Dynamics rammers with two pairs of shock generators

The results of a numerical-analytic study for the dynamics of a vibro-impact mechanism with a crank vibration generator are presented in this paper. We show bifurcation diagrams and stability regions that let us find basic patterns in the reorganization of motion modes when the mechanism’s parameters change

The effect of dry friction forces on the process of dielectric wafer grinding

We have investigated possible motions of the holder on top of the polishing pad during the process of dielectric plate grinding taking into account the forces of dry friction about its axis. A mathematical model of the mechanical device has been elaborated to describe the process of dielectric wafer grinding. The model is in the form of a non-autonomous nonlinear system with a variable structure. The structure of the phase space of the dynamical system was investigated, the qualitative studies of the possible motion modes were carried out. The values of the geometrical and dynamic parameters that qualitatively and quantitatively influence the modes of the holder motion were obtained. It was found that the inclusion of dry friction forces on the axis of the free holder result in a periodic motion of the mechanism with long stops. We present the calculations of the parameters for the type 3PD-320 machine

A continual model of a damaged medium used for analyzing fatigue life of polycrystalline structural alloys under thermal–mechanical loading

The main physical laws of thermal–plastic deformation and fatigue damage accumulation processes in polycrystalline structural alloys under various regimes of cyclic thermal–mechanical loading are considered. Within the framework of mechanics of damaged media, a mathematical model is developed that describes thermal–plastic deformation and fatigue damage accumulation processes under low-cycle loading. The model consists of three interrelated parts: relations defining plastic behavior of the material, accounting for its dependence on the failure process; evolutionary equations describing damage accumulation kinetics; a strength criterion of the damaged material. The plasticity model based on the notion of yield surface and the principle of orthogonality of the plastic strain vector to the yield surface is used as defining relations. This version of defining equations of plasticity describes the main effects of the deformation process under monotone cyclic, proportional and nonproportional loading regimes. The version of kinetic equations of damage accumulation is based on introducing a scalar parameter of damage degree and energy principles, and account for the main effects of nucleation, growth and merging of microdefects under arbitrary regimes of low-cycle loading. The strength criterion of the damaged material is based on reaching a critical value of the damage degree. The results of numerically modeling cyclic thermal–plastic deformation and fatigue damage accumulation in heat-resistant alloys (Nimonic 80A, Haynes 188) under combined thermal–mechanical loading are presented. Special attention is paid to the issues of modeling the processes of cyclic thermal–plastic deformation and fatigue damage accumulation for complex deformation processes accompanied by the rotation of the main stress and strain tensor areas. It is shown that the present damaged medium model accurately enough for engineering purposes describes the processes of cyclic isothermal and nonisothermal deformation and fatigue damage accumulation under combined thermal–mechanical loading and makes it possible to evaluate low-cycle fatigue life of heat-resistant alloys under arbitrary deformation trajectories

Material Origin in Folklore Texts of Predominantly Historical Themes

The article deals with the issues of architectonics of folklore texts of historical content: Russian and Ukrainian historical songs, historical ballads, dooms and epics. The relevance of the study is due to the search for a synchronous typological similarity between folklore texts of different ethnic, generic, genre, and poetic nature. Special attention is paid to three aspects of the organization of the song plot: its compositional layering, the combination of several principles in it; the plot meaning of allomotives, explicating the material principle; their styling. The definitions of the material and spiritual principles are given. The objective existence of typological similarities at the level of the allomotive organization of Russian and Ukrainian texts related to the classical, traditional and stage-by-stage types of creativity in the field of historical song folklore is shown. It is shown that this similarity can be explained by the reflection in the texts of vital, everyday empiricism and can acquire different stylistic incarnations: reduced everyday, ascertaining, idealizing. The question is raised about the reasons for the axiological differences in the Russian and Ukrainian folklore traditions. It is proved that the explication of the material principle can have different meanings in the organization of the song plot: optional, meaningful within a fragment of the text, plot-forming

Polycystic ovary syndrome and periodontal status: a literature review

The review considers the problem of connection the polycystic ovarian syndrome and periodontal disorders of the fertile women. The authors marked that this problem is not virtually touched upon in Russian science. In the foreign literature this issue is discussed in connection with studying the micro-biome and oxidative stress. The authors refer to some articles showing that the quantity of pathogenic microorganisms responsible for periodontal disorders and the level of specific antibodies in blood serum are increased in women with polycystic ovarian syndrome, especially in the cases of gum inflammation. Also the article gives the data where the results show the wider spreading of periodontal disorders in women with polycystic ovarian syndrome in comparison with the healthy ones where controls were matched by age and BMI. The authors think that studies on oral microbiocenose disorders and tissue quality of periodontium of the fertile women with polycystic ovarian syndrome are quite important. The further studying of connection of polycystic ovarian syndrome and oral mucous membrane inflammation could reveal definite periodontal pathogens, which can influence systematic inflammation processes in polycystic ovarian syndrome

