Theses and Dissertations from UMD
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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 give thesis/dissertation in DRUM
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Item MOSQUITOES AND VEGETATION ACROSS SOCIOECONOMIC GRADIENTS(2024) Rothman, Sarah; Leisnham, Paul T; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The biomass and composition of local vegetation is a key resource for juvenile mosquitoes, affecting a suite of life history traits including survival, development rate, and body size. In cities across the United States, both plant and mosquito communities vary with socioeconomics. Vegetation is typically more abundant and biodiverse in high-income neighborhoods, whereas mosquitoes are often more numerous and more likely to vector diseases in low-income neighborhoods. While prior work has examined the effects of plant resources on mosquitoes, my dissertation evaluates how these communities interact across a socioeconomically diverse urban landscape. Chapter 1 is a scoping review of current knowledge of the individual relationships between mosquitoes, plants, and socioeconomics in cities. In Chapter 2, I describe fine-scale vegetation surveys on socioeconomically diverse residential properties in Baltimore, MD and Washington, D.C. that revealed less canopy cover, more vines, and more non-native plant species on lower-income blocks. In Chapter 3, I used leaves from the most frequently observed canopy species on low- and high-income blocks, and species common to both, as detrital resource bases in competition trials between two dominant urban mosquitoes, Aedes albopictus and Culex pipiens. Population performance for both species was greater when reared with characteristically low-income than characteristically high-income detritus, suggesting that socioeconomically diverse plant communities are an important factor in shaping urban mosquito communities. Overall, population performances were greatest when mosquitoes were reared in the regionally representative detritus, and I used this detritus base in Chapter 4 to evaluate the effects of varying temperatures. Aedes albopictus population performance was optimized at higher mean temperatures characteristic of low-income blocks, while C. pipiens performance was best at lower mean temperatures characteristic of high-income blocks. Population performance was often lower, however, when temperatures fluctuated around a high or low mean than when the temperature was stable, suggesting that laboratory studies may need to mimic field conditions to obtain applicable results. My research provides a deeper understanding of the mechanisms behind previously observed relationships, and may help guide management and policy strategies to address environmental injustices and public health threats.Item ADVERSE EFFECTS OF COMPETITION WITH COWORKERS: THE ROLE OF THIRD-PARTY TIES(2020) Yan, Taiyi; Venkataramani, Vijaya; Tangirala, Subra; Business and Management: Management & Organization; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Employees rely on coworkers for support. Through workflow ties and friendship ties with coworkers, employees acquire task support and emotional support that allows them to be effective in their work. At the same time, employees often find themselves having to compete with those very coworkers for limited rewards and recognition (e.g., bonuses, promotion) that organizations provide. In this dissertation, I delineate the negative effects that competition with coworkers who are closely connected to employees in their workflow and friendship networks has on employees’ task performance. I note that such competition can prevent employees from obtaining critical task and emotional support required to remain effective in their roles. Using a social embeddedness perspective, I further highlight that these negative effects of competition can be avoided when employees and their competitors are connected to third-party peers in their teams who can act as mediators and allow for continued flow of task and emotional support via workflow and friendship ties between employees and their competitors. I test these hypotheses in the field (using a sample of 394 employees embedded in 39 R&D teams) and in two experimental studies (using 694 participants). I will discuss implications of my model for theory and practice.Item ESSAYS ON PHARMACEUTICAL ADVERTISING(2015) DAI, WEJIA (DAISY); JIN, GINGER Z; SWEETING, ANDREW; Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The dissertation focuses on two distinctive issues in pharmaceutical advertising. One on the matching choices between advertisers and advertising agencies, and the other on the effect of paid-link advertising on consumer search for online pharmacies. The goal of this dissertation is to empirically uncover the underlying economic mechanisms. Moreover, the analysis of matching problem provides new insights on the formation of vertical relationships between clients and professional service agencies and has implications for professional service market consolidations. And the examination of consumer searches for pharmaceuticals online sheds lights on consumers' concerns over quality and affordability of prescription drugs and draws attention on advertising regulation. In the first two chapters, I focus on two essential features of the market for professional services. One is the necessary mutual agreement in forming relationships, and the other is that a client perceives conflict when hiring the same service agency as his product market competitor. To incorporate these two features, I construct and estimate a two-sided matching model and allow agents' choices to depend on conflict. The results show that conflict does indeed reduce match surplus, and the reduction is greater for a pair of agents who have matched with each other in the previous period. Also, preserving previously formed matches yields much higher surplus than forming new matches. Based on these estimates, I conduct a counterfactual exercise to illustrate the effect of conflict on allocation of matches and another counterfactual exercise to illustrate the effect of a merger between advertising agencies on market equilibrium. In the third chapter, coauthored with Matthew Chesnes and Ginger Jin, we examine how government's sudden ban of foreign online pharmacies from paid search on Google and other search engines changes consumer searches for the banned websites. Using click-through data from comScore, we find that non-NABP-certified pharmacies receive fewer clicks after the ban, and this effect is heterogenous. In particular, pharmacies not certified by the NABP but certified by other sources, referred to as tier-B sites, experience a reduction in total clicks, and some of their lost paid clicks are replaced by organic clicks. These results have implications for the change in consumer search cost and health concern.Item Inpatient Mortality in Emergency Care: Is Competition Always Good?