VictorJuiz/thesis huggingface dataset:
Studies on time-reversal invariant topological insulators [electronic resource]
Keywords: Physics

This dissertation brings together a number of topics in the theory of time-reversal invariant topological insulators. The first four chapters are devoted to the transport properties of the two-dimensional (2D) quantum spin Hall state. We explain nonlocal transport measurements in mercury telluride (HgTe) quantum wells in terms of a Landauer-Büttiker theory of helical edge transport and confirm the discovery of the quantum spin Hall state in this material. We find that decoherence can lead to backscattering without breaking microscopic time-reversal symmetry. As an example of incoherent scattering, we study a Kondo impurity in an interacting helical edge liquid. A renormalization group analysis shows the existence of an impurity quantum phase transition governed by the Luttinger parameter of the edge liquid between a local helical Fermi liquid with T^6 scaling of the low-temperature conductance, and an insulating strongly correlated phase with fractionally charged emergent excitations. In the presence of a time-reversal symmetry breaking magnetic field, it is known that even coherent scattering can lead to backscattering. Through exact numerical diagonalization we find that nonmagnetic quenched disorder has a strong localizing effect on the edge transport if the disorder strength is comparable to the bulk gap. The predicted magnetoconductance agrees qualitatively with experiment. The last two chapters are devoted to 3D topological insulators. We propose a combined magnetooptical Kerr and Faraday rotation experiment as a universal measure of the Z_2 invariant. Finally, we propose a fractional generalization of 3D topological insulators in strongly correlated systems, characterized by ground state degeneracy on topologically nontrivial spatial 3-manifolds, a quantized fractional bulk magnetoelectric polarizability without time-reversal symmetry breaking, and a halved fractional quantum Hall effect on the surface.
Study of the decay of the bottom meson to an omega meson, charged lepton, and neutrino [electronic resource]
Keywords: Physics

Using a sample of 467 million BB pairs recorded by the BABAR detector at the SLAC PEP-II e+e− collider, we measure the partial branching fraction of B^+ \to \omega\ell\nu decays in five ranges of q2, the momentum-transfer squared of the virtual W boson. We observe 1034 ± 131 signal decays, corresponding to a branching fraction of B(B^+ \to \omega\ell\nu) = (1.17 ± 0.15 ± 0.11) x 10^−4 , where the first error is statistical and the second is systematic. The q2 distribution is compared to theoretical predictions based on quark model and light cone sum rule form factor calculations.
Studying bonding and electronic structures of materials under extreme conditions [electronic resource]
Keywords: Applied Physics.

Recent advances in high pressure diamond anvil cell techniques and synchrotron radiation characterization methods have enabled investigation of a wide range of materials properties in-situ under extreme conditions. High pressure studies have made significant contribution to our understanding in a number of scientific fields, e.g. condensed matter physics, chemistry, Earth and planetary sciences, and material sciences. Pressure, as a fundamental thermodynamic variable, can induce changes in the electronic and structural configuration of a material, which in turn can dramatically alter its properties. The novel phases and new compounds existing at high pressure have improved our basic understanding of bonding and interactions in condensed matter. This dissertation focuses on how pressure affects materials' bonding and electronic structures in two types of systems: hydrogen rich molecular compounds and strongly correlated transition metal oxides. The interaction of boranes and hydrogen was studied using optical microscopy and Raman spectroscopy and their hydrogen storage potential is discussed in the context of practical applications. The pressure-induced behavior of the SiH4 + H2 binary system and the formation of a newly formed compound SiH4(H2)2 were investigated using a combination of optical microscopy, Raman spectroscopy and x-ray diffraction. The experimental work along with DFT calculations on the electronic properties of the compound up to the possible metallization pressure, indicated that there are strong intermolecular interactions between SiH4 and H2 in the condensed phase. By using a newly developed synchrotron x-ray spectroscopy technique, we were able to follow the evolution of the 3d band of a 3d transition metal oxide, Fe2O3 under pressure, which experiences a series of structural, electronic and spin transitions at approximately 50 GPa. Together with theoretical calculations we revisited its electronic phase transition mechanism, and found that the electronic transitions are reflected in the pre-edge region.
Subsampling GPS receiver front-end [electronic resource]
Keywords: Electrical Engineering

