A LDL contitui-se de uma fase lipídica, uma esfera composta principalmente de um núcleo de colesterol esterificado envolto por uma camada de fosfolipídeos. A fase lipídica junta-se uma única molécula protéica, a polipoproteina B (apo B). A LDL é removida da circulação por mediação de receptores específicos, os receptores B. E, que reconhecem não só a apo B da LDL mas também a apo E, que está presente em outras lipoproteínas. Estudou-se neste trabalho a influencia da apo B no metabolismo da LDL, através de um modelo de emulsões semelhantes à fase lipídica da LDL, constituídas de oleato de colesterol (29%), fosfatidilcolina (69%) e trioleina (2%), preparadas por sonicação, seguida de ultracentrifugação. As emulsões, com seus componentes lipídicos marcados isotopicamente, foram associadas à apo B e injetadas no rato, determinando-se sua remoção plasmática e captação pelos diversos órgãos do animal. Os resultados foram comparados com o metabolismo da emulsão sem associação da apo B a sua estrutura e com o da LDL natural. Verificou-se que a presença de apo B retardou a remoção plasmática das partículas da emulsão. Por outro lado, o oleato de colesterol da emulsão com apo B foi removido do compartimento plasmático numa taxa semelhante à da LDL natural, o que demonstra a adequação do modelo utilizado à situação fisiológica. Tanto as emulsões quanto a LDL natural foram captadas principalmente pelo fígado. Entretanto, a captação hepática da emulsão sem apo B foi maior a da emulsão com apo B e a da LDL. A incubação das emulsões com HDL do plasma de rato mostrou que a emulsão sem apo B adquiriu mais apo E que a emulsão com apo B. Portanto, essas diferenças de comportamento metabólico provavelmente se devem à maior afinidade dos receptores B, E hepáticos por partículas que contem mais apo E, em comparação às que contêm a apo B. O aumento da atividade dos receptores B, E, induzido pelo tratamento com 17 α-etinil estradiol, resultou no aumento da cinética plasmática das duas emulsões. Porém, à taxa de remoção plasmática da emulsão sem apo B também foi maior no grupo tratado com o estrógeno. Esses dados indicam que as emulsões com apo B associada a sua estrutura apresentam comportamento metabólico muito semelhante ao da LDL. Portanto, o modelo das emulsões análogas à LDL parece ser um instrumento eficiente no estudo do metabolismo daquela lipoproteína. / The effects of apolipoprotein B (apo B) on the metabolism of emulsions constituted of cholesteryl oleate (29%), phosphatidycholine (69%) and triolein (2%) were studied in rats. After intra-arterial injection of the radiolabelled emulsions, plasma removal of the emulsions was reduced in presence of apo B. On the other hand, the cholesteryl ester moiety of the apob B emulsion was removed at the same rate as native LDL. Emulsions and LDL were taken up mainly by the liver 24 h after the injection. However, the hepatic uptake of the apo B emulsion was similar to LDL and lower than that of the apo B-free emulsion. These differences in metabolic behaviour were probably due to the lower hepatic B, E, receptor affinity to apo B contained in the emulsions associated to apo B and in LDL, compared to the apo B-free emulsions. The latter, as confirmed in the in vitro experiments, is capable of adsorbing more apo E, and this apolipoprotein has higher affinity for the receptor. Enhanced receptor activity induced by pre-treatment of the rats with 17 α-ehymylestradiol resulted in augmented plasma removal of both emulsions but nonetheless the cholesteryl ester plasma removal of the apo B-containing particles was still lower, compared to that of the apo B-free emulsion. These data indicate that apo B-containing emulsion exhibits metabolic behaviour similar to that of LDL, and this emulsion can be an adequate tool to test LDL metabolism.

