VictorJuiz/thesis huggingface dataset:
High-Performance Grid-Tied Single-Phase Power Converter Design with Applications in Electric Vehicle Charging and Residential Photovoltaic Systems

Single-phase power converters enable people to connect any electronic device to the ac grid. As the electricity demand of our world continues to grow, it is crucial to continually research and develop novel power electronic technologies that have improved performance. Specifically, traits of minimal power loss, high volumetric power density, high gravimetric power density, high levels of reliability, and long lifetimes are desired./nIn the first part of this thesis, a novel two-stage power converter design is proposed for the application of level-2 electric vehicle on-board charging. For the ac-to-dc rectification stage, a hybrid-switched capacitor converter, which utilizes the ultra-high energy densities of class two ceramic capacitors to minimize the passive component sizing of the converter, is proposed. For the energy buffer stage of the on-board charger, an active buffer topology that minimizes the system's physical volume and weight without compromising efficiency is presented. The active buffer topology in the electric vehicle charger is further investigated, with a novel control and circuit topology introduced that significantly reduces any voltage and current ripple along the dc-link./nIn the second part of this thesis, a novel two-stage inverter solution is proposed for a residential microinverter. The inverting stage of the microinverter is divided into two parts: a step-up stage and an inverting stage. Both parts are implemented with hybrid switched-capacitor converter topologies to (1) reduce system volume through leveraging the high energy densities of capacitors and (2) increase system efficiency by utilizing lower voltage switches with high figures of merit and soft-switching techniques. The passive component volume and switching stress of the step-up stage are theoretically analyzed and compared to other converter topologies, showcasing it as a practical converter choice for the microinverter application space. This two-part inverting stage creates a high voltage dc bus where the energy buffer can be placed in the system. This reduces the required buffer capacitance, enabling the engineer to have a broader range of capacitor choices to design a more reliable and energy-dense system./nOverall, this thesis showcases the design and utilization of several hybrid switched-capacitor converters, active buffer topologies, and control in the single-phase application area. Modeling and theoretical analysis techniques of power converter volume and power stress are explained in detail. High-performance hardware prototypes, experimental results, and test setup designs are included.

Advisor: Pilawa-Podgurski, Robert
Creating and Destroying Rotational Quantum Coherence in a Trapped-Ion Coulomb Crystal Rotor

This work presents the techniques used to create a freely rotating trapped-ion Coulomb crystal and to establish quantum coherent control over this rotational motion. This is done using a highly symmetric surface ion trap with circular trapping electrodes. We derive how a trapped-ion rotor couples to coherent laser light, including the motional transition sideband spectrum and the corresponding coupling strengths. We also show how rotational motion modifies the coupling of the usual trapped-ion vibrational motion to laser light. In our experiments, light which is coupled to the rotor's motion propagates nearly normal to the trap surface, which is thus also sensitive to vibrational motion in this direction. We thus also present the design of and benchmark the performance of a Faraday cage which has successfully protected this motion from harmful electric field noise./nA prerequisite to clean, coherent manipulation of the rotational quantum state of our rotor is preparing it in a rapidly rotating state with a small uncertainty in its angular momentum. This rotational state preparation is done with by accelerating a rotating quadrupole field via time-dependent voltages applied directly to the trap electrodes, resulting in rotation frequencies of 100's of kHz with uncertainties within 1 kHz. We show how this procedure allows for creation of superpositions of angular momentum states, and present considerations and measurements pertaining to optimizing this procedure. We find that the coherence of these superpositions is limited by angular momentum diffusion processes induced by coupling to noisy electric field gradients. Careful measurements of these rotor decoherence dynamics demonstrate close agreement with the corresponding theory for the first time./nFinally, we present a proposal to use angular momentum superpositions of our trapped ion rotor as an interferometer in which we may exchange the positions of two ions. This experiment would serve as a test of the symmetrization of their mutual quantum state, and would be sensitive to the phase of the exchange operation without requiring the two particles to coincide spatially. We interpret the physical meaning of this exchange phase measurement and present detailed considerations of potential errors.

Advisor: Haeffner, Hartmut
Yet Another Local Learner (YALL): a localized machine learning algorithm with applications to precision medicine

We sought to develop an improved decision algorithm for applications in precision medicine. This algorithm should perform as well or better than existing prognostic scores, be interpretable and parsimonious in the predictors it uses for an individual patient, and be able to perform competitively against best-in-class existing ensemble learning algorithms. The algorithm must be flexible enough to predict well in heterogeneous patient populations, where we might expect the covariates that are related to the outcome of interest to be different for different types of patients. To this end, a new supervised classification method is proposed which performs both dimension and instance reduction data-adaptively to hone in on only the most relevant information for a given patient.

