VictorJuiz/thesis huggingface dataset:
Coal and biomass conversion under supercritical water conditions [electronic resource]
Keywords: Mechanical Engineering

Coal has been used as a resource for power generation for over a century. Due to its low cost and abundance, a large amount of coal and biomass is still being used to generate electricity throughout the world. Given that these solid fuels are here to stay for the foreseeable future, the problem of their environmental impact in terms of their emission of CO2 and harmful gas streams will remain unless solutions can be found. In this study, a feasible option to sequester CO2 and harmful gas streams has been investigated. Supercritical water is an attractive medium for power generation because of its special characteristics. Organic compounds extracted from coal and biomass hydrolyze, and they are completely miscible in supercritical water. In contrast, sulfur, chlorine and many trace elements in coal are oxidized and form insoluble salts in supercritical water, which precipitate and can be removed. The coal/biomass-to-electricity scheme proposed in this dissertation takes advantage of these characteristics of supercritical water in using it as a reaction medium. Coal/biomass devolatilization and char gasification models are introduced in the dissertation. Also provided are an analysis for coal gasification with water at various conditions and a description of the experimental facility to conduct experiments for pulverized coal and biomass conversion under supercritical water conditions (P> 218 atm and T> 647 K). The facility includes high-pressure water pumps, pulse-dampening accumulators, a water preheater, an oxygen booster, a supercritical water gasification reactor, and a reaction quenching cooler. This work presents the entire coal/biomass conversion system, built and assembled, which permits the acquisition of data needed to determine the rate coefficients for reactions that are suitable for supercritical water conditions. The focus of the facility is a flow reactor that can be pressurized to up to 340 atm at temperatures of up to 750 K. The continuous flow reactor is 15 meters long, sufficient for residence times of up to 15 minutes when the total mass flow rate (slurry plus supercritical water flow rates) is 20 grams/min. This work also presents the detailed operational procedures for coal/biomass conversion experiments under supercritical water conditions. In addition, the early operational runs for Wyodak coal conversion under 240-245 atm and 350-385°C and their results are discussed.
Coherent feedback and control of linear quantum stochastic dynamical systems [electronic resource]
Keywords: Applied Physics

Coherent feedback will play an important role in the emerging field of quantum control, whose goal is to apply concepts from control engineering and dynamical systems theory to the realm of quantum systems in order to tailor system behavior and performance to suit the needs of scientific and engineering applications. In this thesis I present a system of coupled degenerate optical parametric oscillators (OPOs) that are arranged in a feedback configuration to demonstrate some basic principles of coherent feedback and control. A key point is that the system exhibits gain in the feedback loop, a fundamental component necessary for design flexibility of system dynamics. System behavior will be discussed from a perspective of control goals for narrow band disturbance rejection and amplification, as well stabilization control.
Coherent X-ray diffraction of laser-induced magnetization dynamics and nonlinear X-ray effects [electronic resource]
Keywords: Applied Physics

Coherent x-ray di raction is an attractive tool for studying a wide range of condensed matter systems due to the many unique advantages of x-rays - small wavelengths, large penetration depths, and chemical and elemental specifity. Soft x-rays are particularly important for the study of magnetism, as many of the important magnetic elements have strong resonances in this regime. This dissertation discusses two sets of coherent x-ray experiments. The first part focuses on the development of time-resolved optical pump x-ray probe experiments both at a synchrotron and an x-ray free electron laser (XFEL) source. Using this technique, I studied the femto- to picosecond relaxation dynamics in the labyrinth-like magnetic domains of a Co/Pd multilayer thin film following excitation by a femtosecond optical pulse. From the normalized correlation function, I isolated the elastic and fluctuating portions of the scattering intensity during the relaxation process. The emergence of XFELs such as the Linac Coherent Light Source has dramatically altered the types of experiments that are now possible, including the systematic exploration of nonlinear x-ray-matter interactions. Nonlinear spectroscopy in the optical regime has contributed immensely to our understanding of microscopic interactions and dynamical processes. The hope is to extend these spectroscopic techniques to the x-ray regime, to take advantage of the smaller wavelength, elemental and chemical specificity, and momentum resolution. One of the most promising nonlinear x-ray techniques is stimulated resonant inelastic x-ray scattering (RIXS), analogous to stimulated Raman scattering in the optical regime. The critical question is whether the threshold for stimulated RIXS will be low enough, below the sample damage threshold, for it to be a viable technique for systems of interest. In the second half of this dissertation, I demonstrate strong indications of stimulated RIXS in a high intensity single shot coherent di raction experiment at LCLS. By utilizing the strong resonant enhancements of the scattering cross-section, significant nonlinear changes in the di raction as a function of x-ray pulse intensity were detected. These observations are consistent with calculated intensities for a stimulated inelastic scattering process. Further intensity dependent spectroscopy experiments are planned for LCLS to con rm the threshold for stimulated scattering. The development of nonlinear x-ray spectroscopic techniques will certainly revolutionize existing fields as well as spawn entirely new fields of research.
College students' sense of belonging [electronic resource] : dimensions and correlates
Keywords: Education.

