Digital Commons Network^™

The Layer That Did Not Swim Away: Broadband Acoustic Discrimination And Characterization Of Ocean Stratification, Elizabeth Reed-Weidner

Doctoral Dissertations

Ocean stratification plays a critical role in many oceanographic processes. The magnitude of mixing between stable water masses is regulated, in part, by the intensity of stratification. As such, stratification modulates the vertical transport of heat and many important dissolved constituents in the water column, influencing such processes as ocean ventilation, and ocean heat and carbon uptake. As human induced climate change alters oceanic stratification a thorough understanding of its distribution and variability is critical in the study of the world’s oceans. However, traditional methods are limited in terms of spatial context and rapid, near-synoptic observational methods, such as those …

Advanced Electronics And Post-Processing Algorithm For The Sontrac 3d Neutron Spectrometer, George Suarez

Doctoral Dissertations

The second-generation SONTRAC instrument is being designed by UNH and NASA to detect solar neutrons, a game-changing observation for understanding particle acceleration at the Sun. The new instrument targets small satellites with highly constrained size, mass, and power; bringing a new set of challenges to the design of the instrument electronics. SONTRAC uses silicon photomultiplier detectors to image neutron scattered proton tracks in a scintillating fiber bundle. Individual detector readout provides the best performance, but is not achievable within the size, mass and power constrains for a small satellite. To overcome this problem, we explored detectors configured in strips to …

Disordered Cathode Electrode Materials For Aqueous Zinc Ion Batteries And The Effect Of Conditioned Electrolytes In Cycling Performances, Saewon Kim

Doctoral Dissertations

Electrochemical energy storage is essential to free various electronic devices from electric wiring. Besides the prominent lithium-ion batteries, next-generation batteries using zinc ions as charge carriers in aqueous electrolytes have risen as attractive alternatives due to their superior safety, environmental-friendliness, low cost, and excellent theoretical performance. However, high-performance cathode materials to accommodate the capacity and cyclability of zinc-ion storage have been lacking because of the strong electrostatic interaction between multivalent Zn-ions and host cathode materials. This study suggests a few varieties of vanadium oxide derivatives with large interlayer spaces, excellent structural stability, and finely tuned structural properties. Alkali-intercalated vanadates (MVOs) …

Effectiveness Of Clay Nanotube Blended Coating Materials For Thermal Insulation, Hawa Hashm

Doctoral Dissertations

Studies conducted by the U.S. Department of Energy reported that heating and cooling systems use nearly 60% of the total energy consumed in a building, while approximately 31% of that energy loss occurs through the improperly insulated floor, walls, and ceiling. Hot summers or severely cold weather can make these problems worse. The passing of conditioned air through these building materials is a substantial source of energy loss, which has driven significant investigation into new environmentally friendly, sustainable, and cost-effective solutions. The main objective of the research was to experimentally evaluate the thermal conductivity of paints blended with halloysite nanotubes …

Understanding Physical Properties Of Gas Bubbles In The Ocean: How Does Reality Affect What We Think We Already Know?, Alexandra Michelle Padilla

Doctoral Dissertations

The importance of methane as a greenhouse gas has led to widespread research focused on understanding the sinks and sources for atmospheric methane. One source of atmospheric methane could include methane bubbles released from the ocean’s seafloor. These gas bubbles transport methane from the seafloor through the ocean’s water column, and the methane released during their ascent affects water column geochemistry and microbial populations. Under certain physical and chemical conditions, methane transported by gas bubbles can reach the upper water column and potentially leak across the sea-air interface. The dynamics of gas bubble emission, ascent, and dissolution in the water …

Dynamics Of A Charge Carrier Driven By Oscillating Fields In Materials With Impurities, Dileon Saint-Jean

Doctoral Dissertations

In conductive materials and semiconductors, a charge carrier under the effects of an electric field will suffer collisions due to thermal fluctuations and impurities in the lattice, altering their trajectory. The electronic properties of these materials depend on the nature and frequency of these collisions; thus, they must be accounted for in any model dealing with electrical conduction. Tracking all collisions individually, while it may be possible within certain limits, forces the model to a large degree of approximation. This work introduces a Monte Carlo-based methodology to electrical transport in Ohmic materials that consists of two parts, the utilization of …

