The presented work reflects and analyzes the results of numerical simulation of the electric field strength dependence on the dimensionality and geometry of gold nanostructures as well as their orientation relative to the polarization of the incident radiation. The simulation of the electric field strength near a single nanostructure was performed using the Finite-Difference Time-Domain (FDTD) method. FDTD modeling is an effective theoretical way to study the interaction between electromagnetic waves and plasmonic nanoobjects represented by single gold nanorods with different geometry (cylinder, spherical cylinder, elongated ellipsoid) and variable half-length (L =10–120 nm). The radiation source was a plane-polarized wave (λ = 632 nm). As a result of the simulation, the localization of the electric field near the nanostructures has been determined and the maximum theoretical values of the near-field strength have been obtained. The dependence of the electric field strength maxima has been demonstrated to be nonlinear on the half-length of gold nanostructures in case of their longitudinal orientation to E-vector. The obtained theoretical calculations of the electric field strength near the plasmonic nanoparticles, including gold nanorods, allow us to determine the optimal nanoparticle parameters and excitation conditions for the plasmon resonance occurrence which in turn provides an opportunity to create SERS-structures with a high Raman scattering enhancement.

The article discusses the experimental and theoretical results of studying the optical properties for planar quartz surfaces modified with gold nanostars using Surface-Enhanced Raman Spectroscopy (SERS). Surfaces functionalized with nanoparticles, prototypes of optical sensors, have been obtained. It is shown that the obtained experimental Raman signal enhancement from the dye rhodamine 6G (R6G) can be at least order 104. The paper presents the results of calculation, synthesis and study of the optical and morphological properties of such structures. A complex method for creating and evaluating the optical properties of planar nanostructures and evaluating their optical properties is proposed. The method includes the approaches based on mathematical modeling using finite differences in the time domain (FDTD - Finite-Difference Time-Domain) evaluating electromagnetic field strengths near the surfaces of star-shaped gold nanoparticles in colloidal solutions and on a silicon surface. During the simulation, we studied such parameters as the particle size, the wavelength of the exciting radiation, and the dependence of the effective amplification of the electromagnetic field on the morphological parameters of the star. The theoretical approach to the calculation of such structures is shown to be promising for the subsequent chemical synthesis described in the article and the study of optical properties. In this paper, a theoretical calculation of the parameters of the electric field and optical properties is carried out near star-shaped nanoparticles of varying sizes. These parameters were calculated by the finite difference method in the time domain. The task included finding the optimal sizes of nanoparticles as well as varying the thickness of the surface layers in order to obtain the maximum scattering values and further use of similar structures in SERS experiments. Also, within the framework of this work, syntheses of star-shaped nanoparticles was carried out, their optical and morphological properties were studied, quartz surfaces were functionalized with nanoparticles, and sensor prototypes were created in order to further assess the Raman signal amplification. Based on the results of mathematical modeling, the optimal sizes for the synthesis of star-shaped NPs were determined. Synthesis of NPs was carried out by a chemical method using seeds. To carry out the experimental part, SERS spectra were obtained using Centaur U spectrometer (OOO NanoScanTechnology, Russia). The spectrometer was equipped with three different laser sources: 632.8 nm He-Ne laser (17 mW), 532 nm and 473 nm DPSS lasers (45 mW). During the experiment, a He-Ne laser with λ = 632 nm and DPSS laser with λ = 532 nm were used to match the excitation of the plasmon maximum for the nanostars. The optical scheme of the spectrometer included an Olympus BX41 microscope (Olympus, Japan) with a 100× objective (NA 0.9) for positioning the beam and collecting scattered photons. The monochromator of the spectrometer had a focal length of 800 mm. A holographic diffraction grating of 300 gr/mm, and was equipped with a 1024×256 pixel thermoelectric cooled CCD detector (Andor Tech., UK). As a result of the paper, surfaces functionalized by nanoparticles were obtained prototypes of optical sensors. It is shown that the experimental gain of the Raman signal can be no less than 104 times. The presented data will serve as the basis for obtaining the required sizes of nanostars in the methods of the controlled chemical synthesis of colloidal nanoparticles. The results presented in the article can be applied to the development of biocompatible and highly sensitive optical sensors based on the effect of Raman scattering of light.

