Dissertation Defense Announcements

Candidate Name: Esha Thakur
 February 25, 2022  3:00 PM
Location: https://uncc.zoom.us/j/92529046129

Realizing the next-generation electronic devices with added features, i.e., flexibility, smaller dimension,
higher density (transistors per unit area), lightweight, and low-power consumption would require extensive
work to optimize the processing conditions that would yield high-quality Si wires (microwire/nanowire)
with optimum device performance at an affordable price. To this end, we employed a cost-effective
lithography-free de-wetting technique to fabricate the seed layer for the growth of highly ordered Si
microwires (Si MWs). A quantitative analysis of the impact of various growth parameters on Si MW size
has been reported. This has important implications since the optoelectronic properties of a wire
configuration are strongly dependent on its size and the quality of the as-grown wires, thereby affecting the
device performance. An exponential dependence of MW growth rate has been reported, and the rate-
limiting step has been determined. The electrical transport properties of as-grown Si MWs have been
extracted via two-probe and three-probe measurements. Temperature-dependent IV measurements have
been done to determine the trap state density and trap energy level in the as-grown and passivated Si MWs.
Lastly, we demonstrate an easily constructed, single wire near-infrared (NIR) photodetector device with an
enhancement observed in responsivity, detectivity, and % EQE of low-powered Si MW by a factor of 44.8,
6.8, and 46.7 at the lowest applied voltage.

Candidate Name: Fakhri Abbas
 March 07, 2022  5:00 PM
Location: Virtual

Diet diversification has been shown both to improve nutritional health outcomes and to promote greater enjoyment in food consumption. Conversational Recommender Systems (CRS) has a rich history in direct recommendation of recipes and meal planning, as well as conversational exploration of the possibilities for new food items. But more limited attention has been given to incorporating diversity outcomes as a primary factor in conversational critique for exploration. Critiquing as a method of feedback has proven effective for conversational interactions, and diversifying recommended items during the exploration can help users broaden their food options, which critiquing alone may not achieve. All of these aspects together are important elements for recommender applications in the food domain.

\par This dissertation explores incorporating diversity in a critique based conversational recommender system to support diet diversification. Recommender systems are known to support the task of exploitation while diversity supports the task of exploration. Using a conversational recommender, this dissertation maintains this balance by enabling the exploration through critiquing, and maintains the exploitation by selecting the closest recommendation to the user profile. To enable this balance this dissertation introduces an interactive critique based conversational recipe recommender system called \textit{DiversityBite}, a novel way of dynamically generating critique during recipe recommendation.

\par The contributions of this dissertation are: (i) Development of a novel approach of dynamic diversity-focused critique for conversational recommender system, (ii) Applying dynamic diversity-focused critique in recipes domain to support diet diversification while exploring, and (iii) Identification of recipe features that are helpful in finding diverse recipes using dynamic critique. This study reports on three studies to show the potential of using dynamic critique in increasing diversity. The user studies considered for this dissertation are simulation study, and two user studies. These studies investigate if \textit{DiversityBite} can improve diversity in recipe recommendation.

Candidate Name: Yunfei Xia
Title: Estimation and Simulation for Multivariate Tempered Stable Distributions with Applications To Finance
 March 24, 2022  11:00 AM
Location: Online via Zoom

In this thesis, we introduce a methodology for the simulation and parameter estimation of multivariate tempered stable distributions. Using the fact that tempered stable distributions can be specified indirectly by a Lévy measure, our approach is based on an approximation due to a discretization of the Lévy measure. We derive this discretization in general and give an explicit construction of the discretization in the bivariate case. Also, our approximation results hold for a wide class of multivariate infinitely divisible distributions.

Based on our main approximation, we develop a method for simulations, which we call the discretization and simulation (DS) method. To demonstrate how well the method works, we perform a series of simulations in the bivariate cases and compare it with another approximate simulation method developed by Rosiński's. Further, we use our discretization for parameter estimation by minimizing the distance between the characteristic function of the multivariate tempered stable distribution and the empirical characteristic function. We then apply our methodology to two bivariate financial datasets related to exchange rates. The first is comprised of exchange rates between standard currencies, while the second is based on exchange rates related to cryptocurrencies. We also perform goodness-of-fit tests to show that the multivariate tempered stable model does a good job fitting the model.

