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.
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Item MODELING ADAPTABILITY MECHANISMS OF SPEECH PERCEPTION Nika Jurov(2024) Jurov, Nika; Feldman, Naomi H.; Idsardi, William; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Speech is a complex, redundant and variable signal happening in a noisy and ever changing world. How do listeners navigate these complex auditory scenes and continuously and effortlessly understand most of the speakers around them? Studies show that listeners can quickly adapt to new situations, accents and even to distorted speech. Although prior research has established that listeners rely more on some speech cues (or also called features or dimensions) than others, it is yet not understood how listeners weight them flexibly on a moment-to-moment basis when the input might deviate from the standard speech. This thesis computationally explores flexible cue re-weighting as an adaptation mechanism using real speech corpora. The computational framework it relies on is rate distortion theory. This framework models a channel that is optimized on a trade off between distortion and rate: on the one hand, the input signal should be reconstructed with minimal error after it goes through the channel. On the other hand, the channel needs to extract parsimonious information from the incoming data. This channel can be implemented as a neural network with a beta variational auto-encoder. We use this model to show that two mechanistic components are needed for adaptation: focus and switch. We firstly show that focus on a cue mimics humans better than cue weights that simply depend on long term statistics as has been largely assumed in the prior research. And second, we show a new model that can quickly adapt and switch weighting the features depending on the input of a particular moment. This model's flexibility comes from implementing a cognitive mechanism that has been called ``selective attention" with multiple encoders. Each encoder serves as a focus on a different part of the signal. We can then choose how much to rely on each focus depending on the moment. Finally, we ask whether cue weighting is informed by being able to separate the noise from speech. To this end we adapt a feature disentanglement adversarial training from vision to disentangle speech (noise) features from noise (speech) labels. We show that although this does not give us human-like cue weighting behavior, there is an effect of disentanglement of weighting spectral information slightly more than temporal information compared to the baselines. Overall, this thesis explores adaptation computationally and offers a possible mechanistic explanation for ``selective attention'' with focus and switch mechanisms, based on rate distortion theory. It also argues that cue weighting cannot be determined solely on speech carefully articulated in laboratories or in quiet. Lastly, it explores a way to inform speech models from a cognitive angle to make the models more flexible and robust, like human speech perception is.Item MANAGEMENT OPTIONS FOR FARMERS FACING SALTWATER INTRUSION ON THE EASTERN SHORE OF THE CHESAPEAKE BAY(2023) Schulenburg, Alison Nicole; Tully, Kate; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rising sea levels, storms, and perigean spring tides push saltwater into coastal agricultural fields. This phenomenon, known as saltwater intrusion, alters nutrient cycling and damages crop yields. As sea levels continue to rise, saltwater intrusion will only worsen, with devastating consequences to agroecosystems along the coast of the Chesapeake Bay. Researchers and farmers alike are looking for solutions to adapt to and mitigate the effects of saltwater intrusion. Landowners may respond by altering their management practices. Farmers may 1) adapt by planting a salt-tolerant crop, 2) attempt to remediate soils with trap crops, 3) restore native marsh grasses, or 4) abandon fields altogether. My project investigates the survival of different crops and plant treatments under saltwater-intruded conditions and the potential for these plants to survive and to remove excess nutrients (e.g. sodium and phosphorus) from the soil, with the overall goal to benefit both the farming community and water quality in the Chesapeake Bay. Results from this study will help inform new management practices to increase soil health and maintain crop yields. Finally, the goal of this work is to guide local best management practices and potential easement opportunities for landowners facing saltwater intrusion, and ultimately determine optimal strategies for climate resilience.Item Acknowledging Survival: Political Recognition and Indigenous Climate Adaptation in the United States(2021) Cottrell, Clifton; Bierbaum, Rosina; Sprinkle, Robert; Public Policy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Indigenous peoples in the United States are already disproportionately experiencing the impacts of climate change. Closely related to tribal efforts to manage climate effects are historical endeavors to assert indigenous sovereignty and govern tribal lands, but deficiencies in the process used by the U.S. government to acknowledge tribal sovereignty