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Exploring Soil Microbial Dynamics In Southern Appalachian Forests: A Systems Biology Approach To Prescribed Fire Impacts, Saad Abd Ar Rafie

Doctoral Dissertations

Prescribed fires in Southern Appalachian forests are vital in ecosystem management and wildfire risk mitigation. However, understanding the intricate dynamics between these fires, soil microbial communities, and overall ecosystem health remains challenging. This dissertation addresses this knowledge gap by exploring selected aspects of this complex relationship across three interconnected chapters.

The first chapter investigates the immediate effects of prescribed fires on soil microbial communities. It reveals subtle shifts in porewater chemistry and significant increases in microbial species richness. These findings offer valuable insights into the interplay between soil properties and microbial responses during the early stages following a prescribed fire. …

Understanding The Role Of Impounded Water Bodies In River Network Nutrient Exports In A Dynamic Landscape, Christopher Thomas Whitney

Doctoral Dissertations

Impounded water bodies are a significant component of aquatic networks and various forms have been studied extensively. However, knowledge gaps exist in the research on human-made dams and their reservoirs as well as beaver ponds as both uniquely affect water quality and nutrient exports in different ways. This study fills those knowledge gaps by investigating fluxes of all forms of dissolved nitrogen from small, human-made reservoirs at seasonal timescales. This study found that small reservoirs have a significant effect on nitrogen concentrations but this effect is seasonal and fluxes transported downstream are highly dependent on discharge. Removal of small dams …

Sources And Controls Of Carbon Dioxide In Inland Waters At Watershed, Regional, And Continental Scales, Brian Saccardi

Doctoral Dissertations

Inland waters are significant sources of carbon dioxide to the atmosphere, and estimates of emissions are similar in magnitude to those of the carbon dioxide sequestered by the net terrestrial sink. Currently, methods of estimating carbon dioxide emissions are based on statistical approaches and often do not consider landscape attributes such as human development, agriculture, or the hydrologic connectivity of the stream network. The following research addresses these issues in chapter 1 by developing and validating a reactive transport model at the watershed scale, then in chapter 2 by applying the reactive transport model at the continental scale across US …

Carbon Emissions From Streams And Rivers: Integrating Methane Emission Pathways And Storm Carbon Dioxide Emissions Into Stream And River Carbon Balances, Andrew Robison

Doctoral Dissertations

River networks play an important role in elemental cycling at watershed, regional, and global scales. They not only serve as pipes that transport elements from land to sea, but also as complex processers that can significantly modify the timing, form, and magnitude of these elemental fluxes. For example, recent studies have shown that river networks contribute significantly to the global carbon cycle by emitting greenhouse gases like carbon dioxide (CO¬2) and methane (CH4) to the atmosphere. However, we currently do not fully understand the controls on GHG emissions from river networks, particularly what drives the variability of emissions across space …

Novel Synthetic Methods And Applications Of Porous Materials: Aerogel Foams, Metallic Aerogels, Amorphous And Graphitic Carbon Aerogels, Rushi Soni

Doctoral Dissertations

"We report novel methods for the synthesis of porous materials such as polymeric aerogel foams, pure metallic aerogels, amorphous and graphitic carbon aerogels, and their applications. I. Polyurethane based aerogel foams were synthesized with an aliphatic triisocyanate and ethylene glycol through a pressurized (7 bar) sol-gel method. The foam-like structure is prepared without any chemical foaming agents or templates, resulting in less expensive, more efficient, readily adaptable, and environmentally friendly process. Those materials exhibited lower thermal conductivity (by 25%) and higher oil adsorption capacity (by 36% w/w) than their corresponding aerogels. II. Monolithic, pure metallic Co(0) aerogels were synthesized from …

Design Of Materials And Processing Methods For High Temperature Composites, Chris Monteleone

Doctoral Dissertations

In this dissertation, various studies are described which seek to improve the properties of high temperature ceramic-matrix and carbon-matrix composites. Processes were developed and optimized to control the compositions, microstructures, and morphologies of ceramic materials. Focus was on the chemical vapor infiltration (CVI) of coatings on continuous fiber substrates. Other processes were involved as well, such as polymer impregnation & pyrolysis (PIP) and silicon melt infiltration (SMI). Both carbon and SiC fibers were used as substrates. Materials deposited using CVI include carbon, SiC, TiC, BN, and B4C. Characterization methods include scanning electron microscopy, mechanical testing, X-ray diffraction, and others.

A …

Assessing The Agronomic And Ecological Relevance Of Mineral-Associated Organic Matter, Andrea Jilling

Doctoral Dissertations

As the largest terrestrial sink for carbon (C) and a critical source of nitrogen (N) for plants, soil organic matter (SOM) is a major driver of ecosystem function. It is critical to understand the mechanistic controls on SOM in order to improve models of global C cycling and to develop accurate measures of soil fertility. SOM consists of a wide spectrum of compounds, varying in chemical characteristics and function. The chemical and physical fractionation of SOM is a valuable tool for distilling this complexity into meaningful and distinct pools: detrital or particulate organic matter (POM), which contains mostly recent litter …

Fungal Community And Soil Responses To Invasive Alliaria Petiolata (Garlic Mustard), Soil Warming, And Nitrogen Deposition, Mark Alan Anthony

