The development of analytical techniques is required for the accurate and comprehensive detection and measurement of antibiotic contamination in the environment. Metronidazole is a common antibacterial, antiprotozoal, and antibiotic drug. Thiamine is a vital biological and medicinal ingredient that is involved in the metabolism of proteins, fats, and carbohydrates that produce energy. The study aims to identify the drugs in a mixture without separation to provide more information to confirm if a drug is present in a combination. Metronidazole and thiamine are two examples of pharmaceutical and environmental samples that can be identified using spectrophotometric techniques because of their low cost and simplicity of use. The operating solutions of both drugs were used to scan the UV spectrum between 200 and 400 nm, and the corresponding overlay spectra of the two drugs were recorded. The best absorption peak at 264 nm is exhibited by thiamine, which is observed in the presence of metronidazole with the peak at 320 nm in the suggested method. The working curve for metronidazole and thiamine was set to obey the Beer – Lambert law in the range of (1 – 15) μg/mL for each of them, with molar absorptivity values of 12716.89 and 2053.22 liter/mol/cm for metronidazole and thiamine, respectively. Thiamine and metronidazole showed results in the recovery study that ranged from 99.1 to 100% across three concentrations. For thiamine and metronidazole, the precision study was conducted using estimates of RSD 0.29 and 1.09. The suggested method yielded a relative error of less than 5% when used correctly on pharmaceutical forms. The proposed approach can be used in future research to directly identify the drugs in a mixture without having to separate them.

The chemical composition of solid solutions samples in the SrSO₄ · 0.5H₂O – KCe(SO₄)₂ · H₂O system, synthesized by coprecipitation from aqueous solutions of KNO₃, Sr(NO₃)₂, Ce(NO₃)₃ and H₂SO₄ was studied using X-ray fluorescence analysis. Power approximation functions of calibration dependences of concentration on intensity were used to determine the content of potassium, strontium and cerium (III) sulfates. The coefficients of calibration dependences and their metrological characteristics, such as standard errors s_e and determination coefficients r², were calculated using the least squares method. In the range of determined concentrations (% wt.) K₂SO₄ 5.324 – 22.54, SrSO₄ 11.10 – 89.26, Ce₂(SO₄)₃ 9.243 – 73.32 the standard error for concentration estimation was 0.03, 0.01, 0.02, respectively. The chemical composition of solid solutions was described by the assumed formula K_xSr_{2 – 2x}Ce_x(SO₄)₂ · H₂O, where 0 < x < 1. The X-ray difraction analysis confirmed the presence of a wide existence region of stable solid solutions formed by unstable isostructural trigonal phases SrSO₄ · 0.5H₂O and KCe(SO₄)₂ · H₂O. Stabilization of solid solutions was achieved as a result of heterovalent substitution of cations 2Sr²⁺ ↔ Ce³⁺ + K⁺ in a sulfate anion ambience. Cascade diffraction patterns of 12 solid solution samples and 4 individual compounds — orthorhombic modification of SrSO₄, trigonal modifications of SrSO₄ · 0.5H₂O and KCe(SO₄)₂ · H₂O, monoclinic modification of KCe(SO₄)₂ · H₂O — were presented in this article. The arrangement of reflections in the diffraction patterns of SrSO₄ · 0.5H₂O, KCe(SO₄)₂ · H₂O and solid solutions was completely identical. When changing the chemical composition of solid solution samples, the unit cell parameters remained virtually unchanged. The obtained results indicated the fundamental possibility of using X-ray fluorescence analysis for accurate determination of chemical composition of solid solutions samples in SrSO₄ · 0.5H₂O – KCe(SO₄)₂ · H₂O system.

According to the requirements of GOST ISO/IEC 17025–2019, accredited laboratories must use methods that have previously been validated or verified and calculate the extended uncertainty of measurement results in order to obtain reliable results of analysis. The extended uncertainty of the results of the iodometric determination of sulfur in accordance with GOST 32599.2–2013 was calculated using the numerical Monte Carlo method for the implementation of the described technique in laboratory practice. Using the Ishikawa diagram, sources of uncertainty were identified (repeatability, sampling, determination of the volume and concentration of the titrant solution, recalculation of the mass fraction of sulfur into its mass fraction in dry matter) and the contribution of each of them to the extended uncertainty of the result of determining sulfur in the range of 0.1 – 0.2% was quantified. The values of all uncertainty contributions were entered into an electronic MS Excel spreadsheet, and the analysis result and its extended uncertainty were calculated using created data arrays. The described calculation method is less laborious in comparison with the analytical one, and it can be used in any field where it is necessary to assess the reliability of measurement results.

