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- Creators: Arizona State University
Description
Current Li-ion battery technologies are limited by the low capacities of theelectrode materials and require developments to meet stringent performance demands for
future energy storage devices. Electrode materials that alloy with Li, such as Si, are one
of the most promising alternatives for Li-ion battery anodes due to their high capacities.
Tetrel (Si, Ge, Sn) clathrates are a class of host-guest crystalline structures in which
Tetrel elements form a cage framework and encapsulate metal guest atoms. These
structures can form with defects such as framework/guest atom substitutions and
vacancies which result in a wide design space for tuning materials properties. The goal of
this work is to establish structure property relationships within the context of Li-ion
battery anode applications. The type I Ba 8 Al y Ge 46-y clathrates are investigated for their
electrochemical reactions with Li and show high capacities indicative of alloying
reactions. DFT calculations show that Li insertion into the framework vacancies is
favorable, but the migration barriers are too high for room temperature diffusion. Then,
guest free type I clathrates are investigated for their Li and Na migration barriers. The
results show that Li migration in the clathrate frameworks have low energy barriers (0.1-
0.4 eV) which suggest the possibility for room temperature diffusion. Then, the guest
free, type II Si clathrate (Na 1 Si 136 ) is synthesized and reversible Li insertion into the type
II Si clathrate structure is demonstrated. Based on the reasonable capacity (230 mAh/g),
low reaction voltage (0.30 V) and low volume expansion (0.21 %), the Si clathrate could
be a promising insertion anode for Li-ion batteries. Next, synchrotron X-ray
measurements and pair distribution function (PDF) analysis are used to investigate the
lithiation pathways of Ba 8 Ge 43 , Ba 8 Al 16 Ge 30 , Ba 8 Ga 15 Sn 31 and Na 0.3 Si 136 . The results
show that the Ba-clathrates undergo amorphous phase transformations which is distinct
from their elemental analogues (Ge, Sn) which feature crystalline lithiation pathways.
Based on the high capacities and solid-solution reaction mechanism, guest-filled
clathrates could be promising precursors to form alloying anodes with novel
electrochemical properties. Finally, several high temperature (300-550 °C)
electrochemical synthesis methods for Na-Si and Na-Ge clathrates are demonstrated in a
cell using a Na β’’-alumina solid electrolyte.
ContributorsDopilka, Andrew (Author) / Chan, Candace K (Thesis advisor) / Zhuang, Houlong (Committee member) / Peng, Xihong (Committee member) / Sieradzki, Karl (Committee member) / Arizona State University (Publisher)
Created2021
Description
Image-based deep learning (DL) models are employed to enable the detection of critical heat flux (CHF) based on pool boiling experimental images. Most machine learning approaches for pool boiling to date focus on a single dataset under a certain heater surface, working fluid, and operating conditions. For new datasets collected under different conditions, a significant effort in re-training the model or developing a new model is required under the assumption that the new dataset has a sufficient amount of labeled data. This research is to explore supervised, semi-supervised, and unsupervised machine learning strategies that are formulated to adapt to two scenarios. The first is when the new dataset has limited labeled data available. This scenario was addressed in chapter 2 of this thesis, where Convolutional Neural Networks (CNNs) and Transfer learning (TL) were used in tackling such situations. The second scenario is when the new dataset has no labeled data available at all. In such cases, this research presents a methodology in Chapter 3, where one of the state-of-the-art Generative Adversarial Networks (GANs) called Fixed-Point GAN is deployed in collaboration with a regular CNN model to tackle the problem. To the best of my knowledge, the approaches presented in chapters 2 and 3 are the first of their kind to utilize TL and GANs to solve the boiling heat transfer problem within the heat transfer community and are a step forward towards obtaining a one-for-all general model.
