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Understanding N-Nitrosodimethylamine Formation In Water: Chloramine Chemistry, Kinetics, And A Proposed Reaction Pathway, Huong Thu Pham

Graduate Theses and Dissertations

The formation of N-nitrosodimethylamine (NDMA) in drinking water systems is a concern because of its potential carcinogenicity and occurrence at toxicologically relevant levels. The postulated mechanism for NDMA formation involves a substitution between dichloramine and amine-based precursors to form an unsymmetrical dimethylhydrazine (UDMH), which is then oxidized by ground-state molecular oxygen to form NDMA. However, this latter reaction is spin forbidden, thus likely occurs at a slow rate. It is hypothesized that the reaction between monochloramine and hydroxylamine (a nitrification product) may form an intermediate, which is involved in the NDMA formation pathway. This intermediate may also be generated from …

Computer Simulation Of Pore Migration Due To Temperature Gradients In Nuclear Oxide Fuel, Ian Wayne Vance

Graduate Theses and Dissertations

A phase-field simulation model is being presented that captures the thermal-gradient-driven migration of pores in oxide fuel associated with fuel restructuring. The model utilizes a Cahn-Hilliard equation supplemented with an advection term to describe the vapor transport of fuel material through the pore interior due to gradients in vapor pressure. In addition, the model also captures changes in a migrating pores’ morphology. Simulations demonstrate that the model successfully predicts pore migration towards the hottest portion of the fuel, the centerline. The simulations also demonstrate changes in pore shape that are in agreement with previous experimental observations. Initially isotropic pores are …

Exploring Compaction Effects On Cold In-Place Recycling Mixtures Using Emulsified Asphalt, Erica Ann Yeung

Graduate Theses and Dissertations

Cold in-place recycling (CIR) is a process that takes three to four inches of existing pavement surface and reuses 100% of it by milling and crushing it, adding asphalt emulsions and/or additives to it, before placing and re-compacting it. There is currently very little research regarding the interaction between the crushed aggregate and asphalt emulsion during the CIR process. In this study, the interactions between the combinations of crushed aggregates and asphalt emulsions were investigated along with select compaction metrics and a raveling performance test. The three types of aggregates included coated limestone, recycled asphalt pavement (RAP), and coated syenite. …

Feasibility Of Additive Manufactured Materials For Use In Geotechnical Laboratory Testing Applications, Matthew P. Watters

Graduate Theses and Dissertations

The factors affecting the positive volumetric strain, or dilatancy, typically observed in response to shearing of a dense granular material have long been investigated; however, there still lacks a direct relationship between particle shapes and the resulting dilatant response. The typical Mohr-Coulomb strength parameter associated with granular material is known as the effective friction angle (φ’). For a dense granular assemblage, the peak friction angle has been described as being comprised of a dilatant friction angle (φ’d) component and a critical state friction angle (φ’cv) component. While the topic of dilatancy and factors (both inherent and extrinsic) affecting its behavior …

Characterization Of Plastic Deformation Evolution In Single Crystal And Nanocrystalline Cu During Shock By Atomistic Simulations, Mehrdad Mirzaei Sichani

Graduate Theses and Dissertations

The objective of this dissertation is to characterize the evolution of plastic deformation mechanisms in single crystal and nanocrystalline Cu models during shock by atomistic simulations. Molecular dynamics (MD) simulations are performed for a range of particle velocities from 0.5 to 1.7 km/s and initial temperatures of 5, 300 and 600 K for single crystal models as well as particle velocities from 1.5 to 3.4 km/s for nanocrystalline models with grain diameters of 6, 11, 16 and 26 nm. For single crystal models, four different shock directions are selected, <100>, <110>, <111> and <321>, and dislocation density behind the shock wave …

Total N-Nitrosamine Precursor Adsorption With Carbon Nanotubes: Elucidating Controlling Physiochemical Properties And Developing A Size-Resolved Precursor Surrogate, Erin Needham

Graduate Theses and Dissertations

As drinking water sources become increasingly impaired with nutrients and wastewater treatment plant (WWTP) effluent, formation of disinfection byproducts (DBPs) – such as trihalomethanes (THMs), dihaloacetonitriles (DHANs), and N-nitrosamines – during water treatment may also increase. N-nitrosamines may comprise the bulk of the chronic toxicity in treated drinking waters despite forming at low ng/L levels. This research seeks to elucidate physicochemical properties of carbon nanotubes (CNTs) for removal of DBP precursors, with an emphasis on total N-nitrosamines (TONO).

