4,635 research outputs found
Where does the gas fueling star formation in BCGs originate?
We investigate the relationship between X-ray cooling and star formation in
brightest cluster galaxies (BCGs). We present an X-ray spectral analysis of the
inner regions, 10-40 kpc, of six nearby cool core clusters (z<0.35) observed
with Chandra ACIS. This sample is selected on the basis of the high star
formation rate (SFR) observed in the BCGs. We restrict our search for cooling
gas to regions that are roughly cospatial with the starburst. We fit single-
and multi-temperature mkcflow models to constrain the amount of isobarically
cooling intracluster medium (ICM). We find that in all clusters, below a
threshold temperature ranging between 0.9 and 3 keV, only upper limits can be
obtained. In four out of six objects, the upper limits are significantly below
the SFR and in two, namely A1835 and A1068, they are less than a tenth of the
SFR. Our results suggests that a number of mechanisms conspire to hide the
cooling signature in our spectra. In a few systems the lack of a cooling
signature may be attributed to a relatively long delay time between the X-ray
cooling and the star burst. However, for A1835 and A1068, where the X-ray
cooling time is shorter than the timescale of the starburst, a possible
explanation is that the region where gas cools out of the X-ray phase extends
to very large radii, likely beyond the core of these systems.Comment: to appear in A&
Electron beam transfer line design for plasma driven Free Electron Lasers
Plasma driven particle accelerators represent the future of compact
accelerating machines and Free Electron Lasers are going to benefit from these
new technologies. One of the main issue of this new approach to FEL machines is
the design of the transfer line needed to match of the electron-beam with the
magnetic undulators. Despite the reduction of the chromaticity of plasma beams
is one of the main goals, the target of this line is to be effective even in
cases of beams with a considerable value of chromaticity. The method here
explained is based on the code GIOTTO [1] that works using a homemade genetic
algorithm and that is capable of finding optimal matching line layouts directly
using a full 3D tracking code.Comment: 9 Pages, 4 Figures. A related poster was presented at EAAC 201
Oxygen transport in nanostructured lanthanum manganites
Methods and models describing oxygen diffusion and desorption in oxides have been developed for
slightly defective and well crystallised bulky materials. Does nanostructuring change the mechanism of
oxygen mobility? In such a case, models should be properly checked and adapted to take into account
new material properties. In order to do so, temperature programmed oxygen desorption and
thermogravimetric analysis, either in isothermal or ramp mode, have been used to investigate some
nanostructured La1\u2013xAxMnO3 d samples (A = Sr and Ce, 20\u201360 nm particle size) with perovskite-like
structure. The experimental data have been elaborated by means of different models to define a set of
kinetic parameters able to describe oxygen release properties and oxygen diffusion through the bulk.
Different rate-determining steps have been identified, depending on the temperature range and
oxygen depletion of the material. In particular, oxygen diffusion was shown to be rate-limiting at low
temperature and at low defect concentration, whereas oxygen recombination at the surface seems to
be the rate-controlling step at high temperature. However, the oxygen recombination step is characterised
by an activation energy much lower than that for diffusion. In the present paper oxygen transport
in nanosized materials is quantified by making use of widely diffused experimental techniques and
by critically adapting to nanoparticles suitably chosen models developed for bulk materials
Microbial diversity in innovative mesophilic/thermophilic temperature-phased anaerobic digestion of sludge
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Plasma boosted electron beams for driving Free Electron Lasers
In this paper, we report results of simulations, in the framework of both
EuPRAXIA \cite{Walk2017} and EuPRAXIA@SPARC\_LAB \cite{Ferr2017} projects,
aimed at delivering a high brightness electron bunch for driving a Free
Electron Laser (FEL) by employing a plasma post acceleration scheme. The
boosting plasma wave is driven by a tens of \SI{}{\tera\watt} class laser and
doubles the energy of an externally injected beam up to \GeV{1}. The injected
bunch is simulated starting from a photoinjector, matched to plasma, boosted
and finally matched to an undulator, where its ability to produce FEL radiation
is verified to yield O(\num{e11}) photons per shot at \nm{2.7}.Comment: 5 pages, 2 figure
An agent-based approach to assess drivers’ interaction with pre-trip information systems.
This article reports on the practical use of a multi-agent microsimulation framework to address the issue of assessing drivers’
responses to pretrip information systems. The population of drivers is represented as a community of autonomous agents,
and travel demand results from the decision-making deliberation performed by each individual of the population as regards
route and departure time. A simple simulation scenario was devised, where pretrip information was made available to users
on an individual basis so that its effects at the aggregate level could be observed. The simulation results show that the
overall performance of the system is very likely affected by exogenous information, and these results are ascribed to demand
formation and network topology. The expressiveness offered by cognitive approaches based on predicate logics, such as the
one used in this research, appears to be a promising approximation to fostering more complex behavior modelling, allowing
us to represent many of the mental aspects involved in the deliberation process
First report on Copepoda and Ostracoda (Crustacea) from northern Apenninic springs (N. Italy): a faunal and biogeographical account
The microcrustacean fauna of rheocrene and rheo-limnocrene springs in a protected area of the northern Apennines (Italy) was investigated for the first time. All springs are located in the catchments of the rivers Parma and Enza at altitudes between 800 and 1609 m a.s.l. Several of these springs are still in pristine condition while others are artificially modified or impacted to some degree. Surveys were carried out from April to June 2007. The sampling methods used for invertebrate fauna were: moss washing, artificial traps, and inserting drift tubes at the discharge point. A total of 14 harpacticoid, five cyclopoid, and 13 ostracod taxa were identified. Ostracods were mainly represented by crenophilic taxa; of particular interest was the collection of a specimen belonging to Pseudolimnocythere, a stygobiont genus with only two living species and a reduced distribution. Faunal affinities between northern Apenninic springs and those in other Italian mountain systems are discussed. The investigated ecosystems support a high microcrustacean diversity that must be adequately preserved due to the increasing direct and indirect impacts on mountain springs and groundwater resources
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