Analytical solutions of mushy layer equations describing directional solidification in the presence of nucleation

The processes of particle nucleation and their evolution in a moving metastable layer of phase transition (supercooled liquid or supersaturated solution) are studied analytically. The transient integro-differential model for the density distribution function and metastability level is solved for the kinetic and diffusionally controlled regimes of crystal growth. The Weber–Volmer–Frenkel–Zel’dovich and Meirs mechanisms for nucleation kinetics are used. We demonstrate that the phase transition boundary lying between the mushy and pure liquid layers evolves with time according to the following power dynamic law: at + eZ1(t), where Z1(t) = ßt7/2 and Z1(t) = ßt2 in cases of kinetic and diffusionally controlled scenarios. The growth rate parameters a, ß and e are determined analytically. We show that the phase transition interface in the presence of crystal nucleation and evolution propagates slower than in the absence of their nucleation. This article is part of the theme issue ‘From atomistic interfaces to dendritic patterns’. © 2018 The Author(s) Published by the Royal Society. All rights reserved.Российский Фонд Фундаментальных Исследований (РФФИ), RFBRData accessibility. This article has no additional data. Authors’ contributions. All authors contributed equally to the present research article. Competing interests. The authors declare that they have no competing interests. Funding. This work was supported by project no. 16-08-00932 from the Russian Foundation for Basic Research

Examination of evidence for collinear cluster tri-partition

In a series of the experiments at different time-of-flight spectrometers of heavy ions we have observed manifestations of a new at least ternary decay channel of low excited heavy nuclei. Due to specific features of the effect, it was called collinear cluster tri-partition (CCT). The experimental results obtained initiated a number of theoretical articles dedicated to different aspects of the CCT. We compare theoretical predictions with our experimental data, only partially published so far. The model of one of the most populated CCT modes that gives rise to the so called "Ni-bump" is discussed. Detection of the 68-72Ni fission fragments with a kinetic energy E<25 MeV at the mass-separator Lohengrin is proposed for an independent experimental verification of the CCT.Comment: 16 pages, 14 figure

Approximate analytical solution of the integro-differential model of bulk crystallization in a metastable liquid with mass supply (heat dissipation) and crystal withdrawal mechanism

This paper deals with an approximate analytical solution of an integro-differential model describing nucleation and growth of particles. The model includes a thermal-mass exchange with the environment and the removal of product crystals from a metastable medium. The method developed for solving model equations (kinetic equation for the particle-size distribution function and balance equations for temperature/impurity concentration) is based on the saddle point technique for calculating the Laplace-type integral. We show that the metastability degree decreases with time at a fixed mass (heat) flux. The crystal-size distribution function is an irregular bell-shaped curve increasing with the intensification of heat and mass exchange. © 2022 John Wiley & Sons, Ltd.Russian Science Foundation, RSF: 19-71-10044This work was supported by the Russian Science Foundation (project no. 19-71-10044)

Aromaticity in a Surface Deposited Cluster: Pd4_4 on TiO2_2 (110)

We report the presence of \sigma-aromaticity in a surface deposited cluster, Pd$_4$ on TiO$_2$ (110). In the gas phase, Pd$_4$ adopts a tetrahedral structure. However, surface binding promotes a flat, \sigma-aromatic cluster. This is the first time aromaticity is found in surface deposited clusters. Systems of this type emerge as a promising class of catalyst, and so realization of aromaticity in them may help to rationalize their reactivity and catalytic properties, as a function of cluster size and composition.Comment: 4 pages, 3 figure

Optical absorption in boron clusters B6_{6} and B6+_{6}^{+} : A first principles configuration interaction approach

The linear optical absorption spectra in neutral boron cluster B$_{6}$ and cationic B$_{6}^{+}$ are calculated using a first principles correlated electron approach. The geometries of several low-lying isomers of these clusters were optimized at the coupled-cluster singles doubles (CCSD) level of theory. With these optimized ground-state geometries, excited states of different isomers were computed using the singles configuration-interaction (SCI) approach. The many body wavefunctions of various excited states have been analysed and the nature of optical excitation involved are found to be of collective, plasmonic type.Comment: 22 pages, 38 figures. An invited article submitted to European Physical Journal D. This work was presented in the International Symposium on Small Particles and Inorganic Clusters - XVI, held in Leuven, Belgiu

