182 research outputs found
Investigation of Graded La2NiO4+ Cathodes to Improve SOFC Electrochemical Performance
Mixed ionic and electronic conducting MIEC oxides are promising materials for use as cathodes in solid oxide fuel cells SOFCs due to their enhanced electrocatalytic activity compared with electronic conducting oxides. In this paper, the MIEC oxide La2NiO4+ was prepared by the sol-gel route. Graded cathodes were deposited onto yttria-stabilized zirconia YSZ pellets by dip-coating, and electrochemical impedance spectroscopy studies were performed to characterize the symmetrical cell performance. By adapting the slurries, cathode layers with different porosities and thicknesses were obtained. A ceria gadolinium oxide CGO barrier layer was introduced, avoiding insulating La2Zr2O7 phase formation and thus reducing resistance polarization of the cathode. A systematic correlation between microstructure, composition, and electrochemical performance of these cathodes has been performed. An improvement of the electrochemical performance has been demonstrated, and a reduction in the area specific resistance ASR by a factor of 4.5 has been achieved with a compact interlayer of La2NiO4+ between the dense electrolyte and the porous La2NiO4+ cathode layer. The lowest observed ASR of 0.11 cm2 at 800Ă°C was obtained from a symmetrical cell composed of a YSZ electrolyte, a CGO interlayer, an intermediate compact La2NiO4+ layer, a porous La2NiO4+ electrode layer, and a current collection layer of platinum paste
Analysis of TerraSAR-X data and their sensitivity to soil surface parameters over bare agricultural fields
International audienceCette recherche a pour objectif de mettre en évidence la contribution des capteurs haute résolution pour une meilleure caractérisation de la surface du sol et pour analyser les effets de la polarisation et de l'angle d'incidence radar. L'objectif de cet article est d'analyser la sensibilité des données haute résolution Terrassar-X sur des sols sans couverture végétale et d'étudier la variabilité spatiale. Les relations entre le coefficient de rétrodiffusion et les paramÚtres du sol seront étudiés grùce aux images (TerraSAR, Ikonos, SPOT) ainsi que grùce aux mesures de terrain recueillies pendant plusieurs campagnes de terrain en hiver et printemps 2008-2009. Ce travail a été mené sur le bassin de l'Orgeval (France). / Our research aims to show the contribution of high resolution spatial sensors for a better characterization of soil surface, and to analyze polarization effects and radar incidence angle. The objective of this paper is to analyze the sensitivity of very high resolution TerraSAR-X radar data taken over bare soils, and to study the spatial variability. The relationship between backscattering coefficient and soil's parameters (moisture, surface roughness, and texture) will be examined by means of satellite images (TerraSAR, Ikonos, SPOT), as well as ground truth measurements, recorded during several field campaigns in the winter and spring of 2008 and 2009. This study is carried out on Orgeval catchment (France)
Preparation of NiâYSZ thin and thick films on metallic interconnects as cell supports. Applications as anode for SOFC
In this work, we propose the preparation of a duplex anodic layer composed of both a thin (100 nm) and a thick film (10 lm) with NiâYSZ material. The support of this anode is a metallic substrate, which is the interconnect of the SOFC unit cell. The metallic support limits the temperature of thermal treatment at 800 C to keep a good interconnect mechanical behaviour and to reduce corrosion. We have chosen to elaborate anodic coatings by solâgel route coupled with dip-coating process, which are low cost techniques and allow working with moderate temperatures. Thin films are obtained by dipping interconnect substrate into a sol, and thick films into an optimized slurry. After thermal treatment at only 800 C, anodic coatings are adherent and homogeneous. Thin films have compact microstructures that confer ceramic protective barrier on metal surface. Further coatings of 10 lm thick are porous and constitute the active anodic material
Modelling of the radiative properties of an opaque porous ceramic layer
