Award-winning Theses and Dissertations

Permanent URI for this collection

https://hdl.handle.net/10919/71751
Every year, the Virginia Tech Graduate School honors several outstanding theses and dissertations, and some theses and dissertations have won external awards. Browse these works here. Read about applying for thesis and dissertation awards at graduateschool.vt.edu/academics/awards/.

Browse

Browsing Award-winning Theses and Dissertations by Content Type "Dissertation"

Now showing 1 - 20 of 44
  • Thumbnail Image
    Amplifying the Griot: Technology for Preserving, Retelling, and Supporting Underrepresented Stories
    Kotut, Lindah Jerop (Virginia Tech, 2021-05-24)
    As we develop intelligent systems to handle online interactions and digital stories, how do we address those stories that are unwritten and invisible? How do ensure that communities who value oral histories are not left behind, and their voices also inform the design of these systems? How do we determine that the technology we design respect the agency and ownership of the stories, without imposing our own biases? To answer these questions, I rely on accounts from different underrepresented communities, as avenues to examine how digital technology affect their stories, and the agency they have over them. From these stories, I elicit guidelines for the design of equitable and resilient tools and technologies. I sought wisdom from griots who are master storytellers and story-keepers on the craft of handling both written and unwritten stories, which instructed the development of the Respectful Space for technology typology, a framework that informs our understanding and interaction with underrepresented stories. The framework guided the approach to understand technology use by inhabitants of rural spaces in the United States--particularly long-distance hikers who traverse these spaces. I further discuss the framework's extensibility, by considering its use for community self-reflection, and for researchers to query the ethical implications of their research, the technology they develop, and the consideration for the voices that the technology amplifies or suppresses. The intention is to highlight the vast resources that exist in domains we do not consider, and the importance of the underrepresented voices to also inform the future of technology.
  • Thumbnail Image
    Application of Artificial Intelligence to Wireless Communications
    Rondeau, Thomas Warren (Virginia Tech, 2007-09-20)
    This dissertation provides the theory, design, and implementation of a cognitive engine, the enabling technology of cognitive radio. A cognitive radio is a wireless communications device capable of sensing the environment and making decisions on how to use the available radio resources to enable communications with a certain quality of service. The cognitive engine, the intelligent system behind the cognitive radio, combines sensing, learning, and optimization algorithms to control and adapt the radio system from the physical layer and up the communication stack. The cognitive engine presented here provides a general framework to build and test cognitive engine algorithms and components such as sensing technology, optimization routines, and learning algorithms. The cognitive engine platform allows easy development of new components and algorithms to enhance the cognitive radio capabilities. It is shown in this dissertation that the platform can easily be used on a simulation system and then moved to a real radio system. The dissertation includes discussions of both theory and implementation of the cognitive engine. The need for and implementation of all of the cognitive components is strongly featured as well as the specific issues related to the development of algorithms for cognitive radio behavior. The discussion of the theory focuses largely on developing the optimization space to intelligently and successfully design waveforms for particular quality of service needs under given environmental conditions. The analysis develops the problem into a multi-objective optimization process to optimize and trade-of of services between objectives that measure performance, such as bit error rate, data rate, and power consumption. The discussion of the multi-objective optimization provides the foundation for the analysis of radio systems in this respect, and through this, methods and considerations for future developments. The theoretical work also investigates the use of learning to enhance the cognitive engine's capabilities through feed-back, learning, and knowledge representation. The results of this work include the analysis of cognitive radio design and implementation and the functional cognitive engine that is shown to work in both simulation and on-line experiments. Throughout, examples and explanations of building and interfacing cognitive components to the cognitive engine enable the use and extension of the cognitive engine for future work.
  • Thumbnail Image
    Assessment of the Jones Act Waiver Process on Freight Transportation Networks Experiencing Disruption
    Fialkoff, Marc Richard (Virginia Tech, 2017-10-27)
    In October 2012, Hurricane Sandy caused massive disruption and destruction to the Mid-Atlantic region of the United States. The intensity of the storm forced the Port of New York and New Jersey to close, forcing cargo diversion to the Port of Norfolk in Virginia. Because of the Jones Act restriction on foreign vessels moving between U.S. ports, the restriction on short sea shipping was viewed as a barrier to recovery. Much of the critical infrastructure resilience and security literature focuses on the "hardening" of physical infrastructure, but not the relationship between law, policy, and critical infrastructure. Traditional views of transportation systems do not adequately address questions of governance and behaviors that contribute to resilience. In contrast, recent development of a System of Systems framework provides a conceptual framework to study the relationship of law and policy systems to the transportation systems they govern. Applying a System of Systems framework, this research analyzed the effect of relaxing the Jones Act on freight transportation networks experiencing a disruptive event. Using WebTRAGIS (Transportation Routing Analysis GIS), the results of the research demonstrate that relaxing the Jones Act had a marginal reduction on highway truck traffic and no change in rail traffic volume in the aftermath of a disruption. The research also analyzed the Jones Act waiver process and the barriers posed by the legal process involved in administration and review for Jones Act waivers. Recommendations on improving the waiver process include greater agency coordination and formal rulemaking to ensure certainty with the waiver process. This research is the first in studying the impact of the Jones Act on a multimodal freight transportation network. Likewise, the use of the System of Systems framework to conceptualize the law and a critical infrastructure system such as transportation provides future opportunities for studying different sets of laws and policies on infrastructure. This research externalizes law and policy systems from the transportation systems they govern. This can provide policymakers and planners with an opportunity to understand the impact of law and policy on the infrastructure systems they govern.