Further, we apply our model for the pricing of the bivariate basket option. Toward this end, we provide theoretical results on the existence of equivalent martingale measures. Then combing this with our model for parameter estimation and the DS method for simulation, we develop a Monte Carlo based method for option pricing. We apply it to the pricing of European call options with different strikes and the pricing of the Multi-asset rainbow option.

Candidate Name: Tiancan Pang
Title: Investigations on Multilevel and Surgeless Solid-State Circuit Breakers
 February 24, 2022  1:30 PM
Location: Online

The Solid-State Circuit Breaker (SSCB), as an emerging semiconductor-based circuit protection technology, is featured with its extremely fast fault interruption/isolation speed and regarded as a promising alternative to the electromechanical circuit breakers in the DC systems. However, in the conventional SSCBs, large surge voltages are clamped across their semiconductor switches when the breakers open and the dynamic voltage unbalance is incurred when the series-connected switches are used. With these technical defects, the efficiencies and reliabilities of the SSCBs are impaired and their wide adoption to the DC distribution systems is set back.

To overcome these technical limits of conventional SSCBs, four types of Multilevel and Surgeless Solid-State Circuit Breakers have been proposed in this dissertation. By utilizing the fast switching speeds of the semiconductor switches, the proposed SSCBs can commutate the fault current to the different conduction paths of the circuit breakers and attain significant benefits on efficiency and fault isolation speeds in comparison with the conventional SSCBs. Particularly, for the proposed Multilevel Solid-State Circuit Breaker (MLSSCB), the series-connected switches are clamped to their voltage dividing capacitors during their switching transience and then the dynamic voltage unbalancing issues among the switches can be averted. For the proposed surgeless SSCBs, with surge voltage suppressed, the semiconductor switches do not need to be overdesigned for the voltage ratings and the conduction efficiencies of the SSCBs can be improved on the ground that the semiconductor device with higher voltage block capability has thicker drift regions and larger on-state resistance. Derived from the integration of the Ground-Clamped Surgeless SSCB and the Multilevel SSCB, the proposed Surgeless Multilevel SSCB (SMLSSCB) can solve both the surge voltage and dynamic voltage unbalancing issues in the medium voltage DC SSCBs and attain higher efficiency and an ultra-fast isolation speed prior to the other SSCBs. A fault-tolerant configuration of the SMLSSCB has also been proposed to improve the reliability of SMLSSCB and make it prior to that of the conventional SSCBs.

In this dissertation, the operating principles of the proposed SSCBs have been presented. Besides, to demonstrate the proposed SSCBs’ advantages over the conventional SSCBs on fault isolation speeds, power efficiencies and reliability, the comparisons between the proposed SSCBs and their counterparts of the conventional SSCBs have been made in terms of several key parameters of the circuit breakers. Additionally, the simulation/experiment results and design considerations of the proposed circuit breakers have been introduced to validate their technical feasibilities and practical uses.

Candidate Name: Shannon Clemons
 February 10, 2022  10:15 AM
Location: Zoom

This qualitative study investigates the perceptions of high school-level alternative school administrators in North Carolina about the impact of performance standards (ESSA) on them and their campuses. The study interviewed four alternative high school administrators who are currently serving in alternative schools in North Carolina that were labeled Comprehensive Support and Improvement during the 2018-2019 school year due to low graduation rate and/or low performance. Analysis of the data resulted in the following findings: Alternative high school administrators perceive the ESSA guidelines for school performance as unfair and inequitable to alternative schools, and the guidelines demonstrate a lack of understanding of alternative schools and alternative education on the part of those who develop accountability guidelines.
The impact of these guidelines has resulted in changes to some practices on their campuses and receiving additional funding. Administrators perceive these accountability standards have no impact on their professional career but have increased their stress. Findings indicate that alternative school administrators perceive that the people who assist and are involved in the lives of students, their academic and social-emotional interventions, appear to be the most important strategies that can lead to successful outcomes for their students. Conclusions include a need for more awareness of the differences between traditional and alternative schools, the students served on these campuses, and more awareness of equity in education, specifically accountability and school performance. 

