VictorJuiz/thesis huggingface dataset:
Electric Field Control of Ferromagnetism and Magnetic Devices Using Multiferroics

This dissertation presents a study of a heterostructure composed of room temperature magnetoelectric multiferroic BiFeO3 and ferromagnetic Co90Fe10, with specific interest in understanding the interfacial coupling mechanisms in this system and establishing the electric field control of a magnetization and spintronic devices. The field of spintronics has been plagued with the problem of a large energy dissipation as a consequence of the resistive losses that come during the writing of the magnetic state (i.e. reversing the magnetization direction). The primary aim of the work presented here is to investigate and understand a novel heterostructure and materials interface that can be demonstrated as a pathway to low energy spintronics./nIn this dissertation, I will address the specific aspects of multiferroicity, magnetoelectricity, and interface coupling that must be addressed in order to reverse a magnetization with an electric field. Furthermore, I will demonstrate the reversal of a magnetization/nwith an electric field in single and multilayer magnetic devices. The primary advances made as a result of the work described herein are the use of epitaxial constraints to control the nanoscale domain structure of a multiferroic which is then correlated to the domain structure of the exchange coupled ferromagnet. Additionally, the magnetization direction of the ferromagnetic layer is controlled with only an applied electric field at both macroscopic and microscopic scales. Lastly, using this electric field control of ferromagnetism, the first demonstration of a magnetoelectric memory bit is presented.

Advisor: Ramesh, Ramamoorthy
Solid-Liquid Interdiffusion Bonding of Silicon Carbide to Steel for High Temperature MEMS Sensor Packaging and Bonding

Complex engineering systems ranging from automobile engines to geothermal wells require specialized sensors to monitor conditions such as pressure, acceleration and temperature in order to improve efficiency and monitor component lifetime in what may be high temperature, corrosive, harsh environments. Microelectromechanical systems (MEMS) have demonstrated their ability to precisely and accurately take measurements under such conditions. The systems being monitored are typically made from metals, such as steel, while the MEMS sensors used for monitoring are commonly fabricated from silicon, silicon carbide and aluminum nitride, and so there is a sizable thermal expansion mismatch between the two. For these engineering applications the direct bonding of MEMS sensors to the components being monitored is often required. This introduces several challenges, namely the development of a bond that is capable of surviving high temperature harsh environments while mitigating the thermally induced strains produced during bonding./nThis project investigates the development of a robust packaging and bonding process, using the gold-tin metal system and the solid-liquid interdiffusion (SLID) bonding process, to join silicon carbide substrates directly to type-316 stainless steel. The SLID process enables bonding at lower temperatures while producing a bond capable of surviving higher temperatures. Finite element analysis was performed to model the thermally induced strains generated in the bond and to understand the optimal way to design the bond. The cross-sectional composition of the bonds has been analyzed and the bond strength has been investigated using die shear testing. The effects of high temperature aging on the bond's strength and the metallurgy of the bond were studied. Additionally, loading of the bond was performed at temperatures over 415 °C, more than 100 °C, above the temperature used for bonding, with full survival of the bond, thus demonstrating the benefit of SLID bonding for high temperature applications./nLastly, this dissertation provides recommendations for improving the strength and durability of the bond at temperatures of 400 °C and provides the framework for future work in the area of high temperature harsh environment MEMS packaging that would take directly bonded MEMS to temperatures of 600 °C and beyond.

Advisor: Pisano, Albert P
Reaction-Diffusion Agent Based Models of Nucleocytoplasmic Transport

