UMD Theses and Dissertations
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Item VISUALIZATION, DATA QUALITY, AND SCALE IN COMPOSITE BATHYMETRIC DATA GENERALIZATION(2024) Dyer, Noel Matarazza; De Floriani, Leila; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Contemporary bathymetric data collection techniques are capable of collecting sub-meterresolution data to ensure full seafloor-bottom coverage for safe navigation as well as to support other various scientific uses of the data. Moreover, bathymetry data are becoming increasingly available. Datasets are compiled from these sources and used to update Electronic Navigational Charts (ENCs), the primary medium for visualizing the seafloor for navigation purposes, whose usage is mandatory on Safety Of Life At Sea (SOLAS) regulated vessels. However, these high resolution data must be generalized for products at scale, an active research area in automated cartography. Algorithms that can provide consistent results while reducing production time and costs are increasingly valuable to organizations operating in time-sensitive environments. This is particularly the case in digital nautical cartography, where updates to bathymetry and locations of dangers to navigation need to be disseminated as quickly as possible. Therefore, this dissertation covers the development of cartographic constraint-based generalization algorithms operating on both Digital Surface Model (DSM) and Digital Cartographic Model (DCM) representations of multi-source composite bathymetric data to produce navigationally-ready datasets for use at scale. Similarly, many coastal data analysis applications utilize unstructured meshes for representing terrains due to the adaptability, which allows for better conformity to the shoreline and bathymetry. Finer resolution along narrow geometric features, steep gradients, and submerged channels, and coarser resolution in other areas, reduces the size of the mesh while maintaining a comparable accuracy in subsequent processing. Generally, the mesh is constructed a priori for the given domain and elevations are interpolated to the nodes of the mesh from a predefined digital elevation model. These methods can also include refinement procedures to produce geometrically correct meshes for the application. Mesh simplification is a technique used in computer graphics to reduce the complexity of a mesh or surface model while preserving features such as shape, topology, and geometry. This technique can be used to mitigate issues related to processing performance by reducing the number of elements composing the mesh, thus increasing efficiency. The primary challenge is finding a balance between the level of generalization, preservation of specific characteristics relevant to the intended use of the mesh, and computational efficiency. Despite the potential usefulness of mesh simplification for reducing mesh size and complexity while retaining morphological details, there has been little investigation regarding the application of these techniques specifically to Bathymetric Surface Models (BSMs), where additional information such as vertical uncertainty can help guide the process. Toward this effort, this dissertation also introduces a set of experiments that were designed to explore the effects of BSM mesh simplification on a coastal ocean model forced by tides in New York Harbor. Candidate vertices for elimination are identified using a given local maximum distance between the original vertices of the mesh and the simplified surface. Vertex removal and re-triangulation operations are used to simplify the mesh and are paired with an optional maximum triangle area constraint, which prevents the creation of new triangles over a specified area. A tidal simulation is then performed across the domain of both the original (un-simplified) and simplified meshes, while comparing current velocities, velocity magnitudes, and water levels over time at twelve representative locations in the Harbor. It was demonstrated that the simplified mesh derived from using even the strictest parameters for the mesh simplification was able to reduce the overall mesh size by approximately 26.81%, which resulted in a 26.38% speed improvement percentage compared to the un-simplified mesh. Reduction of the overall mesh size was dependent on the parameters for simplification and the speed improvement percentage was relative to the number of resulting elements composing the simplified mesh.Item PERFORMANCE ENHANCEMENTS OF MICRO CORIOLIS VIBRATORY GYROSCOPES THROUGH LINEARIZED TRANSDUCTION AND TUNING MECHANISMS(2023) Knight, Ryan; DeVoe, Don L; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A quadruple mass Microelectromechanical System (MEMS) Coriolis vibratory gyroscope has been re-engineered with the singular focus of minimizing nonlinear transduction mechanisms, thereby allowing for angle random walk (ARW) noise reduction when operating at amplitudes higher than 2 μm. The redesign involved six primary steps: (i) the creation of an aspect-ratio independent deep reactive ion etch with minimal notching on 100 μm thick silicon-on-insulator device layer, (ii) the creation of micro-torr vacuum packaging capability, enabling operation at the thermoelastic dissipation limit of silicon, (iii) the redesign of Coriolis mass folded flexures and shuttle springs, (iv) the linearization of the antiphase coupler spring rate while maintaining parasitic modal separation, (v) the substitution of parallel plate transducers with linear combs, and (vi) the implementation of dedicated force-balanced electrostatic frequency tuners. Cross-axis stiffness is also reduced through folded-flexure moment balancing to further reduce ARW. By balancing positive and negative Duffing