VictorJuiz/thesis huggingface dataset:
Angle-resolved Photoemission Studies of a Doped Bilayer Iridate

Interest has been rising in systems, such as the iridates, where both spin-orbit coupling and Coulomb correlations play a prominent role, with theoretical proposals for a variety of exotic states. One such state, the spin-orbit Mott insulator, was discovered by Kim et al in Sr$_2$IrO$_4$ using angle-resolved photoemission spectroscopy, the experimental technique used in this work. Such states were later discovered in a variety of materials, including Sr$_3$Ir$_2$O$_7$, Na$_2$IrO$_3$, and RuCl$_3$ and provide a concrete testing ground for the physics of Mott insulators. This includes, naturally, the search for nearby exotic states which are the frequent companion of the Mott state. Indeed, significant attention has been given to doped Sr$_2$IrO$_4$ as an analog to the cuprate high-temperature superconductors, and to Na$_2$IrO$_3$, Li$_2$IrO$_3$, and RuCl$_3$ as candidates for hosting a spin-liquid state./nThis work focuses on (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$, which is notable in the weakness of its parent Mott state and thus its likely proximity to other ground states. The substitution of La on the Sr site adds electrons as carriers to the system. This eventually destroys the insulating state, though manifestations of both Coulomb correlations and spin-orbit coupling remain well beyond the insulator-metal transition. Chapter 1 covers the physics relevant to the ground state of (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$, starting from the effects of Coulomb correlations and spin-orbit coupling in general and including an overview of the current experimental results in doped and undoped Sr$_2$IrO$_4$ and Sr$_3$Ir$_2$O$_7$. Chapter 2 summarizes the theory of (spin- and) angle-resolved photoemission spectroscopy (ARPES), and describes analysis techniques used in the later chapters. The main experimental results of the work obtained using spin-integrated photoemission are in chapter 3, including evidence for a novel ground state in lightly-doped (Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$ and a thorough exploration of the evolving role of Coulomb correlations with doping. Chapter 4 goes into more recent results from several spin-resolved ARPES measurements and their possible implications, including some outstanding puzzles in the results.

Advisor: Lanzara, Alessandra
Heat Conduction in Complicated Nanostructures: Experiments and Theory

The thermal conductivity (k) of a semiconducting nanostructure is dramatically reduced from the bulk value due to boundary and interfacial scattering of energy carriers (phonons). The theoretical understanding of such nanoscale thermal phenomena is based on measurements of relatively simple nanostructures, such as thin films or nanowires. However, qualitatively new heat transfer mechanisms may emerge in more complicated nanostructures such as etched silicon nanomeshes or arbitrarily anisotropic thin films. New theoretical tools are needed to predict k of these nanostructures, and new experimental nanoscale temperature mapping tools would resolve questions about the dominant nanoscale mechanisms. In addition, nanothermometry techniques could be used to improve the thermal performance of technologies utilizing complicated nanostructures, which range from data storage devices to light-emitting diodes and microelectronics./nIn this dissertation, I develop experimental, computational, and analytical tools to answer fundamental questions about heat transfer in complicated nanostructures. I begin by demonstrating two nanothermometry techniques in the scanning transmission electron microscope (STEM) utilizing temperature-dependent thermal diffuse scattering. Temperature mapping of a Joule-heated silicon carbide device in the STEM shows the path forward towards ultrahigh spatial resolution temperature mapping of complicated nanostructures. Then, I describe how phonon ray tracing simulations quantify the boundary scattering reduction of k in complicated nanostructures. Comparing these simulation results with collaborator’s k measurements reveals that thermal phonons behave like incoherent particles rather than like coherent waves in silicon nanomeshes, which are membranes with periodically etched holes. Lastly, I derive solutions of the Boltzmann transport equation for phonon transport in arbitrarily aligned anisotropic thin films, and use these solutions to extend a well-known bulk Onsager relation for anisotropic heat conduction into the boundary scattering regime. In summary, further research using these experimental and theoretical techniques can answer long-standing fundamental thermal questions and can be leveraged in the design of energy-efficient lighting technologies and improved data storage devices.

Advisor: Dames, Christopher
Performing Chinatown: Hollywood Cinema, Tourism, and the Making of a Los Angeles Community, 1882-1943

Examining a period of national debate over immigration and U.S. citizenship, this dissertation foregrounds the social, economic, and political contexts through which representations of Chinatown in Los Angeles were produced and consumed. My dissertation asks: how did Chinese Americans in Los Angeles create, negotiate, and critically engage changing representations of Chinatown? To what extent did popular representations and economic opportunities in Hollywood inform life in Los Angeles Chinatown? And in what ways were the rights and privileges of U.S. citizenship and national belonging related to popular representations of Chinatown? To answer these questions, this project examines four different “Chinatowns” in Los Angeles—Old Chinatown, New Chinatown, China City, and MGM’s set for The Good Earth—between the passage of the Chinese Exclusion Act in 1882 and the law’s symbolic repeal in 1943 during World War II./nWhereas scholars have long argued that the geopolitical context of the Second World War and in particular the U.S. alliance with China led to both to the repeal of the Chinese Exclusion Act in 1943 and a general increase in opportunities for Chinese Americans, my dissertation presents a different narrative. Building on film studies scholars who trace the birth of cinema to the overlapping forces of modernity and urbanization at the turn of the century, I argue that the same transformations in urban visual culture that led to the development of film also transformed Chinatown into a medium of cultural production. Tracing the co-evolution of Chinatown and cinema as overlapping media forms between the arrival of the film industry in Southern California and the openings of New Chinatown and China City in Los Angeles in 1938, I demonstrate the myriad ways that Chinese American merchants, background extras, and others in Los Angeles repositioned Chinatown as part of, rather than distinct from, the idea of a modern cosmopolitan city. In the process, I analyze the ways that Chinese Americans utilized performance in Hollywood film and Chinatown to lay the groundwork for the incorporation of Chinese Americans into the nation-state under the logic of racial liberalism during World War II. In making this argument, my project places the everyday actions and performances of Chinese Americans at the center of discussions of American Orientalism demonstrating that the increasing inclusion of Chinese Americans into the United States was not the product of geopolitical forces alone.

Advisor: Choy, Catherine C
Huhndorf, Shari
Approximate svBRDF Capture From Uncalibrated Mobile Phone Video

I describe a new technique for obtaining a spatially varying BRDF (svBRDF) of a flat object using printed fiducial markers and a cell phone capable of continuous flash video. My homography-based video frame alignment method does not require the fiducial markers to be visible in every frame, thereby enabling me to capture larger areas at a closer distance and higher resolution than in previous work. Clusters of pixels in the resulting panorama that correspond to like materials are fit with a BRDF based on a recursive subdivision algorithm, utilizing all the light and view positions obtained from the video. I demonstrate the versatility of this method by capturing a variety of materials with both one- and two-camera input streams and rendering my results on 3D objects under complex illumination.

Advisor: O'Brien, James K
Embedding Intelligence into Robotic Systems - Programming, Learning, and Planning

Although robots play increasingly important roles in automated production due to their high efficiency, high accuracy, and high repeatability, new challenges for robots arise from different aspects as market demands shift and technology improves. The increasing product complexity and shorter product life cycle bring more difficulties into factories. Hence, higher intelligence for robots is necessary to perform various complicated tasks and to safely assist human workers./nIn order to enhance robot intelligence, one could consider referencing the pattern of human development. When dealing with a completely new task, humans would learn or ask for assistance from experienced people or experts. Once learned, humans would apply such skill to various similar tasks. Furthermore, rather than merely completing the task, humans would make plans to accomplish the mission with better quality and efficiency. The following three phases could be referred to if we apply the same pattern to robot intelligence: 1) Programming, 2) Learning, and 3) Planning. Programming is to retrieve the information/knowledge from human. Learning is to generalize the learned skill to similar tasks. Planning is to plan an optimal policy to achieve the goal given constraints./nFollowing the aforementioned phases, this dissertation is divided into three parts to study the three phases. The programming part investigates several alternative programming approaches and introduces an online collision avoidance algorithm for human guidance programming. Following the framework of learning from demonstration, the learning part proposes remote lead through teaching (RLTT) for assembling and grinding skill learning and applies the non-rigid registration algorithm - coherent point drift (CPD) to transfer the learned grasp examples to similar objects. The planning part presents a fast robot motion planner by using the convex feasible set (CFS) to solve the nonconvex optimization problem in collision avoidance path planning and operational time reduction.

Advisor: Tomizuka, Masayoshi
Risky Subjects: Vulnerability and uncertainty in the global pesticide boom

