Oxymercuration of homoallylic alcohol derived hemiacetals: diastereoselective synthesis of protected 1,3-diols

[reaction: see text] Protected 1,3-diol synthons may be synthesized efficiently from homoallyic alcohols and simple aldehydes by oxymercuration of the derived hemiacetals. The reactions are diastereoselective and proceed without the use of solvent. Both Hg(OAc)2 and HgClOAc are effective in the reaction, and the latter produces isolable organomercurial chlorides directly.     

Probabilistic representation and approximation for coupled systems of variational inequalities

Our study is dedicated to the probabilistic representation and numerical approximation of solutions of coupled systems of variational inequalities. We interpret the unique viscosity solution of a coupled system of variational inequalities as the solution of a one-dimensional constrained BSDE with jumps. This new representation allows for the introduction of a natural probabilistic numerical scheme for the resolution of these systems.     

Sur les représentations linéaires des groupes clos

Sans résumé     

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.     

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

Sans résumé     

Synthesis,Crystal Structure and IR Spectra of Complexes of Mn(II) by Indole-2-Carboxylic or Isoquinoline-1-Carboxylic Acids and 1,10-Phenanthroline

Abstract  

Two ternary complexes of manganese(II) indole-2-carboxylate (2-IC⁻) or isoquinolinecarboxylate (IQC⁻) with 1,10-phenanthroline (phen) in methanol or in dimethylacetamide (DMA) were synthesized and studied by X-ray diffraction and IR spectra. [Mn(C₉H₆NO₂)₂(C₁₂H₈N₂)₂]·CH₄O (1) crystallizes in the triclinic space group P-1 with cell parameters of a = 10.548(2) ?, b = 14.168(3) ?, c = 14.580(3) ?, α = 62.35(2)°, β = 69.16(2)°, γ = 78.61(2)°, V = 1802.4(6) ?³ and Z = 2; [Mn(C₁₀H₆NO₂)₂(C₁₂H₈N₂)].C₄H₉NO (2) crystallizes in the monoclinic space group P2₁/a with cell parameters of a = 15.304(5) ?, b = 12.871(5) ?, c = 17.421(5) ?, β = 114.39(1), V = 3125(2) ?³ and Z = 4. In 1, Mn is six-coordinate by two bidentate phen ligands and two 2-IC⁻ ligands and exhibits a very distorted octahedral geometry. This complex is solvated by methanol involved in hydrogen bonding. In 2, Mn atom is surrounded by one bidentate phen ligand and two bidentate IQC⁻ ligands. The complex exhibits a distorted octahedral geometry around the Mn^II atom. The crystal structure is completed by a disordered DMA solvate molecule. The IR spectra of both compounds are slightly different in the range 4000–2400 cm⁻¹ which may be attributed to hydrogen bond lack in 2.     

Polarization control in spun and telecommunication optical fibers

We consider the counterpropagating interaction of a signal and a pump beam in a spun fiber and in a randomly birefringent fiber, the latter being relevant to optical telecommunication systems. On the basis of a geometrical analysis of the Hamiltonian singularities of the system, we provide a complete understanding of the phenomenon of polarization attraction in these two systems, which allows to achieve a control of the polarization state of the signal beam by adjusting the polarization of the pump. In spun fibers, all polarization states of the signal beam are attracted toward a specific line of polarization states on the Poincaré sphere, whose characteristics are determined by the polarization state of the injected backward pump. In randomly birefringent telecommunication fibers, we show that an unpolarized signal beam can be repolarized into any particular polarization state, without loss of energy.     

Méthode particulaire anisotropeAnisotropic particle method

A particle method has been used to simulate the vorticity transport in a two-dimensional flow of an incompressible inviscid fluid. In this method, not only the location and the circulation of the particle are used but also the moments of the internal vorticity. The transport equation for these moments has been derived from the vorticity transport equation. The method has been compared to the usual particle method as well as to Teng's elliptic vortex model. The test case is that of the evolution of two circular patches of vorticity already used by Teng. To cite this article: A. Beaudoin et al., C. R. Mecanique 330 (2002) 51–56