VictorJuiz/thesis huggingface dataset:
Towards a precision measurement of the half life of neutrinoless double beta decay of 136Xe [electronic resource]

Recent neutrino oscillation experiments provide proof that neutrinos are massive par- ticles, but the absolute neutrino mass scale remains unknown. Observation of neu- trinoless double beta-decay (0vBB), a hypothetical nuclear transition, would provide information on the absolute neutrino mass scale. This decay violates lepton number conservation and requires that neutrinos are massive Majorana particles. Current limits on the half-life of 0vBB are in excess of 10^25 yr. The 200 kg Enriched Xenon Observatory experiment (EXO-200) is a double beta-decay exper- iment designed to improve upon this limit. It is currently in the early stages of commissioning at the Waste Isolation Pilot Plant near Carlsbad, New Mexico. This work discusses first the use of liquid xenon as source and detector medium for double beta decay. The design and construction of EXO-200 is then presented, including a detailed prediction of detector backgrounds and sensitivity.

Keywords: Physics
Advisor: Gratta Giorgio primary advisor. Thesis advisor
Michelson Peter F. advisor. Thesis advisor
Shenker Stephen Hart
Towards an efficient and robust high order accurate flow solver for viscous compressible flows [electronic resource]

Despite the advance in CFD over the past few decades, the field of high-order methods for unstructured grids has not yet reached the level of maturity required to solve real flow problems on complicated geometries. The present thesis work makes an effort towards the realization of a flow solver that is high-order accurate but also efficient, robust and geometrically flexible at the same time. The approach to high-order spatial discretization is based on the Spectral Difference (SD) method for unstructured quadrilateral meshes. High-order (quadratic and cubic) representation is used for curved boundary surfaces. Due to their slow convergence rates with standard explicit time-stepping schemes, the use of high order schemes becomes viable only when there is some kind of convergence acceleration technique used. Towards this end, the multi-order (p-multigrid) method and Implicit time-stepping are implemented, and significant convergence acceleration is achieved for both steady and unsteady flow problems. Another significant challenge with using high-order methods is their inability to handle flow discontinuities. An artificial viscosity based approach is designed and implemented to enable computation of flows with shocks. Adaptive mesh and order refinement have great potential in reducing the computational effort required to reach a specified level of accuracy, particularly in the context of high-order formulations. The capability for adaptive mesh and order refinement is enabled using mortar elements to handle non-conforming solution approximations at the cell interfaces. The flow solver is tested, validated and applied to a variety of flow problems. The current work also demonstrates the effectiveness of computational tools such as convergence acceleration, shock-capturing and adaptive refinement, for enhancing the efficiency and robustness of high order flow computations.

Keywords: Aeronautics and Astronautics
Advisor: Jameson Antony
Lele Sanjiva K. (Sanjiva Keshava)
MacCormack R. W. (Robert William)
Towards clinically viable neural prosthetic systems [electronic resource]

By restoring the ability to move and communicate with the world, brain machine interfaces (BMIs) offer the potential to improve quality of life for people suffering from spinal cord injury, stroke, or neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS). BMIs attempt to translate measured neural signals into the user's intentions and, subsequently, control a computer or actuator. Recently, compelling examples of intra-cortical BMIs have been demonstrated in tetraplegic patients. Although these studies provide a powerful proof-of-concept, clinical viability is impeded by limited performance and robustness over short (hours) and long (days) timescales. We address performance and robustness over short time periods by approaching BMIs as a systems level design problem. We identify key components of the system and design a novel BMI from a feedback control perspective. In this perspective, the brain is the controller of a new plant, defined by the BMI, and the actions of this BMI are witnessed by the user. This simple perspective leads to design advances that result in significant qualitative and quantitative performance improvements. Through online closed loop experiments, we show that this BMI is capable of producing continuous endpoint movements that approach native limb performance and can operate continuously for hours. We also demonstrate how this system can be operated across days by a bootstrap procedure with the potential to eliminate an explicit recalibration step. To examine the use of BMIs over longer timescales, we develop new electrophysiology tools that allow for continuous multi-day neural recording. Through application of this technology, we measure the signal acquisition stability (and instability) of the electrode array technology used in current BMI clinical trials. We also demonstrate how these systems can be used to study BMI decoding over longer time periods. In this demonstration, we present a simple methodology for switching BMI systems on and off at appropriate times. The algorithms and methods demonstrated can be run with existing low power application specific integrated circuits (ASICs), with a defined path towards the development of a fully implantable neural interface system. We believe that these advances are a step towards clinical viability and, with careful user interface design, neural prosthetic systems can be translated into real world solutions.

