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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    RADIATION CHEMISTRY IN PRESSURIZED WATER NUCLEAR REACTORS: H2 GENERATION BY 10B(n,α)7Li, AND THE REACTION OF BORATE WITH •OH
    (2023) Guerin, Steven James; Al-Sheikhly, Mohamad I; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Nuclear power plants (NPPs) are complex engineering systems, with malfunctions having enormous potential to lead to widespread and extreme impacts on society and the environment as a whole. Their safe operation depends on a multitude of factors such as intelligent planning, proper design, quality components, high-level safety operations, and economic viability. Due to requiring high temperature and high pressure of an NPP’s cooling fluid, one of the main concerns for further developing safe operating conditions and evaluating component lifetimes is improving our understanding on the issue of corrosion in nuclear systems. In the U.S., all commercially operated Pressurized Water nuclear Reactors (PWRs) are light-water reactors wherein their coolant waters can reach temperatures up to 350 °C. According to a report in 2005 in association with the U.S. Federal Highway Administration, an annual cost of $4.2 billion was directly attributed to corrosion in NPPs in 1998, out of a total $6.9 billion in the electrical utilities industry (Koch, et al., 2005). Boron is added into commercial PWR primary water in the form of boric acid as a soluble chemical neutron “shim” in order to compensate for fuel burnup and allow smooth long-term reactivity control. After a boron nucleus captures a thermal neutron and becomes unstable, the energy of the recoil ions resulting from its fission accounts for up to 33 % of the total dose to the primary water. This event is an important source for H2 and corrosive H2O2, so its product yields must be accurately included in models of the cooling water radiation chemistry. H2 produced in water from the 10B(n,α)7Li fission reaction has been measured up to 300 °C to aid in quantification of the corrosive H2O2 from the same reaction. Thermal energy neutrons from the Rhode Island Nuclear Science Center 2 MW reactor interacted with boric acid contained in N2O-saturated water in temperature-controlled high-pressure cells made from tubing of either titanium or zirconium alloy. After exposure for a minimum of one hour, the solution samples were extracted and sparged with argon. The H2 entrained by the sparging gas was sampled with a small mass spectrometer. A small amount of sodium was included in the boric acid solution so that after sparging, samples could be collected for 24Na activation measurements in a gamma spectrometer to determine the neutron exposure and thus the total energy deposited in solution. The G-value (µmol/J) for H2 production was obtained for water at a pressure of 25 MPa, over a temperature range from 20 °C to 300 °C. These results have been complemented with Monte Carlo N-Particle® (MCNP®) simulations in collaboration with the National Institute of Standards and Technology, and have been compared with previous experimental results at room temperature and simulated results up to 350 °C. Additionally, boric acid has thus far been accepted as a chemically nondisruptive additive, as it was confirmed long ago to have extremely low reactivity with the two main reactive species produced in reactor primary water by radiolysis, the solvated aqueous electron and the hydroxyl radical (e(aq)- and •OH). However, at the Electric Power Research Institute standard desired pH of 7.3 and the operational temperature of 350 °C, approximately 22% of the boron added in PWR primary water exists in the chemical form of the conjugate base, borate, not boric acid. Although borate was previously confirmed to have no appreciable reactions with e(aq)-, it was not adequately studied for reactions with •OH prior to this work. We have observed a clearly apparent reaction between borate and •OH. Current chemistry models are completely ignorant on both the existence of the resultant species and its reactions. The chemical reaction of [B(OH)4]- (borate) with •OH along with cross-reactions of the product species have been studied up to 200 °C to determine those reactions’ rate constants and the products’ spectra. The University of Notre Dame Radiation Laboratory’s 8 MeV electron linear accelerator (LINAC) was configured to perform pulse radiolysis with pulse widths between 4ns to 20ns providing doses between 5.5 Gy and 62 Gy. High-energy electrons from the LINAC interact with the borated solution which has been N2O-saturated and is continuously flowed through a 316 stainless-steel optical cell. The cell temperature was adjusted by resistive-heating silicon cartridges, and pressure was controlled by two syringe pumps to prevent boiling. The cell had two fused silica windows for transmitting light from a xenon arc lamp through the solution and out to a multichromatic spectrophotometer system. Time-resolved spectral data was obtained over nano- and micro-second timeframes, for wavelengths ranging from the deep UV and into the infrared spectrum (250 nm to 820 nm). The reaction rates and products’ spectra were then obtained by analyzing the data using computational aids, namely IGOR Pro by Wavemetrics and KinTek Explorer by KinTek Corp. The product species of the reaction between borate and •OH is conjectured to be •[BO(OH)3]-, on the basis of ab initio calculations, which likely reacts with boric acid or borate to form a polymer radical.
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    TEMPORAL ANALYSIS OF HYDROXYL RADICAL SCAVENGING IN WATERS.
