This project is concerned with both the study of different Multiple Quantum Wells (MQWs) structures using the In0.53Ga0.47As/In0.52Al0.48As material system lattice matched to InP and a systematic investigation of the properties of InAs QD systems within GaAs with the aim of achieving enhancements of solar cell performance. The key challenge is the growth of QDs solar cell structures which exhibit sufficient absorption (enhanced infrared absorption) to increase short circuit current density (Jsc) but which can still maintains a high open circuit voltage (Voc). The research consists of epitaxial growth using state-of–the-art MBE, optical absorption, photoluminescence and high resolution x-ray diffraction measurements as well as device fabrication and characterization of novel solar cell structures. Optimization was performed on these novel cells to further improve their efficiency by inserting stacks of QD into different regions of the device. The effect of localized doping of such structures was used in an attempt to maintain and enhance the open-circuit voltage which in turn increases the device efficiency. The fabricated devices were characterized using measurements of the dark/light current-voltage (I-V) characteristics and spectral response (50-480 K). Solar cell external quantum efficiencies under standard air mass (AM) 1.5 spectrum were determined and the suitability of these new cells under solar concentration were assessed. Full physical simulations are performed using SILVACO semiconductors modelling software to generate models of multi-junction solar cells that were crucial in informing iterations to growth and fabrication and help to reconcile theory with experiment. One of the key findings, of this thesis, is the fact that Intermediate band photovoltaic devices using material based on InAs/GaAs vertically stacked quantum dot arrays, can be used in applications according to specific configuration criteria such as high temperature operation conditions. The intermediate band cell, including an inter-dot doped configuration, has been found to be a potential candidate as the inter dot doping profile reduces the efficiency degradation below the GaAs values including an enhancement in the open circuit voltage. It has been proved that these devices not only have a good performance at high temperatures but also by changing the vertical stacking QD layer periodicity can enhance the short circuit current density while keeping a large open circuit voltage. It was confirmed in practical device operation that thermal energy is required to enable the intermediate band in InAs/GaAs QD materials. The impact of this works can help in the future improvements of the intermediate band solar cells based on InAs on GaAs QD. The best overall efficiency of 11.6 % obtained in this work is an excellent value for so simple devices configuration. The Si3N4, tested for the first time on InAs/GaAs QD materials, reduces the reflectance on the device surface to a value of 2% and the operational wavelength can be tuned by controlling the layer thickness. A 100 nm Si3N4 antireflective coating proved to be an excellent coating from 700 to 1000 nm. In terms of short circuit current density a 37% enhancement was achieved.

Les travaux présentés contribuent à la modélisation stochastique de la maintenance de systèmes mono- ou multi-composants à détériorations et à modes de défaillances multiples en environnement dynamique. Dans ce cadre, les contributions portent d'une part sur la modélisation des processus de défaillance, et d'autre part sur la proposition de structures de décision de maintenance intégrant les différents types d'information de surveillance en ligne disponible sur le système (état de détérioration mesuré ou reconstruit, état de l'environnement, ...) et le développement des modèles mathématiques d'évaluation associés. Les modèles de détérioration et de défaillances proposés pour les systèmes mono-composants permettent de rendre compte de sources de détérioration multiples (chocs et détérioration graduelle) et d'intégrer les effets de l'environnement sur la dégradation. Pour les systèmes multi-composants, on insiste sur les risques concurrents, indépendants ou dépendants et sur l'intégration de l'environnement. Les modèles de maintenance développés sont adaptés aux modèles de détérioration proposés et permettent de prendre en compte la contribution de chaque source de détérioration dans la décision de maintenance, ou d'intégrer de l'information de surveillance indirecte dans la décision, ou encore de combiner plusieurs types d'actions de maintenance. Dans chaque cas, on montre comment les modèles développés répondent aux problématiques de la maintenance de turbines et de parcs éoliens / The thesis contributes to stochastic maintenance modeling of single or multi-components deteriorating systems with several failure modes evolving in a dynamic environment. In one hand, the failure process modeling is addressed and in the other hand, the thesis proposes maintenance decision rules taking into account available on-line monitoring information (system state, deterioration level, environmental conditions …) and develops mathematical models to measure the performances of the latter decision rules.In the framework of single component systems, the proposed deterioration and failure models take into account several deterioration causes (chocks and wear) and also the impact of environmental conditions on the deterioration. For multi-components systems, the competing risk models are considered and the dependencies and the impact of the environmental conditions are also studied. The proposed maintenance models are suitable for deterioration models and permit to consider different deterioration causes and to analyze the impact of the monitoring on the performances of the maintenance policies. For each case, the interest and applicability of models are analyzed through the example of wind turbine and wind turbine farm maintenance

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Par les représentations qu’elle véhicule et les solutions qu’elle encourage, l’édificationd’une théorie générale n’est jamais neutre au plan axiologique. Sa construction repose certes sur laconnaissance du droit positif de lege lata, mais la mise en ordre qui en résulte demeure quant à elleintimement liée aux perceptions et aux convictions de l’interprète. C’est en ce sens que doit êtreabordée la question de l’apport du droit du travail à la théorie générale de l’acte juridique. La présenteétude met en évidence le caractère protéiforme du phénomène envisagé, sans occulter les situations oùla discipline fait davantage figure de contre modèle que de véritable source d’inspiration. Adoptant unpoint de vue prospectif, cette recherche met en évidence les aspects de droit du travail susceptiblesd’encourager la promotion d’une théorie de l’acte juridique marquée par le pluralisme. La matièrecontribue ainsi à souligner la variété des conditions dans lesquelles se forme la volonté de s’engager,tout comme la diversité de ses modes d’expression. Elle témoigne également d’une capacité certaine àtraduire sur le terrain du Droit, afin de mieux les appréhender, l’altérité des rapports de force et lamutabilité des données factuelles qui accompagnent l’exécution des actes juridiques. / By the representations it conveys and the solutions it encourages, the building of ageneral theory is never neutral in an axiological plan. Although its construction is based on knowledgeof Positive Law de lege lata, the resulting order meanwhile remains closely linked to the perceptionsand beliefs of the interpreter. It is in this sense that must be addressed the question of the contributionof labor law to the general theory of the legal act. This study highlights the protean nature of theconsidered phenomenon, without concealing the situations where the discipline resembles more acounter productive model than a true source of inspiration. Adopting a prospective point of view, thisresearch highlights aspects of the labour law likely to encourage the promotion of a theory of the legalact marked by pluralism. The material thus contributes to underline the variety of conditions in whichforms the willingness to engage oneself, just like the diversity of its modes of expression. It alsoshows a certain capacity to translate in the field of law, in order to understand them better, theotherness of the balances of power and the mutability of the factual data accompanying the executionof legal acts.