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Description
Functional materials can be characterized as materials that have tunable properties and are attractive solutions to the improvement and optimization of processes that require specific physiochemical characteristics. Through tailoring and altering these materials, their characteristics can be fine-tuned for specific applications. Computational modeling proves to be a crucial methodology in the design and optimization of such materials. This dissertation encompasses the utilization of molecular dynamics simulations and quantum calculations in two fields of functional materials: electrolytes and semiconductors. Molecular dynamics (MD) simulations were performed on ionic liquid-based electrolyte systems to identify molecular interactions, structural changes, and transport properties that are often reflected in experimental results. The simulations aid in the development process of the electrolyte systems in terms of concentrations of the constituents and can be invoked as a complementary or predictive tool to laboratory experiments. The theme of this study stretches further to include computational studies of the reactivity of atomic layer deposition (ALD) precursors. Selected aminosilane-based precursors were chosen to undergo density functional theory (DFT) calculations to determine surface reactivity and viability in an industrial setting. The calculations were expanded to include the testing of a semi-empirical tight binding program to predict growth per cycle and precursor reactivity with a high surface coverage model. Overall, the implementation of computational methodologies and techniques within these applications improves materials design and process efficiency while streamlining the development of new functional materials.
ContributorsGliege, Marisa Elise (Author) / Dai, Lenore (Thesis advisor) / Derecskei-Kovacs, Agnes (Thesis advisor) / Muhich, Christopher (Committee member) / Emady, Heather (Committee member) / Zhuang, Houlong (Committee member) / Arizona State University (Publisher)
Created2021
Description
This research presents advances in time-synchronized phasor (i.e.,synchrophasor) estimation and imaging with very-low-frequency electric fields.
Phasor measurement units measure and track dynamic systems, often power
systems, using synchrophasor estimation algorithms. Two improvements to
subspace-based synchrophasor estimation algorithms are shown. The first
improvement is a dynamic thresholding method for accurately determining the
signal subspace when using the estimation of signal parameters via rotational
invariance techniques (ESPRIT) algorithm. This improvement facilitates
accurate ESPRIT-based frequency estimates of both the nominal system frequency
and the frequencies of interfering signals such as harmonics or out-of-band
interference signals. Proper frequency estimation of all signals present in
measurement data allows for accurate least squares estimates of synchrophasors
for the nominal system frequency. By including the effects of clutter signals
in the synchrophasor estimate, interference from clutter signals can be
excluded. The result is near-flat estimation error during nominal system
frequency changes, the presence of harmonic distortion, and out-of-band
interference. The second improvement reduces the computational burden of the
ESPRIT frequency estimation step by showing that an optimized Eigenvalue
decomposition of the measurement data can be used instead of a singular value
decomposition. This research also explores a deep-learning-based inversion
method for imaging objects with a uniform electric field and a 2D planar D-dot
array. Using electric fields as an illumination source has seen multiple
applications ranging from medical imaging to mineral deposit detection. It is
shown that a planar D-dot array and deep neural network can reconstruct the
electrical properties of randomized objects. A 16000-sample dataset of objects
comprised of a three-by-three grid of randomized dielectric constants was
generated to train a deep neural network for predicting these dielectric
constants from measured field distortions. Increasingly complex imaging
environments are simulated, ranging from objects in free space to objects
placed in a physical cage designed to produce uniform electric fields.
Finally, this research relaxes the uniform electric field constraint, showing
that the volume of an opaque container can be imaged with a copper tube antenna
and a 1x4 array of D-dot sensors. Real world experimental results
show that it is possible to image buckets of water (targets) within a plastic
shed These experiments explore the detectability of targets as a function of
target placement within the shed.
