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Flow structure and loads over inclined cylindrical rodlike particles and fibers
Get PDFThe flow past a fixed finite-length circular cylinder, the axis of which makes a nonzero angle with the incoming stream, is studied through fully resolved simulations, from creeping-flow conditions to strongly inertial regimes. The investigation focuses on the way the body aspect ratio χ (defined as as the length-to-diameter ratio), the inclination angle θ with respect to the incoming flow, and the Reynolds number Re (based on the cylinder diameter) affect the flow structure past the body and therefore the hydrodynamic loads acting on it. The configuration θ = 0◦ (where the cylinder is aligned with the flow) is first considered from creeping-flow conditions up to Re = 400, with aspect ratios up to 20 (10) for Re 10^2), separation takes place along the upstream part of the lateral surface of the cylinder, deeply influencing the surface stress distribution. Numerical results are used to build empirical models for the force components and the torque, valid for moderately inclined cylinders
(|θ| ≤ 30◦) of arbitrary aspect ratio up to Re ≈ 300 and matching those obtained at low-to-moderate Reynolds number
Multidisciplinary Design and Architecture Optimization of a Reusable Lunar Lander
Get PDFWith renewed interest in lunar exploration and the upcoming deployment of the lunar space station, the Lunar Orbital Platform-Gateway (LOP-G), a scientific community, is focusing on the design of a lander to bring people back to the lunar surface. This work focuses on optimizing two aspects of the lunar lander concurrently: the mission architecture and the vehicle design, often treated independently in the literature. A methodology is introduced to enumerate and preliminarily rank all possible mission architectures. The best mission architectures are then coupled with a multidisciplinary design optimization process by modeling the various components of the spacecraft and optimizing over a set of design parameters. The need for fast computational models, particularly in trajectory optimization, resulted in an analytical approximation of gravitational losses. This work resulted in a hierarchy of mission architectures that are ranked according to the average mass necessary to perform the mission. This work is intended to help a system engineer designing a lunar lander in choosing the best number of vehicles, the number of reuses, and the mission profile for his/her mission requirements
Experimental and numerical study for direct powder bed selective laser processing (sintering/melting) of silicon carbide ceramic
Get PDFThe study was carried out to investigate the manufacturing possibility of Silicon Carbide (SiC) by direct Powder Bed Selective Laser Processing (PBSLP) experimentally and numerically. The experimental study was carried out by means of PBSLP while the numerical study was accomplished by developing a CFD model. The CFD model simulates accurately realistic conditions of the PBSLP process. A user-defined code, that describes the process parameters such as laser power, scanning speed, scanning strategies, and hatching distance has been developed and compiled to ANSYS FLUENT 2020 R1. Also, the model was validated with the available published data from the literature. The model was used to deeply analyse and support the results obtained through the experimental runs. Different values of laser power and scanning speeds with scanning strategy in the form of a continuous linear pattern and rotated by 90 degrees between layers were studied. The laser power is ranging from 52W to 235 W while the scanning speed is ranging from 300 to 3900 mm s−1. The results showed that the direct PBSLP of SiC is possible with the optimization of the process parameters. Layer thickness and hatching distance are the most important parameters that needed to be optimized. Also, the laser power and scanning speed needed to be adjusted so that the scanning temperature was between the sintering and the decomposition limits. The good agreement between experimental and simulation results proved the power and ability of the developed CFD model to be a useful tool to analyse and optimize future experimental data
Polystyrene Hybrid-Vitrimer Based on the Hemiacetal Ester Exchange Reaction
