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The focus of this dissertation is on the topic of chatter avoidance during machining and the prediction of specific cutting forces and maximum tool temperatures during machining using machine learning. Self-excited regenerative vibration or “chatter” is a significant obstacle in machining which results in poor surface quality. To avoid chatter, a 2D diagram of the depth cut limit vs. the spindle speed, called Stability Lobe Diagram (SLD), is used. The SLD depends on the cutting parameters and structural dynamics parameters. Theoretically, chatter can be avoided using the physic-based SLD. But in practice, there is a gap between the empirical results and what the theory supports due to the uncertainties associated with the in-process structural dynamics parameters. using a multivariate Newton method, given the empirical data sets. The first part of the dissertation focuses on the inverse problem in chatter avoidance where the in-process structural dynamics parameters are extracted using a multivariate Newton method, given the empirical data sets. The SLD and the cutting parameters are assumed to be known and given. Using this knowledge, the structural dynamics parameters are obtained using the inverse approach. In addition, the uncertainty in the value of each structural dynamics parameter derived through the inverse approach is also presented. The results derived from the algorithm are used to discover the sensitivity of the boundary with respect to each parameter. The last part of the dissertation covers the prediction of the specific cutting force and the maximum tool temperature during machining using machine learning models.
This study explored two aspects of K-12 core content area teachers' experiences with digital citizenship through the Connectivism lens (Siemens, 2005). First, it explored how teachers instruct students on digital citizenship topics, including how they define digital citizenship and integrate it into their core content area curriculum. Second, it looked at teachers’ experiences and needs regarding digital citizenship professional development. This study followed a basic qualitative approach and used interviews with a follow up questionnaire to gather data. Participants’ responses were analyzed using Fereday and Muir-Cochrane’s (2006) six-step, hybrid approach of inductive and deductive coding and theme development. Findings and discussion were presented through the learning theory of Connectivism. Information on how core content area teachers define digital citizenship was summarized using the S3 Guiding Principles from Ribble and Park (2019). Information on teachers’ experiences integrating digital citizenship into their core content curriculum revealed five major themes: Responsibility, Student Behavior, News & Media Literacy, Non-Cognitive Competencies, and Technology Use. Findings related to professional development experiences were presented through five broad themes: Personal Learning Networks, Parenting & Family, Self-Exploration, Technology Facilitators & Other Technology Champions, and Participating in the Digital World. Findings related to teachers' professional development needs regarding integrating digital citizenship into their core content curriculum were summarized through three themes: making this content relevant and authentic for their students, raising awareness among their peers to build a community around teaching digital citizenship, and identifying resources to integrate this subject matter into their curricula.
We are developing a real-time infrared image technique, Enhanced Thermal Imaging (ETI), that can detect blood vessels embedded in tissue and assess tissue perfusion. ETI is a combination of standard thermal imaging (8-10 µm) and selective heating of blood relative to surrounding water-rich tissue using LED sources at low power. Blood absorbs strongly at 530 nm. Illumination of water rich tissue and embedded blood vessels at this wavelength selectively increases the temperature of the blood vessels relative to the surrounding tissue causing the vessels to appear brighter in a thermal image. ETI does not require the use of injectable dyes and has a compact footprint allowing for use both during surgery and at the bedside. Previous studies using ETI were limited due to lengthy post-processing times required to delineate vessels. The first study presented in this dissertation shows the real-time capabilities of ETI in mapping vascular structures. Real time application of computational filters highlighting temporal and spatial changes reveal embedded blood vessels. ETI was obtained for a model with simulated blood vessels and a porcine heart tissue, and for both models, temporal and spatial filters outperformed standard thermal imaging. In the second study, ETI was simulated computationally to determine limitations and optimizations. The models were also analyzed to determine parameters that can delineate vessel depth and size and these results were compared with ex vivo tissue studies. The final study involved monitoring the reperfusion of skin flaps in a murine model. ETI appears to be more sensitive to the deeper healing while fluorescent imaging provides information about superficial healing. The use of intra-operative and post-operative optical guidance has beneficial impacts on patient costs and tissue viability.
Given the importance of understanding how gender bias impacts the advancement of women into upper leadership, this second-order meta-analysis attempts to explore and summarize previous developments in the gender and leadership literature in order to present the current state of the literature and identify a roadmap for future research.
This dissertation delivers three primary theoretical contributions. First, I conducted a systematic review of the leadership and gender literature to create a primer, with relevant definitions and theoretical frameworks, for gender and leadership theory. This review highlighted that little theoretical integration exists to synthesize the literature on gender and leadership.
Second, I present a second-order meta-analysis and subsequent relative weights analysis to demonstrate the relationship between personality, gender and follower evaluation of leadership constructs such as leader emergence and other leader behaviors (ex: transformational leadership, ethical leadership, etc.). The final meta-analytic correlation matrix included 89 meta-analytic estimates (total k=1,404; total n=366,329). Results indicate that variation in the evaluation of leaders can be explained by gender, however, the subsequent relative weights analysis indicates that for no construct is gender the dominant predictor.
