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1
Benrabah, Imed-Eddine. "Développement d’alliages métalliques à gradient de composition pour l’exploration combinatoire des microstructures." Thesis, Université Grenoble Alpes, 2021. http://www.theses.fr/2021GRALI005.
Abstract:
La transformation de l'austénite en ferrite dans les aciers présente un intérêt considérable pour le contrôle des propriétés finales des aciers, en particulier des aciers à haute résistance (AHSS) tels que l'acier dual phase (DP). Malgré les efforts considérables déployés pour comprendre les mécanismes qui contrôlent la cinétique de formation de la ferrite, le rôle des éléments substitutionnels pendant la croissance de la ferrite et leur interaction avec l'interface de migration α/γ restent peu clair. Plusieurs modèles ont été développés pour décrire la cinétique de croissance de la ferrite dans les systèmes ternaires et les systèmes d’ordre supérieur. Les modèles ‘solute drag’ ont été utilisés avec succès pour prédire la cinétique de transformation pour plusieurs solutés et à de nombreuses compositions et températures dans les systèmes ternaires. Cependant, l'extension de ce modèle aux systèmes d'ordre supérieur a mis en évidence un comportement complexe de l'interaction entre les différents éléments interstitiels et substitutionnels à l'interface. La validation des modèles développés nécessite une étude expérimentale de l'effet de la composition et de la température sur la cinétique de croissance. L'objectif de cette contribution est de présenter une méthodologie combinatoire à haut débit complète pour accélérer l'étude l’effet de la concentration des solutés sur la transformation austénite-ferrite. Il convient toutefois de noter que cette nouvelle méthodologie pourrait être utilisée pour étudier toute autre transformation de phase dans tout autre alliage métallique. L'essence de la méthodologie est de fabriquer des matériaux avec des gradients de composition macroscopiques, et d'effectuer des expériences in situ de diffraction des rayons X à haute énergie, résolues dans le temps et dans l'espace, pour enregistrer la cinétique de transformation de phases austénite-ferrite en de nombreux points de l'espace de composition. Des couples de diffusion contenant des gradients de soluté à l'échelle millimétrique et une teneur en carbone presque constante ont été générés en utilisant la présente méthodologie et utilisés pour étudier la cinétique de croissance de la ferrite à des températures intercritiques en utilisant des expériences in situ de diffraction des rayons X à haute énergie. Pendant 4 jours d'expériences, plus de 1500 cinétiques ont été mesurées pour différentes compositions et à différentes températures. Cet ensemble de données d'une taille sans précédent a été utilisé pour valider une version modifiée du modèle ‘three-jump solute drag’ pour les systèmes ternaires et quaternaires. Les calculs du modèle correspondent parfaitement à la cinétique de transformation expérimentale à toutes les températures étudiées et sur presque toutes les plages de composition étudiées de Si, Cr, Mn, Ni et Mo, contrairement aux résultats des modèles de para-équilibre (PE) et de partitionnement négligeable à l'équilibre local (LENP). En outre, il a été démontré que l'étalonnage des paramètres thermodynamiques dans les systèmes ternaires reste valable dans les systèmes quaternaires, ouvrant la voie à la modélisation de la transformation dans les systèmes d'ordre supérieurThe transformation of austenite into ferrite in steels is of considerable interest in controlling the final properties of steels, in particular Advanced High-Strength Steels (AHSS) such as Dual Phase (DP) steel. Despite tremendous efforts in understanding the mechanisms controlling ferrite formation, the role of substitutional elements during ferrite growth and their interaction with the migrating α/γ interface remain unclear. Several models have been developed to describe ferrite growth kinetics in ternary and higher systems. The solute drag based models have been successfully used to predict kinetics for multiple substitutional solutes, compositions and temperatures in ternary systems. However, the extension of this model to higher order systems highlighted a complex behavior of the interaction between the different interstitial and substitutional elements at the interface. Validation of the developed models requires an experimental study of the effect of both composition and temperature on growth kinetics. The aim of this contribution is to present a complete combinatorial high-throughput methodology to accelerate the investigation of the dependency of ferrite growth kinetics on substitutional composition in alloy steels. It is noteworthy, however, that this new methodology could be used to study any other phase transformation in any other metallic alloy. The essence of the methodology is to fabricate materials with macroscopic composition gradients, and to perform time- and space-resolved in situ high-energy X-ray diffraction experiments to gather the austenite-to-ferrite phase transformation kinetics in many points of the compositional space. Diffusion couples containing millimeter-scale solute gradients and an almost constant carbon content were generated using the present methodology and used to study ferrite growth kinetics at inter-critical temperatures using in-situ high-energy X-ray diffraction experiments. During 4 days of experiments, more than 1500 kinetics were gathered for different compositions and at different temperatures. This dataset of unprecedented size was used validate a modified version of the three-jump solute drag model for both ternary and quaternary systems. The model calculations matched experimental transformation kinetics at all investigated temperatures and over almost all the investigated composition ranges of Si, Cr, Mn, Ni, and Mo, contrary to results from para-equilibrium (PE) and local equilibrium negligible partitioning (LENP) models. Additionally, it was demonstrated that the calibration of thermodynamic parameters in ternary systems held true in quaternary systems, paving the way towards modeling of the transformation in higher-order systems
2
Villaret, Flore. "Développement d’une jonction austéno-martensitique à gradient de composition chimique par fabrication additive." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI104.
Abstract:
Ces travaux de thèse concernent la problématique des liaisons bimétalliques acier austénitique/acier martensitique. Cette action de recherche se focalise sur une liaison acier austénitique 316L (X2 CrNiMo 18-12-02) / acier martensitique Fe-9Cr-1Mo (X10 CrMo 9-1). L’objectif est de comprendre la problématique métallurgique liée à l’assemblage de ces deux types de nuance et d’évaluer les possibilités de réaliser par métallurgie des poudres et par fabrication additive des transitions aciers austénitiques/aciers martensitiques. Une soudure obtenue par faisceau d’électrons sert de liaison de référence pour cette étude qui se focalise sur l’intérêt de la métallurgie des poudres pour réaliser une transition entre deux aciers. Des matériaux à gradient de composition chimique ont été consolidés par CIC et par SPS et montrent de très bonnes propriétés mécaniques et une excellente jonction entre les deux types de nuances. Par fabrication additive (DED-LB ou PBF-LB), nous obtenons aussi de très bonnes liaisons entre les deux aciers mais les microstructures sont beaucoup plus complexes. On observe curieusement que plus la vitesse de refroidissement du procédé est importante et plus la présence de ferrite dans l’acier martensitique est importante. Différents calculs basés sur la germination et la croissance de la phase austénitique ont permis de proposer un scénario cohérent pour expliquer les fractions de phases présentes dans les matériaux. La zone de transition entre les deux aciers présente, elle, de fortes variations de duretés. Ces variations sont expliquées par les changements de composition chimique, entrainant des modifications dans les températures de changement de phases, et les cycles thermiques particuliers vus lors de la fabrication. D’un point de vue technologique, les matériaux obtenus par fabrication additive présentent en traction des performances très semblables à ce que l’on obtient par soudage par faisceau d’électrons. Il est montré que la fabrication additive permet aussi de piloter le gradient de composition entre un acier martensitique et un acier austénitiqueThis PhD work concerns the problem of bimetallic austenitic/martensitic steel connections. This research action focuses on a 316L austenitic steel (X2 CrNiMo 18-12-02) / Fe-9Cr-1Mo (X10 CrMo 9-1) martensitic steel connection. The objective is to understand the metallurgical problems related to the assembly of these two steels and to evaluate the possibilities of using powder metallurgy and additive manufacturing to produce austenitic/martensitic steel transitions. A weld obtained by electron beam is used as a reference for this study which focuses on the interest of powder metallurgy to achieve a transition between two steels. Materials with a chemical composition gradient have been consolidated by HIP and SPS and show very good mechanical properties and an excellent junction between the two steels. By additive manufacturing (DED-LB or PBF-LB), we also obtain very good bonds between the two steels, but the microstructures are much more complex. Curiously, we observe that the higher the cooling rate, the higher the ferrite fraction in the martensitic steel. Different calculations based on the nucleation and growth of the austenitic phase have made it possible to propose a coherent scenario to explain the phase fractions present in the materials. The transition zone between the two steels shows strong variations in hardness. These variations are explained by changes in chemical composition, leading to modifications in phase change temperatures, and the particular thermal cycles seen during building. From a technological point of view, materials obtained by additive manufacturing have tensile performances very similar to those obtained by electron beam welding. It is shown that additive manufacturing also makes it possible to control the composition gradient between a martensitic and an austenitic steel
3
Jouenne, Stephane. "Structuration et renforcement du polystyrene par des copolymeres styrene/butadiene a gradient de composition." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2005. http://tel.archives-ouvertes.fr/tel-00012106.
Abstract:
Cette étude porte sur le renforcement du polystyrène qui a un comportement fragile à température ambiante. Le mélange avec un copolymère styrène/butadiène à gradient de composition permet d'obtenir un matériau nanostructuré plus tenace, qui conserve sa transparence. Ces copolymères de type polystyrène-b-(polybutadiène-grad-polystyrène)-b-polystyrène (noté S1-(B/S)grad-S2) sont synthétisés en deux étapes par voie anionique. L'asymétrie entre les blocs S1 et S2 et le gradient de composition ont une influence déterminante sur la structuration et les propriétés, en pur ou en mélange. Des synthèses modèles avec mesures de conversion ont permis de déterminer les rapports de réactivité de la synthèse et d'évaluer l'asymétrie et la forme du gradient composition. L'asymétrie est responsable d'un décalage du diagramme de phase vers des compositions plus riches en styrène. Par une modélisation des propriétés mécaniques aux faibles déformations, il est montré que le bloc gradient a pour effet d'élargir l'interphase et augmenter le volume de phase molle. Sous cisaillement, le mélange avec différents polystyrènes de haute masse donne des matériaux nanostructurés transparents malgré l'immiscibilité vérifiée de ces systèmes. La viscosité élevée de la matrice permet de disperser finement le copolymère. Le système est piégé dans un état hors équilibre lors du refroidissement. En traction, les mélanges présentent une augmentation nette de l'élongation à la rupture pour une fraction critique de copolymère qui dépend de l'architecture de ce dernier. Une courbe universelle est obtenue lorsque les propriétés mécaniques sont présentées
4
Furimsky, Anna M. "Characterization of the lipid composition of washed and percoll gradient centrifuged epididymal mouse sperm." Thesis, University of Ottawa (Canada), 2001. http://hdl.handle.net/10393/9396.
Abstract:
Capacitation is an important yet poorly understood process during which the fluidity of the sperm membrane increases to prepare sperm for the acrosome reaction (AR) and subsequent sperm-egg binding. While cholesterol efflux may be partially responsible for this increase, modification of lipid components, such as remodeling of specific phospholipid (PL) bound unsaturated fatty acyl chains, may also be involved, since no change in the cholesterol:PL molar ratio following capacitation in mouse has been previously described. In this study, lipid classes (cholesterol, PL, sulfogalactosylglycerolipid (SGG), diacylglycerol and triacylglycerol) were quantified and the fatty acyl chain compositions of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were characterized in washed non-capacitated (WS), washed capacitated (WCS), and Percoll gradient centrifuged (PGC) capacitated (PGCS) epididymal mouse sperm. Fatty acid methyl esters were generated from PC and PE by acid methanolysis and their identity was analyzed by gas chromatography. (Abstract shortened by UMI.)
