Thesis (B.A.)--Haverford College, Dept. of History, 2003. / Includes bibliographical references.

No description available.

Formation flying is a new paradigm in space mission design, aimed at replacing large satellites with multiple small satellites. Some of the proposed benefits of formation flying satellites are: (i) Reduced mission costs and (ii) Multi mission capabilities, achieved through the reconfiguration of formations. This dissertation addresses the problems of initiatialization, maintenance and reconfiguration of satellite formations in Earth orbits. Achieving the objectives of maintenance and reconfiguration, with the least amount of fuel is the key to the success of the mission. Therefore, understanding and utilizing the dynamics of relative motion, is of significant importance. The simplest known model for the relative motion between two satellites is described using the Hill-Clohessy-Wiltshire(HCW) equations. The HCW equations offer periodic solutions that are of particular interest to formation flying. However, these solutions may not be realistic. In this dissertation, bounded relative orbit solutions are obtained, for models, more sophisticated than that given by the HCW equations. The effect of the nonlinear terms, eccentricity of the reference orbit, and the oblate Earth perturbation, are analyzed in this dissertation, as a perturbation to the HCW solutions. A methodology is presented to obtain initial conditions for formation establishment that leads to minimal maintenance effort. A controller is required to stabilize the desired relative orbit solutions in the presence of disturbances and against initial condition errors. The tradeoff between stability and fuel optimality has been analyzed for different controllers. An innovative controller which drives the dynamics of relative motion to control-free natural solutions by matching the periods of the two satellites has been developed under the assumption of spherical Earth. A disturbance accommodating controller which significantly brings down the fuel consumption has been designed and implemented on a full fledged oblate Earth simulation. A formation rotation concept is introduced and implemented to homogenize the fuel consumption among different satellites in a formation. To achieve the various mission objectives it is necessary for a formation to reconfigure itself periodically. An analytical impulsive control scheme has been developed for this purpose. This control scheme has the distinct advantage of not requiring extensive online optimization and the cost incurred compares well with the cost incurred by the optimal schemes.

A detailed review of existing flying height or head disk spacing testing techniques has been made, and in-depth analyses of the working principles of the currently popular optical interferometry flying height testing methods are presented with simulation results. A new dual-beam normal incidence polarisation inteferometry method is then proposed. One advantage of this dual-beam polarisation interferometry is that it can be used for both the direct spacing measurement (DSM) method and relative displacement measuring (RDM) method. The RDM method is a good way to measure the head-disk spacing and the slider pitch or roll when a real magnetic disk is used for testing. The DSM method has the advantage that the absolute head-disk spacing can be observed and measured directly, especially in the case where it is difficult for the light beam to 'spot' the back surface of the head-slider. When used for the DSM method, the flying height can be measured down to contact without losing sensitivity. Slider pitch or roll can also be measured using the phase information. Another advantage of this polarisation interferometry is that, when used for the DSM method, with the measured intensity and phase information, the optical constants of the slider material can be determined, which is necessary to determine the flying height. By investigation of the application limits and potential problems of the intensity interferometry method, an improved intensity interferometry method is also proposed by using phase-shifting technique to improve the sensitivity of this method when the head-disk spacing is below 10 nm and near contact. An experimental testing system has been built to test the capability and effectiveness of the proposed interferometry methods. Experimental results are presented which show good agreement with the results gained from theoretical analyses and simulation.

As magnetic computer disks are developed to ever-greater data storage densities, the accuracy required for head positioning is moving beyond the accuracy provided by present technology using single-stage voice-coil motors in hard disk drives. This thesis details work to develop a novel active suspension arm with 2-dimensional actuation for use in advanced hard disk drives. The arm developed is capable of high-bandwidth data tracking as well as precision head flying height control motion. High-bandwidth data tracking is facilitated by the use of piezoelectric stack actuator, positioned closer to the head. The suspension arm is also capable of motion in the orthogonal axis. This motion represents active flying height control to maintain the correct altitude during drive operation. To characterise the suspension arm's structural dynamics, a high-resolution measurement system based on the optical beam deflection technique has been developed. This has enabled the accurate measurement of minute end-deflections of the suspension arm in 2-dimensions, to sub-nanometre resolution above noise. The design process of the suspension arm has led into the development of novel piezoelectric-actuated arms. In the work involving lead zirconate titanate (PZT) thick films as actuators, work in this thesis shows that reinforcing the films with fibre improves the overall actuation characteristics of the thick films. This discovery benefits applications such as structural health monitoring. The final suspension arm design has been adopted because it is simple in design, easier to integrate within current hard disk drive environment and easier to fabricate in mass. Closed-loop control algorithms based on proportional, integral and derivative (PID) controller techniques have been developed and implemented to demonstrate high bandwidths that have been achieved. The suspension arm developed presents an important solution in head-positioning technology in that it offers much higher bandwidths for data tracking and flying height control; both very essential in achieving even higher data storage densities on magnetic disks at much reduced head flying heights, compared to those in existing hard disk drives.

<i>Pteropus rufus,</i> Madagascar's largest endemic fruit bat, is widely distributed but declining in number due to habitat loss and over-hunting. The roost of Berenty, located in a 250 ha remnant of gallery forest surrounded by 30,000 ha of sisal plantations and patches of endemic spiny forest, is the largest in southeastern Madagascar and is an important historical breeding site for this species. Compared with conspecifics elsewhere in Madagascar the diet of <i>P. rufus</i> at Berenty is narrow, containing only 17 plant species. Seven gallery forest and four cultivated species are consistently utilised by the bats, but no endemic spiny forest species were identified in their diet. Pollen of <i>Agave sisalana</i>, present in 84% of faecal samples, contains 36% protein, the main digestive extraction of which was high (73%). Native fruits provide more protein that cultivars, but the latter have significantly higher concentrations of soluble carbohydrates. <i>P. rufus</i> has high mean buccal extraction for nitrogen (73%); carbohydrates (86%); condensed tannins (46%) and phenolics (24%). However, contrary to expectation condensed tannin extraction had no significant effect on nitrogen extraction. <i>P. rufus</i> swallows more viable than non-viable <i>Ficus</i> seeds. In 92% and 58% of germination trials, bat-passed seeds had the highest percentage germination and fastest rate of germination, respectively, compared with seeds from ripe fruits, ejecta pellets or faeces of other frugivores. A minimum foraging range of 17 km was established. The role of <i>P. rufus</i> in pollination is inferred from the presence of pollen on the head and thorax of bats and in their faeces. <i>P. rufus </i>is therefore, an important seed disperser and potentially important pollinator. However, at Berenty its' heavy reliance on the introduced cultivator <i>A. sisalana,</i> unique among the Pteropodidae, suggests that without this resource the remaining gallery forest could not support such a large colony of <i>P. rufus.</i>

No description available.

Thesis (M.A.)--Carleton University, 2002. / Includes bibliographical references (p. 117). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1959. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 148-162).

Thesis (M.S. in Management)--Naval Postgraduate School, December 2002. / Thesis advisor(s): Kenneth J. Euske, Jeffrey R. Cuskey. Includes bibliographical references (p. 61-62). Also available online.