ContributorsDrummond, Zachary (Author) / Allee, David R (Thesis advisor) / Claytor, Kevin E (Committee member) / Papandreou-Suppappola, Antonia (Committee member) / Aberle, James (Committee member) / Arizona State University (Publisher)
Created2021
Description
Nanocrystalline (NC) materials are of great interest to researchers due to their multitude of properties such as exceptional strength and radiation resistance owing to their high fraction of grain boundaries that act as defect sinks for radiation-induced defects, provided they are microstructurally stable. In this dissertation, radiation effects in microstructurally stable bulk NC copper (Cu)- tantalum (Ta) alloys engineered with uniformly dispersed Ta nano-precipitates are systematically probed. Towards this, both ex-situ and in-situ irradiations using heavy (self) ion, helium ion, and concurrent dual ion beams (He+Au) followed by isochronal annealing inside TEM were utilized to understand radiation tolerance and underlying mechanisms of microstructure evolution in stable NC alloys. With systematic self-ion irradiation, the high density of tantalum nanoclusters in Cu-10at.%Ta were observed to act as stable sinks in suppressing radiation hardening, in addition to stabilizing the grain boundaries; while the large incoherent precipitates experienced ballistic mixing and dissolution at high doses. Interestingly, the alloy exhibited a microstructure self-healing mechanism, where with a moderate thermal input, this dissolved tantalum eventually re-precipitated, thus replenishing the sink density. The high stability of these tantalum nanoclusters is attributed to the high positive enthalpy of mixing of tantalum in copper which also acted as a critical driving force against atomic mixing to facilitate re-precipitation of tantalum nanoclusters. Furthermore, these nanoclusters proved to be effective trapping sites for helium, thus sequestering helium into isolated small bubbles and aid in increasing the overall swelling threshold of the alloy. The alloy was then compositionally optimized to reduce the density of large incoherent precipitates without compromising on the grain size and nanocluster density (Cu-3at.%Ta) which resulted in a consistent and more promising response to high dose self-ion irradiation. In-situ helium and dual beam irradiation coupled with isochronal annealing till 723 K, also revealed a comparable microstructural stability and enhanced ability of Cu-3Ta in controlling bubble growth and suppressing swelling compared to Cu-10Ta indicating a promising improvement in radiation tolerance in the optimized composition. Overall, this work helps advancing the current understanding of radiation tolerance in stable nanocrystalline alloys and aid developing design strategies for engineering radiation tolerant materials with stable interfaces.
ContributorsSrinivasan, Soundarya (Author) / Solanki, Kiran (Thesis advisor) / Peralta, Pedro (Committee member) / Alford, Terry (Committee member) / Darling, Kristopher (Committee member) / Arizona State University (Publisher)
Created2021
Description
Physical activity (PA) has been shown to increase cognitive function, with higher test scores being reported for students engaged in higher levels PA. Additionally, the integration of the Common Core content into physical education allows for more Common Core content practice while students meet physical education objectives. Integration can be defined as the teaching of two or more subject areas simultaneously to enhance students’ learning and understanding. This novel shift to integration is underpinned by Fullan’s Change Theory where students may learn content in new and meaningful ways that meet the goals of multiple realms in education. The purpose of this crossover, replication design study was to investigate first-grade students’ enjoyment levels (enjoyment exit slips), attitudes (pre- & post-surveys), step counts (accelerometers), reading and listening comprehension (Accelerated Reader testing), as well as students’ and teachers’ perceptions (interviews & field notes) when integrating children’s literature into the fitness segment of physical education. Twenty-one first-grade students, two first-grade classroom teachers, and two physical education teachers from two different schools (Private and Public) in Southwestern, US participated in this study for six weeks each (12 weeks across the two schools). At each school, one first grade class participated as both the control and intervention groups. Overall, the results from integrating children’s literature into the physical education fitness segment were positive. Students’ enjoyment levels were high, their attitudes remained positive, they maintained similar step counts throughout the intervention periods, and the students scored similarly on the Accelerated Reader assessments from content taught in the classroom versus content presented in physical education. Additionally, students’ and teachers’ perceptions were positive, underpinned by Fullan’s Change Theory and resulted in the following three themes for students: (a) Motivation and engagement, (b) learning as perceived by students, and (c) home environment, as well as the following two themes for teachers: (a) Motivation and resources, and (b) stay the course. To my knowledge, this is the first experimental investigation of the integration of children’s literature into physical education which provides necessary evidence and an invaluable start to this important line of inquiry.
