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Research into the mechanisms responsible for the lasting, cyclic activity at Masaya volcano can lead to a better understanding of persistently degassing volcanoes. This study is greatly enhanced by the integration of dynamic micro-gravity, deformation and gas flux measurements. The acquisition of extended temporal and spatial geophysical data will also allow for the development of robust models for the dynamics of magmatic systems. Masaya volcano, Nicaragua, is one of the most active systems in Central America, making it an excellent natural laboratory for this study. It is noted for repeated episodes of lava lake formation, strong degassing and subsequent quiescence. Ground-based geophysical measurements show two episodes of similar magnitude gravity decreases in 1993-1994 and 1997-1999, separated by a period of minor gravity increase. A major increase in S02 gas flux from 1997-1999 correlates well with the most recent episode of gravity decrease. The gravity changes are not accompanied by deformation in the summit areas and are interpreted in terms of sub-surface density changes. The persistent degassing at Masaya suggests that up to -15 krrr' of magma may have degassed over the last 150 years, only a minute fraction of which has been erupted. Furthermore, thermal flux calculations suggest that 0.5 krrr' of magma (the estimated volume of the shallow reservoir) would cool from liquidus to just above solidus temperatures in only 5 years. The high rates of degassing and cooling at open-system volcanoes such as Masaya raise questions as to the ultimate fate of this degassed and cooled magma. A number of models have been proposed to explain this, but the most likely mechanism to explain persistent activity at Masaya and other similar volcanoes is convective removal of cooled and degassed magma and subsequent recharge by volatile-rich magma from depth. Another fundamental question in modem volcanology concerns the manner in which a volcanic eruption is triggered; the intrusion of fresh magma into a reservoir is thought to be a key component. The amount by which previously ponded reservoir magma interacts with a newly intruded magma will determine the nature and rate of eruption as well as the chemistry of erupted lavas and shallow dykes. The physics of this interaction can be investigated through a conventional monitoring procedure that incorporates the Mogi model relating ground deformation (~) to changes in volume of a magma reservoir. Gravity changes (.1.g)combined with ground deformation provides information on magma reservoir mass changes. Models developed here predict how, during inflation, the observed .1.gI~ gradient will evolve as a volcano develops from a state of dormancy through unrest into a state of explosive activity.

Exoskeletons are rapidly emerging from the realm of science-fiction myth to practical reality in everyday life. Various designs have provided viable means for individuals to regain capabilities that were lost or perform tasks not previously possible by their ability alone. In this research, I propose two novel exoskeletons for walking assistance and heavy load carriage. The first exoskeleton can be used to provide assistance for walking in various applications such as industrial productivity, rehabilitation, and military or space training. We introduce a design for a lower body wearable device that supports up to 80% of the user's body weight (667 N peak force) with a single actuator on each leg. Its underactuated design directs force through the user's center of mass with a single sprocket-chain driven prismatic actuator on each leg, allowing for natural gait and mobility. The device is optimized for simplicity, ease of assembly, low cost, and weight. The second design aims to counteract the one of the leading causes of injury in the workplace, repetitive and heavy lifting. The Heavy Lift and Carry Exoskeleton (HeavyLC Exo) is capable of safely lifting and carrying loads up to 36 kg (80 lbs) while minimizing the number of actuators to reduce weight and complexity. The HeavyLC Exo allows the user to direct the object, pause and hold the object steady mid-lift, and follow the natural kinematics of lifting. It is secured to the user with shoulder, chest, and dual thigh straps, along with an adjustable waist belt and overshoe attachment. Powered by two 14.8 V batteries and an off-board air compressor, the HeavyLC Exo has a total of 20 DOF, with 6 actuated DOF and 14 free DOF. The arms use only two actuators each, providing powered lifting and arm retraction/extension, and allowing a wide range of body postures; the legs are powered by single pneumatic actuators on each leg connected to the foot accompanied by a passive spring element to prevent excessive pelvic tilt and leg abduction during swing. The control system requires directional forces from the user at the tool handle of 19 N (4.3 lbf) on average. Current design limitations necessitate the user to provide up to 280 N (62.9 lbf) at the hip during worst load conditions, and future design optimization is proposed. A fully functional prototype of HeavyLC Exo is built, fully tested, and analyzed for improvement. / Master of Science / Exoskeletons, which were once only seen in science fiction, are now becoming a reality in everyday life. Various designs have made it possible for people to do things they couldn't do before or regain abilities they lost. In this research, two new exoskeletons are proposed - one for walking assistance and the other for carrying heavy loads. The first exoskeleton is designed to help people walk. It supports up to 80 % of the user's body weight with a single actuator on each leg, which directs force through the center of mass, allowing for natural gait and mobility. It's simple, easy to assemble, low-cost, and lightweight, making it useful in various applications such as medical rehabilitation, military or space training, and industrial productivity. The second exoskeleton is designed to help people lift and carry heavy objects, which is a common cause of workplace injuries. The Heavy Lift and Carry Exoskeleton (HeavyLC Exo) can safely lift and carry objects up to 36 kg (80 lbs) while minimizing the number of actuators to reduce weight and complexity. It's worn by the user using shoulder, chest, and dual thigh straps, along with an adjustable waist belt and overshoe attachment. The exoskeleton is powered by two batteries and an off-board air compressor, and has 20 degrees of freedom, with 6 powered and 14 non-powered, giving it significant flexibility to conform to lifting and walking motions allowing it to function with normal user range of motion. The arms use two actuators each to provide powered lifting and arm retraction/extension, while the legs are powered by single pneumatic actuators on each leg connected to the foot accompanied by a elastic spring element. The control system requires the user to lift and maneuver about 1.9 kg (4.2 lbs) to direct the object. A fully functional prototype has been built, tested, and analyzed for changes in the future.

