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Gigahertz Bandwidth and Nanosecond Timescales: New Frontiers in Radio Astronomy Through Peak Performance Signal Processing
Get PDFAbstract In the past decade, there has been a revolution in radio-astronomy signal processing. High bandwidth receivers coupled with fast ADCs have enabled the collection of tremendous instantaneous bandwidth, but streaming computational resources are struggling to catch up and serve these new capabilities. As a consequence, there is a need for novel signal processing algorithms capable of maximizing these resources. This thesis responds to the demand by presenting FPGA implementations of a Polyphase Filter Bank which are an order of magnitude more efficient than previous algorithms while exhibiting similar noise performance. These algorithms are showcased together alongside a broadband RF front-end in Starburst: a 5 GHz instantaneous bandwidth two-element interferometer, the first broadband digital sideband separating astronomical interferometer. Starburst technology has been applied to three instruments to date.
Abstract Wielding tremendous computational power and precisely calibrated hardware, low frequency radio telescope arrays have potential greatly exceeding their current applications. This thesis presents new modes for low frequency radio-telescopes, dramatically extending their original capabilities. A microsecond-scale time/frequency mode empowered the Owens Valley Long Wavelength Array to inspect not just the radio sky by enabling the testing of novel imaging techniques and detecting overhead beacon satellites, but also the terrestrial neighborhood, allowing for the characterization and mitigation of nearby sources of radio frequency interference (RFI). This characterization led to insights prompting a nanosecond-scale observing mode to be developed, opening new avenues in high energy astrophysics, specifically related to the radio frequency detection of ultra-high energy cosmic rays and neutrinos.
Abstract Measurement of the flux spectrum, composition, and origin of the highest energy cosmic ray events is a lofty goal in high energy astrophysics. One of the most powerful new windows has been the detection of associated extensive air showers at radio frequencies. However, all current ground-based systems must trigger off an expensive and insensitive external source such as particle detectors - making detection of the rare, high energy events uneconomical. Attempts to make a direct detection in radio-only data have been unsuccessful despite numerous efforts. The problem is even more severe in the case of radio detection of ultra-high energy neutrino events, which cannot rely on in-situ particle detectors as a triggering mechanism. This thesis combines the aforementioned nanosecond-scale observing mode with real-time, on-FPGA RFI mitigation and sophisticated offline post-processing. The resulting system has produced the first successful ground based detection of cosmic rays using only radio instruments. Design and measurements of cosmic ray detections are discussed, as well as recommendations for future cosmic ray experiments. The presented future designs allow for another order of magnitude improvement in both sensitivity and output data-rate, paving the way for the economical ground-based detection of the highest energy neutrinos.</p
A Dark Matter Search Using the Final SuperCDMS Soudan Dataset and the Development of a Large-Format, Highly-Multiplexed, Athermal-Phonon-Mediated Particle Detector
Get PDFOver the past eighty years, numerous complementary observations of our universe have indicated that our current description of physics is far from complete. The "ordinary matter", such as electrons, protons, photons and neutrons, that constitutes the bulk of all human physical experiences is actually only a minority (about 16%) of the total mass of the universe. The remaining 84% is very poorly understood, but has profound effects on the dynamics and evolution of our universe. Because it does not interact with light, and is not observable in telescopes on earth, this extra mass is usually referred to as "dark matter". Although the dark matter is poorly understood, Weakly Interacting Massive Particles (WIMPs) are a well-motivated candidate that can be directly detected via a non-gravitational interaction with normal matter, potentially allowing for direct terrestrial detection and characterization of this dark matter. This dissertation is focused on this direct WIMP detection and will be broken into two main parts.
The first part focuses on the blinded analysis of roughly three years of data collected from March 2012 to November 2015 by the SuperCDMS Soudan experiment. SuperCDMS Soudan consists of an array of 15, 0.6-kg, cryogenic, Ge iZIP particle detectors situated in a decommissioned iron mine in remote northern Minnesota. This analysis is optimized to be sensitive to theoretical WIMP masses above 10 GeV/c2. This result set the strongest limits for WIMP--germanium-nucleus interactions for WIMP masses greater than 12 Gev/c2.
