Un modèle membranaire de coques faiblement courbées valable pour des charges élevées

In this paper, we present the construction of a membrane model for shallow shells using asymptotic approach. This model is valid for important applied loads where the tangential part is supposed to be more important than the normal part. To our knowledge, this membrane model obtained from three-dimensional elasticity, does not exist in the literature. Although it is nonlinear, it resolution can be split into two linear problems.     

Construction d'un opérateur de propagation à partir des équations d'Euler linéarisées

Linearized Euler equations based on a stationary mean flow are used to calculate the propagation of acoustic waves. This method allows one to take into account the mean flow effects on the radiated sound field. The multipolar feature of a source clearly appears in the wave equation. It is shown that these sources are numerically identified in solving directly the linearized Euler equations. The case of a quadrupolar distribution in a jet flow is then investigated.     

Dérivées de fonctionnelles intégrales dans des perturbations de fissures exprimées par intégrales de frontière

This note presents, in the framework of three-dimensional linear elastodynamics in the time domain, a method for evaluating sensitivities of integral functionals to crack shapes, based on the adjoint state approach and resulting in a sensitivity formula expressed in terms of surface integrals (on the external boundary and the crack surface) and contour integrals (involving the direct and adjoint stress intensity factor distributions on the crack front). This method is well-suited to boundary element treatments of e.g. crack reconstruction inverse problems.     

Calcul du rayonnement acoustique d'une couche de mélange à l'aide des équations d'Euler linéarisées

The noise radiated by a mixing layer is computed by an hybrid approach using linearized Euler's equations (LEE) as a wave operator. The acoustic source terms are obtained by substituting the aerodynamic fluctuating velocity field computed by the Large Eddy Simulation (LES) method into the right-hand side of the LEE. The radiated sound field as calculated in this way is in good agreement with the direct calculation obtained by LES. This study provides support to the validity of the acoustic analogy based on the LEE, both for the noise source terms and the mean flow effects on sound propagation.     

Réactions colorées de stéroĭdes

A number of colour reactions for the identification and determination of steroids are described.     

Étude d'un procédé de brassage électromagnétique en écoulement de Stokes

This note deals with a process allowing electromagnetic mixing of a conductor fluid in Stokes flow. The flow, which is generated by two inductor wires (arranged around a cylindrical vat), undergoes a rotation. In order to solve analytically this electromagnetic flow, we use a magnetostatic pattern and we replace the dynamics in the electromagnetic layer by a tangential velocity. We superimpose then a periodic rotation on the flow (triangular signal). The investigated parameters are an a dimensional number (τ), which compares the velocities of the rotation and the flow, the inversion's periodicity of the rotation (k) and the distance of the wires from the vat (d). In studying the stretching and scattering of a drop of the fluid, an optimal choice of these parameters is subsequently suggested. Finally, prospects are considered of the possibilities of stationary three-dimensional and mixing.     

Analyse cytologique de l'expression d'un épitope porté par les glycoprotéines excrétées par Candida albicans

The present study concerns an epitope identified by a monoclonal IgM, named 5B2, generated against the parasitic phase of Candida albicans. The epitope was previously shown to be carried by excreted C. albicans glycoproteins and to be present in the sera of patients suffering from systemic candidiasis. The cytological analysis of the epitope expression was investigated in 3 different yeast strains: the C. albicans strain from which 5B2 was generated (VW.32); a C. albicans mutant, deficient in cell wall mannans (KD.102); and a Sacchromyces cerevisiae strain. Immunofluorescence assays using IgM-5B2 showed discontinoous labelling with the VW.32 strain and no labelling with the 2 other yeast strains; however, the superficial structures of the 3 strains reacted homogeneously with ConA. Ultrastructural immunodetection experiments performed with the VW.32 cells, using gold-conjugated monoclonal antibody, revealed the presence of the epitope in the vacuolo-vesicular system, the periphery of the cytoplasm, the periplasmic space and the cell wall. Under the same conditions, cells from the KD.102 strain only exhibited weak cytoplasmic labelling whereas the presence of the epitope in S. cerevisiae blastoconidia was restricted to the vesicles. Competition and double labelling experiments with IgM and ConA showed that the epitope, distributed on the great majority of VW.32 glycoproteins, is shared by a lesser proportion of the KD.102 glycoproteins and only by some vesicular glycoproteins of S. cerevisiae. Inhibition of the N-glycosylation process of the VW.32 strain by tunicamycin resulted in the absence of cytokinesis and germ tube formation. In such cells, epitope 5B2 was no longer expressed on the bud surface. These cytological results concerning the C. albicans epitope are discussed in relation to recent, more general biochemical data on the yeast glycosylation process.     

