Digital Commons Network^™

Phosphate And Borophosphate Glasses For Optical And Biomedical Applications, Parker Tracy Freudenberger

Doctoral Dissertations

"The goal of this work was to connect the network structures of phosphate and borophosphate glasses to the compositional dependence of properties related to biomedical applications. The glasses were characterized by a variety of techniques, including phosphate ion chromatography, Raman spectroscopy, and ¹¹B and ³¹P Magic Angle Spinning Nuclear Magnetic Resonance spectroscopy, which provide qualitative and quantitative information about the phosphate and borate moieties that constitute the network structures. The systematic addition of borate to a phosphate glass initially creates tetrahedral borate sites that replace P-O-P linkages with B-O-P linkages, and the properties of the resulting borophosphate glasses …

Unsteady Flow Behaviors Generated By Three-Dimensional Lattice Geometries As Measured By Laser Doppler Velocimetry, Yi Qiao

Doctoral Dissertations

"The relation between flow stream turbulence and heat transfer has been known for a long time, that the heat transfer rate is increased if the turbulence or fluctuation level of the flow increases. Open cell foams and compact heat exchangers are two of the most common models applied for heat transfer augmentation. However, the small ligaments of open cell foams limit the heat conducted and smooth passages in compact heat exchangers cannot cause flow unsteadiness. Accordingly, new geometric models are needed to improve the heat transfer enhancement. Three-dimensional (3D) lattice geometries with a range of features and sizes can be …

Advances In Differentially Methylated Region Detection And Cure Survival Models, Daniel Ahmed Alhassan

Doctoral Dissertations

"This dissertation focuses on two areas of statistics: DNA methylation and survival analysis. The first part of the dissertation pertains to the detection of differentially methylated regions in the human genome. The varying distribution of gaps between succeeding genomic locations, which are represented on the microarray used to quantify methylation, makes it challenging to identify regions that have differential methylation. This emphasizes the need to properly account for the correlation in methylation shared by nearby locations within a specific genomic distance. In this work, a normalized kernel-weighted statistic is proposed to obtain an optimal amount of "information" from neighboring locations …

Design, Modeling And Analysis Of An Ac-Ac Dual Active Bridge Converter, Kartikeya Jayadurga Prasad Veeramraju

Doctoral Dissertations

"The Solid-State Transformer (SST) is gaining attention as an alternative to conventional iron-core transformers in the power electronic community. The power industry's increasing demands for smaller size, higher efficiency, and greater energy density have made the SST an attractive option. Among various power electronic converter topologies, the Dual Active Bridge (DAB) has become popular for its bidirectional power flow capability and galvanic isolation, primarily in the DC application space. Advancements in semiconductor technologies have introduced new bidirectional switches, opening avenues for novel SST topologies. This research investigates the application of the DAB as a single-stage SST and focuses on advancements …

Near-Ir Spectroscopic Analysis Of The Primary Volatile Composition Of Long And Short-Period Comets, Younas Khan

Doctoral Dissertations

"Comets are among the most well-preserved objects that formed in the protosolar nebula ∼4.5 Gyr ago. Hence, they are important for understanding various aspects of the formation, evolution, and habitability of the solar system. Multiple primary volatiles (molecules directly sublimating into the coma from the nucleus) emit via rovibrational transitions in the near-IR, providing opportunities to calculate their abundances. To date, only ∼50 comets have been characterized for their primary volatiles, with the short-period Jupiter-family comets (JFCs) being significantly underrepresented. In contrast, hundreds of comets have been sampled at optical/UV wavelengths, primarily for the composition of daughter species, leading to …

Introduction Of A Variable Inductance Transformer For The Design Of Resonant Power Converters, Angshuman Sharma

Doctoral Dissertations

"Magnetic integration is a hot topic in power electronics that concerns the use of a transformer's leakage and magnetizing inductances purposefully in isolated power electronic converters, thereby giving the opportunity to save the cost and footprint of any additional inductor. This is of prime interest, especially in CLLLC resonant converters which require up to three inductors. For a complete integration of these inductances, the concept of a variable inductance transformer (VIT) is introduced in this thesis. A VIT is an adaptive magnetic structure that facilitates an easy adjustment of both magnetizing and leakage inductances to meet their desired values. However, …