Get PDFVitrimer materials, which are permanently cross-linked but reshapable polymers, are a class of materials of growing interest due to their potential in recycling and sustainable development. More precisely, vitrimers derived from commodity polymers could have a drastic impact on plastic consumption in the upcoming years. Here, the development of a polystyrene-based vitrimer harnessing the recently discovered hemiacetal ester exchange reaction of carboxylic acid is presented. 1,4-Cyclohexanedimethanol divinyl ether was reacted with 4-vinylbenzoic acid (VBA) to form a divinyl species containing two hemiacetal ester functions. This dimer was then copolymerized with styrene, butyl acrylate, and VBA to form a cross-linked material presenting pendent acid groups. This material exhibited three distinct behaviors at different temperature regimes: below 80 °C, despite the exchange reactions able to occur at this temperature, the cross-linked material behaved as a frozen material due to the hydrogen bonding formed by the carboxylic acid pendent groups. Between 80 and 130 °C, the vitrimer behavior was demonstrated by rheological creep experiments. At higher temperatures, the dissociation of the hemiacetal ester groups led to the loss of the covalent cross-linking
Densification of surface-modified silicon carbide powder by spark-plasma-sintering
Get PDFSiC was densified by spark plasma sintering (SPS) and the effects of surface modification of the powder particles on its sintering behavior were investigated. The pressure and temperature conditions were set to 50 MPa and 2200 °C, respectively. Specific SPS experiments at a lower temperature (i.e. 1600 °C) was performed to analyze the efficiency of the sintering and the early stage of the densification in softer conditions. The surface functionalization was carried out by grafting a thin molecular layer of a preceramic precursor on the grain surface of SiC particles, which acts as a sintering additive without producing contamination by heteroatoms since, in addition to hydrogen, it contained only Si and C in the same ratio 1:1 as silicon carbide. One of the advantages of this surface functionalization is that it reduces the temperature at which the sintering process begins and therefore it facilitates and increases the densification of the final SiC parts
Covalent Grafting of Ruthenium Complexes on Iron Oxide Nanoparticles: Hybrid Materials for Photocatalytic Water Oxidation
Get PDFThe present environmental crisis prompts the search for renewable energy sources such as solar-driven production of hydrogen from water. Herein, we report an efficient hybrid photocatalyst for water oxidation, consisting of a ruthenium polypyridyl complex covalently grafted on core/shell Fe@FeOx nanoparticles via a phosphonic acid group. The photoelectrochemical measurements were performed under 1 sun illumination in 1 M KOH. The photocurrent density of this hybrid photoanode reached 20 μA/cm2 (applied potential of +1.0 V vs reversible hydrogen electrode), corresponding to a turnover frequency of 0.02 s–1. This performance represents a 9-fold enhancement of that achieved with a mixture of Fe@FeOx nanoparticles and a linker-free ruthenium polypyridyl photosensitizer. This increase in performance could be attributed to a more efficient electron transfer between the ruthenium photosensitizer and the Fe@FeOx catalyst as a consequence of the covalent link between these two species through the phosphonate pendant group
Déterminants psycho-sociaux associés aux pratiques de prescription d'antibiotiques par les vétérinaires : étude en filières avicoles
Get PDFL’usage raisonné des antibiotiques en élevage constitue l’un des leviers majeurs de lutte contre l’antibiorésistance. Dans ce contexte, l’objectif de la thèse vise à identifier les facteurs psycho-sociaux associés aux pratiques de prescription d’antibiotiques par les vétérinaires. Seize entretiens semi-dirigés ont été réalisés auprès de vétérinaires exerçant en production avicole. L’approche retenue est celle de la Méthode Biographique Narrative Interprétative (« BNIM »), complétée d’une analyse thématique qualitative. Ces travaux analysent le cheminement des connaissances - de la théorie à la pratique - des vétérinaires en production aviaires mobilisées lors de la prescription d’antibiotiques. Ils soulignent l’importance des échanges entre pairs (notamment en début de carrière, via un processus de compagnonnage entre vétérinaires) dans les pratiques mises en œuvre sur le terrain. Un deuxième axe d’analyse met en lumière les changements de pratiques de prescription opérés par les vétérinaires, sous l’effet de différents leviers (politiques publiques, attentes sociétales, rôle clé des organisations de production). Enfin, ces travaux mettent en évidence l’importance de nouvelles tensions – entre réduction des usages d’antibiotiques et maintien du bien-être animal, auxquelles se trouvent aujourd’hui exposés les vétérinaires
