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Sobolev S.L.,RAS Institute of Problems of Chemical Physics
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2014

An analytical model has been developed to describe the diffusion-viscous stress coupling in the liquid phase during rapid solidification of binary mixtures. The model starts with a set of evolution equations for diffusion flux and viscous pressure tensor, based on extended irreversible thermodynamics. It has been demonstrated that the diffusion-stress coupling leads to non-Fickian diffusion effects in the liquid phase. With only diffusive dynamics, the model results in the nonlocal diffusion equations of parabolic type, which imply the transition to complete solute trapping only asymptotically at an infinite interface velocity. With the wavelike dynamics, the model leads to the nonlocal diffusion equations of hyperbolic type and describes the transition to complete solute trapping and diffusionless solidification at a finite interface velocity in accordance with experimental data and molecular dynamic simulation. © 2013 Elsevier B.V. Source

Buchachenko A.L.,RAS Institute of Problems of Chemical Physics
Russian Chemical Reviews | Year: 2014

The molecular concept (paradigm) in magnetobiology seems to be most substantiated and significant for explaining the biomedical effects of electromagnetic fields, for the new medical technology of transcranial magnetic stimulation of cognitive activity, for the nuclear magnetic control of biochemical processes and for the search of new magnetic effects in biology and medicine. The key structural element of the concept is a radical ion pair as the receiver of magnetic fields and the source of magnetic effects. The existence of such pairs was recently detected in the two life-supporting processes of paramount importance D in enzymatic ATP and DNA syntheses. The bibliography includes 80 references. © 2014 Russian Academy of Sciences and Turpion Ltd. Source

Sobolev S.L.,RAS Institute of Problems of Chemical Physics
Acta Materialia | Year: 2013

An abrupt transition from diffusion-limited solidification to diffusionless, kinetic-limited solidification with complete solute trapping is explained as a critical phenomenon which arises due to local non-equilibrium diffusion effects in the bulk liquid. The transition occurs when the interface velocity V passes through the critical point V = VD, where V = V D is the bulk liquid diffusive velocity. Analytical expressions are developed for velocity-temperature and velocity-undercooling functions, using local non-equilibrium partition coefficient based on the Jackson et al. kinetic model and the local non-equilibrium diffusion model of Sobolev. The calculated functions demonstrate a sharp break in the velocity-undercooling and velocity-temperature relationships at the critical point V = VD. At this point the local non-equilibrium solidus and liquidus lines coincide with the T0 temperature. The relationship to pertinent experiments and the influence of the local non-equilibrium diffusion effects on grain refinement and disorder trapping phenomena are discussed. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

Denisov E.,RAS Institute of Problems of Chemical Physics
Organic and Biomolecular Chemistry | Year: 2011

The kinetic schemes of intramolecular reactions of five analogs of artemisinin were built. The method of intersecting parabolas was used for the calculation of activation energies and rate constants of each elementary step of these schemes. The competition between monomolecular and bimolecular free radicals was taken into account. It was evidenced that the intramolecular oxidation of these compounds proceeds as a cascade of consecutive free radical reactions with the formation of hydroperoxide groups. The latter decompose via reactions with the Fe(ii) complexes generating free radicals. Among the radicals formed, the hydroxyl radical was proved to play the key role. A correlation between the yield of hydroxyl radicals nOH and antimalarial activity of compounds (IC50) was observed. The dependence of index IC 50 on nOH is linear in the logarithmic coordinates: ln[IC50(Artemisinin)/IC50(Compound)] = -14.10 + 3.85 × nOH. The proposed scheme explains and demonstrates a strong dependence of the antimalarial effectiveness of a drug on the chemical structure. © 2011 The Royal Society of Chemistry. Source

Budyka M.F.,RAS Institute of Problems of Chemical Physics
Russian Chemical Reviews | Year: 2012

The mechanism of photoisomerization of diarylethenes is considered, including its multiplet, conformational and energetic aspects. The experimental data on the 'one bond flip' and 'hula-twist' photoisomerization mechanisms, the adiabatic and diabatic reaction channels and also on one-photon photocyclization of diarylethene trans-isomers are surveyed. The results of quantum chemical calculations of the potential energy surface along the reaction coordinates of diarylethene isomerization and cyclization are analyzed. © 2012 Russian Academy of Sciences and Turpion Ltd. Source

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