The possibility of identification and determination of tetracycline antibiotics (tetracycline, doxycycline, oxytetracycline, demeclocycline, metacycline and chlortetracycline) in natural water using digital colorimetry based on sensitized fluorescence of Eu (III) on europium hydroxide is studied. It is shown that complexes of Eu (III) with tetracyclines in an alkaline medium are adsorbed on europium hydroxide with preservation of their fluorescent properties. When the precipitate is irradiated with monochromatic ultraviolet light, pink fluorescence is observed. The colorimetric parameters of the precipitate in the RGB additive system after centrifugation were measured using a smartphone. The use of chemometric analysis provides shortening of the analysis procedure and visualizing of data obtained. The data set was processed using principal component analysis (PCA), hierarchical cluster analysis (HCA), and k-means method with XLSTAT software. The additional use of chemometric methods for processing of the analytical signal contributes to an increase in the reliability of the analyte identification. The methods used in the study make it possible to quantify the content of antibiotics in water bodies. The calibration dependences in the methods of principal components and k-means have a logarithmic form and are linear in the ranges of the determined contents — 0.005 – 0.1 μg/ml (R² ≥ 0.99). The developed method for determining the total content of tetracycline antibiotics in natural waters is easy to use and is characterized by the availability of instrumentation. The environmental friendliness of this approach is attributed to a small set of inorganic salts required for concentration of the chelate complexes of tetracyclines with Eu (III) ions on europium hydroxide. The use of mobile digital technology (smartphones) and modern software products for data processing contributes to the development of rapid analysis. The approbation of the method was carried out using a sample of river water, the correctness of the analysis was proved by the spike test. The relative error of the analysis results does not exceed 15%.

The effect of matrix components on the results of gas chromatographic determination of methanol in samples of alcoholic and alcohol-containing products was studied using a modified internal standard method for quantitative calculations. Ethanol, which is the main component of alcoholic products was used as an internal standard. The matrix effect can be attributed to the presence of ethanol in various contents, and volatile and non-volatile impurity components characteristic of different kinds of drinks. The matrix effect was evaluated by the spike test in the study of 24 samples of alcoholic and alcohol-containing products with a volume fraction of ethanol from 6.5 to 96.6%. All samples were subjected to distillation: the initial samples and distillates were analyzed at a low sugar content; whereas at a high sugar content, only distillates were analyzed. It is shown that the effect of matrix components on the results of the determination of methanol by the proposed method is statistically insignificant. The developed method is characterized by lower financial, material, labor and time costs compared to the current technical regulatory legal acts of the EAEU, China, India, the EU, USA and Mexico. Validation of the method can be performed on the basis of data regularly obtained by the laboratory during routine study of alcoholic products, without using any additional reagents, equipment and additional measurements. Moreover, the method has good prospects for standardization at the interstate and international levels, i.e., in the framework of the activities of the Euro-Asian Council for Standardization, Metrology and Certification (EASC) and the authoritative International Organization of Vine and Wine (OIV).

A simple and selective method for sorption-photometric determination of thorium (IV) micro amounts in clay using a new chelating sorbent, a copolymer of maleic anhydride with styrene modified with N¹,N¹,N²-triphenylguanidine, is proposed. The sorbent is white substance, insoluble in water, acids, weak alkalis and organic solvents. Sorbents were first ground in an agate mortar and sieved through a sieve (0.14 mm). The effect of pH of the medium, the ionic strength of the solution, contact time of the phases, concentration of thorium (IV) in the solution and on the sorption was studied under static conditions. Thorium concentration was determined by the photometric method using 2,2’,3,4-tetrahydroxy-3’-sulfo-5’-chloro-benzene. The concentration of thorium (IV) was calculated using a calibration curve, the results were processed statistically. The full static sorption capacity of the resulting sorbent on K⁺ ion was 13 mmol/g. An emphasis was also made on the study of the effect of the kinetic properties of sorbents on the sorption process. The maximum degree of thorium extraction by the sorbent was achieved from the solutions with pH 4. The time dependence of sorption was also studied. The results of the study showed that the sorption equilibrium is achieved after 2.5 h of contact of the sorbent with the metal. The sorption of thorium increases with an increase in the thorium concentration in the solution and attains maximum at a concentration of 8 × 10^–3 M (pH 4, = 8 × 10^–3 M, V_gen = 20 ml, m_absorbed = 0.05 g, sorption capacity = 348 mg/g). The degree of thorium (IV) extraction in optimal conditions exceeds 95%. It is shown that the main micro- and macro-components of clay do not affect the results of the determination of thorium. The developed technique was applied to determine thorium in a clay sample from the Shemakhi region of Azerbaijan. The correctness of the obtained results was confirmed by the spike test.

