Influence de la structure chimique de la séquence diimide sur la relaxation γ des polyimides

Dynamic mechanical measurements in the −150 °C /+50 °C temperature range at 1, 3 and 10 Hz were carried out on a series of polyimides based on ODA diamine. A shift of 60 °C towards the lower temperatures of the γ relaxation was found on replacing N,N′-pyromellitimide (PMDA) by bicyclo [2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic di-imide (BCDA). A correlation between the dianhydride monomer structure variation and γ relaxation temperature is interpreted in terms of charge transfer interactions.     

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.     

La théorie exacte de la flexion des plaques

A new approach is introduced for the analysis and computation of homogeneous, isotropic elastic plates subjected to any bending loads. This approach is based upon a partitioning, which is independent of thickness, of the 3D reference solution into both a part with large variation length and localized effects, whose generalized stress-displacement values are zero. The part with large variation length can easily be computed from data as well as from generalized quantities that represent ‘averages’ in the thickness. These generalized quantities coincide with those obtained from the 3D reference solution; they constitute the solution to an ‘exact’ theory of plate bending.     

Modélisation de la durée des sons dans un système de reconnaissance automatique de la parole

A major deficiency of standard Hidden Markov Models (HMM) is that both the spectral and the prosodic features are uniformly processed. To combine more efficiently the prosodic cues with the acoustic ones, a segmental Two Level HMM has been recently studied by Suaudeau. In this paper, we present an adapted version in which the segmental processing is replaced by the classical centisecond one, and the prosodic feature is the sound duration. Experiments on a French database show that such an explicit introduction of prosodic parameters reduces recognition error rates.     

Étude des effets de frottement sur la dynamique des ondes de densité de charge dans les systèmes unidimensionnels

In this work, we present the numerical simulation results of the dynamics of charge density waves in one-dimensional systems. With a classical model, we show that the threshold field depends on the friction coefficient of the system. From the threshold field variation versus impurities concentration, we show the existence of three different pinning regimes and we prove that the pinning regime in witch E_c ∝ n_i^4/3 is an intermediate regime between the weak pinning and the strong pinning one, in the sense of Fukuyama, Lee, Rice. We show also that the transition from one pinning regime to the other is continuous.     

Viscoplasticité dynamique du polycarbonate: Influence de la vitesse de sollicitation et des traitements de recuit

The present paper deals with the study of engineering polycarbonates, investigated at high compressive strain rates (1100–3200 sec⁻¹), by means of Hopkinson pressure bar apparatus. Special attention was devoted to the influence of thermal pre-treatment and the viscoelastic behaviour in the glassy state. The results are compared to those obtained at low strain rates (10⁻²−1 sec⁻¹).     

Étude de la distribution des ions sur colonnes échangeuses

Résumé L'auteur étudie la distribution de divers ions seuls ou mélangés sur une résine cationique, par voie semimicro-analytique.

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Summary A column constructed from eight sacks filled with ion exchangers was used to study the distribution of metal ions of various valency from pure solutions or mixtures. If the chlorides of the metals are used in all cases, sodium and ammonium are retained in the first two sacks; magnesium and zinc in all sacks, especially in the first and sixth; iron and aluminium in all, particularly the first and sixth; nickel and cadmium in the first two, particularly the first; thorium in the first sack. These findings, which are independent of the atomic weight and valency, are possibly related to the formation of solvates and their various stabilities.

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Zusammenfassung Mit Hilfe einer Säule, die aus acht mit einem Ionenaustauscher gefüllten Säckchen bestand, wurde die Verteilung von Metallionen verschiedener Wertigkeit aus reinen Lösungen oder Gemischen untersucht. Verwendet man stets Chloride der betreffenden Metalle, so werden Natrium und Ammonium in den beiden ersten Säckchen, Magnesium und Zink in allen Säckchen, insbesondere im ersten und sechsten, Nickel und Cadmium in den beiden ersten, insbesondere im ersten, Eisen und Aluminium in allen, insbesondere im ersten und sechsten, Thorium im ersten Säckchen zurückgehalten. Diese von Atomgewicht und Wertigkeit unabhängigen Ergebnisse stehen möglicherweise mit der Bildung von Solvaten und deren verschiedener Stabilität im Zusammenhang.

     

Nouvelle synthese des benzodiazepines-1,5 a partir de la γ-pyrone

Reaction of 0-phenylenediamines 2, 3 with 2-hydroxy-6-methyl-4-pyrone leads to:2-butoxycarbonylmethylene-4-methyl-1,5-benzodiazepines 4, 5, 4-acetylmethylene-1,5-benzodiazepin-2-ones 6, 7, and benzimidazoles 8, 11. These compounds results from competitive reactions and different ways of cyclization.     

Étude numérique de la stabilité des écoulements de convection naturelle dans des espaces annulaires horizontaux de faible épaisseur

The mechanisms driving the multiplicity of multicellular natural convective flows found at the top of narrow horizontal air-filled concentric annuli (the inner cylinder temperature exceeding the outer) are considered. For radius ratio less than R = 1.20, the base flow undergoes an imperfect bifurcation. The two stable branches are characterised.     

