1,721,054 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
An extensive VLT/X-shooter library of photospheric templates of pre-main sequence stars
Get PDFContext. Studies of the formation and evolution of young stars and their disks rely on knowledge of the stellar parameters of the young stars. The derivation of these parameters is commonly based on comparison with photospheric template spectra. Furthermore, chromospheric emission in young active stars impacts the measurement of mass accretion rates, a key quantity for studying disk evolution.
Aims. Here we derive stellar properties of low-mass (M⋆≲ 2 M⊙) pre-main sequence stars without disks, which represent ideal photospheric templates for studies of young stars. We also use these spectra to constrain the impact of chromospheric emission on the measurements of mass accretion rates. The spectra are reduced, flux-calibrated, and corrected for telluric absorption, and are made available to the community.
Methods. We derive the spectral type for our targets by analyzing the photospheric molecular features present in their VLT/X-shooter spectra by means of spectral indices and comparison of the relative strength of photospheric absorption features. We also measure effective temperature, gravity, projected rotational velocity, and radial velocity from our spectra by fitting them with synthetic spectra with the ROTFIT tool. The targets have negligible extinction (AV< 0.5 mag) and spectral type from G5 to K6, and from M6.5 to M8. They thus complement the library of photospheric templates presented in our previous publication. We perform synthetic photometry on the spectra to derive the typical colors of young stars in different filters. We measure the luminosity of the emission lines present in the spectra and estimate the noise due to chromospheric emission in the measurements of accretion luminosity in accreting stars.
Results. We provide a calibration of the photospheric colors of young pre-main sequence stars as a function of their spectral type in a set of standard broad-band optical and near-infrared filters. The logarithm of the noise on the accretion luminosity normalized to the stellar luminosity is roughly constant and equal to ~−2.3 for targets with masses larger than 1 solar mass, and decreases with decreasing temperatures for lower-mass stars. For stars with masses of ~ 1.5 M⊙ and ages of ~ 1−5 Myr, the chromospheric noise converts to a limit of measurable mass accretion rates of ~ 3 × 10-10M⊙/yr. The limit on the mass accretion rate set by the chromospheric noise is of the order of the lowest measured values of mass accretion rates in Class II objects
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Unveiling the Star-Disk Interaction in Young Stars with High-Resolution Spectrophotometric Observations
No full textNewly formed stars accrete material from their parent cloud, which, due to conservation of angular
momentum, collapses into a disk-like structure around the young star. After approximately one
million years, the envelope around the star has completely dissipated and the system becomes
observable at optical wavelengths, making it possible to study the interaction between the star and
the disk.
Low-mass stars at this stage, known as Classical T Tauri Stars (CTTSs), have strong magnetic
fields that disrupt the accretion disk at a distance of a few stellar radii from the star. Gas flows from
the disk to the star along the magnetic field lines in a process called magnetospheric accretion,
ending in a shock at the stellar surface, which heats the photosphere and creates a hot spot.
Magnetospheric accretion is a complex process involving the exchange of matter, angular
momentum, and energy between the disk and the star. This process is accompanied by mass loss
via stellar and disk winds, which are driven by open magnetic field lines. These outflows play a
critical role in angular momentum extraction, preventing the star from spinning up.
In this PhD dissertation, I will discuss the main results of my research, which is based on high-
resolution spectroscopic data from the Echelle SPectrograph for Rocky Exoplanet and Stable
Spectroscopic Observations (ESPRESSO), the latest-generation echelle spectrograph at the
European Southern Observatory's Very Large Telescope (VLT), and photometric data from the
Transiting Exoplanet Survey Satellite (TESS).
High-resolution spectroscopy can be used to study the star-disk interaction and investigate the
structure of the magnetosphere and its temperature stratification, as well as the kinematics of CTTS
outflows and their complex, layered structure.
High-cadence photometric data from TESS allow to test magnetohydrodynamic simulations by
analyzing the rotational modulation of the hot spot. The analysis of the frequency spectrum of
CTTSs light curves enables the determination of the radius at which the disk is truncated by the
stellar magnetic field.
When combined together, these two techniques permit the determination of the amount of angular
momentum per unit time transferred from the star to the disk, allowing to constrain the mechanisms
that prevent the stellar spin-up in CTTSs
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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