Colleges and universities often have significantly different graduation rates based on students' ethnicity. Systematic variation in students' sense of belonging at college may be a factor. Existing literature suggests that a better understanding of student belonging at the college level can help to improve college outcomes, particularly for racial/ethnic minorities who are often underrepresented on college campuses and may benefit from well-designed systems of support to bolster their sense of belonging. This study was designed to improve our understanding of student belonging, its components, and its correlates for a diverse group of college students. Self-reported survey data were collected from 159 college sophomores (about a quarter of the class) from one small private and predominantly white college with graduation rates that varied by student ethnicity. Factor analysis produced three reliable and independent measures of belonging: social belonging, academic belonging, and perceived institutional support. Further investigation of this sample indicated that the general measures of college students' 'sense of belonging' found in the literature are mainly social in nature and therefore mask more nuanced associations with important variables that are revealed with separate measurement of academic belonging and perceived institutional support. Results from a set of multivariate stepwise regression analyses suggested that student demographics (ethnicity, parent education, and gender) jointly did not explain a significant amount of variance in any measure of student belonging. Rather, institutional and interpersonal variables (e.g., students' perception of the college's commitment to diversity, students' perception of the personal relevance of the curriculum) jointly explained a significant amount of variance in all three measures of belonging, suggesting that the strongest predictors of student belonging were not fixed student attributes but other variables that can be influenced to various extents by college policies and practices. Additional results indicated that social belonging and academic belonging were significantly and differentially associated with students' self-reported GPA, level of satisfaction with the institution, level of class participation, and frequency of meetings with professors outside of class time. The findings suggest that while social belonging has important associations with measures of academic performance and outcomes, academic belonging is also important and distinct. Differentiating the measurement of 'sense of belonging' into three components may be useful both for research and for guiding institutional policies and practices. It allows us to identify more precisely what facet of belonging is being measured, and how each is differentially associated with 'college experience' variables and educational outputs of interest.
Combining light restriction and optogenetics to dissect the neural circuitry underlying behavior [electronic resource]
Keywords: Neurosciences.

Aberrant states in the nervous system, both acute and chronic are the cause of mental health diseases that affect more than a quarter of Americans over the age of 18. The mechanisms underlying mental health diseases such as Parkinsons, schizophrenia, anxiety, and depression are poorly understood, and thus current treatment approaches are often ineffective or carry with them significant side effects. In order to improve our understanding of these diseases and others, new tools must be developed that take into account the complex dynamics and diversity of circuit elements that make up the neural substrates from which these behaviors arise from. Our lab has pioneered the use of light activated microbial opsins in mammalian neurons in order that we can manipulate neural circuits with cell- type specificity, millisecond temporal precision, and millimeter spatial resolution -- termed 'Optogenetics" . These genetically encoded elements include two broad classes, excitatory channels such as Channelrhodopsin - 2 (ChR2) and inhibitory pumps such as Halorhodopsin (NpHR). The use of these tools allow for bidirectional control ove r cell types and connections that make up the neural circuits that underlie behavior within normal and diseased mental health states using simple gene and light targeting approaches. But, the nervous system's structural complexity -- both in the geometrical arrangement of neurons and connections between neurons - requires more than these basic approaches to dissect its function. T o address this extra layer of complexity, the spatial control of light excitation itself could be a versatile method in combination with optogenetic approaches to dissect neural circuitry. The studies herein look to build upon current optogenetic technology by utilizing light restriction in order to control and dissect neural circuits with high precision. There are two approaches used to accomplish this: (1) in vivo and ex vivo one photon light restriction that utilize simple light restrictive optical elements to more precisely stimulate and inhibit both genetically targeted cells or connections between close brain areas and (2) in vivo and ex vivo two photon techniques that allow for fast excitation, inhibition, and bi- stable modulation at the level of a single - cell, multiple single - cells, or in some cases, sub-cellularly . The tools developed here can be used in a variety of systems and allows for the dissection of neural circuitry using optogenetics to a new level of precision that was otherwise unapproachable via any technique available to researchers. As these tools are further developed, a bridge between the individual cellular contributions to neural circuit function and behavioral neuroscience will hopefully emerge.
Commercial video games as preparation for future learning [electronic resource]
Keywords: Education.

