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Articles 1 - 9 of 9
Full-Text Articles in Physical Sciences and Mathematics
Earth Abundant Thin Film Technology For Next Generation Photovoltaic Modules, Githin Alapatt
Earth Abundant Thin Film Technology For Next Generation Photovoltaic Modules, Githin Alapatt
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With a cumulative generation capacity of over 100 GW, Photovoltaics (PV) technology is uniquely poised to become increasingly popular in the coming decades. Although, several breakthroughs have propelled PV technology, it accounts for only less than 1% of the energy produced worldwide. This aspect of the PV technology is primarily due to the somewhat high cost per watt, which is dependent on the efficiency of the PV cells as well as the cost of manufacturing and installing them. Currently, the efficiency of the PV conversion process is limited to about 25% for commercial terrestrial cells; improving this efficiency can increase …
Toward Understanding The Thermodynamics And Mechanisms Of Actinide Sorption Reactions, Shanna Estes
Toward Understanding The Thermodynamics And Mechanisms Of Actinide Sorption Reactions, Shanna Estes
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The environmental fate of actinides is greatly influenced by interfacial reactions, including sorption onto solid surfaces. Because changes in the primary hydration sphere of the actinide are expected to greatly influence the thermodynamics (i.e., reaction enthalpy and entropy) of these reactions, examining actinide sorption thermodynamics may provide insight into actinide sorption mechanisms. Additionally, examining actinide sorption thermodynamics may enhance the ability to model or predict these reactions in environmental or engineered systems where variable or elevated temperatures are expected. However, few researchers have studied actinide sorption thermodynamics. Therefore, this research examined the thermodynamics of Eu(III) (a trivalent actinide analog), Th(IV), …
A Comprehensive Assessment Methodology Based On Life Cycle Analysis For On-Board Photovoltaic Solar Modules In Vehicles, Mahmoud Abdelhamid
A Comprehensive Assessment Methodology Based On Life Cycle Analysis For On-Board Photovoltaic Solar Modules In Vehicles, Mahmoud Abdelhamid
All Dissertations
This dissertation presents a novel comprehensive assessment methodology for using on-board photovoltaic (PV) solar technologies in vehicle applications. A well-to-wheels life cycle analysis based on a unique energy, greenhouse gas (GHG) emission, and economic perspective is carried out in the context of meeting corporate average fuel economy (CAFE) standards through 2025 along with providing an alternative energy path for the purpose of sustainable transportation. The study includes 14 different vehicles, 3 different travel patterns, in 12 U.S. states and 16 nations using 19 different cost analysis scenarios for determining the challenges and benefits of using on-board photovoltaic (PV) solar technologies …
Experimental Evidence For Colloid-Facilitated Transport Of Plutonium, Hilary Emerson
Experimental Evidence For Colloid-Facilitated Transport Of Plutonium, Hilary Emerson
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Colloid-facilitated transport of the actinides has been observed previously in the field on the kilometer scale. The objective of this work is to investigate the mechanisms of colloid-facilitated transport with controlled settings and conditions. The experimental work in this dissertation investigates transport of a ternary complex with iron oxide colloids, organic ligands and actinides in the presence of quartz or a natural sandy soil as well as simplified systems building up to the ternary complexes. The first three papers investigate the following: (1) unsaturated transport of iron oxide colloids in a natural sandy soil lysimeter with and without natural organic …
Integrating Visual Mnemonics And Input Feedback With Passphrases To Improve The Usability And Security Of Digital Authentication, Kevin Juang
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The need for both usable and secure authentication is more pronounced than ever before. Security researchers and professionals will need to have a deep understanding of human factors to address these issues. Due to their ubiquity, recoverability, and low barrier of entry, passwords remain the most common means of digital authentication. However, fundamental human nature dictates that it is exceedingly difficult for people to generate secure passwords on their own. System-generated random passwords can be secure but are often unusable, which is why most passwords are still created by humans. We developed a simple system for automatically generating mnemonic phrases …
An Experimental Investigation Towards Improvement Of Thermoelectric Properties Of Strontium Titanate Ceramics, Arash Mehdizadeh Dehkordi
An Experimental Investigation Towards Improvement Of Thermoelectric Properties Of Strontium Titanate Ceramics, Arash Mehdizadeh Dehkordi
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The direct energy conversion between heat and electricity based on thermoelectric effects is a topic of long-standing interest in condensed matter materials science. Experimental and theoretical investigations in order to understand the mechanisms involved and to improve the materials properties and conversion efficiency have been ongoing for more than half a century. While significant achievements have been accomplished in improving the properties of conventional heavy element based materials (such as Bi$_2$Te$_3$ and PbTe) as well as the discovery of new materials systems for the close-to-room temperature and intermediate temperatures, high-temperature applications of thermoelectrics is still limited to one materials system, …
Investigation Of Concurrent Energy Harvesting From Ambient Vibrations And Wind, Amin Bibo