The Moderating Role Of Experiential Avoidance Between Child-Caregiver Dynamics And Stem Motivation, Dylan L. Harrell

Doctoral Dissertations

The National Academy of Sciences released a report that discussed the increased need to improve interest and retention of Science, Technology, Engineering, and Math (STEM) careers in the United States. Early childhood factors within one’s family plays an essential role in the process of career decision making, self-concept, and vocational identity. The current study examined the relationship experiential avoidance has on early family dynamics (i.e., family environment, differentiation of self, attachment, and perceived parenting) and perceived motivation in STEM. A total of 231 participants currently enrolled in a Southern University taking a STEM course (Psychology, Biology, Social Science, Computer Science, …

A Comparative Study Of Mono-Stable And Bi-Stable Magnetic Spring Based Energy Harvesters, Hieu Tri Nguyen

Doctoral Dissertations

Continuous advancements in electronics manufacturing have resulted in the widespread use of low-power sensors, necessitating the development of energy harvesters capable of generating electric power from abundant and free energy sources such as ambient vibrations. A rising interest in energy harvesting technology inspires the work discussed herein using magnetic interactions to target nonlinear energy harvesting, which is compatible with ambient vibration energy sources with a broad frequency spectrum and particularly rich in low frequencies. This research aimed to look into a magnetic-levitation-based vibration energy harvester that could be tuned from a mono-stable to a bi-stable configuration. An oscillating magnet is …

Layered Metamaterial Beam Structure With Local Resonators For Vibration Attenuation: Model And Experiment, Winner Chukwuzulum Anigbogu

Doctoral Dissertations

Layered metamaterial beam structures are gaining attention in a variety of fields including vibration attenuation and energy harvesting. Exhaustive research on single-beam metamaterial vibration attenuation structures using local resonators exists in literature. Moreover, there are recent attempts at modelling double-layered beams with different kinds of constraints. The double-layered beam models in literature are limited to simple beams and not extended to metamaterials with local resonators. This research is primarily focused on developing a design criterion and a modelling platform for layered metamaterial structures with multiple beams and local resonators for vibration isolation. The model is developed using Euler-Bernoulli beam equations, …

Understanding The Shear Deformation Mechanism Of Transition Metal/Ceramic Interfaces Using Computational Methods, Nisha Dhariwal

Doctoral Dissertations

The objective of this research was to investigate the deformation behavior of metal/ceramic interfaces under external loadings in a multi-scale framework including first principles density functional theory (DFT) and molecular dynamics (MD) simulations. The mechanical properties of the metal/ceramic interfaces are dominated by defects on a length scale that first principles computations cannot access. Since the DFT calculations become computationally expensive for such large sized systems, therefore, MD simulations are required to deal with such systems. For MD simulations, second nearest neighbor modified embedded atom method (MEAM) potentials were developed to study metal/ceramic interfaces involving Cr, Ti, Al, and N. …

Fully Kinetic Particle-In-Cell Simulations Of Plasma-Surface-Dust Interactions For Lunar Exploration, Jianxun Zhao

Doctoral Dissertations

"The studies involving lunar surface explorations have drawn attentions in recent years. A better understanding of possible potential hazards to astronauts and electronic equipment has become a necessity for future lunar explorations. The lunar surface, lacking an atmosphere and global magnetic field therefore directly exposed to solar radiation and solar wind plasma, is electrically charged by the bombardment of solar wind plasma and emission/collection of photoelectrons. Additionally, lunar dust grains can also get charged and levitated from the surface under the influence of the electric field as well as gravity within the plasma sheath. Since the plasma sheath formed near …

Studies Of Multiphase Distribution And Flow In Bubble/ Slurry Bubble Columns With /Without Internals And Advanced Sustainable Construction Materials Using Sophisticated Measurement Techniques, Omar Farid

Doctoral Dissertations

"Bubble/slurry bubble columns have been widely studied and employed as multiphase flow reactors with and without vertical heat-exchanging tubes. In order to understand more deeply the effect of the dense internals on the hydrodynamics of bubble/slurry bubble column, systematic experiments were performed to visualize and quantify using the radioactive particle tracking (RPT) technique. A new methodology for implementing the radioactive particle tracking (RPT) technique has been developed to investigate the effect of the dense internals on the hydrodynamics of the bubble/slurry column reactor. Monte Carlo N-Particle (MCNP) simulation has been implemented to simulate the system to generate a large number …

