A unifying theme of this thesis is the implementation and characterization of point probes for surface metrology. The implementations include two optical non-contact profiling methods; fiber-based Fabry-Perot interferometry and Confocal microscopy.
Even though Fiber-based Fabry-Perot interferometers are suitable for measuring surface texture in confined space, literature describing its implementation and limitations of this technique are scarce. To explore these knowledge gaps an experimental facility has been built and the feasibility for surface height measurements is validated by measuring two sinusoidal reference surfaces with heights of 1 μm and 1.5 μm and wavelengths of 100 μm and 50 μm respectively.
A second part of this thesis is to implement a flexure-based vertical scanning of an objective lens used for Confocal microscopy to increase the bandwidth of height detection and, therefore, surface scanning speeds. A sinusoidal reference sample is designed and manufactured, which is later measured using a confocal microscope prototype built using a 60X objective lens. A flexure to house the lens stack to provide a surface height scanning range of 10 μm is also designed and fabricated.
A third part of this thesis involves characterizing a stylus-based contact profiler for measuring areal form of freeform optics. Typically, for non-contact optical probes, the probe axis must be orthogonal to the curvature of the part being measured. This is not required for a stylus profiler. Reference objects such as optical flats, prisms, and spheres are measured using the stylus profiler and these measurements are compared with results from a Fizeau interferometer. From these measurements, vertical error of the X scanning carriage, side loading on the stylus probe due to the surface slope of the part being measured are estimated. A geometrical model of the profiler has been developed and used in a Monte Carlo simulation that predicts an uncertainty in the areal form measurements of less than 100 nm PV for a 100 mm measurement aperture.
Deep neural networks (DNN) are proved to be effective and improve the performance dramatically in various kinds of computer vision tasks. The end-to-end learning manner in training DNN consistently shows the powerful modeling ability and consequently mitigates the dedicated efforts for expert feature engineering. On the other hand, it raises the issue that how to improve the black-box network with better representation (feature) learning especially when the learned representations and classifiers are tied together in the manner of supervised learning. In this work, representation learning is studied in four perspectives of different fields, i.e. diversity in ensemble learning, aspect ratio in image aesthetics assessment, invariance in identification task, and composition in color attribute recognition.
In light of analyzing the bottleneck of black-box network and designing better representation learning for target tasks, we introduce that: (a) Ensemble learning relies on the diversity of the complementary neural networks, in both feature representations and classifier representations. A diverse representation learning method, namely learning-difficulty-aware embedding, is proposed to adaptively reconcile learning attentions for different categories by training a series of networks with diversified representations sequentially; (b) Widely-adopted data augmentation method in image recognition deteriorates aspect ratios, which is an important factor in image aesthetics assessment. An aspect ratio representation learning method, namely adaptive fractional dilated convolution, is proposed to explicitly preserve the learning representation related to aspect ratios by adjusting the receptive fields adaptively and natively; (c) Identification tasks, e.g. person re-identification, aim at learning representations that are robust to interfering variances, e.g. lighting variances, view variances, pose variances. An invariance representation learning method, namely anchor loss, is proposed to train a robust feature extractor, which distills the identity-related representations while disentangling and removing interfering variances by global supervision under local mini-batch training; (d) Color recognition is entangled with compositional representation in both visual perception and language attentions. A compositional learning module with attention to key colors is proposed to learn better color representations. Besides, another compositional learning method, namely classifier as descriptor, is proposed for long-tail color recognition by incorporating the rich knowledge in classifier representations to remove the bias from bias-trained
model.
Through extensive experiments and thorough analysis, we demonstrate some novel insights about the impacts of four factors, i.e. diversity, receptive field, invariance, and composition. Several methods are proposed to learn better representations for those factors, achieving state-of-the-art results in different tasks.
This quantitative study explores the potential school-level and school district-level factors associated with North Carolina school performance grades in K-5 elementary schools. The desire was to examine if any of the school- or school district-level factors were associated with the outcome variable of North Carolina school performance grades. This study used the data from the North Carolina school report cards and Civil Rights Data Collection from the 2015 – 2016 school year. The sample had 1096 schools and 92 school districts. A hierarchical linear model was created with the overall school performance grade as the outcome variable and the sixteen school level predictors and thirteen school district predictors. Results indicated that twelve out of sixteen school-level variables were statistically significant. One out of thirteen school district-level variables were statistically significant and two additional variables approached significance. Recommendations for improving student achievement were provided for United States policymakers, university education programs, North Carolina policymakers, local governments, school districts, and schools. These recommendations are presented as opportunities to ensure equitable educational practices and outcomes for all students.