Pesticide use and exposure have reached a truly planetary scale. Pesticide dependence is a defining feature of modern agrarian capitalism, and is growing rapidly in low-income countries. Yet the debates on pesticides, development and health have continued on broadly similar terms for more than 50 years. In this dissertation, I outline the changes in the global political economy of pesticide use in the last twenty years, including changes in the production of off-patent pesticides, and drivers of increased adoption rooted in longstanding processes of agrarian change including expanding global commodity markets, rural-urban migration, and rising consumption in the global south. Understanding what this shift mean, and evaluating its consequences, requires thinking differently. I use a case study in Lao PDR, until recently one of the world’s lowest per-capita pesticide users, to try to chart a different path through these debates, interrogating narratives of development, risk and uncertainty. In a part of the country where maize and herbicides have completely transformed the countryside, I use oral histories, interviews, surveys and agroecology to look at the relationship between modern agriculture, intensification, precarity, and deforestation as old forest-based safety nets were ploughed under for monoculture maize production. I interrogate the diverse -- and divergent -- set of partial knowledges among pesticide users, and ask how pesticide applicators’ direct experiences of toxicity both reinforce and transgress the dominant model for ‘safe use’ of pesticides. Drawing on contextual understandings of risk from feminist science studies and political ecology, I understand how users grapple with risk and uncertainty in ways that produce patterns of unequal exposure on the local level, that produce a class of ‘risky subjects’. I also follow a community-based biomonitoring program and follow the controversy over the data they produced. I use this controversy to illuminate a larger one. Debates about what counts as harm, what evidence is valid, and what science is adequate proof have a history almost as old as chemical agriculture itself. The domain of imperceptibility surrounding exposures, the geographic disparities in terms of the ability to make impacts visible, and the disciplinary ‘tracks’ that limit what kind of evidence count, make it very difficult to produce enough scientific certainty to know the magnitude of the problem.

Advisor: Sayre, Nathan
Kosek, Jake
Net Black Advantage and College Choice

Do black Americans really have a “net advantage” in postsecondary education as suggested by prior studies? What does net black advantage mean and how might we reconcile findings of net black advantage with extensive evidence of black underrepresentation in four-year colleges and highly selective postsecondary institutions in particular? This dissertation applies a model of college choice to address these questions, structuring analysis of postsecondary pathways and developing new and empirically grounded ways of conceptualizing net black advantage. Informed by empirical results, this dissertation argues that net black advantage should be conceptualized primarily as the result of college application behaviors and their antecedents rather than admissions decisions./nThis dissertation applies a college choice model to decompose net black advantage into discrete stages of postsecondary application, admission, enrollment, and degree completion. At each stage in the educational pathway, starting prior to college entry and continuing through college graduation, the dissertation uses statistical models to reveal previously hidden sources of inequality throughout the postsecondary pipeline that are not apparent in prior studies that examine postsecondary enrollment as an isolated outcome./nAfter briefly defining net black advantage in the first chapter and theorizing about its causes in the second chapter, I present findings from an empirical chapter on applications which indicates substantial variation among groups of students in both quantity of college applications and quality of target colleges. Subsequent chapters build on the analysis of college applications to address speculations in the literature about college admissions preferences for black students, especially in elite college settings. Repeating a similar methodology in each empirical chapter, the dissertation tests whether net black advantages exist, conditional upon application to college, for enrollment and graduation. The dissertation concludes by synthesizing findings and implications and recommending ways to more accurately conceptualize net black advantage in light of both empirical findings and a priori theories.

Advisor: Lucas, Samuel R
Identifying Differences in Student Interactions with Near-Peer and Non Near-Peer Instructors in the General Chemistry Laboratory

There is consensus in the literature that peer learning is beneficial for student content learning as well as affective response to courses. Peer learning methods are used frequently in large science and math courses and often show positive outcomes from all participants. Peer learning programs in undergraduate science education rarely distinguish between the types of instructors leading the peer learning sessions, but medical education literature argues that a distinction should be made. This literature reports that the benefits produced as a result of peer learning are produced to an even greater degree when students learn from near-peer instructors. While there is consensus that student content learning and affective gains increase when taught by peers, especially near-peers, there is little real-time data to support these gains to explain how the perceived benefits are produced. Additionally, there is a lack of real-time data to indicate whether there are in fact real time differences between peer instruction and near-peer instruction. Retrospective methods, such as surveys, interviews, and focus groups serve as the primary data collection methods used in existing literature to evaluate the benefits of peer and near-peer learning. The Undergraduate Teacher-Scholar Program was created to investigate this gap in the literature. The program places a near-peer instructor and a non-near peer instructor together in laboratory course sections to teach students simultaneously. This environment allows real-time audio comparison of student interactions with near-peer and non near-peer instructors./nAudio data suggests that the presence of a near-peer instructor in the laboratory section results in increased student-instructor interaction times with both types of instructors. When there is no near-peer instructor present in the laboratory section, graduate student instructors interact with students for fewer minutes per hour of instruction. There is additional evidence to suggest that the presence of a near-peer instructor allows students to ask questions about life outside of the laboratory, which may contribute to increased feelings of comfort in the learning environment. Near-peer instructors also mirror student language and express empathy in conversation at a greater rate than their non near-peer instructor counterparts. Although this happens at a low frequency, it may contribute to positive affective benefits reported by students in surveys, interviews, and focus groups. Findings from this study suggest that the presence of a near-peer instructor in the laboratory is beneficial to all program stakeholders, and that real-time interaction differences may contribute to the perceived content learning and affective benefits expressed by students.