Using Coherence And Interference To Study The Few Body Dynamics In Simple Atomic Collisions Systems, Sujan Bastola

Doctoral Dissertations

"Atomic Collision experiments are best suited to sensitively test the few-body dynamics of simple systems. The few-body dynamics, in turn, can be sensitively affected by interference effects. However, an important requirement to observe interference effects in atomic scattering experiments is that the incoming projectile beam must be coherent. The coherence properties of the incoming projectile can be controlled by the geometry of the collimating slit placed before the target. We performed a kinematically complete experiment where a 75 keV proton beam is crossed with a molecular hydrogen beam to study the dissociative capture process. The motivation for this project was …

Hydroclimate Variability In Central America During The Holocene Inferred From Lacustrine Sediments In Lake Izabal, Eastern Guatemala, Edward Fernando Duarte

Doctoral Dissertations

"Holocene hydroclimate reconstructions have contributed to our understanding of the mechanisms controlling precipitation in Central America. Recent hydroclimate proxy records from the region, however, have revealed considerable spatiotemporal complexity in precipitation variability. This complexity is hypothesized to result from the interaction between multiple oceanic-atmospheric processes that converge in the region. This project analyzed three sediment cores from Lake Izabal, eastern lowland Guatemala, with the goal of understanding changes in precipitation, lake productivity, and lake water chemistry during the Holocene. Our proxy results indicate that precipitation in the region increased from the early to the middle Holocene, when Lake Izabal became …

Advanced Topologies Of High Step-Up Dc-Dc Converters For Renewable Energy Applications, Ramin Rahimi

Doctoral Dissertations

"This research is focused on developing several advanced topologies of high step-up DC-DC converters to connect low-voltage renewable energy (RE) sources, such as photovoltaic (PV) panels and fuel cells (FCs), into a high-voltage DC bus in renewable energy applications. The proposed converters are based on the combinations of various voltage-boosting (VB) techniques, including interleaved and quadratic structures, switched-capacitor (SC)-based voltage multiplier (VM) cells, and magnetically coupled inductor (CI) and built-in-transformer (BIT). The proposed converters offer outstanding features, including high voltage gain with low or medium duty cycle, a small number of components, low current and voltage stresses on the components, …

Development Of Flood Prediction Models Using Machine Learning Techniques, Bhanu Kanwar

Doctoral Dissertations

"Flooding and flash flooding events damage infrastructure elements and pose a significant threat to the safety of the people residing in susceptible regions. There are some methods that government authorities rely on to assist in predicting these events in advance to provide warning, but such methodologies have not kept pace with modern machine learning. To leverage these algorithms, new models must be developed to efficiently capture the relationships among the variables that influence these events in a given region. These models can be used by emergency management personnel to develop more robust flood management plans for susceptible areas. The research …

Social Media Analytics With Applications In Disaster Management And Covid-19 Events, Md Yasin Kabir

Doctoral Dissertations

"Social media such as Twitter offers a tremendous amount of data throughout an event or a disastrous situation. Leveraging social media data during a disaster is beneficial for effective and efficient disaster management. Information extraction, trend identification, and determining public reactions might help in the future disaster or even avert such an event. However, during a disaster situation, a robust system is required that can be deployed faster and process relevant information with satisfactory performance in real-time. This work outlines the research contributions toward developing such an effective system for disaster management, where it is paramount to develop automated machine-enabled …

Evaluating Barriers To And Impacts Of Rural Broadband Access, Javier Valentín-Sívico

Doctoral Dissertations

"The lack of adequate broadband infrastructure persists in many rural communities. Beyond funding, additional barriers persist, such as digital literacy and community-level self-efficacy. As a result, the first contribution articulates barriers at the organizational level. This work proposes a framework based on the Theory of Planned Behavior to highlight stakeholder dynamics that have constrained Regional Planning Commissions from advancing broadband infrastructure in rural areas. One approach to address these barriers is to provide stakeholders with analytical tools to evaluate the benefits and costs of various broadband options for their community since there is not a one-size-fits-all solution. To this end, …

