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Data-driven modeling and control of high-dimensional and nonlinear systems with application to turbulent flows
Get PDFControl of high-dimensional and nonlinear dynamical systems, such as turbulent flows, which are expensive to model due to their large state spaces, has led to the need for approximate models that are computationally tractable and amenable to classical control algorithms. Such complex and uncertain dynamical systems are often easier to observe and collect data from through simulations or experiments than to approximate and control from first principles. The first part of this work focuses on developing methods for reduced-order and control-oriented modeling of such high-dimensional systems from simulation data. In the second part, data-driven modeling methods are used along with optimal control methods to design a novel flow control scheme that targets large-scale motions in turbulent boundary layers for separation delay. Both parametric and non-parametric methods for dimensionality reduction and modeling are explored. Parametric methods focus on dynamic mode decomposition (DMD) - a data-driven, projection-based model reduction method that approximates the evolution of time-resolved data as discrete-time linear dynamics. The widely-used sparsity-promoting DMD is extended to systems with control inputs and non-sequential data, and its amenability to linear optimal control and estimation methods is demonstrated in flow control applications. Furthermore, for systems with unknown parameters where a single linear system fails to sufficiently capture the dynamics, a flowfield and parameter estimation framework, referred to as multiple-model DMD, is proposed. The second class of reduced-order modeling methods is based on Gaussian Process Regression (GPR). These non-parametric probabilistic models offer a number of benefits, including flexibility, uncertainty estimates, smooth performance degradation in unexplored areas of the state space, and the ability to incorporate prior knowledge through the selection of suitable kernel and mean functions. A method that merges the model-reduction capabilities of DMD with the strengths of GPR in handling nonlinearities and uncertainties in the low-dimensional DMD subspace is introduced for high-dimensional systems. The proposed methods are demonstrated in the optimal control of nonlinear partial differential equations, showcasing the ability to control such systems while accounting for model uncertainties. The data-driven modeling methods developed in this work are demonstrated in a novel and challenging turbulent flow control application. Turbulent boundary layers are dominated by large-scale motions (LSMs) of streamwise momentum surplus and deficit that contribute significantly to the statistics of the flow. This work explores the effect of manipulating LSMs in a moderate Reynolds number turbulent boundary layer for separation delay via well-resolved large-eddy simulations. In particular, a model predictive control scheme based on a reduced-order model of the flow that moves LSMs of interest closer to the wall in an optimal way via a body force-induced downwash is developed. The performance gain of targeting LSMs for separation delay versus a naive actuation scheme that does not account for LSMs is demonstrated.Aerospace Engineerin
Modulation of superconductivity in two-dimensional materials
Get PDFSuperconductivity is a phenomenon where under certain conditions the resistance of a material drops to zero and all magnetic fields inside the material are expelled. This state is incredibly useful since zero resistance means that electricity can flow through the superconducting material without losses. However, most materials only become superconductors at very low temperatures, limiting practical applications. Thus, a considerable amount of research has been conducted to try and discover new superconducting materials and find ways to enhance the superconducting critical temperature in existing superconducting materials; this work focuses on the latter subject. The first chapter focuses on the theory and basic physics of superconductivity. Chapter 2 then provides a brief literature review of superconductivity in two-dimensional materials, focusing on the different methods researchers have used to enhance superconductivity in two-dimensional superconductors such as proximity effects and doping/intercalation. Chapter 3 covers our attempt to enhance the critical temperature of NbS₂ using two-dimensional antiferromagnets; chapter 4 discusses our attempts to modulate the critical temperature of FeSeTe using two-dimensional ferroelectrics. While neither experiment yielded the desired critical temperature enhancement, several interesting phenomena were observed, namely a reduction in the critical temperature of NbS₂ when placed in contact with the antiferromagnet MnPSe₃ and the appearance of a two-step superconducting