VictorJuiz/thesis huggingface dataset:
Nonlinear internal waves, internal bores, and turbulent mixing in the nearshore coastal environment [electronic resource]
Keywords: Civil and Environmental Engineering.

The nearshore coastal environment is generally taken to be one of the most productive and ecologically important parts of the ocean. The nearshore is also a complex environment from a physical standpoint, due in large part to the widespread and often irregular occurrence of nonlinear internal waves (NLIWs) that frequently appear more bore-like than wave-like. Indeed, this region of the ocean can be thought of as the "swash zone" for larger-scale internal wave fields on the continental shelf. These nearshore NLIWs and bores have considerable implications for the cross-shelf exchange and transport of nutrients, sediments, contaminants, larvae, and other scalars; turbulent dissipation and diapycnal mixing; and hypoxia development. Despite the ramifications and a growing body of literature on the subject, many questions still remain with respect to the evolution, fate, and impact of NLIWs and internal bores in the nearshore coastal environment. This dissertation addresses these issues in Monterey Bay, CA. Several observational field studies were conducted using a wide variety of instruments and measurement techniques, such as oceanographic mooring arrays and an underwater turbulence flux tower. This work shows that nearshore internal bores produce transient stratification and mixing events, and represent the dominant source of variability, in the nearshore environment of southern Monterey Bay, CA. Specifically, these events control temperature and circulation dynamics, dominate turbulent mixing in the stratified interior, contribute to the majority of the variance in cross-shelf transport, and can create low dissolved oxygen (hypoxic) events. Individual bores also drive substantial changes to local mixing dynamics and the stratified turbulence field, with considerable differences between the various phases of the bores. Furthermore, the strength and structure of the observed internal bores are dependent on a combination of low-frequency upwelling wind forcing, offshore stratification, and the local bathymetric slope. Additionally, high resolution observations of rank-ordered packets of NLIWs in northern Monterey Bay, CA are presented. These NLIWs are some of the largest internal waves ever observed on the continental shelf. They are surmised to be generated at an upwelling front, modified by the presence of a strong background shear, and shown to be unstable to shear instabilities with large overturns and elevated turbulent mixing in the stratified interior. Finally, this dissertation examines the applicability of similarity scaling of turbulence spectra and cospectra in a shallow tidal flow in Elkhorn Slough, CA. Implications of the various findings, including biological processes, ecosystem health, numerical models, and nearshore hypoxia risk are discussed.
Nonlinear Spectroscopy of Rubidium and Frequency Stabilization of a 1560 nm Diode Laser
Keywords:  Department of Physics
laser spectroscopy
metrology
diode laser
second harmonic generation
rubidium
Thesis

Frequency-stabilized lasers are ubiquitous tools in laser spectroscopy and optical metrology. This thesis describes precision nonlinear spectroscopy of rubidium (Rb) at 780 nm that is achieved using the second harmonic of a diode laser at 1560 nm. The frequency of the laser is then actively stabilized to Rb resonances. It will ultimately serve as a frequency reference for optical time transfer and clock comparisons of frequency standards over a free-space optical link.
Non-simple geodesics on surfaces [electronic resource]
Keywords: Mathematics.

In this thesis, we study geodesics on pairs of pants, and then generalize our results to all surfaces. We get bounds on the number of closed geodesics in a hyperbolic surface given certain upper bounds on both length and self-intersection number. Then, we study the image on a pair of pants of certain sets of complete geodesics, which have restrictions for how the self-intersection number of their subarcs grows with subarc length. We show that such sets have low Hausdorff dimension, and in some cases are nowhere dense.
Non-state governance and non-state legitimacy [electronic resource]
Keywords: Political Science.

This project reexamines the way liberal political theory normatively evaluates the legitimacy of the power of non-state actors, including non-profit organizations, for-profit corporations, and international institutions. I argue here that, when these agents participate in governance, when they have independent authority to make, change, and enforce the rules that people must live by, their power raises the same questions of legitimacy that liberal political theory, particularly theories influenced by Rawls, evaluates through a requirement of public justification. I present empirical evidence here that this type of governance is widespread, deeply important for many people's lives, and likely to continue. However, the way that this requirement of public justification is generally understood assumes it is a unified, Westphalian state whose power is being evaluated, and the standard theory therefore cannot be applied to non-state power. The reconstructive portion of this project develops revisions to the standard Rawlsian theory of political legitimacy that, while grounded in the same widely shared liberal values, allow the theory to be applied to governance by non-state actors.
Novel materials for solar energy harvest and storage [electronic resource]
Keywords: Electrical Engineering.

