Du discret au continu pour des modèles de réseaux aléatoires d'atomes

We study in this Note the continuum (macroscopic) limit for some atomistic models for crystals. The purpose is to derive densities of mechanical energies from microscopic models. In contrast to the setting of a previous study, where the microscopic structure was assumed to be periodic, it is modelled here by a stochastic lattice, which enjoys some stationarity and ergodicity properties, following notions previously introduced elsewhere. To cite this article: X. Blanc et al., C. R. Acad. Sci. Paris, Ser. I 342 (2006).     

Synthesis of new fluorescent dyes in the benzoxazinone series: Aminobenzoxazinones with a rigidized structure

The structure of 7-aminobenzoxazinones was modified by enclosing their amino nitrogen atom in a julolidyl ring. This rigidization was expected to enhance the fluorescence performances in this series. Several fluorescent dyes and styryl derivatives were prepared and their spectral characteristics were investigated. Comparison with homologous benzoxazinones with a flexible amino group shows that rigidization does not improve the quantum yield and the photochemical stability, in contrast with the results reported for other classes of dyes, like coumarins or rhodamines.     

Wafer and epilayer improvement for integrated optics devices on InP: the ESPRIT project 2518

Ga _x In_1–x As _y P_1–y alloys lattice matched to InP substrates are currently used to fabricate optoelectronic and integrated optics devices. To achieve devices with high performances and high fabrication yield, the uniformity and reproducibility of the Ga _x In_1–x As _y P_1–y epitaxial layers (composition, thickness, doping, etc.) have become key parameters. These problems have been addressed in the frame of ESPRIT project 2518 and are presented in this paper. Several aspects have been considered starting from the optimization of InP substrates, the MOVPE growth of uniform GalnAsP layers, the material characterization to the validation of material uniformity on passive optical waveguides. Both scanning photoluminescence analysis and waveguide losses measurements performed on 2 inch wafers with a high lateral resolution have shown that high quality uniform GalnAsP layers can be obtained reproducibly on 2 InP substrates using a commercially available LP-MOCVD growth process. In particular, more than 60% of 36 mm long, 3m wide and 100m spaced rib waveguides exhibit losses below 0.8dBcm^–1.     

Structure and conformational analysis of CFC-113 by density functional theory calculations and FTIR spectroscopy

Altitude-resolved volume mixing ratio profiles of CFC-113 have recently become available on a global scale with the Atmospheric Chemistry Experiment (ACE) satellite mission. However, the accuracy of the retrieval is currently limited by the uncertainties on the spectroscopic parameters of CFC-113. This paper reports on the geometrical structure, harmonic frequencies and intensities in the mid-infrared region of the two conformers of CFC-113 and the evaluation of whether theoretical calculations reproduce measurements. The calculations are performed using density functional theory at the B3LYP/6-311+G(3df) level. The molecular geometry parameters, the enthalpy difference and the potential barrier between conformers are calculated. The harmonic frequency of the normal modes of vibration are presented and accurately compared to experimental data. Overtones and combination bands are assigned in the 1200-2500 cm⁻¹ region.     

Approximation locale précisée dans des problèmes multi-échelles avec défauts localisés

We proceed here with our systematic study, initiated in [3], of multiscale problems with defects, within the context of homogenization theory. The case under consideration here is that of a diffusion equation with a diffusion coefficient of the form of a periodic function perturbed by an $L^r({\mathbb{R}}^d)$, $1<r<+\infty$, function modelling a localized defect. We outline the proof of the following approximation result: the corrector function, the existence of which has been established in [3], [4], allows us to approximate the solution to the original multiscale equation with essentially the same accuracy as in the purely periodic case. The rates of convergence may however vary, and are made precise, depending upon the $L^r$ integrability of the defect. The generalization to an abstract setting is mentioned. Our proof exactly follows, step by step, the pattern of the original proof of Avellaneda and Lin in [1] in the periodic case, extended in the works of Kenig and collaborators [12], and borrows a lot from it. The details of the results announced in this Note are given in our publications [2], [11].     

Computing a molecule in its environment: A mathematical viewpoint

This article is the sequel of a previous survey where we presented the mathematical results rigorously known on the models used in quantum chemistry to simulate an isolated molecular system. The emphasis here is on the models that take into account the environment of the molecule, namely, the models of the condensed phase and the models of interaction with electromagnetic fields. Some related issues are also dealt with. A bibliography of more than 150 references are provided. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 227–250, 1999     

Can we outperform the DIIS approach for electronic structure calculations?

This article regroups various results on self-consistent field algorithms for computing electronic structures of molecular systems. The first part deals with the convergence properties of the “conventional” Roothaan algorithm and of the level-shifting algorithm. In the second part, a new class of algorithms is introduced, for which convergence is guaranteed by mathematical arguments. Computational performance on various test problems is reported; advantages of this new approach are demonstrated. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 82–90, 2000     

Synthesis and properties of some 7-dimethylamino-1,4-benzoxazin-2-ones

The synthesis of the 7-dimethylamino-1,4-benzoxazin-2-ones ( 5 ), fluorescent dyes, by condensing α-keto-acids with 2-amino-5-dimethylaminophenol is described. When the 3-substituent is a methyl group, these compounds can be further condensed with aromatic aldehydes to provide the styryl dyes ( 6 ). These products are easily opened by hydrochloric acid in ethanolic solution to afford the corresponding benzalketoacid ethyl esters ( 7 ).     

Selective mono-N-alkylation of triethylenetetraamine. A new versatile route to polylinear aza-ligands

A new route to triethylenetetraamine selective mono-N-alkylation on secondary nitrogen atom using simultaneously bisaminal and diamide protections is presented and applied to the synthesis of poly-linear aza-ligands.     

Synthesis of a New Ditopic Ligand Possessing Linear and Cyclic Tetraaza Subunits

An easy‐to‐run route to a new ditopic ligand possessing linear and cyclic tetraaza subunits is described. In the first step, the reaction consists in the preparation of a triprotected cyclam bearing a 3‐bromopropyl pendant side chain. A subsequent reaction with a bisaminal protected linear tetraamine gives, after deprotection, the desired ditopic ligand.