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Title: Addressing the security and efficiency challenges in Internet of things
Creator: Lei, Xinyu
Date: 2021
Collection: Electronic Theses & Dissertations
Description: Nowadays, Internet of things (IoT) devices (e.g., smart cameras, Amazon Alexa, GPS navigation devices) are increasingly popular in our daily life. In practice, IoT devices are usually supported by their infrastructures (such as cloud servers, blockchain systems) to provide a variety of services. Some examples are given as follows. First, smart home Wi-Fi IoT devices can connect to their IoT vendor servers over the Internet, and they can be remotely monitored and controlled. Second, IoT...
Show moreNowadays, Internet of things (IoT) devices (e.g., smart cameras, Amazon Alexa, GPS navigation devices) are increasingly popular in our daily life. In practice, IoT devices are usually supported by their infrastructures (such as cloud servers, blockchain systems) to provide a variety of services. Some examples are given as follows. First, smart home Wi-Fi IoT devices can connect to their IoT vendor servers over the Internet, and they can be remotely monitored and controlled. Second, IoT devices along with blockchain systems have been implemented in various industries including financial, supply chain management, smart agriculture, cryptocurrency-supported vending machine, etc. Third, IoT devices can produce/collect datasets (e.g., locations) and upload them to powerful public cloud servers for storage. Then, the cloud server (serves as the IoT infrastructure) can deliver different data queries (e.g., kNN queries) services to data users. For both IoT devices and IoT infrastructures, there are many security and efficiency challenges that are needed to be addressed. For example, IoT devices usually have limited hardware capabilities, so they may not support secure communications (i.e., SSL/TLS connections). Moreover, blockchain systems may suffer from double-spending attacks and public clouds may steal the datasets in their storage. In this work, we propose various solutions to address these security and efficiency challenges. They are introduced as follows. To address security and efficiency challenges in IoT devices, we have two studies. First, in our project targeting smart home Wi-Fi-connected IoT devices, we conduct an empirical study on how the cryptographic/security protocols (e.g., SSL/TLS) are supported on 40 popular Wi-Fi smart home IoT devices. Surprisingly, we discover two security vulnerabilities and show that adversaries can exploit them to hijack the victims' IoT devices or peek at victims' activities. To secure these smart home IoT devices, we present SecWIR (Secure Wi-Fi IoT communication Router) framework, which is deployed on the commercial off-the-shelf (COTS) home Wi-Fi routers. Our experimental results show that SecWIR can secure IoT devices at the expense of only a small reduction in the routing performance. Second, in our project on home digital voice assistants (HDVAs), we study the insecurity of HDVA services by using Amazon Alexa and Google Home as case studies. We disclose three security vulnerabilities that root in their insecure access control. The insecure access control means that HDVA devices not only solely rely on single-factor authentication but also take voice commands even if no people are around them. To address the venerability, we devise a Virtual Security Button (VSButton), which leverages a real-time outlier detection algorithm on Wi-Fi signal to detect indoor human motions. Only when indoor human motions are detected, VSButton activates the HDVA devices and allows them to accept voice commands. At last, we conduct experiments to demonstrate the efficiency and effectiveness of VSButton. To address security and efficiency challenges in IoT infrastructures, we have two studies. First, in our project on reducing the transaction validation time on Bitcoin blockchain, we focus on designing fast Bitcoin transaction validation protocols which can help to promote the IoT-blockchain services (e.g., Bitcoin-supported vending machine). Currently, a secure Bitcoin transaction requires the payee to wait for at least 6 block confirmations (one hour) to be validated. In our project, we propose BFastPay scheme to accelerate the Bitcoin transaction validation. BFastPay employs a smart contract called BFPayArbitrator to host the payer's security deposit and fulfills the role of a trusted payment arbitrator which guarantees that a payee always receives the payment even if attacks occur. BFastPay is a routing-free solution that eliminates the requirement for payment routing in the traditional transaction routing network (e.g., Lightning Network). The theoretical and experimental results show that BFastPay is able to significantly reduce the Bitcoin transaction waiting time. Second, in our project on providing secure IoT-cloud service, we focus on k nearest neighbor (kNN) queries service. Nowadays, location service providers (LSPs) often resort to IoT devices (e.g., GPS navigation devices) to collect geospatial data. In practice, LSPs may rely on commercial cloud services, e.g., Dropbox, to store the tremendous geospatial data and deal with a number of user queries. However, it is challenging to achieve a secure and efficient location-based query processing over encrypted geospatial data stored on the untrusted cloud. In this project, we propose SecEQP (Secure and Efficient Queries Processing) scheme to address the secure kNN query problem. Our theoretical analysis and experimental evaluation demonstrate that SecEQP is secure and efficient. In summary, we successfully address the security and efficiency challenges in different IoT devices (including smart home IoT devices and HDVAs) and IoT infrastructures (including blockchain systems and cloud servers) in this work. We believe that our work can promote the fast growth of the IoT industry
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Title: Advanced Operators for Graph Neural Networks
Creator: Ma, Yao
Date: 2021
Collection: Electronic Theses & Dissertations
Description: Graphs, which encode pairwise relations between entities, are a kind of universal data structure for many real-world data, including social networks, transportation networks, and chemical molecules. Many important applications on these data can be treated as computational tasks on graphs. For example, friend recommendation in social networks can be regarded as a link prediction task and predicting properties of chemical compounds can be treated as a graph classification task. An essential...
Show moreGraphs, which encode pairwise relations between entities, are a kind of universal data structure for many real-world data, including social networks, transportation networks, and chemical molecules. Many important applications on these data can be treated as computational tasks on graphs. For example, friend recommendation in social networks can be regarded as a link prediction task and predicting properties of chemical compounds can be treated as a graph classification task. An essential step to facilitate these tasks is to learn vector representations either for nodes or the entire graphs. Given its great success of representation learning in images and text, deep learning offers great promise for graphs. However, compared to images and text, deep learning on graphs faces immense challenges. Graphs are irregular where nodes are unordered and each of them can have a distinct number of neighbors. Thus, traditional deep learning models cannot be directly applied to graphs, which calls for dedicated efforts for designing novel deep graph models. To help meet this pressing demand, we developed and investigated novel GNN algorithms to generalize deep learning techniques to graph-structured data. Two key operations in GNNs are the graph filtering operation, which aims to refine node representations; and the graph pooling operation, which aims to summarize node representations to obtain a graph representation. In this thesis, we provide deep understandings or develop novel algorithms for these two operations from new perspectives. For graph filtering operations, we propose a unified framework from the perspective of graph signal denoising, which demonstrates that most existing graph filtering operations are conducting feature smoothing. Then, we further investigate what information typical graph filtering operations can capture and how they can be understood beyond feature smoothing. For graph pooling operations, we study the procedure of pooling from the perspective of graph spectral theory and present a novel graph pooling operation. We also propose a technique to downsample nodes considering both mode importance and representativeness, which leads to a novel graph pooling operation.
