Cette étude propose d’analyser l’influence de l’architecture du palmier à huile sur sa capacité à intercepter la lumière, en se basant sur des reconstructions 3D de palmiers et en établissant un bilan radiatif sur ses structures végétales reconstruites in silico. Le premier objectif de l’étude était de caractériser et modéliser la variabilité génétique de l’architecture du palmier à huile et de son interception lumineuse. Dans un deuxième objectif l’amélioration potentielle de l’interception de la lumière et de l’assimilation carbonée a été évaluée en modifiant les traits morphologiques et géométriques des feuilles et des idéotypes architecturaux de palmiers à huile ont été proposés.Des relations allométriques ont été utilisées pour modéliser les traits architecturaux en fonction de gradients ontogénétique et de topologie des feuilles dans la couronne. La méthode permet de reconstruire des palmiers à huile virtuels à différents âges au cours du développement. De plus, l’approche allométrique a été couplée à des modèles à effets mixtes pour intégrer au travers de paramètres la variabilité entre et au sein des cinq progénies. Le modèle permet ainsi de simuler les spécificités architecturales des cinq progenies en incluant les variabilités entre individus observés. Le modèle architectural, paramétré pour les différentes progénies, a ensuite été implémenté dans AMAPstudio pour générer des maquettes 3D de palmiers et ainsi estimer leur interception lumineuse, de l’individu à la parcelle entière.Les résultats de ces analyses ont révélé des différences significatives entre et au sein des progenies, dans la géométrie des feuilles (longueur du pétiole, densité de folioles sur le rachis, et courbure du rachis) et dans la morphologie des folioles (gradients de longueurs et largeurs le long du rachis). La comparaison virtuelle des différentes progénies ont aussi montré des efficacités distinctes de l’interception lumineuse.Des analyses de sensibilité ont ensuite été réalisées pour identifier les traits architecturaux influençant l’interception lumineuse et l’assimilation potentielle à différents âges de la plante. Les paramètres les plus sensibles au cours du développement furent ceux reliés à la surface totale foliaire (longueur des rachis, nombre de folioles, morphologie des folioles), mais les attributs géométriques plus fins de la feuille ont montré un effet croissant avec la fermeture de la canopée. Sur un couvert adulte, l’optimum en assimilation carbonée est atteint pour des indices de surfaces foliaires (LAI) entre 3,2 et 5,5 m2.m−2, avec des feuilles érigées, de courts pétioles et rachis et un nombre important de folioles sur le rachis. Quatre idéotypes architecturaux pour l’assimilation carbonée ont été proposés et présentent des combinaisons spécifiques de traits géométriques, limitant l’ombrage mutuel des plantes et optimisant la distribution de la lumière dans la couronne.En conclusion, le modèle 3D de palmiers à huile, dans sa conception et son application, a permis de détecter les traits architecturaux génétiquement déterminés et influençant l’interception lumineuse. Ainsi, le nombre limité de traits dégagés par l’analyse de sensibilité ainsi que les combinaisons de traits révélées au travers des idéotypes pourraient être pris en compte dans de futurs programmes de sélection. En perspective, des travaux dédiés à intégrer dans ce modèle d’autres processus physiologiques, tels que la régulation de la conductance stomatique et le partitionnement du carbone dans la plante, sont à envisager. Ce nouvel FSPM pourrait alors être utilisé pour tester différents scénarii, comme par exemple dans un contexte de changement climatique avec de faibles radiations et des périodes de sécheresse fréquentes. De même, ce modèle pourrait être utilisé pour étudier différentes configurations de plantation et des systèmes de cultures intercalaires, et ainsi proposer de nouveaux idéotypes multicritères / In this study we proposed to investigate the influence of oil palm architecture on the capacity of the plant to intercept light, by using 3D reconstructions and model-assisted evaluation of radiation-use efficiency. The first objective of this study was to analyse and model oil palm architecture and light interception taking into account genetic variability. A second objective was to explore the potential improvements in light capture and carbon assimilation by manipulating oil palm leaf traits and propose architectural ideotypes.Allometric