34,224 research outputs found
Road-traffic pollution and asthma – using modelled exposure assessment for routine public health surveillance
Asthma is a common disease and appears to be increasing in prevalence. There is evidence linking air pollution, including that from road-traffic, with asthma. Road traffic is also on the increase. Routine surveillance of the impact of road-traffic pollution on asthma, and other diseases, would be useful in informing local and national government policy in terms of managing the environmental health risk.
Several methods for exposure assessment have been used in studies examining the association between asthma and road traffic pollution. These include comparing asthma prevalence in areas designated as high and low pollution areas, using distance from main roads as a proxy for exposure to road traffic pollution, using traffic counts to estimate exposure, using vehicular miles travelled and using modelling techniques. Although there are limitations to all these methods, the modelling approach has the advantage of incorporating several variables and may be used for prospective health impact assessment.
The modelling approach is already in routine use in the United Kingdom in support of the government's strategy for air quality management. Combining information from such models with routinely collected health data would form the basis of a routine public health surveillance system. Such a system would facilitate prospective health impact assessment, enabling policy decisions concerned with road-traffic to be made with knowledge of the potential implications. It would also allow systematic monitoring of the health impacts when the policy decisions and plans have been implemented
On the accretion origin of a vast extended stellar disk around the Andromeda galaxy
We present the discovery of an inhomogenous, low-surface brightness, extended
disk-like structure around the Andromeda galaxy (M31) based on a large
kinematic survey of more than 2800 stars with the Keck/DEIMOS spectrograph. The
stellar structure spans radii from 15 kpc out to ~40 kpc, with detections out
to R ~ 70 kpc. The constituent stars lag the expected velocity of circular
orbits in the plane of the M31 disk by ~40 kms and have a velocity dispersion
of ~30 kms. The color range on the upper RGB shows a large spread indicative of
a population with a significant range of metallicity. The mean metallicity of
the population, measured from Ca II equivalent widths, is [Fe/H] = -0.9 +/-
0.2. The morphology of the structure is irregular at large radii, and shows a
wealth of substructures which must be transitory in nature, and are almost
certainly tidal debris. The presence of these substructures indicates that the
global entity was formed by accretion. This extended disk follows smoothly on
from the central parts of M31 disk with an exponential density law of
scale-length of 5.1 +/- 0.1 kpc, similar to that of the bright inner disk. The
population possesses similar kinematic and abundance properties over the entire
region where it is detected in the survey. We estimate that the structure
accounts for approximately 10% of the total luminosity of the M31 disk, and
given the huge scale, contains ~30% of the total disk angular momentum. This
finding indicates that at least some galactic stellar disks are vastly larger
than previously thought and are formed, at least in their outer regions,
primarily by accretion. [abridged]Comment: 20 pages, 30 figures, ApJ submitte
Theoretical calculations and instrument development and test characterization of low intensity X-ray imaging devices
The characteristics of the Lixiscope when excited by X-rays produced by conventional electrically powered X-ray generators are explored to determine the optimum X-ray spectrum and mode of operation of the generator, which yields satisfactory Lixiscope images of medical and industrial specimens
Tidal Remnants and Intergalactic HII Regions
We report the discovery of two small intergalactic HII regions in the loose
group of galaxies around the field elliptical NGC 1490. The HII regions are
located at least 100 kpc from any optical galaxy but are associated with a
number of large HI clouds that are lying along an arc 500 kpc in length and
that have no optical counterpart on the Digital Sky Survey. The sum of the HI
masses of the clouds is almost 10^10 M_sun and the largest HI cloud is about
100 kpc in size. Deep optical imaging reveals a very low surface brightness
counterpart to this largest HI cloud, making this one of the HI richest optical
galaxies known (M_HI/L_V~200). Spectroscopy of the HII regions indicates that
the abundance in these HII regions is only slightly sub-solar, excluding a
primordial origin of the HI clouds. The HI clouds are perhaps remnants
resulting from the tidal disruption of a reasonably sized galaxy, probably
quite some time ago, by the loose group to which NGC1490 belongs.
Alternatively, they are remnants of the merger that created the field
elliptical NGC1490. The isolated HII regions show that star formation on a very
small scale can occur in intergalactic space in gas drawn from galaxies by
tidal interactions. Many such intergalactic small star formation regions may
exist near tidally interacting galaxies.Comment: To appear in the proceedings of the IAU Symposium #217, Recycling
Intergalactic and Interstellar Matter, eds. P.-A. Duc, J. Braine, and E.
Brinks, 6 pages with low resolution figures. The full paper with high
resolution images can be downloaded from
http://www.astron.nl/~morganti/Papers/cloud.ps.g
A Minor Axis Surface Brightness Profile for M31
We use data from the Isaac Newton Telescope Wide Field Camera survey of M31
to determine the surface brightness profile of M31 along the south-east minor
axis. We combine surface photometry and faint red giant branch star counts to
trace the profile from the innermost regions out to a projected radius of 4
degrees (~55 kpc) where the V-band surface brightness is 32 mag per square
arcsec; this is the first time the M31 minor axis profile has been mapped over
such a large radial distance using a single dataset. We confirm the finding by
Pritchet & van den Bergh (1994) that the minor axis profile can be described by
a single de Vaucouleurs law out to a projected radius of 1.4 degrees or ~20
kpc. Beyond this, the surface brightness profile flattens considerably and is
consistent with either a power-law of index -2.3 or an exponential of
scalelength 14 kpc. The fraction of the total M31 luminosity contained in this
component is ~2.5%. While it is tempting to associate this outer component with
a true Population II halo in M31, we find that the mean colour of the stellar
population remains approximately constant at V-i~1.6 from 0.5-3.5 degrees along
the minor axis. This result suggests that the same metal-rich stellar
population dominates both structural components.Comment: 11 pages, 3 figures, ApJ Letters in press, extremely minor
modification
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