95 research outputs found
Mapping small-scale temperature and abundance structures in the core of the Perseus cluster
We report further results from a 191 ks Chandra observation of the core of
the Perseus cluster, Abell 426. The emission-weighted temperature and abundance
structure is mapped detail. There are temperature variations down to ~1 kpc in
the brightest regions. Globally, the strongest X-ray surface brightness
features appear to be caused by temperature changes. Density and temperature
changes conspire to give approximate azimuthal balance in pressure showing that
the gas is in hydrostatic equilibrium. Si, S, Ar, Ca, Fe and Ni abundance
profiles rise inward from about 100 kpc, peaking at about 30-40 kpc. Most of
these abundances drop inwards of the peak, but Ne shows a central peak, all of
which may be explained by resonance scattering. There is no evidence for a
widespread additional cooler temperature component in the cluster with a
temperature greater than a factor of two from the local temperature. There is
however evidence for a widespread hard component which may be nonthermal. The
temperature and abundance of gas in the cluster is observed to be correlated in
a manner similar to that found between clusters.Comment: ~20 pages, colour, accepted by MNRAS. Updates include a more
extensive discussion of the hard component, reference corrections, and a few
other minor changes. A version with good figure quality is at
http://www-xray.ast.cam.ac.uk/papers/perdetail
Extreme AGN Feedback and Cool Core Destruction in the X-ray Luminous Galaxy Cluster MACS J1931.8-2634
We report on a deep, multiwavelength study of the galaxy cluster MACS
J1931.8-2634 using Chandra X-ray, Subaru optical, and VLA 1.4 GHz radio data.
This cluster (z=0.352) harbors one of the most X-ray luminous cool cores yet
discovered, with an equivalent mass cooling rate within the central 50 kpc is
approximately 700 solar masses/yr. Unique features observed in the central core
of MACSJ1931.8-2634 hint to a wealth of past activity that has greatly
disrupted the original cool core. We observe a spiral of relatively cool,
dense, X-ray emitting gas connected to the cool core, as well as highly
elongated intracluster light (ICL) surrounding the cD galaxy. Extended radio
emission is observed surrounding the central AGN, elongated in the east-west
direction, spatially coincident with X-ray cavities. The power input required
to inflate these `bubbles' is estimated from both the X-ray and radio emission
to reside between 4 and 14e45 erg/s, putting it among the most powerful jets
ever observed. This combination of a powerful AGN outburst and bulk motion of
the cool core have resulted in two X-ray bright ridges to form to the north and
south of the central AGN at a distance of approximately 25 kpc. The northern
ridge has spectral characteristics typical of cool cores and is consistent with
being a remnant of the cool core after it was disrupted by the AGN and bulk
motions. It is also the site of H-alpha filaments and young stars. The X-ray
spectroscopic cooling rate associated with this ridge is approximately 165
solar masses/yr, which agrees with the estimate of the star formation rate from
broad-band optical imaging (170 solar masses/yr). MACS J1931.8-2634 appears to
harbor one of most profoundly disrupted low entropy cores observed in a
cluster, and offers new insights into the survivability of cool cores in the
context of hierarchical structure formation.Comment: 19 pages, 15 figures, 5 tables. Accepted by MNRAS for publication
September 30 201
The Observed Growth of Massive Galaxy Clusters II: X-ray Scaling Relations
(Abridged) This is the second in a series of papers in which we derive
simultaneous constraints on cosmology and X-ray scaling relations using
observations of massive, X-ray flux-selected galaxy clusters. The data set
consists of 238 clusters drawn from the ROSAT All-Sky Survey with 0.1-2.4 keV
luminosities >2.5e44 erg/second, and incorporates extensive follow-up
observations using the Chandra X-ray Observatory. Our analysis accounts
self-consistently for all selection effects, covariances and systematic
uncertainties. Here we describe the reduction of the follow-up X-ray
observations, present results on the cluster scaling relations, and discuss
their implications. Our constraints on the luminosity-mass and temperature-mass
relations, measured within r_500, lead to three important results. First, the
data support the conclusion that excess heating of the intracluster medium has
altered its thermodynamic state from that expected in a simple, gravitationally
dominated system; however, this excess heating is primarily limited to the
central regions of clusters (r<0.15r_500). Second, the intrinsic scatter in the
center-excised luminosity-mass relation is remarkably small, being undetected
at the <10% level in current data; for the hot, massive clusters under
investigation, this scatter is smaller than in either the temperature-mass or
Y_X-mass relations (10-15%). Third, the evolution with redshift of the scaling
relations is consistent with the predictions of simple, self-similar models of
gravitational collapse, indicating that the mechanism responsible for heating
the central regions of clusters was in operation before redshift 0.5 (the limit
of our data) and that its effects on global cluster properties have not evolved
strongly since then.Comment: 25 pages, 7 figures, 14 tables. v3: final version (typographic
corrections). Results can be downloaded at
https://www.stanford.edu/group/xoc/papers/xlf2009.htm
The Chemerin/ChemR23 System Does Not Affect the Pro-Inflammatory Response of Mouse and Human Macrophages Ex Vivo
