-
Prospective Students
-
Faculty and Staff
-
Current Students
-
Alumni and Friends
Silicon carbide (SiC) has excellent thermomechanical properties, and it is one of the most promising candidates for many demanding high temperature applications in military, aerospace, space mirrors, nuclear energy stations, filtering, and furnace. Manufacturing of SiC product is difficult due to its thermochemical and mechanical stabilities. The additive manufacturing (AM) of SiC has drawn a lot of attention in recent years due to these excellent materials properties and diverse applications. Previous studies from our lab have shown that the creation of a silica gel layer on the surface of SiC using NaOH solution activated the surface and allowed 3D printing of SiC using water based binder in a powder bed binder jet printer. The dried silica gel layer binds adjacent SiC particles upon hydration during 3D printing at room temperature. The 3D printed green parts require a secondary surface activation by impregnating in NaOH solution and thermal treatment to enhance density and strength. The secondary surface activation technique creates an additional silica layer on the surface of SiC at room temperature which can lead to the growth of silica nanowire inside the pore of 3D printed SiC parts upon heat treatment. The hypotheses underlying this approach are twofold: (i) maximum growth of the silica nanowires will facilitate densification and mechanical properties, and (ii) The silica gel layer can mediate a strong bond between SiC and silicate minerals such as mullite. This thesis has three main objectives. First to understand the effect of processing parameters including concentration of NaOH, thermal treatment temperature and dwelling time on silica nanowires growth and subsequent density and mechanical properties, second, to develop and validate a mathematical model for silica nanowires’ growth and ceramic strengthening, and the third objective is to examine the role of the silica gel layer and thermal treatment parameters on in situ mineralization of mullite bonding agent for SiC composite. This thesis is structured into two parts: (i) experimentally optimizing the processing parameters for silica (SiO2) nanowire growth inside the pore of 3D printed SiC discs based on quantitative SEM analysis and development of a mathematical growth model for silica nanowire growth, and (ii) creating in situ synthesized liquid mullite as a secondary binder phase for the densification and strengthening of 3D SiC manufactured using powder metallurgy technique.
We found that the silica nanowire growth rate and number density depend on the processing parameters such as NaOH concentration, sintering temperature, and time. Therefore, the goal of the first part of this dissertation is to investigate the effect of the processing parameters on nanowire growth and number density. Utilizing quantitative SEM image analysis and a silica nanowire growth model, the focus is on optimizing processing parameters to achieve maximum nanowire growth and density, ultimately enhancing the densification and mechanical properties of 3D printed SiC components. The silica nanowire was grown inside the pore of 3D printed SiC disc through the vapor solid (VS) noncatalytic mechanism. In this process silica (SiO2) vapor condensed directly onto the SiC particle surface, leading to the nucleation and growth of one-dimensional silica nanostructures. Differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis were performed on SiC disc prepared via the powder metallurgy technique using NaOH solutions at varying concentrations (5%, 10%, and 20%). The thermal analysis helped us determine the nucleation temperature of silica droplets at 525 °C and crystallization temperature at 800 °C. The effect of NaOH concentrations analysis showed that the nanowire number density (mm-2) as well as the width and length of the nanowires increased according to the concentration of the NaOH used to pretreat 3D printed SiC in the order 20% > 10% > 5%. The optimal combination of NaOH concentration and heat treatment parameters identified for the highest nanowire number density and nanowire growth involved impregnating with 10% NaOH and heat treating at 550 °C for 6 hours and 1100 °C for 4 hours. The resulting sample exhibited a nanowire number density of 55431 ± 9232 mm-2, majority of the nanowires were in the width range of 0.3 µm – 0.6 µm, and length of 25.6 ± 3.3 µm as determined through quantitative SEM image analysis. The compressive strength, density and porosity were found to be 9.86 ± 1.4 MPa, 2.27 gcm-3, and 38.32%, respectively. Subsequently, a mathematical nanowire growth model was developed in order to investigate the growth mechanism and understand the effect of reaction kinetics on the nanowire growth. The model accounted for the reaction kinetics controlling the formation of silica molecule and its subsequent deposition on nanowire top surface contributing to the growth of the nanowire. The change in nanowire length relation with respect to different processing parameters obtained from the model showed a good agreement with the experimental data.
