Optimal trajectory planning methods that implement convex optimization techniques are applied to the area of satellite rendezvous and proximity operations. This involves the development of linearized relative orbital motion dynamics and constraints for two satellites, where one maintains a near-circular reference orbit. The result is formulated as a convex optimization problem, where the objective is to minimize the amount of fuel required to transfer from a given initial condition to the desired final conditions. A traditional rendezvous and proximity operations scenario is analyzed, which includes examples of initial approach, inspection, final approach, and docking trajectories. This scenario may include trajectory constraints such as maximum allowable control acceleration levels, approach corridors, and spherical keep-out zones. A second scenario that ensures passive safety, in the event of control failures on the maneuvering satellite. The convex optimization problem is ultimately formulated as a second-order cone program. Algorithm CPU and memory requirements are analyzed. Several examples of resulting optimal trajectories are presented for both scenarios, and these trajectories are implemented in a nonlinear simulation.

With the fast development of communication systems, computers and consumer electronics, the power supplies for telecoms, servers, desktops, laptops, flat-panel TVs, LED lighting, etc. are required for more power delivery with smaller spaces. The LLC resonant converter has been widely adopted for these applications due to the advantages in high efficiency, high power density and holdup time operation capability. However, unlike PWM converters, the control of the LLC resonant converter is much more difficult because of the fast dynamic characteristic of the resonant tank. In some highly dynamic processes like the load transient, start-up, over-load protection and burst operation, it is hard to control the current and voltage stresses and oscillations in the resonant tank. Moreover, to meet the high power density requirement, the LLC is required to operate at a high switching frequency. Thus the driving of the synchronous rectifier (SR) poses a design challenge as well. To analyze the fast dynamic characteristic, a graphic state-plane technique has been adopted for a class of resonant converters. In this work, it has been extended to the LLC resonant converter. First of all, the LLC steady state and dynamic behaviors are analyzed in the state plane. After that, a simplified implementation of the optimal trajectory control is proposed to significantly improve the load transient response: the new steady state can be tracked in the minimal period of time. With the advantages of the state-trajectory analysis and digital control, the LLC soft start-up is optimized as well. The current and voltage stress is limited in the resonant tank during the start-up process. The output voltage is built up quickly and smoothly. Furthermore, the LLC burst mode is investigated and optimized in the state plane. Several optimal switching patterns are proposed to improve the light load efficiency and minimize the dynamic oscillations. During the burst on-time, the LLC can be controlled to track the steady state of the best efficiency load condition in one-pulse time. Thus, high light-load efficiency is accomplished. Finally, an intelligent SR driving scheme is proposed and its simple digital implementation is introduced. By sensing the SR drain to source voltage and detecting the paralleled body diode conduction, the SR gate driving signal can be tuned within all operating frequency regions. In conclusion, this work not only solves some major academic problems about analysis and control of the LLC resonant converter based on the graphic state plane, but also makes significant contributions to the industry by improving the LLC transient responses and overall efficiency. / Ph. D.

No description available.

[pt] O presente trabalho, estudando o comportamento de bolhas de ar em água purificada, mostra que na faixa de raios equivalentes de 0,07 a 0,80 cm, a trajetória não é linear. O uso de um equipamento com quatro câmaras fotográficas - situadas duas a duas sobre a mesma vertical e em planos verticais e em planos verticais perpendiculares, contendo o ponto de largada da bolha- dá uma visualização tridimensional do fenômeno. Desenvolveu-se um modelo geométrico para a análise do fenômeno, utilizando-se de um referencial do tipo Lagrangeano. Esse referencial se traslada sobre a curva que liga, os centros das revoluções da trajetória se prejeta no plano perpendicular a esta reta segundo elipses praticamente perfeita. Determinaram-se os valores médicos dos parâmetros dessas elipses, bem como o ângulo da trajetória com a vertical. Constatou-se que esses valores médicos definem uma curva aproximadamente contínua, que apresenta um máximo pra r igual a 0,18 cm, verificando-se que: a ordem de grandeza desses valores médios na região de máximo é muito maior que o desvio, dos valores médicos. Mediu-se a velocidade, U, de translação da bolha uma onde durante uma revolução, bem como o seu período, concluindo-se que a velocidade instantânea da bolha varia dentro de cada revolução. Registrou-se a forma e as pulsações das bolhas durante o seu movimento. / [en] The present work, study the behavior of bubble of air in purified water, shows that in range of equivalent radii between 0.07 to 0.80 cm, the trajectory is not linear. Fours cameras, were used to obtain a theree dimensional visualization of the perpendiculary intersecting planes for this purpose. A geometrical model utilizing a Lagrangean type of reference is developed in order to analyze the phenomenon. This reference is translating parallely to the phenomenon. This reference is translating parallely to the straight line that best approximates the locus of points formed by the center of revolution of the bubble trajectory on a perpendicular plane that straight line is that of a series of practically perfect ellipses. The average values of the parameters a and b of the parameters a and b of these ellipses is determined as well as the angle that the trajectory makes with the vertical. It is found that theses average values a and b can be represented by an appoximately continuose curve as a fuction of bubble radius; whose maximum point is located at a Value of r between the range 0.07 to 0.80 cm. This verifies that the order of maximum point is larger than the deviation from the measured values. It is found that although the vertical component of velocity is constant one revolution to the next, the instantaneous velocity within each revolution vaies. The bubble shape and its fluctuation are also recordede here.