A LDL contitui-se de uma fase lipídica, uma esfera composta principalmente de um núcleo de colesterol esterificado envolto por uma camada de fosfolipídeos. A fase lipídica junta-se uma única molécula protéica, a polipoproteina B (apo B). A LDL é removida da circulação por mediação de receptores específicos, os receptores B. E, que reconhecem não só a apo B da LDL mas também a apo E, que está presente em outras lipoproteínas. Estudou-se neste trabalho a influencia da apo B no metabolismo da LDL, através de um modelo de emulsões semelhantes à fase lipídica da LDL, constituídas de oleato de colesterol (29%), fosfatidilcolina (69%) e trioleina (2%), preparadas por sonicação, seguida de ultracentrifugação. As emulsões, com seus componentes lipídicos marcados isotopicamente, foram associadas à apo B e injetadas no rato, determinando-se sua remoção plasmática e captação pelos diversos órgãos do animal. Os resultados foram comparados com o metabolismo da emulsão sem associação da apo B a sua estrutura e com o da LDL natural. Verificou-se que a presença de apo B retardou a remoção plasmática das partículas da emulsão. Por outro lado, o oleato de colesterol da emulsão com apo B foi removido do compartimento plasmático numa taxa semelhante à da LDL natural, o que demonstra a adequação do modelo utilizado à situação fisiológica. Tanto as emulsões quanto a LDL natural foram captadas principalmente pelo fígado. Entretanto, a captação hepática da emulsão sem apo B foi maior a da emulsão com apo B e a da LDL. A incubação das emulsões com HDL do plasma de rato mostrou que a emulsão sem apo B adquiriu mais apo E que a emulsão com apo B. Portanto, essas diferenças de comportamento metabólico provavelmente se devem à maior afinidade dos receptores B, E hepáticos por partículas que contem mais apo E, em comparação às que contêm a apo B. O aumento da atividade dos receptores B, E, induzido pelo tratamento com 17 α-etinil estradiol, resultou no aumento da cinética plasmática das duas emulsões. Porém, à taxa de remoção plasmática da emulsão sem apo B também foi maior no grupo tratado com o estrógeno. Esses dados indicam que as emulsões com apo B associada a sua estrutura apresentam comportamento metabólico muito semelhante ao da LDL. Portanto, o modelo das emulsões análogas à LDL parece ser um instrumento eficiente no estudo do metabolismo daquela lipoproteína. / The effects of apolipoprotein B (apo B) on the metabolism of emulsions constituted of cholesteryl oleate (29%), phosphatidycholine (69%) and triolein (2%) were studied in rats. After intra-arterial injection of the radiolabelled emulsions, plasma removal of the emulsions was reduced in presence of apo B. On the other hand, the cholesteryl ester moiety of the apob B emulsion was removed at the same rate as native LDL. Emulsions and LDL were taken up mainly by the liver 24 h after the injection. However, the hepatic uptake of the apo B emulsion was similar to LDL and lower than that of the apo B-free emulsion. These differences in metabolic behaviour were probably due to the lower hepatic B, E, receptor affinity to apo B contained in the emulsions associated to apo B and in LDL, compared to the apo B-free emulsions. The latter, as confirmed in the in vitro experiments, is capable of adsorbing more apo E, and this apolipoprotein has higher affinity for the receptor. Enhanced receptor activity induced by pre-treatment of the rats with 17 α-ehymylestradiol resulted in augmented plasma removal of both emulsions but nonetheless the cholesteryl ester plasma removal of the apo B-containing particles was still lower, compared to that of the apo B-free emulsion. These data indicate that apo B-containing emulsion exhibits metabolic behaviour similar to that of LDL, and this emulsion can be an adequate tool to test LDL metabolism.

