Vol 20, No 1 (2024)

The exact solution of the two-dimensional Wiener-Hopf integral equation, which is widely usedin mixed problems, including contact ones, , is given for the first time. The considered equation describingthe contact problem of the action of a rigid die in a quarter plane on an anisotropic deformable medium ofarbitrary rheology is considered. Attempts to solve this problem analytically have been made by many authorsthough resulting in some approximate solutions. The universal modelling method developed by the authors,based on the properties of block elements, as well as solutions of two-dimensional integral equations with ameromorphic function in the kernel suggested an approach that made it possible to construct the exact solutionof a two-dimensional integral equation by factorization.

The study examines steady-state vibrations of a piezoactive bimorph with functionally graded piezoelectric layers that have inhomogeneous properties across the thickness. Direct and inverse problems have been solved. Based on the variational principle, an applied theory of vibrations has been constructed for the quadratic distribution of properties (porosity) over thickness. The problem has been reduced to a system of ordinary differential equations with boundary conditions. During the construction of the theory, Kirchhoff’s hypotheses for mechanical fields were accepted. For the electric field, a quadratic dependence of the distribution of the electric potential over the thickness was adopted. Along the length, the electric potential was considered an unknown function depending on the longitudinal coordinate. The application of quadratic dependence of the distribution of the electric potential over the thickness makes it possible to more accurately describe the behaviour of the electric field in problems of steady-state bending vibrations. Based on the obtained applied theory, the inverse coefficient problem of identifying heterogeneity parameters (porosity in the middle and on the surface of the bimorph) was solved. As the additional information for solving the inverse problem, the characteristics of steady-state oscillations of the bimorph, which can be measured in a full-scale experiment, were considered. The inverse problem was solved on the basis of constructing surfaces and their isolines of the dependences on the porosity parameters: the first resonant frequency of bending vibrations, the output potential during mechanical excitation of vibrations, and the displacement amplitude of the free end of the bimorph during mechanical and electrical excitations of vibrations. It is shown that the selected information is sufficient to unambiguously determine the structure of inhomogeneity of piezoactive material in the class of quadratic functions. The use of these characteristics makes it possible to unambiguously determine the porosity in the middle and on the surface of the bimorph.

The water bodies of the Western Manych valley are the key objects of the dry steppes of European Russia for studying the biogeochemical cycles of elements in the land-aquatic interfaces. The dynamics of water surface areas of these water bodies (according to the MNDWI spectral index) was assessed using Landsat 5 TM and Landsat 8 OLI survey data from 1985 to 2022. The rate of change and the stability grade of water bodies were analyzed. An analysis of the relationship between the dynamics of water bodies areas and hydrometeorological parameters (water discharge, air temperature and relative humidity, precipitation) was carried out using linear regression and correlation methods.In the long-term period (1985-2022), most water bodies in the Western Manych valley tended to decrease in size. The intensity of the decrease in the total areas of different lakes varied from 0.3 to 17%; for the largest water body, the Proletarsk Water Storage Reservoir (including Lake Manych-Gudilo), it was about 3.4% per decade. The water reservoirs of the Kuma-Manych depression have a pulsating, asynchronous change in the boundaries of the water surface, which depends mainly on the weather conditions of the year and the hydrological and geomorphological characteristics of each individual lake. In the most general terms, one can note an increase in the total area of the water surface in the Western Manych valley in the late 1990s - early 2000s and the subsequent (2007-2022) drying trend. As the size of water bodies decreases (total area, depth), the value of the stability grade decreases. Further changes in climatic factors and aridization of the territory will have a negative impact on these lakes (their total areas will decrease), with the exception of two lakes, Gruzskoe and Dzhama, the changes in the total areas of which are more related to the geomorphological structure of lake basins and shores than to climatic factors. Different groups of lakes according to the trends of changes in their sizes have been identified for the first time.

