752 research outputs found
Chemical enrichment of the complex hot ISM of the Antennae galaxies: I. Spatial and spectral analysis of the diffuse X-ray emission
We present an analysis of the properties of the hot interstellar medium (ISM)
in the merging pair of galaxies known as The Antennae (NGC 4038/39), performed
using the deep, coadded ~411 ks Chandra ACIS-S data set. These deep X-ray
observations and Chandra's high angular resolution allow us to investigate the
properties of the hot ISM with unprecedented spatial and spectral resolution.
Through a spatially resolved spectral analysis, we find a variety of
temperatures (from 0.2 to 0.7 keV) and Nh (from Galactic to 2x10^21 cm^-2).
Metal abundances for Ne, Mg, Si, and Fe vary dramatically throughout the ISM
from sub-solar values (~0.2) up to several times solar.Comment: 33 pages, 18 figures, revised version accepted by Astrophysical
Journal Supplement Serie
Hot Interstellar Gas and Stellar Energy Feedback in the Antennae Galaxies
We have analyzed Chandra archival observations of the Antennae galaxies to
study the distribution and physical properties of its hot interstellar gas.
Eleven distinct diffuse X-ray emission regions are selected according to their
underlying interstellar structures and star formation activity. The X-ray
spectra of these regions are used to determine their thermal energy contents
and cooling timescales. Young star clusters in these regions are also
identified and their photometric measurements are compared to evolutionary
stellar population synthesis models to assess their masses and ages. The
cluster properties are then used to determine the stellar wind and supernova
energies injected into the ISM. Comparisons between the thermal energy in the
hot ISM and the expected stellar energy input show that young star clusters are
sufficient to power the X-ray-emitting gas in some, but not all, active star
formation regions. Super-star clusters, with masses >= 1x10^5 M_sol, heat the
ISM, but the yield of hot interstellar gas is not directly proportional to the
cluster mass. Finally, there exist diffuse X-ray emission regions which do not
show active star formation or massive young star clusters. These regions may be
powered by field stars or low-mass clusters formed within the last ~100 Myr.Comment: 36 pages, 6 figures, 8 tables, 2 appendices, to appear in the
Astrophysical Journal, April 20 issu
The Seyfert-Starburst Connection in X-rays. II. Results and Implications
We present the results of X-ray imaging and spectroscopic analysis of a
sample of Seyfert 2 galaxies that contain starbursts, based on their optical
and UV characteristics. These composite galaxies exhibit extended, soft,
thermal X-ray emission, which we attribute to their starburst components.
Comparing their X-ray and far-infrared properties with ordinary Seyfert and
starburst galaxies, we identify the spectral characteristics of their various
intrinsic emission sources. The observed far-infrared emission of the composite
galaxies may be associated almost exclusively with star formation, rather than
the active nucleus. The ratio of the hard X-ray luminosity to the far-infrared
and [O III] 5007 luminosity distinguishes most of these composite galaxies from
``pure'' Seyfert 2 galaxies, while their total observed hard X-ray luminosity
distinguishes them from ``pure'' starbursts. The hard nuclear X-ray source is
generally heavily absorbed (N_H > 10^{23} cm^{-2}) in the composite galaxies.
Based on these results, we suggest that the interstellar medium of the nuclear
starburst is a significant source of absorption. The majority of the sample are
located in groups or are interacting with other galaxies, which may trigger the
starburst or allow rapid mass infall to the central black hole, or both. We
conclude that starbursts are energetically important in a significant fraction
of active galaxies, and starbursts and active galactic nuclei may be part of a
common evolutionary sequence.Comment: 16 pages including 8 figures and 5 tables; to appear in the ApJ, Mar.
10, 200
Understanding why primary care doctors leave direct patient care: a systematic review of qualitative research
This is the final version. Available on open access from BMJ Publishing Group via the DOI in this recordData availability statement: All data relevant to the study are included in the article or uploaded as supplementary information. No additional data available.Background UK general practitioners (GPs) are leaving direct patient care in significant numbers. We undertook a systematic review of qualitative research to identify factors affecting GPsâ leaving behaviour in the workforce as part of a wider mixed methods study (ReGROUP).
Objective To identify factors that affect GPsâ decisions to leave direct patient care.
Methods Qualitative interview-based studies were identified and their quality was assessed. A thematic analysis was performed and an explanatory model was constructed providing an overview of factors affecting UK GPs. Non-UK studies were considered separately.
Results Six UK interview-based studies and one Australian interview-based study were identified. Three central dynamics that are key to understanding UK GP leaving behaviour were identified: factors associated with low job satisfaction, high job satisfaction and those linked to the doctorâpatient relationship. The importance of contextual influence on job satisfaction emerged. GPs with high job satisfaction described feeling supported by good practice relationships, while GPs with poor job satisfaction described feeling overworked and unsupported with negatively impacted doctorâpatient relationships.
