The hamster estrous cycle lasts four days and is considered to be a physiological model for angiogenesis. Angiogenesis is the formation of new capillaries from preexisting vessels, and it occurs extensively during corpus luteum formation in the estrous cycle. Von Willebrand Factor (vWF) is a glycoprotein that is secreted uniquely in endothelial cells and megakaryocytes. It is frequently used as an endothelial cell marker and it is able to detect vessels within tissues when it is used in immunohistochemical staining techniques. This study explores von Willebrand Factor expression within Golden Hamster ovarian tissue. In particular, this study uses cage control and antiorthostatic cage suspension tissue. Antiorthostatic cage suspension is a model developed to mimic and study the physiological effects caused by microgravity, such as that experienced in space flight. It is hypothesized that simulated microgravity caused by antiorthostatic cage suspension would result in lower levels of vasculature and expression of vWF within ovarian tissue. Due to financial considerations, conclusive data was not obtained due to a lack of statistics. However, our study indicates that vasculature and vWF expression may be increased in antiorthostatic cage suspension tissue.

This experiment was designed to determine the involvement of varying levels of whole-body irradiation on ovarian follicular and corpora luteal development in mice. Previous research has indicated reduced counts of ovarian follicles and corpora lutea in mice flown in space. These differences may be the result of microgravity, increased exposure to radiation, or some combination of both. Fifty-six mice were divided into three groups (apocynin-treated, nox2 knockout, and wild-type control) before exposure to 0 Gy, 0.5 Gy, or 2.0 Gy radiation. The tissues were harvested, preserved, run through the appropriate paraffin embedding procedures, serially sectioned, mounted on microscope slides, and stained using a standard H&E staining technique. Total and mean follicular and corpora luteal counts were accessed and compared across treatment groups. Mean ovarian weight, mean total reproductive weight, mean ovarian weight percentage of total body weight, mean total reproductive weight percentage of total body weight, and the apparent estrous phase of the animals were also compared. Radiation from 0.5-2.0 Gy had no significant effect on mean ovarian weight, mean total reproductive weight, mean ovarian weight percentage of total body weight, or mean total reproductive weight percentage of total body weight. Radiation from 0.5-2.0 Gy significantly increased mean early-stage follicular count in the wildtype group only. Radiation of 2.0 Gy increased late-stage follicular count across all groups after accounting for mean ovarian percent of total body weight. Radiation of 2.0 Gy significantly increased mean corpora lutea count in the wildtype group only. This result not only suggests that low-dose radiation accelerates oocyte development in the murine ovary, but also that the inaction of NADPH-oxidase (via apocynin inhibition or genetic knockout) may ameliorate some of these effects.

