Quantum-Chemical Study of the Profiles of Reactions that Form Pyrrole Anion N-Adducts with CS<Subscript>2</Subscript> and CO<Subscript>2</Subscript>

The profiles of reactions leading to pyrrole anion N-adducts with CO₂ and CS₂ have been studied by the ab initio (RHF/6-31+G*, MP2/6-31+G*) and density functional (B3LYP/6-31+G*) methods. Addition of the pyrrole anion to the carbon disulfide molecule is accompanied by the appearance of a minimum corresponding to a pre-reaction complex. The transformation of the complex to the N-pyrrolyldithiocarboxylate anion occurs via a low activation barrier, which is due to repolarization of the C=S bonds. The profile of the reaction leading to the pyrrole anion N-adduct with CO₂ does not contain any intermediate stationary points throughout the whole route from reagents to products.Original Russian Text Copyright © 2004 by V. B. Kobychev, N. M. Vitkovskaya, I. L. Zaitseva, and B. A. Trofimov__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 990–993, November–December, 2004.     

Influence of Pretreatment of Expanded Graphite on Its Sorption Properties with Respect to Petroleum

Petroleum sorption on expanded graphite prepared from residual graphite hydrosulfate at 300-900°C was studied as influenced by pretreatment of the sorbent with water.     

Optical and photoelectric properties of helical quantum wires

The appearance of a steady current in a helical quantum wire under circularly polarized light is predicted. The effect is associated with the appearance of a travelling electromagnetic wave in the coordinate system related to the wire, the wavelength being determined by the period of the helix. The gyrotropy of a medium consisting of parallel quantum wires is considered.     

Annihilation of positrons in hydrogen-saturated titanium

The effect of atomic hydrogen on the electronic structure of α-titanium samples is studied using the electron-positron annihilation methods. It is shown that different states of hydrogen atoms are manifested in different ways in the positron lifetime distribution spectrum. The results of theoretical calculations of the first component of the positron lifetime are in accord with the obtained experimental data.     

Degradation of Metal 2-Acrylamido-2-methylpropanesulfonate-N-Vinylpyrrolidine Copolymers in Aqueous Solutions Containing Different Cations

The influence of single- and double-charged cations on degradation of metal 2-acrylamido-2-methylpropanesulfonate-N-vinylpyrrolidine copolymers in aqueous solutions in the presence of potassium peroxodisulfate, K₂S₂O₈, at 50 and 70°C was studied by viscosimetry.     

Excited-state dynamics in Yb3+-Ho3+-doped fluoroindate glasses

This work has been partially supported by Gobierno Autonomo de Canarias under contact number 226–265/93.     

The Use of Corona Discharge for Rubber Crush Drier Exhaust Control

The rubber crush drier exhaust contains mainly styrene, ethylbenzene, cumene, diizopropylbenzene, alkylphenols, monocyclic terpenes and technological additives as stearic acid, oils an colophony. For possible application of d.c. corona discharge to control styrene in exhaust, the reaction of styrene with additives and air in various d.c. corona discharge tubes was studied. The change of styrene content in the gas phase was measured by IR absorption spectrometry. The decrease of styrene concentration was minimum 83% and reached the 98,9% efficiency. No aromatic compounds remain after corona discharge action in gas phase. The structure of solid products was specified with reflection IR absorption spectrometry and compared with a calibration polystyrene foil (300 μm). The main product has been of malein anhydride-styrene copolymer character for a negative corona discharge and of phenol or quinone-styrene copolymer character for a positive corona discharge.     

Oxidative dehydrogenation of alkylheteroaromatic compounds 1. Catalysts containing vanadium and molybdenum for the oxidative dehydrogenation of alkylpyridines

The dehydrogenation of a series of alkylpyrïdines has been studied on vanadium and molybdenum oxide-containing catalysts in the presence of oxygen of the air and sulfur dioxide gas. A dependence was shown of the catalytic and physicochemical properties of the catalysts indicated on their composition and method of preparation. The optimum catalyst composition and the conditions of carrying out the reaction to provide high activity and selectivity when making vinylpyridines were determined. The relative reactivity of the alkylpyridines investigated on dehydrogenation and further oxidation was determined.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 802–811, June, 1994. Original article submitted April 19, 1994.     

Stochastic resonance in perspective

Summary We outline the historical development of stochastic resonance (SR), a phenomenon in which the signal and/or the signal-to-noise ratio in a nonlinear system increase with increasing intensity of noise. We discuss basic theoretical ideas explaining and describing SR, and we review some revealing experimental data that place SR within the wider context of statistical physics. We emphasize the close relationship of SR to some effects that are well known in condensed-matter physics. Paper presented at the International Workshop ?Fluctuations in Physics and Biology: Stochastic Resonance, Signal Processing and Related Phenomena?, Elba, 5–10 June 1994.