Dissertation Defense Announcements

Candidate Name: Chondon Roy
Title: IN-SITU INSTRUMENTATION FOR DEGRADATION MONITORING OF POWER SEMICONDUCTOR DEVICES IN POWER ELECTRONICS CONVERTERS
 May 12, 2023  1:30 PM
Location: EPIC 2344
Abstract:

Power electronics converters are an integral part of modern power and energy system. Power semiconductor switching devices are the most significant component in a power electronics converter. Power semiconductor devices such as MOSFETs/IGBTs age through different degradation mechanisms in long-term applications. Failure of MOSFETs/IGBTs is one of the primary causes of power electronics failure. And MOSFETs on-state resistance (RDSON) is a key health-indicating parameter. This dissertation presents sensing circuit designs that enable real-time monitoring of on-state voltage of the MOSFETs/IGBTs. In addition a complete online in-situ health monitoring system of the MOSFETs in a three-phase inverter is presented. A new on-state drain-source voltage (VDSON) sensing circuit has been used to monitor the RDSON of the high-side MOSFETs. This sensor references the drain of the high-side transistors for their VDSON measurement and allows VDSON measurement of multiple high-side transistors with respect to the same ground reference. The high-side VDSON measurement circuits combined with low-side VDSON measurement circuits have been used for a complete RDSON monitoring of all the MOSFETs in the inverter. The drain current (IDS) is captured from measurements using an off-the-shelf current sensor located at the output filter inductor. Accounting for propagation delays in the measurement circuitry, both the VDSON and IDS are sampled and converted into digital data multiple times in a switching cycle, filtered, and stored in a digital signal processor (DSP). The DSP, originally used for the inverter control, then processes the sensor data captured over one grid cycle and calculates the average RDSON of the MOSFETs of the inverter. Validations of all the sensing circuits, using theoretical analysis and hardware experiments along with the software implementation for data processing and handling are presented in the dissertation for this real-time, in-situ RDSON measurement. Furthermore, a method of mapping the MOSFET's RDSON to the junction temperature is presented which can be used for real-time accurate junction temperature estimation of the MOSFETs.



Candidate Name: Layne McGuire
Title: The Genomics Revolution and Its Marketing Implications
 April 28, 2023  2:00 PM
Location: Zoom


Candidate Name: Constance Austin Coates
Title: Sexual Violence and Title IX: An Examination of the Nature and Outcomes of Title IX Sexual Violence Complainants
 May 03, 2023  2:00 PM
Location: Join Zoom Meeting https://zoom.us/j/97902136900
Abstract:

Sexual violence on college campus is a salient threat to the health and well-being of students in higher education. Title IX legislation was developed to address and help reduce sex-based discrimination, including incidences of sexual violence, on college campuses. However, existing data suggests that a relatively small number of campus survivors make a formal report and subsequently have an interaction with the Title IX Office (Cantor et al., 2015). Additionally, little is known about the implementation of Title IX processes, the nature of Title IX sexual violence reports, or the outcomes of survivors involved in Title IX reports. The current study adds to our understanding of these survivors’ experiences. Specifically, the study utilized archival Title IX report data obtained from one large public university during the 2018-2019 and 2019-2020 academic years (n = 151) to explore the nature and scope of Title IX sexual violence reports and the academic health outcomes of survivors post-report. The study utilized data extracted from Title IX sexual violence reports to describe the characteristics of Complainants (i.e., survivors), Respondents (i.e., perpetrators), incident characteristics, reporting processes, and characteristics of cases involved in formal university hearings. The study also utilized aggregated data from the Title IX sexual violence reports in conjunction with data obtained from UNC Charlotte Maxient system, which contains student GPA and enrollment status, to examine the academic health of survivors over time. Complainants predominantly identified as Caucasian (65%) and female (93%). Respondents predominantly identified as Caucasian (42%) and male (99%). Complainants most often identified Respondents as friends (16%), ex romantic partners (16%), or acquaintances (14%). Only 11% of Respondents were identified as strangers. Complainants were most often referred to the Title IX Office by mandated reporters (87%). Over half of the Complainants (62%) engaged with Title IX staff following initial outreach. Many cases had incomplete academic data (no pre-report or post-report semester GPA). However, in the sample with three GPA time points (n = 57 survivors), academic outcomes over time were not significantly associated with Respondent’s affiliation to the university, source of referral to the Title IX Office, engagement in the reporting process, or involvement in a formal university hearing. Seventeen percent (n = 25) of Complaints dropped out of the university. However, Complainant engagement with the Title IX Office was not significantly associated with dropout. These findings increase our understanding of the Title IX process and the experiences of campus sexual assault survivors who are involved with the Title IX Office.



