L'utilisation de l'émission acoustique pour le suivi d'essais dynamiques

International audienceThe use of composite material in industry is more and more important especially in the aeronautical field. The use of these materials needs an understanding of their mechanical behavior and in particular the damage mechanisms. Usually the mechanical testing performed on this material is instrumented with different techniques like acoustic emission in order to get the maximum information. Acoustic Emission is very efficient for quasi-static and low frequency fatigue mechanical testing to determine the appearance of the first damage. Nevertheless, when the strain rate is increasing, acquisition of transient signal becomes difficult. In this paper we propose a method based on AE streaming acquisition. This acquisition mode allows us to obtain only one great time sampling without threshold effect. This signal is then “cut” and new genuine features are processed. The use of this method allowed us to study the behavior of epoxy carbon composite specimen during dynamic testing (5 mm/min to 500 mm/min). Two criteria based on the energy have been identified and studied in function the loading rate.L’utilisation de matériau composite dans l’industrie est de plus en plus importante notamment dans le domaine aéronautique. L’utilisation de ces matériaux nécessite une compréhension de leur comportement mécanique et de leur mode d’endommagement. Habituellement les tests mécaniques réalisés sont instrumentés par différentes techniques afin d’en tirer le maximum d’information et notamment l’émission acoustique (EA). Cette technique est très adaptée aux essais mécaniques quasi-statique et de fatigue à faible fréquence pour déterminer l’apparition des premiers endommagements. Cependant lorsque les vitesses de sollicitation augmentent, l’acquisition sous forme de signaux transitoires devient compliquée. La technique proposée dans l’article repose sur la fonction streaming. Cette fonction enregistre un seul intervalle de temps sans tenir compte d’un seuil d’acquisition. Celui-ci est ensuite « redécoupé » et de nouveaux paramètres sont alors calculés. L’utilisation de ce traitement nous a permis d’étudier le comportement d’éprouvette en carbone époxy pour des vitesses de sollicitation allant de 5 mm/min à 500 mm/min. Deux seuils d’endommagement ont été définis et leurs évolutions en fonction des vitesses de sollicitation ont été caractérisés

de Haas-van Alphen oscillations in the underdoped cuprate YBa2_2Cu3_3O6.5_{6.5}

The de Haas-van Alphen effect was observed in the underdoped cuprate YBa$_2$Cu$_3$O$_{6.5}$ via a torque technique in pulsed magnetic fields up to 59 T. Above an irreversibility field of $\sim$30 T, the magnetization exhibits clear quantum oscillations with a single frequency of 540 T and a cyclotron mass of 1.76 times the free electron mass, in excellent agreement with previously observed Shubnikov-de Haas oscillations. The oscillations obey the standard Lifshitz-Kosevich formula of Fermi-liquid theory. This thermodynamic observation of quantum oscillations confirms the existence of a well-defined, close and coherent, Fermi surface in the pseudogap phase of cuprates.Comment: published versio

Far-field mapping and efficient beaming of second harmonic by a plasmonic metagrating

We study numerically and experimentally the second-harmonic generation (SHG) from rectangular meta- gratings of V-shaped gold nanoantennas. We show that by carefully engineering the array pitch to steer the diffraction orders toward the single antenna emission, the extracted signal is maximized. This enhancement is attributed to the angular overlap between the radiation pattern and array factor and is comparable to the improvement yielded by the coupling of surface lattice resonances (SLRs) with local modes. Moreover, we demonstrate a simple technique to experimentally reconstruct the emission diagram of an antenna from measurements of the collective grating response as a function of the excitation angle. Excellent agreement is obtained with simulations when the sample is immersed either in air or in water, which is crucial in view of future sensing application. Thanks to the high signal-to-noise ratio and low dependence on the statistical particle dispersity, this method constitutes an effective alternative to back-focal plane imaging when very weak signals such as SHG are involved

Quantum oscillations in underdoped YBa_2Cu_3O_6.5

Shubnikov-de Haas and de Haas-van Alphen effects have been measured in the underdoped high temperature superconductor YBa$_2$Cu$_3$O$_{6.51}$. Data are in agreement with the standard Lifshitz-Kosevitch theory, which confirms the presence of a coherent Fermi surface in the ground state of underdoped cuprates. A low frequency $F = 530 \pm 10$ T is reported in both measurements, pointing to small Fermi pocket, which corresponds to 2% of the first Brillouin zone area only. This low value is in sharp contrast with that of overdoped Tl$_2$Ba$_2$CuO$_{6+\delta}$, where a high frequency $F = 18$ kT has been recently reported and corresponds to a large hole cylinder in agreement with band structure calculations. These results point to a radical change in the topology of the Fermi surface on opposing sides of the cuprate phase diagram.Comment: proceeding of the ECRYS-200

Etude du comportement de colonies de fissures courtes de Corrosion Sous Contrainte par Corrélation d'Images Numériques (DIC)

