Browsing by Subject "Carbon"
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Item Anthropogenic and Biogenic Carbon Dioxide Fluxes From Typical Land Uses in Houston, Texas(2013-04-29) Werner, Nicholas DA flux measurement setup was established at a communications tower north of downtown Houston, Texas, to measure energy and trace gas fluxes from a variety of emission sources in the urban surface layer. The first part of this study details the development of a correction for latent heat and carbon dioxide (CO2) fluxes due to a low-pass filtering of the true water vapor and CO2 atmospheric signals. A method of spectral analysis was used to develop a correction scheme for this flux underestimation through the observation that the low-pass filtering is a strong function of atmospheric relative humidity and wind speeds. The determined flux corrections for latent heat fluxes (average correction of 34%) were significantly larger than CO2 fluxes (3-4%), suggesting the low-pass filtering had a more dominant effect on the water vapor signal. For the second part of this study, we describe a quadrant analysis technique for separating measured net fluxes into their biogenic (c? < 0 and q? > 0 signals) and anthropogenic (c? > 0 and T? > 0 signals) components, and quantify these fluxes through the use of a refined relaxed eddy accumulation model. A method of minimizing a defined net ? (biogenic + anthropogenic) residual was used to determine an accurate ?hole? around the origin to exclude points in the desired quadrants that appear there randomly. The magnitude of the biogenic flux contribution showed expected relationships with temperature and irradiance. The anthropogenic flux contribution showed a strong correlation with measured traffic counts collected on local thoroughfares. Due to a presumed small bias in the flux calculation methodology, neither flux contribution truly measured zero, so anthropogenic and biogenic ?background? fluxes were calculated (0.01 ?mol mo^-1 m s^-1 and 0.01 ? 0.02 ?mol mol^-1 m s^-1 respectively). Future work involves perfecting the model, with the goal being widespread use of the theory at urban flux sites. The accurate separation of the net flux gives a more complete picture of the carbon cycle and allows for more accurate analysis of the effects of increased temperature and CO2 concentration on urban vegetation as compared to non-urban vegetation.Item Bioaccumulation and correspondent biochemical response of lumbriculus variegatus by exposure to fullerenes (C60)(2012-05) Wang, Jiafan; Cobb, George P.; Anderson, Todd A.; Maul, Jonathan D.; Jackson, Andrew W.; Hope-Weeks, Louisa J.Nanotechnology is one of the most popular and promising technologies in this era. It has been developed from a novel concept to an integral aspect of product advancement. Engineered nanomaterials (NMs) have been massively produced and applied into groups of products, such as automotive, defense, aerospace, electronics and computers, energy production, environmental, food production, agriculture, housing and construction, medical devices, pharmaceuticals, personal care, cosmetics. In 1985, a spherical carbon allotrope fullerene (C60) was discovered by Kroto et al. It is a foundational carbon based NM, widely applied into products due to its physical and chemical properties. However, the likelihood of direct C60 release into the environment has increased due to its applications. In recent decades, research associated with potential C60 environmental and human health risks has been emphasized. However, environmental risks of C60 are not fully understood. This research evaluated the bioaccumulation and correspondent catalase (CAT) activity change in Lumbriculus variegatus exposed to C60. With the challenge to quantify C60 in our experimental matrix, a normal shaking method was developed in this study to extract C60 effectively. Recovery results revealed 90.7 ± 4.5 % efficiency using silanized glass vessels. With relatively low cost of the supplies, this method was applied throughout the subsequent bioaccumulation study. Since few studies have emphasized C60 uptake by organisms in the environment, bioaccumulation factors have not been determined for C60 to L. variegatus. With no mortality observed in the concentration range of 0.05 to 11.33 mg C60 / kg dry weight sediment, biota-sediment accumulation factor (BSAF) was determined. For C60 aggregates in micro-size ranges (µ-C60), BSAF was 0.032 ± 0.008 at day 28, while a negligible (0.003 ± 0.006) BSAF was associated with the bigger C60 aggregates (bulk-C60). In comparison, BSAF of pyrene at day 28 (1.62 ± 0.22) was measured as a reference to determine C60 accumulation risk in the environment. Results demonstrated a lower potential for C60 accumulation in L. variegatus than pyrene. However, size effect for C60 suggests smaller aggregates can increase the accumulation in living organisms. Although C60 shows little accumulation risk in the environment, biological response corresponding to C60 exposure was observed. CAT activity was evaluated after both C60 and pyrene exposure to L. variegatus. Results illustrated a significant CAT activity change (p=0.034) at day 14 for worms exposed to C60 