have left hundreds of indigenous communities unrecognized and especially vulnerable to climate harm. My dissertation aims to determine whether a tribe’s recognition status affects its capacity for climate adaptation. To make this determination, I utilize a case study methodology wherein I analyze the circumstances of one non-federally recognized tribe, the Burt Lake Band of Ottawa and Chippewa Indians, in three critical areas related to adaptation and tribal recognition — access to key species and cultural resources, utilization of federal funding opportunities, and participation in climate decision-making. Tribal access to resources is often predicated by historical treaty rights, so I applied a theme identification technique to extrapolate important strategies on easing barriers to resource access and regulatory authority. I then used the themes to compare the likelihood of the Burt Lake Band and nearby federally recognized tribes to maintain connections to key species in the future. I next employed a comparative statutory analysis methodology to differentiate eligibility for non-federally recognized tribes accessing federal funding. I also assessed tribal climate adaptation plans and interviewed tribal climate plan managers on the barriers to successful implementation of adaptation actions. Finally, I developed criteria from a review of global literature on the inclusion of indigenous peoples in adaptation projects to assess participatory opportunities for the Burt Lake Band in state and regional climate governance. My findings show that the Band’s lack of federal recognition inhibits its adaptive capacity to access key cultural resources, federal funding, and climate governance opportunities. However, I also conclude that state and local perceptions of tribal identity could have a greater influence on the adaptation of non-federally recognized tribes, so I recommend that a more inclusive federal recognition system be implemented to avoid the unequal development of indigenous adaptive capacity based on disparate approaches to indigenous affairs by state and local jurisdictions.Item What makes a successful invader? Population genomics and adaptation to novel environments in the invasive Japanese white-eye (Zosterops japonicus)(2021) Venkatraman, Madhvi; Gruner, Daniel S; Fleischer, Robert C; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Invasive species face many obstacles when colonizing new habitats. Yet, many overcome these hurdles and successfully establish populations. Therefore, understanding how invasive species cope with novel stressors while colonizing new environments is a fundamental goal of evolutionary biology. Additionally, broadening our understanding of how birds adapt to novel environments can help us predict how species will respond to habitat degradation and stressors resulting from climate change in the future. Here, we focus on the Japanese white-eye (Zosterops japonicus), an East Asian bird that was introduced into Hawaii in the early 1900s and is now the most abundant land bird in the archipelago. First, we sequenced and assembled a high-quality Z. japonicus genome and compared genome annotation pipelines. We found that AUGUSTUS was more conservative with gene predictions when compared to BRAKER2, but the final number of annotated gene models was similar between the two workflows. Additionally, we found that while adding more data did not significantly change the number of annotated genes using AUGUSTUS, using BRAKER2 the number increased substantially. Next, we compared whole genomes of Z. japonicus individuals from both their native and introduced ranges to characterize genetic diversity and population history and divergence and to identify genes potentially under selection between the two populations. We saw evidence of mixed ancestry in the introduced population, supported by drastically different demographic histories in Hawaii. This suggests that admixture could have contributed to increased genetic diversity in the introduced population and therefore to overall invasion success. Lastly, we conducted one-, three-, and six-week one-way transplants of individuals from near sea level to 2,790m, with individuals kept at sea level as controls, and later a six-week reciprocal transplant from high to low elevation and vice versa. We assessed morphological and physiological traits as well as gene expression using RNA-seq on heart and lung tissues. We found strong evidence for phenotypic plasticity in hematological and cardiac response to hypoxia and cold stress and some evidence of maladaptive plasticity in pulmonary circulation. We identified two genes potentially under divergent selection in the high elevation population that could be indicative of early-stage genotypic specialization in response to hypoxia and cold stress. Our results suggest that the population of Z. japonicus on Mauna Kea is able to persist at high elevation because of ancestral plasticity, which also could have contributed to its remarkable success as an invasive species.Item Runtime Adaptation in Embedded Computing Systems using Markov Decision Processes(2019) Sapio, Adrian; Bhattacharyya, Shuvra S; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)During