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Title: Advancements in electrochemistry for the sensing of aqueous compounds and persistent compound destruction
Creator: Ensch, Mary
Date: 2020
Collection: Electronic Theses & Dissertations
Description: A significant research question to address is if existing electrochemical methods can be used to advance the sensing of biological compounds and toxic heavy metals, and to destroy persistent toxic pollutants to benefit the planet and humankind. Using the methods of cyclic voltammetry (CV), square wave voltammetry (SWV), square wave stripping voltammetry (SWSV), and electrochemical oxidation (EO), the sensing of isatin and manganese, and the destruction of perfluoroalkyl compounds was...
Show moreA significant research question to address is if existing electrochemical methods can be used to advance the sensing of biological compounds and toxic heavy metals, and to destroy persistent toxic pollutants to benefit the planet and humankind. Using the methods of cyclic voltammetry (CV), square wave voltammetry (SWV), square wave stripping voltammetry (SWSV), and electrochemical oxidation (EO), the sensing of isatin and manganese, and the destruction of perfluoroalkyl compounds was investigated. Each task had the main focus of advancing our understanding of the process and making significant process improvements.Isatin is an endogenous indole that has potential pharmaceutical applications based on its anticonvulsant abilities through reaction pathways in the human body. Due to its low concentrations in blood, serum, and tissues, it is typically detected using gas chromatography mass spectroscopy (GC/MS) which requires a specialized individual and lengthy measurement times. In order to combat this, researchers have begun investigating electrochemical detection methods for this compound. Here, the investigation of isatin detection on a 3-in-1 boron-doped diamond (BDD) sensor was studied to simplify the electrochemical system requirements and set the ground work for a potential plug and play sensor for isatin. Both sensor configurations tested showed applicability to this application with the lowest limit of detection obtained to be 0.04 μM. Not only was isatin able to be detected in a complex sample matrix in a short measurement time with this simplified technical approach, it was done so with the elimination of extensive electrode pretreatment processes that have been required for other electrode materials in the past. This study paves the way for a fully developed BDD sensor that can expand the understanding of isatin reaction pathways and advance its ability to be used in pharmaceuticals.Manganese is an important nutrient but has toxic effects in humans making it imperative to be able to detect it in human blood, urine, and serum as well as drinking water. Indium tin oxide (ITO) has been a typical electrode material for spectroelectrochemical measurements and metal detection experiments on transparent substrates. This study goes through a few process parameters for an ITO film on a non-transparent silicon substrate. It was found that heating and annealing the film created the best film structure for an electrochemical sensing application towards manganese with a limit of detection of 0.1 parts per billion (ppb). This obtained lower detection limit allows for improved accuracy in human serum measurements with no added membranes to the electrode’s surface and uses an electrode material that already has the capabilities to be mass produced with good repeatability. This makes ITO an economical sensing solution.Per- and polyfluoroalkyl substances (PFAS) are toxic to human health and are wide spread in the environment due to their numerous consumer and industrial applications. Most current remediation techniques take advantage of filtration or adsorption technologies to remove these compounds from a water source. However, since they do not destroy the compounds, these remediation techniques yield waste products. This study, utilizing electrochemical oxidation for the destruction of PFAS, looks at tackling waste products from an ion exchange process. By utilizing BDD, a laboratory study showed that PFAS completely mineralize in these complex solutions. Overall, it was foundthat ammonia based solutions allow for the best mineralization of the most common PFAS using electrochemical oxidation for an ion exchange regenerate solution. This study provides valuable knowledge to ion exchange manufacturers who are looking to solve their residual PFAS waste problem.All three studies have shown that existing electrochemical techniques can be used to further sensing and remediation knowledge in today’s world and provide safer, cleaner technology options for the betterment of human health and the environment.
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Title: Advancing Field Emission Technology for High Power Injectors Operating in GHz and Beyond
Creator: Schneider, Mitchell E.
Date: 2022
Collection: Electronic Theses & Dissertations
Description: As the next generation of electron injectors pushes to achieve higher gradient fields than ever before (>300 MV/m), they are driven to operate at higher frequencies (C-band through W-band). This shrinks the fabrication dimensions of these cavities, making field emission cathodes (FECs) an electron source of choice. Photoemission and thermionic sources are increasingly less suited as the complex laser transport schemes and heating source powering these injectors cannot provide the necessary...
Show moreAs the next generation of electron injectors pushes to achieve higher gradient fields than ever before (>300 MV/m), they are driven to operate at higher frequencies (C-band through W-band). This shrinks the fabrication dimensions of these cavities, making field emission cathodes (FECs) an electron source of choice. Photoemission and thermionic sources are increasingly less suited as the complex laser transport schemes and heating source powering these injectors cannot provide the necessary beam quality and may cause damage to the cathode or the injector itself. Carbon-based FECs have dominated the field emission sources R&D portfolio at DOD and DOE for the past 30 years across various high-power vacuum electronic device activities. Compared to traditional metal cathode technology, carbon-based technology cathodes are able to produce higher charge at low electric fields. Small intrinsic electron momentum and simple fabrication means these can become a leading technology, e.g., in the case of carbon nanotubes, nanoscale emitters make them attractive for producing high brightness beams. Specifically, diamond-based cathodes can handle extreme temperature and mechanical stresses that can occur under high gradient conditions.Most promising is a unique form of diamond, ultra-nano-crystalline diamond (UNCD) due to its material and electrical properties, which include being the most conductive form of diamond due to having the largest amount of grain boundaries. This cathode material allows us to explore new frontiers of cathode physics research, revealing a new field emission mechanism that diverges from classical Fowler Nordheim, termed space charge dominated Fowler Nordheim. This form of Fowler Nordheim is space charge dominated but can surpass the 1D Child Langmuir limit and approaches the 2D limit. This is not space charge limited Fowler Nordheim. This ability to decouple the extracted current from the space charge effects allows for the production of extremely xiii bright beams. This can be achieved by expanding the current cathode testing facilities beyond L band into C band so as to access these high fields and explore the temporal dynamics of a field emission source. This will yield the new physics knowledge needed to construct the world’s first custom-built injector specifically designed for field emission sources. Furthermore, exploring other forms of diamond cathode such as Diamond Field Emitter Arrays (DFEA) yields insight into the applications of transversely shaped beams for advanced accelerator applications such as emittance exchange beam lines. DFEA’s allow for the exploration of additional materials effects on the cathode performance such as the ballast resistance. This ultimately allows the derivation of a comprehensive concept map for the field emission dynamic regimes needed for the design of RF injectors. Previously, the theoretical assumption was that everything operated under classical Fowler Nordheim without any additional contributions from other materials properties or beam effects.
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Title: Advancing frontiers in reactive and selective iridium c-h borylation catalysis and targeted silsesquioxane synthesis
Creator: Dannatt, Jonathan E.
Date: 2019
Collection: Electronic Theses & Dissertations
Description: The studies in this dissertation are aimed at uncovering reactive and selective Ir-catalyzed C-H borylation (CHB) catalysts. Due to the high versatility of organoboron species, green methodology to produce the C-B bond is poised to support a myriad of subsequent transformations. These transformations include Suzuki couplings, aminations, oxidations, halogenations, cyanations, and trifluoromethylations.Typical iridium catalyzed CHBs proceed through an iridium trisboryl with a bidentate ligand...
