VictorJuiz/thesis huggingface dataset:
Maximum-efficiency architectures for regenerative steady-flow combustion engines [electronic resource]
Keywords: Mechanical Engineering

Steady-flow combustion engines currently account for about 20% of world-wide electricity generation (gas turbine engines) and almost all of commercial aviation (jet engines). With growing interest in natural gas as a low-carbon alternative to coal, and the economic opportunity associated with the discovery of potentially large natural gas reserves, steady-flow combustion engines are likely to play a larger role in energy conversion. Evidently, increasing engine efficiency is of primary importance and has been an active topic of research for over a century. On the one hand, many advanced engine cycles (e.g., humidified cycles, oxy-fuel cycles, fuel-cell/gas turbine combined cycles) that promise higher efficiency are being proposed and analyzed. But on the other hand, there is a sense of resignation that raising turbine inlet temperature is our only hope for higher efficiency. Simply stated, we do not know what engine architectures provide maximum efficiency. The objective of this dissertation is to establish maximum-efficiency architectures allowed by physics and implementable by engineering for regenerative, steady-flow combustion engines. The goal is also to advance thermodynamic understanding of the tradeoffs in reducing sources of entropy generation (irreversibility) that are the reason for inefficiency in engines. To do so, an irreversibility-minimization approach is developed that has three stages. First, reactive engine architectures are modeled as sequences of energy transfer and transformation processes, and represented as trajectories traced by the working fluid in thermodynamic state space. Second, total irreversibility in any architecture is calculated as a function of the trajectory that represents it. Third, the extremal trajectory is identified that minimizes total irreversibility while satisfying constraints such as the turbine inlet temperature limit. Two methods are employed for identifying the extremal trajectory: optimal-control theory and attractor-trajectory based methodology. The former is an extension of the calculus of variations. The latter is a physics-based methodology, developed in this work specifically for engine-architecture optimization to overcome some of the challenges associated with obtaining solutions using the former. The extremal trajectory represents the optimal architecture that has efficiency greater than any other conceivable architecture subject to the same constraints, and the attractor-trajectory based methodology provides insights into the thermodynamics of regenerative steady-flow combustion engines.
Measuring intentional manipulation [electronic resource] : a structural approach
Keywords: Business.

Using a sample of over 1,800 CEOs in the post-SOX period, I estimate the extent of intentional manipulation and manipulation costs using a dynamic structural model that features a risk-averse manager who receives cash and equity compensation. I find that the expected cost of manipulation is low. The probability of detection is 9%, and the average misstatement results in a 1.5% loss in the manager's wealth. According to the estimated parameters, the implied fraction of manipulating firms is around 63% and the value-weighted bias in the stock price is 2.8%. Among five proxies for earnings management used in the extant literature, only performance-matched discretionary accruals have a positive association with the model-implied measure of intentional manipulation.
Mechanical control of metal-ligand complexation and catalysis through surface immobilization [electronic resource]
Keywords: Chemistry

Heterogenization, or the covalent immobilization of discrete molecular species to a material surface, is a promising strategy in catalyst design to leverage high selectivity and ligand variability with the practical heterogeneous advantages of catalyst separation and recycling. Moreover, heterogenization can be used as a mechanical means to control intermolecular interactions and thereby probe reaction mechanisms in a way not achievable through purely homogeneous characterization. An ideal immobilization approach needs to be modular, with high degree of control over the total surface loading of a species and its overall surface distribution. Here we report the preparation and application of functionalized mesoporous silica SBA-15 with a silioxypropylazide incorporated through a co-condensation approach. These materials serve as the platform for the heterogenization of ethynylated organic moieties through the copper-catalyzed azide alkyne cycloaddition. Surface loading is controlled by the amount of azide incorporation during co-condensation, and the surface distribution of immobilized species correlates well with a statistically random model. Immobilized manganese complexes demonstrate rapid catalytic epoxidation and C−H hydroxylation with peracetic acid as the terminal oxidant. Through a controlled variation of the surface loading and a quantitative understanding of site-interactions, we examine the impact of multi-ligand binding and site-isolation on catalysis.
Mechanical properties and molecular structure of silicon carbide hybrid glasses [electronic resource]
Keywords: Materials Science and Engineering

