UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Analysis of the Stochastic Stability and Asymptotically Stationary Statistics for a Class of Nonlinear Attitude Estimation Algorithms(2018) Galante, Joseph Marshall; Sanner, Robert M; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Attitude estimation algorithms are critical components of satellite control systems, aircraft autopilots, and other applications. Attitude estimation systems perform their task by fusing attitude and gyroscope measurements; however, such measurements are typically corrupted by random noise and gyroscopes may have significant bias. Variations of the extended Kalman filter are commonly used, but this technique relies on instantaneous linearization of the underlying nonlinear dynamics and global stability cannot be guaranteed. Nonlinear attitude observers with guaranteed global stability have been derived and experimentally demonstrated, but only for the deterministic setting where no stochastic effects are present. The first part of this thesis extends a deterministic nonlinear attitude estimator by introducing additional dynamics that allow learning variations of gyro bias as a function of operating temperature, a common source of bias variation in rate gyro readings. The remainder of the thesis formally addresses the problem of stochastic stability and asymptotic performance for this family of estimators when the measurements contain random noise. Analysis tools from stochastic differential equation theory and stochastic Lyapunov analysis are used together to demonstrate convergence of the filter states to a stationary distribution, and to bound the associated steady-state statistics as a function of filter gains and sensor parameters. In many cases these bounds are conservative, but solutions have been found for the associated stationary Fokker-Planck PDEs for two cases. When only the gyro measurement contains noise, the attitude estimation errors are shown to converge to a bipolar Bingham distribution. When the gyro measurement is further assumed to have constant bias, the estimation errors are shown to converge to a joint bipolar Bingham and multivariate Gaussian distribution. Knowledge of the stationary distributions allow for exact computation of steady-state statistics. Further, the analysis suggests a method for modeling a continuous quaternion noise process with specified statistics on SO(3); this model is used for analyzing estimator performance when both the gyro and the attitude measurements contain noise. Bounds and exact predictions for the different noise models are validated using a high fidelity numerical integration method for nonlinear stochastic differential equations.Item Public Opinion, Political Representation, and Democratic Choice(2015) Zenz, Michael; Pacuit, Eric; Morris, Christopher W; Philosophy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this dissertation I argue that political representatives have duties to be responsive to public opinion in their policy decisions. The existence of this duty, I claim, is a basic requirement of a truly democratic system of government. In chapter 2, I show that several standard versions of democratic legitimacy require political representatives to ``respect'' public opinion. However, I argue that a particular version of political legitimacy, based upon popular sovereignty and the importance of self-governance, provides an especially useful background for understanding what this ``respect'' must mean. In chapter 3, I argue that respecting public opinion requires political representatives to integrate public opinion information into their policy decisions. According to one of the standard views of political representation, the liberal conception, representatives deciding between policy alternatives should balance what they believe to be in the interests of the public against public opinion. I argue that this is the only adequate theory of political representation. Although this view of political representation is often discussed in the literature, it is less often given a mathematically precise form. Therefore, I present a formal model of such a balancing procedure, and this reveals several important formal requirements that a conception of public opinion must satisfy; most importantly, it must account for instability in the expression of public opinion, individual differences in opinion strength, and it must be representable along a cardinal scale. Standard measures of public opinion do not satisfy these requirements. I argue that if such a model of public opinion cannot be formulated, then the liberal conception of political representation is incoherent. In chapters 4 and 5, I present a model of public opinion based upon Thurstonian scaling techniques that fulfills the necessary formal requirements. Finally, in chapter 6, I discuss several important implications this model has for the measurement of public opinion, the use of public opinion by political representatives in policy deliberation, and other problems in social choice theory.Item Virtual Team Member Performance and Viability: The Influence of Individual Characteristics(2008-04-23) Hill, Nora Sharon; Bartol, Kathryn M; Business and Management: Management & Organization; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The use of virtual teams is increasing in organizations. Virtual teamwork occurs when team members collaborate using technology-mediated communication rather than face-to-face. Research has shown that virtual teamwork can be challenging. However, currently there is little research to help organizations identify team members who are most likely to be effective in a virtual teamwork environment. Given this, the purpose of my dissertation research was to identify individual characteristics that influence a virtual team member's contribution to team performance and team membership viability. This dissertation developed and tested a theoretical model that integrates literature identifying individual team member characteristics that are directly germane to effective functioning in a team operating virtually. These characteristics include virtual teamwork knowledge, skills, and abilities (KSAs); self-regulatory team orientation; and preference for face-to-face communication with team members. These individual characteristics were hypothesized to influence team member contribution to team performance and membership viability through the intervening variables of virtual teamwork behaviors and attitude toward virtual teamwork with the team. In addition, team technology support and empowering team leadership were two contextual factors predicted to moderate the hypothesized relationships between team member characteristics and virtual teamwork behaviors. The hypotheses were tested using data from 193 team members in 29 virtual teams in the procurement department of one large multinational company. The data were collected from team members and team leaders using online surveys, and hierarchical linear modeling was used to analyze the data. Results showed that both virtual teamwork KSAs and self-regulatory team orientation, although not directly associated with virtual teamwork behaviors, interacted with empowering team leadership to influence virtual teamwork behaviors. Self-regulatory team orientation and preference for face-to-face communication were both found to be positively associated with attitude toward virtual teamwork. Results further showed that virtual teamwork behaviors and attitude toward virtual teamwork were both positively associated with contribution to team performance and membership viability. Finally, no support was found for the hypothesized moderating influence of team technology support on the relationship between team member characteristics and virtual teamwork behaviors.