  • Thumbnail Image
    Atomic Force Microscopy Study of Clay Mineral Dissolution
    Bickmore, Barry Robert (Virginia Tech, 1999-12-09)
    An integrated program has been developed to explore the reactivity of 2:1 phyllosilicates (biotite and the clays montmorillonite, hectorite, and nontronite) with respect to acid dissolution using in situ atomic force microscopy (AFM). Three techniques are described which make it possible to fix these minerals and other small particles to a suitable substrate for examination in the fluid cell of the atomic force microscope. A suite of macros has also been developed for the Image SXM image analysis environment which make possible the accurate and consistent measurement of the dimensions of clay particles in a series of AFM images, so that dissolution rates can be measured during a fluid cell experiment. Particles of biotite and montmorillonite were dissolved, and their dissolution rates normalized to their reactive surface area, which corresponds to the area of their edge surfaces (Ae). The Ae-normalized rates for these minerals between pH 1-2 are all ~10E-8 mol/m2*s, and compare very well to other Ae-normalized dissolution rates in the literature. Differences between the Ae-normalized rates for biotite and the BET-normalized rates (derived from solution chemical studies) found in the literature can be easily explained in terms of the proportion of edge surface area and the formation of leached layers. However, the differences between the Ae-normalized montmorillonite rates and the literature values cannot be explained the same way. Rather, it is demonstrated that rates derived from solution studies of montmorillonite dissolution have been affected by the colloidal behavior of the mineral particles. Finally, the dissolution behavior of hectorite (a trioctahedral smectite) and nontronite ( a dioctahedral smectite) were compared. Based on the differential reactivity of their crystal faces, a model of their surface atomic structures is formulated using Hartman-Perdock crystal growth theory, which explains the observed data if it is assumed that the rate-determining step of the dissolution mechanism is the breaking of connecting bonds between the octahedral and tetrahedral sheets of the mineral structure.
  • Thumbnail Image
    Bacteriophage Felix O1: Genetic Characterization and Bioremedial Application
    Whichard, Jean Marie (Virginia Tech, 2000-10-16)
    Bacteriophage Felix O1 was studied for applicability as a Salmonella intervention. Felix O1's potential as a Salmonella therapeutic was explored, as was its utility as a food application. Felix O1 is specific for and infects most serovars within the genus Salmonella. The entire 86.155-kb sequence of the phage's linear, double-stranded chromosome was determined. 213 open reading frames (ORFs) were found, including 23 homologues of phage genes (e<0.008). Homology searches do not indicate genes that would be expected to increase virulence of Salmonella. Thirteen T4 homologues were found, including rIIA and rIIB, rapid lysis genes of T-even phages. Site-directed mutagenesis of the rIIB region was attempted by homologous recombination with plasmids containing luxAB of Vibrio harveyi. No DrIIB luxAB+ recombinants resulted from the methods tried. Serial in vivo passage was used to select for a longer-circulating Felix O1 mutant using the modified methods of Merril et al., (1996). No difference was found in the clearance of wild-type (WT) and Felix O1 following nine serial passages. Injection of 10⁹pfus yielded 24-hour concentrations of 6.5 and 4.9 log10 pfus/ml plasma for WT and 9th passage, respectively. Both isolates were undetectable in plasma by 72 hours, but remained in spleens at 96 hours. A large-plaque Felix O1 variant (LP) isolated during in vivo serial passage was compared with WT for Salmonella growth suppression. Spectrophotometric measurement of BHI cultures indicated greater suppression of S. typhi by LP than by WT, a difference not seen with S. typhimurium DT104. Both isolates suppressed 24-hour S. typhimurium DT104 growth on experimentally-contaminated chicken frankfurters at 22°C. Untreated frankfurters yielded 6.81 log10 Salmonella cfus/g, whereas WT and LP-treated samples yielded 5.01 and 4.70 log10 cfus/g, respectively. Both phages suppressed the Salmonella typhimurium DT104 growth (p<0.0001), but the isolates did not perform differently (p=0.5088). Presence of Salmonella caused a higher yield of WT phage than from the uninoculated group (p=0.0011), but did not affect LP yield (p=0.4416). With Salmonella present, the 24-hour LP concentration was lower than WT concentration. This supports the surmised LP rapid-lysis phenotype since T4 rapid-lysis mutants typically exhibit lower burst sizes than wild-type phage.
