Capillary electrophoresis, using capillary electrokinetic chromatography, was used for the simultaneous quantitative determination of the dipeptide GSB-106 and sodium hyaluronan with a molecular weight of 130 kDa in a dosage form developed for intranasal delivery of the peptide to the central nervous system. An optimized leading electrolyte composition was established: 15 mM sodium tetraborate and 15 mM sodium dodecyl sulfate. With positive polarity, the peaks of both components on the electropherogram are located in the anion region. The electropherogram development time is 10 min. The developed method enables the selective determination of both components of the nasal formulation with sensitivity sufficient for spectrophotometric detection (8.8 μg/mL for GSB-106 and 76.2 μg/mL for hyaluronan). The efficiency of determining both components was estimated using the number of theoretical plates and was ~13,000 for GSB-106 and ~5500 for hyaluronan. The practical application of the method was demonstrated using the nasal dosage form of GSB-106, which is based on hyaluronic acid. The method can be successfully applied to the analysis of similar hyaluronic acid-based formulations containing peptides.

The use of refractory materials is necessary in various metallurgical units for the production of high-quality steel, such as casting ladles, furnace lining layers to protect against high temperatures and aggressive chemicals during metal processing. The most common refractory materials are magnesia-carbon, aluminum-magnesium-carbon and aluminum-spindle bricks. The problem of oxidation of carbon-containing refractories based on Mg and Al oxides is the main factor affecting their service life. The most effective way to inhibit carbon oxidation in carbon-containing refractories is the addition of antioxidants — metal powders of Al, Mg, Fe and Si. When characterizing refractory materials, bulk analysis methods are usually used, since the selective determination of metal additives is difficult. An approach to the selective determination of metal additives-antioxidants Al, Mg, Fe and Si in refractory composites based on magnesium and aluminum oxides has been developed. The conditions of selective separation of additives in the presence of their oxides, such as the concentration of reagents and the temperature of sample preparation, are investigated. To determine Al and Si, the additives are extracted by dissolving the samples in 1 M NaOH (30 – 60°C), Mg — by 1 M NH₄Cl (30°C), and Fe — by adding 10% CuSO₄ solution when heated. The trueness of the obtained results was confirmed by the recovery test of model mixtures. It is shown that further determination of Al, Si, Mg, Fe is possible by inductively coupled plasma atomic emission spectrometry (ICP AES), as well as by a cost-effective photometric method according to GOST with s_r of no more than 0.05 in an industrial laboratory. The obtained results of the determination of antioxidants in materials were used to study their wear resistance at the enterprises of PJSC Severstal.

Due to its ability to inactivate microorganisms and viruses, β-propiolactone is widely used as a sterilizing and disinfecting agent, as well as an inactivating component in the production of antiviral vaccines. In this regard, it is necessary to control the composition of the finished commercial β-propiolactone. For this purpose, a technique for gas chromatographic determination of the main component and impurities in the synthesis product of β-propiolactone is proposed. The content of related impurities, the main of which are acetic and acrylic acids, acetic anhydride, methylene diacetate and 2-methyl-β-propiolactone, in samples is calculated by internal normalization by peak areas, and the content of the main component is calculated by the mass balance method. During validation, in accordance with the general article of the State Pharmacopoeia of the Russian Federation, the main metrological characteristics of the developed technique were evaluated: the limit of quantification for impurities was less than 0.01%, the linear dependence of the analytical signal on the concentration of the solution was observed in the range of a single impurity content from 0.0016 to 5.0%, the repeatability value was no more than 5.0%, the intermediate precision value was no more than 10.0%, the recovery of a single impurity is in the range from 89.5 to 114.5%. In accordance with the regulated requirements, the obtained values of the key parameters of the technique (specificity, limit of determination, linearity, repeatability, intermediate precision and trueness) are acceptable, which allows it to be used to assess the purity of the finished β-propiolactone at its content from 95 to 100%. The developed technique can be recommended for use in the release control of β-propiolactone.