Silicon carbide hybrid glasses are a class of hybrid organic-inorganic glasses which contain inorganic network bonds and organic monovalent bonds. They exhibit not only excellent thermal and chemical stability, but also unique multi-functionality that is tunable by controlling chemical composition, the number of monovalent bonds, and additional porosity. Perhaps the most significant advantage of silicon carbide hybrid glasses is that they are processed without moisture-sensitive bonds, and therefore they are in theory insensitive to "moisture-assisted cracking, " which significantly deteriorates the mechanical integrity of moisture-sensitive materials. These attractive properties make silicon carbide hybrid glasses promising candidates for emerging nanoscience and energy applications that require protection from moisture and harsh environments. However, the successful integration and application of silicon carbide hybrid glasses are limited by their fragile nature due to the reduced network connectivity and lack of plasticity of the glasses. The central theme of this dissertation is to investigate the fundamental connection between the molecular structure and resulting mechanical properties of silicon carbide hybrid glasses to obtain design guides to improve their mechanical properties, which enables the integration and application of the glasses. The crucial role of glass network connectivity and plasticity in the mechanical properties of the silicon carbide hybrid glasses was first demonstrated. It was shown that the cohesive fracture energy of the silicon carbide hybrid glasses can be dramatically improved by conferring plasticity to the glasses through the incorporation of carbon chains into the molecular structure without sacrificing their excellent thermal and chemical stability. The silicon carbide hybrid glasses with plasticity were also used as toughening layers to dramatically improve adhesion in nanoscale thin-film structures. It was then demonstrated that silicon carbide hybrid glasses exhibited a low sensitivity to moisture-assisted cracking even though they were processed without moisture-sensitive bonds. This low sensitivity was due to the formation of Si--O--Si bonds at Si--Hx bonds in the glasses after the deposition process. A new atomistic kinetic fracture model that incorporates the role of moisture-insensitive bonds was developed to quantitatively predict the low sensitivity and crack growth velocity of the glasses. The developed atomistic kinetic fracture model was further employed to explore how the sensitivity of the glasses to moisture-assisted cracking changed with varying Si--O--Si bonds. Finally, the applicability of a new silicon carbide hybrid glass to an industrial application was explored. This new glass exhibited mechanical properties superior to traditional silica-based hybrid glasses and insensitivity to moisture-assisted cracking.
Media as medium, Raoul Hausmann, 1915-1945 [electronic resource]
Keywords: Art and Art History

This dissertation presents an historical and critical framework for understanding Raoul Hausmann's art and writing from 1915 through 1945. While the confrontational performances, anarchic visual poetry, and boldly discordant photomontages Hausmann produced as a Berlin Dadaist (1918-1921) have long been included in the art-historical canon, his overall project remains largely unexplored. Offering detailed analysis of Hausmann's visual and textual work, I situate him in a "discourse network" that extends well beyond the historical avant-garde as it is normally understood to include theories from the natural sciences as well as both new and outmoded media technologies, which the artist repurposed to subversive effect. This study begins with Hausmann's early work in the applied arts and in German Expressionist circles, then follows his career through his one-man, post-dada "presentist" movement and his experiments as a still photographer. Tracking Hausmann's work across several media, I focus on his project of uncovering and overcoming the deeply ingrained social and perceptual conventions that constrain everyday experience. I situate Hausmann in a tradition of German thought that begins with Ernst Kapp's "philosophy of technology" (1877) and continues in the writings of Walter Benjamin and, more recently, Friedrich Kittler, arguing that the artist's work is best understood through the theory of media it articulates. In so doing, I demonstrate that the crux of Hausmann's project lies in his understanding of sensation as continually renewing human subjectivity, a theoretical gambit that allowed him to avoid the pitfalls of both technological determinism and primitivism. Closely examining the specific challenges that Hausmann posed to audiences through his most important works, this dissertation argues for his central role in the historical avant-garde's critical and creative exploration of media.
Mesograzers of giant kelp (Macrocystic pyrifera) at Hopkins Marine Station, Pacific Grove, CA: community structure and seasonal patterns
Keywords: Hopkins Marine Station
Stanford Biology Department
Marine Life Observatory
MLO
Thesis