Batch experiments with CNTs were completed to assess adsorption of THM, DHAN, and TONO precursors; physiochemical properties of CNTs were quantified through …

Development Of A Multiband Remote Sensing System For Determination Of Unsaturated Soil Properties, Cyrus D. Garner

Graduate Theses and Dissertations

A multiband system including active microwave sensing and visible-near infrared reflectance spectroscopy was developed to measure unsaturated soil properties in both field and laboratory environments. Remote measurements of soil volumetric water content (θv), soil water matric potential (ψ), and soil index properties (liquid limit [LL], plastic limit [PL], and clay fraction [CF]) were conducted. Field-based measurement of θv was conducted using a ground-based radar system and field measurements within 10 percentage points of measurements acquired with traditional sampling techniques were obtained. Laboratory-based, visible and near infrared spectroscopy was found to be capable of obtaining empirical, soil specific regression functions (partial …

Trihalomethane, Dihaloacetonitrile, And Total N-Nitrosamine Precursor Adsorption By Carbon Nanotubes: The Importance Of Surface Oxides And Pore Volume, Erin Needham

Graduate Theses and Dissertations

As drinking water sources become increasingly impaired, enhanced removal of natural organic matter (NOM) may be required to curb formation of disinfection byproducts (DBPs) upon chlor(am)ination. While carbon nanotubes (CNTs) can adsorb NOM, their properties for DBP precursor adsorption have not been elucidated. Nine types of CNTs were assessed for trihalomethane (THM), dihaloacetonitrile (DHAN), and total N-nitrosamine (TONO) precursor adsorption. Batch isotherm experiments were completed with lake water and, to simulate an impaired condition, effluent from a wastewater treatment plant (WWTP). Adsorption varied with CNT type and dose, with TONO precursors having the highest percent removals from WWTP effluent (up …

Rock Art Management And Landscape Change: Mixed Field Assessment Techniques For Cultural Stone Decay, Kaelin M. Groom

Graduate Theses and Dissertations

As tourism continues to grow as one of the world’s most ubiquitous markets, the development and promotion of non-invasive techniques for cultural stone decay analysis and landscape change are vital to establishing conditional base-lines to best aid cultural heritage management (CRM) efficacy. Using rock art as a medium, this dissertation presents three independent case studies employing the Rock Art Stability Index (RASI) and repeat photography to explore the merits of mixed rapid field assessment techniques in relation to CRM and heritage tourism. While rock art is only one example of irreplaceable world heritage resources, examining how they decay and what …

Effect Of Column Axial Load On Skewed Smf Rbs Connection Demands, Clovis Desrochers

Graduate Theses and Dissertations

Steel buildings in high seismic areas often require special structural systems to transfer large lateral forces induced by earthquake accelerations. The selection of an appropriate seismic steel system (braced frame, moment frame, shear wall, etc.) is often influenced by architectural considerations. Moment frame configurations offer the most architectural flexibility, but are limited by code prequalification requirements that limit the use of non-orthogonal (skewed) beam-column connection geometries. A recent study has investigated laterally skewed moment frame connections, indicating that skew increases the potential for column twist and column flange yielding; however, it is unclear how realistic column axial loads will affect …

Numerical Simulation Of Metallic Uranium Sintering, Bruce Berry

Graduate Theses and Dissertations

Conventional ceramic oxide nuclear fuels are limited in their thermal and life-cycle properties. The desire to operate at higher burnups as is required by current utility economics has proven a formidable challenge for oxide fuel designs. Metallic formulations have superior thermal performance but are plagued by volumetric swelling due to fission gas buildup. In this study, we consider a number of specific microstructure configurations that have been experimentally shown to exhibit considerable resistance to porosity loss. Specifically, a void sizing that is bimodally distributed was shown to resist early pore loss and could provide collection sites for fission gas buildup. …

Feasibility Of Using Oxide Thickness Measurements For Predicting Crack Growth Rates In P91 Steel Components, Ralph Edward Huneycutt Iv