aggregates. This elevation was associated with the highest C60 body residue (199 ± 80 µg/kg worm tissue). Worms exposed to pyrene showed no significant CAT activity change while 600-fold higher body residues were found as compared to C60. This suggests that L. variegatus is more susceptible to C60 even through accumulation risk is relatively low. Furthermore, the relationship between C60 body residues and increased CAT activity was analyzed in linear regression to predict biological risk to L. variegatus from exposure to C60. NMs also include other compounds besides C60, such as carbon-nanotubes (CNTs) and metal-based nanoparticles. Current research has demonstrated some potential environmental and human health risks from exposure to NMs due to their special properties. In order to prevent future adverse effects from nanotechnology, an integrated governance approach that is based on scientific research and life cycle assessment is suggested to formulate effective NMs regulation. Advanced scientific research, general public education and engagement, application of well defined agenda-setting theory in public policy are all important norms in this approach to push sustainable NMs management and to prevent any unfriendly accident due to NMs exposure. In sum, this research adds to the knowledge of C60 effects on aquatic invertebrates (Lumbriculus variegatus). Governance approach suggestion is summarized and helpful in a proactive NMs management to not only aquatic ecosystems but also human health.Item Biotic and abiotic controls on carbon dynamics in a Central Texas encroaching savanna(2014-12) Thijs, Ann; Hawkes, Christine V.; Litvak, Marcy E.Anthropogenic activities are responsible for increases in atmospheric CO₂ and climate change. These increases are partly counterbalanced by natural processes, such as carbon uptake in land surfaces. These processes are themselves subject to climate change, creating a coupled carbon-climate system. I investigated the carbon sink that woody encroachment represents, using a Central Texas savanna as study site, and studied how climatic factors influence this carbon sink. Woody plant encroachment, a worldwide structural change in grassland and savanna ecosystems, alters many ecosystem properties, but the net effect on the carbon balance is uncertain. Woody encroachment represents one of the key uncertainties in the US carbon balance, and demands a more detailed understanding. To come to a process-based understanding of the encroachment effect on carbon dynamics, I analyzed patterns of carbon exchange using eddy-covariance technology. I expected the imbalance between carbon uptake and release processes associated with the encroaching trees specifically, to be responsible for the carbon sink. I also expected that the sink would vary in time, due to strong links between carbon fluxes and soil water in this semi-arid ecosystem. I further studied the ecophysiology of the dominant species, as well as soil respiration processes under different vegetation types, and scaled these findings in space and time. I found that the ecosystem was a significant carbon sink of 405 g C m⁻² yr⁻¹. The encroaching trees increased photosynthesis by 180% and decreased soil respiration by 14%, compared to the grassland, resulting in a strong carbon sink due to the encroachment process. The encroaching process also altered carbon dynamics in relation to climatic drivers. The evergreen species Ashe juniper effectively lengthened the growing season and widened the temperature range over which the ecosystem acts as a carbon sink. The drought resistance of the encroaching trees reduced the sensitivity of this savanna to drought. I conclude that encroachment in Central Texas savannas increased the carbon sink strength by increasing the carbon inputs into the ecosystem. Woody encroachment also reduced the sensitivity to climatic drivers. These two effects constitute a direct effect, as well as a negative feedback to the coupled carbon-climate system.Item Carbon based materials for electrodes in electrochemical double layer capacitors(2012-12) Murali, Shanthi; Ruoff, Rodney S.; Goodenough, John B.; Bielawski, Christopher W.; Korgel, Brian A.; Johnston, Keith P.Electrochemical double layer capacitors (EDLCs, also called supercapacitors or ultracapacitors) are high power density energy storage devices that operate through the separation of charge at the electrochemical interface between an electrode and a supporting electrolyte. Numerous types of carbon materials with high surface area and internal porosity, such as activated carbon, carbon fabrics, nanotubes, and reduced graphene oxide have been studied as electrode materials. Electrolytes such as aqueous alkaline and acid solutions usually give high capacitance, while organic and ionic liquids provide a wider operation voltage. Graphene, due to its high theoretical surface area of 2630 m2/g, good electrical conductivity, and relatively low density, is being studied as an electrode material in EDLCs. The objective of this dissertation is thus to study effective methods for synthesis of graphene-based materials, and to investigate their behavior in EDLCs. This work explored microwave assisted