VictorJuiz/thesis huggingface dataset:
The effect of context on children's understanding of negation [electronic resource]

Words like "and", "or", "not", and "if" are powerful tools of human cognition, allowing us to form connections between expressions and reason about the world around us. Past work on children's acquisition of these words suggests a puzzle: Children begin producing these words at a very young age, but struggle on comprehension tasks for several years. In this dissertation, I focus on negation to explore two possible pieces to this puzzle: context and processing demands. I present several experiments demonstrating that context influences our understanding and use of negation. My data indicate that both adults and children expect negative sentences to be produced in relevant and informative contexts, and comprehension is reduced when negative sentences are presented without any context. I also present work suggesting that children have difficulty processing negative sentences, even when the sentences are presented in an informative context. This work collectively suggests that both context and processing demands are important factors to consider in order to understand children's acquisition of complex words.

Keywords: Psychology.
Advisor: Frank Michael C. (Professor of human biology) primary advisor. Thesis advisor
Clark Herbert H. advisor. Thesis advisor
Markman Ellen M.
An effective field theory approach to cosmological structure formation [electronic resource]

One of the main frontiers of observational cosmology is to map out how matter is distributed throughout the universe. The clustering patterns of galaxies and other astrophysical objects contain imprints of the universe's expansion history, the properties of the quantum fluctuations that are believed to have seeded the late-time structures we observe, and possibly other new and exotic physical processes. To extract this information from observations, we require a robust theoretical framework for how gravitational clustering works at large distances. This dissertation presents such a framework, which adapts the ideas of "effective field theory" (originally developed in the context of particle physics and quantum fields) to describe how small perturbations in an initially homogeneous distribution of matter evolve through cosmic time. In this framework, the perturbations are described as an effective fluid at long distances, with a stress tensor that parametrizes the effects of short-wavelength processes on the long-distance dynamics of the fluid. This stress tensor can be written as an expansion in long-wavelength fields (such as the matter overdensity) and spatial derivatives, and the coefficients of this expansion can be matched either to observations or to numerical simulations of gravitational clustering. Through several explicit calculations of correlation functions (particularly the power spectrum) of the cosmic density field, I demonstrate how the presence of this stress tensor renders the theory free of many of the issues that have plagued other perturbative approaches to gravitational clustering. I also perform several comparisons of the theory's predictions to measurements from dark matter-only N-body simulations, demonstrating the theory's ability to reproduce these measurements at over a wider range of scales and at higher precision than previously possible. The results in this dissertation represent significant advances in our understanding of cosmological perturbation theory, and their eventual application to observations of large-scale structure will likely be a great help in furthering our knowledge about the universe we inhabit.

Keywords: Physics.
Advisor: Senatore Leonardo
Kachru Shamit
Wechsler Risa H. (Risa Heyrman) advisor. Thesis advisor
The effective field theory of large-scale structure in cosmology [electronic resource]

So far, the cosmic microwave background has provided most of the significant constraints on cosmological parameters, but because of Silk damping and foreground contamination, the Planck Satellite has essentially reached the limit in constraining non-Gaussianity in scalar modes with the cosmic microwave background. Fortunately, the distribution of galaxies today is correlated with the conditions present in the early universe, so large-scale structure surveys can help us understand the early universe by observing the current-day galaxy distribution. In this way, it is likely that the next leading source of cosmological information will come from large-scale structure surveys like LSST and Euclid. In order for large-scale structure to significantly improve our knowledge of the early universe, for example by constraining f_NL < 1 through bispectrum measurements, the large-scale structure observables must be understood to percent level, even in the quasi-linear regime of structure formation. Recently, a research program called the Effective Field Theory of Large-Scale Structure was launched with this purpose. In this thesis, I will develop two pieces of that program: the effective field theory in redshift space, and the description of baryonic effects in the effective field theory. Finally, I will present work which computes the first slow-roll corrections to the volume of the universe and the universal entropy bound for slow-roll eternal inflation.

Keywords: Physics.
Advisor: Senatore Leonardo
Shenker Stephen Hart
Silverstein Eva
Effects of Public Sector Corruption on the Private Sector: Investigating the Market Value of Political Connections

This paper exploits public announcements of corruption allegations amongst Nigerian political figures to estimate the impact of political connections on firm value. Specifically, I draw results from market reactions to 27 events to determine whether politically connected firms suffer more from financial malpractice amongst government officials. This paper finds heterogeneous impacts of corruption announcements for firms’ returns. For some events involving larger sums of misallocated funds, politically connected firms suffer greater losses in their returns than unconnected firms. For other events involving smaller amounts of missing funds, I find that unconnected firms are actually punished more than connected firms. Still for other events, there appears to be no significantly differential impact of a government corruption scandal on connected and unconnected firms. Furthermore, surprisingly, some events actually show a positive return for all firms, and when this is the case, politically connected firms experience a larger increase in returns than their unconnected counterparts. To identify an overall impact, I run a pooled regression aggregating over all the events studied. I find that on average, there is a negative albeit insignificant impact on the returns of politically connected firms relative to unconnected firms in the aftermath of a corruption scandal.

