Dissertation Defense Announcements

Candidate Name: Michael Zimnoch
Title: Cyclic Analysis of Power Plant Headers and Materials
 April 09, 2024  9:00 AM
Location: Duke 308
Abstract:

This dissertation evaluates the fatigue response of a steam header designed to mirror the specifications of an ex-service unit, with a focus on optimizing material selection through a detailed analysis involving cost, performance, and durability. Beginning with a study comparing three different alloy choices, 2.25Cr-1Mo, 9Cr-1Mo-V, and IN740H, headers are developed and compared using the procedures outlined in ASME BPVC. The design of the headers follows that used in the original development, and their performance is evaluated in representative loading transients. Each of the designs is evaluated for their fatigue response using the finite element program Abaqus. The results demonstrate that cost savings would likely outweigh any performance benefit to the current system.
The second portion evaluates the material characteristics of 2.25Cr-1Mo following years of exposure to a harsh operating environment. Material specimens were machined from the ex-service unit and subjected to uniaxial testing at various temperatures. The process is used to establish the Chaboche NLKH hardening coefficients. The selection of the NLKH model was guided by its capability to capture the cyclic behavior of the material. The material results are used to compare the projected performance of the 2.25Cr-1Mo header found using readily available material acquired from virgin specimens and those found from the existing unit. The results demonstrate a markedly reduced strength in the service-exposed material, illustrating the effects of the material transformation that occurs over time. This study highlights the importance of operational wear on the projected performance of the header.
The final portion introduces an automated crack growth algorithm in combination with Abaqus to model the progression of a seam crack within a 2.25Cr-1Mo header. Traditional fatigue assessments consider the formation of surface cracks as the end of usability. However, it is well established that the existence of cracks in headers may be allowable, depending on several factors such as size, location, and material. Additional challenges exist in headers along the tube-header intersections, which suffer from non-uniform crack propagation stemming from the complex thermal-mechanical loading near the intersection. To address this issue, the present work develops an algorithm in Abaqus to use the seam crack capability and Paris law to efficiently perform iterative crack growth simulations. This approach captures the uneven growth response of the crack, providing more realistic service life estimations.



Candidate Name: William Derrick Johnson
Title: Examining The Quality-Of-Life Experienced By Family Members Affected By A Loved One's Substance Use Disorder As Related to Personal Losses, Substance Use, Level Of Stress, And Perceived Support
 April 04, 2024  10:00 AM
Location: Room #246, Department of Counseling, Cato College of Education
Abstract:

The quality of life for those who support loved ones living with substance use disorder (SUD) is adversely affected due to destructive behaviors and the impact these behaviors have on the family system (Kaur, 2016). Consequently, primary support persons (PSP) often live their lives in silence and experience disenfranchised losses that impact not just the family unit but also impacts the human system, the most significant system among family units (Howard et al., 2010). This same researcher asserts this circular causality is almost always found among human and family systems as the actions of one person create responses or adaptions from other persons living within that same family unit. This is important because it highlights the way alcohol and other drugs (AOD) impact normal functioning of the addict, their loved ones, and society (Cudak & Pedagogika, 2015).
The purpose of this study was to examine variables that impact of quality of life of caregivers to people living with SUD. Perceived losses due to a loved one’s SUD, perceived social support, one’s own substance (ab)use, and stress were all examined to learn the impact these variables have on QOL. Multiple linear regression was utilized to examine the impact on QOL (n = 114) as predicted by losses, perceived support, substance use, and stress. Results indicated that support, losses, and stress are significantly associated with the dependent variable QOL (r2 = .815) to QOL. Results of this study postulate insight into future treatment approaches with PSP and highlight links to treatment that need to be addressed on behalf of PSP as well as the total family unit. These findings have implications for mental health and substance abuse counselors in terms of working with PSP and examining how improved QOL of support persons impacts those being treated for SUD. Future research is needed to examine how more thorough and more inclusive treatment approaches can include working with families of those who are addicted to substances.
Keywords: Quality of life, primary support person, substance use disorder, families, addiction, losses, depression and stress, support, family support, SUD treatment, family treatment involvement, support person



