Une impulsion laser ultra-courte et ultra-intense se propageant dans un gaz de faible densité est capable d'accélérer une partie des électrons de ce gaz à des énergies relativistes, de l'ordre de quelques centaines de MeV, sur des distances de seulement quelques millimètres. Pendant leur accélération et dû à leur mouvement transverse, ces électrons émettent de plus un rayonnement X fortement collimaté et dirigé vers l'avant appelé rayonnement bétatron. Les caractéristiques de cette source la rendent intéressante pour son utilisation en imagerie à ultra-haute résolution.Dans ce manuscrit, nous explorons trois axes de travail autour de cette source à l'aide de simulations réalisées avec les codes Particle-In-Cell CALDER et CALDER-Circ. Nous commençons ainsi par étudier la création d'une source bétatron avec des impulsions laser de durée picoseconde et d'énergie kilojoule, donc plus longues et plus puissantes que celles habituellement utilisées par la communauté. Nous montrons que malgré les paramètres inhabituels de ces impulsions lasers il est toujours possibles de générer des sources X, et ce dans deux régimes différents.Ensuite, afin de comprendre une partie des différences généralement observées entre expériences et simulations, nous montrons dans une autre étude que l'utilisation dans les simulations de profils lasers réalistes au lieu de profils parfaitement Gaussiens dégrade fortement les performances de l'accélérateur laser-plasma et de la source bétatron. De plus, ceci conduit à un meilleur accord qualitatif et quantitatif avec l'expérience.Enfin nous explorons plusieurs techniques pour augmenter l'émission X basées sur une manipulation des profils de plasmas utilisés pour l'accélération. Nous trouvons que l'utilisation d'un gradient transverse ou d'une marche de densité conduisent tous deux à une augmentation de l'amplitude du mouvement transverse des électrons, et donc de l'énergie émise par la source bétatron. Alternativement, nous montrons que cet objectif peut-être atteint par la transition d'un régime de sillage laser vers un régime d'accélération par sillage plasma induit par une augmentation de la densité. L'accélération des électrons est optimisée dans le premier régime, tandis que l'émission X est fortement favorisée dans le second. / An ultra-short and ultra-intense laser pulse propagating in a low-density gas can accelerate in its wake a part of the electrons ionized from the gas to relativistic energies of a few hundreds of MeV over distances of a few millimeters only. During their acceleration, as a consequence of their transverse motion, these electrons emit strongly collimated X-rays in the forward direction, which are called betatron radiations. The characteristics of this source turn it into an interesting tool for high-resolution imagery.In this thesis, we explore three different axis to work on this source using simulations on the Particles-In-Cells codes CALDER and CALDER-Circ. We first study the creation of a betatron X-ray source with kilojoule and picosecond laser pulses, for which duration and energy are then much higher than usual in this domain. In spite of the unusual laser parameters, we show that X-ray sources can still be generated, furthermore in two different regimes.In a second study, the generally observed discrepancies between experiments and simulations are investigated. We show that the use of realistic laser profiles instead of Gaussian ones in the simulations strongly degrades the performances of the laser-plasma accelerator and of the betatron source. Additionally, this leads to a better qualitative and quantitative agreement with the experiment.Finally, with the aim of improving the X-ray emission, we explore several techniques based on the manipulation of the plasma density profile used for acceleration. We find that both the use of a transverse gradient and of a density step increases the amplitude of the electrons transverse motions, and then increases the radiated energy. Alternatively, we show that this goal can also be achieved through the transition from a laser wakefield regime to a plasma wakefield regime induced by an increase of the density. The laser wakefield optimizes the electron acceleration whereas the plasma wakefield favours the X-ray emission.