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La présente thèse est consacrée à l'étude expérimentale et la simulation de la dynamique des gaz granulaires vibro-fluidisés. Les gaz granulaires sont caractérisés par une dissipation due aux collisions inélastiques. Pour maintenir cet état à l'équilibre mécanique (stationnarité), l'énergie est injectée en continu depuis les bords vibrant pour équilibrer la dissipation des vibrations. Ce système fournit une base d'étude de la physique des systèmes non-linéaires, hors équilibre thermodynamique et dissipatifs. Cette thèse insiste sur la nécessité d'intégrer, de comprendre et de rendre compte de la situation inhomogène de la distribution locale dans les gaz granulaires et permet la construction d'un nouveau modèle de gaz granulaires fluidisés par des vibrations. Cette approche inclut (i) des résultats expérimentaux 2d en micro-gravité dans l'Airbus A300 0-g de Novespace, des expériences 2d avec des cellules (et des vibrations) horizontales, des expériences 2d sur plan incliné (avec vibrations et cellules inclinées et avec une gravité effective variable), ainsi que des simulations de dynamique moléculaire par la méthode " event-driven" appliquée à chaque choc. Ces résultats confortent les simulations 3D de Liu et al. Les expériences en micro-gravité dans Airbus A380 (vol parabolique) permettent d'éviter les frottements avec les parois planes et éliminent l'effet de gravité. Les distributions locales de la vitesse dans la direction de vibrations sont asymétriques partout (à l'exception de la zone centrale de la cellule par raison de symétrie). L' équipartition de l'énergie n'est pas vérifiée dans la cellule, l'énergie est distribuée de manière inhomogène, anisotrope et directionnelle. La " température granulaire " n'est plus une mesure efficace pour décrire un tel système. On rend compte de ces résultats à l'aide d'une superposition de deux modèle gaussien pour décrire les profils locaux de vitesse asymétriques le long de la direction de vibration. Les résultats des simulations de dynamique moléculaire 2d en gravité nulle montrent les mêmes tendances et confortent les résultats l'expérimentaux (dissymétrie des distributions de vitesse locales). Cette dissymétrie est un effet à longue portée et est liée à la dissipation du système: Elle augmente si le coefficient de restitution billes-billes diminue ou lorsque le nombre de particules augmente. La dissymétrie disparaît lorsque les chocs billes-billes sont élastiques. Cet effet ne peut être ignoré et doit être traité comme la frontière d'une "nouvelle hydrodynamique". Dans les expériences de vibrations sur cellule 2D et plan inclinés parallèles aux vibrations, l'angle d'inclinaison a été modifié de façon systématique de l'horizontale à la verticale, pour simuler différentes gravités effectives. Les résultats confirment une dissymétrie locale des distributions de vitesse locales, à laquelle se rajoute une dissymétrie supplémentaire liée à la gravité, provoquant une densité différente en haut et en bas de la cellule. Ces études sont les prémices, nous le pensons, d’une nouvelle vision de la mécanique des gaz granulaires réels dissipatifs. / The present thesis is dedicated to the experimental and simulation study of vibro-fluidized granular gases dynamics. Granular gases are characterized by dissipation due to inelastic collisions. To keep a steady state, continuous energy is injected to balance dissipation by vibration. This system provides a platform to study the physics of non-linear, non-equilibrium and dissipative systems. This dissertation insisted on the necessity of understanding the local state in the granular gases and building a new model for vibration-fluidized granular gases. Research approach included experiments in micro-gravity, event-driven molecular dynamic simulation and experiments in tilted plane with various gravity. Micro-gravity experiments were performed on Airbus A380 (Parabolic flight) to avoid friction with the bottom and gravity field. A long range boundary effect is found to exist in 2D vibration granular gases. Local distributions of the velocity component in the vibration direction are asymmetric in the whole cell except for the center bin. In the system, energy equi-partition breaks down. ``Granular temperature" is not efficient to describe such a system. We proposed a superposition of two Gaussian model to describe the local asymmetric velocity profiles along the vibration direction. We demonstrated the performance of this model by the Airbus experimental data and others’ simulation works. Event-driven molecular dynamics simulation was utilized. Results showed support for experiment results. Furthermore, we found this long range boundary effect is related to the system dissipation. This effect becomes pronounced if the coefficient of restitution (e<1) decreased or the number of particles increased. For the elastic situation, there is no such effect. This effect cannot be ignored and treated only as a local boundary effect as in hydrodynamics. We studied a 2D vibration fluidized granular system in a tilted plane systematically. The inclined angle is changed from horizontal to vertical, changing the "effective gravity". These results also showed asymmetric local velocity distributions. Other than the number density profiles deviate from an exponential form, the spatial profiles of the number density of particles moving up and down are not equal, and non symetric from cell center.

