1,721,031 research outputs found
Experimental Studies of the Acoustic Signal generated by Marine Seismic Sources
Full text linkMarine seismic acquisition is the most commonly used geophysical technique to image the subsurface for different purposes, e.g. exploration of reservoirs or investigation of subduction zones as areas where earthquakes are generated. The acquisition consists of a sound source emitting the signal into the subsurface and dedicated sensors which receive the reflected signals from the subsurface structures of interest. The most common sound source used in marine seismics over the last 50 years is the airgun. The airgun is a mechanical device releasing high pressurized air from a chamber into the surrounding water within a few milliseconds. The acoustic source signal consists of a sharp peak when the pressurized air is released followed by an oscillation corresponding to the expanding and contracting air bubble in water. The main advantages of the airgun are its signal repeatability and long lifetime. However, the emitted frequency bandwidth is limited by the oscillation period and the destructive interference of the direct downgoing wavefield with the first reflection from the sea surface, referred to as the ghost. In recent years there has been increasing interest in improving two major aspects of the sound source in marine seismic acquisition. The first aspect is the enhancement of emitted low frequency signals ( 100-200 Hz) which can have an impact on marine life, e.g. masking communication or behavioural disturbances. Therefore, alternative source types, e.g. marine vibrators, are developed and investigations are conducted on how to tune the signal emitted by airguns.
The thesis consists of several, individual manuscripts where the acoustic signal generated by single marine seismic sources, especially from airguns, is experimentally investigated. Several experiments are conducted to study the mechanisms that have an impact on the low frequency content of the emitted sound signal. First, the signal generated by the rising airgun bubble is investigated separately from the main peak and oscillating bubble by dedicated experiments with rising buoys and the results are compared to measured airgun signatures. Secondly, the impact of the spherical wave front on the ghost reflection is studied for different source-interface distances in a tank experiment. Third, the impact of the interaction between the airgun bubble and sea surface on the source signature is investigated for very shallow source depths and the variations of the oscillating bubble and ghost reflection are discussed. In addition, the signal emitted into air is analyzed for these shallow seismic sources. Another study deals with the reduction of high frequency emission from seismic airguns. The impact of bubble curtains surrounding an airgun on the source signature and high frequency emission are investigated for different bubble curtain configurations.
The results from the rising airgun bubble indicate a low frequency signal emitted by this movement. However, the signal strength is low and seems to have no significant impact in marine seismic acquisition. The results for the spherical wave front indicate that the low frequency signal (< 1-2 Hz) could be enhanced with decreasing source depth. However, the noise level at this frequency band is usually strong and it needs to be further investigated how large the impact could be in field applications. The results from the source-interface interaction indicate that the low frequency signal (< 5 Hz) is strongly enhanced when the airgun bubble bursts directly at the water surface and no oscillations occur. This effect seems to be promising to enhance the low frequency signal in field applications. The results from the bubble curtain surrounding the airgun indicate a gradually decreasing frequency content above 50 Hz with increasing air injection into the bubble curtain. Hence, bubble curtains could potentially be considered to reduce high frequency emissions from airguns
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
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
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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