VictorJuiz/thesis huggingface dataset:
Efficient learning in sequential optimization [electronic resource]

We consider a broad class of online optimization problems in which a decision-maker must balance between exploration and exploitation while learning from partial feedback. In these problems, the decision-maker repeatedly chooses among a set of possible actions, observes an outcome, and receives a reward representing the utility derived from this outcome. She is uncertain about the underlying system and is therefore initially unsure of which action is best. However, as outcomes are observed, she is able to learn over time to make increasingly effective decisions. Her objective is to choose actions sequentially so as to maximize the expected cumulative reward. We focus on three algorithmic approaches that accommodate flexible statistical modeling, and are capable of experimenting efficiently in broad classes of problems. The first part of the thesis focuses on a design principle known as optimism in the face of uncertainty, which underlies many of the most effective exploration algorithms. We provide a regret bound for an optimistic algorithm that applies broadly and can be specialized to many specific model classes. Our bound depends on a new notion of dimension that measures the degree of dependence among actions. We compare our notion to the Vapnik-Chervonenkis dimension, and explain why that and other measures of dimension used in the supervised literature do not suffice when it comes to analyzing optimistic algorithms. We then turn our attention to Thompson sampling, an elegant algorithm for learning in online optimization problems with partial feedback. We derive a close theoretical connection between Thompson sampling and optimistic algorithms. Due to the connection we derive, existing analysis available for specific optimistic algorithms immediately translates to expected regret bounds for Thompson sampling. The second part of the thesis pushes beyond the optimistic principle, and offers a fresh, information-theoretic, perspective on the exploration/exploitation tradeoff. We first revisit Thompson sampling from this perspective and provide novel regret bounds that scale with the entropy of the optimal action distribution. Then, we propose a new algorithm--information-directed sampling (IDS)--and study its performance. IDS quantifies the amount learned by selecting an action through an information theoretic measure, and selects actions by optimizing an objective that explicitly balances attaining a high immediate reward and selecting informative actions. We provide a general regret bound for IDS, demonstrate strong performance in simulation, and show through simple analytic examples that it can dramatically outperform Thompson sampling due to the way it quantifies information.

Keywords: Management Science and Engineering.
Advisor: Van Roy Benjamin primary advisor. Thesis advisor
Johari Ramesh
Tse David advisor. Thesis advisor
Electrochemical CO2 and CO reduction on oxide-derived copper catalysts [electronic resource]

The recycling of CO2 to liquid fuel using renewable energy is a longstanding problem that has been stymied by the lack of efficient electrocatalysts for this reaction. We demonstrate here that the reduction of metal oxide layers to generate "oxide-derived nanocrystalline metals" is a general method to increase the energetic efficiency of CO2 reduction and suppress the competitive H2 evolution reaction. Copper is the only metal with appreciable CO electroreduction activity, but requires extreme overpotentials to reduce CO in preference to H2O. Oxide-derived Cu (OD-Cu) lowers this overpotential requirement by at least 500 mV, producing ethanol and acetate with a combined Faradaic efficiency of 57% at --0.3 V vs the reversible hydrogen electrode. Commercial Cu nanoparticles of the same size and morphology exhibit very low selectivity for CO reduction under identical conditions, implicating the participation of surface defects or grain boundaries in the catalysis on oxide-derived nanocrystalline Cu. Using TEM electron diffraction and temperature-programmed desorption, we build grain boundary structure-activity relationships and probe the adsorption energy of CO to the oxide-derived Cu surface. Based on these data, we hypothesize that grain boundary surfaces provide active sites that bind CO more strongly than conventional Cu terrace or stepped facets, and these active sites are implicated in CO reduction catalysis.

