PIV and Electrodiffusion diagnostics of flow field, wall shear stress and mass transfer beneath three round submerged impinging jets

International audienceThis paper reports on measurements of velocities, wall shear rates and mass transfer in an impinging round jet issued from a round nozzle. The effect of the nozzle shape on transfer phenomena was investigated. A round orifice perforated either on a flat plate (RO/P) or on a hemispherical surface (RO/H) was compared to a reference convergent nozzle (CONV). All the nozzles have the same exit diameter D. The exit volumetric flow rate was also conserved and led to the same Reynolds number based on the exit bulk velocity, Reb = 5620. The nozzle-to-wall distance was constant and equal to 2D. The Particle Image Velocimetry technique (PIV) was used to capture the jet flow field. The limitations of the PIV technique in the vicinity of the target disc are addressed by using the electrodiffusion technique (ED) to obtain the wall shear rate distribution. The ED technique was extended for the measurement of local mass transfer distribution and global mass transfer on the target disc. The whole velocity field, wall shear rates and mass transfer in the three impinging round jets were compared. It was shown that at constant volumetric flow rate, the use of an orifice nozzle not only improves wall shear rate, but also increases local and global mass transfer. The global mass transfer on a target disc of a 3.2 D diameter is 25% and 31% higher for RO/H and RO/P nozzles, respectively, compared to the reference CONV nozzle. The orifice nozzles generate narrower exit profiles relatively to the convergent nozzle. The vena contracta effect in orifice jets, more intense with RO/P than with RO/H, generates an increase of the exit centerline velocity. The hemispherical surface of RO/H nozzle stretches the flow at the exit and somewhat attenuates the vena contracta effect. The characteristic scale representation of the data confirms the origin of the observed differences between the three jets. A link between the wall shear stress and the mass transfer is revealed. The wall shear rate and the mass transfer are in a close relationship with the near field flow features, themselves affected by the nozzle geometry. Time-resolved tomographic PIV technique reveals that the wall shear rate fluctuation is related to the dynamics of the jet coherent structures. The instantaneous PIV fields indicates the formation of secondary vortices in the region where a secondary peak in local mass transfer emerges. The level of this secondary peak is sensitive to the nozzle shape. The higher is the jet acceleration, the more intense is the level of the secondary pea

The Genome Sequence of the Grape Phylloxera Provides Insights into the Evolution, Adaptation, and Invasion Routes of an Iconic Pest

Background: Although native to North America, the invasion of the aphid-like grape phylloxera Daktulosphaira vitifoliae across the globe altered the course of grape cultivation. For the past 150 years, viticulture relied on grafting-resistant North American Vitis species as rootstocks, thereby limiting genetic stocks tolerant to other stressors such as pathogens and climate change. Limited understanding of the insect genetics resulted in successive outbreaks across the globe when rootstocks failed. Here we report the 294-Mb genome of D. vitifoliae as a basic tool to understand host plant manipulation, nutritional endosymbiosis, and enhance global viticulture. Results: Using a combination of genome, RNA, and population resequencing, we found grape phylloxera showed high duplication rates since its common ancestor with aphids, but similarity in most metabolic genes, despite lacking obligate nutritional symbioses and feeding from parenchyma. Similarly, no enrichment occurred in development genes in relation to viviparity. However, phylloxera evolved > 2700 unique genes that resemble putative effectors and are active during feeding. Population sequencing revealed the global invasion began from the upper Mississippi River in North America, spread to Europe and from there to the rest of the world. Conclusions: The grape phylloxera genome reveals genetic architecture relative to the evolution of nutritional endosymbiosis, viviparity, and herbivory. The extraordinary expansion in effector genes also suggests novel adaptations to plant feeding and how insects induce complex plant phenotypes, for instance galls. Finally, our understanding of the origin of this invasive species and its genome provide genetics resources to alleviate rootstock bottlenecks restricting the advancement of viticulture

