In avocado, an economically important crop, fruits can store up to 70 % oil in the form of triacylglycerols (TAGs). While TAG synthesis in seed tissues mostly depends on an acyl CoA-dependent enzyme, diacylglycerol (DAG) acyltransferase (DGAT) to catalyze the conversion of DAG to TAG, the enzymes involved in non-seed tissues remains to be elucidated. Recent studies on oil palm suggested participation of an acyl-CoA-independent enzyme, phospholipid:diacylglycerol acyltransferase (PDAT), in TAG synthesis. Our research focuses on identifying acyltransferases involved in oil accumulation in mesocarp tissues of avocado. Furthermore, in ‘Hass’ avocado, where 20-60 % of the fruit are phenotypically small, even under favorable conditions, we are interested in determining the association between oil accumulation and fruit size. To this extent, we quantified gene expression levels for DGAT 1 and 2 and PDAT and the rate of oil accumulation in developing mesocarp (oilrich) and seed (non-oil rich) tissues of phenotypically 'small' and 'normal' fruits, using real-time PCR and gas chromatography, respectively. Candidate acyltransferase genes, highly expressed in mesocarp but not in seed, will be cloned and characterized. Understanding TAG synthesis in non-seed tissues will allow us to develop genetic tools necessary for generating bioenergy-rich crops.

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Cover crops play a part in improving sustainability by reducing negative environmental impacts such as soil erosion and nutrient runoff. Energycane could benefit from cover crops due to its row spacing. This study was conducted at the Bearden Dairy Research Center to determine differences in nitrogen accumulation, weed suppression, and energycane yield among treatments. Four cool-season species (planted in the fall of 2020 and 2021) [balansa clover (Trifolium michelianum), hairy vetch (Vicia villosa), white clover (T. repens) and winter pea (Pisum sativum subsp. arvense)], and four warm-season species (planted in the spring of 2021 and 2022 [alfalfa (Medicago sativa), alyceclover (Alysicarpus vaginalis), soybean (Glycine max), and sunnhemp (Crotalaria juncea)] plus negative and positive controls (0 and 168 kg N ha-1) were used. Regarding cool-season cover crops, significant differences were seen in all previously mentioned metrics. Warm-season cover crops only showed differences regarding nitrogen accumulation and weed suppression abilities.

No description available.

In this study, we develop a method of life prediction of buried pipe using the concepts of a characteristic damage state and damage accumulation. A stress analysis corresponding to the different types of load during service with environmental effects, a moisture diffusion model, and a lifetime prediction analysis combining the above models has been constructed. The model uses an elasticity solution for axial-symmetric loading in the case of pressurized pipe, and an approximate non-linear solution for transverse loading due to soil pressure in the case of buried pipe. The axial-symmetric stress analysis has been constructed taking into account the moisture content and the temperature of each ply of the laminate. The moisture diffusion model takes into account the geometry of the laminate, the different diffusivity coefficients in each ply, and also the geometric changes due to ply failure. The failure mode and material behavior of the pipe has been investigated and identified according to Owens Corning data. Thus, the code that has been developed allows one to predict the time to failure of Owens Corning industrial pipes under any time-dependent profile of environmental and loading conditions. / Master of Science

Sediment and microplastic accumulation in stream systems occur when particulates entrained in overbank flow are retained by the floodplain. Despite overbank flow conditions dictating sediment and microplastic accumulation, the spatial distribution of accumulation within floodplains remains poorly understood. Difficulty quantifying hydraulic flow conditions is due to spatial variation introducing erroneous error. This study hypothesized floodplain sediment and microplastic accumulation would be closely correlated with topographic, vegetative, and hydraulic conditions. To test this hypothesis, sediment and microplastic accumulation were measured along a 1.25 km stretch of Stroubles Creek in Blacksburg, Virginia. Sediment accumulation was measured using tiles with a surface area of 144cm² at 75 locations. Tiles accumulated 4,782g over their two-year deployment. Microplastic accumulation was assessed