Contributions a l'etude cinetique des decompositions endothermiques dans des systemes solide-gaz,a l'aide des donnees thermogravimetriques

Résumé On a déterminé les paramètres cinétiques des réactions de décomposition de quelques combinaisons complexes des halogénures et pseudohalogénures de cobalt, nickel, manganèse, cuivre et cadmium, avec l'ammoniaque, la pyridine et des pyridines substituées. Pour les réactions d'ordre zéro, les valeurs des facteurs préexponentiels, calculées en considérant comme étape limitante la diffusion du composant volatil à travers la couche de la substance décomposée, concordent de façon satisfaisante avec celles déterminées expérimentalement.

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Kinetic parameters were determined for the decomposition reactions of some com plexes of cobalt, nickel, manganese, copper and cadmium halides and pseudohalides with ammonia, pyridine and substituted pyridines. For the zero order reactions, the values of the pre-exponential factors calculated assuming as limiting step the diffusion of the volatile component through the layer of the decomposed substance, are in satisfactory agreement with the experimental values.

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Zusammenfassung Es wurden die kinetischen Parameter der Zersetzungsreaktionen einiger Komplexe der Halogenide und Pseudohalogenide von Kobalt, Nickel, Mangan, Kupfer und Kadmium mit Ammoniak, Pyridin und substituiertem Pyridin bestimmt. Bei den Reaktionen von Null-Ordnung zeigten die preexponentiellen Koeffizienten, berechnet, indem für die limitierende Stufe die Diffusion des flüchtigen Bestandteils durch die Schicht der zersetzten Substanz betrachtet wurde, gute Übereinstimmung mit den experimentellen Werten.

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A theoretical model for core-annular flow of a very viscous oil core and a water annulus through a horizontal pipe

A theoretical model has been developed for core-annular flow of a very viscous oil core and a water annulus through a horizontal pipe. Special attention was paid to understanding how the buoyancy force on the core, resulting from any density difference between the oil and water, is counterbalanced. This problem was simplified by assuming the oil viscosity to be so high that any flow inside the core may be neglected and hence that there is no variation of the profile of the oil-water interface with time. In the model the core is assumed to be solid and the interface to be a solid/liquid interface.By means of the hydrodynamic lubrication theory it has been shown that the ripples on the interface moving with respect to the pipe wall can generate pressure variations in the annular layer. These result in a force acting perpendicularly on the core, which can counterbalance the buoyancy effect.To check the validity of the model, oil-water core-annular flow experiments have been carried out in a 5.08 cm and an 20.32-cm pipeline. Pressure drops measured have been compared with those calculated with the aid of the model. The agreement is satisfactory.     

Nuclear magnetic resonance-compatible furnace for high temperature MR imaging and spectroscopy in situ

A high temperature magnetic resonance compatible furnace for real time in situ monitoring of materials, processes, and chemical reactions with magnetic resonance imaging and spectroscopy is described. Design issues are analyzed. Example applications are demonstrated with a time sequence of proton images of the binder burnout in a porous green ceramic cylinder containing polyethylene glycol binder at 200 degrees C, and 7Li images of the molten salt LiCl at 700 degrees C.     

Selecting distances in arrangements of hyperplanes spanned by points

In this paper we consider a problem of distance selection in the arrangement of hyperplanes induced by n given points. Given a set of n points in d-dimensional space and a number k, , determine the hyperplane that is spanned by d points and at distance ranked by k from the origin. For the planar case we present an O(nlog²n) runtime algorithm using parametric search partly different from the usual approach [N. Megiddo, J. ACM 30 (1983) 852]. We establish a connection between this problem in 3-d and the well-known 3SUM problem using an auxiliary problem of counting the number of vertices in the arrangement of n planes that lie between two sheets of a hyperboloid. We show that the 3-d problem is almost 3SUM-hard and solve it by an O(n²log²n) runtime algorithm. We generalize these results to the d-dimensional (d4) space and consider also a problem of enumerating distances.     

On modules of finite upper rank

For a group and a prime , the upper -rank of is the supremum of the sectional -ranks of all finite quotients of . It is unknown whether, for a finitely generated group , these numbers can be finite but unbounded as ranges over all primes. The conjecture that this cannot happen if is soluble is reduced to an analogous `relative' conjecture about the upper -ranks of a `quasi-finitely-generated' module for a soluble minimax group . The main result establishes a special case of this relative conjecture, namely when the module is finitely generated and the minimax group is abelian-by-polycyclic. The proof depends on generalising results of Roseblade on group rings of polycyclic groups to group rings of soluble minimax groups. (If true in general, the above-stated conjecture would imply the truth of Lubotzky's `Gap Conjecture' for subgroup growth, in the case of soluble groups; the Gap Conjecture is known to be false for non-soluble groups.)     

Gouy phase compensation in quasi-phase matching

In any focussed nonlinear interaction the focus induced phase shift, known as the Gouy phase shift, provides an imperfection in phase matching for any linearly invariant material. However, using an appropriately designed quasi-phase matched structure it is theoretically possible to compensate for the deleterious effects of the Gouy phase shift, allowing a symmetric frequency response and tighter optimal focussing than in a uniform material.