Recent advances in plasma-based propulsion systems have led to the development of electromagnetic Radio-Frequency (RF) plasma generation and acceleration systems, called Helicon Plasma Thrusters (HPT). One of the pioneer companies developing this new type of space propulsion is T4i Technology for Propulsion and Innovation s.p.a., with its cutting-edge project called REGULUS, among which this study has been performed. A crucial part of HPT systems is the acceleration region, where, by the means of a magnetic nozzle, the thermal energy of the plasma is converted into axial acceleration and, in turn, into thrust. This study is focused on the numerically simulation of the plasma dynamics in the acceleration stage, using Xenon gas. A three-dimensional full Particle-In-Cell (PIC) simulation strategy is used to simulate the plume in the magnetic nozzle. The code developed for the plasma simulation is based on the open-source software Spacecraft Plasma Interaction Software (SPIS). The code has been conveniently modified and improved, neutrals and collision processes were added to evaluate their impact on the plasma properties. The features added improved the validity of the results, now one step closer to the physical reality. The code has been proven to be an extremely versatile and powerful tool for optimization and adaptation to different mission scenarios. / De senaste framstegen i plasmaframdrivning har lett till utvecklingen Helicon Plasma Thruster (HPT) som kombinerar elektromagnetisk högfrekvent (RF) plasmakälla och ett accelerationssystem. En av företagen som är pionjärer i att utveckla denna nya framdrivningsteknik är T4i Technology for Propulsion and Innovation s.p.a., med dess banbrytande projekt REGULUS, som detta arbete bygger på. En viktig del av HPT-systemet är accelerationsområde där plasmats termiska energin omvandlas till axiell accelleration i en magnetisk dysa. Denna rapport fokuserar på numeriska modelleringen av plasmadynamiken accelerationsområdet vid användning av Xenongasen. En tredimensionell Particle-In-Cell (PIC) simulering används för att studera plasmautflödet i magnetiska dysan. Koden bygger på den öppna mjukvaran Spacecraft Plasma interaction Software (SPIS). Koden har modifierats och förbättrats, en neutral komponent samt kollisionsprocesser har lagts till och deras påverkan på plasmabeteende har studerats. Dessa nya element förbättrade giltigheten av simulerings-resultaten. Nu ett steg närmre den fysiska verkligheten. Koden är ett mångsidigt och kraftfullt verktyg för optimering och anpassning till olika användningsscenarier.

L'objet du projet CALAS est l'étude de la supergranulation solaire, structure à grande échelle de la photosphère. L'origine de la supergranulation est encore controversée et nécessite des observations à très haute résolution spatiale sur un grand champ de vue. Le projet CALAS répond à ces exigences en proposant de concevoir une caméra rapide combinant grand champ et haute résolution, installée à la Lunette Jean Rösch, réfracteur de 50 cm de diamètre situé au Pic du Midi. Cette caméra utilise des capteurs CMOS (Complementary Metal Oxide Semi-conductor) dont les avantages sont notamment la rapidité de lecture, le coût réduit et de grands formats disponibles.<br />Nous avons conçu une chaîne d'acquisition complète, comprenant la caméra et son électronique de commande, une électronique de lecture couplée à un logiciel de prise de vues, et un système de stockage des données.<br />Le projet a également consisté à concevoir un banc optique sur deux voies permettant l'observation de la surface solaire en mode imagerie mais aussi en mode Doppler et magnétographie, par l'utilisation d'un filtre magnéto-optique. Le travail a également nécessité d'étudier l'intégration de CALAS au sein de la Lunette Jean Rösch, en participant à la jouvence de cet instrument.<br />Enfin, au cours de ce projet, outre de nombreuses missions d'observation à la Lunette Jean Rösch, j'ai également été amené à participer à une campagne internationale d'observations coordonnées consacrée à l'étude des mouvements de la photosphère dans l'environnement de filaments. A l'issue de cette thèse, les premières observations à grand champ et haute résolution de la photosphère solaire ont été réalisées à la LJR, et leur excellente qualité se révèle déjà tout à fait prometteuse pour la suite de l'exploitation scientifique.

