Development of a Standard Test Scenario to Evaluate the Effectiveness of Portable Fire Extinguishers on Lithium-ion Battery Fires

Many sources of fuel are present aboard current spacecraft, with one especially hazardous source of stored energy: lithium ion batteries. Lithium ion batteries are a very hazardous form of fuel due to their self-sustaining combustion once ignited, for example, by an external heat source. Batteries can become extremely energetic fire sources due to their high density electrochemical energy content that may, under duress, be violently converted to thermal energy and fire in the form of a thermal runaway. Currently, lithium ion batteries are the preferred types of batteries aboard international spacecraft and therefore are routinely installed, collectively forming a potentially devastating fire threat to a spacecraft and its crew. Currently NASA is developing a fine water mist portable fire extinguisher for future use on international spacecraft. As its development ensues, a need for the standard evaluation of various types of fire extinguishers against this potential threat is required to provide an unbiased means of comparing between fire extinguisher technologies and ranking them based on performance

Fuel Cell Airframe Integration Study for Short-Range Aircraft

The objective of this study is to define the functionality and evaluate the propulsion and power system benefits derived from a Solid Oxide Fuel Cell (SOFC) based Auxiliary Power Unit (APU) for a future short range commercial aircraft, and to define the technology gaps to enable such a system. United Technologies Corporation (UTC) Integrated Total Aircraft Power System (ITAPS) methodologies were used to evaluate a baseline aircraft and several SOFC architectures. The technology benefits were captured as reductions of the mission fuel burn, life cycle cost, noise and emissions. As a result of the study, it was recognized that system integration is critical to maximize benefits from the SOFC APU for aircraft application. The mission fuel burn savings for the two SOFC architectures ranged from 4.7 percent for a system with high integration to 6.7 percent for a highly integrated system with certain technological risks. The SOFC APU itself produced zero emissions. The reduction in engine fuel burn achieved with the SOFC systems also resulted in reduced emissions from the engines for both ground operations and in flight. The noise level of the baseline APU with a silencer is 78 dBA, while the SOFC APU produced a lower noise level. It is concluded that a high specific power SOFC system is needed to achieve the benefits identified in this study. Additional areas requiring further development are the processing of the fuel to remove sulfur, either on board or on the ground, and extending the heat sink capability of the fuel to allow greater waste heat recovery, resolve the transient electrical system integration issues, and identification of the impact of the location of the SOFC and its size on the aircraft

Etude du depot de nitrure de silicium sur GaAs par pulverisation cathodique reactive RF magnetron

SIGLEINIST T 75238 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Combustion modeling of ethylene /oxygen and allene /oxygen mixtures: Chemical oxidation mechanisms and numerical solution of the non-adiabatic flame equations

The objective of this work is to improve the understanding of combustion chemistry by modeling the chemical and physical characteristics of ethylene and allene reacting mixtures in a wide variety of combustion systems. This is of critical importance for environmental and economic reasons today: formation of air toxics whose emissions are regulated by the U.S. Clean Air Act Amendments, optimization of engines output, and reformulation of fuels, for example. First, a reaction set containing 731 reactions of 85 species was assembled from the literature and theoretical calculations. The mechanism focuses on the C2 and C3 hydrocarbons reactions but it also includes heavier species up to C6 hydrocarbons such as benzene and phenyl. New rate constants for the reactions of the key system C2H 3+O2 were calculated theoretically and rate constants for the C3H3 recombination reaction were inferred from the recent literature. This reaction set was then used in simulations of shock-tubes, flow reactors and especially flame experiments in various conditions. The predictions obtained throughout the study are generally in good agreement with the experimental data and establishes the overall high-quality of the reaction set. However, in the case of a fuel-lean (&phis; = 0.70) ethylene flame, the predicted profiles of key radicals are not within the experimental uncertainty. The modeling of important reactions involving radicals such as H+O2 in this environment may still be inaccurate. A novel approach to flat-flame modeling is also introduced. External heat losses by radiation are included in the energy conservation equation for the first time. This improvement of the model allows the temperature profile to be computed in the case of real, non-adiabatic flames. The analysis of the predictions shows that temperature is greatly affected by the presence of soot in fuel-rich flames. In fuel-lean flames, insufficient heat is generated by the mechanism at low temperature. Finally, net heat flux analysis is used to demonstrate the very good agreement of the predictions with data of the fuel-rich flame and quantify the discrepancy in the case of the fuel-lean flame

Facteurs explicatifs de la démobilisation chez les diplômés universitaires récemment embauchés

Numéro de référence interne originel : A1.328 WP 990

Amorphous to Crystal Conversion As a Mechanism Governing the Structure of Luminescent YV04:Eu Nanoparticles