ContributorsAl-Hindawi, Firas Al (Author) / Wu, Teresa TW (Thesis advisor) / Yoon, Hyunsoo HY (Thesis advisor) / Hu, Han HH (Committee member) / Iquebal, Ashif AI (Committee member) / Arizona State University (Publisher)
Created2021
Description
Humans are biased toward teleological explanations of natural phenomena. The promiscuous teleology account posits that this proclivity is rooted in the detection of supernatural agency behind the design of the natural world. This idea is supported by numerous positive correlations of religious belief and agreement with teleological explanations of natural phenomena, but it is challenged by findings that non-believers often agree with them as well, suggesting the need for an adjudicating experiment. The current experiment tested whether considering similar teleological explanations of nature causes explicitly theistic and atheistic people to think about God, which would suggest that the teleological bias has roots in agency detection. Participants (N = 608) were randomly assigned to consider teleological explanations of either human-caused phenomena or natural phenomena, with the main prediction that considering the natural item set would make theists relatively faster to categorize God as real but make atheists relatively slower to categorize God as imaginary. The data did support this hypothesis, suggesting that people across the theistic belief spectrum automatically think of God when thinking about nature’s purpose, and thus the teleological bias might be rooted in the detection of supernatural agency. Implications for theories of teleology, study limitations, and potential future directions are discussed.
ContributorsScott, Matthew (Author) / Cohen, Adam B (Thesis advisor) / Kenrick, Douglas T (Committee member) / Brewer, Gene A (Committee member) / Becker, David Vaughn (Committee member) / Arizona State University (Publisher)
Created2021
Description
Capacity limits of the human nervous system require important or rewarding information to be prioritized and encoded over less important or rewarding information. The present dissertation aims to identify structural and functional neural correlates of reward-motivated memory encoding. Chapter 1 reviews studies of reward-motivated memory encoding and their neural correlates, as well as the structure and function of dopaminergic midbrain circuits. Chapter 2 presents a study that utilizes electroencephalography (EEG) to determine which of two hypothesized processes underly the influence of reward value on episodic memory. One hypothesis is that value engages prefrontal executive control processes, so that valuable stimuli engage an elaborative rehearsal strategy that benefits memory. A second hypothesis is that value acts through the reward-related midbrain dopamine system to modulate synaptic plasticity in hippocampal and cortical efferents, thereby benefiting memory encoding. The results revealed that EEG signals thought to index dopamine-driven attention allocation were modulated by reward value and were positively correlated with individual differences in behavioral measures of memory prioritization. Chapter 3 employs diffusion-weighted magnetic resonance imaging (MRI) to dissociate heterogenous functional circuits of the midbrain reward system. The results comport with primate histology and show that midbrain circuits are differentially predictive of impulsivity and of attention-deficit hyperactivity disorder (ADHD). Chapter 4 presents a study that also employs diffusion-weighted MRI. The findings replicate Chapter 3 in dissociating heterogenous functional circuits of the midbrain reward system. Additionally, the structural integrity of midbrain-hippocampus circuits was quantified. Structural integrity of these circuits was positively correlated to behavioral measures of memory prioritization. These findings suggest that structural and functional measures of the dopaminergic reward system may underlie reward-motivated memory encoding in humans.
ContributorsElliott, Blake Louis (Author) / Brewer, Gene A (Thesis advisor) / McClure, Samuel M (Committee member) / Sanabria, Federico (Committee member) / Bae, Gi-Yeul (Committee member) / Arizona State University (Publisher)
Created2021
Description
Regolith excavation systems are the enabling technology that must be developed in order to implement many of the plans for in-situ resource utilization (ISRU) that have been developed in recent years to aid in creating a lasting human presence on the surface of the Moon, Mars, and other celestial bodies. The majority of proposed ISRU excavation systems are integrated onto a wheeled mobility system, however none yet have proposed the use of a screw-propelled vehicle, which has the potential to augment and enhance the capabilities of the excavation system. As a result, CASPER, a novel screw-propelled excavation rover is developed and analyzed to determine its effectiveness as a ISRU excavation system. The excavation rate, power, velocity, cost of transport, and a new parameter, excavation transport rate, are analyzed for various configurations of the vehicle through mobility and excavation tests performed in silica sand. The optimal configuration yielded a 28.4 kg/hr excavation rate and11.2 m/min traverse rate with an overall system mass of 3.4 kg and power draw of26.3 W. CASPER’s mobility and excavation performance results are compared to four notable proposed ISRU excavation systems of various types. The results indicate that this architecture shows promise as an ISRU excavator because it provides significant excavation capability with low mass and power requirements.