the design and implementation of embedded computing systems (ECSs), engineers must make assumptions on how the system will be used after being built and deployed. Traditionally, these important decisions were made at design time for a fleet of ECSs prior to deployment. In contrast to this approach, this research explores and develops techniques to enable adaptation of ECSs at runtime to the environments and applications in which they operate. Adaptation is enabled such that the usage assumptions and performance optimization decisions can be made autonomously at runtime in the deployed system. This thesis utilizes Markov Decision Processes (MDPs), a powerful and well established mathematical framework used for decision making under uncertainty, to control computing systems at runtime. The resulting control is performed in ways that are more dynamic, robust and adaptable than alternatives in many scenarios. The techniques developed in this thesis are first applied to a reconfigurable embedded digital signal processing system. In this effort, several challenges are encountered and resolved using novel approaches. Through extensive simulations and a prototype implementation, the robustness of the adaptation is demonstrated in comparison with the prior state-of-the-art. The thesis continues by developing an efficient algorithm for conversion of MDP models to actionable control policies - a required step known as solving the MDP. The solver algorithm is developed in the context of ECSs that contain general purpose embedded GPUs (graphics processing units). The novel solver algorithm, Sparse Parallel Value Iteration (SPVI), makes use of the parallel processing capabilities provided by such GPUs, and also exploits the sparsity that typically exists in MDPs when used to model and control ECSs. To extend the applicability of the runtime adaptation techniques to smaller and more strictly resource constrained ECSs, another solver - Sparse Value Iteration (SVI) is developed for use on microcontrollers. The method is explored in a detailed case study involving a cellular (LTE-M) connected sensor that adapts to varying communications profiles. The case study reveals that the proposed adaptation framework outperforms a competing approach based on Reinforcement Learning (RL) in terms of robustness and adaptation, while consuming comparable resource requirements. Finally, the thesis concludes by analyzing the various logistical challenges that exist when deploying MDPs on ECSs. In response to these challenges, the thesis contributes an open source software package to the engineering community. The package contains libraries of MDP solvers, parsers, datasets and reference solutions, which provide a comprehensive infrastructure for exploring the trade-offs among existing embedded MDP techniques, and experimenting with novel approaches.Item Institutions, Poverty, and Tropical Cyclone Mortality(2019) Tennant, Elizabeth; Patwardhan, Anand; Public Policy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tropical cyclones can result in thousands of deaths when the exposed population is unprepared or ill-equipped to cope with the hazard. Evaluating the importance of institutions and socioeconomic conditions for these deaths is challenging due to the extreme variability in hazard exposure. Studies of socioeconomic risk factors that do not account for exposure will be imprecise and possibly biased, as a storm’s path and intensity are important determinants of mortality and may be correlated with socioeconomic conditions. I therefore model and then control for hazard exposure by spatially interacting meteorological and socioeconomic data, allowing me to develop novel evidence of socioeconomic risk factors. In essay 1, I construct a global dataset of over one thousand tropical cyclone events occurring between 1979 and 2016. Controlling for population exposure to strong winds and rainfall, I find that higher levels of national government effectiveness are associated with lower tropical cyclone mortality. Further, deaths are higher when exposure is concentrated over a subset of the population that is already less well off. In essay 2, I investigate whether local government capacity and poverty alleviation can reduce tropical cyclone deaths, using panel data from 78 provinces and 1,426 municipalities in the Philippines. Tropical cyclone exposure is concentrated in wealthier regions of the Philippines, but once wind exposure and rainfall are controlled for I find robust evidence of a link between local poverty rates and cyclone deaths. In essay 3, I investigate the potential for leveraging policy experiments for causal inference about the effects of development interventions on disaster mortality using an existing randomized control trial in the Philippines. This empirical example illustrates how randomization overcomes issues of multicollinearity and omitted variable bias; however, the presence of outliers in exposure and vulnerability to natural hazards interact to make average treatment effect estimates highly imprecise. Strong evidence of an association between government effectiveness and cyclone deaths suggests that capacity constraints need to be addressed in tandem with risk-specific