3,657 research outputs found

    Empire and Liberty: The Civil War and the West

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    The Inseparable Histories of the Civil War and the American West Virginia Scharff has put together in Empire and Liberty a book that joins together two epic stories in American History; its westward expansion and the Civil War. The writers within this edited work, remind us, that ma...

    Theory and Design of a Highly Compressed Dropped-Channel Polarimetric Synthetic Aperture Radar

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    Compressed sensing (CS) is a recent mathematical technique that leverages the sparsity in certain sets of data to solve an underdetermined system and recover a full set of data from a sub-Nyquist set of measurements of the data. Given the size and sparsity of the data, radar has been a natural choice to apply compressed sensing to, typically in the fast-time and slow-time domains. Polarimetric synthetic aperture radar (PolSAR) generates a particularly large amount of data for a given scene; however, the data tends to be sparse. Recently a technique was developed to recover a dropped PolSAR channel by leveraging antenna crosstalk information and using compressed sensing. In this dissertation, we build upon the initial concept of the dropped-channel PolSAR CS in three ways. First, we determine a metric which relates the measurement matrix to the l2 recovery error. The new metric is necessary given the deterministic nature of the measurement matrix. We then determine a range of antenna crosstalk required to recover a dropped PolSAR channel. Second, we propose a new antenna design that incorporates the relatively high levels of crosstalk required by a dropped-channel PolSAR system. Finally, we integrate fast- and slow-time compression schemes into the dropped-channel model in order to leverage sparsity in additional PolSAR domains and overall increase the compression ratio. The completion of these research tasks has allowed a more accurate description of a PolSAR system that compresses in fast-time, slow-time, and polarization; termed herein as highly compressed PolSAR. The description of a highly compressed PolSAR system is a big step towards the development of prototype hardware in the future

    Theater Of A Separate War: The Civil War West Of The Mississippi River, 1861--1865

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    Neglected Campaigns Recovered For a different perspective on Theater of a Separate War read Robert Welch\u27s review here. Thomas Cutrer, professor emeritus of history at Arizona State ...

    DEEP LEARNING METHODS FOR MULTIBAND EXPLOSIVE HAZARD DETECTION USING L-BAND AND X-BAND FORWARD-LOOKING GROUND-PENETRATING RADAR

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    Explosive hazards are one of the most deadly threats in modern conflicts. The U.S. Army is interested in a reliable way to detect these hazards at range. A promising way of accomplishing this task is using a forward-looking ground-penetrating radar (FLGPR) system. Recently, the Army has been testing a system that utilizes both L-band and X-band radar arrays on a vehicle mounted platform. Using data from this system, we sought to improve the performance of a constant false-alarm-rate (CFAR) prescreener through the use of three deep learning architechtures; deep belief networks (DBNs), stacked denoising autoencoders (SDAEs), and convolutional neural networks (CNNs). We also compare these deep learning classifiers with two more conventional shallow learning classifiers; single kernel support vector machines (SKSVMs) and multiple kernel learning group lasso (MKLGL). By training the deep learners on a combination of image features and comparing the test results to the conventional shallow learners, we were able to significantly increase the probability of detection over both the CFAR prescreener and the shallow learners while maintaining a nominal number of false alarms per square meter. Our research shows that deep learners are a good candidate for improving detection rates in FLGPR systems

    Exhaustion of Nucleation in a Closed System

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    We determine the distribution of cluster sizes that emerges from an initial phase of homogeneous aggregation with conserved total particle density. The physical ingredients behind the predictions are essentially classical: Super-critical nuclei are created at the Zeldovich rate, and before the depletion of monomers is significant, the characteristic cluster size is so large that the clusters undergo diffusion limited growth. Mathematically, the distribution of cluster sizes satisfies an advection PDE in "size-space". During this creation phase, clusters are nucleated and then grow to a size much larger than the critical size, so nucleation of super-critical clusters at the Zeldovich rate is represented by an effective boundary condition at zero size. The advection PDE subject to the effective boundary condition constitutes a "creation signaling problem" for the evolving distribution of cluster sizes during the creation era. Dominant balance arguments applied to the advection signaling problem show that the characteristic time and cluster size of the creation era are exponentially large in the initial free-energy barrier against nucleation, G_*. Specifically, the characteristic time is proportional to exp(2 G_*/ 5 k_B T) and the characteristic number of monomers in a cluster is proportional to exp(3G_*/5 k_B T). The exponentially large characteristic time and cluster size give a-posteriori validation of the mathematical signaling problem. In a short note, Marchenko obtained these exponentials and the numerical pre-factors, 2/5 and 3/5. Our work adds the actual solution of the kinetic model implied by these scalings, and the basis for connection to subsequent stages of the aggregation process after the creation era.Comment: Greatly shortened paper. Section on growth model removed. Added a section analyzing the error in the solution of the integral equation. Added reference