Les missions spatiales et les études de simulation par alitement prolongé ont montré que l’inactivité physique induite par la microgravité affecte l’ensemble des systèmes physiologiques chez l’humain. En condition d’alitement prolongé notre laboratoire (UMR7178, IPHC, DEPE, Strasbourg) a montré que l’adaptation métabolique était proche de celle retrouvée dans le syndrome métabolique associé, dans la population générale, à de nombreuses pathologies. Une hypothèse a été émise pour décrire la cascade des événements entraînant les dérèglements métaboliques en microgravité simulée. Cette cascade d’adaptations aurait pour conséquence le développement d’un état d’inflexibilité métabolique, définie comme une incapacité à ajuster l’utilisation des nutriments comme substrats aux changements de disponibilité des nutriments et dont la compréhension reste toutefois incomplète. Lors de ce projet de thèse, nous nous sommes attachés à caractériser le syndrome d’inflexibilité métabolique chez l’Humain à travers l’investigation clinique de l’état musculaire, de l’inflammation et du stress oxydant, de la sensibilité à l’insuline et de l’oxydation des substrats énergétiques au cours d’une étude de preuve de concept et d’une étude de simulation de microgravité de 60 jours. Sur la base d’études récentes démontrant l’impact de compléments nutritionnels sur les adaptations métaboliques associées à de nombreuses maladies métaboliques chroniques, une étude de preuve de concept a permis de tester l’efficacité d’un cocktail nutritionnel composé de polyphénols, d’oméga-3, de vitamine E et de sélénium. La supplémentation a permis de réduire l’atrophie musculaire, le stress oxydant et le développement d’une inflexibilité métabolique par l’intermédiaire d’une meilleure oxydation lipidique et d’une réduction de la lipogenèse de novo suite à une période d’inactivité physique de 20 jours. Sur la base de ces premiers résultats, une étude d’alitement de 60 jours a été menée chez l’Humain pour tester les effets du cocktail nutritionnel en condition de microgravité simulée. Dans cette seconde étude, la supplémentation nutritionnelle a permis de prévenir au moins partiellement des adaptations aigües et chroniques engendrées par l’inactivité physique au cours de l’alitement. En particulier la supplémentation a augmenté les défenses sanguines anti-oxydantes, a prévenu l’augmentation de la lipidémie et la réduction de l’oxydation lipidique et a contenu le développement d’une inflexibilité métabolique aiguë et chronique en absence de challenge métabolique. Toutefois la contremesure n’a pas eu d’effet protecteur suite à un challenge métabolique sous forme de surnutrition glucidique. L’ensemble des résultats indique que le développement d’une inflexibilité métabolique apparaît comme un événement précoce, qui, décelé à temps pourrait se révéler comme un biomarqueur d’intolérance au glucose dans des stratégies de prévention des maladies chroniques du XXIème siècle. Plus encore, cette étude a permis de démontrer l’atout d’un cocktail antioxydant et anti-inflammatoire en limitant les altérations métaboliques sans avoir d'effets néfastes sur les autres systèmes, tout en étant une contremesure facile à mettre en œuvre et peu coûteuse. Quand bien même la contremesure nutritionnelle utilisée lors de cette étude ne serait pas suffisante pour maintenir l’ensemble des systèmes physiologiques intacts, d’autres études devront être menées afin de trouver la combinaison de contremesures idéale permettant de limiter les dégradations induites par la microgravité et ainsi permettre des nouvelles avancées dans l’exploration spatiale (Lune, Mars) au cours des prochaines décennies. En ce sens, un protocole adapté d’activité physique combiné à une contremesure nutritionnelle sous forme de cocktail semble être une piste prometteuse. / Space missions and bedrest simulation studies have shown that physical inactivity affects all physiological systems in humans. In prolonged bed rest conditions, our laboratory (UMR7178, IPHC, DEPE, Strasbourg) showed that metabolic adaptations were close to that found in the metabolic syndrome associated with metabolic chronic diseases in the general population. Based on these results, we proposed a hypothesis to describe the cascade of events leading to metabolic alterations in simulated microgravity, leading to the development of metabolic inflexibility. Metabolic inflexibility is defined as the inability of the body to adjust fuel use to changes in fuel availability. The first objective of this Thesis was to test this hypothesis and understand the mechanisms underlying the simulated microgravity induced metabolic alterations. Specifically, we focused on characterizing the metabolic inflexibility syndrome in humans through clinical investigation of muscle condition, inflammation and oxidative stress, insulin sensitivity and oxidation of energy substrates in a proof of concept study and a 60-day microgravity simulation study in healthy male adults. Based on recent studies demonstrating the impact of nutritional supplements on metabolic adaptations associated with many chronic metabolic diseases, a proof-of-concept study tested the efficacy of a nutritional cocktail composed of polyphenols, omega-3, vitamin E and selenium. In the feasibility study, we showed that supplementation reduced muscle atrophy, oxidative stress and the development of metabolic inflexibility via an improvement in lipid oxidation and a reduction in de novo lipogenesis following a 20-day period of physical inactivity induced by daily step reduction. Based on these first results, a 60-day bed rest study was conducted in health men to test the effects of the dietary cocktail in simulated microgravity conditions. In this second human clinical research study, nutritional supplementation prevented at least partially acute and chronic adaptations caused by physical inactivity induced by bed rest. In particular, supplementation increased antioxidant blood defenses, prevented increased lipid levels, reduced lipid oxidation and mitigated the development of acute and chronic metabolic inflexibility in absence of metabolic challenge. However, the countermeasure did not have a protective effect following a metabolic challenge in the form of carbohydrate overnutrition. All the results indicate that the development of metabolic inflexibility appears to be an early event, which, if detected in time, could prove to be a useful biomarker to use to prevent chronic diseases in the 21st century. Moreover, this study demonstrated the advantage of an antioxidant and anti-inflammatory cocktail by limiting metabolic alterations without having harmful effects on other systems, while being easy to implement and cost-effective. Even if the nutritional countermeasure used in this study is not sufficient to keep all physiological systems intact, further studies will have to be carried out to find the ideal combination of countermeasures to limit microgravity-induced degradation and thus allow new advances in space exploration (Moon, Mars) over the next decades. In this line, an adapted protocol of physical activity combined with a nutritional countermeasure in the form of a cocktail could be a promising approach.

