multiplexing. Operational amplifier cascade consists of a variable operational amplifier and a current feedback operational amplifier (transimpedance amplifier), which converts the photocurrent from the photodiode to voltage. A signal from the photodetector is transmitted to transimpedance amplifier, which has two operating modes with gain factors equal to 0 and 6 dB, and then to programmed operational amplifier, which additionally amplifies the incoming electric signal in the range from 0 to 40 dB. Further, enhanced signals from the amplifier cascade are fed to analog-todigital converter and then they are demodulated. During the experiment the fiber-optic sensor array under research was closed off from external vibroacoustic impacts on the sensor. Noise signals from four sensors were recorded after demodulation into data files at the various values of gain factors of operational amplifiers. Spectral estimations of noise floor levels of the fiberoptic interferometric sensors were performed by the averaged modified periodogram method depending on the gain factors of operational amplifiers. Main Results. The following minimal average noise floor levels were obtained: 65 urad/Hz0.5 at 1000 Hz with the gain factor of the current feedback operational amplifier equal to 6 dB and the gain factor of the variable operational amplifier equal to 12 dB, and 80 urad/Hz0.5 at 1000 Hz with the gain factor of the current feedback operational amplifier equal to 0 dB and the gain factor of the variable operational amplifier equal to 20 dB. Practical Relevance. The study has shown that optimal operating conditions are achieved with the gain factor of the current feedback operational amplifier equal to 6 dB and in the range of the gain factor of the variable operational amplifier from 5 dB to 20 dB, which provided the minimal average noise floor level of the fiber-optic interferometric sensors at the level of 65–70 urad/Hz0.5. The proposed method of applying operational amplifiers is usable for the amplification of optical signals from the fiber-optic multiplexed sensor array without significant deterioration of their noise performance in case of the optimal operating domain selection.
Subject of Research. The paper presents effective application of the novel imaging photoplethysmography method for receiving data on reaction of peripheral blood flow in lower extremities on venous occlusion. Method. Four digital cameras were used to record synchronously videos of all-around view of the subject’s lower limb illuminated by green light (525 nm). For blood flow reactivity assessment, four consecutive venous occlusions were applied for 10 s by rapid increase of the pressure up to 60 mm Hg in an occlusal cuff situated at the lower third of the thigh followed by 20-second recovery period. Two techniques were used and compared for processing of experimental data: by averaging of camera matrix pixel values in arbitrary chosen regions of interest and by component analysis of camera video signals. It was found out that the technique of the pixel value averaging provides a more reliable quantitative assessment of peripheral blood flow parameters in lower extremities. The data processing algorithm was optimized. Main Results. The study involved 16 healthy volunteers. Data analysis has shown that dynamics of changes in the intensity of light interacting with the lower leg during occlusion was successfully obtained in all subjects. The shape of the optically measured response on venous occlusion was found out to be the same as the curves of classical air plethysmography applied to evaluation of musculocutaneous blood flow in the forearm. Practical Relevance. Taking into account the simplicity and contactless nature of the study, the imaging photoplethysmography method can be widely introduced into clinical practice for research of the functional state of the lower extremity vessels in a wide range of diseases.
Subject of Research. The paper presents research of image restoration quality decrease for the super-resolution structured illumination microscopy in case of defocus and aberrations affecting resulting image. Method. In order to improve restoration image quality, we propose image preprocessing procedure for compensation of defocus and aberrations along with point spread function reconstruction, based on Fourier optics theory and preliminary system calibration. We also propose a technique for automatic point spread function model adaptation to a defocus value by means of acquired images analysis, taking into account input data redundancy of structured illumination microscopy. Main Results. The proposed technique provides opportunity to reduce reconstructed image artifacts for systems with aberrations and unknown defocus to the same level as can be achieved with the diffraction-limited optics. Obtained simulation results demonstrate three-four-fold artifact amplitude decrease for reconstructed images for systems with aberrations, that can be expected for commercially-available objectives. Practical Relevance. Research results are applicable for image restoration quality improvement in super-resolution structured illumination microscopes, and also decrease the cost of new systems by means of non-specific optics without sacrificing high quality of resulting image.