Indiana University-Purdue University Indianapolis (IUPUI) / Pancreatic cancer is the third leading cause of cancer-related deaths and is projected to rank second by 2030 in the United States. However, the etiology of this malignancy remains elusive, with family history, chronic pancreatitis, type 2 diabetes, and cigarette smoking as only established risk factors. Therefore, it is urgent and important to identify risk factors, especially modifiable ones (e.g. diet), for the primary prevention of this lethal disease. In this dissertation, we have investigated the associations of mineral intake, dietary quality, and body adiposity with the risk of pancreatic cancer among participants in the Prostate, Lung, Colorectal, and Ovarian Cancer (PLCO) Screening Trial. Calcium, magnesium, and phosphorus are essential minerals that modulate energy metabolism and glucose homeostasis and may thus be involved in pancreatic carcinogenesis. In the first manuscript, we found that total calcium intake was associated with a reduced risk of pancreatic cancer. In addition, a significant linear inverse association was observed for total magnesium intake. The Healthy Eating Index, 2015 (HEI-2015) and the Dietary Quality Index- revised (DQI-R) have been developed to assess the overall quality or patterns of diet. In the second manuscript, we did not find significant associations between HEI-2015 or DQI-R scores and pancreatic cancer risk. However, a higher intake of some score components (i.e., calcium, vegetables, and whole grains) conferred a lower risk. Although mounting biological mechanisms have linked overweight and obesity to the development of pancreatic cancer, it is largely unclear whether prediagnostic body mass index (BMI) trajectory is associated with the risk of this disease. In the third manuscript, we revealed that prediagnostic adulthood BMI trajectory was not associated with pancreatic cancer risk, but a suggestively or significantly increased risk were identified for individuals who were overweight at age 20 or obese at age 50, compared with those who had a normal weight at the two respective time points. Taken together, the findings of research presented in this dissertation contribute to an improved understanding of the crucial roles of diet and adiposity in the etiology of pancreatic cancer, which may offer some new avenues for the prevention of this intractable malignancy.

The renewed academic interest in using solar sails as a source of spacecraft propulsion has been accompanied by a recent fervor of investigations into non-ideal and off-nominal sail performance considerations. One of the most influential considerations, uncertain optical degradation, has been shown to present significant trajectory design difficulties. This paper investigates the potential of using a mid-course degradation model update to mitigate the risk of missing the target destination in a sample 300 day Earth-Venus trajectory. Using a range of potential degradation profiles, it is shown that correcting in the first half of the mission is highly likely to result in a trajectory that arrives sufficiently close to Venus at the end of the mission timeframe. Depending on the exact extent of the uncertainty, the data suggests that the latest a correction should take place ranges from 150 to 240 days into the mission. The influence of two different parameters, the extent and rate of degradation, are compared to show that the former of the two is more impactful on correcting timing than the latter.

One of the most challenging topics of deep learning (DL) is the analysis of temporal series in complex real-world scenarios. The majority of proposed DL methods tend to simplify such environments without considering several factors. The first part of this thesis focuses on developing video surveillance and sports analytic systems, in which obstacles, social interactions, and flow directions are relevant aspects. A DL model is then proposed to predict future paths, taking into account human interactions sharing a common memory, and favouring the most common paths through belief maps. Another model is proposed, adding the possibility to consider agents' goals. This aspect is particularly relevant in sports games where players can share objectives and tactics. Both the proposed models rely on the common hypothesis that the whole amount of labelled data is available from the beginning of the analysis, without evolving. This can be a strong simplification for most real-world scenarios, where data is available as a stream and changes over time. Thus, a theoretical model for continual learning is then developed to face problems where few data come as a stream, and labelling them is a hard task. Finally, continual learning strategies are applied to one of the most challenging scenarios for DL: financial market predictions. A collection of state-of-the-art continual learning techniques are applied to financial indicators representing temporal data. Results achieved during this PhD show how artificial intelligence algorithms can help to solve real-world problems in complex and time-evolving scenarios.