Advisor: Ng Andrew Y.
Shenoy Krishna V. (Krishna Vaughn) primary advisor. Thesis advisor
Meng Teresa H. advisor. Thesis advisor
Towards Multicultural Education for All: The National and International Influences on Brazilian Educational Policy

Until recently, Brazil has prided itself in being a country free of discrimination and inequalities based on racial or ethnic differences. However, the Brazilian government has changed its posture and began to acknowledge the disadvantaged position of Indigenous People and the descendants of African slaves. Educational policies were among the first to incorporate this concept. Bilingual education, affirmative action and curriculum changes to include cultural diversity were implemented and a new department–Secretary of Continuous Education, Literacy and Diversity (SECAD)–was created in 2004. To explain these changes in policy, the literature on the development of multicultural education in Brazil and globally identify explanatory factors of a domestic nature but do not take the emergence of a global trend of celebration of diversity into account. The present study analyzes the curricular policies of the Brazilian government as well as recommendations from international and national organizations from 1985 to the present to comparatively examine how issues of cultural diversity and inequality are addressed in educational policies. The analysis identifies three discourses that explain (1) why multicultural education is necessary, (2) the goal of multicultural education, and (3) the content of multicultural education. In addition, the findings demonstrate that international movements and values celebrating multiculturalism have been significant factors in the Brazilian government’s surrendering its myth of racial equality, adoption of educational reforms, and embracing old national movements against racial discrimination.

Keywords: Brazil
multicultural education
curricular policies
education policy
Stanford Graduate School of Education International Educational Administration and Policy Analysis
Thesis
Towards precision tests of general relativity using an atom interferometer [electronic resource]

A 10-meter tall, dual-species atomic fountain gravimeter was designed and built for the purpose of testing the Equivalence Principle with freely-falling atoms. Once completed, the apparatus promises to be the most sensitive atom interferometer ever built, with a projected differential acceleration sensitivity of 10^-15 g. This phenomenal force sensitivity opens the door to exciting science applications which are reviewed, including setting new limits on the Equivalence Principle, measuring effects of General Relativity in a laboratory setting, and detecting gravitational waves.

Keywords: Physics
Advisor: Kasevich Mark A. primary advisor. Thesis advisor
Bouyer Philippe advisor. Thesis advisor
Dimopoulos Savas
Toxoplasma gondii co-opts host immune signaling by secretion of a polymorphic tyrosine kinase, ROP16 [electronic resource]

