Méthode de détermination de l'exclusion d'un electrolyte fort par une membrane échangeuse d'ions

We have developed a new method to evaluate the strong electrolyte exclusion of ion exchange membranes. This method is based on the continuous measurement by conductivity of the amount of imbibed electrolyte released into a large excess of permuted water. Its principal advantage is to distinguish between the co-ions in the exchanger and those in the adhering liquid film. The method is tested on two sulfonic membranes: CRP (Rhone-Poulenc) and Nafion (Du Pont De Nemours). The results indicate that the exclusion rate is related to the external concentration and to the molarity of fixed ionic groups.     

De l'analyse de la résistance interne par perçage à la détermination du profil de dureté des aciers traités en surface

The thrust measured during a drilling test is related to the hardness of the material tested. When the test is performed on a superficially heat-treated specimen, the results do not exactly correspond to the hardness profile obtained by the Vickers micro hardness technique. The difference is due to the integration of heterogeneous resistance along the cutting edge of the conic drill. By discretising the drilled thickness, we have developed an algorithm yielding the hardness of each elemental thickness. Results are very close to those obtained by Vickers hardness profile measurements.     

Sur une méthode de projection vectorielle pour la résolution des équations de Navier-Stokes

We propose a method of solving the Navier-Stokes equations in incompressible flow. It is based on the projection of the velocity field, approached by a prediction step on a zero divergence field. The novelty of this method concerns how the projection is made, directly operating on all the components of the velocity field through a coupling. A highly implicit algorithm allows us to maintain all physical boundary conditions of the problem during the solution steps.     

La détermination du vanadium par la méthode spectrophotométrique en solution non-aqueuse

On mixing small quantities of an aqueous solution of vanadium, containing hydrogen peroxide and acidified with HCl, with anhydrous dioxan containing gaseous hydrogen chloride in molar concentration, an intense red-yellow colour appears, in the presence of as little as 5 μg/ml vanadium.If a drop of salicylic aldehyde is added to the solution thus obtained, the colour changes to violet-blue, which shows an absorption maximum at 565 mμ, clearly visible even with 1 μg/ml vanadium.This reaction, though a sensitive method for the detection of vanadium, is not suitable for quantitative measurement of this substance because the small quantity of water introduced in the form of the vanadium solution hydrolyses the coloured compounds.Very good results can be obtained by dissolving the dry residue (at 100°C) of the solution under examination in 0.2 ml of N HCl in 2% aqueous H₂O₂ solution, and then in 5 ml of a solution made up of 40% acetic anhydride containing gaseous HCl (1 N), 40% glacial acetic acid, and 20% methyl Salicylate.By this method as little as 1 μg of vanadium can be determined.Co, Mo, and W, interfere; the other elements do not.     

Détermination du spectre de puissance acoustique émis par une flamme turbulente

This note presents the elaboration of a predictive tool for the acoustic generation of a flame. First, volumetric expansion occurring in turbulent combustion is identified as the main acoustic source term. Following an approach similar to Lighthill's aeroacoustic analogy, a pressure wave equation is derived. By way of a reduced energy relation we express source terms as a function of the temperature fluctuations. Determination of the sound pressure autocorrelation leads to the sound power spectrum. This consists of a double volumetric integration of the production terms weighted by a spatio-frequential coherence function. By means of two characteristic times, this coherence function takes into account combustion and turbulence effects on the acoustic generation. The aerothermoacoustic model is then applied to the turbulent flame produced by an experimental burner and results are compared with experimental spectra.     

Calcul de chiralité quantitative par la méthode des moindres carrés

It is shown how the root mean square chiral index is computed without enumerating all the permutations of a set of n atoms. As an example, the quantitative measure of chirality is achieved for various helicene derivatives. It is also shown that the chiral index of a protein backbone is computable without enumeration.     

Un modèle du spectre des ondes de surface générées par le vent

A model of wind-generated surface waves is discussed. The energy equilibrum between excitation effects, nonlinearity, and dissipation are governed by a self-regulating process. The numerical results are compared with experimental data. © 1999 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS     

Nouvelle méthode de synthèse d’acides et d’esters arylboroniques par électroréduction de dérivés aromatiques halogénés en présence d’agents boratants

Novel synthesis of arylboronic acids and esters by electroreduction of aromatic halides in the presence of borating agents. A novel strategy for the one-step synthesis of arylboronic acids and esters by an electrochemical coupling reaction is described. It is based on the reductive coupling between the aromatic halides and a borating agent (trialkyl borate or pinacolborane). The reactions are carried out in DMF or THF with the use of sacrificial magnesium or aluminium anodes in a single-compartment cell. Arylboronic acids and esters are obtained with moderate-to-good isolated yields. To cite this article: C. Laza, E. Duñach, C. R. Chimie 6 (2003).     