by taking 15cm3 soil grab samples from 40 locations. Microplastics were identified using FTIR spectroscopy and were found to have a concentration of approximately 7MPm-3. Topographic and vegetative variables were measured using digital elevation and canopy height models, while hydraulic variables were calculated with an unsteady flow model in HEC-RAS. Sediment and microplastic accumulation were both found to be significantly influenced by terrain and hydraulic conditions. Sediment accumulation yielded an MLR model with an R2 of 0.72, with a confidence level between 97% - 99%, while the microplastic model yielded an R2 of 0.26 and with a confidence level between 95% - 98%. Differences in sediment and microplastics particle density resulted in hydraulic conditions being more influential on microplastic accumulation with an R2 81.5% greater than any its terrain components. This research identified floodplain accumulation process drivers which could help to guide future management decisions regarding sediment storage and monitoring microplastic accumulation. / Master of Science / Streams act as natural thoroughfares, with the potential to transport materials beneficial and harmful to biological and environmental processes. During flood events, the material carried by stream flow is often deposited in areas adjacent to the main channel. These adjacent areas are called floodplains and contribute to the accumulation of sediment and small pieces of plastic in stream systems. Spatial patterns in floodplain accumulation are believed to be the result of site-specific terrain, vegetation, and flow conditions within a stream system. In the context of a stream system, descriptive characteristics of terrain, vegetation, and flow conditions are heavily confounded making their relationship with floodplain accumulation difficult to interoperate. This study aims to understand the accumulation of sediment and plastics in the Stroubles Creek floodplain by evaluating the terrain, vegetative, and flow conditions believed to influence systematic patterns in accumulation. Floodplain sediment and plastic accumulation were measured along a 2 km reach of Stroubles Creek at 75 and 40 sampling locations. Terrain, vegetative, and flow conditions at each of the sediment (75) and plastic (40) sampling locations were determined to be the characteristics driving their relative accumulation process. The distance and change in elevation of the sampling locations from the channel, flow velocity of water, arrival time and duration of time each location experienced floodwaters were observed to have the most significant impact on accumulation processes. However, the degree to which each of these variables affected sediment and plastic accumulation differed. These findings suggest that sediment and plastic accumulation are both heavily influenced by terrain and flow conditions; however, the processes by which sediment and microplastics accumulate in the floodplain are likely to differ.

La présente thèse s’articule autour de deux sujets. Le premier concerne la localisation des électrons en présence d’impuretés ou d’interfaces dans le réseau hexagonal. Le deuxième, en revanche, traite de l’accumulation de spin dans un supraconducteur hors-Équilibre de type s.Le graphène est la principale motivation de la première partie. Ce matériau bidimensionnel consiste en un feuillet d’atomes de carbones et peut être décrit comme un réseau hexagonal, c’est-à-dire un réseau de Bravais triangulaire avec un motif diatomique. La structure de bande électronique révèle alors l’existence d’électrons de Dirac sans masse et chiraux à basse énergie.D’une part, il est possible d’annihiler ces fermions chiraux en étirant de façon uni-Axiale le matériau. Pour une valeur seuil de l’étirement, les électrons deviennent massiques et non-Relativistes, ce qui définit une transition de phase dite de Lifshitz. Afin de caractériser cette transition, nous étudions la diffusion des électrons sur des impuretés en fonction de l’étirement. Une impureté localisée induit des interférences quantiques dans la densité électronique, connues sous le nom d’oscillations de Friedel. Etant sensibles à la nature chirale des électrons, nous montrons que ces oscillations décroissent selon des lois de puissances qui permettent de caractériser chacune des phases de la transition. La même étude est réalisée dans le cas limite où le diffuseur est une lacune.D’autre part, le motif diatomique du réseau hexagonal propose aussi une incursion dans le monde des isolants et supraconducteurs topologiques. Pour ces systèmes, la caractérisation topologique de la