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Articles 1 - 13 of 13
Full-Text Articles in Physical Sciences and Mathematics
Sorption Of 2-Naphthalene Sulfonate To Organic Carbon In Natural Saturated Porous Media, Jiyan Hatami
Sorption Of 2-Naphthalene Sulfonate To Organic Carbon In Natural Saturated Porous Media, Jiyan Hatami
Theses and Dissertations
Organic carbon (OC) in aquifer sediments serves as a key geochemical control on contaminant fate and transport, potentially immobilizing or delaying mass transport downgradient. Quantifying the abundance of OC in aquifer sediments is therefore imperative in developing a conceptual understanding of local contaminant transport. Traditional methods involve time-intensive coring and lab analyses for total OC (TOC) at distinct intervals with depth. These methods fail to account for the heterogeneity between discrete points and do not interrogate TOC along groundwater flow pathways. 2-naphthalene sulfonate (2-NS), a novel groundwater tracer, was investigated here as a possible sorptive tracer for estimating the relative …
Sp2 Bonded Carbon For Soft X-Ray Detector Windows, Joseph T. Rowley
Sp2 Bonded Carbon For Soft X-Ray Detector Windows, Joseph T. Rowley
Theses and Dissertations
Energy Dispersive X-Ray Spectroscopy (EDS) is a technique used to analyze materials to determine their elemental makeup. This technique is used extensively in the semiconductor industry, metallurgical industry, biology, chemistry, materials science, and other fields. EDS detectors are often attached to scanning electron microscopes (SEM) or transmission electron microscopes (TEM) and are actively cooled by liquid nitrogen or Peltier devices. A thin membrane, or window, is fitted to the front of the detector which allows for an airtight seal as well as transmission of x-rays. The challenge for these windows is maximizing the transmission of x-rays while maintaining mechanical integrity. …
Equations Of State For Warm Dense Carbon From Quantum Espresso, Derek J. Schauss
Equations Of State For Warm Dense Carbon From Quantum Espresso, Derek J. Schauss
Theses and Dissertations
Warm dense plasma is the matter that exists, roughly, in the range of 10,000 to 10,000,000 Kelvin and has solid-like densities, typically between 0.1 and 10 grams per centimeter. Warm dense fluids like hydrogen, helium, and carbon are believed to make up the interiors of many planets, white dwarfs, and other stars in our universe. The existence of warm dense matter (WDM) on Earth, however, is very rare, as it can only be created with high-energy sources like a nuclear explosion. In such an event, theoretical and computational models that accurately predict the response of certain materials are thus very …
A Study Of The Anthropogenic Impact In Farmington Bay Through Isotopic And Elemental Analysis, Nathan Vaun Gunnell
A Study Of The Anthropogenic Impact In Farmington Bay Through Isotopic And Elemental Analysis, Nathan Vaun Gunnell
Theses and Dissertations
The influence of human activity on surrounding environments is an important field of research. With respect to aquatic settings, lacustrine deposits provide excellent proxies of environmental change since the sediment accumulates at a relatively constant rate, recording environmental change. This study employs isotopic, mineral, and chemical records from Farmington Bay freeze cores, in particular δ13C, δ15N, and 210Pb isotopes as well as phosphorus level fluctuation and trace metal analysis. In particular, 210Pb isotopes permit estimation of the age of sediment with depth and δ15N, δ13C, and concentration of P provides a record of changing nutrient sources and level of eutrophication. …
Immobilization Of Copper Nanoparticles Onto Various Supports Applications In Catalysis, Anh Hoang Tu Nguyen Sorenson
Immobilization Of Copper Nanoparticles Onto Various Supports Applications In Catalysis, Anh Hoang Tu Nguyen Sorenson
Theses and Dissertations
Copper-based materials are one of the most promising catalysts for performing transformations of important organic compounds in both academic and industrial operations. However, it is challenging to consistently synthesize highly active and stable copper species as heterogeneous catalysts due to their relatively high surface energy. As a result, agglomeration usually occurs, which limits the catalytic activities of the copper species. The work presented in this dissertation shows different synthetic strategies for obtaining active and stable copper-based materials by modifying chemical/physical properties of copper nanoparticles (NPs). Emphasis is placed on discussing specific catalytic systems, including carbon-supported catalysts (monometallic and bimetallic copper-based …
Regional Drivers Of Organic Carbon Age In Lotic Systems Of The Conterminous United States, Kaycee Faunce
Regional Drivers Of Organic Carbon Age In Lotic Systems Of The Conterminous United States, Kaycee Faunce
Theses and Dissertations
Rivers play a critical role in global carbon (C) budgets despite their comparatively small surface area. A significant portion of the terrestrial C that they receive is transformed, re-mineralized, or stored during transit to the ocean. Radiocarbon (∆14C) data show that a fraction of riverine organic C (OC) has been pre-aged in the terrestrial environment. Lateral export of carbon from these aged pools may contribute to atmospheric carbon dioxide emissions through microbial and photochemical oxidation. However, little is known about the regional climatic, anthropogenic, and landscape factors that promote the mobilization of aged OC to rivers. This study …
Identifying The N Sources For Black Mangrove (Avicennia Germinans) In A South Texas Mangrove Forest, Ashley Elizabeth Murphy
Identifying The N Sources For Black Mangrove (Avicennia Germinans) In A South Texas Mangrove Forest, Ashley Elizabeth Murphy
Theses and Dissertations
