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1.
J Phys Condens Matter ; 34(38)2022 Jul 22.
Article in English | MEDLINE | ID: mdl-35820411

ABSTRACT

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.

2.
J Phys Condens Matter ; 34(24)2022 Apr 18.
Article in English | MEDLINE | ID: mdl-35349984

ABSTRACT

The growth of a parabolic/paraboloidal dendrite streamlined by viscous and potential flows in an undercooled one-component melt is analyzed using the boundary integral equation. The total melt undercooling is found as a function of the Péclet, Reynolds, and Prandtl numbers in two- and three-dimensional cases. The solution obtained coincides with the modified Ivantsov solution known from previous theories of crystal growth. Varying Péclet and Reynolds numbers we show that the melt undercooling practically coincides in cases of viscous and potential flows for a small Prandtl number, which is typical for metals. In cases of water solutions and non-metallic alloys, the Prandtl number is not small enough and the melt undercooling is substantially different for viscous and potential flows. In other words, a simpler potential flow hydrodynamic model can be used instead of a more complicated viscous flow model when studying the solidification of undercooled metals with convection.

3.
Dokl Biochem Biophys ; 507(1): 357-362, 2022 Dec.
Article in English | MEDLINE | ID: mdl-36787002

ABSTRACT

A new series of 1-[ω-(bromophenoxy)alkyl]-uracil derivatives containing naphthalen-1-yl, naphthalen-2-yl, 1-bromonaphthalen-2-ylmethyl, benzyl, and anthracene-9-ylmethyl fragments in position 3 of uracil residue was synthesized. The antiviral properties of the synthesized compounds against human cytomegalovirus were studied. It was found that the compound containing a bridge consisting of five methylene groups exhibits a high anti-cytomegalovirus activity in vitro.


Subject(s)
Cytomegalovirus , Uracil , Humans , Uracil/pharmacology , Uracil/chemistry , Structure-Activity Relationship , Antiviral Agents/pharmacology , Antiviral Agents/chemistry
4.
J Phys Condens Matter ; 34(9)2022 Jan 10.
Article in English | MEDLINE | ID: mdl-34749346

ABSTRACT

Microstructure of Al-40 wt%Si samples solidified in electromagnetic levitation furnace is studied at high melt undercooling. Primary Si with feathery and dendritic structures is observed. As this takes place, single Si crystals either contain secondary dendrite arms or represent faceted structures. Our experiments show that at a certain undercooling, there exists the microstructural transition zone of faceted to non-faceted growth. Also, we analyze the shape of dendritic crystals solidifying from liquid Si as well as from hypereutectic Al-Si melts at high growth undercoolings. The shapes of dendrite tips grown at undercoolings >100 K along the surface of levitated Al-40 wt%Si droplets are compared with pure Si dendrite tips from the literature. The dendrite tips are digitized and superimposed with theoretical shape function recently derived by stitching the Ivantsov and Brener solutions. We show that experimental and theoretical dendrite tips are in good agreement for Si and Al-Si samples.

5.
J Phys Condens Matter ; 33(44)2021 Aug 19.
Article in English | MEDLINE | ID: mdl-34343987

ABSTRACT

This review article summarizes current theories of the steady-state growth mode of dendrites in the form of elliptical paraboloids. The shape of dendrite tips is analyzed, temperature and solute concentration distributions are described in its vicinity, and a solution of the hydrodynamic problem of a viscous incompressible fluid flowing against a dendrite tip is developed. A significant difference in analytical solutions describing a dendrite tip as an elliptic paraboloid as compared to an axisymmetric morphology is shown. The system of nonlinear equations for determining the stationary velocity of dendrite growth and the radii of curvature of the dendrite tip along the major and minor axis of the ellipse, respectively, is derived. The developed theory is compared with experimental data on the growth of ice crystals consisting of D2O or H2O.

6.
J Phys Condens Matter ; 33(36)2021 Jul 09.
Article in English | MEDLINE | ID: mdl-34161932

ABSTRACT

Motivated by an important application of dendritic crystals in the form of an elliptical paraboloid, which widely spread in nature (ice crystals), we develop here the selection theory of their stable growth mode. This theory enables us to separately define the tip velocity of dendrites and their tip diameter as functions of the melt undercooling. This, in turn, makes it possible to judge the microstructure of the material obtained as a result of the crystallization process. So, in the first instance, the steady-state analytical solution that describes the growth of such dendrites in undercooled one-component liquids is found. Then a system of equations consisting of the selection criterion and the undercooling balance that describes a stable growth mode of elliptical dendrites is formulated and analyzed. Three parametric solutions of this system are deduced in an explicit form. Our calculations based on these solutions demonstrate that the theoretical predictions are in good agreement with experimental data for ice dendrites growing at small undercoolings in pure water.

7.
J Phys Condens Matter ; 32(30): 304003, 2020 Jul 15.
Article in English | MEDLINE | ID: mdl-32213674

ABSTRACT

The process of directional crystallization with a quasi-equilibrium mushy region is considered in the steady-state conditions with allowance for the non-linear phase diagram. A complete analytical solution of model equations is found in a parametric form by introducing a new variable-the solid phase fraction in the mushy layer. The temperature and solute concentration, as well as the solid fraction in the mushy layer, its boundaries, and the crystallization velocity, are determined analytically. It is shown that a non-linear phase diagram substantially influences the behavior of solutions obtained.

