VictorJuiz/thesis huggingface dataset:
Locating lightning from slow-tail measurements recorded at a single station [electronic resource]
Keywords: Electrical Engineering

This dissertation analyzes the use of single station measurements of low-frequency electromagnetic waves to locate lightning discharges occurring around much of the world. Lightning detection is a useful tool for many commercial and scientific applications, including early forest fire detection, aircraft route planning, climate modeling and atmospheric studies. There exist lightning location methods that use satellite detectors and others that use networks of ground-based receivers. Using only a single ground-based station is a cost efficient method for lightning detection, though it can often be limited in range and accuracy. The electromagnetic waves generated by lightning discharges are known as radio atmospherics, or sferics. Sferics propagate for great distances away from the radiating discharge in the Earth-ionosphere waveguide and can be detected remotely by radio frequency receiving equipment such as those using magnetic loop antennas. To locate the causal lightning stroke from a recorded sferic, the methodology from this thesis combines an existing direction finding algorithm to compute the arrival azimuth along with a distance of propagation estimate. The new method to estimate the distance of propagation relies on modeling the propagation of the slow-tail, the portion of the sferic that falls in the extremely low frequency (ELF: 3-3000 Hz) range. Slow-tail propagation in the Earth-ionosphere waveguide is modeled for a range of propagation distances, and the recorded sferics are compared with the model output to estimate the actual distance of propagation. A solution is introduced for modeling slow-tails that propagate across the day-night terminator. The lightning location estimates from the new method are compared to the lightning recorded by the National Lightning Detection Network (NLDN), which records lightning in North America. Using the newly developed methodology, the direction of propagation estimates from recorded sferics are accurate to within 5° of the NLDN determined direction while the distance of propagation estimates are accurate to within 10% of the NLDN determined propagation distance. Accuracies in this range make this lightning detection method more appropriate for storm detection than individual lightning discharge detection. Some recorded sferics can not be used for this lightning detection method due to interference in the slow-tail signal by a subsequent lightning discharge, leaving approximately 70% of the recorded sferics viable for locating lightning. Attenuation to station location and the station's signal to noise ratio determine the maximum range specific to that station for lightning detection. Lightning location from two different stations are analyzed: Søndrestrøm station (Greenland) and Palmer station (Antarctica). A single station with low noise, such as Palmer, is shown to locate lightning over approximately half the world, increasing the coverage of lightning detection over other existing single station methods.
The logic of redistributive non-democracies [electronic resource]
Keywords: Political Science.

The "redistributive hypothesis" holds democracy to be the fundamental cause of redistribution from rich to poor. It is based on the following intuition. In contrast to autocracy, under which political power is concentrated among economic elites, democracy empowers all citizens equally by creating a mechanism through which the majority can vote for egalitarian economic policies. This argument traces its intellectual roots at least to Tocqueville, has been formalized through political economy models (Romer 1975; Roberts 1977; Meltzer and Richard 1981) and recently has been expanded to underpin an important set of theories about the economic origins of democracy and dictatorship (Boix 2001, 2003; Acemoglu and Robinson 2000, 2001, 2006). I argue that the prevailing view underestimates the ability of non-democratic regimes to redistribute to the poor and explore alternative mechanisms for redistribution in non-democratic contexts. I use original datasets from archival sources for in-depth case studies, statistical analyses at the cross-national level, and formal models to make my case. My findings offer new insights on the causes of economic redistribution, advance the systematic study of autocracy and contribute to an emerging literature on the autocratic roots of social policy in developing nations.
Long baseline atom interferometry [electronic resource]
Keywords: Physics

Due to its impressive sensitivity, long baseline atom interferometry is an exciting tool for tests of fundamental physics. We are currently constructing a 10-meter scale apparatus to test the Weak Equivalence Principle (WEP) using co-located Rb85 and Rb87 atom interferometers. This apparatus aims to improve the current limit on WEP violation 100-fold, which illustrates the power of this technique. This scientific goal sets stringent requirements on the kinematic preparation of the atomic test masses, the interferometer laser wavefront and stability, as well as the electromagnetic and gravitational field homogeneity of the interferometer region. The efforts to control these sources of systematic error are discussed. Additionally, applications of long baseline atom interferometry to space-based sensors for geodesy and gravitational wave detection are presented.
Low-dimensional neural features reflect central features of muscle activation [electronic resource]
Keywords: Electrical Engineering

