1,721,051 research outputs found
Asymmetries of Radio Galaxies
Full text linkIn this work, we have studied the asymmetries of radio galaxies which are known to be related to the jet-asymmetry. They are the depolarization asymmetry and the spectral index asymmetry. The first part of the thesis is concerned with the polarization asymmetry in GRGs and B2 RGs. After the introductory chapter, we discuss the Ricean bias in the fractional polarization and suggest a hybrid solution in the second chapter. The merit of this new solution is the enhanced reliability of the pixel-to-pixel fractional polarization. Using this hybrid solution, we present DP maps of the five GRGs at the end of the chapter. We conclude that the five GRGs are highly depolarized at low radio frequencies, but the depolarization is not as significant as Burn's law predicts. NGC315 shows an interesting characteristic in that the source is NOT depolarized. The subject of the third chapter is the rotation measure of the five GRGs. After correction for the Galactic contribution to the RM, the GRGs exhibit a few hundred radians per square meters of the Faraday medium. This must be due to field reversals or to changes of the field strength on a scale length of 50 to a few hundred kilo-parsecs. This result indicates that the Faraday media of the GRGs are well resolved, despite the relatively large beam size used. In the fourth chapter, we study the depolarization asymmetry of the B2 sources. Using the hybrid solution of the second chapter, we confirm the result of Morganti et al.(1997) who discovered the `Laing-Garrington' effect in the B2 sources. The Faraday Rotation Measure (hereafter RM) of the B2 sources is estimated using a frequency range similar to that of the GRG sample, but with better angular resolution. The measured RM is about an order of magnitude lower than that of the B2 sources. We test the correlation between the depolarization asymmetry and the asymmetry of the RM dispersion. There is a trend that the more Depolarization (hereafter DP)--asymmetric source is the more RM dispersion--asymmetric. Again, the trend is not as strong as the prediction of Burn's law. The fifth chapter is concerned with the high RM that we found in the GRG sample. We discuss the possible processes producing the high RMs. Since the GRGs with a symmetric morphology, e.g. 3C236, also exhibit a high RM, we favour an `internal' mechanism. Our estimate shows that expansion losses can support the amount of magnetic energy in the Faraday media. However, an external process such as large-scale shock flows may also play a role as we saw in the case of NGC315, where the RM becomes even higher. The sixth chapter deals with the spectral asymmetry. In FR II type sources, there are conflicting results as to this asymmetry. Liu et al.(1991) and Garrington et al.(1991) find a systematic asymmetry where the jet-side spectra are flatter in a sample of FR II type sources. In contrast to these results, Dennett-thorpe(1999) reported in her thesis that there is no systematic asymmetry in a representative FR II sample. Our concern was that the spectral asymmetry could occur not only through the spectral ageing effect but also through the difference in the injection spectral index. This idea may be more relevant for FR I sources and GRGs than for FR II sources, since the latter have a highly symmetric morphology, hence similar physical conditions are expected in both double lobes. Katz-ston et al.(1997) reported that there are possibly two injection spectra in the lobes of the FR I-type radio galaxy 3C449, based on an analysis of the colour-colour diagram. We develop a new analysis, the spectral curvature (SCP) - spectral index (alpha) diagram, in order to easily distinguish different injection spectra. We apply this technique to the GRG sample for which we have multiple frequency data at our disposal. The results show that there exists more than just one injection spectrum in the individual sources. Furthermore, we test this SCP-alpha diagram for a sample of 47 CSS sources whose injection spectra had been thoroughly analyzed by Murgia et al.(1999). This test proves that the SCP-alpha analysis is highly reliable. In the GRG sample we find multiple injection spectra using our new SCP-alpha analysis. On the whole, the subject of this thesis is rather the study of the analysis of the asymmetries, rather than the asymmetries themselves. The behaviour of the two known systematic (jet-asymmetry related) asymmetries is studied. We might verify these results in another way. Recently, RGs were recognized as a promising tool for the process of cosmic structure formation. The linear polarization property of RGs enables us to probe the magneto-ionic intergalactic or intracluster medium. The theory of cosmic particle acceleration is largely based on the observation of the radio spectra of RGs. It will be interesting to investigate a larger and representative sample of RGs with the improved analysis methods suggested in this work
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
Two radio cores in GPS J1543-0757: a new dual supermassive black hole system?
Full text linkWe report on the discovery of a dual supermassive black hole system in the radio galaxy J1543-0757, with a projected separation between the two black holes of 46 mas. The result is based on recent multifrequency observations using the Very Long Baseline Array and European VLBI Network, which reveal two compact, variable, flat-spectrum, active nuclei within the elliptical host galaxy of J1543-0757. Multiepoch observations from the VLBA also provide constraints on the spectral index and proper motions of all components. The flat spectra of both N and S at both frequencies strongly support that these radio components are associated with two separate, accreting supermassive black holes (SMBHs). The two nuclei appear stationary, while the jets emanating from the weaker of the two nuclei appear to move out and terminate in bright hot spots. The discovery of this system has implications for the number of close dual black holes that might be sources of gravitational radiation.18 pages, 5 figures, 4 tables, accepted for publication in Ap
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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