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.     

Effet de la polarité du solvant sur les propriétés des états électroniques excités du 1,1′-binaphtyle: étude par spectroscopie UV-visible

A UV-vis emission spectroscopy study of the flexible molecule, 1,1′-binaphtyl as a function of solvent polarity allows one to obtain information on the excited singlet states. We show the existence of a charge transfer (CT) character state. This CT is evidenced by the solvent polarity effect, the measurement of polarization ratio and finally by comparison of the ratio intensities of phosphorescence and fluorescence.     

Etude du phénomène de dépiégeage des ondes de densité de charge dans les systèmes de basse dimensionnalité

Numerical results of the behaviour of a low dimensional system show that the electric resistivity depends on the friction coefficient generated by the defects. We also show that the electric field dependence of the response time at different friction coefficients follows a power law. The divergence of the charge density wave response time near the threshold field indicates that depinning may be viewed as a dynamical critical phenomenon.     

Critère d'instabilité du front de retrait lors du séchage lent d'une suspension d'argile dans un dièdre

Drying a clay-water suspension within a dihedral leads to the formation of dry clay veils which result from the instability of the withdrawing front. Considering that the suspension dries but no significant gradient of solid fraction develops, the fluid withdrawal can be considered as the flow of a yield stress fluid subjected to the Saffman-Taylor instability. A simple theoretical approach shows that the flow is unstable when the yield stress of the fluid is larger than a critical value proportional to the local distance between the solid surfaces and proportional to the surface tension. The position of the first veils predicted by this theory as a function of the initial solid fraction of the suspension is in agreement with the experiments.     

Généralisation de l'identité de Germano et application à la modélisation sous-maille

In the large-eddy simulation frame, a dynamic procedure based on Germano's identity is often employed to adjust the subgrid-scale model constant. Applying an n-th degree linear operator to the Germano identity, a generalized dynamic procedure is defined to model this operator applied to the subgrid-scale tensor. This procedure leads to very satisfactory results when applied to the divergence operator in the frame of freely decaying turbulence.     

Instabilité du front de retrait lors du séchage d'une suspension d'argile dans un empilement granulaire

Drying a clay-water suspension within a bead pack leads to the formation of dry clay veils between grains. These veils are approximately perpendicular to the direction of advancement of the drying front and may be situated at a distance of the order of grain radius from the point of contact between grains. More generally we demonstrate that such veils result from the instability of the withdrawing front when a suspension dries between solid surfaces. For sufficiently slow drying, no significant gradient of solid fraction develops in the suspension and the different aspects of this instability seem to be in favour of a drying more or less ‘as a whole’.     

Etude des associations phénol-méthyl-2 benzophénones: Influence de la géometrie moléculaire sur la sensibilité du carbonyle aux effets structuraux

The characteristic shifts Δν_OH of ketone-phenol associations have been measured for 40 benzophenones of the Me2, XC₆H₃COC₆H₄Y (Me2, XBY) type in which X and Y are variable substituents. A correlation shows that the CO has a greater sensitivity to the effect of Y for the Me2 BY population. This result is attributed to the destabilization arising from the ortho-methylated aromatic ring thereby rendering the carbonyl group more sensitive to the substituents carried by the other. For two populations of compounds where destabilization by torsion is constant, a second homogeneous correlation allows us to measure the rôle played by the molecular torsion on the attenuation of substituent effects. When the molecule is partially deconjugated and the substituent effect decreased, a third and final correlation shows that these parameters, which have opposite effects, balance each other. A comparison of these results with the pK_BH+ of the benzophenones indicates that in a state nearer the fundamental state, the influence of the molecular geometry on the transmission of the substituent effect is more marked than in a more perturbed state where the phenomenon is masked by electronic interactions between the substituents X and Y     

Utilisation des courbes de polarisation dans les dosages électrochimiques: Coulométrie á intensité constante

The conditions for coulometric determinations at constant intensity can be deduced from the polarisation curves; these are choice of current density and auxiliary systems, and possible accuracy of the determination. We have used for this study the results previously obtained for potentiometry at constant intensity.     

