Pour répondre à la demande mondiale croissante en huile et en protéines, le tournesol apparaît comme une culture très compétitive grâce à la diversification de ses débouchés et son attractivité environnementale et nutritionnelle. Pourtant, les teneurs en huile et protéines sont soumises à des effets génotypiques et environnementaux qui les rendent fluctuantes et difficilement prédictibles. Nous argumentons qu’une meilleure connaissance des effets les plus importants et leurs interactions devrait permettre de mieux prédire ces teneurs. Deux approches de modélisation ont été développées. Dans la première, trois modèles statistiques ont été construits puis comparés à un modèle simple existant. L’approche dynamique est basée sur l’analyse des relations source-puits au champ et en serre (2011 et 2012) pendant le remplissage. Les performances et domaines de validité des deux types de modélisation sont comparés. / Considering the growing global demand for oil and protein, sunflower appears as a highly competitive crop, thanks to the diversification of its markets and environmental attractiveness and health. Yet the protein and oil contents are submitted to genotypic and environmental effects that make them fluctuating and hardly predictable. We argue that a better knowledge of most important effects and their interactions should permit to improve prediction. Two modeling approaches are proposed: statistical one, where we compared three types of statistical models with a simple existing one. The dynamic approach is based on source-sink relationships analysis (field and greenhouse experiments in 2011 and 2012) during grain filling. Performances of both modeling types and their validity domain are compared.

During the summers of 2007-2009, I studied the population growth and reproductive and foraging ecology of the Razorbill (Alca torda) at Matinicus Rock (MR), Maine. This medium-sized marine bird in the family Alcidae (auks) was extirpated from the Gulf of Maine in the late 19th century by hunting, collecting, and colony disturbance. Following legislation protecting seabirds and their nesting habitats, the Razorbill has recolonized probable former nesting habitat in the Gulf of Maine during the past several decades. Six small colonies comprise the Maine population, which is listed as threatened and forms the southern extension of the species breeding distribution. In Chapter 1, I present a population model of the MR breeding colony, based on studies of population growth and reproductive success, and supplemented with previously collected data from the National Audubon Society Seabird Restoration Program (Project Puffin), with whom I collaborated. I also describe chick diet (supplemented with Project Puffin data) and draw connections between diet and reproductive success. I found that reproductive success was too low to account for the observed population growth rate, and conclude that the colony is a sink population supported by substantial immigration. Because annual fledging success was positively associated with prey quality, I suggest that substandard chick diet may contribute to the sink population dynamic via diet-driven depressed fledging success. In Chapter 2, I report on the foraging behavior of chick-rearing Razorbills fitted with bird-borne data-loggers at MR in 2008-2009. I describe diving behavior including depth, duration, and profile shape of dives, as well as diel patterns. Diving activity was restricted to daylight hours, and dives were shallowest and most frequent in the evening. Though generally similar to diving behavior reported at four European and Canadian colonies, Razorbills at MR performed three times as many dives per day as at the Gannet Islands, Labrador, and the mean dive depth was greater than three of four previous studies. Deeper and more frequent dives may indicate higher foraging effort and lower prey availability. Reproductive success would suffer if parents cannot buffer chicks against the effects of low prey availability through increased foraging effort or other behavioral modifications. Together, the pieces of our research indicate that prey availability may be negatively affecting reproduction and population growth at MR. Rapid colony growth cannot be explained by local reproductive success, and is likely the result of substantial immigration from other colonies. Chick diet is varied and includes multiple high-quality forage fish species, yet chicks also consume poor-quality prey (larval fish and euphausiids) that may signal periods of very poor prey availability. Frequency and depth of dives made by chick-provisioning adults are also suggestive of parents allocating extra effort to foraging, relative to other colonies.

Les travaux de la présente thèse porteront sur le raffinement du modèle du potentiel source-puits (SSP) proposé par Ernzerhof en 2006. Cette méthode permet de calculer la conductance qualitative de dispositifs électroniques moléculaires (MEDs). Dans la première partie de ce travail, le modèle SSP sera amélioré en y intégrant la description de l’interaction d’un champ électromagnétique fort avec le MED. Des expériences récentes ont démontré que des molécules pouvaient interagir fortement avec des plasmons de polaritons de surface (SPP). Ces interactions créent des états liés électron-SPP qui seront exploités pour contrôler la conductance de MEDs. Des formules analytiques expliqueront l’impact des paramètres physiques de ces circuits optoélectroniques sur la conductance de ceux-ci. Dans le même esprit, la seconde partie de cette thèse inclura les interactions électron-noyau au modèle SSP afin de décrire entre autres le courant décohérent d’un MED. Dans ce modèle les interactions noyau-électron seront décrites à partir de l’approximation harmonique et intégrées à l’hamiltonien de façon non-pertubative. Des formules analytiques seront dérivées afin de décrire la conductance de tels MEDs. Finalement, les conséquences du bris de la symétrie de la parité et du temps de la matrice hamiltonienne de la méthode SSP seront découvertes dans la densité spectrale et les fonctions d’ondes des MEDs. / The purpose of this thesis is to expand the scope of the source-sink potential (SSP) method originally proposed by Ernzerhof in 2006. The SSP model allows the computation of the qualitative conductance of molecular electronics devices (MEDs). In the first part of this work, the SSP model will be improved by including the description of interaction between the strong electromagnetic field and the MED. Recent experiments have shown that molecules could strongly interact with surface plasmon of polaritons (SPPs). These interactions will create so-called dressed states that can be used to control the conductance of MEDs. In the second part of this work, the SSP model will be augmented by including electron-nucleus interactions to describe the inelastic current. In this model, the electron-nuclueus interaction will be account for with the help of the harmonic approximation and incorporated into the hamiltonian non-pertubatively. Analytical formulas will be derived that will allow one to understand the impact of physical parameters on the conductance of MEDs. Lastly, the impact of the parity and time symmetry breaking of the SSP matrix hamiltonian will be studied and related to change in the spectral density and in the eigenfunctions of the MEDs.