ContributorsGriffo, Janelle Marie (Author) / Kulinna, Pamela H. (Thesis advisor) / Van Der Mars, Hans (Committee member) / Marttinen, Risto H.J. (Committee member) / Johnston, Kelly (Committee member) / Moses, Lindsey (Committee member) / Arizona State University (Publisher)
Created2021
"It's Always A Part Of You and Aloha ʻĀina": Sacred Spaces and Indigenous/Aboriginal People’s Health
Description
Background: Indigenous/Aboriginal People (IAP) since the beginning of colonization have fought for their inherent rights to follow their way of life. They continue to face mistreatment for their beliefs and on the sacred spaces that are apart of them. The purpose of this dissertation is to share how the desecration of sacred spaces impacts Indigenous/Aboriginal Peoples’ health. Two research studies were designed to better understand how Indigenous/Aboriginal Peoples’ health is affected when their sacred spaces are desecrated. Methods: The first research study was conducted in Arizona, and Hawaiʻi with eight participants who are members of American Indian nations and Kanaka Maoli (Native Hawaiian). The first study focused on sacred spaces in general, with some additional focus on the San Francisco Peaks (Nuvtukya’ovi in Hopi) and Mauna A Wākea. The second study was conducted virtually with seven Kanaka Maoli (Native Hawaiians) and focused solely on Mauna a Wākea. Qualitative data collection was through key informant interviews. Qualitative data analysis centered on a thematic analysis characterizing sacred spaces, and the ways in which participants explained how different forms of sacred space desecration impact IAP health. The analysis included the relationship IAP have with sacred spaces, and how their health is connected to sacred spaces. Results: The first qualitative study found that desecrating sacred spaces negatively impacts Indigenous/Aboriginal Peoples’ cultural identity and health. The second study found that participants are connected to sacred spaces, including having a loving relationship with and responsibility to sacred spaces. Conclusions: The conclusions from the study show that Indigenous/Aboriginal Peoples’ health is negatively impacted when their sacred spaces are desecrated, because their relationship to the sacred space is a part of their cultural identity. IAP’s relationship with sacred spaces is one filled with love and the responsibility to care for them. Sacred spaces also heal and maintain IAP health. For the future public health implications, laws and policies need to be upheld and created to protect IAP’s health rights and their sacred spaces.
ContributorsCooper, Danelle (Author) / SturtzSreetharan, Cindi (Thesis advisor) / Wutich, Amber (Thesis advisor) / Riding In, James (Committee member) / Taualiʻi, Maile (Committee member) / Arizona State University (Publisher)
Created2021
Description
Color perception has been widely studied and well modeled with respect to combining visible electromagnetic frequencies, yet new technology provides the means to better explore and test novel temporal frequency characteristics of color perception. Experiment 1 tests how reliably participants categorize static spectral rainbow colors, which can be a useful tool for efficiently identifying those with functional dichromacy, trichromacy, and tetrachromacy. The findings confirm that all individuals discern the four principal opponent process colors, red, yellow, green, and blue, with normal and potential tetrachromats seeing more distinct colors than color blind individuals. Experiment 2 tests the moving flicker fusion rate of the central electromagnetic frequencies within each color category found in Experiment 1 as a test of the Where system. It then compares this to the maximum temporal processing rate for discriminating direction of hue change with colors displayed serially as a test of the What system. The findings confirm respective processing thresholds of about 20 Hz for Where and 2-7 Hz for What processing systems. Experiment 3 tests conditions that optimize false colors based on the spinning Benham’s Top illusion. Findings indicate the same four principal colors emerge as in Experiment 1, but at low saturation levels for trichromats that diminish further for dichromats. Taken together, the three experiments provide an overview of the common categorical boundaries and temporal processing limits of human color vision.