Based on the materials of the study of aquatic vegetation collected in 2006-2022 in various reservoirs and watercourses of the middle and lower reaches of the Don River basin, the classification of aquatic vegetation by the Broun-Blanquet method based on 34 geobotanical descriptions was carried out. As part of the Potamogetonion alliance of the Potamogetonetea class, 7 associations and their characteristics were identified provided: Potamogetonetum pectinati , Potamogetonetum perfoliati , Potamogetonetum nodosi , Potamogetonetum crispi , Potamo-Ceratophylletum demersi , Potamo pectinati-Myriophylletum spicati , Elodeetum canadensis . The communities of associations Potamogetonetum pectinati and Potamogetonetum perfoliati were the most widespread (registered in the delta, lower and middle reaches). Most rarely - Photamogetonetum crispi . The diagnostic species of the association Elodeetum canadensis , Elodea canadensis , is an invasive species and has significantly expanded its geographical range in Rostov Region.Further studies of aquatic vegetation suggest the discovery of 6 more associations in the Don River basin in the indicated area: Potamogetonetum lucentis Hueck 1931, Potamogetonetum natantis Hild 1959, Potamogetono natantis-Polygonetum natantis Knapp et Stoffers 1962, Myriophylletum verticillati Gaudet ex Šumberová in Chytrý 2011, Myriophylletum sibirici Taran 1998, Potamogetonetum berchtoldii Krasovskaya 1959, for the coenose-forming species of associations were indicated in the descriptions. It is possible that the general aridization of climate could lead to a decrease in the role of these species in the southern regions and these types of communities fall out of the vegetation cover.The flora of macrophytes of the Potamogetonion alliance is represented by 29 species of 19 genera of 13 families.The cenotic diversity of the Potamogetonion alliance of the studied territory can be estimated as average or below average (half of the diversity of the alliance has not yet been identified). The data obtained on the flora and vegetation of the Potamogetonion alliance are not final and further new studies of the reservoirs of the Don River basin are required.

Saposhnikovia divaricata (Turcz.) Schischkin is a taproot perennial monocarp and has exclusively seed regeneration. In Zabaykalskiy Region of Russia it grows in steppe and forest-steppe areas, occurring in steppes, thickets of steppe shrubs, on edges of forest-steppe forests, and in fallow lands.The study material was sampled in cenopopulations on fallow lands, mainly in the middle and late stages of the overgrowth, in the steppe and forest-steppe areas of Zabaykalskiy Region in 2022-2023. When determining ontogenetic stages, we used the classification developed by T.A. Rabotnov and supplemented by A.A. Uranov. As a result of the studies, it was found out that the ontogenesis of S. divaricata includes three periods (latent, pregenerative and generative) and eight ontogenetic stages (seeds, seedlings, juvenile, immature, young, middle and late virginile, and generative). A special feature of the ontogenesis of S. divaricata is three virginile stages. The generative period is very short, lasting only one growing season and is not divided into ontogenetic stages. Pregenerative plants have rosette shoots, generative plants have semi-rosette shoots. Virginile, and less often generative, individuals may have not one, but several rosettes, including individuals damaged during theprocurement of root raw materials. No postgenerative S. divaricata individuals were registered.

Currently, there is a rapid growth and development of domestic fodder production, accompanied by the introduction of new formulations of compound feeds. Consequently, there is a growing demand for a reliable evaluation model to assess the effectiveness of various additives included in these feeds. In this study, we conducted an analysis of the morphological and physiological traits, as well as the microbiome status, in sterlet fish consuming feeds of different qualities. Our aim was to determine the physiological parameters most influenced by nutrition.The results indicate that sterlet fish fed with low-quality feed exhibited, on average, a 7% lower final weight and experienced a significant decrease in triglyceride and beta-lipoprotein levels at the end of the experiment. Furthermore, the analysis of the intestinal microbiome revealed an increase in Enterococcus and actinomycetes in the intestines of sterlet fish fed with poor-quality feed. Additionally, we observed a significant presence of lactose-positive bacteria, which were absent in the control group, as well as Bacillus bacteria, which were absent in the other groups. Despite these findings, the fish fed with poor-quality feed remained in good physiological condition. This suggests the potential probiotic activity of the Bacillus bacteria isolated from their microbiome.

The arid territories of Volgograd Region are favourable for the bacterial acute intestinal infections spread. The ecological state of the human environment influences the epidemic process of anthroponotic infections with a fecal-oral transmission mechanism. To examine the quality of the water body, the indicators of biochemical oxygen demand and satellite data of the normalized difference turbidity index were selected. The contribution of natural and climatic factors was evaluated using the calculation of the hydrothermal coefficient by Selyaninov. The assessment of the selected characteristics was carried out on the territory of three zones of the Volgograd urban agglomeration, located downstream of the Volga Hydroelectric Power Plant. There is a sewage treatment plant on Golodny Island, the efficiency of which affects the spread of intestinal infections. This study examines the possibility of using environmental data as indicators of the sanitary well-being of the Volga River basin in order to predict the dynamics of the epidemic process of acute intestinal infections of the unknown aetiology. The incidence rate used as a dependent variable in the proposed model; three predictors reflecting the ecological state of the Volga water area (biochemical, satellite, and climatic) were analyzed as influencing variables. The study established that the greatest contribution to the model predictive power of the incidence of acute intestinal infections in the Volga region is made by the indicator of biochemical oxygen demand, which reflects the degree of surface waters contamination from sewage. The indicator of biochemical oxygen demand formed the basis for a ten-year forecast of the spread of acute intestinal infections. The study calculated the median of the forecast for the dynamics of morbidity, as well as the interval values of the 95th percentile. Our results can be used to adjust measures to assess the quality of sewage treatment plant in the Volgograd urban agglomeration zone.