    Overcrowding and Frequent Moves Undermine Children's Health

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    Children need stability in their lives -- whether it is in their daily routines, the adults that care for them, or their housing. Recent economic conditions are putting families at risk, not just of outright homelessness but of being housing insecure (frequent moves, overcrowding, or doubling up with another family for economic reasons)

    Hypervelocity impact survivability experiments for carbonaceous impactors

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    We performed a series of hypervelocity impact experiments using carbon-bearing impactors (diamond, graphite, fullerenes, phthalic acid crystals, and Murchison meteorite) into Al plate at velocities between 4.2 and 6.1 km/s. These tests were made to do the following: (1) determine the survivability of carbon forms and organize molecules in low hypervelocity impact; (2) characterize carbonaceous impactor residues; and (3) determine whether or not fullerenes could form from carbonaceous impactors, under our experimental conditions, or survive as impactors. An analytical protocol of field emission SEM imagery, SEM-EDX, laser Raman spectroscopy, single and 2-stage laser mass spectrometry, and laser induced fluorescence (LIF) found the following: (1) diamonds did not survive impact at 4.8 km/s, but were transformed into various forms of disordered graphite; (2) intact, well-ordered graphite impactors did survive impact at 5.9 km/sec, but were only found in the crater bottom centers; the degree of impact-induced disorder in the graphite increases outward (walls, rims, ejecta); (3) phthalic acid crystals were destroyed on impact (at 4.2 km/s, although a large proportion of phthalic acid molecules did survive impact); (4) fullerenes did not form as products of carbonaceous impactors (5.9 - 6.1 km/s, fullerene impactor molecules mostly survived impact at 5.9 km/s; and (5) two Murchison meteorite samples (launched at 4.8 and 5.9 km/s) show preservation of some higher mass polycyclic aromatic hydrocarbons (PAHs) compared with the non-impacted sample. Each impactor type shows unique impactor residue morphologies produced at a given impact velocity. An expanded methodology is presented to announce relatively new analytical techniques together with innovative modifications to other methods that can be used to characterize small impact residues in LDEF craters, in addition to other acquired extraterrestrial samples

    Funding Shortfall for Housing Vouchers Could Have Serious Health Consequences for Children

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    In the fourth brief in its Policy Action series, Children's HealthWatch finds that unaffordable housing endangers the health and development of young children. Due to a federal funding shortfall, state and local housing agencies will be forced to reduce or eliminate rental assitance to thousands of families starting this month. Voucher cuts will push more families into the ranks of the "hidden homeless" -- families that move frequently, crowd into apartments that are too small, or live doubled up with other households when they cannot find affordable housing. Children in hidden homeless families are at increased risk for poor health, nutrition, and growth, as well as developmental delays. Timely Congressional action to protect the Housing Choice Voucher Program will ensure that families have stable, affordable housing essential to children's health

    The NASA-UC-UH Eta-Earth Program: IV. A Low-mass Planet Orbiting an M Dwarf 3.6 PC from Earth

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    We report the discovery of a low-mass planet orbiting Gl 15 A based on radial velocities from the Eta-Earth Survey using HIRES at Keck Observatory. Gl 15 Ab is a planet with minimum mass Msini = 5.35 ±\pm 0.75 M⊕_\oplus, orbital period P = 11.4433 ±\pm 0.0016 days, and an orbit that is consistent with circular. We characterize the host star using a variety of techniques. Photometric observations at Fairborn Observatory show no evidence for rotational modulation of spots at the orbital period to a limit of ~0.1 mmag, thus supporting the existence of the planet. We detect a second RV signal with a period of 44 days that we attribute to rotational modulation of stellar surface features, as confirmed by optical photometry and the Ca II H & K activity indicator. Using infrared spectroscopy from Palomar-TripleSpec, we measure an M2 V spectral type and a sub-solar metallicity ([M/H] = -0.22, [Fe/H] = -0.32). We measure a stellar radius of 0.3863 ±\pm 0.0021 R⊙_\odot based on interferometry from CHARA.Comment: ApJ accepted, 11 pages, 8 figures, 3 table
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