Physical Sciences and Mathematics Commons^™

Nanoscale Manipulation Of Pristine And Functionalized Freestanding Graphene Using Scanning Tunneling Microscopy, Matthew Ackerman

Graduate Theses and Dissertations

Over the past ten years the 2D material graphene has attracted an enourmous amount of attention from researchers from across diciplines and all over the world. Many of its outstanding electronic properties are present only when it is not interacting with a substrate but is instead freestanding. In this work I demonstrate that pristine and functionalized freestanding graphene can be imaged using a scanning tunneling microscope (STM) and that imaging a flexible 2D surface is fundamentally different from imaging a bulk material due to the attraction between the STM tip and the sample. This attraction can be used to manipulate …

Investigation Of The Flow And Fate Of Nitrate In Epikarst At The Savoy Experimental Watershed, Northwest Arkansas, Jozef Laincz

Graduate Theses and Dissertations

Many karst aquifers are at high risk of nitrate contamination due to a combination of vulnerable geology characterized by thin soils and conduit flow, and excess inputs of nutrients from animal feeding operations. One zone that is present in many karst regions and could play an important role in nitrate attenuation due to properties such as increased residence time and matrix-water contact is the upper, weathered portion of karst, the epikarst. However, the understanding of this role is lacking, and the objective of this dissertation was to elucidate it. The fate of nitrate in the epikarst was traced along a …

Software Porting Of A 3d Reconstruction Algorithm To Razorcam Embedded System On Chip, Kevin Curtis Gunn

Graduate Theses and Dissertations

A method is presented to calculate depth information for a UAV navigation system from Keypoints in two consecutive image frames using a monocular camera sensor as input and the OpenCV library. This method was first implemented in software and run on a general-purpose Intel CPU, then ported to the RazorCam Embedded Smart-Camera System and run on an ARM CPU onboard the Xilinx Zynq-7000. The results of performance and accuracy testing of the software implementation are then shown and analyzed, demonstrating a successful port of the software to the RazorCam embedded system on chip that could potentially be used onboard a …

Modified-Electrodes For Redox-Magnetohydrodynamic (Mhd) Pumping For Microfluidic Applications, Christena Kayl Nash

Graduate Theses and Dissertations

A new microfluidic pumping and stirring technique was demonstrated for lab-on-a-chip applications. Microfluidics was accomplished via redox-MHD, which takes advantage of a body force (F_B) that is generated when there is a net movement of ions in solution (j) in the presence of a perpendicular magnetic field (B), according to the equation F_B = j×B. In this work the movement of ions in solution was generated using electrodes modified with the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) rather than a redox species in solution, which can interfere with analyte detection and with biological species. …

Self-Assembly Of Gold Nanosphere Dimers By Inertial Force, George Andrew Christopher Sakhel

Graduate Theses and Dissertations

The morphology and composition of a nanoparticle (NP) play a critical role in determining the NP's properties and function. To date, researchers have created a myriad of NPs of different shapes, sizes, and compositions with interesting attributes and applications ushering a revolution in medicine, electronics, microscopy, and microfluidics.

In this study, gold (Au) nanosphere dimers (NSDs) have been synthesized through a novel self-assembly method. These particles were created from Au NPs mono-dispersed in aqueous solution via a process of centrifugation and capping agent replacement. Au NSDs consist of two Au NPs combined together with minimal gaps between them. Optical spectral …

The Significance Of Dolomitized Hunton Strata In The Kinta And Bonanza Fields Of The Arkoma Basin, Christopher William Trotter

Graduate Theses and Dissertations

The Hunton Group has been a prolific hydrocarbon-producing reservoir across much of Oklahoma and western Arkansas. The group is a Silurian-Devonian aged interval that is comprised of sequences of limestone, dolomite, and calcareous shale. The group is divided into several formations. The subdivisions include the Chimneyhill Subgroup, Henryhouse, Haragan and Bois d'Arc Formations. Reservoir quality in the Hunton Group is significantly dependent upon the diagenetic events and depositional environments of the sediments. Most hydrocarbon production, from within the Hunton Group, comes from members that have undergone dolomite replacement of the parent limestone.

