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Growth mechanism study is important to achieve high-quality materials growth using more convenient approaches and to realize controlled growth with compositional and structural tunability. In vapor-based deposition, vapor-solid (VS) and vapor-liquid-solid (VLS) processes have been two classic mechanisms for the growth of micro- and nano-scale structures. The VS process is a non-catalyst growth controlled by vapor supersaturation, while the VLS process is a catalyst-assisted growth initiated and guided by eutectic particles. This research reported a co-growth of three-dimensional (3D) Si crystals with two-dimensional (2D) Si2Te3 crystals and explored its growth mechanism. Chemical vapor deposition (CVD) method has been employed using Te and Si powders as the source materials in the presence of a Cu-coated Si substrate. The growth mechanism study reveals that the Te source plays two different roles in the growth. First, it serves as a reactant which vaporizes and reacts with Si powders to yield 2D Si2Te3 growth via the VS mechanism. A unique “liquid epitaxial growth” was discovered that Te droplets formed prior to the Si2Te3 growth could promote a quasi-epitaxial growth of Si2Te3 crystals on a lattice mismatch substrate. Second, the Te serves as an unstable catalyst for the 3D Si growth. The Si growth is promoted by the synergistic effects of Cu and Te: (1) Cu as a stable catalyst facilitates the reaction of Te vapor species with the Si substrate, forming ternary Te-Cu-Si eutectics; (2) due to the instability of Te, the Te-Cu-Si eutectic particles evaporate and release Si vapor as the precursor for the VS growth of Si crystals. This intermediate process is dubbed as a vapor-liquid-vapor (VLV) process which provides a new approach for the material growth with lower growth temperature, lower cost, and higher compatibility for device fabrications.
There is growing concern about the pervasive underrepresentation of qualified Black women superintendents. despite women significantly outnumbering men in public education. This study sought to shed light on the lived experiences of Black women superintendents in North Carolina. The purpose of this basic interpretive qualitative study was to gain an understanding of the perceptions about inhibiting and enabling factors Black women leaders faced when ascending to the superintendency and while serving in the role. Specifically, this study sought to contribute to the existing body of scholarly work and inform aspiring Black women superintendents about the experiences of Black women superintendents in the role, as this area has not been explored. By considering the intersectionality of race and gender for Black women superintendents, the study findings were grounded in the theoretic frameworks of Black feminist theory and the glass ceiling effect. These informed current practices related to hiring superintendents to create career advancement opportunities for aspiring Black women leaders. Results of the study from semi-structured individual interviews with five Black women superintendents in North Carolina indicated a substantial discrepancy between the number of women, particularly Black women, and men in the superintendent’s role. Implications included the need for career pathway training for prospective Black women superintendents, further research on the topic, new school board policies related to fair hiring and recruitment, and preventing suppression of opportunities by White power structures.
In this dissertation, we develop multivariate Dickman distribution and explore its properties. In addition, we utilize the Dickman distribution to model the small jumps within a broad class of Levy processes. Our central theorem establishes that the limit distribution of an appropriately transformed truncated Levy process with finite variation exhibits a Dickman-type Levy measure. We also provide equivalent conditions to further characterize this result. Drawing inspiration from this, we partition the Levy process into small and large jumps. Small jumps are effectively modeled by the Dickman distribution, while the remaining large jumps follow a compound Poisson distribution. Further, we extend our findings to Ornstein-Uhlenbeck (OU) processes. Our investigation encompasses two scenarios: the truncated OU process and the OU process driven by a truncated Levy process. In general, employing the same transformation outlined in our main theorem, we observe that the limit distribution of the truncated OU process aligns with a Dickman-type Levy measure. Notably, for the OU process with a truncated driving process, the limit distribution remains consistent with that of the OU process with a truncated driving process having a Dickman-type Levy measure.
Graph coloring is commonly used to schedule computations on parallel systems. Given a good estimation of the computational requirement for each task, one can refine the model by adding a weight to each vertex. Instead of coloring each vertex with a single color, the problem is to color each vertex with an interval of colors.
Stencil graphs appear naturally in the parallelization of applications, where the location of an object in a space affects the state of neighboring objects. Rectilinear decompositions of a space generate conflict graphs that are 9-pt stencils for 2D problems and 27-pt stencils for 3D problems. We show that the 5-pt stencil and 7-pt stencil relaxations of the problem can be solved in polynomial time. We prove that the decision problem on 27-pt stencil is NP-Complete. We evaluate the effectiveness of several different algorithms experimentally.
Executing graph algorithms in a parallel or distributed context is a challenging problem. It is possible that the algorithm picks a partial order with long chains, which limits its utility to parallel applications. We investigate how distributed dataflow graph algorithms obtain a partial order and how one could favor orders with shorter long chains. We study the behavior of these different algorithms on randomly generated RMAT graphs and real-world graphs. We show that our ordering methods can significantly reduce the length of the longest chain.