ContributorsKrynen, Richard Chandler (Author) / Mcbeath, Michael K (Thesis advisor) / Homa, Donald (Committee member) / Newman, Nathan (Committee member) / Stone, Greg (Committee member) / Arizona State University (Publisher)
Created2021
Description
This thesis explores several questions concerning the preservation of geometric structure under the Ricci flow, an evolution equation for Riemannian metrics. Within the class of complete solutions with bounded curvature, short-time existence and uniqueness of solutions guarantee that symmetries and many other geometric features are preserved along the flow. However, much less is known about the analytic and geometric properties of solutions of potentially unbounded curvature. The first part of this thesis contains a proof that the full holonomy group is preserved, up to isomorphism, forward and backward in time. The argument reduces the problem to the preservation of reduced holonomy via an analysis of the equation satisfied by parallel translation around a loop with respect to the evolving metric. The subsequent chapter examines solutions satisfying a certain instantaneous, but nonuniform, curvature bound, and shows that when such solutions split as a product initially, they will continue to split for all time. This problem is encoded as one of uniqueness for an auxiliary system constructed from a family of time-dependent, orthogonal distributions of the tangent bundle. The final section presents some details of an ongoing project concerning the uniqueness of asymptotically product gradient shrinking Ricci solitons, including the construction of a certain system of mixed differential inequalities which measures the extent to which such a soliton fails to split.
ContributorsCook, Mary (Author) / Kotschwar, Brett (Thesis advisor) / Paupert, Julien (Committee member) / Kawski, Matthias (Committee member) / Kaliszewski, Steven (Committee member) / Fishel, Susanna (Committee member) / Arizona State University (Publisher)
Created2021
Description
Platform business models have become pervasive in many aspects of the economy,particularly in the areas experiencing rapid growth such as retailing (e.g., Amazon and
eBay) and last-mile transportation (e.g., Instacart and Amazon Flex). The popularity
of platform business models is, in part, due to the asset-light prospect which allows
businesses to maintain flexibility while scaling up their operations. Yet, this ease of
growth may not necessarily be conducive to viable outcomes. Because scalability in a
platform depends on the intermediary’s role it plays in facilitating matching between
users on each side of the platform, the efficiency of matching could be eroded as growth
increases search frictions and matching costs. This phenomenon is demonstrated in
recent studies on platform growth (e.g. Fradkin, 2017; Lian and Van Ryzin, 2021; Li
and Netessine, 2020). To sustain scalability during growth, platforms must rely on effective platformdesign to mitigate challenges arising in facilitating efficient matching. Market design
differs in its focus between retail and last-mile transportation platforms. In retail
platforms, platform design’s emphasis is on helping consumers navigate through
a variety of product offerings to match their needs while connecting vendors to a
large consumer base (Dinerstein et al., 2018; Bimpikis et al., 2020). Because these
platforms exist to manage two-sided demand, scalability depends on the realization of
indirect network economies where benefits for users to participate on the platforms
are commensurate with the size of users on the other side (Parker and Van Alstyne,
2005; Armstrong, 2006; Rysman, 2009). Thus, platform design plays a critical role in
the realization of indirect network economies on retail platforms. Last-mile transportation platforms manage independent drivers on one side andretailers on the other, both parties holding flexibility in switching between platforms.
High demand for independent drivers along with their flexibility in work participation induces platforms to use subsidies to incentivize retention. This leads to short-term
improvements in retention at the expense of significant increases in platforms’
compensation costs. Acute challenges to driver retention call for effective compensation
strategies to better coordinate labor participation from these drivers (Nikzad, 2017;
Liu et al., 2019; Guda and Subramanian, 2019). In addition to driver turnover,
retailers’ withdrawal can undermine the operating efficiency of last-mile transportation
platforms (Borsenberger et al., 2018). This dissertation studies platforms’ scalability
and operational challenges faced by platforms in the growth.