Wearable technology became popular not only in the consumer market, but also in the field of academic research. Studies related to smart wearables have increased dramatically during recent years. However, personal safety perspectives of wearable devices have not been adequately addressed in the literature so far. There have been debates regarding the potential health risk of using wireless technology and batteries from wearable devices. Regardless of the actual health risks from wearable devices, these controversial debates could affect and form users’ perceptions toward purchasing and using the technology. The uniqueness of wearable devices is that they are not only considered as technical devices, but also considered as fashion items. By adding perceived risk and fashnology (combination of fashion and technology) constructs to the Unified Theory of Acceptance and Use of Technology 2 (UTAUT2), this study examines how perceived risks and fashion-related perceptions influence a consumer’s intention to purchase and use wireless earbuds. Based on survey data from a sample group of 205 respondents, Perceived Health Risk, Perceived Fashionability, and wearable comfort have a significant impact on a consumer’s intention to purchase wireless earbuds. These results fill in the gap of wearable technology literature and provide a reason why Perceived Health Risk should be studied more for future research. In addition, practitioners should make sure they produce wearable devices that are safe, fashionable, and comfortable to wear.
The maintenance of genome integrity and fidelity is essential for the proper function and survival of all organisms. Recent studies have revealed that APE2 is required for the activation of an ATR-Chk1 DNA damage response (DDR) pathway in response to oxidative stress and a defined DNA single-strand break (SSB) in Xenopus laevis egg extracts. However, it remains unclear whether APE2 is a general regulator of DDR pathway and what the biological significance of APE2 is in mammalian cells. Here, I provide evidence using mammalian cultured cell lines including human pancreatic cancer cells that APE2 is important for ATR DDR pathway activation in response to different stressful conditions including oxidative stress, DNA replication stress, and DNA double-strand breaks. Fluorescence microscopy analysis shows that APE2-knock-down (KD) leads to enhanced γH2AX foci and increased micronuclei formation. In addition, a small molecule compound is identified as APE2 inhibitor that specifically compromises the binding of APE2 to ssDNA, its 3′-5′ exonuclease activity, and the defined SSB-induced ATR Chk1 DDR pathway in Xenopus egg extracts. Notably, cell viability assays demonstrate that APE2-KD or APE2 inhibitor sensitizes pancreatic cancer cells to chemotherapy drugs. Overall, APE2 is proposed as a general regulator for DDR pathway in genome integrity maintenance in mammalian cells.
This multiple case study explored the characteristics of clinical experiences that support preservice teachers' understandings of culturally responsive literacy in elementary classrooms. In particular, this study focused on capturing the voices and perspectives of three preservice teachers through semi-structured interviews, observations, and the collection of artifacts such as literacy lesson plans, journal entries, and photographs. Findings suggest that preservice teachers generally understand culturally responsive teaching as: (a) using a variety of diverse texts; (b) building a learning community that honors students’ cultures, (c) maintaining high expectations for all students; and (d) teachers knowing their students in order to connect the course content to their lives, cultures, and interests based on their coursework and experiences in the clinical setting. Data also showed that clinical educators are the most influential characteristic of preservice teachers’ understandings of culturally responsive literacy and being in the classroom setting is more influential than only learning about culturally responsive teaching through university coursework. Findings also indicate that preservice teachers are developing superficial understandings of culturally responsive teaching, suggesting implications for teacher education and preparation.
The U.S. Environmental Protection Agency (EPA) report on Municipal Solid Waste (MSW) (EPA, 2018) shows that the amount of MSW generated by Americans increased from 88.1 million tons in 1960 to 262.4 million tons in 2015. Out of the 262.4 million tons, 137.7 million was the estimated amount disposed into landfills. Only 67.8 million tons or about 26% of the total waste generated was recycled. It is clear from the numbers above that the success of existing recycling programs is limited. Increasing populations will continue to put pressure on our existing resources, compelling governments at all levels to take additional action to increase recycling efforts to transition from a linear model of make, use, and dispose to a closed-loop circular economy system, emphasizing reduce, reuse and recycle.