Keywords: Chemistry.
Advisor: Kanan Matthew William
Chidsey Christopher E. D. (Christopher Elisha Dunn)
Stack T. (T. Daniel P.)
Electrochemical CO2 reduction on transition metal surfaces - from thermodynamics to kinetics [electronic resource]

Electrochemical CO2 reduction is a promising technology for the storage of renewable energy in the form of energy-dense hydrocarbons. Although this reaction has been studied experimentally for over a century, only in the last decade have advancements in density functional theory (DFT) and computing power allowed for the theoretical study of heterogeneous electrochemical CO2 reduction to thrive. Our work builds upon advances in the understanding of electrochemical interfaces to model electrochemical CO2 reduction at the fundamental level. First we explore the thermodynamics of CO2 reduction on transition metal surfaces with DFT calculations of binding energies. Then we use explicit simulations of the water-metal interface to calculate proton-electron transfer barriers. Finally we apply trends in barriers to predict electrochemical CO2 reduction reactivity from mean-field microkinetic modeling.

Keywords: Chemical Engineering.
Advisor: Nørskov Jens K.
Jaramillo Thomas Francisco advisor. Thesis advisor
Wilcox Jennifer
Electrochemical studies of III-V heterojunctions and nanowires [electronic resource]

III-V semiconductors exhibit light absorption and charge transport properties that make them ideal for solar energy conversion. However, these materials have been relatively unexplored, as compared to silicon and metal oxides, for photoelectrochemical water splitting. They have also not seen much development in photovoltaics apart from expensive and resource-hungry multijunction architectures. The focus of this work is in the growth of III-V thin film heterojunctions and nanowires, and in electrochemical analysis as an evaluation as electrodes in photoelectrochemical energy conversion and in photovoltaic devices. The first part of this work focuses on the design of two epitaxial heterojunction III-V stacks: InGaP grown on GaAs, and GaP grown on Si. The photovoltaic parameters of these heterojunctions are extracted, and solar-driven hydrogen evolution is demonstrated. Additionally, a new material, AlPN, is grown on GaP. Despite its apparent lack of crystallinity, it demonstrates photoactivity in the visible light range. The second part of this work demonstrates a reduction photocurrent in III-V phosphide nanowires that, due to their reduced dimensionality, can aid in the performance of solar-to-hydrogen systems. Controlled non-aqueous measurements are performed to examine the reduction photocurrent generated in the nanowires, and electrochemical impedance measurements are used to characterize the energetics and electrostatics in the junction created between the nanowires and the electrolyte. Novel phenomena are observed in the materials growth of phosphide nanowires on GaAs, specifically substrate tuning of the growth directions for GaP nanowires, and the formation of an InGaAs interlayer during InP nanowire growth. The third and final part of this work investigates the development of III-V nitride materials for solar energy conversion. With growth control, various micro and nanoscale morphologies of GaN-on-Si heterojunctions are created to drive an oxidation photocurrent in non-aqueous environments. This photocurrent shows that a structured nanowire/film electrode exhibits promising performance in the context of materials usage, and impedance measurements help to build a band diagram of the Si/GaN/electrolyte junction created for all electrodes under study. Single crystal InN nanowires are grown with different morphologies and generate a photovoltage under solar illumination within an electrochemical junction, opening up research in using high-indium InGaN alloys for solar cell and photoelectrode applications.

Keywords: Electrical Engineering.
Advisor: Clemens B. M. (Bruce M.) primary advisor. Thesis advisor
Bent Stacey advisor. Thesis advisor
Harris J. S. (James Stewart)
Electronic and vibrational dynamics of photo-excited A7 structures [electronic resource]

The interaction of intense femtosecond laser pulses with matter leads to highly excited transient states far from equilibrium. The dynamics of these excited states relate to many applications from laser machining to energy conversion. Ultrafast optical and x-ray light-scattering has emerged as a powerful experimental method to study material dynamics on the time-scale of atomic and even electronic motion. Here I report results of ultrafast coherent and squeezed phonon scattering experiments in bismuth and antimony. In response to laser-generated coherent phonons, I find dynamics of the coherent A1g vibrational mode greatly dependent on non-thermal electronic band-occupation. And in response to laser generated squeezed phonons, I find anisotropic changes in dynamical forces evidenced by differentiated high wavevector acoustic mode softening. These results advance our understanding of microscopic electron-electron and electron-phonon interactions in transient systems.