Pont électrolytique et électrode de référence pour titrages potentiométriques

A salt bridge and a reference electrode for potentiometric titrations are described.     

Méthode de détermination des épaisseurs de films conducteurs par mesures de résistance de surface

To evaluate the thickness of the layers of a Ti/TiAl₃/Al system, experiments based on surface resistance measurements have been performed. The thickness of each layer is deduced from a comparison among calculated and measured values of resistance. We present here a solution for the simulation of surface resistance and the results obtained with this method on Ti/TiAl₃/Al systems.     

Structure électronique de la formamide et de l'urée

Résumé La structure électronique de la formamide et de l'urée est étudiée par la méthode L.C.A.O. améliorée. L'énergie de transition N V obtenue pour la formamide (7,3 eV) est en bon accord avec la valeur expérimentale (7,2 eV). La première transition N V de l'urée se situe vers 7,5 eV. Expérimentalement la valeur de celle-ci n'est pas connue, cependant ce résultat paraît correct par comparaison avec les énergies de transition dans la série des dérivés thio correspondants.

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The electronic structure of formamide and urea is studied by the improved LCAO method. The N V transition energy obtained for formamide (7,3 ev) agrees well with the experimental value (7,2 ev). The first urea N V transition should lie at 7,5 ev. An experimental value for it is not known, but this result seems to be correct in view of the transition energies in the corresponding thio derivatives.

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Zusammenfassung Die Elektronenstruktur des Formamids und des Harnstoffs wird mit Hilfe des verbesserten LCAO-Verfahrens untersucht. Die für den N V-Übergang des Formamids berechnete Energie (7,3 eV) stimmt gut mit dem experimentellen Wert (7,2 eV) überein. Der erste N V-Übergang des Harnstoffs sollte bei 7,5 eV liegen. Ein experimenteller Wert dafür fehlt: jedoch scheint der Wert im Vergleich mit den Anregungsenergien der entsprechenden Thioderivate vernünftig zu sein.

     

Transformations de N-acylaziridines catalysées par des supports à base de silice et d’alumine : une élucidation mécanistique

The silica gel, neutral alumina and acid activated clays transform the N-acyl-2,2-dimethylaziridines 1 into a mixture of N-methallylamides 2, oxazolines 3 and amidoalcohols 4. The reaction of N-benzoyl-2,2-dimethylaziridine with benzylcyanid anion leads to a mixture of amidopyrroline 5 and iminopyrrolidine 6. The product 5 was converted into its tautomer 6 by chromatogaphy on silica gel. Ionic mechanisms were then proposed to explain the formation of products 2–6 resulting from the regioselective ring opening on the more substituted C2 carbon side.     

Sur les propriétés électroniques de la phénothiazine et de son radical

Résumé La phénothiazine et son radical sont probablement pliées le long de l'axe passant par les deux hétéroatomes centraux. Des calculs sont effectués par la méthode des orbitales moléculaires sur la modification des caractéristiques électroniques de la phénothiazine en fonction du pliage. On montre, que les densités de spin calculées pour les différentes configurations spatiales possibles du radical phénothiazinique permettent, par comparaison avec les densités expérimentales, de choisir la configuration la plus probable. C'est la configuration pliée dans laquelle le proton attaché à l'azote se trouve placé entre les deux cycles latéraux. L'étude des potentiels d'oxydation polarographique montre qu'au contraire dans les dérivés 10-substitués de la phénothiazine, le substituant aliphatique trop volumineux est placé hors des cycles latéraux.