Candidate Name: Subhasree Srenevas
Title: MORPHOLOGICAL COMPLEXITY AND ORGANIZATIONAL DISORDER OF RANDOM ANTIREFLECTIVE STRUCTURED SURFACES
 April 01, 2024  11:00 AM
Location: GRIGG 132. Zoom link: https://charlotte-edu.zoom.us/j/95363614817?pwd=bzRXNWw1WEZOZ1ZibFd2ZjJEVDBYUT09
Abstract:

Random antireflective surface nanostructures (rARSS) enhance transmission by reducing the electromagnetic impedance between optical indices across a boundary, serving as alternatives for traditional coating techniques. Understanding and quantifying the role of randomness of the surface nanostructures remain elusive, without a comprehensive model that can accurately predict the wideband spectral response of randomly nanostructured surfaces based on causal physical principles. Effective-medium approximations (EMA) emulate the randomly structured surface as a sequence of homogeneous film layers, failing to predict the critical (or cut-off) wavelength above which the enhancement effect is observed and below which bidirectional optical scatter is prominent. Analyzing near-field or far-field radiance due to wavefront propagation through randomly nanostructured surfaces requires high computational budgets, which are challenging for randomly distributed features with varying-scale boundary conditions.
Deterministic periodicity is considered a sufficient surface geometrical descriptor for regular (or long-range repetitive) nanostructured surfaces, whereas characterizing random surface features is based on first-order statistical evaluations or macroscopic averages, such as autocorrelation lengths, which introduce significant ambiguity in subwavelength scales. What constitutes the "randomness" of rARSS, beyond standard surface topography measures, is subjective. Conventional optical surface structure characterization, disregards aspects of nanoscale morphological attributes, mainly spatial configuration or organization, due to resolution limitations of metrological instruments. The organizational aspect of nanostructured features can significantly impact the macroscopic Fresnel reflectivity radiance, bidirectional scattering, and axial transmission enhancement (cooperative-interference effect).
In this work, transverse granule population distributions and their corresponding granular organization at the nanoscale, is determined using a variation of the Granulometric image processing technique. Various rARSS surfaces were fabricated, resulting in unique surface modifications and spectral performance, as observed with respectively scanning electron microscope (SEM) micrographs and spectral photometry. The approach to quantify randomness or complexity of the nanostructures, presented in this work, is based on Shannon’s entropy principles. Resolution limitations from conventional characterization techniques using non-invasive confocal microscopy and spectroscopic ellipsometry is discussed. Statistical quantification of nano-structural randomness using Shannon’s entropy is proposed as a solution to characterize the unique degree of disorder on the surfaces. A figure-of-merit is derived and computed from surface organization state variables, and it is proposed as a heuristic parameter to predict the transition from spectral scattering to the transmission enhancement region. This multivariate problem is addressed by accounting for the conditional probability dependence of granule populations as functions of granule dimensions and their corresponding proximity distributions, thereby laying the foundations for a surface microcanonical ensemble model, establishing a link between surface morphological descriptors and spectral variables.



Candidate Name: Hussein Ghnaimeh
Title: EXTENDING THE EXTENDED UNIFIED THEORY OF ACCEPTANCE AND USE OF TECHNOLOGY (UTAUT2): The moderating Role of Information Privacy Concerns
 April 11, 2024  1:00 PM
Location: Zoom https://charlotte-edu.zoom.us/j/95020353532
Abstract:

This dissertation enhances the Extended Unified Theory of Acceptance and Use of Technology (UTAUT2) by integrating information privacy concerns, examining their influence on the adoption of web-based healthcare portals. Through a survey of 298 U.S. residents using healthcare technologies, the study investigates the interplay between UTAUT2 predictors—Performance Expectancy, Effort Expectancy, Facilitating Conditions, Habit, Social Influence, and Hedonic Motivation—and the intention to use these technologies, while assessing how privacy concerns modulate these relationships. Regression analysis highlights the positive impact of Performance Expectancy, Effort Expectancy, and Habit on adoption intent, with privacy concerns significantly moderating the relationship between Effort Expectancy and usage intention.
The research enriches the UTAUT2 model by showcasing the pivotal role of privacy concerns, thus advancing theoretical understanding and enhancing model predictability in the context of healthcare technology. Practically, it offers insights for practitioners and policymakers on addressing privacy concerns to improve technology adoption. This synthesis of privacy concerns within the technology acceptance framework paves the way for targeted strategies to increase the uptake of healthcare technologies, marking a significant contribution to both academic discourse and practical application in healthcare technology management.



Candidate Name: Ashley Nichole Anderson
Title: Effects of an Instructional Support Package for Community-based Instruction for Young Adults with Extensive Support Needs
 April 01, 2024  11:00 AM
Location: COED 110
Abstract:

Federal legislation for students with disabilities mandates that all students receive appropriate and relevant instruction across environments to improve postsecondary outcomes across domains. Teachers and parents alike have found that one way to meet individual student needs and increase instructional opportunities for students with disabilities is through the use of purposeful and meaningful community-based instruction (CBI). For students with extensive support needs (ESN), however, the practical implementation of CBI within the classroom and community setting may pose several barriers and relies heavily on teacher and family knowledge of community engagement strategies. Previous research in the area of CBI indicates that through the use of evidence-based practices CBI is effective in teaching skills across the four identified domains, which include leisure, vocational, community engagement, and daily living. In an attempt to bridge gaps in the available literature and research in the area of CBI, this study evaluated the effects of an intervention package comprised of three evidence-based practices (video modeling, visual supports, and system of least prompts), goal setting, and collaboration, through peer-implemented instruction, in order to teach leisure skills to young adults with ESN in relevant community settings. The experimental design was a multiple probe across skills replicated across two participants. Two young adults, ages 21 and 22 with ESN participated in the study, along with two of their same aged peers, and relevant team members/key stakeholders (i.e., program director at their university, parents). Three community-based leisure skills across three environments were chosen with a specific skill targeted at each location. The intervention was effective for teaching these leisure skills to the participants across all three community locations. In addition, they were able to generalize and maintain these skills at the conclusion of the study. Social validity measures indicated that all participants felt that these were relevant skills for the participants and that their role in this process was valuable. The findings from this study can be used to guide future research in the area of CBI with students of all ages to support them as they access community settings.



Candidate Name: Monica Rasmussen
Title: The influence of time, rock properties, and climate on mechanical weathering
 April 04, 2024  11:30 AM
Location: McEniry 215
Abstract:

Rock weathering, or the mechanical and chemical breakdown of rock over time, creates the landscape on which all terrestrial life is built. Here, I quantify the rates and controls over mechanical weathering [rock cracking/fracturing] f surficial boulder deposits in Eastern California using by collecting rock and crack field measurements, clast size distribution data from the field, and rock elastic properties using laboratory testing. I used a chronosequence or space-for-time approach, whereby data are collected from rocks or sediments that have been exposed to natural weathering conditions for a range of times, using the properties of the stable deposits to represent the amount of weathering that occurs over the time span of exposure. I studied rocks at three sites, with rocks being exposed to Earth surface conditions from 0 to 148,00 years [148 ka].

I manually measured 8763 crack lengths, widths, and orientations from 2221 in situ boulders on Earth’s surface and found that that rock cracking is initially fastest when rocks are exposed to Earth’s surface conditions, with rocks accumulating cracks at a rate of 9-1502 mm of cracks per m^2 rock surface over a thousand years, or 0.1-36 individual cracks per m^2 rock surface over a thousand years. After this point, rocks continue to crack, but the rate of crack growth slows down. After about 30 ka, the growth rate is <36 mm of cracks/m^2 of rock surface per ka, or <1 individual cracks/m^2 of rock surface per ka. Using all rock and crack data I determined that age itself has the most consistent, positive, statistically significant correlation with the number of fractures per rock surface area [fracture number density] and the total length of fractures measured per rock surface area [fracture intensity].