Cette thèse porte sur l'étude expérimentale de la production d’ions négatifs (H-) par des sources multi-dipolaires microondes (2.45 GHz) fonctionnant à la Résonance Cyclotron des Electrons (RCE). Les sources H- sont nécessaires aux accélérateurs de haute énergie et surtout pour les systèmes d’injection de neutres à haute énergie pour le chauffage des plasmas de fusion. Pour cette étude, deux sources (Prometheus I et ROSAE III) ont été conçues, fabriquées et étudiées. Ces deux sources sont munies de réseaux 2D des sources multi-dipolaires. Il est prouvé que la formation des ions négatifs dans ces sources d'ions, est dû à un mécanisme de production en volume : l'attachement dissociatif des électrons de faible énergie sur des molécules ro-vibrationallement excitées. Contrairement aux sources impliquant des réactions de surface, la production en volume a l’avantage de fonctionner sans césium. Une étude détaillée des principes fondamentaux de la production de H- est réalisée, et les voies possibles pour d'optimisation sont explorées au moyen de : sondes électrostatiques, photodetachment laser, spectroscopie d'émission optique dans la région spectrale du visible et de l'ultraviolet du vide et finalement par spectroscopie d'absorption et de fluorescence induite dans la région spectral de l'ultraviolet du vide en utilisant radiation synchrotron dans un montage expérimental spécial (SCHEME). Analytiquement:La source "Prometheus I" est d'abord étudiée en détails, dans une large gamme de conditions expérimentales (par exemple, pression, puissance, position des zones RCE). Cette étude souligne l’efficacité de production des ions H- en volume, et dévoile une fenêtre de fonctionnement optimal et des voies d'optimisation pour atteindre de plus fortes densités d'ions H-. La contribution du processus d'attachement dissociatif et de l'ionisation résonnante des neutres, à la production H- pour cette source ont été évaluée et la prépondérance de la première finalement confirmée par un modèle rendant compte du bilan des créations et pertes d’espèces.En raison de l'importance des molécules ro-vibrationnallement excitées lors du processus d'attachement dissociatif, l'étude se concentre sur leurs réactions de formation. Deux réactions de formation sont étudiées par des expériences dédiées : la désorption recombinative des atomes d'hydrogène à la surface de divers matériaux ("ROSAE III" et "SCHEME") et l'excitation par impact d'électrons à travers les états singulets temporaires ("Prometheus I"). L'étude de la désorption recombinative a été appréhendée de deux façons différentes. Avec la source ROSAE III, l'impact indirect du processus pour la production d'ions négatifs, à travers la formation de molécules ro-vibrationnellement excitées, a été évaluée dans les plasmas RCE. Dans la deuxième approche, la source "SCHEME" a été conçue pour l'étude de la désorption recombinative des atomes en utilisant le rayonnement synchrotron. La formation des états vibrationnels suite à l’excitation des états singulets, dans la source "Prometheus I" a été étudiée par des mesures d'émission de l'ultraviolet du vide.Une étude qui combine la spectroscopie d'émission de l'ultraviolet du vide, le photodétachement et la caractérisation de la cinétique des électrons par sondes électrostatiques, a permis l'identification des facteurs qui limitent la production d'ions négatifs dans le plasma RCE de "Prometheus I". Des perspectives pour surmonter ces limitations sont finalement proposées. / The present PhD thesis is devoted to the experimental study of hydrogen negative ion (H-) production in microwave-driven (2.45 GHz) multi-dipolar Electron Cyclotron Resonance (ECR) plasma sources. H- sources are required in high-energy accelerators and more importantly in neutral beam injection systems for fusion plasma heating. Towards this directions, two sources (namely, "Prometheus I" and "ROSAE III") are designed, fabricated and studied. Both sources are driven by 2D networks of dipolar ECR elementary sources. It is proven that, negative ion formation in these ion sources is governed by the volume production mechanism, which mostly refers to the dissociative attachment of low energy electrons to vibrationally excited molecules. Contrary to the so called surface sources, volume production sources have the advantage of cesium-free operation. Extended experimental study on fundamental principles of H- production is realized, and possible ways for potential source optimization are tested by means of: electrostatic probes, laser photodetachment, optical emission spectroscopy, both in the visible and vacuum ultra-violet spectral range and finally, vacuum-ultraviolet absorption and induced fluorescence spectroscopy using synchrotron radiation in a specially