Developing sustainable energy is one of the most pressing issue in modern society. Solar energy is clean and abundant. It is the champion of energy resources. However, we derive less than 1% of the total consumed energy from the sunlight. The huge gap between the solar energy we utilize every year and the tremendous undeveloped potential energy from sunlight presents significant challenges. To increase solar energy utilization, an efficient and convenient energy flow path is required. This dissertation presents an energy flow path for solar energy utilization. Solar energy is first converted into electricity using solar cell devices. Due to the intermittent nature of solar energy, the converted solar electricity needs to be integrated with energy storage systems. An electrochemical fuel is employed to store the converted solar electricity through a semi-flow battery. The electrochemical fuel can be transported and distributed to end users, and applied in electric vehicle applications through a refillable battery. The refillable battery can be "recharged" not only by solar electricity like conventional batteries, but also by refilling the electrochemical fuel. It offers a fast driving range extension method to effectively remove the main barriers in the broad adoption of electric vehicles, which in the meanwhile decrease energy dependence on finite fossil fuels in the transportation sector. In developing this solar energy flow path, we studied ultra-thin single-crystalline Si solar cells and transparent conducting electrodes in the solar to electricity conversion part. Recently, there is a strong trend to develop ultra-thin single-crystalline Si solar cells because of their lightweight and flexible form factor. Thin Si, however, absorbs less light, which means that an effective light trapping scheme must be used to improve light absorption in thin cells. Light trapping design using double-sided nanocone array surface textures were studied in this work, presenting very effective light absorption enhancement. Moreover, the processability of the ultra-thin Si in solar cell fabrication is also demonstrated. Besides crystalline Si technology, another major type of solar cell technology is thin film solar cells, where transparent conducting electrodes serve as essential components. In this work, we also demonstrate a hybrid concept for transparent conducting electrodes, which improves the performance of the existing technologies by several orders of magnitudes. In the solar electricity storage part, robust integrated system of solar module and Li/polysulfide semi-flow battery were studied, showing a high round-trip efficiency of 12%. The polysulfide material can be considered as an electrochemical fuel, charged by solar electricity, stored in external tanks, and then applied in a refillable battery to power electric vehicles. The low-lost refillable Li/polysulfide battery shows good rate capability and temperature performance, which are both very important factors for electric vehicle applications.
Novel nanoscale photoelectron and X-ray sources [electronic resource]
Keywords: Materials Science and Engineering.

We report a new optical near-field transducer comprised of a metallic nano-antenna extending from the ridge of a C-shaped metallic nano-aperture. Finite-difference time domain simulations predict that the C-aperture nano-tip (CAN-Tip) provides high intensity (650x), high optical resolution (~ [lambda]/60), and background-free near-field illumination at a wavelength of 980 nm. The CAN-Tip has an aperture resonance and tip antenna resonance which may be tuned independently, so the structure can be made resonant at ultraviolet wavelengths without being unduly small, which can be an ideal nano-optical source for the nano-photoelectron source. In the second part, we report a novel design for and first experimental demonstration of an array of nm-scale, controllable, photoelectron sources using helium ion beam milled 20 nm C-apertures. The apertures were designed and fabricated to resonate at 257 nm and coating with a thin-film photocathode while maintaining photonic resonance. We obtained beams of ~240 pA from each source with estimated emission areas of only 79.2 nm2 (1/e2). Such sources are badly needed for high throughput electron beam lithography and inspection. With far-field projection (> mm) of sub-20 nm photoelectron beams, applications open up in bio imaging, sensing, nano-metrology, and data storage. Lastly we apply the same unity magnification system to build a 3D differential phase contrast X-ray imaging system for identification of explosive materials in luggage. We aim to utilize an optically patterned photoelectron-excited X-ray source to circumvent difficulties of fabrication and power efficiency encountered when relying on conventional X-ray sources. I discuss how electron bombardment activated color centers provide a more efficient way to excite photoelectrons with lower photon energies.
Novel phenomena driven by interactions and symmetry breaking in graphene [electronic resource]
Keywords: Applied Physics.

