States of surface V(IV)-bearing groups in phosphorus-vanadium oxide and titanium-vanadium oxide silica gels made by molecular epitaxy

ESR shows that V(IV) may occur in isolated or interacting vanadium-oxygen groups on the surfaces of catalytically active P-V and Ti-V-bearing silica gels; there is a relationship between the V(IV) content and the phthalic anhydride selectivity in the oxidation of o-xylene.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 3, pp. 277–282, May–June, 1992.     

General method for the liquid-liquid extraction of molybdenum and its application to neutron activation analysis

Summary The liquid-liquid extraction of Mo(VI) from different acid solutions by zinc diethyldithiocarbamate in chloroform is described. This extractant allows the separation of nanogram to milligram quantities of Mo from even gram quantities of many other elements. The separation of Mo can be made selective by appropriate choice of the composition of the aqueous phase, by back-extraction of Mo and/or the coextracted elements, and by masking Mo with hydrogen peroxide. These techniques were adapted for the determination of Mo in several reference materials by radiochemical neutron activation analysis via ⁹⁹Mo.     

Quantum chemical study of molecular ion complexes with hydrogen bonds (Review)

Institute of Bioorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 6, pp. 157–183, November–December, 1992.     

Morphologies of microporous polyethylene and polypropylene crystallized from solution in supercritical propane

The morphologies of solvent-free, microporous, mechanically self-supporting cylinders of linear polyethylene and isotactic polypropylene, crystallized from solution in supercritical propane, were examined by an SEM technique. The morphology of gels (or foams), obtained with little or no shrinkage from 2% to 35% solutions by weight of polyethylene (99% to 85% porosities), is shown in some detail. Lamellae with very little or considerable mutual organization occur, often in the form of stacks with straight or coiled axes (axialites). Further growth of these can lead to particles with a roughly spherical overall shape and a predominantly radial orientation of the lamellae at the particle surface. Subcooled isotactic polypropylene, on the other hand, crystallizes in the form of perfectly shaped birefringent microspheres of very uniform size. ©1995 John Wiley & Sons, Inc.     

Congruences,equational theories and lattice representations

We survey results concerning the representations of lattices as lattices of congruences and as lattices of equational theories. Recent results and open problems will be mentioned.To László Fuchs on the occasion of his 70th birthday