Planar screen-printed potentiometric sensors sensitive to cefepime, cephalosporine antibiotic of the fourth generation, has been developed. Cefepime is an amphoteric antibiotic with carboxyl and aminothiazole groups which exists as a cation in a strongly acidic media, a zwitter-ion in a weakly acidic and neutral media, and as an anion in an alkaline media. The interval of pH = 1.5 - 2.0 is set for obtaining cationic electrode functions for the cefepime determination. Cefepime-tetraphenylborate associates are used as electrode-active components (EAC). The optimal EAC content for planar sensors is 2-3%. The electrode functions are linear in the range of 1 x 10^-5 - 1 x 10^-2 M, angular coefficients 50 ± 2 mV/pC, response time 20 sec for unmodified cefepime sensors. The role of the modifier, ZnO nanoparticles, in improving the electroanalytic properties of sensors is shown. The introduction of a binary mixture of zinc oxide and cetylpyridinium chloride into carbon-containing ink leads to a decrease in the detection limit of cefepime (1 x КГ6 M), an increase in the angular coefficient (58 ± 1 mV/pC) and the interval of linearity of electrode functions (1 x 10^-6 - 1 x 10^-2 mole/liter), sensor response time being 17 sec. The use of a surfactant as an electrode surface comodifier leads to stabilization of the nanoparticle dispersion. The use of modified screen-printed sensors for the cefepime determination in medicinal and biological media, in particular, in saliva, is shown.

A method for quantification of the dose effect of ionizing radiation on the structural characteristics of bovine serum albumin (BSA) in aqueous solution through identification of unique peptides of protein domain structures using high-resolution liquid chromatography-mass spectrometry is proposed. BSA with the initial concentration of 500 mg/liter in a physiological solution was exposed to irradiation at a dose rate of 18. 5 Gy/sec using an accelerated electron beam with the maximum energy of 1 MeV at an average beam current of 1 uA. The absorbed dose in the sample volume was estimated using a Fricke (ferrous sulphate) dosimeter. After irradiation of BSA solution at 0.3, 0.6,1.8, and 20 kGy we analyzed the structural integrity of the protein native form and then quantified the content. For this, masses more than 30 kDa were removed using centrifugation. Then BSA was subjected to enzymatic hydrolysis with the addition of trypsin solution, and the resulting peptides with a mass of more than 10 kDa were repeatedly removed. The resultant samples were then examined using liquid chromatography mass spectrometry (LC-MS) and high-resolution tandem mass spectrometry (HRMS-MS/MS). The content of intact protein molecules was assessed by determining the concentrations of unique peptides corresponding to each of the three domains into which the amino acid sequence of BSA was divided. Using the developed methodology, a change in the natural conformation of bovine serum albumin (denaturation) in water samples induced by ionizing radiation at a dose ranging from 0.3 to 20 kGy was revealed on average in 71% of protein molecules exposed to doses up to 1 kGy in 79% of molecules exposed to doses of 4 kGy and in 99 % to 100% of molecules exposed to doses of 8 and 20 kGy.

A high toxicity of organochlorine compounds, even present in trace amounts in food products, leads to increased requirements for the accuracy of chemical analysis in food safety control. The interstate standard GOST 31858-2012 was taken as a basis for this study. We have improved the method of sample preparation of drinking water for the determination of residual amounts of y-hexachlorocyclohexane (y-HCCH) by gas chromatography with an electron capture detector. Strictly following the instructions of the standard, we failed to obtain the value of the recovery factor of 94% prescribed by GOST for y-HCCH. In this regard, we proposed to use higher-boiling re-heptane instead of re-hexane as an extractant to reduce losses at the stage of sample preparation, and to use sodium chloride instead of ethyl alcohol prescribed by GOST to break the emulsion formed during the extraction of water with hexane. The volume of the analyzed sample, the mass of sodium chloride, the volume of the extragent, and the extraction time were optimized. The use of sodium chloride is shown to provide total emulsion breakage in 100% of experiments and to increase the recovery of pesticides with a concentration of 22 pg/liter from 77 to 96% with a relative standard deviation of 2%. Replacing the extragent with re-heptane led to an increase in the recovery of Y-HCCH to 98% with a relative standard deviation of 1%. It is shown that at a lower concentration of the pesticide, the recovery rate is 98 - 100 %. An increase in the concentration of y-HCCH to 45 pg/liter leads to a sharp decrease in the recovery degree. The proposed method can be considered as an improved method of liquid-liquid extraction with excellent extraction of the pesticide from the aqueous matrix.

X-ray methods in comparison with other control methods are characterized by high information content, clarity and efficiency. The paper presents the results of the use of microfbcus radiography in the control and diagnostics of industrial products. A distinctive feature of the microfbcus radiography method is the use of an X-ray source with a focal spot of micron sizes and a survey geometry with a direct geometric increase in the object of study. The minimum dimensions of the rendered structures in this case are not limited by the pixel size of the image receiver and can be significantly smaller. It is shown that the use of the microfbcus radiography method makes it possible to increase the information content of the resulting radiographs by at least an order of magnitude, due to an increase in spatial resolution. At the same time, the technical means for implementing the described method can be small-sized, designed for use in non-stationary and non-specialized conditions. The results obtained can be used in scientific research and industrial control in the following areas: electronics, additive technologies, instrumentation and others.

