Groundwater provides a fundamental resource for modern life. Throughout the world, groundwater is managed by storing (recharging) it underground in natural aquifers for future withdrawal and consumptive use. In Arizona, over 4 million people benefit from managed aquifer storage, but little effort is made to track the movement of recharged water through the subsurface. Motivated by current limitations in our ability to monitor percolation and groundwater movement at the scale of a recharge facility, an effort to collect time-lapse gravity data was carried out at the Southern Avra Valley Storage and Recovery Project (SAVSARP) operated by the City of Tucson, Arizona. In addition to collecting water-level data 12 wells, there were three primary gravity experiments: (1) five continuously-recording gravity meters (2 iGrav superconducting gravity meters and 3 gPhone gravity meters) were installed semi-permanently in control buildings adjacent to the recharge basins, (2) absolute gravity measurements were made at nine locations over a 17 month period, and (3) three relative-gravity campaigns were carried out on a network of 70 stations. This large-scale controlled experiment, with known infiltration and pumping rates, resulted in one of the most comprehensive datasets of its kind. Gravity data led to several hydrologic insights, both through direct measurement and modeling. First, the infiltration rate could be estimated accurately based on the initial rate of gravity change during infiltration, regardless of the specific yield. Using two gravity meters, the depth, and therefore speed, of the wetting front beneath a recharge basin was observed, including the time at which the water table was reached. Spatial maps of gravity change from relative gravity surveys show areas where infiltration efficiency is highest, and where groundwater accumulates; storage accumulated preferentially to the west of the recharge basins, away from pumping wells. Such information would be valuable for planning the location of pumping wells at a new facility. Gravity data were useful for calibration of a Modflow-NWT groundwater-flow model using the Unsaturated Zone Flow package to simulate recharge; the reduction in the posterior parameter distribution compared to the a priori estimate was substantial and similar to head data. In contrast to model-simulated head data, model-simulated gravity data were less sensitive to more distant model elements and more effective for calibration of a superposition-type model. Observed head data had a strong regional signal reflecting basin-scale conditions with only minor variation associated with individual recharge basins, and were therefore of limited usefulness for model calibration. Together, the methods developed by the study and interpretations they made possible suggest that gravity data are an effective way to better understand large-scale infiltration and groundwater movement.

Pendant la solidification d’alliages se développe au niveau de l’interface solide-liquide une microstructure dont les caractéristiques influencent fortement les propriétés macroscopiques du matériau. Sa formation est un processus dynamique dans lequel le réseau émerge, s’organise et s’ordonne progressivement. Sur terre, la convection dans la phase liquide perturbe la formation de cette microstructure. Pour éliminer la convection tout en conservant des échantillons tridimensionnels, des expériences en solidification dirigée d'alliages transparents (matériaux organiques modèles des alliages métalliques) ont été réalisées dans l’instrument DECLIC–DSI (CNES–NASA), en régime de transport diffusif à bord de la Station Spatiale Internationale. Une quantité considérable de données brutes a été obtenue durant la campagne d’expériences qui s’est déroulée entre 2010 et 2011.L’objectif de ces travaux de thèse est d'analyser la dynamique de formation et d’évolution du réseau interfacial, de sa naissance à l’état stationnaire. Afin d’exploiter les données, il a fallu développer des procédures performantes d’analyse d’images permettant le traitement automatisé de séquences complètes d’images. Nous avons également développé une procédure permettant d’analyser les séquences d’images interférométriques et ainsi de suivre l’évolution temporelle de la forme tridimensionnelle de l’interface.Deux axes principaux structurent ces travaux : d’une part, l’étude des mécanismes de sélection de l’espacement primaire, taille caractéristique de la microstructure; et d'autre part, la caractérisation approfondie du régime oscillant, instabilité secondaire du réseau cellulaire. / The study of solidification microstructure formation is of utmost importance for the design and processing of materials, as solid-liquid interface patterns largely govern mechanical and physical properties. Pattern selection occurs under dynamic conditions of growth. The materials of choice for direct visualization of interface dynamics are transparent organic analogs. On Earth, convection alters the formation of cellular and dendritic microstructures. The micro-gravity of Space is therefore mandatory for fluid flow elimination in bulk samples. Over a hundred days of experiments between 2010 and 2011 were carried out in the DECLIC-DSI, (CNES-NASA) onboard the International Space Station. During the experimental campaign, a huge amount of data, mainly images, was obtained. The objective of this thesis work is to study the dynamics of formation and evolution of the interfacial array, from its birth to its steady state.A significant amount of work was the development of in-house software to robustly treat the white-light and interferometric image sequences.Two major topics are examined in this work: First, the study of the selection of primary spacing (the microstructure's characteristic size). Second, the in-depth characterization of pattern oscillation, which is a secondary instability of the cellular pattern. The analysis of the results is supported by 3D phase-field simulation, undertaken by the modellers in this team and in the team of Pr. A. Karma (Northeastern University, Boston).