strategies and financial transfers. Further, evidence that local poverty rates and socioeconomic conditions matter highlights the need for equitable and inclusive approaches to mitigating the risk from tropical cyclones.Item ‘THE LIFE YET OF HIS LINES SHALL NEVER OUT’: LINEATION AND POETIC AUTHORITY IN THE SHAKESPEAREAN CORPUS(2019) Lind, Sarah; Trudell, Scott A.; English Language and Literature; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The “line” in early modern poetics was a confusing concept due to competing definitions of line length. “Length” could refer to classical, vernacular, or visual measurement. “Length” could figuratively refer to a poet’s “line of life” where a lasting reputation was a measure of a poet’s authority, conflated with the length and measure of his or her lines. Despite the cultural importance of the line, studies of lineation are rare, and few account for the line’s assembly of definitions and vital relationship to poetic authority. This thesis therefore offers an account of lineation and the poetic authority surrounding lineation in editorial and performance traditions. It examines changes to lines in playtexts, songs, and actors’ parts through the seventeenth- and eighteenth-century Shakespearean tradition. It argues that changes in ideas about lineation are both signs and consequences of the continual struggle to adapt Shakespeare’s plays to different performative and textual purposes.Item Integrating Environmental Justice and Social-Ecological Resilience for Successful Adaptation to Climate Change: Lessons from African American Communities on the Eastern Shore of the Chesapeake Bay(2016) Hesed, Christine Danielle Miller; Paolisso, Michael; Anthropology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This research concerns the conceptual and empirical relationship between environmental justice and social-ecological resilience as it relates to climate change vulnerability and adaptation. Two primary questions guided this work. First, what is the level of resilience and adaptive capacity for social-ecological systems that are characterized by environmental injustice in the face of climate change? And second, what is the role of an environmental justice approach in developing adaptation policies that will promote social-ecological resilience? These questions were investigated in three African American communities that are particularly vulnerable to flooding from sea-level rise on the Eastern Shore of the Chesapeake Bay. Using qualitative and quantitative methods, I found that in all three communities, religious faith and the church, rootedness in the landscape, and race relations were highly salient to community experience. The degree to which these common aspects of the communities have imparted adaptive capacity has changed over time. Importantly, a given social-ecological factor does not have the same effect on vulnerability in all communities; however, in all communities political isolation decreases adaptive capacity and increases vulnerability. This political isolation is at least partly due to procedural injustice, which occurs for a number of interrelated reasons. This research further revealed that while all stakeholders (policymakers, environmentalists, and African American community members) generally agree that justice needs to be increased on the Eastern Shore, stakeholder groups disagree about what a justice approach to adaptation would look like. When brought together at a workshop, however, these stakeholders were able to identify numerous challenges and opportunities for increasing justice. Resilience was assessed by the presence of four resilience factors: living with uncertainty, nurturing diversity, combining different types of knowledge, and creating opportunities for self-organization. Overall, these communities seem to have low resilience; however, there is potential for resilience to increase. Finally, I argue that the use of resilience theory for environmental justice communities is limited by the great breadth and depth of knowledge required to evaluate the state of the social-ecological system, the complexities of simultaneously promoting resilience at both the regional and local scale, and the lack of attention to issues of justice.Item Essays on Climate Change Impacts and Adaptation for Agriculture(2013) Ortiz Bobea, Ariel; Just, Richard E; Agricultural and Resource Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Over the past twenty years economists have developed econometric approaches for estimating the impacts of climate change on agriculture by accounting for farmer adaptation implicitly. These reduced-form approaches are simple to implement but provide little insights into impact mechanisms, limiting their usefulness for adaptation policy. Recently, conflicting estimates for US agriculture have led to research with greater emphasis on mechanisms including renewed interest in statistical crop yield models. Findings suggest US agriculture will be mainly and severely affected by an increased frequency of high temperatures with crop yield suggested as a major driver. This dissertation is comprised of three essays highlighting methodological aspects in this literature. It contributes to the