  • Thumbnail Image
    Between Discipline and Profession: A History of Persistent Instability in the Field of Computer Engineering, circa 1951-2006
    Jesiek, Brent K. (Virginia Tech, 2006-12-13)
    This dissertation uses a historical approach to study the origins and trajectory of computer engineering as a domain of disciplinary and professional activity in the United States context. Expanding on the general question of "what is computer engineering?," this project investigates what counts as computer engineering knowledge and practice, what it means to be a computer engineer, and how these things have varied by time, location, actor, and group. This account also pays close attention to the creation and maintenance of the "sociotechnical" boundaries that have historically separated computer engineering from adjacent fields such as electrical engineering and computer science. In addition to the academic sphere, I look at industry and professional societies as key sites where this field originated and developed. The evidence for my analysis is largely drawn from journal articles, conference proceedings, trade magazines, and curriculum reports, supplemented by other primary and secondary sources. The body of my account has two major parts. Chapters 2 through 4 examine the pre-history and early history of computer engineering, especially from the 1940s to early 1960s. These chapters document how the field gained a partially distinct professional identity, largely in the context of industry and through professional society activities. Chapters 5 through 7 turn to a historical period running from roughly the mid 1960s to early 1990s. Here I document the establishment and negotiation of a distinct disciplinary identity and partially unique "sociotechnical settlement" for computer engineering. Professional societies and the academic context figure prominently in these chapters. This part of the dissertation also brings into relief a key argument, namely that computer engineering has historically occupied a position of "persistent instability" between the engineering profession, on the one hand, and independent disciplines such as computer science, on the other. In an Epilogue I review some more recent developments in the educational arena to highlight continued instabilities in the disciplinary landscape of computing, as well as renewed calls for the establishment of a distinct disciplinary and professional identity for the field of computer engineering. I also highlight important countervailing trends by briefly reviewing the history of the software/hardware codesign movement.
  • Thumbnail Image
    Brazil Comes to the Future: Living Time and Space in the International Order of Competition
    Rossone de Paula, Francine (Virginia Tech, 2016-06-20)
    The rise of Brazil as an economic power in the last decade has been celebrated by politicians and analysts as an opportunity for the country to take advantage of its visibility and bargaining power in order to effectively advocate for and promote an institutional and normative reform of the international order toward a less asymmetric and exclusionary space for politics. This dissertation aims to examine the spatial and temporal assumptions in these recent discourses about Brazil's emergence to the global stage and Brazil']s disposition towards the future. Departing from an understanding that there are scripts governing the realm of the possible and the visible in international politics, this dissertation proposes an analysis of what defines the conditions of possibility for Brazil's emergence to the global stage. By looking at discourses about Brazil's position and positioning in international politics, this study explores implicit and explicit rules defining the possibilities for one to be seen as a legitimate presence in the future and what these spatiotemporal constructs reveal about what is allowed as repetition and as change in the world. Contrary to many optimistic accounts of Brazil's emergence as a transformational leader from the developing world, I argue that it is only possible for Brazil to be discursively represented as an emerging global player and/or a country of the future that may have finally arrived because of the same limiting spatial and temporal discursive representations in world politics that translate difference into hierarchy and that contain and define intelligible possibilities for an alternative political order.
  • Thumbnail Image
    Citizen Soldiers and Professional Engineers: The Antebellum Engineering Culture of the Virginia Military Institute
    Miller, Jonson William (Virginia Tech, 2008-09-17)
    The founders and officers of the Virginia Military Institute, one of the few American engineering schools in the antebellum period, embedded a particular engineering culture into the curriculum and discipline of the school. This occurred, in some cases, as a consequence of struggles by the elite of western Virginia to gain a greater share of political power in the commonwealth and by the officers of VMI for authority within the field of higher education. In other cases, the engineering culture was crafted as a deliberate strategy within the above struggles. Among the features embedded was the key feature of requiring the subordination of one’s own local and individual interests and identities (class, regional, denominational, etc.) to the service of the commonwealth and nation. This particular articulation of service meant the performance of “practical” and “useful” work of internal improvements for the development and defense of the commonwealth and the nation. The students learned and were to employ an engineering knowledge derived from fundamental physical and mathematical principles, as opposed to a craft knowledge learned on the job. To carry out such work and to even develop the capacity to subordinate their own interests, the cadets were disciplined into certain necessary traits, including moral character, industriousness, selfrestraint, self-discipline, and subordination to authority. To be an engineer was to be a particular kind of man. The above traits were predicated upon the engineers being white men, who, in a new “imagined fraternity” of equal white men, were innately independent, in contrast to white women and blacks, who were innately dependent. Having acquired a mathematically-intensive engineering education and the character necessary to perform engineering work, the graduates of VMI who became engineers were to enter their field as middle-class professionals who could claim an objective knowledge and a disinterested service to the commonwealth and nation, rather than to just their own career aspirations.
