VictorJuiz/thesis huggingface dataset:
Nanomechanical measurements of thin crystalline perovskite oxide membranes
Keywords: Physics.

Modern oxide materials have garnered significant interest toward them, as they are a class of materials that exhibit a variety of interesting physical properties, ranging from superconductivity to magnetism to ferroelectrics to multiferroics. Modern techniques in thin film fabrication of oxides have made it possible to make freestanding membranes of oxides and their heterostructures with precise control over thickness and composition. By lifting the thin films off from substrates and placing these membranes on a suitable substrate, the membranes can be manipulated mechanically in a desired manner. This serves as a powerful tool to measure the nanomechanical properties of thin oxide membranes by making freestanding structures and probing them using calibrated nanomechanical probes such as atomic force microscopy. Since freestanding structures are devoid of any substrate effects, it becomes straightforward to probe the membranes directly and measure the nanomechanical properties of oxides in the sub-100 nm thickness regime, which was not possible previously. In this work, I will discuss our efforts to measure and understand the nanomechanical properties of single crystalline oxide membranes. We transfer oxide membranes onto porous SiNx membrane to form freestanding circular drum-heads which are used to measure elastic and fracture properties of these oxides using atomic force microscopy. We find that the materials respond mechanically completely differently at the nanoscale compared to their bulk counterparts. We observe that nanoscale elasticity goes beyond the traditional linear and local description of elasticity and exhibits strain gradient elasticity, which stems from a strain gradient induced polarization known as flexoelectricity. Furthermore, we observe that the strain sustenance upon local loading is almost two orders of magnitude higher than the tensile limit for these materials in bulk, along with a fatigue lifetime of a billion cycles. These studies set the platform for studying and manipulating oxide membranes at the nanoscale, and also serve as the foundational experiments for nanomechanical studies of thin oxide membranes
Nano-mechanical testing of colloidal nanostructures and self-assembled films
Keywords: Mechanical Engineering.

Understanding the mechanical behavior of nanostructures is crucial for their use in lightweight, strong, and multifunctional materials. Here, three different colloidal nanocrystals are tested in compression to gain insight into the role of microstructure, structural porosity, surface passivation and roughness, and strain rate on plastic deformation. Single crystal Ag and Cu nanocubes are compressed using in situ scanning electron microscopy to study the effect of surface passivation by the colloidal surfactant ligands on strength. Hollow, single crystal Au-Ag alloy nanoboxes with sub-20 nm wall thickness are found to strain harden. This is related to stacking fault accumulation and interaction which is not observed in solid single crystal nanostructures. In contrast, hollow amorphous cobalt sulfide nanoboxes do not show strain hardening. In addition, deformation and fracture is found to be strain rate dependent. These nanoboxes are self-assembled into lightweight films with pores inside of each nanobox, as well as between neighboring nanoboxes. These films are found to be strain rate independent and similar to granular materials. Finally, I present a workflow for determining the mechanical properties of thin films or other small-scale structures that combines nano-mechanical testing and computational simulations. This approach is validated for the finite element modelling of viscoelastic optically clear adhesive thin films using nanoindentation and rheology experimental data
Narratives of Loss and Loyalty: Gang Membership and Societal Reintegration in El Salvador
Keywords: Division of Literatures, Cultures, and Languages
storytelling
gangs
El Salvador
violence
societal reintegration
Text
Thesis

In this thesis, I explore how an analysis of storytelling can reveal the way gang violence has impacted Salvadoran society and how being a gang member can impact one’s sense of self. I also attempt to provide an alternative version to the story told by the media and popular culture through explaining the often misunderstood root causes of gang violence in El Salvador. I analyze oral literature by looking at gang entry, experiences of gang life, and societal reintegration as different storytelling events. Essentially, I first look at a variety of ethnographic works to understand how storytelling can reveal particular aspects of a society and of an individual. I then use the frameworks of these ethnographic works to analyze books, journal articles, documentaries, and my own interviews with former gang members. Overall, this research contributes to a deeper understanding of how growing up in a culture of violence impacts a person and a nation as a whole, adding to a larger conversation regarding how one's surroundings affect their life, the stories they tell, and the well-being of a nation.
Nation-Being in North Korea: New Perspectives on Human Rights
Keywords:  Stanford Global Studies
Stanford Global Studies
East Asian Studies
Center for East Asian Studies
North Korea
Human Rights
Thesis