BACKGROUND: The DoHAD hypothesis suggests that preterm infants should achieve similar growth and body composition to healthy term-born infants in order to minimize disease risk. Postnatal growth of preterm infants is not fully understood and requires additional characterization, particularly in terms of differences to and transition from intrauterine growth. The period of postnatal adaptation to extrauterine life has been described in preterm infants by Rochow et al., 2016 and was seen to last 21 days. During these first 21 days of life, preterm infants experience a physiological, one-time, permanent contraction of extracellular water spaces (water loss), which causes a downward shift in the growth trajectories. This period of adaptation/water loss and the transition to extrauterine growth rates to achieve WHOGS target trajectories need to be incorporated into individual reference curves for preterm infants. OBJECTIVES: To develop and evaluate approaches to establish individualized growth trajectories for preterm infants to achieve growth similar to the WHO growth standards (WHOGS) for healthy infants at term, using recently published data about the physiological postnatal adaptation. METHODS: Two approaches were compared: 1) Postnatal-Percentile Approach: growth following the percentile at day of life (DOL) 21 until term; 2) Growth-Velocity Approach: using day-specific Fenton median growth velocities between DOL 21 and term. The impact of these approaches were compared using body compositions of 57 healthy preterm infants obtained before discharge (36+0/7 to 42+6/7 weeks PMA). The main outcome was the weight difference between the predicted trajectory and WHOGS target at 42+0/7 weeks PMA for the infants’ birth weight percentile. RESULTS: Postnatal-Percentile Approach: Trajectories deviated by up to 930g and did not match with WHOGS. Growth-Velocity Approach: Trajectories converged with term WHOGS after adjusting growth velocities with a factor of 1.0017 (approximately 10% increase in daily growth velocities). The validation of the Growth-Velocity Approach in preterm infants with minimal medical interventions revealed little deviation between predicted and actual weights. Infants were symmetrically distributed around zero deviation with a mean deviation of -10±370g and an average of 20% fat mass. In contrast, the Postnatal-Percentile Approach showed large deviations between predicted and actual weights and a skewed distribution around zero deviation with a mean deviation of -310±380g or 70±350g, following the birth or DOL 21 percentile, respectively. CONCLUSIONS: Individualized growth trajectories for preterm infants converged with the WHOGS when Fenton daily median growth velocities were applied and optimized with a single factor. The simplicity of the model and its ability to predict target weights that correspond to an appropriate fat mass suggests a biological principle. These results provide a superior understanding of preterm infant’s growth including the physiological postnatal adaptation and new trajectories to achieve WHOGS target trajectories. Results can be used to develop a bedside tool to aid clinicians in monitoring growth, guiding nutrition and preventing chronic adult diseases as a consequence of unguided, inappropriate growth. / Thesis / Master of Science (MSc) / It has been well established that growth of preterm infants has a long-term impact on health in adulthood. Since the survivability of preterm infants has drastically improved in the last decades, there has been a shift in focus to improving quality of life, including improved growth. Infants that grow too quickly or too slowly may develop inappropriate body compositions, with either too much or too little fat. A sub-optimal body composition can put infants at an increased risk for developing cardiovascular, metabolic or neurodevelopmental diseases later in life. In order to prevent these diseases and optimize growth, it is necessary to have a better understanding of how preterm infants should grow. This thesis aims to improve the characterization of growth for preterm infants by providing individual reference growth trajectories for preterm infants that take into consideration postnatal adaptation and aim to minimize later disease risk.

No description available.

Trajectory optimization is a powerful technique to analyze mission feasibility during mission design. High-thrust trajectory optimization problems are typically formulated as discrete optimization problems and are numerically well-behaved. Low-thrust systems, on the other hand, operate for significant periods of the mission time. As a result, the solution approach requires continuous optimization; the associated optimal control problems are in general numerically ill-conditioned. In addition, case studies comparing the performance of low-thrust technologies for space travel have not received adequate attention in the literature and are in most instances incomplete. The objective of this dissertation is therefore to design an efficient optimal control algorithm and to apply it to the minimum-time transfer problem of low-thrust spacecraft. We devise a cascaded computational scheme based on numerical and analytical methods. Whereas other conventional optimization packages rely on numerical solution approaches, we employ analytical and semi-analytical techniques such as symmetry and homotopy methods to assist in the solution-finding process. The first objective is to obtain a single optimized trajectory that satisfies some given boundary conditions. The initialization phase for this first trajectory includes a global, stochastic search based on Adaptive Simulated Annealing; the fine tuning of optimization parameters — the local search — is accomplished by Quasi-Newton and Newton methods. Once an optimized trajectory has been obtained, we use system symmetry and homotopy techniques to generate additional optimal control solutions efficiently. We obtain optimal trajectories for several interrelated problem families that are described as Multi-Point Boundary Value Problems. We present and prove two theorems describing system symmetries for solar sail spacecraft and discuss symmetry properties and symmetry breaking for electric spacecraft systems models. We demonstrate how these symmetry properties can be used to significantly simplify the solution-finding process. / Ph. D.