5
Coppin, Ross Mark. "Ecklonia maxima kelp forests along a thermal gradient: community composition and recovery from disturbance." University of the Western Cape, 2017. http://hdl.handle.net/11394/6163.
Abstract:
Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv & Cons Biol)Climate change will influence species distributions, survival and ecosystem functioning, mostly through changes in sea surface temperatures and storm disturbance. Species are expected to shift poleward in response to ocean warming, which will increase species interaction strength, and cause tropicalisation of temperate ecosystems. Furthermore, if storm frequency and magnitude increases, this could have detrimental effects for species already on their thermal limits. One such group of coastal species is kelp. Kelp are ecosystem engineers that rely on cool-temperate water for survival, and which support an array of fauna and flora. Kelp-based ecosystems are also highly productive, and provide important inorganic input into coastal food webs, largely through detritus. Temperature and disturbance have been shown to be important drivers of kelp ecosystems globally, and we expect that local changes in these drivers may affect kelp ecosystem composition and functioning along the south-western Cape coastline where they form extensive habitats.
6
Jouenne, Stéphane. "Structuration et renforcement du polystyrène par des copolymères styrène / butadiène à gradient de composition." Paris 6, 2005. http://www.theses.fr/2005PA066315.
7
Hutton, Jacob Matthew. "DIET COMPOSITION EXPLAINS REDUCTIONS IN STREAM SALAMANDER OCCUPANCY AND ABUNDANCE ALONG A CONDUCTIVITY GRADIENT." UKnowledge, 2018. https://uknowledge.uky.edu/forestry_etds/40.
Abstract:
Changes in land use such as mountaintop removal mining with valley fills (MTR/VF) affect chemical, physical, and hydrological properties of headwater streams. Although numerous stream taxa have experienced significant declines from MTR/VF, stream salamanders appear to be particularly sensitive. Yet, the specific mechanism(s) responsible for the population declines has eluded researchers. We sampled salamander assemblages across a continuous specific conductivity (SC) gradient in southeastern Kentucky and estimated occupancy rates and abundance estimates along this gradient. We also examined the diet of larval and adult salamanders to determine if autochthony (A/T prey), total prey volume, and body condition is influenced by SC. As SC increased, occupancy and abundance declined consistently among all salamander species and life stages. Diet composition explained the declines; for example, larval salamanders experienced a 12−fold decline in autochthony, a 4.2−fold decline in total prey volume, and a rapid decline in body condition as SC increased. Our results indicate that SC indirectly affects stream salamander populations by eliminating an adequate availability of aquatic prey for salamanders, which in turn lead may lead to reduced population persistence in streams with elevated SC.
8
Simões, Catarina Cordeiro. "Species richness and composition of butterfly assemblages (Lepidoptera:Rhopalocera) along the altitudinal gradient of Serra da Estrela." Master's thesis, Universidade de Évora, 2016. http://hdl.handle.net/10174/20707.
Abstract:
Os gradientes altitudinais são importantes modelos em ecologia pois permitem, numa escala reduzida, estudar a influência da variação de diversas variáveis ambientais nos padrões de biodiversidade existentes. Estes padrões são influenciados por diversos factores, desde variáveis climáticas às relacionadas com a perturbação humana. Nesta tese é estudada a variação na composição das comunidades de borboletas ao longo do gradiente altitudinal na Serra da Estrela e são testadas duas hipóteses sobre os padrões de riqueza específica ao longo do gradiente altitudinal: a regra de Rapoport e o “Mid Domain Effect” (MDE). Foram assinaladas 70 espécies de borboletas neste estudo e constatou-se que a variação na riqueza de espécies de borboletas apresenta um padrão “mid peak” apoiando o MDE. Verificou-se também que as comunidades de borboletas do mesmo nível altitudinal são mais semelhantes entre si independentemente da vertente em que se encontram e são também mais semelhantes com as comunidades dos níveis altitudinais adjacentes. Finalmente, a análise da distribuição de algumas espécies ameaçadas de borboletas torna evidente a necessidade de realização de mais estudos sobre a biologia da conservação deste grupo de animais em Portugal; Abstract:
Altitudinal gradients are important ecological models because they allow us to study the influence of diverse environmental variables in the existing biodiversity patterns. These patterns are influenced by various factors, from climatic variables to variables related to human disturbance. In this thesis we studied the variations in the composition of the butterfly assemblages along the altitudinal gradient of Serra da Estrela and we tested two hypotheses regarding the species richness patterns along the altitudinal gradient: Rapoport’s rule and the Mid Domain Effect (MDE). In this study 70 butterfly species were marked recorded and it was observed that the butterfly species richness presents a mid-peak pattern supporting the MDE. It was also noted that the butterfly assemblages in the same altitudinal level show more similarity within themselves regardless of the slope they are found in, and are also more similar to the assemblages present in the adjacent altitudinal levels. Finally, the distribution of some threatened butterfly species was analyzed and it became evident the need to do more studies regarding the conservation biology of this animal group in Portugal.
9
Hasan, Md Nazmul. "Microstructure and mechanical properties of a CrMnFeCoNi high-entropy alloy with gradient structures." Thesis, University of Sydney, 2020. https://hdl.handle.net/2123/23036.
Abstract:
High-entropy alloys (HEAs) that demonstrate excellent mechanical properties over steel-based alloys are not exempt from the common dilemma of strength–ductility trade-off, which limits their potential applications. One way to improve the property of CrMnFeCoNi HEA is by using the rotationally accelerated shot peening technique to introduce a gradient structure. Two gradient profiles—a thin gradient layer with an undeformed core and a fully deformed structure—are introduced by adjusting the processing parameters. The effects of these gradient profiles on mechanical properties and microstructural evolution at various loading conditions and temperatures are systematically explored. In this thesis, various mechanical tests are performed to investigate the effect of the gradient structure on mechanical properties such as tensile properties at room and cryogenic temperatures, compression at different strain rates and dynamic compression at high strain rates. Material characterisations are performed using various electron microscopic techniques to build a structure–property relationship and investigate microstructural evolution.
10
Dahlø, Eva Sofie. "Variation in chemical composition and genetic differentiation among bilberry (Vaccinium myrtillus L.) populations on a latitudinal gradient." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for biologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-12795.
Abstract:
Bilberry (Vaccinium myrtillus) is native to Europe and North America and constitutes an important nutritional resource for both humans and animals. Over the years, a series of chemical analyses have revealed several health-beneficial compounds in bilberry, and with the current demand of the berries mainly covered by Sweden and Eastern Europe, there has become an increasing desire to cultivate bilberry in Norway. In order for such cultivation to be successful an increased knowledge about bilberry is seen as essential and thus several studies have investigated the chemical composition of the berry. However, the underlying genetic diversity and the variation between populations in biochemical compounds remain to be thoroughly investigated. Therefore, the aim of present study was to investigate the differences in biochemical composition between populations of bilberry distributed on a latitudinal gradient, and estimate the level of genetic variation within and among the populations. This in order to examine whether biochemical composition was reflected by observed levels of genetic variation.Bilberries from four Norwegian populations at three regions differing in latitude were analysed for content of total phenolics (TPH), total anthocyanins (ACY) and antioxidant activity (FRAP). Furthermore, metabolic profiling was performed by gas chromatography-mass spectrometry (GC-MS) to reveal biochemical differences between the populations in content of sugars, acids and some simple phenolics. Multivariate statistics were performed and revealed a clustering of samples from the two locations in Mid-Norway, and a clustering of the northern with the southern population. In addition, there were found significant differences in some of the compounds between the populations.Genetic analyses using four microsatellites were carried out to examine whether metabolic differences between populations were reflected by genetic differentiation. Despite the significant differences between populations in the concentrations of some metabolites no significant genetic differentiation was found. Thus, it seems that the variation in biochemical compounds discovered among populations could be environmentally induced differences on a similar genetic background. However, due to the limited number of working microsatellites and the fact that these molecular markers are neutral, there is still a possibility that the genetic differences causing compound concentrations to differ could be so minor as to remain undetected. Hence, further studies utilizing more microsatellite markers or new state-of-the-art molecular techniques are needed to determine whether this result holds and is valid also for genetic variation in coding parts of the genome.
11
Fromentin, Jean-François. "Réalisation et comportement d'interphases à gradient de composition et de propriétés : application au matériau composite SiC/Ti." Bordeaux 1, 1997. http://www.theses.fr/1997BOR10520.
Abstract:
Les besoins de l'industrie aeronautique en materiaux composites a matrice de titane, capables de conserver leur stabilite thermochimique et thermomecanique pendant de longues durees a 600c, ont motive la realisation d'une zone interfaciale renfort/matrice a gradient de composition et de proprietes. Cet interphasage a base de siliciures de titane a ete synthetise par depot chimique en phase vapeur sur renfort filamentaire de sic. La fiabilite du composite sic/interphases artificielles/ti a ete evaluee a haute temperature par une etude physico-chimique. Les proprietes mecaniques du filament revetu de l'interphasage dcpv ont ete determinees et une approche de son comportement a la rupture a ete effectuee
12
Steinman, Alexis. "Assessment of Wetland Water Quality and Plant Species Composition across the Rural, Peri-Urban, and Urban Gradient." Thesis, North Dakota State University, 2017. https://hdl.handle.net/10365/28381.
Abstract:
The Prairie Pothole Region, specifically eastern North Dakota, has experienced intense disturbance from agricultural demands and urban sprawl. This study assessed wetlands across the rural, peri-urban, and urban gradient to determine the impacts of urbanization on water quality and vegetation composition. Thirty wetlands were randomly selected and compared based on land use type and the impervious to pervious surface ratio within one mile of each wetland. Water quality samples were taken in 2015 and 2016, and a vegetation assessment was completed at all wetlands. Results indicate disturbance from urbanization impacts wetland water quality and vegetation composition. Rural wetland water quality and vegetation significantly differ from both peri-urban and urban wetlands, whereas peri-urban and urban wetland water quality and vegetation do not differ. Information from this study is useful to wetland professionals across the globe as urban development and sprawl continue to impact wetlands.
13
Ndossi, Emanueli Mathayo [Verfasser]. "Composition, degradation and stabilization of soil organic matter along an elevation gradient of Mount Kilimanjaro / Emanueli Mathayo Ndossi." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2020. http://d-nb.info/122410031X/34.
14
Schneider-Maunoury, Catherine. "Application de l’injection différentielle au procédé de fabrication additive DED-CLAD® pour la réalisation d’alliages de titane à gradients de compositions chimiques." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0260/document.
