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41.
M. I. Petrov D. A. Balaev D. M. Gokhfel’d K. A. Shaikhutdinov K. S. Aleksandrov 《Physics of the Solid State》2002,44(7):1229-1234
The temperature evolution of the current-voltage (I-U) characteristic of a contact of the break-junction type with direct conduction is investigated on a polycrystalline HTSC of the Y-Ba-Cu-O system. The experimental I-U characteristics possessing a hysteresis are correctly described in the framework of the Kümmel-Nicolsky theory for an S-N-S contact (S stands for a superconductor; N, for a normal metal) in which the Andreev reflection of quasiparticles from the N-S interface is considered. It is shown that the shape of the I-U curve, as well as the existence of a hysteresis, is determined by the ratio of the number of “long” and “short” intergranular boundaries in the polycrystal under investigation. The coincidence of the calculated and experimental I-U curves made it possible to estimate the effective length of “natural” intergranular boundaries in polycrystalline HTSC materials. The estimate is obtained from the experimental temperature dependence of the critical current in the sample under investigation. 相似文献
42.
M. I. Petrov D. A. Balaev S. V. Ospishchev K. A. Shaikhutdinov B. P. Khrustalev K. S. Aleksandrov 《Physics of the Solid State》1997,39(3):362-368
Composites are prepared from a high-temperature superconductor with the 1-2-3 structure and the low-temperature oxide BaPb3/4Bi1/4O3 with various volume concentrations of the high-temperature and low-temperature superconductors. The temperature dependences
of the electrical resistivities and critical current densities of the composites are measured. It is shown experimentally
that these composites comprise a synthetically created network of Josephson weak links (with a specified degree of coupling).
Fiz. Tverd. Tela (St. Petersburg) 39, 418–424 (March 1997)
Deceased. 相似文献
43.
S. A. Mustafina Yu. A. Valieva R. S. Davletshin A. V. Balaev S. I. Spivak 《Kinetics and Catalysis》2005,46(5):705-711
Efficient methods and algorithms have been developed for the optimization of catalytic processes and reactors. In mathematical terms, these problems reduce to finding the extremum of a functional of a large number of variables whose domain of variation is subject to various constraints as sets of partial differential equations and algebraic inequalities. This implies solving problems in which the domain of extremals is closed. Applying Pontryagin's maximum principle to catalytic processes described by sets of differential equations with constrained phase and control variables allows the necessary set of optimal conditions to be found. A numerical algorithm has been developed for solving nonlinear boundary-value problems that arise when the maximum principle is employed. The efficiency of this algorithm is demonstrated by the example of the catalytic oligomerization of α-methylstyrene, a typical process requiring various kinds of optimization problems to be solved. The theoretical optimization of the process has served as the basis for the engineering optimization of an industrial reactor. Optimal controls were determined in both the theoretical and engineering optimization steps. 相似文献
44.
Isakova V. G. Petrakovskaya E. A. Balaev A. D. Kolpakova T. A. 《Russian Journal of Applied Chemistry》2003,76(4):577-581
Thermal reaction of solid mixtures of fullerene C60 with iron(III) acetylacetonate proceeds in the combustion mode; the composition and characteristics of the reaction products are governed by the Fe : C60 ratio in the initial mixture. The magnetization of iron-fullerene complexes was measured. 相似文献
45.
V. V. Balaev A. A. Lashkov I. I. Prokofev A. G. Gabdulkhakov T. A. Seregina A. S. Mironov C. Betzel A. M. Mikhailov 《Crystallography Reports》2016,61(5):830-841
Pyrimidine nucleoside phosphorylases, which are widely used in the biotechnological production of nucleosides, have different substrate specificity for pyrimidine nucleosides. An interesting feature of these enzymes is that the three-dimensional structure of thymidine-specific nucleoside phosphorylase is similar to the structure of nonspecific pyrimidine nucleoside phosphorylase. The three-dimensional structures of thymidine phosphorylase from Salmonella typhimurium and nonspecific pyrimidine nucleoside phosphorylase from Bacillus subtilis in complexes with a sulfate anion were determined for the first time by X-ray crystallography. An analysis of the structural differences between these enzymes demonstrated that Lys108, which is involved in the phosphate binding in pyrimidine nucleoside phosphorylase, corresponds to Met111 in thymidine phosphorylases. This difference results in a decrease in the charge on one of the hydroxyl oxygens of the phosphate anion in thymidine phosphorylase and facilitates the catalysis through SN2 nucleophilic substitution. Based on the results of X-ray crystallography, the virtual screening was performed for identifying a potent inhibitor (anticancer agent) of nonspecific pyrimidine nucleoside phosphorylase, which does not bind to thymidine phosphorylase. The molecular dynamics simulation revealed the stable binding of the discovered compound—2-pyrimidin-2-yl-1H-imidazole-4-carboxylic acid—to the active site of pyrimidine nucleoside phosphorylase. 相似文献
46.