Within this context, my research evaluates recycling programs in the state of North Carolina, using counties as the unit of analysis. The first part explores county level factors that affect recycling rates. Factors span across the economic, demographic, social, geographic, technical, and programmatic aspects of recycling programs. The second part of my study focusses on exploring the economic and environmental merits of recycling. Specifically, this section explores the GHG emissions and wage creation from recycling certain materials as compared to landfilling them, and the causal mechanism between recycling, and GHG emissions and employment generation. Qualitative interviews with stakeholders in the recycling community inform the findings of my quantitative analysis.
I found that recycling is moving away from being a behavior based in individual taste and preferences to a mainstream behavior—part of everyday life. We must view recycling not only as an individual altruistic action but also as a means to decrease the cost of goods, lower landfill costs, combat climate change, and reduce resource and energy use while engaging the community. Most important is the need for standardized measures for recycling, new ways to measure recycling performance, and greater consistency in solid waste management policies so that scholars and program analysts can conduct more comparative studies. My study provides a unique, yet comprehensive look at recycling in the state of North Carolina, and provides recommendations to decision-makers, leaders, and scholars on how to improve existing recycling programs to achieve the goals of environmental and economic sustainability.
The Tax Cuts and Jobs Act of 2017 (TCJA) provides a novel context in which to examine the effects of U.S. taxation of foreign earnings on the behavior of multi-national corporations (MNCs). Prior to the TCJA, the U.S. levied taxes on an MNC’s worldwide earnings, deferred until firms repatriated the funds to U.S. The worldwide taxation and deferral until repatriation led to firms holding significant amounts of cash offshore. By 2017, there was an estimated $2.8 trillion of repatriatable funds “trapped” offshore. Prior legislation intended to encourage repatriation offered temporary “tax holiday” measures. The TCJA lowered corporate tax rates for all firms and eliminated future U.S. tax on repatriated earnings after payment of a one-time transition tax, creating a “permanent tax holiday” for foreign earnings. I examine the relationship between pre-TCJA foreign cash holdings disclosed by MNCs and their shareholder payout and investment behavior in the two years immediately following enactment of the TCJA. Similar to research into the effects of the temporary tax holidays in prior legislation, I find share repurchases in the post-TCJA period are associated with pre-TCJA foreign cash holdings. I further find that MNCs disclosing pre-TCJA foreign cash holdings increased research and development and capital expenditures in the second year following the TCJA. These findings indicate that the foreign earnings provisions of the TCJA may have had some longer-term effects in line with its legislative intent. This contrasts in some ways with the findings of prior research and should be of interest to policymakers, particularly as the current U.S. administration considers changes to the corporate tax regime, while also providing a basis for future research.
As colleges work to meet performance standards, staff have been placed in key service areas to help students be successful. With the majority of the seven million community college students attending part-time, needing developmental education, and not graduating on time, it is vital that students take advantage of services such as academic advising, financial aid advising, tutoring, career counseling, student organizations, disability services, and military/veteran’s services (American Association of Community Colleges, 2019a; McClenny, 2016; Tippett & Kahn, 2018a). Students who utilize some of these services have been retained and had higher grade point averages (GPA) than students who did not use these services (Bremer et al., 2013; Drake, 2011; Habley et al., 2010; Hatch & Garcia, 2017; McClenney & Dare, 2013; Nakajima et al., 2012; Smith & Allen, 2014). By making use of the provided services, students were more successful, but the frequency of visits to these services has not been analyzed in-depth. Using data from one institution’s Community College Survey of Student Engagement (CCSSE), this study set out to determine if there was an association between the frequency of use of a service and the student’s GPA or intent to return to that college for future semesters. The research questions that guided this study ask if there is a relationship between the frequency of service utilization and student success. By using an analysis of variance to examine the data, it was determined that the reported frequency of using financial aid advising showed a statistically significant difference in the student’s GPA. The research did not find any statistically significant differences in a student’s GPA for the use of multiple services nor a statistically significant difference in a student’s intent to return based on the use of services. Based on this study, community colleges will want to determine the individual services offered by financial aid advising and how to best adapt a financial aid advising program to assist those students who are visiting more often and not seeing academic success.
