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Articles 1 - 7 of 7
Full-Text Articles in Physical Sciences and Mathematics
Thermionic Emission Properties Of Novel Carbon Nanostructures., Andriy Sherehiy
Thermionic Emission Properties Of Novel Carbon Nanostructures., Andriy Sherehiy
Electronic Theses and Dissertations
Materials with low work function values (< 2 eV) are highly in demand for low temperature thermionic electron emission, which is a key phenomenon for waste heat recovery applications. Here we present the study of the thermionic emission of the hybrid structure phosphorus, (P) doped diamond nano crystals grown on conical carbon nanotubes (CCNTs). The CCNTs provide the conducting backbone for the P-doped diamond nanocrystals. In the first part of this thesis thermionic emission properties of conical carbon nanotubes (CCNTs) grown on platinum wires and planar graphite foils were investigated. The work function (Φ) values extracted from the thermionic emission data range from 4.1 to 4.7 eV. The range of Φ values is attributed to the morphological characteristics, such as tip radius, aspect ratio, density, and wall structure of CCNTs. The observed lower values for Φ are significantly smaller than that of multi-walled carbon nanotubes (MWNTs). The reduced Φ values are attributed to field penetration effect as a result of the local field enhancement from these structures having high aspect ratio and an excellent field enhancement factor. The high amplification of the external field at the apex of the nanostructures is capable of reducing both the barrier height and the width, in turn contributing to the improved emission current at lower temperatures. The ultraviolet photoemission spectroscopy data of CCNTs grown on Pt wires are in reasonable agreement with the thermionic emission data. In the next part of the thesis we present work function reduction of phosphorus (P) doped (i) diamond nanocrystals grown on conical carbon nanotubes (CCNTs) and (ii) diamond films grown on silicon substrates. Thermionic emission measurements from phosphorus doped diamond crystals on CCNTs resulted in work function value of 2.23 eV. The reduced work-function is interpreted as due to the presence of the surface states and midband-gap states and no evidence for negative electron affinity was seen. However, Ultraviolet photo-spectroscopy studies on phosphorus doped diamond films yielded a work function value of ~1.8 eV with a negative electron affinity (NEA) value of 1.2 eV. Detailed band diagrams are presented to support the observed values for both cases. In addition we determined the work function values of nanocrystalline P doped diamond films grown on W foil to be significantly lower, 1.0- 1.33 eV compared to the hybrid structure and polycrystalline film on Si substrates. We studied tungsten (W) nanowires as an alternative material in place of CCNT as the supporting and conducting channel for P doped diamond crystals in a new hybrid structure. We described the process of fabrication of arrays of vertical W nanowires by microwave plasma treatment and synthesis of P doped nanocrystalline diamond on top of the reduced W nanowires. Thermionic emission measurements from the alternative hybrid structure resulted in high value of the work function ~ 5.1 eV.
