Amperometric biosensors based on planar graphite electrodes modified by multi-walled carbon nanotubes (CNTs) in chitosan, reduced graphene oxide (RGO), gold nanoparticles (Au NPs) in chitosan, nanocomposites based on them, and immobilized tyrosine enzyme for the determination of tetracycline have been developed. It is shown that tetracycline is a tyrosinase inhibitor, which provides the determination of tetracycline using a tyrosinase biosensor in the concentration range from 1 nM to 1 pM with LOD 0.5 nM. According to the results of kinetic studies of the reaction of the enzymatic conversion of phenol, it is found that in the presence of tetracycline, uncompetitive inhibition is observed on the tyrosinase biosensor. Electrodes modified with nanomaterials can be used as primary transducers of biosensors for fast and accurate determination of the tetracycline concentration. Combination of carbon nanomaterials with metal nanoparticles can form a nanocomposite with a synergistic effect. The use of carbon nanomaterials and metal nanoparticles as modifiers of the electrode surface made it possible to improve the analytical characteristics of the developed sensors: the range of determined concentrations in case of a biosensor modified with CNT/Au NPs and RGO/Au NPs was 1 nM - 1 pM and 0.1 nM - 1 pM, respectively. The correlation coefficient was 0.9925, and the lower limit of the determined concentrations was 50 pM (biosensor with CNT/Au NPs) and 0.7 nM (biosensor with RGO/Au NPs), respectively. The relative standard deviation of the results obtained using biosensors did not exceed 0.078. Methods for the determination of tetracycline using the proposed biosensors in milk and cosmetics have been tested. The compounds present in these samples, structurally unrelated to tetracycline, do not interfere with the determination.

The purpose of the study is development of conditions for the simultaneous determination of caffeine and three isomers of monocaffeoylquinic acids (esters of caffeic and quinic acids: 3CQA, 4CQA and 5CQA) in coffee using "green" reverse-phase HPLC, in which an expensive and environmentally unfavorable acetonitrile is replaced with ethyl acetate as an organic modifier of mobile phases. An approach which provides comparing the efficiency and selectivity of the substance separation in a wide range of concentrations of organic modifiers of selected eluent systems is proposed. It is shown that the replacement of acetonitrile with propanol-2 or ethyl acetate slightly changes the selectivity of the separation of three isomeric chlorogenic acids, but significantly reduces the relative retention of caffeine due to better solvation of caffeine with an organic modifier. This makes it possible to change the position of caffeine elution relative to chlorogenic acids in a targeted way to avoid coelution of caffeine with other extractive substances by changing the concentration and type of the organic modifier of the mobile phase. Ethyl acetate-based eluents are shown to be convenient for simultaneous determination of caffeine and monocaffeoylquinic acids in conditions of reverse-phase HPLC. The replacement of acetonitrile with ethyl acetate makes it possible to re-extract mainly caffeine and monocaffeoylquimc acids from concentrating cartridges (DIAPAK C18) during sample preparation. More lipophilic extractive substances still remain on the concentrating cartridge, which provides the possibility of using a simple isocratic mode thus reducing the duration of analysis and consumption of the organic modifier of the mobile phase.

Gaining current information about the chemical composition of samples from different areas of the deposit during geological exploration necessitates the use of methods of rapid analysis, most often X-ray fluorescence analysis in combination with a method of external standard and its modifications. The existing certified methods assume the construction of calibration characteristics using reference standards. We propose to use a rapid method of X-ray fluorescence analysis (XRF) in aversion of the method of fundamental parameters to determine non-ferrous metals in the samples of titanium-zirconium sands of the Beshpagirskoye deposit and specified conditions of analysis. It is shown that when using the method of fundamental parameters, the accuracy indicators are highly competitive with the indicators obtained by the certified method.

The development and production of effective sound-absorbing materials is an important direction in the construction industry. The results of studying features of the sound-absorbing properties of building structures, i. е., wooden panels, manufactured using CLT technology are presented. Sound insulation and sound absorption of CLT panels are based on the sound resistance. The sound pressure is formed by a frontal wave. The data were processed using the Laplace transform, the decomposition of sound into spectral components was carried out using the Fourier transform. Studies of wooden CLT panels with a cellular structure and given geometric parameters revealed that the acoustic impedance of the composite sound-absorbing CLT panel is higher than that of the massive CLT panel. Moreover, there is a difference in the sound resistance in the opposite direction of sound passage relative to the internal parabolic cavities. It is shown that the internal cavities act as instant resonators, whereas the enclosing elements of the CLT structure (walls, ceilings) with internal parabolic cavities can reduce the noise level by several times. Consequently, a single cavity ("sound pocket") formed by a paraboloid and a plane of a wooden lamella can be considered a module or an element of sound absorption. The results obtained can be used in the design of sound-absorbing materials using CLT composite sound-absorbing panels and modular design.

