29 research outputs found
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/)
L'aquaculture des tilapias : du développement à la recherche
Journée "Tilapia" du 28 Septembre 1987 Cahiers scientifiques : CTFT, 10National audienceCe cahier, consacré à la biologie et à l'aquaculture des tilapias (Oreochromis et Sarotherodon) se compose de sept communications. Contribution à une réflexion sur les stratégies de recherche et de développement en aquaculture des tilapias (Lazard J.). Physiologie de l'adaptation des tilapias à la salinité : aspects fondamentaux et appliqués (Prunet P., Bornancin M.). Alimentation des tilapias (Luquet P.). Physiologie de la reproduction des tilapias : bilan des connaissances et perspectives de recherches d'intérêt appliqué (Baroiller J.F., Jalabert B.). Pathologie des tilapias (Michel C.). Indices de performance de croissance chez les tilapias : utilisation possible en pisciculture et en eaux libres (Moreau J.). Recherches sur les tilapias lagunaires de Côte d'Ivoire (Legendre M., Ecoutin J.M., Hem S., Cisse A.
Temperature evolution in a WC-6% Co cutting tool during turning machining : experiment and finite element simulations
International audienceThe present paper focuses on thermal simulations and temperature measurements in a cutting tool during the machining process. The experimental studies deal with turning an AISI 1045 steel with cemented carbide insert (WC-%6Co). During machining, transient temperatures are measured at two points in cutting tool using the embedded thermocouple method. Three cutting force components are simultaneously recorded. The thermal simulations are based on the calculation of the heat flux from cutting forces and heat partition coefficient. Results obtained by thermal simulations are in good agreement with experimental ones
Temperature evolution in a WC-6% Co cutting tool during turning machining : experiment and finite element simulations
International audienceThe present paper focuses on thermal simulations and temperature measurements in a cutting tool during the machining process. The experimental studies deal with turning an AISI 1045 steel with cemented carbide insert (WC-%6Co). During machining, transient temperatures are measured at two points in cutting tool using the embedded thermocouple method. Three cutting force components are simultaneously recorded. The thermal simulations are based on the calculation of the heat flux from cutting forces and heat partition coefficient. Results obtained by thermal simulations are in good agreement with experimental ones
Wear mechanism of WC-Co cutting tool from turning experiments and high speed tribological tests
International audienc
Friction at high sliding speed of WC-6Co pin versus steel disc AISI 1045 : estimation of the contact temperature
International audienceCemented carbide based cutting tools remain widely used in machining processes for their wear resistance. Knowledge and modelling of wear processes are of prior importance to get models to predict and increase the cutting tool service life. The present paper deals with some results of a research work that study relationships between wear and temperature in the case of pin-on-disc tribological experiments. Topic of the paper is focussed on the estimation of the pin/disc contact temperature by coupling experimental measurements and computational methods. Friction experiments are conducted with WC-6Co pins against steel discs made of an AISI 1045 grade. Furthermore, WC-6Co pins are instrumented with two type-K thermocouples. A large sliding velocity range is considered in the study: from 100m/min up to 600m/min. The present paper is focussed on the 600m/min velocity. During these tribological tests, tangential forces and thermocouple temperatures are measured and monitored. From these values, the heat flux in the WC-6Co pin is estimated by two different ways. On one hand by considering the unidirectional Fourier law, on the other hand by estimating the heat partition coefficient [1] between the disc and the pin. The heat partition coefficient is determined from a physical approach based on the consideration of the mechanical power dissipated in the contact. In both cases, the heat transfer in the pin is then modelled by finite element methods. It is necessary to perform numerical analysis to estimate the pin/disc interface temperature because of the impossibility to measure it directly during friction tests. Results of experiments and of numerical simulations are compared
Microstructural analysis of wear micromechanisms of WC-6Co cutting tools during high speed dry machining
SCIE Article le 06/02/14International audienceThis original study investigates the damages of WC-6Co uncoated carbide tools during dry turning of AISI 1045 steel at mean and high speeds. The different wear micromechanisms are explained on the basis of different microstructural observations and analyses made by different techniques: (i) optical microscopy (OM) at macro-scale, (ii) scanning electron microscopy (SEM), with back-scattered electron imaging (BSE) at micro-scale, (iii) energy dispersive spectroscopy (EDS), X ray mapping with wavelength dispersive spectroscopy (WDS) for the chemical analyses and (iv) temperature evolution during machining. We noted that at conventional cutting speed Vc ≤ 250 m/min, normal cutting tool wear types (adhesion, abrasion and built up edge) are clearly observed. However, for cutting speed Vc > 250 m/min a severe wear is observed because the behavior of the WC-6Co grade completely changes due to a severe thermomechanical loading. Through all SEM micrographs, it is observed that this severe wear consists of several steps as: excessive deformation of WC-6Co bulk material and binder phase (Co), deformation and intragranular microcracking of WC, WC grain fragmentation and production of WC fragments in the tool/chip contact. Thus, the WC fragments accumulated at the tool/chip interface cause abrasion phenomena and pullout WC from tool surface. WC fragments contribute also to the microcutting and microploughing of chips, which lead to form a transferred layer at the tool rake face. Finally, based on the observations of the different wear micromechanisms, a scenario of WC-6Co damages is proposed through to a phenomenological mode
Mécanismes d'endommagement tribologiques du WC-6% CO en usinage
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