Les personnes auto-déclarant une "électrohypersensibilité" (EHS) signalent des problèmes de santé dont des maux de tête, stress, douleurs cutanées, qu'ils lient à l'exposition aux champs électromagnétiques. L'origine, ainsi que le mécanisme de développement des symptômes associés à l'EHS sont à ce jour inexpliqués. L'objectif de la thèse était d'accroître le niveau de connaissance de ce syndrome et ainsi d'identifier d'éventuels troubles biologiques. Ce travail a exploré le fonctionnement des systèmes endocrinien, nerveux autonome, immunitaire et le sommeil chez les EHS à l'aide de marqueurs physiologiques (variabilité du rythme cardiaque, activité électrodermale et rythme respiratoire) et biologiques (marqueurs salivaires et urinaires). Deux études ont été réalisées : une enquête par auto-questionnaire combinée à une étude de caractérisation sans exposition aux champs électromagnétiques et une étude de provocation avec exposition à quatre signaux électromagnétiques successifs. A l'aide du questionnaire, nous avons fourni un aperçu général sur l'EHS en France. Nos résultats sur le sommeil indiquent des perturbations chez les EHS. De plus des marqueurs (alpha amylase et nombre de réponses électrodermales) diffèrent entre les groupes EHS et non EHS. La majorité des marqueurs physiologiques et biologiques n'indiquent pas d'effet en réponse à une exposition électromagnétique chez les EHS. / People suffering from "Electrohypersensitivity" (EHS) report health problems such as headaches, stress, skin pain, that they associate with exposure to electromagnetic fields. So far, origin and underlying mechanism of EHS are unexplained. The aim of this thesis was to bring knew knowledges on this syndrome and identify possible biological markers. This work focused on the endocrine, autonomic, immune functions and sleep in people self-reporting EHS by using physiological (heart rate variability, electrodermal activity and respiration rate) and biological (salivary and urinary) markers. Two studies were performed : a self-questionnaire survey combined with a characterization study without any intentional exposure to electromagnetic fields and a provocation study with exposure to four successive electromagnetic signals. The conducted survey provided an overview of EHS in France. Our results indicate the presence of sleep disturbances in EHS and markers (salivary alpha amylase and number of electro dermal responses) significantly differ between EHS and non EHS group. Most of physiological and biological markers were not affected by electromagnetic exposure in EHS

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En zones marginales, les arbres d'ombrage augmentent la production de café arabica en améliorant le microclimat et la fertilité du sol. En zones optimales, ces effets sont plus controversés mais les systèmes agroforestiers (SAF) procurent toujours d'autres services tels que la lutte antiérosive ou la diversification des productions. Le présent travail compare en zone optimale du Costa Rica une monoculture (MC) et un SAF avec Inga densiflora Benth en termes de microclimat, productivité et bilan hydrique. Par rapport à MC, les arbres d'ombrage ont réduit la radiation globale de 40-50%, les températures maximales foliaires du caféier de 6°C en journée et le VPD foliaire, mais augmenté de nuit les minimales foliaires de 0,5°C. Selon l’année, les arbres ont augmenté l'interception de la pluie (12% à 85%) et la transpiration du système (29% à 33%) mais réduit le ruissellement de 50% et le drainage (1% à 14%). Le SAF a augmenté l'interception (13% de la pluie) par rapport à MC (7%) lorsque le LAI total augmentait de plus d'une unité. Les arbres ont réduit l'égouttement, augmenté l'écoulement le long des troncs et ont contribué pour 40-50% à la transpiration du SAF avec des caféiers transpirant moins qu'en MC. L’assèchement profond du sol sous SAF indique une certaine complémentarité avec les arbres utilisant vraisemblablement des ressources en eau non accessibles au caféier. Malgré l'absence de compétition en eau dans ces conditions de site, la production de café a été réduite de 29% en SAF par rapport à MC du fait d’une radiation et floraison réduites. Par contre, la production de biomasse a été multipliée par 3, contribuant au stockage du carbone et à la production d'énergie. / Under suboptimal site condition for arabica coffee cultivation the shade trees increase the coffee production due to an enhancement of the microclimate and the soil fertility. Under optimal site conditions, the use of shade are more controversial, nevertheless the agroforestry systems (AFS) provide others services as the reduction of erosion and the diversification of production. The present study compare in optimal site conditions in Costa Rica a coffee monoculture (MC) and AFS with Inga densiflora Benth in terms of microclimate, productivity and water balance. In reference to MC, the shade trees reduced the global radiation between 40% to 50%, the maximal coffee leaf temperature to 6°C, the leaf to air VPD during the day and increased the leaf temperature in 0.5°C during night. According to the year of measurement, the trees increased the rainfall interception (12% to 85%) and the total system transpiration (29% to 33%), at the same time trees reduced the runoff (50%) and the drainage (1% to 14%). The trees reduced the throughfall, increased the stemflow and contributed 40% to 50% to the total transpiration of the AFS reducing the coffee transpiration in the AFS. Furthermore, higher reductions in the AFS compared to MC in soil water in deeper soil layers indicate a complementarity interaction in the use of water between coffee and trees. Despite the absence of water competition under these site conditions, the coffee yield was reduced by 29% in the AFS in comparison to the MC, due to a reduction in the radiation and flowering intensity. In other hand, the total aerial biomass was 3 times in the AFS compared to MC, contributing to carbon sequestration and renewable energy.