synthesis of graphite oxide (‘MEGO’, prepared in less than one minute by irradiation of graphite oxide by microwave). This material was further chemically activated to obtain a unique carbon material, activated microwave exfoliated graphite oxide (‘a-MEGO’) with specific surface areas up to 3100 m2/g. Gas adsorption measurements were used to study the specific surface area and porosity of a set of a-MEGO samples, which were also studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for their structure, and by combustion analysis (i.e., elemental analysis) and X-ray photoelectron spectroscopy (XPS) to understand their elemental composition. Cyclic voltammetry (CV), galvanostatic charge/discharge, and frequency response, tests were done in order to study the performance of these new carbon materials as electrodes in both aqueous and organic electrolytes in a two electrode cell set up.Item Climate action strategies for the University of Texas at Austin(2010-05) Hernandez, Marinoelle; Eaton, David J.; Walker, Jim H.This report analyzes the current greenhouse gas emissions inventory for The University of Texas at Austin (UT-Austin), reviews the carbon reduction strategies being implemented at UT-Austin and other peer institutions, and offers recommendations for strategies that could reduce greenhouse gas emissions at UT-Austin in the future.Item Deposition, characterization, and device application of amorphous carbon and amorphous silicon films(Texas Tech University, 1997-05) Liu, ShixiThe purpose of this work is to develop an expertise of deposition of amorphous carbon (a-C) films, especially diamond-like carbon (DLC) films using various deposition systems, to acquire better understandings of this material by various characterization techniques, and finally to study the feasibility of using this material as a new dielectric for Metal-to-Metal antifiise devices to solve the switching problem of the amorphous silicon (a-Si) antifuses. In this work, we report successful deposition of DLC films using a microwave electron cyclotron resonance (ECR) plasma system. We found that a-C:H films deposited without rf biasing are soft and polymer-like and have higher band gaps. DLC films can only be produced under a negative self-bias induced by the rf biasing. The band gap of the film decreases with the increase in rf power, and with the decrease in deposition pressure. This shows that the properties of the films depend mainly on the ion bombardment energy.Item Development of nanofiber protective substrates(Texas Tech University, 2004-08) Subbiah, ThandavamoorthyElectrospinning uses high voltage electric field to produce high surface area fibers in the nanometer range. Polymeric nanofibers were prepared by the electrospinning process and were characterized using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). A study on the relationship between process parameters and fiber characteristics was undertaken. The dependence of fiber morphology on the solvent volatility and collector substrate characteristics was critically analyzed. Results on the self assembling nature of the charged fibers over different collector substrates were obtained and reported in the thesis. Defect free nanofiber webs with high specific surface area and low porosities suitable enough to be used as adsorptive filtration membranes were prepared. Polyurethane nanofibers were used as nano metal oxide catalyst carriers by successfully impregnating the catalyst in a single-step electrospinning process. Aerosol filtration abilities of nanofiber membranes were tested and the results are presented.Item Diamond-like carbon films made by sputtering and PECVD(Texas Tech University, 1997-08) Zheng, ZhongqiangThis thesis describes the work on a-C:H thin films, including their preparation and characterization. It begins with introducing seme basic concepts such as sp1, sp2, sp3, their electronic structure, diamond-like carbon, and their applications to antifuse devices. Then, in Chapter II, film deposition techniques and characterization methods are presented in detail. The techniques of deposition consist of radio-frequency sputtering (r.f sputtering) and plasma-enhanced chemical vapor deposition (PECVD) systems. The methods of characterization are composed of optical absorption used to determine the band gap Eg, and infrared spectroscopy used to study C-C and CH bonding structures. Hew to measure self-biases and how to apply biases on anode are also contained in this chapter. In Chapter HI, the results of a-C:H films prepared by both r.f sputtering and PECVD are listed and discussed. Their growth rate, band gap and concentration of hydrogen are calculated and studied. They change with pressure and power in the same way as we expect according to theory. For instance, the concentration of hydrogen decreases with increasing power since higher power can cause mere removal of hydrogen from the film. Finally, conclusions are made, and future research directions are mentioned. Based en our good and believable results, a-C:H is considered to be a premising material to be used in wide applications.Item Dynamics of Soil Aggregation, Organic Carbon Pools, and Greenhouse Gases in Integrated