VictorJuiz/thesis huggingface dataset:
Controlling injection and propagation of domain walls in magnetic nanowires [electronic resource]

Magnetic domain walls (DWs) are regions where the magnetization changes rapidly from one orientation to another. These magnetic textures are of considerable interest both scientifically as well as technologically with potential applications in novel memory and logic devices based on their controlled creation and manipulation under magnetic field and current. We consider the injection and propagation of DWs in two different materials systems, namely in permalloy (Ni81Fe19) nanowires where the magnetization points in the film plane and in Co/Ni multilayers where the magnetization points perpendicular to the film plane. DWs in permalloy nanowires can be considered as composite objects composed of elementary topological bulk and edge defects with integer and fractional winding numbers, respectively; whose relative spatial arrangement determines the chirality of the DW. Here we show how we can understand and control the trajectory of DWs in magnetic branched networks, composed of connected nanowires, by a consideration of their fractional elementary topological defects and how they interact with those innate to the network. We also demonstrate a highly reliable mechanism for the injection of a DW of a given chirality into a nanowire and show that its chirality determines which branch the DW follows at a symmetric Y-shaped magnetic junction - the fundamental building block of the network. Using these concepts, we unravel the origin of the one-dimensional nature of magnetization reversal of connected artificial spin ice systems that have been observed in the form of Dirac strings. In the second part of this work, we demonstrate that by irradiating small regions in perpendicularly magnetized nanowires to induce in-plane magnetic anisotropy, and thereby creating a 90° DW, we can significantly decrease the energy needed for DW creation. In fact, due to the presence of a 90° DW at the injection site, the process of creating a DW in the nanowire in reality involves extraction of the 90° DW to the perpendicularly magnetized region. We show that this can not only be done by conventional means of creating local magnetic fields near the injection site but more importantly, by exploiting the giant spin transfer torque obtained at the 90° DW (due to the abrupt change in the magnetization), we can inject a series of domain walls using nano-second long, uni-polar current pulses through the nanowire which use much lower energy than conventional techniques.

Keywords: Electrical Engineering.
Advisor: Harris J. S. (James Stewart)
Howe Roger Thomas advisor. Thesis advisor
Parkin Stuart S. P.
White Robert advisor. Thesis advisor
Coordinated regulation of neonatal beta-cell development in mice and humans by calcineurin/NFAT [electronic resource]

To meet host metabolic demands after birth, organs like pancreatic islets increase their physiological function and mass. Compared to fetal islet development, however, little is known about mechanisms governing neonatal islet maturation and expansion. Here I demonstrate calcineurin/Nuclear Factor of Activated T-cells (Cn/NFAT) signaling regulates both [beta]-cell maturation and proliferation in neonatal mice and humans. Inactivation of the gene encoding the calcineurin phosphatase regulatory subunit, calcineurin b1 (Cnb1), in mouse islets resulted in defective dense core granule biogenesis, impaired insulin secretion, and reduced neonatal [beta]-cell proliferation and mass, culminating in lethal, early-onset diabetes. [beta]-cells lacking Cnb1 failed to express genes required for insulin storage and secretion, as well as neonatal replication. Tacrolimus, a calcineurin inhibitor and widely used immunosuppressant, reduces human [beta]-cell secretion and promotes diabetes, toxicities without a clear molecular basis. Exposure of mouse and human islets to tacrolimus reduced expression of genes encoding factors essential for insulin dense core granule formation and secretion, and neonatal [beta]-cell proliferation consistent with our genetic studies. Chromatin immunoprecipitation and other molecular studies revealed these genes as novel, direct NFAT targets in neonatal mouse and human islets. Thus, calcineurin/NFAT signaling coordinately regulates factors that govern [beta]-cell maturation and proliferation, revealing unique models for the pathogenesis and therapy of diabetes mellitus and diverse human islet diseases.

Keywords: Developmental Biology.
Advisor: Kim Seung K. primary advisor. Thesis advisor
Beachy Philip Arden advisor. Thesis advisor
Crabtree Gerald R. advisor. Thesis advisor
Kuo Calvin Jay advisor. Thesis advisor
Utz Paul advisor. Thesis advisor
Copper sulfide resistance change memory and its scalability [electronic resource]