Any time we move, our brains solve the difficult problem of translating our motor intentions to muscle commands. Understanding how this computation takes place, and in particular, what role the motor cortex plays in movement generation, has been a central issue in systems neuroscience that remains unresolved. In this thesis, we took an unconventional approach to the analysis of cortical neural activity and its relationship to executed movements. We used dimensionality reduction to extract the salient patterns of neural population activity, and related those to the muscle activity patterns generated during arm reaches to a grid of targets. We found that salient neural activity patterns appeared to tightly reflect muscle activity patterns with a biologically-plausible lag. We also applied our analyses to movements that were planned before being executed, and found that a muscle-framework view of the cortical activity was consistent with previously-described predictions of movement kinematics based on the state of the cortical population activity. Overall, our results elucidate remarkable simplicity of the motor-cortical activity at the population level, despite the complexity and heterogeneity of individual cell's activities.
Low-noise current readout for in vivo fluorescence detection [electronic resource]
Keywords: Electrical Engineering

Post-treatment follow-up protocols for cancer patients often call for periodic hospital visits for magnetic resonance (MR), positron electron tomography (PET) or computer tomography (CT) scanning. Continuous monitoring through an implantable device would provide doctors and patients with important information between visits. With continuous monitoring, disease progression can be tracked in real-time, therapeutic regimens can be evaluated and adjusted as needed, and abnormal activity can be detected and acted on in a timely fashion. Optical molecular imaging based on fluorescence detection can provide a quantitative measure of many cellular and molecular processes of interest. Fluorescence detection is emerging as a powerful preclinical research tool, and is an attractive candidate for continuous in vivo cancer monitoring. However, in vivo fluorescence imaging is presently possible only with bulky instrumentation that does not permit monitoring of freely-moving subjects. In order to make a fluorescence detection system implantable, and thus portable, a vertical-cavity surface-emitting laser (VCSEL), a detector and a readout circuit for measuring photocurrents need to be integrated in one package. In this work, the design, implementation and testing of a current measuring circuit for fluorescence imaging is presented. The readout architecture is based on current integration using a capacitive transimpedance amplifier (CTIA), followed by analog-to-digital (A/D) conversion based on sigma-delta modulation. Unlike conventional approaches of measuring the voltage signal at the end of the current integration period, the [Sigma][Delta] modulator oversamples the output of the CTIA directly while current integration takes place. Thus, the input to the [Sigma][Delta] modulator is a voltage ramp, and the digital filter at the output of the [Sigma][Delta] modulator implements a line-fitting operation. This technique offers an improvement in the estimation of the CTIA output slope, and removes the limitation introduced in existing architectures by the sample-and-hold (S/H) stage preceding the A/D converter. The tradeoffs among noise power, integration time and oversampling ratio are examined in detail, and a method for extending the dynamic range (DR) of the system by a factor of five, even when voltage saturation occurs, is described. As an experimental demonstration, a prototype readout circuit was integrated in a 0.18-[Mu]m CMOS technology and then interfaced to a fluorescence detector. In vitro fluorescence measurements were performed, and an implantable solution made possible with miniaturized packaging of the two chips was demonstrated. This miniature package was implanted in live animals, which enabled in vivo fluorescence detection in freely-moving mice.
Low-powder and high-rate wireless transmission systems for neural implants [electronic resource]
Keywords: Electrical Engineering

Neural recording systems are fundamental to the advancement of brain-machine interfaces that can significantly improve the quality of lives of patients with neurological diseases, such as spinal cord injuries or quadriplegia. This thesis presents two newly developed wireless neural recording systems that are able to provide a high degree of usability and neural decoding accuracy. They are capable of simultaneously transmitting 32 to 96 channels of neural signals detected by an implanted neural sensor array. This work was carried out within the framework of the Hermes project and its technical design challenges will be addressed. The Hermes project is aimed at primarily developing hardware and software tools that extract neural information from the motor cortex. Those tools can enable practical prosthetic devices used to significantly ameliorate the life of patients with neurological impairments that directly affect motor functions. The first developed system, HermesD, is a 32-channel broadband transmission system using an FSK modulated carrier at 24 Mbit/s in the 3.7-4.1 GHz band. The link range extends beyond 20 m and the total power consumption is 142 mW. The HermesD system uses only COTS components and can be easily replicated. HermesD is fully operational and is currently used to transmit broadband neural data for neuroscience research in the Neural Prosthetic Systems Laboratory (NPSL) at Stanford University. HermesD is also planned as the base platform for future human trials to take place in the same laboratory. The second system that represents the next Hermes generation, HermesE, uses a novel UWB transmitter architecture implemented in a custom IC in the 65-nm CMOS technology. The transmitted signal bandwidth covers the 3.6 to 7.5 GHz frequency range. The time domain waveform is digitally programmable, allowing a very flexible control of the output spectrum to avoid interference and to allow multi-band operation. The UWB transmitter chip is part of a 96-channel broadband recording system delivering 40 Mbit/s. Its power consumption is 230 uW for a communication range of about 5 m. The antenna subsystems for these wireless recording devices presented a design challenge given the requirements for small size, large bandwidth and high efficiency. While HermesD has an operating FBW of 10%, HermesE is much more demanding in this respect, with 70% FBW, requiring unconventional antenna structures. The design techniques and performance of the antennas required to meet the specifications of both systems are also addressed in this work.
Macromolecular motion in vivo [electronic resource] : anomalous diffusion through an "active" viscoelastic medium
Keywords: Biochemistry

