Existence of radial stationary solutions for a system in combustion theory

In this paper, we construct radially symmetric solutions of a nonlinear noncooperative elliptic system derived from a model for flame balls with radiation losses. This model is based on a one step kinetic reaction and our system is obtained by approximating the standard Arrehnius law by an ignition nonlinearity, and by simplifying the term that models radiation. We prove the existence of 2 solutions using degree theory

Micro-raman study of the compressive behaviour of advanced PA66 polyamide fibres in a diamond-anvil cell

International audienceThe micro/nanostructural evolution of ultra-high performance PA66 polyamide fibres has been studied by Raman spectroscopy in a diamond-anvil cell, up to 10 GPa. The nanostructures of these PA fibres consists of amorphous and crystalline (αI-type) regions (oriented + crystalline index not, vert, similar 60%). Information on the “crystalline” part of the fibre is obtained from three probes: (i) a low wave number collective mode at not, vert, similar100 cm−1 representative of the “friction/shear” of crystalline chains; (ii) Nsingle bondH stretching mode at not, vert, similar3300 cm−1, and (iii) Amide I (Cdouble bond; length as m-dashO) stretching mode at not, vert, similar1650 cm−1; the last two modes are representative of the inter-chain and intra-chain behaviour, respectively. A reversible transition between two regimes was evidenced at not, vert, similar3.7 GPa and assigned to the onset of the “contact” between neighbouring polyamide chains, i.e. the onset of possible fatigue. In the first regime (I), the “friction” wave number increased linearly (7.5 cm−1 GPa−1) whilst the distance between neighbouring (crystalline) chains decreased from not, vert, similar0.293 to not, vert, similar0.285 nm; in the second regime (II), the “friction” wave number still increased but at a much slower rate (<4.5 cm−1 GPa−1) and the Cdouble bond; length as m-dashO stretching mode of the amide group started to increase (not, vert, similar1.6 cm−1 GPa−1), indicating that the chains were squeezed together in all directions. The Nsingle bondH stretching mode continued to decrease, slowly (dNcdots, three dots, centeredO down to 0.289 or 0.2865 nm according to the data fitting procedure). Different behaviours are expected for amorphous and crystalline “regions”

Precipitation of C, Si and metals nanoparticles in silicon-based gels induced by swift heavy ion irradiation

Studies of irradiation effects in inorganic polymers and gels performed at CSNSM during the last ten years are summarized, and new results concerning the effect of the density of transferred energy on the precipitation kinetics of C, Si and metal clusters are presented. The precipitation yield as a function of the fluence of ions with different masses and energies was investigated by means of various spectroscopies, depending on the particles nature. The rates of gel to ceramics conversion and of C, Si and metal precipitation are determined by the density of electronic excitations and nuclear collisions have little effect. Particles formed by ion irradiation show a narrower size distribution and, consequently, more interesting characteristics for magnetic or optical applications than those formed in heat treated gels

In situ Raman microscopy study of ceramic fibres in ceramic matrix composites

Communication to : 4th international conference on composites engineering - ICCE/4, Big Island, Hawaii (USA), July 6-11, 1997SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : 22419, issue : a.1997 n.217 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc