717 research outputs found
The Dynamical State and Mass-Concentration Relation of Galaxy Clusters
We use the Millennium Simulation series to study how the dynamical state of
dark matter halos affects the relation between mass and concentration. We find
that a large fraction of massive systems are identified when they are
substantially out of equilibrium and in a particular phase of their dynamical
evolution: the more massive the halo, the more likely it is found at a
transient stage of high concentration. This state reflects the recent assembly
of massive halos and corresponds to the first pericentric passage of
recently-accreted material when, before virialization, the kinetic and
potential energies reach maximum and minimum values, respectively. This result
explains the puzzling upturn in the mass-concentration relation reported in
recent work for massive halos; indeed, the upturn disappears when only
dynamically-relaxed systems are considered in the analysis. Our results warn
against applying simple equilibrium models to describe the structure of rare,
massive galaxy clusters and urges caution when extrapolating scaling laws
calibrated on lower-mass systems, where such deviations from equilibrium are
less common. The evolving dynamical state of galaxy clusters ought to be
carefully taken into account if cluster studies are to provide precise
cosmological constraints.Comment: 8 Pages. Minor changes to match published versio
Using Cluster Abundances and Peculiar Velocities to Test the Gaussianity of the Cosmological Density Field
(Abridged) By comparing the frequency of typical events with that of unusual
events, one can test whether the cosmological density distribution function is
consistent with the normally made assumption of Gaussianity. To this end, we
compare the consistency of the tail-inferred (from clusters) and measured
values (from large-scale flows) of the rms level of mass fluctuations for two
distribution functions: a Gaussian, and a texture (positively-skewed) PDF.
Averaging the recent large-scale flow measurements, we find that observations
of the rms and the tail at the 10 h^-1 Mpc scale disfavor a texture PDF at ~1.5
sigma in all cases. However, taking only the most recent measurement of the
rms, that from Willick et al. (1997b), the comparison disfavors textures for
low Omega_0=0.3, and disfavors Gaussian models if Omega_0=1 (again at ~1.5
sigma). Predictions for evolution of high temperature clusters can also be made
for the models considered, and strongly disfavor Omega_0=1 in Gaussian models
and marginally disfavor Omega_0=1 in texture models. Only Omega_0=0.3 Gaussian
models are consistent with all the data considered.Comment: 34 pg incl. 8 embedded figures, LaTeX, aaspp4.sty, submitted to Ap
A Comparative Study of Dragonfly Flight in Variable Oxygen Atmospheres
i ABSTRACT One hypothesis for the small size of insects relative to vertebrates, and the existence of giant fossil insects, is that atmospheric oxygen levels have constrained body sizes because oxygen delivery would be unable to match the needs of metabolically active tissues in larger insects. This study tested whether oxygen delivery becomes more challenging for larger insects by measuring the oxygen-sensitivity of flight metabolic rates and behavior during hovering for 11 different species of dragonflies that range in mass by an order of magnitude. Animals were flown in 7 different oxygen concentrations ranging from 30% to 2.5% to assess the sensitivity of their behavior and flight metabolic rates to oxygen. I also assessed the oxygen-sensitivity of flight in low-density air (nitrogen replaced with helium), to increase the metabolic demands of hovering flight. Lowered atmosphere densities did induce higher metabolic rates. Flight behaviors but not flight metabolic rates were highly oxygen-sensitive. A significant interaction between oxygen and mass was found for total flight time, with larger dragonflies varying flight time more in response to atmospheric oxygen. This study provides some support for the hypothesis that larger insects are more challenged in oxygen delivery, as predicted by the oxygen limitation hypothesis for insect gigantism in the Paleozoic. ii ACKNOWLEDGEMENT
Construction and validation of a dimensional scale exploring mood disorders: MAThyS (Multidimensional Assessment of Thymic States)
<p>Abstract</p> <p>Background</p> <p>The boundaries between mood states in bipolar disorders are not clear when they are associated with mixed characteristics. This leads to some confusion to define appropriate therapeutic strategies. A dimensional approach might help to better define bipolar moods states and more specifically those with mixed features.</p> <p>Therefore, we proposed a new tool based on a dimensional approach, built with a priori five sub-scales and focus on emotional reactivity rather than exclusively on mood tonality. This study was designed to validate this MAThyS Scale (Multidimensional Assessment of Thymic States).</p> <p>Methods</p> <p>One hundred and ninety six subjects were included: 44 controls and 152 bipolar patients in various states: euthymic, manic or depressed. The MAThyS is a visual analogic scale consisting of 20 items. These items corresponded to five quantitative dimensions ranging from inhibition to excitation: emotional reactivity, thought processes, psychomotor function, motivation and sensory perception. They were selected as they represent clinically relevant quantitative traits.</p> <p>Results</p> <p>Confirmatory analyses demonstrated a good validity for this scale, and a good internal consistency (Cronbach's alpha coefficient = 0.95). The MathyS scale is moderately correlated of both the MADRS scale (depressive score; r = -0.45) and the MAS scale (manic score; r = 0.56).