frequency contributions, net fractional frequency nonlinearity was reduced to -20 ppm. The gyroscope presented in this research has achieved, a first reported of its kind, an ARW of 0.0005 °/√hr, with an uncompensated bias instability of 0.08 °/hr. These advancements hold promise for enhancing navigation and North-finding applications. In tandem with gyroscope performance enhancements, vacuum packaging of ceramic chip carrier physics packages has achieved pressure levels below 1 micro-torr, a first in the field and remains state-of-the-art. Besides high-performance MEMS inertial sensors, ultrahigh vacuum packaging proves beneficial for chip scale atomic clocks, which require micro-torr vacuum levels to maintain fractional frequencies less than 10^-12. Finally, an approach to tuning the quality factor mismatch between degenerate modes in as-fabricated gyroscopes has demonstrated a reduction in gyroscope bias instability. This tuning can be achieved by incorporating lead zirconate titanate into regions where the trade-off between mechanical Q, tuning Q, and bias instability reduction is balanced. Both modeling and empirical frequency data justify this approach, suggesting, for typical MEMS foundry Q mismatch of 7%, a 70× reduction in bias instability.Item Outdoor Localization and Path Planning for Repositioning a Self-Driving Electric Scooter(2023) Poojari, Srijal Shekhar; Paley, Derek; Systems Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The long-term goal of this research is to develop self-driving e-scooter technology to increase sustainability, accessibility, and equity in urban mobility. Toward this goal, in this work, we design and implement a self-driving e-scooter with the ability to safely travel along a pre-planned route using automated, onboard control without a rider. We also construct an autonomous driving framework by synthesizing open-source robotics software libraries with custom-designed modules specific to an e-scooter, including path planning and state estimation. The hardware and software development steps along with design choices and pitfalls are documented. Results of real-world autonomous navigation of our retrofitted e-scooter, along with the effectiveness of our localization methods are presented.Item NAVIGATING RACISM IN HIGHER EDUCATION: A GROUNDED THEORY STUDY OF BLACK MALE ADMINISTRATORS(2017) Rollins, Domonic A.; Fries-Britt, Sharon; Education Policy, and Leadership; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In the United States, racism is alive and well, and the lives of Black men are a complete paradox (Jenkins, 2006). At the same time that the person holding the highest political office in the United States of America is a Black man, Black men are slain in the streets every day. Curiously, in a historic moment more than eight years ago, the United States, a nation founded on prejudice and racial discrimination, elected its first Black man to the presidency. And, in a historic moment less than six months ago, the United States elected the most racist and ethnocentric politician to the presidency in the last half-century. For many people, the election, and subsequent reelection of President Barack Obama signified the end of racism in the United States. Simultaneously, the election of the new president indicates that racism is thriving in the United States. In this Black men are suspended in “dueling realities of history — steady progress and devastating setbacks” (Merida, 2007, p.4). Resultantly, it is commonplace for Black men, regardless of age, socioeconomic class, or location, to wonder whether their life is at risk because they are Black. Simply stated, in an Obama era there was a widely held belief that the United States was post-racial society (Bonilla-Silva & Dietrich, 2011); the subsequent 2016 election indicated this is not that case, and the lives of Black men are in danger (Sanneh, 2015). What’s more is that higher education, an institution founded on inequity, has long harbored institutional racism making it difficult for Black male administrators to achieve equitable outcomes with their White peers. In higher education, there is an extant body of research identifying the barriers that impact the success and progression of underrepresented racial minority students and faculty, including Black people (Baez, 2000; Chesler, Lewis, & Crowfoot, 2005; Christian, 2012; Patitu & Hinton, 2003; Stanley, 2006). Yet, very little is known about the experiences of underrepresented racial minority administrators (Chun & Evans, 2012; McCurtis, Jackson, & O’Callaghan, 2008; Stanley, 2006). Specifically, most research on Black males in the academy focuses on students and faculty, with little research on the experiences of Black male administrators (Jackson, 2003; Patitu & Hinton, 2003; Perna, Gerald, Baum, & Milem, 2006). Using a constructivist grounded theory approach; this dissertation shares and analyzes findings from interview data to unearth the process by which Black male administrators navigate racism. Through this grounded theory investigation, a model for navigating racism for Black male administrators emerged, which illustrates the iterative and contextual nature of navigating racism. The result is that the way one navigates racism in higher education is dependent on major contextual and shaping forces in their life. Further, one learns how to navigate racism early in life, well before one enters higher education. Specific decisions about how to navigate racism also involve an internal and external assessment of the racist incident, current context in which one is steeped, and desired or anticipated outcomes of navigating or managing the incident. Finally, this research, through the creation of a model, moved from the descriptive analysis