  • Thumbnail Image
    Coalition Networks and Policy Learning: Interest Groups on the Losing Side of Legal Change
    Millar, Ronald B. (Virginia Tech, 2005-12-07)
    Network, organizational, and policy learning literatures indicate that when interest groups face failure they will seek out alternative ideas and strategies that will enhance their potential for future success. Research with regard to interest groups and legal change has found that interest groups, using arguments that were once accepted as the legal standard for Supreme Court decisions, were unwilling or unable to alter their arguments when the Court reversed its position on these legal standards. This research project examined the conflicting findings of these literatures. Using the Advocacy Coalition Framework as a guide, this project studied the separationist advocacy coalition in cases regarding state aid to elementary and secondary sectarian schools from 1971 to 2002. The legal briefs filed by members of the separationist advocacy coalition with the Court were examined using content analysis to track changes in their legal arguments. Elite interviews were then conducted to gain an understanding of the rationale for results found in the content analysis. The research expectation was that the separationist advocacy coalition would seek out and incorporate into their briefs new and innovative legal arguments to promote their policy goals. The research results demonstrated that prior to legal change interest groups did seek out and incorporate new legal arguments borrowed from other fora and sought to expand or reinterpret established legal arguments to better aid their policy goals. The changes that seemed to have the potential for adoption by the Court were quickly incorporated into the briefs of the other members of the coalition. Following legal change interest groups continued to analyze the decisions of the Court in order to seek out the best possible legal arguments to use in their briefs; however, the main focus of legal arguments examined and used by the coalition narrowed to those cited by the swing justice in the funding cases. Two innovative arguments were developed, but were either ignored or considered unsuitable, and were not used by the other members of the coalition. Counter to this project's research expectations new and innovative legal arguments were not adopted by the coalition. As the Court discontinued the use of various legal arguments the coalition quickly responded to these changes and dropped those obsolete legal arguments. Therefore, contrary to prior research, the interest groups and the coalition altered their arguments following legal change. Only those interest groups who no longer participated in coalition discussions reverted back to using pre-legal change arguments. Learning continued to occur in the coalition following legal change; however, the focus of analysis and the pool of arguments deemed worthy of use narrowed considerably.
  • Thumbnail Image
    Confronting the West: Social Movement Frames in 20th Century Iran
    Poulson, Stephen Chastain (Virginia Tech, 2002-12-06)
    The Iranian Revolution of 1979 received considerable attention from modern social scientists who study collective action and revolution because it allowed them to apply their different perspectives to an ongoing social event. Likewise, this work used the Iranian experience as an exemplar, focusing on a sequence of related social movement frames that were negotiated by Iranian groups from the late 19th through the 20th century. Snow and Benford (1992) have proposed that cycles of protest are associated with the development of a movement master frame. This frame is a broad collective orientation that enables people to interpret an event in a more or less uniform manner. This study investigated how movement groups in Iran developed master frames of mobilization during periodic cycles of protests from 1890 to the present. By investigating how master frames were negotiated by social movement actors over time, this work examined both the continuity and change of movement messages during periods of heightened social protest in Iran.
  • Thumbnail Image
    Consequences of avian parental incubation behavior for within-clutch variance in incubation temperature and offspring behavioral phenotypes
    Hope, Sydney Frances (Virginia Tech, 2020-01-17)
    Parents can have large effects on their offspring by influencing the early developmental environment. In birds, a major way that parents can influence the early developmental environment is through egg incubation. Not only is incubation necessary for hatching success, but small changes of <1C in average incubation temperature have large effects on post-hatch offspring morphology and physiology. However, incubation is energetically costly and time-consuming for parents, and thus parents must allocate resources between incubation and self-maintenance. This can lead to differences in parental incubation behavior and egg temperatures among and within populations. Understanding which factors influence incubation, and the subsequent effects for offspring, is crucial for understanding parental effects, non-genetic drivers of phenotypic variation, and how environmental changes affect avian populations. I used wood ducks (Aix sponsa) as a study species to investigate how factors (disturbance, clutch size, ambient temperature) that influence parental demands may affect parental incubation behavior, physiology, and egg temperatures, and subsequently how egg temperatures affect offspring behavior and physiology. In a field experiment, I found that nest disturbance (i.e., capture) reduced both parent prolactin concentrations and the amount of time that parents spent incubating (Chapter 1). Further, ambient temperature was positively and clutch size negatively related to egg temperatures. Notably, in large clutches, differences in average incubation temperature among eggs within nests were large enough (i.e., >1C) to lead to different offspring phenotypes within broods (Chapter 2). Then, in a series of experiments in which I controlled incubation temperature, I provided evidence that lower average incubation temperatures lead to a reduced ability of ducklings to exit the nest cavity (Chapter 3), a more proactive behavioral phenotype (Chapter 4), a smaller body size, and a reduced efficiency in food consumption (Chapter 5), compared to those incubated at higher temperatures. Together, my dissertation illustrates how disturbances, clutch size, and ambient temperature can influence an important aspect of avian parental care, which has wide-ranging effects on offspring traits and fitness. This has broad implications for understanding the evolution of clutch size, development of behavior, and the effects of anthropogenic changes on wildlife.