Several Langmuir probe voltage sweeps by a model of the ESA spacecraft Rosetta was simulated in a plasma with solar wind parameters using the ESA open source software SPIS 5. The simulations were carried out to in- vestigate the features of the spacecraft’s environment in the solar wind and the effect of photoemission from the spacecraft surface on the measurements made by the Langmuir probes on board Rosetta. We report a best fit to an existing probe sweep result in the solar wind near the Earth at 1 AU from 9 Nov 2009 for a 4 million particle simulation in SPIS of an 8 V positively charged spacecraft with the following parameters: Tph = 2 eV, Te = 12 eV, Ti = 5 eV, ne = 5 cm−3. We also report that the spacecraft is shielding the Langmuir probes on Rosetta from plasma electrons, and particularly low energy electrons. In one instance, this blocking is shown to lead to an over- estimation of solar wind electron temperature by 12% and underestimate the plasma density by 24% by the Langmuir Probe for a +10 V charged spacecraft in ne= 5 cm−3, Te = 12 eV solar wind. Two models used in lit- erature on photoemission, one for isotropical emission from a plane and the other for radial emission from a point, was used and compared. We report a clear preference to the approximation of a Maxwellian energy distribution of photoelectrons emitted radially from a point source model with our sim- ulation result on the Langmuir Probe aboard Rosetta. We also report the solar aspect angle dependence on the plasma potential and plasma density result, which are in overall agreement with Rosetta measurements from the second Earth fly-by.

Les buts de cette thèse étaient d'explorer les effets de l'obésité et du surpoids sur le contenu minéral osseux (CMO), la densité minérale osseuse (DMO) et la géométrie osseuse de la hanche ches des adolescents et des jeunes adultes libanais. 131 sujets libanais agés de 13 à 30 ans ont acceptés de participer à cette étude (67 de sexe masculin et 64 de sexe féminin) et ont donné leur consentement éclairé. Le poids et la taille ont été mesurés et l'indice de masse corporelle (IMC) a été calculé. La composition corporelle, le CMO du corps entier (CE), la DMO CE, la DMO du rachis lombaire (L2-L4), la DMO de la hanche et la DMO de l'avant-bras ont été mesuréses par la DXA. La géométrie osseuse de la hanche a été évaluée par le logiciel Hip Structure Analysis (HSA). La surface de la section transversale (CSA), le moment d'inertie de la surface transversale (CSMI), le module de section (Z), l'épaisseur corticale (CT) et le buckling ratio (BR) ont été ainsi mesurés par le logiciel HSA. Dans les deux sexes, l'obésité et le surpoids étaient associés à une augmentation des valeurs absolues de CMO, de DMO et d'indicecs géométriques de résistance osseuse (CSA et Z) au niveau de la hanche. Chez les sujets de sexe masculin, le CMO CE, le rapport CMO CE/taille, la DMO CE et la DMO du Radius ultra-distal étaient significativement inférieurs chez le groupe obèse par rapport aux groupes en surpoids et normo-pondérés après ajustement pour le poids (en utilisant une analyse de covariance). Chez les sujets de sexe féminin, après ajustement pour le poids (en utilisant une analyse de covariance), la DMO du rachis lombaire était inférieure chez le groupe obèse par rapport au groupe normo-pondéré alors qu'il n'y avait aucune différence entre les trois groupes (obèse, en surpoids et normo-pondéré) au niveau des indices géométriques de résistance osseuse de la hanche. Cette thèse montre donc que la DMO de certains sites osseux n'est pas correctement adaptée à l'excès de poids chez les jeunes obèses. / The aims of this thesis were to explore the effects of obesity and overweight on bone mineral content (BMC), bone mineral density (BMD) and hip geometry in a group of Lebanese adolescents and young adults. 131 Lebanese subjects (67males and 64 female) whose ages range between 13 and 30 years participated in this study. Informed written consent was obtained from participants. Weight and height were measured, and body mass index (BMI) was calculated. Body composition, whole body bone mineral content (WB BMC), whole body bone mineral density (WB BMD), lumbar spine bone mineral density (L2-L4 BMD), hip BMD and forearm BMD were measured by DXA. To evaluate hip bone strength, DXA scans were analyzed by the hip structure analysis (HSA) program. Cross-sectional area (CSA), section modulus (Z), cross-sectional moment of inertia (CSMI), cortical thickness (CT) and buckling ratio (BR) were measured from hip bone mass profiles using the HSA software. In both sexes, obesity and overweight were associated with higher crude BMC, BMD and geometric indices of hip bone strengh values (CSA and Z). In males, obese group displayed lower WB BMC, WB BMC/height, WB BMD and ultra-distal Radius BMD values in comparison to overweight and normal-weight groups after adjustement for weight (using a one-way analysis of covariance). In females, after adjusting for body weight (using a one-way analysis of covariance), lumbar spine BMD was lower in the obese group compared to the normal-weight group while there were no significant differences among the three groups (obses, overweight and normal-weight) regarding geometric indicesof hip bone strength. This study shows that BMD of some skeletal sites is not well adapted to the increased body weight in young obese.