Abstract:
Depuis 1984, les matériaux à gradients de fonction (FGM) permettent de former une barrière thermique et réduire les fortes discontinuités des propriétés entre deux matériaux de nature différente. Ces multi-matériaux, qui consistent en une variation intentionnelle de la composition chimique entrainant par conséquent une modification des propriétés microstructurales, chimiques, mécaniques et thermiques, permettent de lisser la distribution des contraintes thermiques. L’élaboration in situ de ces alliages sur mesure est rendu possible grâce à l’utilisation de procédés de fabrication additive tel que le procédé par dépôt de poudres DED-CLAD®. Ces procédés connaissent un essor considérable depuis les années 1980 et sont idéaux dans la fabrication de FGM. Dans le cadre de cette thèse CIFRE, des développements techniques ont été effectués pour adapter le procédé DED-CLAD® et permettre la réalisation de FGM. Grâce à plusieurs collaborations industrielles, une étude complète a été réalisée sur les alliages titane-molybdène et titane-niobium. Ces alliages permettent dans le premier cas de réaliser des pièces résistantes à de fortes sollicitations thermiques (secteur spatial), et dans le second cas d’associer les propriétés mécaniques et la biocompatibilité (secteur biomédical). L’originalité de cette thèse repose sur l’étude d’un gradient complet, c’est-à-dire que l’ajout en élément d’alliage varie de 0% à 100%. En effet, les études reportées dans la littérature ne font pas mentions des alliages titane-matériaux réfractaire pour des taux élevés en élément réfractaire. Les analyses microstructurale (DRX, structure cristallographique par EBSD, microstructure), chimique (EDS) et mécanique (microdureté, tests de traction et essais d’indentation instrumentée) ont mis en évidence une évolution des propriétés le long du gradients de composition. La caractérisation mécanique des échantillons par indentation instrumentée s’est par ailleurs révélée particulièrement pertinente dans les cas de ces multi-matériauxSince 1984, the Functionally Graded Material (FGM) allow to create a thermal barrier and to reduce the strong discontinuities of properties between two materials of different composition. These multimaterials,whose consist of an intentional variation in the chemical composition and, consequently, modify the microstructural, chemical, mechanical and thermal properties, lead to a smooth distribution of the thermal stress. The in-situ development of these custom-made alloys is made possible by the use of additive manufacturing processes such as the DED-CLAD® powder deposition process. These processes have grown substantially since the 1980s and are optimal for the manufacture of FGM. During this industrial thesis, technical developments have been carried out to adapt the DED-CLAD® process and to allow the manufacturing of FGM. Thanks to two industrial collaborations, a full study was carried out on titanium-molybdenum and titanium-niobium alloys. These alloys make it possible, in the first case, to produce parts resistant to strong thermal stress (space sector), and in the second case to combine mechanical properties and biocompatibility (biomedical sector). The originality of this thesis rests on the study of a complete gradient, that is the addition in alloy element varied from 0% to 100%. In fact, studies reported in the literature do not mention titanium-refractory material for high levels of refractory element. Microstructural (XRD, crystallographic analysis by EBSD technique), chemical (EDS) and mechanical (microhardness, tensile test and instrumented indentation) analyses revealed an evolution of the properties along the chemical gradient. The mechanical characterization of the sample by instrumented indentation has also proved particularly relevant in the case of these multi-materials
15
Burton, Michele Lee Samuelson Lisa J. "Riparian woody plant diversity, composition, and structure across an urban-rural land use gradient in the Piedmont of Georgia, US." Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Fall/Dissertations/BURTON_MICHELE_14.pdf.
16
Gandhi, Shikha. "Investigation Of The Effect Of Low Molecular Weight Peg On Lysozyme Interactions In Solution Using Composition Gradient Static Light Scattering." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1204599050.
17
Schneider-Maunoury, Catherine. "Application de l’injection différentielle au procédé de fabrication additive DED-CLAD® pour la réalisation d’alliages de titane à gradients de compositions chimiques." Electronic Thesis or Diss., Université de Lorraine, 2018. http://www.theses.fr/2018LORR0260.
Abstract:
Depuis 1984, les matériaux à gradients de fonction (FGM) permettent de former une barrière thermique et réduire les fortes discontinuités des propriétés entre deux matériaux de nature différente. Ces multi-matériaux, qui consistent en une variation intentionnelle de la composition chimique entrainant par conséquent une modification des propriétés microstructurales, chimiques, mécaniques et thermiques, permettent de lisser la distribution des contraintes thermiques. L’élaboration in situ de ces alliages sur mesure est rendu possible grâce à l’utilisation de procédés de fabrication additive tel que le procédé par dépôt de poudres DED-CLAD®. Ces procédés connaissent un essor considérable depuis les années 1980 et sont idéaux dans la fabrication de FGM. Dans le cadre de cette thèse CIFRE, des développements techniques ont été effectués pour adapter le procédé DED-CLAD® et permettre la réalisation de FGM. Grâce à plusieurs collaborations industrielles, une étude complète a été réalisée sur les alliages titane-molybdène et titane-niobium. Ces alliages permettent dans le premier cas de réaliser des pièces résistantes à de fortes sollicitations thermiques (secteur spatial), et dans le second cas d’associer les propriétés mécaniques et la biocompatibilité (secteur biomédical). L’originalité de cette thèse repose sur l’étude d’un gradient complet, c’est-à-dire que l’ajout en élément d’alliage varie de 0% à 100%. En effet, les études reportées dans la littérature ne font pas mentions des alliages titane-matériaux réfractaire pour des taux élevés en élément réfractaire. Les analyses microstructurale (DRX, structure cristallographique par EBSD, microstructure), chimique (EDS) et mécanique (microdureté, tests de traction et essais d’indentation instrumentée) ont mis en évidence une évolution des propriétés le long du gradients de composition. La caractérisation mécanique des échantillons par indentation instrumentée s’est par ailleurs révélée particulièrement pertinente dans les cas de ces multi-matériauxSince 1984, the Functionally Graded Material (FGM) allow to create a thermal barrier and to reduce the strong discontinuities of properties between two materials of different composition. These multimaterials,whose consist of an intentional variation in the chemical composition and, consequently, modify the microstructural, chemical, mechanical and thermal properties, lead to a smooth distribution of the thermal stress. The in-situ development of these custom-made alloys is made possible by the use of additive manufacturing processes such as the DED-CLAD® powder deposition process. These processes have grown substantially since the 1980s and are optimal for the manufacture of FGM. During this industrial thesis, technical developments have been carried out to adapt the DED-CLAD® process and to allow the manufacturing of FGM. Thanks to two industrial collaborations, a full study was carried out on titanium-molybdenum and titanium-niobium alloys. These alloys make it possible, in the first case, to produce parts resistant to strong thermal stress (space sector), and in the second case to combine mechanical properties and biocompatibility (biomedical sector). The originality of this thesis rests on the study of a complete gradient, that is the addition in alloy element varied from 0% to 100%. In fact, studies reported in the literature do not mention titanium-refractory material for high levels of refractory element. Microstructural (XRD, crystallographic analysis by EBSD technique), chemical (EDS) and mechanical (microhardness, tensile test and instrumented indentation) analyses revealed an evolution of the properties along the chemical gradient. The mechanical characterization of the sample by instrumented indentation has also proved particularly relevant in the case of these multi-materials
18
Bolognini, Stéphane. "Propriétés mécaniques à haute température de cermets Ti(C,N)-WC-Mo-Co à gradient de composition pour outils de coupe /." [S.l.] : [s.n.], 2000. http://library.epfl.ch/theses/?display=detail&nr=2161.
19
Hilt, Nadine. "Diversity and species composition of two different moth families (Lepidoptera: Arctiidae vs. Geometridae) along a successional gradient in the Ecuadorian Andes." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=978503872.
20
Duhaime, Johannie. "Predictable Changes in Abundance, Composition, and Size Structure of Fish and Macroinvertebrates Along an Urbanization Gradient in the Ottawa-Gatineau Area." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23309.
Abstract:
As land use transformations are the main driver of biological diversity loss at the global scale, it is essential to provide predictions and understanding of their impacts in order to improve the mitigation of ecosystem perturbations. The first objective of this project was to describe the response of biological assemblages along a gradient of urbanization and to compare metrics of watershed imperviousness in order to determine, as has been suggested in the literature, whether effective imperviousness, which represents the proportion of impervious area directly connected to the stream by storm sewers, is a better predictor of stream impairement than total imperviousness in the watershed. Decline in sensitive taxa abundance is initiated at 14% total imperviousness and 3% effective imperviousness in the Ottawa-Carleton region and, total and effective imperviousness have equivalent predictive power. The second objective of this project was to describe how the structure of metazoan assemblages in urban streams, as described by size spectra attributes (i.e. slopes, intercepts, number of logarithmic size classes occupied, and residual variance), varies with watershed size, land use and water quality. Streams size spectra of the Ottawa-Gatineau region have relatively shallow slopes, reflecting relatively higher densities of organisms in the larger size classes compared to other ecosystem types (e.g. lakes, oceans, soils, coastal waters). Size spectra slopes, density corrected for size, number of size classes, and residual variance vary predictably along gradients of watershed size, watershed proportion of natural land use and periphyton chlorophyll a. A systematic trend of declining spectra slopes with increasing periphyton biomass suggests that ecological efficiency declines in urban eutrophic streams.
21
Corbel, Serge. "Contribution à l'étude de la dévolatilisation d'un grain de charbon sous fort gradient thermique : composition des matières volatiles, modélisation des phénomènes." Mulhouse, 1987. http://www.theses.fr/1987MULH0045.
Abstract:
Dans une première série d'expériences la combustion d'un grain de charbon bitumeux est réalisée dans un four vertical à chute. Les résultats d'observation du phénomène par des techniques optiques ont pu être corrélés à l'aide d'un modèle à réactions multiples. Dans un deuxième temps, l'analyse des produits de volatilisation a été effectuée par chromatographie en phase gazeuse couplée à la spectrométrie de masse. Entre 883 K et 1043 K le méthane constitue le composé majoritaire des produits gazeux, sa vitesse de formation passe par un maximum vers 500°C
22
Corbel, Serge. "Contribution à l'étude de la dévolatilisation d'un grain de charbon sous fort gradient thermique composition des matières volatiles, modélisation des phénomènes /." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37604043m.
23
Keammerer, Holly Barton 1983. "Community structure, plant interactions, seedling performance and seed bank composition of salt marshes along an estuarine gradient in Coos Bay, Oregon." Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/11256.
Abstract:
xviii, 160 p. : ill. (some col.)Salt marshes are intertidal communities dominated by halophytic vascular plants that are subjected periodically to tidal inundation. These species have developed various adaptations to this stress, including tolerances of fluctuating salinity, extended periods of inundation and intervals of anoxic conditions. The marshes are divided into zones of different plant communities based on species' tolerances of ambient estuarine conditions. Abiotic stresses change along the estuarine salinity gradient (marine to riverine), potentially altering development and composition of plant communities. Abiotic gradients associated with tides are not the only factors that contribute to development of plant community composition in salt marshes. Both negative (competition) and positive (facilitation) biological interactions are also important. Factors that influence community structure in salt marshes, particularly on the eastern North American seaboard, have been well studied. In contrast, salt marshes along the Oregon coast are smaller and more discrete and have received comparatively little attention. The community structure and seed bank composition of six marshes along an estuarine salinity gradient were evaluated. Four major community types dominated marshes that varied in the salinity of inundating tidal waters. Community types were relatively consistent throughout the estuary despite the distances between the marshes. Unlike the emergent plant communities, marsh seed bank composition was more similar within a marsh than within a community type. The low and high marsh community types were separated by a distinct boundary in the marine marshes. Although abiotic factors influence the physical separation of communities, competitive interactions commonly determine the upper limit of a species. In Metcalf marsh, however, the upper boundary for two dominant low marsh species was not determined by competition with the high marsh dominant species. Positive biotic interactions between seedlings and existing vegetation in a community are important factors in determining species distributions, particularly in stressful estuarine environments. In salt marshes, where abiotic stress can be harsh, presence of existing vegetation can ameliorate these conditions and enhance germination and seedling establishment. However, interaction between seedlings and the emergent marsh community was highly competitive, though germination of one species was enhanced in the presence of existing vegetation. This dissertation includes un-published co-authored material.
Committee in charge: Dr. Scott Bridgham, Chairperson; Dr. Richard Emlet, Advisor; Dr. Steven Rumrill, Member; Dr. Alan Shanks, Member; Dr. Gregory Retallack Outside Member
24
Nguyen, Ba Doan. "Etude de la transition de phase FM-AFM dans des films de FeRh : à gradient de composition et par application de contraintes." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY016/document.
