Une amélioration de la tomographie ultrasonore en réflexion

Via a simple algorithm given by the Born approximation one can reconstruct a tomographic image of the sound speed of an acoustically penetrable body, knowing its scattered sound field. This method is based on the hypothesis of weak contrast between the body and the external medium. Otherwise the image is a distorted version of the object. The distortion is characterised analytically. Thus we propose a modified algorithm that cancels the image defects so as to obtain a fast and reliable reconstruction method.     

Étude paramétrique de la thermogravitation en milieu poreux

This note reports on a numerical study of the thermogravitational diffusion existing in a porous medium saturated with a binary mixture and subjected to a horizontal thermal gradient. It deals with a study of the influence of the dimensionless characteristic parameters on the species separation, using a two-dimensional numerical code based on a spectral method. The existence of a maximum separation ratio corresponding to an optimal Rayleigh number, associated to an optimal permeability, is shown. The results are also compared with analytical and experimental results coming from previous works.     

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.     

Une généralisation de la théorie de brönsted en chimie analytique

The proposal is made that all reactions be considered as corresponding to the exchange of particles (particules).1. Exchange of electrons between an oxidising agent and a reducing agent. This is the classical conception of oxidation-reduction reactions.2. Exchange of ions (or of polar molecules) between an “acceptor” of the ion and a “donor” of the same ion. In the case of exchange of protons the reaction is one between acids and bases, according to Brönsted.The majority of reactions concern the exchange of different ions. It is proposed to apply to these reactions, and that for each type of particle exchanged, the type of reasoning which Brönsted has used for the exchange of protons.The analogy thus created between the different types of reactions leads to a considerable simplification. It allows identical reasoning and the use of similar formulations for all reactions.Further, the distinction between reactions in terms of the nature of the particle exchanged permits recognition of the respective influence of the factors which are available for controlling the reactions.It is suggested that the use of this conception is advantageous in teaching analytical chemistry.     

Étude physique et numérique de la circulation cérébrale en pathologie carotidienne

A realistic and versatile physical model was built to simulate blood flow through the circle of Willis. Experimental data were then compared to those provided by numerical simulations. When the network is symmetrical and free of stenosis, the results of a linear model closely fit the experimental data. In presence of severe obstructive lesions of internal carotid arteries, the pressure drops induced by sudden changes of section or direction at the level of the communicating arteries must be taken into account. Introducing empirical flow-pressure drop relationships in the theoretical model, leads to an excellent agreement between experimental and simulated data. © 1999 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS     

Étude analytique de la propagation d'ondes en conduites déformables

In this paper, an analytical resolution of a periodic signal propagation equation is presented. At a given site of the conduit, the proposed solution allows one to isolate the part linked to the signal emitted at the extremity of the conduit and the part that would exist in its absence. The investigation of the evolution of this signal located at the extremity allows us to determine the length of the tube (in the particular case of a solitary wave) using the analysis of reflections at a given site.     

Dosage polarographique de la tyrosine,du tryptophane et de la phénylalanine en présence les uns des autres

A polarographic method is described for the determination of tyrosine, tryptophan and phenylalanine in mixtures, in which the animo acids are first converted to their nitro derivatives. Under suitable conditions each of these animo acids can be determined in the presence of the others.     

Amélioration de la tenue à la corrosion atmosphérique de matériaux utilisés en connectique (nickel doré). Traitements de surface par implantations d'ions

Improvement of the atmospheric corrosion resistance of materials used in connectics. Surface treatments by ion implantation. Tests of corrosion of a material, constituted of brass covered with an electrochemical nickel coating (thickness ≈ 5 μm) and with a gold coating (thickness ≈ 0.4 μm or ≈ 1 μm), used in electrical contact applications, have been carried out in humid synthetic air with low contents of NO₂ (0.2 vpm), SO₂ (0.2 vpm) and Cl₂ (0.01 vpm). The results obtained show that the corrosion products are well localised on the surface. The aggregates formed are principally constituted of basic nitrate, sulphate and chloride of nickel and zinc. These studies showed that the corrosion of the material is due to the presence of porosities in the gold and nickel layers. X-ray analysis (SEM/EDS) revealed the presence of carbon in these porosities, probably related to the presence of organic compounds in the electrolytic coating baths. During the galvanic corrosion of nickel and zinc, the carbon is rejected to the periphery of the aggregates. The amount of carbon was determined by Van De Graaff analysis, by (d,p) nuclear reaction. Some treatments of the material by ion implantation (titanium or titanium and nitrogen or helium) have been realised in order to suppress the porosities of the gold layer. These treatments lead to a remarkable improvement of the corrosion resistance of the material. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASatmospheric corrosion / nickel / brass / gold coating / ion implantation     