Solid Oxide Fuel Cells (SOFCs) operate at temperatures above 1,100 K where radiation effects can be significant. Therefore, an accurate thermal model of an SOFC requires the inclusion of the contribution of thermal radiation. This implies that the thermal radiative properties of the oxide ceramics used in the design of SOFCs must be known. However, little information can be found in the literature concerning their operating temperatures. On the other hand, several types of ceramics with different chemical compositions and microstructures for designing efficient cells are now being tested. This is a situation where the use of a numerical tool making possible the prediction of the thermal radiative properties of SOFC materials, whatever their chemical composition and microstructure are, may be a decisive help. Using this method, first attempts to predict the radiative properties of a lanthanum nickelate porous layer deposited onto an yttria stabilized zirconium substrate can be reported
DĂ©veloppement dâun procĂ©dĂ© de revĂȘtement zinc-Nickel rĂ©pondant aux exigences du secteur aĂ©ronautique
La sociĂ©tĂ© MECAPROTEC Industries en collaboration avec les laboratoires CIRIMAT et ELECTRODEP, dĂ©veloppe un procĂ©dĂ© de dĂ©pĂŽt ZnNi rĂ©pondant aux exigences du secteur aĂ©ronautique, en vue de la substitution du cadmiage Ă©lectrolytique. Ces exigences, diffĂ©rentes de celles du secteur automobile, imposent de nouveaux critĂšres de choix qui viennent sâajouter Ă celui du comportement en corrosion. Ainsi, pour des piĂšces en aciers Ă haute rĂ©sistance mĂ©canique, les procĂ©dĂ©s Ă©lectrolytiques peuvent ĂȘtre Ă lâorigine dâune fragilisation des piĂšces par occlusion dâhydrogĂšne. Il est donc indispensable pour le dĂ©veloppement de ce nouveau procĂ©dĂ© et son application Ă des ensembles aĂ©ronautiques, dâĂ©valuer ce risque Ă partir dâessais normalisĂ©s et dây remĂ©dier. De plus, dans le cas d'applications sur des assemblages vissĂ©s, les caractĂ©ristiques tribologiques des alliages ZnNi devront ĂȘtre adaptĂ©es afin dâĂ©viter les risques de grippage. Du point de vue anticorrosion, un post-traitement de finition par chromatation est souvent utilisĂ© pour accroĂźtre les performances des revĂȘtements cadmiĂ©s. Dans le cas des revĂȘtements ZnNi, il conviendra bien sĂ»r dâatteindre des performances identiques en utilisant un traitement de finition sans chromate. Câest ce que nous tentons de faire en dĂ©veloppant un procĂ©dĂ© de finition par voie sol-gel. Pour rendre compatible le procĂ©dĂ© ZnNi avec toutes ou partie de ces contraintes, des recherches amonts sont rĂ©alisĂ©es en parallĂšle des nvestigations industrielles. Le but est de tendre vers une maĂźtrise complĂšte du procĂ©dĂ© et pour cela, de rechercher quels sont les paramĂštres opĂ©ratoires qui conditionnent les aractĂ©ristiques des dĂ©pĂŽts afin dâadapter celles-ci, Ă celles imposĂ©es par les exigences aĂ©ronautiques
Advances in the control of electrophoretic process parameters to tune the ytterbium disilicate coatings microstructure
Suspensions of ytterbium disilicate in isopropanol were prepared using iodine dispersant. Their zeta potential, electrical conductivity, and pH dependence with iodine concentration is detailed. Electrophoretic deposition was performed on silicon substrates at various voltages (100â200 V) and times (until 10 minutes) and the growth dynamic was investigated. It was observed that the deposited mass reaches a maximum value for [I2] = 0.2 g/L, and the coating microstructure becomes porous at higher iodine concentrations. Current density and voltage measurements allowed to correlate this behavior to the increase of free protons concentration in the suspension. In these conditions, it was proved that porosity increases with the increase in applied voltage, and a compaction occurs as the deposition time increases. This has been related to the coating resistance increase and subsequent decrease in effective voltage in the suspension. The denser coatings (20% of porosity) were obtained in the case of suspension without iodine, at the minimum applied voltage and for the longest deposition times
Synthesis of La2NiO4+d oxides by solâgel process: Structural and microstructural evolution from amorphous to nanocrystallized powders
In this paper, the structural and microstructural transition from amorphous to La2NiO4+d nanocrystallized oxides synthesized by a polymeric route based on Pechiniâs work has been studied by several experimental techniques including infrared spectroscopy and wide angle X-ray scattering. The synthesis parameters which govern this transition have been identified in order to synthesize La2NiO4+d oxides with various mean crystallite sizes and non stoichiometry levels. Therefore, it has been demonstrated that the control of the nature and the content of organic compounds in the polymeric sols allows the preparation of La2NiO4+d metastable phases with a mean crystallite size ranging from 100 to 220 nm and a non stoichiometry level ranging from 0.15 to 0.22 at 25 8C. As the cathodic performance strongly depends on the physical characteristics of the oxides, this study shows that our versatile process may be suitable to elaborate electrodes with different electrochemical behaviours