Intermetallic alloys for energy conversion : Anodes for metal / air fuel cells

Ce travail s'inscrit dans une thématique générale centrée sur la production et le stockage de l'énergie. L'étude concerne les systèmes de conversion de type métal-air, MAFC (Métal Air Fuel Cells) qui font partie de la famille des piles à combustible. L'anode consommable joue un rôle essentiel de réservoir d'énergie, déterminant dans les caractéristiques et les performances de ces dispositifs. La recherche de matériaux de substitution au métal de l'anode a été la motivation principale et le cadre de ce travail a été limité aux matériaux à base de magnésium. Les matériaux sélectionnés ont été préparés par différentes voies de synthèse et caractérisés par diffraction des rayons X et microscopie électronique. Les structures cristallines complexes et désordonnées de trois phases intermétalliques ont été résolues. L'étude des comportements électrochimiques de ces matériaux a permis de déterminer leur résistance à la corrosion en milieu salin et alcalin. La méthode de mise en forme s'est avérée importante pour ces matériaux dont les comportements varient en fonction de la compacité de l'électrode. Les performances des matériaux utilisés comme anode ont été évaluées au sein de piles de type métal air face à une cathode de Pd/C alimentée par un flux continu d'oxygène. Parmi les composés sélectionnés figurent MgB2 (structure en feuillets), Mg2Si (structure covalente), Mg3Ag, Mg4Ag et Mg2Al3 aux structures complexes basées sur des empilements polyédriques compacts. C'est le composé intermétallique Mg2Al3 qui a montré les comportements les plus intéressants avec une remarquable stabilité dans le temps au sein d'une pile.This work takes place within a general framework centered on energy production and storage. It concerns the Metal Air Fuel Cell (MAFC) devices which are a part of the fuel cells family. The anode, as an energy reserve, plays an essential part in the characteristics and the performances of these systems. The main goal of this work, which has been limited to Mg-based compositions, was to find substitution materials for the metal at anode. The selected materials have been prepared by various methods and characterized by X-ray diffraction and electron microscopy. Three complex and disordered structures have been solved. Electrochemical studies were employed to determine the corrosion resistance in saline and alkaline media. The conditioning of the electrodes appeared important because materials behavior can vary with the density of the electrode. Performances of materials used as anodes in metal air cells with a Pd/C oxygen cathode have been determined.The selected compounds include MgB2 (layered structure), Mg2Si (covalent simple arrangement), Mg3Ag, Mg4Ag and Mg2Al3 with complex structures that involve compact polyhedral packing. The best results are obtained with Mg2Al3 that presents a remarkably stable behavior in a metal air device

Mg2Al3, a complex and disordered intermetallic compound as anode material for metal-air batteries

International audienc

Alliages intermétalliques du magnésium, anodes pour MAFC ? Magnesium intermetallic alloys, anodes for MAFC?

Des composés intermétalliques sélectionnés ont été étudiés en vue d'une utilisation en remplacement de l'anode métallique dans des batteries de type métal air. Ces composés présentent des structures cristallines très différentes : structure lamellaire pour MgB2, structure covalente simple pour Mg2Si et structure complexe basée sur un empilement compact de polyèdres pour Mg2Al3. Les meilleurs résultats sont obtenus pour ce dernier composé avec une réactivité vis-à-vis des électrolytes testés sensiblement inférieure à celle du magnésium et une cinétique de réaction plus lente. Le potentiel en fonctionnement au sein de la batterie est sensiblement plus faible que celui du magnésium mais il présente une stabilité remarquable au cours du temps. Selected intermetallic compounds have been studied as anodic materials in metal air fuel cells. These compounds have different structural types, MgB2 displays a lamellar structure, Mg2Si a simple covalent structure while Mg2Al3 has a complex structure based on compact polyhedral packing. Best electrochemical results are obtained for the latter, with a lower reactivity towards magnesium in the two electrolytes and with lower kinetics of reaction. The operating potential of the battery with a Mg2Al3 anode is noticeably lower than with a Mg anode, but it presents a very good stability over time

On the adaptability of 1/1 cubic approximant structure in the Mg­Al­Zn system with the particular example of Mg32Al12Zn2Zn37

International audienceIntermetallic Mg alloys are of interest in the development of light materials with specific properties andsome of them are crystalline approximants of quasicrystalline materials. Mg32Al12Zn37 single crystalstructure, cubic, Im3, a = 14.1845(1) Å, is disordered and belongs to the well known 1/1 approximantstructural type commonly called Mg32(Al1-xZnx)49 or T-phase. In this family, Mg32Al12Zn37 is a newmember remarkable for its very special composition nearby intersection of the 2/1 and 1/1 lines thatmark composition domains of cubic 2/1 and 1/1 approximants. Structural features are discussedcomparatively with literature data to emphasize the great adaptability through atom disorder of the 1/1structure

Alliages intermétalliques du magnésium, anodes pour MAFC ?

Des composés intermétalliques sélectionnés ont été étudiés en vue d'une utilisation en remplacement de l'anode métallique dans des batteries de type métal air. Ces composés présentent des structures cristallines très différentes : structure lamellaire pour MgB2, structure covalente simple pour Mg2Si et structure complexe basée sur un empilement compact de polyèdres pour Mg2Al3. Les meilleurs résultats sont obtenus pour ce dernier composé avec une réactivité vis-à-vis des électrolytes testés sensiblement inférieure à celle du magnésium et une cinétique de réaction plus lente. Le potentiel en fonctionnement au sein de la batterie est sensiblement plus faible que celui du magnésium mais il présente une stabilité remarquable au cours du temps

Le malmenage vocal

Thèse : Médecine : Université de Bordeaux : 1906N° d'ordre : 10