Boost Treadmills™, a company specializing in the use of differential air-pressure (DAP) technology in the realm of exercise and rehabilitation, is developing their second-generation micro-gravity treadmill™ named the Boost 2. This machine will allow individuals in all types of fitness environments to move and exercise at a fraction of their normal body weight, reducing the impact forces on lower body extremities and allowing for accelerated returns to activity. The purpose of this thesis was to create an algorithm to be implemented on the Boost 2 that related the percentage of body weight reduction of a user to a required pressure value within the Boost 2 pressure differential space created by the enclosure. This algorithm, when implemented, would allow a Boost 2 user to simply operate the machine at the appropriate pressure(s) automatically by entering their Boost shorts size, approximate height, and desired percentage of body weight reduction from a previously developed user interface screen. The calibration algorithm was developed using collected data and a regression analysis model created in Microsoft Excel®. This analysis creates an equation for a linear fit of predictor variables resulting in a line representing the body weight reduction pattern of a user as pressure is increased within the enclosure. On average, the difference between measured and predicted body weight percentages at measured pressure values was found to be less than 3%.

Les écoulements diphasiques sont couramment utilisés dans de nombreux domaines dont, en particulier, le domaine spatial. La performance de ces systèmes est entièrement régie par les couplages se produisant entre les écoulements et les transferts de chaleur. Cette particularité a conduit, depuis les dernières décennies, au développement de nombreuses études sur les écoulements diphasiques en microgravité. Afin d'accroître la connaissance sur le comportement thermo-hydraulique de ces systèmes thermiques, la présente étude se focalise sur l'étude de la condensation dans un mini-tube en présence ou non de la force gravitationnelle. Pour étudier l'effet de la gravité sur cette configuration, un premier modèle instationnaire d'écoulement diphasique a été développé. Parallèlement, une analyse des effets de la gravité sur l'hydrodynamique et les transferts thermique a été menée dans deux sections d'essai possédant un diamètre interne commun de 3,4 mm et des vitesses massiques faibles à modérées. La première étude a été réalisée au cours de la 62e campagne de vols paraboliques de l'ESA. Elle a été dédiée à la détermination des coefficients de transfert de chaleur quasi-locaux se produisant à l'intérieur d'un tube de cuivre. Afin de visualiser également les régimes d'écoulement présents, un tube en verre a été inséré au sein de cet échangeur. L'effet de la gravité sur les écoulements et les transferts a ainsi été déterminé. La seconde expérience, menée au sol, a porté sur l'étude d'un écoulement de vapeur descendant au sein d'un tube en saphir placé verticalement. Un protocole de mesure permettant d'obtenir simultanément l'épaisseur du film de liquide ruisselant et le coefficient d'échange local associé a été développé. / Liquid-vapor two-phase flows have common applications in many fields including space thermal management systems. The performances of such systems are entirely associated to the coupling between thermal and hydrodynamic phenomena. Therefore, two-phase flows in microgravity condition have emerged as an active research area in the last decades. In order to complete the state of the art and to contribute to the increase in the knowledge of hydrothermal behavior of two-phase thermal management systems, the present study was conducted on convective condensation inside a mini tube, both in normal and micro gravity conditions. To analyze the effect of gravity on such flows, a preliminary transient modeling of the two-phase flow has been established. Simultaneously, an experimental investigation was carried out on the hydrodynamic and thermal behaviors of condensation flows in two test sections of 3.4 mm inner diameter at low and intermediate mass velocities. The first experiment was conducted during the 62nd ESA parabolic flights campaign. The test section was made with copper and allowed measurements of the quasi-local heat transfer coefficient. A glass tube was also inserted in the middle of the test section for the visualization of the two-phase flow regime. From this study, the changes in heat transfer coefficient and flow regime according to gravity variations were determined. The second experiment was carried out on ground in a sapphire tube installed vertically considering downward flow. The set-up was designed in order to measure simultaneously the local heat transfer coefficient and the thickness of the liquid film falling down along the tube wall.

