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Single YVO4:Eu nanoparticle emission spectra using direct Eu3+ ion excitation with a sum-frequency 465-nm solid-state laser
No full textInternational audienceWe report emission spectrum measurements on single YxEu1-xVO4 nanoparticles. The inhomogeneous widths of the emission peaks are identical for single nanoparticles and for ensembles of nanoparticles, while being broader than those of the bulk material. This indicates that individual nanoparticles are identical in terms of the distribution of different local Eu3+ sites due to crystalline defects and confirms their usability as identical, single-particle oxidant biosensors. Moreover, we report a 465 nm solid-state laser based on sum-frequency mixing that provides a compact, efficient solution for direct Eu3+ excitation of these nanoparticles. Both these two aspects should broaden the scope of Eu-doped nanoparticle applications
A three-dimensional analysis of fatigue crack paths in thin metallic sheets
No full textInternational audienceFatigue crack growth in thin sheets of 7075 T651 aluminium alloy and S355 steel were characterised in 3D, using crack front markings and topographic reconstructions of fracture surfaces. Tests performed in air or in salt water produced different crack paths for similar mechanical condit ions, shear lips being reduced by corrosive environment, in the aluminium alloy as well as in the steel. Before the onset of shear lips development, tunnelling crack fronts were observed, due to the difference in closure effects at mid-thickness and near free surfaces. Tunnelling was progressively reduced and cancelled as slanted crack growth developed, even though DK I was reduced locally by crack twisting. This indicates a significant contribution of shear modes to the crack driving force, even though mode I striations are present in slanted zones. Elastic three-dimensional X-FEM computations were performed to analyse the observed crack growth kinetics, based on ΔKI , ΔKII and ΔKIII. The crack growth rates correlated much better to ΔKeq = √(ΔKI^2 + ΔKII^2 + (ΔKIII^2/(1-ν))) than to ΔKI. Elastic–plastic finite element simulations and the local application of a fatigue criterion with an amplitude-dependent critical plane were found to capture qualitatively the transition in fracture mode and its inhibition by side grooves
The JET real-time plasma-wall load monitoring system
No full textÉquipe 107 : Physique des plasmas chaudsInternational audienceIn the past. the Joint European Torus (JET) has operated with a first-wall composed of Carbon Fibre Composite (CFC) tiles. The thermal properties of the wall were monitored in real-time during plasma operations by the WALLS system. This software routinely performed model-based thermal calculations of the divertor and Inner Wall Guard Limiter (IWGL) tiles calculating bulk temperatures and strike-point positions as well as raising alarms when these were beyond operational limits. Operation with the new ITER-like wall presents a whole new set of challenges regarding machine protection. One example relates to the new beryllium limiter tiles with a melting point of 1278 degrees C, which can be achieved during a plasma discharge well before the bulk temperature rises to this value. This requires new and accurate power deposition and thermal diffusion models. New systems were deployed for safe operation with the new wall: the Real-time Protection Sequencer (RTPS) and the Vessel Thermal Map (VTM). The former allows for a coordinated stop of the pulse and the latter uses the surface temperature map, measured by infrared (IR) cameras, to raise alarms in case of hot-spots. Integration of WALLS with these systems is required as RTPS responds to raised alarms and VTM, the primary protection system for the ITER-like wall, can use WALLS as a vessel temperature provider. This paper presents the engineering design, implementation and results of WALLS towards D-T operation, where it will act as a primary protection system when the IR cameras are blinded by the fusion reaction neutrons. The first operational results, with emphasis on its performance, are also presented
Imagerie optique non linéaire ou de polarisation de la matrice exrtracellulaire
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Validation d'un système de déport de lumière à fibres optiques hautement birefringentes pour application à la polarimétrie de Mueller endoscopique
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In-situ spectroscopic ellipsometry of microcrystalline silicon deposited by plasma-enhanced chemical vapor deposition on flexible Fe–Ni alloy substrate for photovoltaic applications
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Permeation barrier performance of Hot Wire-CVD grown silicon-nitride films treated by argon plasma
No full textInternational audienceIn this work SiN x thin films have been deposited by Hot-Wire Chemical Vapor Deposition (HW-CVD) technique to be used as encapsulation barriers for flexible organic electronic devices fabricated on polyethylene terephthal-ate (PET) substrates. First results of SiN x multilayers stacked and stacks of SiN x single-layers (50 nm each) separated by an Ar-plasma surface treatment are reported. The encapsulation barrier properties of these different multilayers are assessed using the electrical calcium degradation test by monitoring changes in the electrical conductance of encapsulated Ca sensors with time. The water vapor transmission rate is found to be slightly minimized (7 × 10 −3 g/m 2 day) for stacked SiN x single-layers exposed to argon plasma treatment during a short time (2 min) as compared to that for stacked SiN x single-layers without Ar plasma treatment
Multiscale investigation of ductile fracture mechanisms and strain localization under shear loading in 2024-T351 aluminum alloy and 36NiCrMo16 steel
No full textInternational audienceDuctile fracture mechanisms under shear loading have been investigated in 2024-T351 aluminum alloy and 36NiCrMo16 steel through interrupted torsion tests followed by SEM observations and through direct monitoring of damage during in situ torsion tests in a SEM. Strain localization was observed at meso-scale, but also at micro-and sub-grain scale. A significant axial elongation was measured in both materials during the torsion tests. This " Swift effect " might partly explain why in the aluminum alloy most voids elongate in one direction and shrink in the orthogonal one but do not completely collapse and why some voids even grow. The crystallographic texture and its evolutions – quite significant in the ductile 36NiCrMo16 steel – play a significant role. No void nucleation was observed in steel. Microcracks initiated at an early stage but did not grow up to a large shear strain. Due to some reorientations, clusters of grains sharing the same orientation appeared. This favored shear bands development and microcracks growth.
Searches for electroweak production of charginos, neutralinos, and sleptons decaying to leptons and W, Z, and Higgs bosons in pp collisions at 8 TeV
No full textReplaced with published version. Added journal reference and DOIInternational audienceSearches for the direct electroweak production of supersymmetric charginos, neutralinos, and sleptons in a variety of signatures with leptons and W, Z, and Higgs bosons are presented. Results are based on a sample of proton-proton collision data collected at center-of-mass energy sqrt(s) = 8 TeV with the CMS detector in 2012, corresponding to an integrated luminosity of 19.5 inverse femtobarns. The observed event rates are in agreement with expectations from the standard model. These results probe charginos and neutralinos with masses up to 720 GeV, and sleptons up to 260 GeV, depending on the model details
Unravelling the mechanism of non-ribosomal peptide synthesis by cyclodipeptide synthases.
No full textInternational audienceCyclodipeptide synthases form cyclodipeptides from two aminoacyl transfer RNAs. They use a ping-pong mechanism that begins with transfer of the aminoacyl moiety of the first aminoacyl tRNA onto a conserved serine, yielding an aminoacyl enzyme. Combining X-ray crystallography, site-directed mutagenesis and affinity labelling of the cyclodipeptide synthase AlbC, we demonstrate that the covalent intermediate reacts with the aminoacyl moiety of the second aminoacyl tRNA, forming a dipeptidyl enzyme, and identify the aminoacyl-binding sites of the aminoacyl tRNAs