S. A. Kharlamova S. G. Ovchinnikov A. D. Balaev M. F. Thomas I. S. Lyubutin A. G. Gavriliuk 《Journal of Experimental and Theoretical Physics》2005,101(6):1098-1105
Magnetic properties of GdFe3(BO3)4 single crystals were investigated by 57Fe-Mössbauer spectroscopy and static magnetic measurements. In the ground state, the GdFe3(BO3)4 crystal is an easy-axis compensated antiferromagnet, but the easy axis of iron moments does not coincide with the crystal C3 axis, deviating from it by about 20°. The spontaneous and field-induced spin reorientation effects were observed and studied in detail. The specific directions of iron magnetic moments were determined for different temperatures and applied fields. Large values of the angle between the Fe3+ magnetic moments and the C3 axis in the easy-axis phase and between Fe3+ moments and the a2 axis in the easy-plane phase reveal the tilted antiferromagnetic structure. 相似文献
47.
Yu.?L.?Ra?kher V.?I.?Stepanov S.?V.?Stolyar V.?P.?Ladygina D.?A.?Balaev L.?A.?Ishchenko M.?Balasoiu 《Physics of the Solid State》2010,52(2):298-305
Ferrihydrite nanoparticles (2–5 nm in size) produced by bacteria Klebsiella oxytoca in the course of biomineralization of iron salt solutions from a natural medium exhibit unique magnetic properties: they
are characterized by both the antiferromagnetic order inherent in a bulk ferrihydrite and the spontaneous magnetic moment
due to the decompensation of spins in sublattices of a nanoparticle. The magnetic susceptibility enhanced by the superantiferromagnetism
effect and the magnetic moment independent of the magnetic field provide the possibility of magnetically controlling these
natural objects. This has opened up the possibilities for their use in nanomedicine and bioengineering. The results obtained
from measurements of the magnetic properties of the ferrihydrite produced by Klebsiella oxytoca in its two main crystalline modifications are reported, and the data obtained are analyzed theoretically. This has made it
possible to determine numerical values of the magnetic parameters of real biomineral nanoparticles. 相似文献
48.
M. I. Petrov D. A. Balaev I. L. Belozerova S. I. Popkov A. A. Dubrovskii K. A. Shaykhutdinov O. N. Mart’yanov 《Technical Physics》2009,54(8):1130-1134
Low-density polycrystalline Bi1.8Pb0.3Sr1.9Ca2Cu3O
x
high-temperature superconductors with a foamlike microstructure and composites consisting of this superconductor and silver
in an amount of 20, 25, and 30 vol % are synthesized. The microstructure, as well as the temperature and field dependences
of the magnetization, M(T) and M(H), are studied. It is found that, in Bi1.8Pb0.3Sr1.9Ca2Cu3O
x
high-temperature superconductors and Bi1.8Pb0.3Sr1.9Ca2Cu3O
x
+ Ag composites, the diamagnetic response is enhanced and the screening properties are improved compared with high-temperature
polycrystalline superconductors with the same composition that are prepared by the standard technology. The observed effect
is explained by the features of magnetic flux penetration into a porous medium. 相似文献
49.
M. I. Petrov D. A. Balaev Yu. S. Gokhfel’d A. A. Dubrovskiĭ K. A. Sha’khutdinov 《Physics of the Solid State》2007,49(11):2047-2051
The Y(1 ? x Ce x Ba2Cu3O7 system with low cerium concentrations has been synthesized. The cerium solubility limit measured using x-ray powder diffraction analysis is about 2.4 at. %. The temperature dependences of the magnetization M(T) are measured for samples cooled in a magnetic field (FC) and in a zero field (ZFC). The difference between the magnetizations M ZFC-M FC at 77.4 K, which is proportional to the pinning potential, passes through a maximum at x = 0.0156. This concentration corresponds to the average distance (equal to eight lattice constants) between the impurity ions in the plane of the rare-earth elements, which is comparable to the diameter of Abrikosov vortices in YBa2Cu3O7. 相似文献
50.
D. A. Balaev A. A. Dubrovskii A. A. Krasikov S. V. Stolyar R. S. Iskhakov V. P. Ladygina E. D. Khilazheva 《JETP Letters》2013,98(3):139-142
The magnetic properties of antiferromagnetic nanoparticles of FeOOH · nH2O with sizes of 3–7 nm, which are products of vital functions of Klebsiella oxytoca bacteria, have been studied. Particles exhibit a superparamagnetic behavior. The characteristic blocking temperature is 23 K. Analysis of the magnetization curves shows that the mechanism of the formation of the uncompensated magnetic moment of particles is the random decompensation of magnetic moments of Fe3+ ions both on the surface and in the bulk of the antiferromagnetic particle. In this mechanism, the exchange coupling between the uncompensated magnetic moment of the particle and its antiferromagnetic “core” is implemented. It has been found that the temperature dependence of the uncompensated magnetic moment has the form 1 — constT 2. 相似文献