Attitude stability and altitude control of a variable-geometry Earth-orbiting solar sail

A variable-geometry solar sail for on-orbit altitude control is investigated. It is shown that, by adjusting the effective area of the sail at favorable times, it is possible to influence the length of the semi-major axis over an extended period of time. This solution can be implemented by adopting a spinning quasi-rhombic pyramidal solar sail which provides the heliostability needed to maintain a passive “sun-pointing” attitude and the freedom to modify the shape of the sail at any time. In particular, this paper investigates the variable-geometry concept through both theoretical and numerical analyses. Stability bounds on the sail design are calculated by means of a first-order analysis, producing conditions on the opening angles of the sail, while gravity gradient torques and solar eclipses are introduced to test the robustness of the concept. The concept targets equatorial orbits above approximately 5,000 km. Numerical results characterize the expected performance, leading to (for example) an increase of 2,200 km per year for a small device at GEO

Attitude and Orbital Dynamics of a Variable-Geometry, Spinning Solar Sail in Earth Orbit

At the ISSS 2013, a novel concept of variable-geometry solar sail was introduced: deployed in the shape of a three-dimensional quasi-rhombic pyramid (QRP), the sail exploited its shape and shift between center of mass and center of pressure to naturally achieve heliostability (stable sun-pointing) throughout the mission. In addition, mechanisms allowed to vary the flare angle of the four booms in opposite pairs, thus allowing to control the area exposed to the sun without the need of slew maneuvers. Using these adjustments in favorable orbital positions, it is possible to build a regular pattern of acceleration to achieve orbit raising or lowering without the need of propulsion system or attitude control. Subsequent more detailed investigations revealed that eclipses, even if lasting only a fraction of the orbit, have a substantial (and negative) impact on the heliostability effect: and even a small residual angular velocity, or disturbance torque, are enough to cause the spacecraft to tumble. In this work, we present a novel and improved concept which allows the sail to preserve its attitude not only with eclipses, but also in presence of disturbance torques such as the gravity gradient. The solution we propose is to add a moderate spin to the solar sail, combined with ring dampers. The gyroscopic stiffness due to the spin guarantees stability during the transient periods of the eclipses, while the heliostability effect, combined with the dampers, cancels any residual unwanted oscillation during the parts of the orbit exposed to the sun, and at the same time guarantees continuous sun-pointing as the apparent direction of the sun rotates throughout the year. Both theoretical and numerical analyses are performed. First, stability bounds on the sail design are calculated, obtaining conditions on the flare angles of the sail, in the different orbital regimes, to test the robustness of the concept. Then, a numerical analysis is performed to validate the study in a simulated scenario where all perturbations are considered, over extended amount of time. The concept targets equatorial orbits above approximately 5,000 km. Results show that an increase of 2,200 km per year for a small device at GEO can be achieved with a CubeSat-sized sail

Interactions between the neural, endocrine and immune systems during the course of experimental allergic encephalomyelitis (eae)

Interactions between the neural, endocrine and immune systems have been investigated during the course of experimental allergic encephalomyelitis (EAE), a cell-mediated autoimmune disease, induced by immunization with myelin basic protein (MBP) in complete Freund's adjuvant (CFA). Activation of the hypothalamic-pituitary-adrenal (HPA) axis and splenic sympathetic noradrenergic pathways was evident during the period of expected lymphoproliteration following immunization with MBP/CFA, or CFA alone, which coincided with an increase in lymphocyte B-adrenergic receptor density. During the stressful clinical stage of EAE, further activation of neural and endocrine pathways was indicated by increased splenic noradrenaline (NA) and serum corticosterone (CS) levels. Similar responses were observed when EAE was induced by the transfer of MBP-sensitized splenocytes, despite the absence of the primary immune challenge from the mycobacterial components of the adjuvant. Activation of both neural and endocrine pathways occurred prior to clinical signs. This is most likely a general response to cytokine production from stimulated cells, since comparable changes were seen in control animals following the transfer of cells sensitized to the antigenic component of the adjuvant. The importance of intact noradrenergic pathways was demonstrated by the altered clinical severity of EAE following either the destruction of central or peripheral sympathetic nerve terminals, or the administration of centrally acting sympathetic drugs. A significant inverse correlation was found between hypothalamic NA content and circulating CS, which was most evident during peak clinical signs of disease and suggests a role for central sympathetic pathways in the regulation of the HPA-axis during the course of EAE. Consistent with the changes in circulating CS, increases in pituitary pro-opiomelanocortin mRNA were found during the pre-clinical and clinical stages of the disease. However the reduced levels of hypothalamic corticotropin-releasing factor mRNA at the time of maximum clinical signs, suggests that activation of the HPA-axis results from either vasopressin release or direct activation at the level of the pituitary. The overriding immunoregulatory influence of CS was demonstrated by the rapid onset of EAE and morbidity in adrenalectomised animals. However, the compensatory increases in splenic NA and lymphocyte 15-adrenergic receptor density seen in these animals and the significant correlation between central NA and circulating CS, indicates that both central and peripheral sympathetic pathways may be activated following immune challenge and play a pivotal role in determining the outcome of disease

