123 research outputs found
Cosmological Effects of Powerful AGN Outbursts in Galaxy Clusters: Insights from an XMM-Newton Observation of MS0735+7421
We report on the results of an analysis of XMM-Newton observations of
MS0735+7421, the galaxy cluster which hosts the most energetic AGN outburst
currently known. The previous Chandra image shows twin giant X-ray cavities
(~200 kpc diameter) filled with radio emission and surrounded by a weak shock
front. XMM data are consistent with these findings. The total energy in
cavities and shock (~6 \times 10^{61} erg) is enough to quench the cooling flow
and, since most of the energy is deposited outside the cooling region (~100
kpc), to heat the gas within 1 Mpc by ~1/4 keV per particle. The cluster
exhibits an upward departure (factor ~2) from the mean L-T relation. The boost
in emissivity produced by the ICM compression in the bright shells due to the
cavity expansion may contribute to explain the high luminosity and high central
gas mass fraction that we measure. The scaled temperature and metallicity
profiles are in general agreement with those observed in relaxed clusters.
Also, the quantities we measure are consistent with the observed M-T relation.
We conclude that violent outbursts such as the one in MS0735+7421 do not cause
dramatic instantaneous departures from cluster scaling relations (other than
the L-T relation). However, if they are relatively common they may play a role
in creating the global cluster properties.Comment: 69 pages, 30 figures, accepted for publication in ApJ Main Journa
The Feedback-Regulated Growth of Black Holes and Bulges through Gas Accretion and Starbursts in Cluster Central Dominant Galaxies
We present an analysis of the growth of black holes through accretion and
bulges through star formation in 33 galaxies at the centers of cooling flows.
Most of these systems show evidence of cavities in the intracluster medium
(ICM) inflated by radio jets emanating from their active galactic nuclei (AGN).
We present a new and extensive analysis of X-ray cavities in these systems. We
find that AGN are energetically able to balance radiative losses (cooling) from
the ICM in more than half of our sample. Using a subsample of 17 systems, we
examine the relationship between cooling and star formation. We find that the
star formation rates are approaching or are comparable to X-ray and far UV
limits on the rates of gas condensation onto the central galaxy. The remaining
radiative losses could be offset by AGN feedback. The vast gulf between
radiative losses and the sink of cooling material, which has been the primary
objection to cooling flows, has narrowed and, in some cases, is no longer a
serious issue. Using the cavity (jet) powers, we place strong lower limits on
the rate of growth of supermassive black holes in central galaxies, and we find
that they are growing at an average rate of ~ 0.1 solar masses per year, with
some systems growing as quickly as ~ 1 solar mass per year. We find a trend
between bulge growth (star formation) and black hole growth that is
approximately in accordance with the slope of the local (Magorrian) relation
between black hole and bulge mass. However, the large scatter in the trend
suggests that bulges and black holes do not always grow in lock step.
(Abridged)Comment: 17 pages, 6 figures, accepted to ApJ. Minor changes to text and
figure
A High Resolution Study of the Hydra A Cluster with Chandra: Comparison of the Core Mass Distribution with Theoretical Predictions and Evidence for Feedback in the Cooling Flow
The cooling flow cluster Hydra A was observed during the orbital activation
and calibration phase of the Chandra Observatory. While the X-ray image of the
cluster exhibits complex structure in the central region as reported in
McNamara , the large scale X-ray morphology of the cluster is fairly
smooth. A spectroscopic analysis of the ACIS data shows that the gas
temperature in Hydra A increases outward, reaches a maximum temperature of 4
keV at 200 kpc, and then decreases slightly at larger radii. The distribution
of heavy elements is nonuniform, with a factor of two increase in the Fe and Si
abundances within the central 100 kpc. Beyond the central 100 kpc the Si-to-Fe
abundance ratio is twice solar, while the Si-to-Fe ratio of the central excess
is consistent with the solar value. One of the more surprising results is the
lack of spectroscopic evidence for multiphase gas within the bulk of the
cooling flow. Beyond the central 30 kpc, the ACIS spectra are adequately fit
with a single temperature model. The addition of a cooling flow component does
not significantly improve the fit. Only within the central 30 kpc (where the
cooling time is less than 1~Gyr), is there spectroscopic evidence for
multiphase gas. However, the spectroscopic mass deposition rate is more than a
factor of 10 less than the morphologically derived mass accretion rate at 30
kpc. We propose that the cooling flow region is convectively unstable due to
heating by the central radio source which significantly reduces the net
accretion rate.Comment: 19 figures include
Attachment of Salmonella strains to a plant cell wall model is modulated by surface characteristics and not by specific carbohydrate interactions
