The effect of the salt composition of water (model aqueous solutions of NaCl and artificial sea salt Instant Ocean, as well as water from the Pechora Sea) on the effectiveness of oil spill dispersants determined in laboratory conditions is studied. The efficiency of dispersants (Finasol OSR 52, Slickgone NS and Slickgone EW) was evaluated three samples of crude oil produced in the Russian Federation. Those oil samples of different composition and properties were used at fixed values of the dispersant-oil ratio  (1:10), water temperature (20 ± 2°C) and salinity (35 ± 2%). It is shown that the effectiveness of the oil spill disper­sant depends on  the nature (composition) of water in which the oil is dispersed, other things being the same. An anomalous behavior of one of the oil samples was found when it was dispersed in an aqueous so­ lution of NaCl under the action of Finasol OSR 52 and Slickgone EW Good convergence of the numerical values of the efficiency of dispersants was obtained when testing them in an aqueous solution of artificial sea salt Instant Ocean and in the water of the Pechora Sea. It is noted that to assess the effectiveness of dispersants in laboratory conditions, it is advisable to use water of the natural object in which this disper­sant is planned to be used. Moreover, the possibility of using an aqueous solution of the artificial salt when its salt composition is similar to that for real sea water was noted.

We present the results of studying and selectiing optimal conditions for the determination of caffeine, catechins and gallic acid in black tea by the method of micellar electrokinetic chromatography. The choice of analytes is determined by the fact that they form the main consumer qualities of tea and, due to their antioxidant properties, have a positive effect on human health. Optimization of the electrophoretic detemination of seven catechins, caffeine and gallic acid in black tea was carried out using the method of ex­ periment design. Optimized conditions — 25 mM phosphate buffer solution with pH 7.4, containing 30 mM SDS and 5% ethyl alcohol — provided a satisfactory resolution of all electrophoretogram peaks, the analysis time was 25 minutes, and the current in the system did not exceed 120 pA. After the assessment of the metrological characteristics of the proposed method the standard deviation of the determina­tion of analytes did not exceed  15%. The  samples of black tea from Ceylon, Chinese, Assamese, Indian, Kenyan and Krasnodar regions of growth were analyzed, and an array of data on the contents of the analytes under study was formed. Discriminant analysis was used to develop a model and obtain classifica­tion functions for six tea groups from different regions of the world. Proceeding from the obtained classifi­cation functions, a scatter diagram of canonical values was constructed, which showed that the samples of Krasnodar and Chinese tea were localized from all the studied groups. Indian, Assamese and Ceylon teas formed a single area with close to the Chinese tea group. The correctness of the model was checked and revealed the total predictive force about 92%.  It is shown that the content of catechins, gallic acid and caf­feine are suitable markers for the classification of black tea samples from different regions of origin.

Biosensor devices including hybrid nanostructures as modifiers of transducer surfaces meet current requirements for the methods of research and determination of drugs, including antidepressants. The fea­tures of amperometric monoamine oxidase biosensors based on printed carbon electrodes modified with nanocomposite compositions C₆₀ / cobalt nanoparticles/amino derivative of polyether polyol of the second generation/chitosan nanocomposite structures used for the detection of tricyclic antidepressant amitriptyline are considered. The choice of the best modifier was made proceeding from the data of transmission electron microscopy, scanning electron microscopy, electrochemical impedance spectroscopy, and differential pulse voltammetry. When developing the biosensor, conditions for depositing the composite composition of cobalt nanoparticles/amino derivative of polyether polyol on the electrode surface were varied: electrochemical deposition, sequential layer-by-layer deposition, and deposition of the mixture. The peak of electrochemical oxidation of hydrogen peroxide, which is formed during the enzymatic reaction of serotonin oxidation under the action of monoamine oxidase was used as an analytical signal of the biosensor. The principle of the biosensor action is based on the inhibitory effect of amitriptyline on the catalytic activity of immobilized monoamine oxidase. The proper choice of a modifier and optimal working conditions provided the range of detectable concentrations of amitriptyline: 1 x 10^-4 - 1 x 10^-8 M, the lower limit of the determined content at a level of 5 x 10^-9 M for monoamine oxidase biosensor. Comparison of the results on the amitriptyline content determination in the pharmaceutical preparation and urine obtained using the monoamine oxidase biosensor and polarization fluorescence immunoassay (dilution of the tracer 1:32, dilution of antibodies 1:128, the range of working concentrations 5 x 10 ^-8 — 5 x 10^-9 M), well-proven in the quantitative determination of medicinal substance, confirmed the correctness of the results obtained.

