Calcul théorique de l'hystérésis thermique de BatiO3 pur et dopé au fer

The value of the thermal hysteresis of pure and iron doped BaTiO₃ was calculated using an effective field model taking into account dipolar and quadripolar interactions. The calculation is performed using a self-consistent method. The calculations show a good agreement with experimental results.     

Indépendance de l'intégrale de contour pour une symétrie de dilatation

Knowles and Sternberg gave the definition of the M integral relative to the dilatational symmetry in the elasticity domain. The path domain independence of this integral correspond to some very restricted applications. We propose to enlarge the field of application in defining for every type of transformation a modified path domain independent M integral. The demonstration that this conservation law is associate to the transformation is considered.     

Propriétés rhéologiques à l'état fondu de polyesters thermoplastiques chargés de fibres de verre

A study of rheological properties in the molten state of two short glass fibre reinforced polyesters (polyethylene terephthalate and polybutylene terephthalate) was carried out, both in steady and dynamic flow. The results lead to information on the flow behaviour of these composite materials. Moreover, this study confirms the presence of fibre tied entanglements and shows the influence of the matrix.     

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.     

Propriétés magnétiques de phosphates et silicophosphates de titane

The magnetic properties of titanium phosphates ATiP₂O₇ (A=Na,K,Rb), A₂Ti₂(PO₄)₃ (A=K,Rb), BaTi₂(PO₄)₃ M g₃Ti₄P₆O₂₄ and titanium silicophosphates ATi₃P₆Si₂O₂₅ (A=K,Cs) have been investigated by magnetic susceptibility and electron spin resonance measurements. All the compounds are paramagnetic and the thermal variation of the susceptibility can be described with a Curie-Weiss law χ_m=χ₀+ C_m/T−θ_p. The values of μ_eff per Ti⁺³ and the spectroscopic data obtained from the 77K E.P.R. spectra are discussed as a function of the structural data.     

Étude Théorique de la Conductivité, Photoconductivité et de l'absorption Photoinduite de BaTiO3:Fe et KNbO3:Fe

Calculation of dark conductivity, and study of photoconductivity and light-induced absorption in BaTiO₃ :Fe and KNbO₃:Fe are performed at many light intensities. The results are interpreted in a two impurity level band model. This model allows to calculate the dark conductivity, to explain the behavior of the photoconductivity with the respect to the light intensities, and to study the light-induced absorption coefficient.     

Le spectre d'absorption infrarouge de l'acétate de méthyle perdeutéré

Résumé Les spectres d'absorption infrarouge de l'acétate de méthyle et de l'acétate de méthyle perdeutéré ont été étudiés de 300 à 4000 cm^–1. La comparaison des spectres a permis l'attribution certaine des bandes de l'acétate de méthyle, en particulier de la bande observée vers 1245 cm^–1 qui correspond à une vibration concernant la liaison C-O.

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Summary The infrared absorption spectra of methyl acetate and the perdeuterated methyl acetate have been studied from 300 to 4000 cm^–1. The comparison of the spectra has made it possible to attribute certain of the bands of methyl acetate, in particular the band observed around 1245 cm^–1, which corresponds to a vibration involving the C-O bond.

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Zusammenfassung Die Absorptionsspektren von Methylacetat der Zusammensetzung CH₃COOCH₃ und CD₃COOCD₃ im Infrarot wurden zwischen 300 und 4000 cm^–1 untersucht. Der Vergleich dieser Spektren führte zur sicheren Zuordnung der Banden des Methylacetats, insbesondere der bei 1245 cm^–1 gelegenen Bande, die der C-O-Bindung zugehört.

     

Étude théorique de la dynamique du réseau de PbTiO3 dans la phase quadratique

The lattice dynamics of lead titanate PbTiO₃ is discussed quantitatively using a shell model taking into account the electronic polarizabilities of the constituent ions, and including Coulomb and short-range interactions. Our calculations highlight the important role played by the anisotropic polarizability of oxygen and show good agreement between calculated and experimental dispersion curves.     

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.     

