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
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Effect of Encapsulation on Electrolyte Leakage in Aluminum Electrolytic Capacitors Under Constant Thermal and Electrical Loading(2014) Parsa, Ehsan; Dasgupta, Abhijit; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study focuses on the influence of encapsulation (with silicone elastomer potting compound) on electrolyte leakage in aluminum electrolytic capacitors. Experiments were conducted on potted capacitors at constant elevated temperature and rated DC voltage, and results were compared to those from a control batch of unpotted capacitors. The weight, ESR and capacitance were periodically monitored. Encapsulation was found to decelerate electrolyte loss rate and ESR degradation. There was an increasingly discernible deceleration of capacitance degradation but the magnitude did not reach statistically significant thresholds within the test period. A simplified axisymmetric finite element model was constructed for theoretical understanding of the electrolyte loss process. The experimental measurements were used to guide the selection of the material properties in the model. The model addresses several possible sources of non-uniformities in the mass flux density in the test specimen: (i) radial nonuniformity of mass transport properties of the rubber seal; and (ii) delamination between the potting compound and the capacitor leads. This model was then used: (i) to conduct parametric investigation of the effect of mass transport properties of the potting compound; and (ii) in conjunction with the experimental results to estimate the electrolyte mass loss from the capacitor through the rubber seal.Item Development of food polymer-based colloidal delivery systems for nutraceuticals(2012) Luo, Yangchao; Wang, Qin; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Colloidal delivery systems have drawn increasing attention in food science area. Biopolymers, i.e. proteins and polysaccharides originated from foods, with low toxicity, high biocompatibility and biodegradability, are the ideal biomaterials to develop delivery systems for nutraceuticals. The present work is dedicated to develop delivery systems for nutraceuticals, using food derived biopolymers, e.g. chitosan and zein. In the first part of this study, different core-shell structured nanoparticles were developed for encapsulating both hydrophilic and hydrophobic nutracetuicals. For chitosan nanoparticles with zein coating, the hydrophilic nutraceutical, selenite, was encapsulated and the physicochemical properties was improved after zein coating. Then, zein nanoparticles with chitosan (CS) or carboxymethyl chitosan (CMCS) coating were developed to encapsulate hydrophobic nutraceuticals, including vitamin E, vitamin D3, indole-3-carbinol and diindolylmethane. The fabrication parameters were systematically studied and the effects of encapsulation on stabilities of nutraceuticals were investigated under different conditions. Subsequently, a novel approach to prepare CMCS hydrogel beads was developed. CMCS, a water-soluble derivative of CS, was known as unable to form hydrogel beads by itself in aqueous solution due to chain rigidity and inefficient entanglement. In this part, the formation of CMCS hydrogel beads was studied in aqueous-alcohol binary solutions. Chemical crosslinking was required to maintain its integrity upon drying. Different drying methods (i.e. freeze and air drying) were also investigated to understand their effects on swelling and release profile in simulated gastrointestinal conditions. Some possible mechanisms were discussed. Lastly, cellular evaluation of zein nanoparticles stabilized by caseinate was carried out. The zein-caseinate nanoparticles had a good redispersibility after freeze-drying and were able to maintain original particle size in different cell culture medium and buffer at 37°C over time. The zein-caseinate nanoparticles had no cytotoxicity at concentrations up to 1 mg/ml over 3 days. Then, coumarin 6, a fluorescent marker, was encapsulated into zein-caseinate nanoparticles to investigate their cell uptake and epithelial transport. The cell uptake was clearly visualized by fluorescent microscopy and the uptake mechanisms were investigated. The epithelial transport was investigated on Caco-2 cell monolayers. The results suggested caseinate not only stabilized zein nanoparticles in different buffers, but also improved cell uptake and epithelial transport.Item Genetic and Phenotypic Differentiation as a Consequence of Host Plant Use by Lepidopteran Herbivores(2011) Shlichta, Jennifer Gwen; Barbosa, Pedro; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this dissertation, I focused on the role of plant hosts as a driving force leading to phenotypic and genotypic changes in insect herbivores. There are three main questions addressed: (1) Do generalist species' populations have broad diet breadth or do they represent a mosaic of sub-populations, each having narrow diet breadths? (2) How do host plants affect the immune response of polyphagous herbivores? and (3) Do host plants or host plant such as allelochemicals, alter the interaction between herbivore defense and parasitoid counter-defense? Do generalist species' populations have broad diet breadth or do they represent a mosaic of sub-populations each having narrow diet breadths? In Chapter 1, I determined, using amplified fragment length polymorphisms (AFLPs), whether host plant-associated genetic differentiation (HAD) was exhibited by a suite of polyphagous tree feeding macrolepidoptera. I determined this by using polyphagous species that exhibit traits expected to be important in the formation of genetically divergent sub-populations. How does host plant affect the immune response of polyphagous species? In Chapter 2, the objective was to examine the effect of host plant species on the immune defenses of polyphagous lepidopteran herbivores, specifically the intensity of encapsulation measured as percent melanization, of three common forest Lepidoptera species. In Chapter 3, I discuss and assessed the potential role of immune responses in insect outbreaks. I present a brief background on immune responses, discuss the methods used to experimentally measure the components associated with immune response and how immune response varies. Lastly, I draw on the studies available and present several potential hypotheses to stimulate further research. Does host plant, or some aspect of host plant such as allelochemicals, alter the interaction between herbivore and parasitoid? In the final chapter, I explored the ecological consequences of viral-plant allelochemical interactions. The objective of this study was to use a model system, Manduca sexta and Cotesia congregata, to directly test the effect of the allelochemical nicotine and the presence or absence of polydnavirus (PDV) on larval immune responses. PDV allows the parasitoid egg to escape encapsulation (an herbivore defense against parasitism).Item Controlled liposome formation and solute encapsulation with continuous-flow microfluidic hydrodynamic focusing(2008-12-11) Jahn, Andreas; DeVoe, Don L; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Liposomes enable the compartmentalization of compounds making them interesting as drug delivery systems. A drug delivery system (DDS) is a transport vehicle for a drug for in vivo drug administration. Drugs can be encapsulated, bound, or otherwise tethered to the carrier which can vary in size from tens of nanometers to a few micrometers. Liposomal DDSs have shown their capability to deliver drugs in a new fashion, allowing exclusive sales of encapsulated drugs to be extended beyond the initial compound's patent expiration date. However, existing methods to form liposomes and encapsulate drugs are based on bulk mixing techniques with limited process control and the produced liposomes frequently require post-processing steps. In this dissertation, a new method is demonstrated to control liposome formation and compound encapsulation that pushes beyond existing benchmarks in liposome size homogeneity and adjustable encapsulation. The technology utilizes microfluidics for future pharmacy-on-a-chip applications. The microfluidic system allows for precise control of mixing via molecular diffusion with reproducible and controlled physicochemical conditions compared to traditional bulk-phase preparation techniques (i.e. test tubes and beakers). The laminar flow and facile fluidic control in microchannels enables reproducible self-assembly of lipids into liposomes in a sheathed flow-field. Confining a water-soluble compound to be encapsulated to the immediate vicinity where liposome formation is expected to occur reduces sample consumption without affecting liposome loading. The ability to alter the concentration and control the amount of encapsulated compounds within liposomes in a continuous-flow mode is another interesting feature towards tailored liposomal drug delivery. The liposome formation strategy demonstrated in this dissertation offers potential for point-of-care drug encapsulation, eliminating shelf-life limitations inherent to current liposome preparation techniques.