282 research outputs found
A Deep Look at the Emission-Line Nebula in Abell 2597
The close correlation between cooling flows and emission-line nebulae in
clusters of galaxies has been recognized for over a decade and a half, but the
physical reason for this connection remains unclear. Here we present deep
optical spectra of the nebula in Abell 2597, one of the nearest strong
cooling-flow clusters. These spectra reveal the density, temperature, and metal
abundances of the line-emitting gas. The abundances are roughly half-solar, and
dust produces an extinction of at least a magnitude in V. The absence of [O
III] 4363 emission rules out shocks as a major ionizing mechanism, and the
weakness of He II 4686 rules out a hard ionizing source, such as an active
galactic nucleus or cooling intracluster gas. Hot stars are therefore the best
candidate for producing the ionization. However, even the hottest O stars
cannot power a nebula as hot as the one we see. Some other nonionizing source
of heat appears to contribute a comparable amount of power. We show that the
energy flux from a confining medium can become important when the ionization
level of a nebula drops to the low levels seen in cooling-flow nebulae. We
suggest that this kind of phenomenon, in which energy fluxes from the
surrounding medium augment photoelectric heating, might be the common feature
underlying the diverse group of objects classified as LINERS.Comment: 33 Latex pages, including 16 Postscript figures, to appear in 1997
September 1 Astrophysical Journa
Prognosis of West Nile virus associated acute flaccid paralysis: a case series
Introduction: Little is known about the long-term health related quality of life outcomes in patients with West Nile virus associated acute flaccid paralysis. We describe the quality of life scores of seven patients with acute flaccid paralysis who presented to hospital between 2003 and 2006, and were followed for up to two years. Case presentations: Between 2003 and 2006, 157 symptomatic patients with West Nile virus were enrolled in a longitudinal cohort study of West Nile virus in Canada. Seven patients (4%) had acute flaccid paralysis. The firs
Stellar Kinematics of Young Clusters in Turbulent Hydrodynamic Simulations
The kinematics of newly-formed star clusters are interesting both as a probe
of the state of the gas clouds from which the stars form, and because they
influence planet formation, stellar mass segregation, cluster disruption, and
other processes controlled in part by dynamical interactions in young clusters.
However, to date there have been no attempts to use simulations of star cluster
formation to investigate how the kinematics of young stars change in response
to variations in the properties of their parent molecular clouds. In this
letter we report the results of turbulent self-gravitating simulations of
cluster formation in which we consider both clouds in virial balance and those
undergoing global collapse. We find that stars in these simulations generally
have velocity dispersions smaller than that of the gas by a factor of ~ 5,
independent of the dynamical state of the parent cloud, so that subvirial
stellar velocity dispersions arise naturally even in virialized molecular
clouds. The simulated clusters also show large-scale stellar velocity gradients
of ~0.2-2 km s pc and strong correlations between the centroid
velocities of stars and gas, both of which are observed in young clusters. We
conclude that star clusters should display subvirial velocity dispersions,
large-scale velocity gradients, and strong gas-star velocity correlations
regardless of whether their parent clouds are in virial balance, and,
conversely, that observations of these features cannot be used to infer the
dynamical state of the parent gas clouds.Comment: 5 pages, 4 figures, accepted to ApJ
Analysis of lesion localisation at colonoscopy: outcomes from a multi-centre U.K. study
Background:
Colonoscopy is currently the gold standard for detection of colorectal lesions, but may be limited in anatomically localising lesions. This audit aimed to determine the accuracy of colonoscopy lesion localisation, any subsequent changes in surgical management and any potentially influencing factors.
Methods:
Patients undergoing colonoscopy prior to elective curative surgery for colorectal lesion/s were included from 8 registered U.K. sites (2012–2014). Three sets of data were recorded: patient factors (age, sex, BMI, screener vs. symptomatic, previous abdominal surgery); colonoscopy factors (caecal intubation, scope guide used, colonoscopist accreditation) and imaging modality. Lesion localisation was standardised with intra-operative location taken as the gold standard. Changes to surgical management were recorded.
Results:
364 cases were included; majority of lesions were colonic, solitary, malignant and in symptomatic referrals. 82% patients had their lesion/s correctly located at colonoscopy. Pre-operative CT visualised lesion/s in only 73% of cases with a reduction in screening patients (64 vs. 77%; p = 0.008). 5.2% incorrectly located cases at colonoscopy underwent altered surgical management, including conversion to open. Univariate analysis found colonoscopy accreditation, scope guide use, incomplete colonoscopy and previous abdominal surgery significantly influenced lesion localisation. On multi-variate analysis, caecal intubation and scope guide use remained significant (HR 0.35, 0.20–0.60 95% CI and 0.47; 0.25–0.88, respectively).