Secured Information Dissemination And Misbehavior Detection In Vanets, Ayan Roy

Doctoral Dissertations

"In a connected vehicle environment, the vehicles in a region can form a distributed network (Vehicular Ad-hoc Network or VANETs) where they can share traffic-related information such as congestion or no-congestion with other vehicles within its proximity, or with a centralized entity via. the roadside units (RSUs). However, false or fabricated information injected by an attacker (or a malicious vehicle) within the network can disrupt the decision-making process of surrounding vehicles or any traffic-monitoring system. Since in VANETs the size of the distributed network constituting the vehicles can be small, it is not difficult for an attacker to propagate an …

Machine Learning Applications In Plant Identification, Wireless Channel Estimation, And Gain Estimation For Multi-User Software-Defined Radio, Viraj K. Gajjar

Doctoral Dissertations

"This work applies machine learning (ML) techniques to selected computer vision and digital communication problems. Machine learning algorithms can be trained to perform a specific task without explicit programming. This research applies ML to the problems of: plant identification from images of leaves, channel state information (CSI) estimation for wireless multiple-input-multiple-output (MIMO) systems, and gain estimation for a multi-user software-defined radio (SDR) application.

In the first task, two methods for plant species identification from leaf images are developed. One of the methods uses hand-crafted features extracted from leaf images to train a support vector machine classifier. The other method combines …

Wind Flow Characteristics Of Multi-Vortex Tornadoes And Their Wind Effects On Residential Houses, Yi Zhao

Doctoral Dissertations

"Tornadoes strike the USA very frequently, with an average of 1200 reports per year, and the average annual tornado-induced property loss has reached $10B. The devastation from recent tornadoes have prompted a renewed interest in better understanding tornado dynamics, their interactions with the built environment, and the performance of civil structures during tornadoes. In the past, the wind effects caused by single-vortex tornadoes have been widely studied, while the multi-vortex tornadoes were rarely considered. In fact, many previous deadly, costly tornadoes involved multiple vortices. Therefore, it is important to understand the wind flow characteristics of multi-vortex tornadoes in order to …

Mitigation Of End Zone Cracking In Precast Prestress Concrete Girders, Oluwatobi F. Babarinde

Doctoral Dissertations

Precast prestressed concrete girders have been widely used to construct bridges in the United States. Recent advancements in high-performance concrete and newly developed girder sections allow the span of girders to be extended significantly. Generally, bridges with longer spans require deeper girders and use more prestressing strands; the latter exacerbates the end zone cracking in pretensioned concrete girders when prestressing strands are released. Various types of end zone cracks have been observed, including horizontal and inclined cracks in the web, and bottom flange cracks.

This dissertation explores two possible options to mitigate the end zone cracking in precast prestressed concrete …

Graphene Nanoscroll Field-Effect Transistor-Based Radiation Sensors, Joshua B. Joffrion

Doctoral Dissertations

Carbon nanomaterials have excited both academia and industry with their extraordinary electronic, mechanical, optical, thermal, and chemical properties for over forty years, providing opportunities for significant advances in fundamental and applied science and leading to the development of disruptive technologies and applications. While graphene and carbon nanotubes have been at the forefront of research, a relatively new one-dimensional carbon allotrope, graphene nanoscrolls, will likely play significant roles in future technologies. Graphene nanoscrolls have structures similar to carbon nanotubes with a key difference in that they are not seamless – there are exposed edges along their lengths. As such, they share …

Assessing Employees’ Perceptions Of The Frequency And Intensity Of Workplace Interpersonal Conflict In Lateral And Hierarchical Dyads, Matthew Shayne Castillo

Doctoral Dissertations

Workplace interpersonal conflict has been identified as a potential major source of stress for several occupations. Occupational stress literature concerning this stressor reveals that interpersonal conflict can have adverse outcomes for organizations including absenteeism, turnover, and workers’ compensation claims for psychological injury. Accordingly, researchers have developed measures aimed at capturing perceptions of workplace interpersonal conflict to remediate and prevent it in organizations. Although workplace interpersonal conflict has received considerable attention, there is little research assessing perceptions of conflict from a dyadic perspective in lateral (coworker-coworker) and hierarchical (supervisor-subordinate) relationships between supervisors and non-supervisors. This is important because conflict may be …