Subject of Research. The digitizing possibility for pictorial holograms is considered aimed at their storage and processing with the use of digital technologies. A novel method is proposed for application of photogrammetric technology with the view to create digital images from holograms. The prospects of obtaining a digital copy are discussed by applying a series of photographs and processing software package. Method. The ceramic sculpture with 89 mm height was chosen as an object for the experiment. Two pictorial sculpture holograms were recorded from the back and front sides by He-Ne laser at the wavelength λ = 633 nm with the power P = 50 mW for 90 seconds. A photograph of the object was taken as it rotates around its axis with a step of 1.8°. The Canon EOS 1100D camera with a resolution of 12.2 million pixels was selected for photography. A series of 300 photos was performed. For recovery of images registered on volume monochrome holograms, a point source of white scattered light was used inclined at an angle of 45° to the normal of the plate. Ninety photos of each hologram were obtained with an angle area coverage of 120°. The sculpture and holograms were photographed around the object at the angles equal to 0 and 45°. Agisoft PhotoScan (version 1.4.5) software was used as a processing software package for a series of photographs. The volume of the processed files was about 4.5 GB. Main Results. The results of a 3D model restoration from two holograms of the same object are presented. Comparative analysis of the obtained 3D-models of the image is carried out. It is shown that the hologram volume model created by photogrammetric method has a visual difference from the model of the object itself. The 3D model quality improvement depends on increasing the number of recorded phase holograms of the same object from different angles. Practical Relevance. The proposed digitizing method for the holograms through the use of photogrammetry technology can find practical application for solving problems in the field of long-term storage of information about cultural heritage sites.
The optimization of lithographic objectives is a quite challenging task due to many conflicting constraints, limitations and numerous variables. We describe the optimization techniques of starting designs for ultraviolet objectives which were previously generated by the global search algorithm. The powerful tools for the global optimization as Automatic Element Insert feature and Saddle points construction were applied to starting points, examining the applicability limited by design considerations. The ray tracing failures and critical lenses in starting designs caused by automatic decisions of the global search algorithm are fixed and replaced by Saddle point construction. The results of this work and presented techniques of the global optimization are valid and relevant for any on-axis complex optical system.
Subject of Research. The paper considers the alternate design of nondestructive jamming in the visible light range. Two different approaches utilizing coherent and incoherent light emitters are approved to suppress visual-optical and electro-optical channels of equipment surveillance. Method. The design relations are examined and graphically illustrated. The numerical calculation of irradiance from energetically equivalent coherent and incoherent narrow beam emitters is performed in the range of exposure distances equal to 100–2000 m while changing radiated power and beam width. Main Results. The quantitative parameters are obtained for irradiance generation above the criterion levels of function destruction, suppression, and negation of applying optical devices. We analyze the usage of optical means for emitters with commercially available compact diode-pumped solid-state visible beam lasers and for emitters utilizing high intensity miniature cermet case short-arc xenon lamps with fixed integrated reflector enhanced with secondary forming optical system. The correlation between the criterion levels and the range of exposure distances is identified. The variation limits of the radiated power and the beam width are established at close distances to satisfy the condition of nondestructive effects. Practical Relevance. Comparative study results and the design relations might be useful for development of nondestructive visual-optical jammers utilizing coherent and incoherent emitters and for determination of function degradation criterion levels for multi-level exposure.
AUTOMATIC CONTROL AND ROBOTICS
Subject of Research. The paper presents a method of dynamical control design for a robot with a parallel kinematic scheme. The stabilization problem of 2-Degree-of-Freedom Ball and Plate system is solved. It is assumed that the rotation angles of the platform are limited. Method. The proposed method is based on transforming the considered nonlinear system to the form of a homogeneous differential inclusion. Since the considered control object is described by a continuous and nonhomogeneous system of ordinary differential equations, the proposed method is based on the use of a homogeneous extension. The differential inclusion obtained by the homogeneous extension method is homogeneous with a negative degree, that provides the finite-time stability of the closed-loop system. Main Results. The dynamical feedback is robust and allows compensating non-Lipschitz disturbances of a certain class. Simulation results demonstrate the efficiency of the proposed approach. Despite the fact that the considered system and the obtained control law are nonlinear, the proposed dynamical feedback has a simple tuning procedure based on the solution of linear matrix inequalities. Practical Relevance. The proposed method is designed for robots with parallel kinematic scheme widely used, for example, in machine tools, flight simulators. The developed algorithm provides robust properties that are necessary in practice.
