1,721,180 research outputs found
The search for radio emission from giant exoplanets
No full textInternational audienceThe intensity of Jupiter's auroral radio emission quickly gave rise to the question whether a comparable coherent emission from the magnetosphere of an extrasolar planet could be detectable. A simple estimation shows that exoplanetary auroral radio emission would have to be at least 1000 times more intense than Jupiter's emission to be detectable with current radio telescopes. Theoretical models suggest that, at least in certain cases, the radio emission of giant exoplanets may indeed reach such an intensity. At the same time, in order to generate such an emission, an exoplanet would need to have a sufficiently strong intrinsic planetary magnetic field. Extrasolar planets are indeed expected to have a magnetic field, but to date, their magnetic field has never been detected. As discussed elsewhere [Griessmeier et al., 2015], the most promising technique to unambiguously observe exoplanetary magnetic fields is to search for the planetary auroral radio emission. The detection of such an emission would thus constitute the first unambiguous detection of an exoplanetary magnetic field. We review recent theoretical studies and discuss their results for the two main parameters, namely the maximum emission frequency and the intensity of the radio emission. The predicted values indicate that detection should be possible using modern low-frequency radio telescopes. We also review past observation attempts, and compare their sensitivity to the predicted emission
Aspects of the magnetosphere-stellar wind interaction of close-in extrasolar planets
Full text linkSince 1995, more than 150 extrasolar planets were detected, of which a considerable fraction orbit their host star at very close distances. Gas giants with orbital distances below 0.1 AU are called “Hot Jupiters”. Current detection techniques are not sensitive enough for the detection of Earth-like planets, but such planets are expected at similar orbital positions. For all these so-called close-in extrasolar planets, the interaction between the stellar wind and the planetary magnetosphere is expected to be very different from the situation known from the solar system. Important differences arising from the close substellar distances include a low stellar wind velocity, a high stellar wind density and strong tidal interaction between the planet and the star. This interaction is shown to lead, for example, to a synchronisation of the planetary rotation with its orbit (“tidal locking”). Taking these points into account, planetary magnetic moments are estimated and sizes of planetary magnetospheres are derived. Two different effects resulting from the magnetospheric interaction are studied in detail. (a) Characteristics of radio emission from the magnetospheres of “Hot Jupiters” are discussed. It is shown that the frequency range and the sensitivity of current radio detectors are not sufficient to detect exoplanetary radio emission. With planned improvements of the existing instrumentation and with the construction of new radio arrays, the detection of exoplanetary radio emission will be possible in the near future. (b) The flux of galactic cosmic rays to the atmospheres of terrestrial exoplanets in close orbits around M stars is studied. Different types of planets are shown to be weakly protected against cosmic rays, which is likely to have implications for planetary habitability. This should be taken into account when selecting targets for the search for biosignatures in the spectra of terrestrial exoplanets
Aspects of the magnetosphere-stellar wind interaction of close-in extrasolar planets
No full textSince 1995, more than 150 extrasolar planets were detected, of which a considerable fraction orbit their host star at very close distances. Gas giants with orbital distances below 0.1 AU are called “Hot Jupiters”. Current detection techniques are not sensitive enough for the detection of Earth-like planets, but such planets are expected at similar orbital positions. For all these so-called close-in extrasolar planets, the interaction between the stellar wind and the planetary magnetosphere is expected to be very different from the situation known from the solar system. Important differences arising from the close substellar distances include a low stellar wind velocity, a high stellar wind density and strong tidal interaction between the planet and the star. This interaction is shown to lead, for example, to a synchronisation of the planetary rotation with its orbit (“tidal locking”). Taking these points into account, planetary magnetic moments are estimated and sizes of planetary magnetospheres are derived. Two different effects resulting from the magnetospheric interaction are studied in detail. (a) Characteristics of radio emission from the magnetospheres of “Hot Jupiters” are discussed. It is shown that the frequency range and the sensitivity of current radio detectors are not sufficient to detect exoplanetary radio emission. With planned improvements of the existing instrumentation and with the construction of new radio arrays, the detection of exoplanetary radio emission will be possible in the near future. (b) The flux of galactic cosmic rays to the atmospheres of terrestrial exoplanets in close orbits around M stars is studied. Different types of planets are shown to be weakly protected against cosmic rays, which is likely to have implications for planetary habitability. This should be taken into account when selecting targets for the search for biosignatures in the spectra of terrestrial exoplanets
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
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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