Influence des réactions chimiques préalables sur la forme des courbes de polarisation

Equations have been established for polarographic waves observed while a chemical reaction slowly takes place before the exchange of electrons.The method of calculation is analogous to that already used by one of the authors in the case of polarisation curves relative to the reversible or irreversible systems.The variation of the two half-wave potentials and the limiting densities of current have been deduced. The results have been verified by means of the experimental results of R. brdicka concerning pyruvic and phenylglyoxylic acids.     

Microdosages des composés caractéristiques de la fermentation butanediolique

Compounds characteristic of the butanediol fermentation are 2–3 butanediol, acetoin and diacetyl; tlie determination of each of these compounds is based on a determination of dimethylglyoxime by nickel (II) (as in the classical methods, which are time-consuming and not very sensitive). The method now deseribed uses the soluble red complex given by dimethylglyoxime with niekel (IV). By this means 4 colorimetric methods have been established which, respcetively, permit: 1. The determination in 5 minutes, to about 1 %, of 120 to 600 μg, of dimethylglyoxime in a 10 ml sample. 2. The determination in 30 minutes, to about 1 %, of 90 to 450 μg, of diacetylin a sample of 10, 50 or 100 ml. 3. The determination in 50 minutes, to about 1 %, of 90 to 450 μg, of acetoin in a sample of 10, 50 or 100 ml. 4. The determination in 70 minutes, to about 3 %, of 100–500 μg, of butanediol in a 10 ml sample. These methods, based on specific reactions of the substances being determined, (in contradistinction to the numerous methods recently proposed for the determination of butanediol) are applicable even when the substances are accompanied by 1000 times their weight of glucose, glycerol, etc.     

Vers un diagnostic optique de la vorticité des tourbillons en hydrodynamique

It is shown in this note that the direct measurement of the rotational part of velocity fluctuations can be achieved within a neutral turbulent fluid by using a scattering technique sensitive to the electric field polarization. Application to the detection of vortices in a fluid by using, optical methods is emphasised.     

Contribution a létude de la standardisation des solutions acides normales

A very convenient and accurate method is proposed for titrating normal acid solutions. Potassium bicarbonate is converted through calcination into neutral potassium carbonate. The base thus obtained is used to determine the titre of acid solutions, following procedure clearly indicated. Results are obtained with an accuracy of 2 per l000.The main traditional methods are critically examined.     

Étude par spectrographie infrarouge de la structure de l'acide iodique,de l'acide anhydroiodique et des polyiodates alcalins

Résumé L'étude par spectrographie infrarouge entre 2 et 33 des divers produits de déshydratation de l'acide iodique et des nombreux iodates «acides» et «pyroiodates» qu'il donne avec les iodates alcalins montre l'existence de ponts I-O-I analogues à ceux qui existent dans l'anhydride iodique I₂O₅. Ces liaisons se caractérisent dans la région explorée par deux groupes de bandes fortes à 400–460 cm^–1 et à 515–646 cm^–1, c'est-à-dire en dehors des régions d'absorption caractéristiques des groupements IO₂ ou IO₃.

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Summary The infrared spectrographic study between 2 and 33, of various products of dehydration of iodic acid and numerous acid iodates and pyroiodates which it yields with alkaline iodates reveals the existence of I-O-I bridges analogous to those in I₂O₅. In the regions explored, these links are characterized by two groups of strong bands at 400–460 cm^–1 and at 515–646 cm^–1, i. e. beyond the absorption regions characteristic of the IO₂ or IO₃ groups.

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Zusammenfassung Die IR-spektrographische Untersuchung verschiedener durch Wasserabspaltung aus Jodsäure hergestellter Produkte, zahlreicher saurer Salze und mit Alkalijodaten gebildeter Pyrojodate zwischen 2 und 33 zeigt das Vorhandensein von J-O-J-Brücken, wie sie analog im Jodsäureanhydrid J₂O₅ vorliegen. Charakteristisch für diese Bindung sind im untersuchten Bereich zwei starke Bandengruppen bei 400 bis 460 cm^–1 und bei 515 bis 646 cm^–1, das heißt jenseits des Bereiches der charakteristischen Absorption der Atomgruppen JO2 oder JO3.

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En l'honneur du ProfesseurF. Feigl, pour son 70^e anniversaire.     

Structuration de la solution stationnaire des écoulements interdisques en configuration rotor-stator

Steady axisymmetric flows in disk systems are investigated numerically. Steady states are calculated by adapting a temporal pseudo-spectral code in order to carry out Newton's method. A self-similar solution is shown to exist surrounding the axis, with a recirculating zone near the end-wall. Between these two zones is a pseudo-similar region where velocity profiles collapse according to a dilatation law which is a function of the aspect ratio.     

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.     

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