The assumptions of mathematical models for calculating the crack resistance of reinforced concrete structures are considered. For each of them, an analysis was carried out to determine whether they correspond to reality throughout the entire life cycle of the structure: from the hardening of the concrete mix to destruction. Based on the results of the analysis, it was proposed to use only one single calculation at the level of standards to assess the crack resistance of structures - according to the crack opening width, acrc. So, for example, at a certain value of acrc, the structure will still remain airtight (the cracks will be non-through), and if this value is exceeded, it will not. At the same time, the calculations already available in the norms for limiting permeability and the safety of reinforcement will still remain in demand. At the junction of the theory of damage accumulation and nonlinear fracture mechanics, a compressed algorithm is proposed for possibly taking into account the influence of cracks at all scale levels of the concrete structure, the key for which is the normalization of the statistical parameters of the distribution of discontinuities by diameters, lengths, openings, depths, directions, distances between discontinuities, etc.

Keywords: reinforced concrete, crack resistance, cracking moment, crack width, plasticity coefficient, damageability, non-linear fracture mechanics

When solving the problem of ensuring the mechanical safety of buildings and structures according to GOST 27551-2014 “Reliability of building structures and foundations. Basic provisions” it is allowed to apply a risk-oriented approach. A mandatory stage of this approach is the forecast of the expected accident risk situation of the facility. Due to the fact that the current regulatory documents on risks do not reflect all the features of the stress-strain state of building structures and foundations of buildings and structures during the operation of structures and, therefore, do not allow for a sufficiently accurate assessment of the safety of structural systems, risk assessment for building structures is a very relevant scientific and technical problem.

Keywords: building, building structures, design, destruction, safety, accident risk, risk assessment, risk management, monitoring and risk analysis

The article considers examples of atmospheric air monitoring in linear and compact cities. The issues of atmospheric air pollution are considered, examples of components of pollutants coming from stationary and mobile sources are given. The analysis of the monitoring system of cities with different urban planning is carried out.

Keywords: linear city, compact city, highway, pollution, monitoring, monitoring posts, motor transport, gas pollution, exhaust gases

A method for recording holograms using digital cameras with high spatial resolution is considered. To register holograms obtained in optical setups with an inclined reference beam, a high resolution of registration systems is required. To do this, it is necessary to use media with a resolution of 2000-4000 lines per mm. The use of photographic plates requires a fairly long exposure and development time, which is usually done separately from the optical setup. In the case of holographic interferometry systems, it is necessary to provide for mounting the hologram back into the optical setup with sufficiently high accuracy. Therefore, digital holography methods have been developed to record holograms on photomatrices with limited resolution. These methods are based on the use of optical schemes at small angles (less than 5 degrees) between interfering beams. Recently, sensors with a single element size of 1.33 µm and 0.56 µm have appeared. This resolution makes it possible to return to registration schemes with angles between interfering beams of 30-60 degrees. This allows us to hope for the revival of holographic methods and methods of holographic interferometry at the modern level without the use of intermediate recording media.

Keywords: holography, holographic interferometry, photomatrices with high spatial resolution, holography with an inclined reference beam, digital holography, Fourier transform

Cement compositions based on slag-Portland cement containing finely ground slag in its composition are considered. Fine-ground slag was obtained by grinding in a laboratory jet mill equipped with an automatic classifier. The upper limit of slag grinding was 20 microns. It was found that the introduction of 1-3% fine-ground slag into the composition of slag-Portland cement made it possible to increase the strength and structural characteristics of cement stone in the early stages of hardening. To ensure the stabilizing effect of finely ground slag particles in the cement matrix, cement compositions were sealed with water with the addition of a sulfonaphthalene-formaldehyde-based plasticizer in an amount of 0.5% of the cement content. In the course of research, it was found that the strength of samples containing finely ground slag and plasticizer increased by 50% at an early age of hardening (1-3 days), by 30% on average at 28 days of hardening, while the porosity of the samples decreased by 19% and 33%, respectively.

Keywords: fine-ground slag, ultrafine grinding, slag-Portland cement, plasticizer, cement stone, strength, porosity, normal density, setting time, degree of hydration

Forecasting the consumption of electrical energy and power is an urgent and significant problem. This paper discusses current methods for predicting the consumption of electrical energy, reflected in various scientific papers, their analysis is carried out with the identification of more promising forecasting methods.

Keywords: energy consumption forecasting, statistical forecasting methods, neural network forecasting methods, hybrid forecasting methods

The article describes the possibilities, advantages and differences of machine learning systems without a teacher from template learning. The definition of clustering is also given, indicating the main methods and tasks solved by this machine learning algorithm. The algorithm for recognizing data from documents using OCR technology is described in detail, the goals and objectives of using OCR technology in the business processes of IT companies are formed. The following are tools for solving the problem of recognizing and clustering data from PDF document scans using the Nanonets and Tesseract machine learning libraries. In conclusion, this article describes the advantages and disadvantages of using these libraries in solving the problem of recognizing and clustering data from document scans.