MATERIAL SCIENCE AND NANOTECHNOLOGIES
Subject of Research. The paper presents the results of an experimental study on morphology and optical properties of AlN films on sapphire. Thin AlN films on sapphire were used as experimental samples. Method. To obtain thin films, an ion beam deposition setup was used, which includes the ion source of the CLAN-53M type with an ion neutralizer. The ion beam energy ranged from 600 to 900 eV. The ion beam current was 60 mA, and it was chosen based on the steady-state plasma burning in the ion source. Deposition was carried out at the residual pressure of gases in the vacuum chamber of at least 1.5×10–3 Pa; the substrates were heated using a group of halogen lamps with the total power of 2500 W; the substrate temperature was 550–850 °C. The precipitation time was one hour. The composition of the nitrogen-argon mixture was changed by increasing the volume fraction of nitrogen from 10 to 90 %. Main Results. The obtained thin films were studied by scanning electron microscopy and energy dispersive analysis. Studies have shown that thin nitrogen AlN films on sapphire obtained with a volume fraction of nitrogen in a nitrogen-argon mixture of more than 50 % have a composition close to stoichiometric one. For AlN films on sapphire, obtained with a volume fraction of nitrogen in a nitrogen-argon mixture of more than 90 %, substrate temperature of 800 °C and the beam energy of 600 eV, the transmittance in the entire optical wavelength range is at least 92 %. The direct dependence of the beam energy on the volume fraction of nitrogen in the nitrogen-argon mixture is determined: at 900 eV, as compared to 600 eV, the nitrogen content in the AlN film rises from 10 % to 30–35 %. When the beam energy is 600 eV, there is an insignificant dependence on the substrate temperature and only the direct dependence on the amount of nitrogen in the nitrogen-argon mixture remains. With partial ionization of the ion beam, the difference between the nitrogen content in the AlN film at different beam energies is in the range of 5–10 %. The increased nitrogen content in the films (more than 20 %) adversely affects the optical perfection of the films. With the partial ionization mode only at 900 eV, the temperature of 800 °C, and with the volume fraction of nitrogen in the nitrogen-argon mixture more than 50 %, the decrease in the quality of the films is observed. Under modes with a volume fraction of nitrogen in a nitrogen-argon mixture of less than 30 %, a large number of microdroplets are observed on the surface with sizes in the range of 1–6 μm. The composition of the gas mixture with the content of the volume fraction of nitrogen in the nitrogen-argon mixture of 10 % increases the concentration of microdroplets on the film surface with the increase in the proportion of large microdroplets. The most optimal mode was revealed with the beam partial ionization, the energy of 600 eV, and the volume fraction of nitrogen in the nitrogen-argon mixture more than 50%. The change in the substrate temperature has practically no effect on the nitrogen fraction in a thin film of aluminum nitride. Practical Relevance. A thin AlN film on sapphire deposited at the substrate temperature of 800 °C and volume fraction of nitrogen in the nitrogen-argon mixture equal to 90 % has a transmittance more than 92 % in the optical range of 200–1100 nm, that characterizes the obtained thin film sample as optically transparent.
Subject of Research. The performed study is devoted to improvement of the text clustering quality indicators. The main attention is paid to the feature extraction that describes the mathematical model of the texts. The k-means method is used for clustering of the resulting vector representation of the texts. Method. An analytical approach was proposed based on the use of semanticosyntactic features of the clustered texts. Feature extraction was performed using the Stanford CoreNLP Toolkit. Some links between the words of the texts in “Enhanced ++ Dependencies” representation were encoded together with the words connecting them. The values of semantico-syntactic features were calculated based on the frequencies of encoded links in the texts. Main Results. An experiment has shown that by comparison of the quality indicators of a prototype developed on the basis of the proposed method and a clustering system based on statistical features, the proposed method application provides for decrease in the number of clustering errors by more than 15 %. Practical Relevance. Pre-training is not required to obtain semanticosyntactic features of the texts. Therefore, the proposed approach can be used to improve clustering quality indicators in the absence of large text corpuses, which are necessary for pre-training of statistical language models based on word embeddings.
