Wastewater-based epidemiology (WBE) has drawn significant attention as an early warning tool to detect and predict the trajectory of COVID-19 cases in a community, in conjunction with public health data. This means of monitoring for outbreaks has been used at municipal wastewater treatment centers to analyze COVID-19 trends in entire communities, as well as by universities and other community living environments to monitor COVID-19 spread in buildings. Precise and accurate quantification of viral copies in wastewater is a prerequisite for a successful WBE surveillance project. Accurate quantification of SARS-CoV-2 is dependent on the choice of an effective and reliable virus concentration method. Sample concentration is crucial, especially when viral abundance in raw wastewater is below the threshold of detection by RT-qPCR analysis. The first objective of my dissertation is the performance evaluation of a rapid ultrafiltration-based virus concentration method using InnovaPrep Concentrating Pipette (CP) Select and how it compares with the electronegative membrane filtration (HA) method. The criteria of the evaluation were based on the SARS-CoV-2 detection sensitivity, surrogate virus recovery rate, and sample processing time. Results suggested that the CP Select concentrator was more efficient at concentrating SARS-CoV-2 from wastewater compared to the HA method. About 25% of samples that tested SARS-CoV-2 negative when concentrated with the HA method produced a positive signal with the CP Select protocol. The optimization of the CP Select protocol by adding AVL lysis buffer and sonication increased Bovine Coronavirus (BCoV) recovery by 19%, which seems to compensate for viral loss during centrifugation. Filtration time decreased by approximately 30% when using the CP Select protocol, making this an optimal choice for building surveillance applications where quick turnaround time is necessary.
The inherent limitation of most of the current virus concentration methods is capable of processing small volumes of wastewater ranging from 20 – 250 mL. While small volume-based virus concentration methods can be successful for detecting and quantifying SARS-CoV-2 viruses during high community infection, these methods may not be informative, especially during the early stage of community infections. The second objective is to develop a large-volume filtration-based virus concentration method for increased sensitivity of molecular detection of SARS-CoV-2 and application in sequencing techniques. A dead-end hollow fiber ultrafilter (UF) and electronegative membrane filtration (HA) were used as primary and secondary concentration methods for concentrating viruses from wastewater. This study found that a modified UF-HA method, incorporating sonication and centrifugation, showed 100% SARS-CoV-2 positive detection in low COVID-19 infection periods compared to only 9% positive detection with the HA method and 63% with the UF alone. During the high COVID-19 infection period, no significant difference in SARS-CoV-2 detection and quantification was observed among the alternatives. The hollow UF-based primary method showed higher BCoV recovery compared to the combined method and HA method. The combined method (UF-HA_soni) can be used to identify the early stages of COVID-19 infection by detecting SARS-CoV-2 viruses from the low-tittered wastewater which can help prevent future outbreaks. Either the combined method or the UF-based primary method can be used to monitor SARS-CoV-2 viruses during the high COVID-19 infection period.
We also aim to apply digital droplet PCR to track the transmission dynamics of the Omicron variants by assessing the relative proportion of the strains circulating in Charlotte, North Carolina. We applied Digital Droplet Polymerase Chain Reaction (ddPCR) technology to detect and quantify Omicron variants using three different mutation assays targeting the S gene (N764K and N856K). Using these two assays, we first detected the Omicron variants on December 6, 2021, from the wastewater sample of Mecklenburg County which was earlier than the first clinical detection on December 10, 2021. The relative abundance of Omicron VOCs determined by the RT-ddPCR from wastewater was strongly and positively correlated with the clinically reported VOCs (r = 0.98, p = < 0.0001). This surveillance method for the variant analysis can give a near real-time transmission dynamic of the Omicron variants enabling quick administrative intervention such as awareness, preparedness, and control measures.
This dissertation proposal examines the relationship between corporate growth/expansions and entrepreneurial start-up activity and failures, the number of jobs created, and wages paid by the corporate relocation. Using data sourced from the North Carolina Secretary of State, Census Bureau, and Job Development Investment Grant, I set out to evaluate changes in entrepreneurial startup activity and failures, tax incentive payouts, and salaries arising from large (greater than 251 employees) corporate expansions located in the state of North Carolina. The analysis suggests that expansions of existing corporations directly affect entrepreneurial start-up activity and failures. We conclude by highlighting the study's theoretical contributions to help further the conversation and direct startup and failure business strategies for small businesses.
The increasing threats posed by climate change and urbanization have elevated the importance of addressing Urban Heat Island (UHI) phenomenon, a critical concern impacting cities across the United States. This dissertation comprises three articles that collectively investigate the effectiveness of trees and greenspaces in managing UHI, creating a Heat Health Score (HHS) to identify areas experiencing UHI effects and investigate the perceived effectiveness of policies and programs aimed at reducing UHI in cities, while providing recommendations for Charlotte, NC in particular. Article 1 shows that urban greenspaces consisting of trees can help reduce the UHI effect by creating shade and cooling spaces, potentially reducing energy costs, improving human living conditions, providing food and habitat to wildlife, and improving aesthetics and land values. In Article 2, measures to mitigate the effect of UHI are evaluated from select cities and a ratio of daily average high temperature between locations and the corresponding difference in land cover of tree and shrub areas, create the Heat Health Score (HHS) (a unique metric) which allows municipalities and community groups to gauge the heat health between locations. These results show that most urban locations remain hotter and with lower vegetative cover than their suburban or rural counterparts, however, changes in tree and shrub cover can impact these results in a positive way. Results from Article 3 elucidate the perceived successes and challenges of current policies through a qualitative survey. These responses offer practical recommendations for policymakers across the US but for Charlotte, NC in particular.
