5,043 research outputs found
Response of the warm absorber cloud to a variable nuclear flux in active galactic nuclei
Recent modeling of the warm absorber in active galactic nuclei has proved the
usefulness of constant total (gas plus radiation) pressure models, which are
highly stratified in temperature and density. We explore the consistency of
those models when the typical variation of the flux from the central source is
taken into account. We perform a variability study of the warm absorber
response, based on timescales and our photoionization code TITAN. We show that
the ionization and recombination timescales are much shorter than the dynamical
timescale. Clouds very close to the central black hole will maintain their
equilibrium since the characteristic variability timescales of the nuclear
source are longer than cloud timescales. For more distant clouds, the density
structure has no time to vary, in response to the variations of the temperature
or ionization structure, and such clouds will show the departure from the
constant pressure equilibrium. We explore the impact of this departure on the
observed properties of the transmitted spectrum and soft X-ray variability: (i)
non uniform velocities, of the order of sound speed, appear due to pressure
gradients, up to typical values of 100 km/s. These velocities lead to the
broadening of lines. This broadening is usually observed and very difficult to
explain otherwise. (ii) Energy-dependent fractional variability amplitude in
soft X-ray range has a broader hump around ~ 1-2 keV, and (iv) the plot of the
equivalent hydrogen column density vs. ionization parameter is steeper than for
equilibrium clouds. The results have the character of a preliminary study and
should be supplemented in the future with full time-dependent radiation
transfer and dynamical computations.Comment: 9 pages, 7 figures, accepted for publication by Astronomy &
Astrophysic
Production of exotic charmonium in interactions at hadronic colliders
In this paper we investigate the Exotic Charmonium (EC) production in interactions present in proton-proton, proton-nucleus and
nucleus-nucleus collisions at the CERN Large Hadron Collider (LHC) energies as
well as for the proposed energies of the Future Circular Collider (FCC). Our
results demonstrate that the experimental study of these processes is feasible
and can be used to constrain the theoretical decay widths and shed some light
on the configuration of the considered multiquark states.Comment: 7 pages, 2 figures, 3 tables. v2: Revised version published in
Physical Review
The puzzle of the soft X-ray excess in AGN: absorption or reflection?
The 2-10 keV continuum of AGN is generally well represented by a single power
law. However, at smaller energies the continuum displays an excess with respect
to the extrapolation of this power law, called the ''soft X-ray excess''. Until
now this soft X-ray excess was attributed, either to reflection of the hard
X-ray source by the accretion disk, or to the presence of an additional
comptonizing medium, giving a steep spectrum. An alternative solution proposed
by Gierlinski and Done (2004) is that a single power law well represents both
the soft and the hard X-ray emission and the impression of the soft X-ray
excess is due to absorption of a primary power law by a relativistic wind. We
examine the advantages and drawbacks of reflection versus absorption models,
and we conclude that the observed spectra can be well modeled, either by
absorption (for a strong excess), or by reflection (for a weak excess). However
the physical conditions required by the absorption models do not seem very
realistic: we would prefer an ''hybrid model''.Comment: 4 pages, 3 figures, abstracts SF2A-2005, published by EDP-Sciences
Conference Serie
Exclusive dilepton production in ultraperipheral collisions at the LHC
In this paper we perform a systematic study of the exclusive dilepton
production by interactions in collisions at the LHC Run
2 energies considering different levels of precision for the treatment of the
absorptive corrections and for the nuclear form factor. The rapidity and
invariant mass distributions are estimated taking into account the experimental
cutoffs and a comparison with the recent ALICE and ATLAS data for the
and production is presented.Comment: 8 pages, 5 figures. Matches the improved version published in EPJ
A negotiation approach to support interoperability in a collaborative manufacturing environment
Maintaining the interoperability in a dynamic competitive manufacturing environment in which different business enterprises collaborate is difficult to achieve. Our approach highlights negotiation as the best solution to solve interoperability problems by reaching the common decision suitable for all managers of various enterprises in the most optimized amount of time. In this context, this paper proposes a multi-agent negotiation model, able to coordinate several negotiations taking place in parallel among multiple participants. It is described the negotiation strategy for evaluating and generating offers and the protocol for sending the offers to the other agents. This model is being implemented in the H2020 C2NET project for supporting manufacturing.info:eu-repo/semantics/acceptedVersio
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