VictorJuiz/thesis huggingface dataset:
Understanding and preventing degradation in organic photovoltaics [electronic resource]
Keywords: Materials Science and Engineering.

Organic photovoltaics (OPVs) are an emerging photovoltaic technology with the potential for low-cost, high-throughput processing. The record laboratory efficiency for these solar cells are now at 9.2% which is approximately half of the efficiency of a traditional rooftop solar module; however, the stability of OPV needs to also reach a lifetime comparable to a 25-year traditional rooftop solar module to be competitive. Here I present the three major modes of degradation in OPV power conversion efficiency for solar cells tested at one-sun illumination in a controlled atmosphere. The first mode is a photo-induced burn-in that occurs in the first few hundred hours of operation and decreases efficiency by ~25%. This burn-in can be avoided by creating a highly aggregated blend of the polymer electron donor material and fullerene electron acceptor material. The second mode is thermal degradation that occurs above the Tg of the material. In the first portion of thermal degradation, the polymer donor material adheres to the top electrode and degrades performance by blocking the transport of electrons. This degradation can be mitigated by making the top electrode the electron withdrawing electrode. The last mode of degradation is long-term degradation and appears to be related to the amount of oxygen that the OPV device is exposed to. The three modes of degradation are shown to be general for several OPV material sets. Lastly, the talk will present rules for highly stable OPV devices and by following these rules we can produce OPVs with a lifetime in excess of 15 years and OPVs with less than half of the typical burn-in.
Understanding the deformation behavior of lithiated silicon and related advances in nanoindentation [electronic resource]
Keywords: Materials Science and Engineering.

In the first part of this dissertation, silicon micropillar lithiation/delithiation studies were employed to assess the robustness of amorphous silicon, relative to crystalline silicon, to lithiation- and delithiation-induced fracture. Even the largest pillars showed no lithiation-induced interior or exterior cohesive fracture. Delithiation of fully lithiated pillars produced internal cohesive fracture initiated by delamination of the pillar/substrate interface at the base of the pillar sidewall. Finite element modeling, indicating concentrated triaxial tensile stresses that move inward and upward with progression of delithiation, provided explanation for the observed fracture evolution. The research findings demonstrate that amorphous silicon is quite robust to fracture during lithiation; the critical size for fracture of amorphous silicon particles upon lithiation is determined to exceed ~2.3 [mu] m. The second part of this dissertation is focused on nanoindentation-based lithiated silicon deformation behavior studies. Prior to indenting lithiated silicon films, advances to general nanoindentation techniques were proposed. A new physically based function for nanoindentation indenter tip shape calibration was developed. The function, which accounts for the rounded shape at the indenter tip as well as the pyramidal shape away from the tip, fits calibration data well and returns physically meaningful calibration constants. Next, modifications to the Agilent Technologies Nanoindenter XP stage were implemented to make possible nanoindentation studies of blistered lithiated silicon films immersed in paraffin oil. Lithium-silicon alloy films of various compositions were probed. Young's modulus and the hardness were found to decrease as lithium content increased. Indentation creep testing was executed on unlithiated, amorphous silicon and heavily lithiated silicon, and the results indicate that lithiated silicon creeps readily compared to unlithiated silicon. In all cases, the viscoplastic flow behavior of lithiated silicon is consistent with power law creep with a large stress exponent (> 20). Interpreting the measured large stress exponents with a model for thermally activated, shear-driven local atomic rearrangement, the activation volume for the transformation is found to be comparable to the volume of a molecular unit of Li15Si4.
Underwater [electronic resource] : essays on American indebtedness
Keywords: Sociology.

This dissertation asks and answers three questions about the nature of mortgage debt and debtors in the contemporary United States. 1) Do individuals from different class backgrounds manage mortgage debt differently? 2) Do existing theories of mortgage debt, mostly in economics and finance, accord with how individuals actually manage debt? 3) And, finally, does consumer solvency or price better predict mortgage default? My findings have implications for theories of consumer credit in economic sociology and inequality as well as relevance to contemporary debates about how to reform housing finance policy in the United States.
Uneasy border state [electronic resource] : the politics and public policy of Latino illegal immigration in metropolitan California, 1971-1996
Keywords: History.