Investigation Of Concurrent Energy Harvesting From Ambient Vibrations And Wind, Amin Bibo
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In recent years, many new concepts for micro-power generation have been introduced to harness wasted energy from the environment and maintain low-power electronics including wireless sensors, data transmitters, controllers, and medical implants. Generally, such systems aim to provide a cheap and compact alternative energy source for applications where battery charging or replacement is expensive, time consuming, and/or cumbersome. Within the vast field of micro-power generation, utilizing the piezoelectric effect to generate an electric potential in response to mechanical stimuli has recently flourished as a major thrust area. Based on the nature of the ambient excitation, piezoelectric energy harvesters are divided …
A Biophysical Understanding Of The Applications And Implications Of Nanomaterials, Nicholas Geitner
A Biophysical Understanding Of The Applications And Implications Of Nanomaterials, Nicholas Geitner
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The last few decades have seen an explosion in the study and application of nanomaterials that continues to grow at a dizzying pace. Despite exciting applications in nano-enabled electronics, materials, medicine, and environmental remediation, an understanding of the interactions of these materials with natural materials and systems and the resulting implications lags severely behind. The purpose of this Dissertation is to illuminate these interactions as well as develop novel environmental applications from a biophysical perspective. Following an introduction and literature review in Chapter 1, Chapters 2-4 will explore the application of dendritic polymers as novel and biocompatible oil dispersants for …
Isolated And Ephemeral Wetlands Of Southern Appalachia: Biotic Communities And Environmental Drivers Across Multiple Temporal And Spatial Scales, Joanna Hawley
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Throughout the world, wetlands are known to support a wide variety of taxa as well as high levels of biodiversity and species richness. Although the ecological significance of wetlands is well documented in the scientific literature, efforts to map and assess wetlands on regional or national scales (e.g., National Wetlands Inventory (NWI)) often overlook wetlands which are either very small (< 1 ha) or have ephemeral hydroperiods. While the vast majority of wetland research in the southeastern United States has focused on wetlands distributed across the coastal plain ecoregion, very little information exists on small and/or ephemeral wetlands in areas of southern Appalachia, although there are several notable exceptions. Despite the paucity of small wetland data in this region, the southeastern US is known as a hotspot for both aquatic biodiversity and species endemism. My goal with this project was to examine the biotic communities inhabiting small, ephemeral and geographically-isolated wetlands to identify the major environmental drivers that contribute to observed community patterns and species' distributions. I studied a set of small, mostly-ephemeral, mostly-isolated wetlands (N = 41) in the upper Piedmont and lower Blue Ridge ecoregions of South Carolina from January-June of 2010 and 2011 and focused my efforts on describing the structure, biotic communities and surrounding habitat characteristics of my study wetlands. I observed high levels of species richness and biodiversity in this previously-undocumented wetland system, despite the small size and ephemeral nature of study wetlands. My results indicated that the amphibian and benthic invertebrate communities of small, ephemeral wetlands responded to different environmental drivers (e.g., wetland depth, area, hydroperiod, canopy cover, surrounding land use types) occurring across multiple spatial and temporal scales. Additionally, the amphibian community was significantly influenced by a number of environmental variables occurring at both the within-pond scale and larger spatial scales (250 m, 500 m and 1 km surrounding land cover variables). By contrast, the benthic invertebrate community was significantly influenced primarily by variables occurring at the within-pond scale. This wetland system also served as both breeding and overwintering habitat for a variety of species such as wood frogs (Lithobates sylvatica), spotted salamanders (Ambystoma maculatum), bullfrogs (Lithobates catesbeiana), cricket frogs (Acris crepitans). This study highlights the ecological importance of small, ephemeral aquatic habitats in a region where little research exists regarding such systems; these often-unnoticed ecosystems are likely the result of a combination of historical anthropogenic and natural environmental process. These legacy wetlands (i.e., wetlands that are the unintended result of some human-induced environmental change in either the recent or long-term past) are found ubiquitously across the landscape and are often missed by coarse-filter mapping approaches (e.g., National Wetlands Inventory). I observed many study wetlands to be extremely small in size (< 0.05 ha) and that many wetlands were habitats of circumstance and opportunity rather than of permanence and predictability. The ephemerality of the majority of study wetlands demonstrates the biological significance of small, temporary habitats for many species requiring these habitats for breeding activity. Despite the small size and ephemeral nature of my study wetlands, I found that these wetlands represented a large proportion of amphibian biodiversity in the regional species pool and thus, are an important conservation feature at the local, landscape and regional scales. My study demonstrates that small, semi-isolated, mostly-ephemeral wetlands in southern Appalachia support high levels of biodiversity and are an important asset deserving of further study and conservation recognition.