Selective yet efficient transport between the cell nucleus and cytoplasm is critical to cellular function as the nuclear pore complex is a major point of regulation for gene expression, signal transduction, immune response, oncogenesis and viral propagation. The combined physical structure of the pore, biochemical interaction of transport factors with pore components and the presence of the cellular milieu create conditions under which selective and efficient nucleocytoplasmic transport can occur. In this dissertation, I explore the significance of structure and interaction on transport of globular proteins and polymeric mRNA cargo through the crowded pore. In the first part of this work, an agent based modeling software framework is developed and validated for accurately simulating discrete and stochastic reaction-diffusion systems. A simulation environment representing the structure of the nuclear pore complex along with rules for the dynamics of protein movement and interaction was created using in vivo and in vitro reported parameters. This setup was then used to perform in silico experiments on the role of pore-cargo affinity in optimizing transport efficiency. These experiments demonstrate the pore's sensitivity to cargo affinity in maintaining efficient transport and suggest that a higher affinity binding site at the side of the pore where transport is terminated increases efficiency by reducing futile shuttling of cargo complexes. In the final part of this dissertation, I extend my agent based modeling framework to look at aspects of mRNA export that have remained unaddressed in experimental works. Variations in the number and spacing of transport receptors bound to the mRNA are shown to play a critical role in transport efficiency. In these experiments, a single transport receptor at the 5' end appeared insufficient for facilitating export. Increasing transport receptor coverage along the length of the mRNA improved the chances of successful export. Additionally, it was observed that the presence of a transport receptor near either the 5' or 3' terminus is required for successful export as it likely promotes the emergence of a favorable threading conformation. Finally, it was observed that the use of a single fluorescent tag to track and report mRNA export time, as is standard in current experimental work, is likely to underestimate true transport times. These findings have implications in the design of targeted delivery and export of polymeric molecules into and out the nucleus.

Advisor: Mofrad, Mohammad
Mechanisms of Heterochromatin Silencing in Saccharomyces cerevisiae

Sir proteins are responsible for maintaining stable transcriptional repression and silencing of telomeres, rDNA, and silent mating-type loci in S. cerevisiae. Decades of research identify a thorough list of the proteins required to establish and maintain silencing at HML and HMR, but despite many models being put forward, the mechanism by which Sir-proteins repress transcription has not been definitively determined. I sought to determine the mechanism of transcriptional silencing within heterochromatin in yeast./nI tested models of transcriptional silencing using a variety of orthogonal in vivo approaches to build a more comprehensive model of the mechanism of silencing by Sir proteins. Specifically, I assayed for RNA Pol II in an engaged, DNA-melted form at the promoter of HMLα1 to conclusively test predictions of the downstream-inhibition model. I then adapted the single-subunit RNA polymerase of T7 phage and its cognate promoter to test the ability of a silenced template to be transcribed by a heterologous transcription assay in vivo. Finally, I adapted the thoroughly studied GAL1 promoter and Gal4 activator to test whether the extent of repression by Sir-proteins at HMR is sensitive to the nature of the transcription factor or to the promoter being repressed./n/nThese studies provided a framework for understanding the mechanism of Sir-protein repression. I propose a dynamic affinity-based competition model for transcriptional silencing where Sir proteins primarily restrict transcription before RNA Polymerase II has melted DNA at its target and competition between Sir proteins and gene-specific activators at promoters determines the efficiency of silencing.

Advisor: Rine, Jasper
A Characteristics-Based Approach to Radioactive Waste Classification in Advanced Nuclear Fuel Cycles

The radioactive waste classification system currently used in the United States primarily relies on a source-based framework. This has lead to numerous issues, such as wastes that are not categorized by their intrinsic risk, or wastes that do not fall under a category within the framework and therefore are without a legal imperative for responsible management. Furthermore, in the possible case that advanced fuel cycles were to be deployed in the United States, the shortcomings of the source-based classification system would be exacerbated: advanced fuel cycles implement processes such as the separation of used nuclear fuel, which introduce new waste streams of varying characteristics. To be able to manage and dispose of these potential new wastes properly, development of a classification system that would assign appropriate level of management to each type of waste based on its physical properties is imperative. This dissertation explores how characteristics from wastes generated from potential future nuclear fuel cycles could be coupled with a characteristics-based classification framework. A static mass flow model developed under the Department of Energy's Fuel Cycle Research & Development program, called the Fuel-cycle Integration and Tradeoffs (FIT) model, was used to calculate the composition of waste streams resulting from different nuclear fuel cycle choices: two modified open fuel cycle cases (recycle in MOX reactor) and two different continuous-recycle fast reactor recycle cases (oxide and metal fuel fast reactors). This analysis focuses on the impact of waste heat load on waste classification practices, although future work could involve coupling waste heat load with metrics of radiotoxicity and longevity. The value of separation of heat-generating fission products and actinides in different fuel cycles and how it could inform long- and short-term disposal management is discussed. It is shown that the benefits of reducing the short-term fission-product heat load of waste destined for geologic disposal are neglected under the current source-based radioactive waste classification system, and that it is useful to classify waste streams based on how favorable the impact of interim storage is on increasing repository capacity. The need for a more diverse set of waste classes is discussed, and it is shown that the characteristics-based IAEA classification guidelines could accommodate wastes created from advanced fuel cycles more comprehensively than the U.S. classification framework.

