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 Transmission Spectra of Rb 87 atoms near an Optical Nanofiber.(2016) Patterson, Burkley D.; Orozco, Luis A; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We present measurements of the transmission spectra of 87Rb atoms at 780 nm in the vicinity of a nanofiber. A uniform distribution of fixed atoms around a nanofiber should produce a spectrum that is broadened towards the red due to shifts from the van der Waals potential. If the atoms are free, this also produces an attractive force that accelerates them until they collide with the fiber which depletes the steady-state density of near-surface atoms. It is for this reason that measurements of the van der Waals interaction are sparse. We confirm this by measuring the spectrum cold atoms from a magneto-optical trap around the fiber, revealing a symmetric line shape with nearly the natural linewidth of the transition. When we use an auxiliary 750 nm laser we are able to controllably desorb a steady flux of atoms from the fiber that reside near the surface (less than 50 nm) long enough to feel the van der Walls interaction and produce an asymmetric spectrum. We quantify the spectral asymmetry as a function of 750 nm laser power and find a maximum. Our model, which that takes into account the change in the density distribution, qualitatively explains the observations. In the future this can be used as a tool to more comprehensively study atom-surface interactions.Item QUANTIFICATION OF IONOPHORE ANTIMICROBIALS ASSOCIATED WITH POULTRY LITTER AND THEIR DYNAMICS IN THE SOILS OF THE MID-ATLANTIC USA(2014) Biswas, Saptashati; McGrath, Joshua M; Sapkota, Amir; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Anticoccidants, biochemically known as ionophores are added to poultry feed for growth promotion, prophylactic and therapeutic purposes to better sorb nutrients and against coccidiosis caused by parasite Eimeria sp. Ionophores belong to the class of emerging contaminants, as they are not regularly monitored in the environment and not specifically treated in the effluents. Potentially, this can cause ionophores to enter into the environment freely. There is little information regarding the dynamics of ionophores in the environment. This has been related to the lack of reliable, sensitive and robust methods that can measure their trace levels from complex environmental matrices like soil, natural water and animal manure. Studies show ionophore toxicity exhibited in flora and fauna, even reported in humans above the dose of 1 mg kg-1. Hence accumulation of ionophores in the environmental can be detrimental. Our multi-scale investigation of ionophores involved, a) method development for trace analysis of ionophores in poultry manure using liquid chromatography triple quadrupole mass spectrometry (HPLC-–MS/MS), b) batch equilibrium studies of ionophores using soils from mid-Atlantic region of the USA and c) influence of soil physico-chemical parameters on dynamics of ionophores in soil-water systems. Our HPLC-–MS/MS method was successful in quantifying ionophores ranging from (19.19 ±± 6.6) µg kg-1 to (97.86 ±± 19.19) µg kg-1 with concentrations of monensin being the highest. This method was further used to investigate partitioning of monensin in soil-ndash;water systems relevant to the occurrence of ionophores in the natural environment. Sorption and desorption isotherms were developed and influence of soil physico-chemical parameters on the sorption-desorption processes were analyzed. C-–type linear isotherms were generated with partition coefficients ranging from (6.41±± 1.34) to (343.83 ±± 5.68) LKg-1. Soil parameters such as cation exchange capacities, pH, organic matter, sand and silt content were found to correlate with sorption in different conditions. A major focus of this dissertation was to develop novel methodologies and design experiments to execute our research objectives.Item Release of inorganic and organic contaminants from fly ash amended permeable reactive barriers(2008-01-25) Morar, Doina Lorena; Aydilek, Ahmet H.; Seagren, Eric A.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Large quantities of fly ash are generated in the United States via coal combustion, most of which is disposed of in lagoons or landfills. The overall goal of this research was to assess the feasibility of using high carbon content (HCC) fly ashes as a reactive medium in permeable reactive barriers (PRBs) for remediation of petroleum hydrocarbon contaminated groundwater. A series of column and batch tests were performed to evaluate the leaching of selected metals from the fly ash, and adsorption/desorption of two target hydrocarbons (naphthalene and o-xylene) onto/from this PRB medium. Leaching of metals in the column experiments exhibited a first-flush, followed by a tailing slope elution pattern for all fly ashes. The naphthalene and o-xylene adsorption/desorption on/from the fly ashes were directly correlated with the organic carbon of the fly ash as measured by loss in ignition. Adsorption/desorption hysteresis was obvious in column and batch tests, suggesting that the adsorption/desorption was not completely reversible during the testing.