UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 given thesis/dissertation in DRUM.
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Item Absorption and metabolism of 3-MCPD 1-monopalmitate in rats(2017) Gao, Boyan; Yu, Liangli (Lucy); Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fatty acid esters of 3-monochloropropane 1,2-diol (3-MCPD esters) are a group of potential chemical toxicants. Their toxic effects primarily include nephrotoxicity and hepatotoxicity. To understand the toxic mechanisms of 3-MCPD esters, one of the key points is to advance the understanding of their metabolic mechanisms in vivo. This dissertation investigated 1) the absorption and kinetics of 3-MCPD 1-monopalmitate in rats, 2) the possible metabolites of 3- MCPD 1-monopalmitate after oral administration to rats, and 3) the possible metabolic pathways of 3-MCPD 1-monopalmitate in vivo. The greatest concentration of 3-MCPD 1-monopalmitate in the plasma was 873.72 ng/mL (Cmax) at about 1.67 hours (Tmax) after oral administration. The concentration of 3-MCPD 1-monopalmitate reduced to half after 3.42 hours (t1/2). No 3-MCPD 1-monopalmitate could be detected after 4 hours, which was its mean resident time (MRT). The area under curve (AUC) for 3-MCPD 1-monopalmitate in rat plasma was 1676.15 h.ng/mL, which represented the maximum amount of 3-MCPD 1-monopalmitate absorbed into plasma under the testing conditions. Beside, 39 possible metabolites were tentatively identified in the liver, kidney, testis, brain, plasma and urine samples at 6, 12, 24 and 48 hours after oral administration of 3-MCPD 1-monopalmitate to rats. In addition, five major metabolic pathways of 3-MCPD esters were derivate to evaluate their metabolic conditions in vivo. These results can greatly enhance the understanding about the absorption, distribution and metabolism conditions of 3-MCPD esters in vivo, and promote further research about the biological actions of 3-MCPD esters.Item EXPERIMENTAL PERFORMANCE EVALUATION OF DESORBER IN A HYBRID ABSORPTION VAPOR COMPRESSION SYSTEM(2013) Mandel, Bracha; Hwang, Yunho; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A single-effect absorption facility was designed and constructed to experimentally investigate the performance of a 3 kW mini-channel desorber using an R134a/POE32 solution mixture. The facility was fabricated to simulate a hybrid absorption/vapor compression system for an off-grid high temperature application utilizing an air-cooled absorber. Desorber design replicated the utilization of waste heat from a generator source. The effects of temperature, pressure, solution mass flow rate and refrigerant concentration variations on desorber and desorption performance were investigated and analyzed through vapor generation, circulation ratio, poor solution concentration, desorber mean heat transfer coefficient and quality difference. Desorber heat transfer coefficient enhancement was found to be a strong function of solution temperature, rising by up to 75% with a 30°C temperature increase. Due to poor absorber performance, increasing solution temperatures and mass flow rates did not result in a proportional desorber vapor generation enhancement, leading to a reduction in desorber quality difference.Item PROBING ATMOSPHERIC AEROSOL AND GAS PROPERTIES WITH PHOTOACOUSTIC SPECTROSCOPY(2011) Bueno, Pedro Antonio; Zachariah, Michael R; Dickerson, Russell R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Absorption by atmospheric aerosols is the wild card for global climate change. Issues regarding atmospheric gases and aerosols have been at the forefront and the work presented within is directed at those issues. Specifically, work has been performed in order to help understand the issue of absorption in the atmosphere and whether this contributes towards positive forcing or warming of the atmosphere. In the process of conducting this research a custom, first-principles photoacoustic spectrometer was improved, calibrated and used extensively in order to obtain knowledge of the interaction of light with atmospherically relevant gases and make the first measurements of absorbing aerosols. The absorption cross-section of uncoated and coated soot was measured and quantified and found to be consistent with other work where amplifications on the order of nearly 100% were observed with uncertainty levels much lower than previously reported. Soot was also found to be optically thin where the total mass of the soot contributes to the absorption. Consequential to the soot work, the photoacoustic spectrometer developed to measure the absorption was utilized as a high precision greenhouse gas sensor. The photoacoustic spectrometer was found to produce results on the absorption of CO2 to within 3% of the theoretically predicted line profile Moreover, the photoacoustic spectrometer was used to determine measurable coating thicknesses of less than 10 nanometers on 100 nm soot particles.Item The effect of surfactant vapor on marangoni convection in absorption and condensation(2005-11-18) yuan, zhe; Herold, Keith E; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mass and heat transfer enhancement by the addition of a class of surfactant additives is in common use in absorption machines based on aqueous lithium-bromide (LiBr). It is observed that the addition of on the order of 100 ppm of a surfactant such as 2-ethyl-hexanol (2EH) introduces Marangoni convection on the liquid surface and thereby enhances absorption and condensation rates. The Vapor Surfactant Theory (Kulankara and Herold, 2000) proposed that such Marangoni convection is driven by the surface tension gradient caused by surfactant that circulates through the machine and arrives at the liquid surfaces as a vapor by bulk flow along with water vapor. The objective of this work was to fully understand the vapor surfactant induced enhancement mechanism and to quantify the relationship between the enhancement and the key variables. This goal was achieved by conducting experimental and numerical analyses including the measurement of surface tension with surfactant 2EH in the vapor, determination of 2EH surface concentrations in aqueous LiBr and water, experimental study of Marangoni convection in an absorption and condensation pool with surfactant 2EH in the vapor and modeling of Marangoni convection in the presence of surfactant vapor. The surface tensions were measured with controlled 2EH concentration in the vapor by using the drop volume method. The results show that for both aqueous LiBr and water the surface tensions are reduced with increased 2EH concentration in the vapor. The 2EH concentration in the vapor is a primary variable in determining the surface tension of aqueous LiBr. Calculated surface concentrations show that the presence of LiBr results in a reduction in 2EH solubility, and that the surface concentration of 2EH is more sensitive to surfactant in the vapor than to surfactant in the liquid. Furthermore, the experimental and numerical analyses show that surfactant in the vapor alone can initiate the Marangoni convection; the strength of Marangoni convection is primarily dependent on the 2EH concentration in the vapor. The current studies show that surfactant in the vapor is a necessary condition for significant absorption and condensation enhancement.