Keywords:  Department of Economics
Stanford Department of Economics
political connections
corruption
firm value
Nigeria
Thesis
Advisor: Chandrasekhar Arun
Effects of virtual environments on pain [electronic resource]

Virtual environments have been shown to alter how people react to painful stimuli. This dissertation explores the effects of different virtual environments on pain threshold and pain rating in induced thermal pain tasks. Results show support for the effectiveness of virtual environments in altering the perception of pain, and suggest directions for future work in finding more effective content for virtual environments designed to reduce pain.

Keywords: Communication.
Advisor: Bailenson Jeremy primary advisor. Thesis advisor
Hancock Jeff advisor. Thesis advisor
Mackey Sean advisor. Thesis advisor
Reeves Byron
Efficient permutation P-value estimation for gene set tests [electronic resource]

In a genome-wide expression study, gene set testing is often used to find potential gene sets that correlate with a treatment(disease, drug, phenotype etc.). A gene set may contain tens to thousands genes, and genes within a gene set are generally correlated. Permutation tests are standard approaches of getting p-values for these gene set tests. Plain Monte Carlo methods that generate random permutations can be computationally infeasible for small p-values. Ackermann and Strimmer (2009) finds two families of test statistics that achieve overall best performances - a linear family and a quadratic family. This dissertation first reviews the relative background of gene set testing and permutation tests, and then provides three alternative approaches to estimate small permutation p-values efficiently. The first approach focuses on the linear statistic. Observing the p-value can be written as the proportion of points lying in a spherical cap, the p-value is approximated by the volume of a spherical cap. Error estimates can be derived from generalized Stolarsky's invariance principal, and alternative probabilistic proofs are provided. The second approach focuses on the quadratic statistic. Importance sampling is used to estimate the area of the (continuous) significant region on the sphere, and the volume of the region is used as an approximation for the (discrete proportion) p-value. Different proposal distributions are studied and compared. The third approach estimates the p-value with nested sampling. It may work for both the linear and the quadratic statistic. Similar ideas can be found in literature spanning from combinatorics, sequential Monte Carlo, Bayesian computation, rare event estimation, network reliability etc., and bears different names, e.g. approximate counting, nested sampling, subset simulation, multilevel splitting etc. We give a thorough review of literature in these different areas, and apply the technique to the gene set testing with the quadratic test statistic. Finally, we compare the proposed methods with plain Monte Carlo and saddle- point approximation on three expression studies in Parkinson's Disease patients. This work was supported by the US National Science Foundation under grant DMS-1521145.

Keywords: Statistics.
Advisor: Owen Art B. primary advisor. Thesis advisor
Hastie Trevor advisor. Thesis advisor
Wong Wing Hung advisor. Thesis advisor
Electrical, mechanical, and optical characterization of two-dimensional materials with molecular overlayers [electronic resource]

A two-dimensional object is entirely surface, with no interior. Its immediate surroundings will accordingly influence its response to electrical, mechanical, and optical stimuli. This thesis explores two different two-dimensional electron systems with molecular overlayers: the surface electron liquid in strontium titanate induced by electrolyte gating, and graphene decorated by ordered adsorbates. Strontium titanate is a band insulator that goes superconducting when doped with remarkably few electrons. By accumulating positive ions at a strontium titanate surface, the electrolyte gating technique can create a two-dimensional electron system with gate-tunable superconductivity. I combine an electrolyte gate with nanopatterned metal-oxide gates to realize the first gate-tunable superconducting weak link in this promising correlated electron system. With the same technique I create a ballistic one-dimensional channel in strontium titanate, and use this channel to perform in-plane tunneling spectroscopy of the superconducting state. Finally, using strontium titanate as a test case, I describe a method to improve mobility of generic electrolyte-gated surface systems by protecting the channel with a thin layer of hexagonal boron nitride. In the second part of this thesis, I use high-resolution atomic force microscopy to reveal a nanotexture that unexpectedly forms on flakes of graphene (and boron nitride) prepared in laboratory air: a "superlattice" of topographic stripes whose period is 4 nm. I argue that these stripes are self-assembled environmental adsorbates, and show that they are responsible for graphene's strongly anisotropic friction--a property previously believed to result from periodic rippling of the graphene sheet itself. In agreement with this self-assembly picture, I demonstrate that the local axis of high friction can be patterned with submicron precision by appropriate mechanical contact. I further show that the stripes produce anisotropic optical response, and I discuss the potential influence of the stripe-superlattice on graphene's electronic properties.

