2,280 research outputs found
The abundance of HCN in circumstellar envelopes of AGB stars of different chemical types
A multi-transition survey of HCN (sub-) millimeter line emission from a large
sample of AGB stars of different chemical type is presented. The data are
analysed and circumstellar HCN abundances are estimated. The sample stars span
a large range of properties such as mass-loss rate and photospheric C/O-ratio.
The analysis of the new data allows for more accurate estimates of the
circumstellar HCN abundances and puts new constraints on chemical models. In
order to constrain the circumstellar HCN abundance distribution a detailed
non-LTE excitation analysis, based on the Monte Carlo method, is performed.
Effects of line overlaps and radiative excitation from dust grains are
included. The median values for the derived abundances of HCN (with respect to
H2) are 3x10-5, 7x10-7 and 10-7 for carbon stars (25 stars), S-type AGB stars
(19 stars) and M-type AGB stars (25 stars), respectively. The estimated sizes
of the HCN envelopes are similar to those obtained in the case of SiO for the
same sample of sources and agree well with previous results from
interferometric observations, when these are available. We find that there is a
clear dependence of the derived circumstellar HCN abundance on the C/O-ratio of
the star, in that carbon stars have about two orders of magnitude higher
abundances than M-type AGB stars, on average. The derived HCN abundances of the
S-type AGB stars have a larger spread and typically fall in between those of
the two other types, however, slightly closer to the values for the M-type AGB
stars. For the M-type stars, the estimated abundances are much higher than what
would be expected if HCN is formed in thermal equilibrium. However, the results
are also in contrast to predictions from recent non-LTE chemical models, where
very little difference is expected in the HCN abundances between the various
types of AGB stars.Comment: Accepted for publication in A&
The proper motion of the Arches cluster with Keck Laser-Guide Star Adaptive Optics
We present the first measurement of the proper motion of the young, compact
Arches cluster near the Galactic center from near-infrared adaptive optics (AO)
data taken with the recently commissioned laser-guide star (LGS) at the Keck
10-m telescope. The excellent astrometric accuracy achieved with LGS-AO
provides the basis for a detailed comparison with VLT/NAOS-CONICA data taken
4.3 years earlier. Over the 4.3 year baseline, a spatial displacement of the
Arches cluster with respect to the field population is measured to be 24.0 +/-
2.2 mas, corresponding to a proper motion of 5.6 +/- 0.5 mas/yr or 212 +/- 29
km/s at a distance of 8 kpc. In combination with the known line-of-sight
velocity of the cluster, we derive a 3D space motion of 232 +/- 30 km/s of the
Arches relative to the field. The large proper motion of the Arches cannot be
explained with any of the closed orbital families observed in gas clouds in the
bar potential of the inner Galaxy, but would be consistent with the Arches
being on a transitional trajectory from x1 to x2 orbits. We investigate a
cloud-cloud collision as the possible origin for the Arches cluster. The
integration of the cluster orbit in the potential of the inner Galaxy suggests
that the cluster passes within 10 pc of the supermassive black hole only if its
true GC distance is very close to its projected distance. A contribution of
young stars from the Arches cluster to the young stellar population in the
inner few parsecs of the GC thus appears increasingly unlikely. The measurement
of the 3D velocity and orbital analysis provides the first observational
evidence that Arches-like clusters do not spiral into the GC. This confirms
that no progenitor clusters to the nuclear cluster are observed at the present
epoch.Comment: 22 pdflatex pages including 12 figures, reviewed version accepted by
Ap
G359.87+0.18: An FR II Radio Galaxy 15 Arcminutes from Sgr A*. Implications for the Scattering Region in the Galactic Center
G359.87+0.18 is an enigmatic object located 15' from Sgr A*. It has been
variously classified as an extragalactic source, Galactic jet source, and young
supernova remnant. We present new observations of G359.87+0.18 between 0.33 and
15 GHz and use these to argue that this source is an Faranoff-Riley II radio
galaxy. We are able to place a crude limit on its redshift of z > 0.1. The
source has a spectral index \alpha < -1 (S \propto \nu^\alpha), suggestive of a
radio galaxy with a redshift z >~ 2.