Candidate Name: Nicholas Constantine Giglio
Title: Infrared laser fusion and bisection of blood vessels with real-time optical diagnostic feedback
 February 18, 2022  9:00 AM
Location: Virtual

The conventional method of suture ligation of vascular tissues during surgery is time consuming, skill intensive, and leaves foreign objects in the body. Energy-based radiofrequency (RF) and ultrasonic (US) devices have recently replaced the use of sutures and mechanical clips, providing rapid hemostasis during surgery. These devices expedite numerous labor-intensive surgical procedures, including lobectomy, nephrectomy, gastric bypass, splenectomy, thyroidectomy, hysterectomy, cystectomy, and colectomy. Though these newer methods provide rapid and efficient blood vessel ligation, both US and RF devices have limitations including the potential for unacceptably large collateral thermal damage zones, with thermal spread averaging greater than 1 mm. This lack of specificity prevents the use of these devices for delicate surgical procedures performed in confined spaces (such as prostatectomy). These devices may also cause thermal damage to healthy tissue through unintended heat conduction in contact with the device jaws. The active jaw of US devices can reach temperatures in excess of 200 oC during a single application and can take greater than 20 s to cool to usable temperatures before proceeding with further applications. The maximum temperatures on the active jaw of RF devices are lower (< 100 C), however, larger thermal spread is observed. This study explores the development of a novel alternative method using near-infrared (IR) lasers for vessel ligation, bisection, and real-time feedback during procedures. This dissertation focuses on the sealing (the act of permanently fusing the lumen of the vessel) and cutting (the act of bisecting a vessel) of the arteries (1-6 mm in diameter), which are the most common vessels sealed with an energy-based device during laparoscopic surgery. There are several potential advantages of laser-based sealing and cutting of vascular tissues compared to conventional US and RF energy-based devices. These include: (1) More rapid sealing and cutting of vascular tissues with seal and cut times as short as 1 s each; (2) More directed deposition of energy into tissue with collateral thermal spread of less than 1 mm; (3) Stronger vessel seals with higher burst pressures (up to 1500 mmHg); (4) An integrated device capable of both optical sealing and cutting of vascular tissues without the need for a separate deployable mechanical blade to bisect tissue seals; (5) Safer thermal profile with lower jaw peak temperatures (< 60 C) compared to ultrasound (~ 200 C) and radiofrequency (~ 100 C) devices; (6) Sealing of large blood vessels greater than 5 mm; and (7) An entirely optical based system with real-time quantitative feedback indicating the success of the thermal seal and/or bisection of the blood vessel. This dissertation will explore these advantages for laser-based technology along with an optical method for real – time optical feedback all with the capability of laparoscopic probe integration.

Candidate Name: Donglin Yang
Title: Building an Efficient and Scalable Learning System on Heterogeneous Cluster
 February 03, 2022  9:30 AM
Location: https://uncc.zoom.us/j/8027725626

Deep Learning (DL) has been widely applied in both academia and industry. System innovations can continue to squeeze more efficiency out of modern hardware. Existing systems such as TensorFlow, MXNet, and PyTorch have emerged to assist researchers to train their models on a large scale. However, obtaining performant execution for different DL jobs on heterogeneous hardware platforms is notoriously difficult. We found that current solutions show relatively low scalability and inefficiencies when training neural networks on heterogeneous clusters due to stragglers and low resource utilization. Furthermore, existing strategies either require significant engineering efforts in developing hardware-specific optimization methods or result in suboptimal parallelization performance. This thesis discusses our efforts to build an efficient and scalable deep learning system when training DL jobs in heterogeneous environments. The goal of a scalable learning system is to pursue a parallel computing framework with (1) efficient parameter synchronization approaches; (2) efficient resource management techniques; (3) scalable data and model parallelism in heterogeneous environments;

In this thesis, we implement robust synchronization, efficient resource provisioning approaches, asynchronous collective communication operators, which optimize the popular learning frameworks to achieve efficient and scalable DL training. First, to avoid the "long-tail effects" for parallel tasks, we design a decentralized, relaxed, and randomized sampling approach to implement partial AllReduce operation to synchronize DL models. Second, to improve GPU memory utilization, we implement an efficient GPU memory management scheme for training nonlinear DNNs by adopting graph analysis and exploiting the layered dependency structures. Third, to train wider and deeper Deep Learning Recommendation Models (DLRMs) in heterogeneous environments, we propose an efficient collective communication operator to support hybrid embedding table placements on heterogeneous resources and a more fine-grained pipeline execution scheme to improve parallel training throughput by overlapping the communication with computation. We implement the proposed methods in several open-source learning frameworks and evaluate their performance in physical clusters with various practical DL benchmarks.

