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Formulation et mise en oeuvre de composites " tièdes " à fibres longues à matrice TP/TD respectueux de la réglementation REACH
Get PDFL’utilisation des composites époxyde/fibre de carbone face aux matériaux métalliques permet l’allègement des structures dans l’aéronautique. Le but de ces travaux est de renforcer la matrice époxyde par un thermoplastique de PEEK afin d’améliorer la stabilité thermique et la résilience de ces composites. Cette famille de thermoplastique à l’avantage d’avoir une ténacité plus importante que les matrice époxyde, tout en conservant une température de transition vitreuse similaire. La difficulté de ce travail repose sur l’immiscibilité du PEEK avec l’époxyde. Pour diminuer l’immiscibilité, un oligomère de PEEK comportant des terminaisons OH a été synthétisé. Les terminaisons ont la capacité de se lier chimiquement au prépolymère époxyde permettant ainsi la création de chaine hybride thermodurcissable et thermoplastique. Les premiers travaux ont consisté à caractériser les matières premières utilisées. Le choix du prépolymère DER 332 a été réalisé en fonction de sa température de dégradation avant réticulation mais aussi de sa viscosité pour faciliter le mélange avec des poudres solides. Le durcisseur choisi est de l’isophorone diamine (IPDA). Il est de la famille des cycloaliphatiques, garantissant une température de transition vitreuse élevé tout en respectant la réglementation REACH. Une poudre de PEEK sans liaison a été sélectionné et sera comparée à l’oligomère de PEEK à terminaisons OH. La réaction entre le prépolymère et l’oligomère de PEEK est visible par analyse thermique et rhéologique. Cette réaction varie en fonction de la température mais aussi en fonction de la proportion du mélange étudiée. La seconde partie de ces travaux a consisté à caractériser les propriétés mécaniques de la matrice et les différentes charges associées. Des essais de traction, flexion, choc, ténacité et de microscopie à force atomique-AFM ont été réalisés. Les premiers essais ont mis en évidence des mouvements des particules dans la matrice. Un protocole ainsi qu’un procédé de rotomoulage ont été adaptés afin d’obtenir une répartition des charges homogènes tout en optimisant le cycle de réticulation des différents mélanges étudiés. La visualisation par AFM a montré une bonne adhésion des oligomères de PEEK au contact de la matrice dans un environnement très majoritairement immiscible. La tenue au choc du matériau n’a pas été augmentée par l’ajout de charges de PEEK à fort taux de cristallinité qu’elles soient liées ou non à la matrice
Mise en pratique d'une grille d'évaluation du profil comportemental du chien (canis lupus familiaris)dans des refuges de la région Occitanie
Get PDFDans une démarche d’amélioration de la qualité de vie des chiens en structure d’hébergement temporaire, telles que les refuges, et pour favoriser le succès des adoptions, il est essentiel de pouvoir décrypter au mieux leur comportement. Pour cela, des outils d’évaluation du comportement canin existent, bien que rares en France. L’étude réalisée ici avait pour objectif de tester la grille 4A développée par ZOOPSY sur 68 chiens issus de 4 refuges d’Occitanie. Leur comportement, ainsi que leurs éventuels troubles, ont été évalués sur quatre axes principaux : l’agressivité, l’anxiété, l’attachement et les autocontrôles. Les évaluations ont été menées au sein des refuges, puis un suivi avec deux évaluations supplémentaires a été réalisé 3 semaines et 3 mois après leur adoption. La mise en pratique de cette grille dans ce contexte très spécifique a permis d’identifier les forces et faiblesses de celle-ci, de proposer des pistes d’amélioration et d’émettre des hypothèses concernant les comportements observés chez ces chiens et leur évolution après l’adoptio
Dynamic transport of the sediment and nutrient in the Mekong River Basin and the role of the Tonle Sap Lake : Assessment coupling data and modelling approaches
