Comparisons of experimental measurements and large eddy simulations for a helium release in a two vents enclosure.

This work takes place in the context of potential hazards in the use of hydrogen in fuel cells. The present article describes comparisons between PIV measurements performed on a two vented cavity with an helium injection and Large Eddy Simulation of the same configuration. A two vented cavity is chosen because a quasi state is reached rapidly and it facilitates both CFD calculations by reducing the CPU costs and also enables statistical treatment of the data, the temporal averaging being possible at steady state. At the same time, this configuration is close to fuel cell designs, except for the set-up reduced size. We also describe the experimental set-up and the care which has to be taken to produce Particle Image Velocimetry velocity fields. The final goal of the paper is to validate a L.E.S approach as a good replacement to experiments, since access to both velocity and con- centration fields is required to improve existing simplified models. Indeed, most of the 2 vents models rely on simplified assumptions such as a constant entrainment coefficient, a bi-layer formation which is not always the case in real situations

Highly resolved large eddy simulations of a binary mixture flow in a cavity with two vents: Influence of the computational domain.

In this article, numerical results from a highly resolved large eddy simulations (LES) of an air-helium buoyant jet developing in a two vented cavity are presented. The simulated configuration mimics the helium-release experiment carried out at CEA Saclay in the framework of security assessment of indoor used hydrogen-based systems. The height of the enclosure was chosen so that a laminar-turbulent transition occurs approximately at the middle of the upstream direction. An exterior region, of different spatial dimensions, has been modeled in the computational domain in order to move the boundary conditions away from the vent surface and to approach the natural inlet/outlet conditions. A sensi- tivity analysis regarding the size of the exterior region is presented to define the minimum horizontal extension so that the flow inside the cavity is not furthermore influenced by bigger computational domains. We observe mainly that applying an ambient equilibrium- hydrostatic pressure outlet condition directly on the surface of the vent reduces the vol- ume of the air inflow, and thus predicts larger helium mass inside the cavity, in contrary with the cases where an exterior region is considered. A qualification analysis shows that the sub-grid scale model plays a small role in the calculations and thus implies that the LES predictions approach the direct numerical simulation (DNS) solution. Analysis carried out on the time-averaged helium field depicts a concentration regime that is not classical in such configurations and thus the theoretical model used in safety pre-calculations can not be served

Monitoring seasonal snow dynamics using ground based high resolution photography (Austre Lovenbreen, Svalbard, 79°N)

International audienceArctic glaciers are reliable indicators of global climate changes. However, monitoring snow and ice dynamics in Arctic regions is challenging: some fast but key events can be missed since they are short in time but significant in the hydrological budget. In the context of long term monitoring with high temporal and spatial resolutions of the snow cover dynamics, automated digital cameras were installed around the Austre Lovénbreen glacier basin (Spitsbergen, Norway, 79 N). Despite data losses due to rough weather conditions and control electronics failure, a dataset of 2411 pictures (out of an expected 3294) was gathered over a 1 year hydrological period to assess the snow coverage of the glacier as a function of time with daily resolution. 73% of the total number of expected images was thus recorded, with gaps associated with temporary electronics or data storage failure. The six camera stations oriented so as to observe the glacier itself provide a surface coverage of 96%. Furthermore, geometric corrections of the pictures, using reference ground control points located on the glacier through GPS receivers, yield a quantitative information from initially qualitative images. Projecting the resulting mosaic of the images gathered from six cameras on a GIS allows for the precise monitoring of ice-related processes, and especially the snow coverage evolution over time. This paper summarizes our current understanding of such dynamics, based on the analysis of daily mosaics of images allowing for the observation of both long term evolution on the seasonal scale and the short term events on a weekly scale. Such results demonstrated over one typical full hydrological season (April-October 2009) that snow coverage evolves following discrete steps, either due to water precipitation or warm events, with a snow coverage ranging from 100% (april) to 37% (September

Large eddy simulations of an air-helium buoyant jet in a two vented enclosure: influence of the outlet boundary condition

