VictorJuiz/thesis huggingface dataset:
The letter and the spirit [electronic resource] : politics, intimacy, and middle class constitution-making in Kenya
Keywords: Anthropology.

My research project arises out of a concern with how a particular response -- constitution-making -- to the particular manifestation of power around the idea of the State and the institutions and practices of Government in Kenya, and to the widespread social and economic inequalities in the country, appears to be closing off, in the name of democracy and democratic reform, the ways in which contingency, uncertainty, and disagreement shape democratic society. Based on sixteen months of fieldwork in Kenya, my doctoral dissertation The Letter and the Spirit: Politics, Intimacy, and Middle Class Constitution-Making in Kenya, is an anthropologically and ethnographically informed historical analysis of class as a political process that focuses on the interests, ideological beliefs, and socioeconomic and sociopolitical strategies of members of the reform movement. I argue that these beliefs and practices are tied to the ways Nairobi, the country's capital, is differentially accessed as a lived and symbolic space, and to the kinds of intimacy that are entered into by these reformers. I show how the reform movement is better understood not as a mass movement but as a small, closely-aligned group of individuals from a mostly cosmopolitan and professional background, who chose to focus on "human rights" and constitution-making because these reflected their class interests.
A light-weight 3-D indoor acquisition system using an RGB-D camera [electronic resource]
Keywords: Electrical Engineering.

Large-scale acquisition of exterior urban environments is by now a well-established technology, supporting many applications in map searching, navigation, and commerce. The same, however, is not the case for indoor environments, where access is often restricted and space can be cluttered. Recent advances in real-time 3D acquisition devices (e.g., Microsoft Kinect) enable everyday users to scan complex indoor environments at a video rate. Raw scans, however, are often noisy, incomplete, and significantly corrupted, making semantic scene understanding challenging, if not impossible. In this dissertation, we present ways of utilizing prior information to understand the structure and semantics of indoor environments starting from noisy scans of real-time 3-D sensors. The presented pipelines are light-weight, and have the potential to allow users to incorporate feedback at interactive rates so as to improve the acquisition. We first present a hand-held system for real-time, interactive acquisition of residential floor plans. We then discuss how we exploit the fact that public environments typically contain a high density of repeated objects (e.g., tables, chairs, monitors, etc.) in regular or non-regular arrangements with significant pose variations and articulations. Last, we present a guided real-time scanning setup, wherein the incoming 3D data stream is continuously analyzed, and the data quality automatically assessed. Overall, the research presented in this talk presents significant advances on how low-quality 3-D scans can be effectively used to understand and acquire indoor environments, while allowing necessary user-interaction in real-time. We believe that user-captured 3D content will become a mainstream medium in the years to come.
Local cosmic-ray measurements with Fermi-LAT [electronic resource]
Keywords: Physics.

The Fermi-LAT (Large Area Telescope) gamma-ray space observatory was launched in June 2008 and has been continuously operating since. By far the brightest gamma-ray source in the sky for Fermi is the Earth. This emission is produced by the interactions between cosmic-ray (CR) particles and the Earth's atmosphere. Various properties of this emission have been measured with unprecedented details. Its energy spectrum is used to infer the spectrum of CR proton. The correlations between the thickness of the atmosphere and the solar cycle are tested by observing the time variation of its profile shape. Also, Fermi has demonstrated an excellent capacity to detect electrons and positrons. This enables the measurements of separate CR electrons and positrons spectra between 20 - 200 GeV, using the geomagnetic field to differentiate the charge sign. The result shows that the positron fraction is increasing with energy in this energy range, which strongly contradicts our standard models of CR productions and propagations. The interpretation of the excess positrons is still at the frontier of current CR physics research. It may be a sign of new phenomena, such as dark matter annihilation signal, or normal astrophysical sources in the local universe that we have to better understand.
Local imaging of high mobility two-dimensional electron systems with virtual scanning tunneling microscopy [electronic resource]
Keywords: Applied Physics.