Keywords: Applied Physics.
Advisor: Reis David A.
Fisher Ian
Reed Evan J. advisor. Thesis advisor
Elucidation of Topographical Design Principles for Electrospun Matrices

Synthetic vascular grafts are characterized by poor long-term patency as low as 50% for small-diameter applications. Thrombosis is a major cause of failure and is attributed to the inability of the neighboring, quiescent endothelium to migrate and proliferate across the graft luminal surface. Hence, there is a large clinical need for implantable biomaterials that promote endothelial migration and proliferation. Recent strategies for engineering implantable biomaterials in the vasculature have leveraged well-defined mechanical and biochemical design principles to achieve such cellular phenotypes. However, despite the clear influence of native extracellular matrix topography on endothelial cell physiology and morphology in vivo, well-defined design principles regarding fibrous matrix topography are lacking. Here, we engineer and characterize an electrospun elastin-like protein platform with mean fiber diameter varied from 0.8 to 2.0 μm, independently of biochemical and mechanical properties. We then demonstrate that an increase in topographical size scale from the submicron to micron level drives an increase in endothelial cell migration and proliferation, specifically through the disruption of VE-cadherin cell junctions. The resulting loss of contact inhibition via VE-cadherin and upsurge in cytoskeletal contractility-induced mechanotransduction signaling is associated with a monolayer-wide shift in intracellular signaling (ERK1/2 phosphorylation, YAP localization), transcriptional activity (nuclear actin accumulation, interleukin 8 expression) and even epigenetic regulation (heterochromatin fraction) in response to more undulant fibrous topography. Finally, we propose and assess a mechanism linking undulant fibrous topography to endothelial cell junction disruption, wherein increased membrane curvature around larger diameter fibers imparts local tensile forces via the cytoskeleton to physically disrupt junction integrity. Results here have implications not only for the design of next generation vascular grafts that maintain long term patency by supporting migratory and proliferative endothelial phenotypes, but also for current understanding of how topographical features of the native vascular extracellular matrix drive cellular organization and organogenesis.

Keywords: Benitez, Patrick
Bioengineering.
Bioengineering
Materials Science and Engineering
electrospinning
vascular grafts
topography
VE-cadherin
mechanotransduction
YAP
endothelial cell
endothelium
matrix
fabric
cytoskeleton
nuclear actin
epigenetic regulation
Firestone Medal for Excellence in Undergraduate Research
Thesis
Advisor: Heilshorn Sarah
Emergent symmetries in quantum impurity experiments [electronic resource]

In systems involving a continuum of energy scales, one can imagine that under renormalization an effective Hamiltonian valid at low energies could possess a symmetry that the bare Hamiltonian does not. We are interested in the extent to which measurements of a physical system may reflect such emergent symmetries. Localized spins coupled to reservoirs of electrons are a natural domain to study these phenomena. Such "quantum impurity" systems can be realized using quantum dots. We report transport measurements of two lithographically patterned quantum dot systems in GaAs/AlGaAs heterostructures: 1. In a capacitively-coupled double quantum dot, gate voltage can be used to tune the system so that it is equally favorable for either dot to hold one electron. The effective Kondo Hamiltonian valid at low energies has been predicted to have an emergent SU(4)-symmetric exchange interaction based on the spin and orbital degrees of freedom. We provide evidence for emergent SU(4) symmetry by carefully comparing temperature-dependent conductance with numerical renormalization group calculations. In our device, conductance may be measured through each dot individually, uniquely enabling orbital state-resolved spectroscopy of the Kondo state. 2. A quantum dot tunnel-coupled to a metallic grain can host a non-Fermi liquid two-channel Kondo state, where a spin-1/2 impurity is exchange-coupled to two independent electron reservoirs. It occurs at the critical point of a second-order quantum phase transition, which surprisingly has exact theoretical descriptions both at and away from the critical point, even at finite temperature. We confirm transport signatures of quantum criticality as first reported by Potok, et al. (Nature 446, 167 (2007)), and then go further by quantitatively validating a universal theory for the crossover to a Fermi liquid. The universality of this crossover in the presence of arbitrary symmetry-breaking perturbations is a consequence of emergent symmetry at the non-Fermi liquid fixed point.

