1,720,956 research outputs found
Evidence for a toroidal magnetic-field component in 5C 4.114 on kiloparsec scales
No full textContext. A monotonic, statistically significant gradient in the observed Faraday rotation measure (RM) across the jet of an active galactic nucleus (AGN) reflects a corresponding gradient in the electron density and/or line-of-sight magnetic (B) field in the region of Faraday rotation. For this reason, such gradients may indicate the presence of a toroidal B field component, possibly associated with a helical jet B field. Although transverse RM gradients have been reported across a number of parsec-scale AGN jets, the same is not true on kiloparsec scales, suggesting that other (e.g. random) magnetic-field components usually dominate on these larger scales. Aims. We wished to identify clear candidates for monotonic, transverse RM gradients across AGN jet and lobe structures on scales larger than those probed thus far, and estimate their statistical significances. Methods. We identified an extended, monotonic transverse Faraday-rotation gradient across the northern lobe of a previously published Very Large Array (kiloparsec-scale) RM image of 5C 4.114. We reanalyzed these VLA data in order to determine the significance of this RM gradient. Results. The RM gradient across the northern kiloparsec-scale lobe structure of 5C 4.114 has a statistical significance of about 4σ. There is also a somewhat less prominent monotonic transverse Faraday-rotation gradient across the southern jet/lobe (narrower range of distances from the core, significance ≠3σ). Other parts of the Faraday-rotation distribution observed across the source are patchy and show no obvious order. Conclusions. This suggests that we are observing a random RM component associated with the foreground material in the cluster in which the radio source is located and through which it is viewed, superposed on a more ordered RM component that arises in the immediate vicinity of the AGN jets. We interpret the transverse RM gradient as reflecting the systematic variations of the line-of-sight component of a helical or toroidal B field associated with the jets of 5C 4.114. These results suggest that the helical field that arises due to the joint action of the rotation of the central black hole and its accretion disc and the jet outflow can survive to distances of thousands of parsec from the central engine
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Evolution of the magnetic field structure in the jet outflows from active galaxies
No full textThis thesis concerns studies into the magnetic fields in the jets from active galactic nuclei (AGN). Helical and toroidal magnetic fields are expected to exist in AGN jets close to the jet base and to assist in the launching and collimation of these structures, however if they can persist to the large kiloparsec scales and whether they still affect the jet on those scales is unknown. The magnetic fields of AGN jets are studied using Faraday rotation measure, which is proportional to the line of sight magnetic field strength, a transverse gradient in this value being an indicator of a toroidal magnetic field. It has been predicted by the “Cosmic Battery” model that the direction of any observed kiloparsec scale toroidal field component is such that an associated outward electrical current is present in the jet. Multiwavelength observations of 9 AGN are studied in this thesis. Of these 9 sources, 6 display significant transverse RM gradients on kiloparsec scales, of which 5 indicate toroidal fields with outward associated electrical currents, as predicted by the Cosmic Battery. Furthermore, the magnetic field environments of the jets are analysed as to how much the jets interact with their external medium. These effects can be studied using spectropolarimetry, where the behaviour of fractional polarization and polarization angle over a wide and continuous range of wavelengths can show evidence of strong depolarization and other complex magnetic field effects, some of which can be attributed to interactions with external media. An in-depth analysis of Coma A using wide band observations is presented here with accompanying Hα observations, showing regions of significant depolarization spatially correlated with observed Hα. The Hα can be used to estimate electron density, and in combination with the rotation measure values, the magnetic field can be calculated directly. It is shown that in a particular region, the depolarizing screen features a magnetic field strength upward of 36 μG, indicating the Hα gas was mixing with the radio lobe. In a similar vein, investigations into the radio galaxies 3C 382 and 3C 433 are also presented albeit without accompanying Hα data. However useful new rotation measure maps are provided for these sources, of which none have been published earlier, made using traditional χ versus λ squared fitting and rotation measure synthesis. Some of the interesting features in these sources are fitted for depolarization models to infer more complex underlying structure and were compared with previous published data at higher resolutions
Variations on the Author
No full text“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
No full textWe 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
No full textWe 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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