Toxoplasma gondii is an obligate, intracellular parasite of the Apicomplexan phylum that is able to infect nearly all warm-blooded vertebrates. This capability for survival in a variety of host niches is reflected in the diversification of Toxoplasma strains. Strains differ dramatically in their interaction with hosts, and a fruitful approach towards understanding the molecular underpinnings of disease has been to identify and characterize drivers of strain-specific differences in host response. Chapter 1 provides a general introduction to Toxoplasma gondii and its ability to modulate host immunity, with special attention given to what is known about the mechanisms behind strain-specific phenotypes and the role of one particular player, ROP16. Chapter 2 describes experiments demonstrating that Toxoplasma secretes a polymorphic tyrosine kinase, ROP16, that can directly phosphorylate host STAT6. These experiments made use of a targeted disruption of the ROP16 locus in Type I parasites to identify ROP16-dependent signaling pathways, and used biochemical approaches to dissect the mechanism by which ROP16 is able to induce rapid STAT6 activation. Chapter 3 describes work demonstrating that ROP16 activation of STAT6 directs murine macrophage polarization towards an alternatively activated (M2) phenotype. In Chapter 4, the avian host response to Toxoplasma is examined to determine whether strain-specific differences in host response might be inverted in non-mammalian hosts. We show that strain-specific transcriptional host response, as well as transcriptional host response modulated by ROP16, appears very similar in chickens as in mice and humans. This suggests that variance between mammalian and avian host species in general may not be the source of selective pressure for the success of these common strains, or of ROP16's variability. Chapter 5 concludes with a discussion of future directions for further characterization of ROP16's role in modulating host response. We show that ROP16 interacts with host chromatin and suggest that investigation of ROP16's function in the host nucleus might yield further molecular insights as to how Toxoplasma is able to co-opt host cells and influence the course of infection.

Keywords: Microbiology and Immunology.
Advisor: Boothroyd John C. primary advisor. Thesis advisor
Bogyo Matthew
Mochly-Rosen Daria advisor. Thesis advisor
Nolan Garry P. advisor. Thesis advisor
Trading mechanisms for financial exchanges [electronic resource]

The first part of this thesis discusses the structure of the US equities market and the regulatory challenges involved, with respect both to particular venues and order types, and to the market as a whole. This part addresses the role of public equities markets, their objectives, and the market-design concepts relevant to evaluating them, it describes the market structure before and after the significant regulatory reforms of 2005, goes on to detail some specific market-design challenges and current proposals from the SEC, and concludes with an analysis and evaluation of several trading mechanisms and three order types, from a mechanism-design perspective. The second part of the thesis presents a theoretical model of an exchange and analyzes optimal order submission in a one-shot game in which a buyer and seller, each of whom can have two (privately known) types, can trade up to two units of an asset through an order book, which is empty at the beginning of the game. In both a setting with private values and interdependent values, equilibria in four games are characterized: a basic game with limit and market orders, and games involving one of the three order types from the first part of the thesis- iceberg, discretionary, and volume orders. The effect of the introduction of the different order types is analyzed with respect to volume and transparency. Each setting also includes an analysis of the buyer-optimal mechanism and its relation to equilibria of the games involving orders.

Keywords: Economics
Advisor: Levin Jonathan D. (Jonathan David)
Niederle Muriel advisor. Thesis advisor
Tertilt Michèle advisor. Thesis advisor
The transformations of Baijie Shengfei [electronic resource] : gender and ethnicity in Chinese religion

The goddess Baijie is worshipped only in the Dali Bai Autonomous Prefecture of Southwest China's Yunnan province, home to the Bai "nationality" (minzu). Most people today see Baijie as the widow martyr of a local ruler from the eighth century, but she first appears as a Buddhist goddess in scriptures of the Dali Kingdom (937-1253). In the Ming (1368-1644) a legend appears in which Baijie is the mother of Duan Siping, founder of the Dali Kingdom. Baijie's widow martyr identity finally emerges in the Ming and Qing (1644-1911). Today, Baijie is worshipped in her widow martyr form as a tutelary village deity throughout Dali Prefecture. This dissertation examines Baijie's transformations in relation to the themes of ethnicity and gender in the religious history of Dali. I argue that the changes in Baijie's identity reflect changes in the representation of ethnicity in Dali religion from the twelfth century to the present. Baijie's gendered symbolism, particularly in her later widow martyr form, additionally illuminates the intersections of ethnicity and gender in Dali religion. The Dali region, and Yunnan as a whole, has long fallen just inside or outside the sphere of Chinese state control. Despite Dali's proximity to India, Tibet, and Southeast Asia, historical records strongly suggest that Dali elites looked to China for their systems of writing, government, and to some extent, religion. Baijie's transformations show how religious symbols reflected and shaped Dali elites' self-representation in relation to Chinese culture and the Chinese state. The first two chapters provide background by examining issues of religion and ethnicity in the independent Nanzhao (649-903) and Dali kingdoms. Chapters three through five cover Baijie's first three identities of Buddhist goddess, king's mother, and widow martyr from the Dali kingdom through the Qing dynasty. Chapter six looks at contemporary Baijie worship and is based primarily on field research conducted in Dali in 2007-08.