Crop-Livestock Agroecosystems in the Texas High Plains(2012-08) Fultz, Lisa; Moore-Kucera, Jennifer; Cox, Robert D.; Maas, Stephan J.; Schwilk, Dylan W.; Zobeck, Ted M.In the Texas High Plains (THP), marked by limited water availability and low soil fertility, management (i.e. tillage, irrigation, crop selection) has great potential to impact soil quality factors, in particular soil organic matter (SOM) and carbon (SOC), and in turn the global C cycle. Soil organic C in whole soil and physically isolated pools can be indicative of a soil’s potential for C sequestration and changes due to management. Measurement of greenhouse gas (GHG) fluxes (CO2 and N2O), can provide insight into soil microbial activity, and allow for tracing losses of SOC. Further analysis of C functional groups using mid-infrared (MidIR) Fourier Transform spectroscopy, a recently (~20 years) developed method, can allow for classification of the C within aggregate fractions. Combination of these methods can provide a detailed outlook of the C interactions and response to management practices in semi-arid systems. The purpose of this research was to thoroughly examine the impacts of alternative agroecosystems on SOC as it relates to aggregation and contributions to GHG concentrations. Conventional production in this area typically consists of continuous cotton (CTN), although the implementation of alternative agroecosystem management practices such as integrated crop-livestock (ICL) systems is growing. Studied systems ranged from those established in 1997 to 2007 and represented various management practices. Specifically, seven systems were selected for monitoring of soil quality factors including mean weight diameter (MWD), aggregate proportions and SOC content, and total nitrogen (TN) content. Additionally, two systems were also utilized for monitoring of GHG fluxes. To examine these changes soil analysis was done at the whole soil level as well as within free aggregates (Elliott, 1986) and intra-aggregate (Six et al., 2000) fractions using physical dispersion. Stability of SOC was examined using the novel technique, MidIR spectroscopy, which can be used to identify C functional groups. Measurements of soil GHG fluxes, specifically CO2 and N2O, were done to aid in the estimation of the global warming potential in these semi-arid systems. Chapters 2 and 3 focus on the impacts of land management practices, including conventional and alternative agroecosystems, in seven systems located in the THP. Chapter 2 examines the changes over time as well as the differences between an ICL and conventional CTN system. Significant increases in SOC were measured within the ICL system, while no significant change was measured in the CTN. In general, MWD and SOC was greatest in systems which utilized alternative management practices (i.e. no-till, perennial vegetation, rotational cropping). Chapter 3 examined the impacts of multiple agroecosystems and associated vegetation components on SOC, aggregate stability, and nutrient content. The complexity of the systems made determination of distinctive impacts difficult. However, similar to the findings in Chapter 2, alternative management techniques resulted in increased SOC content and mean weight diameter. Chapter 4 focuses on fluxes of GHG from two of the systems identified in Chapter 3. This chapter compares fluxes of CO2 and N2O from five vegetation components managed as either irrigated or dryland systems. It was determined that perennial vegetation management resulted in significantly greater fluxes of CO2. In the case of N2O, fluxes were episodic and greatest in bermudagrass, following significant rainfall events but did not contribute significantly to global warming potential. Soil moisture, temperature, and SOC content were the major driving factors for GHG emissions. Chapter 5 examines the use of MidIR to characterize C functional groups from aggregates obtained in Chapter 2. Analysis indicates that SOC within intra-aggregate particulate organic matter was significantly different from all remaining fractions and that further separation based on C functional groups was possible in the intra-aggregate particulate organic matter and silt+clay fractions. The level of degradation associated with the intra-aggregate microaggregate fraction resulted in no significant difference in absorbance spectrum based on vegetation management. Chapter 6 compares the fractionation process when done on field-moist soils (for DNA extraction) and air-dried soils (for SOC analysis). Significant correlation was measured in fractions which produced significantly different results due to pre-fractionation conditions. This correlation may be improved by the inclusion of soil moisture at time of sampling and allow for the estimation of water stable aggregates using fractionation of field-moist soils.Item Electrical transport measurements of individual bismuth nanowires and carbon nanotubes(2005) Jang, Wan Young; Yao, Zhen, Ph. D.Item Estimation and Fate of New Production in the Marine Environment(2014-06-03) McInnes, Allison SkinnerThe fate of carbon in the ocean determines both the amount of CO_(2) that can be sequestered and the amount of sustainable