The study of low-temperature plasma generated in pulsed mode at atmospheric pressure was carried out. The purpose of the presented research is to develop a method of digital holographic interferometry for registration and evaluation of parameters of low-temperature plasma at atmospheric pressure in pulsed mode. This type of plasma is currently applied in medicine and biology. Thus, there is a need to control the exposure dose and plasma environment formation regimes. As plasma parameters, it can be considered its electron concentration which can be calculated through the estimation of the refractive index of plasma pulse in relation to unperturbed state. The plasma pulses were activated in Helium. The plasma pulse frequency was 5 kHz and its duration was 750 ns. During an investigation a laboratory set-up for recording holographic images of plasma pulses was developed. Holograms are acquired on a digital camera and a pulsed laser INNOLAS SpitLight Hybrid II at a wavelength of 532 nm with pulse duration of 10 ns is used as a source of coherent radiation. In order to record plasma pulses, the laser, plasma generator and digital camera were strictly synchronized to each other. During the experiment, a series of about 500 holograms were acquired, and the reconstruction of the phase of the object field was calculated. Analysis of the sequence of holograms allowed calculations of phase difference (interferograms) related to the refractive index of low-temperature pulsed plasma in Helium. It is known that low-temperature plasma leads to low phase delay which forms low phase contrast of the evaluated interferograms. For this purpose, we carried out preliminary experiments with plasma-arc that has similar temporary parameters, however, with a higher phase contrast of the interferograms. The paper presents experimental results obtained by studying the phase contrast of the refractive index of pure Helium, plasma-arc and plasma pulses in Helium. Thus, the effectiveness of both the experimental set-up and the method to evaluate the interferograms related to the refractive index of the plasma pulse was verified. The data obtained can then be used to estimate the electron concentration of the plasma. However, it needs to increase the sensitivity of the method in order to enhance phase contrast. Increase of sensitivity can be done by means of extension of the spectral range, for example, toward to infra-red.

The application of modern and perspective bioradiophotonics methods on the basis of optical and acousto-optic devices for the processing of bioelectric signals (BES) have been considered. The basic application difficulties of these methods are connected with the fact that the studied signals are of low frequencies, and development of special actions are required for the processing devices adapting. It has been proposed to introduce into acousto-optic processing system with time integration the bioelectric signals using method of high frequency carrier with linear frequency modulation which is modulated by low frequency signal. The system configuration has to provide the realization of convolution procedure; hence, the used Bragg cells must be oriented oppositely to each other. The performed analysis has shown that it is possible to realize both signal power spectrum calculation and its wavelet transform; the presence of carrier is obligatory for both kinds of processing. Also, the method of the preliminary BES compression has been proposed for its transmission into the high frequency area. In this case, the possibility occurs to introduce the signal into the acousto-optic processing system with spatial integration. In the simple acousto-optic correlator with the reference transparency the envelope of the correlation function is formed depending on time. Using the set of the reference transparencies in the multichannel correlator, it is possible to realize the prolonged BES wavelet analysis using the mother wavelet. The optical preliminary BES processing can be also performed using liquid crystal arrays. The analysis of the processing of electrocardiac signals obtained from the experimental animals (rats) has been listed using the liquid crystal array for the signal introduction into optical processing system. It has been shown that both spectral and wavelet processing can be realized in this case without using of the high frequency carrier by the low frequency signal. The use of the obtained results will make it possible to create a new family of devices for wavelet processing of bioelectrical signals implemented in real time which will make an important contribution to improving the diagnosis of diseases of the cardiovascular system, the cortex, and the central nervous system.

When diagnosing oncological skin diseases, the problem of untimely detection of pathologies remains relevant. Modern diagnostic methods have a number of disadvantages associated with the limited capabilities of human vision, high requirements for non-invasive studies and digital representation of the results obtained for their transmission over communication channels. The most important tasks of early binary diagnostics of skin neoplasms can be solved using bioradiophotonics methods. The paper considers the author’s multispectral method for processing images of skin areas using a new specialized polychrome light source with software control of the radiation wavelength. The principle of operation of such a source is analyzed and the use of a set of LEDs with a special arrangement is justified which makes it possible to direct a beam of light of any wavelength in one direction. The choice of the wavelength ranges used for LEDs is confirmed, the first version of the layout of such a light source is described, and its optical and structural diagrams are given. It is shown that the optimal way of the wavelength programmable control is its coarse tuning by switching LEDs and fine tuning by acousto-optic tunable filters installed at the source output. A number of test images of a pigment spot on the skin with a size of 40 × 30 mm with wavelengths ranging from near ultraviolet to near infrared ranges using a black and white camera are presented. With digital processing, received monochromatic images, histogram equalization and median filtering of images were carried out to expand the dynamic range of brightness levels and minimize distortion caused by the unevenness of the skin area under study and the presence of shadow illumination. Graphs of the amplitude intensity distribution in the original and filtered images are obtained for the selected wavelengths of the LEDs. It is shown that the presence of a skin neoplasm can be judged by the dips in the light intensity distribution curve. The radial arrangement of LEDs on the board is justified to minimize shadow illumination when illuminating the skin. The conducted studies of multispectral image processing using a realized polychrome light source contribute to the development of new methods for the early diagnosis of skin neoplasms based on photonics and optoelectronics and can find practical application in medical technologies.