This dissertation explores the roots of modern American politics and policy of backlash towards Latino illegal immigration in late twentieth century California, the state with the largest Latino undocumented immigrant population. Drawing on research in dozens of largely untapped archival collections of local, state, and federal officials, agencies, and legislative bodies, and advocates, as well as published media, government, legal, and academic and think tank research sources, I explain evolving debates over labor market impacts, social and fiscal policy, federal immigration policy implementation, local and state immigration policy, and immigration law enforcement. I trace underexplored historical relationships between policymakers at various levels of government and diverse political advocates, political institutional and economic processes, legal developments, and political outcomes of policy shifts. I argue that from the early 1970s to the mid-1990s, Latino illegal immigration transformed from a predominantly liberal political issue into a conservative one in metropolitan California. Economic concerns, over labor market competition and increasingly over fiscal impacts, remained the core focus of debate yet conservatives increasingly seized upon and recast economic concerns in a cultural framework and embraced a cultural politics of illegal immigration law and order. The complex structure of modern American federalism made it extremely difficult to address California illegal immigration concerns, helping to fuel the political contentiousness of debate and fragmented local and state policymaking.
Universal communication and clustering [electronic resource]
Keywords: Electrical Engineering.

Information theory has a history of marrying elegant mathematical models with a wide scope of applications. In an attempt to follow this tradition, we start with questions of universality in communications, and end with surprising connections to clustering, compression, and prediction. Two specific information theoretic scenarios are considered: universal pattern decoding for an unknown codebook across an unknown channel, and universal encoding and decoding across a modulo-additive channel with noiseless feedback. In both settings, fundamental limits are established, and practical algorithms and tools are constructed to achieve these bounds. Applications are briefly discussed both for evaluating the semantic similarity of search queries, and for comparing human populations based on the genotypes of various individuals.
Using Neuroimaging and Optogenetics to Better Understand the Neural Circuit Basis of Major Depression
Keywords: Ferenczi, Emily
bioengineering
neuroscience
psychiatric disease
depression
neural circuits
optogenetics
functional magnetic resonance imaging
fMRI
graph theoretical analysis
Thesis

Depression is a leading global health problem that affects hundreds of millions of people. Though the psychiatric disorder has been known to exist for centuries, its treatment still has yet to be perfected. The inability to clearly define the neurobiological mechanism of depression results in the lack of precise tools for the diagnosis and treatment of depressed patients. Advances in neuroscience research are working towards redefining depression in the language of brain circuits by characterizing the disease's structural, functional, and electrochemical profile. In the pioneering work of Helen Mayberg, one promising brain region that has been shown to be metabolically overactive in depression and therapeutically receptive via deep brain stimulation is the subgenual cingulate cortex. In this thesis, I describe the use of graph theoretical analysis of structural imaging data from depressed humans and optogenetic fMRI in the rat to evaluate the changes in whole-brain connectivity associated with depression, especially with respect to the subgenual cingulate and its associated brain regions. In the graph analysis, it was found that the structural correlation brain network in depressed patients was inefficient and less densely connected than in healthy controls. However, some regions, such as the amygdala and ventral frontal cortex, were found to be hyperconnected. In the optogenetic fMRI study, ventromedial prefrontal cortex (the rodent analog to the subgenual cingulate gyrus) stimulation was able to drive behaviors associated with depression and alter the functional connectivity of the region to other areas in the brain, such as the anterior prefrontal cortices, striatum and amygdala. Together, these studies indicate structural and functional abnormalities of the circuitry between the frontal cortices and subcortical limbic system, a collection of brain regions that control emotion, behavior, and reward processing. The presented data supports and expands upon Helen Mayberg’s hypothesis of an overactive subgenual cingulate cortex in depression. Both graph analysis and optogenetic fMRI require further research and development, but they have the potential to be useful tools in the deciphering of the neural circuit basis of depression and in the creation of impactful clinical tools to help manage the debilitating disorder.
Utilizing photonic crystal Fabry-Perot sensors for high resolution sensing with applications in atomic force microscopy [electronic resource]
Keywords: Electrical Engineering.