The cellular interior is crowded with macromolecules that form highly organized but dynamic structures. While these properties of the cytoplasm have become well known, their physical consequences on intracellular processes such as transport and gene expression are still not well understood. The goal of this dissertation is to begin to elucidate these physical consequences and to develop a new model for macromolecular motion in vivo. Tracking of fluorescently labeled chromosomal loci in live bacterial cells reveals a robust subdiffusive scaling of the mean square displacement (MSD). To identify the source of anomalous behavior, we developed analytical theory and Brownian dynamics simulations of polymers under various physical environments. Specifically, we examined the consequences of confinement, self-interaction, viscoelasticity and random waiting on monomer motion. We found that neither confinement nor self-interaction alter the fundamental Rouse mode relaxations of a polymer. However, viscoelasticity, modeled by fractional Langevin motion (fLm), and random waiting, modeled with a continuous time random walk (CTRW), led to significant and distinct deviations from the classic polymer dynamics model. We propose that the subdiffusive motion of chromosomal loci observed in vivo arises from relaxation of the Rouse modes of the DNA polymer within the viscoelastic environment of the cytoplasm. The time-averaged and ensemble-averaged MSD of chromosomal loci exhibit ergodicity, and the velocity autocorrelation function is negative at short time lags. These observations are most consistent with fLm and rule out a CTRW model as an explanation for anomalous motion in vivo. In contrast to the subdiffusive scaling exponent, the apparent diffusion coefficient is variable across species and sensitive to biological perturbations. When ATP synthesis is inhibited in E. coli, the apparent diffusion coefficient decreases 2-fold while the scaling exponent remains constant. This observation suggests that metabolic activity contributes to the magnitude of locus motion, but does not affect the subdiffusive mechanism (or the viscoelastic properties of the cytoplasm). Furthermore, the temperature-dependence of locus motion is steeper in untreated cells than in ATP-depleted cells. These results suggest that untreated cells have an additional source of molecular agitation that increases with temperature. Such ATP-dependent fluctuations are likely mechanical, as the heat dissipated from glycolysis and oxidative phosphorylation is insufficient to account for the difference in the apparent diffusion coefficient between untreated and ATP-depleted cells. We are currently investigating the dynamic contributions of several molecular candidates. Our data indicate that ATP-dependent enzymatic activity, in addition to thermal fluctuations, may contribute to the molecular agitation driving (sub)diffusion in the cell.
Magnetic resonance imaging of human articular cartilage of the knee in vivo [electronic resource]
Keywords: Electrical Engineering

Osteoarthritis (OA) is a degenerative joint disease that affects over 80% of the population of the U.S. by age 65. However, there is currently no disease-modifying treatment for OA. In order to develop and evaluate potential treatments, it is necessary to assess cartilage health over the course of the disease. Here, an MRI method is presented to obtain sodium images of tissue that pushes the current state of the art of sodium MRI and can provide new information about cartilage. The method presented here enables sodium imaging at high resolution and with lower noise levels than previously reported. This technique uses custom-made radio-frequency (RF) coils and a 3D-cones k-space trajectory and is well suited to imaging at high field strengths like 3 T and 7 T. A second novel method is presented for generating high-resolution, 3D T2 and ADC maps of the human knee in vivo. The maps are derived from diagnostic-quality morphological MR images. This method is based on a new variation of the 3D double echo steady-state (DESS) sequence and solves many of the current challenges of traditional imaging techniques. Finally, a third method is presented allowing independent excitation of two or more volumes with a short RF pulse for MRI. This method enables different volumes to be excited with different RF pulse parameters, including flip angle, slice profile or thickness, phase modulation, etc., increasing the flexibility of the excitation. In summary, the techniques presented here generate measurements of sodium, T2, and ADC in cartilage, all biomarkers of interest for this tissue. These measurements are either less noisy or more efficiently obtained than with previous methods. The methods presented in this dissertation also improve the efficiency of diagnostic image acquisition for the knee.
Magnetic resonance imaging of magnetic fields from radiofrequency ablation at 64 megahertz [electronic resource]
Keywords: Electrical Engineering