structure de bande électronique permet de prédire l’existence d’états de bord aux interfaces. Nous développons notamment un modèle de supraconducteur topologique basé sur le réseau hexagonal du graphène, en présence de supraconductivité de type singulet (s ou d). Lorsque la symétrie par renversement du temps est brisée par un champ Zeeman, et en présence de couplage spin-Orbit Rashba, nous donnons une prescription qui permet de caractériser les différentes phases topologiques possibles et de prédire l’apparition d’états de bord (états de Majorana) dans des nano-Rubans de graphène.La seconde partie discute l’accumulation de spin dans un supraconducteur hors-Équilibre, joint à un ferromagnétique. Lorsqu’il est à l’équilibre, le supraconducteur est composé de quasiparticules et d’un condensat. L’injection de particules polarisées en charge et en spin, à savoir des électrons polarisés en spin, induit une accumulation de spin et de charge à l’intérieur du supraconducteur. Si l’injection cesse, les populations de spin et de charge vont relaxer vers l’équilibre, mais pas nécessairement sur des échelles de temps identiques. Récemment, la réalisation d’une expérience a mis en évidence que le la charge pouvait relaxer bien plus rapidement que le spin. Afin de confirmer cet effet, une nouvelle expérience a été réalisée grâce à des mesures établies dans le domaine fréquentiel. Ici, nous adressons un model relatif à cette dernière expérience, dans le but d’extraire le temps caractéristique de relaxation du spin qui s’avère être de l’ordre de quelques nanosecondes. / Two fields of research define the framework in which the present thesis can be apprehended. The first one deals with impurity and boundary modes in the hexagonal lattice. The second one concerns a spin accumulation in an out-Of-Equilibrium superconductor.Two fields of research define the framework in which the present thesis can be apprehended. The first one deals with impurity and boundary modes in the hexagonal lattice. The second one concerns a spin accumulation in an out-Of-Equilibrium superconductor.Graphene is the main motivation of the first part. From a crystallographic perspective, the carbon atoms in graphene, a graphite layer, design a triangular Bravais lattice with a diatomic pattern. This gives rise to an extra degree of freedom in the electronic band structure that crucially reveals chiral massless Dirac electrons at low-Energy. First of all, it is possible to make these chiral fermions annihilate when a uniaxial strain stretches the graphene layer. For a critical value of the strain, all the fermions become massive and nonrelativistic, which defines a Lifshitz transition. We study the impurity scattering as a function of the strain magnitude. A localised impurity yields quantum interferences in the local density of states that are known as Friedel oscillations. Because they are affected by the chiral nature of the electrons, we show that the decaying laws of these oscillations are specific to the phase the system belongs to. Thus, the impurity scattering offers the possibility to fully characterise the transition.Second, the diatomic pattern of the graphene lattice can also be considered as an invitation to the world of topological insulators and superconductors. The existence of edge states in such systems relies on the topological characterization of the band structure. Here we especially introduce a model of topological superconductor based on the honeycomb lattice with induces spin-Singlet superconductivity. When a Zeeman field breaks the time-Reversal invariance, and in the presence of Rashba spin-Orbit interactions, we give a prescription to describe the topological phases of the system and predict the emergence of Majorana modes (edge states) in strained and doped nanoribbons.The second part discusses the study of a spin accumulation in an out-Of-Equilibrium s-Wave superconductor. At the equilibrium, the superconductor is made of particles coupled by a s-Wave pairing, as well as unpaired quasiparticles. Injecting spin-Polarised electrons into the superconductor induces charge and spin imbalances. When the injection stops, it may happen that charge and spin do not relax over the same time-Scale. The first experiment that points out such a spin-Charge decoupling has recently been realised. In order to confirm this chargeless spin-Relaxation time, a new experiment has been developed [96], based on measurements in the frequency domain. Here, we address a model that fits the experimental data and thus enables the extraction of this characteristic time that is of the order of a few nanoseconds.