SETTING UP A DIGITAL LEARNING ENVIRONMENT IN A PEDAGOGICAL UNIVERSITY

This article is aimed at discovering the development particularities of the digital Russian university management system in Russia in the context of universal digitalisation, and identifying the opportunities for the development of university digital learning environment elements. The leading research method of the issue is a comparative analysis of the level of digital competences of students of professional education in Russia and the European Union member states. The authors of the article discovered the particularities of modern education transformational processes, revealed the main role of the development of information and communication technologies, determined the place of Russia in the world learning space and analysed the dynamics of the position of Russian higher educational institutions in the world university rating.Este artículo tiene como objetivo descubrir las particularidades de desarrollo del sistema digital de gestión de la universidad rusa en Rusia en el contexto de la digitalización universal, e identificar las oportunidades para el desarrollo de elementos del entorno de aprendizaje digital universitario. El principal método de investigación del tema es un análisis comparativo del nivel de competencias digitales de los estudiantes de educación profesional en Rusia y los estados miembros de la Unión Europea. Los autores del artículo descubrieron las particularidades de los procesos de transformación de la educación moderna, revelaron el papel principal del desarrollo de las tecnologías de información y comunicación, determinaron el lugar de Rusia en el espacio de aprendizaje mundial y analizaron la dinámica de la posición de las instituciones de educación superior rusas en La calificación de la universidad mundial.Este artigo tem como objetivo descobrir as particularidades de desenvolvimento do sistema de gerenciamento de universidades digitais da Rússia na Rússia no contexto da digitalização universal e identificar as oportunidades para o desenvolvimento de elementos do ambiente de aprendizado digital das universidades. O principal método de pesquisa da questão é uma análise comparativa do nível de competências digitais de estudantes de educação profissional na Rússia e nos estados membros da União Europeia. Os autores do artigo descobriram as particularidades dos processos transformacionais da educação moderna, revelaram o papel principal do desenvolvimento das tecnologias da informação e da comunicação, determinaram o lugar da Rússia no espaço de aprendizado mundial e analisaram a dinâmica da posição das instituições de ensino superior russas no país. a classificação mundial da universidade

Phase transformations in metastable liquids combined with polymerization

This paper is concerned with the theory of nucleation and growth of crystals in a metastable polymer melt with allowance for the polymerization of a monomer. A mathematical model consisting of the heat balance equation, equations governing the particle-radius distribution function and the polymerization degree is formulated. The exact steady-state analytical solutions are found. In the case of unsteady-state crystallization with polymerization, the particle-size distribution function is determined analytically for different space-time regions by means of the Laplace transform. Two functional integrodifferential equations governing the dimensionless temperature and polymerization degree are deduced. These equations are solved by means of the saddlepoint technique for the evaluation of a Laplace-type integral. The time-dependent distribution function, temperature and polymerization degree at different polymerization rates and nucleation kinetics are derived with allowance for the main contribution to the Laplace-type integral. In addition, the general analytical solution by means of the saddle-point technique and an example showing how to construct the analytical solutions in particular cases are given in the appendices. The analytical method developed in the present paper can be used to describe the similar phase transition phenomena in the presence of chemical reactions. This article is part of the theme issue 'Heterogeneous materials: Metastable and nonergodic internal structures'. ©2019 The Author(s)Published by the Royal Society

Analytical solution of integro-differential equations describing the process of intense boiling of a superheated liquid

In this article, an approximate analytical solution of an integro-differential system of equations is constructed, which describes the process of intense boiling of a superheated liquid. The kinetic and balance equations for the bubble-size distribution function and liquid temperature are solved analytically using the Laplace transform and saddle-point methods with allowance for an arbitrary dependence of the bubble growth rate on temperature. The rate of bubble appearance therewith is considered in accordance with the Dering–Volmer and Frenkel–Zeldovich–Kagan nucleation theories. It is shown that the initial distribution function decreases with increasing the dimensionless size of bubbles and shifts to their greater values with time. © 2021 John Wiley & Sons, Ltd.Russian Foundation for Basic Research, РФФИ: 20-08-00199; Ministry of Education and Science of the Russian Federation, Minobrnauka: FEUZ-2020-0057This study is divided into two parts, theoretical and numerical. The theoretical part is supported by the Russian Foundation for Basic Research (project no. 20-08-00199). The numerical part was made possible due to the support from the Ministry of Science and Higher Education of the Russian Federation (project no. FEUZ-2020-0057)

Changes in neutrophilic granulocytes functional activity in trained athletes

This article presents results of comparative research of the functional activity of neutrophilic granulocytes, expressed through a calculated index of activation, in sportsmen going in for orienteering at the end of competitive period and the control group, consisting mostly of healthy people, who do not expose to high physical load. We detected a reliable decrease of the activation index of neutrophils of sportsmen in more than 2 times in comparison to the control group