transition in FeSeTe when placed in contact with the ferromagnets CuInP₂S₆ and CuInP₂Se₆₋. In chapter 5 we report on our attempt to intercalate lithium ions into FeSeTe, with the main phenomena observed being a reduction in the critical temperature and the appearance of a hysteresis loop in the resistance of sample when rotated in a magnetic field. Next, chapter 6 reviews the growth and superconducting properties of Mo-doped NbSe₂, discussing the non-monotonic relationship the doping level has with the critical temperature, critical current, and critical field with a focus on the samples in which these parameters are enhanced. Finally, in chapter 7 we conclude by discussing potential avenues for future research.Electrical and Computer Engineerin
Undergraduate engineering students' moral sensitivity and effects of ethics education
Get PDFEngineering ethics refers to the ethical requirements of engineering as a profession to ensure the fulfillment of public commitments. Due to the crucial role that engineers play in our society, it is important that they have the appropriate level of awareness of social responsibilities. This research seeks to investigate instructional methods for improving engineering students' moral sensitivity. Moral sensitivity is the first component of James Rest's Four-Component Model of Moral Behavior that places an emphasis on social justice. This study's primary goals are to examine (1) the moral sensitivity of undergraduate engineering students and (2) university-level engineering ethics education in this regard. To accomplish this, we used combined qualitative and quantitative analysis methods applied to 52 semi-structured interviews with undergraduate engineering students at two large public universities. The interviews leveraged a story modified from a New York Times article about Hurricane Ida in Southern Louisiana in 2021 to evaluate students’ moral sensitivity based on the disaster’s complex effects on engineered, natural, and social systems. The findings demonstrate that during the interview, undergraduate engineering students were aware of and discussed socioeconomic inequity issues the most amongst issues present in the case study. Students, while having little access to learning about socioeconomic disparities in their curricula, indicated that they relied heavily on student organizations as a source of ethics education for this topic. Institutional contexts of students’ universities and the type of student organizations had significant relationships with moral sensitivity. This study highlights the lack of university curricula in fostering moral growth in engineering students and the potential for extracurricular activities to fill these gaps. Universities and educators are encouraged to expand their ethics education programs by encouraging extracurricular activities for students. Using a contemporary disaster event to measure moral sensitivity was effective in this exercise as students indicated they were aware of and in many instances experienced similar challenges. This approach, using a contemporary disaster case study, identifies opportunities to develop useful techniques for assessing moral sensitivity as well as other components of moral behavior.Civil, Architectural, and Environmental Engineerin
Antecedents and consequences of changes in self-perceptions in middle childhood and adolescence
Get PDFAdolescence is a time of great social, cognitive, and behavioral change, and work to understand how contextual factors influence beliefs about the self, and how those beliefs are manifested into maladaptive behaviors across this period, is important for understanding the important role self-perceptions play in shaping positive health. This dissertation included two studies that examined antecedents and consequences of changes in self-perceptions in middle childhood and adolescence. In a sample of 8,830 children from the Early Childhood Longitudinal Study Kindergarten Class of 1998-1999 (ECLS-K), the first study explored the links between school context (i.e., school climate, school safety, academic press) and changes in self-perceptions (i.e., reading and mathematics competence, peer relations) in middle childhood and early adolescence. Using data from a longitudinal study of 859 adolescents residing in the Northeast, the second study examined how changes in adolescents’ self-perceptions (i.e., scholastic competence, social acceptance, behavioral conduct, global self-worth) were linked with initiation and changes in risky behaviors (i.e., positive and negative alcohol expectancies, smoking behaviors, delinquency, physical and non-physical aggression) across middle and high school. Findings from the first study revealed school safety and academic press were linked with children’s academic and social self-perceptions. More specifically, children that attended schools with greater safety problems in 3rd grade experienced steeper declines in peer relations self-perceptions