Production of protein and semi-conductor crystals with advanced quality and properties is considered to be possible under microgravity conditions due to the absence of natural convection effects. Such materials have several beneficial properties that can improve the human life. An example is the synthesis of protein crystals with improved structure that can be determined for the production of advanced drugs. In the past experiments conducted aboard several space platforms, however, g-jitter induced convective flow may have resulted in certain effects that reduced the quality of the produced crystals. To investigate the effects of g-jitter on the motion of small particles, experiments were conducted under normal gravity by suspending spherical stainless steel particles of different sizes with a thin wire or synthetic silk thread in a rectangular fluid cell. The fluid viscosities were 350 and 1,000 times higher than water. To produce the g-jitter induced motion in the fluid, the cell was subjected to horizontal sinusoidal vibrations with different frequencies and amplitudes. The focus of the experiments so far has been on vibration-induced force on the particle vibrating parallel to a near wall. Relatively low viscosity fluids such as water have been previously determined to produce a force on the particle which attracts the particle to the nearest fluid cell wall. The present experiments with a more viscous fluid have revealed an interesting change in the force from attraction in low viscosity fluids to repulsion in high viscosity liquids. Moreover, the repulsion force has been observed to increase with an increase in the fluid viscosity and the fluid cell amplitude. A numerical code, Partflow3d, has also been used to predict the vibration effects on the particle. Although, based on the objectives of this study, the numerical simulations were conducted only for a wire-free particle under microgravity, their results were qualitatively in agreement with the experimental results. The numerical simulations also revealed that the physical mechanism of the hydrodynamic attraction-repulsion force on the particle is related to Bernoulli’s principle of reduced pressure in high velocity zones in the fluid surrounding the particle. The results so far have shown new aspects of the g-jitter induced motion of the particle near a fluid cell wall. Better understanding of the forces affecting the particles in a fluid cell subjected to small vibrations, can reveal novel ways to produce new advanced materials and also improve material processing both in microgravity and normal gravity conditions.

Ethylene/Air diffusion flames were studied at sub and super-atmospheric pressures to simulate a microgravity environment at fuel flow rates of 0.482 mg/s and 1.16 mg/s. Flame properties including flame dimensions, soot formation, temperature, and attachment mechanisms were investigated. Overall, luminous flame height decreased with decreasing pressure to the point of visible luminosity disappearance, resulting in blue flames. Flame width increased with decreasing pressure until the flame was almost spherical. Soot formation decreased with decreasing pressure to negligible concentrations in a near vacuum. At 0.482 mg/s, the percentage of carbon converted into soot was between 0.01% and 0.12%, whereas at 1.16 mg/s, this percentage was between 0.5% and 11% at sub-atmospheric pressures. Maximum flame temperatures increased with decreasing pressure. Regardless of fuel flow rate, the diffusion flames remained attached to the exterior of the burner. This attachment point moved further down the burner exterior as pressure decreased until a near vacuum.

Production of protein and semi-conductor crystals with advanced quality and properties is considered to be possible under microgravity conditions due to the absence of natural convection effects. Such materials have several beneficial properties that can improve the human life. An example is the synthesis of protein crystals with improved structure that can be determined for the production of advanced drugs. In the past experiments conducted aboard several space platforms, however, g-jitter induced convective flow may have resulted in certain effects that reduced the quality of the produced crystals. To investigate the effects of g-jitter on the motion of small particles, experiments were conducted under normal gravity by suspending spherical stainless steel particles of different sizes with a thin wire or synthetic silk thread in a rectangular fluid cell. The fluid viscosities were 350 and 1,000 times higher than water. To produce the g-jitter induced motion in the fluid, the cell was subjected to horizontal sinusoidal vibrations with different frequencies and amplitudes. The focus of the experiments so far has been on vibration-induced force on the particle vibrating parallel to a near wall. Relatively low viscosity fluids such as water have been previously determined to produce a force on the particle which attracts the particle to the nearest fluid cell wall. The present experiments with a more viscous fluid have revealed an interesting change in the force from attraction in low viscosity fluids to repulsion in high viscosity liquids. Moreover, the repulsion force has been observed to increase with an increase in the fluid viscosity and the fluid cell amplitude. A numerical code, Partflow3d, has also been used to predict the vibration effects on the particle. Although, based on the objectives of this study, the numerical simulations were conducted only for a wire-free particle under microgravity, their results were qualitatively in agreement with the experimental results. The numerical simulations also revealed that the physical mechanism of the hydrodynamic attraction-repulsion force on the particle is related to Bernoulli’s principle of reduced pressure in high velocity zones in the fluid surrounding the particle. The results so far have shown new aspects of the g-jitter induced motion of the particle near a fluid cell wall. Better understanding of the forces affecting the particles in a fluid cell subjected to small vibrations, can reveal novel ways to produce new advanced materials and also improve material processing both in microgravity and normal gravity conditions.