Research in RFIC design has recently shifted towards direct conversion and subsampling architectures as an alternative to the conventional super-heterodyne architectures. Bandpass sampling architectures, also called subsampling architectures, exhibit several advantages over super-heterodyne architectures, notably, the complexity of subsampling architectures is significantly lower since no phase-locked loop is required. A direct consequence is that downconversion from RF to IF can be achieved with significant power savings as compared to the super-heterodyne architecture. Another significant benefit of such architectures is the capability for processing multiple signals in parallel. The ability to simultaneously handle multiple carriers makes subsampling architectures particularly well suited for GNSS applications, as downconversion of multiple frequency bands is required in GNSS environments. With the advent of the new civilian GPS signals, L2C and L5, and the onset of the new Galileo signal, a receiver that can process multiple signals without adding complexity, is highly desired. An integrated proof-of-concept subsampling GPS receiver front-end in 130 nm BiCMOS is presented in this dissertation. The receiver achieves a noise figure of less than 3.8 dB, the lowest ever recorded noise figure of a subsampling based receiver.
Sunny Side Up: Characterizing the US Military's Approach to Solar Energy Policy
Keywords: solar energy
solar panels
military
multiple streams analysis
microgrid
policy
Thesis

Since 2007, the Department of Defense (DoD) has invested considerable resources and research into deploying solar panels to power its domestic military bases. This thesis seeks to apply theoretical models of policymaking to explain the enactment, implementation, and revision of the DoD‘s solar energy policy. In none of these stages can an idealized rational actor model account for the military‘s decision-making process; the panels purport to enhance energy security but do not do so, they are expensive, and they appear to strive for but fail to achieve federally mandated renewable electricity targets. Kingdon‘s multiple streams analysis best accounts for the timing of the DoD‘s decision to pursue solar, due to an open policy window in 2005. Furthermore, theories of ritualistic bureaucratic compliance in hierarchies explain the haphazard pattern of implementation. Finally, bounded rationality and incrementalism correctly predict the DoD‘s incomplete decision-making process when revising solar energy policy to include secure microgrid technology. These insights can and should inform DoD officials to critically analyze the motivations behind pursuing solar technology, consider nonrenewable microgrids to meet their stated goals of energy security, and lobby Congress to either allocate more funding for expensive renewable technology or relax its mandates in light of national security concerns.
Super string theory and the calculation of metastable ground states [electronic resource]
Keywords: Physics

Super string theory is a candidate theory for the unification of gravity and all the other forces. It is also the arena in which explicit examples of gravity duals of strongly coupled field theories are constructed. In this thesis, we explore various degrees of supersymmetry breaking for strings propagating on gravitational backgrounds which have field theory duals. We analyze a class of cascading quivers arising from near horizon limits of branes at singularities, starting with RG flows which preserve some degree of supersymmetry. We then apply this analysis to cases with supersymmetry breaking. We provide examples in which supersymmetry breaks spontaneously around a metastable groundstate and calculate some of its properties. We finally discuss string models in which supersymmetry is completely broken, including the potential phenomenological applications.
Supply chain contracts for perishable goods with a fixed shelf life [electronic resource]
Keywords: Management Science and Engineering

Managing a supply chain for a perishable good with extremely short shelf life and high value is a challenging task. In such a supply chain, the availability and the utilization of this perishable good become important performance measures. Especially when the supply chain is decentralized, these performance measures may generate conflicting incentives between supply chain partners, where utilization is critical for a supplier and availability for buyers. In this dissertation, we address channel coordination problems for various forms of decentralized supply chains that deal with perishable goods with a fixed shelf life to investigate how to reconcile such misaligned incentives between the supplier and the buyer(s). A platelet supply chain between blood centers and hospitals is a typical example of such a supply chain, where utilization is critical for blood centers and availability for hospitals. Due to such misaligned incentives, blood centers prefer to push older units to hospitals for better utilization of platelets, while hospitals prefer to receive younger units to achieve higher availability. Although there may be various approaches to address the issue of decentralized supply chains, this dissertation particularly focuses on the supply chain contracts.
Suppression of tensor decoherence in QND measurements of atomic ensembles [electronic resource]
Keywords: Applied Physics

Atomic ensembles have assumed a central role in modern high precision sensing applications including atomic clocks, magnetometers, gravimeters, and accelerometers. In the past decade significant advances have been made pushing these sensors to, and in some cases beyond the standard quantum limit of sensitivity. Much recent interest has been in the use of Quantum Non-Demolition (QND) measurements to perform state-preparation and metrology simultaneously. QND measurements are typically accomplished through interaction with an off-resonant optical probe. I present techniques to recreate QND measurements in the case that the Probe-Atom interaction is non-QND due to the presence of a tensor light-shift Hamiltonian. The tensor interaction naturally arises in detuned systems with spin one or higher and leads to a series of effects, including Hamiltonian evolution, technical noise enhancement, inhomogeneous and homogeneous dephasing that reduce measurement accuracy in these systems. I demonstrate several techniques for active cancellation of the tensor Hamiltonian and show compatibility with QND measurement and sub-shotnoise metrology performance.
Surface passivation and junction engineering in silicon / germanium metal-oxide-semiconductor field-effect-transistors for high performance application [electronic resource]
Keywords: Electrical Engineering