biomass. Compartmentalization into new and regenerated production allows a first order estimate of carbon available to the local community versus the amount exported. The goal of this project was to study sources and sinks of production in order to test the general hypothesis that new production is underestimated in the marine environment. Specifically we looked at pulsed new nutrients and the effect on the ecosystem, the effect of currents on our measurements and estimates of export (equivalent to new production), and finally development of a new method which will allow in situ determination of new production in the majority of the global ocean. Specifically, the role of a Pacific herring spawn was investigated as an important stimulant to ecosystem wide carbon and nitrogen cycling in Simpson Bay, Alaska. A consistent pattern was observed each year: a large bloom in June corresponded to the timing of the herring spawn and low nutrients, low phytoplankton diversity, and high POC concentrations; elucidating a previously unidentified pulse of new nutrients to the system. Estimates of carbon export are affected by the physical environment. The model presented and validated herein is used to improve our understanding of C export by including the effect of horizontal transport. We show that measurements of export to shallow water traps are less impacted by currents than deep traps. Spatial extent of variable primary production necessary to affect deep water traps is greater, as such, over half of the traps analyzed in this study are affected by up-current productivity regimes. A method to simultaneously quantify the C and N fixing community in the same sample was developed, eliminating many assumptions introduced when using different techniques and incubations. Cultured and environmental samples were successfully hybridized using TSA-FISH. Strong correlations between positively tagged community abundance and ^(14)C/^(15)N measurements are presented. The findings of this work support the general hypothesis that new production is under-accounted for in marine systems.Item Hierarchical three-dimensional Fe-Ni hydroxide nanosheet arrays on carbon fiber electrodes for oxygen evolution reaction(2014-05) O'Donovan-Zavada, Robert Anthony; Manthiram, ArumugamAs demands for alternative sources of energy increase over the coming decades, water electrolysis will play a larger role in meeting our needs. The oxygen evolution reaction (OER) component of water electrolysis suffers from slow kinetics. An efficient, inexpensive, alternative electrocatalyst is needed. We present here high-activity, low onset potential, stable catalyst materials for OER based on a hierarchical network architecture consisting of Fe and Ni coated on carbon fiber paper (CFP). Several compositions of Fe-Ni electrodes were grown on CFP using a hydrothermal method, which produced an interconnected nanosheet network morphology. The materials were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Electrochemical performance of the catalyst was examined by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The best electrodes showed favorable activity (23 mA/cm², 60 mA/mg), onset potential (1.42 V vs. RHE), and cyclability.Item High Rydberg states and ionization potential of carbon(Texas Tech University, 1997-05) Glynn, Patrick ToddThe ionization potential (IP) as well as the coupling and interactions occurring between the states converging to each of the spin-orbit split states of the ground state of the ion core are analyzed using resonance enhanced multiphoton ionization (REMPI) spectroscopy. Although this is not the first time that the IP for carbon has been measured, the measurement was made to an as yet unseen level of accuracy. Additionally, this is the first time that the interseries interactions have been analyzed for the 2pnp states of carbon. This was accomplished by first exciting from the 2s22p2 3Pj (1 = 0, 1,2) ground state up to the 2p3s 3Pj (1 = 0, 1,2) intermediate state with a vacuum ultraviolet (VUV) photon. This enabled a second transition up to the Rydberg states for the respective transitions. The Rydberg states were scanned from a principal quantum number of about 30 to well beyond the ionization limit. From the analysis of these states, the ionization limit for the series converging to the2P1/2 state of the excited core is determined to an accuracy of ±0.05 cm-1. Additionally, the series interactions occurring within the Rydberg series excited from the 2p3s 3Pj and 2p3s 3P0 states were analyzed to yield quantum defects, interaction matrix elements, and relative dipole matrix elements for comparison to theoretical calculations.Item High-Resolution Carbon Isotope Stratigraphy, Pennsylvanian Snaky Canyon Formation, East-Central Idaho: Implications for Regional and Global Correlations(2012-07-16) Jolley, CaseyNearly 550 samples of fine grained carbonates, collected every 0.5 to 1.0 m from the Bloom Member of the Snaky Canyon Formation at Gallagher Peak, Idaho, were analyzed to determine the high-resolution carbon isotope stratigraphy. To constrain for diagenesis, thin sections were petrographically analyzed and viewed using cathodoluminescence microscopy. Chemical analyses