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.     

Étude de l’activité prébiotique potentielle de l’acide borique

Boric acid has always been neglected in prebiotic chemistry, because it is not a major component of biological macromolecules. We argue here for a potential catalytic role of boric acid in peptides and nucleic acid synthesis. Today boron is an important component of seawater (0.4 mM). Its concentration at prebiotic times was probably higher. In water, boron mainly appears in the form of boric acid or its derivatives (esters and anhydrides).     

Élaboration de ciments apatitiques composites pour la rétention du césium et de l’iode

A composite apatitic cement made of hydroxyapatite loaded with β-tricalcic phosphate, zirconium phosphate and activated carbon has been elaborated and its ability to block cesium and iodine tested. It could be used as a buffer material in order to prevent the rapid release of soluble fission products (cesium and iodine) in aqueous solutions leaching the spent fuel, in the case of direct disposal of spent fuel.     

Analyses de matériaux provenant de la décomposition du benzène liquide au cours de l’interaction avec un faisceau laser pulsé

Materials have been obtained by decomposition of liquid benzene, owing to the acoustic shock wave induced by the stimulated Brillouin and Raman scatterings excited by a pulsed laser beam 〚1〛. First, amorphous carbon containing particles of graphite and chaoite have been characterized by X-ray diffraction; second, after distillation of the treated benzene and heating under vacuum, a solid residue with a yellowish colour is obtained and characterized by means of X-ray diffraction, mass spectrometry, and infrared, visible and ultraviolet spectroscopies. In this last material, there are several constituents: in a main part, monohydrogenated benzene cycles, along with compounds of naphtalene type, and, in a small part, polycyclic aromatic hydrocarbons.     

Étude expérimentale et théorique de la cinétique de l’alcoolyse de la liaison P–N extracyclique du 2-diméthylamino-4,4,5,5-tétraméthyl-1,3-dioxaphospholane monocyclique

This work relates to complementarily experimental and theoretical kinetic aspects of the alcoholysis reaction of an extracyclic P–N bond in monocyclic phospholane. A new mechanism was proposed denying the status of the dimethoxyphosphorane awarded to date as reaction intermediate and replaces it with the status of product despite the fact that it disappears when the reaction is studied in the following stoechiometric conditions 1/1. Transition states were optimized at the B3LYP/6-311G (d, p) level and corresponding reaction pathways were determined by plotting energy profiles as a function of the intrinsic reaction coordinate (IRC). A return to the experience has validated the theoretical results and showed that the disappearance of the formed dimethoxyphosphorane is a consequence to a continuous modification of the equilibrium state with methoxyphospholane highlighting the intervention of chemical relaxation during the reaction by 1/1 and its absence in the case of reaction with a large excess of alcohol.     

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.     

Méthodes de concentration préalable dans la détermination spectrochimique d'éléments à l'état de trace

Résumé La concentration préalable est très intéressante en vue des déterminations analytiques des traces d'éléments qui, en très petite concentration, se trouvent dans les sols de culture, les engrais chimiques, et commes des impuretés, ou des petites quantités des éléments, dans des alliages ou d'autres divers matériaux. Pour cette sorte de microdosage, nous avons spécialement choisi les méthodes spectrochimiques, comme celles les plus convenables pour la détermination simultanée de plusieurs éléments dans les échantillons étudiés. Avec cette concentration préalable des traces d'éléments on obtient dans des méthodes spectrochimiques, l'élimination la plus grande possible des éléments principales qui peuvent troubler ou bien déguiser les lignes appropriées pour le dosage des traces d'éléments. Des divers techniques utilisées pour la concentration préalable nous avons poursuivi spécialement celles qui basent sur l'emploi des réactifs chimiques appropriés, aussi bien qu'à cause de leur spécificité de la précipitation, aussi bien qu'à cause des procès de coprécipitation ou trainage qu'elles provoquent. Parmi les méthodes qui employent des réactifs organiques on a étudié, entre autres, la détermination spectrographique quantitative de petites quantités de bismuth comprises dans des alliages ternaires en base de plomb. On a employé le cupferron comme un réactif sélectif qui précipite le bismuth en présence de plomb et de cadmium, après avoir étudié la zone optime deph (0,5–1,5) dans laquelle ceci est possible. On a aussi étudié la détermination spectrochimique des traces de baryum à l'égard des diverses problèmes, en concentrant préalablement le baryum moyennant un procès de trainage ou coprécipitation provoqué par le ion sulfate en présence de plomb, qui s'ajoute excessivement, et que nous employons comme étalon interne spectral. Cette méthode a été employée pour le dosage de baryum dans certains procès d'adsorption, étudiés dans nos laboratoires.