Black mangrove (Avicennia germinans) in south Texas provide ecosystem services and benefits to humans including: habitat for wildlife, prevention of coastline erosion, and mitigation of natural disasters. One step to preserve their ecological functions is to identify and protect the source of their nitrogen (N). Nitrogen stable isotopes were sampled for one year beginning August 2018 and used as tracers to identify how mangroves obtain N. Total N in (A. germinans) and associated (Batis maritima) (plants) (2.1%) was more abundant than in cyanobacteria (0.6%) and sediment (0.1%). Plant d15N signatures (5.52‰) were more similar to sediment (5.21‰) than cyanobacteria (1.98‰), …
Endolithic Microbial Carbon Cycling In East Antarctica, Natalie Tyler
Endolithic Microbial Carbon Cycling In East Antarctica, Natalie Tyler
Theses and Dissertations
Microbes adapt to inhospitable conditions by colonizing niches that protect them from severe environmental conditions, making them model organisms in the search for life on other planets. Endoliths are globally ubiquitous microbes that colonize structural cavities within rocks, which protect them from environmental stressors while maintaining access to nutrition and light sources. Despite harsh katabatic winds, extreme temperature fluctuations, harmful UV radiation and exposure to desiccation, endolithic communities have been observed in Antarctica. Previous studies have found viable and abundant microbial biomass through microscopy and the addition of isotopic labels. However, due to the slow metabolic activity of these microbes, …
Thin Film Carbon Nanofuses For Permanent Data Storage, Kevin Robert Laughlin
Thin Film Carbon Nanofuses For Permanent Data Storage, Kevin Robert Laughlin
Theses and Dissertations
We have fabricated nanofuses from thin-film, arc-evaporation carbon for use in permanent data storage. Thin film carbon fuses have fewer fabrication barriers and retain the required resistivity and structural stability to work as a data storage medium. Carbon thin films were characterized for their electrical, microstructural, and chemical bonding properties. Annealing the thin-film carbon in an argon environment at 400°C reduced the resistivity from about 4*10-2 Ω cm as deposited down to about 5*10-4 Ω cm, allowing a lower blowing voltage. Nanofuses with widths ranging from 200 nm down to 60 nm were fabricated and tested. They blow …
Photoluminescence From Gan Co-Doped With C And Si, Mykhailo Vorobiov
Photoluminescence From Gan Co-Doped With C And Si, Mykhailo Vorobiov
Theses and Dissertations
This thesis devoted to the experimental studies of yellow and blue luminescence (YL and BL relatively) bands in Gallium Nitride samples doped with C and Si. The band BLC was at first observed in the steady-state photoluminescence spectrum under high excitation intensities and discerned from BL1 and BL2 bands appearing in the same region of the spectrum. Using the time-resolved photoluminescence spectrum, we were able to determine the shape of the BLC and its position at 2.87 eV. Internal quantum efficiency of the YL band was estimated to be 90\%. The hole capture coefficient of the BLC …
Modeling Lake Michigan Nearshore Carbon And Phosphorus Dynamics, Joseph Henry Fillingham
Modeling Lake Michigan Nearshore Carbon And Phosphorus Dynamics, Joseph Henry Fillingham
Theses and Dissertations
Dreissenid mussels, in particular quagga mussels (Dreissena rostiformis bugensis), are transforming the Lake Michigan ecosystem by clearing the water column, recycling phosphorus and modifying benthic habitat. These impacts are thought to have caused observed declines in the spring phytoplankton bloom in Lake Michigan, as well as changes to food web structure and declines in the abundance of critical invertebrate and fish species. In the nearshore zone, the resurgence of benthic Cladophora algae to nuisance levels not observed since phosphorus loading abatement policies instituted in the 1970s has also been attributed to water column clearing and phosphorus recycling by mussels. Using …
Stoichiometric Controls On Denitrification In High Nitrate Watersheds, Brian Grebliunas
Stoichiometric Controls On Denitrification In High Nitrate Watersheds, Brian Grebliunas
Theses and Dissertations
Watershed biogeochemistry throughout Midwestern agroecosystems have been altered through hydrologic manipulation and over-application of nitrogenous fertilizers. As a result, nitrate (NO3-N) export from subsurface drainage has negative impacts on local and downstream ecosystem health. Wetland installation has proven to be a viable option for targeted management where a large proportion of NO3-N is removed through the bacterially mediated process denitrification. For denitrification to maintain high rates under prolonged NO3-N saturation, a stable supply of labile dissolved organic carbon (DOC) is required. The focus of this dissertation was to study how the stoichiometry of agricultural wetlands limits denitrification within a controlled …
Changes To Electrical Conductivity In Irradiated Carbon Nanocomposites, Nickolas A. Duncan
Changes To Electrical Conductivity In Irradiated Carbon Nanocomposites, Nickolas A. Duncan
Theses and Dissertations
Carbon nanotubes (CNT) and carbon nanofibers (CNF) are two nanoparticles incorporated in a polymer to create a composite material. These composites are two potential lightweight materials for use as replacements for aluminum structures on satellite systems. Both composite materials have a low resistivity that is consistent with conductive materials. However, the CNT composite is substantially more conductive than the CNF composite. The CNT and CNF composites were irradiated with electrons and neutrons to fluence levels of and. No changes were observed in the resistivity of the CNF composites following neutron and electron irradiation. A 3.7% increase in resistivity was observed …