Atomic Force Microscopes are known for their high spatial resolution images and are widely used in research and the semiconductor industry. Quantitative Atomic Force Microscopy is a technique which quickly measures the interaction force between the probe and sample, extracting mechanical properties in addition to topography. This technique offers the benefits of nanoindentation while maintaining the high speed and throughput of tapping mode imaging. The challenge of increasing the force resolution of Atomic Force Microscopes for quantitative imaging can be met by miniaturization of the Atomic Force Microscope system and has long been a goal in the field. This thesis outlines how photonic crystal fiber sensors achieve this miniaturization to offer improved resolution and stability and presents improvements and theory relevant to these probes which have applications outside the field of Atomic Force Microscopy. The first part of this work discusses how the properties of a Fabry-Perot sensor are enhanced through control of the reflected phase of its constituent mirrors. This brings up many questions about the fundamental limits of reflected phase in highly reflective mirrors which are addressed through theory, an in-depth analysis of photonic crystals alongside selected mirror alternatives and a discussion of efficiently engineering the desired mirror properties through rigorous coupled wave analysis. Confidence in the ability to engineer mirrors with reflected phase capable of providing better sensors necessitated the testing of our theory through experimental validation which was achieved by precise measurements of Fabry-Perot reflected spectra. The middle of this thesis consists of this methodology alongside experimental results to offer confidence in the theory and limits we initially present. Finally, the fiber facet photonic crystal atomic force microscope is presented. These probes were fabricated using in the Stanford Nanofabrication Facility using standard CMOS fabrication techniques and assembled in the Stanford Nanocharacterization Laboratory using a focused ion beam. These probes use photonic crystal mirrors for high sensitivity and are assembled directly on optical fiber for low measurement noise through fiber coupled detectors. They are thus capable of extracting the tip sample interaction force at a resolution of 10 pN/rtHz with every tap in an image.
Validation and sensitivity analysis of simulations of particle deposition in human airways [electronic resource]
Keywords: Computational and Mathematical Engineering.

The airway is a major entry port into our body. Airborne particles such as tobacco smoke, dust, pollen, bacteria are breathed with every breath. Particles are also used for medical treatment in the form of inhaled aerosols to treat diseases such as asthma. The effect of these particles on our health is highly dependent on where they deposit in our airway. Where particles deposit depends on many different factors including the particles' size, how we breath and differences in our airway geometry. We study the sensitivity of deposition to these factors through simulation. First, we start with the surface of a realistic human airway obtained from segmenting an MRI scan, breathing in from the mouth. The flow field is computed using an unstructured LES fluids solver and is validated against an Magnetic Resonance Velocimetry experiment. We can vary the flow field intensity to model different breathing conditions. Particles of size 1 to 10 microns are injected as Lagrangian point particles after the flow field is developed. Their trajectories are integrated until they either exit the airway into high generations of the bronchial tree or they are deposited on the airway wall. The deposition statistics are then analyzed. Finally, to study the sensitivity to perturbations in airway geometry, we constructed a parameterized synthetic airway that can perturbed. We studied the effects of constrictions and expansions in the main bronchi to particle distribution.
Valuation of private companies using a real options approach and the harmony theorem [electronic resource]
Keywords: Management Science and Engineering.

One of the most interesting and intriguing problems in finance is the valuation of private companies; that is, companies that are not yet publicly traded and for which there is no market. Their pricing is very challenging, since traditional methods used for evaluating tradable assets are not applicable. The problem becomes even more interesting, but more complicated as well, when the company we wish to valuate is also a start up, recently founded by an entrepreneur or a group of entrepreneurs, that designs a new, in most cases innovative, product. The task of performing evaluation of such type of companies is very important. There are people who are interested in knowing the value of a start up company that is still private. These include entrepreneurs, venture capitalists, other investors (e.g. people trading private stocks of the company in the secondary markets), potential or current employees of the company and Wall street analysts. All those individuals try to, at least roughly, approximate the current value of a company that they are interested in. That would help them make decisions (e.g. buying the company, selling it or investing in it), depending on the role that each of them has. The method that we propose incorporates both the Net Present Value (NPV) and the Internal Rate of Return (IRR) criteria, that are typically used by the owner of the company and its investors, respectively. That gives us the ability to include both the entrepreneur and the venture capitalists in the model. Our model is the first one that achieves that, and it does by using a very powerful concept, the Harmony Theorem. According to this, the owner of a venture and someone who invests to it will follow the same operational strategy, although their criteria are different. The Harmony Theorem is not the only tool that is used in our model. Our valuation method is also based on real options approaches and projection pricing concepts. In particular, we used real options to represent the possible alternatives (options) that the company has; several rounds of financing from venture capitals, possible IPO, or possible abandoning of the project and sell of the Intellectual Property (IP). Projection pricing is used in the form of the correlation pricing formula (CPF), since we consider private companies, which means that CAPM or Black-Scholes cannot be used for its valuation. We apply our model for three companies that went public during the next couple of years: LinkedIn, Pandora Media and Groupon. The predictions of our model regarding the IPO's of those companies are much better to the ones proposed by analysts and professionals at the time these companies were still private. It is really important that our model performed well for all three companies that belong in different sectors and had different success level.
Vector deformation time-series from spaceborne motion compensation InSAR processors [electronic resource]
Keywords: Electrical Engineering.

