5,981 research outputs found
Molecular Hydrogen Emission from Protoplanetary Disks
We have modeled self-consistently the density and temperature profiles of gas
and dust in protoplanetary disks, taking into account irradiation from a
central star. Making use of this physical structure, we have calculated the
level populations of molecular hydrogen and the line emission from the disks.
As a result, we can reproduce the observed strong line spectra of molecular
hydrogen from protoplanetary disks, both in the ultraviolet (UV) and the
near-infrared, but only if the central star has a strong UV excess radiation.Comment: 19 pages, accepted for publication in Astronomy and Astrophysic
National and Regional Estimates of the Prevalence of Opiate and/or Crack Cocaine use 2008-09: A summary of key findings
<p>This report summarises the results of a follow-up study
to a three year project to estimate the prevalence of
‘problem drug use’ (defined as use of opiates and/or
crack cocaine) nationally (England only), regionally and
locally. The follow-up was carried out two years after the
final sweep of the original project, so could therefore
be considered as ‘sweep 5’. An overview of the national
and regional estimates are presented in this report, as are
comparisons with the estimates produced by the third
(2006-07) sweep of the study. Estimates for 2007-08 are
not available as a study was not commissioned for that
year.</p>
<p>Information about the number of people who use illicit
drugs such as heroin, other opiates or crack cocaine
is key to formulating effective policies for tackling
drug-related harm as these drugs are associated with
the highest levels of harm. It also helps inform service
provision at the local level and provides a context
in which to understand the population impact of
interventions to reduce drug-related harm.</p>
<p>Direct enumeration of those engaged in a largely covert
activity such as the use of class A drugs is difficult
and standard household survey techniques tend to
underestimate the extent of such activity. Indirect
techniques making use of various data sources offer a
more reliable way of calculating prevalence estimates for
the use of opiates and/or crack cocaine. The estimates
presented in this report are derived using two indirect
measurement techniques: the capture-recapture
method (CRC ); and the multiple indicator (MIM ) method.
These methods are described in detail in Hay et al., 2006
and Hay et al., 2007a. Methodological developments
throughout the course of the previous three sweeps are
discussed elsewhere (Hay et al., 2007b, Hay et al., 2008).
The individuals covered by this study were people aged
15 to 64 and resident in each DAT area, and known to
be using heroin, methadone, other opiate drugs or
crack cocaine.</p>
Chemistry in AGB stars: successes and challenges
Emission and absorption line observations of molecules in late-type stars are
a vital component in our understanding of stellar evolution, dust formation and
mass loss in these objects. The molecular composition of the gas in the
circumstellar envelopes of AGB stars reflects chemical processes in gas whose
properties are strong functions of radius with density and temperature varying
by more than ten and two orders of magnitude, respectively. In addition, the
interstellar UV field plays a critical role in determining not only molecular
abundances but also their radial distributions. In this article, I shall
briefly review some recent successful approaches to describing chemistry in
both the inner and outer envelopes and outline areas of challenge for the
future.Comment: To appear in the refereed proceedings of the 11th Pacific Rim
Conference on Stellar Astrophysics held in Hong Kong, Dec.14-17, 2015, Sun
Kwok (editor). 10 pages, 2 figure
Recommended from our members
CCH <i>N</i> = 4-3 emission from dense interstellar clouds
The authors have searched for N = 4 - 3 rotational line emission from the ethynyl radical CCH, at 349 GHz toward a number of galactic molecular clouds. They have detected emission from ten giant molecular clouds and have derived CCH column densities on the order of 1014 - 1015cm-2. They find that CCH emission arises from dense gas, n(H2) ~ 104 - 105cm-3, but not from very dense material, n(H2) > 106cm-3, nor from hot gas such as the "hot core" region in Orion
Supporting security-oriented, collaborative nanoCMOS electronics research
Grid technologies support collaborative e-Research typified by multiple institutions and resources seamlessly shared to tackle common research problems. The rules for collaboration and resource sharing are commonly achieved through establishment and management of virtual organizations (VOs) where policies on access and usage of resources by collaborators are defined and enforced by sites involved in the collaboration. The expression and enforcement of these rules is made through access control systems where roles/privileges are defined and associated with individuals as digitally signed attribute certificates which collaborating sites then use to authorize access to resources. Key to this approach is that the roles are assigned to the right individuals in the VO; the attribute certificates are only presented to the appropriate resources in the VO; it is transparent to the end user researchers, and finally that it is manageable for resource providers and administrators in the collaboration. In this paper, we present a security model and implementation improving the overall usability and security of resources used in Grid-based e-Research collaborations through exploitation of the Internet2 Shibboleth technology. This is explored in the context of a major new security focused project at the National e-Science Centre (NeSC) at the University of Glasgow in the nanoCMOS electronics domain
Sulphur-bearing molecules in AGB stars I: The occurrence of hydrogen sulfide
Through a survey of (sub-)millimetre emission lines of various
sulphur-bearing molecules, we aim to determine which molecules are the primary
carriers of sulphur in different types of AGB stars. In this paper, the first
in a series, we investigate the occurrence of HS in AGB circumstellar
envelopes and determine its abundance, where possible. We have surveyed 20 AGB
stars with a range of mass-loss rates and of different chemical types using the
APEX telescope to search for rotational transition lines of five key
sulphur-bearing molecules: CS, SiS, SO, SO and HS. Here we present our
results for HS, including detections, non-detections and detailed radiative
transfer modelling of the detected lines. We compare results based on different
descriptions of the molecular excitation of HS and different abundance
distributions, including those derived from chemical modelling results. We
detected HS towards five AGB stars, all of which have high mass-loss rates
of yr and are oxygen-rich. HS
was not detected towards the carbon or S-type stars that fall in a similar
mass-loss range. For the stars in our sample with detections, we find peak
o-HS abundances relative to H between and . Overall, we conclude that HS can play a significant role in
oxygen-rich AGB stars with higher mass-loss rates, but is unlikely to play a
key role in stars of other chemical types or the lower mass-loss rate
oxygen-rich stars. For two sources, V1300 Aql and GX Mon, HS is most likely
the dominant sulphur-bearing molecule in the circumstellar envelope.Comment: 14 pages, 7 figures, accepted in A&
Large scale grain mantle disruption in the Galactic Center
We present observations of C2H5OH toward molecular clouds in Sgr A, Sgr B2
and associated with thermal and non-thermal features in the Galactic center.
C2H5OH emission in Sgr A and Sgr B2 is widespread, but not uniform. C2H5OH
emission is much weaker or it is not detected in some molecular clouds in both
complexes, in particular those with radial velocities between 70 and 120 km/s.
While most of the clouds associated with the thermal features do not show
C2H5OH emission, that associated with the Non-Thermal Radio Arc shows emission.
The fractional abundance of C2H5OH in most of the clouds with radial velocities
between 0 and 70 km/s in Sgr A and Sgr B2 is relatively high, of few 1e-8. The
C2H5OH abundance decreases by more than one order of magnitude (aprox. 1e-9) in
the clouds associated with the thermal features. The large abundance of C2H5OH
in the gas-phase indicates that C2H5OH has formed in grains and released to
gas-phase by shocks in the last aprox. 1e5 years.Comment: In press in Astrophysical Journal Letters 7 pages, 1 table, 1 figur
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