Trois formulations d'un modèle de plasma quasi-neutre avec courant non nul

In this Note, we propose three formulations of a model describing a quasi-neutral plasma with non-vanishing current. In order to study and compare the numerical efficiency of each formulation, two test-problems are implemented in one dimension. The first is a periodic perturbation of a uniform stationary plasma. The second is a case of plasma expansion in vacuum between two electrodes. To cite this article: P. Crispel et al., C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

Détermination des modèles d'imperfections de différentes variétés allotropiques du sulfure cuivreux (digénite cubique,chalcocite hexagonale “haute et basse température”, chalcocite orthorhombique)

From the study of the CuCuBrCu_2?εSC solid cell in the range of cubic digenite and “high temperature” hexagonal chalcocite we have deduced the laws of variation of the deviation from stoichiometry and the holes concentration with the equilibrium partial pressure of sulfur (δ and p are found to be proportional to ). The electronic model corresponding to the formation of associations (V^×_CuV′_Cu) in the presence of neutral vacancies V^×_Cu allows one to explain these laws. In the low temperature range (range of “low temperature” hexagonal chalcocite and orthorhombic chalcocite) the study of thermal variations of Hall coefficient permits us to propose the following models: (a) the deviation from stoichiometry of the “low temperature” hexagonal chalcocite is due to the simple ionized vacancies V′_Cu; (b) the deviation from stoichiometry of the orthorhombic chalcocite is due to the vacancies V′_Cu and to the associations (V^×_CuV^×_Cu).     

Etude des equilibres solide-liquide des systems MIPO3Sm(PO3)3 (MI = Li,Na, Ag)

The M^IPO₃Sm(PO₃)₃(M^I = Li, Na, Ag) systems were studied. Differential thermal analysis and X-ray diffraction were used to investigate the liquidus and solidus relations. Three compounds LiSm(PO₃)₄, NaSm(PO₃)₄, and AgSm(PO₃)₄ were obtained which melt incongruently at 1248, 1143, and 1078 K, respectively. These compounds are isomorphous with their homologs LiLn(PO₃)₄, NaLn(PO₃)₄, AgLn(PO₃)₄ (Ln = Ce, La, Nd). They belong to the monoclinic system. The LiSm(PO₃)₄ unit cell parameters refined by least squares method are a = 16.43(3) Å, b = 7.16(1) Å, c = 9.65(3) Å, β = 125,9°(1), with the space group $\text{C2}\text{c}$ and Z = 4. NaSm(PO₃)₄ and AgSm(PO₃)₄ are isotypic; they cristallize in the $\text{P2}{}_1\text{c}$ space group, Z = 4; their unit cell parameters are, respectively, a = 12.18(1) Å, b = 13.05(1) Å, c = 7.25(5) Å, β = 126,53°(4), $\text{a = 12.25(1)}\text{A}\text{?}$, b = 13.06(1) Å, c = 7.201(9) Å, β = 126,57°(7). The ir spectra of the last two compounds indicate that these phosphates are chain phosphates.     

Théorèmes d'existence pour des inclusions différentielles du second ordre

We prove several existence theorems for second order differential inclusions of the form $\text{x}\text{?}\text{(t)∈K(x(t))}$, $\text{x}\text{?}\text{(t)∈?N(K(x(t));}\text{x}\text{?}\text{(t))+F(t,}\text{x}\text{?}\text{(t)),}$ when K and F are set-valued mappings taking nonconvex and convex values, respectively, in a Hilbert space H. To cite this article: M. Bounkhel, D. Laouir-Azzam, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

Purete enantiomerique et configuration absolue de l'acide β-hydroxy β-trifluoromethyl β-phenyl propionique obtenu par synthese asymetrique

The enantiomeric purity of β-hydroxy β-trifluoromethyl β-phenyl propionic acid, prepared by asymmetric synthesis, was determined by NMR with a chiral europium complex. Its absolute configuration was established by correlation with α-hydroxy α-trifluoromethyl α-phenyl acetic acid. At the same time, the absolute configurations of 2-hydroxy 2-trifluoromethyl 2-phenyl ethylamine, 3-hydroxy 3-trifluoromethyl 3-phenyl 1-amino propane, and 2-trifluoromethyl 2-phenyl 1,2 ethanediol were determined.     

Determinations cinetiques par analyse microcalorimetrique differentielle. XVI. Decomposition du percarbonate de O,O-t-butyle et O-isopropenyle en solution

Kinetic studies by differential scanning microcalorimetry have shown that the free radical decomposition of O,O-t-butyl and O-isopropenylperoxycarbonate is induced, to a great extent, by the addition of free radicals to the vinylic double bond. If the solvent can give stabilized free radicals, then acetonyl radicals add themselves to the double bond leading to acetonylacetone; in this case, the kinetic study allows the characteristic parameters of the thermal stability of the peroxycarbonate to be determined. When the radicals issued from the solvent can add themselves to the double bond, the induced decomposition finds expression in the acetonylation of the solvent; as for kinetics, such an enhancement of the reaction rate takes place that the “spontaneous” homolytic decomposition takes only a minor part even for very low concentrations of the peroxycarbonate solutions.     

Elucidation de structure et comportement de produits naturels sous ionisation chimique—I: Mise en evidence de la cinerubine a par etude des decompositions unimoleculaires des ions produits en phase gazeuse par iBu+

Positive ion chemical ionization mass spectrometry by ⁱBu⁺ is used to determine the structure of anthracycline 4915 A. The metastable decompositions of protonated molecular ion (m/z 828) and fragment ions (aglycone and sugar moieties) show that the antibiotic in cinerubine A. Unimolecular decompositions occuring in the first field-free region are detected by “Linked Scan méthods” B/E and B²/E.