O colágeno é a forma funcional de um oligômero biológico, cujos monômeros são aminoácidos quirais. Tecidos ricos em colágeno são estruturas opticamente anisotrópicas, birrefringentes e não-lineares. O objetivo deste trabalho foi caracterizar o colágeno tipo I não irradiado e após irradiação com laser de He-Ne polarizado, utilizando a microscopia de polarização para investigação da birrefringência, e a geração de segundo harmônico (GSH) para análise da susceptibilidade não-linear. Doze ratos Wistar foram divididos em quatro grupos, de acordo com as idades: 34, 48, 62 e 76 dias. Os grupos receberam, respectivamente, 1; 5; 9 e 13 irradiações de D= 1J/cm2, durante 46s, no tendão de Aquiles que, aleatoriamente, foi escolhido ser o direito ou esquerdo. Os animais foram então sacrificados e os tendões extraídos para a preparação das amostras. Para a microscopia de polarização foram obtidos cortes com 8μm de espessura, e as birrefringências de forma e intrínseca foram avaliadas. Para a GSH foi utilizado um laser de Ti:Safira (150fs) com 76MHz de taxa de repetição, diâmetro do feixe φ= 40μm, comprimento de onda central λ= 800nm e Δλ= 10nm e Pp= 110mW. Um polarizador linear foi posicionado no caminho do feixe. Duas objetivas foram utilizadas para focalizar e coletar a radiação incidente e emergente da amostra, respectivamente. Um analisador, também linear, foi introduzido logo após a objetiva coletora. Um filtro absorvedor na faixa infravermelha do espectro eletromagnético, mas transmissor na faixa azul, foi utilizado para garantir que apenas λ= 400nm era medido. A razão, ρ, entre dois tensores de hiperpolarizabilidade independentes foi estudada. As amostras irradiadas apresentaram maior birrefringência (Δn) e maior susceptibilidade não-linear (ρ), em comparação com as não irradiadas. Estes resultados indicam que o laser de He-Ne polarizado alinha as fibrilas de colágeno ao longo eixo do tendão. / The collagen is the functional form of a biological oligomer whose monomers are chiral amino acids. Tissues filled up of collagen are anisotropic optically structures, birefringent and nonlinear. The purpose of this study was characterizing nonirradiated and polarized He-Ne laser irradiated type I collagen using polarized light microscopy to investigate the birefringence and the second harmonic generation (SHG) to analyze the nonlinear susceptibility. Twelve Wistar rats were alienated into four groups according to the ages: 34, 48, 62 and 76 days. The groups received, respectively, 1; 5; 9; and 13 irradiations of D= 1J/cm2 during 46s on Achilles tendon, which was chosen randomly as right or left. Thereafter, the animals were sacrificed and the tendons were extracted to prepare the specimens. For polarized light microscopy, eight-μm sections were obtained to evaluate the form and intrinsic birefringences. For SHG, it was used a Ti:Safira (150fs) laser at a repetition rate of 76MHz, beam diameter of φ= 40μm, wavelength of λ= 800nm and Δλ= 10nm and Pp= 110mW. The beam passed through a linear polarizer and two microscope objectives were used to focalize and collect the incident and emergent radiation, respectively. A second linear polarizer was placed after of collecting objective. An infrared absorber and blue transmitter filter was used a sure that only λ= 400nm was measured. The ratio, ρ, between two hyperpolarizability tensors was studied. The irradiated samples presented higher birefringence (Δn) and nonlinear susceptibility (ρ) when compared to nonirradiated samples. These results indicate that a polarized He-Ne laser aligns the collagen fibrils to the long tendon axis.

