The study uses the phenomenon of high voltage partial discharge to investigate the phenomenon of percolation and visualisation of the percolation channel. The phenomenon of partial discharges is very similar to the quantum tunneling phenomenon observed in metal-dielectric nanocomposites. In both cases the flow of alternating current occurs in the absence of direct contact between the metallic phase particles.

A measuring stand was developed and constructed to test models of metal dielectric nanocomposites using high voltage partial discharge. The stand consists of a 110 kV high voltage transformer, a voltage regulator protecting the constant rate of high voltage rise, a measuring system consisting of a measuring probe, voltmeters and a computer. The communication between the measuring probe and the voltmeter was made in digital technology with the use of fiber optic technology, which allowed the meter to communicate with the computer without any errors and eliminated the interference caused by a strong electromagnetic field resulting from the use of high voltage.

Systems modelling metal-dielectric composites were built, consisting of metallic elements in the form of disks, randomly distributed on the surface of the dielectric matrix. The number of disks was increased in series of 40 in each. The maximum number of disks was 1520. The dependence was determined of one of the important parameters characterising an partial discharge, i. e. the initial voltage, at which an electric current starts to flow between electrodes, on the concentration of the metallic phase. On the basis of these results, a percolation threshold was established for a matrix with a random distribution of metallic phase elements, the value of which is about 50 %. Films and pictures of partial discharges with visible percolation channels were taken with the camera with which the stand was equipped.

Yttrium aluminium perovskite YAlO₃ (YAP) crystal, doped with rare-earth ions, has been extensively studied as a diode-pumped laser host material. The wide interest to rare-earth ions doped YAP crystals is explained by its good thermal and mechanical properties, high natural birefringence, widely used Czochralski  growth method. The aim of this work was to study the Yb³⁺:YAlO₃  crystal as an active medium for high  power mode-locked laser.

Yb³⁺-doped perovskite-like aluminate crystals have unique spectroscopic and thermooptical properties that allowed using these crystals as an active medium of high power continuous wave (CW) and modelocked (ML) bulk lasers with diode pumping.growth method. The aim of this work was to study the Yb3+:YAlO3  crystal as an active medium for high  power mode-locked laser.

In our work spectroscopic properties of Yb:YAP crystal and laser characteristics in CW and ML regimes are investigated. Maximum output power of 4 W with optical-to-optical efficiency of 16.3 % and 140 fs pulse duration have been obtained for Yb:YAP E //c-polarization with 10 % output coupler transmittance. Tunability range as wide as 67 nm confirms high promise of using Yb:YAP crystal for lasers working in wide spectral range.

The paper presents a measuring stand designed and built for testing direct and alternating current properties of power transformers basic insulation component i.e. electrotechnical pressboard impregnated with transformer oil. Measurements of direct and alternating current parameters are performed using the frequency domain spectroscopy and polarization depolarization current methods.

The measuring station includes a specially developed climatic chamber which is characterized by high accuracy of temperature stabilization and maintenance during several dozen hours of measurements. The uncertainty of temperature maintaining during several dozen hours of measurements does not exceed ± 0.01 °C. The computer software developed to control the station allows for remote measurements, changes in supply voltage and temperature settings and acquisition of the obtained results. A new type of measuring capacitor was developed and manufactured, the structure of which significantly reduces the chance of samples contamination during measurements. By increasing the accuracy of temperature stabilization during measurements, the resolution of measurement temperatures was increased, at which it is possible to perform measurements with the frequency domain spectroscopy and polarization depolarization current methods. This allowed to reduce the step of measurement temperature change and thus to increase the accuracy of determining the activation energy of the measured parameters.

The article also contains basic information on the analysis of the direct and alternating current electrical parameters of the composite electrotechnical pressboard-mineral oil-water nanoparticles. The results of several direct and alternating current parameters measurements of a transformer oil impregnated pressboard sample with a moisture content of (5.2 ± 0.1) % by weight obtained by the use of a measuring stand are presented as examples.

The method of correlation measurement of the coolant flow rate, widely used for operational diagnostics of nuclear power plants, can be extensively used in research practice. The aim of this work was to apply a correlation method based on the conductometric measurement system with wire-mesh sensors for measuring a coolant flow rate.