Advisor: Hubbard, Alan E
History and Archaeological Heritage among the Ch’ol: Ethnographic Dialogues in Northern Chiapas

This dissertation is about Maya Ch'ol understandings of archaeological heritage and their own past, how their current social situation is pulled from and represented in that history. I explore how the Ch´ol experience life from their particular position within the economic, political, touristic, and archaeological landscape today. To understand this situation, I inquire with Maya Ch'ol consultants about their own conceptions of history and heritage, about their relationship with archaeology and archaeologists, and how scholars as mayanists can make our disciplines more open to participation and useful for the interests of Maya peoples of today. A wide variety of relationships between Maya individuals and history was observed, with a few common threads. These include a generalized perception of archaeological practices as opaque, a need for sharing with the Maya peoples and Mexican society the knowledge that archaeology produces. Participants described widespread discrimination against indigenous practices in the life of Ch’oles. A number of layers of cultural erasure and hegemonic policies have made embracing the ancient past of the Maya peoples something to avoid in order to blend into an ideal Mexican subject. Although there are a great number of Ch’ol academics, artists, and activists pushing for embracing the identity with pride, including the archaeological past, most of the Ch’oles do not. The challenges of decolonizing mayanist archaeology were made evident throughout the dialogues, as well as reiterating its necessity.

Advisor: Joyce, Rosemary A
Towards Intrinsic Switching in Ferroelectric Oxide - Materials Synthesis and Fabrication Process

This dissertation presents a systematic study on idealized electrode/ferroelectric/electrode heterostructures, from film synthesis to capacitor fabrication. Single crystal BaTiO3 has shown a small switching field of ~ 1 kV cm-1 and small switching energy of ~ 0.1 J cm-3, making it an excellent candidate for next generation non-volatile ferroelectric applications. However, when BaTiO3 is incorporated into actual nanoscale devices, the ferroelectric properties get significantly worse. BaTiO3 thin films show either large coercive switching field, increasing the total power consumption, or diminished remanent polarization, putting non-volatility into question. In this dissertation, I demonstrate that by carefully controlling the O2 growth pressure in pulsed laser deposition process, we can synthesize SrRuO3/BaTiO3/SrRuO3 heterostructures with BaTiO3 ferroelectric properties comparable to bulk crystal. Thickness scaling is performed to explore the smallest coercive voltage, with BaTiO3 films with thicknesses ranging from 25-50 nm exhibiting best combinations of switching voltage (< 100 mV), switching energy (< 2 J cm−3) and remanent polarization (> 10 μC cm-2). Depolarization field is found to play an important role in suppressing the coercive field, leading to a deviation in coercive field scaling from the Janovec-Kay-Dunn law. Lateral scaling is performed to explore the fastest switching speed, with the projection of achieving sub-nanosecond switching time in capacitor sizes as small as ~ 10 μm2. Integration of SrRuO3/BaTiO3/SrRuO3 heterostructures onto silicon substrate is also shown, with similar switching behavior achieved, as well as good resistance to fatigue and retention. Besides heterostructure synthesis, different fabrication methods are also explored to bring out the best BaTiO3 capacitor performance in various ferroelectric functions. MgO hard mask process introduces surface defects at electrode/ferroelectric interface and results in a large imprint in the hysteresis loops. While the wet chemical etching method gives out idealized ferroelectric loops with almost no imprint, the high selectivity and isotropy makes it unsuitable for fabricating more complex device architectures with high precision. The ion mill methods, on the other hand, have better directionality and can be used to etch almost every type of material and fabricate advanced device structures. However, the Ar+ ion beam bombardment can result in horizontal imprints in the hysteresis loop. Transport studies and deep-level transient spectroscopies reveal the introduction of Ba-related defect types (???′′−??••, ???′′) during the milling process. Post-fabrication annealing in Ba-rich environment significantly lowers the defect levels and reduces the imprints. We also discuss what can be done to further optimize the ferroelectric properties (reducing coercive field, increasing remanent polarization, etc.) in ultrathin BaTiO3 films, for the ferroelectric material to function well for various application purposes.