Ce travail porte sur l’étude des phénomènes induits par implantation d’hydrogène et/ou d’hélium dans le silicium monocristallin. Le cloquage et l’exfoliation dus à la coimplantation d’hélium et d’hydrogène ont été étudiés en fonction des paramètres d’implantation (énergie, fluence, courant, rapport H/He) et des conditions de recuit. Un comportement de type fenêtre à été observé dont le maximum de surface exfoliée dépend uniquement de la fluence. Deux mécanismes d’exfoliation liés aux régimes de fluence ont été identifiés et discutés. D’autre part, la microstructure des échantillons a été étudié par MET, et les déformations ont été mesurées par diffraction des Rayons X. Un modèle décrivant la distribution des contraintes dans le substrat implanté a été proposé. Le phénomène de delamination des substrats qui apparaît pour des conditions particulières d’implantation a également été étudié, comparé aux phénomènes de cloquage et exfoliation, et expliqué en utilisant des concepts de la mécanique de la fracture. Enfin, l’interaction élastique entre précipités d’He et d’H a été étudiée pour des profils d’implantation superposés et décalés. Dans ce dernier cas, nous avons montré que le champ de contraintes générées par les plaquettes d’hélium en surpression pouvait être utilisé comme source locale de contraintes pour contrôler la formation et la croissance de plaquettes d’hydrogène. Afin d’interpréter nos résultats expérimentaux, nous avons développé un modèle basé sur l’interaction élastique pour la nucléation des précipités dans un solide semi-infini. / The present work relates an investigation of H2 + and He+ coimplanted (001)-Si substrates. The phenomena of blistering and exfoliation were studied by SEM as a function of the implantation parameters (energy, fluence, current and H/He ration) and annealing protocol. A window behavior as function of the implanted fluence was observed and two distinct fluence dependents mechanisms of exfoliation were indentified and discussed. The microstructure of the implanted samples was studied using TEM and related to ballistic effects and stress-strain dependent interactions. The strain was measured using DRX and a model to describe the stress-strain distribution into the implanted layer is developed. A new phenomenon of delamination of thin layer from implanted Si substrates was observed to emerge from particular implantation conditions. The behavior was studied and explained using fracture mechanics concepts and contrasted to blistering/exfoliation processes. Finally, the elastic interaction between He and H plate-like precipitates giving rise to arranged nanostructure was demonstrated and studied using TEM. An elasticity based model was developed to understand the behavior. The result set the basis for further developments of nanostructures within a crystalline matrix by manipulating preferential orientations of precipitates in nanometric scale.

Le phénomène de précession cohérente de l'aimantation dans l'hélium 3 superfluide a été découvert en 1984. Il se caractérise par la précession libre de l'aimantation du superfluide sur des échelles de temps très longues (dans certains cas, des heures). Ce phénomène est une signature de la superfluidité de spin, l'analogue magnétique de la supraconductivité ou de la superfluidité. La superfluidité de spin peut se décrire en termes de condensation de Bose-Einstein des excitations magnétiques du superfluide : les magnons. Ce formalisme permet de déterminer simplement les conditions dans lesquelles une telle condensation peut apparaître dans les différentes phases de l'hélium 3 superfluide. Ce travail présente comment l'utilisation d'aérogel anisotrope nous a permis de manipuler le paramètre d'ordre du superfluide et d'obtenir ainsi de nouvelles phases dans lesquelles la condensation de Bose-Einstein des magnons peut être observée. Nous avons ainsi étudié expérimentalement la précession cohérente de l'aimantation dans ces nouvelles phases. Nous avons également étudié l'influence de l'aérogel sur la transition de phase superfluide. Enfin, nous détaillons comment il est possible d'obtenir la précession cohérente de l'aimantation sur les différents niveaux d'un puits de potentiel pour les magnons. / The phenomenon of coherent precession of magnetization in superfluid helium 3 was discovered in 1984. It is characterized by the free precession of the magnetization of the superfluid on very long timescales (up to hours). This phenomenon is a signature of spin superfluidity, the magnetic analogue of superconductivity or superfluidity. Spin superfluidity can be described in terms of Bose-Einstein condensation the magnetic excitations of the superfluid: the magnons. This formalism makes it possible to determine easily the conditions in which such a condensation can appear in the different phases of superfluid helium 3. This work shows how the use of anisotropic aerogel permitted us to manipulate the order parameter of the superfluid and thus to obtain new phases in which the Bose-Einstein condensation of magnons can be observed. We were able to study experimentally the coherent precession of magnetization in these new phases. We also studied the influence of the aerogel on the superfluid transition. Finally, we detail how one can obtain the coherent precession of magnetization on different levels of a potential well for magnons.