Background: Processing of fresh produce exposes cut surfaces of plant cell walls that then become vulnerable to human foodborne pathogen attachment and contamination, particularly by Salmonella enterica. Plant cell walls are mainly composed of the polysaccharides cellulose, pectin and hemicelluloses (predominantly xyloglucan). Our previous work used bacterial cellulose-based plant cell wall models to study the interaction between Salmonella and the various plant cell wall components. We demonstrated that Salmonella attachment was favoured in the presence of pectin while xyloglucan had no effect on its attachment. Xyloglucan significantly increased the attachment of Salmonella cells to the plant cell wall model only when it was in association with pectin. In this study, we investigate whether the plant cell wall polysaccharides mediate Salmonella attachment to the bacterial cellulose-based plant cell wall models through specific carbohydrate interactions or through the effects of carbohydrates on the physical characteristics of the attachment surface. Results: We found that none of the monosaccharides that make up the plant cell wall polysaccharides specifically inhibit Salmonella attachment to the bacterial cellulose-based plant cell wall models. Confocal laser scanning microscopy showed that Salmonella cells can penetrate and attach within the tightly arranged bacterial cellulose network. Analysis of images obtained from atomic force microscopy revealed that the bacterial cellulose-pectin-xyloglucan composite with 0.3 % (w/v) xyloglucan, previously shown to have the highest number of Salmonella cells attached to it, had significantly thicker cellulose fibrils compared to other composites. Scanning electron microscopy images also showed that the bacterial cellulose and bacterial cellulose-xyloglucan composites were more porous when compared to the other composites containing pectin. Conclusions: Our study found that the attachment of Salmonella cells to cut plant cell walls was not mediated by specific carbohydrate interactions. This suggests that the attachment of Salmonella strains to the plant cell wall models were more dependent on the structural characteristics of the attachment surface. Pectin reduces the porosity and space between cellulose fibrils, which then forms a matrix that is able to retain Salmonella cells within the bacterial cellulose network. When present with pectin, xyloglucan provides a greater surface for Salmonella cells to attach through the thickening of cellulose fibrils
Oxford Phase 3 unicompartmental knee arthroplasty: medium-term results of a minimally invasive surgical procedure
PURPOSE: In the last decade, a major increase in the use of and interest in unicompartmental knee arthroplasty (UKA) has developed. The Oxford Phase 3 UKA is implanted with a minimally invasive technique using newly developed instruments. The objective of this prospective study was to evaluate the outcome of UKA in patients with medial osteoarthritis of the knee in a high-volume unit. METHODS: Two-hundred and forty-four UKAs were performed with a minimally invasive approach. The median age was 72 (43-91) years. The median follow-up was 4.2 years (range 1-10.4 years). Fourteen patients died, and nine were considered to be lost to follow-up, but all had a well-functioning prosthesis in situ until their last follow-up. Pain, function and health-related quality of life were evaluated pre- and postoperatively using patient- and assessor-based outcome scores, as well as radiographic evidence. RESULTS: The mean Knee Society knee and function scores, WOMAC-scores, Oxford-score and VAS pain and satisfaction all improved. Nine knees required revision. Eleven patients required an additional arthroscopic procedure due to persisting pain secondary to intra-articular pathology, and four patients required manipulation under anaesthesia because of limited range of motion. The 7-year cumulative survival rate of the arthroplasty was 94.4%. A low incidence (21%) of a radiolucent line beneath the tibial component was observed at 5 years of follow-up. CONCLUSION: This study showed a high survival rate of the Oxford Phase 3 UKA. Patient satisfaction and functional performance were also very high. Major complication rate was low; in addition, the incidence of radiolucency under the tibial component, when compared to present literature, was low. When strict indication criteria are followed, excellent, durable, and in our opinion reliable, results can be expected for this procedur
Climatic predictors of species distributions neglect biophysiologically meaningful variables
This is the final version. Available on open access from Wiley via the DOI in this record.Aim: Species distribution models (SDMs) have played a pivotal role in predicting how species might respond to climate change. To generate reliable and realistic predictions from these models
requires the use of climate variables that adequately capture physiological responses of species to
climate and therefore provide a proximal link between climate and their distributions. Here, we
examine whether the climate variables used in plant SDMs are different from those known to
influence directly plant physiology.
Location: Global.
