Density of states in a mesoscopic SNS junction

The semiclassical theory of proximity effects predicts a gap E _g～?D/L ² in the excitation spectrum of a long diffusive superconductor/normal-metal/superconductor (SNS) junction. Mesoscopic fluctuations lead to anomalously localized states in the normal part of the junction.As a result, a nonzero, yet exponentially small, density of states (DOS) appears at energies below E _g. In the framework of the supermatrix nonlinear σ model, these prelocalized states are due to the instanton configurations with broken supersymmetry. The exact result for the DOS near the semiclassical threshold is found, provided the dimensionless conductance of the normal part G _N is large. The case of poorly transparent interfaces between the normal and superconductive regions is also considered. In this limit, the total number of subgap states may be large.     

Weak antilocalization in a 2D electron gas with chiral splitting of the spectrum

Motivated by the recent observation of the metal-insulator transition in Si MOSFETs, a study is made of the quantum interference correction to the conductivity in the presence of the Bychkov-Rashba spin splitting. For a small splitting, a crossover from the localizing to antilocalizing regime is obtained. The antilocalization correction vanishes, however, in the limit of a large separation between the chiral branches. The relevance of the chiral splitting for the 2D electron gas in Si MOSFETs is discussed. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 118–123 (25 January 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Level statistics inside the core of a superconductive vortex

A microscopic theory of the Efetov supermatrix sigma-model type is constructed for the low-lying electron states in a mixed superconductive-normal system with disorder. This technique is used for the study of the localized states in the core of a vortex in a moderately clean superconductor with τ ⁻¹≫ω ₀∼Δ²/E _F . At low energies ε≪ω _Th∼ (ω ₀/τ)^1/2, the energy level statistics is described by the “zero-dimensional” limit of this supermatrix theory, and the result for the density of states is equivalent to that obtained within Altland-Zirnbauer random matrix model. Nonzero modes of the sigma model increase the mean interlevel distance by the relative amount [2 ln (1/ω ₀ τ)]⁻¹. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 78–83 (10 July 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Investigations on 1-Azabicyclic Compounds. 25. Stereochemistry, Hydrogen Bonds, and Gas-Liquid Chromatography of Pyrrolizidine Alcohols

Data have been summarized of several studies on the separation of isomeric pyrrolizidine alcohols by GLC using liquid polar stationary phases. It was shown that the order of emergence of isomers from the chromatographic column is determined to a significant extent by competition of intermolecular hydrogen bonds formed in the sorbate-sorbent systems and intramolecular hydrogen bonds in the molecules of the same pyrrolizidine alcohols. The preference for one or other type of hydrogen bond depends on the stereochemistry of the pyrrolizidine alcohols. Analysis of the geometric conditions for the formation of intramolecular hydrogen bonds in the investigated compounds in conjunction with chromatographic resolution data enables their configurations to be assigned. The anomalously short retention times of highly strained 5-hydroxyalkyl-3-methylpyrrolizidines are explained by the existence in them of a bicyclic conformation predominantly with a trans linkage and with f avora ble geometric conditions for forming intramolecular hydrogen bonds in them.     

Phosphorus-containing Small Rings: X. Phosphorylation of Derivatives of 1-Methyl-2,2-dichlorocyclopropanecarboxylic Acid

Reaction of derivatives of 1-methyl-2,2-dichlorocyclopropanecarboxylic acid with three- and four-coordinate phosphorus acids was studied. It was established that the nucleophilic substitution on the carbonyl carbon atom proceeds without cleavage of the three-membered ring and leads to new types of phosphorus-containing cyclopropanes. The products were found to enhance the germination energy and laboratory germination of cereal, legume, and vegetable seeds.     