Get PDFThe Asian river basins are great contributors to sediments and nutrient to the seas. These rivers are subject to the influence of climate variability and human activities, which alter the nutrient transport and fate of water quality. The Mekong River is a transboundary river in Southeast Asia and plays an important role in economy, agriculture and also by contributing fluxes into the Mekong delta and into the sea. Within the Mekong basin, the Tonle Sap area is a complex system with a unique reverse flow between Tonle Sap Lake and the Mekong River. Sediment and nutrient in the Mekong River are important to sustain the geomorphology of the floodplains and particularly the Tonle Sap Lake. At the same time, Tonle Sap Lake are contributing the sediment and nutrient for the Mekong delta. Therefore, the sediment and nutrient assessment in the Mekong River and its linkage between the Mekong mainstream and the Tonle Sap Lake would be necessary to evaluate. The study was to assess the dynamic transport of sediment and nutrient in the Mekong River Basin and evaluate the role of the Tonle Sap to the Mekong River through the coupling data and modelling approaches. The physical-based SWAT model was used upstream of the Mekong delta to simulate the water regime and suspended sediment and nutrient flux of the Mekong River. The SWAT model was calibrated based on observed discharge at eight gauge stations, suspended sediment load at six stations and nutrient data at five stations from 1995 to 2016 at a monthly time step. To understand the role of Tonle Sap Lake in sediment and nutrient to Mekong River, the study considered the balanced of the Tonle Sap reverse system at seasonal and annual scales. Before entering the confluence of Mekong and Tonle Sap Lake and delta, the sediment load is found 72±26 Mt/year with a decreasing annual trend from 1995 to 2018. The annual sediment yield of the upper 80% Mekong River basin (310 t/km2/year) is comparable with sediment yields reported for other world major rivers. The Mekong annual average riverine nitrate yield was 202 kg/km2/year with 361.8±83.5 kt/year from 1985-2016 of annual nitrate flux before entering the Mekong delta. The sediment loads variability of the Mekong River and Tonle Sap system presented in this study helps clarify the exchange annual discharge and sediment load toward the Mekong delta. The study also highlighted that the fact that Tonle Sap is the sediment sink (1.35±0.7 Mt annually) in the Mekong basin lead to a reduction in sediment supply, which compounds the threat to the delta from accelerated subsidence and sea-level rise. The study has emphasized the interaction role of Tonle Sap Lake and Mekong in nutrient supply for the Mekong delta. On the annual scale, it is worth discussing these interesting results revealed Tonle Sap Lake contributed 34 kt/year of nitrate and 6.6 kt/year of total phosphorus to the Mekong system or Mekong Delta. In contrast, the Mekong River shared nitrate flux 35.8 kt/year and 8.7 kt/year of total phosphorus to Tonle Sap Lake and its floodplain during the high flow season. Future studies of hydrology together with sediment and nutrients can be carried on based on this model with scenarios of global changes, such as climate changes and land-use changes and include the sediment and nutrient input to Tonle Sap Lake system from the lake tributaries and interconnect with the Mekong River basin model
A geometric encoding for neural network evolution
No full textA major limitation to the optimization of artificial neural networks
(ANN) with evolutionary methods lies in the high dimensionality
of the search space, the number of weights growing quadratically
with the size of the network. This leads to expensive training costs,
especially in evolution strategies which rely on matrices whose
sizes grow with the number of genes. We introduce a geometric
encoding for neural network evolution (GENE) as a representation
of ANN parameters in a smaller space that scales linearly with the
number of neurons, allowing for efficient parameter search. Each
neuron of the network is encoded as a point in a latent space and
the weight of a connection between two neurons is computed as
the distance between them. The coordinates of all neurons are then
optimized with evolution strategies in a reduced search space while
not limiting network fitness and possibly improving search
Plateforme de communication sans fil pour réseaux de capteurs ultra rapides en environnement extrême
Get PDFLa thèse se concentre sur l’acheminement des signaux ultra-rapides délivrés par des capteurs de pression d’onde de souffle lors d’expérimentations de détonique. Ces expérimentations étant très dangereuses, elles impliquent une grande distance de protection à des fins de sécurité. Les signaux de mesure à transmettre sont analogiques et large bande de fréquence. Ils sont en outre altérés par la technique d’acheminement actuelle utilisant des câbles coaxiaux, qui peuvent atteindre plusieurs centaines de mètres. La limitation de la bande passante causée par ce montage filaire, en plus des problèmes posés par les réflexions du signal électrique aux deux extrémités des câbles, est à l’origine d’une modification de l’allure du signal et complique l’évaluation de la surpression maximale de l’onde de souffle. Un système sans fil a