The electronic properties of graphene are well described by a non-interacting Dirac Hamiltonian with an internal symmetry associated with spin and valley, an additional degree of freedom due to the hexagonal crystal lattice of graphene. As a result, graphene exhibits a variety of peculiar phenomena such as an anomalous quantum Hall effect or the absence of backscattering. However, this model breaks down in extremely clean samples, as interactions between electrons and with the substrate become relevant. In this work, we discuss some of the properties of graphene and boron nitride heterostructures, in particular the patterns of broken symmetry phases one can observe in these devices. First, we observe modification in the electronic band structure of graphene due to its interactions with the substrate. The sub lattice symmetry of the Dirac Hamiltonian is broken, which opens an energy gap at charge neutrality, in addition to superlattice Dirac points due to the moire pattern that graphene forms on boron nitride. We then describe transport at high magnetic field, in the quantum Hall regime, where Coulomb interactions yield spin and valley quantum Hall ferromagnetic phases, with polarized one dimensional states propagating along the edges of the device. Using dual-gated device geometries, we can address the transport properties of these edge states and in particular how they equilibrate, depending on their polarization (or absence thereof). At even higher fields, new collective ground states emerge in the fractional quantum Hall regime. In extremely clean samples we observe a plethora of fractional quantum Hall states, described by the composite fermion theory, with unexpected patterns of stability and spin polarizations. Observing these electronic phenomena requires an outstanding device quality with carrier mobility exceeding one million cm2/Vs. We describe in this work the fabrication and characterization methods that allow us to control the quality of graphene/boron nitride, as well as novel device geometries allowing for high quality bipolar transport in graphene.
Novel solar cell designs based on atomic layer deposition [electronic resource]
Keywords: Mechanical Engineering.

With the effects of pollution and global warming playing a larger and larger role in today's world, the case for the development of clean photovoltaic technologies to replace the dirty fuels that we have relied on since nearly the beginning of the Industrial Revolution is a straightforward one. Despite the recent inroads that solar energy has made into the electricity generation markets, there are still no existing technologies that can compete with coal, oil and natural gas from an economic perspective without significant government subsidies. Moreover, the vicious competition in the photovoltaic space has resulted in large solar panel price drops but primarily at the expense of profit margins leading to a mass extinction of cell manufacturers. No existing photovoltaic technology has a significant advantage and the fierce competition between numerous, equally matched adversaries has led to a fractured marketplace and has hindered the growth of the entire industry. In this work, a novel set of solar cell designs centered around the use of atomic layer deposition (ALD) is presented. The overriding goal is the drastic reduction of the installed cost while simultaneously maintaining the high performance achieved in current commercial single-junction solar cells. This is achieved through a three part approach: an ALD-enabled silicon heterojunction architecture chosen to optimize cell efficiency while taking advantage of the low cost ALD process, a technique for synthesizing thin c-Si solar cell absorber sheets that minimizes silicon material cost and reduces the cell weight, and a method for texturing a silicon surface with a shaped nanocone array to enable absorption of the majority of incident light while also eliminating the need for sun-tracking and associated installation costs. Each of the three primary innovations is discussed in detail as is their synthesis into final optimized devices that exhibit overall conversion efficiencies in excess of 22%. With the performance of this architecture nearly matching that of champion commercial cells, it presents a promising new approach with the potential to usher in the next generation of low-cost, high-efficiency photovoltaics.
Nudging drivers [electronic resource] : sensing, smartphone apps and incentives
Keywords: Electrical Engineering.

Societal networks, such as electricity, healthcare and transportation networks, are constructs built around the resources that we consume on a daily basis. Problems surrounding societal networks come from the scarcity and wastage of these resources. These problems can be difficult to solve due to their distributed nature: while the cost of the problem to each network participant is small, the aggregate cost to society can be enormous. Peak demand further complicates the problems: the cost of a resource can be non-linear, and increases dramatically as the resource load increases, affecting all network participants. Two categories of solutions for these problems are capacity addition and demand management. Neither solution is perfect -- capacity addition can be ineffective as demand often increases to fill extra capacity; demand management schemes, often implemented using using charges, can run into public and political reresistance. Incentive programs present a complementary approach for demand management. Instead of charging, incentives are rewarded for behavior change. Incentive programs allow for positive public perception, incremental deployment and personalization, all of which are difficult with charging schemes. Concepts from nudges can be applied to the design of incentive programs; the use of accurate sensing, random rewards, interactive games, social nudging and personalized incentives can synergize to create an effective incentive program. Steptacular and INSINC are programs previously deployed by the Stanford Center for Societal Networks which demonstrate the effectiveness of nudges. Capri, the main thrust of the thesis, is an incentive program for commuters at Stanford University, seeking to reduce peak hour automobile congestion on the Stanford University campus. By incentivizing off-peak and alternative mode commutes, Capri is an effective complement to Stanford's existing transporation demand management programs. By using low-cost, high-accuracy sensing methods of RFID and smartphone geolocationing, and incorporating elements of nudging, personalization and trendjacking, Capri has been effective in shifting the commute times of a large set of users out of peak hours. The rich data generated by Capri participants allow us to quantify the effects of various program features on user performance. More generally, Capri shows that concepts of nudging are widely applicable for incentive programs in societal networks. The architecture espoused by Capri can be used to deploy incentive programs in other settings such as health networks.
Numerical studies of inelastic light scattering in correlated materials [electronic resource]
Keywords: Applied Physics.