The silica gel layer on the surface activated SiC particles transforms into cristobalite (SiO2) upon heat treatment which serves as a binding agent that holds the SiC particles together. However, cristobalite has relatively poor mechanical strength and thermal properties compared to SiC. Therefore, in the second part of this dissertation, an in-situ mullite binding agent was formed which has superior thermomechanical properties compared to SiO2. Additionally, it has thermomechanical and chemical properties comparable to those of SiC. We have reported on using coal fly ash as a source of alumina (Al2O3) that reacts in situ with the silica (SiO2), oxidation product of SiC. The instantaneous mullite formation on the surface of SiC facilitated due to presence of minor concentrations of metal oxides in coal fly ash, resulted in a strong bonding zone between the two phases at relatively low temperature. In this work, SiC was mixed with coal fly ash at weight ratios of 90SiC/10ash, 85SiC/15ash, 80SiC/20ash, and 75SiC/25ash and sintered at 1400 °C. Measurements of mechanical properties showed that the 85SiC/15ash composition had the highest mechanical strength among samples. XRD analysis showed the phase composition of thermally treated 85SiC/15ash to be 81.8 wt% SiC, 11.4 wt% mullite, and 6.8 wt% cristobalite. SEM-EDX revealed a concentration gradient of Al in the cristobalite which enhanced formation of functionally graded bonding zones between phases and resulted in SiC-mullite composite with high thermomechanical properties. The compressive strength, nanoindentation elastic modulus, and Vickers hardness were 434 ± 20 MPa, 370.9 ± 22.6 GPa, and 11.5 ± 1.2 GPa respectively. The thermal shock resistance test showed high dimensional and mechanical stabilities after quenching in liquid nitrogen (−196 °C) from 1400 °C. The SiC-mullite composite showed low thermal expansion co-efficient from 3.17 x 10-7 /K to 5.615 x 10-6 /K when the sample was heated from 182 K to 354 K. The specific heat capacity, thermal diffusivity, and thermal conductivity were 7.83 ± 0.0014 J/g.K, 1.04 ± 0.013 mm2/s, and 17 W/m.K at 100 °C, respectively. The SiC-mullite composite exhibited moderate electrical conductivity of 3.48 x 10-2 S/m at 1000 °C. The resulting SiC-mullite composite is suitable for high temperature applications such as diesel motor parts, gas turbines, industrial heat exchangers, fusion reactor parts, high-temperature energy exchanger systems, and hot gas filters due to its high mechanical strength and thermal shock-resistance. This work demonstrated the potential of utilizing an in-situ mullite bonding agent instead of silica layer in additive manufacturing of SiC in the powder bed binder jet process for achieving a dense SiC parts with high thermomechanical properties.
Superintendent turnover in the state of North Carolina is a concern. Through a qualitative multiple case study, the researcher’s goal in conducting this study was to explore the lived experiences of eight first-year superintendents in North Carolina. Using Hambrick and Fukutomi’s (1991) concept of the seasons of a chief executive officer’s tenure, this study explored participants’ pathways to the superintendency and professional and personal challenges while in the role. Additionally, this study sought further understanding of participants’ priorities, successes, and mistakes, along with advice they had for aspiring superintendents. Eight semi-structured interviews were used to gather data for this study. To identify themes from the eight interviews, data were analyzed using a constant comparison analysis (Marshall & Rossman, 2006). The findings of the study align with existing literature about the experiences of superintendents. Common themes from the eight participants illuminated the importance of a productive partnership with the board of education, professional relationships with stakeholders, and the need for professional networking. Additionally, participants commonly felt a sense of professional isolation and struggled to maintain work-life balance. Implications and recommendations included the need to ensure aspiring superintendents closely consider the alignment between their goals and dispositions and those of the board for which they may work. Additionally, networking and long-range planning were emphasized along with proactive measures to address the social and emotional needs of those serving in highly demanding superintendent positions.
In higher education institutions, the Senior International Officer (SIO), described as an
administrator who manages overall internationalization activities, has been identified as the most
important catalyst for campus internationalization. Institutional context, including structural,
cultural, and environmental aspects, can be highly influential in determining the extent to which
internationalization, led and facilitated by the SIO, is realized. This basic qualitative study
examines the intersection of leadership and institutional context as mediators of the
internationalization process, a perspective which is lacking in the current literature on the SIO
role.
To better understand the perspectives of SIOs on how organizational context and culture
shape their roles as implementers of comprehensive internationalization, semi-structured
interviews were conducted with 11 participants currently working in an SIO role at a university
receiving a national award for internationalization. Strategic planning documents serve as a
secondary data source. A qualitative thematic analysis of the interview and documentary data
was performed using an inductive coding process. Findings suggest that the roles of strategist,
networker, and advocate are key to the SIO’s successful navigation of institutional context.
Furthermore, the specifics of each institution’s distinctive context may be more influential for the
SIO’s role than any commonalities between institutions of the same type, as defined by size,
funding model, or Carnegie classification. Implications for professional practice include a
renewed focus for SIOs on the strategic alignment of internationalization with the institutional
mission, the development of sustainable cross-campus networks to raise visibility and manage
perceptions, and a willingness to experiment as a way of demonstrating value to the wider
campus community.