The scattering diameters of Sgr A* and several nearby OH masers (~ 1" at 1
GHz) indicate that a region of enhanced scattering is along the line of sight
to the Galactic center. If the region covers the Galactic center uniformly, the
implied diameter for a background source is at least 600" at 0.33 GHz, in
contrast with the observed 20" diameter of G359.87+0.18. Using the scattering
diameter of a nearby OH maser OH 359.762+0.120 and the widths of two, nearby,
non-thermal threads, G0.08+0.15 and G359.79+0.17, we show that a uniform
scattering region should cover G359.87+0.18. We therefore conclude that the
Galactic center scattering region is inhomogeneous on a scale of 5' (~ 10 pc at
a distance of 8.5 kpc). This scale is comparable to the size scale of molecular
clouds in the Galactic center. The close agreement between these two lengths
scales is an indication that the scattering region is linked intimately to the
Galactic center molecular clouds.Comment: Accepted for publication in the ApJ, vol. 515, LaTeX2e manuscript
using aaspp4 macro, 19 pages, 8 figures in 11 PostScript file
The role of the novel D2/β2-agonist, Viozan™ (sibenadet HCl), in the treatment of symptoms of chronic obstructive pulmonary disease: results of a large-scale clinical investigation
AbstractViozan™ (sibenadet HCl, AR-C68397AA) is a novel dual D2 dopamine receptor, β2-adrenoceptor agonist, developed specifically to treat the key symptoms of chronic obstructive pulmonary disease (COPD), breathlessness, cough and sputum. The dual sensory nerve modulation and bronchodilator effects of sibenadet have been demonstrated in initial dose-ranging studies of patients with COPD and large-scale clinical evaluation has now been completed. Sibenadet efficacy was determined by assessing symptomatic changes, as defined by the novel assessment tool, the Breathlessness, Cough and Sputum Scale (BCSS©). The findings of two placebo-controlled studies are reported.These multicentre, double-blind, placebo-controlled studies recruited over 2000 patients with stable COPD, randomized to receive sibenadet (500 μg) or placebo, pressurized metered-dose inhaler (pMDI) (three times daily) for a period of 12 or 26 weeks. Diary cards were completed daily by patients throughout the study to record BCSS scores, peak expiratory flow (PEF), study drug and rescue bronchodilator usage, changes in concomitant medication and adverse events. The primary endpoints were defined as change from baseline to the final 4 weeks of the treatment period in mean BCSS total score, and forced expiratory volume in one second (FEV1) measured 1 hour after administration of the final dose of study drug and expressed as a percentage of the predicted FEV1. In addition, clinic assessments were made to determine changes in pulmonary function, health-related quality of life, perception of treatment efficacy and adverse events.Despite initial improvements in mean daily BCSS total scores in patients receiving sibenadet, the difference in the change from baseline to the final 4 weeks of the treatment period between the two treatment groups was neither statistically significant, nor considered to be of clinical importance. Although marked bronchodilator activity was seen early on with sibenadet treatment, the duration of effect diminished as the studies progressed. Sibenadet use was not associated with any safety concerns.These studies, utilizing the novel BCSS, have clearly illustrated that, despite initial symptomatic improvement with sibenadet therapy, this clinical benefit was not sustained over the course of the study
The GOAL study: a prospective examination of the impact of factor V Leiden and ABO(H) blood groups on haemorrhagic and thrombotic pregnancy outcomes
Factor V Leiden (FVL) and ABO(H) blood groups are the common influences on haemostasis and retrospective studies have linked FVL with pregnancy complications. However, only one sizeable prospective examination has taken place. As a result, neither the impact of FVL in unselected subjects, any interaction with ABO(H) in pregnancy, nor the utility of screening for FVL is defined. A prospective study of 4250 unselected pregnancies was carried out. A venous thromboembolism (VTE) rate of 1·23/1000 was observed, but no significant association between FVL and pre-eclampsia, intra-uterine growth restriction or pregnancy loss was seen. No influence of FVL and/or ABO(H) on ante-natal bleeding or intra-partum or postpartum haemorrhage was observed. However, FVL was associated with birth-weights >90th centile [odds ratio (OR) 1·81; 95% confidence interval (CI<sub>95</sub>) 1·04–3·31] and neonatal death (OR 14·79; CI<sub>95</sub> 2·71–80·74). No association with ABO(H) alone, or any interaction between ABO(H) and FVL was observed. We neither confirmed the protective effect of FVL on pregnancy-related blood loss reported in previous smaller studies, nor did we find the increased risk of some vascular complications reported in retrospective studies
EMIC Waves in the Outer Magnetosphere: Observations of an Off-Equator Source Region.