The threonine requirement for reproduction in swine

L-threonine was added to a fortified corn-gelatin diet to attain theonine levels of 3.59, 4.95, 6.31, 7.67 and 9.03 g per day. These diets were fed to twenty-five crossbred gilts at a rate of 1.82 kg per day before mating and during 3 successive pregnancies. During lactation, all animals received the same diet which contained 0.35% theonine. Litter size and feed intake were standardized during both lactations;Five day nitrogen balance trials were initiated on the 45th and 90th day of pregnancy. Increasing the dietary threonine resulted in a significant difference in nitrogen retention, with maximum retention occurring when 4.95 g of threonine were fed. After each balance trial blood samples were drawn before and following feeding. The lowest level of plasma urea nitrogen occurred when 4.95 g of threonine were fed. As threonine intake increased, plasma threonine increased linearly (P \u3c .005) and quadratically (P \u3c .05) with the response curve inflection at 4.95 g. This increase in plasma threonine was accompanied by a significant linear (P \u3c .01) and quadratic (P \u3c .005) decrease in fasted plasma lysine and a significant linear (P \u3c .05) increase in the liver sample activities of lysine\u27s catabolic enzyme, lysine-(alpha)-ketoglutarate reductase;Sow weight gains increased linearly (P \u3c .01) and quadratically (P \u3c .01) with increasing theronine levels. Maximum gestation gains occurred when 6.31 g of threonine were fed, while maximum gains for the entire experiment occurred when 7.67 g were fed;Litter weight, number of pigs born, baby pig gains, daily milk yield and milk protein were not significantly influenced by threonine levels;All sows were slaughtered at 27 (+OR-) 4 days of the third gestation period. There were no significant differences in live weight, hot carcass weight, loin eye area, carcass backfat and percent muscle;The changes in metabolic criteria lead to the conclusion that a daily intake of 4.95 g of L-threonine meets the requirement for reproduction;If it is assumed that the added L-threonine was 100% digestible and that only 75.0% of the threonine present in a typical corn-soybean meal diet is absorbed by the sow, then 5.4 g of threonine per day when supplied by these feedstuffs would meet the requirement for reproduction