Certaines missions d'astrophysique embarquent des détecteurs infrarouges ou X qui sont refroidis à des températures subkelvin via un système cryogénique qui comporte soit un bain d'hélium (comme pour Herschel), soit un réfrigérateur Joule-Thomson (comme pour Planck) pour le pré-refroidissement de l'étage subkelvin. Un doigt froid à tube à gaz pulsé ayant les mêmes performances qu'un Joule-Thomson pourrait offrir un certain nombre d'avantages pour les futures chaines cryogéniques (pas de pré-refroidissement nécessaire, simplicité d'intégration, fiabilité accrue).L'objectif de cette thèse concerne l'étude et la réalisation d'un doigt froid à tube à gaz pulsé 4K qui pourrait remplacer une machine Joule-Thomson. Deux principaux axes d'étude ont été menés parallèlement : des études sur les matériaux régénérateur et des études de performances. Des développements technologiques portant sur le régénérateur (étude et mise en forme de différents matériaux ayant des anomalies de chaleur spécifique à basse température) ont été menés afin d'améliorer les performances d'un doigt froid à tube à gaz pulsé haute fréquence (30Hz) travaillant avec de l'hélium 4.Cette thèse a permis d'obtenir la meilleure performance mondiale en terme de température limite en utilisant de l'hélium 4 et avec un pré-refroidissement à 20K. Une température limite de 3,86K a été obtenue et une puissance froide de 25mW est disponible à 5K. Cette thèse a également permis d'étudier l'effet du gaz réel sur le comportement de la machine, en particulier grâce à des mesures de profils de température du régénérateur. Cinq configurations différentes de régénérateur (variation de la répartition de chaleur spécifique le long du régénérateur froid) ont été testées. Elles ont permis de mieux comprendre le rôle de la répartition de la chaleur spécifique dans le régénérateur. Ces différentes mesures ont été complétées avec des études de fluctuations de températures pariétales réalisées à l'aide d'une centrale d'acquisition rapide (toutes les millisecondes). / Some astrophysics missions embark infrared or X detectors which are cooled down to subkelvin temperatures using a cryogenic cooling system that features helium bath (like for the Herschel satellite) or a Joule-Thomson cryocooler (like for the Planck satellite) for the precooling of the subkelvin cooling stage. A pulse tube cold finger which would have the same performances as a Joule-Thomson cryocooler could offer some advantages for future cryogenic chains (no need of precooling, simplicity of integration, increased reliability).The goal of this PhD is the making and the study of a pulse tube cold finger working at temperature around 4K which could replace a Joule-Thomson cryocooler. Two main lines have been worked on simultaneously : studies on materials for the cold regenerator and studies on the cold finger performances. Technological developments on the cold regenerator (including study and shaping of different materials with specific heat anomalies at low temperature) have been performed to enhance the performances of a cold finger working at high frequency (30Hz) with helium 4.The work done during this PhD led to the best no-load temperature never achieved using helium 4 and with a precooling of 20K. A no-load temperature of 3.86K has been obtained and 25mW of cooling power are available at 5K. In addition the effect of real gas on the cryorefrigerator operation has been studied in particular thanks to the measurement of regenerator thermal profiles. Five configurations with different regenerator fillings (variation of the distribution of the specific heat along the cold regenerator) have been tested. These five tests led to a better understanding of the role of the distribution of the specific heat in the regenerator. These measurements have been completed with studies of regenerator wall temperature fluctuations recorded thanks to a fast data acquisition system (each millisecond).

The aim of the project was to establish rate and mechanisms of solid state reduction of manganese ores. The project studied carbothermal reduction of manganese oxide MnO, two Groote Eylandt (Australian) and Wessels (South African) manganese ores in hydrogen, helium and argon atmospheres at temperatures up to 1400C for MnO and 1200C for manganese ores. Experiments were conducted in the fixed bed reactor with on-line off-gas analysis. The major findings are as follows. ?? Rate and degree of reduction of MnO and ores increased with increasing temperature. ?? Reduction of MnO and manganese ores at temperatures up to 1200C was faster in helium than in argon, and much faster in hydrogen than in helium. The difference in MnO reduction in hydrogen and helium decreased with increasing temperature to 1400C. ?? Addition of up to 7 vol% of carbon monoxide to hydrogen had no effect on MnO reduction at 1200C. ?? In the process of carbothermal reduction of ores in hydrogen at 1200C, silica was reduced. ?? Reduction of both GE ores was slower than of Wessels ore. This was attributed to high content of iron oxide in the Wessels ore. ?? Carbon content in the graphite-ore mixture had a strong effect on phases formed in the process of reduction; thus, in the reduction of Wessels ore with 12-16 wt% C, a-Mn and Mn23C6 were formed; when carbon content was above 20 wt%, oxides were reduced to carbide (Mn,Fe)7C3. ?? Kinetic analysis showed that mass transfer of intermediate CO2 from oxide to graphite in carbothermal reduction in inert atmosphere was a contributing factor in the rate control. ?? High rate of reduction of manganese oxide in hydrogen was attributed to formation of methane which facilitated mass transfer of carbon from graphite to oxide. Hydrogen was also directly involved in reduction of manganese ore reducing iron oxides to metallic iron and higher manganese oxides to MnO. Reduction of Wessels and Groote Eyland Premium Fines ores in the solid state is feasible at temperatures up to 1200C; while temperature for solid state reduction of Groote Eyland Premium Sands is limited by 1100C.

