The development of simple and rapid methods for determining various biomarkers in blood plasma is necessary both to ensure prompt monitoring of the functional state of athletes and to validate new biomarkers. In particular, the key transmethylation intermediates S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) are considered to be potential early markers of impaired long-term adaptation of athletes to physical exertion. A technique for the determination of these compounds in blood plasma by liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) has been developed: acceptable conditions have been found to ensure a balance of sensitivity, selectivity and expressiveness of the analysis. For chromatographic separation of the determined metabolites under gradient elution conditions, a Zorbax Eclipse XDB-C18 reversed-phase column and a water-methanol mixture as the mobile phase were used. The values of the declusterization potential have been optimized, fragmentation of SAM and SAH precursor ions has been studied, and the effect of collision energy on the signal intensity of characteristic fragment ions has been investigated. Product ions with m/z 250 and 136, respectively, were selected to determine SAM and SAH. The metrological characteristics of the developed technique and the matrix effect in the determination of analytes are evaluated: the limit of quantification of SAM and SAH is 1 ng/mL, the linear dynamic range is 1 – 500 and 1 – 1000 ng/mL, respectively. The correctness of the technique within a separate series of analysis and between series was confirmed by analyzing samples of known composition. The duration of the analysis does not exceed 4 min.

An electrochemical method for the determination of sulfur-containing compounds in motor fuels using square-wave voltammetrys developed. The relevance of the research is driven by increasingly stringent environmental regulations governing sulfur content in gasoline and diesel fuels in accordance with the Euro 5 and Euro 6 standards. Carbon-based electrodes fabricated by screen-printing on a dielectric substrate and modified with a bismuth film were employed as sensing elements. The use of such electrodes ensures environmental safety and high reproducibility of analytical characteristics. The conditions for bismuth electrodeposition used to modify the voltammetric sensor were optimized by means of cyclic voltammetry and electrochemical impedance spectroscopy. Model solutions of dibutyl sulfide were used plotting the calibration curve. It has been shown that preliminary accumulation of the analyte for 60 sec increases the sensitivity of determination by 30%. The detection limit calculated according to the 3σ-criterion was 0.05 mg/L, relative standard deviation did not exceed 10%. The developed technique has been tested in the analysis of real samples of gasoline with different octane ratings and diesel fuel. The obtained sulfur contents allowed as to classify all the samples as Euro 5 class. A comparison of the obtained results with those derived from potentiometric titration and X-ray fluorescence analysis according to ASTM D2622 showed good agreement. The developed electrochemical technique can be used for rapid and reliable quality control of motor fuels in both production and analytical laboratory environments.

An overview of the information indicated in the passports of reference materials (RM) or certified reference materials (CRM) from the world’s leading manufacturers for the substances of anticoagulant rodenticides of the 4-hydroxycoumarin series is presented. Most of the characteristics in the passports are presented without taking into account uncertainties and specifying the methods by which the values given were obtained, which does not allow researchers to unambiguously assess the validity of the substance, and the quantity of the standard sample does not allow the consumer to reproduce at least some of these characteristics. As an alternative, the use of technical substances for the analysis of rodenticidal product products is considered. The stages of the input control procedure are proposed as part of the supplier assessment, which would take into account the specifics of the substances under consideration (tautomeric transformations, polymorphism, and rich isomeric composition). Using the example of the dif-nakum substance, the nonequivalence of the spectral characteristics of cis/trans isomers is demonstrated, which must be taken into account when using spectrophotometric or fluorimetric detectors. It is noted that the determination of the isomeric ratio is an important characteristic of the substance and is indicated in the passports for technical substances, but not in the documentation for standards, and this limits the use of the additive method in the analytical determination of the substance. It is proposed to provide the ISI testers with a sample of the technical substance from which the test sample was prepared, indicating in the research assignment the concentration range and the possible range of substances used. In this case, the participants of the ICI have the opportunity to carry out a full-fledged entrance control, confirm the authenticity of the substance, and then quantify its content in the assessment sample. The information provided is of interest both to manufacturers of rodenticide products and to potential providers of interlaboratory benchmarking tests, manufacturers of standard samples of pesticides and laboratories engaged in the analysis of products in the field of «pest control».

