Kinetics and Mechanism of the Reaction of Triphenylphosphine with Methyl Vinyl Ketone

Russian Journal of General Chemistry - Kinetics of the reaction of triphenylphosphine with methyl vinyl ketone has been studied using the stopped flow technique. The experimental data have...     

Observation of dielectronic satellites in the K-spectrum of argon ions in plasma produced by femtosecond laser pulses

The satellite structure of 1s2p ^1,3 P ₁-1s ²¹ S ₀ lines of the He-like argon ion in plasma produced by a 45-fs laser pulse in a gas-jet cluster target is measured with a high spectral resolution. Radiation transitions 2p → 1s from autoionizing states (AISs) are detected for ions ranging from Li-like to F-like. The spectrum observed is theoretically simulated with the use of the spectroscopic data for the AISs of multicharged ions obtained within the multiconfiguration relativistic Hartree-Fock method. Good agreement with experimental data is obtained when the main population channels of these states are taken into account for typical values of cluster-target plasma parameters.     

Can a Metal-Insulator Transition Induce s-Wave Superconductivity?

A recent paper of Capone et al. has studied an extended Hubbard model, in which local orbital degrees of freedom allow an even integer occupation at each site. A strong local repulsion U triggers a metal-insulator transition. Within a DMFT numerical analysis they show that when the ground state is a singlet a pocket of s-wave superconductivity appears in the vicinity of the Mott transition, with a strongly enhanced superconducting gap. A qualitative understanding of their result is proposed, and suggestions are made of possible systems in which this beautiful effect might be searched.     

Eine neue Methode zur gewichtsanalytischen Bestimmung der reduzierenden Zucker unter Anwendung der Zentrifuge

Ohne Zusammenfassung1) Vergl. Meillère und Chapelle, diese Zeitschrift41, 100.     

Effects of localization of the areas of sound scattering by surface wind waves

Experimental studies of the scattering of a monochromatic sound signal by a rough sea surface are carried out. The signal is produced by a point source in a shallow-water basin. The measurements are performed with the use of horizontal and vertical linear receiving arrays. The experimental data are compared with the estimates obtained on the basis of the model developed by the authors for resonant sound scattering by surface roughness. A satisfactory agreement between the experiments and the calculations is achieved. It is shown that the scattered signal is formed within small surface areas, whose sizes have the same order of magnitude as the first Fresnel zone with respect to the source and the receiving system.     

Dérivée des petites valeurs propres des surfaces de Riemann

On estime la dérivée des petites valeurs propres du Laplacien sur une famille de surfaces de Riemann. Ces valeurs propres sont considérées comme des fonctions sur l'espace de Teichmüller, et l'estimation des dérivées peut s'exprimer dans ce contexte. Received: December 21, 1995     

Preparation and Eh--pH diagrams of Fe(II)--Fe(III) green rust compounds; hyperfine interaction characteristics and stoichiometry of hydroxy-chloride, -sulphate and -carbonate

Fe(II)--Fe(III) hydroxy-chloride, -sulphate and -carbonate were prepared by oxidation of a ferrous hydroxide precipitate in anion-containing aqueous solutions. The compounds are characterized by monitoring the redox potential E_h and the pH of stochiometric suspension vs time with the appropriate concentration ratios. X-ray diffraction allows us to characterize the crystal structure by distinguishing “green rust one” (GR1) from “green rust two” (GR2). Since green rusts (GRs) are of a pyroaurite-sjögrenite-like structure, i.e., consisting of intercalated foreign anions and water molecules in the interlayers between the brucite-like layers of Fe(OH)₂, their chemical formulae can be determined from the Mössbauer spectra. Three quadrupole doublets are observed: D₁ and D₂ correspond to a ferrous state with isomershift IS of about 1.27 mm s^-1 and quadrupole splittings QS of about 2.85 and 2.60 mm s^-1, respectively, whereas D₃ corresponds to a ferric state with IS and QS of about 0.4 mm s^-1. The hyperfine parameters of these doublets are similar from one green rust to another but their intensity ratios vary considerably. Finally, E_h and pH equilibrium diagrams of the Fe species in the presence of chloride, sulphate and carbonate anions contained within the water solution are drawn and the thermodynamic conditions of existence and degrees of oxidation of green rusts are discussed.     

Random Classical Fidelity

We introduce a random perturbed version of the classical fidelity and we show that it converges with the same rate of decay of correlations, but not uniformly in the noise. This makes the classical fidelity unstable in the zero-noise limit.     

The role of alkali content in the devitrification mechanisms of SiO2–Fe2O3–Na2O–PbO SYSTEM

Three batch compositions of pure oxides (SiO₂, Fe₂O₃, PbO, Na₂O) with equivalent SiO₂, Fe₂O₃ and PbO contents and a gradually increased Na₂O content were vitrified through heating in a high temperature electric furnace and subsequent quenching. The resulting vitreous products were thermally treated in order to study the devitrification behaviour, under conditions designated from differential thermal analysis experiments. Depending on the Na₂O content, crystal phase separation gave rise to the growth of acmite and hematite or maghemite. A uniformly phase separated glass-ceramic material, with crystallites of similar size and population density, was produced from devitrification of the vitreous product with the higher Na₂O content.