relationships were applied to model these traits according to ontogenetic gradients and leaf position within the crown. The methodology allowed reconstructing virtual oil palms at different stages over plant development. Additionally, the allometric-based approach was coupled to mixed-effect models in order to integrate inter and intra progeny variability through progeny-specific parameters. The model thus allowed simulating the specificity of plant architecture for a given progeny while including observed inter-individual variability. The architectural model, parameterized for the different progenies, was then implemented in AMAPstudio to generate 3D mock-ups and estimate light interception efficiency, from individual to stand scales.Significant differences in leaf geometry (petiole length, density of leaflets and rachis curvature) and leaflets morphology (gradients of leaflets length and width) were detected between and within progenies, and were accurately simulated by the modelling approach. Besides, light interception estimated from the validated 3D mock-ups showed significant variations among the five progenies.Sensitivity analyses were then performed on a subset of architectural parameters to identify the architectural traits impacting on light interception efficiency and potential carbon assimilation over plant development. The most sensitive parameters over plant development were those related to leaf area (rachis length, number of leaflets, leaflets morphology), but fine attribute related to leaf geometry showed increasing influence when canopy got closed. In adult stand, optimized carbon assimilation was estimated on plants presenting a leaf area index (LAI) between 3.2 and 5.5 m2.m−2, with erected leaves, short rachis and petiole and high number of leaflet on rachis. Four architectural ideotypes for carbon assimilation were proposed based on specific combinations of organs geometry, limiting mutual shading and optimizing light distribution within plant crown.In conclusion, this study highlighted how a functional-structural plant model (FSPM) can be used to virtually explore plant biology. In our case of study, the 3D model of oil palm, in its conception and its application, permitted to detect the architectural traits genetically determined and influencing light interception. The limited number of traits revealed in the sensitivity analysis and the combination of traits proposed through ideotypes could guide further breeding programs. Forthcoming work will be dedicated to integrate in the modeling approach other physiological processes such as stomatal conductance and carbon partitioning. The improved FSPM could then be used to test different scenarios, for instance in climate change context with low radiations or frequent drought events. Similarly, the model could be used to investigate different planting patterns and intercropping systems, and proposed new multi-criteria ideotypes of oil palm.

L’interaction des phénomènes de transfert de chaleur et de masse dans un tissu urbain avec les apports anthropiques participent à l’îlot de chaleur urbain et à la dégradation de la performance énergétique des bâtiments. L’objectif de cette étude est de définir l’impact de la modification des propriétés radiatives aux façades des bâtiments qui peut être réalisée par l’utilisation de revêtements sélectifs colorés récemment développés pour les toitures. Les flux sensibles et l’impact sur les bâtiments sont étudiés pour une morphologie caractéristique des milieux urbains denses, la rue canyon. Un suivi expérimental mené sur des surfaces élémentaires de propriétés radiatives différentes nous a permis de développer par une méthode d’optimisation un procédé de détermination simultané du coefficient de convection et des absorptivités solaires effectives sur la période de mesure. L’utilisation de peintures sélectives dans la configuration canyon retenue est ensuite analysée expérimentalement. Pour cela une maquette (1/10ème) de scène urbaine a été conçue sur la base de 5 rangées de cuves de béton creux qui ont fait l’objet de mesures de températures et de flux radiatifs. Dans un premier temps, le traitement de deux mois de mesures a permis de caractériser les évolutions de champs de températures liés à cette forme urbaine. Par la suite, trois configurations de propriétés radiatives aux façades ont été étudiées simultanément et ont permis d’analyser les modifications spécifiques sur les champs de température, de sur-faces