1,720,972 research outputs found
(Log-)epiperimetric inequality and regularity over smooth cones for almost area-minimizing currents.
No full textOptical analysis of the poor clusters Abell 610, Abell 725, and Abell 796, containing diffuse radio sources
No full textAims: We study the dynamical status of the poor, low X-ray luminous galaxy clusters Abell 610, Abell 725, and Abell 796 (at z = 0.1, 0.09, and 0.16, respectively), containing diffuse radio sources (relic, relic, and possible halo, respectively).
Methods: Our analysis is based on new spectroscopic data obtained at the William Herschel Telescope for 158 galaxies, new photometry obtained at the Isaac Newton Telescope with the addition of data recovered from the Data Release 5 of the Sloan Digital Sky Survey. We use statistical tools to select 57, 36, and 26 cluster members and to analyze the kinematics of cluster galaxies, as well as to study the 2D cluster structure.
Results: The low values we compute for the global line-of-sight velocity dispersion of galaxies (σV = 420-700 km s-1) confirm that these clusters are low-mass clusters. Abell 610 shows a lot of evidence of substructure. It seems to be formed by two structures separated by ~700 km s-1 in the cluster rest-frame, having comparable σV ~ 200 km s-1 and likely causing a velocity gradient. The velocity of the brightest cluster member (BCMI; a bright radio source) is very close to the mean velocity of the higher velocity structure. A third small, low-velocity group hosts the second brightest cluster member (BCMII). The analysis of the 2D galaxy distribution shows a bimodal distribution in the core elongated in the SE-NW direction and likely associated to BCMI and BCMII groups. Abell 725 and Abell 796, which are less sampled, show marginal evidence of substructure in the velocity space. They are elongated in the 2D galaxy distribution. For both Abell 610 and Abell 725 we shortly discuss the possible connection with the hosted diffuse radio relic.
Conclusions: Our results show that relic radio sources are likely connected with merger events, but are not limited to massive clusters. About the possible halo source in Abell 796, there is some evidence of a merger event in this non-massive cluster, but a pointed radio observation is necessary to confirm this halo
The dynamical status of the galaxy cluster Abell 115
No full textAims:We present the results of a new spectroscopic and photometric survey of the hot, binary X-ray cluster A115 at z = 0.193, containing a radio relic.
Methods: Our analysis is based on new spectroscopic data obtained at the Telescopio Nazionale Galileo for 115 galaxies and on new photometric data obtained at the Isaac Newton Telescope in a large field. We combine galaxy velocity and position information to select 85 galaxies recognized as cluster members, determine global dynamical properties and detect substructures.
Results: We find that A115 appears as a well isolated peak in the redshift space, with a global line-of-sight (LOS) velocity dispersion σ_v=1362-108+126 km s-1. Our analysis confirms the presence of two structures of cluster-type well recognizable in the plane of the sky and shows that they differ of 2000 km s-1in the LOS velocity. The northern, high velocity subcluster (A115N) is likely centred on the second brightest cluster galaxy (BCM-A, coincident with radio source 3C28) and the northern X-ray peak. The southern, low velocity subcluster (A115S) is likely centred on the first brightest cluster galaxy (BCM-B) and the southern X-ray peak. We estimate that A115S is slightly dynamically more important than A115N having σv = 900-1100 km s-1 vs. σv = 750-850 km s-1. Moreover, we find evidence for two small groups at low velocities. We estimate a global cluster virial mass of 2.2-3.5 × 1015 h70-1 Msun.
Conclusions: Our results agree with a pre-merging scenario where A115N and A115S are colliding with a LOS impact velocity Δ {{v}_rf} ̃ 1600 km s-1. The most likely solution to the two-body problem suggests that the merging axis lies at 20 degrees from the plane of the sky and that the cores will cross after 0.1 Gyr. The radio relic with its largest dimension perpendicular to the merging axis is likely connected to this merger
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
INTERNAL DYNAMICS OF THE RADIO HALO CLUSTER ABELL 2744
No full textAims. We present a detailed dynamical analysis of the rich galaxy cluster A2744, containing a powerful diffuse radio halo.
Methods. Our analysis is based on redshift data for 102 galaxies, part of them recovered from unexplored spectra in the ESO archive. We
combine galaxy velocity and position information to select the cluster members and determine global dynamical properties of the cluster.
We use a variety of statistical tests to detect possible substructures.
Results. We find that A2744 appears as a well isolated peak in the redshift space at z = 0.306, which includes 85 galaxies recognized as
cluster members. We compute the line-of-sight (LOS) velocity dispersion of galaxies, σV = 1767+121
−99 km s−1, which is significantly larger than
what is expected in the case of a relaxed cluster with an observed X-ray temperature of 8 keV. We find evidence that this cluster is far from
dynamical equilibrium, as shown by the non-Gaussian nature of the velocity distribution, the presence of a velocity gradient and a significant
substructure. Our analysis shows the presence of two galaxy clumps of different mean LOS velocities ΔV ∼ 4000 km s−1. We detect a main,
low-velocity clump with σV ∼ 1200−1300 km s−1 and a secondary, high-velocity clump with σV = 500−800 km s−1and located in the S-SW
cluster region.We estimate a cluster mass within 1Mpc of 1.4−2.4×1015 M, depending on the model adopted to describe the cluster dynamics.
Conclusions. Our results suggest a merging scenario of two clumps with a mass ratio of 3:1 and a LOS impact velocity of ΔVrf ∼ 3000 km s−1,
likely observed just after the core passage. The merging is occuring roughly in the NS direction with the axis close to the LOS. This scenario
agrees with that proposed on the basis of recent Chandra results in its general lines although suggesting a somewhat more advanced merging
phase. Our conclusions support the view of the connection between extended radio emission and energetic merging phenomena in galaxy
clusters
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