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Spacecraft trajectory optimization is a near-infinite problem space with a wide variety of models and optimizers. As trajectory complexity increases, so too must the capabilities of modern optimizers. Common objective cost functions for these optimizers include the propellant utilized by the spacecraft and the time the spacecraft spends in flight. One effective method of minimizing these costs is the utilization of one or multiple gravity assists. Due to the phenomenon known as the Oberth effect, fuel burned at a high velocity results in a larger change in orbital energy than fuel burned at a low velocity. Since a spacecraft is flying fastest at the periapsis of its orbit, application of impulsive thrust at this closest approach is demonstrably capable of generating a greater change in orbital energy than at any other location in a trajectory. Harnessing this extra energy in order to lower relevant cost functions requires the modeling of these “powered flybys” or “powered gravity assists” (PGAs) within an interplanetary trajectory optimizer. This paper will discuss the use and modification of the Spacecraft Trajectory Optimization Suite, an optimizer built on evolutionary algorithms and the island model paradigm from the Parallel Global Multi-Objective Optimizer (PaGMO). This variant of STOpS enhances the STOpS library of tools with the capability of modeling and optimizing single and multiple powered gravity assist trajectories. Due to its functionality as a tool to optimize powered flybys, this variant of STOpS is named the Spacecraft Trajectory Optimization Suite - Flybys with Impulsive Thrust Engines (STOpS-FLITE). In three test scenarios, the PGA algorithm was able to converge to comparable or superior solutions to the unpowered gravity assist (uPGA) modeling used in previous STOpS versions, while providing extra options of trades between time of flight and propellant burned. Further, the PGA algorithm was able to find trajectories utilizing a PGA where uPGA trajectories were impossible due to limitations on time of flight and flyby altitude. Finally, STOpS-FLITE was able to converge to a uPGA trajectory when it was the most optimal solution, suggesting the algorithm does include and properly considers the uPGA case within its search space.

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The Suite for Violin and Piano, Op. 6 is one of the least-known compositions by Benjamin Britten. It has been considered unfavorably by critics and scholars due to its puzzling mixture of tonal and post-tonal elements. However, this dissertation argues that the suite is composed with a clear tonal framework, and its unique mixed tonal-post-tonal language justifies an in-depth analysis. This analytical study utilizes a linear progression technique - the voice leading produced by passing tones and neighbor notes around focal pitches - to identify tonal areas of the suite.

Managing mobile ad hoc networks (MANETs) presents new challenges due to the need for a distributed management mechanism that can efficiently adapt to the dynamic nature of these networks. In particular, provisioning and management of Quality of Service (QoS) in such networks remains a challenging task. Previous works in this field have focused largely on the monitoring and data collection aspects of network management; literature on the provisioning of devices and protocol support for MANET configuration is scarce. One approach for QoS provisioning and management in the Internet that has met with considerable interest in the networking community is that of Policy-Based Network Management (PBNM). However, its application has been so far limited mainly to fixed high-bandwidth networks. In this research, we apply the PBNM concept, for the first time, for managing QoS in ad hoc networks. We formulate a framework to understand the various crucial components that should comprise an ad hoc network management system. We propose a taxonomy of policy architectures to classify the various feasible architectures into distinct categories. Based on our assessment using the taxonomy, we identify architectures that seem promising for managing ad hoc networks. We propose a solution suite to address the different challenges in deploying policy-based management in MANETs. These solutions include k-hop clustering, Dynamic Service Redundancy (DynaSeR), inter-domain policy negotiation, and automated service discovery. We propose extensions to the standard Common Open Policy Service (COPS) protocol and suggest methods for cross-layer interaction to implement our solutions. Our methodology focuses on both a prototype implementation and experimental analysis using wired and wireless testbed networks, and modeling and performance evaluation using simulation. The whole exercise of conducting experiments provided valuable insight into the challenges of operating in an actual ad hoc network environment; implementation and testing facilitated assessment of the feasibility of our proposed schemes. Simulation allowed us to evaluate our solutions for different cluster sizes, network densities, and node mobility. The scalability of our solutions was tested with networks of up to 100 nodes. In general, average service availability for the PBNM system improved as the cluster size increased, with decreased COPS connection overhead (the tradeoff is increased unpredictability, longer response time, and resource requirements at intermediate nodes to support larger clusters). We were also able to determine that, for a given cluster size, our proposed delegation scheme resulted in a 10 to 25% improvement in service availability. Using our proposed time-based heuristic, savings on the order of 50 to 400% were obtained in the service discovery overhead for larger cluster sizes. We also validated some of the simulation results against proof-of-concept experiments conducted using the testbed. We presented a working illustration of our PBNM system prototype by demonstrating its application for managing QoS for multimedia and real-time mission critical applications in a multi-domain ad hoc network. The policy-based approach is a promising one for the management of MANETs, but it requires the flexibility to adapt to a constantly changing environment. Through experimental studies and simulation, we were able to determine that using our proposed solution suite and through the addition of a set of extensions to the COPS protocol, we can achieve our objective of a self-organizing, robust, and efficient PBNM system for managing MANETs. / Ph. D.

Despite ample research in the fields of organizational behavior and human resource management regarding employee decisions to voluntarily opt out of corporate leadership positions, there is little research exploring the personal experiences of black women in U.S. companies contemplating leaving executive positions. This research leverages a qualitative interpretative phenomenological study to explore why Black women corporate leaders in the United States are leaving corporate America before reaching the C-Suite. Two studies were conducted to understand the lived experiences of Black women executives in U.S. Fortune 500 companies; moreover, study two further explored and detangled some of the themes from Study One to understand the experiences of the black women leaders in the pipeline for senior management more deeply. The findings identify several environmental factors, explored in depth in this dissertation, that impact executives’ decision to leave corporate America. The findings provide a foundation to understand further the impact of the corporate environment resulting in the loss of top diverse talent in this understudied demographic. These findings also provide critical information for the Black woman executive currently working in corporate America as well as those who have opted to leave early and would like to better digest their experiences. / Business Administration/Human Resource Management

Distant Thoughts: Dreams and Reflections, A Suite for Symphonic Winds, is a seventeen-minute work composed for the high school level wind ensemble. The instrumentation is based on the typical high school band resources. Instrumentation includes piccolo, two flutes, two oboes, English horn, three clarinets, bass clarinet, two alto saxophones, tenor saxophone, baritone saxophone, two bassoons, four trumpets, four horns, two trombones, bass trombone, two euphoniums, two tubas, timpani, and four percussionists.