Insignificant concentration of a salt solution (NaCl or Na2SO4 ) creates a gradient of the conductivity in the flow, which is used as a passive scalar measured by the system. Authors used turbulent pulsations at the interface of two concurrent flows with identical velocities in a square channel as a signal source for the correlation method. The paper presents the methodology of the tests, test facility description, signalto-noise ratio estimation, the results of digital signal processing and comparison of the measured velocities in the model with the flowrate‒averaged velocity determined by the use of flowmeters. The measured velocity values give acceptable agreement for the turbulent flow modes. It was shown that the measurement accuracy drops sharply for low-Reynolds flows.

The obtained results were used for flowrate measurements in core-imitator channels of the nuclear reactor test model. The presented paper is an approbation of this approach for its application as part of an test model of a nuclear reactor in order to determine the each duct flow rates in the channels of the core simulator using wire mesh sensors.

Assessment of the environmental and economic performance of a safety valve requires information about the flow of the substance through the valve when it is actuated. The goal of this paper was to determine the flow rate of the discharged substance and the mass flow rate of the substance entering the safety valve when it is actuated.

Proposed a mathematical model to describe the processes occurring in the valve. The model includes a system of differential equations describing the physical laws of conservation in the internal volume of the valve and differential equations, which link the value of gas flow through the valve with the pressure and the amount of movement of the shut-off disk. Used a modified method by S.K. Godunov to solve gasdynamic equations.

Established that the determination of the flow and power characteristics of the valve requires the preliminary construction of a mathematical model of the safety valve operation. Based on this, proposed a method for determining the flow rate of the discharged substance and the mass rate of the substance entering the safety valve when it is actuated.

Obtained the flow characteristics of the valves under review and the dynamics of movement of the shutoff disc of the valve, as well as the dependence of the pressure change on the opening time of the valve. Comparison of the calculated values with available experimental data gives good agreement of results (no more than 5.6 % for a gas flow rate, under 10 % for the movement of the valve and change the arrival of gas in time using the standard deviation function of the flow characteristics of 0.6 %), confirms the correctness of the defined mathematical model, used numerical schemes and algorithms, as well as the proposed method and recoverability of the arrival of gas in a pressure–time curve.

One of the important characteristics of the surface properties of metal parts subjected to friction is hardness. Hardness measurements are important for determining the operational characteristics of parts and monitoring the technological regimes of surface modification. However, hardness measurements of thin modified layers made by different methods can lead to differences in measurement results. The aim of the article was to study the hardness of a metal surface modified with ultrafine particles of minerals by two different methods (instrumental indentation and Vickers hardness measurement) and a comparative analysis of the measurement results obtained by these methods.

Standard Vickers hardness measurements at loads of 0.025, 0.1 and 0.5 kgf showed a qualitative difference between the hardness values of the two samples modified with different mixtures of ultrafine particles of minerals and a large heterogeneity of the hardness values over the area. By the method of instrumental hardness, standard measurements were performed without preliminary selection of the indentation site (at a load of 1.05 N) and measurements during indentation into even sections (at low loads of 10 mN).

It is noted that the high precision of measurements implemented by instrumental indentation, due to the large roughness of the samples, leads to large values of the error in calculating the measurement results. An additional difference in the results of measurements performed by two methods at shallow indentation depths may be due to the fact that the object under study has a complex structure consisting of a metal matrix and particles distributed over the depth of the sample. A possible way out of the situation lies in the transition from the use of hardness measures when calibrating instruments to standard samples of properties for which the constancy of mechanical properties in the measured range of indentation depths will be ensured, but which are not yet available in research practice. Therefore, at present, when carrying out work related to the search for optimal conditions for obtaining thin wear-resistant layers on the surface of metals modified with ultrafine particles of minerals, comparative measurements performed by one measurement method are recommended.

The nature of the molten electrode metal melting and transfer is the main process parameter of manual metal arc welding (MMA) with coated electrodes. It significantly affects the efficiency of the welding process. For this reason the relevant task is to identify the parameters of the transferred molten electrode metal drops and their further transfer into the weld pool with maximum accuracy. The aim of the given paper is to develop a method and visual representation of the form and the geometrics (volume, area, mass) of a molten electrode metal drop.

We have developed the method of simulation modeling and visualization for molten electrode metal drops transfer and their parameters. It allows obtaining highly reliable input data to be used for developing and verification of mathematical models for the thermal fields distribution along the welded item surface. The algorithm is realized as the calculation programs for specifying the molten metal drop parameters and means of its geometrics and space form visualization.