Advisor: Martin, Lane LM
Nature Acts as our Teacher: Minangkabau Art World Making in Indonesia

This dissertation examines the work of modern and contemporary artists associated with the Minangkabau ethnic group. Today, this group is roughly synonymous with the Indonesian province of West Sumatra. It is also recognized as the world’s largest matrilineal Muslim society. Throughout history because men had no right to immovable property, this contributed to a propensity for outward migration (merantau) and shaped what is imagined as the Minangkabau world (alam Minangkabau). This multi-sited world that is constituted by a homeland and diaspora and is shaped by factors like its members’ association with Minangkabau history, culture, and language rather than fixed geographic boundaries is the focus of this study that spans the late-colonial era (c. 1900) to the present./nMy focus is on artists from Minangkabau because they occupy a double place in Indonesian modern and contemporary art historiography. Not only do artists from Minangkabau hold roles as national pioneers who are credited with achieving successes in the name of Indonesia but also, the work of artists from Minangkabau has consistently been recognized because of how it diverges from dominant streams of expression. Until recently, little attention was paid to what might have contributed to such trends. In this dissertation I show that thanks to the commercial success of certain artists from Minangkabau along with the growth of two artist communities that are part of the Minangkabau diaspora in Java, there is now a greater coherence around Minangkabau identity in art. This makes it possible to trace a history of visual expression specific to Minangkabau that demonstrates a unique relationship to nature and ecosystems and is inseparable from Minangkabau customary norms (adat)./nThis dissertation makes three broad contributions. First, it engages with a history of art making associated with the work of modern and contemporary artists in and from Minangkabau. To date, writing on Indonesian art history has centered on the island of Java. This is because the nation’s preeminent art schools are located there along with the greatest concentration of artists. Second, by focusing on how merantau has shaped the careers of artists associated with Minangkabau and contributed to what I contend is a contemporary Minangkabau art world, it highlights the ways that historical modes of world-making challenge prescriptive constructures like the nation-state and politicized ideas of regional cohesion. Third, through an engagement with adat and alam (nature, universe, and realms of perception), it contributes to scholarship that is focused on decolonizing the Anthropocene by foregrounding local or non-Western bodies of knowledge.

Advisor: Tiwon, Sylvia
Lenssen, Anneka
Ion Distribution Functions in the Near-Sun Solar Wind

Parker Solar Probe (PSP), launched in late 2018, is a mission designed to sample the near-Sun environment and solar corona, and answer broad open questions concerning coronal energy flow and solar wind dynamics. The SPAN-Ion instrument is an on-board electrostatic analyzer responsible for measuring 3D ion velocity distribution functions (VDFs). In the first part of this thesis, we give an overview of SPAN-Ion, its intrinsic uncertainties, and discuss the effect of its finite field-of-view on moment measurements. We then move on to study magnetic switchbacks, rapid radial reversals of the magnetic field. While their role in young solar wind dynamics and precise generation mechanisms are still unclear, their ubiquity marks them out as an important early PSP observation. Using MHD invariants to probe their macroscale structure, we show that they are localised S-shaped folds in the magnetic field with internally backward propagating Alfvénic fluctuations, which has important implications for studies of small-scale turbulence using such invariants. Using fits to SPAN-Ion data, we then investigate alpha particle density, abundance, and velocity fluctuations inside and outside individual switchbacks, showing that there are no consistent compositional changes inside vs outside, but argue that these findings cannot yet be used to definitively rule in favour of one particular switchback generation mechanism (although they may be able to in the future). We also show that alpha particle speeds may be enhanced, decreased, or remain constant during a switchback, depending on the relative values of the alpha proton drift and the local wave phase speed, in contrast to the always positive proton velocity spikes. In the final part we study the alpha VDFs in more detail, focussing on characterising secondary alpha populations or alpha ``beams”. These have been essentially unstudied relative to their proton beam counterparts. We find they are generally more dense and slower moving than proton beams, and occur less frequently. We report time localised correlations between proton and alpha normalised heat flux, suggesting the existence of a common mechanism for producing beams in each species. We then perform a case study of an ion scale wave event, showing for the first time an active role being played by the alphas, specifically the alpha beam population, in driving solar wind plasma unstable and locally generating right-handed fast magnetosonic waves. The predicted wave frequencies, polarisations, and times of occurrence agree remarkably well with the observations. Such wave events are important for understanding the mechanisms of energy exchange between waves and particles that may be responsible for in-situ heating of the solar wind.

Advisor: Wurtele, Jonathan
Bale, Stuart
⟨a⟩-type Screw Dislocation Core Structure and Solute Interaction in α-Ti

α-Ti and α-Ti alloys are of technological interest as high specific strength, corrosion resistant, nonmagnetic, and bio-compatible materials. However, they are costly to process and require strict control of the presence of interstitial impurities that cause significant strength gains, but also loss of ductility. This work uses atomistic simulations to examine the properties of dislocation cores, i.e. the regions in a material surrounding a dislocation that has been deformed beyond it’s ideal strength in α-Ti and α-Ti alloys. Particular attention is paid to the interactions between these dislocations and solute atoms. It is shown that dislocation core structure affects the interaction with interstitial oxygen, and that solute atoms may be used to influence the dislocation core structure of screw dislocations through the so-called Cottrell atmosphere.