The planar silicon MOSFET is facing diminishing performance returns in improvement from device geometry scaling. Two alternative devices are being explored as possible solutions to this problem. The first contender is a multi-gate device (FINFET or surround gate) and the other is a MOSFET with high mobility channel material such as germanium, III-V or carbon. Ge has emerged as an important materials platform during recent years. With its high carrier mobility and the ability to detect and emit photons at telecommunications wavelengths, Ge is an attractive candidate for applications in both high performance electronics and optoelectronics. Moreover due to its compatibility with conventional CMOS fabrication, it can be processed using the standard manufacturing techniques that are currently used for silicon. However Ge does present a number of unique challenges that must be overcome, including issues of surface passivation, low n-type dopant solubility, and high dopant diffusivity. In this work, the unique properties of surface passivation enabled by radical oxidation are discussed. Some of the highlights are low temperature processing, substrate orientation independent growth rate of dielectric and low interface density. Subsequently, this radical oxidation is applied to 3D vertical gate all around (GAA) silicon MOSFET devices. Higher drive current, lower gate leakage and higher gate dielectric breakdown voltage are demonstrated for GAA devices using radical oxidation in comparison to thermal oxidation In the second part, radical oxidation is investigated for GeO2 growth as an interfacial layer in high-k / Ge gate stack. Using MOSCAP and n-MOSFET devices on Ge, low interface state density combined with drive current and electron mobility enhancement is demonstrated for Ge devices. In the third part, the source/drain junctions for Ge are studied. Ultra-shallow junctions using plasma immersion ion implantation are demonstrated. High n-type dopant activation in Ge using laser annealing is realized along with high performance diodes, significant reduction of contact resistance and integration in a MOSFET process flow.
Technological pedagogical content knowledge [electronic resource] : relationships to learning ecologies and social learning networks
Keywords: Education.

Improving learning experiences for all students is the ultimate goal of research in technology use in education. With more availability and better usability of technology in schools, the potential for teachers to use digital tools in schools is greater than ever. However a key factor determining whether new technologies are adopted is the extent to which teachers know how to use them to support students' learning. The special knowledge of how technologies can support students' learning of subject area content is known as technological pedagogical content knowledge (TPACK). This study explored the relationship of accomplished teachers' TPACK confidence to their use of technology with students and to their teaching and learning contexts. In an online survey, 307 National Board Certified teachers provided information about the frequency and breadth of their computer use with students; their use of computers in their personal lives; the school, classroom, and personal resources available to them for learning; and the people in their learning networks supporting their learning to use new technologies for teaching. Although the representativeness of the sample was limited and the measures self-reported, they provided rich opportunities to discover relationships and suggest avenues for supporting teacher learning of new technologies. Analyses showed that these accomplished teachers' confidence in their knowledge of how to use new technologies for teaching was different from their confidence in using technologies more generally. Further, TPACK confidence related to student use of computers in the classroom. No associations were found between TPACK confidence and age, gender, grade levels, subject areas, or student populations. However, confidence in teaching with technology did relate to measures of the teachers' learning resources. More varied learning resources and more productive social learning networks were associated with higher TPACK confidence. Three key types of support provided by learning partners -- learning together, posing challenges, and connecting the teacher to others to learn from -- were significantly more common among high-TPACK teachers. Findings in this study point to ways we might further understand, and subsequently increase, teacher confidence in using new technologies to support student learning. Several questions are raised for future research: Do learning resources lead to confidence in knowledge, or does confidence lead to awareness of existing resources? To what extent can TPACK be measured without first assessing the teacher's PCK? And how might we develop survey measures that reliably capture the complexity of technological pedagogical content knowledge? Understanding TPACK and the conditions under which it develops is an important field of research, as we strive to help teachers learn to use new technologies effectively to support powerful student learning.
Terrain relative navigation for sensor-limited systems with application to underwater vehicles [electronic resource]
Keywords: Aeronautics and Astronautics