    (2013) Donham, Joel Edward; Wigginton, Krista Rule; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The ability to assess hydroxyl radical (*OH) scavenging rates of natural organic matter (NOM) (kNOM,*OH) is necessary for the optimization of advanced oxidation processes (AOPs) for water treatment, and to understand the role of *OH in natural systems. We have developed a rapid method to measure *OH scavenging rates in less than one hour. Using the method, we measured kNOM,*OH for NOM isolates, and performed the first known scavenging analyses of surface waters and treated drinking waters over time. The results are compared with values quantified using more time consuming methods. Our results reveal that kNOM,*OH in water samples can fluctuate with time, which has implications for AOP operation. The methods and benefits of the new measurement technique and implications of observed variability of kNOM,*OH values on AOP operations are presented. Additionally, observations regarding current NOM scavenging measurement and analysis methods are discussed.
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    SOURCE DEPENDENT VARIATION IN HYDROXYL RADICAL PRODUCTION BY AIRBORNE PARTICULATE MATTER AND THE IMPACT ON BEAS-2B AND JB6 CELLS
    (2007-04-30) Alaghmand, Marjan; Blough, Neil V; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Numerous studies have shown an association between increased levels of particulate matter (PM) and the exacerbation of lung diseases. The exact means by which PM produces these effects remain unclear. Generation of reactive oxygen species such as the hydroxyl radical (OH), is one of the hypothesized mechanisms. However, the importance OH of production by PM remains uncertain due to a lack of sensitive and selective methods for its determination. In this work, a highly-sensitive fluorescence-based technique was employed to quantify the magnitude of .OH generated by a wide range of airborne particulate matter. The generated .OH was measured in the presence and absence of biological electron donor. Little or no production of .OH was observed in the absence of the added electron donor. For some but not all particles, .OH production was increased substantially when a biological electron donor was present. No detectable .OH was produced by kaolinite or silica. The mechanism(s) of .OH generation by airborne particulate matter were investigated. The presence of dioxygen, hydrogen peroxide, superoxide and metal chelators significantly affected .OH production by the particles. The results indicate that metals and organic constituents are involved in .OH production by particles and occur through both homogeneous and heterogeneous reactions. The effect of different airborne particles on .OH generation in the presence of two different cell lines, lung epithelial cells (BEAS-2b) and mouse epidermal cells (JB6) were investigated. In addition, two different toxicological methods were employed to investigate cell viability in the presence of different airborne particles. Based on our results, some .OH production was observed in the presence of these cell lines when exposed to diesel particulate matter and urban dust, but rates of cell death did not correlate with the .OH production rate. Further, silica particles, which exhibited no evidence of .OH production, produced the most rapid cell death. On the other hand, both cell death and hydroxyl radical formation were dramatically enhanced when an external biological reductant, NADPH, was added to a suspension of cells and urban dust. In this situation, the high flux of .OH is the likely factor causing cell death.
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    Enhancing the availability of natural antioxidants in wheat-based food ingredients and food products through improved post-harvest treatments and processing conditions
    (2007-04-20) Moore, Jeffrey Calvin; Yu, Liangli; Food Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Wheat grain has significant antioxidant contents concentrated in the bran fraction, most of which may not be bioavailable in humans because they are not released from matrix materials during digestion. The present study developed solid-state enzymatic and yeast post-harvest treatments, and investigated the effects of these treatments and food processing on the extractable antioxidant properties of whole-wheat based food ingredients and food products. Antioxidant properties investigated in this study included scavenging capacities against cation ABTS radicals, peroxyl radicals (ORAC), hydroxyl radicals, and DPPH radicals, and total phenolic contents and phenolic acid compositions. The first part of this research developed and validated a high-throughput fluorometric hydroxyl radical scavenging capacity (HOSC) assay. The HOSC assay utilized a Fe(III)/H2O2 Fenton-like reaction to generate hydroxyl radicals, fluorescein as detector probe, trolox as an antioxidant standard, and area under the curve measurements to quantify scavenging capacity. The hydroxyl radical purity and potential solvent interference in the assay system were evaluated using electron spin resonance. The HOSC assay was found to have acceptable performance characteristics including linear range, accuracy, and reproducibility. The second part of this study investigated the potential of solid-state enzyme and yeast treatments to improve wheat bran antioxidant properties. Both enzyme and yeast treatments were capable of increasing available wheat bran antioxidant properties. Reaction parameters found to influence the effectiveness of these treatments to enhance wheat bran antioxidant properties included enzyme preparation and reaction moisture content for enzyme treatments, and yeast preparation along with dose and treatment time for yeast treatments. The final part of this research evaluated the effects of processing conditions including bran particle size, fermentation time, and baking conditions on the antioxidant properties of a whole-wheat pizza crust. Baking increased extractable antioxidant properties up to 82%. Fermentation time caused some significant increases, while bran particle size had no influence on extractable whole-wheat pizza crust antioxidant properties. This study suggests that post-harvest treatment of wheat bran and optimized processing conditions for whole-wheat food products are potential approaches for increasing their extractable antioxidant properties.