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Summary The preliminary concentration is of great interest with regard to analytical determinations of traces of elements which occur at very low concentrations in agricultural soils, chemical fertilizers, and as impurities, or of minute quantities of elements in alloys or other divers materials. For this kind of microdetermination, we have especially chosen spectrochemical methods as being the most convenient for the simultaneous determination of several elements in the samples studied. With this preliminary concentration of traces of elements, there is obtained in the spectrochemical methods, the greatest possible elimination of the principal elements which may interfere with or entirely disguise the appropriate lines to be followed for determining the traces of elements. Among the various techniques employed for the preliminary concentration, we have followed especially those which are based on the use of appropriate chemical reagents, both because of there specific precipitating action, or because of the process of coprecipitation or entrainment which they provoke. Among the methods, which utilize organic reagents, there have been studied, for instance, the spectrographic quantitative determination of small quantities of bismuth contained in ternary alloys containing principally lead. Cupferron has been used as a selective reagent, which precipitates bismuth in the presence of lead and cadmium, after establishing the optimalph zone (0,5–1,5) in which this separation is possible. A study has also been made of the spectrochemical determination of barium by means of an entrainment of coprecipitation process brought about by sulfate ion in the presence of lead, added in excess, and which we have used as an internal spectral standard. This method has been used for the determination of barium in certain adsorption processes studied on our laboratories.

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Zusammenfassung Die vorhergehende Anreicherung hat für die analytische Bestimmung von Spurenelementen in Ackerböden und im Kunstdünger oder von geringsten Beimengungen und Verunreinigungen in Legierungen oder sonstigem Material große Bedeutung. Wir verwenden für solche Mikrobestimmungen vor allem spektralanalytische Methoden, da sie sich für die gleichzeitige Bestimmung mehrerer Elemente in einer Probe am besten eignen. Mit einer solchen der Spektralanalyse vorangehenden Anreicherung erzielt man die größtmögliche Entfernung der Hauptbestandteile, die die zur spektralanalytischen Bestimmung der Spuren geeigneten Linien stören oder sogar überdecken können. Von den verschiedenen zur Anreicherung geeigneten Verfahren verwenden wir vor allem die mit Hilfe von chemischen Reagenzien, sei es daß sich diese zufolge ihrer Spezifität hierzu besonders eignen, sei es weil sie bei der Niederschlagsbildung die gesuchten Elemente mit ausfällen oder mitschleppen. Unter Zuhilfenahme organischer Reagenzien studierten wir unter anderem die spektralanalytische Bestimmung kleiner Mengen Wismuth, wie sie sich in Legierungen auf Bleibasis finden. Wir verwendeten hierfür als selektives Reagens Cupferron, welches Wismuth in Gegenwart von Blei und Cadmium ausfällt. Als geeignetstesph-Bereich hierfür wurde 0,5 bis 1,5 bestimmt. Weiters untersuchten wir die spektralanalytische Bestimmung von Bariumspuren mit Rücksicht auf gewisse Problemstellungen, indem wir das Barium vorher mit Sulfationen gleichzeitig mit Blei ausfällten, welches im Überschuß zugefügt und von uns als Vergleichssubstanz verwendet wurde. Diese Methode wurde zur Bariumbestimmung bei gewissen Adsorptionsversuchen verwendet, die in unserem Laboratorium durchgeführt werden.

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Avec 4 figures.     

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.     

