VictorJuiz/thesis huggingface dataset:
Permutations with interval restrictions [electronic resource]
Keywords: Mathematics

This thesis studies the problem of the random transposition walk on permutations with interval restrictions. The mixing time of this Markov chain is explored, and a number of different cases are considered. For the case of bounded interval restrictions, a polynomial bound for the mixing time is achieved. For a specific example of bounded interval restrictions called Fibonacci permutations, the correct order of the mixing time is derived. An example of a family of interval restriction matrices for which the random walk mixes in exponential time is provided, showing that the walk in general does not mix in polynomial time. The case of one-sided interval restrictions is also studied, and cut-off is shown for a large class of one-sided interval restriction matrices. Furthermore, examples are provided in which chi-squared cut-off occurs, while total variation mixing occurs significantly earlier without cut-off. Finally, a coupling argument showing the correct order mixing time for the random transposition walk on the whole symmetric group is presented. This is achieved via projection to conjugacy classes and then a path coupling argument.
Phase fluctuations in microcavity exciton polariton condensation [electronic resource]
Keywords: Physics

In a homogeneous two-dimensional system at non-zero temperature, although there can be no ordering of infinite range, an ordered superfluid phase is expected to occur for a Bose liquid. Theory predicts that, in this phase, the correlation function decays with distance as a power law, and quantum vortices are bound to antivortices to form molecular-like pairs. We study the relevance of this theory to microcavity exciton polaritons. These are two-dimensional bosonic quasiparticles formed as a superposition of a microcavity photon and a semiconductor quantum well exciton, and have been shown to condense at high enough densities. Because of the short lifetime, equilibrium is not established, but we instead probe the steady state of the system, in which particles are continuously injected from a pumping reservoir. We employ a Michelson interferometer setup to measure the first order spatial correlation function of such a condensate. The gaussian form of the short-distance decay allows us to define an effective thermal de Broglie wavelength, although the system is not in thermal equilibrium. The long-distance decay is measured to be a power law with an exponent in the range 0.9-1.2, larger than is possible in equilibrium. Our non-equilibrium theory suggests that this can be attributed to laser pumping noise. We also present our observation of a single vortex-antivortex pair in a condensate of the appropriate size. Pairs are generated due to pumping noise, and are formed sequentially at the same point due to the inhomogeneous pumping spot profile. They are revealed in the time-integrated phase maps acquired using Michelson interferometry. Our results suggest that vortex-antivortex pairs can be created in a two-dimensional condensate without rotation or stirring. The observed correlated motion of a vortex and antivortex imply that vortex-antivortex pairs do not dissociate, which is consistent with the measured power law decay of the spatial correlation function. These two experiments uniquely describe the condensate phase fluctuations and provide stringent tests to theories of nonequilibrium condensation. They also highlight the exciton polariton condensate as a very well characterized system showing mesoscopic coherence and deepen our understanding of fundamental two-dimensional bosonic physics. Progress in this field is expected to lead towards long-sought applications such as quantum simulation or low-threshold laser sources.
Photoacoustic molecular imaging and its biomedical applications [electronic resource]
Keywords: Electrical Engineering.

Biomedical imaging has seen a tremendous shift over the past decades, moving to non-invasive and high spatial-resolution imaging, spanning multiple imaging modalities and applications. However, one common limitation of traditional medical imaging is its intrinsic inability to provide information on the molecular levels of various biomarkers. Molecular Imaging solves this limitation by introducing an exogenous imaging agent that upon administration to the subject, binds to or interacts with the molecular target(s) and produces an imaging signal. The agent can be designed to produce the imaging signal in the form of visible fluorescent light, gamma rays, ultrasound waves and other forms of energy. In this thesis, we summarize our work on Photoacoustic Molecular Imaging, a technique where short laser light pulses are converted into ultrasound waves by a nanoparticle that was molecularly targeted to a diseased site. We summarize the physical basis for the technique and its first demonstration -- highlighting angiogenesis markers in living subjects (Chapter 2). We then summarize the development of second generation photoacoustic imaging agents and demonstrate their utility in ultrahigh sensitivity molecular imaging of tumors (Chapter 3) as well as in multiplexing studies (Chapter 4). Next, we describe a novel application for Photoacoustic Imaging in visualizing the retina and the posterior eye segment with unprecedented depth of penetration, giving hope for early diagnosis of age-related macular degeneration and other retinal diseases (Chapter 5). We then describe a novel molecular imaging technology called Optical Coherence Contrast Imaging, and demonstrate it provides ultrahigh resolution and sensitivity images of gold nanoparticles in living mice eyes (Chapter 6). Finally, we conclude with various therapeutic and theranostic (therapy and diagnostic combined) concepts and highlight the synergy between them and the imaging methods presented in earlier chapters (Chapter 7).
Photon management in hydrogenated amorphous silicon solar cells using periodic nanostructures [electronic resource]
Keywords: Materials Science and Engineering

