The presented review of scientific literature on the topic "Digital twins in industry" is based on publications by foreign and domestic researchers. The processes of the concept development starting from the moment of its appearance to the present, are considered. Due to the ambiguity of the term "Digital Twin” interpretation, several definitions of this concept are formulated, and a brief analysis of them is given. Classification of digital twins, as well as approaches to their construction and technologies used are reflected. Scenarios of digital twins application are considered on examples from the experience of Russian and foreign companies. Conclusions are given on the prospects for development in the research area, the advantages and risks of introducing digital twins at industrial enterprises are analyzed.

Nine machine learning methods (ANN, ANFIS, ELM, FM, SVM, GPR, RF, RT, k-NN) are compared using the example of predicting acoustic logging data. With machine learning, the solution to the regression problem can be used not only for predicting geophysical fields, but also for filing in missing data. The constructed curve T(Р) of the P-wave interval time can be considered as a forecasted result, if acoustic logging is expected later; if additional acoustic logging is not possible, then the synthetic curve T(Р) replaces the log-derived one for further interpretation. The RF method is shown to provide the best test results.

An approach to solving the problem of improving the visual quality of objects contours in the earth's surface images is presented. The described approach is based on the use of subband cosine transform matrices. A method is proposed for selecting subband image components corresponding to the object contours. In computational experiments, the described method is applied to several images processing. Results of the experiments are presented.

The problem of the significance of aerometric information for piloting and ensuring the aircraft flight safety is considered, as well as the disadvantages of aerometric systems built based on autonomous receivers of the incoming air flow parameters from sensors distributed over the fuselage. The prospect of a variant of constructing an axisymmetric multifunctional receiver, which ensures the perception of the total and static pressure, as well as pressures, characterizing changes in the angular position of the velocity vector of the incoming air flow and determining the aerodynamic angles of attack and slip of the aircraft, is substantiated. A geometric model of a multifunctional receiver is presented, mathematical models of input informative signals are derived, and requirements for analytical models of the signals processing to determine the aerodynamic angles of attack and slip are formulated. Analytical models of the absolute and relative errors in determining the aerodynamic angles due to the instrumental errors of the used differential pressure sensors are presented. The obtained results provide a theoretical basis for design, study of characteristics and errors of aerometric systems for aircraft air signals measuring with an axisymmetric multifunctional receiver of incoming air flow parameters.

Several algorithms are proposed to solve the problem of increasing the density of points of lidar clouds, including the algorithms based on neural networks. High density lidar clouds can improve the accuracy of scene recognition and localization algorithms. The algorithms quality is assessed by the following metrics: the number of false points, the average error, the root-mean-square error. In contrast to existing ones, the proposed algorithms are aimed at determining not only additional points positions, but also their reflectivity coefficients. Presented results of experiments demonstrate that the neural network algorithm without the use of normalization and sigmoidal weighting of the loss function has the smallest error. The least number of false points is provided by the neural network algorithm with an added normalization.

Results of development of new means for testing magnetic compasses in a dynamic mode are presented. The effect of external influencing factors on a ship's magnetic compass error, caused by the ship's pitching, is shown. Two stands, developed for simulating the impact of rolling on the card of a magnetic compass, including the case of high latitudes conditions, are proposed. A method for assessing its dynamic error under an action corresponding to the actual pitching of the vessel is developed. Particular attention is paid to the stand for evaluating the efficiency of the magnetic compass correction system. Based on the analysis of the results of experimental studies, it is concluded that the developed stands can be used to assess the errors of any magnetic compass.

The method of fluorescence spectroscopy is considered as a high-precision and informative tool for measuring the optical properties of biological and synthetic objects. An automated luminescence spectrometer SDL-2 for determining the fluorescence spectra of the materials under study is presented. The fluorescence spectra of 50 samples of composite materials of hard tissues of teeth of 50 patients of different age groups are obtained. Optical characteristics of the enamel-dentin junction, dentin and enamel are investigated. According to the results of comparative analysis of filling materials, it is revealed that the composites "Estelite Asteria A2B" and "Estelite Asteria OcE" are superior in optical properties to other materials. Recommendations for the use of each material separately are given.

Characteristics and parameters that make it possible to assess the technical condition of overhead power transmission lines are considered. Methods and means of determining the characteristics of power transmission lines are presented and dependences of the resistance of distribution power transmission lines on environmental factors are derived. The investigated parameters include the frequency of the network current, the resistance of the power line, the temperature of the electrical equipment, climatic parameters, the number and frequency of overloads in the network. A method of forecasting and assessing the state of power transmission lines based on the parameters of electrical equipment and the degree of its wear is proposed.

A hardware and software complex developed by the authors is presented. The complex is designed for sorting and classifying samples and small batches of mineral raw materials in a semi-automatic mode according to parameters such as size, color, and purity. The complex contains nodes for the lower and upper illumination, a registration unit with a television camera, as well as a projection unit for displaying the classification results into the analysis zone. The role of the operator is reduced to mechanical actions to place and remove mineral samples from the analysis area. Experimental studies were carried out using beryl, chrysolite, amethyst, lapis lazuli, quartz and aquamarine, 69 samples in total. The relative errors in determining the color tone, saturation and lightness were 2.2, 6.2 and 9.1% of the entire measured range, respectively. The average spread of the determined values of transparency, the number of inclusions and cracks is 3.1, 9.5 and 4.8%, respectively. The error in determining the dimensional parameters is 0.5 mm. The proposed technical solution can be used for the technological assessment of the raw materials suitability for beneficiation by the method of optical sorting with the optimal separation thresholds determination.