Recherches théoriques sur la structure électronique de molécules contenant des atomes hybridés en sp:

Résumé La méthode L. C. A. O. améliorée est utilisée pour étudier la structure électronique des molécules de vinylacétylène, de divinylacétylène et de butatriène, réduites à leur système . Les énergies des premières transitions N V sont en excellent accord avec l'expérience. Une relation entre l'indice de liaison mobile et la distance interatomique, pour des liaisons reliant des atomes hybridés l'un en sp et l'autre en sp ₂, est proposée.

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The improved LCAO theory is used to study the electronic structure of vinylacetylene, divinylacetylene and butatriene molecules, reduced at their system. The first N V transition energies are in excellent agreement with experiment. A relation between mobile bond order and bond distance, for bonds between sp and sp ₂ hybridized atoms, is proposed.

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Zusammenfassung Die elektronische Struktur der auf ihr -System reduzierten Moleküle Vinylacetylen, Divinylacetylen und Butatrien wird mit Hilfe der verbesserten LCAO-Methode untersucht. Die berechneten Energien der ersten N V-übergÄnge stimmen mit dem Experiment ausgezeichnet überein. Eine Beziehung zwischen Bindungsabstand und -Bindungsindex für Bindungen zwischen sp- und sp ₂-hybridisierten Atomen wird vorgeschlagen.

     

Recherches théoriques sur la structure électronique de molécules contenant des atomes hybridés en sp:

Résumé La théorie L. C. A. O. améliorée est appliquée à l'étude de la molécule C₃. Afin de satisfaire l'égalité nécessaire entre les éléments de matrice non diagonaux L _pq et L _qp, nous avons introduit un déplacement électronique le long des liaisons . Les charges nettes portées par les atomes terminaux sont: + 0,09. La distance C-C calculée (1,286 Å) est en bon accord avec l'expérience. Les énergies des deux premières transitions NV: ¹ _g ^{+ 1} _u ^– et¹ _g ^{+ 1}_u sont: 4,7 et 4,8 eV. Ces valeurs ne sont pas en contradiction avec l'expérience qui situe ces transitions au delà de 4,1 eV, limite à partir de laquelle l'absorption de l'atmosphère terrestre rend impossible l'étude des spectres cométaires.

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The improved LCAO theory is applied to the C₃ molecule. In order to satisfy the necessary equality between the non-diagonal matrix elements L _pq and L _qp, we have introduced an electron shift along the bonds. The net charges borne by the terminal atoms are: + 0.09. The computed C-C distance (1.286 Å) is in good agreement with experiment. The two first NV transition energies: ¹ _g ^{+ 1} _u ^– and ¹ _g ^{+ 1}_u are: 4.7 and 4.8 eV. These values are not in contradiction with experiment which places these transitions beyond 4.1 eV, limit from which the terrestrial atmospheric absorption makes impossible to study the comets' spectra.

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Zusammenfassung Die verbesserte LCAO-Theorie wird auf die C₃-Molekel angewandt. Um die nötige Gleichheit der nicht-diagonalen Matrixelemente L _pq und L _qp zu erhalten, haben wir eine Elektronenverschiebung längs der -Bindungen eingeführt. Die Ladungen der Endatome sind: + 0,09. Die berechnete C-C-Bindungslänge (1,286 Å) stimmt mit der Erfahrung überein. Die berechneten Energien der zwei ersten NV-Übergänge: ¹ _g ^{+ 1} _u ^– und ¹ _g ^{+ 1}_u sind: 4,7 und 4,8 eV. Diese Werte sind nicht in Widerspruch mit der Erfahrung, die diese Übergänge über 4,1 eV ansetzt; denn das Stadium der Kometenspektren ist über dieser Grenze wegen der Luftabsorption unmöglich.