Show moreThe studies in this dissertation are aimed at uncovering reactive and selective Ir-catalyzed C-H borylation (CHB) catalysts. Due to the high versatility of organoboron species, green methodology to produce the C-B bond is poised to support a myriad of subsequent transformations. These transformations include Suzuki couplings, aminations, oxidations, halogenations, cyanations, and trifluoromethylations.Typical iridium catalyzed CHBs proceed through an iridium trisboryl with a bidentate ligand such as bipyridine or 1,10-phenanthroline. The selectivity of these standard catalysts is generally driven by sterics; however, many methods of overcoming the steric bias have been developed in the two decades since the first thermal catalytic C-H activation borylation. These methods include both inner- and outer-sphere directed mechanisms. Outer-sphere directed borylations have been accomplished by leveraging hydrogen bonding, Lewis acid-base, and ion-pairing as directing elements. In general this reactivity is activated by precise design of the bidentate ligand framework.Herein is reported a subtle electrostatic interaction to direct ortho-borylation of phenols by simply switching boron source from the common B2pin2 (pin = pinacolate) to B2eg2 (eg = ethyleneglycolate). This electrostatic interaction was revealed by a careful computational analysis of key C-H activation transition states. Understanding gained by the computational studies led to the redesign of the boron source which enabled by selectivities of > 99% ortho borylation. This methodology was extended to the highly selective ortho-borylation of anilines, and the underlying mechanism has been interrogated.Currently, iridium based catalysts have been generated to borylate ortho, meta, and even para to a variety of classes of substrates; however, control of selectivity can breakdown in many fluorinated arenes without a directing group. These substrates are challenging because the fluoro moiety being similar in size to a hydrogen offers little in the way of steric bias. While working to overcome these challenges, a serendipitously discovered hydrazone based ligand was discovered. Exploration of the catalysts generated by this ligand revealed not only impressive activity rivaling dtbpy but also incredible selectivity for meta to a fluoro group.In general iridium CHB catalysts selectively activate sp2 C-H bonds leaving all sp3 C-H bonds intact; however, a method to turn on sp3 C-H activation would be desirable. It was reasoned that a directing group able to increase the effective concentration of the iridium catalyst near a C(sp3)-H bond may enable this transformation. Indeed, it was discovered that catalysts able to accept amide directing groups were able to selectively borylate compounds with amide N-methyl substituents.
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Title: Aerodynamic design and characterization of novel wound composite multistage counter-rotating axial compressors
Creator: Gower, Blake Ernest
Date: 2018
Collection: Electronic Theses & Dissertations
Description: ABSTRACTAERODYNAMIC DESIGN AND CHARACTERIZATION OF NOVEL WOUND COMPOSITE MULTISTAGE COUNTER-ROTATING AXIAL COMPRESSORSByBlake Ernest GowerThis thesis examines two different generations of axial compressor developed within the framework of the patented wound composite impeller technology created at Michigan State University. The technology itself allows for a departure from both the construction and operation of traditional single and multistage axial machines. Rather than using casting and...
Show moreABSTRACTAERODYNAMIC DESIGN AND CHARACTERIZATION OF NOVEL WOUND COMPOSITE MULTISTAGE COUNTER-ROTATING AXIAL COMPRESSORSByBlake Ernest GowerThis thesis examines two different generations of axial compressor developed within the framework of the patented wound composite impeller technology created at Michigan State University. The technology itself allows for a departure from both the construction and operation of traditional single and multistage axial machines. Rather than using casting and machining methods to produce the impellers, they are wound from carbon fiber or other fiber/matrix material on a mandrel with curved slots. Winding layer-by-layer in the axial direction builds the blades while simultaneously creating the outer (and inner) shroud(s). The winding technique ensures that the fibers are closely aligned with the forces associated with high speed rotation, thereby yielding a high strength, light weight composite rotor capable of operating in chemically aggressive environments once cured. Traditional multistage axial compressors typically have a single drive shaft and hence require unidirectional rotation at a single operating speed. Non-rotating stators are utilized between rotors to impose the appropriate velocity distribution at the subsequent rotor inlet. The stators however do not perform useful work in terms of boosting the total pressure, and they contribute substantially to the overall footprint of a multistage machine. The employment of counter-rotating stages serves to eliminate the need for all intermediate stators as they themselves impose the necessary velocity distribution for the subsequent rotor while simultaneously performing useful work. Counter-rotation can be achieved by integrating a permanent magnet motor with each rotor. Rotors can be mounted on a non-rotating shaft and can therefore be driven in opposite directions through the use of variable frequency drives.Initially developed for strength and ease of construction, a full geometric characterization of the first-generation “star pattern” impeller is performed and it is found that it operates under the forced-vortex flow regime. Reductions in terms of polytropic efficiency, mass flow rate, and total pressure ratio are seen from analytical prediction to numerical simulation, and again from simulation to experimental measurement. These reductions have led to the development of the second-generation impeller, which operates under the free-vortex flow regime.Enhanced performance of single stage second-generation impellers in numerical simulation has lead to a vast investigation matching geometrical parameters, rotational speeds, and flow velocities to best-point operating conditions for up to seven counter-rotating stages compressing initially saturated water vapor under vacuum pressure for 22 different inlet temperatures. Numerical simulations of select cases agree well with analytical predictions.For achieving maximum specific work transfer from the rotors to the working fluid, it is determined that the critical relative Mach number at each rotor tip should always be maximized. Hub/tip ratio at the first rotor inlet, aspect ratio, critical absolute Mach number, and turning angle are all temperature-dependent. The number of stages employed also has a large effect on how each rotor behaves (e.g. the second stage of a three stage machine looks and behaves differently from the second stage in a six stage machine), however utilizing an odd vs. an even number of total stages will have a much larger effect on inlet flow angle and the dimensionless flow coefficient, blade loading coefficient, and specific speed of each rotor. Seven other gas mixtures have been investigated in similar fashion and exhibit similar behavior. Overall, billions of designs have been evaluated and the best operating conditions are determined for each individual set of inlet conditions and number of stages used. This research lays the necessary ground work for multistage counter-rotating axial compressor construction.
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Title: Affective and cognitive responses to insects and other arthropods
Creator: Lorenz-Reaves, Amanda R.
Date: 2017
Collection: Electronic Theses & Dissertations
Description: "Insects are the most abundant and diverse group of animals on Earth. Though as a group they do far more ecological good than harm, previous studies have shown that human attitudes toward insects are mainly negative. Attitudes have affective (emotions) and cognitive (beliefs, mental representations) components that interact to influence behavior. Negative attitudes toward insects are associated with negative affect such as disgust and fear, and can have negative consequences, such as a lack...