Correlated electron states in high mobility two-dimensional electron systems (2DESs), including charge density waves and microemulsion phases intermediate between a Fermi liquid and Wigner crystal, are predicted to exhibit complex local charge order, but are not yet well understood. Properties of correlated states in 2D have traditionally been studied using bulk electrical transport measurements, which tend to reflect a spatially averaged response of the system, but can obscure any local ordering phenomena that may be occurring. Scanning probes are well suited to study these systems on a short length scale, but developing useful scanning probe techniques has been difficult due to the fact that high mobility 2DESs are found at buried semiconductor interfaces, typically in the GaAs/AlGaAs materials system. This difficulty can be overcome by using a new scanning technique called "virtual scanning tunneling microscopy" (VSTM) that allows for local tunneling into a high mobility 2DES. This is achieved using a specially designed bilayer GaAs/AlGaAs heterostructure where the tunnel coupling between two separate 2DESs is tunable via electrostatic gating. Scanning gate microscopy measurements on these samples will be presented, which show that the local tunneling can be controlled on a length scale approaching the Fermi wavelength, as well as an overview of the scanning system built to carry out these measurements in a cryogen-free dilution refrigerator, which is able to achieve electron temperatures down to 45 mK.
Local measurements of the superconducting penetration depth [electronic resource]
Keywords: Physics.

Measurements of the superconducting penetration depth, which is closely related to the superfluid density, are among the first characterizations of new superconductors. These measurements give insight into the gap structure, a key stepping stone to a microscopic understanding of the system. I will review several techniques for measuring the penetration depth, and describe how we can use scanning SQUID microscopy to measure it locally. These local measurements often reveal spatial inhomogeneity in the penetration depth. Spatial inhomogeneity is a problem, since every experimental probe of the penetration depth assumes uniformity. This discrepancy motivated us to study penetration depth inhomogeneity in two ways: by creating and measuring a model system with controlled local penetration depth, and by calculation.
Local transport measurement at mesoscopic length scales on epitaxial graphene using scanning tunneling potentiometry [electronic resource]
Keywords: Applied Physics.

Mesoscopic transport is the regime of transport in which quantum interference effects are present. To date there have been no measurements of the local transport potential variation at mesoscopic length scales in macroscopic samples. In this dissertation, we present the first such experimental study. The mesoscopic phenomenon of interest in this study is weak localization in epitaxial graphene. We use scanning tunneling potentiometry (STP) to measure the local transport potential on this material. STP is a scanning-tunneling-microscope-based instrument that is capable of measuring the local transport potential with high accuracy, while obtaining the topography of the sample simultaneously. The spatial resolution under our measurement conditions is of order several nanometers. We will summarize our efforts in developing, understanding and optimizing our STP instrument. Tip jumping artifacts are systematic errors that can occur in STP measurement. It is not possible to completely eliminate such problems if the geometry of the tip is unknown. We limit such problems by using a sharp, slender tip manufactured by focussed ion beam. The practice, benefit, and issues of using such tips in STP experiments are presented. In our data taken at a temperature of 17K, we show that the largest features in the local transport potential are residual resistivity dipoles associated with topographical steps in the sample. On a finer length scale, on the plateau regions of the sample, there are spatially repeatable fluctuations in the measured potential that cannot be understood by simple classical diffusive transport theory. The theoretical understanding of what is measured locally by STP under mesoscopic conditions is not trivial. Lacking a theory on macroscopic samples, we present a heuristic understanding of STP operation to highlight some of the issues one encounters when considering the interpretation of STP results. To understand the effects of quantum interference, the density matrix of the sample is needed. The theory for a macroscopic sample also requires a local description of the density matrix. Such a complete theory requires further development and calculations.
Logic synthesis for fault-tolerant quantum computers [electronic resource]
Keywords: Electrical Engineering.

Efficient constructions for quantum logic are essential since quantum computation is experimentally challenging. This thesis develops quantum logic synthesis as a paradigm for reducing the resource overhead in fault-tolerant quantum computing. The model for error correction considered here is the surface code. After developing the theory behind general logic synthesis, the resource costs of magic-state distillation are quantitatively analyzed. The resource costs for a relatively new protocol distilling multi-qubit Fourier states are calculated for the first time. Four different constructions of the fault-tolerant Toffoli gate, including two which incorporate error detection, are analyzed and compared. The techniques of logic synthesis reduce the cost of fault-tolerant quantum computation by one to two orders of magnitude, depending on which benchmark is used. Using resource analysis for T gates and Toffoli gates, several proposals for constructing arbitrary quantum gates are compared, including ``Clifford+T'' sequences, V-basis sequences, phase kickback, and programmable ancilla rotations. The application of arbitrary gates to quantum algorithms for simulating chemistry is discussed as well. Finally, the thesis examines the techniques which lead to efficient constructions of quantum logic, and these observations point to even broader applications of logic synthesis.
Loop subdivision surface boundary integral simulations for vesicles in shear and extensional flows [electronic resource]
Keywords: Computational and Mathematical Engineering.