Keywords: Physics.
Advisor: Goldhaber-Gordon David
Fisher Ian
Qi Xiaoliang advisor. Thesis advisor
Empirical constraints on the rate and effectiveness of private adaptation to climate change in agriculture [electronic resource]

Changes in climate as a result of greenhouse gas emissions are now well documented but the effects of these changes on people and the social, economic, and natural systems they value are much more difficult to determine. Answering this question is challenging because people are able to adapt so as to preserve the things they care about in the face of a changing climate. These adaptations are an integral determinant of climate change impacts and understanding them is essential for the design of efficient mitigation and adaptation policy. Despite this importance, there is fairly little empirical evidence as to the rate and effectiveness of private adaptation to climate change. This dissertation presents new methods for quantifying climate change impacts and adaptation, with a focus on the agricultural sector. The first chapter quantifies the potential for private adaptation in European agriculture by jointly estimating both the short-run (excluding adaptation) and long-run (including adaption) response of yields and profits to changes in temperature and rainfall. The difference in impacts estimated using these two response curves can be interpreted as the private adaptation potential. I find this potential varies substantially between crops, but is low for wheat and barley, which show large residual effects of warming even with adaptation. The second chapter uses these response curves to quantify the influence of long-term climate trends on European crop yields. I show that climate trends have affected European crop yields but can not account for the stagnation of cereal yields observed since the mid-1990s. I also present a statistical test for constraining the rate of adaptation but show it will have low power in most settings. Finally, chapter three presents a Bayesian model of how farmers might learn about climate change given observations of weather. I test this model with an experiment using an online game simulating the adaptation decision. I show that the process of learning about climate change involves exposure to extreme events and quantify the magnitude of this exposure.

Advisor: Goulder Lawrence H. (Lawrence Herbert) primary advisor. Thesis advisor
Lobell David
Field Christopher B. advisor. Thesis advisor
Naylor Rosamond advisor. Thesis advisor
Empirical studies of expert behavior [electronic resource]

"The Foreclosed Option Fallacy." Foreclosed options influence behavior even when they have no bearing on future outcomes. This paper documents a foreclosed option fallacy in NFL kickoff returns. I compare returns from just behind the goal line, for which the returner declined an option to achieve the 20-yard line with certainty, to returns from just in front of the goal line, for which no such option was available. Consistent with loss aversion around the certain outcome of the declined option, returners are 56% more likely to be tackled at the 20-yard line after the touchback option is foreclosed than when it was never available. "Expertise in the Field Fades in the Lab" (with Justin M. Rao and David Rothschild). We conduct field and laboratory experiments on the same panel of experts, measuring the internal consistency of their predictions 1) in the field, in their domain of expertise, and 2) on a conceptually identical laboratory exercise. Experts make internally consistent predictions in the field, both in absolute terms and relative to a panel of novices, but they exhibit markedly less consistency on the isomorphic lab exercise. Possible explanations for this fading expertise include low motivation in the lab and a failure to transfer skills learned implicitly in the field to the more abstract lab setting. "Impact Aversion in Arbitrator Decisions" (with David P. Daniels). An aversion to salient mistakes leads arbitrators to make mistakes more often, even where directives are clear, incentives strong, and post-hoc evaluation perfect. We study the choices of Major League Baseball umpires, who are directed to make binary decisions according to a single, objective criterion: pitch location. Using state-of-the-art pitch location technology, we examine over one million such decisions and find that every umpire in our sample distorts his directive by avoiding the option that would more strongly change the expected outcome of the game. This impact aversion is consistent with an avoidance of public scrutiny. Umpires face criticism from the public for mistakes that disrupt the course of the game; impact-averse umpires avoid scrutiny by avoiding game-changing options that could be mistaken.