This research focused on optimizing experimental conditions to achieve maximum spectral absorption in the determination of methyldopa. The results demonstrated adherence to Beer – Lambert’s law with excellent linearity within concentration range of 5 – 40 μg/mL and a high coefficient of determination (R², approximately 0.9992). The structural formula of the resulting-colored complex was determined using Job’s method and molar ratio analysis, confirming a 1:1 covalent ratio between the reagent and the drug. Stability constant analysis revealed high chemical stability of the resulting complex, enhancing the accuracy of spectroscopic measurements. The proposed method was successfully applied to the quantification of methyldopa in pharmaceutical formulations (tablets) from various sources, achieving recovery rates of up to 100%, reflecting high precision and selectivity. The values of the LOD (0.495 μg/mL) and LOQ (1.5 μg/mL) demonstrate the high sensitivity of the analytical method used. The fact that these values fall below the approved linear range confirms that the laboratory measurements were performed in a safe area and far from the analytical error limits. The study concludes that this method is a reliable, economical, and suitable analytical tool for quality control and routine pharmaceutical analysis.

Ternary and quaternary alloys based on the Dirac semiconductor Cd₃As₂ with atomic or mesoscopic ferromagnetic inclusions are among the most promising functional materials for spintronics. The aim of this study was to investigate the electrical and magnetic properties of the quaternary alloy α’’-Cd_2.76Mn_0.24As2(MnAs)_0.25. Tests were conducted in the temperature range of 4 – 300 K. Melting was performed using the vacuum-ampoule method from high-purity elements As, Cd, and Mn based on data from the triangular phase diagram of Cd₃As₂ – MnAs – CdAs₂. X-ray diffraction, differential thermal analysis, and microstructural analysis revealed that α’’-Cd_2.76Mn_0.24As₂(MnAs)_0.25 consists of 0.8 M of ternary α’’-Cd_2.76Mn_0.24As₂ alloy with ferromagnetic nanoinclusions of 0.2 M of MnAs. Furthermore, the studied composite is a soft magnetic ferromagnet (coercivity less than 10 Oe) with a Curie point of 328 K and metallic conductivity. The n-type conductivity and significant positive magnetoresistance indicate the predominant influence of the Dirac topological semimetal on the conductivity of the composite. This is evidenced by the effect of weak self-trapping and the diamagnetic response of the conduction electrons of Cd₃As₂. Moreover, the presence of an anisotropic linear magnetoresistance effect indicates the influence of the magnetic moment of the transition Mn cation in the MnAs ferromagnet on the conductivity of the composite. In weak magnetic fields, the material exhibits spin-glass behavior with a spin-glass freezing temperature of 240 K. These results can be used, for example, in the production of precision temperature or magnetic field sensors based on α’’-Cd_2.76Mn_0.24As₂(MnAs)_0.25.

Polyaniline is widely used in the fabrication of organic field-effect transistors. The aim of this work is to investigate the electrophysical properties of organic field-effect transistors based on thin films of polyaniline and its derivatives. During the experiments, the current-voltage characteristics and device parameters measured in an inert atmosphere (nitrogen) of a glove box and in air at room temperature were compared. It was shown that, for bottom-gate top-contact transistor structures exposed to oxygen, the hole mobility decreases significantly (by a factor of 3 – 9), while the maximum drain-source current also decreases. At the same time, a positive shift of the threshold voltage is observed, and the switching speed decreases noticeably, which complicates the direct application of such devices without protection. It was also established that the oxygen stability of the active layer critically depends on the presence of embedded donor-acceptor groups and morphology. The revealed oxygen-induced degradation mechanism consists in the formation of trap states and partial protonation of the surface layer. The obtained results may be used for improving the fabrication technology of stable organic field-effect transistors based on polyaniline.

The development of effective and environmentally friendly ways to reduce oil viscosity is an urgent task for the oil industry. The purpose of the work is to study the properties of oil under thermal, electrostatic and electromagnetic influences. The viscosity of the oil was analyzed using an original experimental setup that allows thermal, electrostatic, and electromagnetic fields to be created in a certain volume. The characteristics of the electromagnetic fields were determined by the EMF induced in the measuring coil placed in the working area. The polarization properties of the Samotlor oilfield were investigated. The densities and viscosities of the samples were measured as a function of temperature and electrostatic and electromagnetic influences. It is shown that the decrease in density and viscosity increases when electrostatic and electromagnetic fields are applied. An increase in the mobility of molecules leads to a weakening of intermolecular forces and a decrease in the viscosity of the reservoir’s oil-containing liquid fluids. This is due to the fact that oil molecules — dipoles — perform forced synchronous oscillations under the influence of an external alternating field. At the same time, alternating conduction currents flow in liquid fluids, which leads to the release of Joule heat in the collector. It has been revealed that the effect of thermal and electromagnetic fields on oil reduces viscosity by 1.5 – 2 times. The results obtained can be used to improve methods for reducing oil viscosity to increase oil production.

