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The H.E.S.S. extragalactic sky survey with the first decade of observations
No full textInternational audienceThe results of the first extragalactic gamma-ray survey by the High Energy Stereoscopic System (H.E.S.S.) are presented. The survey comprises 2720 hours of very high-energy gamma-ray observations of the extragalactic sky, recorded with H.E.S.S. from 2004 up to the end of 2012. These data have been re-analysed using a common consistent set of up-to-date data calibration and analysis tools. From this analysis, a list of 23 detected objects, predominantly blazars, was obtained. This catalogue was assessed in terms of the source class populations that it contains. The level of source parameter bias for the blazar sources, probed by this observational dataset, was evaluated using Monte-Carlo simulations. Spectral results obtained with the H.E.S.S. data were compared with the Fermi-LAT catalogues to present the full gamma-ray picture of the detected objects. Lastly, this unique dataset was used to assess the contribution of BL Lacertae objects and flat-spectrum radio quasars to the extragalactic gamma-ray background light at several hundreds of gigaelectronvolts. These results are accompanied by the release of the high-level data to the astrophysical community
Temps, travail, espace : pourquoi choisir ? Un unisson autostabilisant et ses retombées
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Science Arts & Métiers (SAM) is an open access repository that collects the work of Arts et Métiers Institute of Technology researchers and makes it freely available over the web where possible
No full textInternational audienceThe present paper analyzes separately the effect of the features of the typical AM defects on the fatigue resistance of Ti-6Al-4V alloy. To do so, different defect population in terms of sizes and morphologies were obtained by varying the L-PBF process parameters. The distance of these defects with respect to the surface was also controlled. A uniaxial fatigue testing campaign (R = −1) has then been conducted. The results have showed great influence of the nature of the defect population on the fatigue strength of Ti-6Al-4V alloy, for the case of surface crack initiation. The results have also allowed to quantify the criticality of internal defects with respect to their sizes and showed that the defect morphology has no influence on the fatigue strength for the case of internal crack initiation
Faster SCALLOP from Non-Prime Conductor Suborders in Medium Sized Quadratic Fields
No full textInternational audienceA crucial ingredient for many cryptographic primitives such as key exchange protocols and advanced signature schemes is a commutative group action where the structure of the underlying group can be computed efficiently. SCALLOP provides such a group action, based on oriented supersingular elliptic curves. We present PEARL-SCALLOP, a variant of SCALLOP that changes several parameter and design choices, thereby improving on both efficiency and security and enabling feasible parameter generation for larger security levels. Within the SCALLOP framework, our parameters are essentially optimal; the orientation is provided by a 2^e-isogeny, where 2^e is roughly equal to the discriminant of the acting class group. As an important subroutine we present a practical algorithm for generating oriented supersingular elliptic curves. To demonstrate our improvements, we provide a proof-of-concept implementation which instantiates PEARL-SCALLOP at all relevant security levels. Our timings are more than an order of magnitude faster than any previous implementation.Un ingrédient crucial de nombreuses primitives cryptographiques telles que les protocoles d'échange de clé et les schémas de signature avancés est une action de groupe commutative où la structure du groupe sous-jacent peut être calculée efficacement. SCALLOP fournit une telle action de groupe, basée sur le courbes supersingulières orientées. Nous présentons PEARL-SCALLOP, une variante de SCALLOP qui en change la conception et certains paramètres, améliorant ainsi à la fois l'efficacité et la sécurité et rendant possible la génération de paramètres pour de plus hauts niveaux de sécurité. Dans le cadre de SCALLOP, nos paramètres sont essentiellement optimaux ; l'orientation est donnée par une 2^e-isogénie, où 2^e est approximativement égal au discriminant du groupe de classes. Nous présentons comme important sous-routine un algorithme efficace pour générer des courbes elliptiques supersingulières orientées. Pour mettre en lumière nos améliorations, nous fournissons une implantation preuve-de-concept qui instancie PEARL-SCALLOP à tous les niveaux de sécurité pertinents. Nos temps de calcul sont plus d'un ordre de magnitude plus courts que toute implantation précédente
Procédés laser appliqués aux matériaux composites cuivre/diamant