Utilisation de matériaux à base d’argiles modifiées dans la conversion du toluène

Clay materials, montmorillonite from Maghniya deposits (Algeria), were used as an acidic catalyst in toluene conversion. Toluene disproportionation reaction in gaseous phase was used. These clays were modified by ion exchange with uranyl ions UO₂²⁺. The surface acidity of catalysts was determined by the stepwise desorption technique (STD) of probe molecules using butylamine and ammonia. Thus, total acidity and distribution of the acidity strength were determined. The results show that materials presented an appreciable total acidity and catalytic activity in studied reaction. The acidity strength of catalysts due to UO₂²⁺ ions was kept at a temperature of 550 °C. A relationship was found between the catalytic activity and acidity strength generated by the introduction of uranyl ions in the clay structure.     

Chromatographie sur papier des Molybdates. Titrage direct des taches de Molybdène chromatographié, séparé du Chrome et du Vanadium

Résumé Dans les conditions opératoires précisées ici, le molybdène chromatographié sur papier Whatman n°4, se laisse doser parabsorptiométrie à ± 1% près, pour une quantité de l'ordre de 10 microgrammes.Letitrage direct de la même quantité de molybdène se fait à ± 3,5% près. Séparé du chrome et du vanadium par chromatographie, la précision du titrage après chromatographie reste du même ordre. La titration directe fait gagner trois heures sur l'absorptiométrie.

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Summary Under the conditions outlined here, molybdenum chromatographed on Whatman paper No. 4, may be determined by absorption, within about ± 1%, for an amount of the order of 10 micrograms. The direct determination of this same quantity of molybdenum by titration can be made within about ± 3%. Separated from chromium and vanadium by chromatography, the precision of the titration after chromatography remains of the same order. The direct titration gains three hours over absorption.

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Zusammenfassung Bei Einhaltung der beschriebenen Versuchsbedingungen läßt sich Molybdän nach chromatographischer Adsorption auf Whatman-Papier Nr. 4 in der Größenordnung von etwa 10 mit ± 1% Genauigkeit durch Absorptiometrie bestimmen. Die direkte Titration gleicher Molybdänmengen läßt sich mit einer Genauigkeit von ± 3,5% ausführen. Nach chromatographischer Trennung von Chrom und Vanadium ergibt die Titration die gleiche Genauigkeit. Somit lassen sich durch direkte Titration gegenüber der Absorptionsmessung drei Stunden Zeit gewinnen.

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Cette recherche a bénéficié d'un subside du Fonds National de la Recherche Scientifique. Nous en témoignons ici notre sincère gratitude.

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Avec 3 figures.

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Travail exécuté en vue de l'obtention du grade de Licencié en Sciences Chimiques (Faculté des Sciences, Université Libre de Bruxelles), juillet 1952.     

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.     

Préparation d'aminométhyltributylétains par stannylation de sels d'immonium au moyen du chlorure de tributylstannylmagnésium. Applications à la synthèse de β-aminoalcools

Tributylstannylmagnesium chloride reacts with immonium salts and gives non-substituted, α-substituted or α,α-disubstituted aminomethyltributyltins. The reaction, which can be extended to stannylation by tributylstannylalkalis, is not affected by the nature of the anionic part of the immonium salt. Transmetallation of aminomethyltributyltins with butyllithium, followed by condensation with carbonyl compounds, provides a regiospecific route to β-aminoalcohols.     

Récents progrès dans la chromatographie quantitative sur papier

Résumé Les progrès réalisés dans la chromatographie quantitative sur papier l'ont été par étapes, en vue d'en faire une technique micro et ultra microchimique ayant une réelle valeur pratique; c'est à dire réalisable en un temps très court, applicable aux quantités de matière les plus petites avec le maximum de reproductibilité. Laspectrophotométrie directe sur papier des taches colorées utilisant letransmission de la lumière au travers de celles-ci répond à ces critères. Elle permet de mesurer en quelques minutes la concentration d'un élément contenu dans une taches avec une reproductibilité supérieure à tout ce qui a été obtenu antérieurement et ce jusqu'à des quantités de l'ordre de 0,02 à 0,03 g.D'autres publications feront part de nouvelles améliorations et simplifications, étudiées à l'occasion du cobalt, du cuivre, du zinc, du cadmium, du barium et du plomb.

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Summary The progress made in quantitative chromatography on paper has been in stages with the objective of making it into a micro- and ultramicro technique of real practical value; that is to say, to render it accomplishable in a very short time, applicable to very slight amounts of material, and with the maximum of reproducibility. Direct spectrophotometry on the paper of the colored stains, utilizing the transmission of the light through the latter, meets these criteria. This procedure makes it possible to determine the concentration of an element contained in a stain within several minutes and with a reproducibility surpassing anything obtained previously, and even with amounts of the order of 0,02 to 0,03 g. Later papers will deal with the improvements and simplifications studied with respect to cobalt, copper, zinc, cadmium, barium, and lead.

