5,170 research outputs found
On the size of the Fe II emitting region in the AGN Akn 120
We present a reverberation analysis of the strong, variable optical Fe II
emission bands in the spectrum of Akn 120, a low-redshift AGN which is one of
the best candidates for such a study. On time scales of several years the Fe II
line strengths follow the variations in the continuum strength. However, we are
unable to measure a clear reverberation lag time for these Fe II lines on any
time scale. This is due to the very broad and flat-topped nature of the Fe II
cross correlation functions, as compared to the H-beta response which is much
more sharply localized in time. Although there is some suggestion in the light
curve of a 300-day response time, our statistical analysis does not pick up
such a feature. We conclude that the optical Fe II emission does not come from
a photoionization-powered region similar in size to the H-beta emitting region,
but we cannot say for sure where it does come from. Our results are generally
consistent either with emission from a photoionized region several times larger
than the H-beta zone, or with emission from gas heated by some other means,
perhaps responding only indirectly to the continuum variations.Comment: Accepted for publication in the Ap
The implications of resonant x-ray scattering data on the physics of the insulating phase of V_2O_3
We have performed a quantitative analysis of recent resonant x-ray scattering
experiments carried out in the antiferromagnetic phase of V_2O_3 by means of
numerical ab-initio simulations. In order to treat magnetic effects, we have
developed a method based on multiple scattering theory (MST) and a relativistic
extension of the Schr\"{o}dinger Equation, thereby working with the usual non
relativistic set of quantum numbers for angular and spin momenta.
Electric dipole-dipole (E1-E1), dipole-quadrupole (E1-E2) and
quadrupole-quadrupole (E2-E2) transition were considered altogether. We obtain
satisfactory agreement with experiments, both in energy and azimuthal scans.
All the main features of the V K edge Bragg-forbidden reflections with
odd can be interpreted in terms of the antiferromagnetic ordering only,
{\it ie}, they are of magnetic origin. In particular the ab-initio simulation
of the energy scan around the (1,1,1)-monoclinic reflection excludes the
possibility of any symmetry reduction due to a time-reversal breaking induced
by orbital ordering.Comment: 11 pages, 6 figure
Wetting on Nanorough Surfaces
We present in this Letter a free-energy approach to the dynamics of a fluid
near a nanostructured surface. The model accounts both for the static phase
equilibrium in the vicinity of the surface (wetting angles, Cassie-Wenzel
transition) and the dynamical properties like liquid slippage at the boundary.
This method bridges the gap between phenomenological phase-field approaches and
more macroscopic lattice-Boltzmann models
La reprĂ©sentation sociale du football chez des jeunes adultes issus dâun milieu social dĂ©favorisĂ©
Soccer is a team sport, practiced as a recreational physical activity by amateurs or professionally with elite players. This popular sport has several advantages such as integration of diverse styles and simple rules (Defrance, 1995). A psycho-sociological perspective is adopted in this article, exploring soccer as an object of social representation (Moscovici, 1961/76) with young, adult amateurs from a disadvantaged social background. The results obtained using the free association method and the characterization questionnaire show that there is a social representation of soccer. If, for young amateurs, this representation is based on the values of team sport, the one given to parents is rooted in the professional world. In addition, this study adds to an original phenomenon of the hiddenâ area of social representations. Between amateurism and professionalism, the reference to âZinedine Zidaneâ adds to the controversial nature of this representation for young people
The Challenge Of Including Chemodiversity, And The Potential Economic Use Of New Natural Compounds And Processes, In The Biota/fapesp Program
28339139
Exponential decay for the damped wave equation in unbounded domains
We study the decay of the semigroup generated by the damped wave equation in
an unbounded domain. We first prove under the natural geometric control
condition the exponential decay of the semigroup. Then we prove under a weaker
condition the logarithmic decay of the solutions (assuming that the initial
data are smoother). As corollaries, we obtain several extensions of previous
results of stabilisation and control
On Quasar Masses and Quasar Host Galaxies
The mass of massive black holes in quasar cores can be deduced using the
typical velocities of Hb-emitting clouds in the Broad Line Region (BLR) and the
size of this region. However, this estimate depends on various assumptions and
is susceptible to large systematic errors. The Hb-deduced black hole mass in a
sample of 14 bright quasars is found here to correlate with the quasar host
galaxy luminosity, as determined with the Hubble Space Telescope (HST). This
correlation is similar to the black hole mass vs. bulge luminosity correlation
found by Magorrian et al. in a sample of 32 nearby normal galaxies. The
similarity of the two correlations is remarkable since the two samples involve
apparently different types of objects and since the black hole mass estimates
in quasars and in nearby galaxies are based on very different methods.
This similarity provides a ``calibration'' of the Hb-deduced black hole mass
estimate, suggesting it is accurate to +-0.5 on log scale. The similarity of
the two correlations also suggests that quasars reside in otherwise normal
galaxies, and that the luminosity of quasar hosts can be estimated to +-0.5 mag
based on the quasar continuum luminosity and the Hb line width. Future imaging
observations of additional broad-line active galaxies with the HST are required
in order to explore the extent, slope, and scatter of the black hole mass vs.
host bulge luminosity correlation in active galaxies.Comment: Accepted for publication in ApJ Letters, 7 pages, aas2pp4.st
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