Mesure de la production sébacée chez le chien : comparaison de deux méthodes
Get PDFLa dermatologie est un domaine médical représentant une grande part des consultations vétérinaires et de nombreux produits (lotions, shampoings) sont mis au point grâce aux essais cliniques. Cette thèse expérimentale a pour but de mesurer la production sébacée chez le chien à l’aide d’instruments utilisés en médecine humaine afin de pouvoir utiliser la quantité de sébum comme paramètre supplémentaire lors de ces essais en pratique courante. Dans un premier temps, la peau mais surtout la production sébacée des chiens sont décrites afin de comprendre l’intérêt de la mesure du sébum lors de suivis d’animaux souffrant de pathologies dermatologique. Les expérimentations ainsi que les résultats sont ensuite présentés. Enfin, la discussion est amenée afin de comprendre les résultats obtenus. Ces expérimentations n’ont pas montré de concordance entre les instruments, leur utilisation n’est donc pas possible
Modulation of pollen tube growth by ethylene signaling
Get PDFEthylene is a phytohormone controlling many processes of plant development. The importance of this hormone in fruit set regulation has been reported, but there are still gaps in our knowledge. The first chapter is dedicated to a review of the role of ethylene in the different stages of fruit set, as well as the role of auxin. Briefly, ethylene is involved in the pollen germination in the stigma, the pollen tube growth through the transmission tissues in the style and finally the fertilization of the ovule. The second chapter is centered on pollen tube (PT) elongation. Two opposite lines of Ethylene Receptors (ETRs) mutants were used: etr3-ko, a loss-of-function (LOF) mutant; and NR (Never Ripe), a gain of function (GOF) mutant. We showed that PT of etr3-ko grew faster than WT (Wild Type). On the contrary, NR PT elongation was slower than WT. Moreover, we confirmed that PT growth is enhanced by exogenous ethylene and inhibited by an ethylene perception inhibitor, 1-methylcyclopropene (1-MCP). The transcriptome profiling of PTs in etr3-ko and NR mutants, revealed that ethylene perception has major impacts on cell wall- and calcium signaling-related genes. The third chapter is focused on the role of 1-aminocyclopropane-1-carboxylic acid (ACC), a precursor of ethylene, as a signal by itself, independent of ethylene perception, on PT growth. We discovered that exogenous ACC stimulated PT growth even when ethylene perception was inhibited by 1-MCP treatment or the NR mutation. Furthermore, in EBS:GUS transgenic pollen, GUS activity was stimulated by ACC in the presence of 1-MCP. These data suggest that ACC signaling can bypass the ethylene receptor step to stimulate PT growt
La représentation et la symbolique des animaux dans l'univers Harry Potter créé par J.K. Rowling : un rôle plus politique qu'il n'y paraît.
Get PDFLa saga Harry Potter écrite par J.K.Rowling met en scène plus de 250 espèces d’animaux, parfois réelles, parfois fantastiques, et qui participent activement au récit. Pour façonner son bestiaire, l’auteure s’inspire de divers mythes et légendes, et les représentations animales foisonnent au sein même de son écriture, que ce soit à travers la construction des personnages, l’héraldique ou l’onomastique. Dans un univers où diverses espèces très différentes cohabitent, Rowling questionne la définition de l’animal, sa relation avec l’Homme et sa place au sein de la société magique. Elle met en exergue les travers spécistes du monde politique magique, tout en offrant un panel de personnages prêts à lutter pour les droits des animaux et la protection de leurs habitats. Enfin, bien que cette œuvre littéraire soit initialement destinée à la jeunesse, elle propose un réflexion profonde sur le spécisme et tend à effacer les frontières existantes entre les espèces en invitant le lecteur à reconsidérer la place de l’animal dans sa propre sociét