514 research outputs found
The Nature and Frequency of the Gas Outbursts in Comet 67P/Churyumov-Gerasimenko observed by the Alice Far-ultraviolet Spectrograph on Rosetta
Alice is a far-ultraviolet imaging spectrograph onboard Rosetta that, amongst
multiple objectives, is designed to observe emissions from various atomic and
molecular species from within the coma of comet 67P/Churyumov-Gerasimenko. The
initial observations, made following orbit insertion in August 2014, showed
emissions of atomic hydrogen and oxygen spatially localized close to the
nucleus and attributed to photoelectron impact dissociation of H2O vapor.
Weaker emissions from atomic carbon were subsequently detected and also
attributed to electron impact dissociation, of CO2, the relative H I and C I
line intensities reflecting the variation of CO2 to H2O column abundance along
the line-of-sight through the coma. Beginning in mid-April 2015, Alice
sporadically observed a number of outbursts above the sunward limb
characterized by sudden increases in the atomic emissions, particularly the
semi-forbidden O I 1356 multiplet, over a period of 10-30 minutes, without a
corresponding enhancement in long wavelength solar reflected light
characteristic of dust production. A large increase in the brightness ratio O I
1356/O I 1304 suggests O2 as the principal source of the additional gas. These
outbursts do not correlate with any of the visible images of outbursts taken
with either OSIRIS or the navigation camera. Beginning in June 2015 the nature
of the Alice spectrum changed considerably with CO Fourth Positive band
emission observed continuously, varying with pointing but otherwise fairly
constant in time. However, CO does not appear to be a major driver of any of
the observed outbursts.Comment: 6 pages, 4 figures, accepted for publication in the Astrophysical
Journal Letter
Alice: The Rosetta Ultraviolet Imaging Spectrograph
We describe the design, performance and scientific objectives of the
NASA-funded ALICE instrument aboard the ESA Rosetta asteroid flyby/comet
rendezvous mission. ALICE is a lightweight, low-power, and low-cost imaging
spectrograph optimized for cometary far-ultraviolet (FUV) spectroscopy. It will
be the first UV spectrograph to study a comet at close range. It is designed to
obtain spatially-resolved spectra of Rosetta mission targets in the 700-2050 A
spectral band with a spectral resolution between 8 A and 12 A for extended
sources that fill its ~0.05 deg x 6.0 deg field-of-view. ALICE employs an
off-axis telescope feeding a 0.15-m normal incidence Rowland circle
spectrograph with a concave holographic reflection grating. The imaging
microchannel plate detector utilizes dual solar-blind opaque photocathodes (KBr
and CsI) and employs a 2 D delay-line readout array. The instrument is
controlled by an internal microprocessor. During the prime Rosetta mission,
ALICE will characterize comet 67P/Churyumov-Gerasimenko's coma, its nucleus,
and the nucleus/coma coupling; during cruise to the comet, ALICE will make
observations of the mission's two asteroid flyby targets and of Mars, its
moons, and of Earth's moon. ALICE has already successfully completed the
in-flight commissioning phase and is operating normally in flight. It has been
characterized in flight with stellar flux calibrations, observations of the
Moon during the first Earth fly-by, and observations of comet Linear T7 in 2004
and comet 9P/Tempel 1 during the 2005 Deep Impact comet-collision observing
campaignComment: 11 pages, 7 figure
Rosetta-Alice Observations of Exospheric Hydrogen and Oxygen on Mars
The European Space Agency's Rosetta spacecraft, en route to a 2014 encounter
with comet 67P/Churyumov-Gerasimenko, made a gravity assist swing-by of Mars on
25 February 2007, closest approach being at 01:54UT. The Alice instrument on
board Rosetta, a lightweight far-ultraviolet imaging spectrograph optimized for
in situ cometary spectroscopy in the 750-2000 A spectral band, was used to
study the daytime Mars upper atmosphere including emissions from exospheric
hydrogen and oxygen. Offset pointing, obtained five hours before closest
approach, enabled us to detect and map the HI Lyman-alpha and Lyman-beta
emissions from exospheric hydrogen out beyond 30,000 km from the planet's
center. These data are fit with a Chamberlain exospheric model from which we
derive the hydrogen density at the 200 km exobase and the H escape flux. The
results are comparable to those found from the the Ultraviolet Spectrometer
experiment on the Mariner 6 and 7 fly-bys of Mars in 1969. Atomic oxygen
emission at 1304 A is detected at altitudes of 400 to 1000 km above the limb
during limb scans shortly after closest approach. However, the derived oxygen
scale height is not consistent with recent models of oxygen escape based on the
production of suprathermal oxygen atoms by the dissociative recombination of
O2+.Comment: 17 pages, 8 figures, accepted for publication in Icaru
Ultraviolet Spectroscopy of Comet 9P/Tempel 1 with Alice/Rosetta during the Deep Impact Encounter
We report on spectroscopic observations of periodic comet 9P/Tempel 1 by the
