560 research outputs found
Twitter, YouTube, and Flickr as platforms of alternative journalism: the social media account of the 2010 Toronto G20 protests
This article examines the appropriation of social media as platforms of alternative journalism by the protestors of the 2010 G20 summit in Toronto, Canada. The Toronto Community Mobilization Network, the network that coordinated the protests, urged participants to broadcast news using Twitter, YouTube, and Flickr. This particular use of social media is studied in the light of the history and theory of alternative journalism. Analyzing a set of 11,556 tweets, 222 videos, and 3,338 photos, the article assesses user participation in social media protest reporting, as well as the resulting protest accounts. The findings suggest that social media did not facilitate the crowd-sourcing of alternative reporting, except to some extent for Twitter. As with many previous alternative journalistic efforts, reporting was dominated by a relatively small number of users. In turn, the resulting account itself had a strong event-oriented focus, mirroring often-criticized mainstream protest reporting practices
The magnetic Bp star 36 Lyncis, I. Magnetic and photospheric properties
This paper reports the photospheric, magnetic and circumstellar gas
characteristics of the magnetic B8p star 36 Lyncis (HD 79158). Using archival
data and new polarised and unpolarised high-resolution spectra, we redetermine
the basic physical properties, the rotational period and the geometry of the
magnetic field, and the photospheric abundances of various elements.}{Based on
magnetic and spectroscopic measurements, we infer an improved rotational period
of d. We determine a current epoch of the longitudinal
magnetic field positive extremum (HJD 2452246.033), and provide constraints on
the geometry of the dipole magnetic field (i\geq 56\degr, G, unconstrained). We redetermine the effective
temperature and surface gravity using the optical and UV energy distributions,
optical photometry and Balmer line profiles ( K,
), and based on the Hipparcos parallax we redetermine the
luminosity, mass, radius and true rotational speed ( \kms). We
measure photospheric abundances for 21 elements using optical and UV spectra,
and constrain the presence of vertical stratification of these elements. We
perform preliminary Doppler Imaging of the surface distribution of Fe, finding
that Fe is distributed in a patchy belt near the rotational equator. Most
remarkably, we confirm strong variations of the H line core which we
interpret as due to occultations of the star by magnetically-confined
circumstellar gas.Comment: Accepted by Astronomy and Astrophysic
A cryogenic liquid-mirror telescope on the moon to study the early universe
We have studied the feasibility and scientific potential of zenith observing
liquid mirror telescopes having 20 to 100 m diameters located on the moon. They
would carry out deep infrared surveys to study the distant universe and follow
up discoveries made with the 6 m James Webb Space Telescope (JWST), with more
detailed images and spectroscopic studies. They could detect objects 100 times
fainter than JWST, observing the first, high-red shift stars in the early
universe and their assembly into galaxies. We explored the scientific
opportunities, key technologies and optimum location of such telescopes. We
have demonstrated critical technologies. For example, the primary mirror would
necessitate a high-reflectivity liquid that does not evaporate in the lunar
vacuum and remains liquid at less than 100K: We have made a crucial
demonstration by successfully coating an ionic liquid that has negligible vapor
pressure. We also successfully experimented with a liquid mirror spinning on a
superconducting bearing, as will be needed for the cryogenic, vacuum
environment of the telescope. We have investigated issues related to lunar
locations, concluding that locations within a few km of a pole are ideal for
deep sky cover and long integration times. We have located ridges and crater
rims within 0.5 degrees of the North Pole that are illuminated for at least
some sun angles during lunar winter, providing power and temperature control.
We also have identified potential problems, like lunar dust. Issues raised by
our preliminary study demand additional in-depth analyses. These issues must be
fully examined as part of a scientific debate we hope to start with the present
article.Comment: 35 pages, 11 figures. To appear in Astrophysical Journal June 20 200
Zebrafish as an alternative animal model in human and animal vaccination research
Much of medical research relies on animal models to deepen knowledge of the causes of animal and human diseases, as well as to enable the development of innovative therapies. Despite rodents being the most widely used research model worldwide, in recent decades, the use of the zebrafish (Danio rerio) model has exponentially been adopted among the scientific community. This is because such a small tropical freshwater teleost fish has crucial genetic, anatomical and physiological homology with mammals. Therefore, zebrafish constitutes an excellent experimental model for behavioral, genetic and toxicological studies which unravels the mechanism of various human diseases. Furthermore, it serves well to test new therapeutic agents, such as the safety of new vaccines. The aim of this review was to provide a systematic literature review on the most recent studies carried out on the topic. It presents numerous advantages of this type of animal model in tests of efficacy and safety of both animal and human vaccines, thus highlighting gains in time and cost reduction of research and analyzes
Modelling the light variability of the Ap star epsilon Ursae Majoris
We simulate the light variability of the Ap star epsUMa using the observed
surface distributions of Fe, Cr, Ca, Mn, Mg, Sr and Ti obtained with the help
of Doppler Imaging technique. Using all photometric data available we specified
