Some aspects of the interactions of orthopositronium with perfect and defect surfaces of insulating materials

ETLA (Elastic Thermalisation Lifetime Analysis) is a new model function for the fitting of lifetime spectra of slowly thermalising orthopositronium in the free space between the grains of insulating oxide powders. From this model one can obtain three fundamental parameters; the mass of the cluster of atoms which scatters the o-Ps, the probability that the o-Ps is forced into two-quantum decay at each collision and the emission energyE(0) of the o-Ps from the powder surface. As a consequence of full thermalisation of the Ps it is shown that the o-Ps quenching constant _q () follows atT ^1/2 dependency for MgO, Al₂O₃ and SiO₂ and for temperatures between 77 and 500 K. In MgO powder at low temperatures the irradiation by the positrons induces surface paramagnetic defects which are identified as Mg⁺ sites. These surface defects do not affect the thermalisation, but they induce paramagnetic o-p conversion i.e., an increase in , and they are also responsible for an increase in the emission energyE(0) of the o-Ps.     

Heavy metals as indirect causative factors of capillaropathy

By applying systemic analysis to a set of random variables, representing blood or urine concentrations of certain enzymes, lipids and metals, three direct causative factors of capillaropathy, in its early stage, i.e. leucine amino peptidase, free erythrocyte protoporphyrin and C(3)-complement, have been found. The interactions between the early stage of capillaropathy and these factors have been quantitatively described and a formula for prognosing the capillaropathy occurrence has been proposed. It has also been shown that the following heavy metals Pb, Cd, Cr, Cu, Mg, Fe and Ca, through their direct or indirect interactions with C(3)-complement, exert an influence on the occurrence and intensity of capillaropathy. Since direct causative factors of a given pathology can serve as its markers, the completeness of the set of the capillaropathy markers, formed from the causative factors, and their contributions to this pathology have been evaluated. The results were obtained by examining a population of male residents chronically exposed to heavy metals (Pb, Cu) in the environment.     

Marginal separation in three-dimensional flows

The boundary layer in the vicinity of the zero skin-friction point on the leeward symmetry line of a prolate spheroid placed at an angle of attack is considered. The existence of this flow was established by Cebeci et al. (1980) for an angle of attack =40°. The current study is based on the results of Brown (1985) who described the marginal separation in the symmetry plane for a zero skin-friction point and on the results of Zametaev (1989) who included the spatial extension of Brown's solution but without interaction between the boundary layer and the outer flow. It is found that the three-dimensional boundary-layer equations in the vicinity of the zero skin-friction point are reduced to a single nonlinear partial differential equation of hyperbolic type which governs the longitudinal skin-friction component. Smooth solutions of this equation may be found which contain separation lines as well as double-valued regions. It is likely that the latter regions are related to the tip of the separation line obtained as a result of calculations of the full boundary-layer equations. The influence of interaction is also considered, in which case the flow is governed by a partial integro-differential equation. Numerical solutions are given for each of these problems.This study was supported by the United Technologies Research Center     

Non-reactive metal/semiconductor interfaces: a combined AES,AFM andPAC study

Thin In films on Ge(100), Si(100) andSi(111) are investigated using Auger-electron spectroscopy (AES), atomic force microscopy (AFM) andperturbed -angular correlation (PAC) spectroscopy, respectively. The growth mode of the metal films is characterized by in situ AES measurements, indicating distinct differences between the different substrate surfaces. Additional AFM investigations are used to monitor the film topography at higher metal coverage. Finally, the local crystalline structure of the films is studied by the PAC technique.     

Reaction between piperidine-4-spiro-2′-oxiranes and nucleophilic reagents

An investigation was made into the opening of the epoxide ring of piperidine-4-spiro-2-oxiranes by N-, H-, C-, and P-nucleophiles, which yielded the corresponding 3,4-dihydroxy- and 3-hydroxypiperidine derivatives. When these epoxides were reacted with organomagnesium compounds, regrouping occurred, the piperidine ring reducing in size to a pyrrolidine ring and the latter being functionalized by a hydroxymethyl group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1499–1503, November, 1993.     

Sulfur-containing derivatives of thiolan-1,1-dioxide 3. Reactions of salts of 2-(n,n-dialkyl)iminio-5,5-dioxoperhydrothieno[3,4-d]-1,3-dithiolans with bases

Salts of condensed 2-(N,N-dialkyl)iminio-1,3-dithiolan and 1,1-dioxothiolan rings are converted in alkaline media to 1,1-dioxothiolen esters of N,N-dialkyldithiocarbamic acids and into unsaturated bicyclic compounds. The latter are formed when the initial salts contain a bromine atom to the sulfonyl group.For Communication 2, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 40–47, January, 1993.     

Dispersity and kinetic characteristics of dissociation of mono- and hemiaquo adducts of copper N,N′-ethylenebis(acetylacetoniminate) under nonisothermal conditions

Using optical microscopy and thermogravimetry, we have established that determination of the kinetic characteristics of dissociation for the monoaquo adduct of copper N,N-ethylene-bis(acetylacetoniminate) with particle size 0.5–2 mm is hindered by self-dispersal processes. Using a piezoquartz microbalance, we have obtained the kinetic parameters for thermolysis for a phase whose crystal sizes are substantially smaller than the minimal size after self-dispersal of a block of a large crystal (0.5–2 m). For thermolysis of the hemiaquo adduct not accompanied by self-dispersal, the kinetic characteristics of the process for phases of dispersity 0.5–2 mm and 0.5–2 m are comparable.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 3, pp. 226–231, May–June, 1992.