Candidate Name: Ali Parsa Sirat
Title: Ultra-Wideband Contactless Current Sensors for Power Electronics Applications
 June 20, 2023  2:45 PM
Location: EPIC 2344
Abstract:

Enhanced power density factors can be achieved in the new generation of power electronics by utilizing wide-bandgap semiconductor switching devices with higher switching speeds and lower losses. These characteristics make high-frequency switching (wide-bandgap-based) power converters superior to silicon-based converters in several respects, including better size, weight, efficiency, and power density than silicon-based converters. The design and manufacturing of these power converters have significantly different requirements compared to traditional converters, making it challenging to integrate components and sensors with tighter tolerances. Wideband current sensors are also necessary for diagnosing, monitoring, and controlling wide-bandgap power converters. Speed is not the only concern when developing power converter layouts; size and invasiveness are also significant considerations. Several properties, such as size, speed, noise immunity, accuracy, linearity, capacity, isolation, and non-invasiveness, are required for the next generation of power converters that cannot be achieved with currently available commercial current sensors. Due to size and cost constraints, these converters cannot be equipped with current probes either. Therefore, non-invasive, ultrafast, high-capacity, switch noise-immune sensors are required by wide-bandgap-based power electronics converters.
In this thesis, comprehensive studies of single-scheme and hybrid current sensors are presented as well as issues regarding their integration into power electronics. The present study illustrates that there is no specific method of current sensing that can combine all the required sensing factors at once. The results of a feasibility study have been used to develop guidelines for the design of current sensors that provide high-quality output signals and are readily applicable to the next generation of power converters. Frequency response verification using vector network analyzers and also different types of current waveform comparisons will prove the functionality of proposed light-size and low-cost sensing solutions.



Candidate Name: Cheryl Scott
Title: Facilitators and Barriers in Obstetrics Care in the Identification of Sex-Trafficked Victims
 April 07, 2023  9:00 AM
Location: CHHS 332
Abstract:

Human trafficking is an emergent public health concern that, as noted by the National Institute of Justice (2021), receives attention and support from human rights advocates and law enforcement agencies. The trafficking of women in the sex industry is a growing health concern, as most victims are often unrecognized when seeking healthcare services. Sex-trafficked women suffer adverse health effects and often present to healthcare facilities while still under the control of their traffickers (Rapoza, 2022). A review of the literature revealed a deficit in clinicians' abilities to recognize this vulnerable population. This scholarly project aimed to determine how participation in an educational intervention affects providers’ and clinicians’ knowledge of the facilitators and barriers to identifying and intervening with pregnant sex-trafficking victims. The intervention included the implementation of an educational intervention to enhance knowledge. A pre and posttest design was used to measure a change in confidence, knowledge, and skills. A Likert survey to assess confidence and knowledge of sex trafficking was administered before and 30 days after the educational intervention. This project aimed to demonstrate that education increased confidence, knowledge, and skills among obstetric public health providers and clinicians regarding the identification of sex-trafficked victims.



