Elaboration et proprietes optiques de nouveaux verres fluores actives au neodyme

A vitreous domain has been investigated in the quaternary system BaF₂CaF₂AlF₃BeF₂. Several optical properties have been reported for a typical composition range Ba₁₅Ca_27?xNd_xAl₃₁Be₂₇F_231+x with 0 ≤ x < 8: refractive index, adsorption and fluorescence spectra, oscillator strengths and fluorescence life time. These properties have been compared with those of other glasses previously proposed as laser host structures. The performances are among the best so far obtained for such applications.     

Free radical polymerization engineering—I: A new method for modeling free radical homogeneous polymerization reactions

This paper deals with a new appraisal of free radical polymerization modeling. Classical properties of the distribution of polymerization degrees and methods for studying them thanks to the z-transform are recalled. When simple mechanisms are involved, the kinetics may be represented by a “detailed analytic” model relying on macromolecule balances. This is no longer possible when complex processes are occurring, e.g. transfer to polymer, β-scission, terminal double bond propagation… In order to deal with these more complex cases, a “tendency model” is proposed, relying on balances of quantities such as free radicals, macromolecules and the moments of the distribution of polymerization degrees. The quality of the polymer is described by chemical characters such as double bonds, long and short branching points, terminal double bonds… for which kinetic equations are established. Equations are given for calculating the moments of free radicals and those of instantaneously produced macromolecules via various processes. The simplicity and the usefulness of the method are illustrated by several examples and a comparison is made, when possible, with the detailed approach. Finally, equations are given, making it possible to calculate the quality of polymer produced in any kind of reactor and for different states of segregation.     

Oxydation électrochimique de l'acétylène en solution aqueuse a des électrodes d'or

The electro-oxidation of aqueous solutions of acetylene at gold electrodes is studied by voltammetry and controlled potential electrolysis. A mechanism involving the oxidation of the gold electrode is presented for the electro-oxidation of acetylene at gold electrodes.     

The preparation of (Al2O3)x(SiO2)y thin films using [al(OSiEt3)3]2 as a single-source precursor

Amorphous (Al₂O₃)_x(SiO₂)_y thin films have been grown by atmospheric pressure metal-organic chemical vapour deposition using the single-source precursor [Al(OSiEt₃)₃]₂. Characterisation by X-ray photoelectron spectroscopy indicated that the films consisted of a mixture of Al₂O₃, SiO₂ and an aluminosilicate. The relative amount of each species was dependent on the deposition temperature and the carrier gas composition. Use of NH₃ as the carrier gas resulted in the increased volatility of the precursor by the in situ formation of the low-melting Lewis acid–base adduct Al(OSiEt₃)₃(NH₃); however, no nitrogen incorporation was observed in these deposited films.     

Mirror-image matching and mental rotation problem solving by baboons (Papio papio): Unilateral input enhances performance.

Three experiments, using a matching-to-sample procedure, were conducted to examine hemispheric specialization in mirror-image discrimination and mental rotation in baboons. In Exp 1, no significant difference was found in discrimination of mirror-image and asymmetric pattern stimuli. In Exp 2, orientation was assessed within the left (LVF) and right (RVF) visual half-fields. An RVF advantage was found in accuracy for asymmetric patterns, whereas an LVF advantage was found for discrimination of mirror-image stimuli. No significant relation was found between angular disparity of the stimuli and response time. Exp 3 examined the effect of bilateral visual input on accuracy and response time. Significantly lower accuracy and longer response times were found for bilateral compared with unilateral visual input. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Solid State Hydrolysis of 2-Methyl-4H-benzoxazin-4-one. Mode of Propagation of the Reaction Process During the Hydrolysis

Kinetic studies of hydrolysis and deuteriolysis of microcrystalline 2-methyl-4H-benzoaxazin-4-one 1 into N-acetylanthranilic acid 2 are presented. Hydrolysis of mixtures of microcyrstalline 1 and 2 are given. The results are interpreted and a mechanism is proposed for the solid gas reaction. A theoretical approach of the crystal packing of 1 permits an evaluation of the mode of diffusion of water molecules in the crystal. Both experimental and theoretical results lead to a proposal of the mechanism of water propagation and the hydrolysis process in the solid phase.     

Simple and precise measurements of fibre volume and void fractions in metal matrix composite materials

A method for determining the fibre volume fraction, V _f and the void fraction, V _g, in a metal matrix composite (MMC) material is described. These quantities are determined from specimen weight measurements in air and in a liquid using a laboratory balance. For a material without voids, V _f can be determined with an uncertainty less than 0.5% with a balance precision of 0.01%. By making the same measurements before and after etching away the matrix, using the same balance precision, V _f and V _g can be determined to an uncertainty of about 3 and 6%, respectively. It is also shown theoretically that by indenting a specimen containing no fibres and only a uniform distribution of small voids, the void fraction can also be determined from weight measurements before and after indentation.     

New developments in polybenzhydrolimide resins: Application in the field of heat resistant coatings,adhesives and laminates

The approach to obtaining fully cyclised polyimides is based on the interactions between a benzhydrol group carried in the polyimide main chain and the solvent. The CH of the benzhydrol function is an efficient ¹H-NMR probe in order to follow the extent of imide cyclisation, as shown using benzhydrol tetracarboxylic dimethylester (5.95 ppm), the corresponding diamide diacid (6.20 ppm) and the final imide (6.35 ppm). Three types of polybenzhydrolimides are described. A linear AABB polymide was prepared from benzhydrol tetracarboxylic dimethylester obtained by hydrogenation of the corresponding industrial ketonic tetraacid diester. The solution properties of the polyimide and the extent of imide cyclisation are discussed. The synthesis of a linear AB polymer from (3-aminophenyl)-4-hydroxymethyl monomethylphthalate is described. This product is used as silver filled adhesive for electronic applications. A cyclised nadimide end-capped benzhydrolimide oligomer (M_w=1940, M_n = 1370) is soluble in diglyme. The crosslinking of this oligomer starts at 275°C and the properties of the network according to the curing cycle are discussed.