Show more"Insects are the most abundant and diverse group of animals on Earth. Though as a group they do far more ecological good than harm, previous studies have shown that human attitudes toward insects are mainly negative. Attitudes have affective (emotions) and cognitive (beliefs, mental representations) components that interact to influence behavior. Negative attitudes toward insects are associated with negative affect such as disgust and fear, and can have negative consequences, such as a lack of conservation funding. In addition, negative attitudes can cause people to avoid insects and/or feel distress when insects are present, prompting a disconnection between the public and the insect world. To explore affective responses to insects, Chapter Two focuses on the emotion of disgust. Disgust is associated with avoidance of objects that cause sickness (e.g. rotten meat) or undesirable social conduct (e.g. moral disgust). Disgust is partitioned into distinct domains - pathogen, moral, sexual, etc. To determine whether disgust stimulated by insects belongs in a unique domain, incoming freshmen at a large public university were surveyed (Chapter Two). Survey items pertained to moral, pathogen, and insect-specific disgust. Factor analyses indicate that insect disgust and pathogen disgust are part of the same construct, unique from moral disgust. This implies that insects are perceived with the same feelings of disgust felt for pathogens. To explore cognition associated with insects, Chapter Three and Appendix One focus on mental models of insects and other arthropods. Mental models are internal representations of external entities that are used to reason, make inferences, conduct thought experiments, and anticipate future events. Drawings reflect important qualities of mental models including knowledge categorization and organization. Drawings of insects were collected from participants with high and low expertise in entomology. Salient insect features were indexed and principal components analysis applied to detect underlying patterns. Two distinct components emerged - (1) a non-winged "crawling" insect, and (2) a legless winged "flying" insect, implying that flying and crawling insects are perceived as distinct from each other (Chapter Three). A similar analysis of children's drawings of insects also showed a distinction between crawling and flying insects (Appendix One). Finally, to explore the interaction between affective and cognitive responses to insects, drawings of "disgusting" and "not disgusting" insects from participants sampled in Chapter Three were compared. Participants were also surveyed to gain a quantitative measure of disgust associated with insects. Experts exhibited significantly lower disgust responses than novices. Additionally, the inclusion of legs on drawings of insects deemed not disgusting correlated negatively with disgust. In contrast, the inclusion of legs on drawings of disgusting insects correlated positively with disgust. This suggests that crawling insects may be regarded as being more disgusting than flying insects. A multiple linear regression was conducted on the not disgusting insect drawings to determine whether drawing a crawling insect as well as one's expertise level, could predict insect-associated disgust. Approximately 35% of the variation in disgust was attributable to subject group (expertise) and the degree to which drawings aligned with the crawling insect model. In addition, this study also demonstrates that examining drawings of insects can be a useful tool to shed light on affect and cognition associated with insects."--Pages ii-iii.
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Title: African American athletes, actors, singers, peformers, and the anti-apartheid movement, 1948-1994
Creator: Jackson, Ronald L., 1970-
Date: 2018
Collection: Electronic Theses & Dissertations
Description: “African American Athletes, Actors, Singers, Performers and the Anti-Apartheid Movement, 1948-1994” is the first study to explore the multiple roles African American artists and athletes in the global struggle against apartheid in South Africa. As a transnational study, this dissertation pays attention to the multiple trans-Atlantic dialogues that occurred for over a century between African American entertainers and the people of South Africa. Based on archival sources in the United States...
Show more“African American Athletes, Actors, Singers, Performers and the Anti-Apartheid Movement, 1948-1994” is the first study to explore the multiple roles African American artists and athletes in the global struggle against apartheid in South Africa. As a transnational study, this dissertation pays attention to the multiple trans-Atlantic dialogues that occurred for over a century between African American entertainers and the people of South Africa. Based on archival sources in the United States and South Africa, it argues that many Black Americans in the popular culture industry used their celebrity status to galvanize support for a free South Africa, while others chose paths of accommodation, and, in some cases, collaborated with the Pretoria regime. African American singers, actors, musicians, boxers, golfers, and tennis players were often motivated, both intrinsically and extrinsically, by pan-African connections forged by an empathetic sense of a shared history of racial oppression endured by blacks in both the United States and South Africa during similar time periods. This study addresses questions about the African Diaspora that have not fully been addressed in previous studies. What factors prompted black American entertainers to join the anti-apartheid movement? Did anti-apartheid activists in South Africa consider the support of black American entertainers an essential component of the struggle? Why did some black American entertainers elect to ignore the cultural boycott and tour South Africa?
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Title: Africana women stories : mothering in African centered educational leadership
Creator: Caesar, Tiffany D.
Date: 2019
Collection: Electronic Theses & Dissertations
Description: "The current dissertation examines the stories of black women leaders in African Centered Education (ACE) in South Africa and Detroit using 'mothering' as a core theoretical framework to examine Black women's leadership globally. Pan-Africanism, African Centeredness, and womanism are theories within the study that provide a further understanding of their interwoven narratives. By focusing on the context, emergent themes, and aesthetic whole within a portraiture methodology -- the study hopes...
Show more"The current dissertation examines the stories of black women leaders in African Centered Education (ACE) in South Africa and Detroit using 'mothering' as a core theoretical framework to examine Black women's leadership globally. Pan-Africanism, African Centeredness, and womanism are theories within the study that provide a further understanding of their interwoven narratives. By focusing on the context, emergent themes, and aesthetic whole within a portraiture methodology -- the study hopes to shed light on what it refers to as 'Africana' women's stories. Distinctively, the dissertation study expands on the existing narrative of black women educators presenting them as leaders and using mothering as praxis by adding two originally researched elements - the experiences of black women leaders in African Centered Education and the current racialized and gendered transnational dialogue occurring between women in Detroit, Michigan and South Africa. 'Mothering' as praxis is mentioned throughout the experiences of black women educators (Baylor)(Gumbs)(Msila)(T. Karenga) (Hill-Brisbane) (Johnson L) (Johnson)(Collins). The concept essentially "involves valuing and of itself a commitment to the survival and thriving of other bodies" (Oka, 52). The role of the mother includes the ability to nurture, teach, mold, pass down culture, mentor, and support spiritual regeneration of our ancestors (T. Karenga) (Dove, 520) (Godono). With the current dissertation; these activities extended to 'emancipatory organizations, institutions, and social movements as is reflected in the history of the mothers of the freedom movements in this country and throughout the pan-African world' (Karenga)."--Pages ii-iii.
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Title: Agency in context : a phenomenological study of Chinese college lLearners' intercultural engagement with expatriate instructors
Creator: Larson, Jay B.
Date: 2017
Collection: Electronic Theses & Dissertations
Description: "As China increasingly internationalizes its higher education system, growing numbers of Chinese learners and expatriate instructors meet in the classroom, engaging one another from their disparate cultural and pedagogical standpoints. Despite its widespread occurrence, the phenomenon of Chinese learners and Western instructors engaging one another in pedagogically and culturally Chinese institutions is largely neglected in research. Scholarly literature on Chinese learners is dominated by...