This thesis describes the mesograzer community of the Hopkins Marine Station kelp bed canopy. The community is characterized in terms of both taxonomic and size class composition based on data from samples collected monthly from August 2010 to July 2011. Multivariate analysis revealed seasonal variation in community structure driven primarily by high numbers of copepods in the spring and summer. Larger-bodied taxa known to graze significantly on kelp exhibited higher abundances and sizes in winter months, especially the kelp isopod Idotea resecata. These changes in community structure were correlated with the intensity of seasonal upwelling. Changes in food quality associated with nutrients advected into the system by upwelling may have played a role in altering the relative abundances of different taxa. The increased density of large-bodied grazers in months following low upwelling may have been in part an artifact of their high mobility and a lower standing crop of kelp that coincided with these periods. Regardless of its ultimate cause, the co-occurrence of high mesograzer density and low nutrient availability synergistically elevates tissue degradation and loss by Macrocystis at this time of year with implications for both the kelp forest community and neighboring habitats.
The microbial ecology of the human nasal cavity [electronic resource]
Keywords: Microbiology and Immunology

The establishment and wide acceptance of an abundant and diverse human-associated microbial community has been one of the most important shifts in the field of microbiology in the past decade. From a bacterial perspective, the body is a vast landscape whose shifting geography and fluctuating environmental conditions provide a range of distinct residential possibilities. Some habitats, such as the intestinal tract and the oral cavity, have been characterized more extensively than others; within these environs, an understanding of the interplay between microbial ecology and health and disease has begun to emerge. The nasal cavity, a crucial component of both the respiratory system and innate immune system, has yet to benefit from an exploration of similar depth. Recent examination of the nasal microbial habitat has almost exclusively focused on the anterior nares without examining deeper sites within the cavity which are actively involved in nasal mucociliary clearance and exposed to the efflux of various sinuses. The aim of this work was to explore this biogeography by characterizing the microbial communities in a range of spatial sites along the nasal passageway. Additionally, the nasal cavity has long been a source of pathogens, most notably Staphylococcus aureus. Carriage of S. aureus has been demonstrated to be a significant risk factor for acquisition of antibiotic resistant strains of S. aureus and hospital-acquired infections. The second aim of this project was to understand whether underlying community features may be present that were characteristic of S. aureus carriage. 13 healthy subjects (6 persistent and 7 non-persistent carriers) were sampled weekly at 3 different sites (anterior nares, middle meatus, and sphenoethmoidal recess) within the nasal cavity over a 4-week period. The data shows that biogeographical differences were based less upon spatial factors and more on epithelium type. The data also showed that the S. aureus carriage type of the individual contributed the greatest amount of non-S. aureus variation within the communities. Finally, a carriage-classifying model was generated from the data and examined for important predictive features, revealing a potential intra-genus, interspecific competitive interaction in Corynebacterium with implications on S. aureus carriage. These results highlight the complexity present in human microbial communities even within highly spatially constrained microenvironments.
Microfluidic and optofluidic investigation of biological macromolecule phase transistions [electronic resource]
Keywords: Applied Physics

Phase transitions are ubiquitous in nature. Fundamental study of phase transition phenomena is a cornerstone of condensed matter physics, and theoretical results in this area guide technology development in material science. Phase transitions also play an important role in biology. Biological macromolecule phase transitions occur in many biological processes, for example the gel-liquid transition in lipid bilayers and amyloid formation in protein aggregation disease. From a technological standpoint, the ability to crystallize proteins has enabled one of the most important advances in biology of the last century: protein structure determination with X-ray crystallography. However, biological macromolecule phase transitions often display stark phenomenological differences from their inorganic analogs. This owes to the sheer size and complexity of proteins and nucleic acid complexes. Macromolecular phase transition theory is rich in subtleties, anecdotal & counter-intuitive results, and often diverges from predictions of classical theory. In addition to developing theory, fundamental study in this area is also critical for improvements in high-throughput crystallography efforts and in understanding mechanisms of devastating neurodegenerative diseases. This thesis approaches the study of macromolecule phase transitions through the development of new measurement technology. In this work, spectroscopic and imaging techniques are combined with microfluidic systems to provide insight into three areas of macromolecule phase transitions. First, dynamic light scattering and microscopy are integrated onto a microfluidic platform to study and optimize protein crystallization. Additionally dynamic light scattering is combined with fluorescence spectroscopy to investigate amyloid fibril aggregation. Finally, a new technology is presented that demonstrates high-throughput mapping of macromolecule structure by integrating single-molecule fluorescence resonance energy transfer spectroscopy with a microfluidic mixing platform. This lab-on-a-chip platform enables examination of conformational transitions in nucleic acids in response to changes in the chemical and molecular environment in order to create a conformational "phase diagram". In addition to presenting new insight into the mechanism of protein crystallization and protein aggregation, this thesis introduces new technologies for studying biological macromolecule phase transitions.
Microfluidic chromatin immunoprecipitation [electronic resource]
Keywords: Bioengineering.