  • Thumbnail Image
    Development and testing of recombinant B. abortus RB51 vaccine strains carrying M. tuberculosis protective antigens
    Al Qublan, Hamzeh (Virginia Tech, 2015-06-23)
    Tuberculosis, caused by Mycobacterium tuberculosis, is one of the most prevalent infectious diseases inflicting humankind. The World Health Organization estimates that one third of the world's population, approximately 2.2 billion people, is infected with TB with a mortality of 1.7 million people annually. Currently, the WHO estimates that each year more than 9 million people develop TB. Bacille Calmette-Guérin (BCG), an attenuated strain of M. bovis, is the only licensed TB vaccine in the world. Clinical studies have shown childhood vaccination with BCG to be protective against disseminating and meningeal forms of TB. However, the efficacy of BCG against pulmonary TB in adults has been variable and inconsistent (0-80%). The objective of this study is to develop and test the efficacy of the B. abortus vaccine strain RB51 as a platform for expression of M. tuberculosis antigens (Ag85B, ESAT6 and Rv2660c) and induction of a protective immune response against M. tuberculosis and B. abortus challenge in mice. Here we report the construction of two recombinant strains of B. abortus vaccine strain RB51 capable of expressing mycobacterial antigens Ag85B, ESAT6 and Rv2660c. Our studies show that expression of mycobacterial antigens in strain RB51 lead to induction of antigen-specific immune responses characterized by secretion of IgG2a antibodies as well as of IFN- and TNF-α. Mice immunized with a combination of two strains of RB51 in equal numbers, one carrying Rv2660c-ESAT6 and another carrying Ag85B, led to a 0.90 log reduction in CFU burden with significance nearly reaching borderline (p = 0.052). However, when mice were primed with the same strains of RB51 and boosted with proteins Ag85B and ESAT6, a significant level of protection (1 log reduction) compared to the PBS vaccinated group was achieved. The protection levels conferred by this vaccination strategy was similar to that conferred by BCG vaccine. In conclusion, we have shown that recombinant RB51 strains expressing mycobacterial protective antigens result in stimulation of antigen specific immune response without altering the vaccine efficacy in protecting against the more virulent strain of B. abortus 2308. These recombinant vaccines could potentially be used to protect against M. tuberculosis infection.
  • Thumbnail Image
    Disaggregating Within-Person and Between-Person Effects in the Presence of Linear Time Trends in Time-Varying Predictors: Structural Equation Modeling Approach
    Hori, Kazuki (Virginia Tech, 2021-06-01)
    Educational researchers are often interested in phenomena that unfold over time within a person and at the same time, relationships between their characteristics that are stable over time. Since variables in a longitudinal study reflect both within- and between-person effects, researchers need to disaggregate them to understand the phenomenon of interest correctly. Although the person-mean centering technique has been believed as the gold standard of the disaggregation method, recent studies found that the centering did not work when there was a trend in the predictor. Hence, they proposed some detrending techniques to remove the systematic change; however, they were only applicable to multilevel models. Therefore, this dissertation develops novel detrending methods based on structural equation modeling (SEM). It also establishes the links between centering and detrending by reviewing a broad range of literature. The proposed SEM-based detrending methods are compared to the existing centering and detrending methods through a series of Monte Carlo simulations. The results indicate that (a) model misspecification for the time-varying predictors or outcomes leads to large bias of and standard error, (b) statistical properties of estimates of the within- and between-person effects are mostly determined by the type of between-person predictors (i.e., observed or latent), and (c) for unbiased estimation of the effects, models with latent between-person predictors require nonzero growth factor variances, while those with observed predictors at the between level need either nonzero or zero variance, depending on the parameter. As concluding remarks, some practical recommendations are provided based on the findings of the present study.