light variations of epsUMa modulated by its rotation from far UV to IR. We
employed the LLmodels stellar model atmosphere code to predict the light
variability in different photometric systems. The rotational period of epsUMa
is refined to 5d088631(18). It is shown that the observed light variability can
be explained as a result of the redistribution of radiative flux from the UV
spectral region to the visual caused by the inhomogeneous surface distribution
of chemical elements. Among seven mapped elements, only Fe and Cr significantly
contribute to the amplitude of the observed light variability. In general, we
find a very good agreement between theory and observations. We confirm the
important role of Fe and Cr to the magnitude of the well-known depression
around 5200 \AA\ through the analysis of the peculiar -parameter. Finally,
we show that the abundance spots of considered elements cannot explain the
observed variability in near UV and index which are likely due to some
other causes. The inhomogeneous surface distribution of chemical elements can
explain most of the observed light variability of the A-type CP star epsUMa.Comment: Accepted in A&A, 10 pages, 9 figures, 3 table
First HARPSpol discoveries of magnetic fields in massive stars
In the framework of the Magnetism in Massive Stars (MiMeS) project, a
HARPSpol Large Program at the 3.6m-ESO telescope has recently started to
collect high-resolution spectropolarimetric data of a large number of Southern
massive OB stars in the field of the Galaxy and in many young clusters and
associations. In this Letter, we report on the first discoveries of magnetic
fields in two massive stars with HARPSpol - HD 130807 and HD 122451, and
confirm the presence of a magnetic field at the surface of HD 105382 that was
previously observed with a low spectral resolution device. The longitudinal
magnetic field measurements are strongly varying for HD 130807 from -100
G to 700 G. Those of HD 122451 and HD 105382 are less variable with
values ranging from -40 to -80 G, and from -300 to -600 G,
respectively. The discovery and confirmation of three new magnetic massive
stars, including at least two He-weak stars, is an important contribution to
one of the MiMeS objectives: the understanding of origin of magnetic fields in
massive stars and their impacts on stellar structure and evolution.Comment: 4 pages, 2 figures, accepted for publication in A&A Lette
Characterisation of the magnetic field of the Herbig Be star HD 200775
After our recent discovery of four magnetic Herbig stars, we have decided to
study in detail one of them, HD 200775, to determine if its magnetic topology
is similar to that of the main sequence magnetic stars. With this aim, we
monitored this star in Stokes I and V over more than two years, using the new
spectropolarimeters ESPaDOnS at CFHT, and Narval at TBL. Using our data, we
find that HD 200775 is a double-lined spectroscopic binary system, whose
secondary seems similar, in temperature, to the primary. We determine the
luminosity ratio of the system, and using the luminosity of the system found in
literature, we derive the luminosity of both stars. From our measurements of
the radial velocities of both stars we determine the ephemeris and the orbital
parameters of the system. We have fitted 30 Stokes V profiles simultaneously,
using a chi2 minimisation method, with a decentered-dipole model. The best-fit
model provides a rotation period of 4.3281 d an inclination angle of 60
degrees, and a magnetic obliquity angle of 125 degrees. The polar strength of
the magnetic dipole field is 1000 G, which is decentered by 0.05 R* from the
center of the star. The derived magnetic field model is qualitatively identical
to those commonly observed in the Ap/Bp stars, which bring strong argument in
favour of the fossil field hypothesis, to explain the origin of the magnetic
fields in the main sequence Ap/Bp stars. Our determination of the inclination
of the rotation axis leads to a radius of the primary which is smaller than
that derived from the HR diagram position. This can be explained by a larger
intrinsic luminosity of the secondary relative to the primary, due to a larger
circumstellar extinction of the secondary relative to the primary.Comment: Accepted for publication in MNRAS, 14 pages, 10 figure
Stellar evolution of massive stars with a radiative alpha-omega dynamo
Models of rotationally-driven dynamos in stellar radiative zones have
suggested that magnetohydrodynamic transport of angular momentum and chemical
composition can dominate over the otherwise purely hydrodynamic processes. A
proper consideration of the interaction between rotation and magnetic fields is
therefore essential. Previous studies have focused on a magnetic model where
the magnetic field strength is derived as a function of the stellar structure
and angular momentum distribution. We have adapted our one-dimensional stellar
rotation code, RoSE, to model the poloidal and toroidal magnetic field
strengths with a pair of time-dependent advection-diffusion equations coupled
to the equations for the evolution of the angular momentum distribution and
stellar structure. This produces a much more complete, though still reasonably
simple, model for the magnetic field evolution. Our model reproduces well
observed surface nitrogen enrichment of massive stars in the Large Magellanic
Cloud. In particular it reproduces a population of slowly-rotating
nitrogen-enriched stars that cannot be explained by rotational mixing alone
alongside the traditional rotationlly-enriched stars. The model further
predicts a strong mass-dependency for the dynamo-driven field. Above a
threshold mass, the strength of the magnetic dynamo decreases abruptly and so
we predict that more massive stars are much less likely to support a
dynamo-driven field than less massive stars.Comment: Accepted for publication in MNRAS. 15 pages, 13 figure
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