Conclusions Many GPs report that job satisfaction directly relates to the quality of the doctorâpatient relationship. Combined with changing relationships with patients and interfaces with secondary care, and the gradual sense of loss of autonomy within the workplace, many GPs report a reduction in job satisfaction. Once job satisfaction has become negatively impacted, the combined pressure of increased patient demand and workload, together with other stress factors, has left many feeling unsupported and vulnerable to burn-out and ill health, and ultimately to the decision to leave general practice
Chemical enrichment of the complex hot ISM of the Antennae Galaxies: II. Physical properties of the hot gas and supernova feedback
We investigate the physical properties of the interstellar medium (ISM) in
the merging pair of galaxies known as The Antennae (NGC 4038/39), using the
deep coadded ~411 ks Chandra ACIS-S data set. The method of analysis and some
of the main results from the spectral analysis, such as metal abundances and
their variations from ~0.2 to ~20-30 times solar, are described in Paper I
(Baldi et al. submitted). In the present paper we investigate in detail the
physics of the hot emitting gas, deriving measures for the hot-gas mass (~10^
M_sun), cooling times (10^7-10^8 yr), and pressure (3.5x10^-11-2.8x10^-10 dyne
cm^-2). At least in one of the two nuclei (NGC 4038) the hot-gas pressure is
significantly higher than the CO pressure, implying that shock waves may be
driven into the CO clouds. Comparison of the metal abundances with the average
stellar yields predicted by theoretical models of SN explosions points to SNe
of Type II as the main contributors of metals to the hot ISM. There is no
evidence of any correlation between radio-optical star-formation indicators and
the measured metal abundances. Although due to uncertainties in the average gas
density we cannot exclude that mixing may have played an important role, the
short time required to produce the observed metal masses (<=2 Myr) suggests
that the correlations are unlikely to have been destroyed by efficient mixing.
More likely, a significant fraction of SN II ejecta may be in a cool phase, in
grains, or escaping in hot winds. In each case, any such fraction of the ejecta
would remain undetectable with soft X-ray observations.Comment: 29 pages, 6 figures, accepted by the Astrophysical Journa
In-situ measurement of internal gas pressure within cylindrical lithium-ion cells
Internal gas pressure is a key parameter that varies depending on cell heating and gas formation over the lifetime of a lithium-ion cell under dynamic load conditions and ageing. In our research, for the first time, we present a methodology to directly measure internal gas pressure during pre-instrumentation, cell operation and ageing via an embedded sensor system. Cylindrical format cells (LG-INR21700M50) are instrumented using our proven instrumentation technique. Our study demonstrates that the performance and degradation of instrumented cells are not adversely affected by the instrumentation process. In this study, the effect of state-of-charge (SOC), degradation and temperature on internal gas pressure is evaluated. Initial results highlight a nonlinear relationship between gas pressure and SOC of the cells during charging and discharging and, gas pressure and temperature when the cells are operated under no-load conditions. Our study further highlights that gas pressure accumulation can be correlated with capacity fade or state-of-health (SOH). Monitoring of internal gas pressure could therefore become a useful additional indicator of SOC and SOH and provide new insights into degradation and the safety of lithium-ion cells
Synthesis and characterisation of the perovskite-related cuprate phases YSr2Cu2MO7+y(M = Co, Fe) for potential use as solid oxide fuel cell cathode materials
GAMA: towards a physical understanding of galaxy formation
The Galaxy And Mass Assembly (GAMA) project is the latest in a tradition of
large galaxy redshift surveys, and is now underway on the 3.9m Anglo-Australian
Telescope at Siding Spring Observatory. GAMA is designed to map extragalactic
structures on scales of 1kpc - 1Mpc in complete detail to a redshift of z~0.2,
and to trace the distribution of luminous galaxies out to z~0.5. The principal
science aim is to test the standard hierarchical structure formation paradigm
of Cold Dark Matter (CDM) on scales of galaxy groups, pairs, discs, bulges and
bars. We will measure (1) the Dark Matter Halo Mass Function (as inferred from
galaxy group velocity dispersions); (2) baryonic processes, such as star
formation and galaxy formation efficiency (as derived from Galaxy Stellar Mass
Functions); and (3) the evolution of galaxy merger rates (via galaxy close
pairs and galaxy asymmetries). Additionally, GAMA will form the central part of
a new galaxy database, which aims to contain 275,000 galaxies with
multi-wavelength coverage from coordinated observations with the latest
international ground- and space-based facilities: GALEX, VST, VISTA, WISE,
HERSCHEL, GMRT and ASKAP. Together, these data will provide increased depth
(over 2 magnitudes), doubled spatial resolution (0.7"), and significantly
extended wavelength coverage (UV through Far-IR to radio) over the main SDSS
spectroscopic survey for five regions, each of around 50 deg^2. This database
will permit detailed investigations of the structural, chemical, and dynamical
properties of all galaxy types, across all environments, and over a 5 billion
year timeline.Comment: GAMA overview which appeared in the October 2009 issue of Astronomy &
Geophysics, ref: Astron.Geophys. 50 (2009) 5.1
A limited role for p53 in modulating the immediate phenotype of Apc loss in the intestine
Background: p53 is an important tumour suppressor with a known role in the later stages of colorectal cancer, but its relevance to the early stages of neoplastic initiation remains somewhat unclear. Although p53-dependent regulation of Wnt signalling activity is known to occur, the importance of these regulatory mechanisms during the early stages of intestinal neoplasia has not been demonstrated.
Methods: We have conditionally deleted the Adenomatous Polyposis coli gene (Apc) from the adult murine intestine in wild type and p53 deficient environments and subsequently compared the phenotype and transcriptome profiles in both genotypes.
Results: Expression of p53 was shown to be elevated following the conditional deletion of Apc in the adult small intestine. Furthermore, p53 status was shown to impact on the transcription profile observed following Apc loss. A number of key Wnt pathway components and targets were altered in the p53 deficient environment. However, the aberrant phenotype observed following loss of Apc (rapid nuclear localisation of ÎČ-catenin, increased levels of DNA damage, nuclear atypia, perturbed cell death, proliferation, differentiation and migration) was not significantly altered by the absence of p53.
Conclusion: p53 related feedback mechanisms regulating Wnt signalling activity are present in the intestine, and become activated following loss of Apc. However, the physiological Wnt pathway regulation by p53 appears to be overwhelmed by Apc loss and consequently the activity of these regulatory mechanisms is not sufficient to modulate the immediate phenotypes seen following Apc loss. Thus we are able to provide an explanation to the apparent contradiction that, despite having a Wnt regulatory capacity, p53 loss is not associated with early lesion development
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