1,721,001 research outputs found
Strong spectral variability in NGC 7603 over 20 years
No full textWe present results of a long-term optical variability campaign on the Seyfert 1 galaxy NGC 7603 over a period of nearly 20 years. The optical continuum and the Balmer and Helium lines varied by a factor of 5 to 10 in this broad-line Seyfert 1 galaxy. Furthermore, it is remarkable that the optical FeII line blends varied with the same amplitude as the H alpha and HeI lines. During the first half of the campaign (until 1990) there was a strong correlation between Balmer decrement variations, H beta intensity variations and emission line asymmetry. This behaviour changed afterwards when the H beta line intensity was higher than on average
Strong spectral variability in NGC 7603 over 20 years
No full textWe present results of a long-term optical variability campaign on the Seyfert 1 galaxy NGC 7603 over a period of nearly 20 years. The optical continuum and the Balmer and Helium lines varied by a factor of 5 to 10 in this broad-line Seyfert 1 galaxy. Furthermore, it is remarkable that the optical FeII line blends varied with the same amplitude as the H alpha and HeI lines. During the first half of the campaign (until 1990) there was a strong correlation between Balmer decrement variations, H beta intensity variations and emission line asymmetry. This behaviour changed afterwards when the H beta line intensity was higher than on average
The QSO HE1013-2136 (z = 0.785): Tracing the ULIRG-QSO connection towards large look-back times?
No full textDeep BRIH-images as well as long-slit spectra taken with the ESO-2.2m and VLT-telescopes of the QSO HE1013-2136 (z = 0.785) are presented. They show the QSO apparently in the last phase of a 1:3 merger. Two tidal tails extending 9" and 3.5" (68 and 26 kpc) and several condensations within 3.5" projected distance are clearly detected. The latter could be companion galaxies to the QSO or debris of a merger remnant. Due to the complexity of the system, the morphology of the host galaxy is not well constrained, however, the host galaxy seems to be as bright as 2--3 L*. The I- and H-band images of HE1013-2136 show remarkable differences, which are hard to asses. At present it cannot be ruled out that one of the merging galaxies formed a ring-like structure. The spectrum of the QSO shows it to be an extreme Fe II emitter, which is typical for IR-bright QSOs. At least one of the nearby condensations is most likely at the same redshift as the QSO, however, no signs of (post)starburst activity seen in many nearby interacting QSOs are detected. HE1013-2136 shows many similarities to the low-redshift (z = 0.29) intermediate QSO PG 1700+518 and could thus be a unique probe of the ULIRG-QSO connection at large look-back times
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
Lattice location studies of rare earth impurities in 3C-, 4H- and 6H-SiC
No full textThe lattice location of rare earths Tm in 3C- and 4H-SiC and Yb in 6H-SiC were studied using the emission channeling technique. Radioactive rare earth ions were implanted at the on-line isotope separator ISOLDE at CERN with an energy of 60 keV and fluences of 2 x 10(13) ions/cm(2). in order to determine the lattice location of the implanted impurities, angular dependent electron yields around certain axes were recorded with conversion electrons arising in the decay Tm-167-Er-167 (t(1/2) = 9.28 d) and Yb-169-Tm-169 (t(1/2) = 30.0 d). The effect of annealing on the normalized electron yields was studied up to 873 K for the 3C- and 4H-SiC samples and up to 1073 K for the 6H-SiC sample. In all cases the implanted rare earths are located on near substitutional silicon sites. (C) 2003 Elsevier B.V. All rights reserved
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
Spectral line variability amplitudes in active galactic nuclei
No full textWe present the results of a long-term variability campaign of very broad-line
AGNs with line widths broader than FWHM > 5000 km s-1.
The main goal of our investigation was to study whether the widths of the
optical broad emission lines are correlated with the optical intensity
variations on timescales of years. Our AGN sample consisted of 10 objects.
We detected a significant correlation between optical continuum variability
amplitudes and Hβ emission line widths (FWHM) and, to a lesser degree,
between Hβ line intensity variations and Hβ equivalent widths.
We add the spectroscopic data of variable AGNs from the literature to
supplement our sample.
The AGNs from other optical variability campaigns with different line-widths
helped to improve the statistical significance of our very broad-line AGN
sample. After including the data on 35 additional galaxies, the
correlation between
optical continuum variability amplitudes and Hβ emission line widths
becomes even more significant and the probability that this is a random
correlation drops to 0.7 percent
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
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