Abstract:
Cette thèse porte sur l 'étude et le contrôle des caractéristiques de transition de phase dans les films magnétiques. Dans le cas des films pulvérisés par magnétron à base de FeRh, on a étudié l'influence de la composition et de la souche. La caractérisation magnétique, structurale et électrique a été effectuée en fonction de la position sur des films de composition graduelle. L'ajout d'un troisième élément (Pt ou Ni) a été utilisé pour décaler la température de transition. Nous avons établi qu'un changement dans les propriétés optiques se produit dans les films à base de FeRh en passant de l'état FM à l'état AFM. En étudiant la position dépendant de la température de la transition optique, nous avons pu construire un diagramme de phase du système Fe-Rh-Pt. Un tel diagramme de phase détaillé, basé sur une variation continue de composition, met en évidence une stabilité accrue (température de transition plus élevée) de la phase AFM pour une composition spécifique proche de celle équiatomique. Le contrôle de la souche du changement de phase dans les hétérostructures PMN-PT / FeRh a été étudié par des mesures de transport à l'aide des mises au point développées dans cette thèse. La température de transition pourrait être décalée de 22 K jusqu'à l'application d'un champ électrique faible (10 V ~ 0,32 kV / cm). Le changement de résistance induit par la déformation est important, ce qui est intéressant pour les applications. L'état AFM est stabilisé dans les films contraints. Le caractère anisotrope de la souche piézoélectrique joue un rôle important par rapport au changement de volume isotrope. Nous avons réussi à préparer des films de La (Fe, Si) 13 pour la première fois. Bien que les films optimaux présentent des valeurs de température de Curie, de constante de réseau, de variation d'entropie isotherme induite par le champ et d'aimantation spontanée comparables aux valeurs rapportées pour un matériau en vrac de composition similaire, elles présentent également des caractéristiques inhabituelles, c'est-à-dire des courbes M-T irréversibles et une hystérésis thermique inverse. L'élucidation de l'origine de ces effets nécessite une enquête plus approfondieThis thesis deals with the study and control of phase transition characteristics in magnetic films. In the case of FeRh-based magnetron sputtered films, the influence of both composition and strain were studied. Magnetic, structural and electrical characterization was made as a function of position on compositionally graded films. Addition of a third element (Pt or Ni) was used to shift the transition temperature. We established that a change in optical properties occurs in FeRh-based films on passing from the FM to AFM state. By studying the temperature dependent position of the optical transition, we were able to construct a phase diagram of the Fe-Rh-Pt system. Such a detailed phase diagram based on a continuous variation of composition, evidences an enhanced stability (higher transition temperature) of the AFM phase for a specific composition close to the equiatomic one. Strain control of the phase change in PMN-PT/FeRh heterostructures was investigated through transport measurements using set-ups developed in this thesis. The transition temperature could be shifted by up to 22 K upon application of a low electric field (10 V ~ 0.32 kV/cm). The strain-induced resistance change is large, which is attractive for applications. The AFM state is stabilized in strained films. The anisotropic character of the piezo-electric strain plays a significant role compared to the isotropic volume change. We succeeded in preparing films of La(Fe,Si)13 for the first time. While the optimal films show values of Curie temperature, lattice constant, field-induced isothermal entropy change and spontaneous magnetization comparable with values reported for bulk material of similar composition, they also display unusual features, i.e. irreversible M-T curves and an inverse thermal hysteresis. Elucidation of the origin of these effects requires further investigation
25
Maloney, Caitlin E. "The effects of micronutrient additions on soil invertebrate activity and community structure along a successional gradient." Bowling Green State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1498074605780196.
26
Savelev, Evgenii. "Formation de structures de domaines régulières et conversion de longueur d'onde dans le niobate de lithium modifié par échange protonique." Electronic Thesis or Diss., Université Côte d'Azur, 2023. http://www.theses.fr/2023COAZ4141.
Abstract:
Buts de la recherche: (1) étude de l'évolution de la structure de domaine dans les monocristaux CLN modifiés par la méthode d'échange protonique doux lors de la commutation de la polarisation dans le champ électrique homogène et dans le champ créé par un microscope sonde à balayage, (2) analyse de la génération de seconde harmonique dans les monocristaux CLN dopés au magnésium avec une structure de domaine régulière créée au moyen d'un balayage par faisceau d'électrons.Pour atteindre ces buts, les principaux objectifs suivants ont été formulés:1. Étudier les particularités de la croissance anormale des domaines lamellaires sur la surface polaire pendant la commutation de polarisation dans les monocristaux de niobate de lithium modifiés par échange protonique doux.2. Étudier l'influence des paramètres d'échange protonique sur la distribution spatiale de la composition, la cinétique de la structure de domaine et les champs de seuil dans les monocristaux de niobate de lithium modifiés.3. Élaborer des méthodes de structures de domaine quasi-périodiques et régulières dans les monocristaux de niobate de lithium modifiés.4. Étudier les particularités de la génération de seconde harmonique dans les monocristaux de niobate de lithium dopés au magnésium avec une structure de domaine régulière créée au moyen d'un balayage par faisceau d'électrons focalisés.Méthodologie et méthodes de recherche.Des études expérimentales systématiques de la structure de domaine ont été réalisées à l'aide d'équipements analytiques modernes de haute précision. La visualisation in situ de l'évolution de DS a été réalisée à l'aide de la microscopie optique avec une caméra à grande vitesse. La distribution spatiale des ions H+ dans les plaques étudiées a été mesurée à l'aide de la microscopie confocale Raman (СRM). La visualisation non destructive de DS sur la surface a été réalisée par microscopie à force piézoélectrique à balayage (PFM). La visualisation des domaines en volume a été réalisée à l'aide de CRM et de la microscopie à génération de seconde harmonique (SHG). La commutation de polarisation locale à l'aide d'un microscope sonde à balayage a été utilisée pour créer des domaines isolés et des structures de domaine.PRINCIPAUX RÉSULTATS ET CONCLUSIONS DE L'ÉTUDE1. Il a été étudié pour la première fois la croissance anormale de domaines lamellaires sur la surface polaire Z pendant la commutation de polarisation dans des monocristaux de niobate de lithium modifiés par un échange protonique doux.2. Il a été trouvé que les champs de seuil de formation de domains anormalement bas sur la surface polaire Z dépendaient de la durée du processus d'échange protonique.3. Il a été détecté l'effet de la formation de structures de domaine quasi-périodiques pendant la croissance de domaines lamellaires à partir d'une paroi de domaine planaire.4. La diminution anormale observée des champs de seuil de la croissance des domaines lamellaires à la suite d'un échange protonique doux est attribuée à la formation d'un champ interne de cohérence causé par la présence d'un gradient de composition dans la couche superficielle.5. Il est démontré que la valeur du gradient de composition dans la couche superficielle croît avec l'augmentation de la durée de l'échange protonique, ce qui conduit à une diminution du champ de seuil.6. Il est démontré qu'il est possible de créer une structure de domaine régulière et stable avec une période de 500 nm en commutant localement la polarisation à l'aide d'un microscope sonde à balayage.7. Il a été obtenu pour la première fois une émission de 374 nm de longueur d'onde par génération de seconde harmonique dans un cristal de niobate de lithium dopé au magnésium avec une structure de domaine régulière d'une période de 2 µm créée par balayage à l'aide d'un faisceau d'électrons focaliséConclusion1. The abnormal growth of stripe domains on the Z-polar surface during polarization switching in lithium niobate single crystals modified by soft proton exchange was studied for the first time.2. The dependences of abnormally low values of threshold fields of domain formation on the Z-polar surface on the duration of the proton exchange process are revealed.3. The effect of the formation of quasi-periodic domain structures with the growth of stripe domains from a planar domain wall was found.4. The observed anomalous decrease in the threshold field of stripe domain growth as a result of soft proton exchange is attributed to the formation of bound internal field caused by the presence of a composition gradient in the near-surface layer.5. It is shown that the composition gradient in the near-surface layer increases with an increase in the duration of the proton exchange process, which leads to a decrease in the threshold field.6. The possibility of creating a stable periodic domain structure with a period of 500 nm by local switching using the probe of a scanning probe microscope is demonstrated.7. For the first time, radiation with a wavelength of 374 nm was obtained by the method of the second-harmonic generation in a crystal of magnesium doped lithium niobate with a 2-µm-period domain structure created by scanning with a focused electron beam
27
Merlet-Lacroix, Nathalie. "Auto-assemblage de copolymères à blocs acryliques en milieu apolaire: un exemple de verre colloïdal attractif." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2008. http://pastel.archives-ouvertes.fr/pastel-00005588.
Abstract:
Des copolymères à blocs de type ABA à gradient de composition, s'auto-assemblent en micelles sphériques, dans un solvant apolaire sélectif pour les blocs latéraux. Ces solutions micellaires constituent un très bon exemple de la formation de phases vitreuses dans les suspensions colloïdales, en présence d'interactions attractives. Les structures et les dynamiques à l'équilibre et sous cisaillement sont étudiées par diffusion des rayons X, rhéologie et diffusion de la lumière. A faible concentration, les solutions se comportent comme des suspensions de sphères dures et les variations de la viscosité newtonienne, en fonction de la température et de la concentration, peuvent être décrites par une courbe universelle. A des concentrations plus élevées, des forces attractives à courte portée apparaissent qui affectent la formation du verre et sont responsables de l'existence d'un régime viscoélastique. Cette phase a de nombreux points communs avec un gel faible mais peut solidifier lorsqu'un cisaillement supérieur à une valeur critique est appliqué. Cette gélification sous cisaillement de solutions micellaires attractives est différente du rhéo-épaississement qui se produit dans les suspensions colloïdales conventionnelles et dans les « shake-gels ». Les verres qui se forment aux concentrations plus élevées peuvent être de nature attractive ou répulsive en fonction de la force des interactions attractives à courte portée, qui peut être modifiée en variant la température. Les verres répulsifs présentent les dynamiques lentes et les phénomènes de vieillissement qui sont associés aux dynamiques vitreuses classiques.
28
Brassieur, David Aaron. "An Investigation Into the Origin, Composition, and Commercial Significance of a Sedimentary Subsalt Formation: Keathley Canyon, Gulf of Mexico." ScholarWorks@UNO, 2016. http://scholarworks.uno.edu/td/2245.
Abstract:
Sub-salt oil and gas formations in deep-water northern Gulf of Mexico are high priority targets. Advances in seismic processing allow for high-resolution, below-salt imaging. Understanding the modes of salt emplacement provide insight into sub-salt traps and potential drilling hazards.
A sub-salt sedimentary unit lies in the Keathley Canyon protraction. Autosutures created the transport-parallel lineaments of the upper surface of the unit. In addition, highly variable sediment aggradation rates created ramps, flats, and basal cutoffs along the base of the allochthon as salt and sediment competed for space. Seismic models identify modes of salt emplacement, salt/sediment interactions, and mechanisms responsible for the morphology.
Petrophysical assessments highlight an abnormally pressured, dirty salt environment transitioning into a gouge zone. Dirty salt adds an element of difficulty to managing borehole pressures requiring a unique mud-weight plan designed to resist formation pressures without fracturing lithology.
29
Müller, Guillaume. "Conception, élaboration et caractérisation de matériaux de composition et de microstructure innovants pour les micro-piles à combustible à oxyde solide." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2012. http://tel.archives-ouvertes.fr/tel-00833281.