ContributorsGreen, Marko (Author) / Marvi, Hamid (Thesis advisor) / Emady, Heather (Committee member) / Lee, Hyunglae (Committee member) / Arizona State University (Publisher)
Created2021
Description
Technology has a representation problem. While, in recent years, much more attention has been given to how developing technologies exacerbate social injustices and the marginalization of historically oppressed groups, discussions surrounding the representation of marginalized voices are still in a somewhat nascent state. In pursuing a future where underrepresented groups are no longer underrepresented (or misrepresented) in technological developments, I use this thesis project to draw attention to how gendered technologies are said to represent women as a class. To frame the sort of representation problem I have in mind here, I explore the dynamics of representing others as being a certain way, how individuals can be justified in their practice of representing others as being a certain way, and how such representations might produce harm. I draw special attention to particularly controversial technologies such as Sophia the Robot and sexbots in order to address issues of accountability and dehumanization. I end with some, perhaps, encouraging notes about how the sort of responsible design practices outlined in my project might open the door for some compelling liberatory developments.
ContributorsBradley, Nicole Dawn (Author) / Calhoun, Cheshire (Thesis advisor) / Phillips, Ben (Thesis advisor) / de Marneffe, Peter (Committee member) / Arizona State University (Publisher)
Created2021
Description
The growth of electronic sports (esports) is undeniable. One dimension of esports’ growth can be seen in its adoption as an extracurricular club activity across an increasing number of high schools in the United States. Researchers and educators in literacy have increasingly recognized and emphasized the study of students’ everyday lives and interests, calling for responsiveness to the ways students actually experience literacies versus how they are traditionally taught. In this respect, the popularity of esports in high schools positions it as an activity in the everyday lives of an increasing number of students. As such, this dissertation project explored the topic of esports in high schools through a lens of multiliteracies and digital-age literacies. This work addresses an important knowledge gap because students are converging to reveal an ecosystem where they are drawing from and building on their everyday literacies in non-trivial ways. And although there is a growing body of multidisciplinary scholarly work on esports, relatively little work has explored esports in high schools. Therefore, I asked the overarching question: How are digital-age multiliteracies taking place in high school esports contexts? Specifically, I focused on the digital-age literacy practices, demands, and perspectives in high school esports. Guided by research questions on these three topics, I carried out a study of two high school esports clubs for 22 weeks. This study was guided by qualitative, interpretive, naturalistic, ethnographic, and case study research designs. My findings describe six assertions: (1) literacy practices were used to engage with each other in communal and competitive ways; (2) the social functions of esports’ literacy practices take precedence over scholastic goals; (3) literacy demands of esports emphasize unambiguous and timely multimodal communication for managing teams and scheduling events; (4) literacy demands of high school esports focus on multidimensional fluencies between what is on and what is around the screens; (5) participants characterize the engagement with esports as positively contributing to “belonging”, of a “safe space”, and of opportunities for “critical thinking”; and (6) participants characterize their engagement with high school esports as positively contributing to future occupational or educational preparedness and health.