et d’air. Afin d’estimer les économies d’énergie réalisables sur un bâtiment réel ainsi que l’impact sur son environnement proche, une étude paramétrique des revêtements de façade et de la chaussée a été effectuée par des simulations de l’interaction du bâti et du micro-climat. Les méthodes et expériences établies dans cette étude nous permettent d’envisager le développement du traitement des façades et de la caractérisation de leurs performances globales. / Modified heat and mass transfer in the urban built and anthropogenic loads contribute to the urban heat island phenomenon as to the deterioration of building energy efficiency. The scope of this study is to define the impact implied by the modification of façade radiative properties that can be achieved by using selective cool-coloured coatings initially developed for roofing. Sensible heat transfers and consequences on building comfort are studied through a characteristic morphology from dense urban environment, the street canyon. Monitoring of surface energy budget on elementary discs of different radiative properties allowed us to develop, through optimisation method, a process to determine simultaneously the effective solar absorptivities and a convective heat transfer coefficient on the measurement period. The following step consists in an experimental analysis of cool selective paints in the chosen canyon configuration. A reduced-scale model (1/10th) of an urban scene has been designed with 5 rows of hollow concrete tanks that had temperatures and radiative fluxes monitored. Measured data for uniform coatings allowed highlighting the temperature evolution linked to the particular urban form. Afterwards, three façades radiative properties configurations have been studied simultaneously and allowed the analysis of those specific modifications on air and surface temperature fields. Lastly, in order to estimate energy consumption savings on real scale buildings as well as the impact on the near urban environment, a parametric study on coating of façades and roads has been performed through simulation taking into account interactive heat transfers between the built environment and the microclimate. The experiments and methods designed along the study permit to consider façade coating development and global efficiency characterization.

Human society releases greenhouse gas emissions to the atmosphere while providing housing, heat, mobility and industrial production. Man-made greenhouse gas emissions are the main causes of climate change, coming mainly from burning fossil fuels and land-use changes. Sustainably managed forests play an important role in climate change mitigation with the prospect of sustainably providing essential materials and services as part of a low-carbon economy, both through the substitution of fossil-intensive fuels and material and through their potential to capture and store carbon in the long-term perspective. The overall aim of this thesis was to develop a methodology under a life cycle perspective to assess the climate impact of the sustainable use of forest biomass in bioenergy and material systems. To perform this kind of analysis a methodological framework is needed to accurately compare the different biological and technological systems with the aim to minimize the net carbon dioxide emissions to the atmosphere and hence the climate impact. In such a comparison, the complete energy supply chains from natural resources to energy end-use services has to be considered and are defined as the system boundaries. The results show that increasing biomass production through more intensive forest management or the usage of more productive tree species combined with substitution of non-wood products and fuels can significantly reduce global warming. The biggest single factor causing radiative forcing reduction was using timber to produce wood material to replace energy-intensive construction materials such as concrete and steel. Another very significant factor was replacing fossil fuels with forest residues from forest thinning, harvest, wood processing, and post-use wood products. The fossil fuel that was replaced by forest biomass affected the reductions in greenhouse gas emissions, with carbon-intensive coal being most beneficial to replace. Over the long term, an active and sustainable management of forests, including their use as a source for wood products and bioenergy allows the greatest potential for reducing greenhouse gas emissions.