No full textWith the increasing miniaturization of electronic components, more and more heat has to be dissipated from electronic devices. Without optimal heat dissipation, components overheating can significantly reduce their lifetime and reliability. To meet this need, new thermal management materials, with tailored thermal properties and mechanical strength, have to be developed.Copper (Cu) matrix composites reinforced with diamond (D) particles have the potential to be used as the next-generation of thermal dissipation materials, due to their potentially high thermal conductivity and tailorable coefficient of thermal expansion (CTE). Indeed, Cu has been historically used as heat sink as it is the second-best thermal conductor among metals (λCu = 400 W/(m·K)) after silver. On the other hand, diamond has the highest thermal conductivity (between 1000 and 2500 W/(m·K)) of all bulk materials known in nature, and a low CTE (close to 2 x 10⁻⁶/K).For this type of chemically non-reactive copper-carbon (Cu-C) system, it is necessary to improve the reactivity of the Cu-C interface, in order to enhance the heat transfer between the Cu matrix and the C reinforcement. Furthermore, the use of conventional manufacturing processes, such as powder metallurgy, limits the production of Cu/D composites to simple shapes (cylinders or cubes). The extreme hardness of diamond makes machining very complex, and almost impossible, with conventional machining methods.The development of additive manufacturing (AM) and ultra-short pulse lasers allows the manufacture and processing of parts with complex shapes, whatever the nature of the material. This study aims to optimize the processing of Cu/D composite materials for thermal management applications using a laser-based AM process and their post-processing with an ultra-short pulse laser.First, multilayer and Cu/carbon fiber model composite materials are developed by magnetron sputtering and powder metallurgy, respectively. These model materials are then thermally characterized by photothermal radiometry to assess the influence of the chemical nature of the Cu-C interface on the thermal conductivity of the Cu/C system. Next, the 3D printing of Cu-based materials and Cu/D composites, using the laser powder bed fusion (LPBF) AM process, is investigated using an infrared continuous wave laser. This laser has a ring-shaped intensity distribution, with a minimum at the center and a maximum at the periphery, forming a “donut” intensity profile. Finally, the feasibility of polishing rough surfaces of Cu and Cu/D composite materials with a femtosecond pulsed laser is investigated to achieve a surface with a submicron average roughness.Avec la miniaturisation croissante des composants électroniques, une quantité plus importante de chaleur doit être évacuée des dispositifs électroniques. Sans une dissipation thermique optimale, la surchauffe des composants risque de réduire considérablement leur durée de vie et leur fiabilité. Pour répondre à ce besoin, de nouveaux matériaux de gestion thermique, dotés de propriétés thermiques adaptées et mécaniquement résistants, doivent être développés.Les matériaux composites à matrice cuivre (Cu) renforcée par des particules de diamant (D) ont le potentiel d’être utilisés comme matériaux de dissipation thermique de nouvelle génération en raison de leur conductivité thermique potentiellement élevée et de leur coefficient de dilatation thermique (CTE) ajustable. En effet, le Cu, utilisé historiquement comme drain thermique, est le second conducteur thermique métallique derrière l’argent (λCu = 400 W/(m.K)). Le diamant possède, quant à lui, la conductivité thermique la plus élevée (entre 1000 et 2500 W/(m.K)) de tous les matériaux massifs connus dans la nature, et un faible CTE (voisin de 2 10-6/K).Pour ce type de système (Cu-C) non réactif chimiquement, il est nécessaire d’améliorer la réactivité de l’interface cuivre-carbone (Cu-C), afin d’améliorer le transfert thermique entre la matrice Cu et le renfort C. De plus, l’utilisation des procédés d’élaboration conventionnels, comme la métallurgie des poudres, limite l’élaboration des matériaux composites Cu/D à des formes simples (cylindre ou cube). L’extrême dureté du diamant rend l’usinage très complexe voire impossible avec les méthodes d’usinage conventionnelles.Le développement de la fabrication additive (FA) et des lasers à impulsions ultrabrèves offre désormais la possibilité de fabriquer et de traiter des pièces de formes complexes, et ceci quelle que soit la nature du matériau. Cette étude a pour but d’optimiser l’élaboration de matériaux composites Cu/D pour des applications de gestion thermique par un procédé de FA utilisant un laser, ainsi que leur post-traitement avec un laser à impulsions ultrabrèves.Dans un premier temps, des matériaux modèles multicouches et des matériaux composites Cu/ fibre de carbone sont respectivement élaborés par pulvérisation cathodique magnétron et par métallurgie des poudres. Ces matériaux modèles sont ensuite caractérisés thermiquement par radiométrie photothermique afin d’évaluer l’influence de la nature chimique de l’interface Cu-C sur la conductivité thermique du système Cu/C. Ensuite, la fabrication de matériaux à base de Cu et de matériaux composites Cu/D, par le procédé de FA de fusion laser sur lit de poudre (LPBF), est étudiée en utilisant un laser continu infrarouge. Ce laser présente une distribution d’intensité en anneau, avec un minimum au centre et un maximum en périphérie, formant un profil d’intensité en « donut ». Enfin, la faisabilité de polir des surfaces rugueuses de Cu et de matériaux composites Cu/D par laser à impulsion femtosecondes est investiguée, avec pour ambition d’atteindre un état de surface ayant une rugosité moyenne submicronique