The North Korean government has drawn criticism from the international community for its human rights abuses, which were deemed crimes against humanity by the United Nations Human Rights Council’s 2014 Commission of Inquiry report. Few would argue that these transgressions—which include sexual violence, enslavement, torture, and murder, among others—are anything less than appalling. And yet, the dialogue surrounding the issue of human rights in North Korea is far from straightforward. Rather, a variety of stakeholders—including governments, international bodies, non-governmental organizations, individual actors, and North Korean defectors—are driven to resolve the North Korean human rights problem by a wide range of motivations and with diverging methods. In this thesis, I argue that these discrepancies arise due to stakeholders’ various concepts of historical progress, which have resulted in a human rights dialogue that has largely been subsumed by other goals. To reset and reframe the conversation, I engage with critiques of the global human rights movement as well as with North Korea’s own human rights thinking, unpacking the meaning of “human rights” in the context of North Korea by exploring how both “human” and “rights” are understood in the DPRK. I show that North Korean individuals are conceived of as “nation-beings,” given meaningful existence by their nation. Thus, in contrast to the Western individualist concept, North Korea defines “human rights” as the rights of the North Korean nation itself. I posit that, absent an open human rights dialogue within the country, North Korean fiction offers an invaluable window into the DPRK’s own view of its human rights situation; thus I analyze works of North Korean short fiction to illustrate how human rights are presented within the DPRK. Finally, I offer some implications for how these insights may make the human rights conversation more productive moving forward.
The nature and scope of geometry in the thought of Descartes and Newton
Keywords: Philosophy.

A study of the nature and scope of geometry in the thought of Descartes and Newton. Traces methodological ideas about the appropriateness of appeals to motion and instruments in geometry from their sources in late antiquity through their transmission in early modern editions of classical mathematical works. Shows how the critical reception of these ideas informed attempts by Descartes and Newton to articulate visions of geometry as a unified whole encompassing objects and techniques stemming from the innovations of algebraic geometry and the calculus. Argues that these alternative visions resulted in very different understandings of the relationship of mechanics to geometry, and consequently of the role of these mathematical sciences in the study of nature
“Neither Male Nor Female”: Resurrecting Spiritual Genderlessness in the Life of the Public Universal Friend, 1776 - 1819
Keywords:  Department of History
Public Universal Friend
gender
Department of History
Jemima Wilkinson
New York
early America
prophet
revivalism
burned-over district
nonbinary
genderless
queer history
jerusalem
Thesis

This thesis examines spiritual performances of androgyny in the life of an eighteenth-century preacher named the Public Universal Friend. I argue that the Public Universal Friend’s gender identity has to be understood in analogous terms to their religious beliefs. Gendered in-betweenness reflected the spiritual in-betweenness the Friend embodied as an immortal spirit housed in a mortal body; simultaneously, androgyny visually reinforced their claims to spiritual otherworldliness. From their transformation in 1776, the Friend assumed a gender identity that flowed from their original claim to having been resurrected and reborn as a prophet. In this sense, we can reinterpret the Friend’s gender not as a secular expression of masculinity or femininity, but as a theological practice that expressed the preacher’s immaterial and metaphysical identity. Understanding the Friend in this light allows us to view the eighteenth-century spectrum of gender alongside the religious contexts the Friend existed within: one in which the boundaries between life and death, heaven and hell, mortal world and metaphysical realm were readily collapsed under the banner of God and in the body of the Friend.
A neural network with feature sparsity
Keywords: Statistics.

First, we propose a neural network model with a separate linear (residual) term, that explicitly bounds the input layer weights for a feature by the linear weight for that feature. The model can be seen as a modification of so-called residual neural networks to produce a path of models that are feature- sparse, that is, use only a subset of the features. This is analogous to the solution path from the usual Lasso (L1-regularized) linear regression. We call the proposed procedure LassoNet and develop a projected proximal gradient algorithm for its optimization. This approach can sometimes give as low or lower test error than a standard neural network, and its feature selection provides more interpretable solutions. This thesis illustrates the method using both simulated and real data examples, and shows that it is often able to achieve competitive performance with a much smaller number of input features. We also discuss extensions of this work beyond supervised learning, which includes unsupervised learning, matrix completion, and sparsity in learned features. Second, we consider the problem of local feature attribution and selection for arbitrary black-box models. We introduce a geometric method which we call RbX, for Region-Based Explanations. This method relies on approximating the prediction model's level sets by convex polytopes, thus helping to simplify and interpret the model. We demonstrate the effectiveness of the method on a variety of synthetic and real data sets
‘Neuralizing’ Injustice: How Brain Science Misunderstands Racism, Addiction, and Crime
Keywords: Drug addiction
Neurosciences > Moral and ethical aspects
Racism in the social sciences
Text
Thesis