Microporosity is a dangerous defect of single crystal gas turbine blades cast from nickel-based superalloys (NBS). The volume fraction of the porosity in single crystal alloys does not exceed a few tenths of a percent, however, it can result in manyfold shortening of the lifetime of the blade material under fatigue loading. We present the results of determining the volume fraction of the porosity in single crystal NBS. Single crystals of NBS CMSX-4 obtained according to the industrial technology of manufacturing the single crystal blades of gas turbines were used as a test object. It is found that the applied methods, with the exception of optical microscopy, have an accuracy sufficient for measuring the volume fraction of the microporosity of about 0.2 %vol. The highest accuracy with a statistical error of about ±0.01 %vol. was attained using the Archimedes method using distilled water as a liquid. The method provides the determination of small (up to a few hundredths of a percent by volume) increase of the porosity during high-temperature creep. The results obtained can be used for precise determination of the porosity in NBS single crystals before and after service. Moreover, the process of high-temperature creep can be modeled using a correlation relationship between an increase in the porosity of single crystal material and the accumulated creep strain.

When studying the absorption of X-rays, that the linear absorption coefficient is usually assumed constant throughout the entire volume of the sample under study. However, it can vary in different parts of the crystal, e.g., due to defects present or inhomogeneous inclusion of impurity and doping elements. The results of studying the features of X-ray absorption by a spherical crystalline sample under an assumption that the absorption coefficient is described by a certain function of coordinates are presented. Methods for correcting the diffraction data for such crystals, as well as numerical calculations of the absorption corrections for reflection intensities are proposed. It is shown that the inhomogeneity of absorption in a spherical sample can have a significant effect on the intensity of reflections recorded during a diffraction experiment in the framework of X-ray diffraction analysis (XKD). It is revealed that the attenuation coefficient of a diffracted beam depends on the direction of the absorption coefficient gradient. The results obtained can be used in precision X-ray diffraction analysis of the crystals of some solid solutions. The results of modeling the absorption of X-ray radiation by the samples with different laws of change in the absorption coefficient can be used to identify samples with an inhomogeneous composition.

The possibility of a significant decrease in the growth rate of a fatigue crack is studied. The goal can be attained by creating a local field of residual stresses near the crack tip which arises due to the indentation of a spherical indenter. A methodology and program algorithm (in ANSYS) have been developed for numerical simulation of the problem in a three-dimensional formulation of the process of fatigue crack growth in the field of residual stresses. Considering the prospects of developing the technique with regard to the use of dynamic indentation, the ANSYS Explicit STR solver fully integrated into the calculation module was used in the macro. Proceeding from the solution of the elastoplastic problem the program provides determination of the fields of residual stresses (RS) at the first stage of the calculation and numerical simulation of the fatigue crack growth on the second stage. The effect of the indentation parameters (magnitude of the force applied to the indenter and the location of the indentation point, conditions of fixing) on the crack growth rate is considered. Methods for a significant reduction in the crack growth rate based on multiple preliminary indentation are substantiated. Using the developed program, we managed to solve a series of problems regarding the effect of different types of loading and fastenings on the growth rate of a fatigue crack in a plate with a through crack. The use of one-sided indentation of thin-walled objects with cracks, which are installed on the support surface, greatly simplifies the practical application of the technique for creating a residual stress field in the vicinity of the crack tip. It is shown that with multiple indentation along the crack propagation line, the fatigue crack growth rate is significantly lower than that when using a single indenter.