donc été élaboré pour pallier les inconvénients de la technologie actuelle. Un oscillateur contrôlé en tension module en fréquence une porteuse radiofréquence à 5.8 GHz avec le signal directement issu du capteur. Cette porteuse est ensuite rayonnée par une antenne (dipôle demi-onde), puis captée par une antenne cornet placée à distance de l’explosion. La porteuse radiofréquence est alors numérisée directement à la réception après amplification. La fréquence instantanée de la porteuse peut être estimée au cours du temps sur quelques nanosecondes à l’aide d’une transformée de Fourier glissante, ce qui permet la transmission de signaux analogiques transitoires de temps de montée inférieur à 10 ns, indépendamment de la distance de transmission. Pour retrouver le signal de pression appliqué à l’entrée de modulation du VCO à partir de la fréquence instantanée de la porteuse mesurée en réception, l’oscillateur est préalablement calibré à l’aide d’un signal de référence, ce qui permet de déterminer sa caractéristique tension/fréquence. Différents modèles ont été étudiés pour simuler au mieux la caractéristique de l’oscillateur. Au final, des résultats de transmission sans fil de signaux de type échelon (fonction de Heaviside) et de signaux de type pic-détente (fonction de Friedlander) sont d’abord présentés, puis des signaux de mesures réels transmis sans fil depuis l’intérieur de boules de feu formées par la détonation d’explosifs condensés sont obtenus et analysés pour la première fois
Influence of alloying on the tensile strength and electrical resistivity of silver nanowire: copper composites macroscopic wires
Get PDFComposite powders made up of 1 vol. %Ag nanowires (NW) dispersed in Cu were prepared and consolidated into cylinders by spark plasma sintering. One cylinder was sintered at only 400 °C resulting in a nanocomposite sample with no dissolution of the Ag NW into the Cu matrix. The second cylinder was sintered at 600 °C and the Ag NW are dissolved forming Ag/Cu alloy NW. The cylinders served as starting materials for room temperature wire-drawing, enabling the preparation of wires of decreasing diameters. The microstructure of the cylinders and the wires was investigated by electron microscopy and associated techniques. The tensile strength and electrical resistivity were measured at 293 K and 77 K. The nanocomposite and alloy wires show similar UTS values (1100 MPa at 77 K), but alloying, although spatially limited, provoked a significant increase in electrical resistivity (0.56 µΩ cm at 77 K) compared to the nanocomposite wires (0.49 µΩ cm at 77 K)
Thermal stability and mechanical behavior of technical bamboo fibers/bio-based polyamide composites
Get PDFThe objective of this research is to tailor composites with continuous bamboo fibers as reinforcement of a bio-based polyamide (RilsanXD). Using mild chemical and mechanical treatment, technical bamboo fibers were extracted from Phyllostachys viridiglaucescens. They have an average diameter of 397 µm. Their average tensile strength is 323 MPa, and their average Young modulus is 26 GPa. Single ply bamboo fibers/polyamide composites were processed. Gravimetric analyses show that polyamide allows mild processing conditions at 200 °C, therefore permitting to make composites without degrading the fibrous reinforcement. Composites composition was determined from peak analyses of the mass derivative curve associated with bamboo situated at 330 °C. Composites with 60 m % of bamboo fibers were prepared and analyzed. SEM images observation of cryo-cuts shows the absence of voids between technical fibers and polyamide matrix. The cohesion in shear was tested by dynamic mechanical analyses. Comparative data recorded on the bio-based polyamide and the 60/40 bamboo fibers/polyamide composite show a significant improvement of the shear glassy modulus which is multiplied by 1.6 at 20 °C. This result is consistent with the continuity of matter between bamboo fibers and polyamide observed by SEM. This effect may be due to a dense network of static hydrogen bonds
Low-velocity impacts into granular material: application to small-body landing
Get PDFWith the flourishing number of small body missions that involve surface interactions,
understanding the mechanics of spacecraft - surface interactions is crucial for improving our
knowledge about the landing phases of space missions, for preparing spacecraft operations,
and for interpreting the results of measurements made during the surface interactions. Given
their regolith-covered surfaces, the process of landing on a small body can be considered as
an impact at low-velocity onto a granular material in reduced-gravity.
