1,721,081 research outputs found
The survival of gas clouds in the circumgalactic medium of Milky Way-like galaxies
Full text linkObservational evidence shows that low-redshift galaxies are surrounded by extended haloes of multiphase gas, the so-called circumgalactic medium (CGM). To study the survival of relatively cool gas (T < 105 K) in the CGM, we performed a set of hydrodynamical simulations of cold (T = 104 K) neutral gas clouds travelling through a hot (T = 2 × 106 K) and low-density (n = 10−4 cm−3) coronal medium, typical of Milky Way-like galaxies at large galactocentric distances (∼50–150 kpc). We explored the effects of different initial values of relative velocity and radius of the clouds. Our simulations were performed on a two-dimensional grid with constant mesh size (2 pc), and they include radiative cooling, photoionization heating and thermal conduction. We found that for large clouds (radii larger than 250 pc), the cool gas survives for very long time (larger than 250 Myr): despite that they are partially destroyed and fragmented into smaller cloudlets during their trajectory, the total mass of cool gas decreases at very low rates. We found that thermal conduction plays a significant role: its effect is to hinder formation of hydrodynamical instabilities at the cloud–corona interface, keeping the cloud compact and therefore more difficult to destroy. The distribution of column densities extracted from our simulations is compatible with those observed for low-temperature ions (e.g. Si ii and Si iii) and for high-temperature ions (O vi) once we take into account that O vi covers much more extended regions than the cool gas and, therefore, it is more likely to be detected along a generic line of sight
A comprehensive set of elemental abundances in Damped lyman alpha systems: revealing the nature of these high redshift objects
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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
Highly ionized region surrounding SN Refsdal revealed by MUSE
No full textSupernova (SN) Refsdal is the first multiply imaged highly magnified and spatially resolved SN ever observed. The SN exploded in a highly magnified spiral galaxy at z = 1.49 behind the Frontier Fields cluster MACS1149 and provides a unique opportunity to study the environment of SNe at high z. We exploit the time delay between multiple images to determine the properties of the SN and its environment before during and after the SN exploded. We use the integral-field spectrograph MUSE on the VLT to simultaneously target all observed and model-predicted positions of SN Refsdal. We find Mg II emission at all positions of SN Refsdal accompanied by weak Fe II* emission at two positions. The measured ratios of [O II] to Mg II emission of 10-20 indicate a high degree of ionization with low metallicity. Because the same high degree of ionization is found in all images and our spatial resolution is too coarse to resolve the region of influence of SN Refsdal we conclude that this high degree of ionization has been produced by previous SNe or a young and hot stellar population. We find no variability of the [O II] line over a period of 57 days. This suggests that there is no variation in the [O II] luminosity of the SN over this period or that the SN has a small contribution to the integrated [O II] emission over the scale resolved by our observations
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
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