1,720,962 research outputs found
Three-dimensional simulations of near-surface convection in main-sequence stars - III. The structure of small-scale magnetic flux concentrations
No full textContext. The convective envelopes of cool main-sequence stars harbour magnetic fields with a complex global and local structure. These fields affect the near-surface convection and the outer stellar atmospheres in many ways and are responsible for the observable magnetic activity of stars.
Aims. Our aim is to understand the local structure in unipolar regions with moderate average magnetic flux density. These correspond to plage regions covering a substantial fraction of the surface of the Sun (and likely also the surface of other Sun-like stars) during periods of high magnetic activity.
Methods. We analyse the results of 18 local-box magnetohydrodynamics simulations covering the upper layers of the convection zones and the photospheres of cool main-sequence stars of spectral types F to early M. The average vertical field in these simulations ranges from 20 to 500 G.
Results. We find a substantial variation of the properties of the surface magnetoconvection between main-sequence stars of different spectral types. As a consequence of a reduced efficiency of the convective collapse of flux tubes, M dwarfs lack bright magnetic structures in unipolar regions of moderate field strength. The spatial correlation between velocity and the magnetic field as well as the lifetime of magnetic structures and their sizes relative to the granules vary significantly along the model sequence of stellar types
Three-dimensional simulations of near-surface convection in main-sequence stars I. Overall structure
No full textContext. The near-surface layers of cool main-sequence stars are
structured by convective flows, which are overshooting into the atmosphere. The flows and
the associated spatio-temporal variations of density and temperature affect spectral line
profiles and thus have an impact on estimates of stellar properties such as effective
temperature, gravitational acceleration, and abundances.
Aims. We aim at identifying distinctive properties of the thermodynamic
structure of the atmospheres of different stars and understand their causes.
Methods. We ran comprehensive 3D radiation hydrodynamics simulations of
the near-surface layers of six simulated stars of spectral type F3V to M2V with the
MURa
Radial velocity observations of the 2015 Mar. 20 eclipse A benchmark Rossiter-McLaughlin curve with zero free parameters
No full textSpectroscopic observations of a solar eclipse can provide unique information for solar
and exoplanet research; the huge amplitude of the Rossiter-McLaughlin (RM) effect during
solar eclipse and the high precision of solar radial velocities (RVs) allow detailed
comparison between observations and RV models, and they provide information about the
solar surface and about spectral line formation that are otherwise difficult to obtain. On
March 20, 2015, we obtained 159 spectra of the Sun as a star with the solar telescope and
the Fourier Transform Spectrograph at the Institut für Astrophysik Göttingen, 76 spectra
were taken during partial solar eclipse. We obtained RVs using I2 as wavelength
reference and determined the RM curve with a peak-to-peak amplitude of almost
1.4 km s-1 at
typical RV precision better than 1 m s-1. We modeled the disk-integrated solar RVs using
well-determined parameterizations of solar surface velocities, limb darkening, and
information about convective blueshift from 3D magnetohydrodynamic simulations. We confirm
that convective blueshift is crucial to understand solar RVs during eclipse. Our best
model reproduced the observations to within a relative precision of 10% with residuals
lower than 30 m s-1. We cross-checked parameterizations of velocity fields
using a Dopplergram from the Solar Dynamics Observatory and conclude that disk-integration
of the Dopplergram does not provide correct information about convective blueshift
necessary for m s-1
RV work. As main limitation for modeling RVs during eclipses, we identified limited
knowledge about convective blueshift and line shape as functions of solar limb angle. We
suspect that our model line profiles are too shallow at limb angles larger than
μ =
0.6, resulting in incorrect weighting of the
velocities across the solar disk. Alternative explanations cannot be excluded, such as
suppression of convection in magnetic areas and undiscovered systematics during eclipse
observations. To make progress, accurate observations of solar line profiles across the
solar disk are suggested. We publish our RVs taken during solar eclipse as a benchmark
curve for codes calculating the RM effect and for models of solar surface velocities and
line profiles
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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