Résolution du problème à deux électrons en mécanique quantique par détermination directe des orbitales naturelles

Résumé La fonction d'onde et l'énergie de l'état fondamental de l'atome d'hélium et des ions isoélectroniques sont calculées selon un procédé proposé antérieurement [10]. Les équations intégrodifférentielles relatives aux orbitales naturelles (NO) sont résolues approximativement dans une représentation matricielle utilisant les fonctions complètes de Laguerre comme base, ainsi qu'avec de simples approximations analytiques des NO. On réussit à tenir compte de 95% environ de l'énergie de corrélation. La convergence du développement naturel est telle que les NO dont le nombre quantique principal est plus petit ou égal à 4 sont les seules à apporter une contribution appreciable à l'énergie. Les contributions de l'énergie cinétique et des énergies potentielles, d'attraction nucléaire et de répulsion interélectronique à l'énergie de corrélation sont examinées. Une certaine simplification du potentiel de corrélation aboutit à une justification du principe des intégrales interélectroniques réduites.

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The wave function and the energy of the ground state of the helium atom and the corresponding isoelectronic ions are calculated by a procedure recently proposed by the author [10]. The integro-differential equations of the natural orbitals (NO) are resolved approximatively in a matrix representation using the complete Laguerre functions as its basis as well as in a simple analytical approximation for the NO. The natural expansion converges so rapidly that only those NO whose principal quantum number is 4 or less contribute significantly to the energy. This method succeeds in accounting for some 95% of the correlation energy. The kinetic, potential and interelectronic energy contributions to the correlation energy have been examined separately. By simplifying the correlation potential in a certain manner the principle of reduced electron interaction integrals is justified.

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Zusammenfassung Die Wellenfunktion und die Energie des Grundzustandes des Heliumatoms und der mit ihm isoelektronischen Ionen wird gemäß einer vom Verfasser vorgeschlagenen Methode [10] berechnet. Dazu löst man die Integrodifferentialgleichungen für die natürlichen Einelektronenfunktionen (NO) näherungsweise in einer Matrixdarstellung unter Benutzung der vollständigen Laguerre-Funktionen als Basis. In dieser Näherung erfaßt man etwa 95% der Korrelationsenergie. Die natürliche Entwicklung konvergiert so gut, daß nur die NO mit der Hauptquantenzahl kleiner oder gleich 4 wesentlich zur Energie beitragen. Die Anteile der kinetischen Energie, der potentiellen Einelektronenenergie und der Elektronenwechselwirkungsenergie an der Korrelationsenergie werden untersucht. Ausgehend von einer bestimmten Näherung für das Korrelationspotential läßt sich die Methode der reduzierten Wechselwirkungsintegrale rechtfertigen.

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L'auteur a bénéficié d'une bourse de recherches de l'OTAN qui lui a été accordée par l'intermédiaire de «Deutscher Akademischer Austauschdienst». M. Gaston Berthier, Maitre de recherches au CNRS a pris un grand intérêt à ce travail et y a beaucoup contribué. Qu'il soit remercié cordialement.     

Détermination spectrale du phosphore et du carbone dans les aciers par la méthode de profilage

Sans résuméLes recherches ont été effectués sous les auspices de l'I. R. S. I. A. (Institut pour l'encouragement de la Recherche Scientifique dans l'Industrie et l'Agriculture) et du C. N. R. M. (Centre National des Recherches Métallurgiques) Section Hainaut.     

Microstructure et détermination des ramifications alkyle dans une série de copolymères éthylène acétate de vinyle

Compounds suitable as models for copolymers of ethylene with vinyl acetate have been prepared and studied by ¹³C-NMR (62.89 MHz). By mixing model compounds, various branched copolymers were simulated. The results have permitted an assignment more complete than previously reported for these copolymers. An investigation was made on the number of branches in nine separate copolymers. The number of ethyl, butyl, pentyl and longer branches per 1000 carbons in the main chain were determined. The number of ethyl branches was around four branches per 1000 carbons; the number of branches longer than butyl decreased from about 20 to 8 per 1000 carbons with increase in vinyl acetate content; the butyl branches predominated over those of other types when the vinyl acetate content was ⩽25% by weight.     

Mécanisme de décomposition des composés M(NEt2)4 (M = V,Cr) lors de leur utilisation comme mono-source pour la croissance de films M-C-N par MOCVD

Both NMR identification of the decomposition by-products of the organometallic compounds M(NEt₂)₄ (M = V, Cr) and on line mass spectrometry analyses in the MOCVD reactor have been used, in relation with the main features of the films, to discuss a decomposition pathway which accounts for the lability of the NEt₂ ligands and accordingly the low nitrogen content of the films.     

Influence de l'excentration des aspérités sur la résistance thermique de constriction statique ou glissante

A three-dimensionnal analytical model is developed to calculate the thermal constriction resistance for a solid presenting multiple contacts at the surface. The solid can be considered static or sliding. The non-unifomity of contact distribution is studied by the introduction of an eccentricity parameter referred to the uniform case. The results of the proposed model are compared to existing experiments adapted to a static contact.     

