1,426 research outputs found
Evolution in the iron abundance of the ICM
We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies
at , which cover a temperature range of keV. Our analysis
is aimed at measuring the iron abundance in the ICM out to the highest redshift
probed to date. We find that the emission-weighted iron abundance measured
within in clusters below 5 keV is, on average, a factor of
higher than in hotter clusters, following , which confirms the trend seen in local samples. We made use of
combined spectral analysis performed over five redshift bins at
to estimate the average emission weighted iron abundance. We find a constant
average iron abundance as a function of redshift,
but only for clusters at . The emission-weighted iron abundance is
significantly higher () in the redshift range
, approaching the value measured locally in the inner radii for a mix of cool-core and non cool-core clusters in the
redshift range . The decrease in with can be
parametrized by a power law of the form . The observed
evolution implies that the average iron content of the ICM at the present epoch
is a factor of larger than at . We confirm that the ICM is
already significantly enriched () at a look-back time
of 9 Gyr. Our data provide significant constraints on the time scales and
physical processes that drive the chemical enrichment of the ICM.Comment: 4 pages, 4 figures, to appear in the Proceedings of "The Extreme
Universe in the Suzaku Era", Dicember 2006, Kyoto (Japan
The invisible environmental impact of tourism in show caves: microplastic pollution in three Italian show caves
Show caves are the most important geological heritage in the world, a significant economic resource and unique ecosystems characterized by speleothems, particular species and important drinking water reserves, however, microplastic (MP) pollution in caves is poorly studied. The deposits of three NW Italian show caves were investigated: for each cave, six sediment samples were collected along the tourist paths and one in a non-touristic area. MPs were identified and characterized using MUPL automated software, observed with and without UV light under a microscope, and verified under μFTIR-ATR. MPs were present in sediments of all examined caves: an average of 4300 MPs/kg were found along the tourist paths and of 2570 MPs/kg in the speleological zones. MPs less than 1 mm, fibre-shaped, polyesters and polyolefins dominated the samples suggesting that synthetic clothes are the main source of pollution in show caves. Our results highlight a high pollution of MPs in the examined show caves, despite the different touristic and environmental characteristics. The subterranean environment monitoring gives useful information to assess risks posed by MPs in show caves and consequently define strategies for the conservation and management of caves and natural resources
An X-ray view of Mrk 705: A borderline narrow-line Seyfert 1 galaxy
Mrk 705 exhibits optical properties of both narrow- and broad-line Seyfert 1
galaxies. We examine the X-ray properties of this borderline object utilising
proprietary and public data from Chandra, ASCA, ROSAT and RXTE, spanning more
than twelve years. Though long-term flux variability from the pointed
observations appears rather modest (about 3 times), we do find examples of rare
large amplitude outbursts in the RXTE monitoring data. There is very little
evidence of long-term spectral variability as the low- and high-energy spectra
appear constant with time. A 6.4 keV emission line is detected in the ASCA
spectra of Mrk 705, but not during the later, higher flux state Chandra
observation. However, the upper limit on the equivalent width of a line in the
Chandra spectrum is consistent with a constant-flux emission line and a
brighter continuum, suggesting that the line is emitted from distant material
such as the putative torus. Overall, the X-ray properties of Mrk 705 appear
typical of BLS1 activity.Comment: 7 pages, 7 figures. Accepted for publication in A&A (Research Note
Tracing the evolution in the iron content of the ICM
We present a Chandra analysis of the X-ray spectra of 56 clusters of galaxies
at z>0.3, which cover a temperature range of 3>kT>15 keV. Our analysis is aimed
at measuring the iron abundance in the ICM out to the highest redshift probed
to date. We find that the emission-weighted iron abundance measured within
(0.15-0.3)R_vir in clusters below 5 keV is, on average, a factor of ~2 higher
than in hotter clusters, following Z(T)~0.88T^-(0.47)Z_o, which confirms the
trend seen in local samples. We made use of combined spectral analysis
performed over five redshift bins at 0.3>z>1.3 to estimate the average emission
weighted iron abundance. We find a constant average iron abundance Z_Fe~0.25Z_o
as a function of redshift, but only for clusters at z>0.5. The
emission-weighted iron abundance is significantly higher (Z_Fe~0.4Z_o) in the
redshift range z~0.3-0.5, approaching the value measured locally in the inner
0.15R_vir radii for a mix of cool-core and non cool-core clusters in the
redshift range 0.1<z<0.3. The decrease in Z_Fe with redshift can be
parametrized by a power law of the form ~(1+z)^(-1.25). The observed evolution
implies that the average iron content of the ICM at the present epoch is a
factor of ~2 larger than at z=1.2. We confirm that the ICM is already
significantly enriched (Z_Fe~0.25Z_o) at a look-back time of 9 Gyr. Our data
provide significant constraints on the time scales and physical processes that
drive the chemical enrichment of the ICM.Comment: 6 pages, 6 figures, to appear in the Proceedings of "Heating vs.
Cooling in Galaxies and Clusters of Galaxies", August 2006, Garching
(Germany
Feature Selection Based on a Genetic Algorithm for Optimizing Weaning Success
Finding the right time for weaning from ventilator is a difficult clinical decision. Several systems based on machine or deep learning are reported in literature. However, the results of these applications are not completely satisfactory and may be improved. An important aspect is represented by the features used as input of these systems. In this paper we present the results of the application of genetic algorithms to perform feature selection on a dataset containing 13688 patients under mechanical ventilation characterizing by 58 variables, extracted from the MIMIC III database. The results show that all features are important, but four of them are essential: 'Sedation_days', 'Mean_Airway_Pressure', 'PaO2', and 'Chloride'. This is only the initial step to obtain a tool to be added to the other clinical indices for minimize the risk of extubation failure
Flux of Primordial Monopoles
We discuss how in supersymmetric models with D and F-flat directions, a
primordial monopole flux of order 10^{-16} - 10^{-18} cm^{-2} sec^{-1} sr^{-1}
can coexist with the observed baryon asymmetry. A modified Affleck-Dine
scenario yields the desired asymmetry if the monopoles are superheavy (~
10^{13}-10^{18} GeV). For lighter monopoles with masses ~ 10^{9}-10^{12} GeV,
the baryon asymmetry can arise via TeV scale leptogenesis.Comment: 17 pages, 4 figures, revtex
Production of Mesons in the Reaction at 3.67 GeV/c
The ratio of the total exclusive production cross sections for
and mesons has been measured in the reaction at
GeV/c. The observed ratio is
from which the exclusive
meson production cross section is determined to be
. Differential cross section
distributions have been measured. Their shape is consistent with isotropic
meson production.Comment: 14 pages, 5 figures, accepted by Phys.Lett.
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