Vesicles are fluid droplets enclosed by a deformable lipid membrane. The most prominent features of vesicles fluids problems are the incompressibility of the membrane and a membrane bending energy that requires a smooth and accurate determination of curvature. In this thesis we use boundary integral simulations with curvature determined via Loop subdivision surfaces to model vesicles in fluid flow. This method ensures that curvature is measured on a surface that is guaranteed to be at least C1 continuous everywhere. We are able to examine vesicles that are highly non-spherical in shape. When vesicles are placed in a shear flow they undergo motions of tank treading, trembling, and tumbling. We validate our code versus spectral simulations and extend the vesicle phase diagrams to vesicles of increasing aspect ratio. In addition to the prolate shape family of vesicle shapes, we present simulations of biconcave and stomatocyte vesicles. We show that reduced volume 0.65 vesicles experience different responses to the same viscosity ratio and capillary number depending on whether their initial shape is prolate or biconcave. We investigate how the presence of a wall near a vesicle gives the vesicle a lift velocity and how the wall affects the phase diagram. We find vesicles far from a wall experience an induced lift velocity inversely proportional to the square of the height of the centroid of the vesicle and proportional to the wall normal component of the particle stresslet. The presence of a nearby wall also requires a higher critical viscosity ratio for the vesicle to advance from tank treading to trembling or tumbling motions. Finally, we re-examine over a wider range of reduced volumes the instability originally reported by Zhao and Shaqfeh in 2013 of a vesicle placed in an extensional flow. At sufficiently high aspect ratio and capillary number, we find the steady elongated dumbbell shape is unstable to odd perturbations and the vesicle's dumbbell ends become unequal in size. We also find that the critical capillary number as a function of reduced volume is similar between uniaxial and planar extensional flow. We simulate vesicles with an aspect ratio of up to 10:1 and compare to experimental results. Observing the continuation of this instability from modest to high aspect ratio vesicles helps us reconcile the asymmetric nature of the reported instability with the apparently symmetric appearance of high aspect ratio experiments.
Low bitrate image retrieval with compressed histogram of gradients descriptors [electronic resource]
Keywords: Electrical Engineering.

Mobile Visual Search (MVS) enables a new class of applications which use the camera on mobile devices like smart phones and tablets to initiate search queries. For MVS applications, transmitting a JPEG image could take tens of seconds over a slow wireless link. The size of the data transmitted over the network needs to be as small as possible to reduce network latency. In this thesis, we show that we can reduce the amount of data by an order of magnitude by transmitting compressed features compared to transmitting JPEG images. Most popular descriptors in computer vision are based on histograms (or distributions) of gradients.To that end, we study techniques for quantization and coding of distributions, and use these techniques to obtain compact representations for HoG descriptors. The proposed descriptors are fast to compute, do not require storage of codebooks and can be compared in the compressed domain. We discuss how to build an analytical model for each step of an image matching and retrieval pipeline. We show how image level True Positive Rate and False Positive Rate can be modeled from feature level Receiver Operating Characteristic. We also propose a model for the bag-of-words retrieval pipeline. We use the model for optimizing system parameters in a low bitrate image retrieval system. We show that high performance retrieval can be achieved with a database of 1 million images using only a few KB of compressed feature query data.
Low energy excitations in cuprate high temperature superconductors [electronic resource] : angle-resolved photoemission spectroscopy studies
Keywords: Applied Physics.

The mechanism of superconductivity in the cuprate high temperature superconductors is an enduring problem in condensed matter physics, and a detailed experimental phenomenology is a crucial starting point for microscopic understanding. Angle-resolved photoemission spectroscopy (ARPES) measures electronic structure in momentum-space. Low-energy excitations in the cuprates, including the superconducting gap, are known to be anisotropic in momentum space, so the momentum resolution afforded by ARPES is key to understanding the physics and uncovering the mechanism. In this dissertation, I present experiments which pursue the cuprate superconductivity problem from several angles: understanding electron-boson coupling which may be involved in mediating superconductivity (Chapters 6 and 7 and Appendix B), understanding the momentum-space structure of the normal state pseudogap (Chapter 5 and Appendix A), understanding how superconductivity coexists with the pseudogap and other phases (Chapters 3 and 4). Much of this work took advantage of a recent development in ARPES technology, using a UV laser as a light source, which allows experiments to be performed with superior energy and momentum resolution. These experiments highlight the wealth of information that is available in ARPES data, including dispersions, scattering rates, and spectral gaps, and they demonstrate the importance of exploring these variables comprehensively as a function of temperature, doping, and momentum.
Low resistance contacts to n-type germanium [electronic resource]
Keywords: Electrical Engineering.