Influence de l’énergie interne sur la réactivité de l’ion Fe(CO)2+ avec le diméthyléther, étudiée dans un spectromètre de masse FT–ICR

The influence of the internal energy on the reactivity of iron carbonyl cations with dimethylether CH₃OCH₃ (DME) has been studied using a triple cell Fourier Transform Ion Cyclotron Resonance mass spectrometer. The experimental set-up as well as the data analysis are briefly presented before being detailed on the example of the reactivity of Fe(CO)₂⁺. The strong energy dependence upon the reactivity of the ion is shown: when working with thermalised ions, the only channels observed are the two successive substitutions of a CO ligand by one DME molecule, whereas other channels are opened up for excited ions (the cleavage of the C–O bond may be homolytic or due to a rearrangement). A reaction mechanism of the C–O bond activation is then proposed.     

Applications de la photométrie de flamme à l'analyse des éléments différents aux alcalins et alcalino-terreux

Résumé On a étudié les possibilités de l'usage du photomètre de flamme pour la détermination quantitative de quelques éléments fréquents dans diverses alliages ferreuses. Parmi ces éléments on a étudié spécialment le cobalt, le nickel, le chrome et le manganèse. La sensibilité de ces éléments dans les méthodes de photométrie de flamme est petite et leur émissions sont affectées par la grande concentration du fer des échantillons, même dans les aciers avec des teneurs élevées de nickel et de chrome. On doit donc faire une séparation préalable du fer, que nous avons effectuée par extraction avec des solvants organiques, ayant étudié de même les récupérations quantitatives des autres métaux dans les solutions privées de fer. D'autre part on a étudié les interférences mutuelles de ces éléments pour arriver à des conclusions sur les erreurs que peuvent apparaître on cours des mesures. On discute aussi la séparation préalable du nickel et les modes opératoires. Quelques résultats sont donnés sur l'analyse de divers échantillons d'acier et de ferromanganèse. Les différences entre les valeurs photométriques et obtenues par voie chimique sont aussi indiquées.

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Summary A study has been made of the use of the flame photometer for determining quantitatively some of the elements found in various ferrous alloys. Among these elements, special studies have been made of cobalt, nickel, chromium, manganese. The sensitivity by the high concentration of iron in the samples, even in steels containing much nickel and chromium. Consequently, the iron should be removed beforehand. The writers accomplished this by extraction with organic liquids, after they studied the quantitative recovery of other metals in solutions freed of iron. A study has also been made of the mutual interferences of these elements to arrive at conclusions regarding the errors which may appear during the course of the measurements. A discussion is given of the preliminary separation of nickel and the procedures. Analyses of different samples of steel and ferromanganese are reported. The differences between the photometric values and those obtained by chemical methods are also pointed out.

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Zusammenfassung Die Möglichkeit der Verwendung der Flammenphotometrie zur quantitativen Bestimmung einiger Elemente, die sich häufig in Eisenlegierungen finden, wurde untersucht. Besonders Kobalt, Nickel, Chrom und Mangan wurden hierbei in Betracht gezogen. Die Empfindlichkeit der Flammenphotometrie für diese Elemente ist gering. Deren Emission wird durch hohe Eisenkonzentrationen beeinträchtigt, auch wenn der Gehalt an Nickel und Chrom im Stahl beträchtlich ist. Daher muß das Eisen vorher abgetrennt werden. Dies wurde durch Extraktion mit organischen Lösungsmitteln durchgeführt, da festgestellt werden konnte, daß sich die übrigen Elemente in den von Eisen befreiten Lösungen quantitativ auffinden lassen. Weiters wurde die gegenseitige Störung dieser Elemente untersucht, um auf allenfalls dadurch bedingte Fehler aufmerksam zu werden. Die vorhergehende Abtrennung des Nickels und die dazu geeigneten Methoden werden erörtert. Einige Analysenergebnisse von verschiedenen Stählen und Mangan-Eisen-Legierungen werden angeführt. Die sich zwischen photometrischer und chemischer Analyse ergebenden Differenzen werden angegeben.