Since the inverse problem in Diffusive Optical Tomography (DOT) is nonlinear and severely ill-posed, only low resolution reconstructions are feasible when noise is added to the data nowadays. The purpose of this thesis is to improve image reconstruction in DOT of the main optical properties of tissues with some novel mathematical methods. We have used the Landweber (L) method, the Landweber-Kaczmarz (LK) method and its improved Loping-Landweber-Kaczmarz (L-LK) method combined with sparsity or with total variation regularizations for single and simultaneous image reconstructions of the absorption and scattering coefficients. The sparsity method assumes the existence of a sparse solution which has a simple description and is superposed onto a known background. The sparsity method is solved using a smooth gradient and a soft thresholding operator. Moreover, we have proposed an improved sparsity method. For the total variation reconstruction imaging, we have used the split Bregman method and the lagged diffusivity method. For the total variation method, we also have implemented a memory-efficient method to minimise the storage of large Hessian matrices. In addition, an individual and simultaneous contrast value reconstructions are presented using the level set (LS) method. Besides, the shape derivative of DOT based on the RTE is derived using shape sensitivity analysis, and some reconstructions for the absorption coefficient are presented using this shape derivative via the LS method.\\Whereas most of the approaches for solving the nonlinear problem of DOT make use of the diffusion approximation (DA) to the radiative transfer equation (RTE) to model the propagation of the light in tissue, the accuracy of the DA is not satisfactory in situations where the medium is not scattering dominant, in particular close to the light sources and to the boundary, as well as inside low-scattering or non-scattering regions. Therefore, we have solved the inverse problem in DOT by the more accurate time-dependant RTE in two dimensions.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-08-01T13:42:24Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) JDiogo_Tese Final_Quimica.pdf: 8861608 bytes, checksum: b9ce8a33624820a531c0a5c298600d94 (MD5) / Made available in DSpace on 2017-08-01T13:42:24Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) JDiogo_Tese Final_Quimica.pdf: 8861608 bytes, checksum: b9ce8a33624820a531c0a5c298600d94 (MD5) Previous issue date: 2017-01-26 / CNPQ / Metodologias te´oricas s˜ao ´uteis para complementar investigac¸˜oes experimentais e guiar novos experimentos envolvendo compostos luminescentes de lantan´ıdeos. A ausˆencia de uma ferramenta computacional contendo tais m´etodos motivou o desenvolvimento do LUMPAC. Se por um lado o LUMPAC difundiu o uso dessas metodologias, por outro as suas limitac¸˜oes tamb´em foram evidenciadas. Nesse sentido, pˆode-se conhecer melhor quais m´etodos merecem uma atenc¸˜ao especial, a saber: c´alculo dos parˆametros de intensidade (Ωλ), c´alculo da energia dos estados excitados dos ligantes e c´alculo da taxa de emiss˜ao n˜ao-radiativa (Anrad). O objetivo geral do presente trabalho de doutoramento consiste em corrigir algumas dessas limitac¸˜oes. Quantoaoc´alculodosΩλ,conseguimosatenuaroproblemacomumanovaformadeajustedos fatores de carga e das polarizabilidades atrav´es de um procedimento que foi denominado de Modelo da UnicidadeQDC, o qual faz uso de um conjunto bastante reduzido de parˆametros (Q,D eC). A importˆancia do ajusteQDC ´e que todas as quantidades derivadas se tornam tamb´em ´unicas para uma dada geometria do complexo, incluindo um esquema proposto de partic¸˜ao qu´ımico da taxa de emiss˜ao radiativa (Arad) em termos dos efeitos dos ligantes. Para demonstrar uma das poss´ıveis aplicac¸˜oes dessa partic¸˜ao, foi considerado o caso de complexos tern´arios de Eu3+ de ligantes n˜ao-iˆonicos repetidos e com os ligantes betadicetonatos DBM, TTA e BTFA. A partic¸˜ao ordenou perfeitamente a combinac¸˜ao n˜ao ´obvia de pares de ligantes n˜ao-iˆonicos que levam aos compostos misturados com os maiores valores deAexp rad. Quanto ao c´alculo dos estados excitados dos ligantes, ´e proposta uma parametrizac¸˜ao do m´etodo CIS baseadonaaproximac¸˜aoNDDO,exclusivamenteparasistemaslantan´ıdicos. Al´emdisso,realizamosumestudoavaliativodemetodologiasTDDFTaplicadasaoc´alculodeestadosexcitados de ligantes em complexos de lantan´ıdeos. Dentre os funcionais e func¸˜oes de base avaliados, a combinac¸˜ao LC-ωPBE/6-31G(d) foi aquela que forneceu as energias tripleto mais concordantes com os dados obtidos na