Keywords: Physics.
Advisor: Goldhaber-Gordon David
Heinz Tony F. advisor. Thesis advisor
Moler Kathryn A. advisor. Thesis advisor
Electromagnetic actuation for ferrofluid-based droplet microfluidics [electronic resource]

Magnetic actuation is an attractive method for microfluidic manipulations, given that strong magnetic fields can be applied on biological materials or fluids with negligible physiological impact. Despite its common use in passive microfluidic systems, there's been limited development for active microfluidic systems, mainly due to the limitations of conventional magnetic sources. Permanent magnets, although magnetically strong, lack switching capability. Strong electromagnets are too large to be integrated in microfluidic systems and small electromagnets generate weak forces. This dissertation demonstrates the use of miniature electropermanent magnets (EPMs) for the first time in microfluidic systems. EPMs combine the switching capability of electromagnets with the strength of permanent magnets into a compact package. In this work, EPMs are integrated with PDMS microfluidic chips and used to manipulate aqueous droplets in an oil-based ferrofluid. A PDMS compatible ferrofluid is presented and used as the continuous phase for the droplet microfluidic system. Using fast EPM switching (under 100 microseconds), magnetic fields of up to 300 mT are generated in close proximity (under 200 micrometers) to the microchannels. On-demand droplet displacement is demonstrated and used for sorting. Displacement velocities up to 300 micrometers/s are demonstrated for 50 micrometer droplets. EPM-driven droplet size modulation is demonstrated and used to control the sizes of droplets during generation. Droplet size increases of up to 44% are demonstrated for a continuous stream and for a single droplet. In addition, cell viability is tested in the ferrofluid-based droplet microfluidic system. Cells are encapsulated in serum-free media droplets, surrounded by the ferrofluid continuous phase, and their viability is tracked over several hours. Results show that cell viability is not significantly affected by encapsulating them in droplets surrounded with ferrofluids with 4.5% concentration of passivated iron oxide nanoparticles. The work presented in this dissertation demonstrates that EPMs are a viable magnetic source for active microfluidic systems. Coupled with ferrofluids, EPM-driven microfluidics could present an attractive new direction for the field and enable new applications.

Keywords: Electrical Engineering.
Advisor: Howe Roger Thomas primary advisor. Thesis advisor
Dutton Robert W. advisor. Thesis advisor
Santiago Juan G. advisor. Thesis advisor
Electron transport engineering in photon-enhanced thermionic energy converters [electronic resource]

A new physical mechanism for direct conversion of solar energy to electricity, called photon-enhanced thermionic emission (PETE), has attracted significant attention as a technology with the promise of very high power conversion efficiencies. The PETE mechanism involves thermionic emission of photoexcited electrons from a high temperature semiconductor cathode, followed by collection at a lower temperature, low work function anode. Due to its combination of photovoltaic and thermal processes, PETE has the potential to achieve efficiencies far above the fundamental limits for single-junction photovoltaics. In this work, two approaches to engineering electron transport in PETE energy converters are presented. A triode device with an electron-transparent gate electrode can be used to overcome space charge limitations that may reduce PETE converter efficiency. Graphene is considered as a candidate gate material, and SEM-based experimental measurements of its transparency to low energy (down to ~5 eV) electrons are reported. Even with an effective gate, the PETE process requires emission of electrons into vacuum, posing significant challenges to realizing efficient converters. To overcome this challenge, a solid-state PETE device structure is proposed, in which the vacuum gap is replaced by semiconductor nanowires that bridge the electrodes. These nanowires provide a path for electron transport while minimizing thermal conduction between the electrodes. Theoretical efficiencies for this device architecture are reported, and the implications of these results for realizing solid-state PETE converters are discussed.

Keywords: Materials Science and Engineering.
Advisor: Melosh Nicholas A. primary advisor. Thesis advisor
Howe Roger Thomas advisor. Thesis advisor
Salleo Alberto
Electronic readout strategies for silicon photomultiplier-based positron emission tomography detectors [electronic resource]