ongoing debate and shows the preeminent role of extreme temperature is overestimated while the role of soil moisture is seriously underestimated. This stems from issues related to weather data quality, the presence of time-varying omitted weather variables, as well as from modeling assumptions that inadvertently underestimate farmers' ability to adapt to seasonal aspects of climate change. My work illustrates how econometric models of climate change impacts on crop production can be improved by structuring them to admit some basic principles of agronomic science. The first essay shows that nonlinear temperature effects on corn yields are not robust to alternative weather datasets. The leading econometric studies in the current literature are based on a weather dataset that involves considerable interpolation. I introduce the use of a new dataset to agricultural climate change research that has been carefully developed with scientific methods to represent weather variation with one-hour and 14 kilometer accuracy. Detrimental effects of extreme temperature crucially hinge upon the recorded frequency at the highest temperatures. My research suggests that measurement error in short amounts of time spent at extreme temperature levels has disproportionate effects on estimated parameters associated with the right tail of the temperature distribution. My alternative dataset suggests detrimental temperature effects of climate change over the next 50-100 years will be half as much as in leading econometric studies in the current literature. The second essay relaxes the prevalent assumption in the literature that weather is additive. This has been the practice in most empirical models. Weather regressors are typically aggregated over the months that include the growing season. Using a simple model I show that this assumption imposes implausible characteristics on the technology. I test this assumption empirically using a crop yield model for US corn that accounts for differences in intra-day temperature variation in different stages of the growing season. Results strongly reject additivity and suggest that weather shocks such as extreme temperatures are particularly detrimental toward the middle of the season around flowering time, which corrects a disagreement of empirical yield models with the natural sciences. I discuss how this assumption tends to underestimate the range of adaptation possibilities available to farmers, thus overstating projected climate change impacts on the sector. The third essay introduces an improved measure of water availability for crops that accounts for time variation of soil moisture rather than season-long rainfall totals, as has been common practice in the literature. Leading studies in the literature are based on season-long rainfall. My alternative dataset based on scientific models that track soil moisture variation during the growing season includes variables that are more relevant for tracking crop development. Results show that models in the literature attribute too much variation in yields to temperature variation because rainfall variables are a crude and inaccurate measure of the moisture that determined crop growth. Consequently, I find that third of damages to corn yields previously attributed to extreme temperature are explained by drought, which is far more consistent with agronomic science. This highlights the potential adaptive role for water management in addressing climate change, unlike the literature now suggests. The fourth essay proposes a general structural framework for analyzing the mechanisms of climate change impacts on the sector. An empirical example incorporates some of the flexibilities highlighted in the previous essay to assess how farmer adaptation can reduce projected impacts on corn yields substantially. Global warming increases the length of the growing season in northern states. This gives farmers the flexibility to change planting dates that can reduce exposure of crops during the most sensitive flowering stage of the crop growth cycle. These research results identify another important type of farmer adaptation that can reduce vulnerability to climate change, which has been overlooked in the literature but which becomes evident only by incorporating the principles of agronomic science into econometric modeling of climate change impact analysis.Item "Coffee & Biscuit": A Variation on Henrik Ibsen's "A Doll's House"(2013) Bayer, Teresa Ann; Felbain, Leslie; Theatre; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Artistic adaptation is most often defined as the process of transporting or transforming a particular work of theatre to a different location, time period, or situation. This choice allows a play to be seen and understood in a new light, illuminating particular themes or ideas inherent to the script or story. Coffee & Biscuit is a 1950's Technicolor variation on Henrik Ibsen's A Doll's House in which we see Nora Helmer's perfect world of Hoovers and Jell-O molds topple around her. This darkly whimsical romp, featuring both puppets and live actors, is an adaptation that examines how a contemporary theatre audience can be provoked to question the gender roles constructed by society and the media.