The increase of portable electronic devices such as cellular phones, digital cameras, and mp3 players is driving a rapid growth of the market for nonvolatile memories (NVMs). Today's most established NVM technologies are based on charge storage method. However, the scaling of current NVM technologies beyond 32 nm node of International Technology Roadmap for Semiconductors (ITRS) poses severe problems such as poor retention and unacceptable cross-talks among devices. To overcome these disadvantages and achieve high-speed, high-density, long-retention, and low-power NVMs, several new memory materials and technologies have been extensively investigated. Among new emerging materials and concepts, we investigate copper sulfide resistance change memory, which is one of the most promising candidates for future NMV, whose electrical resistance can be changed reversibly between two stable states. In the first part of the study, we report fabrication and electrical characterization of micrometer-scale copper sulfide NVM devices. We have achieved synthesis of stoichiometric Cu2S using anodic polarization whose composition is analyzed by Rutherford backscattering (RBS), and fabricated [micrometer]-sized NVM devices in the sandwiched structure of a Cu/Cu2S/top electrode. The resistive switching is consistent and reproducible over 50 cycles for large-area devices and 200 cycles for small-area devices. Low SET and RESET voltages below 0.3 V for switching and a high OFF-state resistance to ON-state resistance ratio over 10^5 have been achieved. The ON-state resistance value, RON, does not change as the size of the devices shrinks indicating the conduction is localized while the OFF-state resistance, ROFF, increases with the device scaling. As a result, we can obtain a fascinating scaling result that ROFF/RON ratio increases as the devices scale down. In the second part of the study, we present for the first time a simple fabrication method of copper sulfide nanopillar arrays with a high aspect ratio using nanoporous templates created from self-assembled nanostructures of block copolymers (BCP) for NVM applications. With our proposed process, the high aspect ratio of copper sulfide nanopillars with 25 nm in diameter and 170 nm in height is generated. Due to the small distance of 40 nm between the nanopillars, characterization is performed using conductive atomic force microscope (CAFM). Our nanopillar arrays exhibit a huge ROFF/RON ratio of 10^7 at a 2 [microampere] current level. This low level of switching current demonstrates the possibility of low-power NVM devices.

Keywords: Electrical Engineering.
Advisor: Nishi Yoshio
McIntyre Paul Cameron advisor. Thesis advisor
Wong Hon-Sum Philip
Corporate performance in light of congressional conflicts of interest [electronic resource]

While members of Congress must disclose information about their financial assets, there are no restrictions on the types of assets they can hold. This creates conflicts of interest as legislators vote on issues that will affect their personal investments. This dissertation explores the shareholder relationships between members of Congress and the corporations in which they are invested. I begin by examining how they allocate their investments. I use the S& P 500 as a benchmark portfolio to show that legislators' portfolios do not diverge widely from the rest of the market, with a few notable exceptions. In particular, I find mixed evidence that legislators allocate investments to sectors in which they have increased influence. I then assess whether assets issued by firms in which members of Congress have financial stakes yield higher returns than those from otherwise similar firms. I provide several theoretical explanations that would support a finding of excess returns and find no evidence to suggest that firms with congressional shareholders outperform their peers. If anything, the firms with political connections perform slightly worse. This result holds over both long- and medium-term time horizons and is robust to differentiating asset holdings by party, leadership positions, or committee assignments. Lastly, I test whether markets expect these shareholder connections between politicians and firms to be valuable. I conduct three event studies using narrow elections, the public release of the financial disclosure reports, and sudden resignations of members of Congress to demonstrate that market participants do not expect firms with congressional ties to outperform their peers.

Keywords: Business.
Advisor: Shotts Kenneth W. primary advisor. Thesis advisor
Jha Saumitra advisor. Thesis advisor
Malhotra Neil Ankur advisor. Thesis advisor
Correlation analyses of encoded music performance [electronic resource]

Correlation analyses of encoded music performance by a large and diverse international community of amateur performers afford insights into fundamental questions of musical behavior. By observing demographic data associated with a corpus of performance recordings, we can conjecture about cultural, geographical, topographical, socio-political, economic and other potential influences, and explore possible 'universals' in musical thought and practice. This study attempts to address questions of musical practices from an entirely novel perspective, specifically taking advantage of massively popular game-oriented music performance programs on mobile devices.

Keywords: Music.
Advisor: Berger Jonathan
Aquilanti Giancarlo
Chafe Chris advisor. Thesis advisor
Cosmological Evolution of Gamma-Ray Bursts

Gamma-ray bursts (GRBs) are among the most powerful electromagnetic events in the universe, luminous enough to be detected across vast stretches of space and time. This makes them invaluable cosmological probes of the early universe. However, to use GRBs as probes, we must first determine the evolution of their characteristics, such as the co-moving density rate and the luminosity function. This process is complicated by an extensive collection of observational biases, truncations, and questionable assumptions about the parametric forms of the various functions. We apply non-parametric methods, developed by Efron & Petrosian for truncated data, directly to a sample of Swift long GRBs with known redshifts, and obtain the co-moving density rate evolution and luminosity function and evolution. Furthermore, we derive a GRB rate which is very different from star formation rate, particularly below redshift z~2, indicating perhaps a distinct class of low-z GRBs.