A new principal optical scheme for automatic recognition of the shape and relative position of inclusions in moving translucent objects is presented. A new criterion for automatic identification of structures (their localization) based on the analysis of the interference pattern projected on the surface of a CCD matrix, which is an element of the proposed scheme of an optical correlator based on the confocal laser tomograph, has been introduced. The results of this work may be of interest to the specialists in the field of non-destructive control; it can find application in the relevant fields

Opportunity research of using neural networks and computer vision to analyze images of skin lesion and identify features of various pathologies, including oncological neoplasms. A methodology has been developed that makes it possible to evaluate the significance of combinations of color components and spaces in feature extraction using local binary patterns (LBP) and histogram of oriented gradients (HOG) computer vision technologies to extract features of skin changes binary classification of human skin lesions. Optimization of extracted feature makes it possible to more effectively solve the problem of data separability in classification. Research reveals an accessible way to classify skin lesions on a small dataset (less than 1000 images). Research is supposed to be applied to data sequences obtained using a new unique method of multispectral processing of skin lesions. In the course of the work, data from the ISIC-19 and ISIC-20 datasets were used. Samples were formed with a limit of 1000 images for training and validating the models. Additionally, a test sample of 250 images was formed. All images were reduced to 128 × 128 pixels and converted to YCrCb, BGR, Grayscale, HSV color spaces. Features were extracted for each color channel using the HOG and LBP methods. Mathematical models, including neural networks have been used for data classification. The effectiveness of features combinations by color channels and feature extraction methods was evaluated. The preprocessed images were divided into training and validation subsets in a 70/30 ratio. The accuracy, recall, precision and f1-score metrics were used to evaluate the models. The models were evaluated using stratified cross-validation and a test dataset. Optimization of model parameters was carried out based on the loss function represented by the average of cross-validation and evaluation on the validation set. In the process of research, more than 15 000 different optimizations of model parameters were executed. The most stable results on the validation dataset were achieved using ensemble of models, which were trained on a combination of features using local binary patterns (LBP) and histogram of oriented gradients (HOG) technologies. Models which used only local binary patterns technology had the best metrics values, but these models are not recommended to be used in practice without ensemble with stronger models. The results gained can be applied for usage with an ensemble of state-of-the-art convolutional and recurrent neural networks. The proposed approach is universal and applicable both for the analysis of individual images of skin neoplasms and for the analysis of their sequences obtained by the method of multispectral image processing. The technique can be applied to datasets with a limited amount of data. The results obtained will be of interest to specialists in the fields of computer vision and medical images analysis.

Residual amplitude modulation in LiNbO3 phase modulator is one of the key factors that limit the accuracy of high-sensitive fiber-optical sensors. A fiber-optical gyroscope is an angular velocity sensor whose sensitivity is better than 0.001 °/h. Optical light intensity changes after phase modulator is a reason for wrong phase difference that introduces an error in the angular velocity signal. Most existing residual amplitude modulation suppression methods are based on reduction of back reflections between an optical fiber and integrated optical waveguide, absorbing groove to suppress or reduce reflection on the bottom face, and algorithmic compensation. In this paper, new approach to reduce residual amplitude modulation in LiNbO3 for fiber optical gyroscope application is presented. Method feature is an application of additional differential signal modulation with uniform amplitude distribution in the input signal voltage range of the phase modulator. The proposed method allows to suppress residual amplitude modulation of the multifunctional integrated optical circuit phase modulator more than 3 times using additional triangle signal modulation with the frequency f = 200.09 MHz and power P = 36 dBm. This method is suitable for improving fiber optical gyroscope accuracy. Moreover, it could be applied for any fiber-optic sensors based on LiNbO3 phase modulator. The paper will be of interest to specialists in the field of highly sensitive fiber optical sensors, fiber, and integrated optics.

Optical system consisting of single-mode optical fiber and p-i-n photodiode semiconductor chip with InGaAs active layer was investigated. Considered photodetector module has responsivity in 1.3–1.6 µm. The problem of optical power loss due to inaccurate matching between the optical fiber and the active medium of photodiode in photodetector modules is investigated; resolving the power loss problem will lead to an increase in the spectral photosensitivity and external quantum efficiency of the photodetector module. Optimization of optical fiber coupling with semiconductor chip was implemented in Zemax® software with built-in Levenberg–Marquardt algorithm. Also, numerical calculations of the influence of the transverse and longitudinal displacement on optical coupling efficiency in the photodetector module were carried out. The optical system of photodetector module based on standard metal can package was built in Zemax® software. Optimal distances between elements of the photodetector module were calculated, and maximum efficiency of 93.1 % optical coupling between single-mode fiber and photodiode aperture was achieved. The necessary sensitivity of linear micro translators used during the assembly of photodetector modules was determined to ensure the alignment of optical elements with coupling efficiency more than 90 %. The results of this work can be used in the design of photodetector modules. The proposed solutions can be relatively easily modified to create photodetector modules of other spectral ranges.

An extensive growth of serial remote sensing images paves the way for abundant data intended for the sequential spatial pattern determination in several fields like monitoring of agriculture, development of urban areas, and the vegetative area. However, conventional spatial sequential pattern mining is not applied efficiently or directly in the aspect of serial remote sensing images. Therefore, a residue feature analysis with empirical mode decomposition is proposed so as to enhance the spatial sequential pattern mining efficacy from the raster serial remote sensing images. At first, input images are being extracted by means of minima and maxima pattern by computing the mean of envelops and the intrinsic mode function components. If the intrinsic mode function condition is satisfied, then it is being subtracted from the original image; finally, the image is decomposed into many intrinsic mode functions and residue. The experimental outcomes attained indicate that the proposed strategy is proficient of mining spatial sequential pattern from the images of serial remote sensing. Though the support values of the patterns might not be attained accurately, the presented scheme guarantees that the whole patters are being extracted at lower consumption of time.