were performed using an electron microprobe. Average delta18O and delta13C values from the Bloom Member are -4.5% +/- 1.6% (1 sigma) and 2.1% +/- 1.1%, respectively. Maximum delta13C values are about 1% higher for the Desmoinesian and Missourian than the Morrowan and Atokan, similar to results from the Yukon Territory. delta18O and delta13C values are lowest for crystalline mosaic limestones and siltstones, moderate for packstones, wackestones, and mudstones, and highest for boundstones and grainstones. The delta13C profile from Gallagher Peak consists of high frequency 1% oscillations with several larger excursions. No large delta13C increase at the base of the section suggests the Mid-Carboniferous boundary is in the underlying Bluebird Mountain formation. delta13C of Gallagher Peak and Arrow Canyon, NV, correlate well from 318 to 310 Ma, but correlation becomes more difficult around 310 Ma. This may result from increased restriction of the Snaky Canyon platform beginning in the Desmoinesian. Most of the short term (<1 Ma) isotopic excursions are the result of diagenesis. Two of the largest negative excursions at Gallagher Peak correlate with two large negative excursions at Big Hatchet Peak, NM, possibly due to sea level lowstands of the Desmoinesian. Phylloid algal mounds at Gallagher Peak are associated with positive excursions because of original aragonite composition and increased open marine influence. Positive excursions related to other facies characteristics also result from increased marine influence. The delta13C curve for the upper half of Gallagher Peak contains three repeated cycles of increasing delta13C over 1-1.5 Ma, which are possibly related to long-term sea level fluctuations. Given the complexity of each local environment, without detailed biostratigraphy, detailed rock descriptions, and analysis of the various rock components, delta13C stratigraphy of whole rocks can be misinterpreted.Item Human Appropriation of Net Primary Productivity (HANPP) in Texas: A Statewide Analysis of Sustainability in the Agricultural and Timber Sectors(2010-07-14) Graff, Christopher P.The sustainability of the Texas agricultural and timber sectors is measured using the ratio of human appropriation of net primary productivity (HANPP) to available net primary productivity (NPP) on a county-by-county basis for the entire state. By combining NPP and HANPP, a measure of ecologic sustainability in terms of carbon dynamics is achieved. This is based on a six-year average from 2000 to 2005 obtained from the NASA MODIS sensor, as well as the calculated NPP harvested from agricultural and timber activities reported by USDA Agricultural and Texas Forest Department timber statistics covering the same years. The spatial pattern of NPP in Texas is strongly influenced by moisture availability and is naturally highest in the Gulf Coastal Plains, and parts of east Texas. Areas of artificially-high NPP can often rival or surpass naturally occurring NPP and occur primarily due to irrigation, such as in the Panhandle and lower Rio Grande Valley. Human appropriation of this carbon is greatest in the Panhandle and lower Rio Grande Valley where, in many counties, >45% of all carbon produced is appropriated. HANPP values throughout the rest of the state are moderate (10-24%) corresponding well with global and national HANPP literature. These results support two conflicting findings: increased HANPP indicates decreased ecological sustainability, but is also a measure of increased agricultural efficiency.Item Magnetic, thermoelectric, and electronic properties of layered oxides and carbon materials(2007) Caudillo, Roman, 1977-; Goodenough, John B.; Jose-Yacaman, MiguelThe structure and physical properties of layered oxides and carbon materials were studied. Two layered carbon materials were studied: carbon nanotubes (CNTs) synthesized by electron irradiation from amorphous carbon in situ in a transmission electron microscope (TEM) and a carbon and silver nanocomposite consisting of graphitic carbon nanospheres encapsulating Ag nanoparticles. In the CNT experiments, the effect of electron irradiation in the TEM is shown to alter drastically their structure and properties, even being able to transform amorphous carbon into a CNT. This suggests a possible alternative synthesis technique for the production of CNTs, in addition to providing a method for tailoring their properties. The structure and magnetic properties of the carbon and silver nanocomposite was characterized with x-ray diffraction, scanning and transmission electron microscopy techniques, and magnetic susceptibility measurements with a superconducting quantum interference device (SQUID) magnetometer. While the sp² bonding gives a grapheme sheet its mechanical properties, the p[subscript pi] electrons are responsible for its electronic and magnetic properties. In a flat graphene sheet the p[subscript pi] electrons are itinerant, but in a narrow p[subscript pi] band. The introduction of curvature to the graphene sheets that encapsulate the Ag nanoparticles is demonstrated to narrow the p[subscript pi] band sufficiently to result in "ferromagnetic" behavior. A model that is able to explain spin