1,721,533 research outputs found
New Results from the X-Ray and Optical Survey of the Chandra Deep Field-South: The 300 Kilosecond Exposure. II.
No full textOpicino de Canistris e Galvano Fiamma: l'immagine della città e del territorio nel Trecento lombardo
No full textSaggio dedicato alla figura di Galvano Fiamma come fonte primaria per la conoscenza della città di Milano nel tardo Medioevo
Testing the rotation versus merger scenario in the galaxy cluster Abell 2107
Full text linkWe search for global rotation of the intracluster medium in the galaxy cluster Abell 2107, where previous studies have detected rotational motion in the member galaxies with a high-significance level. By fitting the centroid of the iron Kα line complex at 6.7–6.9 keV rest frame in Chandra ACIS-I spectra, we identify the possible rotation axis with the line that maximizes the difference between the emission-weighted spectroscopic redshift measured in the two halves defined by the line itself. Then, we measure the emission-weighted redshift in linear regions parallel to the preferred rotation axis, and find a significant gradient as a function of the projected distance from the rotation axis, compatible with a rotation pattern with maximum tangential velocity vmax = 1380 ± 600 km s−1 at a radius λ0 ∼ 160 kpc. This result, if interpreted in the framework of hydrostatic equilibrium, as suggested by the regular morphology of Abell 2107, would imply a large mass correction of the order of ∆M = (6 ± 4) × 1013 M☉ at ∼160 kpc, which is incompatible with the cluster morphology itself. A more conservative interpretation may be provided by an unnoticed off-centre, head-on collision between two comparable haloes. Our analysis confirms the peculiar dynamical nature of the otherwise regular cluster Abell 2107, but is not able to resolve the rotation versus merger scenario, a science case that can be addressed by the next-generation X-ray facilities carrying X-ray bolometers on board
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
On the origin of central abundance drops in the intracluster medium of galaxy groups and clusters
Full text linkA central drop of ICM Fe abundance has been observed in several cool-core clusters. It has been proposed that this abundance drop may be due, at least partially, to the depletion of Fe into dust grains in the central, high-density regions. According to this scenario, noble gas elements such as Ar and Ne are not expected to be depleted into dust, and therefore should not show any drop, but follow the general increase of metal abundance towards the centre. In this work, we test this scenario by measuring with Chandra data the radial profiles of Ar and Ne in a sample of 12 groups and clusters where a central drop in Fe abundance has been detected. We confirm the presence of the Fe drop in 10 out of 12 clusters at more than 2σ c.l., and 4 Ar drops with similar significance. We also find 4 Ne drops, with the caveat that Ne abundance measurement from CCD spectra suffers from systematics not completely under control. Our results are consistent with an abundance drop common to the three elements. When comparing the profiles, we find that, on average, the abundance profiles of Ar and Ne are significantly higher than Fe and steeper towards the centre, while they all gradually become consistent with solar composition at r ≥ 0.05r 500 . We also check that Si and S profiles are mostly consistent with Fe. This result confirms a scenario in which some fraction of Fe is depleted into dust grains in the inner regions, although the global central abundance drop is mostly due to mechanical processes, like the displacement of metal-rich ICM from the very centre to larger radii by AGN-driven feedback. Finally, we report the detection of an Fe drop in the cluster MACSJ1423.8+2404 at z = 0.543, showing that this feature appears early on in cool-core clusters
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
Scaling laws in X-ray galaxy clusters at redshift between 0.4 and 1.3
No full textWe present a study of the integrated physical properties of
a sample of 28 X-ray galaxy clusters observed with Chandra at
a redshift between 0.4 and 1.3. In particular, we have twelve objects in
the redshift range 0.4–0.6, five between 0.6 and 0.8, seven between
0.8 and 1 and four at , compounding the largest sample
available for such a study. We focus particularly on the properties
and evolution of the X-ray scaling laws.
We fit both a single and
a double model with the former which provides a good representation
of the observed surface brightness profiles, indicating that these
clusters do not show any significant excess in their central brightness.
By using the best-fit parameters of the model together with
the measured emission-weighted temperature (in the range 3–11 keV),
we recover gas luminosity, gas mass and total gravitating mass
out to R500. We observe scaling relations steeper than expected from
the self-similar model by a significant (>) amount in the
and relations and by a marginal value in the and relations. The degree of evolution of the
relation is found to be consistent with the
expectation based on the hydrostatic equilibrium for gas within
virialized dark matter halos. We detect hints of negative
evolution in the , and relations,
thus suggesting that systems at higher redshift have lower X-ray
luminosity and gas mass for fixed temperature.
In particular,
when the 16 clusters at are considered, the evolution becomes
more evident and its power-law modelization is a statistically
good description of the data.
In this subsample, we also find significant evidence for
positive evolution, such as , in the
relation, where the entropy S is defined as
and is measured at 0.1.
Such results point toward a scenario in which a relatively lower gas
density is present in high-redshift objects, thus implying a
suppressed X-ray emission, a smaller amount of gas mass and a higher
entropy level. This represents a non-trivial constraint for models
aiming at explaining the thermal history of the intra-cluster medium
out to the highest redshift reached so far
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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