A Pressão intracraniana (PIC) é um dos principais parâmetros fisiológicos em animais e humanos e sua morfologia é extremamente importante. Entretanto, todos os métodos de monitoramento existentes no mercado são invasivos, existindo uma ampla demanda por sistemas não invasivos, expandindo assim o campo de pesquisas acerca desse importante parâmetro neurológico, que só não é melhor estudado devido a forma invasiva de ser monitorado. A motivação é fazer com que o monitoramento da PIC seja tão comum e tão essencial quanto é hoje o monitoramento da pressão arterial, facilitando o diagnóstico e até prognóstico de diversas doenças. Este trabalho analisa e implementa melhorias de um sistema não invasivo de monitoramento da pressão intracraniana, baseado em extensometria. Um dos objetivos, no que tange o desenvolvimento do produto, é analisar o equipamento como um todo - Sensor, Hardware, Firmware e Software - e propor melhorias a partir dos testes realizados. Os testes realizados In vivo mostraram uma boa correlação do sinal com um sistema Gold Stardard, evidenciando o potencial promissor do método. / The intracranial pressure (ICP) is one of the main physiological parameters in animals and humans and its morphology is extremely important. However, all monitoring methods available in the market are invasive and there is a large demand for non-invasive systems, thus expanding the scope of research on this important neurological parameter, that just is not further studied because of the invasive method of monitoring. The motivation is to make monitoring the ICP as common and as essential, as monitoring the blood pressure is nowadays, facilitating diagnosis and even prognosis of various diseases. This work analyzes and implements improvements in a non-invasive intracranial pressure monitoring system based on extensometer. One of the goals, regarding product development, is to analyze the unit as a whole- Sensor, Hardware, Firmware and Software- and propose improvements from the tests. The in vivo tests showed a good correlation with a Gold Stardard system signal showing the promising potential of the method.

A pressão intracraniana (PIC) é um dos principais parâmetros neurológicos em animais e humanos. A PIC é uma função da relação entre o conteúdo da caixa craniana (parênquima cerebral, líquido cefalorraquiano e sangue) e o volume do crânio. O aumento da PIC (hipertensão intracraniana) pode acarretar graves efeitos fisiológicos ou até mesmo o óbito em pacientes que não receberem rapidamente os devidos cuidados, os quais incluem o monitoramento em tempo real da PIC. Todos os métodos de monitoramento da PIC atualmente utilizados são invasivos, ou seja, é necessário introduzir um sensor de pressão no sistema nervoso central, acarretando aos pacientes riscos de infecções e traumas decorrentes do método. Neste trabalho desenvolvemos um método minimamente invasivo de monitoramento da pressão intracraniana, que consiste na utilização de sensores de deformação do tipo strain gauge fixados sobre a calota craniana. Os sinais oriundos deste sensor foram amplificados, filtrados e enviados para um computador com software apropriado para análise e armazenamento dos dados. O trabalho aqui apresentado objetivou os testes &quot;in vivo&quot; do sistema, onde foi utilizada mais de uma centena de animais em diversos testes, sendo que em todos os casos os resultados foram satisfatórios, apontando a eficácia do método. / The intracranial pressure (ICP) is one of the most important neurological parameter in animals and humans. The ICP is a function of the relation between the contents of the skull (brain parenchyma, cerebrospinal fluid and blood) and the volume of the skull. The increase in ICP (intracranial hypertension) may cause serious physiological effects and death in patients that do not receive appropriate care quickly, which includes real-time monitoring of ICP. All monitoring methods currently used in ICP are invasive, ie requiring invasion of the central nervous system by a pressure sensor, causing infections and traumas risks to patients. In this work we present a new minimally invasive method to monitor the intracranial pressure. This uses strain gauge deformation sensors, externally glued on the skull. The signal from this sensor is amplified, filtered and sent to a computer with appropriate software for analysis and data storage. &quot;In vitro&quot; and &quot;in vivo&quot; experiments let to the following results: (1) Our minimally invasive system is capable of adequately monitoring the ICP. (2) The measurements are in real and online time providing excellent signal and stability. (3) Simultaneous comparison with invasive methods not only validated our results but showed increased performance. The equipment cost effective will allow the use of our system in the Public Health System, with a important social aspect of our contribution.