Abstract:
Les micro-piles à combustible à oxyde solide (micro-SOFC) apparaissent comme des sources d'énergie miniatures attractives et constituent une réelle rupture technologique permettant une solution alternative aux accumulateurs Li-ion actuels. Dans ce contexte, ce travail concerne la synthèse, la caractérisation structurale, microstructurale et électrochimique de films minces denses et poreux de composition et de structure variées : LSCF-CGO, Ni(O)-CGO et CGO. Ces matériaux ont été intégrés comme cathode, anode et électrolyte respectivement dans un dispositif type micro-SOFC fonctionnant vers 400-600°C à partir de H2 comme carburant. L'architecture de la cellule et son procédé de synthèse diffèrent de ceux proposés dans la littérature. En effet, des gradients de porosité et de composition ont été réalisés aux électrodes de manière à limiter les phénomènes de polarisation d'activation et de concentration. De plus, le choix du procédé de synthèse, sol-gel couplé à la méthode de trempage-retrait pour la mise en forme des matériaux, a été guidé par des critères économiques et de facilité de mise en œuvre. Pour la synthèse des films minces denses d'électrolyte (CGO), une autre méthode de synthèse (ALD) a également été utilisée. Dans ce travail, nous avons étudié plus particulièrement les relations qu'il existe entre les propriétés structurale, microstructurale et électrique des films minces poreux d'électrodes, dans les conditions de synthèse et de fonctionnement in fine de la cellule. Sur la base de cette étude, la fabrication et l'évaluation des propriétés électriques de ces micro-SOFC déposées sur un support poreux de Pt/Al2O3 ont été réalisées
30
Ranasinghe, Purnika Damindi. "Use of next generation sequencing for analysing taxonomical and functional composition of bacteria in an insect gut microbiome." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/116377/1/Purnika%20Damindi_Ranasinghe_Thesis.pdf.
Abstract:
This thesis describes the difference between the baseline composition of Diamondback moth (Plutella xylostella L.) insect colonies' gut microbiomes collected from field- and laboratory-reared populations. Results indicates that variation of gut bacterial community composition between individual insect influences baseline microbiome composition estimates at the population scale. The gut bacteria diversity and functional composition change in response to external challenges, and those changes reflect on insect development. This explains the need to discover the specific symbiotic gut bacteria that respond to environmental variables - such findings will be essential for controlling insect hosts, and this knowledge can be applied to develop insect pest management and control.
31
Корнієнко, Анатолій Олександрович. "Формування триботехнічних властивостей композиційних електролітичних покриттів на основі нікелю створенням градієнтних структур. Автореферат дисертації на здобуття наукового ступеня кандидата технічних наук." Thesis, Національний авіаційний університет, 2007. http://er.nau.edu.ua/handle/NAU/35678.
Abstract:
Дисертацію присвячено розробленню градієнтних композиційних електролітичних покриттів зміцнених макро- та наночастинками з керованими триботехнічними властивостями. Проведено аналітичні дослідження напружено-деформованого стану одно- та багатошарових градієнтних КЕП, навантажених силами тертя. Експериментально встановлено оптимальні щодо зносостійкості будову та режими нанесення КЕП Ni-SiC. Визначено вплив кількості та розміру частинок наповнювача на триботехнічні властивості покриттів. Проведенням експериментальних досліджень впливу градієнта будови КЕП на триботехнічні властивості встановлено, що більш високою зносостійкістю характеризуються градієнтні КЕП з “прямим” градієнтом будови, що узгоджується з теоретичними розрахунками напружено-деформованого стану. Дослідженнями встановлено, що із введенням одночасно макро- та наночастинок в КЕП значно підвищується зносостійкість таких покриттів. Показано, що оплавленням покриттів Ni-SiC, які містять додатково бор, можна значно підвищити їх фізико-механічні властивості та зносостійкість. При цьому для оплавлення більш ефективним є застосування лазера, а створення дискретно-оплавлених покриттів дозволяє отримати значно вищі триботехнічні властивості порівняно з повністю оплавленими покриттями.Thesis is aim at development of gradient composition electrolytic coatings hardened by macro- and nanoparticles with the guided tribotechnical properties. Analytical researches of the tensely deformed state of single- and multi-layered gradient CEC loaded with forces of friction are conducted. The opti-mum structure and parameters process of CEC Ni-SiC are experimentally established in relation to wear-proofness. Influencing of amount and size of particles of stuff on tribotechnical property of coatings is determined. Experimental researches of influencing of gradient of structure of CEC are conducted on tri-botechnical property. It is established that the higher wearproofness is characterize gradient CEC with the “direct” gradient of structure, that conforms to the theoretical calculations of the tensely deformed state. Researches is established, introduction simultaneously of macro- and nanoparticles into CEC raise wear-proof of such coatings. It is established, meltback of coatings Ni-SiC, which contain the boron additional-ly, it is possible considerably to raise their physical-mechanical properties and wearproofness. Thus for meltback more effective is application of laser, and the creation of discretely meltback coatings allows to get considerably higher tribotechnical properties comparatively with fully meltback coatings
32
Tardif, Antoine. "Pr??diction des taux de d??composition des liti??res v??g??tales par les traits fonctionnels agr??g??s." Thèse, Universit?? de Sherbrooke, 2014. http://savoirs.usherbrooke.ca/handle/11143/84.
Abstract:
Sommaire : Comprendre le fonctionnement des e??cosyste??mes est un enjeu crucial, en particulier dans un contexte de changements globaux. Afin de mieux pre??dire les processus e??cosyste??miques, j???ai teste?? la pre??cision et les limites des hypothe??ses du biomass-ratio de Grime (HBMR) et de l???annulation idiosyncratique (HAI), cette dernie??re e??tant une hypothe??se originale de cette the??se. Pour cela, j???ai applique?? le principe du biomass-ratio aux traits fonctionnels, en employant la me??thode des traits agre??ge??s en communaute??, pour estimer la re??ponse globale des espe??ces en me??lange.
La de??composition des litie??res plurispe??cifiques constitue un bon mode??le biologique, pour lequel je me suis pose?? les questions suivantes : (1) est-ce que l???HBMR pre??dit bien les taux de de??composition en me??langes plurispe??cifiques ? ; (2) est-ce que le degre?? de variabilite?? de ces taux diminue pour des raisons biologiques avec l???augmentation de la richesse spe??cifique (RS) des me??langes (HAI) ? ; (3) est-ce que la variabilite?? des taux entre me??langes diminue quand les conditions abiotiques du site deviennent plus limitantes ? ; (4) conside??rant que les me??langes plus contraste??s fonctionnellement sont susceptibles de de??velopper plus d???interactions, est-ce que la de??viation a?? la pre??diction augmente avec la dispersion fonctionnelle des me??langes (?? FDis ??, Laliberte?? & Legendre 2010) ?
Cette the??se inclut deux expe??riences de de??composition en sachets a?? litie??res : (1) a?? Sherbrooke (QC, Canada) avec des microcosmes, impliquant des litie??res de six espe??ces d???arbres, de??composant seules et en me??langes et (2) sur trois sites au climat contraste?? dans la re??gion de Clermont-Ferrand (France) avec des litie??res de quatre espe??ces d???herbace??es, de??composant seules et en me??langes.
Les re??sultats montrent des de??viations positives et ne??gatives par rapport aux taux pre??dits, mais l???HBMR de??crit bien la re??ponse moyenne des litie??res plurispe??cifiques. Bien que l???HAI ait e??te?? rejete??e, les re??sultats montrent une convergence des taux observe??s vers les taux pre??dits quand (1) la RS des me??langes augmente, (2) l???e??chelle spatiale augmente et (3) le climat est plus limitant pour la de??composition. Enfin, malgre?? des corre??lations entre FDis et interactions entre espe??ces dans les litie??res, cette relation n???est pas ge??ne??ralisable et l???hypothe??se de corre??lation positive entre FDis et de??viation a?? l???HBMR a e??te?? rejete??e. // Abstract : Understanding ecosystem functioning is a key goal in ecology, especially in the context of global changes. To better predict ecosystem processes, I tested the accuracy and the limits of Grime???s biomass-ratio (BMRH) hypothesis and a novel idiosyncratic annulment (IAH) hypothesis. I applied the biomass-ratio to functional traits, using the community-weighted means (CWM) to estimate the global response of species in mixtures. I studied the decomposition of litter species mixtures as a biological model and asked the following questions : (1) does the BMRH predict well the decomposition rates of mixed species litters? ; (2) does the degree of variability of these rates decrease with increasing species richness (SR) beyond that expected from purely mathematical causes (IAH)? ; (3) does the variability of rates between mixtures decrease with less favourable abiotic conditions for decomposition? ; (4) as more functionally contrasted mixtures are expected to develop more interactions, does the deviation from prediction increase with increasing functional dispersion in mixtures (?? FDis ??, Lalibert?? & Legendre 2010)? This study involves two decomposition experiments using litterbags: (1) at Sherbrooke (QC, Canada), in microcosms, involving litters from six tree species, decomposed alone and in mixtures and (2) in three climatically contrasted sites in the region of Clermont-Ferrand (France) with litters from four herbaceous species, decomposed alone and in mixtures. Despite both positive and negative deviations from expectation occurring at all levels of SR, the BMRH well described the average response of mixed species litters. Although I rejected the IAH, the results showed a convergence to the predicted values based on CWM with (1) increasing the SR in mixtures, (2) increasing the spatial scale of the study and (3) a less favourable climate to decomposition. Finally, although there was a correlation between litter interactions and functional divergence, this relationship was not generalizable and I rejected the hypothesis of a positive correlation between FDis and the deviations from BMRH.
33
Farcet, Céline. "Polymérisation radicalaire contrôlée par les nitroxydes en miniémulsion aqueuse." Paris 6, 2002. http://www.theses.fr/2002PA066133.
34
Merlet-Lacroix, Nathalie. "Auto-assemblage de copolymères à blocs acryliques en solvant apolaire : un exemple de verre colloïdal attractif." Paris 6, 2008. https://pastel.archives-ouvertes.fr/pastel-00005588.
Abstract:
Des copolymères à blocs de type ABA à gradient de composition, s’auto-assemblent en micelles sphériques, dans un solvant apolaire sélectif pour les blocs latéraux. A faible concentration, les solutions se comportent comme des suspensions de sphères dures et les variations de la viscosité newtonienne, peuvent être décrites par une courbe universelle. A des concentrations plus élevées, des forces attractives à courte portée apparaissent, qui affectent la formation du verre et sont responsables de l’existence d’un régime viscoélastique. Cette phase peut solidifier lorsqu’un cisaillement supérieur à une valeur critique est appliqué. Les verres qui se forment aux concentrations plus élevées peuvent être de nature attractive ou répulsive en fonction de la force des interactions attractives à courte portée, qui varie avec la température. Les verres répulsifs présentent les dynamiques lentes et les phénomènes de vieillissement qui sont associés aux dynamiques vitreuses classiques.
35
Ther, Olivier. "Élaboration de carbures cémentés à gradient de propriétés par procédé d’imbibition réactive : Application aux inserts WC-Co et aux taillants en diamant polycristallin pour le forage pétrolier en conditions sévères." Thesis, Paris, ENMP, 2014. http://www.theses.fr/2014ENMP0067.