Keywords: Religious Studies.
Advisor: Bielefeldt Carl primary advisor. Thesis advisor
Faure Bernard advisor. Thesis advisor
Harrison Paul advisor. Thesis advisor
Transport measurements on graphene p-n junctions [electronic resource]

Klein tunneling is a relativistic quantum effect standing at the base of the Quantum Electrodynamics (QED) theory. It describes a relativistic process where a particle obeying the Dirac equation - called a Dirac Fermion - propagates through a strong repulsive potential step without the exponential attenuation typical to quantum tunneling. Counter-intuitively, the stronger the potential step, the more transparent it becomes for the particle. Although the QED theory had proven to be a successful theory describing reality accurately, Klein tunneling has not yet been observed experimentally. The extreme conditions required to observe such an effect may occur in collisions of super-heavy nuclei or pair production at the horizon of a black hole, difficult or impossible to realize in a laboratory. However, a recently discovered material called graphene, which is a one atom-thick lattice of carbons, can be used as a testbed for such an effect. Since graphene carriers have been proven to be Dirac-like Fermions, the analog of Klein tunneling can be investigated in a commonly used condensed matter setup via electrical transport measurements. In this work we present experimental evidence for graphene carriers obeying Klein tunneling transport using a set of metallic gates on graphene to create p-n junctions. These p-n junctions incorporate a potential step for graphene Dirac-like Fermions allowing us to investigate Klein tunneling in graphene. Finally, we also discuss the existence of p-n junction-like structures between metal contacts and graphene, a topic that has an impact on graphene's electronic device applications.

Keywords: Physics
Advisor: Goldhaber-Gordon David
Beasley Malcolm advisor. Thesis advisor
Kapitulnik Aharon advisor. Thesis advisor
Transposable regularized covariance models with applications to high-dimensional data [electronic resource]

High-dimensional data is becoming more prevalent with new technologies in biomedical sciences, imaging and the Internet. Many examples of this data often contain complex relationships between and among sets of variables. When arranged in the form of a matrix, this data is transposable, meaning that either the rows, columns or both can be treated as features. To model transposable data, we present a modification of the matrix-variate normal, the mean-restricted matrix-variate normal, and introduce transposable regularized covariance models by placing penalties on inverse covariance matrices. We give theoretical results exploiting the structure of our transposable models that give computationally feasible algorithms for parameter estimation and calculation of conditional expectations. These contributions make the matrix-variate normal accessible for application to high-dimensional data. We apply our model to two applications: missing data imputation and large-scale inference with the matrix-variate normal distribution. Examples, simulations and results are given using the Netflix movie-rating data and microarrays, demonstrating the flexibility and functionality of our transposable models.

Keywords: Statistics
Advisor: Tibshirani Robert primary advisor. Thesis advisor
Owen Art B. advisor. Thesis advisor
Taylor Jonathan E. advisor. Thesis advisor
Tuning the shape of semiconductor nanowires for advanced photovoltaics [electronic resource]

