1,720,969 research outputs found
Compressive Sensing and Fast Simulations: Applications to Radar Detection
No full textIn most modern high-resolution multi-channel radar systems one of the major problems to deal with is the huge amount of data to be acquired, processed and/or stored. But why do we need all these data? According to the well known Nyquist-Shannon sampling theorem, real signals have to be sampled at at least twice the signal bandwidth to prevent ambiguities. Therefore, sampling of very wide bandwidths may require Analog to Digital Converter (ADC) hardware that is unavailable or very expensive; especially in multi-channel systems, the cost and power consumption can become critical factors. In applications involving interleaving of radar modes in time or space (antenna aperture), multi-function operation often leads to conflicting requirements on sampling rates in both time and spatial domains. So while, on one hand, the increased number of degrees of freedom improves the system performance, on the other hand it puts a significant burden on both the off-line analysis and performance evaluation of sophisticated detectors, and on the real time acquisition and processing. For example, space-time adaptive processing algorithms significantly enhance the detection of targets buried in noise, clutter and jamming. However, evaluating the optimal filter weights is an immense computational load when simulating such detectors in the design phase as well as in real time implementation. In some cases, measurement time may also be a constraint, as in 3D radar imaging for airport security inspection of passengers. Conventional acquisition of a full 3D high resolution image requires a measurement time that can be unacceptable in this situation. In this thesis we investigate sampling methods that can deal with the problems of processing complexity as well as analysis (or performance evaluation) extremely efficiently by reducing the required amount of samples. By cleverly using properties of the signals or random variables involved, the considered techniques, namely Compressive Sensing (CS) and Importance Sampling (IS), both alleviate the burden related to data handling in complex radar detectors. These methods, although very different in nature, provide an alternative to classical sampling techniques. The first, compressive sensing, is based on a revolutionary acquisition and processing theory that enables reconstruction of sparse signals from a set of measurements sampled at a much lower rate than required by the Nyquist-Shannon theorem. This results in both shorter acquisition time and reduced amount of data. The second, importance sampling, has roots in statistical physics and represents a fast and effective method for the design and analysis of detectors whose performance have to be evaluated by simulations. By efficiently sampling the underlying probability density function, importance sampling provides a very fast alternative to conventional Monte Carlo simulation. The first part of the thesis deals with the design and analysis of adaptive detectors for compressive sensing based radars. In systems using compressive sensing, the target signal, which is assumed to be sparse, is estimated from the noisy, undersampled measurements via L1-norm minimization algorithms. CS recovery algorithms require proper setting of parameters (thresholds) and are therefore not inherently adaptive. Classical radar systems employ a matched filter, matched to the transmitted waveform, followed by a Constant False Alarm Rate (CFAR) processor for the detection of targets embedded in unknown background clutter and noise. However, the non-linearity introduced by a CS recovery algorithm does not allow straightforward application of conventional adaptive detector design methodology. In the work reported here, by making use of the properties of the Complex Approximate Message Passing algorithm, we are able to propose an adaptive non-linear recovery stage combined with classical CFAR processing, and derive a novel adaptive CS detector. Additionally, our theoretical findings are also demonstrated via both simulated and experimental results. Furthermore, we provide a methodology to predict the performance of the proposed detectors that can be used to evaluate how transmitted power can be traded against undersampling, making it possible to incorporate CS-based sampling and detection in radar system design. The second part of this thesis focuses on deriving methods of importance sampling for fast simulation of rare events especially applicable to Space Time Adaptive Processing (STAP) radar detectors. These type of methods are, however, of much wider applicability. They can and have been used in many other situations that require intensive and time-consuming Monte Carlo simulations. In conducting rare event simulations of systems that involve signal processing operations that are mathematically complex, there are two principal issues that contribute to simulation time. The first issue concerns the rare event itself whose probability is being sought. The second concerns the computational intensity that accompanies the signal processing. It is a daunting task to conduct conventional Monte Carlo simulations that involve several millions of trials to estimate low false alarm probabilities, with as many matrix inversions, as required in STAP. We demonstrate how fast simulation schemes can deal with these aspects, and devise tailored importance sampling biasing schemes for evaluating the performance of STAP detectors which are analytically difficult or impossible to analyze, such as low rank STAP detectors. By comparing our results with traditional Monte Carlo methods, we show that importance sampling can achieve tremendous gain in terms of computational time.Geoscience and Remote SensingCivil Engineering and Geoscience
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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