Doctoral Dissertations

Non-native, invasive plants can fundamentally alter soil fungal communities and edaphic properties. In this dissertation, I first measured fungal and edaphic responses and recovery to invasive, Alliaria petiolata (garlic mustard; Brassicaceae) eradication across Southern New England. I conducted an experimental eradication and tracked fungal communities and soil properties for three years in relation to reference uninvaded plots and actively invaded plots. Neither the fungal community nor soil properties recovered (i.e. became similar to reference uninvaded plots) following eradication, and I discuss how altered soil properties likely prevented fungal communities from recovering via environmental filtering. I also measured fungal and edaphic …

Lignin-Based Li-Ion Anode Materials Synthesized From Low-Cost Renewable Resources, Nicholas William Mcnutt

Doctoral Dissertations

In today’s world, the demand for novel methods of energy storage is increasing rapidly, particularly with the rise of portable electronic devices, electric vehicles, and the personal consumption and storage of solar energy. While other technologies have arguably improved at a rate that is exponential in accordance with Moore’s law, battery technology has lagged behind largely due to the difficulty in devising new electric storage systems that are simultaneously high performing, inexpensive, and safe.

In order to tackle these challenges, novel Li-ion battery anodes have been developed at Oak Ridge National Laboratory that are made from lignin, a low-cost, renewable …

Design, Synthesis And Characterization Of Transition Metal Oxide Nanomaterials As Efficient Sorbents And Emerging Catalysts And Investigation Of Carbon Structure-Oxidation Activity Correlations, Lakshitha R. Pahalagedara

Doctoral Dissertations

Design, Synthesis and Characterization of Transition Metal Oxide Nanomaterials as Efficient Sorbents and Emerging Catalysts and Investigation of Carbon Structure-Oxidation Activity Correlations

Lakshitha Randimal Pahalagedara, Ph. D

University of Connecticut, 2015

Keywords: Mesoporous, Metal oxides, Desulfurization, Microwave, Hydrothermal, microwires, Doped, Carbon, Soot, Oxidation

This thesis is delineated into three parts. The first part describes the synthesis of mesoporous cobalt oxides with tunable porosity, and crystallinity based on an inverse micelle soft template method and investigation of these materials as desulfurizing sorbents in a fixed bed reactor in the temperature range of 25-250ºC. Very high S sorption capacities were observed in …

Single Fiber Mechanical Properties Using Nano-Tensile Testing And Carbon Fiber Structure-Property Relationship, Matthew Erich Kant

Doctoral Dissertations

Single carbon fibers are studied using a nano-tensile testing system. This system has unprecedented load and displacement resolution, nN and nm respectively, and the ability to perform dynamic testing for storage and loss modulus during quasi-static tensile extension. Furthermore, improved fiber mounting and alignment procedures coupled with the precision of the nano-tensile testing system assist in unprecedented resolution in single fiber mechanical testing for axial modulus and strength. Hence, using these unique capabilities, the moduli and their statistical distribution of many high performance carbon fibers are reported here. From this, a simplified single parameter model describing the strain dependent modulus …

Role Of Nitrogen Defects In Nitrogen-Doped Carbon For Catalyst Support And Electric Double-Layer Capacitor, Sujan Shrestha

Doctoral Dissertations

Electrochemical applications of carbon are wide and varied. They are used as electrodes for batteries, capacitors and proton exchange membrane fuel cells (PEMFCs). This is possible due to their excellent electrical conductivity, variable nanostructure and cost-effectiveness. Besides these properties, physicochemical properties such as microstructure and surface chemistry play a significant role in the performance of carbon as electrodes in these applications. In supercapacitors or ultracapacitors, surface oxygen functionalities can increase capacitance due to non-faradaic reactions between redox couples such as quinine and hydroquinone while in PEMFCs, surface functionalities can determine catalyst size distribution and dispersion. However, surface oxygen functionalities also …

Carbon And Sulfur Cycling In Early Paleozoic Oceans, Cara Kim Thompson

Doctoral Dissertations

Here, I evaluate biospheric evolution during the Ordovician using high-resolution inorganic carbon and sulfur (carbonate-associated sulfate and pyrite) isotope profiles for Early Ordovician to early Late Ordovician strata from geographically distant sections in Western Newfoundland and the Argentine Precordillera. Additionally, I present new, high-resolution U-Pb ages for volcanic ash beds within strata of the Argentine Precordillera. Carbon isotope data record subdued variation that is typical of Early- to Middle Ordovician strata worldwide. By contrast, sulfur-isotopic compositions of carbonate-associated sulfate reveal a complex signal of short-term, rhythmic variation superimposed over a longer-term signal. This short-term, rhythmic variation occurs in all sections …

Kinetics Of Laser Chemical Vapor Deposition Of Carbon And Refractory Metals, Feng Gao

Doctoral Dissertations

Three-dimensional laser chemical vapor deposition (3D-LCVD) has been used to grow rods of carbon, tungsten, titanium, and hafnium from a variety of hydrocarbons and metal halide-based precursors. A novel computerized 3D-LCVD system was designed and successfully used in the experiments. A focused Nd:Yag laser beam (λ = 1.06 μm) was utilized to locally heat up a substrate to deposition temperature. The rods, which grew along the axis of the laser beam, had a typical diameter of 30–80 μm and a length of about 1 mm. The precursors for carbon deposition were the alkynes: propyne, butyne, pentyne, hexyne, and octyne. Propyne …