Experimental analysis of wear resistance of compacts of fine-dispersed iron powder and tungsten monocarbide nanopowder produced by impulse pressing

The paper presents the results of studying the structure and wear resistance of compacts produced from fine dispersed reduced iron powder (average particle size 3–5μm) with the addition of tungsten carbide (WC) nanopowder with the average particle size of 25–30 nm. The mass fraction of tungsten carbide (wolfram carbide) in the powder composition was 5% and 10% of the total mass. Impulse pressing was conducted using the modified Kolsky method at compacting temperatures of 20 °C to 300 °C. The produced compacts had relative density of over 90%. Metallographic studies using the scanning electronic microscopy method on a TESCAN VEGA II electronic microscope have shown that the produced compacts have a fairly homogeneous fine-grained structure, with a uniform pattern of pore distribution, the form of the pores being close to spherical. X-ray microanalysis using an INCA Energy 250 energy-dispersion spectrometer with scanning along the surface line and transversal laps testifies to the fact that, in the considered temperature range, dynamic compaction does not lead to any noticeable changes in the distribution of the Fe, W and C elements over the bulk of the specimens. The conducted measurements of micro-hardness of the compacts have shown that it increases considerably with the pressing temperature. The produced compacts were tested for wear resistance in a dry friction regime, using the ‘rotating disk – stationary specimen’ configuration. Mass loss of the compacts as a function of testing time is presented. Wear resistance of compacts depends on pressing temperature and concentration of the WC powder in the matrix of reduced iron. It has been experimentally determined that maximal wear resistance is observed in the compacts with the mass fraction of WC equal to 10%, produced at a pressing temperature of 300 °C

Features of Chronic Endometritis in Women of Reproductive Age with Polycystic Ovary Syndrome

Background. The prevalence of chronic endometritis among women of reproductive age reaches 68 %. Polycystic ovary syndrome (PCOS) is a common cause of reproductive disorders. Data on the characteristics of the manifestation of chronic endometritis in patients with PCOS are incredibly insufficient. PCOS is known as closely associated with metabolic syndrome and chronic systemic inflammation. However, there is no information on the role of chronic systemic inflammation in the pathogenesis of chronic endometritis in women with PCOS.The objective. Determination of the clinical and morphological features of chronic endometritis in women  with polycystic ovary syndrome and to establish the role of systemic inflammation and hormones of the  hypothalamic-pituitaryovarian axis in chronic endometritis associated with PCOS. Materials and methods. We performed a cross-sectional study from May 2017 to December 2019 and examined 198 women of reproductive age (33.71 ± 5.93 years) during annual preventive examinations. We used clinical, instrumental, and laboratory research methods, including hormonal, biochemical,  immunohistochemical techniques, and statistical analysis.Results. Of the 198 women examined chronic endometritis was diagnosed in 76 patients, including 15 patients with PCOS. Chronic endometritis in PCOS is characterized by a relative decrease in the duration of the menstrual cycle and less pronounced lymphoid infiltration of endometrial tissue. The risk of chronic endometritis in women of reproductive age is not associated with changes in gonadotropins, prolactin, and  manifestations of clinical and biochemical hyperandrogenism. Chronic endometritis is not accompanied by an increase in the concentration of C-reactive protein. At the same time, BMI, waist circumference, and leptin are considered «anti-risk» factors for chronic endometritis.Conclusion. The specific clinical manifestations of chronic endometritis in PCOS allows us to consider them as diagnostically significant. The revealed negative associations of chronic endometritis with BMI, waist  circumference, and leptin require further investigation of the role of adipose tissue products in the control of local and systemic inflammation

Metabolic syndrome: Epidemiology, diagnostic criteria, racial characteristics

Metabolic syndrome (MS) is a very serious pathological condition that occurs in the clinical practice of doctors of various specialties. Often, the presence of MS aggravates the course of comorbidities, while various diseases can serve as a risk factor for its development. The significant prevalence of MS determines the need for its early diagnosis for timely correction and prevention of its long-term complications.The aim. To systematize data on the prevalence of metabolic syndrome in various countries and populations and to discuss the most frequently used diagnostic criteria, including racially and ethnically differentiated ones.Materials and method. A literary search was carried out using scientific databases: eLIBRARY, PubMed.NCBI, CyberLeninka, the official website of IDF for the period from 1999 to 2020.Results. It was found that despite different diagnostic criteria used for MS, its prevalence in many countries is comparable (10–30 %) but differs in different populations. Thus, MS occurs more often in Caucasians than among Asians, and its prevalence is significantly higher in the newcomer vs the indigenous population. Nevertheless, a comparative analysis of the frequency of MS is difficult due to the use of research results based on different approaches to its diagnosis in the literature presented in the literature. Although the analysis of literature data indicates the existence of specific features of the prevalence of MS in different populations, the differentiated approaches to detecting MS depending on the race of patients, which are necessary for many countries, have not yet been sufficiently developed