This work is devoted to the security assessment of systems using hydrogen as energy carriers, where the problematic is mainly with the hydrogen leakage which is not only dangerous, but can be destructive when mixed with air. The french Atomic Energy Commission (CEA) is showing a great interest to the presented problem and have been participating in several concerned projects that focus on reducing the risks in such systems. We present a numerical Large Eddy Simulation (LES) study to mimic the experiment held at CEA-Saclay, where the above problem is modelled by injecting Helium gas (replacing the Hydrogen in the real problem) through a cylindrical pipe that enters a two-vented parallelepiped cavity filled initially with air. Understanding the mixing/dispersion of the binary fluids at the transient and quasi-steady state is one of the goals that we target on. In spite of the fact that the experiments had been held over a wide range of varied injection flow-rates, we restrict our study to the case of a 5 Nl/min injection resulting in a formation of a buoyant jet that is mainly influenced by momentum in the near source and buoyancy dominant upstream. The dimensions of the cavity had been chosen so that the interesting physical phenomena of the problem is captured; basically the transition from a laminar regime to a turbulent one and the self-similarity of the jet horizontal profiles. In this paper, we present some of our LES results obtained by making use of the CEA code TRUST and the Smagoranski model. We point out basically to the influence of the exterior domain, if it is/isn't considered in the computational domain, on the flow inside the cavity. We demonstrate that imposing classical fixed pressure boundary conditions directly at the vents positions, when compared with the experimental Particle Image Velocitimetry (PIV) measurements, tends to under-estimate the air flow in the cavity and thus leading to over-estimate the maximum Helium concentration. Different simulations had been achieved by varying the size of the exterior domain which is opened from all directions not in contact with the plexi-glass of the cavity. Following a space and a temporal convergence study, our statistical results seems to be satisfactory when compared to the experimental data. This work is a first step as we look on developing new outlet boundary conditions which can be directly applied at the vents positions for a perfect Direct Numerical Simulation (DNS), at the Kolmogorov scales, with a better computational cost

Improved Energy Supply Regulation in Chronic Hypoxic Mouse Counteracts Hypoxia-Induced Altered Cardiac Energetics

Hypoxic states of the cardiovacular system are undoubtedly associated with the most frequent diseases of modern time. Therefore, understanding hypoxic resistance encountered after physiological adaptation such as chronic hypoxia, is crucial to better deal with hypoxic insult. In this study, we examine the role of energetic modifications induced by chronic hypoxia (CH) in the higher tolerance to oxygen deprivation.P-NMR), and to describe the integrated changes in cardiac energetics regulation by using Modular Control Analysis (MoCA). Oxygen reduction induced a concomitant decrease in RPP (−46%) and in [PCr] (−23%) in Control hearts while CH hearts energetics was unchanged. MoCA demonstrated that this adaptation to hypoxia is the direct consequence of the higher responsiveness (elasticity) of ATP production of CH hearts compared with Controls (−1.88±0.38 vs −0.89±0.41, p<0.01) measured under low oxygen perfusion. This higher elasticity induces an improved response of energy supply to cellular energy demand. The result is the conservation of a healthy control pattern of contraction in CH hearts, whereas Control hearts are severely controlled by energy supply.As suggested by the present study, the mechanisms responsible for this increase in elasticity and the consequent improved ability of CH heart metabolism to respond to oxygen deprivation could participate to limit the damages induced by hypoxia

Odyssey 2 : A mission toward Neptune and Triton to test General Relativity

Odyssey 2 will be proposed in December 2010 for the next call of M3 missions for Cosmic Vision 2015-2025. This mission, under a Phase 0 study performed by CNES, will aim at Neptune and Triton. Two sets of objectives will be pursued. The first one is to perform a set of gravitation experiments at the Solar System scale. Experimental tests of gravitation have always shown good agreement with General Relativity. There are however drivers to continue testing General Relativity, and to do so at the largest possible scales. From a theoretical point of view, Einstein's theory of gravitation shows inconsistencies with a quantum description of Nature and unified theories predict deviations from General Relativity. From an observational point of view, as long as dark matter and dark energy are not observed through other means than their gravitational effects, they can be considered as a manifestation of a modification of General Relativity at cosmic scales. The scientific objectives are to: (i) test the gravitation law at the Solar System scale; (ii) measure the Eddington parameter; and (iii) investigate the navigation anomalies during fly-bys. To fulfil these objectives, the following components are to be on board the spacecraft: (i) the Gravity Advanced Package (GAP), which is an electrostatic accelerometer to which a rotating stage is added; (ii) radio-science; (iii) laser ranging, to improve significantly the measure of the Eddington parameter. The second set of objectives is to enhance our knowledge of Neptune and Triton. Several instruments dedicated to planetology are foreseen: camera, spectrometer, dust and particle detectors, and magnetometer. Depending on the ones kept, the mission could provide information on the gravity field, the atmosphere and the magnetosphere of the two bodies as well as on the surface geology of Triton and on the nature of the planetary rings around Neptune.Comment: 61st International Astronautical Congress (Prague, Czech Republic - September 2010), 7 page

