VictorJuiz/thesis huggingface dataset:
Broken rotational symmetry in iron based superconductors [electronic resource]

High-temperature superconductivity often emerges in the proximity of a symmetry-breaking ground state in strongly interacting electronic materials. In the case of the superconducting iron pnictides, in addition to the antiferromagnetic ground state of the parent compounds, a ubiquitous but small structural distortion breaks the crystal C4 rotational symmetry in the underdoped part of the phase diagram. It has been proposed that this structural transition is driven by an electronic nematic phase transition, below which the electronic system spontaneously organizes with an orientational order without developing additional spatial periodic order. In this thesis I show how the effects of this electronic nematic order can be explicitly revealed by observing the response of the system to in-plane uniaxial stress. I present transport measurements of single crystal samples of various iron-based superconductors held under an in-situ tunable strain at temperatures above the phase transition, which explicitly confirm that the structural transition is fundamentally driven by a thermodynamic instability in the electronic part of the free energy. I will also discuss the nematic fluctuations prevailing throughout the overdoped part of the phase diagram, which suggests that a quantum phase transition occurs at the optimal doped composition. Finally, I will describe the in-plane resistivity anisotropy measurements of detwinned samples at temperatures below phase transition, which potentially reveals an intriguing interplay between topological protected Dirac pockets and spin/orbital ordering.

Keywords: Applied Physics
Advisor: Fisher Ian R. (Ian Randal) primary advisor. Thesis advisor
Kivelson Steven advisor. Thesis advisor
Shen Zhi-Xun advisor. Thesis advisor
Building a creative community [electronic resource] : emergent practices and learning at a seven-week innovation camp

Supporting creativity and innovation has emerged as a top priority across fields from Education to Environmental Sciences and even the Humanities. Accordingly, there has been a recent surge of experimental contexts to spark and sustain creativity and innovation. The Globul5 innovation camp, an extreme example of such an exploration, provided an unstructured context for twenty-eight young adults as they lived and worked together in a factory for seven weeks to redesign "the future of work." Through analysis of field notes, video records, photographs, and interviews, I investigated the conditions of the camp design, the community's emergent collaborative practices, and the residents' learning processes. The research questions guiding this study are: 1) What were the incoming conditions of the innovation camp? 2) How did collaborative teams address challenges that arose at the camp? 3) How did participants forge individual learning pathways at the camp? 4) What insights about creative collaboration did participants articulate after the camp? Results of this research suggest that the relational intensity and lack of structure at the camp posed challenges to team project work; however, a significant factor of the residents' learning may be attributable to these challenges and the resultant need to invent ways to manage them. Residents learned through observation, experimentation, critical reflection, and reflective discourse; ultimately, they described the camp as a transformative learning experience (Mezirow, 1991). Residents adapted, adopted, and developed practices at the camp to manage their collaborative work, including a ritual for abandoning projects that were failing due to attempts at consensus, methods for differentiating idea generation and idea evaluation, and implicitly designated spaces for open and informal communication. Based on post-camp interviews, residents came away from the Globul5 experience feeling increased confidence and having convictions about how to best support creative collaboration. The residents articulated insights related to: 1) how to support critique while maintaining group cohesion, 2) how to structure teams in order to foster autonomy and productivity, 3) how to find a common vision while valuing multiple perspectives, and 4) how to simultaneously achieve a sense of flexibility and clear direction. Results indicate that residents may have developed repertoires of collaborative practice (Barron et al., 2009), or adaptive understandings of how to apply practices and insights to future collaborations.

Keywords: Education.
Advisor: Barron Brigid primary advisor. Thesis advisor
Goldman Shelley
Schwartz Daniel L. advisor. Thesis advisor
Capacitive micromachined ultrasonic transducer (CMUT) chemical sensor and its interface circuits [electronic resource]

Miniaturized chemical sensors based on microelectromechanical-systems (MEMS) offer competitive advantages over existing bench-top chemical analyzers, such as small size, low power consumption, low cost due to batch fabrication, and CMOS compatibility. The potential for system integration of these chemical sensors with on-chip CMOS circuitry expands the spectrum of use, including consumer, industrial, and homeland security applications. This thesis introduces a miniaturized resonant chemical sensor based on a 50-MHz capacitive micromachined ultrasonic transducer (CMUT). With a high mass sensitivity of 4.3 ag/Hz, this CMUT-based chemical sensor achieves excellent volume sensitivity of 21.2 ppt/Hz to dimethyl methylphosphonate (DMMP), a common simulant for Sarin gas. In addition, a direct application of a mesoporous silica thin-film on a CMUT for relative humidity and carbon dioxide detection is presented. Using a mesoporous silica thin-film with a pore size of ~11 nm, this sensor achieves one of the lowest volume resolutions and a sensitive detection of 5.1 × 10-4%RH/Hz to water vapor in nitrogen. In addition, a mesoporous thin-film that is functionalized with an amino-group is directly applied on the resonant sensor, which exhibits a volume sensitivity of 1.6 × 10-4%/Hz and a volume resolution of 1.82 × 10-4% to carbon dioxide in nitrogen. Lastly, this thesis describes the sensor interface circuitry for CMUT and discusses the frequency noise analysis of CMUT-based oscillators. Specifically, a multi-channel interface integrated circuit (IC) implemented using 0.18-um CMOS technology, which results in reduced area and power consumption for each channel is presented. Two-channel detection of relative humidity is demonstrated using this circuit.