Abstract:
Dans l'industrie du forage pétrolier, les conditions de travail de plus en plus sévères requièrent sans cesse de nouveaux outils plus résistants à l'usure abrasive et à l'impact. Afin de répondre à ce défi, les travaux présentés ici, ont pour but l'élaboration de matériaux en carbure cémenté à gradient de composition par le procédé d'imbibition réactive. Ce procédé peut être décomposé en deux procédés de gradation, à savoir : l'imbibition et le revêtement réactif. L'imbibition a pour rôle d'enrichir graduellement, en phase liante, le coeur d'une pièce en carbure cémenté dense et repose sur le principe de migration de phase liquide dans un corps solide-liquide. Le revêtement réactif est un procédé qui s'applique également sur un carbure cémenté dense sur lequel est déposé un revêtement de nitrure de bore. Après avoir atteint le liquidus de la phase liante du carbure cémenté, une précipitation de borures ternaires prend place à la surface du matériau et s'étend graduellement sur des distances millimétriques. Dans le cas de pièces industrielles (inserts tricône et supports de taillants PDC (Polycrystalline Diamond Compact)), le traitement d'imbibition réactive permet de générer des gradients de dureté pouvant atteindre 450 HV sur 25 mm. L'élaboration de tels gradients a nécessité une meilleure compréhension des cinétiques ainsi que des phénomènes mis en jeu durant l'imbibition et le revêtement réactif. Dans le cas des taillants PDC, l'influence des paramètres du procédé HPHT de synthèse de la plaquette diamantée, sur le gradient de composition présent dans le support WC-Co après imbibition réactive, a été étudiée. Ces travaux se sont également intéressés à l'effet de ces gradients de composition sur les propriétés des plaquettes diamantées ainsi obtenues. A la suite d'essais mécaniques, les inserts WC-Co et taillants PDC gradués montrent une augmentation significative de leur résistance à l'abrasion (de 30 à 100%) et de leur tenue à l'impact (de 20 à 40%)In oil drilling industry, harsher working conditions require ever new and more abrasive wear and impact resistant tools. To meet this challenge, the work presented here, is to develop graded cemented carbide materials by reactive imbibition process. This method can be divided into two gradation processes, namely, reactive coating and imbibition. Imbibition gradually enriches the core of dense cemented carbide with binder phase and is based on the principle of liquid phase migration in a solid-liquid body. Reactive coating also takes place in dense cemented carbide on which a boron nitride coating is deposited. After reaction with the WC-Co liquid binder, some ternary boride precipitations take place from surface to several millimeters deep. For industrial parts (inserts for roller cone bits and PDC (Polycrystalline Diamond Compact) cutters substrates), hardness gradients obtained can reach 450 HV on 25 mm. Such gradients development is passed through a better understanding of kinetics and phenomena occurring during imbibition and reactive coating. In case of PDC cutters, influence of HPHT process parameters, allowing diamond table synthesis, on the WC-Co substrate gradient, generated by reactive imbibition, was studied. This work was also interested in gradient effect on the obtained diamond tables properties. After mechanical tests, graded WC-Co inserts and graded PDC cutters show a significant increase of both wear resistance (from 30 to 100%) and impact resistance (from 20 to 40%)
36
BONARI, GIANMARIA. "DIFFERENT HABITAT AND TAXA: VARIOUS APPROACHES AND THEIR IMPLICATIONS FOR A LONG-SIGHTED MANAGEMENT AND CONSERVATION." Doctoral thesis, Università di Siena, 2017. http://hdl.handle.net/11365/1010508.
Abstract:
The thesis starts in the continental context of the White Carpathians Protected Landscape Area and UNESCO Biosphere Reserve (Czech Republic), a protected area famous for its grasslands with the globally highest fine-scale plant species richness. The effects of management on species richness and composition of both plants and animals were tested in relation to different management practices (mowing, grazing, abandonment and mixed management) for several years at several sites, clarifying the disagreements that have occurred among conservationists and practitioners to date. The thesis continues with a focus on the Mediterranean context. Here, the distribution patterns of understorey assemblages of coastal pine stands on sand dunes were studied, given the scarcity of literature due to scholarly disdain. Using more than a hundred plots along Italian coastlines in different pine forest types, community similarity and specificity was assessed in order to provide lacking management clues. Subsequently, focusing on a pine forest stand located in Southern Tuscany, the thesis aimed to solve another pivotal question, namely by investigating the concordance of species assemblages between vascular plants, oribatid mites and soil chemical properties with special attention to the role of vegetation structure (i.e. tree, shrub and herbaceous cover) for biological components. This part provides new answers about congruence among communities and following appropriate management practices to be fulfilled for communities. The last part, performed along a wide range of Tuscan coasts, deals with one of the most extreme habitats in the Mediterranean basin: coastal dunes. Here, the understanding of the response of plant species to soil factors was estimated. This provides concrete proposals for the effective conservation of coastal habitats.
37
Abohwo, Olubusola. "Reservoir analysis based on compositional gradients /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
38
Tanniou, Anaëlle. "Etude de la production de biomolécules d'intérêt (phlorotannins, pigments, lipides) d' algues brunes modèles par des approches combinées de profilage métabolique et d'écophysiologie." Thesis, Brest, 2014. http://www.theses.fr/2014BRES0055/document.
Abstract:
Notre étude s’inscrit dans un processus de recherche de nouveaux composés d’origine naturelle à activités biologiques avérées à partir de macroalgues brunes, avec d’éventuelles perspectives d’exploitation industrielle. Ainsi, dans un premier volet nous avons testé des méthodologies innovantes en matière d‘extraction en utilisant trois espèces d’algues brunes comme modèles. Nous avons optimisé le protocole d’extraction solide/liquide en estimant divers paramètres cruciaux qui influent sur le rendement d’extraction et sur les activités antiradicalaires des composés extraits. Soucieux de trouver une méthodologie innovante d’extraction plus « verte » répondant aux normes européennes, nous avons donc testé des méthodes d’extraction utilisant des solvants dans leur état supercritique ou sous forme pressurisés. La comparaison avec le procédé d’extraction solide/liquide nous a permis de sélectionner l’extraction par fluides pressurisés (PLE) employée avec un mélange Ethanol-Eau pour l’extraction de composés antiradicalaires avec une haute efficacité. Dans une deuxième partie nous nous sommes intéressés aux variations quantitatives et qualitatives des principales macromolécules présentes chez l’espèce invasive Sargassum muticum en Europe. L’emploi de deux techniques analytiques, RMN HR-MAS et spectroscopie IR, nous a permis d’avoir une vue d’ensemble des compartiments susceptibles de subir des variations selon la position géographique d’une même espèce à large répartition. Cette étude nous a montré comment une espèce est capable de changer sa composition biochimique en fonction de son environnement et ainsi s’acclimater à des milieux assez différents. Ce travail a mis en évidence les effets de différents paramètres environnementaux sur les compartiments lipidique (analysés en GC), protéique ainsi que sur les quantités de carbohydrates et de pigments (analysés en HPLC). L’influence de ces paramètres sur la taille des individus de Sargassum muticum a également été discutée. La dernière partie de cette étude nous a permis de décrire les variations quantitatives et qualitatives des phlorotannins chez l’espèce invasive Sargassum muticum sur une grande échelle spatiale, le long d’un gradient latitudinal (Norvège-Portugal). Dans un premier temps cette variabilité a été appréhendée grâce à un suivi temporel et spatial des teneurs en phlorotannins. L’étude des variabilités intra-spécifiques et intra-individuelles nous a permis de mettre en évidence un effet du stade de développement et de la partie de l’algue considérée : les teneurs et activités des phlorotannins sont plus importantes dans les crampons et chez les individus matures. Après la recherche d’un protocole simple pour la semi-purification des composés phénoliques présent chez Sargassum muticum, nous avons pu mettre en évidence la présence de composés de type phlorethol au moyen de techniques de RMN à deux dimensions (2D). Ces fractions semi-purifiées possèdent des activités antiradicalaire et antibactérienne notoires. Enfin, l’utilisation de plusieurs techniques de séparation membranaires nous a permis d’estimer le poids moléculaire des différents composés présents dans le pool de composés phénoliques extrait. Enfin, suite aux constats effectués sur les populations, l’effet de l’intensité lumineuse et de la température de l’eau a pu être apprécié isolément : les radiations UVA et UVB boostent la production de CP alors qu’une augmentation de la température fait chuter la production de CP chez S. muticumOur study is part of the research process for new compounds of natural origin with biological activities and possible industrial perspectives. In a first part, we tested innovative extraction methodologies using three brown algae species as model. We optimized the solid/liquid extraction protocol by estimating diverse crucial parameters which influence the extraction yield and radical scavenging activities of extracts. In order to find an innovative and more "green" extraction methodology answering the European standards, we thus tested more recent extraction methods using solvents in their supercritical state or under pressure. The comparison with the solid/liquid process allowed us to select pressurized liquid extraction (PLE) using an ethanol-water mixture for the extraction of active compounds with a high efficiency, but also to select Sargassum muticum as an interesting model for further investigations. In a second part, we were interested in the quantitative and qualitative variations of the main macromolecules present in the invasive species S. muticum in Europe. The employment of two analytical techniques (NMR HR-MAS and IR spectroscopy), allowed us to have an overview of biochemical parts of the algae, which vary according to the geographical position of this wide spread species. This study showed how a species is able to modify its biochemical composition, and then to acclimate, according to the environment. We then focused on molecules, which showed important variations along the latitudinal range of S. muticum. This work highlighted the effects of environmental parameters on lipid (GC analysis) and protein compartments as well as on carbohydrates and pigments quantities (HPLC analysis). The influence of these parameters on the size of individuals was also discussed. The last part of this study allowed us to describe the quantitative and qualitative variations of phlorotannins in S. muticum on a large spatial scale, along a latitudinal gradient (Norway-Portugal). At first this variability was measured thanks to temporal and spatial follow-up of the phlorotannins contents. The study of intra-specific and intra-individual variabilities allowed us to highlight an effect of the development stage and of the seaweed part: phlorotannins contents and activities are more important in holdfast and in mature individuals. After the research of a simple protocol for the phenolic compounds semi-purification present in Sargassum muticum, we were able to highlight the presence of compounds of only phlorethol type in this species by means of 2D RMN techniques. These semi-purified fractions possess notorious radical scavenging and antibacterial activities. Finally, the use of several membrane separation techniques allowed us to consider the molecular weight of the various compounds present in the extracted pool of phenolic compounds. Finally, under controlled conditions, the effects of the light quality and the seawater temperature were tested: UV-A and UV-B radiations boost the production of CP while an increase of the temperature makes the phlorotannins production decreasing in S. muticum
39
Everard, David Alexander. "Composition, structure and processes along woodland gradients in the Weald." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385319.
40
Boman, Daniel. "Compositional gradients in sputtered thin CIGS photovoltaic films." Thesis, Uppsala universitet, Fasta tillståndets elektronik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-355462.
Abstract:
Cu(In,Ga)Se2 (CIGS) is a semiconductor material and the basis of the promising thin-film photovoltaic technology with the same name. The CIGS film has a typical thickness of 1-2 mm, and solar cells based on CIGS technology has recently reached efficiencies of 23.3%. Ultra-thin CIGS solar cells use sub-micrometer thick films that require significantly less material and can be manufactured in a shorter amount oftime than films with typical thicknesses. With decreasing thickness, both electrical and optical losses get more significant and lower the overall performance. Electrical losses can be decreased by increasing the overall film quality and by utilising a graded bandgap throughout the CIGS layer. The band gap can be changed by varying the[Ga]/([Ga]+[In]) (GGI) ratio. Higher overall film quality and a higher band-gap towards the back of the absorber are expected to increase the performance. In this work, sputtered CIGS solar cells were made with different CIGS layer thicknesses, that ranged between 550-950 nm. Increased heat during deposition was examined and shown to increase the film quality and performance for all thicknesses. Two different ways of doping CIGS with Na was examined and it was found that higher Na content lead to an increasing predominance of the (112) plane. The bandgap was graded by varying the GGI composition throughout the CIGS layer and depth profiles were made with Glow-Discharge Optical Emission Spectroscopy (GDOES). It was found that a sputtered CuGaSe2 (CGS)layer below the CIGS-layer lead to a steep increase of the GGI near the back contact. When CGS made up 10% of the total CIGS layer thickness, a significant increase in performance was observed for all thicknesses. CIGS-absorbers with a less graded region with low GGI, making up 30% or 60% of the total CIGS layer thickness were made. A decrease in GGI in that region, was shown to increase the current but lower the voltage. No substantial increase in total performance compared to a fully graded CIGS layer was seen regardless of layer thickness. For further work the optical losses needs to be addressed and work on increasing the optical path in the CIGS layer needs to be done.