Electromagnetic ion cyclotron (EMIC) waves at large L shells were observed away from the magnetic equator by the Magnetospheric MultiScale (MMS) mission nearly continuously for over four hours on 28 October 2015. During this event, the wave Poynting vector direction systematically changed from parallel to the magnetic field (toward the equator), to bidirectional, to antiparallel (away from the equator). These changes coincide with the shift in the location of the minimum in the magnetic field in the southern hemisphere from poleward to equatorward of MMS. The local plasma conditions measured with the EMIC waves also suggest that the outer magnetospheric region sampled during this event was generally unstable to EMIC wave growth. Together, these observations indicate that the bidirectionally propagating wave packets were not a result of reflection at high latitudes but that MMS passed through an off-equator EMIC wave source region associated with the local minimum in the magnetic field
On the Calibration of Full-polarization 86GHz Global VLBI Observations
We report the development of a semi-automatic pipeline for the calibration of
86 GHz full-polarization observations performed with the Global Millimeter-VLBI
array (GMVA) and describe the calibration strategy followed in the data
reduction. Our calibration pipeline involves non-standard procedures, since
VLBI polarimetry at frequencies above 43 GHz is not yet well established. We
also present, for the first time, a full-polarization global-VLBI image at 86
GHz (source 3C 345), as an example of the final product of our calibration
pipeline, and discuss the effect of instrumental limitations on the fidelity of
the polarization images. Our calibration strategy is not exclusive for the
GMVA, and could be applied on other VLBI arrays at millimeter wavelengths. The
use of this pipeline will allow GMVA observers to get fully-calibrated datasets
shortly after the data correlation.Comment: 10 pages, 10 figures. Accepted for publication in A&
Dayside response of the magnetosphere to a small shock compression: Van Allen Probes, Magnetospheric MultiScale, and GOES-13.
Observations from Magnetospheric MultiScale (~8 Re) and Van Allen Probes (~5 and 4 Re) show that the initial dayside response to a small interplanetary shock is a double-peaked dawnward electric field, which is distinctly different from the usual bipolar (dawnward and then duskward) signature reported for large shocks. The associated E × B flow is radially inward. The shock compressed the magnetopause to inside 8 Re, as observed by Magnetospheric MultiScale (MMS), with a speed that is comparable to the E × B flow. The magnetopause speed and the E × B speeds were significantly less than the propagation speed of the pulse from MMS to the Van Allen Probes and GOES-13, which is consistent with the MHD fast mode. There were increased fluxes of energetic electrons up to several MeV. Signatures of drift echoes and response to ULF waves also were seen. These observations demonstrate that even very weak shocks can have significant impact on the radiation belts
Role of tyrosine 129 in the active site of spinach glycolate oxidase
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66136/1/j.1432-1033.1993.tb17852.x.pd
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