Subject of Research. The paper presents the study of computer systems in providing exchanges through redundant channels in order to analyze the possibilities of reliability increase and timeliness of computer systems interaction as a result of redundant transfers through aggregated channels, taking into account the implementation options in computer nodes of distributed separate queues for access to each channel, or general queue for access to all channels. Method. The method is based on the development of simulation models of the considered options for redundant exchange through aggregated channels. Main Results. The redundant exchange efficiency is shown taking into account the organization of distributed queues in the nodes for access to aggregated channels. For the first option of redundant exchange, separate queues are organized at each computer node for access to each channel. The incoming request is copied k times (depending on the criticality to the timeout), and each copy is placed in one of the queues. For the second option, one common queue is organized for all channels in each computer node, and each incoming packet is entered in this queue (a request for its transmission). When a request is issued from the general queue, k copies of the transmitted packet are generated, and each copy is transmitted through one of the n channels as far as the node is granted access rights to it. A specific feature of the reserved service is the formation of k copies for each request, issued for service in different channels. A service is considered to be successfully completed if at least one of the k created copies of the request (package) is correctly executed in the specified time. The existence of the optimal reservation multiplicity of transmitted copies of packets is shown; the efficiency area of the reserved machine-to-machine exchange is determined. Practical Relevance. The results can be used in the design of highly reliable computer systems, including real-time ones.
Subject of Research. We propose an approach to the research of the frequency properties of the sea surface images sequence (video frames) on the basis of sub-band analysis within the cosine transform. The study of frequency properties makes it possible to solve the problem of object detection on the agitated sea surface. Method. The main theoretical propositions of the sub-band analysis within the cosine transform are given. The paper presents the method of formation of the cosine transform sub-band matrices used in data analysis and method of calculation of the analyzed vector energy parts in different frequency intervals. The sub-band approach to the analysis of the image component energy distribution in the frequency domain is described. Realization of separate components of the sea surface image sequence (video frames) in the vector form is shown. The vectors contain the pixel values with the same coordinates in the image set and give the possibility to calculate the energy parts in specified frequency intervals. Main Results. Video of the sea surface with various agitation levels were used in computing experiments. The distribution analysis of the energy part values of the matching components in the used video records showed that different sea surface agitation corresponds to different distributions of the matching component energy in the frequency domain. It has been found that at low agitation, the energy of the image components is concentrated in the low-frequency region and with the increase of the sea surface agitation, the energy part values of the corresponding image components increase in the high-frequency region. Practical Relevance. The obtained distribution features of the sea surface image component energy parts can be used when solving the detection problems for objects, floating on the sea surface, based on the analysis of their frequency characteristics.
Subject of Research. The paper presents research of software development tools. The study analyzes existing integrated software development environments with structured editing support. We consider the design process and experimental testing of the modified integrated development environment architecture. Method. Analysis of the existing integrated software development environments with structured editing support was performed and their shortcomings were identified. A development environment architecture was proposed. It provides the development of system prototype for such problems as circular translation from textual representation of source code to intermediate one and vice versa, the lack of functionality (compared to classical development environments), design complexity of new development environments with structured editing support. Main Results. In this architecture design we have proposed to abandon the textual representation of the source code at all stages of software development. As a result, the circular translation has been eliminated, the number of system components has been reduced, and development environment performance has been increased. The created prototype of development environment with support for structured editing has tested experimentally the effectiveness of the proposed architecture modification. Experiments have been carried out including comparison of compilation speed of software projects and the speed of automatic source code refactoring.Practical Relevance. The proposed solution can be used by organizations engaged in the industrial software development and by creators of new software development environments.
