12,748 research outputs found
XMM-Newton observations of three poor clusters: Similarity in dark matter and entropy profiles down to low mass
(Abridged) We present an analysis of the mass and entropy profiles of three
poor clusters (A1991, A2717 and MKW9) observed with XMM-Newton. The clusters
have similar temperatures (kT=2.65, 2.53 and 2.58 keV), and similar redshifts
(0.04 < z < 0.06). We trace the surface brightness, temperature, entropy and
integrated mass profiles up to 0.5 (0.35 for MKW9) of the virial radius
(r_200). The integrated mass profiles are very similar in physical units and
are reasonably well fitted with the NFW mass model with concentration
parameters of c_200=4-6 and M_200=1.2-1.6 X 10^14 h_70^-1 \msun. The entropy
profiles are similar at large scale, but there is some scatter in the central
region (r<50 kpc). None of the clusters has an isentropic core. Including XMM
data on A1983 (kT=2.2 keV), and A1413 (kT = 6.5 keV), we discuss the structural
and scaling properties of cluster mass and entropy profiles. The scaled mass
profiles display <20% dispersion in the 0.05 - 0.5 r_200 radial range. The
c_200 parameters of these clusters, and other values from the literature, are
fully consistent with the c_200 - M_200 relation derived from simulations. The
dispersion in scaled entropy profiles is small, implying self-similarity down
to low mass (kT ~2 keV), and is reduced by 30-40% (to ~20%) if we use the
empirical relation S \propto T^0.65 instead of the standard self-similar
relation, S \propto T. The mean scaled profile is well fitted by a power law
for 0.05 < r_200 < 0.5, with a slope slightly lower than expected from pure
shock heating (\alpha = 0.94+/-0.14), and a normalisation at 0.1 r_200
consistent with previous studies. The gas history thus likely depends both on
gravitational processes and the interplay between cooling and various galaxy
feedback mechanisms.Comment: Final refereed version to appear in A&A. Minor changes. 15 pages, 12
figures (Figs 1 & 3 low res
Anisotropic thermal expansion of bismuth from first principles
Some anisotropy in both mechanical and thermodynamical properties of bismuth
is expected. A combination of density functional theory total energy
calculations and density functional perturbation theory in the local density
approximation is used to compute the elastic constants at 0 K using a finite
strain approach and the thermal expansion tensor in the quasiharmonic
approximation. The overall agreement with experiment is good. Furthermore, the
anisotropy in the thermal expansion is found to arise from the anisotropy in
both the directional compressibilities and the directional Gr\"uneisen
functions.Comment: accepted for publication in PR
Pseudographs and Lax-Oleinik semi-group: a geometric and dynamical interpretation
Let H be a Tonelli Hamiltonian defined on the cotangent bundle of a compact
and connected manifold and let u be a semi-concave function defined on M. If E
(u) is the set of all the super-differentials of u and (\phi t) the Hamiltonian
flow of H, we prove that for t > 0 small enough, \phi-t (E (u)) is an exact
Lagrangian Lipschitz graph. This provides a geometric
interpretation/explanation of a regularization tool that was introduced by
P.~Bernard to prove the existence of C 1,1 subsolutions
Looking for Light Pseudoscalar Bosons in the Binary Pulsar System J0737-3039
We present numerical calculations of the photon-light-pseudoscalar-boson
conversion in the recently discovered binary pulsar system J0737-3039. Light
pseudoscalar bosons (LPBs) oscillate into photons in the presence of strong
magnetic fields. In the context of this binary pulsar system, this phenomenon
attenuates the light beam emitted by one of the pulsars, when the light ray
goes through the magnetosphere of the companion pulsar. We show that such an
effect is observable in the gamma-ray band since the binary pulsar is seen
almost edge-on, depending on the value of the LPB mass and on the strenght of
its two-photon coupling. Our results are surprising in that they show a very
sharp and significant (up to 50%) transition probability in the gamma-ray (
tens of MeV) domain. The observations can be performed by the upcoming NASA
GLAST mission.Comment: to appear in Phys. Rev. Let
An SZ/X-ray galaxy cluster model and the X-ray follow-up of the Planck clusters
Sunyaev-Zel'dovich (SZ) cluster surveys will become an important cosmological
tool over next few years, and it will be essential to relate these new surveys
to cluster surveys in other wavebands. We present an empirical model of cluster
SZ and X-ray observables constructed to address this question and to motivate,
dimension and guide X-ray follow-up of SZ surveys. As an example application of
the model, we discuss potential XMM-Newton follow-up of Planck clusters.Comment: 4 pages, 5 figures. To appear in the proceedings of the XXXXIIIrd
Rencontres de Morion
Development of GCP Ontology for sharing crop information
Poster presented at 3rd International Biocuration Conference. Berlin (Germany), 17 Apr 200
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