The new generation of positron emission tomography (PET) scanners based on silicon photo-multiplier (SiPM) technology require thousands of readout channels. Due to the complexity of such systems, potential advances in PET such as 3D position sensitive detectors, depth of interaction (DOI) and optimized time of flight (TOF) design have not been fully implemented in commercial scanners. This thesis proposes and tests readout strategies that greatly simplify the readout of advanced PET detectors. A pulse width modulation (PWM) readout strategy that allows for multiplexing without signal degradation is demonstrated on an ultra-high resolution 3D position- ing PET detector. The readout successfully resolves 0.5 mm x 0.5 mm x 1.0 mm LYSO crystals. The effects of multiplexing readout channels of state-of-the-art SiPM arrays on timing resolution are also thoroughly investigated. A TOF DOI detector with sub 300 ps full width half maximum (FWHM) coincidence time resolution is demonstrated with a 32:1 crystal to timing channel multiplexing ratio, and a passive binary positioning scheme. This module is then tested using analog and digital electro-optical readout to enable MR compatibility for a simultaneous PET/MR design. Finally, 3D printed phantoms to test the effects of these novel PET detectors on image quality are introduced. The strategies presented in this thesis significantly simplify PET readout, while increasing its imaging capabilities.

Keywords: Electrical Engineering.
Advisor: Levin Craig primary advisor. Thesis advisor
Khuri-Yakub Butrus T.
Murmann Boris advisor. Thesis advisor
Electrons in quantum confined nanoparticle assemblies [electronic resource]

Electrostatic capacitors have wide applications in energy storage and power quality management. Compared to electrochemical batteries, they offer higher power densities and superior cycling performances as neither chemical bond formation nor ion transport processes are involved in these devices. Nevertheless, their energy densities need to be improved. One possible way is to replace conventional metallic electrodes by nanoparticle electrodes with respectful electron conductivity and discrete energy levels in the conduction band. Electronic structures of individual quantum dots of the same material can be modified by their sizes. The degree of symmetry loss and surface/volume atom ratio affect the degree of differences in energy levels from those of their bulk form. Mediated by capping ligands, similar-sized colloidal quantum dots can self-assemble into superlattice films or solids. When quantum dots are assembled into monolayers at the water-air interface by Langmuir-Blodgett method, density of dislocations can be reduced by providing mechanical perturbations that facilitate thermal equilibrium. Electronic structures of quantum dot assemblies can be affected by interparticle spacing, sizes, and size variation. They change the degree of electronic coupling, which is in the form of electron wavefunction extension between quantum dots. Electron mobility can be estimated according to the electronic structures of the quantum dot assemblies, and high electron mobility are associated with monodisperse quantum dots with short ligands. Improved capacitance are obtained on capacitors where quantum dots are incorporated. It is possibly attributed to enlarged surface area of quantum dot arrays. Evidence on breakdown voltage improvement suggest potential of storing charges with higher energy density.

Keywords: Mechanical Engineering.
Advisor: Prinz F. B. primary advisor. Thesis advisor
Salleo Alberto
Zheng Xiaolin
Elevated temperature photo-electrochemical water splitting [electronic resource]

In order for solar energy to become a major contributor to utility-scale electricity production across the country, it is critical to tackle the inherently intermittent nature and geographically uneven distribution of solar energy. Due to the high energy densities and transportability, solar fuels, such as hydrogen and hydrocarbons, remain the most promising media to store and provide solar energy when and where it is needed. Photo-electrochemical (PEC) water splitting is a particular cost-effective and efficient approach to store solar energy into hydrogen. An overwhelming majority of the work has focused on ambient-temperature PEC cells, as it is believed that the efficiency of photovoltaic devices decreases with increasing temperature. While that the photovoltage generally decreases with temperature due to the rising intrinsic carrier concentration, electrocatalytic activity and minority/majority carrier transport properties in many materials actually improve with temperature. Therefore, it leaves an open question whether it is optimal to operate PEC cells at ambient temperatures. Motivated by that, I have carried out extensive investigation in elevated temperature photo-electrochemical water splitting. In this thesis, I will first discuss the non-trivial effect of temperature on PEC cells in aqueous solutions based on hematite (a-Fe2O3) thin film photoanode, grown by pulsed-laser deposition, as a model system. Building on top of that, I explicitly demonstrate that thermal energy significantly improves the saturation photocurrent in BiVO4 photoanode with only slight loss of the onset potential, the mechanism of which is rigorously attributed to the thermally activated minority carrier hopping. Furthermore, I extend the investigated temperature range even beyond 100 oC where the existing design of PEC cells in aqueous electrolyte are no longer applicable. This is achieved by an innovative design of liquid-free PEC cell with both theoretical analysis and experimental demonstration. Our observation confirms that increasing temperature could be an effective route to activing PEC cells, which contrasts with the prevailing understanding that the decreasing photovoltage dominates the temperature dependence of the energy conversion efficiency.

Keywords: Materials Science and Engineering.
Advisor: Chueh William
Melosh Nicholas A. primary advisor. Thesis advisor
McIntyre Paul Cameron advisor. Thesis advisor