From two sites, I collected a granitic boulder from each dated deposit for rock mechanics testing. These data show that rock compliance increases over time while mechanical weathering leads to an increase in microscale cracks, which alter the rock’s strength and elastic strain response under stress. Using the laboratory analyses and local weather station data, I implemented a simple daily stress model applying Paris’ law of subcritical crack growth to predict single crack growth after each day of weather conditions, for a period of 5000 years. Cracking occurred over only a limited number of unusually intense weather days when the daily range of air temperatures was the largest. In the two semi-arid sites, these cracking days were hot, dry summer days; in the arid site, the day when the most crack growth was predicted coincided with summer monsoonal rains. The model is highly sensitive to rock elastic properties, which supports the theory that a gradual increase in bulk compliance allows rocks to withstand stress without cracking over thousands of years.

Finally, I present clast size data to show that for volcanic and carbonate rocks, there is a correlation between the geometry of cracking observed on the rocks and the shape of sediments on older deposits: when many cracks are parallel to the rock surface, older deposits tend to have more flattened rocks on them. This shows that cracking rates and crack geometries can play a strong role in clast size and shape evolution over geologic time, and mechanical weathering should be considered when interpreting sediments in the geologic record.

These findings are directly applicable to geoscientists attempting to understand weathering, landscape evolution, and geological hazards. More broadly, the decreasing rock cracking rates that accompany slow mechanical property changes represent a real-world example of material fatigue vs. material failure.



Candidate Name: Sergei Miles
Title: Dynamics of the shift action on linear sequence spaces over groups beyond Z
 March 27, 2024  2:00 PM
Location: Fretwell room 379
Abstract:

In linear dynamics, bounded linear operators over infinite-dimensional Banach spaces have been shown to be able to exhibit interesting characteristics including topological transitivity, topological mixing, and even chaos in the sense of Devaney. This dissertation will examine weighted l^p sequence spaces together with the shift action as the operator. In the case the shift action is over the semi-group N, the above topological properties have been previously characterized by conditions on the weight sequence associated with a given weighted l^p space. This work will present recent results for new characterizations of these properties when the group action over a countable group is instead considered. Additionally, an example choice of the weight sequence in this setting will be presented which yields points which are periodic while having an infinite orbit.

Lastly, new implications for infinite and 0 topological entropy for the weighted l^p space with the shift action over N will be given. In particular, when the weight sequence is summable over a subset of N with positive upper density then infinite entropy may be achieved. Furthermore, when an arbitrary ratio of the weights is bounded above then 0 entropy is guaranteed.



Candidate Name: Mohiuddin Ahmed
Title: Distributed Hierarchical Event Monitoring for Security Analytics
 March 29, 2024  10:00 AM
Location: Online (Zoom): https://charlotte-edu.zoom.us/j/96478264051?pwd=Sk81SVBFYjRTelhRQ0tsY2dHaEJ4dz09
Abstract:

In recent years, there has been an increase in attacks, including advanced persistent threats (APTs), and the techniques used by the attacker in these attacks have reached unprecedented sophistication. Threat hunters use various monitoring tools to monitor and collect all these attack actions (which blend in with benign user activities) for cyber threat hunting—the end devices store monitored activities as generated logs/events. Moreover, Organizations like NIST and CIS provide guidelines (CSC) to enforce cyber security and defend against those attacks.

Although the end hosts and networking devices can record all benign user and adversary actions, it is infeasible to monitor everything. In existing approaches, high memory usage and communication overhead to transfer events to the central server create scalability issues on the monitored network. Single event matching on the end-host devices approach to detect attacks generates false alerts, causing the alert fatigue problem. This dissertation presents a distributed hierarchical monitoring agent architecture to overcome those limitations of existing tools and research works.