Macrophages constitute a major component of innate immunity and play an essential role in defense mechanisms against external aggressions and in inflammatory responses. Chemerin, a chemoattractant protein, is generated in inflammatory conditions, and recruits cells expressing the G protein-coupled receptor ChemR23, including macrophages. Chemerin was initially expected to behave as a pro-inflammatory agent. However, recent data described more complex activities that are either pro- or anti-inflammatory, according to the disease model investigated. In the present study, peritoneal macrophages were generated from WT or ChemR23â/â mice, stimulated with lipopolyssaccharide in combination or not with IFN-Îł and the production of pro- (TNF-α, IL-1ÎČ and IL-6) and anti-inflammatory (IL-10) cytokines was evaluated using qRT-PCR and ELISA. Human macrophages generated from peripheral blood monocytes were also tested in parallel. Peritoneal macrophages from WT mice, recruited by thioglycolate or polyacrylamide beads, functionally expressed ChemR23, as assessed by flow cytometry, binding and chemotaxis assays. However, chemerin had no effect on the strong upregulation of cytokine release by these cells upon stimulation by LPS or LPS/IFN-Îł, whatever the concentration tested. Similar data were obtained with human macrophages. In conclusion, our results rule out the direct anti-inflammatory effect of chemerin on macrophages ex vivo, described previously in the literature, despite the expression of a functional ChemR23 receptor in these cells
A conceptual framework for implementation fidelity
<p>Abstract</p> <p>Background</p> <p>Implementation fidelity refers to the degree to which an intervention or programme is delivered as intended. Only by understanding and measuring whether an intervention has been implemented with fidelity can researchers and practitioners gain a better understanding of how and why an intervention works, and the extent to which outcomes can be improved.</p> <p>Discussion</p> <p>The authors undertook a critical review of existing conceptualisations of implementation fidelity and developed a new conceptual framework for understanding and measuring the process. The resulting theoretical framework requires testing by empirical research.</p> <p>Summary</p> <p>Implementation fidelity is an important source of variation affecting the credibility and utility of research. The conceptual framework presented here offers a means for measuring this variable and understanding its place in the process of intervention implementation.</p
An agenda for integrated system-wide interdisciplinary agri-food research
© 2017 The Author(s)This paper outlines the development of an integrated interdisciplinary approach to agri-food research, designed to address the âgrand challengeâ of global food security. Rather than meeting this challenge by working in separate domains or via single-disciplinary perspectives, we chart the development of a system-wide approach to the food supply chain. In this approach, social and environmental questions are simultaneously addressed. Firstly, we provide a holistic model of the agri-food system, which depicts the processes involved, the principal inputs and outputs, the actors and the external influences, emphasising the systemâs interactions, feedbacks and complexities. Secondly, we show how this model necessitates a research programme that includes the study of land-use, crop production and protection, food processing, storage and distribution, retailing and consumption, nutrition and public health. Acknowledging the methodological and epistemological challenges involved in developing this approach, we propose two specific ways forward. Firstly, we propose a method for analysing and modelling agri-food systems in their totality, which enables the complexity to be reduced to essential components of the whole system to allow tractable quantitative analysis using LCA and related methods. This initial analysis allows for more detailed quantification of total system resource efficiency, environmental impact and waste. Secondly, we propose a method to analyse the ethical, legal and political tensions that characterise such systems via the use of deliberative fora. We conclude by proposing an agenda for agri-food research which combines these two approaches into a rational programme for identifying, testing and implementing the new agri-technologies and agri-food policies, advocating the critical application of nexus thinking to meet the global food security challenge
Planck 2013 results. XX. Cosmology from Sunyaev-Zeldovich cluster counts
We present constraints on cosmological parameters using number counts as a
function of redshift for a sub-sample of 189 galaxy clusters from the Planck SZ
(PSZ) catalogue. The PSZ is selected through the signature of the
Sunyaev--Zeldovich (SZ) effect, and the sub-sample used here has a
signal-to-noise threshold of seven, with each object confirmed as a cluster and
all but one with a redshift estimate. We discuss the completeness of the sample
and our construction of a likelihood analysis. Using a relation between mass
and SZ signal calibrated to X-ray measurements, we derive constraints
on the power spectrum amplitude and matter density parameter
in a flat CDM model. We test the robustness of
our estimates and find that possible biases in the -- relation and the
halo mass function are larger than the statistical uncertainties from the
cluster sample. Assuming the X-ray determined mass to be biased low relative to
the true mass by between zero and 30%, motivated by comparison of the observed
mass scaling relations to those from a set of numerical simulations, we find
that , , and
. The value of
is degenerate with the mass bias; if the latter is fixed to a value
of 20% we find and a
tighter one-dimensional range . We find that the larger
values of and preferred by Planck's
measurements of the primary CMB anisotropies can be accommodated by a mass bias
of about 40%. Alternatively, consistency with the primary CMB constraints can
be achieved by inclusion of processes that suppress power on small scales
relative to the CDM model, such as a component of massive neutrinos
(abridged).Comment: 20 pages, accepted for publication by A&
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