The higher amounts of porosity and permeability are …

From Graphite To Graphene Via Scanning Tunneling Microscopy, Dejun Qi

Graduate Theses and Dissertations

The primary objective of this dissertation is to study both graphene on graphite and pristine freestanding grapheme using scanning tunneling microscopy (STM) and density functional theory (DFT) simulation technique. In the experiment part, good quality tungsten metalic tips for experiment were fabricated using our newly developed tip making setup. Then a series of measurements using a technique called electrostatic-manipulation scanning tunneling microscopy (EM-STM) of our own development were performed on a highly oriented pyrolytic graphite (HOPG) surface. The electrostatic interaction between the STM tip and the sample can be tuned to produce both reversible and irreversible large-scale movement of the …

Effects Of Large Scale Growing Season Prescribed Burns On Movement, Habitat Use, Productivity, And Survival Of Female Wild Turkey On The White Rock Ecosystem Restoration Project Of The Ozark-St. Francis National Forest, Henry Tyler Pittman

Graduate Theses and Dissertations

Restoration of woodland and savanna ecosystems has become a common management strategy in the Central Hardwoods region. Over the past two decades forest managers have implemented woodland and savanna restoration at the landscape level (≥10,000 ha), especially using early growing season prescribed fire. The implementation of the restoration strategy has coincided with declines of Eastern Wild Turkey (Meleagris gallopavo silvestris) in many treated areas causing concern that early growing season prescribed fire was impacting wild turkey. We initiated our study to examine the effect of woodland and savanna restoration on the ecology and habitat of wild turkey in the Ozark …

Overcoming Roadblocks In Introducing Virtual World Technology To High Schools, Casey Dylan Bailey

Graduate Theses and Dissertations

The EAST (Environmental And Spatial Technology) Initiative is a non-profit educational organization that provides students in over two hundred schools in eight states with access to advanced computing technologies for the purpose of enabling students to develop technical skills early and to produce solutions to local community problems. Although many high-end technologies are available through EAST, they are desktop solutions that individual students use and there are none that enable students within a school or between schools to collaborate.

This thesis is a saga that documents the identification and removal of many roadblocks to introducing a 3D multi-user virtual simulation …

A Mixed Methods Approach Of Communication Campaign Development And Assessment: Identifying The Needs Of An Audience And Determining The Value In Evaluation, Tara Johnson

Graduate Theses and Dissertations

The two articles presented in this thesis used both quantitative and qualitative research methods to examine two distinct stages of communication campaigns: research and evaluation. In the quantitative study, students (n = 440) at the University of Arkansas were surveyed to determine their perceptions of the Arkansas Water Resources Center (AWRC), water resources, and water issues. A questionnaire was developed from an existing instrument, reviewed by a panel of experts, pilot tested, and revised. The researchers found participants were most aware (M = 3.23, SD = 1.14), concerned (M = 4.07, SD = 0.86), and interested (M = 4.10, SD …

Characterizing Nanoparticle Size By Dynamic Light Scattering Technique (Dls), Marzia Zaman

Graduate Theses and Dissertations

The Dynamic Light Scattering Technique was used to determine the size, shape and diffusion coefficient of nanoparticle. The intensity auto correlation functions of light scattered by particles in a solution were measured by using a photomultiplier tube and analyzed to get the relaxation rates for decay of intensity correlations, which correspond to the diffusion constants pertaining to the motion of the particle. In the case of nanorods there are two types of motion - translational and rotational. By dis-entangling the relaxation rates, corresponding to these two types of motion, the shape and size of nanoparticle could be characterized. These experiments, …

Comparisons Of Hydrogeologic Modeling Methods To Define Capture Zones For Public Water Supply Wells In Northern Arkansas, Paula Anderson

Graduate Theses and Dissertations

The usefulness, applicability, and practicality of more complex and resource consuming methods for groundwater modeling has been in question since computer based groundwater modeling was established (Anderson, 1992). In many situations, computer modeling of groundwater flow is a necessity and useful for extrapolating data where none exists or it is impossible or impractical to acquire. However, when delineating a recharge area around a public water well for protection purposes, it is unknown if more detailed computer modeling results are better than simpler hydrologic calculations and site study. In the case of public drinking water supply wells located in various aquifers …

In-Season Drought Monitoring: Testing Instrumentation And Developing Methods Of Measurement Analysis, Tyson Brant Raper