8.
J Phys Condens Matter ; 32(19): 194002, 2020 May 08.
Article in English | MEDLINE | ID: mdl-31931496

ABSTRACT

The dendritic growth of pure materials in undercooled melts is critical to understanding the fundamentals of solidification. This work investigates two new insights, the first is an advanced definition for the two-dimensional stability criterion of dendritic growth and the second is the viability of the enthalpy method as a numerical model. In both cases, the aim is to accurately predict dendritic growth behavior over a wide range of undercooling. An adaptive cell size method is introduced into the enthalpy method to mitigate against 'narrow-band features' that can introduce significant error. By using this technique an excellent agreement is found between the enthalpy method and the analytic theory for solidification of pure nickel.

9.
Sci Rep ; 8(1): 6879, 2018 May 02.
Article in English | MEDLINE | ID: mdl-29720623

ABSTRACT

This work presents results in the field of advanced substrate solutions in order to achieve high crystalline quality group-III nitrides based heterostructures for high frequency and power devices or for sensor applications. With that objective, Low Temperature Co-fired Ceramics has been used, as a non-crystalline substrate. Structures like these have never been developed before, and for economic reasons will represent a groundbreaking material in these fields of Electronic. In this sense, the report presents the characterization through various techniques of three series of specimens where GaN was deposited on this ceramic composite, using different buffer layers, and a singular metal-organic chemical vapor deposition related technique for low temperature deposition. Other single crystalline ceramic-based templates were also utilized as substrate materials, for comparison purposes.

10.
J Phys Condens Matter ; 30(10): 105702, 2018 03 14.
Article in English | MEDLINE | ID: mdl-29380745

ABSTRACT

A stable growth of dendritic crystal with the six-fold crystalline anisotropy is analyzed in a binary nonisothermal mixture. A selection criterion representing a relationship between the dendrite tip velocity and its tip diameter is derived on the basis of morphological stability analysis and solvability theory. A complete set of nonlinear equations, consisting of the selection criterion and undercooling balance condition, which determines implicit dependencies of the dendrite tip velocity and tip diameter as functions of the total undercooling, is formulated. Exact analytical solutions of these nonlinear equations are found in a parametric form. Asymptotic solutions describing the crystal growth at small Péclet numbers are determined. Theoretical predictions are compared with experimental data obtained for ice dendrites growing in binary water-ethylenglycol solutions as well as in pure water.

11.
Philos Trans A Math Phys Eng Sci ; 376(2113)2018 Feb 28.
Article in English | MEDLINE | ID: mdl-29311208

ABSTRACT

Transport processes around phase interfaces, together with thermodynamic properties and kinetic phenomena, control the formation of dendritic patterns. Using the thermodynamic and kinetic data of phase interfaces obtained on the atomic scale, one can analyse the formation of a single dendrite and the growth of a dendritic ensemble. This is the result of recent progress in theoretical methods and computational algorithms calculated using powerful computer clusters. Great benefits can be attained from the development of micro-, meso- and macro-levels of analysis when investigating the dynamics of interfaces, interpreting experimental data and designing the macrostructure of samples. The review and research articles in this theme issue cover the spectrum of scales (from nano- to macro-length scales) in order to exhibit recently developing trends in the theoretical analysis and computational modelling of dendrite pattern formation. Atomistic modelling, the flow effect on interface dynamics, the transition from diffusion-limited to thermally controlled growth existing at a considerable driving force, two-phase (mushy) layer formation, the growth of eutectic dendrites, the formation of a secondary dendritic network due to coalescence, computational methods, including boundary integral and phase-field methods, and experimental tests for theoretical models-all these themes are highlighted in the present issue.This article is part of the theme issue 'From atomistic interfaces to dendritic patterns'.

12.
J Phys Condens Matter ; 28(3): 035102, 2016 Jan 27.
Article in English | MEDLINE | ID: mdl-26732456

ABSTRACT

The evolution of particle coarsening due to a combined effect of Ostwald ripening and coagulation at the concluding stage of phase transition processes in metastable media is considered. A complete analytical solution of integro-differential equations with a memory kernel is found in special self-similar variables for supersaturated solutions and supercooled liquids. It is shown that the particle distribution function becomes narrower and bell-shaped when decreasing the metastability level. The analytical solutions obtained are in good agreement with experimental data.

13.
Bull Exp Biol Med ; 146(1): 116-9, 2008 Jul.
Article in English | MEDLINE | ID: mdl-19145367

ABSTRACT

A technology for obtaining a biomatrix on the basis of polypropylene mesh, used in clinical surgery, and cultured fetal fibroblasts is proposed. The method was developed on experimental animal cells. It includes culturing of rat fetal fibroblasts on fibers of a polypropylene mesh, treated with wheat germ lectin. This technology can be used for obtaining a biomatrix with fibroblasts of different origin. This biomatrix can be used in experimental and clinical surgery for dressing and stimulation of effective healing of mechanical injuries to the connective tissue.


Subject(s)
Biocompatible Materials/metabolism , Fibroblasts/physiology , Polypropylenes/metabolism , Surgical Mesh , Animals , Biocompatible Materials/chemistry , Cell Culture Techniques , Cells, Cultured , Fibroblasts/cytology , Materials Testing , Mice , Polypropylenes/chemistry , Rats , Wheat Germ Agglutinins/metabolism
14.
J Phys Condens Matter ; 20(11): 114105, 2008 Mar 19.
Article in English | MEDLINE | ID: mdl-21694198

ABSTRACT

A model is presented that describes nonstationary solidification of binary melts or solutions from a cooled boundary maintained at a time-dependent temperature. Heat and mass transfer processes are described on the basis of the principles of a mushy layer, which divides pure solid material and a liquid phase. Nonlinear equations characterizing the dynamics of the phase transition boundaries are deduced. Approximate analytical solutions of the model under consideration are constructed. A method for controlling the external temperature at a cooled wall in order to obtain a required solidification velocity is discussed.

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