L'expérience E89-044, réalisée dans le Hall A du Jefferson Lab, a mesuré les sections efficaces de la réaction 3He(e,e'p).<br> L'extraction des fonctions de réponse longitudinale et transverse de la réaction de désintégration à deux corps 3He(e,e'p)d en cinématique parallèle doit permettre l'étude des propriétés électromagnétiques du proton à l'intérieur du noyau d'3He ainsi que des mécanismes nucléaires mis en jeu au-delà de la description en ondes planes, pour des impulsions manquantes de 0 et +- 300 MeV/c et des quadrimoments transférés de 0.8 à 4.1 GeV2. Les sections efficaces préliminaires ont été obtenues après calibration du dispositif expérimental en utilisant une méthode d'ajustement des modèles théoriques intégrés sur l'espace de phase expérimental à l'aide d'une simulation Monte-Carlo. L'erreur systématique de 8% sur les sections efficaces est principalement liée à la normalisation absolue de la densité de la cible : l'analyse des données en diffusion élastique permettra de réduire cette erreur. Les résultats préliminaires font apparaître certains désaccords avec les prédictions théoriques pour les cinématiques aux angles avant à petite impulsion manquante (<100 MeV/c), notamment à grands Q2, et des comportements sensibles aux effets d'interaction dans l'état final ainsi qu'aux fonctions d'ondes de l'3He utilisées pour les impulsions manquantes voisines de 300 MeV/c. La séparation des composantes longitudinale et transverse déjà amorcée devrait contraindre plus fortement les modèles.

Cette thèse présente l'étude de la dynamique d'un atome ou d'une molécule en interaction avec un agrégat en vue d'étudier comment un petit système (l'atome, la molécule) échange de l'énergie électronique, cinétique et vibrationnelle avec un système possédant de très nombreux degrés de liberté (l'agrégat).Le premier système est l'étude, expérimentale et théorique, de la dynamique en temps réel d'un atome de baryum déposé sur agrégat d'argon (BaArn). L'atome de baryum est excité dans des niveaux de Rydberg, il en résulte une dynamique extrêmement riche entre le chromophore et l'agrégat. L'interprétation théorique a nécessité la conception d'une méthode de dynamique originale, permettant de traiter à la fois le grand nombre d'états excités mis en jeu, couplés à de nombreux degrés de libertés atomiques. La mise en commun des informations théoriques et expérimentales a permis d'établir l'ensemble du chemin réactionnel ayant lieu au cours de cette dynamique.Le deuxième système concerne l'étude par fluorescence de la photo-dissociation de Ca2 déposé sur agrégat d'hélium ou sur agrégat mixte hélium-argon (Ca2Hen ou Ca2ArmHen). Ces résultats sont comparés à ceux obtenu sur agrégat d'argon pur (Ca2Hen). Les différences entre ces trois types de solvant montrent que les interactions sont différentes suivant que le solvant est ''quantique'' (l'hélium) ou ''classique'' (l'argon). Plusieurs canaux réactionnels ont été mis en évidence selon que l'atome de calcium excité qui résulte de la photo-dissociation est libre ou reste solvaté par de l'hélium et/ou de l'argon. Les rapports de branchement entre ces différents canaux ont également été mesurés.