The present paper is devoted to the comprehensive study of the effect of crystallographic mesoscale texture (CMT) in the critical zone of titanium disks in the aircraft engines low-pressure compressor first stage on the kinetics of low cycle dwell fatigue (LCDF) cracks in the start-stop cycles. The theoretical basis of the study is the previously developed concept of fatigue crack kinetics stages and model of their stable growth. In the process of fractocrystallographic studies, using high-resolution scanning electron microscopy and electron backscatter diffraction, a relationship was established between the CMT parameters, the kinetics of the LCDF cracks and the microrelief of the fracture surface (fractorelief). An unfavorable CMT (UCMT) has been identified, which consists the mesoscale clusters of the α-phase with predominant orientation of the basal plane (0001) normal to the direction of the crack driving stress. In the UCMT clusters, the LCDF crack propagates in the basal plane under the action of the low-energy mechanism, which leads to rapid crack growth and the fractorelief formation in the form of microcleavages. The kinetics of the LCDF cracks in the presence of UCMT was fractographically reconstructed and compared with their stable growth (in the absence of UCMT). The influence of two types of UCMT detected in critical zones of the disks on the LCDF crack growth period has been assessed. UCMT in the form of quasi-plates located across the crack growth direction led to reduction of the crack growth period (compared with the its stable growth) by half, and UCMT in the form of quasi-fibers — by seven times.

To ensure the operation safety and to extend the durability of engineering systems, it is necessary to develop a methodology for experimental and computational experimental studies of material fracture. The first review part of this article presents the results of an analysis of known approaches to accelerated fatigue testing; methods of high-frequency longitudinal and transverse vibrations to determination of experimental fatigue curve depending on the loading frequency; and modern equipment and measuring technologies. The authors of the analyzed papers consider the «resonant» frequency of oscillations of all testing machine and specimen power elements equal to the first own frequency of oscillations under the boundary condition of free ends. Based on this, the «resonant» length of the specimen is calculated. The purpose of this work is to show that so-defined «resonant» frequency is not resonant. The formulations and solutions of the corresponding problems of elasticity theory for a straight cylindrical rod are given in the article second part. It is shown that the «resonant» frequency is located in the midway between the first and second resonant frequencies of specimen free vibrations with one end clamped. The example illustrates that maximum stresses may be in the clamped section, distributed irregular along the rod length depending on the oscillation frequency and specimen length, and it is possible the case of maximum stresses of opposite signs in several specimen sections. The sample length is selected to provide zero displacements and maximum stresses in the sample center. Resonant vibrations with finite displacements are not considered in this work. It can be noted that the effect of energy dissipation on the stress-strain state of oscillating bodies is significant only in resonant zones with a considerable increase of displacement amplitude, and so in the considered cases this effect can be assumed small.

This study examined the dependence of the mechanical properties of secondary carbon fibers obtained by pyrolysis of carbon fiber-reinforced plastic waste on the oxygen content in the pyrolysis furnace. The study was conducted in a continuous-action pilot pyrolysis furnace, with three temperature zones set along its length by an automatic temperature control system: the first pyrolysis zone, the transition zone, and the second pyrolysis zone. The test material was ASM 102-C00T woven prepreg made from UMT42S-3K-EP carbon fibers containing 38% ASM 102 thermosetting binder. The oxygen content in the furnace working space was varied by changing the feed rate of the material, using the relationship between the weight of the processed carbon fiber reinforced plastics and the volume of gases released during the pyrolysis process, which displace oxygen from the gas environment and thereby change its content in the furnace working space. It was found that, at atmospheric oxygen content in the furnace gas environment, the tensile strength of secondary carbon fibers is approximately 55% of the initial value. As the oxygen content decreases, the strength increases, and a mechanical property level of ~90% of the initial value is achieved with an oxygen content in the second pyrolysis zone of less than 16%. However, at an oxygen content of less than 12%, sintering of carbon fiber monofilaments with coke residue occurs, which significantly reduces the textile properties of secondary carbon fibers. It has been established that the optimal coke residue value is no more than 7%. The elastic modulus of secondary carbon fibers is slightly dependent on the oxygen content and is close to the initial value.