Graduate Theses and Dissertations

There are only few methods available for predicting the age of cracks that are found in high

temperature structural components during service; among the promising ones is the oxide

thickness measurement technique. Oxide thickness profiles are taken from crack surfaces of

components and used for predicting the rates of crack propagation. This technique is particularly

suitable for high temperature components fabricated from ferritic steels commonly used in power

plants that run on fossil fuels. To implement this technique, it is necessary to fully understand the

kinetics of high temperature oxidation in these steels. In this study, the oxidation characteristics

of …

The Spatial Ordering Of Nabataea: An Integrated Analysis Of The Geography, Architecture, And Morphology Of Nabataean Petra, Christopher Clifton Angel

Graduate Theses and Dissertations

The Nabataean city of Petra is well known for its sandstone architecture and rock-hewn funerary landscape. Over the last few decades, numerous studies examined their history, culture, art, and architecture. The few studies that assessed the urban space of Petra focused on the functional properties of individual architectural forms and their nominal placement within the overall landscape. This study focused on the spatial configurations of architecture as relational to the dynamics of Nabataean politics and ritual where shifts in social order manifested similar shifts in spatial order which in turn produced and reproduced forms of social order. The production of …

A Comparison Of Force And Pressure Coefficients On Dome, Cube And Prism Shaped Buildings Due To Straight And Tornadic Wind Using Three Dimensional Computational Fluids Dynamics, Majdi A. A. Yousef

Graduate Theses and Dissertations

Tornadoes induce very different wind forces than a straight-line (SL) wind. A suitably designed building for a SL wind may fail when exposed to a tornado-wind of the same wind speed. It is necessary to design buildings that are more resistant to tornadoes. Most studies have been conducted to investigate tornado forces on cubic, gable-roof and cylinder buildings. However, little attention has been paid to investigate tornado force on dome buildings; hence, further research is conducted in this study. The forces on a dome, cube and prisms were analyzed and compared using Computational Fluid Dynamics (CFD) for tornadic and SL …

Influence Of Stream Permanence, Predation, And Invasive Species On Crayfish In The Ozark Highlands With An Emphasis On Species Of Greatest Conservation Need (Orconectes Marchandi, Orconectes Eupunctus And Cambarus Hubbsi), Allyson Noelle Yarra

Graduate Theses and Dissertations

Due to the ecological importance of crayfish and the increasing vulnerability of freshwater systems due to habitat loss, invasive species, and hydrologic alteration, understanding crayfish-environment relationships is crucial in the context of aquatic species conservation. I sought to examine the influence of hydrologic variation among intermittent and permanent streams on crayfish occupancy, abundance, predation risk, and potential vulnerability to invasive species effects. I conducted crayfish and environmental data sampling during two consecutive summers across 20 Ozark streams of differing permanence levels (10 intermittent, 10 permanent). In these same streams, I conducted fish and scat surveys over the course of four …

Influence Of Histidine Residues, Ph And Charge Interactions On Membrane-Spanning Peptides, Ashley N. Henderson

Graduate Theses and Dissertations

Designed transmembrane peptides were employed for investigations of histidine residues within the hydrophobic environment of the lipid bilayer by means of oriented solid-state deuterium NMR spectroscopy. Using the model peptide GWALP23 sequence (GGALW(LA)6LWLAGA) as a host framework, the effects of single and double histidine mutations were explored. Replacement of leucine residue 12 to polar neutral histidine had little influence on the peptide average orientation, however under strongly acidic pH conditions in DOPC bilayers, the histidine becomes positively charged (pKa 2.5) and the GWALP23-H12 peptide exits the membrane and adopts a surface-bound orientation. Conversely, mutation of leucine 14 to neutral histidine …

Temporal Evaluation Of Corn Respiration Rates Using Pressure Sensors, Gagandeep Singh Ubhi

Graduate Theses and Dissertations

High respiration rate of a grain indicates faster degradation of its dry matter. Proper grain management requires chronological and precise measurements of carbon dioxide evolved from grain respiration during the postharvest storage duration. Therefore the main goal of this research was to develop a new technique that evaluates temporal corn respiration rate using pressure sensors. It was based on measuring pressure drop associated with the grain respiration in a closed container and using it to calculate the grain respiration rates.