Solar technology is a leading candidate for clean energy production. Silicon is an excellent material for photovoltaic (PV) applications due to its low toxicity, abundance, long term stability, and well developed processing technologies. Crystalline Si solar cells currently dominate the photovoltaic market despite requiring more material and more energy-intensive manufacturing processes than their thin-film counterparts. Thin-film silicon, e.g. amorphous silicon (a-Si:H), provides the advantage of decreasing material costs over crystalline silicon. Because the material is amorphous, there are many defects, which results in a small minority carrier diffusion length. Thus, a thinner absorber is required. However, thinner absorber layers do not absorb light effectively, resulting in poor cell performance. If the active material could be made to absorb all of the light in a film with a thickness approximately equal to the minority carrier diffusion length, the open-circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF) of the device would be greater than those of a thicker cell. My research is comprised of three parts: (1) developing a nanostructure fabrication process, (2) designing device geometries for alternative light trapping strategies in both substrate and superstrate configurations, and (3) investigating the effects of nanostructures' morphologies on the optical and electrical properties of devices. In contrast to the use of randomized surface texturing to improve the coupling of light into the active material, we employed periodic nanostructures to couple incident light into guided modes that propagate in the plane of the absorber. This approach can significantly increase the optical path length inside a thin absorber layer. To achieve this goal, I first developed a nanostructure fabrication process by combining self-assembly and reactive ion etching. We then employ these as-made nanostructures in a-Si:H solar cells. The periodic-nanostructure devices show an enhanced absorption and photocurrent generation in comparison with planar cells. We used FTDT studies to confirm that the increased photocurrent was indeed caused by enhanced absorption. We also systematically studied the effects of morphological parameters on light-trapping efficiency and electrical characteristics of the device. With my optical and electrical findings, we have achieved efficiencies up to 9.7% for devices with substrate configurations and 11.2 % for devices with superstrate configurations.
Phylogenetic inference of the Tibeto-Burman languages or on the usefulness of lexicostatistics (and "megalo"-comparison) for the subgrouping of Tibeto-Burman [electronic resource]
Keywords: Anthropological Sciences

It has been argued that lexicostatistical methods cannot be fruitfully applied to the Tibeto-Burman (or the larger Sino-Tibetan) language family. This dissertation first develops a statistical method for determining linguistic cognates (or sound correspondences) between arbitrarily many languages. This method is then applied to a subset of the Sino-Tibetan languages to infer the correspondences and further develops a method for lexicostatistical analysis for subgrouping those languages. The output of these methods agrees very well with that determined by the traditional comparative method. Furthermore, this method yields both greater resolution of the subgroupings, and provides statistical inference of the confidence in the various groupings.
Physics and technology of tensile-strained germanium for high-performance silicon-compatible optoelectronics [electronic resource]
Keywords: Electrical Engineering

Modern high-bandwidth communications systems primarily use optical links to support data transmission across a range of length scales, from metro/long-haul for infrastructure backbones to shorter-range cables in data centers. As performance, cost, and energy-efficiency requirements become more demanding, optical links are expected to eventually supplant copper-based interconnects at the board-to-board, chip-to-chip, and on-chip levels as well. Most optoelectronic devices use III-V materials to achieve high performance. Though efficient, these materials are expensive, toxic, and incompatible with the standard high-volume silicon-based manufacturing used to build microprocessors. In order for the transition to optics to take place at the smaller length scales, a fully silicon-compatible photonics technology is needed to replace the III-Vs and allow us to leverage the practical advantages of silicon-based manufacturing. This dissertation presents a foundational set of new platform technologies that make major improvements to the current state of silicon-compatible optoelectronics research. In the first part, we present the development of a new method for manufacturing germanium--on--insulator substrates, an attractive materials platform for optical devices. In the second part of the dissertation, we introduce a new silicon-compatible platform technology that can be used to dramatically enhance the optical performance of germanium-based light emitters and detectors.
Pivot thinking and the differential sharing of information within new product development teams [electronic resource]
Keywords: Mechanical Engineering