ContributorsWang, Lina (Author) / Rabinovich, Elliot (Thesis advisor) / Richards, Timothy (Committee member) / Webster, Scott (Committee member) / Guda, Harish (Committee member) / Arizona State University (Publisher)
Created2021
Description
Wurtzite (B, Ga, Al) N semiconductors, especially (Ga, Al) N material systems, demonstrate immense promises to boost the economic growth in the semiconductor industry that is approaching the end of Moore’s law. At the material level, their high electric field strength, high saturation velocity, and unique heterojunction polarization charge have enabled tremendous potentials for high power, high frequency, and photonic applications. With the availability of large-area bulk GaN substrates and high-quality epilayer on foreign substrates, the power conversion applications of GaN are now at the cusp of commercialization.Despite these encouraging advances, there remain two critical hurdles in GaN-based technology: selective area doping and hole-based p-channel devices. Current selective area doping methods are still immature and lead to low-quality lateral p-n junctions, which prevent the realization of advanced power transistors and rectifiers. The missing of hole-based p-channel devices hinders the development of GaN complementary integrated circuits.
This thesis comprehensively studied these challenges. The first part (chapter 2) researched the selective area doping by etch-then-regrow. A GaN-based vertical-channel junction field-effect transistors (VC-JFETs) was experimentally demonstrated by blanket regrowth and self-planarization. The devices’ electrical performances were characterized to understand the regrowth quality. The non-ideal factors during p-GaN regrowth were also discussed. The second part (chapter 3-5) systematically studied the application of the hydrogen plasma treatment process to change the p-GaN properties selectively. A novel GaN-based metal-insulator-semiconductor junction was demonstrated. Then a novel edge termination design with avalanche breakdown capability achieved in GaN power rectifiers is proposed. The last part (Chapter 6) demonstrated a GaN-based p-channel heterojunction field-effect transistor, with record low leakage, subthreshold swing, and a record high on/off ratio. In the end, some outlook and future work have also been proposed.
Although in infancy, the demonstrated etch-then-regrow and the hydrogen plasma treatment methods have the potential to ultimately solve the challenges in GaN and benefit the development of the wide-ultra-wide bandgap industry, technology, and society.
ContributorsYang, Chen (Author) / Zhao, Yuji (Thesis advisor) / Goodnick, Stephen (Committee member) / Yu, Hongbin (Committee member) / Vasileska, Dragica (Committee member) / Arizona State University (Publisher)
Created2021
Description
While understanding of failure mechanisms for polymeric composites have improved vastly over recent decades, the ability to successfully monitor early failure and subsequent prevention has come of much interest in recent years. One such method to detect these failures involves the use of mechanochemistry, a field of chemistry in which chemical reactions are initiated by deforming highly-strained bonds present in certain moieties. Mechanochemistry is utilized in polymeric composites as a means of stress-sensing, utilizing weak and force-responsive chemical bonds to activate signals when embedded in a composite material. These signals can then be detected to determine the amount of stress applied to a composite and subsequent potential damage that has occurred due to the stress. Among mechanophores, the cinnamoyl moiety is capable of stress response through fluorescent signal under mechanical load. The cinnamoyl group is fluorescent in its initial state and capable of undergoing photocycloaddition in the presence of ultraviolet (UV) light, followed by subsequent reversion when under mechanical load. Signal generation before the yield point of the material provides a form of damage precursor detection.This dissertation explores the implementation of mechanophores in novel approaches to overcome some of the many challenges within the mechanochemistry field. First, new methods of mechanophore detection were developed through utilization of Fourier transform infrared (FTIR) spectroscopy signals and in-situ stress sensing. Developing an in-situ testing method provided a two-fold advantage of higher resolution and more time efficiency over current methods involving image analysis with a fluorescent microscope. Second, bonding mechanophores covalently into the backbone of an epoxy matrix mitigated property loss due to mechanophore incorporation. This approach was accomplished through functionalizing either the resin or hardener component of the matrix. Finally, surface functionalization of fibers was performed and allowed for unaltered fabrication procedures of composite layups as well as provided increased adhesion at the fiber-matrix interphase. The developed materials could enable a simple, non-invasive, and non-detrimental structural health monitoring approach.
ContributorsGunckel, Ryan Patrick (Author) / Dai, Lenore (Thesis advisor) / Chattopadhyay, Aditi (Thesis advisor) / Lind Thomas, Mary Laura (Committee member) / Liu, Yongming (Committee member) / Forzani, Erica (Committee member) / Arizona State University (Publisher)
Created2021