</p> <p>When considering the Kaiser-Guttman rule and the scree plot, our model of 5 factors seems to be valid. The four first factors have an eigenvalue greater than 1.0 and the eigenvalue of the factor five is 0.97. In the scree plot, the "elbow", or the point at which the curve bends, indicates 5 factors to extract. This 5 factors structure explains 68 per cent of variance.</p> <p>Conclusion</p> <p>The characterisation of bipolar mood states based on a global score assessing inhibition/activation process (total score of the MATHyS) associated with descriptive analysis on sub-scores such as emotional reactivity (rather than the classical opposition euphoria/sadness) can be useful to better understand the broad spectrum of mixed states.</p
Predicting the Clustering of X-Ray Selected Galaxy Clusters in Flux-Limited Surveys
(abridged) We present a model to predict the clustering properties of X-ray
clusters in flux-limited surveys. Our technique correctly accounts for past
light-cone effects on the observed clustering and follows the non-linear
evolution in redshift of the underlying DM correlation function and cluster
bias factor. The conversion of the limiting flux of a survey into the
corresponding minimum mass of the hosting DM haloes is obtained by using
theoretical and empirical relations between mass, temperature and X-ray
luminosity of clusters. Finally, our model is calibrated to reproduce the
observed cluster counts adopting a temperature-luminosity relation moderately
evolving with redshift. We apply our technique to three existing catalogues:
BCS, XBACs and REFLEX samples. Moreover, we consider an example of possible
future space missions with fainter limiting flux. In general, we find that the
amplitude of the spatial correlation function is a decreasing function of the
limiting flux and that the EdS models always give smaller correlation
amplitudes than open or flat models with low matter density parameter. In the
case of XBACs, the comparison with previous estimates of the observational
spatial correlation shows that only the predictions of models with Omega_0m=0.3
are in good agreement with the data, while the EdS models have too low a
correlation strength. Finally, we use our technique to discuss the best
strategy for future surveys. Our results show that the choice of a wide area
catalogue, even with a brighter limiting flux, is preferable to a deeper, but
with smaller area, survey.Comment: 20 pages, Latex using MN style, 11 figures enclosed. Version accepted
for publication in MNRA
The Representative XMM-Newton Cluster Structure Survey (REXCESS) of an X-ray Luminosity Selected Galaxy Cluster Sample
The largest uncertainty for cosmological studies using clusters of galaxies
is introduced by our limited knowledge of the statistics of galaxy cluster
structure, and of the scaling relations between observables and cluster mass.
To improve on this situation we have started an XMM-Newton Large Programme for
the in-depth study of a representative sample of 33 galaxy clusters, selected
in the redshift range z=0.055 to 0.183 from the REFLEX Cluster Survey, having
X-ray luminosities above 0.4 X 10^44 h_70^-2 erg s^-1 in the 0.1 - 2.4 keV
band. This paper introduces the sample, compiles properties of the clusters,
and provides detailed information on the sample selection function. We describe
the selection of a nearby galaxy cluster sample that makes optimal use of the
XMM-Newton field-of-view, and provides nearly homogeneous X-ray luminosity
coverage for the full range from poor clusters to the most massive objects in
the Universe. For the clusters in the sample, X-ray fluxes are derived and
compared to the previously obtained fluxes from the ROSAT All-Sky Survey. We
find that the fluxes and the flux errors have been reliably determined in the
ROSAT All-Sky Survey analysis used for the REFLEX Survey. We use the sample
selection function documented in detail in this paper to determine the X-ray
luminosity function, and compare it with the luminosity function of the entire
REFLEX sample. We also discuss morphological peculiarities of some of the
sample members. The sample and some of the background data given in this
introductory paper will be important for the application of these data in the
detailed studies of cluster structure, to appear in forthcoming publications.Comment: 17 pages, 17 figures; to appear in A&A. A pdf version with
full-quality figures can be found at
ftp://ftp.xray.mpe.mpg.de/people/gwp/xmmlp/xmmlp.pd
Measuring and Modelling the Redshift Evolution of Clustering: the Hubble Deep Field North
(abridged) The evolution of galaxy clustering from z=0 to z=4.5 is analyzed
using the angular correlation function and the photometric redshift
distribution of galaxies brighter than I_{AB}\le 28.5 in the HDF North. The
reliability of the photometric redshift estimates is discussed on the basis of
the available spectroscopic redshifts, comparing different codes and
investigating the effects of photometric errors. The redshift bins in which the
clustering properties are measured are then optimized to take into account the
uncertainties of the photometric redshifts. The results show that the comoving
correlation length has a small decrease in the range 0<z<1 followed by an
increase at higher z. We compare these results with the theoretical predictions
of a variety of cosmological models belonging to the general class of CDM. The
comparison with the expected mass clustering evolution indicates that the
observed high-redshift galaxies are biased tracers of the dark matter with an