Ceramic matrix composites (CMC) exhibit increased crack resistance and resistance to mechanical and thermal shock impacts retaining at the same time the valuable properties of monolithic ceramics. Therefore, they are widely used as parts of heat-loaded elements of aviation and rocket technology, in nuclear power industry, etc. LPI-method (liquid polymer infiltration) of CMC production is based on the impregnation of a skeleton of ceramic fibers with an organosilicon polymer, formation of a preceramic matrix by polymer technology, and subsequent high-temperature pyrolysis resulting in formation of a reinforced ceramic matrix. Ceramics obtained from polymer precursors have a predominantly amorphous structure which determines its high thermal stability. Moreover, introduction of the nanosized particles of carbides, borides and nitrides of refractory metals (Zr, Ti, Hf) into the matrix of a ceramic composite stabilizes its amorphous structure up to temperatures of 1500 - 1600°C. We present the results of studying the preceramic compositions based on polycarbosilane and polyorganosilazanes modified with Hf and Ta atoms. It is shown that introduction of the modifying additives Hf and Ta into the polyorganosilazane composition shifts the curing interval of the compositions towards lower temperatures. The yield of the gel fraction is 73.3 and 82.7 wt.%, respectively. The weight loss of pyrolysate samples heated to 1400°C in air does not exceed 0.5%. The physical and mechanical properties, as well as the thermal oxidative stability of novel ceramic composite materials obtained on the base of the studied compositions and carbon reinforcing filler are analyzed. It is shown that the density of CMC samples increases by 1.5 times with an increase in the number of impregnation cycles and reaches the maximum value of 1950 kg/m³ with five impregnation cycles of the filler with a composition based on polyorganosilazane modified with Ta. The results obtained can be used in the development of new CMCs.

Thermodilatometric methods of analysis are used to study the structural parameters of polymer materials, however, when studying moisture-saturated compositions certain difficulties arise in their identification. The results of thermophysical tests of VKU-25 carbon fiber samples in the initial state and after moisture saturation are presented. It is shown that heat treatment of materials affects the recorded values of the glass transition temperature of the epoxy matrix. When the samples are exposed in water or above the water surface, the sorbate penetrates into the polymer at the same rate, which is confirmed by almost identical values of water absorption at the same exposure time. The estimates of the thermal coefficient of linear expansion (TCLE) of the samples in the range of 20 - 250°C are given. Moreover, it is shown that the glass transition temperature of the plasticized polymer matrix depends on the direction of fiber reinforcement. In the case of moisture-saturated carbon fiber (CF)heated to 210°C, the formation of main cracks occurs mainly at the fiber-matrix interface. The glass transition temperature (GTT) of the material in the dry state (176 - 177°C), appeared almost independent on the heating rate, whereas for water-saturated samples, GTT changes significantly and can be described by a polynomial of the 2nd order. After exposure of the carbon fiber under conditions of high temperature and humidity, two relaxation transitions corresponding to the systems occur in the polymer matrix: epoxidian oligomer— amine hardener and polyfunctional resin— amine hardener. The glass transition temperature is 132 and 159°C in the first and in the second, respectively. The results obtained can be used in the development of new polymer composite materials.

Discontinuities in the products that occur during manufacture, mounting or upon operation can be missed during non-destructive testing which do not provide their complete detectability at a current level of the technology. Therefore, it is necessary to take into account that certain structural elements may have discontinuities of significant dimensions. We present the results of using the methods of probability theory in studying the residual imperfections that remains in the structure after non-destructive control and repair of the previously identified defects. We used the results of operational control of units carried out by ultrasonic and radiographic methods. We present a method for determining a multifactorial coefficient that takes into account the detectability of defects, the number of control procedures and the errors in the instrumentation and methodological support, as well as a generalized equation for the probability distribution of detecting discontinuities. The developed approach provides assessing of the level of damage to the studied objects, their classification proceeding from the quantitative data and determination of the values of postulated discontinuities for deterministic calculations. The results obtained can be used to improve the methods of monitoring NPP facilities.