Les structures d’échappement de fluides et leurs mécanismes de migration à travers la pile sédimentaire sont un phénomène connu sur les marges continentales. Elles ont été largement étudiées depuis une vingtaine d’années, notamment en raison de l’amélioration de la résolution des données sismiques, et de l’abondance des données dans ces zones, du fait de la prospection pétrolière. Le bassin du Bas Congo, au large de l'Afrique de l’ouest, est une province pétrolière prolifique qui a été largement étudiée et qui est exploitée depuis plus de 30 ans. La zone d’intérêt est située au-dessus d'un champ pétrolier producteur (la zone de Moho), dans laquelle les hydrocarbures sont piégés dans des chenaux turbiditiques. Le travail est principalement basé sur l'analyse de données géophysiques comprenant de la sismique 3D et 2D-THR, de la bathymétrie multifaisceaux et la rétrodiffusion correspondante, ainsi que des données de fond (échantillons prélevés, photos ROV, analyses géochimiques). L'analyse de cet important jeu de données sismiques a révélé de nombreuses évidences de migration de fluides dans la pile sédimentaire mio-pliocène. Ces dernières correspondent principalement à des indices de migration focalisée de fluides, incluant des structures actuelles d’expulsion de fluides sur le fond de l’eau et des structures enfouies, interprétées comme fossiles, et indiquant une activité ancienne du système d’expulsion de fluides. Les indices de migrations de fluides étudiés correspondent principalement à des pockmarks (dépressions) et à des cimentations carbonatées. Ces deux types d’indices peuvent s’empiler sur plusieurs centaines de mètres, mettant en évidence la pérennité des échappements et suggérant le développement de véritables conduits.Un nouveau type de pockmarks a été mis en évidence, les structures en araignée, qui sont localisées au-dessus d'un réservoir turbiditique, et qui résultent d'une migration focalisée des hydrocarbures thermogéniques. Leur fonctionnement est lié aux hydrates de gaz dans le contexte d’un BSR penté (Bottom Simulating Reflector), du fait de la présence du biseau des hydrates. Un modèle dynamique de leur fonctionnement est développé, montrant que ces structures se développent vers l'amont de la pente, du fait de la migration du gaz sous le BSR penté. Une étude du BSR, dans le contexte particulier du biseau des hydrates, permet de proposer un modèle des échappements de gaz liés à la dissociation des hydrates, lors d'une baisse du niveau marin. Ce modèle met en scène une dissociation des hydrates de gaz d'échelle régionale (associée à du gaz biogénique), localisée au niveau du biseau des hydrates du dernier bas niveau marin. Enfin, le réseau de structures d’échappements de fluides de l’intervalle Mio-Pliocène a été investigué dans le but de comprendre son architecture et les mécanismes de migration de fluides dans la zone d’étude. Les hydrocarbures semblent migrer principalement le long de certaines portions de failles et verticalement à travers la pile sédimentaire sous forme de « pipes » ou de cheminées. La base du Pliocène, associée à une baisse du niveau marin, marque la formation des premières paléo-araignées ainsi que d'un niveau contenant de nombreux indices de présence de gaz. Un modèle de ce réseau de migrations de fluides est proposé, intégrant les chemins de migrations des hydrocarbures à travers la pile sédimentaire, et l’événement majeur de la base Pliocène. Cette étude semble indiquer que les phases de baisse du niveau marin constituent des déclencheurs pour la migrations des fluides dans les bassins.Ce travail marque ainsi le point de départ d'une investigation à plus grande échelle qui consiste d'une part à rechercher des structures similaires (araignées et bandes de pockmarks) dans d'autres bassins et d'autres part à comparer les événements d'échappement de fluides à la courbe eustatique. / Evidence of fluid flow features and their mechanisms of migration through the sedimentary pile are a known phenomenon on continental margins. It has been widely studied over the past twenty years, notably due to the improved resolution of seismic data and the abundance of data in these areas due to oil and gas exploration.The Lower Congo basin, offshore West Africa, is a prolific petroleum province that has been extensively studied, and has been in operation for over 30 years. The area of interest is located above a producing oil field (the Moho license), in which hydrocarbons are trapped in turbidite channels. The work is primarily based on the analysis of geophysical data including 3D and 2D-THR seismic, multibeam bathymetry and corresponding backscatter, as well as background data (samples taken from ROV photos, geochemical analyses).The analysis of this important seismic dataset revealed abundant evidence of fluid migration in the Mio-Pliocene sedimentary pile. They mainly correspond to indications of vertically focused migration, including current fluid expulsion structures on the seafloor, and buried structures, interpreted as fossile and indicating former activity of the fluid expulsion system. The studied fluid migration features mainly consist of pockmarks (depressions) and carbonate cementations. These two types of indicators can build vertical stacks, over several hundred meters, highlighting the durability