We used this method to specify a number of molten electrode metal drop parameters: volume, mass, center-of-gravity position, surface area.

We have established that it is possible to conduct the measurements with maximum

The suggested method significantly decreases the labor intensity of experimental studies aimed at specifying the size of electrode metal drops in comparison to the standard methods. When we know the size of the drops under certain welding conditions we can control the drop transfer process, i. e. reduce the heat input into the welded item and produce weld joints with the tailored performance characteristics.

The article notes the advantages of the method of constructing absolutely invariant measuring transducers for working in conditions with disturbing influences. However, this method is not universal. Its limitations are due to the impossibility of "symmetric" transmission of all disturbing influences into parallel measuring channels. A broader interpretation of the two-channel principle is proposed to overcome these limitations. The aim of the study was to substantiate and implement a method for constructing quasi-invariant measuring transducers and systems that retain their metrological characteristics under external disturbances of unknown physical nature.

The theory that develops the two-channel principle to a full-fledged technological method is presented in the article. The theory includes the necessary and sufficient conditions for physical feasibility this method. Two fundamental tasks have been solved in the work. The first task is to identify signs that reflect the essence of the technological method in to specific cases and the second is to implement a methodology that allows these signs to be effectively applied in practice.

In the examples, a complex of technologies is defined for groups of elements of quasi-invariant transducers that provide compensation of the influencing factors acting on them with acceptable accuracy.

There are significant advantages in discussed method. It gives hope for acceptable measurement results under conditions when character and even physical principle of influencing a priori are unknown.

All measurements of mechanical properties of materials in the magnetic structural analysis are indirect and relationships between the measured parameters are correlated. An important physical parameter of steel is hardness. An increase in the correlation coefficient R and a reduction in the standard deviation (SD) are achieved when controlling the hardness of steels with two-parameter magnetic methods compared to methods that use a single measured parameter. However, the specific conditions and requirements for application of the two-parameter methods remain unclear. The purpose of this article was to analyze conditions and the achievable error reduction limit for two-parameter indirect determination of steels hardness and to compare those with one-parameter methods.

In particular, we considered the mean Square Deviation (SD), σF , of indirect calculation of the physical quantity F using two measured parameters x1 and x2 that are correlated with F. It was found that reduction of σF is most pronounced when x1 and x2 are inversely correlated with the maximum modulus |R| of the correlation coefficient R between them. The most significant reduction in σF occurs at similar values of the SDs σ1 and σ2 between the true value of F and the values calculated based on the results of indirect measurements of F using

each of the parameters x1 and x2 . The Results of the analysis are confirmed by an example of reduction in SD when determining the hardness of carbon steels by measuring their remanent magnetization and coercive force compared to use any one of these parameters.

This result can be applied to measurements in non-destructive testing and in related fields of physics and technology. The Results of the analysis allow us to compare different parameters for indirect two-parameter determination of a physical quantity, to select the optimal parameters, and to evaluate the minimum achievable measurement error of a physical quantity by a two-parameter method before performing the measurements.

The aim of the work was to study the contrasts of the images of an object observed in a smoky environment, using polarizing filtering of radiation scattered by smoke particles towards the observer, and without filtering. Prospects for developing optical accessories for firefighters to improve the observation of objects in smoke were evaluated by comparing image contrasts.

The goal was achieved by experimentally simulating the process of transmitting images of a blackandwhite object with a sharp black/white transition boundary through various types of smoke aerosols using polarizing filtering of radiation scattered by smoke particles, and without filtering and evaluating image contrasts.

Studies of image contrasts for different optical densities of smoke in two registration schemes were performed, when the receiving optical system is located near the illumination source of the object at a distance of ≈ 150 mm from it, and when it is located at a distance from the illumination source of the object at a distance of ≈ 800 mm.

It is established that the method of forming the image of the object using polarization filtering of radiation backscattering (RBS) reduces the rate of image contrast reduction with an increase in optical smoke density compared to image registration without filtering (RBS).

A significant difference in the contrasts of images recorded with filtration (RBS) and in the absence of it is observed for "light" fumes (smoldering of wood, cotton) at average optical densities of smoke.

The results obtained can be used in the development of optical accessories for firefighter-rescuer to improve the conditions of observation of objects in adverse conditions of vision: smoke, vaporization, fog.