In order to study the influence of the surface material, projectile shape, and gravity on
the collision dynamics we used two experimental configurations (one for terrestrial gravity
experiments and one for reduced-gravity experiments) to perform low-velocity collisions into
different types of granular materials: quartz sand, and two different sizes of glass beads (1.5
and 5 mm diameter). Both a spherical and a cubic projectile (with varying impact orientation)
were used.
The experimental data support a drag model for the impact dynamics composed of both a
hydrodynamic drag force and quasi-static resistance force. The hydrodynamic and quasi-static
contributions are related to the material frictional properties, the projectile geometry, and the
gravity.
The transition from a quasi-static to a hydrodynamical regime is shown to occur at lower
impact velocities in reduced-gravity trials than in terrestrial gravity trials, indicating that
regolith has a more fluid-like behaviour in low-gravity. The reduced quasi-static regime of a
granular material under low-gravity conditions leads to a reduction in the strength, resulting
in a decreased resistance to penetration and larger penetration depths
First Assessment of the Benthic Meiofauna Sensitivity to Low Human-Impacted Mangroves in French Guiana
Get PDFBioindicators assess the mangroves ecological state according to the types of pressures but they differ with the ecosystem’s specificities. We investigated benthic meiofauna diversity and structure within the low human-impacted mangroves in French Guiana (South America) in response to sediment variables with various distances to the main city. Contaminant’s concentrations differed among the stations, but they remained below toxicity guidelines. Meiofauna structure (Foraminifera, Kinorhyncha, Nematoda) however varied accordingly. Nematode’s identification brought details on the sediment’s quality. The opportunistic genus Paraethmolaimus (Jensen, 1994) strongly correlated to the higher concentrations of Hg, Pb. Anoxic sediments were marked by organic enrichment in pesticides, PCB, and mangrove litter products and dominance of two tolerant genus, Terschellingia (de Man, 1888) and Spirinia (Gerlach, 1963). In each of these two stations, we found many Desmodora individuals (de Man, 1889) with the presence of epibionts highlighting the nematodes decreased fitness and defenses. Oxic sediments without contaminants were distinguished by the sensitive genera Pseudocella (Filipjev, 1927) and a higher diversity of trophic groups. Our results suggested a nematodes sensitivity to low contaminants concentrations. Further investigations at different spatio-temporal scales and levels of deterioration, would be necessary to use of this group as bioindicator of the mangroves’ ecological status
Dense upflow fluidized bed (DUFB) solar receivers of high aspect ratio: Different fluidization modes through inserting bubble rupture promoters
Get PDFA fluidized bed of Geldart-A particles is promoted as heat transfer fluid in the tubular solar receivers of solar towers. A pressure-driven upward particle flow affects the hydrodynamic flow structure and properties of the fluidized bed. Experiments involved a tube of 0.05 m internal diameter but of very high height/diameter ratio (>120), representative of the future solar receiver and of numerous chemical reactors. Solid circulation fluxes and aeration velocities were varied. Configurations of a bare tube and a tube with bubble rupture promoters were compared. In the bare tube, freely bubbling is transformed into axi-symmetric slugging at a bed level of ~1 m. With bubble rupture promoters, freely bubbling prevails to about a bed level of 3 m, and a turbulent fluidization mode develops higher up the tube (a more chaotic two-phase system with elongated and unstable “gas voids” and “dense solid clusters”), without axi-symmetric slugging detected. Experimental results for both tube configurations were assessed and compared with CFD predictions by the Euler n-fluid code, NEPTUNE_CFD. A good agreement of bed properties was obtained for slug/void frequencies and solids volume fraction in both tube configurations. BRPs moreover enhance the bubble through flow of the fluidizing gas, thus limiting the visible bubble flow rate and bubble sizes while increasing the gas/particle contact, and hence important in designing multi-tube chemical reactors. Whereas slugging limits the heat transfer from the tube wall to the suspension at ~200 W/m2K, the presence of BRPs maintains a heat transfer coefficient in excess of 600 W/m2K