literatura, sendo o erro m´edio absoluto correspondente em torno de 1600 cm−1. Atrav´es da parametrizac¸˜ao do modelo NDDO-CIS implementado no programa ORCA foi poss´ıvel obter um modelo semiemp´ırico para o c´alculo da energia tripleto de complexosdelantan´ıdeocom qualidade bem superiora da melhormetodologiaTDDFT avaliada. / Theoretical methodologies are useful to complement experimental investigations, and to guide new experiments involving luminescent lanthanide compounds. The lack of a software containing these methods motivated us to the development of the user friendly software package LUMPAC. And indeed, LUMPAC is slowly popularising the use of these theoretical methodologies - methodologies that are being put to more frequent tests, and are, consequently, slowly revealing their limitations. In this sense, we identified which aspects of the methods would deserve a more special attention, namely: intensity parameters calculations (Ωλ), calculation of the excited state energies of the ligands, and the calculation of the non-radiative decay rate (Anrad). The overall objective of this doctoral work is to correct some of these limitations as wellastoadvancenewdevelopments. RegardingtheΩλ calculation,wemitigatedthisproblem with a new way to adjust the charge factors and polarizabilities through a procedure we called theQDC Uniqueness Model, which makes use of a fairly small set of adjustaeble parameters (Q,D, andC). The importance of theQDC adjustment is that all derived quantities become also unique for a given complex geometry, including the chemical partition of the radiative emission rate (Arad) in terms of the effects of the ligands, which is being advanced here. To demonstrate one of the possible applications of this chemical partition, we address the case of repeating non-ionic ligand ternary complexes of europium(III) with DBM, TTA, and BTFA. The chemical partition perfectly ordered the non-obvious combination of pairs of non-ionic ligands that led to the mixed ligand compounds with the highest values ofAexp rad . Regarding the calculation of the excited states of the ligands, a new parametrization of the CIS method based on the NDDO approximation is being proposed, exclusively for lanthanide complexes. In addition, we carried out a study to evaluate some TDDFT methodologies for the calculation of excited states of ligands in lanthanide complexes. Among the functionals and basis sets evaluated, the combination LC-ωPBE/6-31G(d) was the one that led to the lowest UME (unsigned mean error), of around 1600 cm−1, for the triplet energies in comparison with data from the literature. The parametrization of the NDDO-CIS model implemented into ORCA provided a semiempirical method for the triplet energy calculation of lanthanide complexes with better predictionpower thanthebestassessed TDDFT method.

Master’s thesis deals with numerical finding the global minimum. A theoretical part of project presents a problem of global optimization, her basic division and shows basic examples the specific problems of global optimization. Further, the reader is familiar with the basics of some numerical methods and with description of their strengths and weaknesses. A practical part shows concrete algorithm of global optimization, its use on data of specified function. Data refer to the issue of radiative heat transfer.

This thesis deals with an experimental determination of heat transfer coefficients from the surface of the thermal manikin. The main focus of the work lies on separating radiative and convective heat fluxes from the surface of the thermal manikin. Both nude and clothed, standing and seated postures were investigated respectively. The tests were conducted in a constant air temperature (cca 24°C) and a constant wind speed (cca 0,05 m.s-1) environment. The major part of the radiative heat flux was eliminated by a low emissivity coating applied to the surface of the nude thermal manikin, and in the case of clothed manikin by a low emissivity two-piece dress. Favorable results were achieved only in the case of the nude manikin measurements. The measurements were performed across 34 zones that logically represent parts of a human body. Experimental work confirms theoretical expectations in the means of a heat transfer. In addition, the results of this work were compared to results of a similar experimental work. The outcomes of this thesis provide essential information in order to create detailed computational models of a thermal environment. Such models require anatomically specific, separate values of convective and radiative heat transfer coefficients.