Show more"As China increasingly internationalizes its higher education system, growing numbers of Chinese learners and expatriate instructors meet in the classroom, engaging one another from their disparate cultural and pedagogical standpoints. Despite its widespread occurrence, the phenomenon of Chinese learners and Western instructors engaging one another in pedagogically and culturally Chinese institutions is largely neglected in research. Scholarly literature on Chinese learners is dominated by studies of their experiences as international students on Western campuses. In Chinese environments, authors most often examine perspectives of expatriate instructors on their cultural adjustments. The voice of the Chinese learner in China is rarely heard in research. In this study, I turned a phenomenological lens toward 17 Chinese learners' lived experiences of intercultural classroom engagement at China's Southwest University. Drawing on works of Hall (1997a, 1997b), Said (1978), and Simmel (1971), I devised a Progression Model of Intercultural Engagement to frame participants' evolving perceptions of expatriate instructors as culturally foreign Others. I focused my analysis of learners' perceptions through three overlapping areas of inquiry: (a) learners' sense-making processes and management of intercultural teaching and learning; (b) their perceptions of the expatriate instructor as a physical, social, and cultural presence; and, (c) perceptions of expatriate instructor's course design and teaching. I collected data over a two-month period at Southwest University through methods including classroom observations, Chinese language participant essays, and English language interviews. Findings revealed learners exercised ownership and agency in interpreting and managing intercultural engagement with their instructors. Participants expressed ownership of a perceived physically, linguistically, and academically Chinese environment. Within that environment, they initially characterized expatriate instructor by foreign-ness. Learners made further sense of intercultural experience by situating their instructors' foreign-ness in constructed social, pedagogical, linguistic, and cultural roles. These roles assigned purpose to the expatriate instructor's foreign presence, and framed the meanings learners constructed from intercultural engagement. Finally, participants interpreted their relationships with written and spoken English through engagement with expatriate instructors perceived as social, pedagogical, and cultural embodiments of language. In sum, findings indicate perceived cultural context of the environment, and senses of ownership and agency learners exercised in this environment. These findings contribute to the academic dialogue on intercultural teaching and learning, not only in Chinese institutional contexts, but anywhere knowledge construction must bridge cultural assumptions, epistemologies, and pedagogies. This study can inform further inquiry into international learners on Western campuses, multinational classes in education hubs, and Western learners studying abroad. I address these applications, and others, as I conclude this dissertation with recommendations for practice, and implications for research and theory."--Pages ii-iii.
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Title: Alignment Control for Optical Communication between Underwater Robots
Creator: Solanki, Pratap Bhanu
Date: 2021
Collection: Electronic Theses & Dissertations
Description: Light-emitting diode (LED)-based optical communication is emerging as a promising low-power, low-cost, and high-data-rate alternative to acoustic communication for underwater applications. However, it requires a close-to-line-of-sight (LOS) link between the communicating parties.Achieving and maintaining the LOS is challenging due to the constant movement of underlying mobile platforms caused by propulsion and unwanted disturbances. In this dissertation, a novel, compact LED-based wireless...
Show moreLight-emitting diode (LED)-based optical communication is emerging as a promising low-power, low-cost, and high-data-rate alternative to acoustic communication for underwater applications. However, it requires a close-to-line-of-sight (LOS) link between the communicating parties.Achieving and maintaining the LOS is challenging due to the constant movement of underlying mobile platforms caused by propulsion and unwanted disturbances. In this dissertation, a novel, compact LED-based wireless communication system with active alignment control is presented that maintains the LOS despite the movement of the underlying platform. Multiple alignment control algorithms are developed for scenarios that range from a simple one-way two-dimensional (2D) setting to a practical three-dimensional (3D) bi-directional underwater setting. An extended Kalman filter (EKF)-based approach is first proposed to estimate the relative orientation between the heading angle and the LOS direction, which is subsequently used for alignment control. The EKF uses only the measurement of light intensity from a single photo-diode, where successive measurements are obtained via a scanning technique that ensures the full observability of the underlying system. The approach is first examined in a 2D setting, and then extended to the 3D scenario with improvements in both the hardware and the algorithm. The amplitude of the scanning is modulated according to the alignment performance to achieve a sound trade-off between estimation accuracy, signal strength, and energy consumption. The efficacy of the approach is tested and verified via simulation and on an experimental setup involving two robots with relative 3D motion. The EKF approach uses an assumption that the relative motion between the robots is small, and consequently, requires the communicating robots to take the scanning in an alternating fashion for the convergence of the estimator. An alternative approach, first explored in the 2D setting, is developed that allows simultaneous, bi-directional alignment control for both parties. Because of the convex nature of the measured intensity functions, model-free approaches, including both hill-climbing (HC) and extremum-seeking (ES), are explored. The hill-climbing approach is found to be superior to the ES approach in terms of convergence time and computational efficiency. Theoretical analysis is provided for the hill-climbing approach that guarantees finite time convergence to an $O(\delta)$ neighborhood of the LOS, for control step size $\delta$.Finally, a model-free approach for the 3D setting is proposed that maximizes light intensity based on three consecutive intensity measurements from an equilateral triangle configuration. The efficacy of the approach is demonstrated experimentally, first with an underwater robot controlled by a joystick via LED communication and then with two robots performing bi-directional communication and tracking in an underwater setting.
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Title: Allied studies on total sythesis of cyclic tripeptide TMC-95 via an iridium catalyzed borylation/deborylation strategy and teaching organic chemistry in "words"
Creator: Shen, Fangyi
Date: 2019
Collection: Electronic Theses & Dissertations
Description: Arylboronate esters are versatile synthetic building blocks. Iridium catalyzed C-H activation/borylation reactions are a green way of making such building blocks as these reactions often obviate the need for prior functionalization (e.g. halogenation), the use of pyrophoric reagents, cryogenic conditions, etc. Installation of multiple boron substituents about the starting arene and then Ir catalyzed selective deborylation of the individual borons can allow for the formation of an even greater...
Show moreArylboronate esters are versatile synthetic building blocks. Iridium catalyzed C-H activation/borylation reactions are a green way of making such building blocks as these reactions often obviate the need for prior functionalization (e.g. halogenation), the use of pyrophoric reagents, cryogenic conditions, etc. Installation of multiple boron substituents about the starting arene and then Ir catalyzed selective deborylation of the individual borons can allow for the formation of an even greater diversity of borylated building blocks.The regioselectivity of Ir-catalyzed borylation is usually driven by sterics, however heterocycles are known to borylated at positions that exhibit heightened C-H acidity through the influence of the heteroatom. The regioselective borylation attained with a tryptophan derivative has been utilized in the development of a novel convergent route to the TMC-95 core. While pursuing a model synthesis of this natural product, the ability of bismuth salts to catalyze deborylations was discovered. These bismuth salts mediated methods can be highly selective in the in the deborylation of di and triborylated indoles. Furthermore, bismuths compounds are safe and less expensive as compared to the Ir-catalysts that facilitated deborylation. Numerous screening experiments on both substrates and other metal salts afforded a better understanding of how these novel deborylations can be applied in various synthetic settings and provided insight into possible mechanisms.Also, while I was a teaching assistant and a fixed-term instructor during my graduate studies at Michigan State University, I gradually realized that teaching is my passion and I am prepared to start my independent career and be an independent thinking teacher for the organic chemistry area.Owing to the nature of the subject, organic chemistry can be very visually distracting, and the image can be overpowering during student's learning. Like it or not students will try memorization first, our hypothesis is that once they know the "organic transformation formula" in words, via memorization or any other method, then introducing them to the structures of these functional groups will come with added context, and once they make that jump from word to structure they will be in a better position to understand reaction mechanisms. More importantly, understanding those reaction mechanisms will enable the student to progress to more complex topics.By introducing functional group transformations without the "clutter" of structures, we predict that once structures are introduced students will prioritize what's important because they will have trained their minds to ask what is the functional group, not "where did I see that structure in my notes".In short, we aim to train students to focus their attention on the reactive functional group of an organic molecule by emphasizing the use of WORDS to describe functional group transformation and teach the organic chemistry as the second language.