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Phenothiazine and its free radical are probably folded along the axis passing through the two central heteroatoms. Calculations are carried out by the molecular orbital method on the modification of the electronic characteristics of the phenothiazine ring as a result of folding. It is shown, in particular, that the spin densities calculated for the different possible geometrical configurations of the phenothiazine free radical permit, by comparison with experimental spin densities, to deduce which configuration is the most probable. In the present case, this is the folded configuration in which the proton attached to the nitrogen atom is placed between the two lateral rings. The energy of the highest filled molecular orbital is also a sensitive function of the geometrical configuration of the molecule. The study of the polarographic oxidation potential of substituted phenothiazines shows that, in contrast to the parent molecule, in the N-alkyl substituted derivatives the voluminous alkyl substituent is probably pushed out to an external position with respect to the lateral rings.

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Zusammenfassung Phenothiazin und sein Radikal sind wahrscheinlich längs der N-S-Verbindungslinie geknickt. Wir berechneten nach der MO-Methode die Änderungen der elektronischen Eigenschaften des Moleküls mit dem Knickwinkel. Der Vergleich der für die verschiedenen denkbaren Konfigurationen des Radikals berechneten Spindichten mit Meßwerten erlaubt, eine von ihnen als am wahrscheinlichsten auszuwählen. Es ist die geknickte Form, in der das H-Atom am Stickstoff zwischen den aromatischen Ringen liegt. Die Untersuchung der polarographischen Oxydationspotentiale zeigt dagegen, daß in den N-alkyl-substituierten Phenothiazinderivaten die aliphatische Gruppe von den Seiten-Ringen wegsteht.

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Ce travail a bénéficié de la subvention CY-3073 du Public Health Service des Etats-Unis (National Cancer Institute).     

Non-monotonie numérique de courbes de dispersion en élasticité linéaire

This study concerns the behaviour of dispersion curves stemming from a problem of guided waves in a plane elastic medium that is invariant by translation in one spatial direction and stratified with respect to the other one. We formulate an equivalent problem in a bounded domain using transparent boundary conditions. The dispersion curves that are shown are not monotonous, a phenomenon not yet been encountered but suspected.     

Mesure de la dispersion pour la solution éléments finis de l'équation de Helmholtz

The numerical solution of the Helmholtz equation suffers from a dispersion error. A general method to calculate a priori the dispersion error is formulated and applied to the methods suggested in the literature in order to minimize the dispersion.     

Réduction électrochimique de porphyrines portant un groupement électroactif pyridinium

The electrochemical reduction of meso-tetraphenylporphyrins β-substituted by a pyridinium group was investigated in N,N-dimethylformamide. The measurements showed the presence of two distinct electroactive sites – the pyridinium cation and the porphyrin ligand – involved in three successive one-electron charge transfers. The pyridinium cation is reduced before the porphyrin ligand, leading to the formation of a neutral radical species. The reduction of the porphyrin ligand takes place at more cathodic potentials that are close to those of the corresponding unsubstituted porphyrin. This result was expected taking into account the neutral state of the pyridinium group that follows its reduction. The decrease of the reduction potentials of the pyridinium cation fits well with the evolution of the electronic densities of the porphyrin ligand in the series H₂ < Cu < Zn. The depicted evolution clearly demonstrates the presence of the mutual electronic interactions between the two different electroactive sites in these molecules and the important electrodonating effect of the porphyrin ligand. The reduction of the pyridinium group, which is reversible for the free base, becomes irreversible for the metalloporphyrin. A possible dimerisation of the molecules via the reduced pyridinium group is proposed. These results are discussed on the basis of the d–π interactions existing in the metalloporphyrins.     

Séparation de traces de manganèse par électrolyse sur cathode de mercure renouvelée

The authors describe conditions of electrolysis which permit a quantitative deposit of traces of manganese to be obtained from sulphate and perchlorate solutions. Theoretical considerations based on the application of polarisation curves lead to a quantitative explanation of some of the experimental results, especially those concerned with the effect of different factors on the kinetics of deposition.