54,520 research outputs found
The Chinese-French SVOM mission for Gamma-Ray Burst studies
We present the Space-based multi-band astronomical Variable Objects Monitor
mission (SVOM) decided by the Chinese National Space Agency (CNSA) and the
French Space Agency (CNES). The mission which is designed to detect about 80
Gamma-Ray Bursts (GRBs) of all known types per year, will carry a very
innovative scientific payload combining a gamma-ray coded mask imagers
sensitive in the range 4 keV to 250 keV, a soft X-ray telescope operating
between 0.5 to 2 keV, a gamma-ray spectro-photometer sensitive in the range 50
keV to 5 MeV, and an optical telescope able to measure the GRB afterglow
emission down to a magnitude limit M with a 300 s exposure. A particular
attention will be also paid to the follow-up in making easy the observation of
the SVOM detected GRB by the largest ground based telescopes.
Scheduled for a launch in 2013, it will provide fast and reliable GRB
positions, will measure the broadband spectral energy distribution and temporal
properties of the prompt emission, and will quickly identify the optical
afterglows of detected GRBs, including those at very high redshift.Comment: Proceedings of the SF2A conference, Paris, 200
Relativistic description of magnetic moments in nuclei with doubly closed shells plus or minus one nucleon
Using the relativistic point-coupling model with density functional PC-PK1,
the magnetic moments of the nuclei Pb, Pb, Tl and
Bi with a closed-shell core Pb are studied on the basis of
relativistic mean field (RMF) theory. The corresponding time-odd fields, the
one-pion exchange currents, and the first- and second-order corrections are
taken into account. The present relativistic results reproduce the data well.
The relative deviation between theory and experiment for these four nuclei is
6.1% for the relativistic calculations and somewhat smaller than the value of
13.2% found in earlier non-relativistic investigations. It turns out that the
meson is important for the description of magnetic moments, first by
means of one-pion exchange currents and second by the residual interaction
provided by the exchange.Comment: 11 pages, 7 figure
Stability of spikes in the shadow Gierer-Meinhardt system with Robin boundary conditions
We consider the shadow system of the Gierer-Meinhardt system in a smooth bounded domain RN,At=2A−A+,x, t>0, ||t=−||+Ardx, t>0 with the Robin boundary condition +aAA=0, x, where aA>0, the reaction rates (p,q,r,s) satisfy 1<p<()+, q>0, r>0, s0, 1<<+, the diffusion constant is chosen such that 1, and the time relaxation constant is such that 0. We rigorously prove the following results on the stability of one-spike solutions: (i) If r=2 and 1<p<1+4/N or if r=p+1 and 1<p<, then for aA>1 and sufficiently small the interior spike is stable. (ii) For N=1 if r=2 and 1<p3 or if r=p+1 and 1<p<, then for 0<aA<1 the near-boundary spike is stable. (iii) For N=1 if 3<p<5 and r=2, then there exist a0(0,1) and µ0>1 such that for a(a0,1) and µ=2q/(s+1)(p−1)(1,µ0) the near-boundary spike solution is unstable. This instability is not present for the Neumann boundary condition but only arises for the Robin boundary condition. Furthermore, we show that the corresponding eigenvalue is of order O(1) as 0. ©2007 American Institute of Physic
Glauber-based evaluations of the odd moments of the initial eccentricity relative to the even order participant planes
Monte Carlo simulations are used to compute the centrality dependence of the
odd moments of the initial eccentricity , relative to the even
order (n) participant planes in Au+Au collisions. The results
obtained for two models of the eccentricity -- the Glauber and the factorized
Kharzeev-Levin-Nardi (fKLN) models -- indicate magnitudes which are essentially
zero. They suggest that a possible correlation between the orientations of the
the odd and even participant planes ( and
respectively), do not have a significant influence on the calculated
eccentricities. An experimental verification test for correlations between the
orientations of the the odd and even participant planes is also proposed.Comment: 3 pages, 1 figure. Version accepted for publicatio
Towards Identification of Relevant Variables in the observed Aerosol Optical Depth Bias between MODIS and AERONET observations
Measurements made by satellite remote sensing, Moderate Resolution Imaging
Spectroradiometer (MODIS), and globally distributed Aerosol Robotic Network
(AERONET) are compared. Comparison of the two datasets measurements for aerosol
optical depth values show that there are biases between the two data products.
In this paper, we present a general framework towards identifying relevant set
of variables responsible for the observed bias. We present a general framework
to identify the possible factors influencing the bias, which might be
associated with the measurement conditions such as the solar and sensor zenith
angles, the solar and sensor azimuth, scattering angles, and surface
reflectivity at the various measured wavelengths, etc. Specifically, we
performed analysis for remote sensing Aqua-Land data set, and used machine
learning technique, neural network in this case, to perform multivariate
regression between the ground-truth and the training data sets. Finally, we
used mutual information between the observed and the predicted values as the
measure of similarity to identify the most relevant set of variables. The
search is brute force method as we have to consider all possible combinations.
The computations involves a huge number crunching exercise, and we implemented
it by writing a job-parallel program
Functional Forms for the Squeeze and the Time-Displacement Operators
Using Baker-Campbell-Hausdorff relations, the squeeze and harmonic-oscillator
time-displacement operators are given in the form , where ,
, , and are explicitly determined. Applications are
discussed.Comment: 10 pages, LaTe
- …