Monitoring systems of automated production lines requires high accuracy and processing speed of acquired data. Nowadays digital twin technologies are rapidly developing as part of Industry 4.0. Digital twin is a virtual representation of a physical system that mimics the behaviour of a real object, and is used in real-time control, monitoring and disturbance prediction, without influence on a real object. Digital twin is being used in many fields of application such as: healthcare, manufacturing, education, city development, etc. Nonetheless, despite the rising popularity of digital twin researches, there is no basic approach to digital twin synthesis. Mostly, in state of the art articles, systems with known parameters are considered. In this paper, approach to development of digital twin, based on internal model for multi-link mechanisms with unknown motion parameters, is presented. Described approach intended to ease the task of production line monitoring and extend digital twin technology application field. In this article adaptive controller design, based on internal model, is presented, theoretical explanations of design process are provided, and application of the control algorithm in the task of multi-link mechanism motion trajectory parameters estimation is described. In this work the experimental synthesis of digital twin for Kuka youBot manipulator based on presented approach in real time is described. Adaptive motion parameters estimation was made for two links of the manipulator for the sake of confirmation of presented approach usage in the task of digital twin for systems with unknown parameters. Motion trajectory parameters of the robot links were defined manually with the use of chaotic generators to estimate the accuracy of the adaptive control system. This approach was used in order to calculate the error of reference tracking by comparing the control signal for digital twin with the reference exogenous input for manipulator links. As the results of the experiment, the graphs of the error reference tracking for both links are presented. As the goal of the experiment, the convergence of reference tracking error to the field [–0.005, 0.005] radian was set, and as can be seen from graphs this goal was achieved. There is a small disturbance of the error convergence on the graphs within the desired field which was caused by noised measurements and delays of the chosen modelling environment real-time simulations. In the conclusion of this paper, further work to reduce the influence of mentioned causes is described. The results of this paper can be used in further digital twin technology researches. Presented approach can be implemented in robots remote control tasks, production lines technical condition monitoring and in general motion trajectory parameters estimation tasks for multi-link mechanisms

Within the framework of the scientific project “Investigation of spectral-luminescent properties of CsPb(BrCl)3 quantum dots in fluorophosphate glasses” CsPbX3 (X = Br, Cl) quantum dots were synthesized and investigated. The absorption spectra were studied using a Perkin Elmer lambda 650 double beam spectrophotometer. A Perkin Elmer LS50B spectrofluorimeter was used to obtain luminescence spectra. The temperature dependences were studied by means of an original setup, including a spectrofluorimeter, a multimode optical fiber, a cryostat and a temperature stand. The exciting light from the spectrofluorimeter lamp was focused on the input channel of the optical fiber. After leaving the channel, the radiation was collected by a lens in the focus of which was a sample fixed in a thermostat. The luminescence of the sample was collected in the opposite direction with the output to the receiver of the spectrofluorimeter, which is connected to the computer. The thermostat, in turn, was connected to a cryogenic set-top box with variable temperature, which allows adjusting the temperature in the range from 74 to 472 K. It is shown that an increase in the heat treatment time leads to an increase in quantum dots and, accordingly, to a decrease in the band gap due to the quantum confinement effect. When replacing bromine in CsPbBr3 with chlorine, mixed CsPb(BrCl)3 nanocrystals were obtained which leads to a shift of the absorption and luminescence bands to the short-wavelength region. Thus, by choosing different ligands for CsPbX3 (X = Br, Cl), changing their ratio and heat treatment conditions, it is possible to adjust the wavelength of luminescence in a wide area of the visible range. The study of the dependence of the band gap width on temperature clearly showed the presence of phase transformations of the crystal structure. The sequence of phase transitions for various chemical compositions was determined, namely, the contribution of chlorine to the change in dependence in the range from 180 to 400 K. It is assumed that the main causes of luminescence quenching above 300 K are phase transitions. As a result, it is proved that fluorophosphate glass is a chemically stable medium for protecting quantum dots from external influences. The possibility of creating stable phosphors, new laser media and luminescent coatings of both white light and in the entire visible range has been obtained

A study is presented in the field of development and creation of modernized multi-layer color separation multispectral systems with increased color resolution. The types of structures of the developed patterns of matrix photodetectors based on multilayer silicon with working layers for use in the blue, green, red and infrared spectral ranges are considered. A method for calculating silicon layers in the form of optical films with specified characteristics is proposed. The silicon layers act as both a sensing element and a specific wavelength filter to highlight the blue, green, red and infrared ranges of the spectrum. The reflection and transmission coefficients were calculated for the selected wavelengths at various angles of incidence on the sensor. The Brewster angle for these wavelengths is also calculated. The possible presence of a microlens sensor surface is taken into account. Calculations are presented for cells with four-layer and two-layer structures for various combinations of layers. The dependences of the reflection and transmission coefficients for two-layer and four-layer structures of semiconductor sensors for p- and s-polarization, also for unpolarized light, are obtained. It is shown that the combination of layers in the red and infrared ranges of the spectra has the minimum reflection coefficient and the maximum transmission coefficient. The results obtained can be used in the development of multilayer multispectral systems with registration of infrared radiation. As a result, it is possible to use a pair of red and infrared spectra as the basis of a matrix photodetector pattern, and layers of blue and green spectra as auxiliary ones for building a full-color image.