Keywords: machine learning, clustering, data recognition, library Nanonets, library Tesseract

The purpose of the study was to find methods to reduce the construction time of special purpose structures. The analysis of the factors influencing the terms of construction of nuclear power plants is carried out. Using the example of calculating the parameters of the ventilation pipe installation of a really erected nuclear power plant, the advantages of replacing the traditionally used for the construction of these structures with the method of "falling arrows" are noted.

Keywords: falling boom, set of machines, installation of structures, scope of work, traction mechanisms, continuity of work, cost, construction period, commissioning period, work cycle

The assumptions of mathematical models for calculating the crack resistance of reinforced concrete structures are considered. For each of them, an analysis was carried out to determine whether they correspond to reality throughout the entire life cycle of the structure: from the hardening of the concrete mix to destruction. Based on the results of the analysis, it was proposed to use only one single calculation at the level of standards to assess the crack resistance of structures - according to the crack opening width, acrc. So, for example, at a certain value of acrc, the structure will still remain airtight (the cracks will be non-through), and if this value is exceeded, it will not. At the same time, the calculations already available in the norms for limiting permeability and the safety of reinforcement will still remain in demand. At the junction of the theory of damage accumulation and nonlinear fracture mechanics, a compressed algorithm is proposed for possibly taking into account the influence of cracks at all scale levels of the concrete structure, the key for which is the normalization of the statistical parameters of the distribution of discontinuities by diameters, lengths, openings, depths, directions, distances between discontinuities, etc.

Keywords: reinforced concrete, crack resistance, cracking moment, crack width, plasticity coefficient, damageability, non-linear fracture mechanics

The article studies the relevance of online tutoring, considers various existing systems for organizing online tutoring, identifies their strengths and weaknesses, and identifies the most relevant functions of the considered services. The design of the architecture of the developed software product is considered. The goals for further research are defined.

Keywords: online tutoring, tutor, online learning, design patterns, application architecture, information system

This article describes methods for measuring the characteristics of drinking water using microwave technologies, provides their comparative characteristics, advantages and disadvantages. The advantages of research by resonance methods are shown, the prospects for their application for further research are shown. Dielectric constant of substances, its influence on resonance.

Keywords: microwave technologies, resonant and non-resonant methods, water purification, drinking tests, dielectric constant

In this paper, based on Russian and foreign experience in mathematical modeling of photovoltaic installations, the authors consider the approaches to the construction of these models. The relevance of the research is confirmed by the wide spread of electric energy sources using solar energy. The scheme of photovoltaic element substitution and the dependences describing the processes occurring in it are given. The authors conclude that despite the large number of various mathematical models of photovoltaic elements, all of them can be grouped into two categories. The first category includes models that consider photovoltaic panels as a separate element, and the second category includes models where the photovoltaic panel is a component of a generating complex. Despite the difference in the analyzed approaches, the authors single out a number of parameters that characterize the operation of a photovoltaic panel and are sufficient to obtain simulation results with the required accuracy.

Keywords: photovoltaic panel, mathematical modeling, substitution scheme, distributed generation, power generation

The article discusses the features of the use and applicability of identification of parameters of the equivalent circuit of an submersible electric motors. The possibilities of technical implementation with a given accuracy are evaluated for definition the parameters of submersible electric motors substitution circuits under various external influences, as well as when designing submersible electric motors as an integral part of the electro-technical complex of electrical submersible pump units.

Keywords: submersible electric motor, electrical submersible pump unit, identification of parameters of the equivalent circuit of an asynchronous electric machine, mathematic simulation, crude oil production

The application of the gas-dynamic method with the use of nonlinear dynamics to the calculation of an underground structure built into the lower floor on the impact of an air shock wave is considered, taking into account the collapse of the above-ground part of the building. It is known that one of the impacts on built-in underground structures designed to protect the population and territory from natural and man-made emergencies is the impact of a possible collapse or blockage from a higher building when exposed to an air shock wave. This task is relevant because the current methods are based on linear static calculation methods and involve certain assumptions, including when calculating for collapse, and all this can lead to difficult to estimate errors in the calculation results. Therefore, when solving these problems, which are highly non-linear and the processes under consideration themselves are fast, it is necessary to consider the use of more adequate and accurate methods based on more rigorous formulations, which is the gas-dynamic method using nonlinear dynamics.

Keywords: emergency explosive effects, air shock wave, impulse effects, non-linear gas dynamics, compression phase, rarefaction phase, underground structures, “Ambient” elements, Eulerian grids, progressive collapse, collapse of structures, destruction of structure

The testing of technique for modeling the local atomic structure and X-ray absorption spectra for zinc ions in an aqueous solution in the presence of arachidic acid has been adjusted. Models of the local structure of zinc with different coordination geometries are considered: planar, pyramidal, tetrahedral, and octahedral. The cases of increasing distances between the zinc ion and water molecules in the plane and in the axial direction are simulated for octahedral coordination. It has been established that the most probable change in the local structure of the zinc environment in solution in the presence of arachidic acid is the removal of water molecules from zinc ions in the axial position and their further replacement with the formation of a bond with the carboxyl group of arachidic acid.

Keywords: arachidic acid, lipid layer, local atomic structure, X-ray absorption spectroscopy, total external reflection, zinc, biomembrane, finite difference method, monolayer