Reaction of Organoelement Hydrides R<Subscript>3</Subscript>EH (E = Si,Ge) with Metal <Emphasis Type="Italic">tert</Emphasis>-Butylate (M = Al,Ti)-<Emphasis Type="Italic">tert</Emphasis>-Butyl Hydroperoxide Oxidative Systems

Trialkyl(aryl)silanes and -germanes effectively react with metal (Al, Ti) tert-butylate-tert-butyl-hydroperoxide under mild conditions (room temperature, benzene or tetrachloromethane) mainly by the element-hydrogen bond. The character of the products depends on the nature of the element, the structure of the radical bound to it, and the solvent. The process is radical in nature. It includes the stages of formation of element-centered radicals and their reaction with the oxygen generated by the system. The intermediate organometallic peroxides can also acts as oxidants for the element (Si, Ge)-hydrogen bonds.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 7, 2005, pp. 1161–1170.Original Russian Text Copyright © 2005 by Stepovik, Gulenova, Martynova, Skvortsov, Cherkasov.     

Reaction of 1,1,3,3-tetramethyldisiloxane with p-substituted acetophenones in the presence of platinum and rhodium complexes

Hydrosilylation of p-substituted acetophenones XC₆H₄COCH₃ (X = H, Me, MeO, HO, F, Cl, NO₂) with 1,1,3,3-tetramethyldisiloxane in the presence of rhodium and platinum complexes was studied. The Pt(II) complexes are less active but more selective catalysts of hydrosilylation of acetophenones. Six new 1-(1-arylethoxy)-1,1,3,3-tetramethyldisiloxanes were prepared.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1804–1811.Original Russian Text Copyright © 2004 by Zuev, de Vekki, Kuchaev, Vorobev, Skvortsov.This revised version was published online in April 2005 with a corrected cover date.     

Cyanoacetylenes in reaction with benzimidazol-2-one

The reaction of 1-phenyl-2-cyanoacetylene and 4-hydroxy-4-methyl-2-pentynenitrile with benzimidazol-2-one was studied. The respective N,N-diadducts were obtained. It was shown that the addition of benzimidazol-2-one to the tertiary cyanoacetylenic alcohol catalyzed by bases is accompanied by intramolecular cyclization.Irkutsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, 664033 Irkutsk. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1140–1443, June, 1992.     

Liquid adsorption chromatography of polyethers: experiments and simulation

The adsorption behavior of poly(ethylene glycol) (PEG) in reversed-phase chromatography is studied both experimentally and theoretically and a computer simulation of chromatograms is performed on the basis of these studies. The experimental conditions were: different reversed-phase adsorbents and a solvent methanol–water system as the mobile phase. At varying mobile phase compositions highly resolved chromatograms of PEG samples were obtained, in which all peaks could be identified, and the dependencies of the distribution coefficient on the degree of polymerization for PEG molecules were evaluated by processing these chromatograms. The data were interpreted by using a theory of homopolymers based on a continuum Gaussian chain model of flexible macromolecules and a slit-like model of pores of stationary phase. The theory proved to describe well the experimental data in the whole range of studied molecular masses, and the thermodynamic parameters characterizing interactions of ethylene oxide repeating units in PEG molecules with the adsorbent pore walls have been determined from the comparison of the theory with the experimental data. The dispersion of chromatographic peaks corresponding to individual oligomer molecules is also estimated. In the system studied the peak width occurred to be proportional to the distribution coefficient of corresponding macromolecule. The theory is used to develop a computer-assisted procedure for simulation of chromatograms for samples of linear homopolymers. Using the obtained data on the thermodynamic parameters and the estimates of peak dispersion, chromatograms are simulated for PEG samples at two different chromatographic conditions. These simulated chromatograms were in good quantitative agreement with the real chromatograms.     

Reaction of 1,2,4-triazole-3-thione with acetylene

A mixture of 1,2,4-triazol-3-yl vinyl sulfide and N,S-divinyl derivatives is formed in the reaction of 1,2,4-triazole-3-thione with acetylene under pressure. The mixture of N,S-divinyl derivatives was separated into two isomers by gas-liquid chromatography. The hydrogenation, polymerization, and complexing of 1,2,4-triazol-3-yl vinyl sulfide were studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1561–1563, November, 1977.