Dénombrement de cascades de colonnes de rectification complexes

A recursive procedure for enumerating separation sequences involving columns with one or two feed streams and several sidestreams is presented in t     

Méthode de dosage spécifique de l'alanine et de la somme sérine + acide aspartique

Résumé La méthode indiquée parKendall etFriedemann pour le dosage de l'alanine n'est nullement spécifique de cet acide aminé; les modifications queFürth et ses collaborateurs ont apporté à cette méthode dans le but de la rendre spécifique, n'ont atteint ce but que partiellement, et par des moyens compliqués.Le présent travail montre qu'il suffit d'ajouter à la solution des hydroxyacides provenant de la désamination des acides aminés, le dixième de son volume d'une solution d'acétate mercurique à 5% pour empêcher au cours del'oxydation ulterieure par le permanganate, toute production d'acétaldéhyde à partir de la sérine et de l'acide aspartique; dans ces conditions, l'acétaldéhyde formé ne provient plus que de l'alanine. La réaction colorimétrique donnée par l'acétaldéhyde avec le nitroprussiate de soude et la pipérazine, permet d'en faire le dosage spécifique en présence des autres aldéhydes fournis pas les autres acides aminés. Il est ainsi possible de doser l'alanine d'une façon rigoureusement spécifique en présence d'acides aminés quelconques. Cette méthode permet la détermination, à 5% près, de 2 mgr. et plus d'alanine.En modifiant les conditions d'oxydation par le permanganate (augmentation de la concentration en SO₄Mn, et de la durée d'oxydation) et en supprimant l'addition d'acétate mercurique, on obtient une production quantitative d'acétaldéhyde à partir de l'ensemble alanine + sérine + acide aspartique; il est ainsi possible de doser la somme de ces trois acides aminés en présence d'acides aminés quelconques, et de déterminer, par conséquent, la teneur d'un mélange d'acides aminés quelconques en alanine d'une part et en l'ensemble sérine + acide aspartique de l'autre. Les chiffres obtenus correspondent à 95 à 97% de la teneur réelle en alanine, et à 93 à 95% de la teneur réelle en sérine + acide aspartique.

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Summary The method given byKendall andFriedemann for the determination of alanine is by no means specific for this amino acid.Fürth and his co-workers introduced some modifications in order to make the method specific. The aim, however, was obtained but partially and by complicated means.It is shown in the paper present that it is sufficient to add to the solution of the hydroxy-acids formed by desamination of the amino-acids, one tenth of its volume of a 5% mercuric acetate solution, in order to inhibit the formation of acetaldehyde from serine and aspartic acid during the ultimate oxidation by permanganate. Acetaldehyde formed under those circumstances solely originates from alanine. The colour reaction which acetaldehyde gives with sodium nitroprussiate and piperazine, is specific. Thus, a colorimetric determination of acetaldehyde in presence of other aldehydes originating from the other amino-acids, is made possible. It ensues that a strictly specific determination of alanine in the presence of any other amino acid can be performed. This method allows to determine, at least, 2 mgs. of alanine, the limit of error being about 5%. By altering the conditions of the permanganate oxidation (i. e. by augmenting the concentration of manganous sulphate or by extending the time of oxidation) and by omitting the addition of mercuric acetate, acetaldehyde is formed quantitatively as a product of the sum of alanine + serine + aspartic acid. It is possible, in this way, to determine the sum of these three amino acids in presence of any other amino acids and to calculate therefrom the quantity of both alanine and the sum of serine + aspartic acid, contained in a mixture of whatsoever amino acids. The figures obtained represent 95–97% of the true alanine content, and 93–95% of the true content of serine + aspartic acid.