designed setup ("SCHEME"). Analytically:The source "Prometheus I" is initially studied in detail (EEDF, H- density, optical emission spectra etc), under a wide range of experimental conditions (e.g., pressure, power, ECR-zone location), proving its efficiency for H- volume production, and unveiling optimum operational window and paths for obtaining higher H- densities. The contribution of the dissociative attachment process and neutral resonant ionization to H- production in this source, is evaluated, and the dominance of the former is finally confirmed by an equilibrium model.Due to the importance of the ro-vibrationally excited molecules to the dissociative attachment process, the study is focused on their formation reactions. Two formation reactions are considered by adequately adapted experiments: the recombinative desorption of hydrogen atoms on the surface of various materials (ROSAE III and SCHEME) and the electron impact excitation through temporary singlet states (Prometheus I). The study of recombinative desorption is approached in two different ways. With the source ROSAE III, the indirect impact of the process to the production of negative ions, through the formation of ro-vibrationally excited molecules, is evaluated in ECR plasmas. In the second approach, the source SCHEME is designed for the independent investigation of the recombinative desorption of unexcited atoms using synchrotron radiation based diagnostics. The formation of vibrational states through singlet excitation in the source "Prometheus I" is studied by vacuum-ultraviolet emission measurements.A study that combined vacuum-ultraviolet emission spectroscopy, photodetachment and the characterization of electron kinetics with electrostatic probes, allowed the identification of the factors that limit negative ion production in the ECR plasma of "Prometheus I". Perspectives for overcoming these limitations are finally proposed.

L’un des plus grands défis des missions prévues sur Mars est la phase d’entrée atmosphérique, lorsque le vaisseau spatial entre dans l’atmosphère de Mars à l’aller, ou de la Terre au retour. Les capsules spatiales entrent dans l’atmosphère à des vitesses hypersoniques ce qui comprime le gaz à l’avant de l’appareil et résulte en une augmentation de température jusqu’à la dissociation et l’ionisation du gaz. Ces phénomènes engendrent un rayonnement intense du gaz. Le flux radiatif arrivant sur la capsule est la principale source de chauffage de l’appareil mais de grandes incertitudes demeurent dans sa prédiction. En conséquence, le bouclier thermique est surdimensionné, augmentant la masse totale de l’appareil et diminuant sa charge utile. Ces incertitudes sont maximales sur l’arrière-corps de l’appareil où le plasma l’entourant est forcé de se recombiner hors équilibre. Cette thèse présente une caractérisation expérimentale de plasma hors équilibre d’air et d’azote en recombinaison, typique des plasmas d’arrière-corps. Les distributions de la population de l’azote atomique et moléculaire sont mesurées, ainsi que le rayonnement hors équilibre de ces espèces. Des comparaisons avec les prédictions de codes numériques sont données, et de larges différences sont observées, soulignant les limites des modèles de mécanique des fluides numériques. Ces données expérimentales ont pour but d’être utilisées dans la validation des modèles présents dans les codes d’entrée atmosphérique. / One of the main challenges for the upcoming Mars missions is the atmospheric entry phase when the spacecraft enters the Martian atmosphere or the Earth’s atmosphere upon return. The hypersonic velocity of the capsule entering the atmosphere leads to extreme gas heating and results in intense gas radiation. The radiative flux emitted by the plasma in front and around the capsule is the main source of heating, but its prediction suffers from large uncertainties, leading engineers to apply safety margin on the heat shield, thereby decreasing the useful payload of the capsule. These uncertainties are maximal in the afterbody region where the plasma is forced to recombine and can depart from equilibrium. This thesis presents an experimental characterization of recombining non-equilibrium air and nitrogen plasma flows to mimic the chemical kinetic dynamics encountered in the afterbody region. The population distributions of radiating atomic and molecular species of nitrogen are measured, along with the nonequilibrium radiation emitted by these species. Comparisons with predictions from numerical codes are made and large differences are observed even in simple test cases, thus highlighting the limits of current computational fluid dynamics models. These data are intended to serve as a basis to validate the models used in reentry codes.