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Nous remercions le Professeur P. Swings (Institut d'Astrophysique, Cointe-Sclessin, Belgique) ainsi que le Professeur Ch. Fehrenbach (Observatoire de Marseille), pour les échanges de vue que nous avons eu avec eux sur ce sujet.     

Recherches théoriques sur la structure électronique de molécules contenant des atomes hybridés en sp:

Résumé La méthode L. C. A. O. améliorée est utilisée pour étudier la structure électronique des molécules d'acétylène, de diacétylène et d'azote. Les énergies des transitions verticales calculées sont en bon accord avec l'expérience. Une relation entre l'indice de liaison mobile ( + ) et la distance interatomique, valable même lorsque les atomes sont de nature différente, est proposée.

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The improved LCAO theory is used to study the electronic structure of acetylene, diacetylene and nitrogen molecule. Calculated vertical transition energies are in good agreement with experiment. A relation between total mobile bond order ( + ) and bond distance is proposed, which applies also to atoms with different effective nuclear charges.

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Zusammenfassung Die elektronische Struktur der Moleküle Acetylen, Diacetylen und Stickstoff wird mit Hilfe der verbesserten LCAO-Methode untersucht. Die für die vertikalen Übergänge berechneten Energien stimmen mit dem Experiment befriedigend überein. Eine Beziehung zwischen Bindungsabstand und Gesamt--Bindungsindex, die auch für Atome verschiedener effektiver Kernladung gilt, wird vorgeschlagen.

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Que Monsieur G. Berthier (Laboratoire de Chimie Théorique de la Faculté des Sciences de Paris) qui a bien voulu relire notre manuscrit trouve ici l'expression de tous nos remerciements.     

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.     

Relation entre la morphologie des précurseurs et la microstructure de la céramique WO3 frittée

Relationship between the morphology of precursors and the microstructure of sintered WO₃ ceramics. The aim of this study is to perfect an elaboration process of ceramic WO₃, to control the main parameters, to understand the nature and the role of the precursors and to establish a relationship between the morphology of the powder and the microstructure of the final ceramic. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASpowder / granulometric / microstructure / precursors / sintering / ceramics     

Etude theorique de la dynamique du réseau de batio3 en phase quadratique

The lattice dynamics of barium titanate BaTiO₃ is discussed quantitatively in the framework of a shell model taking into account the electronic polarizabilities of the constituent ions and including Coulomb and short-range interactions. The results of calculations point out the important role of the anisotropic oxygen polarizability. There is a good agreement between calculated and experimental dispersion curves.     

Linéarisation et homogénéisation en viscoélasticité

Constitutive equations for non-linear viscoelastic materials are expressed first using a causal operator which relates a response function to any loading history. The corresponding tangent linear equations are then defined through the Fréchet derivative of this operator. This definition is used to propose a step-by-step treatment in view of the derivation of the overall behaviour of non-linear non-ageing viscoelastic heterogeneous materials.     

Récentes réalisations en analyse thermogravimétrique

Résumé Récentes applications en chimie minérale de la thermogravimétrie, en association avec d'autres techniques comme l'analyse thermique différentielle, les rayons X, la spectrographie d'absorption infrarouge, etc.

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Summary Recent applications in inorganic chemistry of thermogravimetry, in association with other techniques such as differential thermal analysis, X-rays, infra red absorption, etc.

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Zusammenfassung Eine Übersicht über neuere Anwendungsmöglichkeiten der Thermogravimetrie in der anorganischen Chemie wird gegeben. Die Verbindung mit anderen Verfahren, wie IR-Spektrographie, thermische Differenzanalyse, Röntgenanalyse u. dgl., wird erörtert.

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Conférence donnée à Luton, le 16 avril 1962     

Synthèse et étude d'une prodrogue de dipyridamole: application de la stratégie ADEPT à la résistance multiple (MDR) en chimiothérapie anticancéreuse

A glucuronyl-spacer-dipyridamole prodrug has been synthesized from dipyridamole, a reversal agent of MDR. Combined use of this compound with a glucuronyl-spacer-doxorubicin prodrug (HMR 1826), restored in vitro the sensibility of a resistant cancerous strain. This prodrug was therefore selected for in vivo tests according to ADEPT strategy on MDR resistance expressing tumours.