Peatland-Stream Hydrological And Biogeochemical Connectivity In The James Bay Lowland, Ontario, Meghan Kline
Peatland-Stream Hydrological And Biogeochemical Connectivity In The James Bay Lowland, Ontario, Meghan Kline
Electronic Thesis and Dissertation Repository
The Hudson-James Bay Lowlands are the second largest peatland dominated area on the planet, and are expected to be particularly vulnerable to future climate change. Changes in climate will affect peatland hydrology and biogeochemistry, impacting the aquatic ecosystems this region supports, however there is limited information about the hydrology and biogeochemistry of this landscape under current conditions. This thesis focuses on assessing the nature of hydrological and biogeochemical connectivity between a fen and 2nd order channel in the Central James Bay Lowland, Ontario. Specifically the study focuses on the role of preferential hydrological flowpaths in the riparian area, such …
Using Green Building To Mitigate Climate Change In The Twenty-First Century, Lisa Battiste
Using Green Building To Mitigate Climate Change In The Twenty-First Century, Lisa Battiste
Honors Theses
The need for green buildings are rapidly becoming more important as the nation faces impending energy crises and the world heats up from the overabundance of greenhouse gases. Buildings in America are one of the largest consumers of energy and one of the greatest contributors to CO2 emissions; more than the total emissions from all the transportation vehicles used every day. By making the construction and use of buildings more resource efficient, this can help alleviate the environmental strain of climate change. Neutralizing or eliminating carbon emissions from building use will significantly reduce the amount of greenhouse gases in the …
Hydrology And Biogeochemistry Of A Bog-Fen-Tributary Complex In The Hudson Bay Lowlands, Ontario, Canada, Thomas A. Ulanowski
Hydrology And Biogeochemistry Of A Bog-Fen-Tributary Complex In The Hudson Bay Lowlands, Ontario, Canada, Thomas A. Ulanowski
Electronic Thesis and Dissertation Repository
The Hudson Bay Lowlands (HBL) contains 26 Gt C sequestered in a 2 meter thick layer of peat which blankets a quarter of Ontario, Canada. The hydrological and chemical influence of the HBL peatlands to surface waters is recognized, but information on peatland runoff processes and the evolution of groundwater through this vast, carbon-rich landscape remain scant. This study focused on elucidating the groundwater flow patterns of a bog-fen-tributary complex in the central region of the HBL, and estimating exports of groundwater, dissolved organic carbon (DOC), total (THg), and methyl (MeHg) mercury during the 2011 ice-free season. Hydrometric data, combined …
Impacts Of Climate Change On Soil Microorganisms In Northern Hardwood Forests, Carley Jane Kratz
Impacts Of Climate Change On Soil Microorganisms In Northern Hardwood Forests, Carley Jane Kratz
Dissertations, Master's Theses and Master's Reports - Open
As global climate continues to change, it becomes more important to understand possible feedbacks from soils to the climate system. This dissertation focuses on soil microbial community responses to climate change factors in northern hardwood forests. Two soil warming experiments at Harvard Forest in Massachusetts, and a climate change manipulation experiment with both elevated temperature and increased moisture inputs in Michigan were sampled. The hyphal in-growth bag method was to understand how soil fungal biomass and respiration respond to climate change factors. Our results from phospholipid fatty acid (PLFA) analyses suggest that the hyphal in-growth bag method allows relatively pure …
Modeling The Effects Of The Hemlock Woolly Adelgid On Carbon Storage In Northern New England Forests, Jeffrey John Krebs
Modeling The Effects Of The Hemlock Woolly Adelgid On Carbon Storage In Northern New England Forests, Jeffrey John Krebs
Graduate College Dissertations and Theses
The hemlock woolly adelgid (HWA, Adelges tsugae Annand) is an invasive insect that threatens to eradicate native eastern hemlock (Tsuga canadensis (L.) Carr.) across the eastern United States. In southern New England and southern Appalachian forests, HWA-induced hemlock mortality has impacted carbon (C) flux by altering stand age, litter composition, species composition, and coarse woody debris levels. However, no one has examined how total C storage and sequestration may be impacted by these changes. Further, while projections are that HWA will ultimately infest hemlock across its entire geographic range, the majority of studies have been limited to southern New …
Carbon And Nitrogen Isotope Analysis Of Archaeological Faunal Material From Dutchess Quarry Caves, Ny, Jessica Zuhlke
Carbon And Nitrogen Isotope Analysis Of Archaeological Faunal Material From Dutchess Quarry Caves, Ny, Jessica Zuhlke
Legacy Theses & Dissertations (2009 - 2024)
The purpose of this study was to do an isotopic analysis to determine the carbon and nitrogen isotope concentrations of archaeological faunal material found in the Dutchess Quarry Caves in Orange County, NY. These isotope values were then used to compare the taxa from which the samples were taken to determine if and how trophic relationships were formed. The main focus of this comparison spotlighted a sample from a human femur; to establish the human's position trophically with the other large and small mammal samples collected. The human had been previously radiocarbon dated to have lived between 2877 and 3180 …