Finally, this dissertation presents a research agenda based on the current findings that will advance the field, including research questions ranging from resolving methodological issues related to the measurement of evaluations of behaviors rather than actual behaviors, to further understanding further moderators of the relationship between gender and leader evaluations.
Energy efficiency and scalability continue to be key considerations for the development of low-cost wireless networks for meeting the needs of the emerging world of the Internet of Things (IoT). Recent developments in low-power wide area networks (LPWAN) promise to meet these requirements by achieving long communication ranges at low data rates without increasing the energy cost.
Consequently, LPWAN technologies are rapidly gaining prominence in the development of IoT networks in comparison to legacy WLANs. LPWANs address the challenges of legacy wireless technologies that use multi-hop mesh networking for increasing connectivity and coverage. Long Range (LoRa) technology is receiving increasing attention in recent years for addressing the challenges of providing wireless connections to a large number of end devices in the field of IoT. LoRa has become the most prominent LPWAN standard due to its long transmission range, low power consumption, and large network capacity. Despite these benefits, LoRa networks may not be able to achieve their full potential unless additional improvements are achieved in the network scalability domain. Specifically, the probability of success under heavy network traffic loads or a large number of end devices needs to be improved.
In this dissertation, we present the causes of performance degradation of LoRa networks and propose several approaches to enhance their performance. Next, we present a novel framework to employ AI tools to make IoT applications smarter. The effectiveness of all the proposed approaches is validated using mathematical analysis as well as via simulations thereby creating the basis for further research in this area.
In higher education institutions, as the number of online language courses continues to increase, it is paramount to provide training and support for faculty and equip them with the appropriate tools to improve students’ learning experiences, specifically those with visual impairments. This qualitative study aims to examine online language faculty’s experiences teaching students with vision impairments. The goal is to make a novel contribution by exploring accessibility issues for online accessibility in language courses in the United States. 10 in-depth, semi-structured interviews were conducted with 10 language faculty around the country. After analyzing each transcript, several themes were identified to answer each research question: 1) Faculty Experiences in Delivering Online Language Courses to Learners with Visual Impairments, 2) Training and Support in Delivering Accessible Online Language Courses, and 3) Strategies and Tools to Teach Students with Vision Impairments. These findings revealed that ADA compliance and online languages should be prioritized in higher education. Despite the increasing number of online courses to teach languages, it is salient that students with visual impairments require further support and attention in higher education language courses. Additionally, faculty require further training and support to help them implement accessibility strategies and tools to their courses.
The Triodopsis genus of Stylommatophoran land snails has been confusing to malacologists for decades. Twenty-eight species have been described in the eastern and southern US, but some original descriptions are insufficient to correctly identify specimens, and misidentifications are common. Phylogenetic approaches have not been applied for species in this genus as the usual mitochondrial markers are extremely variable and difficult to sequence. DNA extraction is complicated by the presence of mucopolysaccharides. A mollusk-specific DNA extraction protocol and custom primers are developed in this study to better facilitate genetic analysis of the family Polygyridae. Triodopsis genus phylogenies based on 16S, ITS2, and H3 genes are presented, with FST values suggesting a reduction in the number of named species. The phylogenetic clades are related to morphology and biogeography to attempt to better identify the recognized species and change the species status of some based on morphology measurements and overlapping distributions. An H3 molecular clock tree suggests a recent and rapid expansion in the family. New hypotheses are also presented that may explain the genetic variation in the Stylommatophoran mitochondrial genome, and a possible explanation of the morphological variation within a clade that could still be undergoing rapid speciation after repeated refugia isolation.
Mollusks are a highly diverse phylum with some of the most extremes of body forms. The relationship between phenotype and phylogeny is studied here in two very different groups of mollusks, the bivalves and the terrestrial gastropods. The eastern oyster, Crassostrea virginica, being a nearly amorphic organism, expresses its phenotype as physiological responses to its environment. This ancient group has a huge distribution over a range of climates and conditions. The physiology of the eastern oyster is investigated to determine its response as a physiological phenotype to different tidal elevations, salinities, and environmental conditions. This research investigates the immunity gene expression and mitochondrial genes to determine if selection has any effect in the oyster response. Triodopsis snails, on the other hand, generally have small ranges that appear to be similar habitats but have many morphological forms. The morphology, biogeography and phylogenetics of the Triodopsis genus is studied to determine the status of recognized species, and probable evolutionary history. Both groups of mollusks have incredible adaptations to their respective lifestyles. The oyster and the snail are extreme examples of diversity and adaptation to adverse habitats and conditions with different life strategies.