Graduate Theses and Dissertations

Soil moisture sensor use in crop production systems has the potential to give inference on plant water status for the purpose of irrigation scheduling and site-drought characterization. These processed measurements could serve as the framework on which to compile trial results across locations, thereby more accurately defining varietal yield response to drought. Still, the ability to characterize drought within a given field or initiate irrigations from these data hinge upon the ability of the instrument to characterize soil moisture at the sampled point and extrapolate that information across the landscape and time. Therefore, the objectives of this research were to: …

Optimization Of Plasmon Decay Through Scattering And Hot Electron Transfer, Drew Dejarnette

Graduate Theses and Dissertations

Light incident on metal nanoparticles induce localized surface oscillations of conductive electrons, called plasmons, which is a means to control and manipulate light. Excited plasmons decay as either thermal energy as absorbed phonons or electromagnetic energy as scattered photons. An additional decay pathway for plasmons can exist for gold nanoparticles situated on graphene. Excited plasmons can decay directly to the graphene as through hot electron transfer. This dissertation begins by computational analysis of plasmon resonance energy and bandwidth as a function of particle size, shape, and dielectric environment in addition to diffractive coupled in lattices creating a Fano resonance. With …

Discrete Strain Engineering In Graphene, Cedric Marcus Horvath

Graduate Theses and Dissertations

Graphene has a number of fascinating mechanical and electrical properties. Strain engineering in graphene is the attempt to control its properties with mechanical strain. Previous research in this area has come up with an approach using a continuum theory to describe the strain induced gauge fields in graphene; however, this approach is only valid for small strains (5% at most). A discrete framework is being developed in Arkansas that can more accurately calculate the deformation (electrical) and (pseudo-)magnetic gauge fields created by large strains. Computational simulations were carried out and used to get discrete atomic positions for strained, suspended graphene …

Estimating Nitrogen Fixation Rates, Importance, And Short-Term Efficiency In Small, Temperate Reservoirs Using Delta15n Techniques, Bryant Christopher Baker

Graduate Theses and Dissertations

Nitrogen (N2) fixation can give certain species of cyanobacteria a competitive advantage in lake and reservoir phytoplankton. These species of cyanobacteria, along with others that cannot fix N2, can form toxic compounds that impair water quality when present in high concentrations. N2 fixation rates may be substantial in small (< 1.0 km2), temperate reservoirs since these systems experience thermal stratification and often nitrogen (N) limitation throughout a substantial proportion of the year. However, the effects of N2 fixation on N cycling, alleviation of short-term N limitation, and water quality are not well-understood. A mesocosm experiment and ecosystem-scale observational study were conducted to 1) determine the efficiency of N2 fixation under varying N relative to phosphorus (P) supply, 2) examine the effects of N2 fixation on autotrophic biomass accumulation and microcystin production, and 3) measure N2 fixation rates and importance to autotrophic N demand and zooplankton N assimilation. Results of the mesocosm experiment indicated that N2 fixation was increased at low N:P supply under high P. However, N2 fixation was inefficient at alleviating N limitation when fixed N was the primary source of N. Additionally, microcystin production occurred only at high N:P supply when N2 fixation was low, indicating that reducing external N inputs may have a positive effect on water quality. Results of whole-reservoir determination of N2 fixation using seston δ15N natural abundances indicated that N2 fixation rates throughout the warm season were substantial and influenced by water temperature. Annual N2 fixation rates ranged from 2.2 - 6.6 g N m-2 yr-1, and contributed up to 19% of the annual autotrophic N demand. Zooplankton were assimilating fixed N in most of the study reservoirs, representing a possible mechanism of ecosystem fixed N retention. Collectively, these results suggest that N2 fixation plays a substantial role in N cycling in small, temperate reservoirs, but likely cannot alleviate short-term N limitation.

Power To The People? An Evaluation Of State-Level Environmental Justice Policies, Angela Michelle Hines

Graduate Theses and Dissertations

Communities of color in America lacking economical, educational, and political power have been largely invisible in the process of making major policy decisions. This is lack of access to decision-making venues has been viewed by many as the reason behind marginalized populations bearing the brunt of many societal burdens. The Environmental Justice Movement legitimized the claims of inadequate access to the decision-making process concerning environmental conditions in which African-Americans lived and worked. Through the use of disruptive actions reminiscent of those used throughout the Civil Rights Movement, the plight of communities plagued by the daily presence of hazardous waste gained …

Mechanical Stratigraphy Of The Mississippian In Osage County, Oklahoma, Caleb James Jennings

Graduate Theses and Dissertations

The Mississippian formation of Oklahoma and Kansas has recently developed as a world class unconventional reservoir with wells producing up to 800 bbl/day. The Mississippian is composed of multiple distinct lithologic zones including limestone, hard chert, and soft tripolitic chert. These zones are difficult to discern with traditional log correlation, but mechanical stratigraphy has the potential to improve previous correlations of the Mississippian.