La planète Mars est le siège d'un climat complexe, caractérisé par des cycles du dioxyde de carbone et de l'eau, ainsi qu'un transport de poussière à toutes les échelles. Ces cycles se manifestent par la condensation saisonnière aux pôles de dépôts de glace de CO₂ et d'eau pendant la nuit polaire, et leur sublimation pendant le printemps local. Les cycles du CO₂ , de l'eau et des poussières sur Mars sont intimement liés. Un processus saisonnier actif illustre bien ces liens : les jets de gaz froid, déclenchés par la sublimation saisonnière des dépôts de CO₂ , pouvant mettre en suspension des poussières du régolite de manière durable dans l'atmosphère, et dont l'activité semble être modulée par les échanges d'eau à la surface.L'objectif de cette thèse est de permettre l'utilisation des données d'imagerie hyperspectrale disponibles au maximum de leur potentiel, pour apporter de nouvelles contraintes sur les échanges saisonniers entre surface et atmosphère et sur les interactions entre les différents cycles (CO₂ , eau, poussières), en se focalisant sur les jets de gaz froid. Pour cela, un modèle semi-analytique de transfert radiatif dans les glaces compactes, ainsi qu'une méthode efficace d'inversion ont été développés et validés.Le modèle de transfert radiatif permet de décrire l'interaction de la lumière avec une couche de glace de manière quantitative d'après les paramètres suivants : épaisseur de la couche, proportions volumiques et tailles des impuretés, rugosité de la surface. Il repose sur plusieurs hypothèses majeures : optique géométrique, milieux continus par morceaux, inclusions quasi-sphériques. L'approximation des deux flux est utilisée pour le transfert au sein de la couche mais la réflexion spéculaire en surface est estimée en tenant compte de la variabilité des facettes de la rugosité surfacique. Ce modèle a été validé numériquement et sur des données de laboratoire et des tests numériques. La méthode d'inversion consiste à créer des bases de données synthétiques d’après le modèle de transfert radiatif pour déterminer les jeux de paramètres les plus probables pour reproduire une mesure donnée. L'inversion repose sur le formalisme bayésien : les grandeurs manipulées sont décrites par des densités de probabilités. Ceci permet la prise en compte de manière réaliste des incertitudes sur la donnée et le calcul d'une incertitude a posteriori sur le résultat de l'inversion.Une étude ciblée d'un site d'intérêt a été menée pour tester et démonter l'applicabilité de cette démarche à l'inversion massive de données de spectro-imagerie.Nous avons déterminé l’état de surface du champ de dunes du cratère de Richardson (72°S, 180°W), choisi car il présente de fortes interactions entre cycle de l'eau et du CO₂ , une important activité saisonnière de jets froids mais aussi une grande quantité de données disponible et une haute qualité du suivi temporel. Le suivi des caractéristiques de surface sur ce site montre une diminution de l'épaisseur de la couche de glace pendant le printemps cohérente avec les estimations des modèles de climat. Nous avons pu estimer et faire le suivi du contenu en eau et en poussière pour discuter le scénario de formation des jets froids. Nous avons proposé un nouveau mécanisme de mise en suspension des petits grains d’eau. / Mars has a complex climate, characterized by carbon dioxide and water cycles, and dust transport at all scales. These cycles are mainly controlled by the seasonal condensation of CO₂ and water ice deposits at high latitudes during the polar night and their sublimation during the local spring. There are a lot of interactions between the CO₂ , water and dust cycles on Mars and they influence each other. An active seasonal process illustrates particularly well these links: the cryoventing, cold CO₂ gas jets triggered by seasonal sublimation of CO₂ deposits, which can put dust from the regolith in suspension into the atmosphere durably, and whose activity seems to be modulated by the exchange of water at the surface.The purpose of this thesis is to allow the use of the available hyperspectral imaging data to their full potential, to bring new constraints on seasonal exchanges between surface and atmosphere and the interactions between the different cycles (CO₂ , water , dust), focusing on cold gas jets. To achieve this, a semi-analytical radiative transfer model in compact ices and an effective inversion method were developed and validated.The radiative transfer model describes the interaction of light with a surface quantitatively, using the following parameters: thickness of the layer, volume proportions and grain-sizes of impurities, surface roughness. It is based on several key assumptions: geometrical optics, piecewise-continuous media quasi-spherical inclusions. The two-stream approximation is used for the radiative transfer inside the layer, but the surface specular reflectance is estimated taking into account the variability of the facets orientations from the surface roughness. This model was validated both numerically and on laboratory data.The inversion method consists in exploring synthetic databases generated by the radiative transfer model and determining the most likely sets of parameters to reproduce a given measure. The inversion is based on the Bayesian formalism: the manipulated variables are described by probability density functions. This allows to take into account realistic uncertainties on the data and enables to calculate a posteriori uncertainties on the result of the inversion.A focused study was conducted on a area of particular interest, to test and prove the applicability of this approach to the massive inversion of spectro-imaging data. The dune-field of Richardson Crater (72°S, 180°W) was chosen because it shows strong interactions between the water and CO₂ cycles, a major seasonal cryoventing activity, but also a large amount of data available and a high quality temporal monitoring. The monitoring of surface characteristics on this site shows a decrease in the thickness of the ice during the spring consistently with climate models simulations. We were able to estimate and monitor the content of water and dust in order to discuss the formation scenario of cold jets.