Nucleate boiling is widely used as a means of heat transfer in thermal management systems because of its high heat transfer rates. This study explored the effects of heat flux and surface geometry on heat transfer behavior and bubble dynamics of nucleate pool boiling in microgravity. A single platinum wire, a twist of three platinum wires, and a twist of four platinum wires were used as boiling surfaces for two separate experiments performed in microgravity on board NASA’s parabolic flight aircraft. Wire temperature, thermocouple, and video measurements were taken during a total of 44 microgravity parabolas. Results show that the crevices formed by wire twisting provide regions of localized superheating and are able to reduce the heat flux necessary for boiling onset to occur. This localized heating results in a lower average heater temperature and shortened superheating periods, but this effect decreases when more wires are present in the twist. This behavior was investigated and confirmed with a finite volume, transient conduction model. This model also showed that the water temperature profile at the bubble onset indicates that water at a certain distance from the wire surface, in this experiment 50 μm, needs to be heated to above saturation temperature in order to initiate and generate a burst of bubbles. A relative bubble area analysis method was able to quantify vapor production and bubble behavior across multiple frames of video. Application of this method revealed a transition of bubble behavior from large isolated bubbles to jet flows of small bubbles, and this method allowed the heat flux contribution of jet flows to be approximated. Additionally, a new mode of jet flows was observed. Particle image velocimetry was used to provide approximate velocities of small bubble jet flows and their influence on heat transfer to the bulk fluid.

Les écoulements diphasiques avec ou sans changement de phase sont présents dans les applications terrestres et spatiales avec notamment le contrôle thermique des satellites par boucle diphasique, l’alimentation en propergol des moteurs de fusée et le traitement des eaux usées pour les missions d’exploration spatiale. Des expériences d’ébullition convective dans un tube chauffé avec du HFE7000 ont été menées en écoulement vertical ascendant au sol et en microgravité conditions afin de caractériser les régimes d’écoulements et de mesurer les transferts de chaleur, le taux de vide et les pertes de pression. Les mesures de taux de vide ont permis de caractériser la vitesse moyenne de la phase vapeur et l’épaisseur du film liquide en écoulement annulaire. En microgravité, l’épaisseur du film liquide et le frottement interfacial sont inférieurs aux conditions de gravité terrestre. La structure du film liquide a été caractérisée par des visualisation rapides. L’impact de la gravité, des vitesses superficielles du liquide et de la vapeur sur la célérité et la fréquence des ondes perturbatrices a été mis en évidence. Deux techniques de mesure ont été implémentées et comparées pour la mesure du coefficient d’échange de chaleur. En ébullition convective saturée pour des titres massiques supérieurs à 0.2, le transfert de chaleur est peu sensible à la gravité et en bon accord avec des corrélations de la littérature. En ébullition nucléée sous refroidie pour des titres inférieurs à 0.1, le transfert de chaleur est significativement plus faible en microgravité. / Two-phase flows with or without phase change are present in terrestrial and space applications like thermal control of satellites, propellant supply for launchers, and waste water treatment for space exploration missions. Flow boiling experiment with HFE7000 were conducted in a heated tube in vertical upward flow on ground and in microgravity conditions to collect data on flow patterns, pressure drops, heat transfers, void fraction. Void fraction measurements allowed to measure mean gas velocity and the liquid film thickness in annular flow. In microgravity condition, the liquid film thickness and the interfacial shear stress are significantly lower than in normal gravity. A detail analysis of the film structure was performed by image processing. The impact of gravity and liquid and vapour superficial velocities on the disturbance waves velocities and frequencies was investigated. Two different measurement techniques were used and compared to determine the heat transfer coefficient. For quality values greater than 0.2, HTC is not sensitive to gravity and is in good agreement with classical correlations of the literature. For qualities smaller than 0.1, in the subcooled nucleate boiling regime HTC is significantly smaller in microgravityconditions.

No description available.