Functionally diverse team members bring unique sets of cognitive styles to team interaction; it is less clear how these differences affect the exchange of critical, mutually required team information. This cognitive diversity in new product design (NPD) teams increases the likelihood that individual team members will perceive the team's task differently, leading to "cognitive representational gaps" between teammates' interpretations of both the task and potential solution. This research shows that cognitively diverse NPD teams develop representational gaps based on individual cognitive preferences between convergent and divergent information types and these cognitive preferences influence both task definition and solution. A second experiment shows that team leadership that bridges cognitive preferences, called "pivot thinking, " can overcome this limiting behavior. Understanding these general mechanisms deepens understanding of group information processing and conflict in cognitively diverse NPD teams. Implications for design education are discussed.
Plasmonic optical antennas for enhanced light detection and emission [electronic resource]
Keywords: Materials Science and Engineering

Antennas are used across a wide range of frequencies in the electromagnetic spectrum to concentrate wave energy into electronic circuits. The principles that govern the operation of conventional radio-frequency antennas can be extended to much higher frequencies and be applied to produce nano-metallic (i.e. plasmonic) antennas that act as "receivers" and "transmitters" for visible light. These traits make them excellent candidates for light trapping in solar cells, light concentration in sub-wavelength photodetectors, or even localized heating for cancer therapies. The unique optical properties of metals at visible frequencies make it difficult to apply traditional antenna design rules. Using full-field electromagnetic simulations and analytical antenna models, we developed new design rules for producing optical antennas with a desired set of optical properties. We then applied these design rules to create antennas that resonantly enhance absorption on thin silicon detectors as well as enhance emission of cathodoluminescence (CL). Through spatial and spectral mapping of both photocurrent and CL we clearly show the fundamental and higher-order resonant modes of these antennas. With CL we are also able to map the spatial distribution of these resonant modes with nanometer resolution. In addition to these specific demonstrated applications, the results of this work enable optical engineers to more easily design a myriad of plasmonic devices that employ optical antenna structures, including nanoscale photodetectors, light sources, sensors, and modulators.
The political economy of anti-poverty programs in Indonesia [electronic resource]
Keywords: Political Science.

This dissertation consists of three papers: 1) Targeting the Poor: Evidence from a Field Experiment in Indonesia; 2) Do Village Politics Matter?: Evidence from a Natural Experiment on the Distribution of a Cash Transfer in Indonesia; and 3) Assessing the Political Impacts of a Conditional Cash Transfer: Evidence from a Randomized Policy Experiment in Indonesia. The papers collectively explore several different aspects of the political economy of anti-poverty programs in Indonesia. In the first paper, a randomized experiment compares different methods of targeting an unconditional cash transfer to poor households. By testing the effectiveness of community-based methods versus government-centered methods on community satisfaction and accuracy in reaching the poor, the paper addresses several important questions relevant to the political economy of development and decentralization. The second paper analyzes the extent to which the distribution of Indonesia's unconditional cash transfer -- the world's largest cash transfer program to date -- is influenced by local political factors. Using a natural experiment, I explore how the quasi-random timing of village head elections affects the distribution of benefits to poor and non-poor households. Finally, my third paper analyzes the political effects of a randomized conditional cash transfer (CCT) pilot program to test its impacts on support for incumbent politicians, political participation, and several other indicators relevant to local democracy.
The political economy of publicly-provided goods [electronic resource]
Keywords: Business.

