Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1974. / Bibliography: p. 565-568. / by Greg L. Zacharias. / M.S.

Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. Thesis. 1970. M.S. / MICROFICHE COPY ALSO AVAILABLE IN AERO LIBRARY. / Ten blank pages included in paging. / Bibliography: p. 289. / by Louis Anthony D'Amario [and] Stephen Patrick Synnott. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1991. / Includes bibliographical references (leaves 135-138). / by David Thomas Roberts. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2003. / Includes bibliographical references (p. 75-76). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / The impact of geometric variability on compressor performance is investigated using a compressor repeating-stage model based on well-known correlations for profile losses, endwall blockage, deviation, and the onset of stall. Previous computations with a quasi-two dimensional cascade analysis code are used to link geometric variability to performance deviations. Performance variability is then introduced probabilistically through random perturbations to tip clearances, profile losses and turning. For the variation input, at design incidence, the mean efficiency is found to decrease by 1%, mostly due to the mean shift in profile losses, and the mean pressure rise is reduced by 2.5%, mostly because of the mean shift in turning. A parametric study for compressor stages of different designs shows a lower degradation of mean performance and a lower performance variability for stages which have higher work coefficient, lower degree of reaction, and higher blade aspect ratio. It was found that the influence of blade profile effects was well represented, but the impact of tip clearance variation was not well captured when compared to three-dimensional computations. It is concluded that to address the effects of tip clearance variability, emphasis should be placed on development of models which both can include the alteration of end-wall displacement thickness within the compressor stage and are appropriate for probabilistic description. / by Antoine Vincent. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 109-115). / With demand for aviation projected to grow by 5% per year over the next 20 to 25 years, policy makers must not only consider ways to ensure that the air transportation system can accomodate significant growth, but also how their policy decisions will affect the environment. Because environmental issues are becoming increasingly apparent, the sustainability of policy measures will likely constrain responses to this potential increase in aviation demand. Policy makers will need to consider various trade-offs that come with policy decisions, and find ways to balance the demands of the air transport system with the need to reduce the environmental impact of aviation. This thesis assesses the environmental impacts of implementing a policy scenario, which employs both operational and technological improvments to the air transport system. The impacts are presented in both physical and monetary metrics using the Aviation environmental Portfolio Management Tool, to allow for a comparison of trade-offs among different environmental effects. This thesis discusses the limitations of this particular scenario, while also providing an overview of policy-making models, and the observed weaknesses in current policy-making processed involving technical data. In particular, it identifies the mismatch between needs of those involved in the policy-making process, and the information provided by analysts, which can be an obstacle to developing credible and objective support for a policy proposal. It finally provides suggested methods for improving the relationship between different groups involved in developing policy to allow for better informed decision-making, and a more fluid policy-making process. / by Alice Fan. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2002. / Includes bibliographical references (p. 181-185). / Optimal performance and optimal allocation of resources, such as pointing accuracy and onboard fuel utilization, are of primary concern in the design and operation of precision pointing spacecraft. Ironically, internal spacecraft instruments and reaction control actuators often act as sources of narrowband disturbances and impede the optimal performance of these precision systems. The fundamental objective of this work is the development of an active control methodology capable of rejecting disturbances with narrowband nonstationary spectral distributions with particular focus on spacecraft reaction wheel induced disturbances. A closed-form symbolically parameterized optimal feed-forward disturbance rejection methodology for flexible systems has been developed. The methodology combines disturbance modeling for narrowband disturbances together with quasi-stationary optimal control to yield a parameterized feed-forward control architecture. In the case of the reaction wheel disturbance rejection problem, the symbolic optimal control gains are parameterized in terms of wheel spin rate, enabling continuous and analytically exact gain adjustments as a function of the measurable scheduling parameter. The methodology was shown to be compatible with loop-shaping control design methods such as frequency-weighted optimal control. This quasi-stationary disturbance rejection methodology has been generalized and applied to the nonstationary reaction wheel imbalance problem. The nonstationary formulation involves expanding the reaction wheel's angular states in terms of a general series representation. Bessel functions and their properties are employed to define an equivalent finite-dimensional quasi-stationary disturbance signal. / (cont.) The effectiveness of the methodology has been experimentally demonstrated on a highly compliant system with non-collocated sensors and actuators. Experimental results show peak performance yielding nearly a 40 dB improvement over conventional broadband control with improved performance across a wide range of frequencies. / by Sean P. Kenny. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2004. / Includes bibliographical references (leaves 51-57). / (cont.) days) post-implantation. Histological and immunohistochemical analyses showed severe fibrous and glial scar formation in Groups I and III, less fibrous scarring in Group II and very little scar manifesting in Groups IV and V. A quantitative analysis of myelinated axons in the center of the explants corresponded with the assessment of scar as a physical barrier to competent axon growth. Groups I and III exhibited the least regenerated axons, Groups IV and V the most. The findings also validated the effectiveness of the dorsal barrier in promoting spinal cord regeneration. Overall, the combination of wrap membrane and dorsal barrier (Group V) proved most effective in creating a hospitable environment for regenerative success. / Traumatic injury to the adult mammalian spinal cord results in varying degrees of lost motor and sensory nerve function. Damaged axons of the central nervous system (CNS) exhibit a severely limited regenerative capacity; paralysis induced by severe trauma is generally permanent. Previous studies have attempted to simulate the peripheral nerve environment, where axonal regeneration is spontaneous, through the implantation of peripheral nerve graft tissue, exogenous growth factors or prosthetic devices. Such intervention has demonstrated the ability of central nerve axons to regrow over significant distances and partially restore distal limb function. The current work aims at evaluating the efficacy of two distinct collagen implants towards promoting spinal cord regeneration. The experimental spinal lesion is a 5mm mid-thoracic gap created by transections at T7 and T9 and removal of intermediary cord and peripheral roots. The two implants offered different entubulation schemes; one implant was a thin walled tube composed of Type I bovine collagen, the other a commercially available bilayered membrane composed of Types I and III porcine collagen. Whereas the tube was fitted directly into the spinal lesion, the membrane was wrapped around the cord stumps like a tubular bandage. Five experimental groups defined the current research: Groups I and II received no implant, Groups III and IV were implanted with tubes, and Group V was implanted with the membrane wrap. A secondary aim of the research was to validate the use of a dorsal barrier in further reducing scar infiltration to the wound. This additional collagen membrane was simply draped over the implant (or lesion) of Groups II, IV and V. Mid-thoracic spinal cord sections were explanted from all groups 4 weeks (28 / by Sajjad S. Matin. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006. / Includes bibliographical references (p. 121-126). / This thesis proposes, develops and validates a methodology to quantify the complexity of air traffic control (ATC) human-machine interaction (HMI). Within this context, complexity is defined as the minimum amount of information required to describe the human machine interaction process in some fixed description language and chosen level of detail. The methodology elicits human information processing via cognitive task analysis (CTA) and expresses the HMI process algorithmically as a cognitive interaction algorithm (CIA). The CIA is comprised of multiple functions which formally describe each of the interaction processes required to complete a nominal set of tasks using a certain machine interface. Complexities of competing interface and task configurations are estimated by weighted summations of the compressed information content of the associated CIA functions. This information compression removes descriptive redundancy and approximates the minimum description length (MDL) of the CIA. The methodology is applied to a representative en-route ATC task and interface, and the complexity measures are compared to performance results obtained experimentally by human-in-the-loop simulations. / (cont.) It is found that the proposed complexity analysis methodology and resulting complexity metrics are able to predict trends in operator performance and workload. This methodology would allow designers and evaluators of human supervisory control (HSC) interfaces the ability to conduct complexity analyses and use complexity measures to more objectively select between competing interface and task configurations. Such a method could complement subjective interface evaluations, and reduce the amount of costly experimental testing. / by Christos George Tsonis. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1998. / Includes bibliographical references (p. 219-221). / by Arnaud Irving Wisnia. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005. / Includes bibliographical references (p. 99-102). / As the field of robotics continues to mature, individual robots are increasingly capable of performing multiple complex tasks. As a result, the ability for robots to move autonomously through their environments is a fundamental necessity. If perfect knowledge of the robot's position is available, the robot motion planning problem can be solved efficiently using any of a number of existing algorithms. Frequently though, the robot's position can only be estimated using incomplete and imperfect information from its sensors and an approximate model of its dynamics. Algorithms which assume perfect knowledge of the robot's position can still be applied by treating the mean or maximum likelihood estimate of the robot's position as certain. However, unless the uncertainty in the agent's position is very small, this approach is not reliable. In order to perform optimally in this situation, planners, such as the partially observable Markov decision process, plan over the entire set of beliefs (distributions over the robot's position). Unfortunately, this approach is only tractable for problems with very few states. Between these two extreme approaches, however, lies a continuum of possible planners which plan over a subset of the belief space. The difficulty that these planners face is choosing and representing a minimal subset of the belief space which spans the set of beliefs that the robot will actually experience. In this paper, we show that there exists a very natural such set, the set, of Gaussian beliefs. By combining an extended Kalman filter with an augmented Markov decision process, we create a path planner which efficiently plans over a discrete approximation of the set of Gaussian beliefs. / (cont.) The resulting planner is demonstrated via simulation to be both computationally tractable and robust to uncertainty in the robot's position. / by Peter Hans Lommel. / S.M.