Nanocomposite Si/C/N Powder Production by Laser–Aerosol Interaction

Ultrafine preceramic Si/C/N powders were obtained via ultrasonic injection of aerosol particles into a highpower CO₂ laser beam, using hexamethyldisilazane, which strongly absorbs the CO₂ laser radiation at 10.6 μm, as the precursor. Introduction of aerosol droplets via a flowing argon or argon–NH₃ mixture into the laser beam yielded nanosized (30 to 60 nm), amorphous powders. Yield and particle composition were controlled by varying the synthesis conditions. Powder changes, such as crystallization during heat treatment under nitrogen or argon, were studied.     

On the plastic and viscoelastic behavior of methylmethacrylate-based random copolymers

Both plastic and Viscoelastic properties were investigated on neat polymethyl-methacrylate (PMMA) and methylmethacrylatc-based random copolymers including N-substituted maleimide units. A strong coupling was evidenced between the glass transition motions and the secondary transition motions for PMMA samples rapidly quenched from the molten state. This coupling was shown to diminish markedly in the case of aged PMMA and to disappear almost completely in the case of MMA-maleimide copolymers having a maleimide content as small as 5 mol%. Thus, it strongly suggests tnat a greater compacity of the glassy PMMA matrix and (or) the presence of stiff maleimide units in the copolymers are sufficient to hinder the early occurrence of large scale conformational motions in the secondary transition region. In addition, it was shown that the strain softening that follows the yield point is also important for aged PMMA and maleimide-rich copolymers, but tends to vanish in the other samples. Therefore, the probable origin, at least in this series of materials, of the strain softening would be the different nature of the molecular motions that occur in the secondary relaxation region and in the glass transition region.     

Hydrogen bonding in PMMA-fluorinated polymer blends: FTi.r. investigations using ester model molecules

The sensitivity of the carbonyl stretching vibration of methyl acetate to interactions with the surroundings is re-examined through FTi.r. analyses and Fourier self deconvolution. The relevant conclusions permit a study of the mixtures of methyl acetate and methyl pivalate with various fluorinated polymers. Evidence is given for the existence of hydrogen bonding between poly(vinylidene fluoride) and these model compounds of poly(methylmethacrylate). Arguments are put forward in favour of a similar behaviour in poly(vinylidene fluoride)/poly(methylmethacrylate) blends.     

Panorama des outils d’analyse et d’optimisation de la consommation dans les systèmes sur puce (SoC)

Power and energy consumption is currently a critical problem in digital signal and image processing applications; the emergence of Systems-on-Chip (SoCs) makes the power analysis difficult by increasing the system heterogeneity, density and performances. To take into account this problem and efficiently focus the actions, we will first examine the main sources of the power consumption and its distribution in circuits and systems; then we will propose a non exhaustive overview of estimation and optimization methods and available tools together with the needs and perspectives in low power SoC design.     

Catalytic wet-air oxidation of carboxylic acids on carbon-supported platinum catalysts

Catalytic wet-air oxidation (CWAO) of aqueous solutions (5 g · l⁻¹) of car☐ylic acids (formic, oxalic, and maleic) was carried out with air at 293–463 K on carbon-supported platinum catalysts. Platinum was loaded on active charcoal by cationic exchange, then reduced under H₂. Homogeneous dispersions of 1–2 nm metal particles were obtained. CWAO reactions were performed at 1 or 15 bar air pressure in stirred, batch reactors. Total conversion of formic and oxalic acids into carbon dioxide was obtained under very mild conditions (air at atmospheric pressure, 326 K). The Pt/C catalyst was almost inactive for the oxidation of acetic acid but maleic acid was oxidized under moderate conditions (15 bar of air pressure, 405 K) which indicates that the degradation of this acid does not occur via acetic acid.     

Local composition heterogeneities occurring during crystallization in PVF2/PMMA blends as studied by high-resolution solid-state 13C n.m.r.

High-resolution solid-state ¹³C n.m.r. has been used to study the amorphous phase of PVF₂/PMMA blends. The decrease of the carbon magnetization as a function of the contact duration in a cross-polarization sequence was analysed in terms of the local composition heterogeneities occurring during PVF₂ crystallization. The influence of the composition and thermal history of the samples is discussed.     

Santémental et relations conjugales ches les travilleurs exposés à des substances neurotoxiques.

55 workers and their spouses took part in assessment of the effect of exposure to nerve agents in the workplace on mental health and marriage. Standardized measurements were used to assess exposure level, mental health problems and marital discord. Significant levels of exposure were related to a high incidence of psychological symptoms. Workers' psychological symptoms mediated the impact of exposure on spouses' perceptions of marital discord. Exposure regulated the related the relationship between mental health and marital discord. Exposure therefore posed a risk to marital stability. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intermolecular interaction in polymer alloys as studied by crack healing

The “method of crack healing” permits measuring the mechanical effects resulting from an interdiffusion of chain molecules across an interface. Having shown that in highly cross-linked ruptured styrene-acrylonitrile (SAN) a two-stage healing mechanism is active, a similar phenomenon was expected in blends of polystyrene (PS) with a more flexible component such as poly(vinyl methyl ether) (PVME), or with a more rigid component such as poly(?2,6 dimethyl 1,4 phenylene oxide) (PPO). However, in both cases crack healing at a temperature 10 K above the respective glass transition temperature (T_g) was linear with the healing time to the power of 1/4 and slower than with pure PS. This unexpected observation is explained by analysis of the thermal and viscoelastic behavior of these blends and by the different contribution to the stress intensity factor resulting from the entanglements formed by the interdiffusing molecules.