Dissertation Defense Announcements

Part I: An equilibrium statistical mechanics framework for investigating microfracture in rocks is proposed and tested. The framework consists of three elements: A) A simplified energy-based model describing atomic- to grain-scale mechanical and thermal rock fracture, B) A macroscopic, grain-scale statistical mechanics model that postulates existence of (thermomechanical) equilibrium, where (over appropriate timescales) rates of grain-scale microfracture (nominally) match rates of microfracture healing, and C) A resultant theoretical prediction connecting measurable fracture-induced acoustic emission (AE) with rock temperature. Comparisons of theoretical, temperature-dependent AE with AE observed during cyclic rock heating and cooling experiments support the validity of the model. Importantly, the results suggest that, for a given rock type - whether in pristine volumes devoid of grain-scale cracks or within volumes containing such cracks - the number of microfractures within the volume can be reasonably estimated as a calculable function of temperature and confining pressure, regardless of the rock's geological and weathering history.
PART II: The second part of the dissertation recasts traditional dimensional correlations between experimentally measured (tensile-driven) subcritical fracture speed, da / dt, and imposed stress intensity, KI, in dimensionless form. To the best of our knowledge, all existing correlations are well-described by the so-called (dimensional) Charles crack growth law: da / dt=AKIn where a, t, A, KI and n are, respectively, crack length, time, a rock-dependent (constant) prefactor, stress intensity, and subcritical crack growth index. Puzzlingly, however, in granite and similar fine-grained rock, experimentally determined n's are anomalously large, on the order of 40 to 150.
To tackle this puzzle, we apply dimensional analysis to existing (and difficult to obtain) Charles law correlations, recasting these in dimensionless form. While this practice is de rigueur in, e.g., fluid mechanics, physics, and heat transfer, it is new in the area of fracture mechanics. Importantly, recasting Charles' law in appropriate dimensionless form exposes two distinct regimes of subcritical fracture in rock: A) A slow growth regime, extant at stress intensities below a well-defined threshold, in which sub grain-scale cracks grow slowly along grain boundaries; and B) A fast subcritical growth regime, extant at stress intensities above the threshold, in which cracks grow intermittently across multiple grains. We show that each regime is well-captured by dimensionless Charles' law correlations, where slow regime n's are on the order of 1, and fast regime n's are clustered around approximately 4 to 6.
Crucially, these findings will allow development of improved, predictive crack growth models, suitable for predicting and interpreting geologically ubiquitous subcritical fracture in surface and near-surface rock, both on earth and on extraterrestrial bodies.

College readiness has been a primary focus of U.S. secondary education for over 40 years. Despite the continued focus on college readiness at the national, state, and local levels, researchers have claimed that educational reforms have resulted in little gains in students’ college readiness, warranting continued emphasis and research. To advance college readiness, secondary and postsecondary institutions offer rigorous advanced courses with college competencies. While these courses may positively impact college readiness, research has shown gaps for students of color, students from economically disadvantaged backgrounds, and rural students. Despite much college-readiness research, the issue remains relevant; specifically, teacher perspectives still need to be studied. This gap in the literature warrants acknowledgment and further investigation.
This exploratory, multiple-case, qualitative study sought to bridge this gap by exploring Advanced Placement secondary teachers’ and Dual Enrollment postsecondary instructors’ perspectives of college readiness regarding advanced courses in a rural North Carolina setting. The results from two focus group interviews, an Advanced Placement focus group and a Dual Enrollment focus group, indicated that advanced-course teachers perceived college readiness as multifaceted, extending beyond knowledge and performance, and they perceived a rigorous program design enhances college readiness. However, they perceived differences between the two educational systems, leading to frustration for the secondary teachers. Implications reflect the dire need for better communication and curriculum alignment between the two systems and support recommendations for expanding the scope of qualitative research with continued quantitative methods.

This dissertation explores the impact of diversity, intersectionality, and diversity management on job satisfaction within the federal workforce. The three constituent studies use disaggregated ethnoracial data from the Federal Employee Viewpoint Survey (FEVS) to examine the effects of demographic congruence, demographic heterogeneity, and perceptions of diversity management practices on the outcome variable of job satisfaction.

The first study tests the effects of demographic congruence (representation) and heterogeneity (diversity) on job satisfaction across federal agencies for members of different ethnoraces by employing mixed-effects models to a combination of 2020 FEVS data and FedScope data on agency-level demographics. Findings from this study show that increased demographic congruence is positively associated with job satisfaction for all minority groups and that demographic heterogeneity, in contrast, presents a more complex relationship, where initial increases in diversity are linked to lower job satisfaction but later rebound past a certain threshold. The second study explores how intersectional identities—race and gender—influence job satisfaction and are mediated by perceptions of DEI management. By using mixed-effects models on 2022 FEVS data, the results show that minority status is generally associated with higher job satisfaction but that gender and perceptions of DEI Management moderate this relationship. For all ethnoracial groups and genders, perceptions of positive DEI management—especially equity and inclusion—are positively associated with job satisfaction. The third study employs Random Forest models on 2022 FEVS data to predict job satisfaction based on demographic and job-related factors. All models achieve high predictive accuracy across various racial and gender subgroups, with intrinsic work experience, job inspiration, satisfaction with pay, and personal attachment to the organization emerging as the most influential factors for all. Noticeable differences between ethnoracial and intersectional groups emerge. These results highlight the potential for AI techniques to enhance public administration by offering practical tools for HR managers to proactively address issues related to employee satisfaction, especially as it pertains to specific populations.

This dissertation advances the theoretical understanding of social identity and diversity management while offering practical guidance for improving job satisfaction in the federal workforce. All three studies show that targeted and effective DEI management practices can improve employees' job satisfaction. As public managers respond to policy changes and adjust their approach to diversity, this research can help improve data-driven strategies to better address their workforces’ needs.

With the rise in antibiotic resistance (AR) and multidrug-resistant (MDR) bacteria, there is a need for novel antimicrobials that can exert antibacterial action via multiple mechanisms. Nanoparticles such as silver nanoparticles (AgNP) can serve as a potential alternative due to their unique optical and physiochemical properties along with their innate broad-spectrum antibacterial activity. AgNPs antibacterial property is associated with the release of silver ions (Ag+), which is a slow process taking up to days to achieve effective antibacterial levels. Recent findings indicate that combining photodynamic inactivation (PDI) with AgNP shows antibacterial synergy. This research is aimed at developing light-activated silver nanoparticles and investigating their light-responsive Ag+ release kinetics to understand their role in antibacterial synergy.
Herein, protoporphyrin IX conjugated on the AgNP surface (PpIX-AgNPs) was developed and Ag+ release kinetics were investigated to correlate the Ag+ release kinetics to the antibacterial synergy of PS-AgNP. These PpIX-AgNPs serve as excellent light-activated antimicrobial agents and this antibacterial action was demonstrated in antibiotic-resistant bacteria (ARBs). The antibacterial action of this light-activated PpIX-AgNP was further modulated by adopting a dual-step irradiation strategy to ensure the controlled release of Ag+. Finally, this research includes a preliminary study demonstrating the transport of nanoparticles within biofilms and light-activated inhibition of Vibrio cholerae biofilms. This research provides crucial knowledge for designing light-responsive silver-based antimicrobials for potential wound-healing applications.