6,640 research outputs found
SN/GRB connection: a statistical approach with BATSE and Asiago Catalogues
Recent observations suggest that some types of GRB are physically connected
with SNe of type Ib/c. However, it has been pointed out by several authors that
some GRBs could be associated also with other types of core-collapse SNe (type
IIdw/IIn). On the basis of a comphrensive statistical study, which has made use
of the BATSE and Asiago catalogues, we have found that: i) the temporal and
spacial distribution of SNe-Ib/c is marginally correlated with that of the
BATSE GRBs; ii) we do not confirm the existence of an association between GRBs
and SNe-IIdw/IIn.Comment: Proceeding of the 4th workshop on Gamma Ray Bursts in the Afterglow
Era, Rome, 2004; 4 page
L∞ -estimates in optimal transport for non quadratic costs
For cost functions c(x, y) = h(x- y) , with h∈ C2(Rn\ { 0 }) ∩ C1(Rn) homogeneous of degree p> 1 , we show L∞-estimates of Tx- x on balls, where T is an h-monotone map. Estimates for the interpolating mappings Tt= t(T- I) + I are deduced from this
A microscopic description of the aging dynamics: fluctuation-dissipation relations, effective temperature and heterogeneities
We consider the dynamics of a diluted mean-field spin glass model in the
aging regime. The model presents a particularly rich heterogeneous behavior. In
order to catch this behavior, we perform a **spin-by-spin analysis** for a
**given disorder realization**. The results compare well with the outcome of a
static calculation which uses the ``survey propagation'' algorithm of Mezard,
Parisi, and Zecchina [Sciencexpress 10.1126/science.1073287 (2002)]. We thus
confirm the connection between statics and dynamics at the level of single
degrees of freedom. Moreover, working with single-site quantities, we can
introduce a new response-vs-correlation plot, which clearly shows how
heterogeneous degrees of freedom undergo coherent structural rearrangements.
Finally we discuss the general scenario which emerges from our work and
(possibly) applies to more realistic glassy models. Interestingly enough, some
features of this scenario can be understood recurring to thermometric
considerations.Comment: 4 pages, 5 figures (7 eps files
Probing the diffusive behaviour of beam-halo dynamics in circular accelerators
Circular particle accelerators at the energy frontier are based on superconducting magnets that are extremely sensitive to beam losses as these might induce quenches, i.e. transitions to the normal-conducting state. Furthermore, the energy stored in the circulating beam is so large that hardware integrity is put in serious danger, and machine protection becomes essential for reaching the nominal accelerator performance. In this challenging context, the beam halo becomes a potential source of performance limitations and its dynamics needs to be understood in detail to assess whether it could be an issue for the accelerator. In this paper, we discuss in detail a recent framework, based on a diffusive approach, to model beam-halo dynamics. The functional form of the optimal estimate of the perturbative series, as given by Nekhoroshev’s theorem, is used to provide the functional form of the action diffusion coefficient. The goal is to propose an effective model for the beam-halo dynamics and to devise an efficient experimental procedure to obtain an accurate measurement of the diffusion coefficient
The GRB Variability/Peak Luminosity Correlation: new results
We report test results of the correlation between time variability and peak
luminosity of Gamma-Ray Bursts (GRBs), using a larger sample (32) of GRBs with
known redshift than that available to Reichart et al. (2001), and using as
variability measure that introduced by these authors. The results are puzzling.
Assuming an isotropic-equivalent peak luminosity, as done by Reichart et al.
(2001), a correlation is still found, but it is less relevant, and inconsistent
with a power law as previously reported. Assuming as peak luminosity that
corrected for GRB beaming for a subset of 16 GRBs with known beaming angle, the
correlation becomes little less significant.Comment: 11 pages, 10 figures, MNRAS, accepte
The Bethe approximation for solving the inverse Ising problem: a comparison with other inference methods
The inverse Ising problem consists in inferring the coupling constants of an
Ising model given the correlation matrix. The fastest methods for solving this
problem are based on mean-field approximations, but which one performs better
in the general case is still not completely clear. In the first part of this
work, I summarize the formulas for several mean- field approximations and I
derive new analytical expressions for the Bethe approximation, which allow to
solve the inverse Ising problem without running the Susceptibility Propagation
algorithm (thus avoiding the lack of convergence). In the second part, I
compare the accuracy of different mean field approximations on several models
(diluted ferromagnets and spin glasses) defined on random graphs and regular
lattices, showing which one is in general more effective. A simple improvement
over these approximations is proposed. Also a fundamental limitation is found
in using methods based on TAP and Bethe approximations in presence of an
external field.Comment: v3: strongly revised version with new methods and results, 25 pages,
21 figure
Spectral catalogue of bright gamma-ray bursts detected with the BeppoSAX/GRBM
The emission process responsible for the so-called "prompt" emission of
gamma-ray bursts is still unknown. A number of empirical models fitting the
typical spectrum still lack a satisfactory interpretation. A few GRB spectral
catalogues derived from past and present experiments are known in the
literature and allow to tackle the issue of spectral properties of gamma-ray
bursts on a statistical ground. We extracted and studied the time-integrated
photon spectra of the 200 brightest GRBs observed with the Gamma-Ray Burst
Monitor which flew aboard the BeppoSAX mission (1996-2002) to provide an
independent statistical characterisation of GRB spectra. The spectra were fit
with three models: a simple power-law, a cut-off power law or a Band function.
The typical photon spectrum of a bright GRB consists of a low-energy index
around 1.0 and a peak energy of the nuFnu spectrum E_p~240 keV in agreement
with previous results on a sample of bright CGRO/BATSE bursts. Spectra of ~35%
of GRBs can be fit with a power-law with a photon index around 2, indicative of
peak energies either close to or outside the GRBM energy boundaries. We confirm
the correlation between E_p and fluence, with a logarithmic dispersion of 0.13
around the power-law with index 0.21+-0.06. The low-energy and peak energy
distributions are not yet explained in the current literature. The capability
of measuring time-resolved spectra over a broadband energy range, ensuring
precise measurements of parameters such as E_p, will be crucial for future
experiments (abridged).Comment: 28 pages, 20 figures, 3 tables, accepted to A&
Analyses of shocked quartz at the global K-P boundary indicate an origin from a single, high-angle, oblique impact at Chicxulub
Accepted versio
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