Crise social extrema, processos identificatĂłrios e resistĂȘncia psĂquica Os Druzos na guerra do LĂbano
Functional modulation and directed assembly of an enzyme through designed non-natural post-translation modification
Post-translational modification (PTM) modulates and supplements protein functionality. In nature this high precision event requires specific motifs and/or associated modification machinery. To overcome the inherent complexity that hinders PTM's wider use, we have utilized a non-native biocompatible Click chemistry approach to site-specifically modify TEM ÎČ-lactamase that adds new functionality. In silico modelling was used to design TEM ÎČ-lactamase variants with the non-natural amino acid p-azido-L-phenylalanine (azF) placed at functionally strategic positions permitting residue-specific modification with alkyne adducts by exploiting strain-promoted azideâalkyne cycloaddition. Three designs were implemented so that the modification would: (i) inhibit TEM activity (Y105azF); (ii) restore activity compromised by the initial mutation (P174azF); (iii) facilitate assembly on pristine graphene (W165azF). A dibenzylcyclooctyne (DBCO) with amine functionality was enough to modulate enzymatic activity. Modification of TEMW165azF with a DBCOâpyrene adduct had little effect on activity despite the modification site being close to a key catalytic residue but allowed directed assembly of the enzyme on graphene, potentially facilitating the construction of protein-gated carbon transistor system
Influenza Infectious Dose May Explain the High Mortality of the Second and Third Wave of 1918â1919 Influenza Pandemic
BACKGROUND:
It is widely accepted that the shift in case-fatality rate between waves during the 1918 influenza pandemic was due to a genetic change in the virus. In animal models, the infectious dose of influenza A virus was associated to the severity of disease which lead us to propose a new hypothesis. We propose that the increase in the case-fatality rate can be explained by the dynamics of disease and by a dose-dependent response mediated by the number of simultaneous contacts a susceptible person has with infectious ones.
METHODS:
We used a compartment model with seasonality, waning of immunity and a Holling type II function, to model simultaneous contacts between a susceptible person and infectious ones. In the model, infected persons having mild or severe illness depend both on the proportion of infectious persons in the population and on the level of simultaneous contacts between a susceptible and infectious persons. We further allowed for a high or low rate of waning immunity and volunteer isolation at different times of the epidemic.
RESULTS:
In all scenarios, case-fatality rate was low during the first wave (Spring) due to a decrease in the effective reproduction number. The case-fatality rate in the second wave (Autumn) depended on the ratio between the number of severe cases to the number of mild cases since, for each 1000 mild infections only 4 deaths occurred whereas for 1000 severe infections there were 20 deaths. A third wave (late Winter) was dependent on the rate for waning immunity or on the introduction of new susceptible persons in the community. If a group of persons became voluntarily isolated and returned to the community some days latter, new waves occurred. For a fixed number of infected persons the overall case-fatality rate decreased as the number of waves increased. This is explained by the lower proportion of infectious individuals in each wave that prevented an increase in the number of severe infections and thus of the case-fatality rate.
CONCLUSION:
The increase on the proportion of infectious persons as a proxy for the increase of the infectious dose a susceptible person is exposed, as the epidemic develops, can explain the shift in case-fatality rate between waves during the 1918 influenza pandemic.TD acknowledges the support of the Faculdade de Ciencias e Tecnologia through grant PPCDT/AMB/55701/2004. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript
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