The functional characteristics of strontium hexagonal ferrites, widely used in instrument making, depend significantly on the technology of their production. The paper presents the results of studying the crystal structure of hexagonal isotropic polycrystalline ferrites SrFe₁₂O₁₉. The samples were obtained by radiation-thermal sintering (RTS) in a fast electron beam of the ILU-6 electron accelerator. The phase composition and crystal lattice parameters of the samples were controlled by X-ray diffractometry, the X-ray spectra were recorded on a DRON-8 diffractometer using CoKα₁ radiation, the density of the objects of study was determined on a UW620H electronic balance. It was found that the obtained single-phase samples are characterized by the P63/mmc space group (corresponding to the structure of hexagonal ferrite). For the synthesized samples, the dependences of the unit cell parameters and volume on the temperature and duration of sintering are given. The multidirectional nature of the change in the parameters of the crystal lattice is revealed, which indicates anisotropic distortion of the unit cell. It is shown that in RTS the sintering temperature plays a much greater role than the sintering time. The results obtained can be used to improve microwave electronics and terahertz photonics devices.

To optimize the processes of obtaining graphene nanoplatelets based on polyacrylonitrile (PAN), it is necessary to study the thermal transformations and reactivity of PAN during heat treatment. The paper presents the results of a study of the thermal properties of PAN and its interaction with solvents. Using UV and IR spectroscopy, differential scanning calorimetry, thermogravimetric analysis and molecular modeling, it was found that the nitrile group CN is the key reaction center affecting the PAN structure. Calculations showed a decrease in the total energy of the system during heat treatment from 14.87 to 12.51 J/g. When PAN interacted with dimethylacetamide (DMA) and dimethylformamide (DMF), the total energy calculated per 1 atom was 6.02 and 5.64 J/g. It was also revealed that the temperature of solvent removal from the PAN/DMF film with a PAN content of 0.2 wt.% — 141.56, and the carbonization temperature is 300°C. The maximum reactivity is observed in hydrogen atoms connected to tertiary carbon atoms and located near CN groups. The combination of the applied experimental methods of analysis and molecular modeling allowed us to establish the key patterns of thermal transformations of PAN and its interaction with solvents. The results obtained can be used to improve the methods for obtaining graphene-like materials.

Modern production requires new technological solutions that meet the requirements of environmental safety, saving energy resources while increasing the efficiency of technological processes. The paper presents the results of a study of the polymer composite materials in the form of fiberglass rebar curing with the use of a microwave unit. Microwave technologies were used for the polymer composite materials curing (at the electromagnetic field oscillation frequency of 2450 MHz), thermosetting epoxy resins and glass fibers were used as binders and fillers. A uniform temperature distribution over the volume of polymer composite materials in the form of rods (of 20 and 40 mm diameters) was formed using the microwave installation electrodynamic systems. It is shown that the microwave radiation energy as a heat source makes it possible to realize a qualitatively new level of polymer composite materials production, characterized by the ability to produce products with higher physical and mechanical characteristics. In addition, microwave installations significantly save energy consumption compared to traditional installations for the fiberglass rebar production. The calculation of microwave installation parameters and fiberglass rebar heat treatment technological modes are presented as well as data on the temperature distribution over the rods cross-section. The obtained results can be used in technological production processes of the polymer composite rod materials heat treatment.

The existing pipelines are constructed from pipes manufactured in accordance with different technological eras. One of the main features of the production of modern rolled products for pipes is the thermomechanical processing of metal, in which it is subjected to high degrees of plastic deformation without subsequent phase transformations and recrystallization. In addition to the positive effect of such treatment, it may also have a negative effect of preserving undesirable technological heredity, especially in the near-surface layers of contact deformation. It is also known that due to the operational characteristics of pipelines, the outer surface of the pipes is a zone of increased stress concentration and initiation of destruction. In connection with the above, the study of the state of the surface layer of new and used oil and gas pipelines and connecting parts of pipelines made using the most common rolling technologies was carried out. The study consisted in determining the brittleness index of the pipe metal at various depths, calculated using a specially developed technique: based on processing the values of microhardness and morphology of localized shifts next to the print during microindentation. It has been established that embrittlement of metal can be caused at all stages of the design life cycle. At the same time, the modes of controlled sheet rolling have a decisive influence on the formation of the initial embrittlement of the metal of pipes. It begins to appear in the production of steels of strength class K60, and increases in steels of strength class K65. In this case, there is also a significant heterogeneity of metal embrittlement in depth: in the near-surface layers with a depth of 0.5 – 1.0 mm, there is a sharp increase in metal embrittlement relative to the central volume. Such a feature can have a decisive influence on the origin and development of stress-corrosion cracks, since it correlates well with the existing statistics on the detection of these defects. The possibility of assessing the degree of embrittlement of metal during the operation of pipelines using specialized equipment has also been confirmed.