The use of internal protective coating of steel pipes is one of the most effective and reliable ways to prevent corrosion. The most widespread coatings based on epoxy film-forming exhibit high adhesion to steel and chemical resistance to various aggressive factors. The formation of epoxy coatings is intimately connected with the interactions occurring on the metal surface, the physicochemical properties of the polymer itself and with the process of curing (polymerization), as well as with the thermophysical parameters that change during curing (glass transition temperature, degree of curing). The method of differential scanning calorimetry is widely used in practice to determine glass transition temperature which provide detecting phase transitions and their values in different materials. The accuracy of this method depends on many factors related to the instrument properties and methodological approaches which leads to a lack of repeatability and reproducibility of test results in various laboratories, and as a result, to the absence of a unified criteria for assessing the quality of protective coatings. We present the results of studying the degree of curing the epoxy coatings of oil and gas pipes by differential scanning calorimetry. The effect of instrumental conditions for laboratory tests, sample preparation methods, and methods of data processing by specialized software on the determination of thermophysical properties of epoxy coatings by differential scanning calorimetry was revealed. The results obtained can be used in developing a refined procedure for determining the degree of curing protective coatings.

The estimates of the reference temperature T₀, obtained for the base metal and the weld-seam metal of the Cr - Ni - Mo - V type (shell 200 mm thick) on the basis of statistical modeling by the Monte Carlo method are presented. T₀ was determined according to the ASTM E1921 standard taking into account the inhomogeneity of the material. The sample size of the fracture toughness values KJC for T₀ modeling was 12, 24 and 70. The Monte Carlo method was used for analysis of the correctness of metal identification (homogeneous/inhomogeneous). It is shown that sampling of 12 samples do not provide a reliable determination whether the metal is homogeneous or inhomogeneous (incorrect results were obtained in 50% of cases for the base metal and in 37% of cases for the weld-seam metal). When the sample size increased to 24 samples, the incorrect results were obtained in 5% of cases. The T₀ values with allowance for the material inhomogeneity were determined by two ways: using a screening procedure and proceeding from the actual bimodal representation of the fracture toughness distribution (parameters of the bimodal distribution were determined by the maximum likelihood method). It is shown that both methods give close results for the base and weld-seam metal, the magnitude of the shift towards positive values in the average T₀ values determined with allowance for the inhomogeneity being about 22°C. Using the obtained T₀ estimates, the lower envelopes of the temperature curves of the fracture toughness are constructed (master curves for 5 % failure probability).

Shear and interlayer characteristics of polymer fiber composites, in contrast to metals, play a decisive role in the deformation and fracture processes. In this regard, special methods have been developed to determine the interlayer bending strength of a short beam and the interlayer shear modulus by deflection correction. At the same time, the accepted hypotheses about the distribution of shear stresses, for example, by the Zhuravsky formula, are too simple and do not provide the determination of the correction and calculation of the shear modulus with a rather high accuracy. The use of the Saint-Venant - Lekhnitzky solution for an orthotropic beam instead of the simplest parabolic distribution potentially makes it possible to take into account all the shear stresses occurring in the beam, as well as their distribution over the height and width of the beam, which should increase the accuracy of determining the deflection correction and interlayer shear modulus, respectively. Since the strict solution is presented in a series of hyperbolic functions, its practical use is rather difficult. We present an exact approximation of the strict solution by simpier quadratic dependences, which provides determination of the deflection correction and the shear modulus with a high accuracy. It is shown that for real composite beam-type specimens the use of the refined shear stress distribution with allowance for the heterogeneity of stresses along the beam width gives a negligibly small correction for the deflection compared to the simplified parabolic distribution according to the Zhuravsky formula. The numerical verification was carried out using the finite element. Special tests of fiberglass specimens of different widths for three-point bending also showed no increase in the deflection with increasing beam width, which indicates an insignificant influence of the heterogeneity of tangential stresses on the deflection.

The failure probability and the reliability index have been determined for a pipe submitted to internal pressure, exhibiting a corrosion defect, embedded in a soil with a ground reaction, and underwent the displacement due to seismic activity. Results are obtained by computing the condition of failure: strain demand higher than strain resistance which is typically the Strain Based Design (SBD) basis. From the probabilistic point of view, this condition results in the overlay of the two probability distributions, namely, demand and resistance. An analytical method is proposed to compute the common area between the strain demand and resistance distribution and then to get the probability of failure. The strain demand is assumed to follow a power-law distribution and the strain resistance is a Normal one. The strain demand is computed assuming that the probability density of seismic waves follows a Gutenberg - Richter distribution law. This simple method is also used to predict the failure probability of different reference periods or seismic zone. It is also used to examine the influence of the coefficient of variation of the strain resistance distribution when using vintage pipe steels. 

The article develops an idea that the stress-strain curve for an arbitrary material is the extremum of some functional. However, for irreversible processes, the using of the principle of stationarity of some functional is incorrect, because due to the dissipation of the deformation process, the possible work of internal forces is non-integrable. Therefore, it is proposed to use the generalized variational principle of L. I. Sedov for modeling the stress-strain curve of elastoplastic materials. A concept of sequential inclusion of certain deformation mechanisms on different segment of the stress-strain curve is proposed. According to this concept, each section of the stress-strain curve must correspond either to the stationary value of the corresponding functional, or to the stationary value of the non-integrated form of variations of the corresponding stress derivatives. The combination of naturally obtained spectra of boundary conditions at the ends of each segment leads to a variation-consistent formulation of the system of boundary and contact conditions of solutions of different differential equations on each segment of stress-strain curve. As a result, it is possible to construct a differentiable stress-strain curve over the entire area of the stress-strain curve definition. The resulting solution, in contrast to the Ramberg - Osgood empirical law, has a strictly liner segment. The obtained mathematical model was tested on experimental data of materials for various industrial purposes. The achieved accuracy of the mathematical model is sufficient for engineering applications.