localization and ferrimagnetic spin-spin interactions in graphitic materials with positive curvature is presented. Layered oxides from the family of the P2 Na[subscript x]CoO₂ structure were synthesized and their properties studied. Na[subscript x]CoO₂ has a rich phase diagram ranging form a promising Na-rich thermoelectric composition to the hydrated Na-poor composition Na[subscript 0.33]CoO₂· 1.3H₂O that is superconductive. Intermediate to these two Na compositions exists an insulating phase with x [approximately equal to] 0.5 that presents a variety of interesting structural, magnetic, thermoelectric, and electronic behavior. Investigations of Na[subscript x]CoO₂ that probe the role of H₂O in the superconductive Na[subscript 0.33]CoO₂· 1.3H₂O are presented and conclude that H₂O plays a more active role than a passive lattice spacer. The relationship between Na ordering and an interesting magnetic behavior observed with [chi](T) measurements of annealed NaxCoO₂ and Sr[subscript x/2]CoO₂ samples is determined and found to correspond to a (2a x 2a) superstructure. The properties of NaxCoO₂ (x [approximately equal to] 0.5) are reviewed and thermoelectric S(T) measurements are made in order to develop a model that is able to explain the salient features of the NaxCoO₂ (x [approximately equal to] 0.5) phase.Item Municipal economic growth through green projects and policies(2012-05) Lindner, Harry Dreyfus; Gamkhar, ShamaCities generally need economic growth. Green policies and projects are environmentally beneficial, desirable, expected by the public, and pragmatic in the long term. However, there is insufficient research on what, if any, municipal green projects and policies generate economic growth. To address this question, the author created a database of green and economic indicators, and modeled the green indicators to predict the economic indicators. The database included carbon usage, transportation metrics, water usage, the number of green jobs, and the gross domestic product (GDP) for the 100 largest cities, defined by metropolitan statistical area (MSA), in the U.S. To gather data on green indicators, existing green rankings, indices, and reports were evaluated for methodology and usability for this paper. The results of the data-gathering step show the need for more and better data collection. That means an increased number of green indicators should be collected, and data should be collected at the MSA (or county) level for more of the largest cities. Specifically to name some green indicators, data collection on energy usage, buildings, waste, land use, air quality, and food could be improved. Those green indicators would likely be included in a model that uses green indicators to predict green jobs or GDP. However, those were not included for the regressions in this paper. The results of the regressions in this paper show two indicators with promise for predicting economic growth as defined by GDP and number of green jobs: (1) percent of people using public transportation, biking, or walking to work, and (2) public water consumption per person. The first explanatory variable indirectly measures the adoption of policies that promote public transportation, biking, and walking. The results suggest that these policies have a positive effect on GDP and number of green jobs. This means the results suggest that as the percent increases, so does GDP and number of green jobs. The second explanatory variable measures the water conservation policies. The results suggest this variable has a negative, albeit weaker relationship with GDP per person. This means the results suggest as water conservation increases (less water usage per person), the GDP per person increases. This paper offers a methodology and some of the groundwork for building a model to show which, if any, municipal green projects and policies predict economic growth.Item Nanoscale graphene for RF circuits and systems(2013-08) Parrish, Kristen Nguyen; Akinwande, DejiIncreased challenges in CMOS scaling have motivated the development of alternatives to silicon circuit technologies, including graphene transistor development. In this work, we present a circuit simulator model for graphene FETs, developed to both fit measured data and predict new behaviors, motivating future research. The model is implemented in Agilent ADS, a circuit level simulator that is commonly used for non-standard transistor technologies, for use with parameter variation analyses, as well as easy integration with CMOS design kits. We present conclusions drawn from the model, including analyses on the effects of contact resistance and oxide scaling. We have also derived a quantum-capacitance limited model, used to intuit intrinsic behaviors of graphene transistors, as well as outline upper bounds on performance. Additionally, the ideal frequency doubler has been examined and compared with graphene, and performance limits for graphene frequency multipliers are elucidated. Performance as a demodulator is also discussed. We leverage this advancement in modeling research to advance circuit- and system-level research using graphene transistor technology. We first explore the development of a GHz planar carbon