The results obtained after tests using the slow strain rate test method (SSRT) to determine the tendency to sulfide stress cracking (SSC) of corrosion-resistant steels of ferritic, austenitic, austenitic-ferritic and martensitic classes as well as aluminum alloy are considered. The selected materials are used in the oil and gas industry and operated in an acidic aqueous environment when saturated with hydrogen sulfide. The deformation rate at the level of 10^–6 sec^–1 is recommended by the NACE TM 0198 standard and was selected during the initial study of these materials (due to low illumination of the SSC results on them) in order to assess the tendency to sulfide stress cracking of corrosion-resistant steels and alloys. In fact, using the promising SSRT method, materials with varying structures are evaluated. The method of stretching with a low deformation rate directly in a corrosive environment has shown its suitability for comparative evaluation of the resistance of steels of various classes to sulfide stress cracking. From the consideration of the tensile curves of the studied materials in a hydrogen sulfide medium, it follows that the destruction of steel samples of grades 08Kh13, 08Kh18N10T, 08Kh22N6T occurs only in the area of plastic deformation, and the destruction of steel samples of grades 17-4PH was noted in the area of elastic deformation on a linear section of the tensile curve. Martensitic class steel 17-4PH showed the greatest sensitivity to the effects of hydrogen sulfide and a threshold stress below the permissible one. Aluminum alloy 1953T1 has not shown a tendency to sulfide cracking (the tensile curves in air and in a hydrogen sulfide medium are almost completely the same) and can be considered as a standard of resistance to this type of corrosion failure. Metallographic analysis of the structure of the studied steels and the nature of the propagation of the formed corrosion cracks allowed us to confirm the influence of the structure, phase composition and strength level of the material on the development of the sulfide stress cracking process.

The paper presents the results of long-term operation, improvement and modernization of a specialized friction machine designed and manufactured to study fretting wear of materials and coatings in gross slip regime. Four different regimes of friction contact surfaces behavior during fretting are known: full stick (seizing) and partial slip (stick-slip) regimes, which are characterized by fatigue failure and cracking, and regimes of gross slip and its transition to reciprocating sliding, for which the main damage contacting surfaces is wear process. It is typical for friction units in which moving contacts of friction surfaces are limited or specially designed, inherent in a large number of plants, machines and mechanisms, and in particular, friction units of gas turbine engines (GTE) and power plants based on them. The work examines not only the stages of modernization of a specialized friction machine, but also presents the main results obtained from studies of fretting wear of various friction units at each stage. The advantages of this machine are determined not only by the ability to control one of the main wear fretting factors — the amplitude of sliding (relative cyclic motion), but also, thanks to the use of collet clamps for fastening experimental samples, to test various forms of friction contacts, such as sphere – plane, plane – plane, cylinder – cylinder, cylinder – plane and others. At all stages of modernization of a specialized friction machine, various coating designs were developed and tested for fretting resistance to protect against fretting wear the friction surfaces, in particularly, of fan blade locks and friction pairs of the mid-span shrouds of gas turbine engine blades operating in gross slip regime. A comparison of the linear and volumetric fretting wear values of various coating options and their components made it possible to establish that the developed and proposed coatings have a good fretting resistance under the operating conditions specified and implemented on the friction machine. Using an analysis of variants of the dependences of the tangential friction force on the displacement values (amplitudes) of gross slip, the values of dissipation energy (friction energy) were obtained and fretting hysteresis loops were constructed. They made it possible to estimate the service life of each of the coatings under consideration with its known thickness and a given displacement, and by comparing the energy coefficients of volumetric wear to determine the most effective coating in terms of fretting resistance and service life. Based on the results of testing materials and coatings under plane-to-plane friction conditions at temperatures of 175 – 180°C, recommendations were developed for the utilization of these materials and technologies for use in friction pairs of mid-span shrouds of gas turbine engine blades. Thus, the considered and implemented capabilities of the modernized friction machine make it possible, under laboratory evaluation conditions, to study various materials and coatings under fretting wear conditions in model friction units of various power plants, machines and mechanisms under given operating conditions at normal and elevated temperatures.

Fisher information is a fundamental concept in the theory of statistical inference and plays a crucial role in the estimation of parameters in statistical models. It represents a measure of the informativeness of observed data with respect to the unknown parameters of the model. In situations involving random censoring, where some observations may be incomplete or censored, calculating Fisher information becomes a complex task that has garnered significant attention from researchers. In this paper, we compute and investigate the Fisher information in a competing risks model under inhomogeneous random interval censoring. The results obtained indicate that under certain conditions, Fisher information retains its properties even in the presence of incomplete observations, which is crucial for improving the accuracy of parameter estimation in statistical models.