Methods: We carry out an extensive, systematic review of the climate variables used to model the
distributions of plant species and provide comparison to the climate variables identified as
important in the plant physiology literature. We calculate the top ten SDM and physiology
variables at 2.5 degree spatial resolution for the globe and use principal component analyses and
multiple regression to assess similarity between the climatic variation described by both
variable sets.
Results: We find that the most commonly used SDM variables do not reflect the most important
physiological variables and differ in two main ways: (i) SDM variables rely on seasonal or annual
rainfall as simple proxies of water available to plants and neglect more direct measures such as
soil water content; and (ii) SDM variables are typically averaged across seasons or years and
overlook the importance of climatic events within the critical growth period of plants. We
identify notable differences in their spatial gradients globally and show where distal variables
may be less reliable proxies for the variables to which species are known to respond.
Main conclusions: There is a growing need for the development of accessible, fine-resolution
global climate surfaces of physiological variables. This would provide a means to improve the
reliability of future range predictions from SDMs and support efforts to conserve biodiversity in a
changing climate
Host galaxies, clustering, Eddington ratios, and evolution of radio, X-ray, and infrared-selected AGNs
We explore the connection between different classes of active galactic nuclei
(AGNs) and the evolution of their host galaxies, by deriving host galaxy
properties, clustering, and Eddington ratios of AGNs selected in the radio,
X-ray, and infrared. We study a sample of 585 AGNs at 0.25 < z < 0.8 using
redshifts from the AGN and Galaxy Evolution Survey (AGES) and data in the radio
(WSRT 1.4 GHz), X-rays (Chandra XBootes), and mid-IR (IRAC Shallow Survey). The
radio, X-ray, and IR AGN samples show modest overlap, indicating that to the
flux limits of the survey, they represent largely distinct classes of AGNs. We
derive host galaxy colors and luminosities, as well as Eddington ratios
(lambda), for obscured or optically faint AGNs. We also measure the two-point
cross-correlation between AGNs and galaxies on scales of 0.3-10 h^-1 Mpc, and
derive typical dark matter halo masses. We find that: (1) radio AGNs are mainly
found in luminous red galaxies, are strongly clustered (with M_halo ~ 3x10^13
h^-1 M_sun), and have very low lambda <~ 10^-3; (2) X-ray-selected AGNs are
preferentially found in galaxies in the "green valley" of color-magnitude space
and are clustered similarly to typical AGES galaxies (M_halo ~ 10^13 h^-1
M_sun), with 10^-3 <~ lambda <~ 1; (3) IR AGNs reside in slightly bluer, less
luminous galaxies than X-ray AGNs, are weakly clustered (M_halo <~ 10^12 h^-1
M_sun), and have lambda > 10^-2. We interpret these results in terms of a
simple model of AGN and galaxy evolution, whereby a "quasar" phase and the
growth of the stellar bulge occurs when a galaxy's dark matter halo reaches a
critical mass between ~10^12 and 10^13 M_sun. Subsequently, star formation
ceases and AGN accretion shifts from radiatively efficient (optical- and IR-
bright) to radiatively inefficient (optically-faint, radio-bright) modes.Comment: 30 emulateapj pages, 21 figures, 3 tables, v2: minor changes match
version to appear in Ap
Haplotype Analysis Improved Evidence for Candidate Genes for Intramuscular Fat Percentage from a Genome Wide Association Study of Cattle
In genome wide association studies (GWAS), haplotype analyses of SNP data are neglected in favour of single point analysis of associations. In a recent GWAS, we found that none of the known candidate genes for intramuscular fat (IMF) had been identified. In this study, data from the GWAS for these candidate genes were re-analysed as haplotypes. First, we confirmed that the methodology would find evidence for association between haplotypes in candidate genes of the calpain-calpastatin complex and musculus longissimus lumborum peak force (LLPF), because these genes had been confirmed through single point analysis in the GWAS. Then, for intramuscular fat percent (IMF), we found significant partial haplotype substitution effects for the genes ADIPOQ and CXCR4, as well as suggestive associations to the genes CEBPA, FASN, and CAPN1. Haplotypes for these genes explained 80% more of the phenotypic variance compared to the best single SNP. For some genes the analyses suggested that there was more than one causative mutation in some genes, or confirmed that some causative mutations are limited to particular subgroups of a species. Fitting the SNPs and their interactions simultaneously explained a similar amount of the phenotypic variance compared to haplotype analyses. Haplotype analysis is a neglected part of the suite of tools used to analyse GWAS data, would be a useful method to extract more information from these data sets, and may contribute to reducing the missing heritability problem
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