VictorJuiz/thesis huggingface dataset:
Computational Research on Adiposity, Nutrition, and Energy expenditure (CRANE) [electronic resource]
Keywords: Electrical Engineering

The rapid rise in obesity in the US over the last several decades parallels a decrease in infectious disease incidence and a rise in antimicrobial usage. The role of the microbiome—which is influenced by both disease and by biocidal chemicals—on body weight is of increasing interest. We desired to quantify effects of changes in disease patterns and microbiome shifts on body weight of the population; however, no population-level model of body weight existed. Drawing from a collection of literature describing models of individual body weight, a model was built to quantify weight changes across the population using publicly available data from the National Health and Nutrition Examination Survey (NHANES). The model used an energy balance perspective, quantifying energy intake and expenditure. First, dietary data was obtained to describe energy intake. Dietary data comes primarily from self-report and is notoriously inaccurate as individuals tend to under-estimate their food consumption. A dataset was obtained from a study where participants had completed dietary recall surveys and had had energy expenditure measured. Using this as a "training dataset", Chapter 3 describes two predictive models developed which adjust dietary intake to a more biologically plausible range. The models were validated, with a simulation of NHANES data, for their ability to produce estimates within bounds established a priori. They produced substantially more realistic estimates than those derived from the raw data. With better estimates of energy intake, a simulation model of body weight in a population was built (Chapter 4). A population was drawn from NHANES which represented a realistic cross-section of the U.S. population based on age, sex, and survey sampling weights. Energy intake and expenditure were tracked for each individual in the model, and an excess or deficiency of energy was converted to a gain or loss of body weight. The effect of ageing on the weight distribution of the population was calculated. The excess energy necessary to produce the shift in the body weight distribution of the US population over a 20-year period was estimated. The effect of an infectious agent's alteration of energy intake and expenditure and associated body weight was also calculated. Finally, the relationship between NHANES data on triclosan and body mass index (BMI) was studied (Chapter 5). Triclosan is a biocide that likely affects the gut microbiome. The effect of triclosan on BMI in a linear regression was studied with triclosan expressed in two ways: (1). as a binary variable (present vs. absent) and (2). in quartiles (in order to assess whether increased quantity of triclosan led to a trend in BMI). Triclosan presence was found to be associated with an increase in BMI. By quartile, BMI was higher in lower levels of triclosan compared to higher levels, suggesting the possibility of multiple mechanisms of action.
Computer modeling of human lower limb muscles to study how muscle fiber lengths and velocities affect muscle force generation during walking and running [electronic resource]
Keywords: Mechanical Engineering

Walking and running rely on the complex coordination of the neurological, muscular, and skeletal systems. The role of muscles in this system is to produce force, a task that is dramatically affected by the dynamics of muscle fibers. In walking and running, we do not know how fiber dynamics affect force generation because experimental tools are ill suited to these measurements. Computer models can be powerful tools for estimating muscle dynamics that cannot be measured experimentally. During my doctoral research I created a model based on state-of-the-art muscle architecture data that estimates fiber lengths and velocities during movement. I used this model to create simulations of muscle fiber dynamics for five subjects walking and running at multiple speeds. Analysis of my simulations revealed how walking or running speed affects force generation, explained how running enables some muscles to produce more force than they do in walking, and yielded normative muscle fiber lengths and velocities of eleven muscles during walking and running. The results support the hypothesis that the walk-to-run transition in human gait is related to the force generation ability of the plantarflexors, offer insights into dynamic properties of muscles that have not yet been measured during walking and running, and permit comparisons among muscles with diverse architecture. The model and simulations created as part of this work can be applied to many other research areas in biomechanics and have been made freely available at simtk.org.
Conditional Stochastic Disasters and the Equity Premium Puzzle
Keywords:  Department of Economics
Stanford Department of Economics
Thesis

Motivated by Barro’s (2006) approach towards modeling the equity premium, we study the original formulation of the equity premium puzzle as posed by Mehra and Prescott (1985). Firstly, we build a single-regime stochastic model capable of simulating the effects of rare economic disasters. We then extend that into a multi-regime model which allows study of conditional disaster regimes and shocks that are not i.i.d., allowing for the simulation of a robust variety of economic phenomenon. Finally, we examine the results of modeling depression-recession economic cycles with the possibility of recessionary aftershocks following severe depressions. Compared to historical economic data, we conclude that a multi-regime model can account for the observed equity premium while simultaneously producing a plausibly low real rate.
Confidence-building measures [electronic resource] : a theoretical and empirical assessment
Keywords: Political Science.

