Sélections approchées dans les espaces métriques de dimension finie

We prove an existence result of approximate selections for multi-valued maps defined on finite dimensional metric spaces. We impose to our applications to be upper semi continuous and to have a values having contractible small neighborhoods. To cite this article: Y. Askoura, C. R. Acad. Sci. Paris, Ser. I 339 (2004).     

Further results of existence of positive solutions of elliptic Kirchhoff equation with general nonlinearity of source terms

The paper deals with some existence results for elliptic Kirchhoff equations with respect to general nonlinear source terms and changing sign data, where we have used three different methods: direct variational method, Galerkin approach, and subsolution–supersolution method.     

Development of an electron paramagnetic resonance methodology for studying the photo-generation of reactive species in semiconductor nano-particle assembled films

An experimental approach involving electron paramagnetic resonance is proposed for studying photo-generated reactive species in semiconductor nano-particle-based films deposited on the internal wall of glass capillaries. This methodology is applied here to nano-TiO₂ and allows a semi-quantitative analysis of the kinetic evolutions of radical production using a spin scavenger probe.     

Fixed point theorem in subsets of topological vector spaces

We prove new existence results of fixed points for upper semicontinuous multi-valued maps with not necessarily convex values. The definition domains are assumed to have the simplicial approximation property. To cite this article: Y. Askoura, C. Godet-Thobie, C. R. Acad. Sci. Paris, Ser. I 340 (2005).     

Ab initio calculations study of the electronic, optical and thermodynamic properties of NaMgH3, for hydrogen storage

The structural stability, electronic structure, optical and thermodynamic properties of NaMgH₃ have been investigated using the density functional theory. Good agreement is obtained for the bulk crystal structure using both the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation energy. It is found from the electronic density of states (DOS) that the valence band is dominated by the hydrogen atoms while the conduction band is dominated by Na and Mg empty states. Also, the DOS reveals that NaMgH₃ is a large gap insulator with direct band gap 3.4 eV. We have investigated the optical response of NaMgH₃ in partial band to band contributions and the theoretical optical spectrum is presented and discussed in this study. Optical response calculation suggests that the imaginary part of dielectric function spectra is assigned to be the interband transition. The formation energy for NaMgH₃ is investigated along different reaction pathways. We compare and discuss our result with the measured and calculated enthalpies of formation found in the literature.     

Optical channel drop filters based on photonic crystal ring resonators

A new optical channel drop filters (CDFs) configuration based on photonic crystals ring resonators (PCRRs) is provided. The transmission characteristics for single-ring and multiple-ring configurations have been investigated by using the two-dimensional (2D) finite-difference time-domain (FDTD) technique in triangular lattice photonic crystal (PC) silicon rods. Both forward and backward dropping were achieved in dual-ring PCRR structures. In this filter, 100% drop efficiency and acceptable quality factor can be obtained at 1550 nm. The present device can be used in the future photonic integrated circuits.     

Ab initio study of the structural,electronic, elastic and magnetic properties of Cu2GdIn,Ag2GdIn and Au2GdIn

We preformed first-principle calculations for the structural, electronic, elastic and magnetic properties of Cu₂GdIn, Ag₂GdIn and Au₂GdIn using the full-potential linearized augmented plane wave (FP-LAPW) scheme within the generalized gradient approximation by Wu and Cohen (GGA-WC), GGA+U, the local spin density approximation (LSDA) and LSDA+U. The lattice parameters, the bulk modulus and its pressure derivative and the elastic constants were determined. Also, we present the band structures and the densities of states. The electronic structures of the ferromagnetic configuration for Heusler compounds (X₂GdIn) have a metallic character. The magnetic moments were mostly contributed by the rare-earth Gd 4f ion.     

Organocatalytic asymmetric syntheses of functionalized tetrahydropyridazines

Four tetrahydropyridazines, respectively, substituted at the C-3 position with hydroxymethyl, a silyloxymethyl, a carboxylic acid, and a methyl ester have been prepared in good yields and high enantiomeric purities using organocatalytic α-amination of aldehydes as the key step. These compounds have then been tested as organocatalysts for the same reaction.