The scaling of conventional silicon transistors faces several obstacles including the need to introduce materials such as germanium which have higher carrier mobilities. Several challenges need to be addressed in these new materials systems. In the case of germanium, contact resistance to n-type Ge is particularly problematic. This thesis presents two approaches to address this issue. The first is the use of metal-insulator-semiconductor contacts, whereby inserting a thin insulator between the metal and semiconductor can reduce the barrier height and reduce contact resistance. Tunneling resistance and series resistance effects are studied experimentally and theoretically. The second approach is the use of germanide contacts in conjunction with high doping techniques. Low contact resistances are obtained due to the high dopant activation level and dopant segregation effects.
Low-cost, highly-efficient Si solar cell [electronic resource] : for the 1.4 billion people who do not have access to electricity
Keywords: Electrical Engineering.

Women in Africa walk more than four miles every day to collect water because they do not have electricity to pump the water in their wells. Villagers in India travel more than ten miles to charge their gadgets such as cell phones. Today, more than 1.4 billion people in the world do not have any access to electricity, and most of them are poor families in remote locations. One viable solution to the world's energy problem is to utilize solar power with inexpensive and efficient photovoltaic systems. Si solar cells, which have no limitation for use in terms of abundance, toxicity, and stability, will be the most attractive solution, but the current Si photovoltaic system still remains more expensive than traditional fossil fuels. In order to be cost-competitive, a Si solar cell needs to be thinner: it can reduce not only the material cost but also the balance-of-system (BOS) cost, because thin and light-weight Si solar cells can be packaged with cheap plastics substrates and can be delivered and installed easily. Thinner material, however, absorbs less amount of light, which requires a smart design for a thin Si solar cell to improve light absorption as much as possible. Nanostructuring, such as nanowires or nanocones, emerges as a promising solution: its absorption improvement can be significantly larger than that from a conventional texturing method. Various nanostructured solar cells, however, have not achieved high power conversion efficiency (PCE). Although their light absorption is much higher than that of a conventional solar cell, their PCE is much lower. This problem is due to the increased Auger and surface recombination in nanostructured solar cells. It is a very critical problem, but it has been overlooked. This dissertation presents two novel design concepts of nanostructured solar cells as solutions to the problem: a hybrid Si nanocone/polymer solar cell and an ultra-thin Si solar cell with an all-back-contact design. Both devices achieved more than 80% external-quantum-efficiency (EQE) over the entire visible spectrum, which demonstrated their success as a solution. Their EQEs are superior to the EQEs of any other nanostructured Si solar cells reported so far. The hybrid Si solar cell showed 11.1% PCE with a simple solution-based process. The ultra-thin Si solar cell showed 13.7% PCE from a sub-10-µm-thick substrate. These achievements were based on three key design principles: no highly-doped layer at the front, less surface area, and higher light absorption. My research for low-cost, highly-efficient Si solar cells show the potential of the nanostructured Si solar cell to be a cost-effective solution to the world's energy problem.
Machine learning in the search for dark matter with the ATLAS detector [electronic resource]
Keywords: Physics.

The results of a search for pair production of the scalar partners of the bottom quarks in 4.7 fb1 of pp collisions at ps = 7 TeV using the ATLAS detector at the LHC are reported. Scalar bottoms are searched for in events with large missing transverse momentum and two jets identified as originating from a b-quark in the final state. In an R-parity conserving minimal supersymmetric scenario, assuming that the scalar bottom decays exclusively into a bottom quark and a neutralino, 95% confidence-level upper limits are obtained in the b1 c10 mass plane. Exclusions are first calculated using the frequentist method. For c 10 masses less than 150 GeV, b1 masses up to 500 GeV are excluded. The exclusion is extended up to 600 GeV by the use of machine learning methods.