A Qualitative Study Of Ableism On The Postsecondary Campus, George Stuart Fuller

Doctoral Dissertations

This study aimed to learn about the experiences and challenges of disabled students on college campuses. The qualitative research gave voice to the nine disabled students so we can hear, in their own words, their lives, successes, failures, most enjoyable aspects of campus life, and the least pleasant parts of the campus environment. Zoom interviews took place with nine undergraduate disabled students, eight with non-visible disabilities and one with visible disabilities, located on four different campuses within the United States. During the nVivo data analysis, three themes emerged. The three themes identified were: the disabled students' connections with the campus, …

Geometry-Aware Methodology For Coupling Mechanism Analysis And Radiation Mechanism Analysis, Xu Wang

Doctoral Dissertations

"Due to the wide-band spectrum of digital signals, a variety of noise generators, including microprocessors, liquid crystal displays, digital microphones, high-speed traces, and double-data-rate memory modules, are found in consumer electronics products. Noise generated by digital circuits can couple to the antennas and degrade their sensitivity. Additionally, it also couples to metallic housings or heatsinks and produces a significant amount of emission. In this research, methodologies are presented to analyze the coupling and radiation mechanism in electronic devices.

To investigate the coupling between the distributive geometries in the radio frequency interference (RFI) problem, a mesh-dependent partition-based coupling mechanism analysis method …

Applied Geochemistry, Geochronology And Biostratigraphy: Case Studies From The 38th Parallel Structures In Missouri And Orange Basin, Offshore Western South Africa, Marissa Kay Spencer

Doctoral Dissertations

"The unique alignment of the Decaturville, Crooked Creek, and Weaubleau geological structures in central Missouri, three of nine known such structures along the 38th parallel in Illinois, Missouri, and Kansas, has puzzled geoscientists for decades. Research using palynology (palynomorphs and particulate organic matter) and radiometric dating of impact spherules were used to constrain age and a relationship between these enigmatic structures and infer their paleoenvironmental conditions. Novel melting damages, unique to impact, were documented in the palynomorphs in all the three structures. Early Ordovician acritarchs with melted processes correlate with ⁴⁰Ar-³⁹Ar stepwise heating age of impact spherules …

Investigation And Enhancement Of Students’ Conceptions Of Ph Buffers, Mary Alice Woodland Sheppard

Doctoral Dissertations

Understanding how students construct knowledge of pH buffer concepts is essential to developing effective instructional strategies to support student learning. A resource theoretical framework and the phenomenographic method were used to explore 12 general chemistry students’ conceptions of pH buffers using three buffer questions ranging from algorithmic to conceptual. Open coding of student responses revealed a diverse array of resources that varied in productivity and connectedness. A layered resource graph was introduced to visually compare resource activations across question contexts, highlighting some resources as important for all sensemaking about pH buffers, while others were specific to particular topics. The phenomenographic …

Studying Us Iranian Immigrant Parents Negotiating Movements Toward Future Belonging, Fatemeh Hajnaghizadeh

Doctoral Dissertations

In this dissertation, I reflect on how my work with Iranian immigrant parents in the US is informed by my lived experiences and research as a member of the minoritized group both in post-revolutionary Iran and the US. I recognize these experiences as informing my research on diasporic parenting throughout different stages, from designing the methodology to curating the theoretical framework and analyzing data.The desire to engage with minoritized ways of being and knowing beyond static essentializing viewpoints informs my approach to designing methodological processes that centralize confusion/disagreements with dominant practices and ideologies. In my study’s methodology, I use stories …

Development And Characterization Of Electrospray Ionization Modes In Mass Spectrometry: Applications In Protein Analysis And Beyond, Huishan Li

Doctoral Dissertations

Electrospray ionization (ESI) has emerged as a widely used soft ionization method, facilitating the introduction of intact molecular ions into mass spectrometers for diverse applications. Despite its popularity, ESI in its current form still faces certain non-ideal limitations. One ongoing research direction is focused on reducing the flow rate for ESI, a crucial parameter that correlates with the size of initial charged droplets generated. Smaller initial charged droplets have exhibited improved performances, including enhanced ionization efficiency, reduced nonspecific adducts, and minimized sample consumption. It would be of significant interest to measure and investigate ultra-low ESI flow rates for downscaled study. …

Trend Stationary Time Series: Simultaneous Estimation Of Trend And Autocorrelated Errors, Jakub Michel

Doctoral Dissertations

The world of time series analysis is predominantly focused on nonstationary time series, which exhibit various patterns and behaviors that researchers across different industries aim to analyze. Decomposing nonstationary time series into a trend component and a stationary process is a common approach, with trend and stationary process estimation achieved through parametric and nonparametric methods.