Alice ultraviolet spectrograph on the Rosetta spacecraft in conjunction with
NASA's Deep Impact mission. Our objectives were to measure an increase in
atomic and molecular emissions produced by the excavation of volatile
sub-surface material. We unambiguously detected atomic oxygen emission from the
quiescent coma but no enhancement at the 10% (1-sigma) level following the
impact. We derive a quiescent water production rate of 9 x 10^27 molecules per
second with an estimated uncertainty of 30%. Our upper limits to the volatiles
produced by the impact are consistent with other estimates.Comment: 11 pages, 4 postscript figures. Accepted for publication in Icarus
special issue on Deep Impac
Country differences in the diagnosis and management of coronary heart disease : a comparison between the US, the UK and Germany
Background
The way patients with coronary heart disease (CHD) are treated is partly determined by non-medical factors. There is a solid body of evidence that patient and physician characteristics influence doctors' management decisions. Relatively little is known about the role of structural issues in the decision making process. This study focuses on the question whether doctors' diagnostic and therapeutic decisions are influenced by the health care system in which they take place. This non-medical determinant of medical decision-making was investigated in an international research project in the US, the UK and Germany.
Methods
Videotaped patients within an experimental study design were used. Experienced actors played the role of patients with symptoms of CHD. Several alternative versions were taped featuring the same script with patients of different sex, age and social status. The videotapes were shown to 384 randomly selected primary care physicians in the three countries under study. The sample was stratified on gender and duration of professional experience. Physicians were asked how they would diagnose and manage the patient after watching the video vignette using a questionnaire with standardised and open-ended questions.
Results
Results show only small differences in decision making between British and American physicians in essential aspects of care. About 90% of the UK and US doctors identified CHD as one of the possible diagnoses. Further similarities were found in test ordering and lifestyle advice. Some differences between the US and UK were found in the certainty of the diagnoses, prescribed medications and referral behaviour. There are numerous significant differences between Germany and the other two countries. German physicians would ask fewer questions, they would order fewer tests, prescribe fewer medications and give less lifestyle advice.
Conclusion
Although all physicians in the three countries under study were presented exactly the same patient, some disparities in the diagnostic and patient management decisions were evident. Since other possible influences on doctors treatment decisions are controlled within the experimental design, characteristics of the health care system seem to be a crucial factor within the decision making process
Identification of sex hormone-binding globulin in the human hypothalamus
Gonadal steroids are known to influence hypothalamic functions through both genomic and non-genomic pathways. Sex hormone-binding globulin ( SHBG) may act by a non-genomic mechanism independent of classical steroid receptors. Here we describe the immunocytochemical mapping of SHBG-containing neurons and nerve fibers in the human hypothalamus and infundibulum. Mass spectrometry and Western blot analysis were also used to characterize the biochemical characteristics of SHBG in the hypothalamus and cerebrospinal fluid (CSF) of humans. SHBG-immunoreactive neurons were observed in the supraoptic nucleus, the suprachiasmatic nucleus, the bed nucleus of the stria terminalis, paraventricular nucleus, arcuate nucleus, the perifornical region and the medial preoptic area in human brains. There were SHBG-immunoreactive axons in the median eminence and the infundibulum. A partial colocalization with oxytocin could be observed in the posterior pituitary lobe in consecutive semithin sections. We also found strong immunoreactivity for SHBG in epithelial cells of the choroid plexus and in a portion of the ependymal cells lining the third ventricle. Mass spectrometry showed that affinity-purified SHBG from the hypothalamus and choroid plexus is structurally similar to the SHBG identified in the CSF. The multiple localizations of SHBG suggest neurohypophyseal and neuroendocrine functions. The biochemical data suggest that CSF SHBG is of brain rather than blood origin. Copyright (c) 2005 S. Karger AG, Base
Advanced Camera for Surveys Observations of Young Star Clusters in the Interacting Galaxy UGC 10214
We present the first Advanced Camera for Surveys (ACS) observations of young
star clusters in the colliding/merging galaxy UGC 10214. The observations were
made as part of the Early Release Observation (ERO) program for the newly
installed ACS during service mission SM3B for the Hubble Space Telescope (HST).