over the later elementary school years, and children in schools with less academic press reported lower reading competence self-perceptions at that time point. The second study found that steeper declines in youth’s self-perceptions in early adolescence were related to steeper increases in substance use cognitions and antisocial behaviors over the middle and high school years. Youth with increasing middle school behavioral conduct self-perceptions reported increases in negative alcohol expectancies across the high school transition. Students with less steep declines in global self-worth and social acceptance self-perceptions were more likely to report steeper declines in non-physical aggression across adolescence. Similarly, adolescents with more attenuated declines in middle school scholastic competence reported decreasing delinquent behaviors over the later middle school years. Taken together, the results from these two studies suggest that school processes do play a role in youth’s declining self-perceptions, and these declining self-perceptions put students at risk for engagement in unhealthy behaviors, which can carry serious mental and psychical health risks across the life course (Kann et al., 2016). Findings from the current study can inform public health and school policy efforts to prepare youth for healthy, successful futures.Human Development and Family Science
Spatiotemporal dynamics of groundwater flow and transport along Arctic coasts: exploring subterranean estuaries, fluxes, and seasonal drivers
Get PDFSubmarine groundwater discharge (SGD) along coastlines serves as a potent, but invisible conduit for materials and energy, and therefore, has significant implications for coastal biogeochemistry. SGD is particularly crucial in the Arctic subterranean estuaries (STEs), as it interacts with organically rich soils and thermally vulnerable ice-bounded permafrost before reaching the freshwater-saltwater mixing zone nearshore. Yet, its magnitude has been largely downplayed and its flow and transport dynamics remain understudied. The distinct hydrological and climatic processes imposed on Arctic STEs during thawing, summer, freeze-up, and winter periods differentiate these systems from well-studied STEs of temperate regions. With changing climate, altered thawing period onset, prolonged above-zero temperatures (i.e. extended summers), increased storm activities due to decreased sea-ice extent, and enhanced degradation of terrestrial and coastal permafrost are expected to cause major changes in groundwater storage, and potentially, discharge. Therefore, improved comprehension of coastal groundwater hydrology is essential for predicting future changes in Arctic hydrology and ecosystems. This dissertation investigates the spatiotemporal dynamics of groundwater flow and transport along the lagoon coasts of the Alaskan Beaufort Sea. Specifically, this work aims to constrain (1) how important in magnitude the fresh terrestrial SGD and organic-inorganic matter fluxes are for Arctic coastal water budgets and biogeochemistry in the summer, (2) how the hydro-thermal regime of coastal supra-permafrost aquifer evolves over short (hourly-daily) and seasonal timescales, and (3) how major climatic and oceanic factors influence variations in Arctic coastal groundwater availability and discharge. The chapters utilize geophysical, hydraulic, thermal, and chemical field data collected along shore-perpendicular piezometer transects installed in Kaktovik and Simpson Lagoons along the Beaufort Sea coast in the North Slope of the Alaska. Ex situ techniques including numerical (groundwater flow-transport) models (Chapters 2 and 3) and explainable artificial intelligence tools (Chapter 4), further supported our observations and elevated understanding in multi-dimensional system dynamics. The studies indicated that Arctic STEs deliver significant amounts of fresh SGD, dissolved organic carbon, organic nitrogen, and inorganic carbon (i.e. CO₂) in summer. Heat advection due to flow of groundwater was found significant for the thermal regime of STEs, and thus, the distribution of ice nearshore. Terrestrial fresh groundwater availability and discharge were sporadic, abundant, and absent in thawing, summer, and early freeze-up seasons, respectively. They were majorly influenced by potential evaporation in the daily and monthly time-scales, and by precipitation on the daily event-based scale. Easterly-westerly winds near coastlines were a major marine driver of SGD.Earth and Planetary Science
Development of a machine-learning platform for the autonomous analysis of 3D+T calcium imaging data
