1,2,2-Trimethyldisilane-1,1,2-triol: intermediate formation and conversion to condensation products

1,2,2-Trimethyldisilane-1,1,2-triol (1) is formed as an unstable intermediate upon hydrolysis of oligo(trimethyldisilanylsesquiazane). In the absence of trapping agents it undergoes rapid condensation to give ether-soluble poly(trimethyldisilanyloxane) which contains silanol groups. Treatment of the hydrolysis products with chlorotrimethylsilane in the presence of triethylamine affords trimethylsiloxy derivatives, (Me₃SiO)₂MeSiSiMe₂(OSiMe₃),5,6, and [Si₂Me₃O _x (OSiMe₃) _y ] _n . The isolation of these products indicates that disilanetriol1 readily undergoes condensation to form hydroxylcontaining six-membered rings and polysiloxanes. The condensation of compound1 in the presence of Me₃SiOH has been studied. The ratio between the isomeric cyclosiloxanes5 and6 has been determined both by¹H NMR spectroscopy and by a chemical method (chlorinolysis). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1788–1792, October, 1993.     

Fluorimetric determination of anionic surfactants by extraction as safranine-T ion-pairs

A simple and rapid method is proposed for the spectrofluorimetric determination of anionic surfactants. It is based on formation of an ion-pair at pH 2 with safranine-T and its subsequent extraction into chloroform. Fluorescence intensity is increased by a factor of about 5 with respect to that of the reagent. The calibration graph is linear in the concentration range 0.015–0.40 mg l^?1 dodecyl sulfate; the relative standard deviation is 5.6% at 0.22 ml l^?1 surfactant. The method is applied to determine anionic surfactants in city waste-waters, giving recoveries close to 100%.     

Cathodic Reduction of Chromium on a Surface of Nickel Modified by Aromatic Carboxylic Acids

Effect of organic compounds (salicylic, acetylsalicylic, and p-nitrobenzoic acids) adsorbed on a nickel surface or introduced into solution on the cathodic reduction of Cr(VI) is studied by measuring voltammetric curves in a wide potential range up to the beginning of electrodeposition of black chromium. If the adsorbate is salicylic or p-nitrobenzoic acid, only the maximum current corresponding to incomplete reduction Cr(VI) Cr(III) increases in cathodic polarization curve (PC). On a surface modified by acetylsalicylic acid, in addition to an increase in the maximum current, all parts of PC shift towards positive potentials. The Cr(VI) reduction on modified surfaces accelerates presumably due to the electron transfer from the cathode surface onto Cr(VI) atoms, accelerated by the formation of bridges with an increased electron conduction.     

Vanadium oxide surface studies

The vanadium oxides can exist in a range of single and mixed valencies with a large variety of structures. The large diversity of physical and chemical properties that they can thus possess make them technologically important and a rich ground for basic research. Here we assess the present status of the microscopic understanding of the physico-chemical properties of vanadium oxide surfaces. The discussion is restricted to atomically well-defined systems as probed by surface techniques. Following a brief review of the properties of the bulk oxides the electronic and geometric structure of their clean single crystal surfaces and adsorption studies, probing their chemical reactivity, are considered. The review then focuses on the growth and the surface properties of vanadium oxide thin films. This is partitioned into films grown on oxide substrates and those on metal substrates. The interest in the former derives from their importance as supported metal oxide catalysts and the need to understand the two-dimensional overlayer of the so-called “monolayer” catalyst. On the single crystal metal substrates thin oxide layers with high structural order and interesting properties can be prepared. Particular attention is given to ultrathin vanadium oxide layers, so-called nano-layers, where novel phases, stabilised by the substrate, form.     

Beryllium diffusion across GaAs/(Al,Ga)As heterojunctions and GaAs/AlAs superlattices during MBE growth

Beryllium diffusion during MBE growth of (Al, Ga)As layers, (Al, Ga)As/GaAs heterojunctions and GaAs/AlAs superlattices has been studied by electrochemical C-V and secondary ion mass spectrometry (SIMS) concentration profiling, in conjunction with transmission electron microscopy. Diffusion times were comparatively short since they were limited to part of the growth sequence, so non-equilibrium effects had a significant influence. The results are consistent with an interstitial-substitutional mechanism in which lattice site incorporation becomes more difficult with increasing band gap enthalpy. Incorporation involves a kick-out reaction which leads to the observed disordering of the superlattices.     

New nonlinear σ-model with N=4 extended supersymmetry

A new nonlinear -model with N=4 supersymmetry in d=2 is constructed in terms of a N=2 tensor multiplet in d=4. Four equivalent formulations of the theory in superspace are obtained. The component structure of the model is considered by means of the Legendre transformation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 70–74, September, 1987.     

Some inequalities for partial orders

We establish some inequalities connecting natural parameters of a partial order P. For example, if every interval [a,b] contains at most maximal chains, if some antichain has cardinality v, and if there are ₁ chains whose union is cofinal and coinitial in P, then the chain decomposition number for P is ₁v (Theorem 2.2), and the inequality is sharp in a certain sense (Section 3).This paper was written while the authors were visitors at the Laboratoire d'algèbre ordinale, Département de Mathématiques, Université Claude Bernard, Lyon 1, France.Research supported by NSERC grant # A5198.     

Density of the set of attractive compacta

A compact set K in a smooth closed manifold M is said to be attractive, if on M there exists a system of differential equations, for which K is an asymptotically stable invariant set. It is proved that the set of attractive compacta is dense and its complement contains a dense set of type G in the space of all compacta of the manifold M endowed with two natural topologies.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 143, pp. 170–175, 1985.