Retrosynthetic analysis of fullerene C(60): structure, stereochemistry, and calculated stability of C(30) fragments.

The total number of possible retrosynthetic bisections of C(60) leads to nine different isometric C(30) fragments. These molecules include five chiral units, four of which derive from partitions corresponding to four distinct "Coupes du Roi". The energies, curvatures, and homodesmotic stabilization energies of the C(30) fragments are evaluated at the ab initio 6-31G level.     

Chromium (II) chloride : a new reagent for cross-aldol reactions

The proposed cross aldolization of α-bromoketones with aldehydes in presence of Chromium (II) chloride is an excellent stereospecific reaction. One exception to the stereospecific orientation is reported.     

Stabilité élastique des structures unidimensionnelles

In this paper, we consider the problem of stability of one-dimensional structures and give a general formulation by means of the energy method. We propose then a numerical method of deriving the critical rate requiring eigenvalues of a sequence of small matrices rather than of a big one.

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Cet article est le résumé d'une thèse présentée à l'Ecole Polytechnique de l'Université de Lausanne [17]. Je tiens à exprimer ma vive gratitude au ProfesseurCh. Blanc, directeur de l'Institut de Mathématiques Appliquées, dont les conseils et encouragements m'ont été très précieux.     

Perhydro dioxazepines-1,5,3 : Methode generale de synthese

Perhydrodioxazepines-1,5,3 are obtained by reacting a primary amine with a 1,2-diol and paraformaldehyde.     

Proprietes magnetiques et electriques de la phase Ca2MnO4−xFx

The magnetic properties of the antiferromagnetic Ca₂MnO_4?x solid solution (0?x?0,30) are essentially characterized by a weak ferromagnetism with a maximum value for x = 0,20. Spin canting results from the competition between the antiferromagnetic super-exchange couplings and the double exchange ferromagnetic interactions due to the presence of manganese in oxidation states + III and + IV. It seems independent of the site of fluorine in the framework. The variation of Weiss constant and ordering temperature withx is also discussed. Electrical conductivity results from a hopping mechanism between Mn³⁺ and Mn⁴⁺ ions. The electrical conductivity presents a maximum when x = 0.10, corresponding to an activation energy minimum.     

Efficient laser action of Yb:LSO and Yb:YSO oxyorthosilicates crystals under high-power diode-pumping

We report here on the efficient laser action of a new Yb-doped crystal Yb³⁺:Lu₂SiO₅ (Yb:LSO) under high power diode-pumping (15 W). Its performances were compared to another Yb-doped crystal belonging to the oxyorthosilicate family: the Yb:YSO. For both crystals, more than 7 W of laser radiation around 1 m was obtained under 14.4 W of incident pump power at 978 nm, leading to high optical conversions of more than 50%. Finally, both crystals demonstrate little sensitivity to pump wavelength drift and exhibit broad tunability at a multiwatt level (more than 4 W over 50 nm and 60 nm, respectively for Yb:LSO and Yb:YSO). PACS 42.55.Xi; 42.60.Pk; 42.70.Hj     

Z-scan measurements of the nonlinear refractive indices of novel Yb-doped laser crystal hosts

We report on the z-scan characterization of the nonlinear refractive indices of three borate crystals (GdCOB, YCOB, and BOYS), which are new promising Yb-doped laser hosts. The results indicate the possibility of substantial Kerr-lensing and self-phase modulation effects in femtosecond oscillators and amplifiers. High values of the nonlinear refractive indices suggest possible KLM operation of such lasers. PACS 42.65.An; 42.65.Hw; 42.55.Rz; 42.65.Re