A cloud system for geographically distributed data centers is presented. An approach is based on the principle of multi-agent structure (microservices). A special interaction protocol was developed for agents’ communication operating in asynchronous mode. The asynchronous behavior of the agent interaction system is achieved through the use of a specially developed algorithm. The program that implements the proposed algorithm is written in the Python programming language. This solution uses relational databases and queuing systems. A relational database stores requests and responses from the agents. A message broker is necessary for exchanging YAML messages with identifiers of these requests and responses. The developed software was tested a prototype of a scalable geographically distributed data center. An original technical solution was obtained that successfully passed a series of tests and was implemented within existing cloud infrastructure. Features of applying the RabbitMQ queuing system and PostgreSQL database management system in cluster mode with traffic encryption are indicated. The use of the developed model appears to be promising oriented for highly loaded distributed systems.
MODELING AND SIMULATION
Subject of Research. The paper proposes a novel organization technique for preventive maintenance systems (including condition-based and predictive maintenance systems) based on the use of modern machine learning methods. The systems are operating using an original, non-parametric identification method for the current degradation phase of serviced equipment. Method. The proposed method comprises reducing the task of the current phase identification of the equipment degradation phase to interval estimation of the value of the so-called “health index” parameter of the equipment. This parameter is represented as a step function with the arguments in terms of a set of the measurable equipment objective parameters. The current equipment degradation phase is determined by classification approach. At this, based on the analysis of the observed data, it is decided upon what class (state phase) these data correspond to. Measurements from a group of sensors, in general, of various physical nature, which are located both on the surface and inside the equipment being monitored are used as data for identification of the equipment degradation stage. Mathematically, the proposed approach is reduced to a weighted combination of two classifiers. One of the classifiers of this combination is based on solving a group of binary classification problems. The second classifier is based on “Remaining Useful Life” parameter estimation by the method of nonparametric regression. Main Results. As distinguished from traditional approaches, the proposed approach uses a minimum of a priori information about the principles of operation and the internal structure of the equipment being serviced. The approach is based on the usage of the “health index” equipment parameter presented in the form of a step function. The novelty of the approach lies in the simultaneous use of the “health index” step function and the weighted combination of two classifiers with various structure. The proposed method showed good results when being tested on the C-MAPPS Dataset database, which contains data on failures of turbofan engines modeled using a thermodynamic simulation model. The pre-failure status of the equipment is identified with the probability of 99%. Practical Relevance. The obtained results and algorithms can be used in preventive maintenance systems aimed at reliable identification of the equipment degradation current stage.
Subject of Research. The paper analyzes design methods of locomotion robots on the example of high-speed, energy-efficient cheetah robot creation which is able to move over rough terrain. The paper describes a femur mechanism energy analysis of the cheetah robot leg. The operation principle is based on flexible element resonance caused by self-oscillations of the robot inertial mass. The developed design is considered as a spring-loaded inverted pendulum with the flexible element necessary to ensure the harmonic behavior of the robot body, stable interaction with the ground, absorption of impact force and recuperation of the locomotion energy. Method. We proposed the application of biomimetic methods in the design of bio-inspired robotic devices. Their essence lies in reproducing the unique qualities and characteristics of living systems, rather than only an imitation of physical configuration. The design presented in the paper imitates the dynamics of a jumping animal due to the movement harmonic nature caused by a periodic inertia force of the robot body mass. The harmonic force, which causes self-oscillations, is derived by the Lagrange dynamic equation. A generalized description of the robot dynamics is represented in the Poisson structure used in the system concept by means of the Port-Hamilton approach Main Results. As a result of the simulation, we have obtained energy and power exchange graphs for a spring pendulum with and without external harmonic force. The same graphs with and without internal inertial force for jumping in place are given for a femur mechanism, called “minitaur”. The diagrams of dependencies between the cost of transport coefficients and the configuration of the mechanism and the spring stiffness for a running behavior are presented. Practical Relevance. The given analysis is required for determination of the amount of energy in the system, the ways of energy budget conservation, the reasons for its consumption and how it can be replenished. In the following publications, a similar analysis will be presented for the entire leg of the cheetah-robot, imitating the tibia and metatarsus bones.
