1,720,953 research outputs found
Harmonic Phase Processing In Magnetic Resonance Susceptibility Imaging
Get PDFThe popularity of magnetic resonance imaging (MRI) owes much to its flexibility. Sensitive to a host of different biophysical phenomena, parameters of the scan can be fine-tuned to highlight specific pathologies. One such mechanism for generating image contrast is magnetic susceptibility—the material property that defines how an object will distort an applied magnetic field such as that of the MR scanner. In functional MRI (fMRI), for instance, the unique magnetic signatures of oxygenated (diamagnetic) and deoxygenated (paramagnetic) blood are what permit the indirect measure of neuronal activity. However, rather than measuring the susceptibility itself, fMRI registers haemodynamic change as subtle gains and losses in the signal magnitude due to haem-iron induced dephasing of the proton spins. Susceptibility mapping, an emerging area in MRI, attempts to retrieve a direct measure of bulk susceptibility itself. Generally this is done, not by means of the standard magnitude image, but through the phase component of the signal which, in the idealized case, relates the magnetic field perturbation by a simple multiplicative constant. Several issues interfere with the construction of accurate susceptibility maps. Foremost is the obfuscation of the small-scale “local” field (i.e., that pertaining to susceptibility vari- ation within tissue) by the so-called “background” field, which owes predominantly to the comparatively substantial susceptibility shift between tissue and air. Whether the goal is to produce qualitatively useful images of the local field, or to map the susceptibility itself, the local field must first be isolated from the background. To isolate overlapping signals which are a priori unknown, the unique characteristics of the expected signals need to first be cod- ified. One family of methods for isolating the local field begins by asserting that, away from air-tissue interfaces, the background field should satisfy the partial differential equation of Laplace, whereas the local field should satisfy that of Poisson (viz., the background field should be harmonic, the local field non-harmonic). This classification informs a filtering technique based on the spherical mean value (SMV) property of harmonic functions: the mean of a harmonic function calculated over a spherical surface equates to the specific value taken by the function at the centre of the sphere. This thesis introduces another property of harmonic functions to the task of local field estimation: a harmonic function can be locally expressed by means of a convergent power series (viz., it is an analytic function). This property is first employed to characterize the SMV kernel as an estimator for the central field value when the field is discretized. Analysis reveals that when the field data is of a finite spatial resolution, the aim of accurate elimination of the background field via the SMV is fundamentally at odds with the aim of preserving the local field. Fortunately, given the rapid decay of the background field and its derivatives with distance from its field sources, the discrete SMV is nevertheless a robust estimator for field geometries such as those observed in the brain. In addition to the problem of finite image resolution, MR imaging of the head has finite spatial support as signal is generally absent in the skull and ever-absent in the surrounding air. The SMV cannot be used to estimate the background field wherever the spherical kernel extends beyond the edges of this support. Hence, in conventional SMV-filtering, field points within a distance from the edges equal to the radius of the employed kernel are discarded outright. This is a considerable obstacle to a number of clinical applications as it precludes analysis of features such as subdural haematomas and cortical lesions in pathologies such as multiple sclerosis. To recover local field across the edges of the brain, this study presents an extension to conventional SMV-filtering by appealing to the analytic nature of the back- ground field: by obtaining an initial SMV-estimate of the harmonic background field over a reduced inner portion of the brain, a three-dimensional Taylor expansion was performed to extend field coverage to the edges of the brain. The method is quantitatively assessed through a numerical experiment and qualitatively demonstrated on in vivo human brain data acquired at 4.7 T. Using a kernel radius typical of conventional methods, the extension recovered on average 26 % more in vivo brain volume
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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