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Zusammenfassung Die vonKendall undFriedemann für die Bestimmung des Alanins angegebene Methode ist für diese Aminosäure keineswegs spezifisch. Die Modifikationen, die vonFürth und seinen Mitarbeitern eingeführt wurden, um die Methode spezifisch zu gestalten, erreichen dieses Ziel nur teilweise und durch komplizierte Mittel.Die vorliegende Arbeit zeigt, daß es genügt, der Lösung der Oxysäuren, die bei der Desaminierung der Aminosäuren entstehen, ein Zehntel ihres Volumens an 5%iger Quecksilberacetatlösung zuzufügen, um die Entstehung von Acetaldehyd aus dem Serin und der Asparaginsäure bei der schließlichen Oxydation mit Permanganat zu verhindern. Der unter diesen Umständen gebildete Acetaldehyd entsteht lediglich aus dem Alanin. Die Farbreaktion, die der Acetaldehyd mit Nitroprussidnatrium und Piperazin gibt, ist spezifisch und ermöglicht eine kolorimetrische Bestimmung in Gegenwart anderer Aldehyde, die aus den anderen Aminosäuren entstehen. Es ist mithin eine streng spezifische Bestimmung des Alanins in Gegenwart irgendeiner anderen Aminosäure möglich. Diese Methode gestattet die Bestimmung von wenigstens 2 mg Alanin bei einer Fehlergrenze von ungefähr 5%. Wenn man die Bedingungen bei der Permanganatoxydation ändert (durch Erhöhen der Konzentration von MnSO₄, bzw. der Oxydationsdauer) und das Zufügen von Quecksilberacetat unterläßt, erfolgt die Bildung des Acetaldehyds quantitativ, und zwar aus der Summe Alanin + Serin + Asparaginsäure; es ist auf diese Weise möglich, die Summe dieser drei Aminosäuren in Gegenwart beliebiger anderer Aminosäuren zu bestimmen und daraus den Gehalt eines Gemisches beliebiger Aminosäuren an Alanin einerseits und an der Summe Serin + Asparaginsäure andererseits zu bestimmen. Die erhaltenen Zahlen entsprechen 95 bis 97% des wahren Alaningehaltes und 93 bis 95% des wahren Gehaltes an Serin + Asparaginsäure.

     

Polymérisation et post-polymérisation de l'acrylate de méthyle en milieu précipitant

The radiation initiated polymerization of methyl acrylate was investigated under precipitating conditions in n-hexane In 10 and 25% monomer solutions, the conversion curves are auto-accelerated and post-polymerization is observed in the dark. The initial rate of this post-polymerization steadily increases with the degree of conversion reached during irradiation, suggesting that trapped growing chains are responsible for the effect. The post-polymerization was followed at 23, 40 and 60°. From the results, it is concluded that chain termination is negligible under such conditions. The addition of methanol to the monomer solutions results in decreased rates and in a reduction of the extent of auto-acceleration. No influence of any “matrix effect” could be detected in these systems.     

Application de la chrono-ampérométrie par redissolution anodique au dosage de traces d'acétate de triphényl-étain

Using a hanging dropping mercury electrode (according to Vogel) the autliors find a better sensitivity of measurements in the determination of triphenyl tin acetate as fungicide residues on vegetable inatter.     

Contribution à l'étude du mécanisme de mûrissement de résines polyesters insaturées en présence de MgO

The thickening process for unsaturated polyester resin in styrene monomer and with magnesium oxide (MgO) has been evaluated by gel permeation chromatography (GPC). The GPC analysis n tetrahydrofuran (THF) shows that with time the distribution shifts towards higher molecular weight. This effect disappears when the products are analysed in a polar solvent. The process of thickening is attributed to the formation of reversible ionic association. The existence of strong ionic bonds in the final products is confirmed by the presence of a rubber-like plateau in dynamic mechanical properties. The effects of water and magnesium oxide concentrations are given.     

étude thermodynamique de certains médicaments

Two compounds of sulphamide type:p-amino-benzene sulphonamide (I) and 3,4-dimethylisoxazol 5-sulphanylamide (II) were studied by combustion calorimetry and by differential scanning calorimetry (DSC).The enthalpies in solid state at 298,15 K of combustion, _c H _m ^o (I)=-2788,5±1,6 kJ mol^–1, _c H _m ^o (II)=-5036±3,8 kJ mol^–1 and of formation, _f H _m ^o (I)=-458,3±1,6 kJ mol^–1, _fH _m ^o (II)=-180,1±3,8 kJ mol^–1 were determined.The thermal effects concerning the melting and phase transition of this compounds were also measured.

     

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.     

Transitions de phases multiples et propriétés ferroïques de Pb5Al3F19

Pb₅Al₃F₁₉, a member of the isostructural Pb₅M₃F₁₉, family with M = Al, Ti, V, Cr, Fe and Ga, differs from the remaining members in having three additional phases between its ferroelectric phase V and its paraelectric phase I. Phase IV is shown to be antiferroelectric, phase III ferroelastic and phase II paraelastic. Each phase has been fully characterized. Formation of the three extra phases is attributed to interactions between the 6(sp)² lone electron pair of the Pb² ion and volume effects related to the small Al³⁺ ion.