Subject of Research. We study the procedure of natural frequencies calculation for a system consisting of a human spine with fixing elements. Resonant effects can occur in the vicinity of such system leading to stability violation or structure destruction. Method. A mathematical model of the conditional vertebral column is proposed, consisting of two anatomically-physiologically isolated columns: the spinal cord (dorsal longitudinal column) and its musculoskeletal “case” (ventral longitudinal column). The model includes complementary boundary condition — an additional fixing element. To solve this problem, the vertebral complex is modeled using a geometric graph. A fourth-order differential operator on the edges of a geometric graph is considered. The graph is a model of a biomechanical system — the spine and metal structure. It is assumed that there are point potentials at the vertices of the graph that model the bond character between the graph elements. A system of differential equations with boundary conditions (conditions for matching solutions on adjacent edges) is solved to find the spectrum of the operator dangerous for the integrity of the mechanical frequency system. Main Results. A technique is proposed for detection of biomechanical system eigenfrequencies that lead to resonant effects. A correct model of a metric graph is created with a fourth-order operator on the edges and the conditions of point interaction at the vertices. Frequency values are obtained for specific values of the system parameters. Practical Relevance. The described method for detection of hazardous frequencies can be used in the treatment of patients with scoliosis to prevent breakage of the installed metal structure and save the patient’s life.
Subject of study. The paper presents the results of the experimental study of a wavelet-based pre-processing that was used to increase the amount of statistically-discoverable information leakage in a side-channel signal. The studied signal was acquired via an electromagnetic channel of the ARM-Cortex M4F processor. The signal was recorded at the distance of 1 mm and 3 cm. During signal collection, the Advanced Encryption Standard (AES) algorithm was executed on the board. Method. After the acquisition, electromagnetic signal is processed using a discrete wavelet transform with shrinkage of the detail coefficients. The influence of various shrinkage thresholds, mother wavelet, and wavelet decomposition level is studied. After processing of the signal records, the leakage analysis is performed using the Test Vector Leakage Assessment (TVLA), a method based on the Welch statistical test. The obtained estimates are used to compare wavelet transform pre-processing with the leakage estimate of the original signal. Main Results. The signal processed by a wavelet transform shows higher values of the statistical test, that means more confidence in the presence of an information leakage. The universal threshold and zeroing detail coefficients increase the value of the t-criterion by 1.4 times. The third level of decomposition shows the highest result for all wavelet functions. The discrete wavelet of Meyer shows the best result in all experiments. Symlets and Coiflets also show stable results in the experiments. Practical Relevance. Statistical methods, such as the Welch statistical test, can detect leakage without costly and time-consuming stages such as research and attacks. The wavelet transform and processing of the received signal increases the informational components of the signal providing close-to-real statistical signal profiles. Pre-processing based on wavelet transform also allows for leakage detection on fewer signal records.
Subject of Research. The paper presents an advanced model and experimental study results considering an unorganized group behavior in case of emergency. An approach to simulation of human behavior is based on the Dirk Helbing and Peter Molnar model of social forces (Social force model). Such model takes into account the informational impact on the individual behavior of group agents. The developed model is adapted for crowd behavior description in emergency situations. Method. The essence of the proposed model of behavior lies in the idea that at every instant the agent solves the problem of finding the optimal transition direction from a current location to some safer place. The implementation of AnyLogic simulation tool is proposed as a software platform for the simulator with the built-in Pedestrian library, which gives the possibility to build models with a large amount of information about pedestrian movements (traffic). The tool used has a graphical interface, provides a description of the interaction between agents within the group and the possibility for the Java programming language application. Main Results. The proposed model is implemented in the form of a simulator using open information about the fire in the Lame Horse Club (December 5, 2009) in the city of Perm. Comparison of information about a real fire with the simulation results by the proposed method is performed, as well as according to the existing method of group behavior in a multi-level branched room, and by the method of moving agents along the shortest path. It is shown that the results obtained by the proposed model most closely match the real results. Practical Relevance. The presented model of an unorganized group behavior makes it possible