Confidence-building measures (CBMs) are a unique class of international agreement intended to reduce mistrust between rival states by minimizing the risk of surprise attack, political exploitation of military power, and of inadvertent conflict or escalation. This dissertation offers four related papers that firmly ground the concept of CBMs in international relations theory. The first paper provides a conceptual definition of CBMs premised on the idea that uncertainty over a rival's intentions is a basic cause of mutual fears between states. CBMs attempt to build confidence in intentions by either credibly revealing a state's preferences or demonstrating that specific actions are non-hostile. Three strategic structures enable CBMs to overcome the obstacles of sustaining compliance in the face of incentives to defect. The first two strategic structures are familiar in international relations theory: Harmony and the repeated Prisoner's Dilemma. However, one important type of CBM - notification CBMs - cannot be sustained by either Harmony or the repeated Prisoner's Dilemma. The second paper offers a game theoretic model of notification CBMs that explores their unique strategic structure. They rely on a tradeoff between the utility of exploitation and the cost of accidents to make notification both possible and informative. The third paper explores the empiric landscape of CBM practice. Analysis of a new dataset of CBMs shows wide variation in the prevalence and type of CBM agreements. Statistical analysis of a number of theoretically and empirically derived determinants identifies several factors that are associated with increased probability of CBM agreements. The fourth paper examines the roots and effectiveness of the 1972 U.S.-Soviet Incidents at Sea Agreement, one of the most important early CBMs. The paper is the first quantitative test of whether or not the INCSEA Agreement succeeded in reducing dangerous naval incidents. Collectively, these papers provide a systematic exploration of an important but under-studied class of international agreement.
Conflict, community and crime in fin-de-siècle Sichuan [electronic resource]
Keywords: History.

The 350 legal cases from the ming'an ["cases of unnatural death"] category of the Ba County archive that survive from the final decade of the nineteenth century create a textured picture of social life and state-society relations at the grassroots near the end of the Qing Dynasty (1644-1912). Close analysis of these cases enhances our understanding of the lives of ordinary people in the last decades of the old regime by untangling the webs of social relations, practices, and norms that bound people together and gave their actions meaning. At the same time, this study illuminates the role that local courts played, even at the end of the dynasty, in settling disputes and in enforcing the normative forms of authority that underpinned social order. Together, these chapters offer a vivid and unprecedented picture of life in late-Qing China. This study employs death to illuminate the webs of social life in the county. Despite the frequent opacity of the actual event (suicide, homicide or other violence), these acts explode into view the surrounding social connections and cleavages, revealing how both death and violence were instrumental in local life.
Conic degeneration and the determinant of the laplacian [electronic resource]
Keywords: Mathematics

We consider a family of smooth Riemannian manifolds which degenerate to a manifold with a conical singularity. Such families arise in various settings in spectral theory, including the study of the isospectral problem. We investigate the behavior of the determinant of the Laplacian under the degeneration. Our main result is an approximation formula for the determinant, including all terms which do not vanish in the limit. The key idea is a uniform parametrix construction for the heat kernel on the degenerating family of manifolds, which enables us to analyze the determinant via the heat trace. It becomes clear in the construction that we need to understand both the short-time and long-time behavior of the heat kernel on an asymptotically conic manifold. Using techniques of Melrose and building on previous work of Guillarmou and Hassell, we give a complete description of the asymptotic structure of this heat kernel in all spatial and temporal regimes.
Content in the digital era [electronic resource] : multiplex configuration and online pricing
Keywords: Business.

In the first chapter, the movie exhibitor's problem is analyzed in the light of two forces vying for the limited footprint of their properties. Recent advances have enabled exhibitors to satisfy consumers' long-standing desire for increasingly larger screens. On the other hand, digital technology has reduced the cost of playing the same movie on multiple screens, thereby creating an incentive for screen expansion to increase the number of show times for a given movie. Increasing the screens also has the added benefit of allowing the exhibitor to expand the number of unique movies screened at a given time. The goal of this chapter is to evaluate consumers' relative valuations of the large screens vs. more shows tradeoff in determining space allocations. Using a new data set on movie showings in India at the movie-chain-market-week level, an aggregate discrete-choice demand model is estimated providing measures of customer preferences for the number of movie showings and screen size. India provides a valuable setting to study this question because the densely populated cities face substantial space constraints and regional heterogeneity in tastes and languages suggest the option of more shows may be more important in some cities than others. The findings generally indicate that while adding more shows is beneficial, the additional expenses associated with building more screens as opposed to larger screens is not justified by the increased demand in some markets. In the second chapter, I explore how the digital era is changing purchase and rental movie markets. Low transaction costs make it easier for consumers to access online content and Digital Rights Management enables studios to provide durable and non-durable versions of their movies. I design a conjoint experiment to recover consumer preferences to determine the studio's best strategy in the online space. I find that heterogeneity in one-time versus repeat consumption preferences drives purchase and rental offerings. I also find that when consumers place a premium on accessing new content, they are less likely to inter-temporally substitute thereby increasing the firm's pricing power. Consistent with theory, commitment to future prices increases profits considerably. This supports retailers', such as Apple's, rigid pricing structure despite studios' push towards more pricing flexibility.
Continuous-time sigma-delta modulation using digitally linearized Gm-C integration [electronic resource]
Keywords: Electrical Engineering

