Microdosage colorimétrique de la cystéïne et de la cystine

Thiofluorescein is bleached in alkaline medium by light but reforms its colour on reaction with —SH groups. This can be used for the colorimetric determination of cystine and cysteine in the micromolar range.     

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.     

Analyse de la réduction passive de la traînée laminaire

A theoretical multi-layer model is used to describe the influence of wall perturbations on the boundary layer flow. The originality and interest of the method lies in the use of non-regular second-order asymptotic expansions arising from the presence of two longitudinal length scales. From the lower deck canonical problem, the influence of wall perturbations on laminar drag reduction is inferred.     

Détermination de la dissipation caractéristique dans la propagation d'un front de recristallisation

We study the displacement of the boundary between the two grains of an ideal two-dimensional bicrystal having a hexagonal lattice within the plane. The boundary we deal with is a discontinuity straight line for the lattice orientation function that may move at a different velocity from the underlying matter; hence dissipation occurs, eventually equal to the rate of released energy. We estimate the characteristic dissipation in the propagation of the discontinuity.     

Effet de la température,de la pression et de la composition sur l'intensité diffusée par un mélange de deux polymères

Phase diagrams of polymer blends and solutions are usually studied by measuring the scattered intensity (by light or neutrons) as a function of composition, temperature and pressure. If one expands Flory's χ parameter as a function of the composition, one sees that in order to have deviations from Flory's laws, thermodynamic quantities such as volume, heat capacity or compressibility should vary with respect to composition by a power law of degree larger than two. In some cases, the direct measurement of these quantities could lead to a more precise and rapid determination of the miscibility conditions.     

Applications analytiques de la phénothiazine

Spot tests carried out with the help of phenothiazine as reagent permit the detection of silver on a drop plate or on paper. D = 10^-5 or even 6.7.IO^-6 with a little less certainty. The reactions obtained are described in detail in the case of palladium, gold and platinum. Use of the reagent allows the detection of iron in presence of uranium (0.15γ iron in 0.053 ml in the presence of 107 times its weight of uranium). It also enables mercury to be detected in the presence of silver, even in the case of silver which is practically free from mercury. Finally, by the combined use of phenothiazine and diphcnylcarbazide it is possible to detect 0.54γ of silver in the presence of 100 times its weight of mercury.     

Étude de la phényl-2 oxine et de ses chélates: Constantes de dissociation de la phényl-2 oxine

The authors determined, by spcctrophotometric and potentiometric methods, the ionization constants of 2-phenyl-8-quinolinol in hydroalcoholic solutions.     

Description eulerienne de la mécanique d'un front de discontinuité avec apparition d'une localisation de la déformation

We study the exchanges occurring through a discontinuity front in a continuum. We focus in particular on the jump condition corresponding to the Clausius-Duhem inequality. We analyse the possibility of a localised glide on a discontinuity surface, emphasizing two different terms in the dissipation on the surface: one resulting from a possible movement of the front, the other ensuing from localisation.     

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.     

Simulation numérique déterministe de la turbulence

We first present techniques of large-eddy simulation (LES) in physical und Fourier spaces. We show how LES allows vortex control in mixing layers, and good prediction of velocity statistics in a turbulent channel. We study also in a developed boundary layer the dynamics of high- and low-speed streaks at the wall, and the associated pressure fluctuations. Following this, we show in rotating shear flows a universal behaviour ol the mean velocity in regions whosw local Rossby number is sirictly inferior to — 1. Finally, we present for LES of compressible flows a formalism based on Favre averages.     

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.     

Statu quo sur la méthanation du dioxyde de carbone : une revue de la littérature

This review summarizes the statu quo and the perspectives of chemical methanation. CO₂ methanation, including catalyst deactivation, reactors, mechanisms, and thermodynamics are presented. This reaction serves as a test bed for our fundamental understanding of heterogeneous catalysis and is used in various industrial processes, including the removal of oxo-compounds (CO_x) in the feed gas for the ammonia synthesis, in connection with the gasification of coal, where it can be used to produce methane from synthesis gas, and in relation to Fischer–Tropsch's synthesis. Moreover, CO₂ methanation became of interest as a renewable energy storage system based on a “power-to-gas” conversion process by SNG (synthetic natural gas) production integrating water electrolysis and CO₂ methanation as a highly effective way to store the energy produced by renewables sources. The effectiveness and efficiency of the “power-to-gas” plants strongly depends on the CO₂-methanation process.     

