432 research outputs found
A Sunyaev-Zel'dovich map of the massive core in the luminous X-ray cluster RXJ1347-1145
We have mapped the Sunyaev-Zel'dovich decrement (hereafter SZ) in the
direction of the most luminous X-ray cluster known to date, RXJ1347-1145, at
z=0.451. This has been achieved with an angular resolution of about 23'' using
the Diabolo photometer running on the IRAM 30 meter radio telescope. We present
here a map of the cluster central region at 2.1mm. The Comptonization parameter
towards the cluster center, \yc=(12.7^{+2.9}_{-3.1})\times 10^{-4},
corresponds to the deepest SZ decrement ever observed. Using the gas density
distribution derived from X-ray data, this measurement implies a gas
temperature \te=16.2 \pm 3.8 keV. The resulting total mass of the cluster is,
under hydrostatic equilibrium, for a corresponding gas fraction .Comment: 16 pages, 2 figures, accepted for publication in ApJ Letter
Explicit approximate controllability of the Schr\"odinger equation with a polarizability term
We consider a controlled Schr\"odinger equation with a dipolar and a
polarizability term, used when the dipolar approximation is not valid. The
control is the amplitude of the external electric field, it acts non linearly
on the state. We extend in this infinite dimensional framework previous
techniques used by Coron, Grigoriu, Lefter and Turinici for stabilization in
finite dimension. We consider a highly oscillating control and prove the
semi-global weak stabilization of the averaged system using a Lyapunov
function introduced by Nersesyan. Then it is proved that the solutions of the
Schr\"odinger equation and of the averaged equation stay close on every finite
time horizon provided that the control is oscillating enough. Combining these
two results, we get approximate controllability to the ground state for the
polarizability system
The Diabolo photometer and the future of ground-based millimetric bolometer devices
The millimetric atmospheric windows at 1 and 2 mm are interesting targets for
cosmological studies. Two broad areas appear leading this field: 1) the search
for high redshift star-forming galaxies and 2) the measurement of
Sunyaev-Zel'dovich (SZ) effect in clusters of galaxies at all redshifts. The
Diabolo photometer is a dual-channel photometer working at 1.2 and 2.1 mm and
dedicated to high angular resolution measurements of the Sunyaev--Zel'dovich
effect towards distant clusters. It uses 2 by 3 bolometers cooled down to 0.1 K
with a compact open dilution cryostat. The high resolution is provided by the
IRAM 30 m telescope. The result of several Winter campaigns are reported here,
including the first millimetric map of the SZ effect that was obtained by
Pointecouteau et al. (2001) on RXJ1347-1145, the non-detection of a millimetric
counterpart to the radio decrement towards PC1643+4631 and 2 mm number count
upper limits. We discuss limitations in ground-based single-dish millimetre
observations, namely sky noise and the number of detectors. We advocate the use
of fully sampled arrays of (100 to 1000) bolometers as a big step forward in
the millimetre continuum science. Efforts in France are briefly mentionned.Comment: 7 pages, 6 figures, to appear in the Proceedings of the 2K1BC
``Experimental Astronomy at millimeter wavelengths'', Breuil-Cervinia (AO)
Italy - July 9 - 13, 2001, Eds. M. De Petris et a
A parabolic approach to the control of opinion spreading
We analyze the problem of controlling to consensus a nonlinear system
modeling opinion spreading. We derive explicit exponential estimates on the
cost of approximately controlling these systems to consensus, as a function of
the number of agents N and the control time-horizon T. Our strategy makes use
of known results on the controllability of spatially discretized semilinear
parabolic equations. Both systems can be linked through time-rescalin
Observations of the Sunyaev-Zel'dovich effect at high angular resolution towards the galaxy clusters A665, A2163 and CL0016+16
We report on the first observation of the Sunyaev-Zel'dovich effect with the
Diabolo experiment at the IRAM 30 metre telescope. A significant brightness
decrement is detected in the direction of three clusters (Abell 665, Abell 2163
and CL0016+16). With a 30 arcsecond beam and 3 arcminute beamthrow, this is the
highest angular resolution observation to date of the SZ effect.Comment: 23 pages, 8 figures, 6 tables, accepted to New Astronom
The SciCryo Project and Cryogenic Scintillation of for Dark Matter
International audienceWe discuss cryogenic scintillation of Al2O3. Room-temperature measurements with α particles are first carried out to study effect of Ti concentration on response. Measurements under X-rays between room temperature and 10 K confirm a doubling of light output. The integration of a scintillation-phonon detector into an ionization-phonon dark matter search is underway, and the quenching factor for neutrons has been verified
On the lack of robustness of hydrologic models regarding water balance simulation: a diagnostic approach applied to three models of increasing complexity on 20 mountainous catchments
This paper investigates the robustness of rainfall–runoff models when their
parameters are transferred in time. More specifically, we propose an approach
to diagnose their ability to simulate water balance on periods with different hydroclimatic
characteristics. The testing procedure consists in a series of parameter
calibrations over 10 yr periods and the systematic analysis of mean flow volume
errors on long records. This procedure was applied to three conceptual models
of increasing structural complexity over 20 mountainous catchments in southern France.
The results showed that robustness problems are common. Errors on 10 yr mean
flow volume were significant for all calibration periods and model structures.
Various graphical and numerical tools were used to investigate these errors and
unexpectedly strong similarities were found in the temporal evolutions
of these volume errors. We indeed showed that relative changes in simulated
mean flow between 10 yr periods can remain similar, regardless of the calibration
period or the conceptual model used. Surprisingly, using longer records for parameters
optimisation or using a semi-distributed 19-parameter daily model instead of a simple
1-parameter annual formula did not provide significant improvements regarding these
simulation errors on flow volumes. While the actual causes for these robustness problems
can be manifold and are difficult to identify in each case, this work highlights that the
transferability of water balance adjustments made during calibration can be poor,
with potentially huge impacts in the case of studies in non-stationary conditions
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