Many young star clusters can be identified in the tails of UGC 10214, with ages
ranging from ~3 Myr to 10 Myr. The extreme blue V-I (F606W-F814W) colors of the
star clusters found in the tail of UGC 10214 can only be explained if strong
emission lines are included with a young stellar population. This has been
confirmed by our Keck spectroscopy of some of these bright blue stellar knots.
The most luminous and largest of these blue knots has an absolute magnitude of
M_V = -14.45, with a half-light radius of 161 pc, and if it is a single star
cluster, would qualify as a super star cluster (SSC). Alternatively, it could
be a superposition of multiple scaled OB associations or clusters. With an
estimated age of ~ 4-5 Myr, its derived mass is < 1.3 x 10^6 solar masses. Thus
the young stellar knot is unbound and will not evolve into a normal globular
cluster. The bright blue clusters and associations are much younger than the
dynamical age of the tail, providing strong evidence that star formation occurs
in the tail long after it was ejected. UGC 10214 provides a nearby example of
processes that contributed to the formation of halos and intra-cluster media in
the distant and younger Universe.Comment: 6 pages with embedded figures, ApJ in pres
Dual oscillator model of the respiratory neuronal network generating quantal slowing of respiratory rhythm
We developed a dual oscillator model to facilitate the understanding of dynamic interactions between the parafacial respiratory group (pFRG) and the preBötzinger complex (preBötC) neurons in the respiratory rhythm generation. Both neuronal groups were modeled as groups of 81 interconnected pacemaker neurons; the bursting cell model described by Butera and others [model 1 in Butera et al. (J Neurophysiol 81:382–397, 1999a)] were used to model the pacemaker neurons. We assumed (1) both pFRG and preBötC networks are rhythm generators, (2) preBötC receives excitatory inputs from pFRG, and pFRG receives inhibitory inputs from preBötC, and (3) persistent Na+ current conductance and synaptic current conductances are randomly distributed within each population. Our model could reproduce 1:1 coupling of bursting rhythms between pFRG and preBötC with the characteristic biphasic firing pattern of pFRG neurons, i.e., firings during pre-inspiratory and post-inspiratory phases. Compatible with experimental results, the model predicted the changes in firing pattern of pFRG neurons from biphasic expiratory to monophasic inspiratory, synchronous with preBötC neurons. Quantal slowing, a phenomena of prolonged respiratory period that jumps non-deterministically to integer multiples of the control period, was observed when the excitability of preBötC network decreased while strengths of synaptic connections between the two groups remained unchanged, suggesting that, in contrast to the earlier suggestions (Mellen et al., Neuron 37:821–826, 2003; Wittmeier et al., Proc Natl Acad Sci USA 105(46):18000–18005, 2008), quantal slowing could occur without suppressed or stochastic excitatory synaptic transmission. With a reduced excitability of preBötC network, the breakdown of synchronous bursting of preBötC neurons was predicted by simulation. We suggest that quantal slowing could result from a breakdown of synchronized bursting within the preBötC
- …