A fermented functional food enriched in phytosterol and carotenoids improves lipid profile and insulin resistance and restores vitamin A status in high-fat diet-induced metabolic syndrome rats
No full textInternational audienceTackling metabolic syndrome (MetS) using functional fermented food has recently attracted much attention. A vegetable-fermented maize - and fruit-based probiotic functional food (maize 5% and fruits 30%) was previously designed, which was enriched in papaya/melon carotenoids and dispersible phytosterols to obtain a cholesterol-lowering effect. The aim of this work was to investigate the effect of this new functional food on an HFD (high-fat diet)-induced MetS rat model focusing on lipid and glucose metabolic disorders and considering vitamin A status. Male Sprague-Dawley rats (n = 36) were randomly divided into 4 groups (n = 9): a control group (C); an HFD group; and two HFD groups receiving 1.44 g per rat per day of the functional fermented food during the three months of the experiment following a preventive (HFD-P) or a curative (HFD-C) mode. The intake of the functional food decreased the adipose tissue amount by 1.5 times in preventive and curative mode groups and restored their LDL cholesterol and triglyceride levels to C level. The area of hepatic lipid droplets was reduced in both HFD-P and HFD-C groups compared with HFD group, which was associated with a reduction in inflammation and lipid oxidation. Both the HFD-P and HFD-C groups alleviated HFD-induced insulin resistance, as evidenced by the return of fasting insulin levels and the HOMA-IR index to control levels. However, only the HFD-C group improved the glucose tolerance test and skeletal muscle insulin sensitivity. Notably, alteration in vitamin A status in HFD rats was restored with HFD-C and HFD-P. Altogether, these results support the potential of this nutritional strategy to prevent MetS
D'une famille à l'autre. La dimension transitoire du Docteur Pascal d'Emile Zola
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Le contrôle de proportionnalité de la liberté d’expression militante en France
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Assessing the invasion risk of the cnidaria Blackfordia virginica Mayer, 1910: a threat to the Baltic Sea ecosystem?
No full textInternational audienceThe ecological role, bloom extent and long-term dynamics of jellyfishes are mostly overlooked due to sampling limitations, leading to the lack of continuous long-term datasets. A rise in frequency and magnitude of jellyfish invasion around the world is shedding new light on these organisms. In this study, we estimate the current and future distribution of the introduced jellyfish Blackfordia virginica in the Baltic Sea. We determine the combination of favorable levels of temperature and salinity for this species by analyzing presence/absence data from areas outside the Baltic Sea and project the distribution of suitable habitat in the Baltic Sea across different scenarios with variable climate forcing and eutrophication levels. Our results show that suitability increases with rising temperature and optimal salinity range from 13 to 20 for this species. In addition, a relatively large area of the Baltic Sea represents favorable abiotic conditions for B. virginica , enhancing the concerns on its potential range expansion. Spatial analysis illustrates that the coastal areas of the southern Baltic Sea are particularly at risk for the invasion of the species. The observation of the projection of habitat suitability across time highlights that future Baltic Sea environmental conditions increase suitability levels for B. virginica and suggest a potential expansion of its distribution in the future
Pregnancy and birth outcomes in women with multiple sclerosis: Comparison of the RESPONSE study to the general French population
No full textInternational audienceBackground: Retrospective studies did not show strong evidence of higher risk of adverse neonatal or pregnancy outcomes in women with multiple sclerosis (MS) compared to general population, but there are contradictory data on prematurity, cesarean section, and small birthweight for gestational age (SGA).Methods: We compared pregnancy and birth outcomes in MS women included in RESPONSE, a French prospective cohort, with a recent survey (Enquête Nationale Périnatale (ENP)) describing leading indicators in perinatal epidemiology in France.Results: On 7 April 2023, 476 pregnancies (461 MS women, 482 expected newborns) from RESPONSE were available. The ENP study reported 12,723 women and 12,939 expected newborns in March 2021. MS patients were older (mean age 32.6 ± 4.4 vs. 30.9 ± 5.3 years, p < 0.001), with similar rate of cesarean (23.8% vs. 21.4%, p = 0.115) and use of locoregional analgesia (86.6% vs. 85.1%, p = 0.51). Preterm birth was less frequent (4.0% vs. 7.0%, p = 0.001). Birthweight of children from MS mothers was similar to general population (3240 ± 477.2 vs. 3264.5 ± 552.9 g, p = 0.22), with slightly more children with SGA (13.4% vs. 9.8%, p = 0.04).Conclusion: This prospective and contemporary comparison of pregnancy in MS women and the French population provides reassuring results. In the future, we need to assess the impact of disease-modifying treatment exposure during conception