This study uses full wave sonic logs from Osage County, OK to analyze the elastic properties of the Mississippian. Our work computes isotropic elastic parameters in an effort to partition the Mississippian section into units that may …

Atomic-Scale Characterization And Manipulation Of Freestanding Graphene Using Adapted Capabilities Of A Scanning Tunneling Microscope, Steven Barber

Graduate Theses and Dissertations

Graphene was the first two-dimensional material ever discovered, and it exhibits many unusual phenomena important to both pure and applied physics. To ensure the purest electronic structure, or to study graphene's elastic properties, it is often suspended over holes or trenches in a substrate. The aim of the research presented in this dissertation was to develop methods for characterizing and manipulating freestanding graphene on the atomic scale using a scanning tunneling microscope (STM). Conventional microscopy and spectroscopy techniques must be carefully reconsidered to account for movement of the extremely flexible sample.

First, the acquisition of atomic-scale images of freestanding graphene …

Effects Of Instrumentation On Dental Microwear Textures: Reanalysis And Augmentation Of An Early Hominin Sample, Anna Jacquelyn Ragni

Graduate Theses and Dissertations

Dental microwear texture analysis has been refined to a methodology relying upon scanning confocal microscopy for its advantages of repeatability and standardized quantification. A new instrument, the Plu Neox (Sensofar Corp.) confocal profiler recently entered the market, sparking questions among dental anthropologists related to the advantages and efficacy of this new technology, which has better resolution and lighting properties than previously available white-lighted based confocal profilers. This thesis reports on three complementary studies that set out to evaluate the comparability of the Plu Neox to the Plu Standard system and assess its ability to distinguish primates on the basis of …

General Sampling Schemes For The Bergman Spaces, Newton Foster

Graduate Theses and Dissertations

A characterization of sampling sequences for the Bergman spaces was originally provided by Seip and later expanded upon by Schuster. We consider a generalized notion of sampling using the infimum norm of the quotient space. Adapting some old techniques, we provide a characterization of general sampling sequences in terms of the lower uniform density.

Closed-Range Composition Operators On Weighted Bergman Spaces And Applications, Shanda Renee Fulmer

Graduate Theses and Dissertations

We will discuss necessary and sufficient conditions for a Composition Operator to be closed range on the weighted Bergman spaces. The function phi is an analytic self map of the unit disk and our results extend those previously intended for the classical Bergman space. We will also give applications.

Properties Of Multiferroic Bifeo3 From First Principles, Dovran Rahmedov

Graduate Theses and Dissertations

In this dissertation, a first-principle-based approach is developed to study magnetoelectric effect in multiferoic materials. Such approach has a significant predictive power and might serve as a guide to new experimental works. As we will discuss in the course of this work, it also gives an important insight to the underlying physics behind the experimentally observed phenomena.

We start by applying our method to investigate properties of a generic multiferroic material. We observe how magnetic susceptibility of such materials evolves with temperature and compare this evolution with the characteristic behavior of magnetic susceptibility for pure magnetic systems. Then we focus …

The Szego Kernel Of Certain Polynomial Models, And Heat Kernel Estimates For Schrodinger Operators With Reverse Holder Potentials, Michael Tinker

Graduate Theses and Dissertations

We present two different results on operator kernels, each in the context of its relationship to a class of CR manifolds M={z,w1,...wn) element of Cn⁺¹ : Im wifi(Re z)} where n d 2 and (phi)i( x) is subharmonic for i = 1,...,n. Such models have proven useful for studying canonical operators such as the Szegö projection on weakly pseudoconvex domains of finite type in C², and may play a similar role in work on higher codimension CR manifolds in C³. Our study in Part II concerns the Szegö kernel on M for which the (empty set)i are subharmonic nonharmonic polynomials. …