Polynomial regression and nonparametric methods, such as Kernels and B-Splines, are employed to estimate the trend. Once the trend is estimated, the residuals are obtained by subtracting the estimated trend from the data, allowing for the fitting of an ARMA stationary process. However, the estimation …

Epigenetic Regulation During The Differentiation Of Embryonic Stem Cells Into Cardiomyocytes, Nan Yang

Doctoral Dissertations

Heart disease is the leading cause of death in the United States, constituting a quarter of total deaths. A major reason behind the high mortality of heart disease is the low regenerative capacity of cardiomyocytes (CMs), which carry out the contractile function of the heart. Lineage- specific differentiation of pluripotent stem cells into CMs provides a promising therapeutic strategy. However, current methods suffer from challenges in generating mature and homogenous CMs in sufficient quantities for practical application. Moreover, little is known about the underlying epigenetic regulations in CM differentiation, which is essential during the establishment and maintenance of cell identity …

Clarifying The Role Of Microorganisms And Their Traits In Soil Organic Matter Formation, Emily Whalen

Doctoral Dissertations

Soil organic carbon (C), the largest actively cycling reservoir of C on earth, is ultimately derived from plant photosynthesis. Once in soils, a significant proportion of this C is processed by microbial communities prior to its incorporation into soil organic matter (SOM) pools, and microbial-derived organic matter inputs are increasingly recognized as a dominant source of SOM. Conceptual theory therefore posits that microbial physiological traits (e.g., growth efficiency) are central controls on SOM formation and stabilization. However, recent observations are mixed, and the specific traits that promote the formation and retention of different SOM functional pools (e.g., total vs. stable …

Meta-Analysis Of The Effectiveness Of Project-Based Learning Approach On Academic Achievement In Higher Education Worldwide, Ziyu Meng

Doctoral Dissertations

This research study conducted a meta-analysis to integrate the studies that investigated the effectiveness of project-based learning on academic achievement based on a worldwide higher-education population. The researcher explored the variables that previous meta-analysis studies used to evaluate academic achievements, such as student grade point average (GPA), course grades, and test scores, to explore the use of these variables in project-based learning. There were 17 studies in total included in the meta-analysis evaluating the effect size of academic achievement, which was influenced in moderator variable by subject-matter areas, school location, hours of instruction, technology support, and group size. The researcher …

We Are Still Playing: A Meta-Analysis Of Game-Based Learning In Mathematics Education, Thomas Conmy

Doctoral Dissertations

The purpose of this meta-analysis was to investigate the effectiveness of the use of games as part of mathematics instruction on academic achievement in grades Kindergarten to 12 in the United States. There were 17 studies selected for investigation published from 2010 to 2023 that focused on game-based learning and mathematics. This meta-analysis fills the gap in the knowledge by examining classes that are using game based learning across three platforms of instruction: nondigital games, digital on computers, and mobile devices. The findings from this meta-analysis suggest that the usage of game-based learning in a classroom has a positive effect …

Data Analytics Of Wettability Alteration With Surfactants In Carbonate Reservoirs, Ya Yao

Doctoral Dissertations

"Wettability alteration with surfactants has been widely applied to improve oil recovery in carbonate reservoirs. An effective surfactant huff-puff application design requires comprehensive guidelines about where, how, and when this method could be applied. Besides, traditional methods to design an effective application and optimize surfactant performance are dependent on extensive experiments and are time-consuming. This study is to assist in the design of surfactant huff-puff via statistical methods and machine learning techniques.

