Application des relation de Mislow et Raban a la determination de configuration (mesothreo) par resonance magnetique nucleaire

The meso or threo configuration of diastereoisomeric molecules is elucidated on the basis of respective NMR spectra of either isomers. The symmetry relationship (according to Raban and Mislow) between protons or groups are not identical in each isomer, and the consequent differences in chemical shifts and spin-coupling constants permit assignment of configurations.     

Décomposition du fibré des spineurs d''une variété spin Kähler-quanternionenienne sous l''action de la 4-forme fondamentale

On a spin quaternionic-Kähler manifold M^4m, we give the spectral decomposition of the spin bundle the action of the fundamental 4-form Ω. Moreover, we compute the eigenvalues of Ω which, in the compact case, play an essential role in the problem of estimating the eigenvalues of the Dirac operator. The proof is based on the decomposition of the spin representation into irreducible components under the action of the group Sp(1) × Sp(m). We show that this algebraic results induces a Whitney decomposition of the spin bundle which, when restricted to the fibres, is the spectral decomposition under the action of Ω.     

Variétés unirationnelles non rationnelles: au-delà de l'exemple d'Artin et Mumford

Sans résumé     

A Non-Serial Dynamic Programming Model with an Application to the Optimal Design of Distribution Networks

A non-serial dynamic programming (NSDP) formulation, aimed at the decomposition and optimization of interconnected systems, is presented. A new model is proposed for the system decomposition. It is used to optimize an electrical distribution system, and the results on a 25-node network are reported.     

Benefits of chemical beam epitaxy for micro and optoelectronic applications

This paper reviews the benefits that Chemical Beam Epitaxy (CBE) growth technique can bring to micro and optoelectronic devices. The characteristics of the technique are first underlined for a better understanding of the specific advantages it offers compared to other growth techniques. The first one is the low growth temperature, which pushed the thickness limit in strained InGaAsP multi-quantum well structures. Carbon doping of GaAs and In_0.53Ga_0.47As, and its application to GaAs and InP based npn heterojunction bipolar transistors is another important contribution of CBE which has resulted in successful device development. The last developments in surface cleaning and in situ etching with new amine and chloride sources are presented. The capabilities of CBE for selective and uniform growth on partially masked substrates are illustrated through examples of device planarization and integration. Finally, the most recent improvements in the technology of CBE equipment and their impact on CBE production capabilities are presented.     

Stereochimie en Serie Aziridine—III Etude de l'Isomérie de Rotation d'un Aldéhyde Aziridinique

From the ASIS effect on chemical shifts and from solvent and temperature dependence of the vicinal spin-spin coupling constant of 1-tertiobutyl 2-formyl aziridine, the following conclusion is reached: the less polar rotamer is the s-trans rotamer, which is of lower energy than the s-cis rotamer.     

The CP1 model on the torus: Contribution of instantons

The contribution of instantons to the partition function is calculated for the two-dimensional CP₁ model defined on the torus.     

Electronic and ionic conductivities and point defects in ytterbium sesquioxide at high temperature

From the study of complex impedance diagrams applied to a symmetric cell Pt-Yb₂O₃-Pt, the authors have shown the mixed character of electrical conduction within the ytterbium sesquioxide. The measurements were performed at thermodynamic equilibrium in the temperature range from 1423 to 1623 K and the partial pressure of oxygen range from 10^?12 to 1 atm. The variations of ionic and electronic conductivity as a function of P_O2, were interpreted in terms of point defects e′, ?, V?_Yb and Yb_{$\text{I}\text{?}$}, in the general case of a Frenkel disorder. The relative contributions and the activation energies of conduction of these different defects were determined.