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Title: An Experimental Study of the Steadily Plunging Airfoil in Uniform-Shear Flow
Creator: Albrecht, Mitchell Baxter
Date: 2022
Collection: Electronic Theses & Dissertations
Description: Freestream shear may be found in many unsteady aerodynamic situations, such as the fighter jet landing through the air wake of an aircraft carrier and the micro air vehicle (MAV) navigating wind currents around buildings in urban environments. Despite the prevalence of shear in aeronautics, literature concerning its effects on unsteady airfoils is scarce. To address the need to understand the fundamental, complex aerodynamics of moving airfoils coupled with freestream shear, a novel...
Show moreFreestream shear may be found in many unsteady aerodynamic situations, such as the fighter jet landing through the air wake of an aircraft carrier and the micro air vehicle (MAV) navigating wind currents around buildings in urban environments. Despite the prevalence of shear in aeronautics, literature concerning its effects on unsteady airfoils is scarce. To address the need to understand the fundamental, complex aerodynamics of moving airfoils coupled with freestream shear, a novel experimental setup was implemented to investigate the case of the airfoil steadily plunging across a canonical uniform-shear approach flow in a water tunnel. The effect of unsteadiness on the NACA 0012 airfoil in shear is examined by using a servo motion system to plunge the airfoil from the high- to low-speed extremes of the shear zone and varying the steady plunge speed. The aerodynamic load (lift and drag coefficients), streamwise velocity component of the flow, separation and reattachment locations, and boundary layer thickness are characterized such that the flow measurements are correlated to the observed behavior of the load measurements. First, uniform flow measurements are performed that confirm the unique experimental setup reproduces the expected Galilean transformation between the stationary and steadily plunging airfoils. It is confirmed that minimal blockage, confinement, or other artifacts result from the airfoil traversing over a large fraction of the test section's width. Molecular tagging velocimetry is uniquely implemented such that tag lines are created over the entire airfoil surface, image pairs are formed with the entire airfoil in view, and flow measurements are enabled for the moving airfoil. The airfoil aerodynamics are characterized in uniform flow at the same Reynolds numbers of the shear flow at three primary cross-stream locations of interest to provide baselines for the measurements in shear. For Reynolds numbers 13,500 and 16,500, a multi-region behavior is observed in the slope of the lift coefficient curve where the observed rapid rise in lift is related to the flow switching from an open separation to a closed separation bubble. By contrast, a steady rise in lift is observed at Reynolds number 9,800 which correlates to only open separation being observed.Next, the basic effect of shear on the stationary airfoil is studied by placing the airfoil at the three primary cross-stream locations in the shear flow, which also provides baseline measurements for the plunging airfoil in shear. It is observed that the current study reproduces the negative lift at zero angle of attack that is opposite of inviscid theory but consistent with recent computational and experimental literature from our group. A common observation in the lift and drag coefficient curves for the stationary airfoil in shear is asymmetry, as exemplified by the different stall behavior between positive and negative angles of attack. A multi-region behavior is observed among the lift curves which is connected to the airfoil switching from open separation to a closed separation bubble, like for uniform flow. Except for the Reynolds number 13,500 case, there is no observed difference in the angle of attack at which the flow switches from open separation to a closed separation bubble in shear compared to uniform flow. For the highest shear, lowest Reynolds number case, only open separation is observed at positive angles of attack, like the corresponding results in uniform flow.Finally, the effect of the steadily plunging airfoil motion in shear is studied in comparison with its stationary airfoil counterpart. For the range of dimensionless shear rates (0.40-0.69) and chord Reynolds numbers (9,800-16,500) in this study, it is observed that the slope of the lift coefficient curve for the plunging airfoil begins to rapidly increase at lower effective angle of attack than for the stationary airfoil, which is found to be a result of the flow reattaching at a lower effective angle of attack for the former than for the latter. Near stall, the magnitude of the lift coefficient on the plunging airfoil is typically greater than that on the stationary airfoil, which is found to be related to the reattachment point occurring farther upstream for the former than for the latter. It is found that the airfoil must plunge as slowly as 1% of the freestream speed for the load on the plunging airfoil to be well-approximated by that on the stationary airfoil for the same effective angle of attack and freestream conditions.
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Title: An accurate, efficient, and robust fingerprint presentation attack detector
Creator: Chugh, Tarang
Date: 2020
Collection: Electronic Theses & Dissertations
Description: The individuality and persistence of fingerprints is being leveraged for a plethora of day-to-day automated person recognition applications, ranging from social benefits disbursements and unlocking smartphones to law enforcement and border security. While the primary purpose of a fingerprint recognition system is to ensure reliable and accurate user recognition, the security of the system itself can be jeopardized by the use of fingerprint presentation attacks (PAs). A fingerprint PA is...
