Solidification of ternary melts with a two-phase layer

This review is concerned with the nonstationary solidification of three-component systems in the presence of two moving phase transition regions—the main (primary) and cotectic layers. A non-linear moving boundary problem has been developed and its analytical solutions have been defined. Namely, the temperature and impurity concentration distributions were determined, the solid phase fractions in the phase transition regions and the laws of motion of their boundaries were found. It was shown that variations in the initial impurity concentration affect significantly the ratio between the lengths of the two-phase layers. A non-linear liquidus surface equation is theoretically taken into account as well

Evolution of a Polydisperse Ensemble of Spherical Particles in a Metastable Medium with Allowance for Heat and Mass Exchange with the Environment

Motivated by a wide range of applications in various fields of physics and materials science, we consider a generalized approach to the evolution of a polydisperse ensemble of spherical particles in metastable media. An integrodifferential system of governing equations, consisting of a kinetic equation for the particle-size distribution function (Fokker–Planck type equation) and a balance equation for the temperature (concentration) of a metastable medium, is formulated. The kinetic equation takes into account fluctuations in the growth/reduction rates of individual particles, the velocity of particles in a spatial direction, the withdrawal of particles of a given size from the metastable medium, and their source/sink term. The heat (mass) balance equation takes into account the growth/reduction of particles in a metastable system as well as heat (mass) exchange with the environment. A generalized system of equations describes various physical and chemical processes of phase transformations, such as the growth and dissolution of crystals, the evaporation of droplets, the boiling of liquids and the combustion of a polydisperse fuel. The ways of analytical solution of the formulated integrodifferential system of equations based on the saddle-point technique and the separation of variables method are considered. The theory can be applied when describing the evolution of an ensemble of particles at the initial and intermediate stages of phase transformation when the distances between the particles are large enough, and interactions between them can be neglected. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.Russian Foundation for Basic Research, РФФИ: 20-08-00199; Ministry of Education and Science of the Russian Federation, Minobrnauka: FEUZ-2020-0057Funding: This paper comprises two parts of research studies, including (i) the model generalization and discussion of governing equations, analytical solutions, analysis of the results obtained, and (ii) checking the mathematics, numerical calculations, visualization, and discussion of the functions obtained. Two parts of this review article were supported by two financial sources. The first part was supported by the Russian Foundation for Basic Research (grant no. 20-08-00199). At the same time, the authors are grateful to the Ministry of Science and Higher Education of the Russian Federation (grant no. FEUZ-2020-0057) for the support of the second part of the research studies

Nucleation and Growth of an Ensemble of Crystals during the Intermediate Stage of a Phase Transition in Metastable Liquids

In this paper, an analytical method of solving the integro-differential system of kinetic and balance equations describing the evolution of an ensemble of crystals during the intermediate phase of the bulk crystallization process is described. The theory is developed for kinetic equations of the first-and second order corresponding to the absence and presence of fluctuations in particle growth rates. The crystal-size distribution function as well as the dynamics of metastability reduction in a supercooled melt (supersaturated solution) are analytically found using the saddle-point and the Laplace transform methods. The theory enables us to obtain the crystal-size distribution function that establishes in a supercooled (supersaturated) liquid at the beginning of the final stage of a phase transformation process when Ostwald ripening, coagulation and fragmentation of crystals are able to occur. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.Russian Science Foundation, RSF: 21-79-10012Funding: Authors gratefully acknowledge financial support from the Russian Science Foundation (project no. 21-79-10012)

Prehospital Period in Patients with COVID-19: Cardiovascular Comorbidity and Pharmacotherapy During the First Epidemic Wave (Hospital Registry Data)

Aim. Based on the data from the register of patients with COVID-19 and community-acquired pneumonia (CAP), analyze the duration of the prehospital period, cardiovascular comorbidity and the quality of prehospital pharmacotherapy of concomitant cardiovascular diseases (CVD).Material and methods. Patients were included to the study which admitted to the FSBI "NMHC named after N.I. Pirogov" of the Ministry of Health of the Russian Federation with a suspected or confirmed diagnosis of COVID-19 and/or CAP. The data for prehospital therapy, information from medical histories and a patients’survey in the hospital or by telephone contact 1-2 weeks after discharge were study. The duration of the prehospital stage was determined from the date of the appearance of clinical symptoms of coronavirus infection to the date of hospitalization.Results. The average age of the patients (n=1130; 579 [51.2%] men and 551 [48.8%] women) was 57.5±12.8 years. The prehospital stage was 7 (5,0; 10,0) days and did not differ significantly in patients with the presence and absence of CVD, but was significantly less in the deceased than in the surviving patients, as well as in those who required artificial lung ventilation (ALV). 583 (51.6%) patients had at least one CVD. Cardiovascular comorbidity was registered in 222 (42.7%) patients with hypertension, 210 (95.5%) patients with coronary heart disease (CHD), 104 (91.2%) patients with atrial fibrillation (AF). The inclusion of non-cardiac chronic diseases in the analysis led to an increase in the total proportion of patients with concomitant diseases to 65.8%. Approximately a quarter of hypertensive patients did not receive antihypertensive therapy, a low proportion of patients receiving antiplatelet agents and statins for CHD was revealed – 53% and 31.8%, respectively, anticoagulants for AF – 50.9%.Conclusion. The period from the onset of symptoms to hospitalization was significantly shorter in the deceased than in the surviving patients, as well as in those who required ALV. The proportion of people with a history of at least one CVD was about half of the entire cohort of patients. In patients with CVD before COVID-19 disease, a low frequencies of prescribing antihypertensive drugs, statins, antiplatelet agents and anticoagulants (in patients with AF) were recorded at the prehospital stage