With student discipline becoming a growing area of concern in public schools, the staggering number of office referrals and student suspensions following incidents of student misbehavior has caused principals to seek alternative methods. Restorative practices aim to teach students appropriate behaviors by focusing on reflection, repair, and open communication following incidents of misbehavior. The purpose of this basic, interpretive qualitative study was to explore school principals’ perceptions and experiences related to the implementation of restorative practices. The researcher hopes key findings will assist with future implementation efforts in schools and support principals seeking to change their practices from traditional discipline efforts to restorative approaches. The findings from this study revealed numerous implications for future research as well as recommendations for practice. Results from semi-structured one-on-one interviews with six public school principals revealed that there are advantages, processes, and pitfalls that can guide future research and implementation efforts. Participants consistently reported the benefits of implementing restorative practices in their schools to include improved relationships and fewer suspensions. Findings suggest that relationships, expectations, accountability, professional development, and mindset all play an important role in successful implementation. Additional research investigating the balance of restorative practices and traditional consequences and the impact on student academic performance is still needed.
Echinoderms are highly regenerative animals that share a common ancestor with chordates, including humans. While the two phyla share a common ancestor, echinoderms defeat humans when it comes to regeneration. Regeneration is the replacement of damaged cells or regrowth of damaged tissues or organs naturally. Despite the significant differences in the body plan of echinoderms and humans, the similarities in their genome structure, the genes these two groups share, the phylogenetic relationship they have, and the simplicity of experimentation make echinoderms a valuable group to study regeneration. We expect that understanding tissue regeneration in echinoderms can set a stage for improved treatments and provide insights for developing therapeutic approaches to treat human injuries in the future.
Even within such a highly regenerative phylum as echinoderms, some species regenerate more readily than others. Holothurians, commonly known as sea cucumbers, occupy a special place in this regard, as they can fully and rapidly regenerate their body parts and major organs, including: the viscera, central nervous system, body wall, and muscles. However, the available genomic resources are very limited to implement holothuroids as animal models to study regeneration. Moreover, the available genomic resources do not represent diversity within the phylum. Hence, to fill this gap, I have updated an easy-to-use web-based application, EchinoDB, a database resource that includes the genomic and transcriptomic data on 42 unique echinoderm species, spanning the deepest divergences within the five extant classes of the phylum in addition to the 2 new major datasets: the RNA-Seq data of the brittle star Ophioderma brevispinum and the high-quality genomic assembly data of the green sea urchin Lytechinus variegatus.
Among sea cucumbers, the vast majority of molecular studies have been done on a single species, Holothuria glaberrima which do not represent the diversity of various regenerative events, including: regeneration of the gut luminal epithelium (mesodermal to endodermal) and regeneration of the pharyngeal bulb. However, other sea cucumber species, especially, those of the order Dendrochirotida are capable of such exceptional regeneration events. Therefore, I sequenced and annotated the draft genome of a dendrochirotid Sclerodactyla briareus to gain a deeper understanding of the regulatory molecular mechanisms controlling regeneration and genomic aspects behind the diversity of regeneration, seen in echinoderms.
To illustrate the practical utility of the dendrochirotid genome for regeneration studies, key components of the Notch and Wnt signaling pathways were selected and identified in the genome of hairy sea cucumber S. briareus. This is a biologically relevant example as these pathways are crucial for tissue regeneration in echinoderms. They are highly conserved across all multi-cellular animals and are known to coordinate many cellular events, including: cell proliferation, de-differentiation, cell division, and apoptosis. Therefore, I aimed to retrieve 29 selected genes of the Notch pathway and 25 selected genes of the canonical Wnt signaling pathway. Except for Mesp2 (a Notch pathway gene), all other genes were identified in the newly assembled draft genome of S. briareus.
I also studied S. briareus for primordial host-viral interactions and to learn about the evolution of their immune system by looking at the recombination activating genes (RAG) in relation to Strongylocentrotus purpuratus and other echinoderms. The objective was to discover and characterize novel viral sequences within S. briareus alongside the evolution of immune genes (RAG-Like) in marine environment. However, because of the gaps in the assembly, I was unable to find any evidence of viral markers in the genome of S. briareus. The paucity of full-length contigs in the genome assembly also resulted into only 3 protein sequences that may potentially share a sequence homology with RAG1-Like gene, but further investigation is needed. The lack of results require improvements in the genome assembly and the availability of increased data for RAG-Like genes on echinoderms. Nevertheless, this work is still useful for regeneration studies on echinoderms.