  • Thumbnail Image
    Discovery of Novel Strains of Animal Hepatitis E Viruses in the United States: Antigenic and Genetic Characterization, Cross-Species Infection, and Public Health Implications
    Cossaboom, Caitlin Marie (Virginia Tech, 2015-03-17)
    Hepatitis E virus (HEV) is an important human pathogen, with pigs and likely other animal species serving as natural reservoirs. There are currently four recognized HEV genotypes that infect humans within the genus Hepevirus of the family Hepeviridae. Genotypes 1 and 2 are human viruses that are associated with waterborne and fecal-oral transmission in developing countries, while genotypes 3 and 4 have been identified in humans and other animal species and are zoonotic and endemic in both industrialized and developing countries. In my dissertation research, we identified the first strain of HEV from rabbits in the United States. We subsequently determined the complete genome sequence of the virus. Phylogenetic analyses of the full-length sequence indicated that U.S. rabbit HEV is a distant member of the zoonotic genotype 3, thus raising a potential concern for zoonotic infection. In order to investigate the cross-species potential of rabbit HEV, we then determined its antigenic cross-reactivity with other animal strains of HEV. Additionally, we demonstrated that the novel rabbit HEV could cross species barriers and infect pigs under experimental conditions. Finally, we attempted to determine the risk factors and sources of foodborne HEV infection in the United States. We detected HEV for the first time from non-liver pork commercial products in the United States and demonstrated consumption of undercooked meat a risk factor for HEV infection. HEV sequences of genotype 3 origin were detected from pork products purchased from grocery stores in Southwest Virginia. Approximately 6.3% (21/335) of university students tested seropositive for HEV antibodies and, importantly, those with a history of consuming undercooked meats were 13 times more likely to be seropositive. These results further underscore the importance of cooking pork thoroughly and using proper hygiene when preparing meals.
  • Thumbnail Image
    Distributed Machine Learning for Autonomous and Secure Cyber-physical Systems
    Ferdowsi Khosrowshahi, Aidin (Virginia Tech, 2020-07-31)
    Autonomous cyber-physical systems (CPSs) such as autonomous connected vehicles (ACVs), unmanned aerial vehicles (UAVs), critical infrastructure (CI), and the Internet of Things (IoT) will be essential to the functioning of our modern economies and societies. Therefore, maintaining the autonomy of CPSs as well as their stability, robustness, and security (SRS) in face of exogenous and disruptive events is a critical challenge. In particular, it is crucial for CPSs to be able to not only operate optimally in the vicinity of a normal state but to also be robust and secure so as to withstand potential failures, malfunctions, and intentional attacks. However, to evaluate and improve the SRS of CPSs one must overcome many technical challenges such as the unpredictable behavior of a CPS's cyber-physical environment, the vulnerability to various disruptive events, and the interdependency between CPSs. The primary goal of this dissertation is, thus, to develop novel foundational analytical tools, that weave together notions from machine learning, game theory, and control theory, in order to study, analyze, and optimize SRS of autonomous CPSs. Towards achieving this overarching goal, this dissertation led to several major contributions. First, a comprehensive control and learning framework was proposed to thwart cyber and physical attacks on ACV networks. This framework brings together new ideas from optimal control and reinforcement learning (RL) to derive a new optimal safe controller for ACVs in order to maximize the street traffic flow while minimizing the risk of accidents. Simulation results show that the proposed optimal safe controller outperforms the current state of the art controllers by maximizing the robustness of ACVs to physical attacks. Furthermore, using techniques from convex optimization and deep RL a joint trajectory and scheduling policy is proposed in UAV-assisted networks that aims at maintaining the freshness of ground node data at the UAV. The analytical and simulation results show that the proposed policy can outperform policies such discretized state RL and value-based methods in terms of maximizing the freshness of data. Second, in the IoT domain, a novel watermarking algorithm, based on long short term memory cells, is proposed for dynamic authentication of IoT signals. The proposed watermarking algorithm is coupled with a game-theoretic framework so as to enable efficient authentication in massive IoT systems. Simulation results show that using our approach, IoT messages can be transmitted from IoT devices with an almost 100% reliability. Next, a brainstorming generative adversarial network (BGAN) framework is proposed. It is shown that this framework can learn to generate real-looking data in a distributed fashion while preserving the privacy of agents (e.g. IoT devices, ACVs, etc). The analytical and simulation results show that the proposed BGAN architecture allows heterogeneous neural network designs for agents, works without reliance on a central controller, and has a lower communication over head compared to other state-of-the-art distributed architectures. Last, but not least, the SRS challenges of interdependent CI (ICI) are addressed. Novel game-theoretic frameworks are proposed that allow the ICI administrator to assign different protection levels on ICI components to maximizing the expected ICI security. The mixed-strategy Nash of the games are derived analytically. Simulation results coupled with theoretical analysis show that, using the proposed games, the administrator can maximize the security level in ICI components. In summary, this dissertation provided major contributions across the areas of CPSs, machine learning, game theory, and control theory with the goal of ensuring SRS across various domains such as autonomous vehicle networks, IoT systems, and ICIs. The proposed approaches provide the necessary fundamentals that can lay the foundations of SRS in CPSs and pave the way toward the practical deployment of autonomous CPSs and applications.