International audienceThe development of functional materials by taking advantage of the physical properties of nanoparticles needs an optimal control over their size and crystal quality. In this context, the synthesis of crystalline oxide nanoparticles in water at room temperature is a versatile and industrially appealing process, but lacks control especially for "large" nanoparticles (> 30 nanometres), which commonly consist of agglomerates of smaller crystalline primary grains. Improvement of these syntheses is hampered by the lack of knowledge on possible intermediate, non-crystalline stages, although their critical importance has already been outlined in crystallisation processes. Here, we combine time-resolved, in situ SAXS/WAXS and EXAFS to demonstrate that during the synthesis of luminescent Eu-doped YV04 nanoparticles, a transient amorphous network forms with a two-Ievel structuration. These two pre-structuration scales constrain topologically the nucleation of the nanometre-sized crystalline primary grains within the amorphous network, and their aggregation in nanoparticles, respectively. The amorphous network, which forms within 40 ms, therefore determines the nanocrystalline structure, which forms in the minute range. This template effect not only clarifies why the crystal size is found independent of the nucleation rate, in contradiction with the classical nucleation theory, but also supports the possibility to control the final nanostructure with the amorphous phase

Cytotoxic and Genotoxic Impact of TiO2 Nanoparticles on A549 Cells

International audienceTitania nanoparticles are produced by tons, and included in commercial products, raising concerns about their potential impact on human health. This study relates their cytotoxic and genotoxic impact on a cell line representative of human lung, namely A549 alveolar epithelial cells

Oxide nanoparticles in water : amorphous to crystal conversion of luminescent yttrium vanadate

International audienc

Prévalence à la maternité des facteurs de risque de développer une obésité infantile

Introduction : Durant la période périnatale plusieurs facteurs de risque maternels et obstétricaux sont connus pour être associés au surpoids et à l’obésité infantile. Méthode : Une étude de la prévalence des facteurs de risque d’obésité infantile a été menée à partir du dossier médical de 1977 femmes ayant accouché à la maternité du CHU de Bordeaux entre le 01/06/2016 et le 30/06/2017. Résultats : Les femmes avaient un âge moyen de 31,6 ans [±5,2] et un IMC moyen était de 23,9 kg/m2 [±4,9] en début de grossesse. Un tiers d’entre-elles était en surpoids ou obèses, et la moitié ont eu une prise de poids excessive. Un diabète gestationnel était survenu chez 15,9 % des femmes, 15,9 % ont fumé pendant la grossesse, et 18,1 % étaient en situation de précarité. Les enfants sont nés par césarienne dans 15,3 % des cas. Selon la définition utilisée, poids exact de naissance (PN) ou formule Audipog (percentile), ils étaient macrosomes dans respectivement 6,7 % des cas (PN> 4000 g) ou 11 % (>90e percentile) et hypotrophes dans respectivement 3 % des cas (PN 4000 g) respectively, or 11% (> 90th percentile) and small for gestational age in 3% of cases (BW < 2500 g) and 6.8% (< 10th percentile) respectively. They were immediately formula fed in 28.7% of cases. Conclusion : This study gives informations on the prevalence of childhood obesity risk factors present at birth. Based on them, the development of a risk score will allow the identification of newborns at risk in order to put in place early actions to prevent childhood obesity from maternity unit

Elucidating non-classical nucleation of nanocrystals from an amorphous intermediate state

International audienceWhile nanoparticles are attractive because of their peculiar properties, their production remains a challenge. Their attributes mostly depend on size and surface state, but also on their microstructure. However, this structure (size, shape, porosity, crystalline quality) is currently only controlled via trial-error experimentations and poorly described by the only tool available, the classical nucleation theory (CNT), especially for oxide nanoparticles synthesised in water. Luminescent, europium-doped yttrium vanadate (YVO$_4$: Eu) illustrates nicely how important tuning the properties at the nanometric scale is. For light emission applications, a good crystalline quality and low surface to volume ratio is required, whereas porosity and high surface area will be key for chemical sensor applications. This branching makes it crucial to understand the mechanisms of formation of these objects in order to have precise control on their structure and thus on their properties. In this work, we focused on elucidating how crystalline YVO4 is formed in water. A first striking result is that tuning the initial pH leads to two critical microstructures : (i) the "expected" [4], porous, one, with nanoparticles ~20nm wide composed of subunits of 2nm, (ii) a new, monocrystalline-like one, with particles 30nm large and no primary unit detected. To understand this difference, we conducted luminescence, pH, ICP-MS, and SAXS/WAXS/XRD studies during the reaction from reaction times as short as 5ms. In particular, we could show the existence of an amorphous intermediate state in both cases and its impact on the particles' size and microstructure, and measure nucleation rates within the disordered network to improve nucleation theories