1,721,104 research outputs found
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Exploring the Dynamic Radio Sky with the Allen Telescope Array
Full text linkThe revolution in digital technology that has had so many obvious effects in recent decades has not spared the field of astronomy. It has led to an enormous improvement in astronomers’ ability to study the “time domain,” the expected and unexpected ways in which celestial objects change on timescales ranging from milliseconds to centuries. In the field of radio astronomy a variety of advances have led to a new breed of observatories that are orders of magnitude more efficient at surveying the sky than previous facilities. These new observatories produce data at prodigous rates, however, and require sophisticated analysis to take full advantage of their capabilities. With several major facilities coming online in the next few years, there is an urgent need to prove that terabytes of data can be reliably turned into genuine astrophysical results.This dissertation develops tools and techniques for coping with this challenge and applies them to data obtained with the Allen Telescope Array (ATA), a pioneering next-generation radio observatory located in Northern California. The ATA was built from the ground up to be a fast survey instrument, incorporating a suite of the new technologies that figure prominently in the new telescopes.I develop and describe miriad-python, a framework for the rapid development of interferometric analysis software that is used in a variety of ways in my subsequent research. I also present a robust software system for executing multiple observing campaigns cooperatively (“commensally”) at the ATA. Data from the ATA are difficult to analyze due to nontraditional features such as a large instantaneous field of view; continuous coverage of a large, interference-prone frequency range; and broadband, movable feeds; I describe and implement several methods for coping with these challenges.This technical work is driven by the needs of a variety of astrophysical applications. I use broadband spectra of starforming galaxies to investigate the “calorimeter” interpretation of their cosmic ray energetics. The data are consistent with a recent hypothesis that the magnetic fields in these galaxies are stronger than traditionally thought. I use the survey capabilities of the ATA to conduct ASGARD, a large survey of the Galactic component of the dynamic radio sky, which has remained poorly-explored due to the limitations of previous obseratories and the technical challenges involved. I discuss in detail the methods used to analyze the data and provide catalogs, maps, completeness functions, and variability statistics. I map extended radio structures in Galactic fields and show how they can be subtracted from the data to simplify the search for transient Galactic sources. I limit the density of transient sources brighter than 10 mJy to be <0.5 deg-2 at 95% confidence. One of the areas of emphasis in this survey was the fascinating system Cygnus X-3, which shows prominent flares across the electromagnetic spectrum. Observations from 2010 May show a bright (1 Jy) radio flare followed by a 4.3σ γ-ray flare (E > 100 MeV) ∼ 1.5 days later. This timing is inconsistent with standard inverse-Compton models, suggesting that multiple mechanisms may be responsible for the system’s high-energy emission
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
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Searches for Exotic Radio Sources and Intelligent Life on Other Worlds
Full text linkHere I describe several experiments that explore some of the rarest and most intriguing phenomena in the sky: short duration radio transients and possible electromagnetic emission from advanced extraterrestrial technology. Motivated by new discoveries and new technologies, we have performed, and are performing, some of the most thorough searches for these sources ever attempted. Our experiments include a "fly's eye" search for bright radio pulses at the Allen Telescope Array, commensal searches for extraterrestrial intelligence at the Arecibo Observatory, a targeted search of extrasolar planets for narrow-band radio emission using the Green Bank Telescope and an ongoing effort to discover pulsars in orbit around SgrA*. Although our experiments explore very different physics, they share common tools and techniques, notably a need for high performance digital signal processing. The experiments described here are prime examples of the synergy that exists between science and technology. Aided by dramatic advances in computing technology and the use of commodity components, we have enabled the processing of heretofore unheard of quantities of observational data. By taking advantage of a reusable design paradigm in which instruments do not have to be built from scratch, we have been able to develop new instruments quickly and efficiently. Our experiments are exploring wavelengths and signal types never before searched with high sensitivity, presenting the exciting chance for serendipitous discovery of unexpected phenomena. With an optimistic spirit, we venture into unexplored territory and expect the unexpected.This thesis is structured as follows: Chapter 1 presents an introduction to the scientific motivations for our experiments and the tools with which we conduct them, Chapter 2 describes our Fly's Eye Search for short duration radio transients at the Allen Telescope Array, Chapter 3 discusses our ongoing SETI experiments at radio and optical wavelengths and our plans for the future, Chapter 4 describes a 1.1-1.9 GHz search for narrow-band emission from planet candidates identified by the Kepler mission and Chapter 5 details our ongoing search for pulsars near Sgr A*
Variations on the Author
Full text link“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
Full text linkWe 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
Full text linkWe 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
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