These results draw from the real-world experiences and lessons uncovered in the three articles, in aggregate, these provide a valuable resource for city leaders and policymakers striving to create a more sustainable and climate-resilient city. It stresses the importance of urban greenspaces and urban trees in particular, provides community leadership with an easily accessible, not previously defined tool to discern urban heat health through the use of free, open-source data to score heat health, and provides insight into the perceived effectiveness of policies and programs used to mitigate UHI in cities in the United States.
As the entry point into higher education for over half of the bachelor’s degree earners, (Trapani & Hale, 2019), community colleges are positioned to have a positive impact of bringing a more diverse student group into science, technology, engineering, and mathematics (STEM) majors. However, the vertical transfer function from community colleges into a four-year university is often not clear resulting in a gap between those with transfer aspirations and bachelor degree attainment. There are unique barriers that women of color transfer students encounter that can threaten persistence in STEM. This study contributed to the few studies (Allen et al., 2022, Jackson, 2013, & Reyes, 2011) that have focused on the experiences of women of color in STEM and transfer. The purpose of this qualitative phenomenological transfer student study was to understand how pre- and post-transfer women of color in STEM majors experience the transition into university from community college in North Carolina. This longitudinal study used interview data from 14 women who participated in a larger transfer study. Six of the women provided three interviews. Guided by the reconceptualized model of multiple dimensions of identity (Abes et al., 2007), the role of social identities and the impact on educational decisions was explored. Five major themes were identified: (1) the internalization of community college stigma, (2) blindsided: post-transfer rigor, (3) the loss of personal connection post-transfer, (4) feeling behind and other perceived roadblocks for STEM transfer students, and (5) can’t do it alone: leaning on support networks for success. The findings from this study led to recommendations to the current articulation agreement structure in North Carolina, and recommendations for post-transfer institutions to better support women of color in STEM.
In this dissertation we present new results on the classification of limit distributions of random geometric processes. In particular, that develop on the work of Penrose and Wade, who were the first to document the phenomenon with limited initial variables. In this dissertation we put forth not only new results, but a new method of obtaining results through analyzing the sequence of moments produced by random variables. Additionally we have new results in cycle decomposition of the related Dickman-Goncharov distribution. We present a novel proof of the distribution of the three highest order cycles in a random partition of Sn.
Seasonal cold weather and frost action has a major effect on the design, construction, performance, and maintenance of roadways. Frost heaving and thaw weakening are especially problematic, subjecting all elements of a pavement system to significant changes in moisture content, stress, and strain. Nationally, this leads to recurrent annual maintenance costs estimated at over 2 billion dollars, as well as additional economic impacts because of related vehicle damage, road closures, and weight restrictions. Studies identify three basic requirements for frost action; freezing temperatures, availability of water, and frost-susceptible soils. While advances have been made in designing for freezing temperatures and providing for groundwater separation, very little progress has been made in terms of in situ soil improvement. A cost and labor-intensive approach is to replace unsuitable soils. As an alternative, Engineered Water Repellency (EWR), a process in which soils are made hydrophobic is presented as a suitable barrier limiting the transport of water through these soils, resulting in frost heave mitigation. This is achieved by combining soils with cost-effective and environmentally compatible polymers and other complex organic molecules. This process explored through a multi-year project funded by the U.S. National Science foundation, involved laboratory, field, and numerical studies.
Since the early 1980s, American educational reformers have tried to improve schools through standards, high-stakes tests, and punishments for those schools that failed to meet the mark. In North Carolina, many schools with diverse populations and low socioeconomic status have struggled to succeed, receiving the state performance grade of D or F and the consequent “low-performing” label. Meanwhile, some teachers in these schools have achieved at high levels and attempted to improve not only their classrooms, but their schools and districts. Few researchers have sought the opinions and expertise of high-performing teachers in order to better understand their experiences, their role as change agents, and their recommendations for other so-called “low-performing” schools. This qualitative multiple case study used in-depth interviews with these high-performing teachers in “low-performing” elementary schools in North Carolina. Specifically, this research gathered information about their backgrounds, their actions for school transformation, and their lessons learned about education and equity. Findings from the study indicated that high-performing elementary teachers tried to reform their “low-performing” schools through teacher agency but were blocked by multiple factors. School administrators and district officials reduced teacher agency and opportunities for school improvement. North Carolina’s “low-performing” schools policy harmed children, reinforced school failure, and produced discriminatory and inequitable results. Teacher agency theory provided a promising approach for the state to change course and improve failing schools.
