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 FUSARIUM SPECIES OF CUCUMIS MELO IN THE MID-ATLANTIC REGION OF THE US AND THEIR IMPACT ON SALMONELLA ENTERICA NEWPORT SURVIVAL AND INTERNALIZATION ON VARIOUS MELON CULTIVARS.(2019) Korir, Robert Cheruiyot; Everts, Dr. Kathryne L; Micallef, Dr. Shirley A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fruit rots caused by Fusarium spp. can lead to economic yield losses on melon (Cucumis melo). However, which Fusarium spp. are the most prevalent in Maryland and Delaware has not been documented. Several Salmonella enterica subsp. serovar Newport (S. Newport) outbreaks on melon have occurred over the past 25 years. Fusarium spp. infestation on melon have potential impact on survival and colonization of Salmonella. Our objectives were to identify Fusarium spp. infestations on melons within the Delmarva region, and evaluate their impact on survival and internalization of S. Newport on various melon cultivars. Fifty-six isolates were molecularly identified, according to Fusarium-ID online database, as Fusarium spp. (Fusarium fujikuroi-20, Fusarium proliferatum-18, Fusarium oxysporum-15, Fusarium graminearium-2, Fusarium verticilloides-1). Our findings revealed that most of the Fusarium isolates we collected were not pathogenic to melon fruit. We evaluated the impact of four Fusarium spp. (F. armeniacum, F. oxysporum, F. fujikuroi, and F. proliferatum) on S. Newport survival in five melon cultivars; ‘Arava’ (C. melo var. reticulatus, Galia), ‘Athena’ (var. reticulatus, muskmelon), ‘Dulce Nectar’ (var. inodorus, honeydew), ‘Jaune de Canaries’ (var. inodorus, Canary), and ‘Sivan’ (var. cantalupensis, Charentais). Impact of F. proliferatum on survival and interlization of S. Newport was evaluated on honeydew (smooth) and cantaloupe (netted) melons. Generally, Fusarium did not impact the survival of S. Newport, however greater survival of S. Newport was observed on the netted cultivars compared to the smooth surface melons. Fusarium fujikuroi significantly enhanced survival of Salmonella when inoculated on riper ‘Jaune de Canaries’ melons (above ¾ slip). However, when the experiments were replicated with less ripe (about ¾ slip) melon, F. fujikuroi did not significantly influence the growth of S. Newport. Salmonella Newport internalized in all treatments and the cantaloupe and honeydew melons, but variation in population levels were observed across the treatments. Overall, Fusarium proliferatum did not impact internalization of S. Newport on either melon type. This may be attributed to that Fusarium species used during this study were non-pathogenic. Salmonella Newport recovered gradually decreased with time. Fusarium species on melon, influence S. Newport colonization differently. Also, melon rind type affects the ability of S. Newport to survive and colonize differently.Item A Systematic and Minimalist Approach to Lower Barriers in Visual Data Exploration(2016) Yalcin, Mehmet Adil; Bederson, Benjamin B; Elmqvist, Niklas E; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the increasing availability and impact of data in our lives, we need to make quicker, more accurate, and intricate data-driven decisions. We can see and interact with data, and identify relevant features, trends, and outliers through visual data representations. In addition, the outcomes of data analysis reflect our cognitive processes, which are strongly influenced by the design of tools. To support visual and interactive data exploration, this thesis presents a systematic and minimalist approach. First, I present the Cognitive Exploration Framework, which identifies six distinct cognitive stages and provides a high-level structure to design guidelines, and evaluation of analysis tools. Next, in order to reduce decision-making complexities in creating effective interactive data visualizations, I present a minimal, yet expressive, model for tabular data using aggregated data summaries and linked selections. I demonstrate its application to common categorical, numerical, temporal, spatial, and set data types. Based on this model, I developed Keshif as an out-of-the-box, web-based tool to bootstrap the data exploration process. Then, I applied it to 160+ datasets across many domains, aiming to serve journalists, researchers, policy makers, businesses, and those tracking personal data. Using tools with novel designs and capabilities requires learning and help-seeking for both novices and experts. To provide self-service help for visual data interfaces, I present a data-driven contextual in-situ help system, HelpIn, which contrasts with separated and static videos and manuals. Lastly, I present an evaluation on design and graphical perception for dense visualization of sorted numeric data. I contrast the non-hierarchical treemaps against two multi-column chart designs, wrapped bars and piled bars. The results support that multi-column charts are perceptually more accurate than treemaps, and the unconventional piled bars may require more training to read effectively. This thesis contributes to our understanding on how to create effective data interfaces by systematically focusing on human-facing challenges through minimalist solutions. Future work to extend the power of data analysis to a broader public should continue to evaluate and improve design approaches to address many remaining cognitive, social, educational, and technical challenges.Item Impact of Cryptosporidium spp. interaction with co-occurring microorganisms on moderate-to-severe diarrhea in the developing world(2015) Reid, Molly Carroll; Sapkota, Amy R; Maryland Institute for Applied Environmental Health; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Diarrheal illness is responsible for over a quarter of all deaths in children under 5 years of age in sub-Saharan Africa and South Asia. Recent findings have identified the parasite Cryptosporidium as a contributor to enteric disease. We examined 9,348 cases and 13,128 controls from the Global Enteric Multicenter Study to assess whether Cryptosporidium interacted with co-occurring pathogens based on adjusted odds of moderate-to-severe diarrhea (MSD). Cryptosporidium was found to interact negatively with Shigella spp., with multiplicative interaction score of 0.16 (95% CI: 0.07 to 0.37, p-value=0.000), and an additive interaction score of -9.81 (95% CI: -13.61 to -6.01, p-value=0.000). Cryptosporidium also interacted negatively with Aeromonas spp., Adenovirus, Norovirus, and Astrovirus with marginal significance. Odds of MSD for Cryptosporidium co-infection with Shigella spp., Aeromonas spp., Adenovirus, Norovirus, or Astrovirus are lower than odds of MSD with either organism alone. This may reduce the efficacy of intervention strategies targeted at Cryptosporidium.Item Nonparametric Estimation and Testing of Interaction in Generalized Additive Models(2011) Li, Bo; Smith, Paul J; Mathematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The additive model overcomes the "curse of dimensionality" in general nonparametric regression problems, in the sense that it achieves the optimal rate of convergence for a one-dimensional smoother. Meanwhile, compared to the classical linear regression model, it is more flexible in defining an arbitrary smooth functional relationship between the individual regressor and the conditional mean of the response variable Y given X. However, if the true model is not additive, the estimates may be seriously biased by assuming the additive structure. In this dissertation, generalized additive models (with a known link function) are considered when containing second order interaction terms. We present an extension of the existing marginal integration estimation approach for additive models with the identity link. The corresponding asymptotic normality of the estimators is derived for the univariate component functions and interaction functions. A test statistic for testing significance of the interaction terms is developed. We obtained the asymptotics for the test functional and local power results. Monte Carlo simulations are conducted to examine the finite sample performance of the estimation and testing procedures. We code our own local polynomial pre-smoother with fixed bandwidths and apply it in the integration method. The widely used LOESS function with fixed spans is also used as a pre-smoother. Both methods provide comparable results in estimation and are shown to work well with properly chosen smoothing parameters. With a small and moderate sample size, the implementation of the test procedure based on the asymptotics may produce inaccurate results. Hence a wild bootstrap procedure is provided to get empirical critical values for the test. The test procedure performs well in fitting the correct quantiles under the null hypothesis and shows strong power against the alternative.