Approximately 25% of United States mental health practitioners are employed in private practice settings (BLS Data Viewer, 2021). However, the Council for Accreditation of Counseling and Related Educational Programs, which sets standards for graduate level counseling programs, neither specifies private practice settings as a specialization nor an area for graduate programs to emphasize. In addition, research specific to private practice counselors is limited to the challenges of working in the setting (Harrington, 2013; Legge, 2017). The purpose of this study was to explore the career development and current work experiences of new licensed counselors who earned the required direct client and supervision hours in the private practice setting. Basic qualitative research design, as described by Merriam and Tisdell (2016), was paired with Braun and Clarke’s (2021) Reflexive Thematic Analysis for this exploration. Due to the limited empirical research, Krumboltz’s (1979) Social Learning Theory of Career Decision Making was used as a theoretical framework. Supporting evidence from eight participants was analyzed and five patterns emerged: (1) Non-Counseling Experience is an Asset, (2) Graduate School Does a Great Job Giving you a Foundation to Build On, (3) Practical Experience Makes Up for Academic Gaps, (4) I’m Going to Start Private Practice and See What I Can Do, and (5) Private Practice Yields for My Career Development. These patterns and the accompanying ten subpatterns are discussed in alignment with extant literature and the theoretical framework. A private practice counselor development model was proposed amongst the other implications of the findings.
The purpose of this study was to explore the impact of the social construct of masculinity on the fraternity members’ experiences with accountability. This study focused on the methods fraternities used to hold their members accountable, how the members’ behavior changes, and the impact masculinity had on accountability methods. This study is rooted in an understanding of the concept of masculinity and how it is often engrained deeply in the fraternity experience (Harris & Edwards, 2010; Harris & Harper, 2015). This study used document review to understand espoused expectations and accountability process. Additionally, four participants each from two different fraternity chapters participated in semi-structured interviews. This qualitative phenomenological study sought to understand the experience each member had with accountability in their fraternity. After multiple rounds of coding, five themes were created encompassing the experiences fraternity members had with accountability: formal accountability only a formality, herd mentality: informal expectations of the group, informal accountability is the real accountability, being a man prioritized, and culture and context set the tone. The study largely found that masculinity had a strong influence over the accountability experience in the chapter. Additionally, informal accountability was used daily to enforce several informal expectations. Formal accountability and formal expectations, however, did not take priority in fraternities. The expanded understanding of accountability can be used by fraternity members and their advisors to help empower men to mitigate high-risk behavior. Doing so will be critical to ensuring fraternities remain a viable opportunity for undergraduate student involvement.
Values-based leader behavior is commonly referenced by scholars and practitioners as an effective style of leadership. Problematically, multiple definitions of the concept exist that are either ambiguous, tautological, or valanced. Additionally, the concept has been researched almost entirely via questionnaires with little triangulated evidence. The current study reviews previous conceptualizations of values-based leader behavior as well as the key components of leadership, values, and behavior to arrive at a new conceptualization framed from a signaling theory perspective: goal-oriented action or inaction signaling an individual’s, organization’s, or society’s value structure. Then, I review three commonly referenced manifestations of values-based leader behaviors (charismatic leader tactics, ethical leader signals, and transformational leader behaviors) and make the case that pay-for-performance strategies too are strategies that can signal one’s value structure. Using a pre-registered experimental design, I explore the extent to which each of these values-based leader behaviors influence stakeholder in- and extra-role behavior compared to a control condition in a realistic text labeling task. Results found that the pay-for-performance strategies were strong predictors of both in- and extra-role behavior, charismatic leader tactics were strong predictors of extra-role behavior, and the control condition produced the least net output for in- and extra-role behavior combined. I conclude with a discussion of the theoretical and practical implications as well as future research directions.
Materials science aims to explore the properties and behaviors of different materials, from metals to advanced carbon structures. This dissertation focuses on three distinct areas of study: Inconel Alloy 740H, polycrystalline graphene, and tetragraphene (TG).
The first part of this work concentrates on developing and validating a Chaboche unified constitutive model. This model incorporates both nonlinear isotropic and kinematic hardening rules to accurately predict the stress-strain behavior of Inconel Alloy 740H, a high-temperature nickel-based superalloy. The material parameters of the model are determined and its accuracy validated through experimental data obtained from uniaxial strain-controlled loading tests across a wide temperature and strain ranges.
The second part explores the mechanical properties of polycrystalline graphene, bridging scales from nanoscale to macroscale through a multiscale molecular dynamics (MD)–finite element (FE) modeling approach. By studying the behavior of graphene sheets with different grain boundaries and atomic structures, insights are gained into the influence of grain size on mechanical properties like the Young modulus and fracture stress.
The third part of this dissertation investigates the mechanical properties of tetragraphene (TG), a quasi-2D semiconductor carbon allotrope, with a focus on addressing graphene's limitations in electronic applications. Through MD simulations, the research examines TG's fracture properties under mixed mode I and II loading, considering variables such as loading phase angle, crack structure, and temperature.
The expectation for educators to engage in evidence-based decision-making has become standard protocol in public education, yet translating research into effective practice can often be mired with implementation challenges. Research-practice partnerships (RPP) support research-informed practice by engaging key stakeholders to address real and contextual problems encountered by K-12 educators. This qualitative critical realist case study investigated the inner workings and attributes of a teacher-centric RPP formed to address ongoing implementation challenges with the North Carolina Early Learning Inventory. Data sources included observations of RPP meetings, teacher interviews, communications, and analysis of artifacts. Thematic findings suggest that teacher-centric RPP models strengthen trust and credibility between educational agencies through a series of preconditions: Expanding access, diversifying perspectives, developing alliances, and deepening knowledge. This resulted in increased implementation practices and enhanced the production of usable information to address implementation fidelity. Simultaneously, this framework also heightened teachers’ sense of professional identity. This study contributes to a dearth of literature on applying RPP models to support evidence-based policy mandates and offers a new model for leveraging classroom practitioners. This investigation contributes to the field of evaluation by providing a sustainable model to maintain implementation fidelity and strengthen teachers’ perceptions of their professional identity and agency.