Candidate Name: Ryan Benson Feemster
Title: Pan-Africanism in Establishing Culturally Affirming Racialized Gendered Identities in African American Cis-gendered Heterosexual Males attending Counselor Education Doctoral Programs with Respect to Archetypal Imagery and Ancestral Assistance
 January 26, 2022  10:00 AM
Location: Virtual


HERU RYAN BENSON FEEMSTER: Pan-Africanism in Establishing Culturally Affirming Racialized Gendered Identities in African American Cis-gendered Heterosexual Males attending Counselor Education Doctoral Programs with Respect to Archetypal Imagery and Ancestral Assistance

Academic literature suggests that institutions of higher learning can oftentimes embody the systemic racist attitudes of the collective society resulting in African American males experiencing challenges in completing their doctoral degree because of 1.) Spending more time and energy wondering if they are being accepted or tolerated; 2.) Discerning if the words, actions, and intentions of white people are supportive or destructive, and 3.) Contemplating different methods to resist oppression as opposed to accommodating to it (Smith et al., 2011; Pierce, 1988). These concerns are prevalent in counselor education and supervision degree programs. The purpose of this dissertation research study is to determine the role of Pan African epistemology and ontology in the development of African American male doctoral student’s culturally affirming identity development in counselor education and supervision programs. This dissertation research study is significant because it can assist with providing counselor education and supervision doctoral programs in understanding the minoritized culture’s view upon social reality and how they experience their social conditions. The following three research questions guided the study: 1.) How do African American male doctoral students in counselor education and supervision programs subjective interpretations of the images relate to the African archetypal meanings? 2.) How do African American male doctoral students in counselor education and supervision programs make sense of their racialized gendered identity with respect to culturally affirming African images; 3.) In what ways can Pan-African epistemology inform counselor education and supervision programs to enhance African American male inclusion? This dissertation research study employed a visual methodology of photo elicitation. Photo Elicitation is a qualitative methodology using photographs as prompts for rich discussion about the research topic. There were three findings: 1) African American males experience ancestral assistance to reconcile the cognitive dissonance experienced between the identity racialized and gendered by European supremacy and the identity captured by a Pan-African paradigm; 2.) African American male exposure to culturally affirming images increased connection to ancestral guidance that encouraged visibility, inclusion, sense of belonging and acceptance of their racialized gendered identities; and 3.) The execution of multiculturalism, social justice advocacy, and racial equity and inclusion programs are seen as a rhetorical ethic that attempts to disarm African American males into the belief that the fullness of their racialized gendered identities is acceptable within counselor education programs. An implication to the field of counselor education is to incorporate Pan-African programming within the core curriculum and as specialty areas that include art, religion, music, communications, literature, popular culture, history, anthropology, education, sociology, and political science of the Pan-African world.

Candidate Name: Rui He
Title: Experimental Study and Numerical Modeling of the Performance of Flue Gas Desulfurization (FGD) Brine/Coal Fly Ash Co-disposal
 January 12, 2022  2:00 PM
Location: Zoom https://uncc.zoom.us/j/96101011514?pwd=V1lMeldwZ2dManYzVjdtVXhDbThEZz09