High-performance continuous-time sigma-delta modulators that utilize rectangular DAC feedback pulses suffer from a relatively high sensitivity to timing jitter. In order to overcome this problem, many state-of-the-art designs rely on SC feedback pulses. Unfortunately, the large peak currents generated by the SC waveform dictate higher power dissipation, primarily due to the increased slew rate requirements in the active RC circuit that is typically employed as the modulator's first integrator. This research reports on a proof-of-concept evaluation of an alternative jitter-insensitive approach that replaces the slew-rate limited active RC circuit with a low-power Gm-C integrator that can efficiently absorb SC feedback waveforms. To further reduce the requirements on the Gm-C circuit in terms of linearity, we employ a polynomial-based digital-domain nonlinearity compensation. The required coefficients are background calibrated using a highly linear, but low SNR auxiliary modulator. In this scheme, the estimates of the linearization coefficients are obtained by minimizing the mean squared error between the two outputs using an LMS algorithm. A 65-nm CMOS experimental prototype achieves 79 dB dynamic range, 74.3 dB peak SNR and 73.3 dB peak SNDR for a signal bandwidth of 1.95 MHz and 124.8 MHz sampling rate. The IC dissipates 8.55 mW from a 2.5 V supply.
Control and suppression of laminar vortex shedding off two-dimensional bluff bodies [electronic resource]
Keywords: Mechanical Engineering

The focus of this research is on the control and suppression of vortex shedding of flow past bluff bodies. The motivation of this research stems from the aerodynamic problems encountered in the design and development of hard disk drives (HDD's). Two different computational fluid dynamic methods have been used in this research-- the Semi-Implicit Method for Pressure Linked Equation (SIMPLE), that is widely employed in today's commercial incompressible flow solvers, and the high-order spectral difference (SD) method, recently developed for compressible flow solution. In addition to numerical simulation and verification, complementary experimental measurements have been performed to further validate the results. This research leads to two very different suppression techniques: 1) a passive control using a thin splitter plate positioned downstream of the bluff body; 2) an active control by way of counter rotating a cylinder pair. The passive suppression technique places a thin splitter plate downstream of the bluff body in order to interfere with the vortex wakes and thereby suppress the vortexinduced forces on the bluff body itself. The present investigation examines the suppression of wake instabilities in the laminar shedding regime. Both bounded and unbounded flow conditions are examined. It is found that in the bounded flow condition, the channel walls have an additional stabilizing effect on the shedding control. With proper positioning of the splitter plate, vortex shedding is completely suppressed in a bounded flow with moderate blockage factor. Wind tunnel empirical experiments have also confirmed the effectiveness of a splitter plate in a bounded flow. Active flow control by counter-rotating a pair of cylinders has been numerically investigated. It has also been investigated experimentally in partnership with the Gas Dynamics Laboratory at Princeton University. It is demonstrated that it is possible to suppress unsteady vortex shedding for gap sizes from one to five cylinder diameters, at Reynolds numbers from 100 to 200. The degree of unsteady wake suppression is proportional to the speed and the direction of rotation, and there is a critical rotation rate where a complete suppression of flow unsteadiness can be achieved. In the doublet-like configuration at higher rotational speeds, a virtual elliptic body that resembles a potential doublet is formed, and the drag is reduced to zero. The shape of the elliptic body primarily depends on the gap between the two cylinders and the speed of rotation. Prior to the formation of the elliptic body, a second instability region is observed, similar to that seen in studies of rotating single cylinders. It is also shown that the unsteady wake suppression can be achieved by rotating each cylinder in the opposite direction, that is, in a reverse doublet-like configuration. This tends to minimize the wake interaction of the cylinder pair and the second instability did not make an appearance over the range of speeds investigated here.
Control of DNA capture by nanofluidic transistors [electronic resource]
Keywords: Electrical Engineering