In his capstone thesis, Christopher Iyer examines the pitfalls of applying modern psychology and neuroscience to racism, addiction, and criminality. He considers how the individual-focused methods of brain science have "over-individualized" our views of (and proposed solutions to) these issues, obscuring structural and environmental root causes. Moreover, he criticizes how applying brain science to these issues has "over-neuralized" them, leading us to believe that racism, addiction and crime should be understood (and intervened upon) as features of our brains—divorced from social conditions, and divorced even from ourselves as empowered agents. Scapegoating the brain allows us to show mercy towards individuals without grappling with collective responsibility for the conditions of social injustice truly at the heart of racism, addiction, and criminality. Finally, he outlines recommendations for conscientious and socially embedded brain science research that is responsive to social injustice.
New optics for low-damage electron microscopy
Keywords: Applied Physics.

While transmission electron microscopes are in principle capable of atomic resolution, the practical resolution limit for many samples of critical interest (i.e. biological molecules, polymers, battery materials) is determined by beam-induced damage. This leads to a dose-limited resolution far inferior to the resolution limit set by diffraction and aberrations. Multi-Pass Transmission Electron Microscopy (MPTEM) is a new technique for improving dose-limited resolution. I will motivate MPTEM with theory and simulation and present a detailed design of the novel optical elements which enable this protocol. I will also discuss the design of a programmable electron phase plate, which controls electron wavefronts and enables a variety of new measurement techniques. Finally, I will describe a new approach to understanding phase imaging for strongly scattering samples, which will be critical for extracting the maximum possible information from a multi-pass measurement
New results in the mathematics of string theory
Keywords: Physics.

In addition to being a promising candidate for a UV-complete theory of quantum gravity, string theory provides a rich breeding ground for relationships between physics and pure mathematics. Importantly, these relationships can go in both directions: string theory has both been enriched by the direct application of existing results in mathematics, and has also inspired profound new ideas in math. In this thesis, consisting of four papers co-written by the author, we present new developments in both of these directions. In the former direction, we use existing results in number theory and dynamical systems to determine aspects the BPS spectra of certain four-dimensional supersymmetric theories, including both string compactifications and quantum field theories. In the later, we conjecture a physical criterion for the modularity of some Calabi-Yau threefolds defined over the rational numbers
New theoretical insights for oxygen electrocatalysis
Keywords: Chemical Engineering.

Oxygen electrocatalysis, defined here as the study of electrocatalytic reactions consisting of O2, H2O, H2O2, has applications in a wide variety of industries from clean transportation to water purification. By utilizing electrochemical synthesis via either the 2-electron water oxidation reaction (2e-WOR) or the 2-electron oxygen reduction reaction (2e-ORR), we can produce hydrogen peroxide remotely for use as a water disinfectant in places with limited access to clean drinking water. By reducing oxygen to water in fuel cells, we can produce electricity to propel vehicles and power cities. In this work, we use a combination of density functional theory (DFT), microkinetic modelling, and ab initio molecular dynamics (AIMD), to develop new understanding of catalysts for these reactions.Specifically, we show that binding energies can help us understand and predict catalysts for the2e-WOR and 2e- and 4e-ORR, as well as predict more general electrochemical behavior of transition metal surfaces. First we use limiting potential analysis to predict ZnO as an active and selective catalyst for the 2e-WOR. We demonstrate that ZnO is not only the most active catalyst for this reaction known to date, but is also remarkably stable in reaction conditions. This result demonstrates the power of simple tools like limiting potential analysis in predicting catalysts for electrochemical reactions. Next, we demonstrate some of the limitations of limiting potential analysis in the ORR in two specific scenarios. First, we show that on transition metals, incorporating electric field ejects into microkinetic modeling allows us to accurately predict varying pH dependencies on several model catalysts. We use this newly developed model to create activity volcanoes which help us understand how and why electric field affects different catalysts in different ways in both the 2e- and 4e-ORR. We extend this understanding to transition metal oxides, where the intercept of the O-OH scaling relation is much higher than in metals. We show that by applying a similar microkinetic model to these new scaling relations, we can explain the relative inactivity of oxides in the 4e-ORR. Finally, we demonstrate that using similar principles as used in oxygen electrocatalysis, we can predict trends in work function reduction, and consequently, potential of zero charge (PZC), across transition metal surfaces. We connect work function reduction directly to water coverage using AIMD, and show that even simple vacuum binding energy calculations have predictive power for PZC. Throughout this thesis we attempt to show that by using simple descriptors to explain binding energies, reaction rates, and other electrochemical properties, we are not only able to predict new catalysts, but also better understand the physical phenomena which govern the way existing catalysts behave
"No, I'm Puerto Rican": An Exploration of Identity Formation and Anticolonial Resistance in Chicago's Puerto Rican Community
Keywords: identity
race
Puerto Ricans
Chicago
anti colonialism
resistance
displacement
Thesis

