Study of magnetic flux pinning in granular YBa2Cu3O7 − y /nanoZrO2 composites

In this work, the effect of ZrO₂ nanoparticles prepared in a low-pressure arc discharge plasma on magnetic flux pinning of granular YBa₂Cu₃O_{7 ? y} /nanoZrO₂ composites has been studied. It has been shown that the ZrO₂ nanoparticles do not change the superconducting transition and the microstructure of superconductors. At a temperature of 5 K, the addition of 0.5 and 1 wt % of ZrO₂ nanoparticles may lead to the additional effect of magnetic flux pinning and the increase in the critical current density J _c. The J _c value for composites with 1 wt % is two times larger than that for the reference sample. The fishtail effect is observed for YBa₂Cu₃O_{7 ? y} /nanoZrO₂ composites at the temperatures of 20 and 50 K. The problems associated with the additional effect of magnetic flux pinning of granular YBa₂Cu₃O_{7 ? y} /nanoZrO₂ composites and the appearance of the fishtail effect have been discussed.     

Differential games with fixed terminal time and estimation of the instability degree of sets in these games

This paper contributes to the theory of differential games. A game problem of bringing a conflict-controlled system to a compact target set is analyzed. Sets in the position space that terminate on the target set and are not stable bridges are considered. The notion of stability defect of these sets is examined. It is demonstrated how the notion of stability defect can be used to construct sets with relatively good geometry that are at the same time convenient for the first player to play the game successfully.     

Effect of annealing on the deformation and fracture of metallic glass under local loading

An investigation is undertaken into the variations observed in the cracking resistance, the plasticity, and the structure of an 82K3KhSR metallic glass upon annealing. A method of evaluating the mechanical properties and the structural state of metallic glasses is proposed. This method is based on the indentation of the metallic glass deposited onto a substrate prepared from a polyester material and a metal. The critical annealing temperature that corresponds to drastic changes in the mechanical properties of the metallic glass is determined. It is found that dependences of the cracking resistance of metallic glasses on the indenter load exhibit a linear behavior at annealing temperatures above the critical point. An exponential decrease in the cracking resistance upon indentation is observed with an increase in the annealing temperature of metallic glasses.     

From acylethynylpyrroles to pyrrole-pyrone ensembles in a one step

Functionalized pyrrole-pyrone ensembles have been synthesized in up to 87% yields by KOH/MeCN [4+2]-cyclization of available acylethynylpyrroles with methylene active esters. The synthesized compounds, due to their potential rich chemistry, are rewarding building blocks for novel pyrrole-integrated complex molecules and promising precursors of medicine targeted compounds.     

Thermoinitiated polymerization of 1,1,3,3-tetramethyl-1-sila-3-germacyclobutane and the polymer chain structure

Russian Chemical Bulletin -     

New Approach to the Synthesis of Strained Cyclic Systems: I. Iminocyclobutenes and Iminothietanes from 1,3-Dilithio-3-phenylpropyne and Methyl Isothiocyanate

The reaction of 1,3-dilithio-3-phenylpropyne with methyl isothiocyanate in THF-hexane at -90 to -55°C, followed by successive treatment of intermediate product with a donor of protons, superbase, and alkyl halide, yields isomeric iminocyclobutenes and iminothietanes in addition to the expected aminothiophene. The ratio of the products depends on the amount and nature of proton donor (MeOH, t-BuOH), base (MeONa, t-BuOM, M = Li, Na, K; t-AmOK), co-solvent (DMSO, HMPA), and alkyl halide (MeI, EtI, BuBr). The system t-BuOH(MeOH)-t-BuOK-DMSO is the most favorable for the formation of the corresponding iminocyclobutene.     

Cyclooligomerization of Acetylene with Acetonitrile to 2-Amino-3-(1-iminoethyl)-6-methylpyridine in the System KOH-CH3CN

Russian Journal of Organic Chemistry -     

Coincidence criteria for maximal stable bridges in two game problems of approach

We consider a finite-dimensional conflict-controlled system whose behavior on a finite time interval is described by a vector differential equation. We analyze two game problems of approach in the phase space. In both problems the same terminal set is considered: in the first case, one should guarantee that the phase vector of the system reaches the terminal set at the final instant of time; in the second case, the phase vector should reach the terminal set no later than the final time instant. It is natural to assume that the construction of a solution to the first problem is much simpler than the construction of a solution to the second problem; this fact is confirmed by available experience. The paper is devoted to finding conditions on the system and the terminal set under which the solutions to the above problems coincide. Using these conditions, one can replace the solution of the second problem by the simpler solution of the first problem.     

Selective on-line deuteration in gas chromatography - mass spectrometry for the investigation of dissociative ionization of silicon-containing compounds

A method for specific gas-phase deuteration of unsaturated silicon-containing compounds over pre-heterogenized Wilkinson's catalyst (a solution of (Ph₃P)₃RhCl in Carbowax 20M coated on Chromaton) in the reaction column connected to the mass spectrometer is described. This method was employed to study the dissociative ionization of the corresponding saturated analogues. With the aid of the mass spectra of the dideutero derivatives thus obtained, the main electron-impact-induced reactions of 1,1-dimethyl-1-silacyclopentane, 1,1,2,2-tetramethyl-1,2-disilacyclohexane, 1-methyl-1-ethyl-1-silacyclobutane and ethyl triethoxysilane were elucidated.