A biaxial apparatus for the study of heterogeneous and intermittent strains in granular materials

We present an experimental apparatus specifically designed to investigate the precursors of failure in granular materials. A sample of granular material is placed between a latex membrane and a glass plate. A confining effective pressure is applied by applying vacuum to the sample. Displacement-controlled compression is applied in the vertical direction, while the specimen deforms in plane strain. A Diffusing Wave Spectroscopy visualization setup gives access to the measurement of deformations near the glass plate. After describing the different parts of this experimental setup, we present a demonstration experiment where extremely small (of order $10^{-5}$) heterogeneous strains are measured during the loading process

Evidence and modeling of mechanoluminescence in a transparent glass particulate composite

International audienceMechanoluminescence (ML) of a transparent alkali-phosphate glass composite with SrAl2O4:Eu, Dy particles is reported. Uniaxial compression experiments show the linear dependence of the mechanoluminescence intensity with the mechanical power. A theoretical model, based on the physics of delayed processes (in analogy of viscoelasticity), is proposed. This model accurately predicts the ML intensity changes induced by a complex mechanical loading and provides a convincing description of the mechanoluminescence response

Electrochemical measurements of the kinetics of inhibition of two FeFe hydrogenases by O2 demonstrate that the reaction is partly reversible

International audienceThe mechanism of reaction of FeFe hydrogenases with oxygen has been debated. It is complex, apparently very dependent on the details of the protein structure, and difficult to study using conventional kinetic techniques. Here we build on our recent work on the anaerobic inactivation of the enzyme [Fourmond et al, Nat. Chem. 4 336 (2014)] to propose and apply a new method for studying this reaction. Using electrochemical measurements of the turnover rate of hydrogenase, we could resolve the first steps of the inhibition reaction and accurately determine their rates. We show that the two most studied FeFe hydrogenases, from Chlamydomonas reinhardtii and Clostridium acetobutylicum, react with O2 according to the same mechanism, despite the fact that the former is much more O2 sensitive than the latter. Unlike often assumed, both enzymes are reversibly inhibited by a short exposure to O2. This will have to be considered to elucidate the mechanism of inhibition, before any prediction can be made regarding which mutations will improve oxygen resistance. We hope that the approach described herein will prove useful in this respect

A relationship between non-exponential stress relaxation and delayed elasticity in the viscoelastic process in amorphous solids: Illustration on a chalcogenide glass

International audienceInorganic glasses are viscoelastic materials since they exhibit, below as well as above their glass transition temperature, a viscoelas-tic deformation under stress, which can be decomposed into a sum of an elastic part, an inelastic (or viscous) part and a delayed elastic part. The delayed elastic part is responsible for the non-linear primary creep stage observed during creep tests. During a stress relaxation test, the strain, imposed, is initially fully elastic, but is transformed, as the stress relaxes, into an inelastic and a delayed elastic strains. For linear viscoelastic materials, if the stress relaxation function can be fitted by a stretched exponential function, the evolution of each part of the strain can be predicted using the Boltzmann superposition principle. We develop here the equations of these evolutions, and we illustrate their accuracy by comparing them with experimental evolutions measured on GeSe 9 glass fibers. We illustrate also, by simple equations, the relationship between any kind of relaxation function based on additive contribution of different relaxation processes and the delayed elastic contribution to stress relaxation: the delayed elasticity is directly correlated to the dispersion of relaxations times of the processes involved during relaxation

Evidence and modeling of mechanoluminescence in a novel transparent glass particulate composite

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Damage in silica glass due to laser shock: Experiments and simulations

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Prosopographie des contributeurs

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Fabrication of low-loss chalcogenide photonic-crystal fi bers by a moulding process

conference 7598 " Optical Components and Materials VII ", Topic " Optoelectronic Materials and Devices ", Session 5 " Optical Fibers and Devices II " [7598-22]International audienceChalcogenide glasses are known for their large transparency in the mid infrared and their high refractive index (>2). They present also a high non linear refractive index (n2), 100 to 1000 times larger than for silica. An original way to obtain single-mode fibers is to design photonic crystal fibers (PCFs). Until now, chalcogenide PCFs are realized using the stack and draw process. However this technique induces defects, like bubbles, at the capillaries interfaces, causing significant scattering losses. Until now, the best transmission obtained was 3dB/m at 1.55µm. The poor PCF transmission reduces significantly their application potential. So, we present a new efficient method to realize low-loss chalcogenide PCFs. This original method by molding permits to reduce the optical losses down to 1dB/m at 1.55µm and less than 0.5dB/m between 3 and 5µm for an As-Se PCF. Furthermore, this molding method can be used for different compositions. Single mode fibers were realized. Moreover, very small core fibers were realized with this method, obtaining a non linear coefficient of 15 000W-1km-1 with an As-Se PCF. We also observed self phase modulation at 1.55µm on a fiber with a 2.3µm2 mode area

Casting method for producing low-loss chalcogenide microstructured optical fibers

Topic: Fiber Optics and Optical CommunicationsInternational audienceWe report significant advances in the fabrication of low loss chalcogenide microstructured optical fiber (MOF). This new method, consisting in molding the glass in a silica cast made of capillaries and capillary guides, allows the development of various designs of fibers, such as suspended core, large core or small core MOFs. After removing the cast in a hydrofluoric acid bath, the preform is drawn and the design is controlled using a system applying differential pressure in the holes. Fiber losses, which are the lowest recorded so far for selenium based MOFs, are equal to the material losses, meaning that the process has no effect on the glass quality

Mai-juin 68, l’Espace géographique et la mémoire d’une communauté. Débat, 16 juin 2008

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