This article covers the development of methodological issues, software, experimental equipment, and practical application of the method of sequentially increasing cracks for studying inhomogeneous high-gradient fields of residual stresses (RS) that occur in areas of structural heterogeneity in flat construction parts (e.g., welded joints). Method of electronic speckle pattern interferometry (ESPI) is used to detect the deformation response in the form of the fields of displacement of the surface of the object under study arising from formation of successively increasing crack. ESPI provide contactless registration of movements directly in a digital form with high accuracy. The scheme of a specialized interferometer is described along with the features of the procedure for registering the displacement fields arising from a stepwise increase of the crack length. A return device provided removing of the object under study out of the optical zone and then return it to the initial position after performing the necessary mechanical operations. The accuracy of the procedure for calculating RS is estimated on the basis of mathematical processing of the experimentally obtained dependences of SIF on the crack length. An example of using the developed methods, equipment and programs for studying the RS distribution in stir welding joint of the sheets of aircraft alloy 1163T with a high level of crack resistance is given.

The evolution of the structure and assessment of the age limit of steel 12Cr18Ni10Ti upon fatigue loading is considered using neural network modeling and approaches of fractal analysis of the microstructure. An algorithm for processing images of the microstructures has been developed to improve their quality. An indicator of the fractal dimension of the image is used as a quantitative indicator for assessing the evolution of the microstructure of the surface metal layer. A quantitative assessment of the structures at different stress amplitudes is carried out in a wide range of low temperatures using the fractal dimension index. Correlation of the fractal dimension index with the run of the sample material is shown. The appearance of the main crack was observed in the range of 0.7 - 0.8 from the number of cycles to failure, after which the crack growth rate increased. At a lower temperature, the main crack is formed later, but further loading results in a higher crack growth rate. Formation of the secondary phases in austenitic steel at a lower temperature occurred at earlier stages than that at a temperature of t = +20°C, which led to hardening of the material. An artificial neural network (ANN) has been developed and trained for assessing structural changes in metal proceeding from the fractal dimensionality of the microstructure images at different stages of fatigue loading. The developed neural network made it possible to estimate with a sufficiently high accuracy the number of cycles before damage of the sample and the residual life of the material. Thus, the developed ANN can be used to assess the current state of the material in a wide range of low temperatures.

Three variants of the engineering solution of inverse problems regarding the strength of pipeline sections bent as a result of ground movements or during an earthquake are proposed. The feature of this approach consists in calculation of stresses not by the forces acting on the pipe, but by the displacements or deflections. Therefore, full-scale measurements of the detected deviation of the pipe position from the planned pipeline route should be taken as initial data for estimating the values of additional bending stresses. The first problem considered is the assessment of the risk of pipeline malfunction upon sagging or bulging of the supports of aboveground pipelines. The problem is solved in the beam approximation. The pipeline is considered a statically indeterminate beam, one of the supports of which is forcibly moved to a given distance. For a once statically indeterminate beam, a system of four equations — two equilibrium equations and two integral equations for deflections — was solved numerically. The calculated values of three reactions of the supports and the angle of rotation of the pipe section on the first support are used to calculate bending moments, stresses and deflection lines. The problem for a thrice statically indeterminate beam under strain loading was also solved. The second goal is to model the stress-strain state of the pipeline proceeding from the tables of experimental data on the values of pipe deflections and their coordinates. The problem was also solved numerically, using the procedures of smoothing, linear interpolation and sequential differentiation. It is shown that taking into account the possible ambiguous solution of the inverse problem, we should not rely on the calculated values of transverse forces and distributed loads. It is enough to limit ourselves to the second coordinate derivative of the deflection. The third goal is to prevent accidents at the design stage. It is proposed to create a list of normalized deflection functions for modeling possible emergency situations for pipeline sections placed in difficult ground-geological conditions and seismically dangerous zones. The examples of such functions are given.