In this study, a dataset including 402 effective surfactant imbibition tests is established by collecting information from nearly 50 publications. The dataset provides a foundation for further data …

Essays On Conditional Heteroscedastic Time Series Models With Asymmetry, Long Memory, And Structural Changes, K C M R Anjana Bandara Yatawara

Doctoral Dissertations

"The volatility of asset returns is usually time-varying, necessitating the introduction of models with a conditional heteroskedastic variance structure. In this dissertation, several existing formulations, motivated by the Generalized Autoregressive Conditional Heteroskedastic (GARCH) type models, are further generalized to accommodate more dynamic features of asset returns such as asymmetry, long memory, and structural breaks. First, we introduce a hybrid structure that combines short-memory asymmetric Glosten, Jagannathan, and Runkle (GJR) formulation and the long-memory fractionally integrated GARCH (FIGARCH) process for modeling financial volatility. This formulation not only can model volatility clusters and capture asymmetry but also considers the characteristic of long …

White Womanhood: Finding Oppositional Epistemologies And Community At The Intersection Of Whiteness And Womanhood, Hannah Joy Fischer

Doctoral Dissertations

White women continue to contribute to the reproduction and maintenance of White supremacy even when they attempt to pursue antiracism. To better understand their antiracist agency, this study analyzed White women’s experiences and comprehension of White womanhood. Using phenomenology and critical autoethnography, this qualitative study invited six self-proclaimed antiracist White women to participate in individual interviews, attend two focus groups, and reflect on five guided prompts on White womanhood and antiracist action. The study revealed antiracist White women’s feelings of responsibility and lack of perceived agency for antiracist action. Participants demonstrated attempts to disengage from whiteness while also expressing desires …

Identity Formation And Role Expansion For Nurse Practitioner Residency Preceptors: A Qualitative Thematic Analysis, Angel Chen Kuo

Doctoral Dissertations

Employer-based nurse practitioner residency programs have been implemented to address the significant shortage of primary care providers in the community clinic settings. However, there continues to be a shortage of clinicians who serve as preceptors to nurse practitioner residents and students. Preceptors, also referred to as clinician educators, are essential in the training of learners and their socialization into the profession. Just as there is a shortage of clinicians of diverse backgrounds to reflect the population served in the community, there is also a significant shortage of preceptors of color to train learners from diverse backgrounds. The purpose of this …

Fluorination Of Rubisco-Mimetic Co2 Capture Systems. Theoretical And Experimental Studies Of Ammonium Ion Acidity Depression And Carbamylation, Brian Michael Jameson

Doctoral Dissertations

"RuBisCO-inspired CO₂ capture and release (CCR) systems featuring amines have been developed for the purpose of reversable CO₂ capture from air. The enzyme active site consists of the tetrapeptide sequence Lys-Asp-Asp-Glu. The Lys sidechain amine undergoes carbamylation and an Mg²⁺ cation stabilizes the resulting carbamate. The N^a-acyl-lysinyl-aspratyl-aspartyl-glutamide (Lys-Asp-Asp-Glu, KDDE) peptide featured maximum capture at pH ≈ 10; a pH region too high for Mg²⁺ ions to remain in solution. This work aims to achieve pKa depression by introducing fluorine in the proximity of the lysine’s sidechain amine. A comparative analysis was made of butylamine, …

Efficient High Order Ensemble For Fluid Flow, John Carter

Doctoral Dissertations

"This thesis proposes efficient ensemble-based algorithms for solving the full and reduced Magnetohydrodynamics (MHD) equations. The proposed ensemble methods require solving only one linear system with multiple right-hand sides for different realizations, reducing computational cost and simulation time. Four algorithms utilize a Generalized Positive Auxiliary Variable (GPAV) approach and are demonstrated to be second-order accurate and unconditionally stable with respect to the system energy through comprehensive stability analyses and error tests. Two algorithms make use of Artificial Compressibility (AC) to update pressure and a solenoidal constraint for the magnetic field. Numerical simulations are provided to illustrate theoretical results and demonstrate …

Effects Of Downwash When Measuring Gas Concentration With Uav-Mounted Gas Sensors, Jacob Lane Brinkman

Doctoral Dissertations

"This research concludes that the downwash region of a rotary-wing unmanned aerial vehicle (UAV) does not produce pressure variations substantial enough to cause significant changes in density-based gas concentration measurements. US regulations evaluate gas concentration as a function of gas density, and accurate concentration measurements are critical for protecting health and safety, which means evaluation of actual downwash effects on measured gas concentration is essential.

