1,721,058 research outputs found
Probing the Reionization History Using the Spectra of High-Redshift Sources
No full textWe quantify and discuss the footprints of neutral hydrogen in the intergalactic medium (IGM) on the spectra of high-redshift (z ∼ 6) sources, using mock spectra generated from hydrodynamical simulations of the IGM. We show that it should be possible to extract relevant parameters, including the mean neutral fraction in the IGM and the radius of the local cosmological Strömgren region, from the flux distribution in the observed spectra of distant sources. We focus on quasars, but a similar analysis is applicable to galaxies and gamma-ray burst (GRB) afterglows. We explicitly include uncertainties in the spectral shape of the assumed source template near the Lyα line. Our results suggest that a mean neutral hydrogen fraction, xH, of unity can be statistically distinguished from xH ≈ 10-2 by combining the spectra of tens of bright (M ≈ -27) quasars. Alternatively, the same distinction can be achieved using the spectra of several hundred sources that are ∼100 times fainter. Furthermore, if the radius of the Strömgren sphere can be independently constrained to within ∼10%, this distinction can be achieved using a single source. The information derived from such spectra will help in settling the current debate as to what extent the universe was reionized at redshifts near z ∼ 6
Implications of the Lyα Emission Line from a Candidate z=10 Galaxy
No full textThe z = 10 galaxy recently discovered by Pello and coworkers has a strong Lyα emission line that does not appear to have the expected asymmetry with more transmission on the red side. The blue wing of a Lyα line originating at high redshift should be strongly suppressed by resonant hydrogen absorption along the line of sight, an expectation borne out by the observed asymmetric shapes of the existing sample of Lyα-emitting sources at lower redshifts (3 < z < 6.7). The observed line is inconsistent with the galaxy being embedded in a fully neutral intergalactic medium (IGM) and having no receding peculiar velocity relative to the surrounding absorbing gas at the 95.0%-98.8% confidence level. Absorption on the blue side of the line of the Pello et al. source could be reduced if the IGM in the vicinity of the galaxy is highly ionized, but we show that this requires an unrealistically high ionizing emissivity. We suggest instead that the Lyα-emitting gas is receding relative to the surrounding gas with a velocity of ≳35 km s-1, which reduces the inconsistency confidence level to less than 76.0%-94.5%. We find that with this velocity shift, the observed strength and shape of the line is more consistent with the galaxy being surrounded by its own Strömgren sphere embedded in a fully neutral IGM. More generally, we predict that at any given redshift, the bright Lyα emitters with broader lines would exhibit stronger asymmetry than fainter ones. Bright galaxies with symmetric Lyα lines may be signposts for groups and clusters of galaxies, within which they can acquire random velocities comparable to or larger than their line widths. © 2005. The American Astronomical Society. All rights reserved
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
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