In this work, the conversion efficiency of Cr4+ ions and the optical properties of ceramics based on chromium-doped yttrium aluminum garnet were investigated. Increasing the conversion efficiency of Cr3+ to Cr4+ opens up broad prospects for using YAG ceramics as saturable absorbers for passive Q-switching of Nd- and Yb-solid-state lasers. The aim of this work was to study the effect of magnesium oxide concentration on the conversion efficiency of Cr3+ to Cr4+ under conditions of Al3+ (4.8 mol.%) and Y3+ (2.9 mol.%) cations excess in the garnet structure as well as the stoichiometric ratio Y3+/Al3+ = 3/5. The possibility of changing the concentration of Cr4+ ions in both the octahedral and tetrahedral positions due to the formation of magnesium substitution defects when the composition deviates from the yttrium-aluminum garnet stoichiometry has been studied. Chromium-doped transparent optical ceramics based on yttrium-aluminum garnet with different ratios of Y3+/Al3+ cations was obtained by the two-stage coprecipitation method. Magnesium oxide was used as a sintering additive and charge compensator for converting chromium ions from the trivalent to the tetravalent state in concentrations of 0 to 0.2 wt.%. It was found that aluminum excess in the yttrium-aluminum garnet matrix leads to a decrease in the Cr3+ to Cr4+ conversion efficiency. A deviation of stoichiometry towards an excess of yttrium leads to a decrease of air annealing temperature for oxidizing chromium ions to the tetravalent state and their transition to the tetrahedral position. However, the samples optical transmittance with an excess of yttrium was lower than in the cases of an excess of aluminum and stoichiometry. It was found that with an increase in the vacuum sintering temperature from 1780 to 1820 °C in the samples with an excess of aluminum, an increase in the concentration of Cr4+ ions in the tetrahedral position occurs, as evidenced by higher absorption intensity at a wavelength of 1030 nm. For the cases of stoichiometry and an excess of yttrium in garnet, this effect is less pronounced. Samples of optical ceramics of yttrium-aluminum garnet with a light transmission of more than 75 % in the visible and near-IR ranges with pronounced absorption bands of chromium have been obtained. The results of the work can be applied to the creation of passive switches for solid-state lasers.

The results of the study of the optical properties of low-density InGaPAs quantum dots, as well as the effect of low temperatures and thermal annealing parameters on their optical and structural properties were presented. InGaPAs quantum dots were formed by substituting phosphorus with arsenic in InGaP layer directly during epitaxial growth. The optical properties of InGaPAs quantum dots were studied by photoluminescence (PL) spectroscopy. Photoluminescence spectra at liquid nitrogen temperature (–196 °С) made it possible to determine the features of nonradiative recombination in heterostructures. The heterostructures were subjected to short-term thermal annealing at temperatures of 600 and 650 °C for 2 min to estimate the effect of annealing on the optical and structural properties of quantum dots. It was shown that at –196 °С the contribution of nonradiative recombination can be considered insignificant for the entire measured range of pumping power rage but at temperatures above –73 °С, the contribution of nonradiative Shockley-Reed recombination can be observed. Rapid thermal annealing of InGaPAs quantum dots led to reduce the number of point defects and growth of PL intensity. InGaPAs quantum dots and substitution method can find their application in the creation of single photon sources. The presented experimental results should be considered for implementing such sources, especially for optimizing the width and intensity of the radiation line.

This paper discusses the effect called undesirable extrusion dynamics that occur during material extrusion printing or fused deposition modeling. This effect is revealed during high acceleration and deceleration of printing head and results in over-extrusion on corners of parts and printed layer unevenness. To minimize this effect, modern control systems use Advance algorithms for dynamics control. However, such disadvantages as inertia, reduced printing speed, need for manual calibration, as well as uncertainty of the influence of material, nozzle geometry, and printing process parameters on the algorithm performance do not allow this group of solutions to be applied on an industrial scale. The paper presents a study of the influence of printing characteristics, such as material type, extruder type, printing temperature, layer and nozzle geometry, on extrusion dynamics through a series of experiments. The experiments were carried out on a Creality Ender 3 printer. The obtained experimental data will allow us to deepen the understanding of extrusion dynamics influence in FDM printing; they are also used in the present study to modify existing dynamics control algorithms. The paper proposes a modification of Advance algorithm based on machine learning. It is proposed to implement an algorithm containing two trained neural network models. One model predicts changes in printing head motion to minimize residual defects and increase average print speed. The second model predicts the compensation parameter for specific printing conditions without the need for manual calibration. A neural network model was trained to determine the compensation parameter depending on the type of material, layer thickness, nozzle geometry and printing temperature. The model was trained based on experimental data. The developed algorithm was introduced into Linear Advance algorithm of the Marlin firmware and tested on Creality Ender 3. The experiments showed that the developed model can successfully predict the required compensation and can be applied during the printing process. The proposed algorithm helps to facilitate and automate the process of extrusion dynamics compensation which will expand the possibilities of FDM printers’ application in industrial conditions. The obtained algorithm can improve the accuracy and printing speed which will subsequently help to increase the economic independence and competitiveness of small design organizations and enterprises in Russia that use 3D printers. This research expands the possibilities of rapid prototyping and may help to ensure the rapid creation of pilot batches.