Show moreThe individuality and persistence of fingerprints is being leveraged for a plethora of day-to-day automated person recognition applications, ranging from social benefits disbursements and unlocking smartphones to law enforcement and border security. While the primary purpose of a fingerprint recognition system is to ensure reliable and accurate user recognition, the security of the system itself can be jeopardized by the use of fingerprint presentation attacks (PAs). A fingerprint PA is defined as a presentation, of a spoof (fake), altered, or cadaver finger, to the data capture system (fingerprint reader) intended to interfere with the recording of the true fingerprint sample/identity, and thereby preventing correct user recognition.In this thesis, we present an automated, accurate, and reliable software-only fingerprint presentation attack detector (PAD), called Fingerprint Spoof Buster. Specifically, we propose a deep convolutional neural network (CNN) based approach utilizing local patches centered and aligned using fingerprint minutiae. The proposed PAD achieves state-of-the-art performance on publicly available liveness detection databases (LivDet) and large-scale government controlled tests as part of the IARPA ODIN program. Additionally, we present a graphical user interface that highlights local regions of the fingerprint image as bonafide or PA for visual examination. This offers significant advantage over existing PAD solutions that rely on a single spoof score for the entire fingerprint image.Deep learning-based solutions are infamously resource intensive (both memory and processing) and require special hardware such as graphical processing units (GPUs). With the goal of real-time inference in low-resource environments, such as smartphones and embedded devices, we propose a series of optimizations including simplifying the network architecture and quantizing model weights (for byte computations instead of floating point arithmetic). These optimizations enabled us to develop a light-weight version of the PAD, called Fingerprint Spoof Buster Lite, as an Android application, which can execute on a commodity smartphone (Samsung Galaxy S8) with a minimal drop in PAD performance (from TDR = 95.7% to 95.3% FDR = 0.2%) in under 100ms.Typically, deep learning-based solutions are considered as "black-box" systems due to the lack of interpretability of their decisions. One of the major limitations of the existing PAD solutions is their poor generalization against PA materials not seen during training. While it is observed that some materials are easier to detect (e.g. EcoFlex) compared to others (e.g. Silgum) when left out from training, the underlying reasons are unknown. We present a framework to understand and interpret the generalization (cross-material) performance of the proposed PAD by investigating the material properties and visualizing the bonafide and PA samples in the multidimensional feature space learned by deep networks. Furthermore, we present two different approaches to improve the generalization performance: (i) a style transfer-based wrapper, called Universal Material Generator (UMG), and (ii) a dynamic approach utilizing temporal analysis of a sequence of fingerprint image frames. The two proposed approaches are shown to significantly improve the generalization performance evaluated on large databases of bonafide and PA samples.Lastly, fingerprint readers based on conventional imaging technologies, such as optical, capacitive, and thermal, only image the 2D surface fingerprint making them an easy target for presentation attacks. In contrast, Optical Coherent Tomography (OCT) imaging technology provides rich depth information, including the internal fingerprint, eccrine (sweat) glands, as well as PA instruments (spoofs) placed over finger skin. As a final contribution, we present an automated PAD approach utilizing cross-sectional OCT depth profile scans which is shown to achieve a TDR of 99.73% FDR of 0.2% on a database of 3,413 bonafide and 357 PA OCT scans, fabricated using 8 different PA materials. We also identify the crucial regions in the OCT scans necessary for PA detection.
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Title: An agent model of vertical integration in telecommunications and content
Creator: Koning, Kendall Jay
Date: 2017
Collection: Electronic Theses & Dissertations
Description: "This dissertation explores several important telecommunications policy issues in light of recent developments in the wireline broadband and online video markets." -- Abstract.

Title: An analysis of content knowledge and cognitive abilities as factors that are associated with algebra performance
Creator: McLean, Tamika Ann
Date: 2017
Collection: Electronic Theses & Dissertations
Description: "The current study investigated college students' content knowledge and cognitive abilities as factors associated with their algebra performance, and examined how combinations of content knowledge and cognitive abilities related to their algebra performance. Specifically, the investigation examined the content knowledge factors of computational fluency, numeracy skills, fraction knowledge, understanding of equivalence, and algebraic reasoning skills, and the cognitive abilities of spatial...
Show more"The current study investigated college students' content knowledge and cognitive abilities as factors associated with their algebra performance, and examined how combinations of content knowledge and cognitive abilities related to their algebra performance. Specifically, the investigation examined the content knowledge factors of computational fluency, numeracy skills, fraction knowledge, understanding of equivalence, and algebraic reasoning skills, and the cognitive abilities of spatial visualization, crystallized intelligence, and fluid intelligence. A multiple regression analysis found that while controlling for gender, the highest math course taken, and the number of years since an algebra course, fraction knowledge and the spatial visualization ability of spatial imagery were statistically significant predictors of algebra performance along with the control variable identifying whether or not participants had taken at least one calculus course. In addition, cluster analysis identified six content knowledge and cognitive ability profiles, with varying levels of both content knowledge and cognitive abilities observed across the six clusters. The six profiles - characterized as Low All, Moderate-Low All, Moderate-High MASMI, Moderate-Low Spatial, Moderate-High All, and High Spatial - varied somewhat in terms of their algebra performance scores. In particular, the participants in the High Spatial cluster group and participants in the Moderate-High All cluster group had similarly high algebra performance scores, which were significantly higher than performances scores observed for participants in the other cluster groups. Additionally, the participants in the other cluster groups exhibited similar low algebra performance scores to each other except for participants in the in the Moderate-Low Spatial and Low All cluster groups. Participants in the Moderate-Low Spatial cluster group had significantly higher algebra performance scores than participants in the Low All cluster group. The differences in algebra performance scores among cluster groups suggested that the observation of higher algebra performance occurred when participants had strong spatial visualization skills, strong fluid intelligence skills, and high content knowledge or when participants had strong fraction knowledge, numeracy skills, algebraic reasoning skills, and spatial imagery skills."--Pages ii-iii.
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Title: An assessment of protective factors in predicting juvenile reoffending
Creator: Barnes, Ashlee R.
Date: 2017
Collection: Electronic Theses & Dissertations
Description: Juvenile court practitioners use risk assessment to evaluate level of risk and criminogenic areas of need to determine the most appropriate consequence for young offenders, and to determine goals for case planning. Recently, juvenile court practitioners and researchers have gained interest in evaluating young offenders' internal and external strengths, or protective factors. Some scholars assert that incorporating measures of protective factors into the risk assessment process can increase...
Show moreJuvenile court practitioners use risk assessment to evaluate level of risk and criminogenic areas of need to determine the most appropriate consequence for young offenders, and to determine goals for case planning. Recently, juvenile court practitioners and researchers have gained interest in evaluating young offenders' internal and external strengths, or protective factors. Some scholars assert that incorporating measures of protective factors into the risk assessment process can increase the accuracy of identifying young offenders' odds of recidivating. Relatively few juvenile risk assessment validation studies have evaluated the predictive validity of protective factor items. Moreover, protective factor items that are included in many existing risk assessment tools are narrow in scope, particularly within family-, school-, and community-level protective factor domains. The current study examined the relationship between protective factors and recidivism for 278 young probationers from a Midwestern juvenile county court. The study was conducted in two parts. First, a strengths-based measure of risk of recidivism (Protective Factors for Reducing Juvenile Reoffending, PFRJR) was created and its factor structure and reliability was evaluated. Second, the predictive validity, incremental validity, and differential predictive validity of the PFRJR were examined. In the first study, the author identified two factors, Individual/Community and Family/Social; both subscales demonstrated strong internal consistency. In the second study, the author found no significant differences in mean level composite protective factor scores across gender, however African American offenders had significantly lower protective factor scores than White offenders. The PFRJR significantly predicted recidivism and time-to-recidivism, and produced AUC effect sizes that ranged from small to large for the total sample and across young offender subgroups. The author did not find evidence of differential predictive validity across gender, however the author found differential predictive validity by race/ethnicity. Regarding the incremental validity of protective factor scores, the PFRJR composite scores did not increase the amount of variance explained in recidivism after accounting for the variance explained by composite risk factor scores (as measured by the Youth Level of Service/Case Management Inventory). Broadly, the current study highlights the feasibility of integrating a complementary strengths-based measure into traditional risk assessment procedures. Findings from the current study also contributed to the paucity of risk assessment validation studies that emphasized the predictive validity of protective factor scores.
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Title: An ecological exploration of sport specialization pathways
Creator: DiSanti, Justin S.