Keywords: Electrical Engineering
Advisor: Howe Roger Thomas primary advisor. Thesis advisor
Khuri-Yakub Butrus T.
Bahai Ahmad R. S.
Murmann Boris advisor. Thesis advisor
Carbon nanotube containing electrodes for organic electronics applications [electronic resource]

Flexible transparent electrodes are critical for use in large-area or flexible touch screens, solar cells, and flat panel displays. An ideal material should be inexpensive, nontoxic, flexible, solution processable, thin and uniform, with a sheet resistance of less than 50 ohms per square at 90% transmission. No current material satisfies this set of specifications. One promising candidate is the carbon nanotube (CNT) network. There are two key challenges in making CNT electrodes. Firstly, in dispersion, van der Waals forces drive CNT aggregation into bundles, which are less efficient conductors than single tubes. Secondly, transport through a CNT network is typically dominated by large intertube resistances. The work in this thesis develops and studies composite materials addressing each of these challenges. In the first part of this thesis, we develop a method for making four-probe conductivity measurements on CNT bundles in networks, and compare these with data taken via electrostatic force microscopy. We confirm that bundles are less efficient at charge transport than single tubes, and that intertube rather than interbundle junctions limit transport in bundled networks. We then explore the use of poly-3-hexylthiophene (P3HT), as a dispersing agent for CNTs. While P3HT debundles CNTs, improves film morphology considerably and facilitates processing immensely, we find that too much P3HT can still substantially reduce the overall conductivity of the films. To improve this, and to address the tube junction resistance problem in general, the second part of the thesis focuses on p-type doping of CNTs, which increases free carrier concentration and lowers or eliminates intertube Schottky barriers. Known CNT dopants, including nitric acid and thionyl chloride, are toxic, corrosive, and/or ephemeral. We develop a new mild, stable and competitive process to dope CNT networks with molybdenum oxide, and explore the doping mechanism. We then compare this process with doping by thionyl chloride and by tetrafluorotetracyano-p-quinodimethane, a known mild molecular dopant. Lastly, to affirm the utility of these CNT composites as electrodes for organic semiconductor devices, we optimize methods to pattern them with high fidelity on dielectric surfaces and show that they can drive organic thin film transistors, in some cases better than can typical Au bottom contact electrodes.

Keywords: Applied Physics
Advisor: Bao Zhenan primary advisor. Thesis advisor
Fisher Ian R. (Ian Randal) primary advisor. Thesis advisor
McGehee Michael
Causes and consequences of fungal disease in cottonwoods [electronic resource]

Plant pathogens are microorganisms that cause disease and are therefore of great economic and ecological importance. Tremendous effort has been devoted to understanding plant genetic resistance to individual pathogens. Yet we know less about how natural genotypic variation in host plants affects the structure of pathogen communities. Here I test how both plant genotype and the environment influence the structure of fungal leaf pathogen communities, and how pathogens in turn affect plant herbivores. First, I test how the evolutionary history of plants affects their pathogen communities. I show that the pathogens of Populus angustifolia, the narrow leaf cottonwood of the Rocky Mountains, are consistent with a hypothesis of Beringian migration into North America by the ancestor of P. angustifolia. Second, in common garden studies and in the wild, I test how inter- and intraspecific genetic variation in Populus affects the structure of pathogen communities. I found that pathogen communities varied both among Populus species and genotypes within species, mostly in the severities of damage inflicted by constituent pathogens rather than in composition. These results suggest that quantitative genetic resistance, which is neither complete nor pathogen-specific, is affecting these communities. Third, I test how environmental variation affects both pathogen communities, and genetic resistance to pathogens. I found that the influence of plant genotype on pathogen communities attenuates as spatial scale and environmental heterogeneity increase, and that plant genetic resistance to pathogens is correlated to the level of disease risk within the environment where the plant occurs. Finally, I test how plant genotypic variation in pathogen severity influences pathogens' indirect effects on herbivores. I found that pathogens reduce the richness and abundance of herbivores most strongly on severely infected Populus species. Pathogens also reduced herbivory, but this effect was modulated by genotypic variation in herbivore resistance. Pathogens most strongly deterred herbivores on herbivore-susceptible genotypes, suggesting that they induce defenses. Overall, this thesis demonstrates that the genetic-based interactions of relatively few species (e.g., a plant and a pathogen) can be fundamental to understanding community structure.