Additionally, there are no well-defined automated measures and metrics to validate the enforcement of CSC. Manually analyzing and developing measures and metrics to monitor and implementing those monitoring mechanisms are resource-intensive tasks and massively dependent on the security analyst's expertise and knowledge. To tackle those problems, we use LLM as a knowledge base and reasoner to extract measures, metrics, and monitoring mechanism implementation steps from CSC descriptions to reduce the dependency on security analysts with the help of few-shot learning with chain-of-thought prompting. This dissertation presents CSC enforcement assessment with the help of our distributed hierarchical monitoring agent architecture and prompt engineering.



Candidate Name: Arash Shiri
Title: Orbital Angular Momnetum of Partially Coherent Beams through Turbulence
 March 19, 2024  9:00 AM
Location: Grigg Hall, 238
Abstract:

The orbital angular momentum of light is a promising candidate as an information carrier in optical communication systems to enhance the capacity of data channels. However, the effects of atmospheric turbulence significantly degrade the quality of light beams, thereby imposing limitations on the range of reliable data transmission. To address this issue, researchers have been actively seeking methods to enhance the resilience of light against fluctuations of refractive index due to the atmospheric turbulence. It has long been recognized that partially coherent beams exhibit greater robustness in propagation through turbulence. Consequently, transitioning from full coherence to partial coherence has been suggested as a solution. Conversely, in OAM-based communications, reducing coherence results in broadening of the OAM spectrum, thus increasing cross-talk between adjacent channels. Therefore, utilizing partially coherent beams in free space communications entails both Benefits and drawbacks.
The main objective of this dissertation is to explore various classes of partially coherent beams through analytical approaches in order to identify a robust OAM spectrum in the presence of atmospheric turbulence. The results are presented in three different articles. The first article introduces a simplified version of the extended Huygens-Fresnel principle which is a widely used method of turbulence propagation. The discoveries outlined in the first article substantially alleviate the mathematical complexity associated with propagation in random media, thereby enabling analytical exploration of the propagation of partially coherent beams in random media.
The second article presents an optimization criterion associated with a specific class of partially coherent beams, substantially enhancing their resistance against turbulence. Finally, the third article thoroughly investigates the behavior of three categories of partially coherent beams in interaction with atmosphere, providing a detailed comparison of their respective resistance. The compilation of these three articles presents a comprehensive study of the impact of atmospheric fluctuations on the orbital angular momentum spectrum of partially coherent beams.



Candidate Name: Arash Shiri
Title: Orbital Angular Momentum of Partially Coherent Beams through Turbulence
 March 19, 2024  9:15 AM
Location: Grigg Hall, 238
Abstract:

The orbital angular momentum of light is a promising candidate as an information carrier in optical communication systems to enhance the capacity of data channels. However, the effects of atmospheric turbulence significantly degrade the quality of light beams, thereby imposing limitations on the range of reliable data transmission. To address this issue, researchers have been actively seeking methods to enhance the resilience of light against fluctuations of refractive index due to the atmospheric turbulence. It has long been recognized that partially coherent beams exhibit greater robustness in propagation through turbulence. Consequently, transitioning from full coherence to partial coherence has been suggested as a solution. Conversely, in OAM-based communications, reducing coherence results in broadening of the OAM spectrum, thus increasing cross-talk between adjacent channels. Therefore, utilizing partially coherent beams in free space communications entails both Benefits and drawbacks.
The main objective of this dissertation is to explore various classes of partially coherent beams through analytical approaches in order to identify a robust OAM spectrum in the presence of atmospheric turbulence. The results are presented in three different articles. The first article introduces a simplified version of the extended Huygens-Fresnel principle which is a widely used method of turbulence propagation. The discoveries outlined in the first article substantially alleviate the mathematical complexity associated with propagation in random media, thereby enabling analytical exploration of the propagation of partially coherent beams in random media.
The second article presents an optimization criterion associated with a specific class of partially coherent beams, substantially enhancing their resistance against turbulence. Finally, the third article thoroughly investigates the behavior of three categories of partially coherent beams in interaction with atmosphere, providing a detailed comparison of their respective resistance. The compilation of these three articles presents a comprehensive study of the impact of atmospheric fluctuations on the orbital angular momentum spectrum of partially coherent beams.