Date: 2019
Collection: Electronic Theses & Dissertations
Description: Youth sport specialization has been a sustained area of interest in academic and practical settings. Though preliminary findings of the relationship between athletes' pathways of sport participation and their sport outcomes posit early specialization in a single sport as potentially harmful to an athlete's physical and psychological well-being, concern that athletes are specializing earlier, and to a greater degree, than ever before remains pervasive. In analyzing potential explanations for...
Show moreYouth sport specialization has been a sustained area of interest in academic and practical settings. Though preliminary findings of the relationship between athletes' pathways of sport participation and their sport outcomes posit early specialization in a single sport as potentially harmful to an athlete's physical and psychological well-being, concern that athletes are specializing earlier, and to a greater degree, than ever before remains pervasive. In analyzing potential explanations for this logical gap between recommendations and perceived behaviors, one notable gap of the literature is the lack of ecological, systems-based research that may better clarify what drives athletes to specialize in a single sport. In this study, a developmental, ecological, perception-based approach was used to explore youth athletes' pathways of sport participation (specifically, why they chose to specialize or play multiple sports) in relation to their ecological characteristics and subsequent sport experiences. To do so, a conceptual, ecological framework was developed to inform the design of this study, and the nature and strength of relationships between variables of this novel heuristic provided an initial understanding of the ecology of sport participation pathways. 132 current high school athletes participated in this study's testing battery, which surveyed elements of their sport participation, personal and contextual characteristics, their sport specialization behaviors and perceptions, and their expectations and subsequent experiences related to their chosen pathway. Results of this study highlighted several significant group differences and relationships between variables, and due to the exploratory nature of this study the non-significant findings also served as a hypothesis-generating mechanism for future research. Implications of these findings were explored in their relation to previous sport specialization literature and the study's guiding theoretical framework (i.e., the Developmental Model of Sport Participation and the Person-Process-Context-Time Ecological Model), and the results underscored the importance of accounting for the influence of context and competitive climate in understanding youth athletes' selected sport pathways and subsequent experiences.
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Title: An experimental parametric study on the efficiency of hybrid fastening system
Creator: Ramli, Salina
Date: 2020
Collection: Electronic Theses & Dissertations
Description: As the use of fiber-reinforced polymer composites in mass-produced structural components in all domains of industry has grown, appropriate advancements in joining systems are necessary. Bolted joints are a common method used due to the simplicity of the process. Drilling holes in composites for fastening results in delamination, creation of locations for the onset of failure, and can reduce load-carrying capacities. Hybrid fastening techniques and other approaches for joining composite...
Show moreAs the use of fiber-reinforced polymer composites in mass-produced structural components in all domains of industry has grown, appropriate advancements in joining systems are necessary. Bolted joints are a common method used due to the simplicity of the process. Drilling holes in composites for fastening results in delamination, creation of locations for the onset of failure, and can reduce load-carrying capacities. Hybrid fastening techniques and other approaches for joining composite materials have been developed as a way to address problems related to conventional bolted joints. One such technique is the hybrid fastening system in which a structural adhesive insert is placed in the bolt-hole clearance. This approach has been shown to eliminate bolt-adherend slip, reduce delamination, and increase load-bearing capacities. Nevertheless, the extant work on such a hybrid fastening system is limited. In this work, experimental characterizations of hybrid fastening systems comprised of glass fiber reinforced polymer (GFRP) composite substrates fastened using a fully threaded grade 5 steel bolts in 1/2" (12.5 mm.) diameter with varying bolt hole clearance and three structural insert materials were performed. The GFRP substrates were manufactured using the vacuum-assisted resin transfer molding (VARTM) process. The preload was maintained at 75% of the bolt yield strength for all joints. The objective of this work was to characterize/quantify the effect of: a) the adhesive insert and b) the bolt-hole clearances on the efficiency of the hybrid fastening system. For the first parameter, namely the effect of the adhesive insert, four configurations, namely the hybrid fastening system with three different structural insert materials and one control/conventional joint without any structural insert were studied. Adhesive insert materials used were PRO-SET epoxy resin, DEVCON epoxy carrying aluminum particles, and polyurethane. All resulting joints were cured at room temperature for 48h prior to testing. For the second parameter, namely the effect of bolt clearance, four different bolt-hole clearances: close fit (0.5mm), normal fit (1.0 mm.), loose fit (1.5 mm.), and extra loose fit (2.0 mm.) were studied for each of the insert materials along with the control/conventional joint without any structural insert. The resulting joints were tested in a tensile-shear configuration at a rate of 5 mm./min. Hybrid joints were found to have 7 to 9 times higher load carrying capacities relative to slip-loads for conventional joints. All hybrid fastening systems showed no bolt-adherend slip along with delayed onset of delamination relative to conventional joints. Most of the joints with close fit (0.5mm) clearance were found to experience a catastrophic failure which resulted in bolt shearing failure. All other joints experienced progressive delamination failure without any bolt-shear failures. Further, the results indicate that the failure mechanism changed with the changes of bolt-hole clearances. The larger the clearances, the more the bolt tilts/rotates and experiences a combination of bending and shear. For small clearances, such as close-fit, shear dominates and bolt-shear occurs leading to bolt fracture. The combination of slightly larger clearance along with a structural adhesive insert allows tailoring the bolt- joint performance, leading to 7-9 times better performance than conventional joints with similar clearances. Future work should focus on quantifying the stress-concentrations and its reductions due to the addition of structural inserts. Overall, this work is novel and the first to report on the effect on clearance and varying adhesive insert materials for hybrid mechanical joints.
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Title: An exploration of mid- to high-valent transition metal complexes for application to catalysis
Creator: Aldrich, Kelly E.
Date: 2019
Collection: Electronic Theses & Dissertations
Description: "The valency or oxidation state of a transition metal in a complex plays a large role in determining the reactivity of the complex. With transition metal chemistry, historically accessible chemistry has often focused on metals in a low oxidation state. However, transformations involving transition metals in high oxidation states are of equal importance in providing complex products for use in consumer products. Expanding the applications and understanding of transition metal complexes in high...
Show more"The valency or oxidation state of a transition metal in a complex plays a large role in determining the reactivity of the complex. With transition metal chemistry, historically accessible chemistry has often focused on metals in a low oxidation state. However, transformations involving transition metals in high oxidation states are of equal importance in providing complex products for use in consumer products. Expanding the applications and understanding of transition metal complexes in high oxidation states is the focus of the research presented in this dissertation. Fundamental studies of how ligands interact with high valent metals is presented in chapters 2 and 3, where a chromium(VI) model complex has been used to study bonding interactions between this d0 transition metal and phosphine ligands. Practical application of high valent titanium(IV) catalysts to C--N bond forming reactions is presented in chapters 4--6. Finally, chapters 7 and 8 focus on the changes in the character of M--N double bonds, with M=Fe and Ru, as the metal is forced to higher oxidation states. Collectively, these studies demonstrate different approaches to the same general problems and questions of how chemists can better understand and utilize high valent transitions metals to do catalytically-target desired transformations."--Page ii.
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