     

Étude de l’élimination du Cr(VI) par l’oxyde mixte obtenu par calcination de l’hydroxyde double lamellaire MgAl

A magnesium aluminium hydrotalcite-like compound (HT) containing carbonate anions in the interlayer space and with a final Mg/Al ratio of 2 was synthesized by the co-precipitation method. The obtained material was characterized by powder X-ray diffraction (XRD), Fourier-Transform–Infrared spectroscopy (FT–IR), thermal analysis (ATG/ATD), and surface area measurements (BET). The interaction of the clay with Cr(VI) has been studied by ultraviolet–visible (UV–vis) spectroscopy. The calcined hydrotalcite (HT-C) showed the highest capacity of removal of chromium ions, and their sorption capacities for Cr(VI) are 4.85 mmol/g. The effect of various parameters on the preparation conditions for the removal of chromium, such as the contact time, the amount of sorbent, the initial concentration of Cr(VI), and the pH values of aqueous solution were also investigated to identify their influence on Cr(VI) sorption. The characterization of the calcined hydrotalcite (HT-C) after interaction with Cr(VI) ions by FT–IR spectroscopy showed that Cr(VI) was adsorbed and intercalated by the solid.     

Mesures de la perfusion cérébrale chez le rat à l’aide de la RMN du 129Xe hyperpolarisé : étude de fluides biologiques vecteurs du 129Xe

The high xenon solubility in blood and tissues makes hyperpolarized ¹²⁹Xe a potential MR tracer for tissue perfusion studies. Two biocompatible fluids were studied with a view to be used as delivery media for hyperpolarized xenon injection: the carrier agents were ¹²⁹Xe micro-bubbles in Echovist (2–3 μm in diameter), and Intralipid ¹²⁹Xe suspension. Xenon chemical shifts and longitudinal relaxation time T₁ were measured at 2.35 T in both fluids. Xenon chemical shift of the dissolved phase in Echovist was 204.1 ± 0.5 ppm from the micro-bubbles gas phase resonance data (0 ppm). Xenon T₁ was 20.0 s in micro-bubbles in Echovist and 19.0 s for the dissolved phase. Xenon chemical shift in Intralipid was 194.6 ± 0.5 ppm. T₁ was 15.2 ± 4.9 s (n = 5) in Intralipid 20 % and 20.9 ± 2.9 s (n = 4) in Intralipid 30 %. Using an intra-carotid injection of a small volume (0.15 mL) of hyperpolarized xenon dissolved in Intralipid 30 %, cerebral blood flow was measured in rats (160 ± 30 mL·(100 g)^–1·min^–1, n = 10). Rat brain xenon images were performed with 2-D projection–reconstruction pulse sequence, enabling regional blood flow measurements.     

Dispersion dans l’environnement routier et urbain de Pt,Pd, et Rh émis par les pots d’échappement catalytiques. Étude de la spéciation des éléments

This study highlights the dispersion into the French urban environment of platinum group elements (PGEs) used in catalytic converters. Differences were observed between Pt and Rh on the one hand, and Pd on the other one. One experiment, consisting in passing the corrosive gas emissions from engines over the metals heated to 1000 °C, showed that Pd was severely corroded by nitrogen oxides. It was concluded that Pd is emitted in nitrate form. Hydrolysis of this nitrate form leads to the formation of soluble species. In situ pH and E_h measurements in the soils concerned confirm this theory when the results are compared with the Pd species predominance diagram.     

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.     

Effet de l'accélération d'un écoulement sur le transfert de masse ou de chaleur à la surface d'une bulle sphérique

Numerical results concerning mass or heat transfer on a spherical bubble embedded in axisymmetrical accelerated flows are presented. The Reynolds number is varied between 0.1 and 500. Two different situations are considered, namely an unsteady flow with a constant acceleration, and a pure straining flow where the homogeneous strain induces a spatial acceleration. In the latter case, the acceleration is seen to have little effect on the transfer. In contrast in the unsteady case, computations reveal that dramatic history effects may happen. A comparison of characteristic times allows us to explain the various evolutions shown by the computations. These numerical results are confirmed by analytical solutions obtained in the corresponding situations by assuming a potential flow.     

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.