3D Map of the Human Corneal Endothelial Cell

Corneal endothelial cells (CECs) are terminally differentiated cells, specialized in regulating corneal hydration and transparency. They are highly polarized flat cells that separate the cornea from the aqueous humor. Their apical surface, in contact with aqueous humor is hexagonal, whereas their basal surface is irregular. We characterized the structure of human CECs in 3D using confocal microscopy of immunostained whole corneas in which cells and their interrelationships remain intact. Hexagonality of the apical surface was maintained by the interaction between tight junctions and a submembraneous network of actomyosin, braced like a drum. Lateral membranes, which support enzymatic pumps, presented complex expansions resembling interdigitated foot processes at the basal surface. Using computer-aided design and drafting software, we obtained a first simplified 3D model of CECs. By comparing their expression with those in epithelial, stromal and trabecular corneal cells, we selected 9 structural or functional proteins for which 3D patterns were specific to CECs. This first 3D map aids our understanding of the morphologic and functional specificity of CECs and could be used as a reference for characterizing future cell therapy products destined to treat endothelial dysfunctions

The project of the technological line of the electronic-beam drains disinfection in the infected hospitals’ divisions and tubercular centres

The purpose of the project was to create the electrophysical facility for the environmental protection from contamination by drains of the infected hospitals’ divisions and tubercular centres and prevention of open water reservoirs. In this project two main problems are solved: Development of the economically approved methods of the radiative disinfection of contaminated drains; development of the inexpensive compact facility for the electron-beam disinfection of small volume drains (up to 25 cubic meters daily)

Potamia-Agios Sozomenos (Chypre): La constitution des paysages dans l'Orient médiéval

International audienceCompte-rendu de prospection sur la constitution des paysages dans l'Orient médiéval à Potamia-Agios Sozomenos (Chypre)

039: Platelet reactivity predicts both ischemic and bleeding events at one year follow-up in acute coronary syndome patients receiving prasugrel

There are evidences of a link between platelet reactivity inhibition and thrombotic and bleeding events. We have previously demonstrated that PR after prasugrel loading dose (LD) predicts short-term thrombotic events. We aimed to further investigate the relationship between PR under prasugrel and one-year thrombotic and bleeding events.MethodPatients were prospectively included in this multicentre study if they had a successful PCI for an acute coronary syndrome (ACS) and received prasugrel. Vasodilator-Stimulated Phosphoprotein (VASP index) was measured after prasugrel LD. Endpoint included the rate of thrombotic events (cardiovascular death, myocardial infarction and stent thrombosis) and bleeding events (TIMI) at one year.ResultsThree hundreds and one patients were enrolled. Nine patients (3%) were lost to follow-up at one year. The rates of thrombotic and bleeding events at one year were 7.5 and 6.8% respectively. The mean VASP index after a 60mg LD of prasugrel was 34}23% and 76 patients (25%) were considered as having high on-treatment platelet reactivity (HTPR). Patients with HTPR had a higher rate of thrombotic events compared to good responders (19.7 vs 3.1%;p<0.001). Patients with a minor or major non-CABG related TIMI bleeding had lower PR compared to patients with no bleeding events (21}18 vs 35}23%;p=0.008). In multivariate analysis, the VASP index predicted both thrombotic and bleeding events (OR: 1.44 (95% CI: 1.2–1.72; p<0.001 and 0.75 (95% CI: 0.59–0.96;p=0.024 (respectively, per 10% increase)).ConclusionPlatelet reactivity measurement after prasugrel LD predicts both ischemic and bleedings events at one year follow-up for ACS patients undergoing PCI