SuperKEKB est un collisionneur à très haute luminosité construit pour l’expérience Belle II, constitué d’un anneau de basse énergie (LER) transportant des positrons de 4 GeV et d’un anneau de haute énergie (HER) où circulent des électrons de 7 GeV. Sa mise en service -ou commissioning- se déroulera en trois phases : La phase 1, durant laquelle des faisceaux circulent sans être focalisés au point de collision, a pour but de nettoyer la chambre à vide du gaz résiduel. La seconde phase, où le détecteur Belle II sera en partie installé, permettra le réglage du système de focalisation finale des faisceaux, jusqu’à atteindre une luminosité de 10³⁴ cm⁻² s⁻¹. La troisième phase correspondra au démarrage de l’expérience Belle II avec une luminosité visée de 10³⁵ cm⁻² s⁻¹ à 8×10³⁵ cm⁻² s⁻¹. Dans ce cadre, ma thèse porte sur la conception et la mise en place d’un système permettant le monitorage rapide de la luminosité, système nécessaire pour pouvoir corriger en temps réel les instabilités des faisceaux et ainsi maintenir une luminosité optimale. Afin d’atteindre la haute précision relative souhaitée, de l’ordre de 10⁻³ en 1 ms, la mesure sera basée sur le taux de comptage des particules issues de la diffusion Bhabha radiative à angle nul, processus bien connu et dont la section efficace est importante. Ces particules seront détectées au moyen d’un capteur en diamant, matériau résistant aux radiations et permettant une acquisition très rapide du signal, situé à l’extérieur de la chambre à vide et en aval du point d’interaction. La première partie de cette thèse est consacrée à la recherche des localisations optimales pour le positionnement des capteurs diamants dans chacun des deux anneaux. Au moyen de simulations détaillées, nous avons étudié la dynamique des particules Bhabha lors de leur transport dans les anneaux ainsi que leur interaction avec la matière de la chambre à vide. Ces études ont permis d’ une part d’ identifier un emplacement à 11.9m dans le LER et un autre à 30 m dans le HER, et d’autre part de redéfinir pour l’une d’ entre elle la géométrie locale du tube à vide. La seconde partie, plus expérimentale, s’articule autour de la première phase du commissioning de SuperKEKB et des mesures réalisées au moyen des capteurs diamants que nous avons installés. Dans un premier temps, une étude détaillée des processus de perte single beam (Bremsstrahlung, effet Touschek, diffusion coulombienne) a été réalisée pour le LER en fonction des paramètres du faisceau et du collisionneur (courant, pression, taille transverse des faisceaux). Dans un deuxième temps les résultats de cette étude ont été comparés aux données que nous avons prises de février à juin 2016. Nous avons pu mettre en évidence un bon accord qualitatif et quantitatif entre nos simulations et nos mesures. Cela nous a permis d’estimer que le niveau de bruit de fond attendu dans le cadre des mesures pour le monitorage de la luminosité sera de plus de deux ordres de grandeurs inférieurs au taux du processus Bhabha radiatif à angle nul. / SuperKEKB is a very high luminosity collider dedicated to the Belle II experiment, it consists of a Low Energy Ring (LER) of 4 GeV positrons and a High Energy Ring (HER) of 7 GeV electrons. The commissioning of this machine is split into three phases: phase 1 (single-beam phase) is dedicated to vacuum scrubbing, where beams circulate without focusing at the collision point. Phase 2, for which the major part of the Belle II detector will be installed, will enable the tuning of the final focus system to achieve a luminosity of 10³⁴ cm⁻² s⁻¹. During phase 3, Belle II physics runs will start with an aimed luminosity up to 8×10³⁵ cm⁻² s⁻¹. In this context, the aim of my thesis is to develop and install a fast luminosity monitoring system, which is