Future contributions to Journal of Chemical Crystallograpy

Future contributions to Journal of Chemical Crystallograpy     

Autopsy of superflow collapses and multiple phase slips

Although phase slippage across an orifice in its purest form takes place by individual phase increments by 2π, there are many instances of flow in which the energy dissipation occurs by lumps involving much larger phase difference changes. Such events, the observation of which has been reported first by Sabo and Zimmermann, reduce the flow through the micro-aperture of two-hole resonators to residual values which can be close to zero. We have studied experimentally their detailed features and report the existence of two rather distinct manifestations of superflow collapses as well as the strong effect of hydrostatic pressure on their occurrence. Possible mechanisms are reviewed to explain a phenomenon that involves many vortex lines which evolve in time in such a way as to change the phase difference across the micro-aperture by 2nπ.     

A stochastic theory of chemical reaction rates. I. Formalism

A class of stochastic processes is studied that can be used to model elementary and complex chemical reactions composed of a series of several distinct steps. Formal correlation function expressions are directly computed for the stochastic model to yield the overall rate constant for the reaction. One of the main results is a formula connecting the overall rate constant to the rate constants characterizing the elementary steps of the reaction.     

X-Ray and 1H-NMR Configurational Assignment of Valofan (α-Allphanoyl-α-allyl-γ-valerolactone) Diastereoisomers

The two diastereoisomers of valofan were separated by semi-preparative HPLC. The preferred solution conformation of the two diastereoisomer was established by ¹H-NMR spectroscopy. The spectra could be interpreted in confirgurational terms. The configuration of the more lipophilic isomer was ascertained bty X-ray crystallography as r-2-allophanoyl-2-allyl-t-4-methylbutyrolactone.     

A generalization of the theory of normal forms

Summary Normal forms allow the use of a restricted class of coordinate transformations (typically homogeneous polynomials) to put the bifurcations found in nonlinear dynamical systems into a few standard forms. We investigate here the consequences of relaxing the restrictions of the form of the coordinate transformations. In the Duffing equation, a logarithmic transformation can remove the nonlinearity: in one interpretation, the nonlinearity is replaced by a branch cut leading to a Poincaré section. When the linearized problem is autonomous with diagonal Jordan form, we can remove all nonlinearities order by order using these singular coordinate transformations. Deceased, November 4, 1993.     

Adoucissement des eaux calciques par échange d''ions transmembranaire à travers des membranes homogenes obtenues par greffage radiochimique

The potential application of DONNAN dialysis to water softening has been studied. The selective transportation of calcium and alkaline-earth ions through a cationic membrane appeared to be an interesting process, since materials with both optimal exchange capacity and transportation properties exist now.

Preliminary investigations allowed us to optimize some of these materials, as well as the conditions of their use. Thus we have found that for the membranes handled, the 3.10-2 M concentration of brine represented the best compromise between the extraction of calcium and the leakage of chlorine through the membrane (relating to the water to be softened).

We also observed that for a low and a medium flow, the extraction rate was high enough to allow the release of calcium at a rate comparable to the classical ion-exchange process using a resin bed.     

A Tabu Search with Slope Scaling for the Multicommodity Capacitated Location Problem with Balancing Requirements

In this paper, a tabu search heuristic is combined with slope scaling to solve a discrete depot location problem, known as the multicommodity location problem with balancing requirements. Although the uncapacitated version of this problem has already been addressed in the literature, this is not the case for the more challenging capacitated version, where each depot has a fixed and finite capacity. The slope scaling approach is used during the initialization phase to provide the tabu search with good starting solutions. Numerical results are reported on various types of large-scale randomly generated instances. The quality of the heuristic is assessed by comparing the solutions obtained with those of a commercial mixed-integer programming code.