24,286 research outputs found
Public health and landfill sites
Landfill management is a complex discipline, requiring very high levels of organisation, and considerable investment. Until the early 1990’s most Irish landfill sites were not managed to modern standards. Illegal landfill sites are,
of course, usually not managed at all. Landfills are very active. The traditional idea of ‘put it in the ground and forget about it’ is entirely misleading. There is a lot of chemical and biological activity underground. This produces complex changes in the chemistry of the landfill, and of the emissions from the site.
The main emissions of concern are landfill gases and contaminated water (which is known as leachate). Both of these emissions have complex and changing chemical compositions, and both depend critically on what has been
put into the landfill. The gases spread mainly through the atmosphere, but also through the soil, while the leachate (the water) spreads through surface waters and the local groundwater. Essentially all unmanaged landfills will discharge large volumes of leachate into the local groundwater. In sites where the waste accepted has been
properly regulated, and where no hazardous wastes are present, there is a lot known about the likely composition of this leachate and there is some knowledge of its likely biological and health effects. This is not the case for
poorly regulated sites, where the composition of the waste accepted is unknown.
It is possible to monitor the emissions from landfills, and to reduce some of the adverse health and environmental effects of these. These emissions, and hence the possible health effects, depend greatly on the content of the landfill, and on the details of the local geology and landscape.
There is insufficient evidence to demonstrate a clear link between cancers
and exposure to landfill, however, it is noted that there may be an association
with adverse birth outcomes such as low birth weight and birth defects. It
should be noted, however, that modern landfills, run in strict accordance with
standard operation procedures, would have much less impact on the health of
residents living in proximity to the site
Destruction of Interstellar Dust in Evolving Supernova Remnant Shock Waves
Supernova generated shock waves are responsible for most of the destruction
of dust grains in the interstellar medium (ISM). Calculations of the dust
destruction timescale have so far been carried out using plane parallel steady
shocks, however that approximation breaks down when the destruction timescale
becomes longer than that for the evolution of the supernova remnant (SNR)
shock. In this paper we present new calculations of grain destruction in
evolving, radiative SNRs. To facilitate comparison with the previous study by
Jones et al. (1996), we adopt the same dust properties as in that paper. We
find that the efficiencies of grain destruction are most divergent from those
for a steady shock when the thermal history of a shocked gas parcel in the SNR
differs significantly from that behind a steady shock. This occurs in shocks
with velocities >~ 200 km/s for which the remnant is just beginning to go
radiative. Assuming SNRs evolve in a warm phase dominated ISM, we find dust
destruction timescales are increased by a factor of ~2 compared to those of
Jones et al. (1996), who assumed a hot gas dominated ISM. Recent estimates of
supernova rates and ISM mass lead to another factor of ~3 increase in the
destruction timescales, resulting in a silicate grain destruction timescale of
~2-3 Gyr. These increases, while not able resolve the problem of the discrepant
timescales for silicate grain destruction and creation, are an important step
towards understanding the origin, and evolution of dust in the ISM.Comment: 30 pages, 8 figures, accepted for publication in the Astrophysical
Journa
‘Dominant ethnicity’ and the ‘ethnic-civic’ dichotomy in the work of A. D. Smith
This article considers the way in which the work of Anthony Smith has helped to structure debates surrounding the role of ethnicity in present-day nations. Two major lines of enquiry are evident here. First, the contemporary role of dominant ethnic groups within 'their' nations and second, the interplay between ethnic and civic elements in nationalist argument. The two processes are related, but maintain elements of distinctiveness. Smith's major contribution to the dominant ethnicity debate has been to disembed ethnicity from the ideologically-charged and/or anglo-centric discourse of ethnic relations and to place it in historical context, thereby opening up space for dominant group ethnicity to be considered as a distinct phenomenon. This said, Smith's work does not adequately account for the vicissitudes of dominant ethnicity in the contemporary West. Building on the classical works of Hans Kohn and Friedrich Meinecke, Anthony Smith has also made a seminal contribution to the debate on civic and ethnic forms of national identity and nationalist ideology. As well as freeing this debate from the strong normative overtones which it has often carried, he has continued to insist that the terms civic and ethnic should be treated as an ideal-typical distinction rather than a scheme of classification
Near-Optimal Evasion of Convex-Inducing Classifiers
Classifiers are often used to detect miscreant activities. We study how an
adversary can efficiently query a classifier to elicit information that allows
the adversary to evade detection at near-minimal cost. We generalize results of
Lowd and Meek (2005) to convex-inducing classifiers. We present algorithms that
construct undetected instances of near-minimal cost using only polynomially
many queries in the dimension of the space and without reverse engineering the
decision boundary.Comment: 8 pages; to appear at AISTATS'201
Multi-photon effects in energy losses spectra
Effect of radiation of many photons by a single electron traversing a target
is discussed. When the summary energy of emitted photons (the energy losses
spectrum) is measured only, the photon spectrum is distorted comparing with the
photon spectrum in one interaction. Influence of this effect is discussed for
the cases (1) bremsstrahlung (described by Bethe-Heitler formula), (2) the
strong Landau-Pomeranchuk-Migdal effect and (3) transition radiation.
Qualitative picture of the phenomenon is discussed in detail. Comparison with
the recent SLAC experiment in relatively thick target (2.7% of the radiation
length), where the effect of emission of many photons by a projectile is very
essential, shows perfect agreement of the theory and data.Comment: LaTeX2.09, 19 pages, 5 PostScript figure
A uvbyCaHbeta CCD Analysis of the Open Cluster Standard, NGC 752
Precision uvbyCaHbeta photometry of the nearby old open cluster, NGC 752, is
presented. The mosaic of CCD fields covers an area ~42' on a side with internal
precision at the 0.005 to 0.010 mag level for the majority of stars down to
V~15. The CCD photometry is tied to the standard system using an extensive set
of published photoelectric observations adopted as secondary standards within
the cluster. Multicolor indices are used to eliminate as nonmembers a large
fraction of the low probability proper-motion members near the faint end of the
main sequence, while identifying 24 potential dwarf members between V=15.0 and
16.5, eight of which have been noted before from Vilnius photometry. From 68
highly probable F dwarf members, we derive a reddening estimate of E(b-y)=
0.025 +/- 0.003 (E(B-V) = 0.034 +/- 0.004), where the error includes the
internal photometric uncertainty and the systematic error arising from the
choice of the standard (b-y), Hbeta relation. With reddening fixed, [Fe/H] is
derived from the F dwarf members using both m_1 and hk, leading to [Fe/H] =
-0.071 +/-0.014 (sem) and -0.017 +/- 0.008 (sem), respectively. Taking the
internal precision and possible systematics in the standard relations into
account, [Fe/H] for NGC 752 becomes -0.03 +/-0.02. With the reddening and
metallicity defined, we use the Victoria-Regina isochrones on the Stromgren
system and find an excellent match for (m-M) = 8.30 +/- 0.05 and an age of 1.45
+/- 0.05 Gyr at the appropriate metallicity.Comment: 37 pages, 11 figures, 4 tables. Accepted to Astronomical Journa
- …