Sur les représentations linéaires des groupes clos

Sans résumé     

Zum Nachweis des Thoriums mit Alizarin S und seine Bestimmung am Ringofen nach Weisz

Zusammenfassung Zum Nachweis des Thoriums bewährte sich als Reagens eine wäßrige, perhydrol- und ammomumnitrathaltige Alizarin S-Lösung. Da Alizarin kein spezifisches Reagens für Thorium ist, wird ein Analysengang beschrieben, der sich zur Entfernung störender Substanzen aus Mineralen eignet. Das dabei erhaltene Thoriumnitrat kann am Ringofen quantitativ bestimmt werden.

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Summary Aqueous alizarin S solution along with perliydrol and ammonium nitrate was found suitable for the detection of thorium. Since alizarin is not a specific reagent for thorium, an analytical procedure is described, which is suitable for the removal of interfering substances from minerals. The thorium nitrate obtained in this way can be determined quantitatively on the ring oven.

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Résumé On a utilisé pour la recherche du thorium, une solution aqueuse d'alizarine S avec le perhydrol et le nitrate d'ammonium. Comme l'alizarine n'est pas un réactif spécifique du thorium, on a décrit un procédé d'analyse qui permet l'élimination des substances gênantes à partir des minéraux. On peut doser quantitativement le nitrate de thorium alors obtenu, à l'aide du four annulaire.

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Wir danken an dieser Stelle dem Conselho Nacional de Pesquisas von Brasilien, der uns die Durchführung dieser Arbeiten ermöglicht hat.     

Surface morphology of Ge‐modified 3C‐SiC/Si films

The influence of Ge deposition prior to carbon interaction with 3° off‐axis Si(111) substrates on the structural and morphological properties of the formed silicon carbide (SiC) layer is studied. In situ reflection high‐energy electron diffraction (RHEED) and X‐ray diffraction (XRD) revealed the formation of the cubic silicon carbide (3C‐SiC) modification. In situ spectroscopic ellipsometry measurements revealed a decreasing 3C‐SiC thickness with increasing Ge predeposition. Atomic force microscopy (AFM) studies revealed that the surface overlayer morphology is mainly formed by periodic step arrangements whose relevant geometric parameters, i.e. lateral separation, height and terrace width, depend on the Ge content. Besides the changes of the step morphology, the surface roughness and the grain size and the strain of the formed 3C‐SiC decreases with increasing germanium precoverage. Copyright © 2008 John Wiley & Sons, Ltd.     

SiC polytypes process affected by Ge predeposition on Si(111) substrates

Structural and optical measurements were performed on silicon carbide (SiC) samples containing several polytypes. The SiC samples investigated were grown on (111) Si substrates by solid source molecular beam epitaxy (SSMBE). Several quantities of Ge were predeposited before the growth procedure. The influence of Ge on the SiC polytypes formation was studied by X-Ray, FTIR and μ-Raman characterizations methods. The spectra of the samples with less than one Ge monolayer exhibit a mixture of 2H, 15R and 3C–SiC polytypes. This mixture is due to the mismatch between the heterostructure layers. We propose that the Ge predeposition in the heterostructure can be used to stabilize and unify the polytypes formation.     

Study of the electron transfer reaction between [Co(EDTA)]− and [Ru(NH3)5py]2+ in methanol–water mixtures

The title reaction was studied in different water–cosolvent (methanol) mixtures. The results have been rationalized employing the Marcus–Hush treatment. To apply this treatment, the true, unimolecular, electron‐transfer rate constants (k_et) were obtained from the experimentally measured rate constants after calculation of the equilibrium constant for the processes of formation of the encounter complex. This calculation was carried out using Eigen–Fuoss (EF) and exponential mean spherical (EMSA) approaches employing effective values of the solvent dielectric constant. These effective values were obtained from the measured association constants corresponding to other ion pairs. The results reveal that in these media there is an additional component of reorganization energy, absent in neat solvents. An explanation of the origin of this component is given. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 658–666, 2009     

New aryl-containing fluorinated sulfonic acids and their ammonium salts, useful as electrolytes for fuel cells or ionic liquids

Several aryl-containing ammonium sulfonates have been prepared either by cationic metathesis from the corresponding lithium sulfonates or from the corresponding sulfonic acids. The latter have been obtained by elution of an Amberlite resin with alcoholic solutions of the lithium sulfonates. These ammonium sulfonates exhibit interesting conductivities and thermal properties which allow them to be promising candidates as electrolytes for electricity storage.     

Sur des familles remarquables d'hypersurfaces isoparamétriques dans les espaces sphériques

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Relaxations in chitin: Evidence for a glass transition

Relaxations in chitin have been investigated in the temperature range 298–523 K using impedance spectroscopy in the frequency range 10⁻¹–10⁸ Hz. The objective was to detect a glass‐transition temperature for this naturally occurring, semicrystalline polysaccharide. The impedance study was complemented with X‐ray diffraction, thermogravimetric, and differential scanning calorimetry measurements. Preliminary impedance data treatment includes the subtraction of the dc conductivity contribution, the exclusion of contact and interfacial polarization effects, and obtaining a condition of minimum moisture content for further analysis. When all these aspects are taken into account, two relaxations are clearly revealed in the impedance data. For the first time, evidence is presented for a relaxation process, which exhibits a non‐Arrhenius temperature dependence, in dry α‐chitin (∼0.1% moisture content), and likely represents the primary α‐relaxation. This evidence suggests a glass transition temperature for chitin of 335 ± 10 K estimated on the basis of the temperature dependence of the conductivity and of the relaxation time. A second relaxation in dry α‐chitin, not previously reported in the literature, is observed from 353 K to the onset of thermal degradation (∼483 K) and is identified as the σ‐relaxation often associated with proton mobility. It exhibits a normal Arrhenius‐type temperature dependence with activation energy of 113 ± 3 kJ/mol. The latter has not been previously reported in the literature. A high frequency secondary β‐relaxation is also observed with Arrhenius activation energy of 45 ± 1 kJ/mol. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 932–943, 2009