2,420 research outputs found
Media Ownership Control: To What Extent Is Competition Law And Policy Sufficient to Provide for Diversity and Plurality in the Media?
In modern economies and societies, the availability of information is central to better decision making by citizens and consumers. In most countries, citizens and consumers receive the information they need through the media, including newspapers, television radio, internet and etc. After 1990s, technological and economic developments have evolved the media sector by converging it to telecommunications and IT sectors and by leading to new interactive broadcasting services transmitted by different technologies. These developments also increased mergers and joint ventures both at global level and national level. As well as these developments, the private benefits of media have increased concentration of ownership in these sectors. There are many people who argue that concentration in media markets has a negative effect on diversity and plurality. Because of increasing concentration in media markets in recent years all over the world, many concerns as to whether competition law and policy is sufficient to ensure the diversity and pluralism in media have arisen. Competition rules can address issues of concentration, efficiency and choice and will tend to encourage dispersed ownership and new entry. However, they cannot guarantee any of it. Competition law cannot therefore provide the certainty we need that a significant number of different media voices will continue to be heard, or that prospective new entrants to the market will be able to add their voice. Moreover, it cannot directly address concerns over editorial freedom or community voice. Therefore, if competition law and policy is assessed as a whole in the context of media, it can be stated that it guarantees diversity to some extent. However, because of the objectives and criteria of competition law is an important part of regulation, it is not designed to deliver diversity and plurality in the media. Special media ownership rules exist across the world because the market alone, even regulated by competition law, is not thought to provide the best results for society and for democracy.
SDSS Absolute Magnitudes for Thin Disc Stars based on Trigonometric Parallaxes
We present a new luminosity-colour relation based on trigonometric parallaxes
for thin disc main-sequence stars in SDSS photometry. We matched stars from the
newly reduced Hipparcos catalogue with the ones taken from 2MASS All-Sky
Catalogue of Point Sources, and applied a series of constraints, i.e. relative
parallax errors (), metallicity
( dex), age ( Gyr) and surface gravity
(), and obtained a sample of thin disc main-sequence stars. Then, we
used our previous transformation equations (Bilir et al. 2008a) between SDSS
and 2MASS photometries and calibrated the absolute magnitudes to the
and colours. The transformation formulae between 2MASS
and SDSS photometries along with the absolute magnitude calibration provide
space densities for bright stars which saturate the SDSS magnitudes.Comment: 7 pages, including 7 figures and 2 tables, accepted for publication
in MNRA
Luminosity-Colours relations for thin disc main-sequence stars
In this study we present the absolute magnitude calibrations of thin disc
main-sequence stars in the optical (), and in the near-infrared
(). Thin disc stars are identified by means of Padova isochrones, and
absolute magnitudes for the sample are evaluated via the newly reduced
Hipparcos data. The obtained calibrations cover a large range of spectral
types: from A0 to M4 in the optical and from A0 to M0 in the near-infrared.
Also, we discuss the of effects binary stars and evolved stars on the absolute
magnitude calibrations. The usage of these calibrations can be extended to the
estimation of galactic model parameters for the thin disc individually, in
order to compare these parameters with the corresponding ones estimated by
statistics (which provides galactic model parameters for thin
and thick discs, and halo simultaneously) to test any degeneracy between them.
The calibrations can also be used in other astrophysical researches where
distance plays an important role in that study.Comment: 8 pages, including 12 figures and 4 tables, accepted for publication
in MNRA
Population types of cataclysmic variables in the solar neighborhood
The Galactic orbital parameters of 159 cataclysmic variables in the Solar neighbourhood are calculated, for the first time, to determine their population types using published kinematical parameters. Population analysis shows that about 6 per cent of cataclysmic variables in the sample are members of the thi
ck disc component of the Galaxy. This value is consistent with the fraction obt
ained from star count analysis. The rest of the systems in the sample are found to be in the thin disc component of the Galaxy. Our analysis revealed no halo CVs in the Solar vicinity. About 60 per cent of the thick disc CVs have orbital periods be low the orbital period gap. This result is roughly consistent with the predictions of population synthesis models developed for cataclysmic variables. A kinematical age of 13 Gyr is obtained using total space velocity dispersion of the most probable thick disc CVs which is consistent with the age of thick disc component of the Galaxy
Absolute Magnitude Calibration for Giants based on the Colour-Magnitude Diagrams of Galactic Clusters. II-Calibration with SDSS
We present an absolute magnitude calibration for red giants with the colour
magnitude diagrams of six Galactic clusters with different metallicities i.e.