required for online correction of beam instabilities and maintenance of optimal luminosity. To reach the aimed relative precision of 10⁻³ in 1 ms, the measurement will be based on the radiative Bhabha process at zero photon scattering angle, whose cross-section is large and well-known. These particles will be detected using diamond sensors, resistant to radiation and enabling very fast signal acquisition, to be placed outside of the beam-pipe and downstream of the interaction point. The first part of this work is dedicated to the investigation of the best locations for the diamond sensor positioning in both rings. Using detailed simulations, we studied the dynamics of Bhabha particles during their tracking in the rings and their interaction with the beam pipe material. This led to the identification of two positions, at 11.9 m in LER and at 30 m in HER, and to considering a new geometry for the vacuum pipe in the LER. The second part is related to the phase 1 of the SuperKEKB commissioning and concerns the measurements performed with the diamond sensors that were installed. Single beam loss processes (Bremsstrahlung, Touschek, beam-gas Coulomb scattering) were studied in detail with respect to the LER beam and ring parameters (current, pressure, transverse beam sizes). The results of this study were then compared to the data collected from February to June 2016. We found good qualitative and quantitative agreement between our simulations and measurements. From this we could estimate that the level of background to be expected during luminosity monitoring will be two orders of magnitude smaller than the rate of the radiative Bhabha scattering signal.

Thermal radiation is a fundamental heat transfer process, with certain basic aspects still not fully understood. Furthermore, tailoring its properties has potential to affect a wide range of applications, particularly thermophotovoltaics (TPV) and radiative cooling. TPV converts heat into electricity using thermal radiation to illuminate a photovoltaic diode, with no moving parts. With its realistic efficiency limit up to 50% (heat source at 1200 ^oC), TPV has garnered substantial interest. However, state-of-the-art TPV demonstrations are still well below theoretical limits, because of losses from generating and efficiently converting or recycling thermal radiation. In this thesis, tailored integrated photonic crystal structures are numerically simulated to enhance the efficiency of solar TPV. Next, a high-temperature thin-film Si-based selective absorber and emitter is designed, fabricated and experimentally characterized. It exhibits great potential to open up new applications, as it lends itself to large-scale production with substantial mechanical flexibility and excellent spectral selectivity for extended time periods, even when operating under high operating temperatures (600 ^oC) for up to 6 hours, with partial degradation after 24 hours. To perform this high-temperature characterization, an emittance measurement setup has been built; its performance agrees well with numerical simulations. Second, a unique passive cooling mechanism known as radiative cooling is developed to reduce the operating temperature of the photovoltaic diode. The significant effect of radiative cooling as a complement for an all-passive-cooling TPV system is proposed and numerically analyzed under a range of conditions. Furthermore, an outdoor experiment has been performed to demonstrate the effect of radiative cooling on a concentrating photovoltaic system, which can potentially be applied to the thermal management of a TPV system. In summary, this work paves the way towards the development of reliable, quiet, lightweight, and sustainable TPV and radiatively cooled power sources for outdoor applications.