  • Thumbnail Image
    Equilibria of a Gyrostat with a Discrete Damper
    Sandfry, Ralph Anthony (Virginia Tech, 2001-07-09)
    We investigate the relative equilibria of a gyrostat with a spring-mass-dashpot damper to gain new insights into the dynamics of spin-stabilized satellites. The equations of motion are developed using a Newton-Euler approach, resulting in equations in terms of system momenta and damper variables. Linear and nonlinear stability methods produce stability conditions for simple spins about the nominal principal axes. We use analytical and numerical methods to explore system equilibria, including the bifurcations that occur for varying system parameters for varying rotor momentum and damper parameters. The equations and bifurcations for zero rotor absolute angular momentum are identical to those for a rigid body with an identical damper. For the more general case of non-zero rotor momentum, the bifurcations are complex structures that are perturbations of the zero rotor momentum case. We examine the effects of spring stiffness, damper position, and inertia properties on the global equilibria. Stable equilibria exist for many different spin axes, including some that do not lie in the nominally principal planes. Some bifurcations identify regions where a jump phenomenon is possible. We use Liapunov-Schmidt reduction to determine an analytic relationship between parameters to determine if the jump phenomenon occurs. Bifurcations of the nominal gyrostat spin are characterized in parameter space using two-parameter continuation and the Liapunov-Schmidt reduction technique. We quantify the effects of rotor or damper alignment errors by adding small displacements to the alignment vectors, resulting in perturbations of the bifurcations for the standard model. We apply the global bifurcation results to several practical applications. We relate the general set of all possible equilibria to specific equilibria for dual-spin satellites with typical parameters. For systems with tuned dampers, where the natural frequency of the spring-mass-damper matches the gyrostat precession frequency, we show numerically and analytically that the existence of certain equilibria are related to the damper tuning condition. Finally, the global equilibria and bifurcations for varying rotor momentum provide a unique perspective on the dynamics of simple rotor spin-up maneuvers.
  • Thumbnail Image
    Evaluating System Performance in a Complex and Dynamic Environment
    Vaneman, Warren Kenneth (Virginia Tech, 2002-12-04)
    Realistically, organizational and/or system efficiency performance is dynamic, non-linear, and a function of multiple interactions in production. However, in the efficiency literature, system performance is frequently evaluated considering linear combinations of the input/output variables, without explicitly taking into account the interactions and feedback mechanisms that explain the causes of efficiency behavior, the dynamic nature of production, and non-linear combinations of the input/output variables. Consequently, policy decisions based on these results may be sub-optimized because the non-linear relationships among variables, causal relationships, and feedback mechanisms are ignored. This research takes the initial steps of evaluating system efficiency performance in a dynamic environment, by relating the factors that effect system efficiency performance to the policies that govern it. First, this research extends the concepts of the static production axioms into a dynamic realm, where inputs are not instantaneously converted into outputs. The relationships of these new dynamic production axioms to the basic behaviors associated with system dynamics structures are explored. Second, this research introduces a methodological approach that combines system dynamics modeling with the measurement of productive efficiency. System dynamics is a modeling paradigm that evaluates system policies by exploring the causal relationships of the important elements within the system. This paradigm is coupled with the fundamental assumptions of production theory in order to evaluate the productive efficiency of a production system operating within a dynamic and non-linear environment. As a result, a subsystem within the system dynamics model is introduced that computes efficiency scores based on the fundamental notions of productive efficiency. The framework's ability to combine prescriptive and descriptive modeling characteristics, as well as dynamic and combinatorial complexity, can potentially have a greater impact on policy decisions and how they affect system efficiency performance. Finally, the utility of these concepts is demonstrated in an implementation case study. This methodology generates a prescriptive dynamical production frontier which defines the optimal production resources required to satisfy system requirements. Additionally, the dynamical production frontier allows for analysis for comparisons between options during a transient period, insight into possible unintended consequences, and the ability to forecast optimal times for introducing system or process improvements.
  • Thumbnail Image
    The Formation of Cultural Capital using Symbolic Military Meanings of Objects and Self in an Adult Agricultural Education Program serving Military Veterans
    Kyle, Crystal Anne (Virginia Tech, 2018-10-04)
    The purpose of this qualitative ethnographic case study was to investigate how an adult agricultural educational program generates new learning spaces for military veterans. Utilizing Symbolic Interactionism and Cultural Capital Theories this study illustrates how military veterans use and making new meanings of military symbols in an agricultural educational context. After leaving their military service, veterans often discharge with not only the physical scars of battle, but sometimes harboring mental and emotional distress that can prevent their abilities to successfully reintegrate into a civilian setting. For several veterans, adult agricultural programs can provide a vital educational experience to help them address physical and mental challenges, launch a new career in agriculture, and form new civilian identities. Findings from this research indicate that participants of this study transformation of a civilian identity is positively impacted when familiar symbols of the military are used in the implementation of agriculture education and that these symbols then take on new meanings supporting Blumer (1969) Symbolic Interactionism Theory. Further, mutually beneficial experiences occurred between veterans and community members, allowing for the veteran to build positive connection with civilians and move up in civilian society. This supports the concept of Pierre Bourdieu (1986) Cultural Capital Theory. Further, these finding show that military veterans are employing this adult agricultural education program to transform their cultural identity and re-assign symbolic military meanings of objects and self. They connect with familiar military constructed language, behaviors, and physical symbolism to represent their identity, during and after their service. For them, it is important to be able to express their military identity to civilians and other veterans. It is also, vital for them to participate and express their military identities through symbolic military behaviors. This military symbolism is critical to their ability to socialize with others, acquire a civilian identity, and navigate social mobility. When the use of symbolism is not applied, or is not recognized by civilians, it influences their civilian identity and for some, creates transition challenges and challenges to their connection to civilian population.