Dépassement de la limite de réflexion de la lumière des cristaux liquides cholestériques : de Plusiotis resplendens aux gels à inversion d'hélicité

Beyond the reflectance limit of cholesteric liquid crystals: from Plusiotis resplendens to helicity-inversion gels. Due to its helical structure, a cholesteric liquid crystal (CLC) selectively reflects the light when its wavelength matches the helical pitch. The reflectance is limited to 50% of ambient, unpolarized light, because circularly polarized light of the same handedness as the helix is reflected. We report the elaboration procedure and the properties of a CLC gel for which the reflectance limit is exceeded in the infrared region. Photopolymerizable mesogens are introduced in the volume of a CLC exhibiting a thermally induced helicity inversion, and the blend is then cured with ultraviolet light when the helix is right-handed. The reflectance exceeds 50% when measured at the temperature assigned at a cholesteric helix with practically the same pitch, but a left-handed sense before reaction. From scanning electron microscopy investigations, it is shown that the organization of the mesophase is transferred onto the structure of the network. The gel structure is discussed as consisting of a polymer network with a helical structure containing two populations of LC molecules. Each of them was characterized by a band of circularly polarized light, which is selectively reflected. Novel opportunities to modulate the reflection over the whole light flux range are offered. Potential applications are related to the light and heat management for LC smart windows or reflective polarizer-free displays with a larger scale of reflectivity levels.     

Nitration et dosage de la phénylalanine

This paper comprises a study of the conditions for nitrating phenylalanine and an investigation of the compounds obtained, polarographic and chromatographic methods being employed. At the same time some nitrobenzoic acids that are found among the nitration products of nitrophenylalanine were examined by both these methods.A method has been proposed for the polarographic determination of phenylalanine, by means of which as little as 30γ of this substance can be detected in 10 ml solution. With concentrations between 2.4.10^-4M and 6.10^-3Mt, the error is less than 2.5%, with those of the order of 2.10^-5M it approaches 12%.     

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.

     

Emploi de la thermogravimétrie et de la spectrophotométrie infrarouge pour suivre les réactions à l'état solide

Résumé L'auteur indique sur des exemples variés comment on peut combiner les indications de la thermobalance et du spectromètre infrarouge pour suivre les réactions à l'état solide, qu'il se dégage ou non un produit gazeux: action de la strontiane sur les pyrophosphates, polymérisation spontanée des métaborates, adsorption du permanganate par le sulfate de baryum, combinaison supposée SiO₂ + 12 MoO₃, action de l'iode sur la magnésie. Ensuite, il étudie plus longuement la synthèse des chromites et la mise en solution par l'oxylithe des oxydes métalliques; cette dernière réaction s'effectue suivant quatre mécanismes différents illustrés par des exemples concrets.

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Summary The writer shows by means of varied examples how the information furnished by the thermobalance may be combined with that derived from the infra red spectrometer in following solid state reactions, which may or may not produce gaseous products. Examples are: action of strontium oxide on the pyrophosphates, spontaneous polymerization of metaborates, adsorption of permanganate by barium sulfate, alleged compound SiO₂ + 12 MoO₃, action of iodine on magnesia. The investigation also included a lengthy study of the synthesis of chromites and the solution of metal oxides by sodium peroxide. The latter reaction, effected by four different mechanisms, is illustrated by concrete examples.

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Zusammenfassung An Hand verschiedener Beispiele wird gezeigt, wie man mit Hilfe der Thermowaage und des IR-Spektrophotometers Festkörperreaktionen mit oder ohne Gasentwicklung verfolgen kann. Als solche Beispiele werden angeführt: die Einwirkung von Strontiumoxyd auf Pyrophosphat, die Spontanpolymerisation von Metaboraten, die Absorption von Permanganat durch Bariunisulfat, die Bildung des Gemisches SiO₂ + 12 MoO₃ durch Erhitzen von Oxin-Silicomolybdat, Einwirkung von Jod auf Magnesiumoxydhydrat. Weiters wird die Synthese von Chromiten und die Auflösung von Metalloxyden mit Natriumperoxyd ausfuhrlich erörtert. Der letztgenannte Vorgang verläuft nach vier verschiedenen Reaktionsmechanismen, die an konkreten Beispielen erklärt werden.

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Conférence prononcée le 25 avril 1961, au Congrès de chimie analytique de Budapest.     

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.