Role of impurities on the spark plasma sintering of ZrCx–ZrB2 composites

The study of the spark plasma sintering (SPS) of ZrCx and ZrCx–ZrB2 composites was carried out considering the effect of experimental parameters such as the applied load, the temperature and the heating time. In addition, the role of the main impurities, detected in the raw materials, on the sintering behaviour has been explored by Transmission Electron Microscopy (TEM). The analyses of monoliths and composites showed up the liquid phase formation from silica impurities and the complete structural reorganisation of free carbon into the graphite form during the sintering treatment. It is also shown that within composites, the plastic strain is preferentially accommodated by ZrB2 crystals

Optical investigation of a cavitating flow in a 2D nozzle

International audienceIn heat engines (vehicle), cavitation plays an important role in fuel atomization mechanisms. The physics of cavitation as well as its impact on spray formation and injector efficiency are not well documented yet. Experimental investigations are required. The complexity of modern injectors and the extreme conditions of injection do not facilitate experimental investigations. In this paper, experiments are conducted in a simplified geometry. The model nozzle consists of a transparent 2D micro-channel supplied with a test-oil (ISO 4113). Velocity fields are obtained by means of a shadowgraph-like imaging arrangement using PIV components (double pulsed laser and double-frame camera). Pressure fields are obtained by interferometry coupled with a Schlieren technique

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Experimental investigation on tow mechanical behaviour under multiaxial loads

Les procédés de mise en œuvre de type pultrusion ou enroulement filamentaire permettent d’obtenir des structures avec une très bonne répétabilité. Ils offrent l’avantage d’un haut degré d’automatisation, des temps de mise en œuvre courts et permettent de réaliser des pièces présentant un taux de renfort élevé. Le choix optimal des conditions opératoires (vitesse, tension, température, ...) implique une capacité à décrire finement les phénomènes physiques mis en jeu. La particularité de ces procédés est de solliciter en traction les mèches de manière continue toute en appliquant des sollicitations transverses à certaines étapes du procédé: compression dans le convergent d’un outillage de pultrusion, écrasement sur le mandrin dans le cas de l’enroulement.Dans le but de caractériser le comportement des mèches dans des conditions de mise en œuvre, un moyen d’essai prototype a été conçu pour caractériser le comportement en compression de mèches textiles soumises à un niveau de tension contrôlé. Les premiers résultats, réalisés sur des mèches de carbone, sont présentés. L’analyse de ces essais est ensuite exploitée pour proposer des pistes d’amélioration du dispositif.Continuous processes such as pultrusion or filament winding allow manufacturingcomposite with very good repeatability. They offer the advantage of a high degree of automation, short manufacturing times and make it possible to produce parts with high fibre volume fraction.The optimal choice of operating conditions (speed, yarn tension, temperature ...) requires beingable to accurately describe the physical phenomena involved. The particularity of these processes is to continuously pullthe yarns while simultaneously applying transverse loads during some steps of the process: compression in the convergent of pultrusion tooling, crushing on the mandrel in the case of filament winding.In order to characterize the behaviour of the yarns under manufacturing conditions, a prototype test device has been designed to characterize the compression behaviour of yarns subjected to a controlled tension level. The first results, made on carbon yarns, are presented. The analysis of these preliminary tests is then exploited to propose ways to improve the devic

Compression of 3D Triangular Meshes with Progressive Precision

International audienceIn this paper we introduce a novel approach for progressive transmission of three-dimensional (3D) triangular meshes. This algorithm is based on a new reversing approach of the irregular mesh subdivision that enables a wavelet representation of any mesh geometry. In this paper, we show how to achieve progressive compression of 3D models by transmitting more and more wavelet coef cients computed from the original mesh vertices coordinates. The connectivity of the reconstructed mesh remains the same as the original one, but its geometry is progressively re ned by means of bitplane encoding. This approach processes directly oating point coordinates which is the most common representation for 3D meshes, and does not need quantization, which is a lossy transformation. Experimental results are given and demonstrate the efficiency of our encoding scheme versus other approaches

Etude expérimentale du comportement mécanique de mèches sous sollicitations multiaxiales.

International audienceContinuous processes such as pultrusion or filament winding allow manufacturingcomposite with very good repeatability. They offer the advantage of a high degree of automation, short manufacturing times and make it possible to produce parts with high fibre volume fraction.The optimal choice of operating conditions (speed, yarn tension, temperature ...) requires beingable to accurately describe the physical phenomena involved. The particularity of these processes is to continuously pullthe yarns while simultaneously applying transverse loads during some steps of the process: compression in the convergent of pultrusion tooling, crushing on the mandrel in the case of filament winding.In order to characterize the behaviour of the yarns under manufacturing conditions, a prototype test device has been designed to characterize the compression behaviour of yarns subjected to a controlled tension level. The first results, made on carbon yarns, are presented. The analysis of these preliminary tests is then exploited to propose ways to improve the deviceLes procédés de mise en œuvre de type pultrusion ou enroulement filamentaire permettent d’obtenir des structures avec une très bonne répétabilité. Ils offrent l’avantage d’un haut degré d’automatisation, des temps de mise en œuvre courts et permettent de réaliser des pièces présentant un taux de renfort élevé. Le choix optimal des conditions opératoires (vitesse, tension, température, ...) implique une capacité à décrire finement les phénomènes physiques mis en jeu. La particularité de ces procédés est de solliciter en traction les mèches de manière continue toute en appliquant des sollicitations transverses à certaines étapes du procédé: compression dans le convergent d’un outillage de pultrusion, écrasement sur le mandrin dans le cas de l’enroulement.Dans le but de caractériser le comportement des mèches dans des conditions de mise en œuvre, un moyen d’essai prototype a été conçu pour caractériser le comportement en compression de mèches textiles soumises à un niveau de tension contrôlé. Les premiers résultats, réalisés sur des mèches de carbone, sont présentés. L’analyse de ces essais est ensuite exploitée pour proposer des pistes d’amélioration du dispositif

Experimental Investigation of Roughness Effects on Cavitating Flow in Diesel Injectors

International audienceIn diesel injectors, the wall roughness of the nozzle holes is thought to influence cavitation formation during the injection cycle. In order to highlight the roughness effect, an experimental setup has been designed. This setup consists of a 2D-orifice that confines a cavitating flow. Specific tools are used to control-by means of femtosecond laser-and finely characterise wall roughness, and the cavitating flow is visualised using optical techniques. The different devices are introduced and the first results are presented

Perception des plages et des politiques de rechargement : réflexions à partir du cas du golfe d’Aigues Mortes (Hérault/Gard)

Beaches, which are of strategic importance for both the environment and the tourism industry in coastal zones, are subject to worsening erosion. Public policies first addressed the erosion issue through the construction of sea defenses but are now moving towards soft measures, in particular beach sand nourishment. A large-scale nourishment operation was carried out in 2008 in the Gulf of Aigues Mortes and lessons can be learned from the study of user perceptions. This article begins by addressing both the positive and negative impacts of such measures. It then discusses users’ perceptions of beaches, in particular the significance that they attach to their size, and their viewpoints on beach nourishment practices. The results clarify the communication and awareness-raising efforts needed to promote such actions