(2014) Kwok, Veronica; Chen, Jie; Health Services Administration; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The objective of this study was to measure the association between regional competition and emergency care outcomes. Competition was measured using the Herfindahl-Hirschman Index for three hospital referral regions in Maryland. Preliminary regression analysis using a logistic binary model showed that higher competition was associated with lower odds of mortality. Further investigation suggested that competition could be endogenous. Further regression analysis using an instrumental variable of hospital system affiliation and two-stage least squares estimation showed that lower competition was associated with lower odds of mortality for sepsis and trauma (OR = 0.7, p-value <0.001, OR = 0.5, p-value <0.001, respectively). Future investigation perhaps on a national level could help identify a stronger, more uniform association between competition and emergency care outcomes including large scale events, and as such provide policy guidance for quality of emergency care.Item Green Rivalry and Performance(2014) Kumar, Anupam; Grimm, Curtis M; Business and Management: Logistics, Business & Public Policy; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study analyzes the competitive interactions between focal and rival firms in the domain of environmental management (EM) practices and the associated impacts on environmental performance and financial performance. Using competitive dynamics and institutional theory as a basis, the study contends that firm performance is impacted by behavior of both focal and rival firms, and perceptions of legitimacy. Our findings indicate that firms competing aggressively do benefit from their proactive approach, but significant dissimilarity of behavior from their rivals tends to negatively impact firm performance bringing issues of legitimacy to the forefront. Subsequently, the study expands the work outlined above with a larger set of performance measures to look at the impact of rivalry on growth and long term shareholder value. Furthermore, this section also looks into the joint impact of environmental behavior and environmental performance on financial performance via a mediating model using various environmental performance measures. The findings indicate a partial mediation between EM behavior and financial performance from EM reputation and EM policy. In the final part of the dissertation, the study presents exploratory work on two future research topics. The first topic expands the work from focal-rival dyads to include supplier networks as well. The second topic lays out a roadmap for future work in the area of credible EM signaling. This topic takes on issues surrounding greenwashing that has been reported in the popular media. Given the visibility on sustainable activities across the entire spectrum, and the burden of green on firms, it is important to understand how firms are responding and if the returns justify their investments. This study contributes to this discourse by tying theory with behavior and adds additional clarity to firm behavior vis-à-vis green. From a methodological perspective, this study uses an original panel dataset using secondary data sources, which adds to the credibility of the results. The study has important managerial relevance at both the firm level and for policy making.Item Community Ecology and Sirex noctilio: Interactions with Microbial Symbionts and Native Insects(2013) Thompson, Brian Matthew; Gruner, Daniel S; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Sirex noctilio is an invasive woodwasp with a global distribution that feeds on the sapwood of pine trees. Wood-feeding in the basal Hymenoptera (sawflies) arose out of sequential adaptations to feeding on nutrient poor and digestively refractive internal plant organs (xylem). Symbiotic association with White-rot fungi are thought to aid overcoming nutritional and digestive barriers, including exceedingly low nitrogen (N) and refractory lignocellulosic polymers. In this dissertation I evaluate wood-feeding relative to nutrition, symbiosis and biotic resistance to invasion of exotic North American habitats in Sirex noctilio [Hymenoptera: Siricidae]. I evaluated nutrient relations within fungal mutualism using: 1) functional morphological analysis of insect feeding, 2) sterol molecules to determine diet sources and 3) metagenomic and isotopic analyses for discovery of novel microbial associates and their associated nutrient pathways. Nutritional constraints of wood feeding are potentially compounded by the presence of diverse fungal and insect communities as they divide the tree resource. I examined the role biotic resistance to Sirex and its fungal mutualist, Amylostereum, in North America using field and laboratory experiments. Morphological evidence supported a role for Amylostereum in external digestion of wood. Observational evidence confirmed Sirex larvae did not ingest wood biomass but preferentially extracted liquid substances via specialized structures of mandibles. Sterol analysis indicated plant compounds as the primary constituent of the diet, while metagenomic analysis of bacteria and their metabolic pathways showed a bacterial microbiome adapted to short chain plant polymers, starch and sugar metabolism. Stable isotopes suggested an additional symbiotic association with