effective bias b strongly increasing with redshift. Assuming an Einstein-de
Sitter universe, we obtain b\simeq 2 at z=2 and b\simeq 5 at z=4. A comparison
of the clustering amplitudes that we measured at z=3 with those reported for
LBG suggests that the clustering depends on the abundance of the objects: more
abundant objects are less clustered, as expected in the paradigm of
hierarchical galaxy formation. The strong clustering and high bias measured at
z=3 are consistent with the expected density of massive haloes predicted for
the various cosmologies here considered. At z=4, the strong clustering observed
in the HDF requires a significant fraction of massive haloes to be already
formed by that epoch. This feature could be a discriminant test for the
cosmological parameters if confirmed by future observations.Comment: 23 pages, Latex using MN style, figures enclosed. Version accepted
for publication in MNRA
Regulatory interactions between IRG resistance GTPases in the cellular response to Toxoplasma gondii
Members of the immunity-related GTPase (IRG) family are interferon-inducible resistance factors against a broad spectrum of intracellular pathogens including Toxoplasma gondii. The molecular mechanisms governing the function and regulation of the IRG resistance system are largely unknown. We find that IRG proteins function in a system of direct, nucleotide-dependent regulatory interactions between family members. After interferon induction but before infection, the three members of the GMS subfamily of IRG proteins, Irgm1, Irgm2 and Irgm3, which possess an atypical nucleotide-binding site, regulate the intracellular positioning of the conventional GKS subfamily members, Irga6 and Irgb6. Following infection, the normal accumulation of Irga6 protein at the parasitophorous vacuole membrane (PVM) is nucleotide dependent and also depends on the presence of all three GMS proteins. We present evidence that an essential role of the GMS proteins in this response is control of the nucleotide-bound state of the GKS proteins, preventing their GTP-dependent activation before infection. Accumulation of IRG proteins at the PVM has previously been shown to be associated with a block in pathogen replication: our results relate for the first time the enzymatic properties of IRG proteins to their role in pathogen resistance
Effect of surrounding environment on atomic structure and equilibrium shape of growing nanocrystals: gold in/on SiO2
We report on the equilibrium shape and atomic structure of thermally-processed Au nanocrystals (NCs) as determined by high resolution transmission electron microscopy (TEM). The NCs were either deposited on SiO2surface or embedded in SiO2layer. Quantitative data on the NCs surface free energy were obtained via the inverse Wulff construction. Nanocrystals inside the SiO2layer are defect-free and maintain a symmetrical equilibrium shape during the growth. Nanocrystals on SiO2surface exhibit asymmetrical equilibrium shape that is characterized by the introduction of twins and more complex atomic defects above a critical size. The observed differences in the equilibrium shape and atomic structure evolution of growing NCs in and on SiO2is explained in terms of evolution in isotropic/anisotropic environment making the surface free energy function angular and/or radial symmetric/asymmetric affecting the rotational/translational invariance of the surface stress tensor
First simultaneous optical/near-infrared imaging of an X-ray selected, high-redshift cluster of galaxies with GROND: the galaxy population of XMMU J0338.7+0030 at z=1.1
The XMM-Newton Distant Cluster Project is a serendipitous survey for clusters
of galaxies at redshifts z>=0.8 based on deep archival XMM-Newton observations.
... Low-significance candidate high-z clusters are followed up with the
seven-channel imager GROND (Gamma-Ray Burst Optical and Near-Infrared Detector)
that is mounted at a 2m-class telescope. ... The test case is XMMU
J0338.7+0030, suggested to be at z~1.45+/-0.15 from the analysis of the z-H vs
H colour-magnitude diagram obtained from the follow-up imaging. Later VLT-FORS2
spectroscopy enabled us to identify four members, which set this cluster at
z=1.097+/-0.002. To reach a better knowledge of its galaxy population, we
observed XMMU J0338.7+0030 with GROND for about 6 hr. The publicly available
photo-z code le Phare was used. The Ks-band number counts of the non-stellar
sources out of the 832 detected down to z'~26 AB-mag in the 3.9x4.3 square
arcmin region of XMMU J0338.7+0030 imaged at all GROND bands clearly exceed
those computed in deep fields/survey areas at ~20.5 - 22.5 AB-mag. The
photo-z's of the three imaged spectroscopic members yield z=1.12+/-0.09. The
spatial distribution and the properties of the GROND sources with a photo-z in
the range 1.01 - 1.23 confirm the correspondence of the X-ray source with a
galaxy over-density at a significance of at least 4.3 sigma. Candidate members
that are spectro-photometrically classified as elliptical galaxies define a red
locus in the i'-z' vs z' colour-magnitude diagram that is consistent with the
red sequence of the cluster RDCS J0910+5422 at z=1.106. XMMU J0338.7+0030 hosts
also a population of bluer late-type spirals and irregulars. The starbursts
among the photometric members populate both loci, consistently with previous
results. The analysis of the available data set indicates that XMMU
J0338.7+0030 is a low-mass cluster (M_200 ~ 1E14 M_sun) at z=1.1. (Abridged)Comment: accepted for publication in Astronomy & Astrophysics Main Journal, 27
pages, 24 figures, 1 tabl
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