M92, M13, M3, M71, NGC 6791 and NGC 2158. The combination of the absolute
magnitudes of the red giant sequences with the corresponding metallicities
provides calibration for absolute magnitude estimation for red giants for a
given colour. The calibration is defined in the colour interval
0.45 1.30 mag and it covers the metallicity interval
+0.37 dex. The absolute magnitude
residuals obtained by the application of the procedure to another set of
Galactic clusters lie in the interval mag.
However, the range of 94% of the residuals is shorter,
mag. The mean and the standard deviation of (all) residuals are 0.169 and 0.140
mag, respectively. The derived relations are applicable to stars older than 2
Gyr, the age of the youngest calibrating cluster.Comment: 12 pages, including 5 figures and 10 tables, accepted for publication
in PASA. arXiv admin note: substantial text overlap with arXiv:1204.429
New colour-transformations for the Sloan photometry and revised metallicity calibration and equations for photometric parallax estimation
We evaluated new colour-transformations for the Sloan photometry by 224
standards and used them to revise both the equations for photometric parallax
estimation and metallicity calibration cited by Karaali et al. (2003). This
process improves the metallicity and absolute magnitude estimations by
[Fe/H]<=0.3 dex and M^{H}_{g} <= 0.1 mag respectively. There is a high
correlation for metallicities and absolute magnitudes derived for two systems,
UBV and Sloan, by means of the revised calibrations.Comment: 11 pages, including 7 figures and 2 tables, accepted for publication
in PAS
Estimation of Galactic Model Parameters and Metalicity Distribution in Intermediate Latitudes with SDSS
We estimated the galactic model parameters for a set of 20
intermediate-latitude fields with galactic longitudes 0<l<100 and 160<l<240,
included in the currently available Data Release 6 (DR6) of SDSS, to explore
their possible variation with galactic longitude. The local space densities of
the thick disc and halo are almost the same for all fields,
=6.52% and =0.35%, respectively, a result
different than the one cited for high-latitude fields. The thin disc's
scaleheight is 325 pc in the galactic centre changes to 369 pc in the third
quadrant, which confirms the existence of disc flare, whereas the thick disc
scaleheight is as large as 952 pc at galactic longitude l=20 and 10% lower at
l=160, which confirms the existence of the disc long bar in the direction l=27.
Finally, the variation of the axis ratio of the halo with galactic longitude is
almost flat, =0.56, except a slight minimum and a small maximum in the
second and third quadrants, respectively, indicating an effect of the long bar
which seems plausible for a shallow halo. We estimated the metallicities of
unevolved G-type stars and discussed the metallicity gradient for different
vertical distances. The metallicity gradient is d[M/H]/dz=-0.30 dex kpc
for short distances, confirming the formation of this region of the Galaxy by
dissipational collapse. However, its change is steeper in the transition
regions of different galactic components. The metallicity gradient is almost
zero for inner halo (5<z<10 kpc), indicating a formation of merger or accretion
of numerous fragments such as dwarf galaxies.Comment: 31 pages, 18 figures and 4 tables, accepted for publication in New
Astronom
Spatial distribution and galactic model parameters of cataclysmic variables
The spatial distribution, galactic model parameters and luminosity function
of cataclysmic variables (CVs) in the solar neighbourhood have been determined
from a carefully established sample of 459 CVs. The sample contains all of the
CVs with distances computed from the Period-Luminosity-Colours (PLCs) relation
of CVs which has been recently derived and calibrated with {\em 2MASS}
photometric data. It has been found that an exponential function fits best to
the observational z-distributions of all of the CVs in the sample, non-magnetic
CVs and dwarf novae, while the sech^{2} function is more appropriate for
nova-like stars and polars. The vertical scaleheight of CVs is 15814 pc
for the {\em 2MASS} J-band limiting apparent magnitude of 15.8. On the other
hand, the vertical scaleheights are 12820 and 1605 pc for dwarf novae
and nova-like stars, respectively. The local space density of CVs is found to
be pc^{-3} which is in agreement with the lower limit of
the theoretical predictions. The luminosity function of CVs shows an increasing
trend toward higher space densities at low luminosities, implying that the
number of short-period systems should be high. The discrepancies between the
theoretical and observational population studies of CVs will almost disappear
if for the z-dependence of the space density the sech^{2} density function is
used.Comment: 29 pages, 9 figures and 5 tables, accepted for publication in New
Astronom
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