of the fluid escapes and suggesting the development of real pipes.A new type of pockmarks has been discovered, the spider structures, which are located above a turbiditic reservoir, and which result from a focused migration of thermogenic hydrocarbons. They are related to gas hydrates, in the context of a sloping BSR (Bottom Simulating Reflector), due to the presence of the hydrate wedge. A dynamic model of their functioning is proposed, showing that these structures develop upslope, due to the gas migration under the sloping BSR. A study of the BSR, in the particular context of the hydrates wedge, allows to propose a model of gas escapes, linked to the dissociation of the hydrates, during a sea level fall. This model presents a dissociation of gas hydrates of regional scale (associated with biogenic gas), localized at the gas hydrate wedge zone of the last lowstand. Finally, the network of fluid escape structures of the Mio-Pliocene interval was investigated in order to understand its architecture and the mechanisms of fluid migration in the study area. Hydrocarbons appear to migrate mainly along certain portions of faults and vertically crosscutting the sedimentary pile through pipes or chimneys. The base of the Pliocene, associated with a sea level fall, marks the formation of the first paleo-spiders, as well as a level containing numerous evidence of gas. A model of this network of fluid migrations is proposed, integrating the indicators of hydrocarbon migrations through the sedimentary pile, and the major event of the Pliocene base. This study seems to indicate that a the sea level fall constitute a trigger for the fluids migrations, in the basin.This work thus marks the starting point of a larger-scale investigation which consists in, on the one hand, searching for similar structures (spiders and bands of pockmarks) in other basins ; and, on the other hand, by comparing fluid flow events with the eustatic curve.

Si vous voulez prendre votre train à l'heure, vous devez estimer à quelle distance se trouve la gare et combien de temps vous allez mettre pour y aller. Plusieurs études ont montré qu'il existe des interactions dans la perception de différentes dimensions. En 2003, Walsh a suggéré que le Temps, l'Espace et les Nombres faisaient partie d'un système de magnitudes commun qui serait localisé dans le cortex pariétal. Dans cette thèse nous avons étudié l'existence d'un tel système. La manipulation de la magnitude de dimensions non-temporelles n'a pas interféré avec les jugements de durée. En revanche, l'estimation du nombre et de l'espace a été biaisée par le taux d'accumulation d'évidence sensorielle. Dans une première expérience nous avons cherché à savoir si un système de magnitudes basé sur des probabilités Bayesiennes nécessitait l'utilisation d'un " prior " unique, amodal, ou alors nécessitait plusieurs " priors ". D'un point de vue Bayesien, nos résultats indiquent que l'estimation de différentes dimensions requiert plusieurs " priors ", ce qui ne supporte pas l'existence d'un système de magnitude commun. Pour étudier l'effet du nombre sur l'estimation de la durée, nous avons effectué une seconde étude dans laquelle les participants devaient reproduire des intervalles de temps et également juger la valeur numérique du stimulus visuel. Les résultats ont montré que l'interaction temps-nombre dépend essentiellement du format numérique utilisé (symbolique ou non symbolique). Ces résultats suggèrent que la magnitude numérique est automatiquement traitée alors que des ressources attentionnelles sont requises lorsque l'information numérique est présentée symboliquement. / If you want to catch your train on time you have to estimate how far the station is from your current position and how long it will take you to go there. A growing body of evidence suggests that interferences may exist in the perception of different magnitude dimensions. These relationships fascinate researchers for decades and led Walsh (2003) to hypothesize that Time, Space and Number were part of a generalized magnitude system which may be located in the parietal cortex. In this thesis, we first investigated the possible existence of such system. Manipulating non-temporal magnitude dimensions did not interfere with duration judgments. Instead, numerical and spatial estimates were biased when we manipulated the rate of accumulation of sensory evidence. In this first experiment we asked whether a generalized Bayesian magnitude estimation system would sample evidence using a common, amodal prior, as expected by a generalized magnitude system. Our results suggested that from a Bayesian perspective, computations would necessitate multiple priors. This work provides substantial evidence against the existence of a generalized magnitude system. To further investigate interferences of numerical magnitude on perceived duration, we built a second experiment in which participants were required to reproduce intervals of time and also judge the numerical magnitude of the stimulus. Our results revealed that the number-time interaction depended on the numerical format that was used. Our work suggests that the numerical magnitude is automatically processed at a non-symbolic level whereas it requires attentional resources when numerical information is symbolically conveyed.