A Pressão intracraniana (PIC) é um dos principais parâmetros fisiológicos em animais e humanos e sua morfologia é extremamente importante. Entretanto, todos os métodos de monitoramento existentes no mercado são invasivos, existindo uma ampla demanda por sistemas não invasivos, expandindo assim o campo de pesquisas acerca desse importante parâmetro neurológico, que só não é melhor estudado devido a forma invasiva de ser monitorado. A motivação é fazer com que o monitoramento da PIC seja tão comum e tão essencial quanto é hoje o monitoramento da pressão arterial, facilitando o diagnóstico e até prognóstico de diversas doenças. Este trabalho analisa e implementa melhorias de um sistema não invasivo de monitoramento da pressão intracraniana, baseado em extensometria. Um dos objetivos, no que tange o desenvolvimento do produto, é analisar o equipamento como um todo - Sensor, Hardware, Firmware e Software - e propor melhorias a partir dos testes realizados. Os testes realizados In vivo mostraram uma boa correlação do sinal com um sistema Gold Stardard, evidenciando o potencial promissor do método. / The intracranial pressure (ICP) is one of the main physiological parameters in animals and humans and its morphology is extremely important. However, all monitoring methods available in the market are invasive and there is a large demand for non-invasive systems, thus expanding the scope of research on this important neurological parameter, that just is not further studied because of the invasive method of monitoring. The motivation is to make monitoring the ICP as common and as essential, as monitoring the blood pressure is nowadays, facilitating diagnosis and even prognosis of various diseases. This work analyzes and implements improvements in a non-invasive intracranial pressure monitoring system based on extensometer. One of the goals, regarding product development, is to analyze the unit as a whole- Sensor, Hardware, Firmware and Software- and propose improvements from the tests. The in vivo tests showed a good correlation with a Gold Stardard system signal showing the promising potential of the method.

We create a dual-species ultracold neutral plasma (UNP) by photo-ionizing Yb and Ca atoms in a dual-species magneto-optical trap. Unlike single-species UNP expansion, these plasmas are well outside of the collisionless (Vlasov) approximation. We observe the mutual interaction of the Yb and Ca ions by measuring the velocity distribution for each ion species separately. We model the expansion using a fluid code including ion-ion friction and compare with experimental results to obtain a value of the Coulomb logarithm of Λ= 0.04.

Un spectrographe hyper-Raman très lumineux a été développé pour étudier les vibrations des matériaux. Les résultats obtenus sur ce dispositif sont comparés aux spectroscopies vibrationnelles classiques (Diffusion inélastique des neutrons, absorption infrarouge, diffusion Raman). L'analyse des règles de sélection a permis de préciser la nature des modes de vibrations dans les verres d'oxydes v-SiO2 et v-B2O3. Il a été nécessaire de s'appuyer sur les données obtenus dans des verres binaires xNa2O(1-x)SiO2 et xLi2O(1-x)B2O3, ainsi que dans une série de verres de silices densifiées de manière permanente. Nous montrons en particulier que les modes du pic boson des verres d'oxydes sont essentiellement associés à des mouvements de libration des unités structurales élémentaires qui composent le verre: tétraèdres SiO4 pour la silice et essentiellement les anneaux boroxols B3O3 dans v-B2O3. Nous observons aussi que pour ces deux verres les spectres Raman et hyper-Raman sont dominés par des modes de vibrations associés à des mouvements d'anneaux.