We have developed an algorithm, which we call V-SBAS, that extends existing InSAR time-series techniques to estimate the temporal evolution of three-dimensional vector deformation. Our approach uses several LOS-InSAR geometries and an along-track technique called multiple aperture interferometry (MAI) to increase the temporal sampling and dimensionality over time-series in a single radar geometry. By combing multiple observations, we reduce the effect of noise, allowing us to estimate deformation in regions where other multidimensional approaches might typically fail. V-SBAS can be implemented at the backend of any InSAR data processor, but since we use hundreds of interferograms, we develop the processing chain in the context of efficient motion compensation processors. Motion compensation uses the satellite orbit information to shift the position and phase of the receive signal to that of an ideal noninertial circular reference orbit where the focusing equations are simplified and SAR scenes are produced in a common coordinate system. This approach reduces the computational complexity of interferogram formation and is well suited to produce stacks of InSAR data for time-series analysis. We first present our approach to motion compensation and develop the equations to produce stacks of interferograms in a single radar geometry. We find that processing to a common reference orbit introduces spectral shifts, which can reduce coherence for large motion compensation baselines. We derive expressions for these shifts and propose processor modifications to restore coherence. We then develop the V-SBAS algorithm and define a set of constraints that are based on the concept of space-time separability. We present an algorithm to verify the existence of this property through a principal component analysis of existing GPS data, which we use to determine whether or not the constraints should be applied. The separability constraints are nonlinear in the time-series components, thus we also propose a linear approximation to maintain the efficiency of our approach. The linear solution involves an initial unconstrained estimate, followed by a constrained re-estimate of the northward component. We choose this approach because the north is defined primarily by the noisy MAI measurements, while the east and up are defined by InSAR. Finally, we present results of the 2007 Father's Day eruption and intrusion at Kilauea Volcano, Hawaii, where we see agreement with GPS on the order of 2 cm in the east and up directions and 6 cm in the north. The separability constraints reduce the overall average errors to approximately 4 cm, however, some individual stations saw a reduction in error by as much as 10-20 cm.
Verilog piecewise linear behavioral modeling for mixed-signal validation [electronic resource]
Keywords: Electrical Engineering.

Mixed-signal systems-on-chip (SoC's) are complex entities that contain very tightly coupled analog and digital circuits. Validating these complex systems requires simulating the entire design through a large number of test vectors, and each test vector might in turn lead to a long simulation. Due to traditionally differing views of validation as well as design tools for analog and digital, validation of an SoC is not easy. Behavioral modeling is an attractive approach that tries to address this issue by replacing analog circuits with high-level functional models to speed up simulation while retaining some of the analog behavior. This dissertation proposes a method for creating these models in an event-driven, digital modeling language. Piecewise linear approximation is used to represent continuous time analog signals as value-slope pairs that update at discrete instances in time. By breaking analog circuits into sub-blocks with mostly unidirectional ports and leveraging the (nearly) linear intent of analog circuits, an efficient method of computing module output that avoids time integration is possible. The overall result is analog behavioral models that are pin-accurate, fast to simulate and capture the key dynamics in analog circuits. Models of various types of circuits (a simple RC filter, a phase interpolator, a comparator and a current DAC) are used to illustrate the wide applicability of the proposed modeling method. A 250MS/s track and hold, a 2.5-1.8V switching regulator, and a 1GHz PLL are also modeled to verify the preservation of important circuit behaviors as well as to gauge these models' computation complexity.
Vision-based hazard estimation during autonomous lunar landing [electronic resource]
Keywords: Aeronautics and Astronautics.

This thesis develops an information-seeking controller to augment a standard lander descent guidance algorithm in order to improve the performance of vision-based Hazard Detection and Avoidance for autonomous lunar landers. One of the main goals of HDA is to construct a map of the local terrain during the descent so that safe sites can be identified. A vision-based hazard sensing system has the considerable benefit of being lightweight such that it could be used on a small landing craft. However, the quality of hazard measurements derived from imagery is dependent on the spacecraft trajectory, and mapping performance can be degraded if this dependency is not properly accounted for. The new information-seeking controller developed in this thesis actively modifies the descent trajectory in response to the observed terrain to increase the quality and quantity of images used for hazard map creation. This is accomplished by using a novel, online framework to trade fuel against potential information gain. The hazard maps produced using this new information-seeking method show increased coverage and reduced uncertainty regarding the local hazard field when compared to the standard guidance approach. Simulated results using a variety of lander and environmental configurations are presented to demonstrate the effectiveness of the method.