Protein--DNA interactions are responsible for numerous critical cellular events: for example, gene expression and silencing are mediated by transcription factor protein binding and histone protein modifications, and DNA replication and repair rely on site specific protein binding. Chromatin immunoprecipitation (ChIP) is the only molecular assay that directly determines, in a living cell, the binding association between a protein of interest and specific genomic loci. It is an indispensible tool in the biologists' toolbox, but the many limitations of this technique prevent broad adoption of ChIP in biological studies. The typical ChIP assay can take up to one week to complete, and the process is technically tricky, yet tedious. ChIP assay yields are also low, thus requiring on the order of millions to billions of cells as starting material, which makes the assay unfeasible for studies on rare or precious samples. Cancer stem cells (CSCs), for instance, are obtained from primary tumors, and FACS sorting of the dissociated tumor cells rarely yields more than ~100,000 CSCs per tumor. This thesis describes the microfluidics-based strategies for performing ChIP. The first design for a microfluidic ChIP design utilizes the automation and scalability aspects of microfluidics to reduce both total and hands-on assay time, and improve throughput. It can take chromatin prepared using any existing ChIP protocol as input, and generate ChIP-qPCR results in just 1 day. The device is shown to be comparable to existing ChIP protocols, and can detect cellular epigenetic changes induced by external cytokine stimulants. It was used to investigate transcription factor binding dynamics in an aging-related pathway, and was able to link transcription factor binding to local changes in histone modifications. The second design of the microfluidic ChIP platform focuses on addressing the cell number requirements of ChIP. In addition to reducing assay time through automation, this design incorporates microfluidic designs that allow whole fixed cells as input, and enables automated ChIP from as few as 2,000 cells. Finally, using this high-sensitivity ChIP device in conjunction with next-generation sequencing technology, a protocol for determining genome-wide epigenetic landscapes from as few as 2,000 cells is developed, with the ultimate goal of performing protein-DNA association studies on CSCs.
Microfluidic platforms for single-cell analyses [electronic resource]
Keywords: Chemistry

This dissertation describes several microfluidic platforms for single-cell analysis. They represent the continuing advance of analytical technologies to provide ever increasingly detailed information of cellular populations. Microfluidics offers several advantages for working with samples at the single-cell level, including the ability to manipulate nanoliter volumes and enhancement of interactions in confined volumes. In order to demonstrate the scientific utility of these new platforms, the devices are used to process and study various strains of cyanobacteria, which represent an important class of organism of interest to the environmental microbiology community. A microfluidic device that incorporates a membrane of conical nanopores is described and used to capture hundreds of single cells, one per pore. The conical nanopores are created using simple chemical etching of a polycarbonate membrane containing heavy-ion damage tracks. The geometries can be tuned to create nanopores capable of capturing single cyanobacteria cells based on size. Capture and observation of single cells, as well as size-based separation of a cellular mixture, is demonstrated. A second method for capture of single cells using a molecular-imprinted film integrated into a microfluidic device is also described. Films are imprinted with target strains of cyanobacteria and used to selectively capture single cells of the same strain as the imprint template. The imprints are shown to be selective even between different strains of the same genus of cyanobacteria. It is thought that this selectivity derives from diverse chemistries present on these organisms, allowing the imprints to prefer template-matching individuals. The separation efficiency of microfluidic molecularly imprinted films, as well as how that efficiency can be tuned with pH, is demonstrated. Microfluidic single-cell genetic amplification is extended to a new class of organisms through the development of chemical lysis protocols for cyanobacteria that remain sufficiently compatible with the amplification reaction. Previously, such methods were limited to organisms susceptible to simple alkaline lysis. Issues of contaminating genetic material and complications of the MDA reaction, such as coverage variance, are also characterized. The utility of the technique is demonstrated by amplifying a heterogeneous sequence of interest, CRIPSR, and sequencing it.