Radiofrequency ablation (RFA) is an effective minimally invasive treatment for tumors, using RF currents to deposit energy and create local heating. MRI has been proposed to monitor RFA due to its ability to acquire images of heating. If the ablation is performed at 64 MHz (the Larmor frequency of a 1.5 Tesla MRI system) instead of the typical 460-500 kHz, the magnetic fields associated with the RF currents can be used as the MR excitation. RF field mapping techniques can then be used to image those magnetic fields, providing information about the underlying current density. The current distribution will change during the course of ablation due to changes in the complex conductivity of the treated tissue. Knowledge of the magnetic fields could be used to steer currents into a more efficient ablation pattern as well as evaluate the process of the ablation by monitoring changes in the electrical properties of the tissue. In this thesis, I show results from performing RFA at 64 MHz and discuss improvements to MRI RF field mapping techniques for imaging the fields from the ablation currents. I have optimized the Actual Flip-Angle (AFI) RF field mapping sequence to achieve the best SNR of the field maps within a given scan time by considering noise propagation, errors from T1 relaxation and incomplete spoiling of transverse magnetization. I have then designed an adiabatic partial passage pulse that, when used in the AFI sequence, captures a much larger dynamic range, up to 16:1. Finally, I have performed RFA at 64 MHz and imaged the RF magnetic fields.
Making belief [electronic resource] : religion and the state in Korea, 1392-1960
Keywords: Religious Studies

This dissertation investigates the relationship between religion and the state in the formation of a new belief about modern Korea. It examines how religion has shaped the idea of nation, an ostensibly novel way of imagining the collective. I argue that two types of religion have been central to that imagination: the state religion of the Chosŏn and the imported notion of religion as a category for legitimate belief. In the first chapter, I consider the way in which the Chosŏn used religion to present itself as a divinely mandated polity located outside the Ming's sphere of influence. By utilizing official chronicles, astrological literature, ceremonial manuals, and private writings of the elites, I demonstrate that official religion under the Choson dynasty served to instill a sense of collective belonging before the advent of nationalism. In the second chapter, I examine the creation of a new national identity by Koreans who denied that Japan and State Shinto were the only roads into the light of civilization and modern nationhood. In the third chapter I focus on the definition of superstition by the colonial state and how colonial Korean identity became grounded in that definition in the run up to the official campaign to promote State Shinto. In the final chapter I discuss how Korean Buddhism became the vehicle for claiming a new national identity by the nascent Republic of Korea, which inherited both the religious policies of the colonial state and ideas about religion and nation harbored by Koreans thinkers of the past.
Manipulating light with nanostructured metals [electronic resource]
Keywords: Electrical Engineering

Plasmonics has emerged as a technology that enables the creation of a wide range of miniaturized photonic devices. Nanostructured metals provide numerous new opportunities for manipulating light at a deep-subwavelength scale. This dissertation covers our work on exploiting nanostructured metals to create new and improved optical functionality. We provided the first experimental demonstration of far-field lensing using an aperiodic plasmonic slit array. This approach offers large design freedom, since these structures derive their behavior from local geometry. We illustrated this flexibility through simulations of efficient and compact planar nanoslit lenses that compensate for various angles of incidence. We further demonstrated the ability to perform phase front design in two dimensions by varying the local geometry in metallic nanoscale pillar arrays. We also considered aperiodic arrays of coupled metallic waveguides and numerically demonstrated that, for an incident plane wave, a focus of as small as one-hundredth of a wavelength can be achieved for a focal distance that is much longer than the wavelength. Moreover, the focusing behavior can be controlled by changing either the incident wavelength or the angle of incidence. We showed that this behavior can be understood using Hamiltonian optics ray tracing. Lastly, we developed the coupled-mode theory for resonant apertures. Such apertures are of fundamental interest, and form the basic building blocks for many applications in subwavelength optics and optoelectronics. We showed that the maximum transmission and absorption cross sections for subwavelength resonant apertures are only related to the wavelength of the incident light and the directivity of the aperture's radiation pattern and explained the spectral behavior of structures that support multiple resonances.
Meaningful engagement in educational activity and purposes for learning [electronic resource]
Keywords: Education.

The American political culture that encourages competition on standardized tests, epitomized by the policy of Race to the Top, oversimplifies students' motivation for learning. This dissertation argues that educational research on student learning and activity engagement should consider motives beyond the pursuit of good grades in the classroom, prestigious college credentials, and going to school because it is what students are supposed to do. In particular, the studies highlight the moral inspirations and cultural habits behind students' engagement in life activities, and how inspiration and habits help to direct learning in life. A case study of an ordinary high school senior articulates a common motive to enroll in college to achieve success in life. Comparative case studies contrast emotional experiences with social responsibilities in order to articulate purposes for learning beyond standardized achievement. Findings suggest that volunteer community service, engagements with family, involvement in religious activities, and working for pay could provide inspiration for students to engage in learning in life.