Ethylene/Air diffusion flames were studied at sub and super-atmospheric pressures to simulate a microgravity environment at fuel flow rates of 0.482 mg/s and 1.16 mg/s. Flame properties including flame dimensions, soot formation, temperature, and attachment mechanisms were investigated. Overall, luminous flame height decreased with decreasing pressure to the point of visible luminosity disappearance, resulting in blue flames. Flame width increased with decreasing pressure until the flame was almost spherical. Soot formation decreased with decreasing pressure to negligible concentrations in a near vacuum. At 0.482 mg/s, the percentage of carbon converted into soot was between 0.01% and 0.12%, whereas at 1.16 mg/s, this percentage was between 0.5% and 11% at sub-atmospheric pressures. Maximum flame temperatures increased with decreasing pressure. Regardless of fuel flow rate, the diffusion flames remained attached to the exterior of the burner. This attachment point moved further down the burner exterior as pressure decreased until a near vacuum.

NASA goals include long-term International Space Station (ISS) missions and the ambitious objective of eventually sending astronauts to Mars. Unfortunately, exposure to unloading due to microgravity during spaceflight has been shown to cause detrimental health effects on bone. Therefore, NASA is seeking a ground-based animal model to study the long-term effects of unloading on bone in order to better insure the health and mission capability of astronauts. The hindlimb unloaded (HU) rat model was used to study the effects of multiple unloading exposures and aging on bone properties. Six month old, adult, male Sprague-Dawley rats were separated into the following groups: baseline (BL, sacrificed when received at 6 months age), aging cage control (AC, normal weight-bearing cage activity), 1HU7 (unloaded for 1 month starting at 7 months of age and allowed to recover for 3 months), 1HU10 (normal cage activity until 10 months of age, unloaded for 1 month, recovered for 2 months), and 2HU10 (unloaded for 1 month at 7 months of age, allowed to recover for 2 months, unloaded again for 1 month at 10 months of age, followed by 2 months of recovery). Every 28 days a subset of animals (n=15) were euthanized and both femurs were excised. A peripheral quantitative computed tomography (pQCT) scanner was used to collect densitometric and geometric properties at the right and left femoral neck and at the left femoral midshaft. Mechanical testing (axial and lateral compression of the femoral neck and 3pt bending of the midshaft) was performed at each location and strength indices based on pQCT parameters were calculated. Femoral neck properties decreased due to HU but recovered with respect to increase over HU, BL, and AC by the end of the recovery periods. Femoral midshaft properties were relatively unaffected, but did show slight decreases for older animals at month 10, which recovered during the two month recovery period. Femoral neck geometry exhibited increased endocortical resorption and periosteal apposition of the cortical shell which suggests that trabecular bone plays an important role in how the total bone is affected by HU. Densitometric properties were affected less by HU with respect to BL than were mechanical strength values. Results suggest that femoral neck is more affected by unloading than midshaft, particularly for multiple exposures of unloading. Also, aging does not appear to be a critical factor for bone loss due to HU for either femoral neck or midshaft.

Liquid and gas do not separate naturally in microgravity, presenting a problem for twophase space systems. Increased integration of multiphase systems requires a separation method adaptable to a variety of systems. Researchers at Texas A&M University (TAMU) have developed a microgravity vortex separator (MVS) capable of handling both a wide range of inlet conditions and changes in these conditions. To optimize the MVS design, the effects of nozzle area, separator geometry, and inlet flow rate must be understood. Computational fluid dynamics (CFD), in the form of Adapco’s Star-CD, is used, along with laboratory testing, to accomplish this goal. Furthermore, as analysis aids for the laboratory data and CFD results, relationships for radial pressure, bubble transit time, and momentum transfer were developed. Ground testing data showed a linear relationship between rotational speed and inlet flow rate. The CFD results compared well with the ground data and indicated that the majority of the rotational flow travels at nearly the same rotational speed. Examination of the tangential velocity profile also showed that a reduction of nozzle outlet area resulted in increased tangential velocities. Using dimensional analysis, a relationship between separator radius, inlet momentum rate, fluid properties, and rotational speed was found. Applying this relationship to the ground data and CFD results showed a strong correlation between the two dimensionless groups. Linear regression provided an equation linking rotational speed to the separator parameters. This equation was tested against the ground data and shown to predict average rotational speed well for all separator models. These results were used to calculate the radial and axial transit times of gas bubbles within the separation volume. Radial transit time was found to decrease more rapidly than axial transit time as gas volume increased, indicating axial and radial transit times are closest in value for the all liquid case and increasing gas core diameter improves the operational characteristics of the separator. From a design standpoint, the all liquid case provides a minimum flow rate for successful phase separation. Maximum flow rate depends on the pressure resources of the system.