During experimentation, the UAV was fixed to a stand in a sealed chamber filled with NOx (NO and NO₂) of constant concentration. The UAV rotors ran at hovering speeds, and gas concentrations were …

Fiber Optic Sensors For Liquid Identifications, Wassana Naku

Doctoral Dissertations

"The fiber optic Fabry-Perot interferometer (FPI) is a widely utilized sensing configuration, offering numerous advantages over conventional electronic sensors, including high accuracy, distributed sensing capabilities, immunity to electromagnetic interference, and compact size. In this study, we propose a remarkably simple fiber optic-tip sensor system combined with machine learning techniques for the identification of pure and volatile organic liquids (VOLs).

A liquid droplet forms an extrinsic FPI (EFPI), with its effective reflectance being a function of the droplet's length. As the droplet evaporates, its length decreases. We conducted immersion tests using optical fiber tip sensors and monitored the time-transient responses of …

Cfd Analysis For Beyond Bubbly Gas-Liquid Two-Phase Flows In A Large Diameter Pipe, Sungje Hong

Doctoral Dissertations

"Due to the complexity of multiphase flow phenomena, numerical analysis for multiphase turbulent flow is not as reliable as single-phase computational fluid dynamics (CFD). A literature review has revealed that the current efforts on multiphase flow simulation have focused on small diameter channels under very restricted flow conditions and have been conducted without identifying some important procedures. To expand CFD applications to a wide range of two-phase flow conditions in large diameter channels, this study aims to validate the current CFD models for vertical concurrent air-water two-phase flow simulations beyond bubbly flows. First, a numerical model developed to describe dynamical …

Identification, Mapping, Analysis, And Dating Of Composite Mega Landslides In The Colorado Plateau, Conor Maris Watkins

Doctoral Dissertations

"This research consists of three articles focusing on landslide complexes within the Grand Canyon region of the Colorado Plateau. This is a vast and remote region of rugged topography. The landslide complexes in this study are greater than 10 million cubic meters in volume. The slides are located within different areas of the region and consist of differing geology but share multiple commonalities. Stratigraphic and structural controls tend to dictate where the slides occur. All of the landslides occur where carbonates and/or sandstones overlie over consolidated shales. The shales are susceptible to creep and strain softening where lateral confinement has …

Sustainable Development: A Data Analysis Investigation For A New Conceptual Model, Case Study Comparison And Validation Techniques, Tiffanie Marie Toles

Doctoral Dissertations

"The three pillars model for sustainability, often represented with three intersecting circles described as economic, environmental, and social factors with sustainability being at the center is a complex and philosophically open model [1]. As society promotes efforts to reduce carbon impacts, there becomes a need to critically review the models employed for understanding. This research presents a validated methodology, an updated conceptual configuration of sustainability for overall use, as well as a sustainable development performance measurement system. Using the 2020 Sustainable Development Goals Index Data, 232 indicators from 193 countries were used to evaluate the efficacy of using more than …

Development Of A Mission Design Tool For Computing Libration Point Formations Using Differential Corrections Initialized With A Genetic Algorithm, Donna Jennings

Doctoral Dissertations

"The growing interest in deep space spacecraft missions and distributed spacecraft formations has established the need for state-of-the-art advancements in the areas of relative dynamics and mission design. The focus of this research is to develop methods for identifying natural (i.e. ballistic) relative formation trajectories in the vicinity of the collinear libration points. A natural formation decreases the station keeping costs, lowering the consumption of spacecraft resources and extending mission lifetime. This research adapts both numerical and machine learning approaches to the problem of mission design. A genetic algorithm was first used to identify a multi-agent spacecraft formation in the …

Recurrent Event Data Analysis With Mismeasured Covariates, Ravinath Alahakoon Mudiyanselage

Doctoral Dissertations

"Consider a study with n units wherein every unit is monitored for the occurrence of an event that can recur with random end of monitoring. At each recurrence, p concomitant variables associated to the event recurrence are recorded with q (q ≤ p) collected with errors. Of interest in this dissertation is the estimation of the regression parameters of event time regression models accounting for the covariates. To circumvent the problem of bias and consistency associated with model's parameter estimation in the presence of measurement errors, we propose inference for corrected estimating functions with well-behaved roots under additive measurement errors …