An in-depth analysis of a distinctive electric machine topology characterized by a doubly salient structure and integrated permanent magnets within the stator is presented in this dissertation. The machine demonstrates high power density (up to 50 kW/L) with capabilities such as a rated torque of 95 Nm at 12,500 rpm and a maximum speed of 37,500 rpm. An analytical model using lumped parameter magnetic equivalent circuits (LPMEC) is developed, examining spatial harmonics and validating results through finite element analysis. A high-fidelity model-based motor drive system employs a field-oriented control approach and introduces a complex vector current (CVC) regulation strategy, enhancing stability compared to classical methods. Comparative analyses highlight the robustness of CVC regulation. Experimental tests have been conducted to validate the analytical outcomes and proposed control methodologies employing an open frame laboratory prototype (OFLP) of the proposed machine and SiC based traction inverter.
This dissertation explores the perception of social skills in structured virtual interviews, with a focus on how verbal, nonverbal, and vocal signals influence Social Skills Perception (SSP). The study explores the impact of specific behaviors on observers' perceptions of social skills and why particular behaviors are associated with low social skills perception scores. A central finding is the "just right" effect, which reveals that both excessive and insufficient displays of certain behaviors can negatively affect SSP, emphasizing the importance of balanced social skills demonstration in structured interviews. The findings contribute to social skills literature by building on the Heggestad et al. (2023) Social Skills Framework and highlight the complex dynamics of SSP in professional settings, particularly in structured interviews. This study suggests that such interviews might not fully capture exceptional social skills, offering insights into interview practices and evaluating social competencies in the workplace. Future research is encouraged to explore SSP across various contexts and cultures to deepen our understanding of these phenomena.
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.
Energy storage plays a crucial role in addressing the growing demand for energy and electricity while simultaneously reducing greenhouse gas emissions. Most of the power infrastructure in the U.S. heavily relies on water-cooling technology, leading to significant freshwater withdrawals. To mitigate high water withdrawal rates and the thermal pollution of water sources, an alternative solution involves implementing dry cooling towers (DCT) or air-cooled condensers (ACC). However, the effectiveness of dry cooling techniques depends on the dry bulb temperature of the ambient cooling air, resulting in a plant performance penalty equivalent to approximately a 2%-point efficiency loss compared to wet cooling.
The current research focuses on designing a cost-effective latent heat cold thermal energy storage (LCTES) system to enhance the performance of DCT/ACC during the summer months. This is achieved by storing cold energy during the nighttime in inexpensive materials like phase change materials (PCM), such as CaCl2 hexahydrate or CC6. To guide the LCTES design, a numerical analysis of the melting and solidification processes of PCM within the tube array was conducted. Transient two-dimensional Navier-Stokes equations and a Realizable k-ɛ turbulence model were used to predict fluid flow and heat transfer in LCTES heat storage modules. The enthalpy-porosity technique was employed to model PCM melting and solidification.
The numerical results show excellent agreement with experimentally obtained values. The resulting design successfully met the predefined performance criteria, achieving a cooling effect of 4 °C for a four-hour duration while maintaining a pressure drop of less than 100 Pa. The proposed prototype-scale tube array design can efficiently cool the incoming ambient air, and PCM in the LCTES can be fully frozen overnight. The energy storage density of the system falls within the range of 22 to 27 kWh/m3, with the maximum energy efficiency reaching around 75% during the system charging and discharging processes. Apart from its primary focus on coal power plant dry cooling technology, the suggested concept can also be used for industrial, commercial, and residential applications, including concentrated solar power (CSP).
The rising rates of mental health issues among college students (WHO, 2022) can be compounded by the challenges of STEM (Henry et al., 2022) and any experiences of minority stress (Helling & Chandler, 2019), yet little research has been done on college student wellness (Beauchemin, 2018), in particular low income STEM college students. Moreover, the concept of ecowellness (Reese & Myers, 2012) is still new and growing within the field of counseling, indicating the need for further study and application. Previous authors have asserted the potential for nature-based social groups in supporting wellness (Adams & Morgan, 2018; Reese & Gosling, 2020). The purpose of this research study was to understand the ecowellness experiences of STEM college students who are recipients of a scholarship serving low income students. Using a phenomenological case study design (Vagle, 2018), I collected demographic information and interviewed 9 participants for the study then analyzed the data. Analysis involved constant comparative coding (Dye et al., 2000) followed by final development of the findings through iterative dialogue with two external reviewers. Analysis produced two major findings, ecology of wellness and nature as partner in nourishment, including five themes and 14 sub-themes. Implications of these results for higher education, STEM, and the counseling field are discussed, along with limitations of the study and recommendations for future research. Higher education stakeholders may consider employing nature-based social groups to promote the wellness, academic achievement, and career success of college students. The results of this study add to the understanding of the relationship between nature, access, and wellness for this case study of diverse low income STEM college students.