The lack of automatic control is a drawback of mine interferometric analyzers of methane and carbon digestion concentration in air. We present the results of developing an algorithm for automating the process of measuring the concentration of methane and carbon dioxide in air with a mine interferometric analyzer. An automatic determination of the shift of the interference pattern by the gas under study is proposed using an opto-electronic device. The main automated functions, i.e., control of the radiation source and electric pump, measurement channels and movement of the movable gas-air chamber along with processing of digital images of interferograms are implemented in a device with the metrological characteristics corresponding to the parameters of the mine interferometer SHI-11. The algorithm for digital processing of the interference pattern (interferogram) is implemented in the MATLAB package. The result of using the developed algorithm for measuring methane concentration showed the effectiveness and required accuracy of the procedure. Automation of carbon dioxide measurements provided for the appropriate calibration of the scale by loading the calibration coefficients into the memory of the microcontroller. The results obtained can be used to automate the determination of the gas concentration in air at the enterprises of oil and gas, chemical and mining industries.

The characteristics of gas turbine engines depend on the structural state of the material of the turbine blades and are largely determined by the technology of their manufacture. Identification of the specific defects of casting is an important goal aimed at improving the quality of blade castings since the castings of turbine blades with a monocrystalline structure made of high-alloyed nickel superalloys (NS) are subject to increased requirements for macro- and microstructure. We present the results of studying the effect of directional crystallization parameters on the morphology of the dendritic structure of NS and their tendency to form casting defects of the single-crystal structure. The structure of alloys in single-crystal blade castings and the effect of technological parameters on the dispersion of the structural components of NS were analyzed upon casting of turbine blades with <001> axial orientation on installations with liquid-metal cooling. It is shown that the parameters of the dendritic cells of castings vary in height from 220 to 330 μg and volume fraction of micropores changes from 0.02 to 0.2%. Electron probe microanalysis revealed that the phase and local elemental compositions of the alloy in the areas of the blade tip and isolated grains are identical. The appearance of isolated grains that violate the monocrystalline structure of castings is observed when the rate of NS cooling decreases. To increase the temperature gradient and reduce the probability of formation of extraneous crystals in castings ahead of the crystallization front, optimized temperature-speed modes of casting and directional crystallization are proposed. The obtained results can be used in the development of temperature-velocity parameters of the process of directional crystallization of blades of promising turbines made of new superalloys.

A probabilistic approach to assessing fatigue strength and cyclic life based on Wheeler’s model is presented. The approach provides the possibility of estimating the probability of failure of the structural component under consideration, with allowance for the effect of crack retardation after the overload. The initial crack size, the parameters of the Paris equation, and the exponent of the crack retardation power function are assumed random parameters. The kinetics of a fatigue crack is described by cycle-by-cycle integration of the Paris equation written in finite differences. The probabilistic estimate is performed using the Monte Carlo statistical simulation method by repeatedly solving the Cauchy problem for various combinations of the values of random model parameters that are generated under the adopted laws of the probability distributions of those parameters. The probabilistic distributions of random parameters are selected proceeding from the level of the uncertainty of the problem using available statistical data without taking into accounting for data on the actual state of a particular structural component in real operation conditions. A computer code in Matlab environment has been developed for statistical description of the fatigue crack growth in structural components which allows accounting for the effect of crack retardation. An example of assessing the probability of the fatigue failure of a pipeline component with a longitudinal crack on the inner surface loaded by the internal pressure which varies according to a periodic law with a constant amplitude is presented for single tensile overload of the pipeline component. The dependencies of the fatigue failure probability on the number of loading cycles for various combinations of model parameters were obtained. The sensitivity of the fatigue failure probability under a given number of loading cycles to changes of the values of structural parameters was assessed.

The rheology of the KhN55MVTs alloy has been studied at finite quasi-static strains and at operational and elevated temperatures to develop methods for calculating the emergency conditions of heat-stressed equipment. Some basic features of the stress-strain response of the alloy and the physical mechanisms responsible for them were revealed. Constitutive models are proposed to describe the most significant and crucial effects in assessing the structural integrity. The rheological properties of the alloy were studied under isothermal uniaxial compression within a temperature range of 24 – 1150°C with log-strains up to 1.0 and deformation rate of 0.001 – 0.125 sec^–1. The main deformation mechanisms have been revealed via optical microscopy. A constitutive model predicting the shape of stress-strain curves (a modification of the Bergström dislocation-based model of rigid-plasticity) is proposed which make it possible to obtain the rate and temperature dependencies of the mechanical properties. The dependence of maxima (peak values) of stresses on the deformation rate and temperature exhibits a non-monotonic character, while the yield stresses are weakly rate-dependent, and the linear slope is almost rate and temperature independent. The microstructure tests revealed the absence of a correlation between the softening stage and the onset of dynamic recrystallization process. No microcracks were found. Serrated flow and acoustic emission were observed within a temperature interval of 24 – 900°C probably attributed to dynamic aging (above 500°C), deformation twinning, and autowave effects during localization of the plastic strain. The proposed models of rheological effects differ from the existing dislocation models in a wider range of application — in terms of strain rates (10^–8 – 1,0 sec^–1) and temperatures (0 – 80% of the melting point). The rheological effects revealed in the experiments, analysis of their physical nature and constitutive description can be used in assessing failures of heat-stressed equipment and improving the methods for calculating emergency situations.