This dissertation consists of three chapters which explore various aspects of the political economy of publicly-provided goods. I shed light on why governments do or do not invest in goods of different types, and also how government versus private provision affects consumers. What follows are three empirical analyses testing the implications of competing theoretical models. My first chapter addresses the question, what drives governments with similar revenues to publicly provide very different amounts of goods for which private substitutes are available? Key examples are education and health care. I compare spending by Brazilian municipalities on pre-primary education--a good that is also provided privately--with spending on public infrastructure like parks and roads, which lacks private substitutes. I find that municipalities with higher median income and more inequality are less likely to allocate revenue to education or to expand pre-primary enrollment. They are more likely to allocate revenue to public infrastructure. This seems to occur for two reasons. In rich and unequal municipalities, fewer total people support public education spending (the collective choice channel), and also, any given poor person wanting public education has less influence over policymakers there (the political power channel). My second chapter addresses the question, can private sector participation (PSP) in the urban piped water sector improve child health? A fixed effects analysis suggests that the introduction of PSP decreases diarrhea among under-five children by between 2.2 and 2.6 percentage points, or 14-16%. An instrumental variables analysis that uses variation in the share of the world water market controlled by former colonizing countries suggests that the effects are twice as large. The difference between the OLS and the IV results can be explained by the fact that PSP is more likely when the water sector is distressed and causing health problems. Importantly, PSP appears to benefit the health of children from the poorest households the most. It also leads to higher rates of reliance on piped water as the primary water source, which is a likely channel explaining child health improvements. My third chapter, joint with John Hatfield, examines how competition between governments affects economic growth. We find that doubling the number of local governments in a metropolitan area increases the income growth rate over 1969-2006 by 18%, which implies an approximate 900 difference in 2006 income. Decomposing this effect, we find that 60% stems from inter-jurisdictional competition changing the composition of the workforce, while 40% comes from making existing workers more productive. The results support a formal model showing that competition for capital drives local governments to provide productive public goods at levels which maximize economic growth (Hatfield 2010).
Political origins of firm strategies [electronic resource]
Keywords: Political Science.

What explains the emergence of different kinds of capitalist systems across advanced industrialized democracies? In particular, why do highly coordinated employer associations form in some states and not others, and why do such organizations change over time? Because different kinds of contemporary employer coordination or varieties of capitalism are linked to long-term outcomes of unemployment, inequality, social policy generosity, and product innovation, it is important to understand their historical origins and development. I propose a new theory of the development of highly coordinated employer associations and their absence in advanced industrialized states. I argue that the key decisions firms faced involved addressing the redistributive threat posed by the political organization of workers, and the collective action problem of organizing themselves. The cross-national and temporal variation in firm strategies depends on two variables: levels of industrial heterogeneity and the political mobilization of workers. The former affects the incentives of firms to act collectively or individually; the latter shapes their incentives to pursue a collaborative or repressive approach. This parsimonious framework accounts for a much wider range of variation in firm strategies. To test the theory I use extensive qualitative and quantitative evidence from the development of employer associations in Germany and the United States. I also test the portability of the theory with cross-national evidence. I conclude with discussion of broader implications for comparative politics, in particular the importance of understanding collective action among firms and instruments of repression.
Political regimes and redistribution [electronic resource]
Keywords: Political Science

How do political institutions affect wealth redistribution initiatives and their efficacy? While influential current theory holds that redistribution should be both higher and more targeted at the poor under democracy, many newly democratic states have failed to implement redistributive policies that would benefit the majority of newly enfranchised voters. Using original data, primarily though not exclusively on land reform and bank and natural resource expropriations in Latin America, I find that redistribution has actually been greatest during periods of autocratic rule. I demonstrate empirically that where institutional constraints to rule are higher, as in democracy, large-scale redistribution is more difficult to implement. But why do some autocratic rulers choose to redistribute while others do not? I argue that when there is a split between a dictator's support coalition and elites out of government that can pose a threat to his rule, the dictator may choose to expropriate rival elites. Simultaneously redistributing much of the assets of those elites to the poor can gain the support of lower classes and reduce potentially destabilizing pressure from below. One important consequence is that dictators who have expropriated tend to survive longer in office than those that do not. Although redistribution is often more likely under autocracy, there are nonetheless cases of redistribution under democracy. When elites are politically weak during the democratic transition process, as during revolution, there is a long-run relationship between democracy and redistribution. So although democracy may sometimes be a credible commitment to redistribution, it is more often captured by elites and does not induce redistribution.