Advisor: Peterson, Per F
Making a good match: How schools and external service providers negotiate needs and services in support of school improvement

This study investigated a problem facing policy makers, education leaders, and external providers of service that support or facilitate school-based change designed to improve teaching and learning: How to match school needs with providers' services in ways that maximize school improvement. A growing number of organizations provide service to schools, and considerable amounts of money set aside by state and national policy makers to facilitate school improvement. Despite escalating pressures for performance and the availability of both funding and external expertise, more and more schools and districts across the country are failing to meet expectations and experiencing an array of sanctions./nAlthough research on the role of intermediary organizations is growing in some areas, lack of attention to the match between partners during the formation of working relationships warranted this inquiry. This was a comparative case study focused on two partnerships that were at the beginning of the negotiation and contracting process, and drew from both the education and the management literature to frame the investigation. Each partnership was intended to focus on improving student performance on standardized tests./nThe relationship most critical to the success or failure of a match existed between the principal and the external provider. Early congruence between these two key players overcame lack of teacher buy-in over time in one case, and lack of early congruence between these two undermined the match in the other. The communication strategy during early negotiations enabled or impeded the development congruent understanding about the nature of the work to be undertaken. The level of early congruence between principal and provider regarding the problem they were going to work on, and how they would assign and enact their different leadership roles, was associated with later-stage progress and perceived satisfaction with the match. Finally, school-level (versus district) control over school improvement decisions, efforts to place the initiative in the context of a coherent school improvement plan, and willingness to adapt the initiative to prevailing school conditions were the aspects of context most relevant to match formation. The findings have implications for school leaders and external providers seeking to foster more productive relationships in the service of school improvement.

Advisor: Warren Little, Judith
Incentives in Firm's Unobservable, Endogenous Decisions: Diversity and Service Effort

Firms make optimal decisions on the level of various marketing-mix variables to maximize profits. Some of these marketing-mix variables are unobserved by researchers, yet they are important to understand when they are endogenous in that a firm has incentives to increase or decrease them depending on how they change its profit. This thesis is focused on understanding a firm's incentive in two unobservable, endogenous decisions: workforce diversity and service effort. This thesis further builds theoretical frameworks around these two concepts, validates/estimates the model using public and proprietary data, and draws implications in market competition and policy experiment./nThe literature in business, psychology, and sociology shows that there is a trade-off in hiring diverse workforce: diversity brings creative ideas that help solving problems, but it also creates friction among members. Under competition, the decision on the level of diversity of workforce is an important strategic decision that gives firms a competitive edge. We build a theoretical model with symmetric firms and find that the better a firm can deal with a diverse workforce or the more competition there is in the market, the more diverse workforce the firm will hire. We also find that a firm's profit decreases with the intensity of market competition as expected, but increases with the firm's inability to deal with diverse workforce as the inability deters competition between firms. Finally, we extend the model to firms with asymmetric private marginal costs and empirically validate the positive relationship between the diversity of workforce and the intensity of competition (industry concentration ratio, in particular) using two datasets from 1997: National Organizations Survey and Economics Census./nService effort, often referred to as customer service, is also another important unobservable, endogenous decision that firms must make. Empirically quantifying or measuring the service effort is difficult because it is often unobservable. This paper proposes an empirical framework of the role of service effort in demand, along with other traditional marketing mix instruments. This model allows us to measure the unobserved effort level without data on effort, which is hardly available in most empirical settings. The paper also presents an application to a unique data set obtained from a franchise operating in the car radiator market. This framework can be useful in examining various aspects of service-intensive industries. In particular, this study investigates a much-debated public policy question regarding resale price ceiling in franchising. A policy evaluation shows that resale price ceiling lowers franchisees' profits and weakens their incentive to exert effort, which reduces consumer welfare. However, I find that, overall, resale price ceiling enhance consumer welfare in the car radiator market due to the lower price generated by the price ceiling.