Advisor: Chrzan, Daryl C
Settling Debts: Early Native American Authorship and the Credit Economy

In this dissertation, I argue that the economic knowledge adapted from the early American credit economy influenced Native American authors’ literary and rhetorical compositions. By applying a political-economic lens to the works of Samson Occom, Jane Johnston Schoolcraft, and Elias Boudinot, I argue that debt and indebtedness offered these Native authors a means of interrogating the dynamics of settler-colonialism and Indigenous sovereignty in the years between 1760 and 1836. Debt and economic principles allowed Native authors to secure the means of Native advancement, critique the program of removal, and reassign dependency and obligation within the rapidly changing milieu of Native-settler relations.

Advisor: Wong, Hertha
Piatote, Beth
Monitoring Distributed, Dynamic Strain in Civil Infrastructure using Phase-Sensitive Optical Time-Domain Reflectometry

The micro-scale mechanical behavior of civil infrastructure and the earth immediately sur-rounding it is indicative of material properties, condition and use level. In addition, the geometry of infrastructure systems can be complex and spanning large extents. Phase- sensitive optical time domain reflectometry (φ-OTDR), also known as distributed acoustic sensing (DAS) or distributed vibration sensing (DVS), is a revolutionary technology that uses interferometry within optical fibers to make distributed measurements of strain at higher precision than ever before possible. This technology can measure extremely small strains (nanostrain level) at high spatial resolutions (several meters) and over long distances (10’s of kilometers). Since φ-OTDR can measure such small perturbations, it has gained widespread attention within the earth and planetary science community for measuring seismic wave propagation. These measurements have been predominantly focused on capturing the phase behavior of seismic waves at a crustal or exploration scale. However, for application to mea- suring dynamic strain in civil infrastructure the measurements must be understood for their strain magnitude as well as phase behavior. This dissertation serves to demonstrate the use of φ-OTDR for monitoring civil infrastructure systems through the presentation of several practical verification cases. Optical fibers were coupled to a soil site, a pavement system, and a superstructure to demonstrate how φ-OTDR can be used to quantitatively measure dynamic strain in these elements. The φ-OTDR measurements were verified through the use of velocity transducers (geophones), strain gauges, and another distributed fiber optic sens- ing technique called optical frequency-domain reflectometry (OFDR). Numerical modeling of φ-OTDR measurements is demonstrated for describing the measurements in a pseudo- static case as well as during stress-wave propagation. It is shown that φ-OTDR provides capabilities for monitoring civil infrastructure that currently-used techniques cannot due to its superior measurement precision and high acquisition rates. φ-OTDR is demonstrated as a new tool for monitoring civil infrastructure.

Advisor: Soga, Kenichi
Of Islands, Ensembles, and Eigenstates

This work furthers the program of understanding the black hole information paradox, the firewall paradox, and the relevance of concepts from quantum information to quantum gravity. A gravitational calculation was recently shown to yield the Page curve for the entropy of Hawking radiation. In this work, we generalize the Ryu-Takayanagi (Quantum Extremal Surface) prescription for von Neumann entropies to various settings relevant for this calculation. We examine a puzzle in the calculation, which we call the state paradox: that the calculation makes use of Hawking's result that the radiation entropy becomes large at late times. The paradox is resolved if the gravitational path integral computes averaged quantities in a suitable ensemble of unitary theories. We apply the insights from these calculations to cosmology by searching for entanglement islands in cosmologies with spatial curvature containing thermal radiation purified by a reference spacetime. We show arbitrarily small positive curvature guarantees that the entire universe is an island. Proper subsets of the time-symmetric slice of a closed or open universe can be islands, but only if the cosmological constant is negative and sufficiently large in magnitude. We extend this analysis to cosmologies containing a general fluid, finding that flat universes with time-symmetric slices always have islands on that slice. We find islands in the Simple Harmonic Universe model, which has no classical singularity at the background level. We then argue that the Page curve calculations do not resolve the firewall paradox. We exhibit a sharpened version of the paradox which consists of the Hayden-Preskill thought experiment in which the message thrown into the black hole is itself a smaller black hole. We argue that accounting for decoherence resolves the paradox. Finally, we conclude with an argument that quantum complexity theory can quantify the difficulty of distinguishing eigenstates obeying the Eigenstate Thermalization Hypothesis (ETH).

Advisor: Bousso, Raphael