The main static design characteristics of sheet semi-finished aircraft materials are obtained from the results of tests for uniaxial tension, compression and bearing. At the same time, the Ramberg - Osgood equation is widely used for the analytical description of strain diagrams under static tension in the region of small plastic deformations. The inverse anisotropy resulted from the crystallographic texture after rolling is characteristic of the sheets of aluminum-lithium alloys. We have studied the mechanical characteristics of 1441RT1 alloy sheets under static loading (tension, compression, bearing) in three rolling directions (longitudinal, long transverse, at 45° angle to the longitudinal direction), with an estimate of the Taylor factor characterizing the texture of the material. Tension tests were carried out at a temperature of-70, +20, + 85, and +125°C, compression and beading tests were carried out at a temperature of 20°C. Test temperatures were chosen proceeding from operating conditions of panel skin materials. The Ramberg - Osgood coefficient was determined from the tensile and compressive strain diagrams. To determine the Taylor factor, the X-ray texture analysis was performed with the construction of inverse pole figures. It is shown that for 1mm- and 3-mm sheets of aluminum-lithium alloy 1441RT1 the test temperature corresponding to the operation temperature has a weak effect on the tensile strength characteristics in the region of small plastic deformations. At the same time, the Ramberg - Osgood coefficient is a characteristic most sensitive to the exposure temperature, rolling direction and sheet thickness. The functional dependence of the Ramberg - Osgood coefficient on the rolling direction and the exposure temperature has been determined for 1-mm and 3-mm sheets of 1441RTlalloy.

A number of methods for testing bending of thin discs on an annular support designed to determine the tensile strength of brittle materials, are considered. The methods differ in the type of a loading indenter (with flat, spherical, or toroidal tips), support devices, and calculation equations for determination of the breaking stress. The results of testing samples on an annular support made of two model materials which differ in the degree of brittleness, i.e., cast iron and graphite, are presented. It is shown that the calculated strength of the tested materials depends on the character of the sample destruction and on the type of bending diagram. Cast iron samples were destructed under a significant plastic deformation (characteristic bending diagram passed through the maximum), and the tensile strength of the samples corresponded to the compressive strength of the material being several times higher than the tensile strength of the material. Graphite samples underwent brittle fracture (within the linear section of the bending diagram), and the calculated strength value was comparable to the tensile strength of the material. A conclusion is made that the use of the test method of thin disk samples on an annular support for determination of the tensile strength of the material is substantiated only in the case of absolutely brittle fracture of samples with a bending diagram similar to the fracture diagram of graphite samples. Disk samples made of aluminum oxide obtained by electro-pulse sintering were tested using two methods (with flat and spherical tips). In both cases, the bending diagram of aluminum oxide samples was similar to that of graphite samples, i.e., their destruction occurred at the initial linear section of the diagram and was absolutely brittle. The results of comparative testing of the samples made of aluminum oxide, taking into account the results of testing samples made of model materials (cast iron and graphite), showed that tests on the annular support of disks using a flat-tipped indenter are the most grounded. The samples should be made of brittle materials having a linear bending diagram up to the sample destruction.

The issues of modeling processes occurred in drum-type rotary kilns in steady-state (static) modes are considered in details in the literature, unlike the processes occurred in dynamic conditions (transient modes). However, management and optimization of technological regimes require gaining information about the dynamics of those processes. The goal of the study is analysis of the process of alumina calcination. The quality indicators of the process have a significant impact on the process of aluminum electrolysis. Calcination of aluminum hydroxide is a final stage in all technologies of alumina production. We present the results of theoretical construction of mathematical models of the dynamics of heat and mass transfer processes upon heat treatment of the initial aluminum hydroxide. Three types of models are constructed under different initial conditions which describe the main regularities of the process with different degree of accuracy. Proceeding from the data of the theoretical study a methodology has been developed for experimental study of the dynamics of the process along the main control channels: "hydrate loading - flue gas temperature," "natural gas consumption - temperature in the calcination zone," and "natural gas consumption - flue gas temperature." Transfer functions and differential equations of the process were thus obtained for the studied channels. The revealed good agreement between the structures of theoretical and experimental models made it possible to formulate recommendations for the construction of a process control system for alumina calcination. The temperature in the calcination zone affects the fuel (gas) consumption and determines the quality of the resulting alumina. The flue gas temperature must be maintained at the desired level using a two-circuit system which stabilizes the aluminum hydroxide charge with correction for the flue gas temperature. The temperature in the lower head of the furnace is an integral indicator of the interaction of two flows: the flow of burning gas and the counter-moving flow of the material. This temperature in the steady state operation of the furnace is a control parameter associated with the quality of the resulting alumina. When managing gas consumption, it is also necessary to maintain an optimal fuel-air ratio to ensure complete fuel combustion with maximum efficiency.