ContributorsPerez Cortes, Luis (Author) / Nelson, Brian C (Thesis advisor) / Gee, Elisabeth R (Committee member) / Anderson, Kate T (Committee member) / Arizona State University (Publisher)
Created2021
Description
This qualitative study begins with the supposition that all schools have cultural biases and that even within the same school culture, people see things differently. Internal biases can negatively affect the approach to school improvement. To disrupt these culture bound realities, parent perspectives were sought out to provide an alternate view into Zaharis Elementary School. Two critical assumptions were built into this study. One, that the vast reservoir of cultural knowledge among parents could be tapped, and two, once that cultural knowledge was uncovered, they the schoolpeople (1986) of Zaharis Elementary could do something with it to make a difference in the lives of children. A focus group framework was employed over a series of parent group interviews to explore the following research question: What are the multiple realities expressed by parents and what similarities and differences exist across these realities? Focus group discussions were transcribed, participant responses were coded, and a thorough and comprehensive analysis revealed that the majority of parent perceptions expressed fell within three emergent parent realities that were defined and presented. One, parents perceived that teaching and learning were social processes that support the development of student voice and nurture rich relationships. Two, parents perceived that learning through inquiry elevated class work to purposeful student learning, activates critical thinking, and fosters authentic real-world experience. And the third parent perception was teaching is teamwork and all members of the classroom community were teachers and learners.
ContributorsOliver, Michael (Author) / Marsh, Josephine P (Thesis advisor) / Serafini, Frank (Committee member) / Moses, Lindsey (Committee member) / Arizona State University (Publisher)
Created2021
Description
The field of computer vision has achieved tremendous progress over recent years with innovations in deep learning and neural networks. The advances have unprecedentedly enabled an intelligent agent to understand the world from its visual observations, such as recognizing an object, detecting the object's position, and estimating the distance to the object. It then comes to a question of how such visual understanding can be used to support the agent's decisions over its actions to perform a task. This dissertation aims to study this question in which several methods are presented to address the challenges in learning a desirable action policy from the agent's visual inputs for the agent to perform a task well. Specifically, this dissertation starts with learning an action policy from high dimensional visual observations by improving the sample efficiency. The improved sample efficiency is achieved through a denser reward function defined upon the visual understanding of the task, and an efficient exploration strategy equipped with a hierarchical policy. It further studies the generalizable action policy learning problem. The generalizability is achieved for both a fully observable task with local environment dynamic captured by visual representations, and a partially observable task with global environment dynamic captured by a novel graph representation. Finally, this dissertation explores learning from human-provided priors, such as natural language instructions and demonstration videos for better generalization ability.
ContributorsYe, Xin (Author) / Yang, Yezhou YY (Thesis advisor) / Ren, Yi YR (Committee member) / Pavlic, Theodore TP (Committee member) / Fan, Deliang DF (Committee member) / Srivastava, Siddharth SS (Committee member) / Arizona State University (Publisher)
Created2021
Description
Activity in the sympathetic branch of the autonomic nervous system tends tocovary amongst romantic partners. Studies of interpersonal physiology suggest that
romantic partners possess the ability to influence each other’s physiological states, which
may be observable through systematic covariation in partners’ physiological activity (i.e.,
physiological synchrony). However, very few studies have directly tested physiological
synchrony across conversation contexts, which is a notable gap in the literature given that
social context may modulate the implications of physiological synchrony on relational
functioning. Using electrodermal skin conductance as a measure of autonomic activity,
this study used multilevel vector autoregressive modeling to test for time-lagged
physiological synchrony across different-gender romantic partners while they discuss 1) a
mutual stress and 2) a topic of mutual enjoyment. Strong carryover (i.e., autoregressive)
effects were observed in both female and male partners in both conversations.
Unidirectional time-lagged synchrony was observed in the mutual stress conversation,
with female skin conductance preceding and predicting male skin conductance, on
average. No time-lagged synchrony effects were observed in the enjoyment conversation,
on average. Across both conversations, physiological synchrony varied greatly between
each couple. Findings prompt future studies to further explore physiological synchrony
using multiple physiological indicators to identity couple-specific dynamics.
ContributorsLeon, Gabriel Aaron (Author) / Randall, Ashley K (Thesis advisor) / Bludworth, James (Committee member) / Burleson, Mary H (Committee member) / Duran, Nicholas D (Committee member) / Arizona State University (Publisher)
Created2021