Dry corn (Zea Mays L.) was procured from a local farmer and stored at 4ºC. Corn rewetting technique was applied …

Comparison Of Flow Dynamics And Bifurcation Angles In Tributary And Distributary Channel Networks, Thomas Coffey

Graduate Theses and Dissertations

The dynamics of channel mouth bifurcations on river deltas can be understood using theory developed in tributary channel networks. Bifurcations in groundwater-fed tributary networks have been shown to evolve dependent on diffusive ground water flow patterns

directly adjacent to the channel network, producing a critical angle of 72°. We test the hypothesis that bifurcation angles in distributary channel networks are likewise dictated by a diffusive external flow field, in this case the shallow surface water surrounding the subaqueous portion of distributary channels in a deltaic setting. We measured 25 unique distributary bifurcations in an experimental delta and 197 bifurcations in …

Linear Quadratic Optimal Control For A Cascaded Converters-Based Microgrid, Amlam Niragire

Graduate Theses and Dissertations

There is a constant transformation of the electric grid due to an ongoing interest in the deployment of renewable energy resources and electric microgrid formation. This transformation, though advantageous in many ways, poses great challenges for the energy industry and there must be a constant improvement in modeling, simulation, analysis and control techniques in order to characterize and optimize the system design and operation. In this light, the scope of this thesis is focused on developing a linear model, analyzing the stability and designing an optimal linear quadratic regulator (LQR) for a microgrid system. The microgrid system used is inspired …

Service Consistency In Vehicle Routing, Kunlei Lian

Graduate Theses and Dissertations

This thesis studies service consistency in the context of multi-period vehicle routing problems (VRP) in which customers require repeatable services over a planning horizon of multiple days. Two types of service consistency are considered, namely, driver consistency and time consistency. Driver consistency refers to using the fewest number of different drivers to perform all of the visits required by a customer over a planning horizon and time consistency refers to visiting a customer at roughly the same time on each day he/she needs service. First, the multi-objective consistent VRP is defined to explore the trade-offs between the objectives of travel …

The “Apparent” Diffusion Coefficient Of Electrons Through A Nafion Membrane, Marissa Kayle Reynolds

Graduate Theses and Dissertations

The hydrogen/oxygen fuel cell is a greener, more efficient energy solution. However, there are many problems with the fuel cell including storage, infrastructure, cost, the oxygen reduction reaction, and the durability of the proton exchange membrane (PEM). The PEM is not only used as the electrolyte for the cell but also as a physical barrier between the anode and the cathode. The integrity of this membrane is crucial to the functioning of the fuel cell. This thesis will examine using ferricyanide as a probe molecule for diagnostic experiment of Nafion membrane integrity. Using hydrodynamic voltammetry with a rotating disk electrode …

Molecular Dynamics Simulations Of Dna-Functionalized Nanoparticle Building Blocks On Gpus, Tyler Landon Fochtman

Graduate Theses and Dissertations

This thesis discusses massively parallel molecular dynamics simulations of nBLOCKs using graphical processing units. nBLOCKs are nanoscale building blocks composed of gold nanoparticles functionalized with single-stranded DNA molecules. To explore greater simulation time scales we implement our nBLOCK computational model as an extension to the coarse grain molecular simulator oxDNA. oxDNA is parameterized to match the thermodynamics of DNA strand hybridization as well as the mechanics of single stranded DNA and double stranded DNA. In addition to an in-depth review of our implementation details we also provide results of the model validation and performance tests. These validation and performance tests …

Development Of An Oxygen Saturation Monitoring System By Embedded Electronics, Manikandan Venkatesan Gomathy

Graduate Theses and Dissertations

Measuring Oxygenation of blood (SaO2) plays a vital role in patient’s health monitoring. This is often measured by pulse oximeter, which is standard measure during anesthesia, asthma, operative and post-operative recoveries. Despite all, monitoring Oxygen level is necessary for infants with respiratory problems, old people, and pregnant women and in other critical situations.

This paper discusses the process of calculating the level of oxygen in blood and heart-rate detection using a non-invasive photo plethysmography also called as pulsoximeter using the MSP430FG437 microcontroller (MCU). The probe uses infrared lights to measure and should be in physical contact with any peripheral points …

Development Of A One Pass Microwave Heating Technology For Rice Drying And Decontamination, Deandrae Lynette Smith

Graduate Theses and Dissertations

An industrial microwave (MW) system operating at 915 MHz frequency was used to dry high moisture content (MC) (23% to 24% wet basis) medium-grain rough rice samples (cv. Jupiter). The rice beds were contained in a modified tray that accommodated up to 9 kg of rice separated by thin fiberglass mesh in 3 kg increments. Each layer of rice was fitted with fiber optic sensors connected to a real time data logger during MW treatments. It was determined that drying rice to a MC of 14% to 16% was feasible with the application of MW specific energy at 600 kJ/kg-grain …