Keywords:  Department of Physics
gamma-ray bursts
cosmology
high-energy astrophysics
Thesis
Advisor: Petrosian Vahe
Church Sarah
"A country with land but no habitat" [electronic resource] : travel and belonging in colonial southern Rhodesia and post-colonial Zimbabwe

THE ABSTRACT Throughout Zimbabwe's history the political imagination has based belonging to the country on the idea of land ownership and settlement. While the political imagination has been content to simply tie belonging to the land. The creative-imagination, on the other hand, has always, intentionally or not, undermined such a simple notion of belonging by focusing on movement and travel. My dissertation, therefore, mainly charts out literary efforts to use travel to problematize the over-simplified political sense of "national" belonging. Authors of Rhodesian and Zimbabwean works of fiction and non-fiction alike, reveal ways that travel makes all belonging unsettled; I argue that this unsettledness can be productive in making us re-think and interrogate "Zimbabwean" and, by extension, "African" identity in a post-colonial, post-essentialist, and post-nativist era. Applying New Diaspora Theory to the unlikely context of an African country generates both new ways to understand African nationalism and productive transformations in the theory itself.

Advisor: Hanretta Sean
Majumdar Saikat primary advisor. Thesis advisor
Elam Michele advisor. Thesis advisor
Lunsford Andrea A.
Covalent modification of mRNAs in S. cerevisiae [electronic resource]

While the presence of modified nucleotides in cellular RNA has been known about for over 60 years, it is only recently that such nucleotides have become studied and mapped in mRNAs. With recent transcriptome-wide maps of N6-methyladenosine and 5-methylcytosine showing widespread mRNA modification and evolutionary conservation of many sites, it is clear that site-specific mRNA modification may represent a new level of post-transcriptional regulation of gene expression. With this in mind, we set out to map other mRNA modifications to begin to get an idea of the role they may play in gene expression. We developed a high-throughput sequencing technique that identified the first known pseudouridines in mRNA. We were able to identify the enzymes that modified a few of the top hits, as well as show that modification of at least one of the top sites is conserved throughout the fungal lineage. We have made progress toward developing an improved high-throughput sequencing technique, which could allow elucidation of a transcriptome-wide map of pseudouridines. Adapting the same technique as was used to identify mRNA pseudouridylation, we also found a few dozen possible 2'-O-methylation sites in mRNA with an interesting functional theme, though these potential modifications still need to be validated. In addition, we attempted to map and find a functional role for N6-methyladenosines in yeast undergoing meiosis, and while this failed, it led to our discovery of a target set of bound mRNAs and role in gene expression of a meiosis-specific RNA binding protein, Rim4p. The work described in this thesis identifies the third known internal, site-specific modified nucleotide in mRNA, suggesting that mRNA modifications may be more common than previously thought and may play an important, under-explored role in post-transcriptional control of gene expression.

Keywords: Biochemistry.
Advisor: Brown Patrick O'Reilly
Das Rhiju
Straight Aaron
Creating effective magnetic field for photons [electronic resource] : principles and applications

In this dissertation, I present the results of study of creating effective magnetic field for photons. I will show two routes to achieve such a goal: dynamic modulations and magneto-optic effects. The essence of the dynamic modulation scheme is that the phase of dynamic modulations can be related to an effective gauge potential for photons. Such an identity is exclusively demonstrated through a photonic Aharonov-Bohm effect. Based on this observation, when a two-dimensional photonic resonator lattice undergoes dynamic modulation, photons propagating in this lattice experience an effective magnetic field. The consequence of the achievement of effective magnetic field for photons is two-fold. On one hand, one can generate photonic phenomena that are reminiscent to the electronic correspondence, which is intellectually fascinating. In particular, I will show a photonic de Hass-van Alphen effect, and a photonic quantum Hall effect with one-way edge modes. On the other hand, effective magnetic field and effective gauge potential bring in new ingredients to the control of light propagation, which is of practical importance. I will numerically show concrete examples of such flexible, non-reciprocal light propagation effects using effective magnetic field, including negative refraction, one-way mirror, as well as on- and off-axis focusing in a same resonator lattice under dynamic modulation.

Keywords: Physics.
Advisor: Fan Shanhui
Zhang Shoucheng primary advisor. Thesis advisor
Kivelson Steven advisor. Thesis advisor
Miller D. A. B. advisor. Thesis advisor
Crisis decision analysis [electronic resource] : how to save more lives?