Conclusion:
Lesion localisation at colonoscopy is incorrect in 18% of cases leading to potentially significant surgical management alterations. As part of accreditation, colonoscopists need lesion localisation training and awareness of when inaccuracies can occur
The COMPLETE Survey of Star-Forming Regions: Phase I Data
We present an overview of data available for the Ophiuchus and Perseus
molecular clouds from ``Phase I'' of the COMPLETE Survey of Star-Forming
Regions. This survey provides a range of data complementary to the Spitzer
Legacy Program ``From Molecular Cores to Planet Forming Disks.'' Phase I
includes: Extinction maps derived from 2MASS near-infrared data using the NICER
algorithm; extinction and temperature maps derived from IRAS 60 and 100um
emission; HI maps of atomic gas; 12CO and 13CO maps of molecular gas; and
submillimetre continuum images of emission from dust in dense cores. Not
unexpectedly, the morphology of the regions appears quite different depending
on the column-density tracer which is used, with IRAS tracing mainly warmer
dust and CO being biased by chemical, excitation and optical depth effects.
Histograms of column-density distribution are presented, showing that
extinction as derived from 2MASS/NICER gives the closest match to a log-normal
distribution as is predicted by numerical simulations. All the data presented
in this paper, and links to more detailed publications on their implications
are publically available at the COMPLETE website.Comment: Accepted by AJ. Full resolution version available from:
http://www.cfa.harvard.edu/COMPLETE/papers/complete_phase1.pd
The Extended Blue Continuum and Line Emission around the Central Radio Galaxy in Abell 2597
We present results from detailed imaging of the centrally dominant radio
elliptical galaxy in the cooling flow cluster Abell 2597, using data obtained
with the Wide Field and Planetary Camera 2 (WFPC2) on the Hubble Space
Telescope (HST). This object is one of the archetypal "blue-lobed" cooling flow
radio elliptical galaxies, also displaying a luminous emission-line nebula, a
compact radio source, and a significant dust lane and evidence of molecular gas
in its center. We show that the radio source is surrounded by a complex network
of emission-line filaments, some of which display a close spatial association
with the outer boundary of the radio lobes. We present a detailed analysis of
the physical properties of ionized and neutral gas associated with the radio
lobes, and show that their properties are strongly suggestive of direct
interactions between the radio plasma and ambient gas. We resolve the blue
continuum emission into a series of knots and clumps, and present evidence that
these are most likely due to regions of recent star formation. We investigate
several possible triggering mechanisms for the star formation, including direct
interactions with the radio source, filaments condensing from the cooling flow,
or the result of an interaction with a gas-rich galaxy, which may also have
been responsible for fueling the active nucleus. We propose that the properties
of the source are plausibly explained in terms of accretion of gas by the cD
during an interaction with a gas-rich galaxy, which combined with the fact that
this object is located at the center of a dense, high-pressure ICM can account
for the high rates of star formation and the strong confinement of the radio
source.Comment: Astrophysical Journal, in press, 34 pages, includes 6 PostScript
figures. Latex format, uses aaspp4.sty and epsf.sty file
Pahs, Ionized Gas, and Molecular Hydrogen in Brightest Cluster Galaxies of Cool Core Clusters of Galaxies
We present measurements of 5-25 {\mu}m emission features of brightest cluster
galaxies (BCGs) with strong optical emission lines in a sample of 9 cool-core
clusters of galaxies observed with the Infrared Spectrograph on board the
Spitzer Space Telescope. These systems provide a view of dusty molecular gas
and star formation, surrounded by dense, X-ray emitting intracluster gas. Past
work has shown that BCGs in cool-core clusters may host powerful radio sources,
luminous optical emission line systems, and excess UV, while BCGs in other
clusters never show this activity. In this sample, we detect polycyclic
aromatic hydrocarbons (PAHs), extremely luminous, rotationally-excited
molecular hydrogen line emission, forbidden line emission from ionized gas ([Ne
II] and [Ne III]), and infrared continuum emission from warm dust and cool
stars. We show here that these BCGs exhibit more luminous forbidden neon and H2
rotational line emission than star-forming galaxies with similar total infrared
luminosities, as well as somewhat higher ratios of 70 {\mu}m / 24 {\mu}m
luminosities. Our analysis suggests that while star formation processes
dominate the heating of the dust and PAHs, a heating process consistent with
suprathermal electron heating from the hot gas, distinct from star formation,