The second part focuses on the development new kind of particle detector in the style of a SuperCDMS iZIP, designed to simplify fabrication and readout, improve phonon-based position reconstruction, and help to scale to larger target arrays. These detectors replace the TES-based phonon sensors of the iZIP with Microwave Kinetic Inductance Detectors (MKIDs).</p
Tensile Failure and Fracture of Three-Dimensional Brittle Nanolattices
Get PDFThe emergence of a new class of cellular solids, i.e., nano- and micro-architected materials, poses the question of whether they can be characterized as a continuum solid. Extensive research has shown that these ultralight and strong structural metamaterials are particularly attractive for mechanically-demanding applications; yet their susceptibility to flaws, fracture behavior, and discrete-continuum duality remains relatively unexplored. In the course of this work, we report the fabrication and tensile-to-failure response of three-dimensional ceramic nanolattices, comprised of 50nm-thick alumina tubes that are arranged into periodic 5um-wide octet-truss unit cells, with and without pre-fabricated through-thickness center notches oriented at different angles to the loading direction. In-situ uniaxial tensile experiments revealed that for all notch orientations, failure always initiated at the notch root, as would be in a monolithic material, with the tube walls at nodal junctions fracturing first, followed by instantaneous crack propagation through the discrete lattice architecture along nodal planes orthogonal to the loading direction. Measured tensile strength of 27.4 MPa was highest for the unnotched samples and decreased systematically with the increase of notch orientation to its minimum of 7.2 MPa in the orthogonally-notched samples. We found the specific tensile strength of hollow-tube octet alumina nanolattices to be 4 times higher than what has been reported for architected and bulk materials at similar low densities. Three-dimensional finite element simulations closely reproduce the observed failure mechanism and trends in failure strength. A direct comparison is made between the experimental measurements, finite element simulations, and predictions of linear elastic fracture mechanics for a self-similar monolithic tensile samples made out of an ideally-brittle solid. Results are in good agreement with the scaling of failure strengths from classical mode I fracture criteria and suggest that trajectory of crack propagation can be adequately explained by considering the connectivity of the lattice architecture. These findings imply that the continuum nature of nano-architected materials offers predictability of failure stresses, which helps enable the development of advanced materials through informed architectural design
iLost: A Tale for our Time
No full text[Introduction] "There are seven billion transistors on a single computer chip - as many transistors as there are people on earth. And unlike people, every one of them works." I laughed at my professor's remark. He was genuinely a great lecturer, and watching him perform and articulate about the little miracle in his hand as he waved his phone around didn't feel like a lecture. After class ended, I filed out with the rest of the class and marched up the stairs, from the basement lecture hall, and back to the realm where the sun shone. The sun, and cell signal. Pausing briefly, I milled around by the door and flipped through my texts. Around me, two other students did the same
A System for Cancellation of Two-Level System Noise in Kinetic Inductance Devices
Get PDFKinetic Inductance Detectors (KIDs) are showing promise in a variety of low-light applications photometry applications, notably in observing B-mode polarization of the cosmic microwave background. These devices are read out by modulating the inductance of an LC resonator through light, and observing the shift in resonant frequency. Among several contributing sources of noise is Two-Level System noise (TLS noise) that causes low-loss drift in the frequency. Under certain assumptions of the source of the noise, we propose a new dual-resonator design that would allow the TLS noise to be observed independently of the signal, and thus cancelled out. This design comes at a roughly factor-of-2 cost in component size and sensitivity. We designed a manufactured a niobium-on-silicon chip, but encountered issues in that we were unable to observe enough TLS noise to conclusively say that the cancellation works
Improvement of Integral Membrane Protein Expression via Optimization of Simulated Integration Efficiency
Get PDFIntegral membrane protein characterization is limited by the low levels of protein obtainable from heterologous overexpression in hosts such as Escherichia coli. Differences in the efficiencies of subdomains of the co-translational integration processes of membrane proteins into the membrane could explain the observed variation in the experimental expression of closely related homologs in E. coli. We have developed a method to predict and increase the expression of individual membrane proteins by optimizing the efficiency of their translocon-mediated integration into the membrane. The integration efficiency of each component of a membrane protein is calculated using a coarse-grained co-translational simulated integration model. The results of model simulations, experimental expression levels quantified by integral membrane protein-GFP fusion fluorescence, and a novel antibiotic survival test that reports on misintegration in vivo are applied to test the relationship between the integration efficiency of specific domains and experimental expression. Changes in simulated integration efficiencies due to sequence modifications agree with the effects on experimental expression in vivo. In the case of the TatC protein family, misintegration of the C-tail is found to be a major contributor to expression failure in E. coli. Beneficial sequence modifications that improve both simulated integration efficiency and experimental expression levels can be identified using the model. Preliminary evidence shows that simulated integration efficiency could potentially predict the effects of mutations on Haemophilus influenzae GlpG experimental expression in E. coli. The process described herein allows for the rational overexpression of integral membrane proteins through the identification and mitigation of inefficiencies in the underlying co-translational membrane integration process.</p
Unveiling the Physical Conditions in Star-Forming Galaxies at the Peak of Galaxy Assembly
Get PDFGalaxies at the peak of cosmic star formation (z~2-3) exhibit significantly higher star formation rates and gas fractions at fixed stellar mass than nearby galaxies. These z~2-3 galaxies are also distinct in terms of their nebular spectra, reflecting important differences not only in the physical conditions of their interstellar medium (e.g., electron density and gas-phase metallicity), but also in the details of their massive stellar populations. Jointly observing galaxies' HII regions, at rest-UV and rest-optical wavelengths, and massive stars, at rest-UV wavelengths, is central to constructing a framework for understanding the differences between z~2-3 and z~0 star-forming galaxies and also vital for self-consistently explaining the trends observed in the high-z population.
