1,613 research outputs found
X-ray AGN in the XMM-LSS galaxy clusters: no evidence of AGN suppression
We present a study of the overdensity of X-ray selected AGN in 33 galaxy
clusters in the XMM-LSS field, up to redhift z=1.05. Previous studies have
shown that the presence of X-ray selected AGN in rich galaxy clusters is
suppressed. In the current study we investigate the occurrence of X-ray
selected AGN in low and moderate X-ray luminosity galaxy clusters. Due to the
wide contiguous XMM-LSS survey area we are able to extend the study to the
cluster outskirts. We therefore determine the projected overdensity of X-ray
point-like sources out to 6r_{500} radius. To provide robust statistical
results we also use a stacking analysis of the cluster projected overdensities.
We investigate whether the observed X-ray overdensities are to be expected by
estimating also the corresponding optical galaxy overdensities. We find a
positive X-ray projected overdensity at the first radial bin, which is however
of the same amplitude as that of optical galaxies. Therefore, no suppression of
X-ray AGN activity with respect to the field is found, implying that the
mechanisms responsible for the suppression are not so effective in lower
density environments. After a drop to roughly the background level between 2
and 3r_{500}, the X-ray overdensity exhibits a rise at larger radii,
significantly larger than the corresponding optical overdensity. Finally, using
redshift information of all optical counterparts, we derive the spatial
overdensity profile of the clusters. We find that the agreement between X-ray
and optical overdensities in the first radial bin is also suggested in the
3-dimensional analysis. However, we argue that the X-ray overdensity "bump" at
larger radial distance is probably a result of flux boosting by gravitational
lensing of background QSOs. For high redshift clusters an enhancement of X-ray
AGN activity in their outskirts is still possible.Comment: 16 pages. Accepted for publication in A&
Universal shape law of stochastic supercritical bifurcations: Theory and experiments
A universal law for the supercritical bifurcation shape of transverse
one-dimensional (1D) systems in presence of additive noise is given. The
stochastic Langevin equation of such systems is solved by using a Fokker-Planck
equation leading to the expression for the most probable amplitude of the
critical mode. From this universal expression, the shape of the bifurcation,
its location and its evolution with the noise level are completely defined.
Experimental results obtained for a 1D transverse Kerr-like slice subjected to
optical feedback are in excellent agreement.Comment: 5 pages, 5 figure
Inter Simple Sequence Repeat Fingerprints for Assess Genetic Diversity of Tunisian Garlic Populations
Garlic ( Allium sativum L.) that is cultivated in Tunisia is heterogeneous and unclassified with no registered local cultivars. At present, the level of genetic diversity in Tunisian garlic is almost unknown. Inter Simple Sequence Repeats (ISSR) genetic markers were therefore used to assess the genetic diversity and its distribution in 31 Tunisian garlic accessions with 4 French classified clones used as control. It was the first time that ISSR markers were used to detect diversity in garlic. Seventeen ISSR primers were screened; seven primers detected 73 polymorphic bands. A high level of polymorphic loci (p) was found in Tunisian populations (54%). Nei’s total genetic diversity coefficient was 0.45 and 0.34 respectively for Tunisian and French garlic. Genetic distances observed between Tunisian accessions, ranged between 38.4 and 78.1%. Factor analysis of distances’ table (AFTD) did not classify accessions on the base of geographical origin or morpho-physiological characters, particularly bolting ability, but confirmed the appurtenance of analyzed accessions to s ativum botanical subspecies. There was sufficient diversity detected to start a national collection of garlic germplasm which is crucial for the conservation of genetic diversity and its valorization. Keywords: Allium sativum L., ISSR markers, genetic diversity, Tunisian garlic populations
Zig-zag instability of an Ising wall in liquid crystals
We present a theoretical explanation for the interfacial zigzag instability
that appears in anisotropic systems. Such an instability has been
experimentally highlighted for an Ising wall formed in a nematic liquid crystal
cell under homeotropic anchoring conditions. From an envelope equation,
relevant close to the Freedericksz transition, we have derived an asymptotic
equation describing the interface dynamics in the vicinity of its bifurcation.