Keywords: Biology.
Advisor: Dirzo Rodolfo primary advisor. Thesis advisor
Field Christopher B.
Newcombe George M.
Whitham Thomas
Vitousek Peter Morrison advisor. Thesis advisor
Centrosome protein fusions and leukemia [electronic resource]

Chromosomal translocations fusing genes that encode centrosome proteins and tyrosine kinases are frequently observed in myeloproliferative neoplasms (MPNs). Although the function of centrosome proteins in these fusions is not well understood, roles that may contribute to proliferative signaling including kinase centrosome localization and constitutive kinase dimerization have long been postulated. To test the relative contributions of localization and dimerization on kinase signaling efficiency, we targeted inducibly dimerizable FGFR1 to several subcellular locations and generated a centrosome localization mutant of the FOP-FGFR1 MPN fusion. Expression in mammalian tissue culture cells followed by substrate phosphorylation assays reveals a statistically significant decrease in kinase signaling effectiveness upon loss of FOP-FGFR1 centrosome localization. Interestingly, wild-type FOP-FGFR1 expression also caused a centrosome localization-dependent ciliogenesis defect. Further studies revealed that the fusion partner, FOP, localizes to centriolar satellites in addition to its previously described centrosomal localization. Centriolar satellites are granules clustered around the centrosome suspected to function in microtubule anchoring, protein trafficking, and ciliogenesis, though their precise function and composition remain unknown. Satellite localization is retained in the FOP-FGFR1 fusion and an increase in phosphotyrosine activity occurs at satellites in FOP-FGFR1 expressing cells. Given the importance of centriolar satellites in ciliogenesis, and the link between ciliogenesis and proliferative signaling, it is possible that increased phosphotyrosine activity at satellites is functionally significant in the progression of MPN. Finally, we assayed for ciliary signaling proteins in chronic myelogenous leukemia (CML) cells. Although FOP-FGFR1 causes a ciliogenesis defect, MPN affects blood cells, which have not been reported to contain cilia. We show here that, although CML cells do not appear to form a primary cilium, they contain masses of stabilized tubulin that co-localize with ciliary proteins. This may be evidence for a form of ciliary signaling in unciliated mammalian cells.

Keywords: Biological Sciences
Advisor: Stearns Tim primary advisor. Thesis advisor
Ferrell James Ellsworth advisor. Thesis advisor
Kopito Ron Rieger
Nelson W. J. (W. James) advisor. Thesis advisor
Chain conformation and disorder in high mobility semiconducting polymers [electronic resource] : understanding charge transport in complex microstructures

A critical step to understanding charge transport in complex systems is being able to characterize them accurately and extensively. In particular, the microstucture of conjugated polymers exhibits a coexistence of ordered and amorphous regions, with the size of the ordered regions being smaller than the length of individual polymer chains. In order to study the ordered regions we use advanced X-ray diffraction analysis in combination with computational modeling and measurements of optical and electrical properties. It was possible to uncover fundamental relationships between short-range order in pi-aggregates, aggregate connectivity and macroscopic charge transport in semiconducting polymers. An unusually high and materials-independent amount of paracrystalline disorder was found in all high-performing polymers. Computer simulations and analytical models made the connection between fluctuations in molecular arrangement and electronic traps. Charge transport studies elucidated the predominant role of paracrystallites in semicrystalline and strongly disordered polymer films. The other component of the microstructure -- the amorphous regions -- deserves our attention as well since aggregate connectivity depends on it. A model for charge transport in strongly disordered polymers was developed for this reason. The morphology of individual polymer chains can be determined by well-known statistical models. Likewise, the electronic coupling between units along a polymer chain and on different molecules can be determined by Marcus theory. Combining knowledge from both areas into an analytical and computational model that incorporates the structural and electronic properties of polymers, it is possible to explain observations that previously relied on phenomenological models. The multi-scale behavior of charges in these materials (high mobility at short scales, low mobility at long scales) is naturally described with this framework. Additionally, the dependence of mobility with electric field and temperature is explained in terms of conformational fluctuations and correlations. Bringing all these concepts together it is possible to provide a more complete description of the way in which charges move in conjugated polymers, a set of materials that occupies an intermediate region between ordered and disordered systems, with a great amount of complexity at various length scales. Doing so will facilitate the feedback cycle between molecular design, microstructure optimization, and device performance.

