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 Application of Ultrahigh Resolution Mass Spectrometry and Deuterium Labeling to Determine the Contribution of Ketone/ Aldehyde-Containing Species to the Composition and Optical Properties of Dissolved Organic Matter(2020) Bianca, Marla; Blough, Neil V; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dissolved organic matter (DOM) is a complex, heterogeneous mixture comprised of thousands of chemical species, found in almost all aquatic environments and is one of Earth’s largest carbon reservoirs. DOM is known to affect many biogeochemical processes and may be a crucial component of the global carbon cycle. However, due to the inherent complexity of DOM, understanding and relating its photophysical and photochemical properties to its composition is difficult. This dissertation describes and applies a mass labeling method using ultrahigh resolution mass spectrometry and deuterium labeling to determine the contribution of ketone/ aldehyde-containing species to the composition and optical properties of DOM. Sodium borodeuteride (NaBD4) selectively and irreversibly reduces ketone/aldehyde groups and the changes due to reduction were observed through mass spectrometry and ultraviolet/visible (UV-Vis) and fluorescence spectroscopy. The reduction of ketone/aldehyde-containing species by NaBD4 results in loss of absorption and creates unique mass markers (deuterated species at mass M+3.021927n) in the mass spectrum. The internal consistency of this algorithm for identifying reduced species was tested using two additional methods, both of which resulted in consistently identified reduced species in the mass spectra. This method was applied to Suwannee River fulvic acid (SRFA) with increasing concentrations of NaBD4 to evaluate the extent of reduction which differed depending on the concentration used. Additionally, the extent of reduction resulting from the increasing concentrations of NaBD4, was shown to correlate well with changes in the absorption and emission spectra of the corresponding untreated and reduced samples; thus, providing evidence that ketone/aldehyde functional groups contribute substantially to the bulk optical properties of SRFA. Furthermore, SRFA that was irradiated as well as reduced revealed insights into the structural components in SRFA that were lost or decreased due to irradiation and contributed to the observed optical properties. Also, it was demonstrated that irradiation made terrestrial material appear more like marine DOM. DOM samples from several different aquatic environments were compared using this method to reveal differences and similarities within the composition of DOM. This method has proven to be a useful tool in relating the changes in the optical properties upon the reduction by NaBD4 to the changes observed by mass spectrometry to reveal information on the composition and well as source and structure of DOM.Item Development and characterization of high-strain electrodes(2006-08-31) Delille, Remi Alain; Smela, Elisabeth; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis, composed of three journal articles, presents a compliant electrode material, based on a novel fabrication procedure. The compliant electrodes consisted of a photopatternable, urethane matrix embedded with platinum nanoparticles. The first in the series of journal articles, "Benchtop Polymer MEMS," characterized the unloaded urethane matrix's compatibility with microfabrication and patterning processes. The second, "Compliant Electrodes Based on Platinum Salt Reduction in a Urethane Matrix," presented a unique manufacturing process for compliant electrodes, which exhibited a secant modulus under 10 MPa, an electrical conductivity of 1 S/cm, and maintained electrical conductivity under mechanical strains of 30%. The third, "High-Strain, High-Conductivity Photopatternable Electrodes," explored a modification to this fabrication method that yielded a dramatic improvement in performance: an electrical conductivity of 50 S/cm, mechanical strains of 150% without loss of conductivity, robustness after thousands of strain cycles, and low hysteresis.