27,498 research outputs found
Weak decays of medium and heavy Lambda-hypernuclei
We have made a new evaluation of the Lambda decay width in nuclear matter
within the Propagator Method. Through the Local Density Approximation it is
possible to obtain results in finite nuclei. We have also studied the
dependence of the widths on the N-N and Lambda-N short range correlations.
Using reasonable values for the parameters that control these correlations, as
well as realistic nuclear densities and Lambda wave functions, we reproduce,
for the first time, the experimental non-mesonic widths in a wide range of mass
numbers (from medium to heavy hypernuclei).Comment: 22 pages, including 5 figure
Real-time multiframe blind deconvolution of solar images
The quality of images of the Sun obtained from the ground are severely
limited by the perturbing effect of the turbulent Earth's atmosphere. The
post-facto correction of the images to compensate for the presence of the
atmosphere require the combination of high-order adaptive optics techniques,
fast measurements to freeze the turbulent atmosphere and very time consuming
blind deconvolution algorithms. Under mild seeing conditions, blind
deconvolution algorithms can produce images of astonishing quality. They can be
very competitive with those obtained from space, with the huge advantage of the
flexibility of the instrumentation thanks to the direct access to the
telescope. In this contribution we leverage deep learning techniques to
significantly accelerate the blind deconvolution process and produce corrected
images at a peak rate of ~100 images per second. We present two different
architectures that produce excellent image corrections with noise suppression
while maintaining the photometric properties of the images. As a consequence,
polarimetric signals can be obtained with standard polarimetric modulation
without any significant artifact. With the expected improvements in computer
hardware and algorithms, we anticipate that on-site real-time correction of
solar images will be possible in the near future.Comment: 16 pages, 12 figures, accepted for publication in A&
Sparse inversion of Stokes profiles. I. Two-dimensional Milne-Eddington inversions
Inversion codes are numerical tools used for the inference of physical
properties from the observations. Despite their success, the quality of current
spectropolarimetric observations and those expected in the near future presents
a challenge to current inversion codes. The pixel-by-pixel strategy of
inverting spectropolarimetric data that we currently utilize needs to be
surpassed and improved. The inverted physical parameters have to take into
account the spatial correlation that is present in the data and that contains
valuable physical information. We utilize the concept of sparsity or
compressibility to develop an new generation of inversion codes for the Stokes
parameters. The inversion code uses numerical optimization techniques based on
the idea of proximal algorithms to impose sparsity. In so doing, we allow for
the first time to exploit the presence of spatial correlation on the maps of
physical parameters. Sparsity also regularizes the solution by reducing the
number of unknowns. We compare the results of the new inversion code with
pixel-by-pixel inversions, demonstrating the increase in robustness of the
solution. We also show how the method can easily compensate for the effect of
the telescope point spread function, producing solutions with an enhanced
contrast.Comment: 13 pages, 8 figures, accepted for publication in A&
Fungos em sementes de especies florestais com potencial agrossilvicultura no Parana.
Edição dos Anais do Congresso Florestal Brasileiro, 6., 1990, Campos do Jordão
Decay rates of medium-heavy Lambda-hypernuclei within the Propagator Method
The Lambda decay rates in nuclei has been calculated in ref. 1 using the
Propagator Method in Local Density Approximation. We have studied the
dependence of the widths (including the one for the two-body induced process
Lambda NN -> NNN) on the N-N and Lambda-N short range correlations. Using a
reasonable parametrization of these correlations, as well as realistic nuclear
densities and Lambda wave functions, we reproduce, for the first time, the
experimental non-mesonic widths from medium to heavy hypernuclei.Comment: 8 pages, 1 figure. Talk given at the APCTP Workshop Strangeness
Nuclear Physics, Seoul National University, Seoul, Korea, 19-22 February 199
{\it Ab initio} NMR chemical shifts and quadrupolar parameters for phases and their precursors
The Gauge-Including Projector Augmented Wave (GIPAW) method, within the
Density Functional Theory (DFT) Generalized Gradient Approximation (GGA)
framework, is applied to compute solid state NMR parameters for in
the , , and aluminium oxide phases and their gibbsite
and boehmite precursors. The results for well-established crystalline phases
compare very well with available experimental data and provide confidence in
the accuracy of the method. For -alumina, four structural models
proposed in the literature are discussed in terms of their ability to reproduce
the experimental spectra also reported in the literature. Among the considered
models, the structure proposed by Paglia {\it et al.} [Phys. Rev.
B {\bf 71}, 224115 (2005)] shows the best agreement. We attempt to link the
theoretical NMR parameters to the local geometry. Chemical shifts depend on
coordination number but no further correlation is found with geometrical
parameters. Instead our calculations reveal that, within a given coordination
number, a linear correlation exists between chemical shifts and Born effective
charges
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