Eddy current testing of the quality of soldering of current-carrying joints of stators of hydro- and turbogenerators is carried out when commissioning new units, as well as after their scheduled repairs. The objective of this study is to investigate the specific electrical conductivity of connecting strips of current-carrying joints made of M1 copper semi-finished products and to eliminate the influence of adjacent joints on the testing results. When hot-rolled busbars are used as connecting strips in current-carrying joints of turbogenerator stator windings, significant variability (from 2 to 4.4%) in their electrical conductivity across their thickness and from product to product is observed. The error in determining the solder integrity of sidewalls using an eddy current transducer (ECT) can reach 52.8%. This must be taken into account when developing eddy current testing tools for soldering such joints, with electrical conductivity determined at the same frequencies at which the testing will be performed. It has been demonstrated that conductivity variability does not affect solder quality testing results when inspecting current-carrying joints in hydrogenerator stator windings, as the current-carrying rods and connecting strips in this case consist of soft copper busbars manufactured from rod using the upward casting method. However, the influence of adjacent connections on the ECT signals is significant. A method for eliminating this influence is proposed, consisting of shielding the ECT windings with a two-layer screen made of transformer steel. The obtained results can be used to improve the reliability of solder joint inspection in power equipment and to refine the methodology for use with other types of connections, as well as in conditions of complex electromagnetic interference.

Ceramic materials based on aluminum oxide (Al₂O₃) are widely used in industry due to their unique combination of high hardness, thermal stability, and chemical inertness. The objective of this work is to review studies on the performance characteristics of ceramic cutting tools based on aluminum oxide. Key factors determining tool performance were examined, including the chemical purity of starting powders, composition modification of ceramics tailored to operating conditions, material microstructure (grain size, porosity, grain boundary state), and residual stresses arising during sintering. It is demonstrated that the wear resistance of Al₂O₃-based ceramics is primarily governed by the stability of grain boundaries (absence of amorphous phases and pores located along grain boundaries). Hardness, which depends on grain size, also exerts an influence. It was found that the lowest wear occurs in ceramics with grain sizes of 0.4 – 0.65 μm. A procedure for evaluating ceramic strength is proposed, incorporating the calculation of critical stress required for crack propagation along grain boundaries. It was established that, following grinding, the strength of conventional sintered ceramics increases by 30%, whereas the strength of ceramics sintered in a hydrogen atmosphere decreases by 10%. The research findings can be applied to develop new methods for controlling grain boundary structure and mitigating the impact of structural defects on the performance characteristics of ceramic cutting tools.

Anisotropic thick films of hexagonal barium ferrite BaFe₁₂O₁₉ are used in the design and manufacture of microstrip microwave electronics devices, spinwave electronics devices and magnonics. The aim of the work is to study the crystal structure and magnetic properties of BaFe₁₂O₁₉ films of different thicknesses. The films were obtained by the method of slip casting. The starting material is ferritized barium hexaferrite powder synthesized using standard ceramic technology. Polyvinyl butyral was used as a film-forming agent, ethyl alcohol, butyl acetate and dibutyl phthalate were used as solvents. The ratio of BaFe₁₂O₁₉ powder to solvent film-forming agent was 70/30, and the thickness of the obtained films after sintering was 73, 340, and 770 μm. X-ray phase analysis of the samples was performed using an automated X-ray diffractometer DRON-4, the magnetic hysteresis loops of the study objects were recorded at room temperature. It is established that the main phase of the films is barium hexaferrite (crystal lattice parameters: a = 5.88 Å, c = 23.19 Å). The impurity found on the diffractograms probably refers to the film-forming agent and solvent. It is shown that the coercive force of the synthesized films is ~3 kOe, the residual specific magnetization is 20 – 26 emu/g, and the degree of magnetic texture is in the range of 10.98 – 15.7, which indicates the anisotropy of the samples. The results obtained can be used in the manufacture and improvement of devices for magnetoelectronics, microwave microelectronics, as well as spinwave electronics and magnonics.