Get PDFThe role of live imaging within the biological sciences is to observe a system and its dynamic evolution over time. To understand neural pathways and signaling, Ca²⁺ imaging is a key technology as it allows for the non-invasive observation of neural activity. Advances in high-speed imaging has led to the creation of Ca²⁺ imaging systems that can capture all neurons in the nervous system of animal models such as Caenorhabditis elegans. While tens of minutes of continuous imaging can be performed, the manual analysis takes tens of hours and limits the throughput of functional Ca²⁺ imaging studies. This dissertation develops a machine learning platform specialized for the processing of volumetric videos. Enabled by work in low-rank 4D convolutions, our platform consists of two key technologies: a self-supervised video denoising method to increase the underlying data quality and a two-stage object detector for neuron recognition and tracking. We package these items in an interactive software such that advanced computational tools are accessible irrespective of computational experience. We develop and apply this platform to twenty-minute recordings of the model organism C. elegans. The raw volumetric video, acquired by a laser-scanning confocal microscope, is first restored with our self-supervised denoising method. For the dimmest neurons, our method increases the signal-to-background ratio by more than 30 times as compared to the raw data. This data is then processed by a novel-two stage object detector that identifies and segments objects in 3D. Further, a contrastive tracking loss is included as it allows for this model to learn both segmentation and tracking in an end-to-end fashion. Applied in this fashion to twenty-minute recordings, our platform accurately detects 245 of the 302 neurons in the C. elegans. Requiring no human intervention, approximately 80% of the nervous system can be detected and extracted in 6-8 hours on a local desktop.Biomedical Engineerin
Relating GNSS and VLBI antenna positions through co-observation of radio frequency sources
Get PDFTerrestrial References Frames (TRFs) underpin all modern navigational techniques, which depend on the accuracy and stability of these reference frames to derive consistent positions that can be related to each other at different epochs and locations. Many important areas of science also depend on the long-term stability of station positions such as studies of sea level rise, ice mass balance, glacial isostatic adjustment, and tectonic plate motion. The most precise and accurate TRFs consist of observations submitted by multiple geodetic techniques that are combined through local tie vectors. These local tie vectors are high accuracy vector differences in position between the reference points of instruments that contribute to each of these techniques individually, occurring at specialized locations called collocation sites where the instruments are placed close to each other.
For many years, these local tie vectors have been produced primarily through one technique–laser ranging between reflectors placed near the reference points of the instruments with a total station. This dissertation lays out the necessary measurement theory, digital signal processing techniques, high-fidelity models, and experiment setup to realize an entirely new methodology of producing these local tie vectors via co-observation of radio frequency sources with a Global Navigation Satellite Systems (GNSS) antenna and receiver and a Very Long Baseline Interferometry (VLBI) radio telescope. The technique is then thoroughly demonstrated through a series of experiments with GNSS antennas colocated with telescopes of the Very Long Baseline Array (VLBA). In preliminary experiments, it is demonstrated that a GNSS antenna and receiver that can produce baseband samples can co-observe with a radio telescope to detect natural radio sources more than 5 billion light years from the Earth in addition to GNSS satellites. Using GNSS processing techniques to account for clock variation, it is also shown that coherent accumulations of up to 20 minutes are possible with a rubidium frequency standard that is much cheaper than the typical H maser used in
VLBI processing.
A second set of experiments intended for precision geodesy includes the estimation of the first GNSS-VLBI tie vectors directly through the reference points of the participating instruments with both GNSS and VLBI analysis techniques. Preliminary results suggest that on the sub-100 m baselines used in these experiments, the technique may yield ties of mm-level accuracy and precision. Upcoming experiments in late 2025 promise to bring this technique to each telescope in the Very Long Baseline Array and to produce the first repeatability measurements for these tie vectors. Through GNSS analysis via correlation of the samples recorded by the radio telescope with the pseudorandom noise sequence of an observed GNSS satellite, we have shown that any radio telescope with an L band feed can use this technique to produce tie vectors with any colocated GNSS receiver, including International GNSS Service (IGS) stations. This technique is thus easily extensible, and the software developed for this effort can be used to produce many more ties worldwide at geodetic colocation sites.