nitrogen fixing bacteria enriched the nitrogen deficient food substrate. These studies point toward herbivory with microbial supplementation of nutrients as a tri-partite relationship, pending conclusive identification of the bacterial symbiont for Sirex. Specific constraints of wood feeding by the Sirex-Amylostereum symbiotic complex were antagonized by intraguild predation and fungal competition in North America. Competition interfered with Amylostereum, while intraguild predation accounted for an additional 15% mortality of larval populations. This research describes the evolutionary role of microbial symbionts in wood-feeding in the Hymenoptera and the internal and external constraints to foraging this ubiquitous, yet nutrient poor food resource.Item Relative roles of aggregation, competition, and predation in the North American invasion of the Asian Bush mosquito, Aedes japonicus(2012) Freed, Thomas Z.; Leisnham, Paul T; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The success of an invasion can be mediated by biological interactions (e.g. competition and predation). The newly invasive mosquito Aedes japonicus has established in the range of the competitively superior resident mosquito Aedes albopictus and the predatory indigenous mosquito Toxorhynchites rutilus. I tested the hypotheses that intraspecific aggregation, fluctuating resources, or keystone predation are facilitating the invasion of A. japonicus into the range of A. albopictus. Populations of A. japonicus and A. albopictus were negatively correlated with each other and intraspecifically aggregated in field studies, suggesting that aggregation is facilitating coexistence. Resources showed a high amount of spatial variability, and A. japonicus populations were strongly associated with resource-rich containers, providing evidence for the fluctuating resource hypothesis. A laboratory experiment showed that predation suppresses A. japonicus populations to a greater extent than interspecific competition when all three species co-occur, and provided no evidence for keystone predation.Item Essays on Issues in New Product Introduction: Product Rollovers, Information Provision, and Return Policies(2011) Koca, Eylem; Souza, Gilvan C; Xu, Yi; Business and Management: Decision & Information Technologies; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this dissertation we study several key issues faced by firms while introducing new products to market. The first essay looks at product rollovers: introduction of a new product generation while phasing out the old one. We study the strategic decision of dual vs. single roll jointly with operational decisions of inventory and pricing during this transitional period. Our results confirm previous findings and uncover the role and interaction of several parameters that were not examined before. In the second essay, we investigate the role of information provision and return policies in the consumer purchasing behavior and on the overall market outcome. We build a novel model of consumer learning, and we attain significant analytical findings without making any distributional assumptions. We then fully study the joint optimization problem analytically under uniform valuations. In the third essay, we study competition in the framework described in the second essay and we identify the potential Nash equilibria and associated conditions. Our findings demonstrate the effect of competition on return policy and information provision decisions and provide insight on some real-life observations.Item PLANT PRODUCTIVITY AND COMPETITIVE RESPONSE TO PRESCRIBED FIRE IN MID-ATLANTIC BRACKISH MARSHES(2011) Bickford, Wesley Alan; Needelman, Brian A; Weil, Raymond R; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Prescribed fire may increase productivity of some brackish marsh species. An understanding of the mechanisms behind this stimulatory effect is important for land managers to maximize the benefits to the ecosystem. I found that canopy removal is the dominant mechanism through which fire stimulates biomass production in the marshes at the Blackwater National Wildlife Refuge in Dorchester County, Maryland. The stimulatory effect of canopy removal was stronger in sedge-dominated systems than grass-dominated systems. Faster sprouting sedge species may be able to take fuller advantage of light and soil temperature increases following canopy removal than later-sprouting grass species. Results of a greenhouse study indicated that canopy removal gives sedges a competitive advantage over grasses. These studies have numerous implications for land managers using anthropogenic disturbances as a management technique. Canopy-level disturbances, such as fire may increase productivity in sedge-dominated marshes and may suppress grass species in mixed compositions.Item SEPARATING PRODUCT FAMILY DESIGN OPTIMIZATION PROBLEMS(2010) Karimian Sichani, Peyman; Herrmann, Jeffrey W.; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In order to improve productivity and reduce costs, manufacturing firms use product families to provide variety while maintaining economies of scale. In a competitive marketplace, designing a successful product family requires considering both customer preferences and the actions of other firms. This dissertation will conduct fundamental research on how to design products and product families in the presence of competition. We consider both single product and product family design problems. We use game theory to construct a model that includes the competition's product design decisions. We use separation, a problem decomposition approach, to replace complex optimization problems with simpler problems and find good solutions more efficiently. We study the well-known universal electric motor problem to demonstrate our approaches. This dissertation introduces the separation approach, optimizes product design with competition, models product family design under competition as a two-player zero-sum game, and models product family design with design and price competition as a two-player mixed-motive game. This dissertation formulates novel product design optimization problems and provides a new approach to solve these problems.