Renewable energy resources advancement and offerings are steadily increasing, a major factor leading to its global fast adoption. The connection of these resources to the electric grid, however, needs to be studied to ensure efficiency both from an operational and regulatory standpoint. The IEEE 1547 has been used to establish standards for grid interconnection of some renewable energy resources (RERs). In this dissertation, the operations of RERs connected to the grid with respect to their control, management, and optimization are studied. It is of note that RERs are intermittent in nature and this can have effects on the power quality metrics or utility objectives on either network separately or collectively. For instance, the stability of the grid can be affected due to the low inertia of these resources, which can impact the voltage or the grid frequency. A novel adaptive controller was developed to damp the oscillations caused by these RERs, the controller was initially tested with RERs in one network architecture, and it offers advantages such as dynamically responsive support to the grid to control the frequency, a frequency spectrum was used to determine the amount of support required in an adaptive manner. The architecture was then expanded to a network model that has both transmission and distribution networks integrated together with the interconnection of multiple RERs connected to the grid, the capabilities of the proposed architecture were evaluated with different test cases with different grid events. The architecture had the capability to control multiple generators as well as damp the oscillations observed during the test cases and simulations performed, by adaptively updating the gain of the power system stabilizers (PSS).
On the management side, A new technique was developed with grid-connected RERs that provide real-time visibility of two integrated networks during operation. Presently, the operations don't offer such capabilities as the transmission system operator (TSO) is often times blind to the distribution system operator (DSO). Our technique makes it possible for the transmission network to adjust itself in real-time in case of sudden changes in the distribution network with RERs connected, A stochastic linear optimization technique; Linear decision rule (LDR) that establishes the relationship between the generators in the transmission network and the RERs in the distribution network was implemented, the technique addresses one of the major issues with integrated T&D networks which is boundary mismatch caused by the reverse power flow from the distribution network, in addition to offering the operational advantages required by most utilities like minimization of voltage deviation, and minimization of cost of operation, as it eliminates the need for curtailing RERs which is the current implementation used by most utilities, the technique theorem proof was also discussed. Furthermore, Grid Connected RERs are multiperiod in nature, it is therefore imperative to study their behavior at each time interval, the optimization framework was extended to such studies to handle the reverse power flow operation due to the irradiance daily curve, and the optimal power flow formulation was transformed to multiperiod optimal power flow MPOPF. The effectiveness of the proposed architecture was tested with an irradiance curve, and a typical residential load curve, it demonstrated the capability to reduce the boundary mismatch while ensuring the grid objectives for each network were achieved. Finally, the impact of electric vehicle charging was studied and a management approach was developed, Electric vehicles (EVs) adoption is also increasing impacts of the distribution network on the transmission network with respect to grid penetration, we developed a two-stage stochastic linear optimization in the integrated T&D to handle the uncertainty with electric vehicle charging and compared with effective EV charging management technique that was developed.
Sexually transmitted infections (STIs) affect an estimated 347 million people worldwide. These diseases can potentially incur significant long-term negative health outcomes, including lifetime treatment regimens, cancer, or infertility. Outcome severity, clinical manifestations, and acquisition rates show a sexually dimorphic variability, with women experiencing a higher disease burden than men. While the exact mechanism for this disparity is unknown, it is likely due to a combination of biological and social influences disproportionately affecting the sexes. This study investigates some of these gendered variables, particularly those involving birth control and sexual healthcare, and their relationship with STI acquisition. Data analysis using the National Health and Nutritional Examination Survey, and a cross-sectional sexual health survey disseminated to college women concluded that women in the United States follow the classic gendered trend with higher rates of STIs. Our cross-sectional sexual health survey included information from 522 sexually active women. We found significant associations regarding a positive self-reported STI history with sexual partner number and inconsistent screening frequency. We also found associations between women who do use some form of hormonal contraceptive with condom use, STI screening frequency, and age. Free-response questions also gave us qualitative insight regarding comfort with sexual health physicians, feelings regarding positive STI diagnosis, and physician’s approach toward their positive STI history. This study addressed several variables associated with women's sexual health care and outcomes and was able to identify several risk factors that may influence the gendered disparity we see in STI prevalence.
A significant change that employees in the United States have experienced because of the COVID-19 pandemic is the rise of remote work. There are many benefits of remote work, including increased performance and productivity. However, many remote workers struggle to separate work and life, leading to increased work-life conflict. Parents working remotely during the pandemic were the most likely to report challenges keeping work and life separate. The goal of this study was to better understand how parents’ work-life boundaries have changed during the pandemic. Based on interviews with 16 mothers and 16 fathers, this study examined how parents’ preferences for keeping work and life separate have adjusted and what factors affect their work and life. This research also looked at how mothers and fathers differ in their strategies to navigate between work and life when working remotely. This research uncovered six themes on how parents managed their work-life boundaries: two mindset shifts and four work-life separation strategies. Parents adapted their mindsets by redefining their priorities and setting realistic work and family expectations. The four boundary management strategies were turning off technology, sticking to a schedule, designating a home office space, and using a door-closed policy.
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