The technique also serves as a direct comparison between the signal processing and data analysis techniques used in the GNSS and VLBI communities. This inter-comparison has yielded a robust phase wind-up model applicable to both radio telescopes and GNSS antennas and observations of both natural radio sources and transmitting satellites. In addition, for the first time rigorous and automated integer ambiguity resolution techniques are adapted from the GNSS community to
consistently resolve the phase ambiguity in both satellite observations and traditional geodetic VLBI observations of natural radio sources. This methodology can be adopted in the wider VLBI community to make the use of phase delay measurements a routine part of geodetic processing.Aerospace Engineerin
From hobby to side hustle : fan artist professionalization in the post-network era
Get PDFIn the U.S. broadcast industries, there exists a long history of commodifying fan art and co-opting fan labor for promotional purposes, whether to increase market penetration, lower advertising cost, demonstrate audience value, leverage subcultural capital, or all of the above. However, in the wake of post-Fordist production practices, neoliberal market logics, and post-exposure marketing challenges, that commodification has escalated. Industrial perceptions of and approaches toward fan art have made a telling transition, from strange hobby to side hustle, pastime to profession. Fan artists are no longer just used for free labor or increased access to key demographics; they are now being hired as contingent workers and touted as such. Between 2008 and 2018, broadcast networks, cable channels, and streaming platforms have evolved their marketing strategy from appropriation to professionalization—enclosing the artist, not just the art. In so doing, they are able to leverage the affective labor and aspirational labor of fan artists, mobilizing their economic precarity and fannish subjectivity for television promotion. This project uses historical research, as well as content and discourse analysis, to evidence these changes in the mechanics and motivations of fan art promotion within the U.S. post-network era television industry. But the professionalization of fan artists is only a microcosm of a larger labor ecosystem. At the bleeding edge of contemporary media employment models, labor laws, professionalization processes, and union jurisdictions, these professionalized fan artists are artifacts of the post-recession era. They are both actor and archive, in many ways the only record of the shifting strategies, transitory norms, ephemeral ideologies, and lived realities of media work. As they are professionalized, their identity and productivity are enclosed and formalized, monetized and commodified. However, given the state of flexible labor markets and waning labor organizations, that commodification comes without the protections historically afforded media professionals. By situating professional fan artists as a case study of post-recessional, post-network era television promotional labor, this project explores both structural problems of and potential solutions to contemporary contingent media work.Radio-Television-Fil
Guards at the games: the International Olympic Committee and security, 1972-1996
Get PDFThe 1972 Munich Olympic Games marked a pivotal moment in Olympic history. An attack by Palestinian terrorists on Israeli athletes and coaches in the Olympic Village marred the image of the Olympic Games as a mere sporting event. In the ensuing decades, the task of providing security at the Olympics evolved as Organizing Committees sought to nullify all threats, real and perceived. Yet, outside of one two-decade old manuscript, sport historians have virtually ignored this topic. While initially lackluster in their efforts, the International Olympic Committee (IOC) eventually played an important, yet rarely discussed role in the preparation and provision of security at Olympic events. This dissertation examines the evolution of IOC policy towards security from the Munich Olympics in 1972 to the last attack at an Olympic competition, the 1996 Centennial Park bombing in Atlanta. In the years prior to the attack in Munich, the IOC attempted to side-step political problems existing in the larger world. Following the massacre, the IOC initially forced the various Organizing Committees for the Olympic Games to provide security with their own resources (ie. without any monetary or logistical aid from the IOC). A change in leadership and one dynamic IOC member altered the course of this policy. Consequent to these developments, IOC leaders were forced to finally admit, at least internally, that politics mattered greatly. By applying transnational relations theory from the field of political science, this study explores the IOC’s role as a non-state actor that, at times, coordinated the security efforts of national governments, non-governmental organizations, and national sporting bodies.Kinesiology and Health Educatio