Keywords: Business.
Advisor: Barnett William P. primary advisor. Thesis advisor
Levav Jonathan
Rao Hayagreeva
Energy-efficient coarse-grain out-of-order execution [electronic resource]

Throughout the past decade, energy efficient computing has been a major problem in the computer system space from device technologies, to chip design, to computer architecture and software systems. Today, we have more smartphone devices in the hands of consumers than ever before, and we generate more data on the internet than ever before. This trend implies that moving forward, building energy efficient systems remains an increasingly significant challenge both in the mobile industry and in the server industry. Building energy efficient processors is at the forefront of solving these technological challenges. This doctoral dissertation describes the Coarse-Grain Out-of-Order (CG-OoO) processor architecture. Block-level code processing is at the heart of the CG-OoO architecture; CG-OoO speculates, fetches, schedules, and commits code at block-level granularity. CG-OoO eliminates unnecessary accesses to energy consuming tables, and turns large tables into smaller and distributed tables that are cheaper to access. CG-OoO leverages compiler-level code optimizations to deliver more efficient static code. It exploits instruction-level parallelism and block-level parallelism. CG-OoO introduces the Skipahead model which is a complexity effective, limited out-of-order instruction issue model. It is an energy-performance proportional design that can scale according to the program load. Through the energy efficiency techniques applied to the compiler and processor pipeline stages, CG-OoO delivers over 50% energy reduction at the performance of the baseline out-of-order processor.

Keywords: Electrical Engineering.
Advisor: Dally William J. primary advisor. Thesis advisor
Aamodt Tor M.
Aiken Alexander advisor. Thesis advisor
Kozyrakis Christoforos
Energy-efficient optical access/in-building networks [electronic resource]

This dissertation focuses on the design of energy-efficient optical access/in-building networks and their protocols. We introduce the Cascaded Bit-interleaved optical network protocol, an energy-efficient solution aiming to achieve low power consumption in converged optical access/in-building networks while providing high data rates to end-users, and propose a novel network architecture for optical access/in-building networks. In the proposed network architecture, optical-electrical-optical (OEO) regeneration is employed at the interface between access and in-building networks. The downstream frames are generated in the central office using a two-stage bit-interleaving scheme. In the downstream direction, the network nodes only process the data destined for them at a lower clock rate than that of the aggregate passive optical network (PON). In the upstream direction, no word alignment or decoding is performed in the intermediate nodes. We present detailed simulation and experimental results we obtained and show that a significant reduction in the power consumption of access/in-building networks can be achieved when the proposed Cascaded Bit-interleaved Protocol is employed in conjunction with the proposed network architecture.

Keywords: Electrical Engineering.
Advisor: Kazovsky Leonid G. primary advisor. Thesis advisor
Chembil Palat Ramesh
Solgaard Olav advisor. Thesis advisor
Engaging Children in Discussions of Disfigurement and Disability: The Wonder of Palacio’s Wonder

This study examined children's engagement with Wonder by RJ Palacio and explored the ways in which the children's literature could be used to promote critical, reflective and broad discussions of complex themes, such as disfigurement and disability, among young children. Eight students between the ages of 9 and 12 were assigned the reading of Wonder. They participated in an individual interview followed by a group interview. Interviews were coded with the objective of classifying each participant by type of engagement and examining references to specific themes of appearance, bullying, disability and disfigurement. Results indicated that children differentially engage with Wonder: four were engaged with both the novel and discussion, two were engaged with only the novel, one was engaged with only the discussion, and one was engaged with neither. Some children are capable of using Wonder to inform their own real-life experiences of and encounters with bullying, disfigurement and disability and/or discuss these social issues beyond the scope of the novel. Furthermore, some children are not only capable of discussing Wonder through critical lenses such as disfigurement and disability studies, but doing so adds crucial nuance to their simplistic initial interpretations of the novel and its themes.

Keywords:  Program in Human Biology
Graduate School of Education
disfigurement
disability
children's literature
Thesis
Advisor: Padilla Amado
Willinsky John
Moorhead Laura