The mechanism of high temperature superconductivity has been a puzzle for almost three decades. With the rapid development of synchrotron light sources, photon spectroscopies such as x-ray absorption (XAS), inelastic x-ray scattering (IXS) and resonant inelastic x-ray scattering (RIXS), have shown to provide more and more useful information for the study of elementary excitations in strongly correlated ma- terials. In particular, RIXS at the Cu K-edge has been shown to be a probe of charge excitations. RIXS at the Cu L-edge in hole-doped cuprates has been shown to measure high energy collective spin excitations which persist well into the overdoped regime. We perform numerical simulations to study light scattering cross-sections using the single and multi-orbital Hubbard models. Our calculations highlight the ability to obtain spin and charge dynamical structure factors using Cu L or K-edge RIXS, respectively, and the importance of incident energy dependence (or the res- onant pro le) and the full in uence of light polarization. Our results ll in the gap between theoretical understanding and inelastic light scattering experiments on correlated materials, and further provides useful information for understanding the superconducting mechanism.
Objective probability and the art of judgment [electronic resource]
Keywords: Philosophy.

This dissertation argues that for many purposes, it is often useful to regard probability as objective; and, furthermore, that we can do so without any metaphysically heavyweight commitments. Those claims will be defended within three broad domains: quantum mechanics, classical statistical mechanics, and macroscopic chance events such as coin tosses. It will be explored how taking objective probability as a function of two arguments (i.e., taking it as primitively conditional) contributes to its overall usefulness. Finally, it will be discussed how objective probability can guide our actual degrees of belief. A pluralist picture will be presented in which many variants of Lewis's Principal Principle are all of some use, each with their merits and demerits.
On higher q, t-Catalan numbers [electronic resource]
Keywords: Mathematics.

The purpose of this thesis is two-fold: to give a self-contained evaluation of the symmetric function version of higher , t$-Catalan numbers $SC_n^{(m)}(q, t) = \langle \nabla^m e_n, e_n \rangle$ as a summation of rational functions of $ and $ indexed by partitions, and to prove the conjecture that the combinatorial version $WC_n^{(m)}(q, t)$ and the symmetric function version $SC_n^{(m)}(q, t)$ of higher , t$-Catalan numbers are equivalent for $ up to 6, thus strengthening a result of Lee, Li, and Loehr (see~\cite[Section 5]{LLL14}) which shows the equivalence for $ up to 4.
On the acceleration, dynamics, and propagation of cosmic rays [electronic resource]
Keywords: Physics.

The complete story of the origin, acceleration, and propagation of cosmic rays has remained a mystery for over a century. No conclusive evidence exists for how supernova remnants, the known sources of at least a large fraction of galactic cosmic rays, can accelerate cosmic rays up to the required energies. The origin of extragalactic cosmic rays is still completely unknown, with active galactic nuclei, gamma-ray bursts, certain types of neutron stars, and large scale shocks being the most popular candidates. This dissertation focuses on three separate but related topics: the interaction of anisotropic plasmas and cosmic rays, the propagation of cosmic rays in the presence of dense gas clouds, and the acceleration of extragalactic cosmic rays by strong accretion shocks around clusters and filaments of galaxies. The first major topic relaxes the common assumption that astrophysical plasmas have an isotropic pressure distribution caused by the presence of a magnetic field. We derive the dispersion relation for such a plasma with anisotropic magnetohydrodynamics as well as instabilities that are likely to amplify the magnetic field. This amplification may help to explain how shock fronts amplify the ambient magnetic field and accelerate cosmic rays to higher energies. The second major section examines the effect of dense gas clouds on the magnetic field and consequently on the propagation and emission of cosmic rays. This chapter is an attempt to gain insight on the gamma-ray spectrum of supernova remnants in such environments, where the spatial distribution and the spectral index of cosmic rays remains unexplained. The third topic uses new observations and simulations to modify a model of ultra-high-energy cosmic rays from strong accretion shocks. New evidence suggests that shocks around the large-scale structure of the universe --- not only shocks around galaxy clusters --- are adequate for accelerating cosmic rays up to the highest energies. Though the composition of these particles remains unknown, we propose two potential composition models, one with only protons and one with protons and heavy nuclei. Though the applications and environments discussed in each chapter varies, the underlying principles are similar. The full story of cosmic rays is not a simple one, and we hope that additions we have added to the standard theory provide useful tools for understanding other aspects of cosmic rays and perhaps other areas of astrophysics.