One major step needed for fusion to become a reliable energy source is the development of materials for the extreme conditions (high temperature, radioactivity and erosion) caused by hot plasmas. The main goal of the present study is to use and optimise ion beam methods (lateral resolution and sensitivity) to characterise the distribution of hydrogen isotopes that act as fuel. Materials from the test reactors JET (Joint European Torus), TEXTOR (Tokamak Experiment for Technology Oriented Research) and Tore Supra have been investigated. Deuterium, beryllium and carbon were measured by elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA). To ensure high 3D spatial resolution a nuclear microbeam (spot size &lt;10 µm) was used with 3He and 28Si beams. The release of hydrogen caused by the primary ion beam was monitored and accounted for. Large variations in surface (top 10 µm) deuterium concentrations in carbon fibre composites (CFC) from Tore Supra and TEXTOR was found, pointing out the importance of small pits and local fibre structure in understanding fuel retention. At deeper depths into the CFC limiter tiles from Tore Supra, deuterium rich bands were observed confirming the correlation between the internal material structure and fuel storage in the bulk. Sample cross sections from thick deposits on the JET divertor showed elemental distributions that were dominantly laminar although more complex structures also were observed. Depth profiles of this kind elucidate the plasma-wall interaction and material erosion/deposition processes in the reactor vessel. The information gained in this thesis will improve the knowledge of first wall material for the next generation fusion reactors, concerning the fuel retention and the lifetime of the plasma facing materials which is important for safety as well as economical reasons.

A cryogenic (325-80 K) ion mobility-mass spectrometer was designed and constructed in order to improve the analytical figures-of-merit for the chemical analysis of small mass analytes using ion mobility-mass spectrometry. The instrument incorporates an electron ionization source, a quadrupole mass spectrometer, a uniform field drift cell spectrometer encased in a cryogenic envelope, and an orthogonal geometry time-of-flight mass spectrometer. The analytical benefits of low temperature ion mobility are discussed in terms of enhanced separation ability, ion selectivity and sensitivity. The distinction between resolving power and resolution for ion mobility is also discussed. Detailed experimental designs and rationales are provided for each instrument component. Tuning and calibration data and methods are also provided for the technique. Proof-of-concept experiments for an array of analytes including rare gases (argon, krypton, xenon), hydrocarbons (acetone, ethylene glycol, methanol), and halides (carbon tetrachloride) are provided in order to demonstrate the advantages and limitations of the instrument for obtaining analytically useful information. Trendline partitioning of small analyte ions based on chemical composition is demonstrated as a novel chemical analysis method. The utility of mobility-mass analysis for mass selected ions is also demonstrated, particularly for probing the ion chemistry which occurs in the drift tube for small mass ions. As a final demonstration of the separation abilities of the instrument, the electronic states of chromium and titanium (ground and excited) are separated with low temperature. The transition metal electronic state separations demonstrated here are at the highest resolution ever obtained for ion mobility methods. The electronic conformational mass isomers of methanol (conventional and distonic) are also partially separated at low temperature. Various drift gases (helium, neon, and argon) are explored for the methanol system in order to probe stronger ion-neutral interaction potentials and effectuate higher resolution separations of the two isomeric ions. Finally, two versatile ion source designs and a method for axially focusing ions at low pressure (1-10 torr) using electrostatic fields is presented along with some preliminary work on the ion sources.

Presented in this thesis is the design and characterization of a new, high-flux source of cold atoms based on continuous, post-nozzle injection of lithium atoms into a cryogenic, supersonic helium jet. To date, experiments have been performed with lithium injection fractions up to [approximately equal to]10⁻⁶, where fluorescence spectroscopy reveals successful capture and thermalization of lithium atoms within the helium jet. The observed lithium beam copropagates with the helium jet and has a temperature of less than 10 mK, a brightness of 1.1x10¹⁹ m⁻² s⁻¹ sr⁻¹, and a brilliance of 3.1x10²⁰ m⁻² s⁻¹ sr⁻¹. Lithium atoms contained within a solid angle of [approximately equal to]0.018 sr are good candidates for future magnetic extraction. This results in a potentially capturable lithium flux of 1.1x10¹² s⁻¹, comparable to the existing record for a cold atomic beam. Also presented is preliminary data showing lithium fluorescence nearly 1 m downstream, demonstrating that the cold lithium beam can be successfully extracted from the seeding region. Numerical simulations reproduce capture efficiency to within 50%, suggesting that the process is well understood. We believe that successful seeding may be possible at a fraction up to 10⁻⁴. Seeding at this rate could produce an atomic beam with a flux as high as 1.3x10¹⁴ s⁻¹ at a phase-space density up to 1.6x10⁻⁷, corresponding to brightness and brilliance of order 10²² m⁻² s⁻¹ sr⁻¹ and 10²⁴ m⁻² s⁻¹ sr⁻¹ , respectively. If this novel cooling method performs as well at higher incident lithium flux, it could serve as a pump source and pave the way to the realization of the first truly continuous atom laser. / text