A crisis creates a decision situation in which it is challenging to apply decision analysis as a normative decision-making approach. The existing literature on crisis decision making lacks discussions on three aspects developed in this dissertation: (1) how a crisis decision maker can prepare for crisis responding decisions; (2) how to determine the optimal timing of actions balancing the quality of information against the effectiveness of intervention; and (3) how to handle unexpected new observations. Chapters 3, 4, and 5 develop and characterize a set of tools for structuring, making, and updating strategic decisions when responding to a variety of crises. A "Crisis World Map" is a conceptual map customized for each individual crisis decision maker. Such a tool helps clarify the boundaries of what can be planned and what cannot before crises happen, and therefore helps prepare for crisis responding decisions. The second tool incorporates time into the decision analysis model and helps the decision maker describe time-varying values and probabilities. As a result, the decision maker can more effectively balance the trade-off between waiting for more information versus taking quick actions in moments of crisis. When unexpected new observations arise before the decision maker takes actions, the "Value of Further Modeling" helps him decide whether to introduce new uncertainties that potentially change the decision. Chapter 6 and Chapter 7 examine two historical case studies in detail. One case study is on the 1999 United Nations Peacekeeping mission planning for Sierra Leone and the other is on the 2011 Fukushima nuclear crisis. Although the two case studies discuss completely different types of crisis under different time scales with different sources of value, they both provide concrete validation of the proposed methodologies and generate many valuable practical insights for application.

Keywords: Management Science and Engineering.
Advisor: Howard Ronald A. (Ronald Arthur)
Robinson Burke Edward
Schultz Kenneth A. advisor. Thesis advisor
Shachter Ross D. advisor. Thesis advisor
Current- and wave-driven flow and nutrient exchange in natural and model submerged vegetated canopies [electronic resource]

In the coastal ocean, seagrass canopies attenuate near-bed current velocities and modify flow in the region above. In so doing, they help to reduce sediment erosion and resuspension. Vertical profiles of mean water velocity and key turbulent quantities have characteristic features that indicate these underlying dynamics. While such profiles have been especially studied well in the laboratory, detailed measurements are rare in natural seagrass canopies. We addressed that deficiency with a comprehensive set of natural canopy flow measurements, analyzed in the context of the laboratory-derived models. Seagrasses depend on these hydrodynamic interactions for their health and basic biological functions. The rates of many of their core metabolic processes are limited by nutrient availability; in many environments, availability is constrained most by the slow diffusive transfer across element boundary layers. Boundary layer thickness is reduced by flow, and evidence has shown that seagrass nutrient uptake rates rise as mean water velocities are increased. However, uptake rates are enhanced even more significantly in wave-driven, oscillatory flows - flows that are less effectively attenuated within the canopy space. In another portion of the work described here, we measured flow-modulated seagrass community uptake directly in both current-driven and wave-driven flow. We found that uptake rate efficiency depends not just canopy depth-averaged flow magnitude, but also on the characteristic wave frequency. Finally, we found that at some field locations, flexible canopy-forming seagrasses were complemented with a dense understory of secondary species. In wavy-environments, understory biomass may fill distinct ecological niches while also helping to protect the bed from wave-driven disturbances. We created a simple numerical model to encapsulate the theory, and tested it in the laboratory with a collection of heterogeneous canopy mimics. Results supported the idea that understories may indeed significantly alter near-bed hydrodynamics.

Keywords: Civil and Environmental Engineering.
Advisor: Koseff Jeffrey Russell primary advisor. Thesis advisor
Fong Derek advisor. Thesis advisor
Fringer Oliver B. (Oliver Bartlett) advisor. Thesis advisor
Monismith Stephen Gene advisor. Thesis advisor
Data exploration with multi-persistent density clustering [electronic resource]

This research proposes the multi-persistent density clustering method as a data ex- ploration and profiling tool, which enables users to easily investigate the clustering structure in the data. The main procedure is to construct different versions of neigh- borhood graph from the data regarding to different density level sets with different scale parameters. Then the persistence information of each cluster is summarized into a persistent diagram by tracing the evolution of connected components of those neighborhood graphs, and the information can be used to discover reliable clustering structure. The method extends the goal of scale persistence in most existing persistence- based topological data analysis approaches, so that the results can be robust to the presence of noise and outliers. The method is related to the single linkage hierarchical clustering method and the cluster tree analysis, but it does not suffer from their main shortcomings such as the chaining problem of single linkage. In contrast to most clustering analysis approaches, the method does not require users to provide information about the clustering structure that is usually unknown before running the algorithm such as the number of target clusters. The second part of this dissertation demonstrates four different applications of multi-persistent density clustering, including exploring metastable states in the molec- ular dynamics simulation data, studying treatment variations of breast cancer from electronic health records, discovering disease subtypes from gene expression data and investigating research topics from dissertation titles and abstracts. The demonstra- tions show that the proposed method can be applied to various kinds of data and discover clustering structures with different characteristics.

Advisor: Carlsson Gunnar
Guibas Leonidas J. advisor. Thesis advisor
Pande Vijay advisor. Thesis advisor