 Identifying community structures within network dynamics is important for analysing the latent structure of the network, understanding the functions of the network, predicting the evolution of the network as well as detecting unusual events of the network. From various perspectives, a diversity of approaches towards dynamic community detection has been advised. However, owing to the difficulty in parameter adjustment, high temporal complexity and detection accuracy is diminishing as time slice rises; and recognizing the community composition in dynamic networks gets extremely complex. The basic models, principles, qualities, and techniques of latent factor models, as well as their various modifications, generalizations and extensions, are summed up systematically in this study which focuses on both theoretical and experimental research into latent factor models across the latest ten years. Latent factor model like non-negative matrix factorization is considered one of the most successful models for community identification which aims to uncover distributed lower dimension representation so as to reveal community node membership. These models are mostly centred on reconstructing the network from node representations while requiring the representation to have special desirable qualities (non-negativity). The purpose of this work is to provide an experimental as well as theoretical comparative analysis of the latent factor approaches employed to detect communities within dynamic networks. Parallelly we have devised the generic and improved non-negative matrix factorization-based model which will help in producing robust community detection results in dynamic networks. The results have been calculated from the experiments done in Python. Moreover our models methodology focuses on information dynamics so as to quantify the information propagation among the involved nodes unlike existing methods that considers networks first-order topological information described by its adjacency matrix without considering the information propagation between the nodes. In addition, this paper intends to create a unified, state of the art framework meant for non-negative matrix factorization conception which could be useful for future study.

A visual display system of changes in the physiological state of patients and their data transmission via optical wireless communication is presented. Existing methods such as bedside monitors do not provide the possibility of visual display of information near the object in conditions of high workload of personnel and allow transmitting data via an electric cable or remotely in the radio frequency range. Such disadvantages reduce the responsiveness of personnel and lead to numerous errors in the transmitted data. A remote operational monitoring system is more effective, providing data collection from sensors, display with minimal delay time and data transmission over an interference-free communication channel in the optical range. A simple and visual way of displaying information allows to quickly and accurately recognize critical situations. The proposed system has two channels. The first channel provides a visual representation of changes in the physiological state on the visual display device in the form of a bracelet. The second channel allows transmitting data about the deviation in the patient’s condition via optical wireless communication in the infrared range of the spectrum for detailed display on a computer. The visual representation of changes in the physiological state is based on programmable change in the color of the LED indicators and on change in their operation modes. The block diagram and design of the visual display and data transmission system are presented. As part of the evaluation of the system operability, the heating of the visual display device in the COMSOL Multiphysics was evaluated. It is shown, that the average heating temperature of the indicator part in contact with human skin does not exceed 24 °C and is safe for the patient. The optical scheme of the receiving unit and the transmitting module is presented. The optical model of the module is presented in the Zemax program. It is shown, that the required average optical power of the working spectral region is 235 μW for the four infrared LEDs and four photodiodes located at a distance of 1 meter. A description of the working layout of a visual display and data transmission device is presented, including a digital pulse sensor and blood oxygen level, a color control and data processing unit, a visual display device, and a data transmission unit. The LEDs operation modes and its compliance with the deviation of the controlled parameters were checked by a special microcontroller program of practical significance. The implementation of the developed system is relevant when monitoring the condition of the object of observation in cases where the use of the radio frequency range is limited and the stability of the data transmission channel to electromagnetic interference plays an important role.

A practically effective solution to the problem of automated processing of ice reconnaissance data in high latitudes is proposed. The intermediate result of ice reconnaissance is huge aerial survey data set consisting of images of low quality; this is a consequence of the difficult conditions of aerial survey in high latitudes. The goal of the study is to create a high-level method that can either efficiently process this pre-collected data set or perform real-time processing of similar images while ensuring high reliability in solving the problem of recognizing ice class distribution on the water surface with minimal computing resources. In particular, the problem of automatic classification of ice-floe size distribution (FSD) type for a three-class model based on aerial survey data is solved. The practically important case of low-quality images is considered, a common situation for the meteorological conditions of the Far North. The proposed approach is based on the use of machine learning methods, in particular on the well-known multi-class SVM (Support Vector Machine), which is extremely undemanding to computing resources and therefore can be implemented even by the onboard computer of an ice reconnaissance UAV. From the input images of low quality some numerical characteristics of the image are calculated which informatively characterize the image. These characteristics (features) are invariant to scaling, rotation and illumination as well as have a much smaller dimensionality than the original image. The main idea underlying the proposed method is to form an original set of features which are implemented in the original feature space. These features characterize large fragments of the analyzed image and are “stable”, in contrast to the features that characterize small details. A new method of FSD type classification based on the processing of aerial survey data by using machine learning methods, which is sufficiently effective for processing low-quality images, has been proposed. Also, the original feature space for classification was proposed which ensured high practical efficiency of this method. The method has shown high efficiency when it is tested on a data set composed of low-quality real images (high blurriness, vagueness, presence of meteorological noises). The developed algorithm can be used for express analysis of ice reconnaissance data, including an ice reconnaissance UAV on-board software component.