Orthostatic intolerance following exposure to simulated or actual microgravity is observed following spaceflight and extended periods of bed rest, and is not always associated with simultaneous hypotension. Differential adaptation of cephalic and caudal arterial vasculatures (as a result of removal of the normal hydrostatic gradient) is proposed as a potential mechanism underlying this phenomenon. A potential role for changes to the L-arginine/nitric oxide pathway in such adaptations has been suggested, predominantly from previous in vitro studies; using an established model of simulated microgravity (head-down tilt; HDT). This thesis investigates whether findings in isolated vessels are reflected by in vivo measurements of cephalic and caudal vascular function. Using carotid or iliac artery flow normalized to mean arterial pressure as an index of cerebral or hind limb vascular conductance, autoregulatory cerebral vasodilatation in response to lower body negative pressure was found to be impaired following HDT. In addition, α¬1-adrenoceptor agonist-mediated vasoconstriction was decreased in the cerebral vasculature and increased in the peripheral and hind limb vasculature. Administration of acetylcholine or the non-selective nitric oxide synthase (NOS) inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) demonstrated a decreased contribution of NOS to cerebrovascular tone, but an increased contribution of NOS to peripheral vascular resistance and tone of the hind limb vasculature. Together with a lack of difference in the response to the selective inducible NOS (iNOS) inhibitor 1400W, these results suggest that differential adaptation of eNOS may account for the observed differences between control and HDT animals. Further investigation of the changes to the L-arginine/nitric oxide pathway suggest that these changes are not associated with changes in eNOS expression, but may be related to altered activity of eNOS. Furthermore, the bioavailability (as measured by pharmacokinetic half life) or the vascular effector mechanisms (as measured by the haemodynamic response to exogenously administered nitric oxide) responsible for the effects of nitric oxide were also shown to be unaffected by HDT. These findings suggest that differential adaptation of the L-arginine/nitric oxide pathway may contribute to the inability to raise total peripheral resistance and impaired cerebral autoregulation following HDT, thereby representing a mechanism of orthostatic intolerance following exposure to microgravity.

Orthostatic intolerance following exposure to simulated or actual microgravity is observed following spaceflight and extended periods of bed rest, and is not always associated with simultaneous hypotension. Differential adaptation of cephalic and caudal arterial vasculatures (as a result of removal of the normal hydrostatic gradient) is proposed as a potential mechanism underlying this phenomenon. A potential role for changes to the L-arginine/nitric oxide pathway in such adaptations has been suggested, predominantly from previous in vitro studies; using an established model of simulated microgravity (head-down tilt; HDT). This thesis investigates whether findings in isolated vessels are reflected by in vivo measurements of cephalic and caudal vascular function. Using carotid or iliac artery flow normalized to mean arterial pressure as an index of cerebral or hind limb vascular conductance, autoregulatory cerebral vasodilatation in response to lower body negative pressure was found to be impaired following HDT. In addition, α¬1-adrenoceptor agonist-mediated vasoconstriction was decreased in the cerebral vasculature and increased in the peripheral and hind limb vasculature. Administration of acetylcholine or the non-selective nitric oxide synthase (NOS) inhibitor Nω-nitro-L-arginine methyl ester (L-NAME) demonstrated a decreased contribution of NOS to cerebrovascular tone, but an increased contribution of NOS to peripheral vascular resistance and tone of the hind limb vasculature. Together with a lack of difference in the response to the selective inducible NOS (iNOS) inhibitor 1400W, these results suggest that differential adaptation of eNOS may account for the observed differences between control and HDT animals. Further investigation of the changes to the L-arginine/nitric oxide pathway suggest that these changes are not associated with changes in eNOS expression, but may be related to altered activity of eNOS. Furthermore, the bioavailability (as measured by pharmacokinetic half life) or the vascular effector mechanisms (as measured by the haemodynamic response to exogenously administered nitric oxide) responsible for the effects of nitric oxide were also shown to be unaffected by HDT. These findings suggest that differential adaptation of the L-arginine/nitric oxide pathway may contribute to the inability to raise total peripheral resistance and impaired cerebral autoregulation following HDT, thereby representing a mechanism of orthostatic intolerance following exposure to microgravity.