Advisor: Baranger, Anne M
Atom interferometry in an optical cavity

Matter wave interferometry with laser pulses has become a powerful tool for precision measurement. Optical resonators, meanwhile, are an indispensable tool for control of laser beams. We have combined these two components, and built the first atom interferometer inside of an optical cavity. This apparatus was then used to examine interactions between atoms and a small, in-vacuum source mass. We measured the gravitational attraction to the source mass, making it the smallest source body ever probed gravitationally with an atom interferometer. Searching for additional forces due to screened fields, we tightened constraints on certain dark energy models by several orders of magnitude. Finally, we measured a novel force mediated by blackbody radiation for the first time./nUtilizing technical benefits of the cavity, we performed interferometry with adiabatic passage. This enabled new interferometer geometries, large momentum transfer, and interferometers with up to one hundred pulses. Performing a trapped interferometer to take advantage of the clean wavefronts within the optical cavity, we performed the longest duration spatially-separated atom interferometer to date: over ten seconds, after which the atomic wavefunction was coherently recombined and read out as interference to measure gravity. This work demonstrates the feasibility and utility of bringing a cavity to atom interferometry.

Advisor: Mueller, Holger
Mind-Reading and Telepathy for Beginners and Intermediates: What People Think Machines Can Know About the Mind, and Why Their Beliefs Matter

What can machines know about the mind, even theoretically? This dissertation examines what people (end-users and software engineers) believe the answer to this question might be, where these beliefs come from, and what effect they have on social behavior and technical practice. First, qualitative and quantitative data from controlled experiments show how basic biosignals, such as heartrate, meet with both social context and prior beliefs about the body to produce mind-related meanings, and affect social decision-making. Second, a working brain-computer interface probes the diverse beliefs that software engineers hold about the mind, and uncovers their shared belief that the mind can and will be read by machines. These cases trace an unstable boundary–one heavily mediated by human beliefs–between sensing bodies and sensing minds. I propose the porousness of this boundary as a site for studying the futures of computer-mediated communication, of security, privacy and surveillance, and of minds themselves.

Advisor: Chuang, John
Convection, Radiation, and Climate: Fundamental Mechanisms and Impacts of a Changing Atmosphere

A hierarchy of models is used to connect fundamental mechanisms to impacts in a changing atmosphere. On the subject of forcings, an intermediate-complexity model for the radiative forcing of carbon dioxide is developed. This model is used to provide simple explanations for well-known properties of carbon dioxide (CO2) forcing such as its magnitude, dependence on atmospheric conditions, and logarithmic scaling. In the realm of impacts, climate models are used to investigate the impact of global warming on the kind of severe thunderstorms that produce hail and damaging winds. The results suggest that severe thunderstorms will become more damaging in the future, and that increases in Convective Available Potential Energy (CAPE) are the culprit. This motivates the subsequent use of cloud-resolving simulations to develop of a theory of CAPE and its dependence on temperature, which highlights the importance of the atmospheric saturation deficit. Another result of that theory for CAPE is an explanation for why cloud buoyancy and updraft strength are largest in the upper troposphere, a property that has traditionally been attributed to the release of the latent heat of fusion above the melting line. It is shown that this ice-based explanation is a fallacy: cloud buoyancy and updraft strength are the same in a world with or without ice. Finally, on the topic of feedbacks, the relationship between high clouds and the tropopause is investigated in cloud-resolving simulations. The results support the existence of a Fixed Tropopause Temperature (FiTT) rather than a Fixed Anvil Temperature (FAT), which implies a decoupling of anvil clouds from the tropopause. This decoupling motivates further investigation into the formation mechanisms of anvil clouds; it is found that anvil clouds do not result from enhanced detrainment below the tropopause, as is the traditional view, but from the slow evaporation of cloudy air in the cold upper troposphere.

Advisor: Romps, David M.
Thin-Film Electrostatic Actuators and Adhesives for High-Voltage Robotics

Thin-film electrostatic actuators and adhesives operating at high-voltages have potential as light-weight, low-cost force sources in mm- to cm-scale robotics./nFirst, new designs for repulsive-force electrostatic actuators (RFAs) were fabricated and evaluated, including: 2-layer linear and rotary RFAs, multi-layer RFAs for increased stroke, and RFAs with work-optimized electrode geometries. Second, a new bidirectional repulsive-/attractive-force electrostatic actuator (RAFA) was introduced, which employs the RFA electrode patterns but can controllably generate either repulsive or attractive forces by simply varying two input voltages. Third, a flexible, 8-fingered robotic gripper was developed, which employs electrostatic adhesion to grasp and manipulate flexible films (such as satellite multi-layer insulation)./nRFAs exhibit interesting characteristics – including stable open-loop operation and peak force at rest – and are compatible with thin-film / planar manufacturing processes. Demonstrated applications include RFA-powered 1- and 2-DoF micro-mirror systems, and a RAFA-powered 132 mg crawling robot.

Advisor: Fearing, Ronald S.