Evaluation Of Safening Effects To Herbicides Conferred Via Insecticide Seed Treatments In Soybean (Glycine Max) And Grain Sorghum (Sorghum Bicolor), Nicholas Robert Steppig

Graduate Theses and Dissertations

Interactions between herbicides and insecticides in crop production have been documented for a number of years. Research has shown that applications of some organophosphate insecticides at planting can reduce cotton injury following applications of the soil-applied herbicide clomazone. Additionally, recent research has shown that, when applied as seed treatments prior to planting, some neonicotinoid insecticides can safen rice to drift from both glyphosate and imazethapyr. Since insecticide seed treatments are commonly used in many crop production systems throughout the Midsouth, exploring their ability to reduce injury from herbicides in other crops besides rice is of great interest. Presently no research …

Ecological Importance Of Invader Source Population And Disturbance In Aquatic Invasions, Nicole Elizabeth Graham

Graduate Theses and Dissertations

Invasive species are a global problem and their effects on recipient ecosystems may be mediated by disturbance and intraspecific variation. Crayfish can substantially influence stream structure and function, and invasive crayfish often have differential impacts than native crayfish in aquatic ecosystems. Since species traits often vary across a distribution, it is possible that invasive crayfish from different source populations may have distinct impacts on recipient ecosystem structure and function. In the Ozark Highlands of Arkansas and Missouri, USA, invasive O. neglectus (the Ringed Crayfish) may be leading to the displacement of native O. eupunctus (the Coldwater Crayfish). The objective of …

Characteristics And Behaviors Of School Board Members In "Grade A" Arkansas Public School Districts, Bridget Lynn Polk

Graduate Theses and Dissertations

The purpose of this grounded theory study was to describe characteristics and behaviors of school board members in Arkansas school districts where 50% or more of their campuses earned a letter grade of “A” on the 2014 Arkansas School Performance Report (Arkansas Department of Education [ADE], 2015). This purpose was achieved through analysis of artifacts from selected school districts including: achievement patterns; board minutes; and board member professional development records. A web-based survey of school board members was also utilized to gather demographic and background information. Finally, personal interviews were completed with a small group of board members to collect …

Reduction In Recombination Current Density In Boron Doped Silicon Using Atomic Hydrogen, Matthew Garett Young

Graduate Theses and Dissertations

The solar industry has grown immensely in recent years and has reached a point where solar energy has now become inexpensive enough that it is starting to emerge as a mainstream electrical generation source. However, recent economic analysis has suggested that for solar to become a truly wide spread source of electricity, the costs still need to plummet by a factor of 8x. This demands new and innovative concepts to help lower such cost. In pursuit of this goal, this dissertation examines the use of atomic hydrogen to lessen the recombination current density in the boron doped region of n-type …

Controlled Synthesis And Utilization Of Metal And Oxide Hybrid Nanoparticles, Cameron Cowgur Crane

Graduate Theses and Dissertations

This dissertation reports the development of synthetic methods concerning rationally-designed, hybrid, and multifunctional nanomaterials. These methods are based on a wet chemical, solution phase approach that utilizes the knowledge of synthetic organic and inorganic chemistry to generate building blocks in solution for the growth of nanocrystals and hybrid nanostructures. This work builds on the prior knowledge of shape-controlled synthesis of noble metal nanocrystals and expands into the challenging realm of the more reactive first row transition metals. Specifically, a microemulsion sol-gel method was developed to synthesize Au-SiO2 dimers as precursors for the synthesis of segmented heterostructures of noble metals that …

Assessment Of The Arkansas Horse 4-H Program: Perspectives From Multiple Stakeholders, Fawn Lee Kurtzo

Graduate Theses and Dissertations

Assessment of the Arkansas horse 4-H program utilized stakeholders’ perceptions to describe inputs, outcomes, preferences and impacts provided by the Arkansas Cooperative Extension Service. Stakeholders’ perceptions were captured through three studies. Studies included the following: a pre- and post-test evaluation of the 2016 summer horse camp, purposive interviews with county agents (n = 6), volunteer leaders (n = 4), and parents (n = 4) of horse 4-H clubs, and a statewide survey provided to Extension staff (n =26) and volunteer leaders (n = 28) affiliated with horse 4-H clubs.

The 2016 summer camp evaluation found the goals to improve horsemanship, …