41
Cook, Clinton John. "Compositional gradients in photopolymer films utilizing kinetic driving forces." Diss., University of Iowa, 2014. https://ir.uiowa.edu/etd/1308.
Abstract:
Independent control of the surface and bulk properties is advantageous for many applications such as adhesives, release coatings, and antimicrobial films. Traditional methods for achieving independent control typically require multiple processing steps such as wet-on-wet or wet-on-dry coating methods. Independent control over the surface properties can achieved in a single step utilizing the temporal and spatial control inherent to photopolymerization. Specifically, a co-photopolymerization of monomers with different reactivities in the presence of a light gradient is capable of producing a polymer film with a surface chemistry that differs from the bulk chemistry. The light gradient, produced via the concentration of photoinitiator in the formulation, results in a reaction gradient through the film with the higher rates of reaction occurring in the high light intensity regions of the film. The preferentially reacting monomer adds at a greater rate in the high light intensity regions resulting in non-uniform consumption yielding a concentration gradient. Consequently, diffusion of the preferentially reacting monomer from the bulk to the surface of the film and a counter-diffusion of the other monomer from the surface to the bulk of the film occurs from the non-uniform monomer consumption thus producing a film with a concentration gradient through the depth of the film with the preferentially reacting monomer enriching the high light intensity regions. A variety of kinetic differences capable of producing a stratified film will be presented including inherent monomer reactivity, number of functional groups per monomer, oxygen inhibition, thiol-ene chemistry, and Norrish type two initiation. Additionally, parameters that control the degree of stratification, such as methods of varying polymerization rate and the light gradient, will be examined. Changes in surface properties (such as contact angle, surface hardness, adhesion) and bulk properties (such as mechanical properties measured by dynamic mechanical analysis and polymer swelling) are studied as a function of stratification. Finally, a mathematical model which describes and predicts the production of stratified films via photopolymerization is presented. Photopolymerization allows for a facile, single step method of generating stratified films with controllable surface chemistries.
42
Morris, Tracy Catharine. "Tree Composition Along Edaphic and Hydrologic Gradients in Nonriverine Wet Hardwood Forests." NCSU, 2005. http://www.lib.ncsu.edu/theses/available/etd-04102005-161445/.
Abstract:
We sampled seven intact nonriverine wet hardwood forests to establish target ranges for vegetation, soils and hydrology and to examine trends in plant species composition along a wetness gradient. Although quantitative vegetation analysis for this community has been published, broad drainage classes were used to represent a moisture gradient. We investigated trends along a finer-scaled wetness gradient utilizing a novel wetness index that incorporated indicators of saturated soils. Understanding small-scale patterns in plant community composition is useful in planning wetland restoration projects. Although no strong relationship was found between wetness index classes and plant community composition, these data represent the vegetative community supported by soils specific to each wetness class. Absence of this relationship is most likely a result of the dominance of A. rubrum and L. styraciflua in all wetness classes as well as a history of disturbance in each forest and other unknown stochastic variables. For the restorationist hoping to restore a historic nonriverine wet hardwood forest, once known as oak flats, we can suggest guidelines for restoring hydrology to the wetness classes in which we found oaks with high importance.
43
Largiller, Grégory. "Maîtrise du frittage de matériaux céramique-métal à gradients de composition et de structure." Grenoble INPG, 2010. http://www.theses.fr/2010INPG0160.
Abstract:
Les matériaux à gradient de composition et de structure permettent d'associer des propriétés complémentaires dans une pièce donnée. Les cermets (matériaux composite céramique métal) développés par Rio Tinto Alcan seront potentiellement utilisés en tant qu'anodes inertes pour l'électrolyse de l'aluminium. Pour connecter cette pièce à matrice céramique au réseau électrique, ce matériau doit être associé avec un matériau conducteur électrique en une seule opération de frittage. En associant les connaissances issues de la métallurgie des poudres avec une analyse microstructurale, des calculs thermodynamiques et des considérations mécaniques, une gamme de matériaux appelés metcer (composite métal céramique) a été développée. Selon la proportion et composition de la phase métallique initiale de ces metcers, ils peuvent être cofrittés en une seule opération avec un cermet. Nous avons montré que la proportion de phase métallique influençait fortement la tenue mécanique de l'ensemble pendant le frittage ; que la composition des phases oxydes et métalliques permettait de maîtriser les phénomènes de diffusion entre les parties cofrittées pour construire une interface graduelle. Des lois phénoménologiques basées sur la mécanique des milieux continus ont été développées pour modéliser le frittage d'un cermet et d'un metcer. Ces lois ont été introduites dans un logiciel de calcul par éléments finis pour simuler le frittage d'assemblages bicouches et identifier les éventuels points de fragilité de différentes géométries. En comparant ces résultats de simulation numérique à des observations optiques in situ sur des pièces centimétriques, nous avons montré que l'amorçage de fissures proche de l'interface a lieu lorsque les contraintes sont élevées. A basse température, de faibles écarts de déformations entre les couches suffisent à amorcer des fissures lorsque les viscosités des matériaux sont grandes et qu'ils ont un comportement fragile. A haute température, lorsque les écarts de déformation sont grands et les viscosités faibles, les contraintes entre les couches sont relaxées. En utilisant les connaissances acquises à la fois sur la chimie et la mécanique du système, une pièce centimétrique tricouche à gradient exempt de fissure a été réaliséeGraded materials are used to gather complementary physical and/or chemical properties into a single part. Cermet material (ceramic metal composite) developed by Rio Tinto Alcan may be used as inert anode for aluminium electrolysis. To connect these ceramic matrix materials to the current network, we propose to associate them with a conductive material in a single sintering step. Using our knowledge on powder metallurgy with microstructure analysis, thermodynamical and mechanical calculations, a new range of material called metcer (metal ceramic composite) has been developed. According to their metal phase proportion and composition, the metcer materials can be cosintered with cermets in a single sintering step. By modifying the metal phase proportion, we enabled the parts to keep joined during the whole sintering thermal cycle. The composition of oxides and metal phases change the diffusion phenomena and enable one to build a graded interface between the layers. Based on continuum mechanics, constitutive equations have been used to simulate the sintering of a cermet and a metcer. Constitutive equations have been implemented into a finite element software to identify the weak regions of bilayers parts of complex geometry. We compared numerical simulation results with optical observations made during sintering on large scale bilayers. Cracks near the interface occur at low temperature when the strain mismatch between the layers is low and the viscosities of the layers are high. Thus, the materials have a fragile behaviour. At high temperature, when the viscosities are low and the strain mismatch is high, the stresses in the vicinity of the interface are released. Combining our knowledge on the chemistry and interactions between these materials, we developed a trilayer material. This material showed up a graded interface without any crack
44
Mrázek, Zdeněk. "Snímání a zpracování digitálních obrazů s vysokým dynamickým rozsahem." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2016. http://www.nusl.cz/ntk/nusl-241953.
Abstract:
The target of this thesis is sumarize the theory of metods used for composition image sequence into single high dynamic range image. Selected methods and algorithms are described in theoretical part and implemented in practical part of this thesis. It was used C++ language with using OpenCV library.
45
Zhang, Zhipeng, Wenckstern Holger von, Jörg Lenzner, and Marius Grundmann. "Wavelength-selective ultraviolet (Mg,Zn)O photodiodes: Tuning of parallel composition gradients with oxygen pressure." American Institute of Physics, 2016. https://ul.qucosa.de/id/qucosa%3A23555.
Abstract:
We report on ultraviolet photodiodes with integrated optical filter based on the wurtzite (Mg,Zn)O
thin films. Tuning of the bandgap of filter and active layers was realized by employing a
continuous composition spread approach relying on the ablation of a single segmented target in
pulsed-laser deposition. Filter and active layers of the device were deposited on opposite sides of a
sapphire substrate with nearly parallel compositional gradients. Ensure that for each sample position
the bandgap of the filter layer blocking the high energy radiation is higher than that of the
active layer. Different oxygen pressures during the two depositions runs. The absorption edge is
tuned over 360 meV and the spectral bandwidth of photodiodes is typically 100 meV and as low as
50 meV.
46
Artioli, Luiz Guilherme Schultz. "As assembléias de peixes da Zona Litoral de Lagoas Costeiras Subtropicais do Sistema do Rio Tramandaí/RS : aspectos amostrais, variações espaciais e temporais de descritores ecológicos e suas relações com a variabilidade ambiental." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/72376.