Dans cette étude, un système expérimental est développé pour l'étude par corrélation d'images numériques (DIC) de colonies de fissures courtes de Corrosion Sous Contrainte (CSC). Un alliage d'Inconel 600est étudié par DIC, puis par des techniques plus conventionnelles (émission acoustique, bruit électrochimique), dans une solution de tétrathionate de potassium à 0.01 M et acidifié à pH 3. Il a été aussi développé une méthode permettant d'identifier les fissures en fonction du temps, ainsi que la classification des fissures selon leur activité dynamique (actives ou dormantes). La même méthode a aussi permis le suivi du processus et l'identification de coalescences de fissures

Omega-3 fatty acids, polymorphisms and lipid related cardiovascular disease risk factors in the Inuit population

Background : Tissue concentrations of fatty acids (FAs) and genetic variations are well-known factors which affect the cardiovascular disease (CVD) risk. The objective was to examine whether the genetic variability of 20 candidate genes and red blood cells (RBCs) percentage of total n-3 polyunsaturated fatty acids (PUFA), a biomarker of dietary n-3 PUFA intake, modulate lipid related CVD risk factors in the Inuit population. Methods : Data from the Qanuippitaa Nunavik Health Survey (n = 553) were analysed via multivariate regression models with 40 known polymorphisms, RBCs percentage of n-3 PUFA, and the interaction term to take into account the effect on plasma lipid and apolipoporotein levels. Results : Individuals being heterozygotes for CETP C-4502T (rs183130) or G-971A (rs4783961) together with higher n-3 PUFA had lower triacylglycerol (TG) concentrations compared to homozygotes for the minor allele. Further, effects of a stronger beneficial association between n-3 PUFA in RBCs and plasma lipid parameters- including lower total cholesterol (TC), lower low-density lipoprotein cholesterol (LDL-C) or higher high-density lipoprotein cholesterol (HDL-C) concentrations- were associated with AGT M235T (rs699) TT genotype, CETP G-971A (rs4783961) AG genotype, T allele carriers of CETP C-4502T (rs183130), and T allele carriers of CETP Ile405Val (rs5882). In contrast, higher n-3 PUFA in RBCs were associated with adverse lipid profiles- including increased LDL-C, increased apolipoprotein B100 or decreased HDL-C concentrations- in G allele carriers of the APOA5 -3 A/G (rs651821), C allele carriers of APOA5 T-1131C (rs662799), G carriers of APOC3 SstI (rs5128) and G carriers of APOA4 Asn147Ser (rs5104). Conclusion : Overall, these results suggest that percentage of total n-3 PUFA of RBCs are associated with lipids related CVD risk factors conferred by genetic variations in the Inuit population

Transport and Phototransport in ITO Nanocrystals with Short to Long-Wave Infrared Absorption

Nanocrystals are often described as an interesting strategy for the design of low-cost optoelectronic devices especially in the infrared range. However the driving materials reaching infrared absorption are generally heavy metalcontaining (Pb and Hg) with a high toxicity. An alternative strategy to achieve infrared transition is the use of doped semiconductors presenting intraband or plasmonic transition in the short, mid and long-wave infrared. This strategy may offer more flexibility regarding the range of possible candidate materials. In particular, significant progresses have been achieved for the synthesis of doped oxides and for the control of their doping magnitude. Among them, tin doped indium oxide (ITO) is the one providing the broadest spectral tunability. Here we test the potential of such ITO nanoparticles for photoconduction in the infrared. We demonstrate that In2O3 nanoparticles presents an intraband absorption in the mid infrared range which is transformed into a plasmonic feature as doping is introduced. We have determined the cross section associated with the plasmonic transition to be in the 1-3x10-13 cm2 range. We have observed that the nanocrystals can be made conductive and photoconductive due to a ligand exchange using a short carboxylic acid, leading to a dark conduction with n-type character. We bring further evidence that the observed photoresponse in the infrared is the result of a bolometric effect

Hidden magnetism at the pseudogap critical point of a high temperature superconductor

The mysterious pseudogap phase of cuprate superconductors ends at a critical hole doping level p* but the nature of the ground state below p* is still debated. Here, we show that the genuine nature of the magnetic ground state in La2-xSrxCuO4 is hidden by competing effects from superconductivity: applying intense magnetic fields to quench superconductivity, we uncover the presence of glassy antiferromagnetic order up to the pseudogap boundary p* ~ 0.19, and not above. There is thus a quantum phase transition at p*, which is likely to underlie highfield observations of a fundamental change in electronic properties across p*. Furthermore, the continuous presence of quasi-static moments from the insulator up to p* suggests that the physics of the doped Mott insulator is relevant through the entire pseudogap regime and might be more fundamentally driving the transition at p* than just spin or charge ordering.Comment: 26 pages, supplementary info include