SARS-CoV-2, the new coronavirus underlying the development of the COVID-19 pandemic, has led to a sharp increase in the burden on healthcare systems, high mortality and significant difficulties in organizing medical care. The aim of the study was to conduct a systematic analysis of factors affecting the course of infectious disease in patients with diagnosed COVID-19 hospitalized. In order to predict the course of the disease and determine the indications for more aggressive treatment, many different clinical and biological markers have been proposed, however, clinical and laboratory assessment of the condition is not always simple and can clearly predict the development of a severe course. Technologies based on artificial intelligence (AI) have played a significant role in predicting the development of the disease. One of the main requirements during a pandemic is an accurate prediction of the required resources and likely outcomes. In the present study, a machine learning (ML) approach is proposed to predict the fatal outcome in patients with an established diagnosis of COVID-19 based on the patient’s medical history and clinical, laboratory and instrumental data obtained in the first 72 hours of the patient’s stay in the hospital. A machine learning algorithm for predicting the lethal outcome in patients with COVID-19 during 72 hours of hospitalization demonstrated high sensitivity (0.816) and specificity (0.865). Given the serious concerns about limited resources, including ventilators, during the COVID-19 pandemic, accurately predicting patients who are likely to require artificial ventilation can help provide important recommendations regarding patient triage and resource allocation among hospitalized patients. In addition, early detection of such persons may allow for routine ventilation procedures, reducing some of the known risks associated with emergency intubation. Thus, this algorithm can help improve patient care, reduce patient mortality and minimize the burden on doctors during the COVID-19 pandemic.

Symbolic execution is a widely used method for the systematic study of program execution paths; it allows solving a number of important problems related to verification of correctness: searching for errors and vulnerabilities, automatic test generation, etc. The main idea of symbolic execution is generation and use of symbolic expressions in the program analysis in direct order, i.e., from the entry point to the points of interest. At the same time, since the time of E.W. Dijkstra, the method of backward symbolic execution has been popular when the conditions for hitting the point of interest are extended to the entry point of the program due to the iterative calculation of the weakest preconditions. This method is usually much more difficult to implement than direct symbolic execution, so even the artifacts of the latter cannot be used in the implementation. In this paper, the relationship between direct and backward symbolic execution based on the calculation of the weakest preconditions is investigated. In particular, it is shown that the latter can be implemented using the former. A formal presentation of symbolic execution with lazy initialization for programs with dynamic memory is given. An algorithm for calculating the weakest preconditions for arbitrary symbolic executed program branches is proposed. The lazy initialization mechanism and the algorithm for calculating the weakest preconditions are implemented in KLEE, a symbolic virtual machine for the well-known LLVM platform. The proposed method allows performing backward symbolic analysis using direct symbolic execution. This is important for the implementation of bidirectional program execution which can be used both for program verification and for automatic test generation.

The paper presents the results of a study of the possibility of expanding the dynamic ranges of hot-wire methods. The relevance of the work is due to the demand in new methods for measuring the thermal and hydrodynamic parameters of high-speed gas flows for the purposes of scientific instrumentation. The novelty of the presented technical solution lies in the use of two hot-wires anemometers with significantly different thermal inertia for simultaneous measurement of the flow velocity and the heat transfer coefficient in it. The theoretical basis of the proposed method is based on the phenomenon of the inertia of the response of any thermodynamic system under a stepwise thermal effect on it. The method consists in placing in the investigated flow two bodies of the same shape and size which have significantly different thermal inertia. The bodies are subjected to a stepped thermal effect, and the non-stationary temperature delay of the bodies relative to each other is recorded. Using the maximum value of the temperature delay, the value of the heat transfer coefficient of the bodies with the investigated flow can be evaluated by calculation. The flow rate is found from the value of the moment of time corresponding to the maximum temperature delay while using the calibration characteristic previously obtained on the reference flow. The new thermal anemometry method is scientifically substantiated, the measurement equation of the method is obtained, the measurement algorithm and the generalized scheme of the device implementing the method are developed, and the value of the expected uncertainty of the measurement results is given. The simulation results showed that the relative uncertainty provided by the presented method does not exceed 1.5 %. The developed method makes it possible to significantly increase the accuracy and expand the studied dynamic ranges of the required values for a wide range of gas flows. The method can be used in the flow measurement of gas-air flows.