Two-phase liquid-gas flow has a wide variety of applications in space, including active thermal control systems, high-power communications satellites, heat pumps and space nuclear reactors. Two-phase systems have many potential advantages over current single-phase systems due to reductions in system size, weight and power consumption. The mechanisms of pressure drop, heat transfer coefficients, void fractions, and flow regimes must be well understood under microgravity conditions in order to design reliable two-phase systems. The main objective of this present research is to develop a new mathematical model that can accurately predict the annular two-phase friction pressure drop to optimize the design of two-phase systems. The two-phase flow tests were conducted aboard the NASA KC-135 aircraft by the Interphase Transport Phenomena (ITP) group from Texas A&M University. The two-phase flow pressure drops were measured across a single transparent test section 12.7 mm ID and 1.63 m long in annular regimes under microgravity conditions during two flight campaigns. Different from previous work, this was the first time both the void fraction and the film thickness were measured under microgravity conditions. The empirical correlations for the interfacial friction factor and void fraction were developed from 57 experimental data using a linear least squares regression technique. The annular two-phase friction pressure drop can be predicted by the new mathematical model requiring only knowledge of the length and diameter of the tube, liquid and vapor mass flow rates, and properties of the working fluid. In addition, the new mathematical model was validated using Foster-Miller & ITP data collected over twelve flights aboard the KC-135 with working fluid R-12 (77 data points), Sundstrand data collected aboard the KC-135 with working fluid R-114 (43 data points) and Zhao and Rezkallah data aboard the KC-135 with working fluid water and air (43 data points). Compared with the LockhartMartinelli model, Wheeler model, Chen model and homogeneous model, the new mathematical model is the optimal model for predicting the two-phase friction pressure drop in annular regimes. The majority of the data falls within +-20% of the proposed correlation and the average error is 12%.

No description available.

This thesis investigates the design of a CubeLab Module frame to facilitate biological research aboard the International Space Station (ISS). With the National Laboratory designation of the ISS by the United States Congress the barriers for use of the facility have been lowered for commercial and academic entities, allowing greater volume and diversity in the research that can be done. Researchers in biology and other areas could benefit from development and adoption of a plug-and-play payload containment system for use in the microgravity/space environment of the ISS. This research includes design and analysis of such a system. It also includes production and testing of a prototype. The relevant NASA requirements are documented, and they were considered during the design phase. Results from finite element analyses to predict performance of a proposed design under expected service conditions are reported. Results from functional testing of the prototype are also provided. A discussion of future work needed before the structure outlined in this thesis can become commercially viable is also presented.

Mechanical unloading has deleterious effects on the musculoskeletal system and results in significant reductions in bone density, mass, and strength, which do not fully recover even years after returning to weightbearing. For example, the rate of bone loss in microgravity is 10-fold more rapid than the rate of loss seen in elderly Caucasian females, the population group most predisposed to osteoporosis. This raises concern with individuals who are exposed to multiple bed rest periods or crewmembers who make repeated missions. Exercise offers a way to reduce or reverse these effects. Dual-energy X-ray absorptiometry (DXA) densitometry and bone mineral density (BMD) alone are generally insufficient for capturing the complex changes in bone mass, structure, and integrity and not an accurate predictor of fracture risk. Therefore, it is essential to measure the mechanical properties of bone tissue directly using animal models. The hindlimb unloaded (HU) rat model is a well-established ground-based analog for studying bone response to disuse and effects of spaceflight. The current study is one of the very few that has measured longitudinally densitometric and mechanical properties of bone after repeated simulated microgravity and long-term recovery at multiple anatomic sites in skeletally mature rats. The specific aims were to characterize 1) loss and recovery dynamics of bone following a period of unloading, 2) bone response after a second exposure to 28 days of HU, following an initial 28 days of HU and a recovery period equal to twice the duration of initial exposure, and 3) effects of resistance exercise during recovery period following an initial HU exposure and its effects on a subsequent exposure. In general, our data showed that bone response to unloading and recovery is site-specific. More specifically, we found that: 1) the rat proximal tibia metaphysis modeled the loss and discordant recovery dynamics as seen in the International Space Station (ISS) crewmembers proximal femur better than the rat femoral neck; 2) the initial exposure to HU has minimal effect on the subsequent HU exposure, and detrimental effects of the second HU exposure were milder than the initial due to reduced mechanosensitivity of the bone; 3) exercise significantly enhanced recovery following the initial HU exposure, and losses during the second exposure were not affected by exercise in most cases.