This thesis presents the main results from the near-infrared (NIR) component of the Keck Baryonic Structure Survey (KBSS), a targeted spectroscopic survey of z~2-3 galaxies that uniquely combines observations in the rest-UV (1000-2000Å) and rest-optical (3500-7500Å) bandpasses. The NIR spectroscopic campaign conducted using Keck/MOSFIRE, described in Chapter 2, includes observations over 1200 high-z galaxies and represents one of the largest samples of high-quality rest-optical spectra of z~2-3 galaxies ever assembled. These measurements offer new insights regarding the physical conditions in galaxies forming during one of the most active periods in the universe's history.
Chapter 3 describes the rest-optical spectra of ~380 KBSS galaxies at z~2-2.7 and shows that the primary difference between HII regions in z~2.3 galaxies and those at z~0 is an enhancement in the degree of nebular excitation. KBSS galaxies are also 10 times more massive than z~0 galaxies with similar ionizing spectra and have higher gas-phase N and O abundances at fixed excitation. These results indicate the presence of harder ionizing radiation fields at fixed gas-phase enrichment relative to typical z~0 galaxies, consistent with Fe-poor stellar population models that include massive binaries.
Chapter 4 builds on this analysis to develop a new technique for determining the physical conditions in individual high-z galaxies -- independent of diagnostics tuned to local calibration samples. This method produces self-consistent measurements of the chemical enrichment and excitation conditions in ~150 galaxies at z~2-2.7.
Together, these results provide compelling evidence that the distinct chemical abundance patterns observed in z~2-3 star-forming galaxies result from systematic differences in their star formation histories relative to galaxies with similar stellar masses today. The thesis concludes by considering the importance of accounting for differences in galaxies' past star formation when interpreting spectroscopic observations and briefly discusses opportunities for extending the framework for analyzing high-z galaxies presented here to future studies of star-forming galaxies throughout cosmic time.</p
Data Driven Computing
Get PDFData Driven Computing is a new field of computational analysis which uses provided data to directly produce predictive outcomes. This thesis first establishes definitions of Data-Driven solvers and working examples of static mechanics problems to demonstrate efficacy. Significant extensions are then explored to both accommodate noisy data sets and apply the deveoloped methods to dynamic problems within mechanics. Possible method improvements discuss incorporation of data quality metrics and adaptive data sampling, while new applications focus on multi-scale analysis and the need for public databases to support constitutive data collaboration
Why Was The Feminine Mystique Such a Phenomenon?: A Clarification
No full text[Introduction] Since The Feminine Mystique was published in 1963, it has become so influential that it has gathered a mystique of its own. The controversial book has drawn both high praise for "[pulling] the trigger on history" and strong criticism from conservative groups for threatening family values, as well as from scholars for being riddled with methodological errors and for focusing only on white, middle-class women. Confusion abounds in the general public, too. In Stephanie Coontz’s A Strange Stirring, which is about the impact of Friedan’s book, Coontz reveals that many of the women that she interviewed in conducting research for her book believed that they had read it when in fact they had not, and, furthermore, that they often had completely erroneous ideas about its contents (Coontz xvi).</p
Measuring R(D(*)) for B → ‾D(*)τν_τ using Semileptonic Tags and Tau Decays to Hadrons
Get PDFWe perform a measurement of R(D(*)) for B → D(*)τντ using semileptonic tagging and τ decays to hadrons on the 429 fb-1 of data that BABAR collected at the Υ(4S) resonance. This is the first measurement of R(D(*)) using the specied reconstruction channels. Candidate selection was performed with supervised learning, where the training labels were obtained by solving an instance of subgraph isomorphism. The signal extraction was performed by solving an optimization problem whose objective function required the evaluation of kernel density estimates that were accelerated by a branch-and-bound algorithm as well as with a GPU. The training data for the density estimates were themselves the output of two classier scores. We present a 68% and 95% confidence regions of R(D(*)), which do not show enough evidence to reject the standard model prediction.</p