Elastic-relaxation properties of uniaxial oriented polymer materials under dynamic deformation mode are investigated. A theoretical explanation of the phenomenon of the occurrence of beats is proposed. Experimental confirmation of the obtained theoretical results is given. Using the barrier theory and applying the balance equation of the number of cluster transitions through the energy barrier, taking into account the transition time, a refined constitutive equation of the viscoelasticity of the polymer materials is obtained. Experimental studies in the dynamic mode were carried out by the method of the longitudinal low-amplitude oscillations. For a polymer material, taking into account the time of transition of the cluster through the energy barrier, a refined constitutive equation is obtained. The resulting equation is a second-order differential equation and admits a periodic solution. The application of the obtained equation to the study of free longitudinal low-amplitude oscillations in uniaxial oriented polymer materials is considered. It is shown that the solution of the equation admits two close complex roots, the existence of which leads to the effect of the observed beats. The relations between the parameters of the oscillatory process and viscoelastic characteristics are obtained. The experiment showed that the polymer materials under study have a complex form of the oscillatory process, similar to the phenomenon of beats, in a certain range of load. The dependence of the tangent of the mechanical losses angle calculated from the main frequency on the stress has an acute maximum in the stress range where beats are observed. According to the obtained theoretical ratios and experimentally determined attenuation coefficient and main frequency, the time of transition of the cluster through the energy barrier or the lifetime of the cluster in this energy state is determined. The use of additional information obtained during experiments in static modes made it possible to determine the relaxation time for this material. The calculation on the example of polyethyleneterephthalate (PET) filament showed that the theory is consistent with the experiment. Based on the experimental data obtained during the study of free longitudinal oscillations and the solution of the refined constitutive equation, it is possible to determine the necessary viscoelastic characteristics which makes it possible to predict dynamic deformation processes in polymer materials.

The problem of creating high-lift propulsive aerodynamic is considered. A method was developed for constructing an aerodynamic profile by solving the inverse problem of aerodynamics. The dependence of the lifting force of this profile on the volume of air sucked from its upper surface and from the angle of attack is studied. The profile under study was developed on the basis of the well-known Griffin/Goldschmid profile with air suction at the upper critical point. Three aerodynamic profiles have been developed. The first profile has a flat lower surface to obtain the ground effect. The second profile is similar to the first but has a slit nozzle near the trailing edge. The third profile is similar to the second but has a non-flat bottom surface and increased thickness. The solution of the inverse problem of aerodynamics was used to construct aerodynamic profiles within the model of an ideal gas. The pressure distribution on the upper part of the profile, its construction height and the range of angles of attack are from 0° to 16°, as well as the degree of rarefaction up to 0.5 atm in the gap through which the air was taken were set. For the second and third profiles, the ratio of the amount of air ejected through the nozzle to the amount of air taken from the upper surface of the profile was set. This ratio ranged from 50 % to 200 %. Numerical calculations were performed for each variant using the Spalart-Allmaras turbulence models and the Transition Shear Stress Transport (SST) and Langtry model. The parameters of the turbulence models were adjusted according to known reference data. The Reynolds number was in the range of 1.5·105–1.5·106. The profiles have a high lift coefficient Cy = 3–3.4 which is achieved when creating a vacuum in the air intake of 0.5 atm. Cy depends on the angle of attack almost linearly up to the maximum values. The greater the air flow through the slot nozzle, the greater is the Cy at a vacuum in the air intake of 0.5 atm. Significance for practical application. The developed profiles have a large thickness and create traction. These profiles are convenient to use in aircraft with large internal volumes, for example, those running on hydrogen fuel.

 A numerical method for calculating the thrust of a wide-range rocket engine nozzle has been developed. This type of engine is equipped with an annular nozzle with a flat central body and is designed to operate in the upper atmosphere and in vacuum. The nozzle forms a jet converging to the axis of symmetry due to which a more compact torch of the working fluid is formed. Nozzles of this type have important design advantages over conventional external expansion nozzles. They are more compact, simpler in terms of cooling, but they have increased losses in the bottom region due to the presence of a flat bottom near the central body. Therefore, the design of such engines needs parametric optimization. Currently, for engines equipped with an annular nozzle with a flat central body, there are no validated methods that would allow parametric optimization. The characteristics of the jet, the loss of specific impulse, and the magnitude of thrust for a given type of nozzle depend on three main parameters: the area of the bottom region of the central body, the area of the throat section, and the angle of rotation of the inner edge of the nozzle to the axis of symmetry. The gas flow in the bottom region is accompanied by complex shock-wave processes that require a lot of time for numerical calculations. To optimize the design of the nozzle, it is required a simple engineering method to calculate the thrust of the nozzle according to its main parameters. The calculation of the nozzle thrust is based on the integral distribution of pressure forces over its surface obtained by performing numerical calculations in a wide range of external pressure. The Reynolds-averaged Navier-Stokes equations closed by the SST-modification of the k-ω turbulence model are solved. Based on the results of numerical simulation, the calculated coefficients for one-dimensional engineering dependencies are determined; they make it possible to calculate the speed and pressure in a random section of the combustion chamber and engine nozzle. A simple engineering method for calculating the thrust of the chamber nozzle of a wide-range rocket engine has been developed. The technique is verified by comparison with the results of a numerical experiment. The problem of parametric optimization of the rocket engine combustion chamber, capable to operate in a wide range of altitudes, was solved, and it is of interest to the space industry. The developed method of calculation makes it possible to carry out a wide range analysis of the influence of the ratio of geometric dimensions, regime parameters on the thrust of the combustion chamber and nozzles of a wide-range rocket engine, and to estimate the thrust value at different engine operating heights.