Efficient Ray Tracing For Mobile Devices, Rafael De Melo Aroxa

Graduate Theses and Dissertations

The demand for mobile devices with higher graphics performance has increased substantially in the past few years. Most mobile applications that demand 3D graphics use commonly available frameworks, such as Unity and Unreal Engine. In mobile devices, these frameworks are built on top of OpenGL ES and use a graphics technique called rasterization, a simple concept that yields good performance without sacrificing graphic quality. However, rasterization cannot easily handle some physical phenomena of light (i.e. reflection and refraction). In order to support such effects, the graphics framework has to emulate them, thereby leading to suboptimal results in term of quality. …

Structural And Stratigraphic Transition From The Arkoma Shelf Into The Arkoma Basin During Basin Subsidence; Arkoma Basin, Northwest Arkansas, Elizabeth Whitney Studebaker

Graduate Theses and Dissertations

The Arkoma basin is an arcuate Paleozoic structural feature in the Ouachita foreland that extends from central Arkansas and westward into southeastern Oklahoma. The Arkoma shelf lies immediately north of the basin and is comprised of Cambrian to Pennsylvanian age sedimentary rocks. In northwestern Arkansas, the stratigraphic and structural transition from the shelf into the northern portion of the Arkoma basin is poorly defined.

Wireline logs were used to construct a series of three north to south cross sections, as well as two along-strike west to east cross sections to examine Morrowan and lower Atokan age strata. In addition to …

A Framework For Constructing Serious Games, Taylor Glen Yust

Graduate Theses and Dissertations

Communicating ideas and knowledge through serious games is a trend that is currently gaining in popularity. However, at present, there is a distinct lack of a game development methodology that takes a critical approach to transforming information into gameplay. This thesis presents a framework that can be followed to construct compelling serious games that are effective at transferring knowledge to the player. This is accomplished through an analysis of atomic knowledge items and their relationships to one another, followed by a meaningful and synergetic implementation of these ideas at a foundational mechanics level.

This thesis also describes the development of …

Methane Emissions And Ammonia Volatilization From Drill-Seeded, Delayed-Flood Rice On A Silt-Loam Soil In Arkansas, Christopher Wade Rogers

Graduate Theses and Dissertations

The Environmental Protection Agency (EPA) currently uses a single methane (CH4) emissions factor of 160 kg CH4-C ha-1 for a primary rice (Oryza sativa L.) crop. The emissions factor is based on studies that do not adequately represent current management practices in Arkansas. Another concern is pre-flood fertilizer nitrogen (N) management, as the common N source, urea, is prone to loss via ammonia (NH3) volatilization. Thus, the objective of this research was to investigate trace gas emissions from rice on a silt-loam soil, including CH4 emissions as influenced by nitrogen (N) fertilization (i.e., optimal N and no N) in 2011, …

Porosity Development Within Lobes To Downslope Ramp Deposits On A Prograding Carbonate Shelf Of The Kinderhookian To Osagean Series In Northwest Arkansas, Elizabeth Marchese

Graduate Theses and Dissertations

Carbonate bodies with lobate geometries form a substantial part of the Osagean (early Mississippian) section in northwest Arkansas. The purpose of this study is to isolate and describe a single lobe from three-dimensional exposures in quarry walls to provide criteria by which lobe and lobe porosity can be recognized in the subsurface. Carbonate sediment generated on the Mississippian Burlington shelf moved southward by gravity flows from the shelf margin to positions on a prograding ramp in Arkansas where overlapping deposits with lobate geometries accumulated. These deposits are recognized in outcrops of the Boone Formation. Stratigraphic units within the Boone are …

Understanding The Influence Of Interfacial Chemistry In Core, Core/Shell And Core/Shell/Shell Quantum Dots On Their Fluorescence Properties, Omondi Bernard Omogo

Graduate Theses and Dissertations

Colloidal semiconductor nanocrystals (quantum dots) have received a great deal of attention due to their superior size tunable properties and promising applications in many areas. Some of the most practical areas of their applications include light emitting diodes (LED), photovoltaic and biological studies. Synthetic methods of these crystals is becoming more established with new strategies being reported every now and then. However, quantitative studies connecting the processes at the interface, namely core-ligand, core-shell and shell-shells, to the overall quantum dots fluorescence properties are not well understood. Specifically for cores, relating surface-atoms interactions, solvents, ligands nature, density and functional groups on …