A. James Clark School of Engineering
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Desing of Click Hydrogels for Cell Encapsulation(2011) Breger, Joyce; Wang, Nam Sun; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The long-term stability of ionically crosslinked alginate hinders the development of a bioartificial pancreas for the treatment of Type I Diabetes. Ionically crosslinked alginate with divalent cations is traditionally utilized to encapsulate islets of Langerhans serving as a protective barrier between the host's immune system and the donor islets of Langerhans. However, due to ion exchange with monovalent ions from the surrounding serum, alginate degrades exposing donor tissue to the host's immune system. The overall goal of this dissertation was to explore the possibility of utilizing `click' chemistry to introduce covalent crosslinking in alginate for therapeutic cell encapsulation. `Click' chemistry is customarily defined as the Cu (I) catalyzed reaction between an azide and alkyne to form a 1,2,3 triazole ring. To achieve the goal of covalently crosslinked polysaccharides, the following aims were determined: (1) synthesis and characterization of functionalized polysaccharides (alginate and/or hyaluronic acid) with alkyne or azide end groups; (2) measurement and comparison of the stability and transport properties of covalently crosslinked alginate hydrogels to that of ionically crosslinked alginate hydrogels; (3) determination of the inflammatory potential and cytotoxicity of these functionalized polysaccharides and `click' reagents by employing RAW264.7, a murine macrophage cell line under various simulated inflammatory states (with or without endotoxin, with or with out the inflammatory cytokine gamma-interferon); (4) optimization of the `click' reaction for therapeutic cell encapsulation utilizing RIN-5F, a rat insulinoma cell line, while minimizing cytotoxicity and maintaining insulin production; (5) encapsulation of primary porcine islets of Langerhans in either ionically and/or covalently crosslinked alginate capsulation and comparing insulin response to a glucose challenge. The results of these experiments demonstrate the utility of employing `click' chemistry to increase the overall stability of alginate hydrogels while maintaining therapeutic cell function.Item Relating pollutant and water quality parameters to landuse in a subwatershed in the Choptank River watershed(2010) Nino de Guzman, Gabriela Tejeda; Torrents, Alba; Hapeman, Cathleen J; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Agriculture and animal feeding operations have been implicated as sources of water pollution along the Choptank River, an estuary and tributary of the Chesapeake Bay. This survey examined a subwatershed within the Choptank River watershed for impacts of a poultry facility on its adjacent surface water. Water and sediment samples were collected May - October 2009 under mostly baseflow conditions and analyzed for antibiotics, nutrients, heavy metals, and selected bacteria. Of the antibiotics recovered, no significant difference was observed spatially, but a significant difference emerged between spring and fall/winter. For nutrients, the greatest phosphorus concentrations were at the subwatershed outlet (4) and at two branches not containing the poultry house (3 and 5); nitrogen concentrations at sites 2 and 5 were as high as site 4. Arsenic concentrations at 2 were lower than both the low-agriculture (control) site and a site neighboring 3. Bacterial counts in water and sediment remained fairly constant throughout the sampling regime.Item Using MODIS Satellite Images to Confirm Distributed Snowmelt Model Results in a Small Arctic Watershed(2009) Choy, David F.; Brubaker, Kaye; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Environmental analysts face the problem of obtaining distributed measurements to evaluate the performance of models with increasingly small spatiotemporal resolution. While U.S. government agencies readily provide both measurement products and data tools for the study of global change occurring over entire seasons and across continental areas, analysts need access to the low-level data that provides the basis for global products. Finally, analysts need to consider sensor errors inherent in low-level products that are accounted for in global, composite products. Hydrologists using tools for managing low-level snow swath measurements, in particular, must consider how measurements are affected by sensor errors like snow-cloud confusion and sensor errors due to low ground illumination at night. This thesis aims to explore the use of remotely sensed snow maps to confirm a time series of model maps. Specifically, snow covered area (SCA) measurements remotely sensed by the National Aeronautics and Space Administration (NASA) are used to confirm SCA predictions modeled by the United States Agriculture Department (USDA). The measurements come from the two Moderate Resolution Imaging Spectroradiometer (MODIS) sensors aboard near-polar, sun-synchronous satellites named Aqua and Terra. The USDA calls the model TOPMODEL-Based Land-Atmosphere Transfer Scheme (TOPLATS). The Upper Kuparuk River Watershed (UKRW) on the North Slope of Alaska acts as the case study location. To meet the map-comparison goal, the Kappa statistic, Kappa statistic variants, and probability density functions expressing measurement uncertainty in discrete scenes all evaluate the ability of MODIS measurements to confirm the accuracy of TOPLATS model maps. Data management objectives to make measured data accessible and comparable to the model output comprise a supporting goal. Results show that individual composite statistics, like the proportion of agreement between two maps, can easily obscure spatiotemporally distributed confirmation information without additional statistics and side-by-side images of measurement maps and model maps. These tools show some promise for using MODIS to confirm model predictions of snowmelt that occur across less than 150 km2 and less than a few days, however, clouds and malfunctioning sensors limit such use.Item Environmental Performance and Sustainability of Bioretention Cells(2009) Jones, Philip Sumner; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bioretention cells use vegetation and soil media for source control of urban stormwater runoff, alleviating waterway impairment. Environmental performance of two cells was investigated. First, a cell capturing road runoff was monitored for one year. At a second cell, media were sampled to measure lifetime metal accumulation and evaluate the environmental, health, and maintenance implications of metal sequestration. Monitoring found high metal and suspended solids removal, generally poor nutrient performance, and chloride export. Runoff volume and peak flow rate reduction occurred for small storm events. For larger events, outflow volume consistently exceeded inflow because of unique site conditions. Lead, copper, and zinc media concentrations in the second cell were elevated but well below cleanup thresholds. Metals were strongly bound to bioretention media and largely immobile; lead bioavailability was comparable to generic soil estimates. Most metal accumulation was near the inflow point in the top 3 to 12 cm of media.Item A QUANTITATIVE FRAMEWORK FOR UNDERSTANDING THE COMPLEX INTERACTIONS OF COMPETING INTERFACIAL PROCESSES AND IN-SITU BIODEGRADATION(2004-08-30) Johnson, Mark Adam; Seagren, Eric A; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In Situ bioremediation of contaminated groundwater is made technologically challenging by the physically, chemically, and biologically heterogeneous subsurface environment. Subsurface heterogeneities are important because of influences on interfacial mass transfer processes which impact the availability of substrates to microorganisms. The goal was to develop a quantitative understanding of the impact of interfacial heterogeneities effecting contaminant biodegradation. A quantitative framework of dimensionless parameters was developed to capture the effects of competing physiochemical and biokinetic processes. Two numerical modeling experiments were completed, demonstrating the framework, and how it can be used to determine what engineered enhancements will alleviate the rate-limiting process. Baseline conditions were established to examine intrinsic biodegradation with a set rate-limiting process (either dispersion or biokinetics). Three different engineering controls were then examined. In each case, the control predicted to be appropriate based on the quantitative framework more successfully alleviated the limitation and enhanced biodegradation more than the alternative enhancements.Item Substrate Specificity and Molecular Characterization of PAH-Degrading Anaerobic Enrichment Cultures Under Methanogenic Conditions(2004-05-06) Baldwin, Brandi; Holoman, Tracey R. P.; Chemical EngineeringOver the past several years, this lab has cultivated enriched anaerobic mixed cultures capable of degrading the low-molecular-weight polycyclic aromatic hydrocarbons (PAHs), naphthalene or phenanthrene, as a sole carbon source. Characterization of the enrichment cultures by 16S rDNA analysis revealed two unique populations, though they were initiated from the same sediment source. This study set out to determine the ability of these highly enriched communities to utilize a new carbon source, and to identify the effect of this shift on the population profile. The phenanthrene-degrading culture demonstrated significant naphthalene-degrading activity; however, the naphthalene-degrading culture was unable to degrade phenanthrene. Molecular characterization of these cultures showed a single species common to both original enrichment cultures and dominating in the population able to degrade both substrates. These results suggest that very few members of the mixed cultures participate in the degradation of PAHs, whereas the remaining members live off the metabolic byproducts.