Numerical Study on the Influence of Tip Clearance

Due to a constant rise in costs and a continuous demand for travel from customers, airlines look to new technologies as a way of potentially reducing operational costs, such as fuel costs. With such objectives in mind, NASA and other organizations are studying and experimenting new configurations of gas turbines to determine if this could be a viable solution for the near future. Several simulations are run for an axial compressor blade in order to verify the influence in total pressure ratio and flow velocity between the No-Tip Gap model and the Tip Gap model. This will determine the impact of tip clearance on the aforementioned parameters. The CFD simulations will be carried out using FLUENT where it is possible to determine the inlet and outlet conditions of the experiment as well as other boundary conditions to properly present the problem and a realistic solution. In this study two distinct models will be simulated, No-Tip Gap and Tip Gap, each at three different rotational speeds to simulate the impact for different velocities of blade rotation and determine which model would be more beneficial for future turbines. It was concluded that the pressure along the blade using the No-Tip Gap model was higher when compared to the Tip Gap model. This could be explained by simply analysing the surface area of the blade. Being that the blade occupies the area up to the engine casing it will have a greater surface area, hence, transferring more work and having higher pressure at the compressor exit. As for the velocity, the results were reversed, meaning that a higher velocity of flow was found when using the Tip Gap model. The explanation for this higher speed could be the existence of a tip clearance, allowing the flow to pass through this area with no contact with the blade and therefore not reducing the speed of the airflow resulting in a higher outlet velocity.Devido a um aumento constante dos custos e ao continuado aumento na procura por parte de clientes, as companhias aéreas investigam novas tecnologias como forma de reduzir custos operacionais, como os custos de combustível. Com tais objectivos em mente, a NASA e outras organizações estão a estudar e a testar novas configurações de turbinas a gás para determinar se poderá ser uma solução viável num futuro próximo. São realizadas várias simulações numéricas para uma pá de um compressor axial, de forma a verificar a influência da razão de pressão total e velocidade de escoamento na diferença entre a folga na ponta e a ausência de folga no topo da pá. As simulações de CFD foram realizadas utilizando o FLUENT onde é possível determinar as condições de entrada e de saída da experiência bem como as condições de fronteira que permitem colocar o problema corretamente para que seja obtida uma solução realista. Nesta tese foram estudados dois modelos diferentes, No-Tip Gap (sem espaçamento) e Tip Gap (com espaçamento). Cada um destes modelos foi depois simulado com três diferentes velocidades de rotação da pá para que seja possível determinar qual o seu impacto e perceber qual seria mais benéfica em projectos futuros. Após a realização das simulações foi possível determinar que existe uma pressão maior no modelo No-Tip Gap. Esta pressão superior pode ser explicada analisando a área de superfície da pá em ambos os modelos. No modelo No-Tip Gap a pá do compressor ocupa toda a área desde a raiz até à nacele do motor, logo a sua área será superior, transferindo mais trabalho e consequentemente criando uma maior pressão à saída do que o modelo Tip Gap. No que toca à velocidade, os resultados foram o inverso. Uma maior velocidade foi obtida quando simulado o modelo Tip Gap. Esta maior velocidade pode ser explicada devido à existência do espaçamento na ponta da pá. O escoamento passando por este espaço não entra em contacto com a pá, não reduzindo a sua velocidade, resultando numa velocidade de saída mais elevada

Missouri River Open Lands Preservation: A Great Falls Case Study

South of Great Falls, Montana, adjacent to the city lies a 72-acre undeveloped parcel of state school trust land. For decades, this land has been used by the community for recreation including mountain biking, dog walking, fishing, and wildlife viewing. During the COVID-19 pandemic, these recreational values were especially pertinent as city attractions such as bars, restaurants, and other entertainment were shuttered or suffered from greatly reduced capacity. The community, while aware of this treasure, became especially attached as it served as a refuge from the throes of the modern world. When the Fox Farm neighborhood learned of the State’s plans to sell or lease the property, they bound together to fight the development of the ever-shrinking amount of undeveloped riverfront ecosystem which exists along the Missouri River

Incidence and Predictors of Adolescent's Early Sexual Debut After three Decades of HIV Interventions in Tanzania: A time to Debut Analysis.

To determine the incidence and predictors of adolescent's early sexual debut after three decades of HIV interventions in Tanzania. In a cross-section study of adolescents aged 16-19 residing in Morogoro Municipality, information on socio-demographic, parental-and-peer communication, and sexual behaviors were collected. Cox-regression analysis was used to examine predictors of time to sexual debut. A total of 316 adolescents with mean age of 17.5±0.9 were recruited. Half (48.7%) of adolescent were sexually active with mean age at sexual debut of 14.6±2.3. Of these, 57.8% had sex before their 15(th) birthday with incidence of early sexual debut of 17.4/1000 person-years at risk. Adolescent family characteristics, peer pressure, alcohol use, parental and peer communication were key predictors of early sexual debut. Parental and peer communication strategies works calling for efforts to increase its scope to reach all adolescents alongside promoting family stability and reducing adolescent alcohol consumption

Evaluating the Effect of Woodchips on Soil Matric Potential, Temperature, Weed Biomass, and Yield of Selected Crops

Organic mulches are very popular for weed control in sustainable agricultural systems where the application of synthetic herbicides is restricted. A study was conducted to evaluate the effectiveness of organic mulch in controlling weeds, enhancing soil matric potential, and soil temperature. Blended hardwood mulch was applied to the soil surface at a thickness of 10 cm. The experimental design was laid out as a completely randomized design with two treatments, viz., mulch and no-mulch, replicated 5 times. Data were collected during the growing period for weed biomass, soil matric potential, soil temperature, and yield of selected crops. Results from a two-way ANOVA revealed that the mulch treatments significantly (p≤0.50) reduced weed biomass, and soil temperature while increasing the soil matric potential and yields of okra, tomatoes, squash, and basil. It was concluded that the use of organic mulch was beneficial for weed control and increasing crop yield