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Zusammenfassung Die fortschreitende Entwicklung der quantitativen Papierchromatographie führte zur Ausarbeitung mikrochemischer und ultramikrochemischer Verfahren für die Praxis; diese beanspruchen wenig Zeit, sind auf sehr kleine Mengen anwendbar und ausgezeichnet reproduzierbar. Die unmittelbare Spektrophotometrie der Chromatogrammflecken auf dem Papier durch Messung ihrer Lichtdurchlässigkeit entspricht diesen Anforderungen und ermöglicht die Bestimmung der Konzentration eines Elementes im Chromatogramm besser als alle bisherigen Verfahren bis zu einer Größenordnung von 0,02 bis 0,03 g. Weitere Mitteilungen über Verbesserungen und Vereinfachungen für die Bestimmung von Kobalt, Kupfer, Zink, Cadmium, Barium und Blei sind in Vorbereitung.

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A M. le Professeur de l'Université Dr.Hans Lieb à l'occasion de son 70^ème anniversaire.     

Activité antiplasmodiale in vitro des composés isolés des écorces du tronc de Vitex thyrsiflora

Phytochemical study of Vitex thyrsiflora (Verbenaceae), a medicinal plant commonly used in traditional medicine to treat malaria, have allowed to isolate six compounds identified 20(R),24(E)-3-Oxo-9β-lanosta-7,24-dien-26-oic acid (1), α-amyrin (2), β-amyrin (3), friedelin (4), β-sitosterol palmitate (5) and a sterol glucoside (6). All these compounds were isolated for the first time in this plant. Their structures were determined on the basis of their physical and spectroscopic data (IR, MS, UV, NMR) and by comparison of these data with those reported in the literature. Compound 5 showed significant antiplasmodial activity with IC₅₀ of 3,09 and 8,98 μg/mL against multi-resistant strains Dd2 and K1 of P. falciparum. All these constituents were isolated from this plant for the first time. The tested compounds were non-cytotoxic on the LLC-MK2 monkey kidney epithelial cells. The results obtained can justify the use of Vitex thyrsiflora stem bark in traditional medicine for the treatment of malaria.     

La modélisation statistique de la turbulence: ses capacités et ses limitations

Statistical turbulence modelling has experienced some very differnent and even contradictory fortunes: il can lead in highly satisfactory results in complex industrial geometries, like in flows around aeroplanes, but can meet with almost insurmountable problems when applied to apparently simple geometries. This paradoxical situation arises mainly because the hypotheses on which the different models of turbulence are based vary in their suitability (sometimes completely unsuitable) for the specific physics that is relevant for each studied flow. The aim of this paper is to display some of the great difficulties that remain to be resolved in order that statistical turbulence modelling can become a truly reliable tool, both in attempts to understand phenomena (the objective of the research scientist) and for the optimal development of industrial systems (the engineer's objective). From the starting point of straightforward observations made, on running computational simulations of turbulent jets, we attempt to show in stages where the sources of weakness in present turbulence models lie, especially in the case where energy spectra are no longer in equilibrium. These analyses have resulted in our divising a new approach, while still drawing on the established knowledge attained by classical statistical modelling. The new method is based on a new way of breaking down physical values into two parts: coherent and incoherent. We will also deal in this paper with the choice of the level of modelling turbulent viscosity models and models using Reynolds stress transport equations. The Boussinesq behaviour law has also been questioned, in many situations. This leads to the elaboration of non linear models and to certain kinds of constants which are in reality structure functions. In conclusion, new prospects are put forward concerning continued follow-up research in this area.     

Un modèle de transfert énergétique rotation-translation lors de dissociations unimoléculaires à trois atomes

A model of rotational-translational energy transfer in the exit-channel of a three-atom unimolecular reaction. For a three-atom unimolecular reaction of the type ABC → AB + C performed in a supersonic molecular beam experiment, we propose an analytical model to describe how the rotational angular momentum of AB varies from the transition state onto the separated products. This model is compared with quasiclassical trajectory calculations on a model potential energy surface and the agreement found is very satisfying. Including this model in a statistical treatment could possibly extend its ability to describe processes involving non-negligible exit-channel rotational-translational energy transfers.