Evidence for the existence of two kinds of orthopositronium in condensed rare gases and for irreversible transitions between them

With reference to time-differential measurements of the momentum distribution of annihilating positron–electron pairs (AMOC) in the condensed rare gases Ne, Ar, and Kr, the paper discusses the question whether in condensed matter positronium (Ps) forms only at predetermined trapping sites or “anywhere”, with subsequent processes leading to Ps trapping or to the formation of Ps bubbles. Ne, in which Ps bubbles are formed not only in the liquid but also in the solid state, may serve as model material for more complex Ps-formers, such as polymers.     

核桃油中脂肪酸含量的测定

核桃油中脂肪酸含量的测定岳红（西北工业大学化工系西安７１００７２）翟文俊（陕西教育学院西安７１００６１）关键词核桃油脂肪酸气相色谱中图分类号Ｏ６２３．６１２油脂营养一直是人们所关注和研究的重要课题，尤其是油脂中富含的不饱和脂肪酸，不仅有较高的营养价值...     

The formation of formic acid upon low-temperature condensation of a methane-carbon dioxide mixture dissociated in a microwave discharge

Formic acid was found as the main product upon low-temperature (77 K) condensation of the CH₄+CO₂ mixture dissociated in the microwave discharge at a low pressure. The yield of HCOOH was studied as a function of the experimental conditions: flow rate of the initial gas mixture. CH₄ content in the initial mixture, pressure in the reactor, and output power of the microwave generator. The concentrations of H, O, OH, and O₂ in the gas phase were measured by ESR spectroscopy. Mathematical modeling of the kinetics of the gas phase chemical reactions in the connecting channel was performed. The mechanism of formic acid formation by the interaction of active species of the gas phase on the condensate surface was proposed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 826–831, May, 2000.     

Prospects of ion-mobility measurements in superheavy element research

The element specific electron configuration of ions directly reflects the two quantum mechanical observables 〈r²〉 and r_max, which denote the r² expectation value of the electron density and the principle maximum of the wave function of the outermost electron orbital, respectively. Thus, the determination of these observables may present a new access to element identification of single superheavy nuclides. In this paper, we discuss how these observables are related to ionic radii deduced from ion-mobility data using the most simple hard sphere model and semi-empirical (n,6,4) model potentials for the interaction of heavy ions with noble gases. A concept for a high resolution ion-mobility spectrometer is presented. Optimum extraction efficiency of the ions will be achieved by decoupling the ion motion from the electric field drift by the friction force of the suitably shaped gas flow at the exit nozzle.     

石墨炉原子吸收光谱法直接测定城市污泥中有机态镉

建立了真空冷冻干燥法制备有机相标准系列,氯化钯-磷酸氢二钾作基体改进剂,分步斜坡升温石墨炉原子吸收光谱法直接测定城市污泥中痕量有机态Cd的方法,有效地消除了基体干扰.方法的精密度(RSD,n=11)为5.7%,用于污泥样品的测定加标回收率在91%-107%之间,与常规消解法测定值比较结果令人满意.     

Quantum-well resonances and image states in the Ar/Cu(1 0 0) system

A theoretical study of the effect of an atomically thin rare gas layer on the dynamics of excited electronic states at metal surfaces is presented for the case of a few mono-layers of Ar on a Cu(1 0 0) surface. We develop a 3D-microscopic model with predictive capabilities of the interaction of an electron with an Ar layer physisorbed on a metal surface. It takes into account the 3D structure of the Ar layer as well as its dielectric character. The dynamics of the excited electron on the surface is treated within a wave-packet propagation approach. The calculations show that two different types of excited states are present at the Ar/Cu(1 0 0) surface. (i) Image states that are repelled into vacuum as compared to their position on clean Cu(1 0 0) surfaces, leading to a decrease of their binding energies and to an increase of their lifetimes. (ii) Quantum-well resonances, corresponding to quasi-stationary states localised inside the Ar layer; they are associated with the quantisation of the conduction band in the finite size Ar layer. The present results on image states nicely agree with very recent time-resolved two-photon-photo-emission experiments by Berthold, Feulner and Höfer.     

Separation of small molecules using novel rolltruded membranes. I. Apparatus and preliminary results

A novel membrane production technique, rolltrusion, has been developed for the preparation of permselective polymeric membranes for both gas and vapor separations and pervaporation applications. Pinhole-free thin films with a regulated three-dimensional morphology comprising crystalline and amorphous regions have been produced with improved mechanical properties in three dimensions. Because rolltrusion is a solid-state processing technique, it is not restricted by solubility constraints inherent in the common solvent-based thinfilm production techniques. Consequently it can be extended to include commercially available engineering plastics that have not been used as membranes previously because of their limited solvent solubility. These polymers are interesting because of their applicability to temperatures in excess of 200 to 300°C in harsh chemical environments, compared with the ca. 150°C ceiling usually encountered in the most rugged of solvent-cast polymers. In the first part of this series we detail an automated experimental permeation apparatus that permits testing of both single-component and multicomponent gases and vapors over a temperature range of ?73 to 273°C. Currently, modifications to the permeation cell are underway to permit pervaporation studies in the apparatus. To illustrate the operation of the apparatus, and to some degree the effect of rolltrusion processing, experimental permeability, diffusivity, solubility, and actual gas separation factors (via gas chromatography) are detailed for several light gases in rolltruded isotactic poly(propylene) (iPP) and in the thermally and chemically resistant thermoplastic, poly(ether ether ketone) (PEEK). Permeation temperatures to at least 225°C have been studied using PEEK, representing the first published experimental permeability and gas-separation results for such engineering polymers at temperatures above 200 °C. © 1992 John Wiley & Sons, Inc.     

Simulating three-dimensional hydrodynamics on a cellular automata machine

We demonstrate how three-dimensional fluid flow simulations can be carried out on the Cellular Automata Machine 8 (CAM-8), a special-purpose computer for cellular automata computations. The principal algorithmic innovation is the use of a lattice gas model with a 16-bit collision operator that is specially adapted to the machine architecture. It is shown how the collision rules can be optimized to obtain a low viscosity of the fluid. Predictions of the viscosity based on a Boltzmann approximation agree well with measurements of the viscosity made on CAM-8. Several test simulations of flows in simple geometries—channels, pipes, and a cubic array of spheres-are carried out. Measurements of average flux in these geometries compare well with theoretical predictions.