Existence of minimizers for non-quasiconvex integrals

Communicated by H. Brezis     

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.     

Réseau intégré ou réseaux spécialisés

The increase of telecommunications services demand has been so far satisfied by the creation of new networks or dedicated equipments. The emergence of new networks could stress through the density of competition, the liberalization of infrastructures and the market preemption strategies. Paradoxically this situation leading to burst the general network occurs as technology evolution matures into the alternative of providing a great broadband network, able to support the whole set of today’s and tomorrow’s services. In this paper, first will be considered the case in which the monopoly promotes the broadband network. Then the effects of cream-skimming competition will be introduced. This shall allow to observe how the fragile sustainability of the broadband network disturbs the theoretical solution based on a single integrated network. This will lead to draw up a balance sheet of the respective advantages and drawbacks of integrated and dedicated solutions, and consider the opportunity of half-integrated networks emergence.     

Caractérisation des composants de protection soumis à des impulsions électromagnétiques à pente raide de I’ordre de 1 kV/ns

This paper presents the experimental and theoretical methods to characterize protective devices under fast transient perturbations with rising fronts of 1 kV/ns. This study concerns the main parallel protective components used in telecommunications equipments. Under high voltage rise, these components have a dynamic behaviour due to their intrinsic capacitance and inductance. The influence of these elements on component responses is analysed numerically with a parametric study by varying simultaneously their value. The comparison of these responses with experimental results permits to fix the values of capacitance and inductance.     

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.     

Synthesis and X-ray crystal structure of cis-dichloro(cyclopentylamine) (dimethyl sulphoxide)platinum(II)

Summary cis-Dichlorocyclopentylamine(dimethyl sulphoxide)-platinum(II) is obtained, in addition to small quantities of the corresponding trans compound, by reaction of K₂PtCl₄ with cyclopentylamine in DMSO solution, where it is formed as the thermodynamically favoured isomer. An X-ray crystal structure analysis confirms the cis configuration. Coordination around the metal centre is square planar, and the ligand bond angles at the Pt atom are close to the expected values of 90 and 180°. The DMSO ligand is S-coordinated to Pt. The Pt-Cl bond lengths, 2.299(2) and 2.317(2) Å, are normal for structures of this type, as are the Pt-N and Pt-S bond distances, 2.059(5) and 2.191(2) Å, respectively.Author to whom all correspondence should be directed.     

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.