antenna for use on an RF frontend. This research is further developed in work towards the first standalone carbon radio on flexible plastics. A front end receiver, comprised of an integrated carbon antenna, transmission lines, and a graphene transistor for demodulation, are all fabricated onto one plastic substrate, to be interfaced with speakers for a full radio demo. This complete system will motivate further research on graphene-on-plastic systems.Item New insights into the carbon isotope composition of speleothem calcite : an assessment from surface to subsurface(2012-05) Meyer, Kyle William; Banner, Jay L.; Breecker, Dan O.; Musgrove, MaryLynnThe purpose of this study was to provide new insights into the interpretation of speleothem (cave calcite deposit) δ13C values. We studied two caves in central Texas, which have been actively monitored for over 12 years. We compared δ13C values of soil CO2 (δ13Cs), cave drip water (δ13CDIC), and modern cave calcite (δ13Ccc). Measured average δ13C values of soil CO2 were -13.9 ± 1.4‰ under mixed, shallowly-rooted C3-C4 grasses and were -18.3 ± 0.7‰ under deeply-rooted ashe juniper trees (C3). The δ13CDIC value of minimally-degassed drip water in Natural Bridge Caverns was -10.7 ± 0.3‰. The carbon isotope composition of CO2 in equilibrium with this measured drip water is -18.1 ± 0.3‰. The agreement between juniper soil CO2 and drip water (within ~0.2‰) suggests that the δ13C value of drip water (δ13CDIC) that initially enters the cave is controlled by deeply-rooted plants and may be minimally influenced by host-rock dissolution and/or prior calcite precipitation (PCP). At Inner Space Caverns, δ13CDIC values varied with vegetation above the drip site, distance from the cave entrance, and distance along in-cave flow paths. Whereas CO2 derived from deeply-rooted plants defines the baseline for drip water δ13CDIC entering the caves, kinetic effects associated with the degassing of CO2 and simultaneous precipitation of calcite account for seasonal variability in δ13CDIC and δ13Ccc. We documented increases in δ13CDIC at a rate of up to 0.47‰/hour during the season of peak degassing (winter), suggesting that δ13CDIC variations may be controlled by total elapsed time of CO2 degassing from drip water (Ttotal). We also observed seasonal shifts in the δ13C values of modern calcite grown on glass substrates that are correlated with shifts in drip water δ13CDIC values and drip-rate. Therefore, we suggest that increased aridity at the surface above a given cave results in, slower drip-rates, higher Ttotal, and therefore higher δ13CDIC values. We propose that large variability (>2‰) in speleothem δ13Ccc values dominantly reflect major vegetation changes, and/or increasing Ttotal by slowing drip-rates. Based on these findings, variability in speleothem carbon isotope records may serve as a proxy for paleoaridity and/or paleovegetation change.Item Preparation and characterization of nitrogen doped carbon nanotube electrode materials(2006) Maldonado, Stephen; Stevenson, Keith J.This dissertation describes the preparation and characterization of nitrogen doped carbon nanotube films by a chemical vapor deposition (CVD) process. Thorough description of the preparation method is given. A variety of techniques are used to demonstrate the relationship between the physicochemical properties and electrochemical properties of nitrogen doped carbon nanotubes, shedding insight to the influence of nitrogen doping on observed electrocatalysis phenomena. Chapter 1 comprises a general overview of the presented material and scope of the work. Chapter 2 details the CVD preparation of nitrogen doped carbon nanotubes. Scanning electron microscopy, thermal gravimetric analysis, and x-ray photoelectron spectroscopy are used to demonstrate the degree of control afforded by the CVD process over the resultant properties of the prepared carbon nanotubes. The direct preparation of carbon nanotube films on a current collector is shown. Chapter 3 consists of a thorough characterization and comparison of nitrogen doped carbon nanotubes and non-doped carbon nanotubes. Transmission electron microscopy, thermal gravimetric analysis, and Raman spectroscopy demonstrate the increased disorder caused by nitrogen doping into the graphitic lattice structure of carbon nanotubes. X-ray photoelectron spectroscopy highlights the existence of multiple carbon-nitrogen surface functionalities that change in relative abundance as the nitrogen content is varied. Titration analyses indicate that nitrogen doped carbon nanotubes are basic and acquire a cationic surface charge in solutions of neutral pH. Chapter 4 presents a collection of voltammetric responses of several outer-sphere and innersphere redox probes. The similarities and differences between the responses at non-doped carbon nanotube electrodes and nitrogen doped carbon nanotube electrodes are noted and discussed in the context of the conclusions of the physical characterizations. A detailed mechanistic analysis of the O2 reduction process at nitrogen doped carbon nanotube electrodes is presented. Chapter 5 details continuing work with carbon nanotube materials for fundamental and applied studies.