Tuning the shape of nanostructures can have a strong effect on photon management and charge carrier collection for photovoltaics. Here two examples of nanowire shape designing are demonstrated: nanocones and branched nanowires. Photon management, involving both absorption enhancement and reflection reduction, is critical to all photovoltaic devices. It can improve the efficiency by minimizing optical and electrical losses, and cut cost by reducing material usage, process time and capital investment. Here I demonstrate a novel solar cell structure with an efficient photon management design. The centerpiece of the design is a novel nanocone structure, which is fabricated by a scalable low temperature process. With this design, devices with very thin active layer can achieve near perfect absorption because of both efficient antireflection and absorption enhancement over a broad spectral range and a wide range of angles of incidence. More strikingly, the design and process is not in principle limited to any specific material system, hence it opens up exciting opportunities for all classes of photovoltaic devices. I have used amorphous silicon and dye sensitized solar cells as two examples to demonstrate the concept. The device efficiencies of this design are significantly better compared to conventional devices. Moreover, I also have explored absorption enhancement on a sub-wavelength scale, compared to "classical" light trapping limits. PbSe nanocrystals have shown a greatly enhanced multi exciton generation (MEG) effect, one important step toward third generation solar cells. However, it is difficult to extract generated carriers from nanocrystals without good transport pathways. Three dimensional branched nanowire or nanotube networks, with strong quantum confinement within two dimensions, and the connected third dimension as an efficient charge carrier pathway, could be ideal for enhancing the MEG effect, light absorption, and carrier collection. I successfully demonstrate a large area growth of PbSe hyperbranced and chiral branched nanowires on a variety of substrates. More excitingly, Chiral branched nanowires reveal a new nanowire growth mechanism, dislocation driven growth, which can be applied to a variety of materials.

Keywords: Electrical Engineering
Advisor: Cui Yi
Howe Roger Thomas advisor. Thesis advisor
McGehee Michael
Tunnel barrier engineering for flash memory technology [electronic resource]

The conventional Flash memory faces two critical obstacles in the future: density and voltage scaling. Density is associated with scaling the gate length. The gate length cannot be reduced beyond a point because it requires a commensurate gate stack, specifically, tunnel oxide scaling for maintaining good gate control and short channel effects. However, the gate-tunnel oxide (TO) reduction has a practical lower bound of ~ 7-9nm (depending upon NAND or NOR flash architecture) due to leakage and data retention constraints. Below this TO thickness, irrespective of how inter-poly dielectric (referred as ONO) is scaled, the electric field across it during charge retention increases, leading to unacceptable levels of tunneling current. The second major challenge with scaling is to reduce the programming and erase operation voltages. The usual operation voltages for these processes are much greater (15-18 Volts). With scaling, it is imperative for operating voltages to reduce. Typically, read voltages are low, while erase and program operations stress the charge pump requirements and dictate the maximum voltages. The major impediment in erase voltage scaling is, once again, the inability to scale the gate oxide. Recently, engineered tunnel barriers were proposed as solutions to scaling gate oxide. It is postulated that engineered barriers offer faster program/erase yet maintain excellent retention. However, a detailed characterization of engineered tunnel dielectrics and a deeper understanding of the erase/program mechanism are sought to establish its implementation. In the first half of the thesis, we perform simulations to establish the feasibility of tunnel barriers under Flash memory device constraints. We look at different higher-k materials as a replacement for SiO2 and perform global optimization over different materials. This is first done under absence of traps in these materials. Later the assumptions are relaxed and traps are incorporated in these materials. In the second part, we implement engineered tunnel barriers based on the simulation results. However, it is observed that presence of traps in these materials degrades performance. Retention loss and endurance degradation are identified as two major problems, hindering implementation and scaling. In the third and final part, we discuss solutions to these problems. Fluorine is well known as a passivating agent for traps in high-k dielectrics. We incorporate fluorine in engineered tunnel stacks and show electrical & physical characterization results to emphasize its advantages. Finally, alternative tunnel barrier structures and materials are discussed to continue scaling of gate dielectrics.

Keywords: Materials Science and Engineering
Advisor: McIntyre Paul Cameron primary advisor. Thesis advisor
Saraswat Krishna primary advisor. Thesis advisor
Cui Yi