The coal-fired steam electricity plants are interested in finding efficient ways to manage by-products from the combustion process out of environmental and regulatory considerations. As one of the major solid by-products, the coal fly ash (CFA) is required by the Coal Combustion Residuals (CCRs) rules to be disposed of in an engineered landfill to protect groundwater. While the disposal of the CFA in the landfill needs water for moisture conditioning and dust control measures, it is convenient to use liquid by-products as alternative moisture sources. The concentrates (brines) generated from the volume reduction of the flue gas desulfurization (FGD) wastewater, such as reverses osmosis and evaporation treatment, can be an alternative liquid source to achieve zero-liquid-discharge (ZLD) for its economic benefit and environmental responsibility considerations. It is reasonable to investigate the potential methods to co-dispose the CFA and FGD brine in the ash landfill. In this study, chloride was the dominant anion with a significant presence of sulfate and bromide in the hypersaline FGD brine, and the cations were mainly calcium and magnesium. The class F CFA used in this study was acquired from an electric plant in the southeast U.S. and did not possess cementitious properties needed for stabilization/solidification (S/S) of co-disposal material. Methods investigated were the co-disposal through compaction and paste encapsulation technology. Instrumented testbeds with leachate and runoff collection systems for each co-disposal method were used to study their field behaviors under the weather conditions of Charlotte, North Carolina.
The chemical analysis of leachate and runoff samples from the compacted testbed found that the method released 79.1% of chloride and 88.6% of bromide in added FGD brine due to the absence of solidification/stabilization of the material. While the electrical conductivity (EC) was used as an indicator of the pore solution’s salinity, the chemical compositions of the fluid could vary as observed in the shifting of dominant anion from chloride to sulfate in the leachate. This study established a set of empirical equations to translate the permittivity to volumetric water content (VWC) for the pore solution's of a known EC (salinity). The low intensity, high-frequency precipitation provided high infiltration during the winter, resulting leachate generation by the testbed with a little amount of runoff. In contrast, the summer's high intensity, low-frequency rains resulted in a high runoff with little infiltration, coupled with extensive evaporation, causing a pause in leachate generation.
Compared to the compacted method, the paste encapsulation method successfully sequestered the halides mainly through the solidification process of the material, as indicated by the leaching test. Further analysis of the chemical composition of inner and annulus leachate coupled with the low hydraulic conductivity (1.44×10-8) of parallelly tested laboratory samples and the negligible leachate volume collected from the inner section of the leachate collection system suggests the leachate collected in the annulus section originated from side leakage. The chemical analysis of leachate and runoff showed on average 80% of retention of chloride and bromide during the experiment period and 97% retention if the side leakage could have been eliminated. The relatively impermeable paste suggests storm management of a paste landfill should expect runoff quantity approximately equivalent to the local precipitation. The surface temperature of the paste was elevated by solar radiation during the summer, which indicated the paste landfill could serve as a heat source that could impact the local microclimate. The mineralogy study of different samples showed the formation of poorly structured minerals which caused interpretation challenges of XRD results. The anticipated halide stabilization pathway through the precipitation of Fridel’s salt and Kuzel’s salt was complicated by the significant presence of magnesium in the brine.
Although the compacted method failed to retain halides under current weather conditions (Charlotte, NC, US), it does not necessarily disqualify its use in different environments. Therefore, a physics-based COMSOL-MATLAB (CM) model was established to simulate the field behaviors of the compacted co-disposal material, which was validated with the field data. The CM model consisted of three main components: heat transfer (HT), unsaturated flow (UF), and solute transport (ST) processes. The model also simulated the runoff, evaporation, and solar heating at the surface of the testbed. The CM model could appropriately reproduce the field leachate/runoff generation pattern, moisture content variation, temperature profile, and the change of chloride and bromide concentrations in the leachate during the washoff stage. The accuracy of simulation results could be improved with a better estimation of the conditions on the testbed surface.
While the validated physics-based model could be used to explore potential management methods for the compacted landfill and its behaviors under different weather conditions, the abundance of data spurred the interest in developing data-driven models. Since the bulk dielectric permittivity, which could be translated into VWC, was the measured property, a data-driven model simulating the change of permittivity in the compacted testbed was developed. The data-driven model was structured as three layers of material stacked in spatial order to address the standard operation of implementing new layers on top of old materials during landfill operation. With a forecast interval of 24 hours, the prediction over time of three years had an average R2 of 97.6% with the data-driven model trained with the first-year data, and R2 of 99.5% if two years of data were used in the training. The scenario studies showed that the data-driven model could only accurately predict permittivity values included in the training dataset, which indicates that a failure to predict could happen when unprecedented values occurred. Further investigation showed the data-driven model could simulate processes that would have conventionally required additional physics-related information through unique pattern recognition in the training dataset.

Candidate Name: Madiha Tabassum
Title: Understanding end-users' privacy perceptions, concerns, behaviors, and needs in the smart home
 December 13, 2021  1:30 PM
Location: meet.google.com/ihw-tior-odp

Smart homes are more connected than ever before, with a variety of commercial internet of things devices available. The use of these devices introduces new security and privacy risks in the home and needs for helping users to understand and mitigate those risks by providing them some level of control over their data. For doing so, it is necessary to have a thorough understanding of smart home users' security and privacy perceptions, behaviors, preferences, and needs.
My thesis aims to investigate the current state of end-user knowledge of smart home device data practices, available privacy controls, and their security and privacy concerns and behaviors. I have utilized different research methods throughout this exploration, including semi-structured interviews, surveys, and experience sampling studies. The contributions of this dissertation are: 1) it uncovers several factors that contribute to the privacy perceptions, concerns, and behaviors of smart home users, 2) it provides in-depth analysis of the current interface support (or lack thereof) to address end-user privacy needs, and finally 3) it contributes several design guidelines to empower users with their privacy in the smart home.