Candidate Name: Jan T. Mooney
Title: And I’m Hungry Like the Mom: Influences on Appetite During Pregnancy and Postpartum
 May 04, 2023  10:00 AM
Location: https://zoom.us/j/95002583635
Abstract:

Maternal eating patterns during pregnancy and the first year postpartum contribute to short and long term maternal and child health outcomes. Food choices are thought to result from an interaction between individual-level appetite and the diversity and quantity of foods available to the individual. Appetite, the motivational drive to eat, is regulated by both internal and environmental factors and occurs both within and outside of physiological energy deprivation. Through a series of three manuscripts, this work examined psychophysiological influences on maternal appetite and their interrelations to understand how these factors present in pregnancy and postpartum, how they change over time, and their role in predicting the development of specific food desires. The Power of Food Scale (PFS), a measure of hedonic hunger, assesses perceived responsiveness to food stimuli in the environment. PFS retains stable psychometric properties and remains at similar levels across its subscales through pregnancy and the first year postpartum. In contrast, leptin, a hormone with roles in satiety, reward, and reproduction, shows positive mean change over the same time. Neither of these appetitive influences nor dietary restraint were associated with variability in cravings concurrently or prospectively, during pregnancy or postpartum. Overall, results of these studies suggest that these appetite influences vary relatively independently during pregnancy and postpartum, in contrast to relationships observed outside this time. Future research could build upon these findings by incorporating additional appetitive influences and/or increasing the frequency of assessments to capture fluctuations within trimesters or within the first year postpartum.



Candidate Name: Madhumita Paul
Title: SPECTRAL THEORY OF SCHRÖDINGER TYPE OPERATOR ON SPIDER GRAPH
 April 13, 2023  12:45 PM
Location: Fretwell 302
Abstract:

We construct the definition of Brownian motion on the N-legged spider graph with infinite legs and Kirchhoff’s gluing conditions at the origin and calculate the transition probability of this process. In addition, we study several important Markov moments, for instance the first exit time τL from the spider with the length L of all legs. The calculations give not only the moments of τL but also the distribution density for τL (all results of this section are new ones). For the spectral theory on the spider like quantum graphs, we start by constructing the spectral analysis on the finite interval of a three-legged spider graph and then pass it to infinity. Spectral analysis is performed for three different types of potentials. The fast-decreasing potentials, the fast-increasing potentials, mixed potentials, and its spectral theory. The details contain, the absolute continuous spectrum of multiplicity 3 and its construction using the reflection-transmission coefficients on each leg for the fast-decreasing potential, Bohr’s asymptotic formula for N(λ) (the negative eigenvalues), instability of the discrete spectrum for the mixed potential on each leg of the spider graph. Furthermore, we have done symplectic analysis, and its representation on the spider quantum graph.



Candidate Name: Min-Seung Kim
Title: How Information Frictions Impacted the Efficacy of the Paycheck Protection Program in Mitigating the Economic Constraints Faced by Small Businesses from COVID-19
 April 10, 2023  1:00 PM
Location: https://charlotte-edu.zoom.us/j/93615128218?pwd=ZXplczFQWStHazE4aTJmN0tac2hxUT09
Abstract:

This research uses PPP loan data from the Small Business Administration (SBA) to investigate whether information frictions contributed to disproportionate PPP loan disbursements to certain racial and socioeconomic groups. This analysis makes several contributions. First, it adds to the body of literature on the PPP program, the impact of COVID-19 on small businesses, and government subsidy programs designed to mitigate economic crises. Prior research on the PPP program examined whether loans were allocated to business owners based on socio-demographic factors. Atkins et al. (2022) find a negative relationship between a community’s minority share of business owners and disbursed PPP loan amounts. Likewise, Howell et al. (2021) report that minority business owners were less likely to obtain PPP loans. We build on these existing studies by conceptualizing information frictions. To our knowledge, this is the first study to conceptualize information frictions into three main drivers, socio-demographic bias, financial institution access, and digital literacy, and to explain the relationship between information frictions and the efficacy of the PPP program.