Circadian rhythms refer to the physiological and biological processes that fluctuate over a 24-hour period. These rhythms are found in most living things such as animals, plants and fungi. In mammals, circadian rhythms are mainly generated and regulated by the suprachiasmatic nucleus (SCN).The period (Per1) gene in the SCN plays a key role in directing circadian rhythms. Per1 expression increases during the day and decreases at night. The neurons which express the Per1 gene show different behaviours to non-Per1 neurons during the day-night cycle. Per1 neurons are in a state of repetitive firing in the morning while in the late morning they display a bursting behaviour. In the afternoon, Per1 neurons divide into two groups: GA and GB, where GA is in a repetitive firing state and GB is silent. At night, these neurons are generally in a quiescent state but late at night they generate spikes. In this study, a standard Hodgkin-Huxley type model was used to study the behaviours of Per1 neurons over the day-night cycle using bifurcation analysis. In this model, the potassium and calcium currents carry the circadian rhythms which are modelled by their conductance. The currents had a significant impact on Per1 neuron behaviours. Furthermore, by changing some of the model parameters, different bistability mechanisms were examined. The study was extended to explore the effect of noise from other neurons on Per1 neuron behaviours. It was shown that noise plays a crucial role in inducing some of the Per1 neuron behaviours and that some Per1 neuron behaviours are fully induced by this noise, e.g. the late morning and late night behaviours. In contrast, the noise was found not to have any significant effect on other Per1 neuron behaviours other than the two behaviours that are observed in the afternoon.

Sixty years after the works of Wigner and Dyson, Random Matrix Theory still remains a very active and challenging area of research, with countless applications in mathematical physics, statistical mechanics and beyond. In this thesis, we focus on rotationally invariant models where the requirement of independence of matrix elements is dropped. Some classical examples are the Jacobi and Wishart-Laguerre (or chiral) ensembles, which constitute the core of the present work. The Wishart-Laguerre ensemble contains covariance matrices of random data, and represents a very important tool in multivariate data analysis, with recent applications to finance and telecommunications. We will first consider large deviations of the maximum eigenvalue, providing new analytical results for its large N behavior, and then a power-law deformation of the classical Wishart-Laguerre ensemble, with possible applications to covariance matrices of financial data. For the Jacobi matrices, which arise naturally in the quantum conductance problem, we provide analytical formulas for quantities of interest for the experiments.