of what racism is, towards the practical implications of having to navigate racism in higher education. By integrating the identified racist incidents, shaping contexts, and the navigation model together, applications were created for individuals, institutions, and future research. The resulting implications focused primarily on critical self-reflection for individuals, an increase in reflection and audits for institutions, and a new direction for race and racism research to explore the primary learning sites of how to manage racism in one’s life.Item Bee-ing There: The Systematicity of Honeybee Navigation Supports a Classical Theory of Honeybee Cognition(2006-04-27) Tetzlaff, Michael James; Rey, Georges; Philosophy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Classical theory of cognition proposes that there are cognitive processes that are computations defined over syntactically specified representations, "sentences" in a language of thought, for which the representational-constituency relation is concatenative. The main rival to Classicism is(Nonimplementational, or Radical, Distributed) Connectionism. It proposes that cognitive processes are computations defined over syntactically simple, distributed representions, for which the constituency relation is nonconcatenative. I argue that Connectionism, unlike Classicism, fails to provide an adequate theoretical framework for explaining systematically related cognitive capacities and that this is due to its necessary reliance on nonconcatenative constituency. There appears to be an interesting divergence of attitude among philosophers of psychology and cognitive scientists regarding Classicism's language of thought hypothesis. On one extreme, there are those who argue that only humans are likely to possess a language of thought (or that we at least have no evi- dence to the contrary). On the other extreme, there are those who argue that distinctively human thinking is not likely to be explicable in terms of a language of thought. They point to features of human cognition which they claim strongly support the hypothesis that human cognitive-state transition functions are computationally intractable. This implicitly suggests that the cognitive processes of simpler, nonhuman minds might be computationally tractable and thus amenable to Classical computational explanation. I review much of the recent literature on honeybee navigation. I argue that many capacities of honeybees to acquire various sorts of navigational information do in fact exhibit systematicity. That conclusion, together with the correctness of the view that Classicism provides a better theoretical framework than does Connectionism for explaining the systematicity of the relevant cognitive capacities, gives one reason in support of the claim that sophisticated navigators like honeybees have a kind of language of thought. At the very least, it provides one reason in support of the claim that the constituency relation for the mental representations of such navigators is concatenative, not nonconcatenative.Item The Use Of Variable Celestial X-ray Sources For Spacecraft Navigation(2005-09-22) Sheikh, Suneel Ismail; Pines, Darryll J.; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Accurate control and guidance of spacecraft require continuous high performance three-dimensional navigation solutions. Celestial sources that produce fixed radiation have demonstrated benefits for determining location near Earth and vehicle attitude. Many interplanetary navigation solutions have also relied on Earth-based radio telescope observations and substantial ground processing. This dissertation investigates the use of variable celestial sources to compute an accurate navigation solution for autonomous spacecraft operation and presents new methodologies for determining time, attitude, position, and velocity. A catalogue of X-ray emitting variable sources has been compiled to identify those that exhibit characteristics conducive to navigation. Many of these sources emit periodic signals that are stable and predictable, and all are located at vast distances such that the signal visibility is available throughout the solar system and beyond. An important subset of these sources is pulsar stars. Pulsars are rapidly rotating neutron stars, which generate pulsed radiation throughout the electromagnetic spectrum with periods ranging from milliseconds to thousands of seconds. A detailed analysis of several X-ray pulsars is presented to quantify expected spacecraft range accuracy based upon the source properties, observation times, and X-ray photon detector parameters. High accuracy time transformation equations are developed, which include important general relativistic corrections. Using methods that compare measured and predicted pulse time of arrival within an inertial frame, approaches are presented to determine absolute and relative position, as well as corrections to estimated solutions. A recursive extended Kalman filter design is developed to incorporate the spacecraft dynamics and pulsar-based range measurements. Simulation results demonstrate that absolute position determination depends on the accuracy of the pulse phase measurements and initial solutions within several tens of kilometers are achievable. The delta-correction method can improve this position solution to within 100 m MRSE and velocity to within 10 mm/s RMS using observations of 500 s and a 1-m2 detector. Comparisons to recorded flight data obtained from Earth-orbiting X-ray astrophysics missions are also presented. Results indicate that the pulsed radiation from variable celestial X-ray sources presents a significant opportunity for developing a new class of navigation system for autonomous spacecraft operation.