1,721,020 research outputs found
The local high-velocity tail and the Galactic escape speed
Full text linkWe model the fastest moving (v_{tot}>300km s^{−1}) local (D ≲ 3 kpc) halo stars using cosmological simulations and six-dimensional Gaia data. Our approach is to use our knowledge of the assembly history and phase-space distribution of halo stars to constrain the form of the high-velocity tail of the stellar halo. Using simple analytical models and cosmological simulations, we find that the shape of the high-velocity tail is strongly dependent on the velocity anisotropy and number density profile of the halo stars – highly eccentric orbits and/or shallow density profiles have more extended high-velocity tails. The halo stars in the solar vicinity are known to have a strongly radial velocity anisotropy, and it has recently been shown the origin of these highly eccentric orbits is the early accretion of a massive (M_{star}∼10^{9}M⊙) dwarf satellite. We use this knowledge to construct a prior on the shape of the high-velocity tail. Moreover, we use the simulations to define an appropriate outer boundary of 2xr_{200}, beyond which stars can escape. After applying our methodology to the Gaia data, we find a local (r_{0} = 8.3 kpc) escape speed of v_{esc}(r_{0})=528 +24 −25 km s^{−1}. We use our measurement of the escape velocity to estimate the total Milky Way mass, and dark halo concentration: M_{200,tot}=1.00 +0.31 −0.24 ×10^{12}M⊙, c_{200}=10.9 +4.4 −3.3. Our estimated mass agrees with recent results in the literature that seem to be converging on a Milky Way mass of M_{200,tot}∼10^{12}M⊙
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
The Local Group and its dwarf galaxy members in the standard model of cosmology
No full textAccording to the current cosmological paradigm, ``Lambda Cold Dark
Matter'' (LambdaCDM), only ~20% of the gravitating matter in
the universe is made up of ordinary (i.e. baryonic) matter, while the
rest consists of invisible dark matter (DM) particles, which existence
can be inferred from their gravitational influence on baryonic matter
and light. Despite the large success of the LambdaCDM model in
explaining the large scale structure of the Universe and the
conditions of the early Universe, there has been debate on whether this
model can fully explain the observations of low mass (dwarf)
galaxies. The Local Group (LG), which hosts most of the known dwarf
galaxies, is a unique laboratory to test the predictions of the
LambdaCDM model on small scales.
I analyze the kinematics of LG members, including the
Milky~Way-Andromeda (MW-M31) pair and dwarf galaxies, in order to
constrain the mass of the LG. I construct samples of LG analogs from
large cosmological N-body simulations, according to the following
kinematics constraints: (a) the separation and relative velocity of
the MW-M31 pair; (b) the receding velocity of dwarf galaxies in the
outskirts of the LG. I find that these constraints yield a median
total mass of 2*10^{12} solar masses for the MW and M31, but with a
large uncertainty. Based on the mass and the kinematics constraints, I
select twelve LG candidates for the APOSTLE simulations project. The
APOSTLE project consists of high-resolution cosmological
hydrodynamical simulations of the LG candidates, using the EAGLE
galaxy formation model. I show that dwarf satellites of MW and M31
analogs in APOSTLE are in good agreement with observations, in terms
of number, luminosity and kinematics.
There have been tensions between the observed masses of LG dwarf
spheroidals and the predictions of N-body simulations within the
LambdaCDM framework; simulations tend to over-predict the mass of
dwarfs. This problem is known as the ``too-big-to-fail'' problem. I
find that the enclosed mass within the half-light radii of Galactic
classical dwarf spheroidals, is in excellent agreement with the
simulated satellites in APOSTLE, and that there is no too-big-to-fail
problem in APOSTLE simulations. A few factors contribute in solving
the problem: (a) the mass of haloes in hydrodynamical simulations are
lower compared to their N-body counterparts; (b) stellar mass-halo
mass relation in APOSTLE is different than the ones used to argue for
the too-big-to-fail problem; (c) number of massive satellites
correlates with the virial mass of the host, i.e. MW analogs with
virial masses above ~ 3*10^{12} solar masses would have faced
too-big-to-fail problems; (d) uncertainties in observations were
underestimated in previous works.
Stellar mass-halo mass relation in APOSTLE predicts that all isolated
dwarf galaxies should live in haloes with maximum circular velocity
(V_max) above 20 km/s. Satellite galaxies, however, can inhabit
lower mass haloes due to tidal stripping which removes mass from the
inner regions of satellites as they orbit their hosts. I examine all
satellites of the MW and M31, and find that many of them live in
haloes less massive than V_max=20 km/s. I additionally show that the
low mass population is following a different trend in stellar
mass-size relation compared to the rest of the satellites or field
dwarfs. I use stellar mass-halo mass relation of APOSTLE field
galaxies, along with tidal stripping trajectories derived in Penarrubia
et al., in order to predict the properties of the progenitors of the LG
satellites. According to this prediction, some satellites have
lost a significant amount of dark matter as well as stellar
mass. Cra~II, And~XIX, XXI, and XXV have lost 99 per-cent of their
stellar mass in the past.
I show that the mass discrepancy-acceleration relation of dwarf
galaxies in the LG is at odds with MOdified Newtonian Dynamics (MOND)
predictions, whereas tidal stripping can explain the observations very
well. I compare observed velocity dispersion of LG satellites with the
predicted values by MOND. The observations and MOND predictions are
inconsistent, in particular in the regime of ultra faint dwarf
galaxies.Graduat
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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