Over the years, housing has always been one of the basic human needs. Stones, clay, wood and cement are common construction materials. Currently, cement structures are highly solicited both in our country and all over the world. However, cement structures suffer from stress-induced cracks attributed to overloading. The study was carried out to find out the possibility of minimizing the crack formation and increasing the stability of cement structures to fracture. The goal of the study is to characterize the physical and mechanical properties of the cement mortar reinforced with oil palm mesocarp fibers (OPMF) to increase the crack resistance of the structures built with cement mortar, as well as to simulate nucleation and growth of cracks up to the fracture. Composition of the prepared samples differed in the content of OPMF: 0.25, 0.5, 0.75, 1, 1.25, and 1.5 of sand weight. Analysis of the physical and mechanical characteristics of the samples carried out after 7, 28 and 45 days revealed that the rate of water absorption increases in proportion to the increase in fiber content and ranges from 2.4 to 11.6. The three-point bending test was used to determine the flexural strength and Young’s modulus (YM) upon bending. The flexural strength and YM increase as the fiber content of the sample increases from 0 to 0.25 and then decrease. The maximum values of the flexural strength (5.475_MPa) and YM (283.633_MPa) in bending were obtained after 45 days on a sample containing 0.25_% fibers. The compression test was used to determine the compressive strength and YM under compression. The compressive strength and YM decrease with increasing fiber content in the samples. The maximum values of the compressive strength (23.18_MPa) and YM (310.044_MPa) were obtained for the sample containing 0 of fibers. Analysis of the destruction of organic fiber cement samples revealed that the crack propagation occurs by the mechanism of coalescence of micropores. Stochastic modeling carried out for different fiber content showed that the crack growth rate also increases in proportion to the increase in the fiber content. Thus, the main cause of fracture in compressive and bending tests is the viscous growth of the pores and ductile-brittle crack growth through the cement grains.

The problem of optimal control of a linear dynamic object in conditions of incomplete information about the initial data is considered. The approaches based on various models of the uncertainty description are analyzed. It is shown that the use of the approach based on a probabilistic model for describing uncertainty is advisable when the uncertainty is associated only with randomness, the description of other sources of uncertainty within this model is rather difficult and the formal application of the regression analysis provides the results that are far from true. Though the fuzzy model is suitable for describing a wide range of the uncertainty sources, application of the model faces methodological difficulties when comparing and ranking fuzzy numbers and smoothing fuzzy data. In this regard, it seems promising to use an approach based on an interval model which allows description of a wide class of uncertain and inaccurate initial data. To unify control algorithms for the systems described by equations of state of different types with interval-given parameters, we developed an algorithm of equivalent transformations that provides the transition to special forms of representing the state matrix while maintaining preservation of all the dynamic properties of the original system. The problems of constructing the range of values of the roots of the matrix of the system and its description by an approximation in the form of an interval vector are solved to ensure the implementation of the algorithm. An approach is proposed to solve the problems of terminal control and maximum performance, when the uncertainty of the initial data is described by the interval model and the apparatus of interval analysis is used to solve the problem. It is shown that in this case with the direct use of the classical formulation of the optimal control problem without taking the uncertainty into account, there is no single optimal control which guarantees the exact transfer of the object to the required final state for any value of the parameters from a given range of their possible values. Therefore, in the presence of the interval uncertainty of the initial data, the solution of the problem can’t be obtained in the sense in which it is understood with precisely known parameters and the approach to the formulation of the control problem itself should be revised in order to determine in the future a solution that ensures guaranteed accuracy of the system translation. In this regard, we propose to formulate the control problem in conditions of the interval uncertainty as a problem of determining the set of control actions that guarantee the solution with the accuracy set up to the interval, on the set of initial data known up to the interval. Using an example of the problem with an inaccurately known initial state, it is shown that if the set of possible initial states of an object belongs to a n-dimensional rectangular parallelepiped, then when implementing a control on an object calculated for any initial state from a given set, the set of final states is convex and represents a n-dimensional parallelepiped. To construct the parallelepiped, it is sufficient to determine the coordinates of the vertices corresponding to the vertices of the abovementioned n-dimensional rectangular parallelepiped. We propose a system of inequalities which determines the condition for the membership of a set of finite states of the object obtained upon implementation of control for any possible value of the initial state from a given set to the required set of finite states. On the basis of this system of inequalities, conditions are formulated that provide a priori determination of the solvability of the problem.