is heating the molecular gas and contributing to the heating of the ionized gas
in the galaxies. The survival of PAHs and dust suggests that dusty gas is
somehow shielded from significant interaction with the X-ray gas.Comment: 27 preprint pages, 18 figures, accepted by Astrophysical Journa
Comparison of prestellar core elongations and large-scale molecular cloud structures in the Lupus 1 region
Turbulence and magnetic fields are expected to be important for regulating molecular cloud formation and evolution. However, their effects on sub-parsec to 100 parsec scales, leading to the formation of starless cores, are not well understood. We investigate the prestellar core structure morphologies obtained from analysis of the Herschel-SPIRE 350 mum maps of the Lupus I cloud. This distribution is first compared on a statistical basis to the large-scale shape of the main filament. We find the distribution of the elongation position angle of the cores to be consistent with a random distribution, which means no specific orientation of the morphology of the cores is observed with respect to the mean orientation of the large-scale filament in Lupus I, nor relative to a large-scale bent filament model. This distribution is also compared to the mean orientation of the large-scale magnetic fields probed at 350 mum with the Balloon-borne Large Aperture Telescope for Polarimetry during its 2010 campaign. Here again we do not find any correlation between the core morphology distribution and the average orientation of the magnetic fields on parsec scales. Our main conclusion is that the local filament dynamics---including secondary filaments that often run orthogonally to the primary filament---and possibly small-scale variations in the local magnetic field direction, could be the dominant factors for explaining the final orientation of each core
Differing effects of high-fat or high-carbohydrate meals on food hedonics in overweight and obese individuals.
Although the effects of dietary fat and carbohydrate on satiety are well documented, little is known about the impact of these macronutrients on food hedonics. We examined the effects of ad libitum and isoenergetic meals varying in fat and carbohydrate on satiety, energy intake and food hedonics. In all, sixty-five overweight and obese individuals (BMI=30·9 (sd 3·8) kg/m2) completed two separate test meal days in a randomised order in which they consumed high-fat/low-carbohydrate (HFLC) or low-fat/high-carbohydrate (LFHC) foods. Satiety was measured using subjective appetite ratings to calculate the satiety quotient. Satiation was assessed by intake at ad libitum meals. Hedonic measures of explicit liking (subjective ratings) and implicit wanting (speed of forced choice) for an array of HFLC and LFHC foods were also tested before and after isoenergetic HFLC and LFHC meals. The satiety quotient was greater after ad libitum and isoenergetic meals during the LFHC condition compared with the HFLC condition (P=0·006 and P=0·001, respectively), whereas ad libitum energy intake was lower in the LFHC condition (P<0·001). Importantly, the LFHC meal also reduced explicit liking (P<0·001) and implicit wanting (P=0·011) for HFLC foods compared with the isoenergetic HFLC meal, which failed to suppress the hedonic appeal of subsequent HFLC foods. Therefore, when coupled with increased satiety and lower energy intake, the greater suppression of hedonic appeal for high-fat food seen with LFHC foods provides a further mechanism for why these foods promote better short-term appetite control than HFLC foods
Psychopolitics: Peter Sedgwick’s legacy for mental health movements
This paper re-considers the relevance of Peter Sedgwick's Psychopolitics (1982) for a politics of mental health. Psychopolitics offered an indictment of ‘anti-psychiatry’ the failure of which, Sedgwick argued, lay in its deconstruction of the category of ‘mental illness’, a gesture that resulted in a politics of nihilism. ‘The radical who is only a radical nihilist’, Sedgwick observed, ‘is for all practical purposes the most adamant of conservatives’. Sedgwick argued, rather, that the concept of ‘mental illness’ could be a truly critical concept if it was deployed ‘to make demands upon the health service facilities of the society in which we live’. The paper contextualizes Psychopolitics within the ‘crisis tendencies’ of its time, surveying the shifting welfare landscape of the subsequent 25 years alongside Sedgwick's continuing relevance. It considers the dilemma that the discourse of ‘mental illness’ – Sedgwick's critical concept – has fallen out of favour with radical mental health movements yet remains paradigmatic within psychiatry itself. Finally, the paper endorses a contemporary perspective that, while necessarily updating Psychopolitics, remains nonetheless ‘Sedgwickian’
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