For decades, scaling of semiconductor devices has allowed massive parallelization and faster devices for higher processing throughput at a lower cost. Similar benefits can be reaped for biotechnological systems. Miniaturized microfluidic sensors and actuators have dramatically improved the throughput of biomolecular analysis by parallelization. The development of further miniaturized biotechnological sensors and actuators (in the nanoscale) is a thriving field of research today. A promising group of such nanofluidic devices are based on nanopores. Over the past 15 years nanopores have garnered significant interest as single-molecule analytical tools, particularly for DNA sequencing, and actuators to manipulate ionic and biomolecular transport. In this work, we report the use of electrically-gated ~200 nm pores as a reversible, electronically-tuneable biomolecular switch, namely, a nanofluidic transistor (NFT). We demonstrate highly effective electrostatic control of the nucleic acid capture rate with > 1000-fold modulation using sub-1V gate biases. These devices were fabricated to exploit the barrier-limited operation arising from the balanced interplay between electroosmotic flow (EOF) and electrophoresis for pores of this size and aspect ratio. The method relies on varying the gate voltage to modulate the shape of the electric double layer (EDL) to finely tune the strength of the EOF opposing the DNA's electrophoretic motion. We have determined that operating these NFTs within the sub- to near-threshold regime allows for exponential (or super-linear) control of the DNA capture rate. We present detailed numerical simulations to quantitatively elucidate the underlying mechanism of NFT operation and the effects of electrical biases, solution pHs, NFTs surface properties and NFT device dimensions. This dissertation will contain an overview of electrokinetics of nanopores, a survey of nanofluidic device research, the specifics of nanofluidic transistor fabrication used, the details of instrument development and behavior, the results of the DNA capture rate modulation experiments, and potential applications of the nanofluidic transistors studied.
Controlled electrode aging and nanoscale electrolytes for solid oxide fuel cells [electronic resource]
Keywords: Materials Science and Engineering

Solid oxide fuel cells (SOFCs) are a compelling energy conversion technology due to their high efficiency and fuel flexibility, but their commercialization has largely been limited by high operating temperatures (800-1000°C). Recent research efforts have focused on nanoscale SOFC membranes via MEMS-type fabrication and have demonstrated low-to-intermediate temperature operation (250-550°C) with improved device performance. Porous platinum is commonly used as the electrode material in these research devices, but it is unfortunately subject to coarsening at even moderate temperatures, leading to degradation of the electrodes and ultimately reduction of device performance. In order to investigate the evolution of porous Pt electrodes and evaluate nanoscale YSZ electrolytes, we fabricated two types of SOFCs with identical electrodes: bulk-YSZ (100um-thick) electrolyte with 115nm-thick porous Pt electrodes; and atomic layer deposited (ALD) nano-YSZ (30nm-thick, varying compositions) electrolyte with 115nm-thick porous Pt electrodes. This dissertation begins with a general introduction to solid oxide fuel cells, fundamentals of their operation, and key metrics for their evaluation. The second part of this dissertation focuses on bulk-YSZ SOFCs, which were the subject of an electrode pre-treatment study, and which also served as baseline devices for comparison with nano-YSZ SOFCs. In this pre-treatment study, we observed that cycling air and forming gas over the anode resulted in an immediate, sustained, and significant enhancement of the current density compared to devices tested without pre-treatment. The apparent enhanced current density was accompanied by a 10x enhancement of SOFC performance and a 93% reduction in total electrode resistance. The third and fourth parts of this dissertation focus on the ALD of YSZ and subsequent characterization of SOFCs fabricated with 30nm-thick YSZ membranes of varying composition. These SOFC membranes tested are among the thinnest reported.
Controlling ramification in number fields [electronic resource]
Keywords: Mathematics

This thesis focuses on two aspects of limited ramification and is split up into two independent sections. The first section (which comprises the second and third chapters) is on the distribution of class groups of cyclic cubic fields. We propose an explanation for the discrepancy between the observed number of cyclic cubics whose 2-class group is C_2 x C_2 and the number predicted by the Cohen-Lenstra heuristics, in terms of an invariant living in a quotient of the Schur multiplier group. We also show that, in some cases, the definition of the invariant can be simplified greatly, and we compute 10^5 examples. The second section (which comprises the fourth and fifth chapters) discusses branched covers of algebraic curves, especially covers of elliptic curves with one branch point. We produce some techniques that allow us to write down explicit equations for such maps, and then we give examples of number fields which arise from such covers. Finally, we present some possibilities for future works that the author hopes to pursue.