Détermination de la composition énantiomérique dˈesters dˈacides aminés par spectroscopie de RMN à lˈaide dˈune chiroporphyrine de cobalt(III) comme agent chiral de déplacement chimique

We wish to propose a novel chiral shift reagent for the determination of enantiomer composition of amino acid derivatives. This reagent, chlorocobalt(III) tetramethylchiroporphyrin CoCl(TMCP), effects quantitative in situ derivatization of amino compounds in the NMR tube, without any detectable kinetic resolution. The influences of the chiral cavity and of the porphyrin ring current on the signals of the coordinated amino acid methyl ester L* can be seen in the high-field region of the ¹H NMR spectrum of the bis-adduct [Co(L*)₂(TMCP)]⁺Cl^–. The signatures of the (R) and (S) ligands are well resolved at 200 MHz, and their relative intensities can be readily determined by peak integration. To cite this article: M. Claeys-Bruno et al., C. R. Chimie 5 (2002) 21–25     

Microlensing photométrique et détermination des masses stellaires

Microlensing was suggested for stellar mass determination of nearby stars by several authors (e.g. Paczyński). There are two aspects in gravitational microlensing: photometry and astrometry. Here only the photometric aspect, i.e. magnification of a background source by a stellar lens, will be considered. The first study in this domain was done by Paczyński. An attempt to investigate some observational constraints (Alard et al.) takes its origin in this study. It will be shown here that blending of the source by the lens not only induces a degeneracy which has been pointed out by Woźniak and Paczyński and can be removed by measuring the flux of the source outside the microlensing event, but also strongly reduces the photometric cross section as well as the duration of microlensing events. The expected number of events decreases strongly with blending. Blending effects can be reduced by selecting faint lens candidates. Unfortunately however, it is difficult to monitor a sufficient number of lens candidates per night, and restricting oneself to nearby and high proper motion objects would lead to a very small number of lens candidates. In the case of short duration events, the light curve must be sampled at short time intervals. When sampling daily, the condition is very strong and the expected rate of events very small. Observing from space would increase significantly the rate, but this gain is still insufficient. We conclude that the event rate will be very small and that the project does not seem to be feasible, at least under current observing conditions and even in the near future.     

Interprétation des mesures potentiométriques au moyen des courbes de polarisation

The observed experimental results of the potentiometric determinations can be explained by means of the polarisation curves. Thus explanations are given of the following phenomena: Electro-activity and non-electro-activity of ions. Nature of the potential taken by an electrode. Time required to establish a stable potential. Significance of the limiting potentials and the limiting concentrations. Influence of oxygen on the value of the measured potentials and on the limit of electro-activity of the oxidants. Significance of the “irreversible” potentials. Formulas giving the potentials in the presence of oxygen. Utility of removing the oxygen from the solution in view of potentiometric determinations. It appears that for all the “slow” redox systems, which are very numerous in inorganic and organic chemistry, the knowledge of the polarisation curves is fundamental.     

Caractérisation des propriétés électriques des parois de pores d’une membrane

The characterisation of the surface electrical properties of membrane materials is critical for understanding and predicting the filtration performances of membranes. In this paper, four simple experimental methods – streaming potential, electro-osmosis, pore conductivity and membrane potential –, allowing the characterisation of the charge state of membrane pore walls are presented. The four experimental parameters provide information about the sign of the electrical net charge. Examples illustrating the influence of the pH, electrolyte concentration and nature on the four experimental parameters are given. The zeta potential can be then deduced from these measurements by means of a model.     

Tube de Thiele à mercure pour la détermination des points de fusion et la cryoscopie

Résumé L'emploi de mercure comme bain liquide dans le tube deThiele présente l'avantage d'assurer une meilleure constance de température, l'effet de conduction venant s'ajouter à l'effet de convection.Afin de permettre la lecture, le tube à substance est aplati et il est fixé contre la paroi, également aplatie, du tube deThiele.

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Summary The use of mercury as the liquid in theThiele tube has the advantage of guaranteeing a better constancy of temperature; the effect of conduction being added to the convection effect. To permit reading, the sample tube is flattened, and it is fastened against the side of theThiele tube, which is likewise flattened.

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Zusammenfassung Die Verwendung von Quecksilber als Badflüssigkeit im Schmelzpunktapparat vonThiele bietet durch Ausnützung der Flüssigkeitsströmung und der Wärmeleitfähigkeit des Materials den Vorteil erhöhter Temperaturkonstanz.Zwecks Beobachtung der zu untersuchenden Substanz wird die abgeplattete Schmelzpunktskapillare unmittelbar an einer gleichfalls planen Stelle der Innenwandung des Schmelzpunktsapparates angebracht.

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Avec 1 figure.