A Qualitative Study Of The Collaborative Relationships Between District Leaders And School Principals In High-Performing And Low-Performing Schools Within A Single High-Performing School District, Shaunna Pierrelee

Doctoral Dissertations

Research on effective collaborative relationships between district leaders and school principals have shown to exhibit characteristics that positively impact student achievement. Characteristics such as reciprocal communication, shared decision making, intensive support, and quality professional learning opportunities are repeated in literature. Therefore, this qualitative case study examined whether there are differences in collaborative relationships between district leaders and school principals in high-performing and low-performing schools within a single school district based on those common characteristics. The following research questions guided the current study: (a) What are the differences, if any, in communication between district leaders and principals of high- and low-performing …

Assessing Gender Bias In Student Evaluations Of Teaching In Collegiate Aviation, Kary M. Randall

Doctoral Dissertations

Student evaluations of teaching (SET) are commonly used to assess teaching effectiveness and influence personnel decisions in higher education. This quantitative study sought to determine if gender and years of teaching experience were related to SET ratings for collegiate aviation faculty. Constructs evaluated related to gender stereotypes and consisted of expressiveness and immediacy as stereotypically female and professionalism and openness as stereotypically male. The overall rating was also analyzed as a fifth construct. Evaluation ratings from 54 participants associated with nine Aviation Accreditation Board International affiliated institutions were analyzed for the 2017 to 2020 academic years. Findings from the two-way …

Science Instructional Leadership Knowledge: A Qualitative Case Study, Mary Ann Chapman

Doctoral Dissertations

This qualitative case study aimed to investigate instructional leaders’ depths of science content knowledge and pedagogical content knowledge and how their depths of that knowledge supports effective instructional leadership. Implementation efforts around the Next Generation Science Standards (NGSS) have highlighted the need for science instructional leaders to have in-depth content and pedagogical knowledge to function as effective instructional leaders in secondary science classrooms across the United States. Semi-structured interviews with 19 teachers and instructional leaders in a public high school in the southern United States informed the study. The findings revealed that teachers expect instructional leaders to have higher levels …

Novice Teachers As Teacher Leaders: A Mixed Methods Study Of Years Of Experience And Teacher Leadership Development, Miranda Owens Allen

Doctoral Dissertations

The aim of this research was to address the gap in the literature on novice teacher leadership development from novice teachers’ perspectives. An explanatory sequential mixed methods design was used to identify the differences that years of experience may or may not have on southern US public school novice teachers’ teacher leadership identity, readiness, and engagement. Distributed leadership theory provided the theoretical lens and Sinha and Hanuscin’s (2017) Teacher Leadership Development Process Model was used as the conceptual framework.

Survey data were collected from 306 full-time pre-k through fifth grade teachers from 71 public elementary schools. One-way ANOVAs measured statistical …

Finding Change Agents: A Qualitative Case Study On Perceptions Of Education Leaders During The Implementation Of The Next Generation Science Standards, Billy Dwain Niell Iii

Doctoral Dissertations

This study is a qualitative case study of middle schools located in a rural public school district in a southern state in the United States that has implemented the Next Generation Science Standards (NGSS) which explored the roles of education leaders in the implementation of NGSS. Participants included teachers, instructional coaches, and district administrators. The findings of the study include how a lack of training for NGSS impacted the effectiveness of education leaders, district leadership focused on curriculum instead of the standards, the response to teacher frustrations led to an adversarial relationship with the district, and education leaders exist in …

What Do Facial Products Have To Do With A Waterfall? The Role Of Remoteness, Social Comparison, And Envy In The Purchasing Effectiveness Of Sponsored Product Social Media Content, Louis J. Zmich

Doctoral Dissertations

Advertising has gone from magazines, to television, and now social media. However, unlike the robust advertisement literature, the influencer marketing literature has not caught up to explain how social media sponsored content can perform its best. While companies rely on follower count and interaction (i.e., likes) to determine who to partner with, the need for clarity on how to best predict digital advertisement success is needed. This study brings the literature of advertising and cognitive psychology, and applies the associative memory, visual persuasion, and remote conveyor theories into the influencer marketing context. This study specifically looks at how creativity through …