48,048 research outputs found
Stokes Inversion based on Convolutional Neural Networks
Spectropolarimetric inversions are routinely used in the field of Solar
Physics for the extraction of physical information from observations. The
application to two-dimensional fields of view often requires the use of
supercomputers with parallelized inversion codes. Even in this case, the
computing time spent on the process is still very large. Our aim is to develop
a new inversion code based on the application of convolutional neural networks
that can quickly provide a three-dimensional cube of thermodynamical and
magnetic properties from the interpretation of two-dimensional maps of Stokes
profiles. We train two different architectures of fully convolutional neural
networks. To this end, we use the synthetic Stokes profiles obtained from two
snapshots of three-dimensional magneto-hydrodynamic numerical simulations of
different structures of the solar atmosphere. We provide an extensive analysis
of the new inversion technique, showing that it infers the thermodynamical and
magnetic properties with a precision comparable to that of standard inversion
techniques. However, it provides several key improvements: our method is around
one million times faster, it returns a three-dimensional view of the physical
properties of the region of interest in geometrical height, it provides
quantities that cannot be obtained otherwise (pressure and Wilson depression)
and the inferred properties are decontaminated from the blurring effect of
instrumental point spread functions for free. The code is provided for free on
a specific repository, with options for training and evaluation.Comment: 18 pages, 14 figures, accepted for publication in Astronomy &
Astrophysic
Recent results on the nonmesonic weak decay of hypernuclei within a one-meson-exchange model
We update our previous results for the nonmesonic decay of C
and He. We pay special attention to the role played by Final State
Intreractions on the decay observables. We follow a One-Meson-Exchange model
which includes the exchange of the and
mesons. We also present recent predictions for different observables concerning
the decay of the doubly strange He hypernucleus.Comment: 4 pages. Contribution to the Mesons and Light Nuclei'01 Conference,
Prague, 2-6 July 200
The Weak Decay of Hypernuclei
The nonmesonic weak decay of hypernuclei is studied in a shell
model framework. A complete strangeness-changing weak
transition potential, based on one boson exchange, is constructed by including
the exchange of the pseudoscalar mesons , K, as well as the vector
mesons , and K, whose weak coupling constants are obtained
from soft meson theorems and SU(6). General expressions for nucleons in
arbitrary shells are obtained. The transition matrix elements include realistic
N short-range correlations and NN final state interactions based on
the Nijmegen baryon-baryon potential. The decay rates are found to be
especially sensitive to the inclusion of the strange mesons, K and K, even
though the role of kaon exchange is found to be reduced with recent couplings
obtained from next-to-leading order Chiral Perturbation Theory. With the weak
couplings used in this study the rates remain dominated by the pion-exchange
mechanism since the contributions of heavier mesons either cancel each other or
are suppressed by form factors and short-range correlations. The total decay
rate therefore remains in agreement with present measurements. However, the
partial rates which are even more sensitive to the inclusion of heavier mesons
cannot be reconciled with the data. The proton asymmetry changes by 50% once
heavier mesons are included and agrees with the available data.Comment: 70 pages, 8 figures, epsf.tex, revtex, submitted to Phys. Rev.
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