In the field of digital game-based learning there has been much focus on the development of educational games—games designed specifically to teach. Attention has also been paid to commercial, off-the-shelf (COTS) games, but that work has focused mostly on the motivation, engagement, and community participation engendered by such games. Relatively little work has been done to examine the potential of incorporating COTS games into formal curricula, and to the best of my knowledge no one has studied what school-relevant learning benefits might accrue from simply playing COTS games in one's leisure time. This dearth of research is unsurprising: there is no reason to expect that games designed entirely to entertain would produce learning benefits on school content that are measurable by traditional assessments. A novel assessment framework called Preparation for Future Learning (PFL), however, is designed specifically to measure immature forms of knowledge that traditional assessments miss, by incorporating learning resources into the assessment process to determine what test takers' immature knowledge has prepared them to learn. In this study, I used the PFL framework to investigate whether being randomly assigned to receive and play one of two COTS games (Call of Duty 2, n = 34, or Civilization IV, n = 35) at home over the course of five weeks would prepare community-college students to learn from a lecture about World War II compared to a control condition that received no game (n = 33). Learning was measured by performance on pre- and post-lecture multiple-choice tests comprising items from the National Assessment of Educational Progress (NAEP), the California Standards Test (CST), and a purpose-built test from a World-War-II study guide produced by the company SparkNotes. Results indicated no condition differences in performance on the pre-lecture test but a significant positive effect of gameplay on the post-lecture test, suggesting that gameplay experiences had prepared participants in those conditions to learn more from the lecture. Additionally, responses to open-ended questions about two scenarios that had not been covered in the lecture suggested that the two games had influenced participants' attention to the lecture differently: CoD2 players were more attentive to local tactical elements, and Civ4 players to global strategic elements. Demonstrating school-relevant benefits of COTS gameplay strengthens the broader argument for digital game-based learning, suggests that educators could leverage recreational gameplay with appropriately designed formal instruction, and shows COTS game designers that incorporating even modestly school-relevant experiences in their games could help their players without compromising the appeal of their games.
Compactifying picard stacks over degenerations of surfaces [electronic resource]
Keywords: Mathematics

Moduli spaces of smooth varieties can be partially compactified by the addition of a boundary parametrizing reducible varieties. We address the question of partially compactifying the universal Picard stack (the moduli space of line bundles) over a moduli space of smooth varieties by extending it over such a partial compactification. We present a stability condition for line bundles on reducible varieties and use it to specify what boundary points should be added to the universal Picard stack to obtain a proper moduli space. Over surfaces with exactly two irreducible components, we give specific results on enumerating stable line bundles, which support the conjecture that these are the right boundary points to add. This generalizes work of Caporaso and others in the 1990s on compactifying the universal Picard variety over the moduli space of curves.
Comparative modeling and protein-like features of hydrophobic-polar models on a two-dimensional lattice [electronic resource]
Keywords: Physics

Lattice models of proteins have been extensively used to study protein thermodynamics, folding dynamics and evolution. Our study considers two different hydrophobic-polar (HP) models on the two-dimensional square lattice: the purely HP model and a model where a compactness-favoring term is added. We exhaustively enumerate all the possible structures in our models and perform the study of their corresponding folds, HP arrangements in space and shapes. The two models considered differ greatly in their numbers of structures, folds, arrangements, and shapes. Despite their differences both lattice models have distinctive protein-like features: (1) Shapes are compact in both models, especially when a compactness-favoring energy term is added. (2) The residue composition is independent of the chain length and is very close to 50% hydrophobic in both models, as we observe in real proteins. (3) Comparative modeling works well in both models, particularly in the more compact one. The fact that our models show protein-like features suggests that lattice models incorporate the fundamental physical principles of proteins. Our work supports the use of lattice models to study questions about proteins that require exactness and extensive calculations, such as protein design and evolution, which are often too complex and computationally demanding to be addressed with more detailed models.
Competition and strategic interaction in new markets [electronic resource]
Keywords: Management Science and Engineering