The asymptotic limit used accounts for a strong difference between two of the
elastic constants. The model is characterized by a conservative order parameter
which satisfies a Cahn-Hilliard equation. It provides a good qualitative
understanding of the experiments.Comment: 4 pagess, 4 figures, lette
Monte Carlo simulation of the transmission of measles: Beyond the mass action principle
We present a Monte Carlo simulation of the transmission of measles within a
population sample during its growing and equilibrium states by introducing two
different vaccination schedules of one and two doses. We study the effects of
the contact rate per unit time as well as the initial conditions on the
persistence of the disease. We found a weak effect of the initial conditions
while the disease persists when lies in the range 1/L-10/L ( being
the latent period). Further comparison with existing data, prediction of future
epidemics and other estimations of the vaccination efficiency are provided.
Finally, we compare our approach to the models using the mass action
principle in the first and another epidemic region and found the incidence
independent of the number of susceptibles after the epidemic peak while it
strongly fluctuates in its growing region. This method can be easily applied to
other human, animals and vegetable diseases and includes more complicated
parameters.Comment: 15 pages, 4 figures, 1 table, Submitted to Phys.Rev.
Lower gastrointestinal bleeding-Computed Tomographic Angiography, Colonoscopy or both?
Lower endoscopy (LE) is the standard diagnostic modality for lower gastrointestinal bleeding (LGIB). Conversely, computed tomographic angiography (CTA) offers an immediate non-invasive diagnosis visualizing the entire gastrointestinal tract. The aim of this study was to compare these 2 modalities with regards to diagnostic value and bleeding control.
Tertiary center retrospective analysis of consecutive patients admitted for LGIB between 2006 and 2012. Comparison of patients with LE <i>vs.</i> CTA as first exam, respectively, with emphasis on diagnostic accuracy and bleeding control.
Final analysis included 183 patients; 122 (66.7%) had LE first, while 32 (17.5%) had CTA; 29 (15.8%) had neither of both exams. Median time to CTA was shorter compared to LE (3 (IQR = 8.2) <i>vs.</i> 22 (IQR = 36.9) hours, <i>P</i> < 0.001). Active bleeding was identified in 31% with CTA <i>vs.</i> 15% with LE ( <i>P</i> = 0.031); a non-actively bleeding source was found by CTA and LE in 22 <i>vs.</i> 31%, respectively ( <i>P</i> = 0.305). Bleeding control required endoscopy in 19%, surgery in 14% and embolization in 1.6%, while 66% were treated conservatively. Post-interventional bleeding was mostly controlled by endoscopic therapy (57%). 80% of patients with active bleeding on CTA required surgery.
Post-interventional LGIB was effectively addressed by LE. For other causes of LGIB, CTA was efficient, and more available than colonoscopy. Treatment was conservative for most patients. In case of active bleeding, CTA could localize the bleeding source and predict the need for surgery
The XMM-LSS survey: the Class 1 cluster sample over the extended 11 deg and its spatial distribution
This paper presents 52 X-ray bright galaxy clusters selected within the 11
deg XMM-LSS survey. 51 of them have spectroscopic redshifts
(), one is identified at , and all together make
the high-purity "Class 1" (C1) cluster sample of the XMM-LSS, the highest
density sample of X-ray selected clusters with a monitored selection function.
Their X-ray fluxes, averaged gas temperatures (median keV),
luminosities (median ergs/s) and total mass
estimates (median ) are measured, adapting to
the specific signal-to-noise regime of XMM-LSS observations. The redshift
distribution of clusters shows a deficit of sources when compared to the
cosmological expectations, regardless of whether WMAP-9 or Planck-2013 CMB
parameters are assumed. This lack of sources is particularly noticeable at . However, after quantifying uncertainties due to small
number statistics and sample variance we are not able to put firm (i.e. ) constraints on the presence of a large void in the cluster
distribution. We work out alternative hypotheses and demonstrate that a
negative redshift evolution in the normalization of the relation
(with respect to a self-similar evolution) is a plausible explanation for the
observed deficit. We confirm this evolutionary trend by directly studying how
C1 clusters populate the space, properly accounting for selection
biases. We point out that a systematically evolving, unresolved, central
component in clusters and groups (AGN contamination or cool core) can impact
the classification as extended sources and be partly responsible for the
observed redshift distribution.[abridged]Comment: 33 pages, 21 figures, 3 tables ; accepted for publication in MNRA
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