The story of migration from the island of Puerto Rico to and throughout cities such as Chicago is one of serial displacement and resistance to the colonial structure of the United States. Puerto Ricans residing in mainland US cities are pulled between a national identity that characterizes the island and a dualistic racial identity that categorizes American people. Because the values that inform the formation of identity are intertwined with the social context one is raised in, where Puerto Ricans are raised can powerfully shape how they accept or reject various identities. Humboldt Park became known as a nucleus of Puerto Rican culture in Chicago after decades of social and residential discrimination and displacement as Puerto Rican migrants worked to settle and gain access to resources and rights. Initiatives led by Puerto Rican activists in Chicago led to the creation of organizations such as Casa Central Evangelical and the Puerto Rican Cultural Center, which were instrumental in the prevalence of a united Puerto Rican community. I am seeking to answer two questions in this research project: 1. How has the creation of Casa Central Evangelical and the Puerto Rican Cultural Center created and upheld a national identity? And 2. How has this sense of national pride impacted the racial identities of Puerto Ricans in Chicago?
My findings show that the creation of the Puerto Rican Cultural Center (PRCC) and Casa Central Evangelical strengthened the presence of Puerto Rican pride in Humboldt park by preserving traditional Puerto Rican culture and providing organized spaces for Puerto Rican identities. More specifically, the PRCC is modeled after principles and societies with anticolonial frameworks. The anticolonial nature embedded in PRCC has strongly shaped the paradigms of Puerto Ricans in Chicago, centering their Puerto Rican identity as an act of resistance to colonialism.
North American biospheric carbon exchange variability explained by climatological and meteorological regimes
Keywords: Environmental Earth System Science.

The ability of the terrestrial biosphere to absorb more carbon from the atmosphere than it releases may prove to be an important mechanism for climate change mitigation. However, the effects of climate on biospheric net carbon uptake and sequestration remain highly uncertain. This dissertation examines how the North American biosphere, a large carbon sink, responds to climate and meteorological events. First, this work addresses the vulnerability of the carbon balance of high-latitude North American biomes to warming, with a focus on Alaska. This question is investigated using a geostatistical inverse model with a novel configuration to determine the potential attribution of the interannual variability of carbon fluxes to climate conditions. This study finds that Alaskan tundra and other Alaskan ecosystems dominated by grasses and shrubs are highly vulnerable to net losses of carbon during the autumn and early winter under the warm temperatures that are quickly becoming the norm in this region. In contrast, the net carbon losses of high-latitude boreal forests under warming may be substantially smaller because of an extension of the growing season that occurs under warm conditions in this biome. Then, this dissertation addresses the effects of large-scale atmospheric systems on regional and continental biospheric carbon fluxes over midlatitude North America, via two studies that employ a clustering algorithm to identify continental-scale meteorological events. First, several observational sites across a highly productive forested region near the Great Lakes are studied to determine regional-scale responses to nearby storm track activity and associated anomalies of temperature and cloud cover. This work finds that during storm track activity that occurs with strong southerly atmospheric inflow from the Gulf of Mexico, net carbon uptake is suppressed in the Great Lakes region due to a combination of cloud cover and sharp increases in temperature. In the final chapter, the response of the North American carbon sink to continental atmospheric dynamics is generalized across the continent and across summertime midlatitude cyclonic events. More than 50 observational sites across the continent are used in a geostatistical interpolation to map carbon flux anomalies associated with various cyclonic placements, and meteorological variables are evaluated for their ability to explain geographical patterns in flux anomalies and are assimilated into the interpolation. This analysis finds that net carbon uptake is consistently suppressed in the warm sector and enhanced in the cold sector of cyclonic systems, with these anomalies extending throughout vast regions of the continent. Both temperature and cloud cover can explain the large spatial extent of these carbon flux anomalies. This work demonstrates how atmospheric systems can be studied to infer large geographical patterns of carbon uptake suppression or enhancement
Novel astrophysical signatures of beyond the standard model physics
Keywords: Physics.

Astrophysical systems provide novel opportunities to search for new physics in regions of parameter space inaccessible to Earth-based experiments. Supernovae, for example, are some of the hottest environments in the Universe, achieving temperatures upwards of tens of MeV; they are consequently uniquely suited to test models of new physics at the MeV scale. In this dissertation, I will show that supernovae (and other astrophysical systems) allow us to probe a wide range of models of new physics, both placing new constraints and suggesting future signals by which we might one day uncover what lies beyond the Standard Model