Keywords: Applied Physics
Advisor: Fisher Ian R. (Ian Randal) primary advisor. Thesis advisor
Salleo Alberto
Stebbins Jonathan Farwell advisor. Thesis advisor
Challenging monoliths [electronic resource] : Henry Wallace, Herbert Hoover, and the rise of America in the world, 1874-1965

This dissertation examines the politics, ideas, and cultural beliefs of the Cold War's two most prominent American dissenters: Henry Wallace and Herbert Hoover. From the nation's liberal left wing and conservative right wing, respectively, Wallace and Hoover presented the two most powerful alternative perspectives on the Cold War—and, beyond that, on America's role in the post-World War II world. Focusing primarily on World War II and the Korean War, this study investigates Wallace and Hoover's attempts to contest the nation's global security policies during a critical period in the global Cold War. They failed, and as a result the U.S.-led anti-Communist and U.S.S.R.-led Communist blocs fought an expanded war in Korea that drastically escalated the Cold War arms race and bipolar confrontation for years to come. But their efforts to shape alternatives had a lasting impact on both men and many of their contemporaries into the Vietnam War era and beyond.

Keywords: History
Advisor: Bernstein Barton J. primary advisor. Thesis advisor
Chang Gordon H. primary advisor. Thesis advisor
Holloway David
Characterization by X-ray absorption spectroscopy of the biosynthesis of the cofactors of nitrogenase [electronic resource]

A group of catalytic enzymes known as nitrogenases is able to perform the chemical feat of reducing atmospheric N2 to NH3, a bioavailable nitrogen source for the assembly of biological macromolecules, due largely to the complex electronic and geometric structures of their associated transition metal cofactors. The nitrogenase of Azotobacter vinelandii consists of a two-component system, the MoFe protein, a substrate fixing enzyme, and its specific reductase, the Fe protein. Together the two form a catalytic complex under turnover. An electron transport sequence is formed originating with the [Fe4S4] cofactor of the Fe protein proceeding to the P-cluster (Fe8S7) of the MoFe protein and ending with the iron-molybdenum cofactor (FeMoco), a MoFe7S9C cluster also of the MoFe protein, where substrate reduction occurs. The biosynthesis of these cofactors is an exceedingly involved process still not fully understood, but which serves as a model for cofactor assembly in other biological systems and a template for generation of functional synthetic analogues. Using a carefully constructed series of experiments involving genetic manipulation, reconstitution assays, and structural determination by X-ray Absorption Spectroscopy, a sequence of critical and essential events in cofactor synthesis, requisite gene products, and previously unidentified intermediates have been characterized. Despite a high degree of sequence homology, remarkable differences were detected in the structure of the [Fe4S4] cofactor of alternative nitrogenase Fe proteins. The stepwise fusion of P-cluster on [delta]nifH and [delta]nifB[delta]nifZ MoFe protein was observed to involve an iterative mechanism and the involvement of a new gene product was confirmed. An all iron precursor bound to the NifEN scaffold was determined to have a novel structure and suggest a new mechanism for insertion of heterometal. The solution potential and protein channel were found to have important roles in the maturation of a molybdenum-containing FeMoco precursor. Finally, the structural differences in the iron core of FeMoco and FeVco (a vanadium containing analogous cofactor) were correlated with the differences in substrate reducing profile. Together, these results help to unlock the puzzle of nitrogenase structure and function, a function essential for all life on Earth.

Keywords: Chemistry
Advisor: Hedman B. (Britt)
Hodgson Keith
Solomon Edward I. advisor. Thesis advisor
Characterization of fractured geothermal reservoirs based on production data [electronic resource]

Reservoir characterization is one of the most important and challenging parts of running a successful geothermal operation. Characterization requires thorough understanding of the physics that govern the flow of mass and energy through the reservoir. As for most subsurface modeling endeavors, the inability to measure the actual value of properties in the geothermal system make it necessary to strike a balance between what is included in the reservoir model and what is known about the physical processes that might take place in the subsurface. This balance should reflect the decisions that need to be made based on the model, and the data available for model calibration. In this work, a number of methods were developed for characterizing well-to-well connections in fractured geothermal reservoirs. These methods were based on production data that are commonly recorded in geothermal fields, i.e. pressure, flow rate, tracer and temperature. A key aspect in the developing this work, for multiwell applications, was to find the link between the various types of models, and understand how they could be combined to estimate well-to-well properties. The estimation of these properties relied on regression analysis, where an effort was made to balance the complexity of the regression model with the information required from the given data source. The combined characterization defined a work flow that would be well-suited to characterize fractured geothermal systems, with low compressibility characteristics. An effort was made to illustrate the usefulness of the characterization method to tackle important reservoir engineering problems. This was done by formulating and solving a flow rate scheduling problem for a geothermal field. The results showed that considerable gains in efficiency could be made, given a set of well-calibrated interwell relationships.

Keywords: Energy Resources Engineering
Advisor: Horne Roland N. primary advisor. Thesis advisor
Caers Jef advisor. Thesis advisor
Durlofsky Louis advisor. Thesis advisor