Abstract:
Lagoas costeiras são ecossistemas cruciais para conservação da biodiversidade local e global. O sistema do rio Tramandaí (SRT) apresenta uma série de lagoas costeiras rasas conectadas por canais naturais, e uma saída, via estuário de Tramandaí, para o oceano. Esse sistema é dividido em dois subsistemas, ao norte e ao sul do estuário, resultado de padrões hidrodinâmicos e da influência do vento e que definem características ambientais distintas a esses subsistemas. Um gradiente decrescente, de norte a sul, no estado trófico dessas lagoas já foi verificado. No presente estudo é testada hipótese de variabilidade espacial (lagoas e subsistemas) e temporal (estações do ano) na magnitude de variáveis abióticas e de descritores ecológicos das assembleias de peixes (composição, riqueza, diversidade, dominância) do SRT. Também é avaliada a relação entre variáveis abióticas e descritores das assembleias nesses subsistemas. É comparada a seletividade de captura de um amostrador ativo (rede de arrasto de praia) e de um amostrador passivo (redes de emalhe). Amostragens foram conduzidas de novembro de 2008 a abril de 2010 com rede de arrasto de praia e redes de emalhe, na zona litoral das lagoas Itapeva, Quadros e Malvas no subsistema norte, e nas lagoas Fortaleza, Rondinha e Barros no subsistema sul. Entre abril de 2009 e março de 2010, amostras de água foram coletadas e dez variáveis foram mensuradas em laboratório. Análises de ordenação (NMDS) mostraram clara diferença de composição, abundância numérica (CPUEn) e em biomassa (CPUEb) de espécies entre amostradores. A análises de ANOSIM e SIMPER mostraram baixa similaridade desses parâmetros entre amostradores. Houve diferença no tamanho dos peixes coletados com redes de arrasto e emalhe. Turbidez e DBO5 tiveram médias superiores no subsistema norte, enquanto que condutividade, salinidade, dureza, sólidos totais dissolvidos e transparência de Secchi no subsistema sul. Temporalmente foram verificadas diferenças de temperatura, pH, salinidade, turbidez, dureza, sólidos totais dissolvidos, oxigênio dissolvido, sólidos suspensos e profundidade, mas somente os dados de pH, condutividade, turbidez e DBO5 mostraram interação entre os fatores espaço e tempo. As assembleias das margens rasas da zona litoral foram dominadas por dez espécies, resultando em alta similaridade de composição, CPUEn e CPUEb entre os subsistemas. A riqueza de espécies variou espacial e temporalmente. Diversidade e equitabilidade espacialmente, e CPUEn e CPUEb temporalmente. As assembleias das regiões pelágicas da zona litoral foram dominadas por sete espécies, com dominância numérica das espécies L. anus e A. aff. fasciatus no subsistema norte. A NMDS mostrou similaridades maiores de composição, CPUEn e CPUEb entre amostras de um mesmo subsistema, no entanto, a ANOSIM não apresentou resultados significativos para rejeição das hipóteses nulas. CPUE n e b, diversidade e equitabilidade variaram espacialmente, enquanto a riqueza, temporalmente. A análise de correlação canônica (CCA) mostrou que temperatura, DBO5, sólidos suspensos e dureza responderam por 46% da variabilidade dos dados de abundância numérica das espécies. Os resultados sugerem que amostradores ativos e passivos reproduzem diferentes imagens da assembleia por eles amostrada, indicando que o delineamento amostral para estudos com peixes nesses ecossistemas deve contemplar tais diferenças. As diferenças ambientais dos subsistemas refletem em diferenças na qualidade da água e os resultados obtidos confirmam os pressupostos do gradiente trófico. A estrutura das assembleias de peixes foi mais variável em resposta as condições ambientais em escala espacial, enquanto que temporalmente, houve maior coerência na variabilidade dos dados. As relações das espécies com as variáveis ambientais são discutidas com base no comportamento alimentar e/ou reprodutivo das mesmas e na qualidade do habitat. Tais resultados podem ser úteis como subsídio a elaboração de estudos de manejo costeiro do SRT, sobretudo com relação aos recursos pesqueiros, e na proposição de modelos de estrutura das assembleias de peixes de lagoas costeiras subtropicais.Coastal lakes ecosystems are crucial for conserving biodiversity both locally and globally. The river Tramandaí system (SRT) comprises a series of shallow coastal lagoons, connected by natural channels, and has an output via Tramandaí estuary into the ocean. This system is divided into two subsystems, north and south of the Tramandaí estuary, as result of hydrodynamic patterns, influence of wind and environmental characteristics that define the subsystems. A trophic gradient decreasing from north to south in those lagoons was identified. In this study is tested the hypothesis of spatial (lagoons and subsystems) and temporal (seasons) variabilities in the amplitude of abiotic variables and descriptors of the fish assemblages (species composition, richness, diversity, dominance) in the SRT. It also assessed the relationship between abiotic variables and descriptors of the fish assemblages in these subsystems. Is compared the selectivity of the active fishing (beach seining) and passive (gill netting) fishing. Sampling was conducted from November 2008 to April 2010 with beach seine and gill nets in the littoral zone of lakes Itapeva, Quadros and Malvas in north subsystem, and Fortaleza, Rondinha and Barros lakes, in south subsystem. Between April 2009 and March 2010 water samples were collected and ten variables were measured in the laboratory. Analyses of ordination (NMDS) showed clear differences in composition, numerical abundance (CPUEn) and biomass (CPUEb) of species between samplers. The analysis of similarity (ANOSIM and SIMPER) showed low similarity of these parameters between nets. There was a difference in the size of the fish caught with beach seine and gill nets. Turbidity and BOD5 averages were higher in the northern subsystem, while the conductivity, salinity, hardness, total dissolved solids and Secchi transparency in the south subsystem. Temporally were observed differences in temperature, pH, salinity, turbidity, hardness, total dissolved solids, dissolved oxygen, suspended solids and depth, but only the data for pH, conductivity, turbidity, BOD5 showed interaction between the factors space and time. The assemblages of the shallow margins of the coastal zone were dominated by ten species resulting in high similarity of composition, CPUEn and CPUEb between subsystems. Species richness varied spatially and temporally, while diversity and evenness only spatially and CPUEn and CPUEb only temporally. The assemblages of the pelagic regions of the coastal zone were dominated by seven species with numerical dominance of L. anus and A. aff. fasciatus in north subsystem. The NMDS showed greatest similarity in composition, CPUEn and CPUEb between samples of the same subsystem, the ANOSIM however, showed no significant results for rejection of the null hypothesis. CPUE n and b, diversity and equitability varied between lakes and subsystems, while the richness between seasons. The canonical correlation analysis (CCA) showed that four variables (temperature, BOD, suspended solids and hardness) account for 46% of data variability of species abundance. Samples of the north subsystem were directly influenced by temperature, BOD and suspended solids while the south subsystem by the hardness. The results suggest that active and passive samplers reproduce different images of the assemblage sampled and indicate that the sampling design for studies of these ecosystems should include such differences. The environmental differences in subsystems reflect in water quality differences and the results confirm the assumptions of a trophic gradient decreasing from north to south in the SRT. The structure of the fish assemblages was more variable in response to environmental conditions in spatial scale between subsystems, while there was greater consistency in the temporal variability of the data. The relationships between the species and environmental variables are discussed based on the feeding behavior and / or reproduction of the same and by habitat quality. These results may be useful as an aid to preparing studies of coastal management of SRT, especially with respect to fisheries, and in proposing models of the structure of the fish assemblages of subtropical coastal lagoons.
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Banerjee, Sagarika. "EFFECTS OF LIVESTOCK ANTIBIOTICS ON NITRIFICATION, DENITRIFICATION, AND MICROBIAL COMMUNITY COMPOSITON IN SOILS ALONG A TOPOGRAPHIC GRADIENT." UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_theses/43.
Abstract:
Several types of antibiotics (roxarsone, virginiamycin, and bacitracin) are widely included in poultry feed to improve animal growth yields. Most of the antibiotics are excreted in manure which is subsequently applied to soils. One concern with this practice is that antibiotics may affect several microbially-mediated nutrient cycling reactions in soils that influence crop productivity and water quality. The main objectives of this study were to determine the effects of livestock antibiotics on nitrification, denitrification, and microbial community composition in soils along a topographic gradient. These objectives were addressed in a series of lab experiments by monitoring changes in inorganic N species and ester-linked fatty acid methyl ester profiles after exposing soil microorganisms collected from different topographic positions to increasing levels of antibiotics. It was discovered that roxarsone and virginiamycin inhibited nitrification and soil microbial growth and also influenced microbial community composition, but only at levels that were much higher than expected in poultry litter-applied soils. Bacitracin did not affect nitrification, microbial growth, or microbial community composition at any concentration tested. None of the antibiotics had a strong affect on denitrification. Thus, it is unlikely that soil, water, or air quality would be significantly impacted by the antibiotics contained in poultry litter.
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Crawford, Wayne Fortune Ron. "Criteria for evaluating composition their place in students' composing processes /." Normal, Ill. Illinois State University, 1997. http://wwwlib.umi.com/cr/ilstu/fullcit?p9819891.
Abstract:
Thesis (Ph. D.)--Illinois State University, 1997.Title from title page screen, viewed June 14, 2006. Dissertation Committee: Ron Fortune (chair), Doug Hesse, Janice Neuleib, Maurice Scharton. Includes bibliographical references (leaves 191-201) and abstract. Also available in print.
49
Bhuta, Arvind Aniel Rombawa. "Variation in the structure, composition, and dynamics of a foundation tree species at multiple scales and gradients." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/40487.
Abstract:
Scientists and land managers often focus on the Southeastern Plains and Coastal Plain of the southeastern United States when considering the ecology, restoration, and management of longleaf pine (Pinus palustris P. Mill.) communities and ecosystems. However, the range of this foundation tree species and its associated communities and ecosystems also extend into the Piedmont and Montane Uplands: the Piedmont of Alabama, Georgia, North and South Carolina and Virginia; the Ridge and Valley of Alabama and Georgia; and the Southwestern Appalachians of Alabama. The composition, structure, and dynamics of Piedmont and Montane Uplands longleaf pine communities have been understudied compared to their Southeastern Plains and Coastal Plain counterparts, and knowledge is based on historical accounts and a handful of studies at site-specific scales. The biogeography and ecology of Piedmont and Montane Uplands longleaf pine communities differ significantly from those in the Southeastern Plains and Coastal Plain. My research combines geospatial and ecological approaches to provide insights on current composition, structure, and dynamics of longleaf pine communities in the Southeastern Plains, Piedmont, and Ridge and Valley at multiple scales and highlights differences and similarities with communities in the Coastal Plain. The Piedmont and Montane Uplands longleaf pine communities showed high variation in canopy tree diversity compared to those in the Coastal Plain. Longleaf pine was sometimes the only canopy tree, while in other communities longleaf pine was one constituent in a mixed oak-pine canopy. My study showed that longleaf pine communities were not just restricted to south-facing slopes as previously thought, but were found on northwestern-facing slopes as well. Analysis of tree rings across my study sites showed that as longleaf pine approaches its northern range margin in the Piedmont and Montane Uplands, its radial growth is restricted by minimum temperature especially at longleaf pineâ s elevational, latitudinal, and longitudinal extremes; at all sties radial growth was influenced by drought and precipitation. At the local scale, I found that an Alabama Piedmont longleaf pine community showed a diameter-class distribution typical of an old-growth site but contrary to current knowledge, diameter was not a good indicator of age.Ph. D.
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Ombres, Erica H. "Gradients in Season, Latitude, and Sea Ice: Their Effect on Metabolism and Stable Isotopic Composition of Antarctic Micronekton." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4554.
Abstract:
Respiration, metabolic enzyme assays, and body composition parameters were measured in the Antarctic krill Euphausia superba during the summer, fall and winter on the Western Antarctic Peninsula (WAP). E. superba of all sizes decrease their metabolism from the summer to the winter. These same parameters were also measured along the WAP during the austral fall 2010. E. superba's enzyme activity indicated that there was a latitudinal gradient to the decline in metabolism along the WAP with the more northerly sites having significantly higher metabolic enzyme activities than the sites to the south.
Carbon (δ13C) and nitrogen (δ15N) stable isotopes were measured in E. superba along the WAP to determine if there were any latitudinal trends. δ13C showed a significant trend with latitude with more depleted δ13C values in the southern portion of the WAP. Carbon (δ13C) and nitrogen (δ15N) stable isotopes were also measured in two important prey fishes along the WAP, the silverfish Pleuragramma antarcticum and the myctophid Electrona antarctica. P. antarcticum had a more variable and more enriched δ13C value than E. antarctica indicative of P. antarcticum's more neritic habitat. There were no significant differences between the δ15N values of the two fish, indicating that although they feed in different areas they were feeding at the same trophic level.
Carbon (δ13C) and nitrogen (δ15N) stable isotopes were measured in twenty species in the marginal ice zone (MIZ) of the Weddell Sea at the beginning of the austral summer. Samples were taken from under the ice, at the ice edge and in the open ocean. A significant trend in the δ13C values of all species was found with the under-ice δ13C values being more depleted than those in the open ocean. This is most likely due to the reduced atmospheric exchange of CO2, upwelled water with depleted δ13C values, and continuous biological respiration under the ice, all of which contribute to very depleted δ13C values. δ15N values were significantly lower in the open ocean than the other ice conditions due to the increased reliance on primary production. The diapausing copepods Calanoides acutus and Rhincalanus gigas showed similar patterns in their isotopic signatures across the ice zones. Cluster analysis revealed trophic shifts between the different ice zones. The ice edge zone proved to contain the most species and was the best habitat for most species. The trophic shifts observed within species in the differing ice conditions mimicked the seasonal changes they undergo during the course of the productive season every year.