  • Thumbnail Image
    Gender, Politics, and Radioactivity Research in Vienna, 1910-1938
    Rentetzi, Maria (Virginia Tech, 2003-03-25)
    What could it mean to be a physicist specialized in radioactivity in the early 20th century Vienna? More specifically, what could it mean to be a woman experimenter in radioactivity during that time? This dissertation focuses on the lived experiences of the women experimenters of the Institut für Radiumforschung in Vienna between 1910 and 1938. As one of three leading European Institutes specializing in radioactivity, the Institute had a very strong staff. At a time when there were few women in physics, one third of the Institute's researchers were women. Furthermore, they were not just technicians but were independent researchers who published at about the same rate as their male colleagues. This study accounts for the exceptional constellation of factors that contributed to the unique position of women in Vienna as active experimenters. Three main threads structure this study. One is the role of the civic culture of Vienna and the spatial arrangements specific to the Mediziner-Viertel in establishing the context of the intellectual work of the physicists. A second concerns the ways the Institute's architecture helped to define the scientific activity in its laboratories and to establish the gendered identities of the physicists it housed. The third examines how the social conditions of the Institute influenced the deployment of instrumentation and experimental procedures especially during the Cambridge-Vienna controversy of the 1920s. These threads are unified by their relation to the changing political context during the three contrasting periods in which the story unfolds: a) from the end of the 19th century to the end of the First World War, when new movements, including feminism, Social Democracy, and Christian Socialism, shaped the Viennese political scene, b) the period of Red Vienna, 1919 to 1934, when Social Democrats had control of the City of Vienna, and c) the period from 1934 to the Anschluss in 1938, during which fascists and Nazis seized power in Austria. As I show, the careers of the Institute's women were shaped in good part by the shifting meanings, and the politics, that attached to being a "woman experimenter" in Vienna from 1910 to the beginning of the Second World War.
  • Thumbnail Image
    Identification and Characterization of Y Chromosome and M Locus Genes in Anopheles and Aedes Mosquitoes Using the Chromosome Quotient Method
    Hall, Andrew Brantley (Virginia Tech, 2016-03-22)
    In mosquitoes, sex determination is initiated by a dominant male-determining factor located on the Y chromosome in Anopheles mosquitoes or in a small Y-like region called the M locus in Aedes mosquitoes. Before my research, not a single gene from the Anopheles Y or Aedes M locus had ever been discovered. During the course of my undergraduate research in the Tu lab, I developed the chromosome quotient (CQ) method which identifies Y chromosome/M locus sequences by comparing the ratio of alignments from separate pools of female and male Illumina sequencing data. The focus of my dissertation is using the CQ method to identify potential male-determining factors in Aedes and Anopheles mosquitoes. First, we identified a novel gene tightly-linked to the M locus in Aedes aegypti called myo-sex. Myo-sex encodes a myosin heavy chain protein that is highly expressed in the pupa and adult male. Myo-sex is generally only found in males, but can sporadically be found in females due to a rare recombination. The fact that myo-sex can be found in females combined with a lack of early-embryonic expression suggests that myo-sex is not the male-determining factor. Next, we identified a gene in Aedes aegypti, Nix, which appeared to be persistently linked to the M locus and was expressed in the early embryo. Nix shows distant similarity at the amino acid level to Transformer2, a gene involved in the sex determination pathway of Drosophila melanogaster. Nix knockout with CRISPR/Cas9 resulted in feminization of genetic males and the production of the female isoforms of doublesex and fruitless, two key regulators of downstream sexual differentiation. Ectopic expression of Nix resulted in masculinization of genetic females. Based on these results, we concluded that Nix is a male-determining factor in Aedes aegypti. We also characterized large portions of the Anopheles gambiae Y chromosome using PacBio sequencing and the CQ method. We discovered that 92.3 percent of predicted Y sequences fell into two classes, the zanzibar amplified region (ZAR) and the satellite amplified region (SAR). This analysis fills in a large piece of the Anopheles gambiae genome missing since 2002.