Advisor: Villas-Boas, J. Miguel
Life and Libraries in the Roman World

I argue that the physical media through which literature was experienced (books, statues, and especially libraries) are crucial for understanding how liberal studies functioned in the economy of prestige. This is a study of the interactions between literature and society. The focus is not strictly on how society influenced literature, or how literature influenced society, but rather on how material manifestations of literature can shed light on the power dynamics of Roman society. In a domestic context, libraries could be used to define the meaning of places in the house, and their physical structure could be used by a dominus to reinforce and justify his place in the social hierarchy, in particular in relation to guests. At the same time, the very materiality of libraries had a tendency to undermine their place in elite ideology by implicating them in the discourse of luxuria. Finally, control over the material trappings of the library (especially author portraits) could function as a proxy for the exercise and establishment of cultural authority, which was inextricably bound up with political power. As such, fights over library statuary provide a window into the inter-relationship between power and paideia.

Advisor: Sailor, Dylan
Switching Dynamics of Thin Film Ferroelectric Devices- A Massively Parallel Phase Field Study

In this thesis, we investigate the switching dynamics in thin film ferroelectrics. Ferroelectric materials are of inherent interest for low power and multi-functional devices. However, possible device applications of these materials have been limited due to the poorly understood electromagnetic and mechanical response at the nanoscale in arbitrary device structures. The difficulty in understanding switching dynamics mainly arises from the presence of features at multiple length scales and the nonlinearity associated with the strongly coupled states. For example, in a ferroelectric material, the domain walls are of nm size whereas the domain pattern forms at micron scale. The switching is determined by coupled chemical, electrostatic, mechanical and thermal interactions. Thus computational understanding of switching dynamics in thin film ferroelectrics and a direct comparison with experiment poses a significant numerical challenge. We have developed a phase field model that describes the physics of polarization dynamics at the microscopic scale. A number of efficient numerical methods have been applied for achieving massive parallelization of all the calculation steps. Conformally mapped elements, node wise assembly and prevention of dynamic loading minimized the communication between processors and increased the parallelization efficiency. With these improvements, we have reached the experimental scale - a significant step forward compared to the state of the art thin film ferroelectric switching dynamics models. Using this model, we elucidated the switching dynamics on multiple surfaces of the multiferroic material BFO. We also calculated the switching energy of scaled BFO islands. Finally, we studied the interaction of domain wall propagation with misfit dislocations in the thin film. We believe that the model will be useful in understanding the switching dynamics in many different experimental setups incorporating thin film ferroelectrics.

Advisor: Salahuddin, Sayeef
Helping Developers Construct Secure Mobile Applications

Mobile phones are no longer static devices that simply make phone calls and send SMS messages. Modern smartphones are now closer to general purpose computers. They allow users to customize their phones by installing third-party applications that let them browse the web, check social networking sites, and do online banking. Platform manufacturers, such as Android, introduce new APIs to facilitate the creation of rich applications that interact with other applications, system resources, and external resources (such as web applications). Given the level of trust users put in their phones and the number of sensitive tasks they perform, it is important to understand and improve the security of mobile applications./nAndroid provides tools to enable rich interaction, but if developers do not know how to use them correctly, they will not use them securely. In this dissertation, we examine how mobile applications interact with each other and their environment. We uncover threats to application security due to developer confusion and general misuse of the features provided by the mobile platform. Specifically, we perform an in-depth analysis of how Android applications interact with each other through inter-process communication mechanisms, how they interact with system resources through Android permissions, and how they interact with web content through WebViews. We build static analysis tools to identify vulnerable applications and measure the prevalence of the vulnerabilities. Through automated and manual analysis, we identify patterns that illustrate how developers misuse these features and make their application vulnerable to attack. We further provide platform-level, API-level, and design-level solutions to help developers and platform designers build secure applications and systems.

Advisor: Wagner, David A.