: cette thèse porte sur l’étude d’un accéléromètre à ondes de matière fonctionnant à bord d’un avion effectuant des vols paraboliques et permettant des expériences en micro-gravité (0-g). Un interféromètre à atomes de 87Rb refroidis par laser, et dont les états quantiques sont manipulés à l’aide de transitions Raman stimulées, constitue l’élément physique du capteur. Lors de la conception du dispositif expérimental, un effort particulier a été apporté au choix d’une source laser transportable, stable, et robuste. Nous démontrons pour la première fois le fonctionnement aéroporté d’un senseur inertiel à ondes de matière, à la fois en 0-g et durant les phases de gravité des vols (1-g). Nous proposons une technique combinant le signal de l’interféromètre à celui d’accéléromètres mécaniques auxiliaires pour effectuer des mesures au dela de la dynamique intrinsèque du capteur atomique. Nous expliquons comment bénéficier du haut niveau de sensibilité de l’interféromètre dans l’avion, et indiquons des voies d’améliorations significatives de notre dispositif pour le futur. En 0-g, nous montrons une amélioration de la sensibilité de l’accéléromètre jusque 2 x 10-4 m.s-2 à une seconde, et étudions une réjection des vibrations de l’avion à l’aide d’un interféromètre à quatre impulsions Raman. L’objectif de notre projet consiste en un test du principe d’universalité de la chute libre avec un double accéléromètre à atomes de 87Rb et de 39K. Notre système laser double-espèce emploie des composants optiques fibrés aux longueurs d’onde de 1.56 et 1.54 μm, ainsi qu’un doublage de fréquence pour obtenir la lumière utile à 780 et 767 nm pour le refroidissement et la manipulation des deux atomes. Nous étudions théoriquement la sensibilité d’une mesure de leur différence d’accélération en tenant compte des vibrations de l’avion, et précisons comment une résolution de l’ordre de 10-10 m.s-2 pourra être atteinte dans le futur avec notre expérience aéroportée. / This thesis reports the study of a matter-wave accelerometer operated aboard a 0-g plane in ballistic flights. The acceleration measurements are performed with a cold 87Rb atom interferometer using stimulated Raman transitions to manipulate the quantum states of the atoms. When designing the instrument, we took special care to make the laser source transportable, robust, and stable. With our setup, we demonstrate the first operation of a matter-wave inertial sensor aboard a plane, both in 0-g and during the gravity phases of the flights (1-g). Thanks to additional mechanical accelerometers probing the coarse inertial effects, we are able to detect acceleration fluctuations much greater than the intrinsic measurement range of the interferometer. We explain our method to benefit from the full sensitivity of the matter-wave sensor in the plane, and suggest significant improvements of our system for the future. In 0-g, we show the enhancement of the accelerometer sensitivity up to 2 x 10-4 m.s-2 in one second, and investigate a rejection of the vibrations of the plane with a four Raman pulses interferometer. The goal of our project is to perform a test of the universality of free fall with two atom accelerometers using 87Rb and 39K. The laser system for the two-species interferometer is based on fiber optical components at wavelengths of 1.56 and 1.54 μm, and optical frequency doubling to generate the useful light at 780 and 767 nm to cool and manipulate the atoms. We study theoretically the sensitivity of the differential acceleration measurement by taking into account the vibrations of the plane, and discuss how a resolution of the order of 10-10 m.s-2 could be achieved in the future with our airborne experiment.

This dissertation presents the design and development of a mixed-signal low noise second-order integrated circuit (IC) for the open-loop and closed-loop operation of integrated capacitive micro- and nano-gravity accelerometers. The micromechanical accelerometers are fabricated in thick (less than 100 m) silicon-on-insulator (SOI) substrates. The IC provides the 1-bit digital output stream and has the versatility of interfacing sensors with different sensitivities while maintaining minimum power consumption (less than 5 mW) and maximum dynamic range (90 dB). A fully-differential sampled-data scheme is deployed with the ability of low-frequency noise reduction through the use of correlated double sampling (CDS) scheme. In this work, the measured resolution of the closed-loop CMOS-SOI accelerometer system, in the presence of high background accelerations, is in the micro-g (g: gravity) range. In this design, a second-order SC modulator is cascaded with the accelerometer and the front-end amplifier. The accelerometer operates in air and is designed for non-peaking response with a BW-3dB of 500 Hz. A 22 dB improvement in noise and hence dynamic range is achieved with a sampling clock of 40 kHz corresponding to a low oversampling ratio (OSR) of 40. The interface IC consumed a current of 1.5 mA from a supply of 3 V.