Cryogenic composites find critical application in the manufacture of fuel tanks for reusable launch vehicles due to significant reduction in overall structural weight of the tank. These fuel tanks contain pressurized cryogen such as hydrogen at cryogenic temperatures. Exposure to varying temperatures and mechanical loads resulting from flight cycle, containment of pressurized cryogen causes thermo-mechanical loading of the composite. The thermo-mechanical loading cycles combined with anisotropy of the composite and mismatch in the thermal and mechanical properties of fibers and matrix lead to transverse matrix cracks (TMC) in each ply. TMC in adjacent plies intersect in localized regions at ply interfaces called crack junctions, which open up due to delamination on application of thermo-mechanical load. TMC and crack junctions usually form a network of leakage paths that assists leakage of cryogen through the composite. In this study, the volumetric flow rate of cryogen leaking through a damaged cross-ply composite with five plies is determined by estimating the effective conductance of the leakage paths. For a given damage state and applied load, crack junction and TMC openings are obtained by finite element analysis. A computational fluid dynamics model is first used to estimate the effective conductance of a leakage path to hydrogen leakage and then a simplified analytical model is used to compute the effective conductance from individual conductances of each crack junction and TMC through a series-parallel combination. A single phase flow model is considered for the numerical analysis of hydrogen flow through TMC and crack junctions. The simulations are carried out using a commercial computational fluid dynamics software, FLUENT. Parametric studies are carried out to investigate the dependence of leak rate of hydrogen on the irregularities of the TMC geometry and TMC, crack junction openings. The simplified model predictions of the effective conductance for the five ply composite show good comparison with numerical simulations.

Cryogenic composites find critical application in the manufacture of fuel tanks for reusable launch vehicles due to significant reduction in overall structural weight of the tank. These fuel tanks contain pressurized cryogen such as hydrogen at cryogenic temperatures. Exposure to varying temperatures and mechanical loads resulting from flight cycle, containment of pressurized cryogen causes thermo-mechanical loading of the composite. The thermo-mechanical loading cycles combined with anisotropy of the composite and mismatch in the thermal and mechanical properties of fibers and matrix lead to transverse matrix cracks (TMC) in each ply. TMC in adjacent plies intersect in localized regions at ply interfaces called crack junctions, which open up due to delamination on application of thermo-mechanical load. TMC and crack junctions usually form a network of leakage paths that assists leakage of cryogen through the composite. In this study, the volumetric flow rate of cryogen leaking through a damaged cross-ply composite with five plies is determined by estimating the effective conductance of the leakage paths. For a given damage state and applied load, crack junction and TMC openings are obtained by finite element analysis. A computational fluid dynamics model is first used to estimate the effective conductance of a leakage path to hydrogen leakage and then a simplified analytical model is used to compute the effective conductance from individual conductances of each crack junction and TMC through a series-parallel combination. A single phase flow model is considered for the numerical analysis of hydrogen flow through TMC and crack junctions. The simulations are carried out using a commercial computational fluid dynamics software, FLUENT. Parametric studies are carried out to investigate the dependence of leak rate of hydrogen on the irregularities of the TMC geometry and TMC, crack junction openings. The simplified model predictions of the effective conductance for the five ply composite show good comparison with numerical simulations.

Thermal contact conductance is highly important in a wide variety of applications, from the cooling of electronic chips to the thermal management of spacecraft. The demand for increased efficiency means that components need to withstand higher temperatures and heat transfer rates. Many situations call for contact heat transfer through nominally cylindrical interfaces, yet relatively few studies of contact conductance through cylindrical interfaces have been undertaken. This study presents a review of the experimental and theoretical investigations of the heat transfer characteristics of composite cylinders, presenting data available in open literature in comparison with relevant correlations. The present investigation presents a study of the thermal contact conductance of cylindrical interfaces. The experimental investigation of sixteen different material combinations offers an opportunity to develop predictive correlations of the contact conductance, in conjunction with an analysis of the interface pressure as a function of the thermal state of the individual cylindrical shells. Experimental results of the present study are compared with previously published conductance data and conductance models.

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