My dissertation focuses on how firms compete effectively in new markets, and explores several strategic issues faced by firms in these contexts. These include how firms strategically interact with their rivals, how they quickly and efficiently craft successful strategies and develop viable business models, and how they successfully position themselves as the cognitive referent in the new market they are creating. While prior research has examined many of these issues in the context of established markets, my research investigates new markets and traces the activities of entrepreneurial rivals. Through an in-depth, longitudinal field study of five firms in the online investing market, I develop new theory to explain how firms successfully achieve these objectives. The first theoretical framework offers an explanation for how firms win the race to develop a viable business model. As the new market emerged, high performing firms enacted three strategies in sequence, which helped them get to a business model quickly and efficiency. First, executives attended to substitutes and copied from rivals. Next, they actively tested assumptions and made major resource commitments to the most lucrative business model opportunity. Finally, they maintained loose links in the organizational activity system to accommodate emergent sources of value. The resultant middle range theory has implications for research on competition in new markets and the strategic processes of developing business models. The second theoretical framework offers an explanation for how some firms become the cognitive referent in a new market while others fail to do so. Although prior research has shown how firms and other actors use rhetoric and symbolic activities to create new markets, I analyze how entrepreneurial firms use the same cultural strategies to position themselves in a new market they are creating. Successful firms conceptualize market creation as problem solving and follow a sequence that begins with narrowly directed rhetorical attacks aimed at current solutions, progresses to shifting stories to coincide with emergent logics, and culminates with eschewing labels that audiences attach to them as these firms introduce novel products to the market. By contrast, unsuccessful firms undermine their own positions through improper use of symbolic market creation activities. The resultant theory is relevant to the literatures on cultural strategy and the performance of entrepreneurial firms.
Computational efficiency in internet economics and resource allocation [electronic resource]
Keywords: Management Science and Engineering

The Internet has created an environment for operations research to play a role in solving practical problems with large networks and a tremendous amount of data. In this thesis, I am interested in developing mathematical principles and computational methodologies underlying the huge multiple-agent environment created by social economic systems over the Internet. The three major topics covered are: 1. Social network advertising, modeling, and pricing: I propose an analytic model and solution for advertisement on a social network based on the concept of forwarding power. Forwarding power is a concept I derive to quantify the amount of information each node is able to gather from the network, or the power to forward information from its predecessors. In other words, the forwarding power is an individual's ability to forward others' opinions. Based on this new concept for a social network, I formulate an optimization model that maximize social welfare, a goal often favored by system designers. This has the advantage of being a convex program that can be solved in polynomial time. Furthermore, it derives a polynomial-time, implementable, and truthful mechanism for advertisement pricing. 2. Envy-free resource allocation: I study the computational efficiency of the envy-free cake-cutting problem. A solution to this problem would be a resource allocation among several partners such that no one entity would envy the anothers' allocated part. I am interested in understanding the query complexity to achieve this task, under both the oracle function model as well as the polynomial function model. I characterize the complete query complexity by developing an (asymptotically) matching query bound for the oracle function model. I also prove PPAD-completeness for the query complexity under the polynomial time function model. In deriving these results, I developed a comprehensive characterization of query complexity for discrete fixed points and the Tucker problem. 3. Finding pure Nash equilibria in supermodular games: A supermodular game abstracts relations in the players' strategic alternatives, among the participation agents. Tarski's fixed point on lattices forms the mathematical foundation for the supermodular game. For both supermodular games and Taski's fixed points, I find the first efficient algorithm to find one solution and prove hardness results to determine uniqueness (matching bounds for query complexity in the oracle function model and Co-NP-hardness in the polynomial function model). The modeling techniques, fundamental mathematical insights, and algorithmic tools developed in this thesis are expected to be useful for many related applications in Internet economics and resource allocation.