In use of technical systems and impact on them total loadings, physical fields and corrosion environments initiation in zones of high concentration of stresses of their elements not only fields of stresses and strains, but also fields of damages takes place. At the same time depending on conditions of loading and environment various mechanisms of damages accumulation and fracture are realized. Among these mechanisms are the most dangerous such which taking into account of long static and thermomechanical cyclic loading lead to catastrophic (avalanche) fracture. At the same time identification and analysis of physically connected specificities of not isothermal and statistical mechanisms of accumulation of damages to material plays a very important role when forming criteria of achievement of various types of limit states which are described by the corresponding state equations with the parameters of criteria characteristics of mechanical properties of materials entering them. It is shown that in the direction of working out of materials criteria base of structural strength and technogenic safety justification of models of damages summation at complex impact conditions of the damaging operational factors is perspective. At the same time in addition to standard characteristicses of mechanical properties of structural materials it is necessary to include in the content of criteria base of structural materials science characteristicses of crack resistance, fatigue, cold resistance, corrosion resistance, characteristics of resistance to elastic and plastic strains, characteristics of cyclic hardening, softening and stabilization of material at repeated elastoplastic deformation in the wide range of temperatures of operational loading. New, perspective integrated criteria of safety of operation of technosphere objects is the criteria of unacceptable (critical) technogenic risk considering on the basis of criteria base of structural materials science probability of initiation to them of damages, refusals, fractures, emergency and catastrophic situations at all stages of a lifetime at design, beyond design basis and hypothetical situations.

The study presents the methodology and results of investigation into the viscoelasticity of polymethyl methacrylate (PMMA) and polyamide PA-6 in tensile and compressive testing. The experiments enabled the separation of the volumetric and deviatoric components of the strain tensor. A significant dependence of the shear modulus and a weak dependence of the bulk modulus on hydrostatic stress were revealed. The features of PMMA viscoelastic deformation were studied over a wide range of operating temperatures. It was found that the ratio of the elastic and viscous strain intensities is weakly dependent on both hydrostatic stress and temperature of the medium. Constitutive equations are presented for viscoelasticity under a volumetric stress state at various combinations of elastic and viscous strain rates in the stress range from the creep limit to the forced elasticity limit, as well as during recovery after complete unloading. The equations do not explicitly include time and accumulated viscous strain, so they are applicable to processes with arbitrary strain or stress growth patterns. Comparison with experiment confirmed the high modeling accuracy of viscous PMMA deformation for prescribed law of elastic strain change. Several successive stages of viscoelastic deformation during loading and subsequent unloading were revealed. At the first stage, viscous strain does not increase, at the second stage, it increases only with increasing load, at the third stage, it also increases under constant load. Upon load reversal, the viscous strain rate decreases to zero, then changes sign and increases, approaching the elastic strain rate. The developed mathematical apparatus is intended for modeling the cyclic alternating loading of a spherical shell with internal and external pressure under operating conditions of a manned submersible vehicle.

For mechanical multi-cycle tests and fatigue strength studies of steel specimens, a simple portable bench unit has been created. Such tests are especially relevant in the study of specimens obtained with the help of additive technologies, which have specific features due to the specific production technology, consisting in the construction of the finished product by layer-by-layer build-up of powder material. The most convenient scheme of cyclic loading of the test specimen based on cantilever bending and possessing a number of advantages: simplicity of realization, testing performance, relatively low cost, adaptability and variability to loading conditions and additive technologies research, versatility, etc., was used when creating the stand. The block diagram of the stand, its appearance, the shape of the specimen loading cycle are presented, and the operation of the portable stand is described. The micromagnetic method — the Barkhausen effect method, which is closely related to the domain structure of the material, was used as a method for studying the kinetics of fatigue damage accumulation in the samples. Multi-cycle bending tests were carried out on specimens made of 09G2S low-alloy structural steel manufactured in accordance with GOST by additive technology (by selective laser fusion/sintering) and by casting. Experimental dependences of the influence of the number of loading cycles on the intensity of magnetic noise in the samples of one of the batches at low stress amplitude in the range of loading cycles variation from 1.5 × 10⁶ to 6.9 × 10⁶ are presented, as a result, the performance and efficiency of the stand are demonstrated. The bench allows to test small-sized specimens and to study in detail the process of fatigue damage accumulation with the growth of the basic value of the number of loading cycles and has the ability, if necessary, to set the required loading algorithm for multi-cycle tests and can be used in factory and laboratory conditions.