Terrain Relative Navigation (TRN) provides bounded-error localization relative to an environment by matching range measurements of local terrain against an a priori map. The environment-relative and onboard sensing characteristics of TRN make it a powerful tool for return-to-site missions in GPS-denied environments, with potential applications ranging from underwater and space robotic exploration to pedestrian indoor navigation. For many of these applications, available sensors may be limited by mission power/weight constraints, cost restrictions, and environmental effects (e.g. inability to use a magnetic compass in space). Such limitations not only degrade the accuracy of traditional navigation systems, but further impact the ability to successfully employ TRN. Consequently, despite numerous advances in TRN technology over the past several decades, the application of TRN has been restricted to systems with highly accurate and information-rich sensor systems. In addition, a limited understanding of the effects of map quality and sensor quality on TRN performance has overly restricted the types of missions for which TRN has been considered a viable navigation solution. This thesis develops two new capabilities for TRN methods, resulting in significantly increased TRN applicability. First, a tightly-coupled filtering framework is developed which enables the successful use of TRN on vehicles with both low-accuracy navigation sensors and simple, low-information range sensors. This new filtering framework has similarities to tightly-coupled integration methods for GPS-aided navigation systems. Second, a set of analysis and design tools based on the Posterior Cramer-Rao Lower Bound are developed which allow for reliable TRN performance predictions as a function of both sensor and map quality. These analyses include the development of a new terrain map error model based on the variogram which allows for performance prediction as a function of map resolution. These developed capabilities are validated through field demonstrations on Autonomous Underwater Vehicles (AUVs) operated out of the Monterey Bay Aquarium Research Institute (MBARI), where available sensing has been limited primarily by cost. These trials include a real-time, closed-loop demonstration of the developed tightly-coupled TRN framework, enabling 5m accuracy return-to-site on a sensor-limited AUV where traditional TRN methods failed to provide better than 150m accuracy. The results further demonstrate the accurate prediction capability of the developed performance bounds on fielded systems, verifying their utility as design and planning tools for future TRN missions.
The Demise and Rise of Governance in Health Systems: A Path Forward
Keywords: CISAC
Center for International Security and Cooperation
Stanford University
global health
health governance
Thesis

How can global health initiatives (GHIs) focused on funding service provision in the short term simultaneously encourage indigenous health governance? This thesis first offers a taxonomy of nine mechanisms at the community, district, and national levels identified from the literature as capable of improving health governance. Second, it utilizes the proposed taxonomy to evaluate the funding patterns of one GHI – the Global Fund to Fight AIDS, Tuberculosis and Malaria. Analysis of the first nine rounds of Global Fund grants awarded to 123 countries revealed that the Global Fund appears to base its funding decisions upon need – high disease burden and low GDP per capita – rather than on quality of governance. Upon further examination, a complicated relationship exists between grant size and disease burden with countries facing the greatest disease prevalence paradoxically receiving relatively fewer dollars per case than other recipient countries. The governance-improving activities offered in the taxonomy appeared in less than one-half, and in most cases less than one-fifth, of 287 grants analyzed from forty countries. This insufficient emphasis on governance improvement is likely due to an overriding emphasis on vertical disease eradication driven by donor demands of short term results rather than on broadly strengthening health systems for which measurement of results is more difficult and outcomes are slower to develop. Inadequate investment in governance threatens to hamper progress towards the health Millennium Development Goals and to jeopardize sustainability of short term improvements in health outcomes, especially as developing countries with large disease epidemics often face poor governance.
The Effect of Health Insurance on Health Care Spending in Young Adults
Keywords:  Department of Economics
Stanford Department of Economics
United States
young adults
health insurance
Medical Expenditures Panel Survey
Thesis

Nearly a quarter of young adults between the ages of 19 and 23 are uninsured, making them the demographic most vulnerable to being uninsured in the United States. Young adults experience a sharp drop in health insurance rates at the age of 19 when they “age out” of their parents’ insurance plans. Exploiting this fact, I use a regression-discontinuity framework to explore the effect of health insurance on health care spending and to circumvent the usual problems of endogeneity. With data from the Medical Expenditures Panel Survey from 1996 through 2008, I estimate a 7% drop in insurance rates at the age of 19. I find that men spend significantly less on health care after this drop, and women spend more. With the passing of the 2010 Health Care Bill, we can expect young adults to rapidly become more insured. This paper’s results may provide insight into the policy’s potential consequences on health care spending.
The Effect of Hole Transport Material Pore Filling on Device Performance in Solid-State Dye-Sensitized Solar Cells
Keywords: photovoltaic devices
solar cells
organic electronics
titanium dioxide
photochemistry
Thesis

This thesis documents a detailed investigation of the effect of hole transport material (HTM) pore filling on the photovoltaic performance of solid-state dye-sensitized solar cells (ss-DSCs). The efficiency and photovoltaic characteristics of ss-DSCs improve significantly with the pore filling fraction (PFF) of the HTM 2,2’,7,7’-tetrakis-(N,N-di-p-methoxyphenylamine)9,9’- spirobifluorene (spiro-OMeTAD), and the mechanisms for these improvements were studied with transient absorption spectroscopy and transient photovoltage/photocurrent measurements. As the spiro-OMeTAD PFF is increased from 26% to 65%, there is a higher hole injection efficiency from dye cations to spiro-OMeTAD because more dye molecules are covered with spiro-OMeTAD, an order-of-magnitude slower recombination rate because holes can diffuse further away from the dye/HTM interface, and a 50% higher ambipolar diffusion coefficient due to an improved percolation network. Device simulations predict that if 100% PFF could be achieved for thicker devices, the efficiency of ss-DSCs using a conventional ruthenium-dye would increase by 25% beyond its current value.