Subject of Research. Efficiency study of cameral signal recovery algorithms is carried out in the presence of single long gaps and rare arrival of measurements. Quantitative comparison of the algorithms is performed by modeling and cameral processing of satellite navigation receiver real solutions. The standard error is an algorithm measure of efficiency. Method. The algorithm is considered based on a quadratic model taking into account constraints on the signal size and its derivative. The algorithm is known from the literature, however, it is used for the first time in satellite navigation problems. Moreover, comparison is made with the other two algorithms: quadratic approximation without regard to constraints and linear interpolation. Main Results. After analyzing the results, the following recommendations have been developed on the use of recovery algorithms in order to achieve the minimum mean square error of recovery. It is established that the quadratic approximation with constraints is the best of the considered algorithms in terms of accuracy; however, when recovering the signal during the long-term measurement absence at the beginning and at the end of the gap, it is better to use linear interpolation. In order to achieve the minimum standard error in the central part of the gap, it is recommended to use the algorithm with constraints and break down a fragment of the processed measurement implementation so that no more than one polynomial interval junction of the restored signal is located on the measurement absence section. For short measurement intervals to the left and to the right of the gap, the best option is to split the implementation fragment into 2 intervals. In case of the signal restoration under conditions of rarely received measurements, it is advisable to choose the interval duration of the polynomial representation less than the period of measurement discreteness. Practical Relevance. The application of the developed algorithms can improve the positioning accuracy for the users of global-positioning satellite systems, however, their application area may be more extensive and include post-processing of field measurements in geodesy and mapping tasks.
Subject of Research. The paper studies one of the possible design and research approaches relating to wireless networks in the OMNeT ++ simulation environment by applying the INET framework. We show the modeling process of both the models themselves and their various operation modes. The model analysis methodology is considered on the example of a time diagram.
Method. When considering the approach, the method of serial complication of the modelled wireless networks is used with reference to their operation features. The simplicity of the approach implementation is shown, as it uses ready-made components from the INET framework for models of wireless networks. The process of the time diagram research and the explanation of the simulation model behavior are demonstrated on the problem situation example. Main Results. We present the design method for wireless networks with the use of ready-made components from the INET framework. The redefining possibility of the composite module embedded components is demonstrated to create a model of the device that meets the necessary requirements. Possible operation modes of wireless networks are considered, both at the direct and indirect interaction of nodes through intermediate ones. The modeling approach for physical level and phenomena of interference is demonstrated. The approach for the problem situation research is considered involving the time diagram analysis. Practical Relevance. The proposed simulation environment allows for the study of design decisions in the design of the wireless networks. The applicability of the developed projects in real life is proved.
INFORMATION TECHNOLOGIES IN EDUCATION
Subject of Research. The paper considers the process of generating reports in electronic learning systems. The aim is to optimize learning process management in generating reports using blockchain technologies. The paper analyzes existing learning management systems and their tools for generating and analyzing reports. Blockchain technology is reviewed in terms of educational opportunities. Method. The process of generating reports in the learning management system is presented as a mathematical model. It has been proven that the use of blockchain technology simplifies this process, since blockchain tools automatically register network events. A model for generating reports in the learning system using blockchain transactions has been developed. The model is implemented in a test version of the Ethereum blockchain using the smart contract mechanism. A smart contract records heterogeneous data of learning events to the blockchain without using special data structures. The blockchain stores data in a unified registry and registers event timestamp and event author’s address by itself. Event data is available through the geth console oriented for the Ethereum blockchain. Main Results. A method of learning process documenting using blockchain technology has been developed. The method does not require any special data model for storing learning events data, as well as special mechanism for recording event timestamp and event author’s address. Practical Relevance. Research results show that blockchain application provides for optimization of the learning process management.
Subject of Research. The paper analyzes design and development issues of web portals for cloud services of data centres. We consider a web portal for administrators and users and a portal for service configuration. The portals are applied for access to cloud services according to differentiation of user access rights. Method. The design of referred portals was presented based on international practice of cloud service providers. Implementation of the portal for administrators based on Openstack Horizon and our own solution of the portal for service configuration were proposed. Main Results. The functionality of the portals has been tested effectively with Openstack virtualization platform on the prototype of a geographically distributed data centre deployed by SMARTS telecom provider (the city of Samara). Practical Relevance. The proposed approach can be used for similar portal development in the other cloud service projects.