The flow of plastic disperse systems in the presence of the wall effect

Summary The results of studies of the wall effect in the flow of lubricating greases of different types are presented. It has been shown that the wall effect substantially influences the flow curves obtained for smooth capillaries, especially at low shear rates; the magnitude of this effect is estimated as a function of the capillary radius and shear rate at the capillary wall. It has been proved experimentally that the use of grooved surfaces eliminates the wall effect completely.The properties of a wall layer were assessed on the basis of the concept of the activation nature of the viscous flow of disperse systems. The following parameters of the wall layer have been determined from the variations of the free activation energy in the wall layer and in the bulk of the grease: thickness, disperse phase concentration and viscosity characteristics. The mechanism of flow generation and development in the wall layer is explained on the basis of the data obtained.Good agreement of theory with experiment is shown.

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Zusammenfassung Es werden die Ergebnisse von Untersuchungen des Wandeffekts beim Fließen von Schmierfetten unterschiedlichen Ursprungs mitgeteilt. Dabei wird gezeigt, daß der Wandeffekt die Fließkurven in glatten Kapillaren wesentlich beeinflußt, besonders bei niedrigen Schergeschwindigkeiten. Die Größe dieses Effekts wird in Abhängigkeit vom Kapillarradius und der Schubspannung an der Kapillarwand ermittelt. Experimentell wird nachgewiesen, daß bei Verwendung gerillter Oberflächen der Wandeffekt vollkommen verschwindet.Die Eigenschaften der Wandschicht werden unter Zugrundelegung der Vorstellungen von der Aktivierungsnatur der Prozesse des viskosen Fließens der Dispersionssysteme beurteilt. Aus der Veränderung der freien Aktivierungsenergie in der Wandschicht und im Volumen werden die Parameter der Wandschicht ermittelt: Dicke, Konzentration der Dispersionsphase und Viskositätskennlinie. Aufgrund dieser Kennwerte wird der Mechanismus der Bildung und der Entwicklung der Strömung in der Wandschicht erörtert.Es wird gezeigt, daß eine gute Übereinstimmung zwischen Theorie und Experiment besteht.

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With 10 figures and 1 table     

On the tri-n-octylammonium chlorocomplexes of Sn(IV) in benzene solution

Extracts with tri-n-octylammonium chlorocomplexes of Sn(IV) of various compositions, included the N-deuterated compounds, were prepared and investigated by IR spectroscopy and conductivity measurements. Three Sn(IV) complexes were found: (TOAH⁺)₂SnCl₆^2? (2:1-complex), TOAH⁺SnCl₅^? (1:1-complex) and a complex with the stoichiometric ratio TOA:Sn(IV) > 2. The cation of the latter contains the groups (TOAH…Cl…HTOA)⁺ and TOAH⁺ and that species is supposed to be a 3:1-complex (TOAH…Cl…HTOA)⁺TOAH⁺SnCl₆^2?.     

Synthesis of certain 3,5,7-disubstituted pyrazolo[3,4-e][1,3]oxazines. Derivatives of a new heterocyclic ring system

The synthesis of several 3,5,7-trisubstituted pyrazolo[3,4-e][1,3]oxazines by ring annulation of the appropriately substituted pyrazoles is described.     

Some aspects of reduced quinoline chemistry

Different synthetic paths that produce the reduced quinoline cycle are discussed: among them intramolecular cyclization, intra- and inter [4+2] cycloaddition reactions and other methods. Some chemical properties of tetrahydroquinolines are also analyzed.     

Almost flat planar diagrams

We continue our study of matrix models of dually weighted graphs. Among the attractive features of these models is the possibility to interpolate between ensembles of regular and random two-dimensional lattices, relevant for the study of the crossover from two-dimensional flat space to two-dimensional quantum gravity. We further develop the formalism of largeN character expansions. In particular, a general method for determining the largeN limit of a character is derived. This method, aside from being potentially useful for a far greater class of problems, allows us to exactly solve the matrix models of dually weighted graphs, reducing them to a well-posed Riemann-Hilbert problem. The power of the method is illustrated by explicitly solving a new model in which only positive curvature defects are permitted on the surface, an arbitrary amount of negative curvature being introduced at a single insertion.In memoriam Claude ItzyksonThis work is supported by funds provided by the European Community, Human Capital and Mobility Programme.Unité Propre du Centre National de la Recherche Scientifique, associée à l'École Normale Supérieure et à l'Université de Paris-Sud.     

Syringaldazine

The prostaglandin H synthase (PGHS) reaction has been studied with syringaldazine as the electron donor. Kinetic parameters of the reaction agreed with those for commonly used electron donors. The sensitivity of the PGHS activity detection in the presence of syring aldazine increases 10 times. A sensitive spectrophotometric assay for polyunsaturated fatty acid (PUFA) detection using syringaldazine as a new electron donor has been proposed.     

The influence of sample extremes on the maximum of partial sums of independent random variables

Many papers exist dealing with the distribution of the maximum of partial sums of independent random variables and studying the relationship between the sums and the sample extremes (see [L. Takacs,Combinator Methods in the Theory of Stochastic Processes, Wiley, New York (1967)], [J. Calambos,The Asymptotic Theory of Extreme Order Statistics, Wiley, New York (1978)]). The present paper deals with the effect the sample extremes have on the distribution of the maximum of sums of independent random variables. Proceedings of the Seminar on Stability Problems for Stochastic Models, Moscow, 1993     

Supersonic Flow Past an Obstacle with a Clearance at the Base

The supersonic air flow structure and the pressure distribution in the vicinity of a vertical cylinder suspended over the surface of a plate with a turbulent boundary layer are studied experimentally. The effects of the free-stream Mach number and the width of the clearance between the cylinder base and the surface on the dimensions of the separated flow region and the pressure distribution in the latter are examined.