68,626 research outputs found
The application of compressive sampling to radio astronomy I: Deconvolution
Compressive sampling is a new paradigm for sampling, based on sparseness of
signals or signal representations. It is much less restrictive than
Nyquist-Shannon sampling theory and thus explains and systematises the
widespread experience that methods such as the H\"ogbom CLEAN can violate the
Nyquist-Shannon sampling requirements. In this paper, a CS-based deconvolution
method for extended sources is introduced. This method can reconstruct both
point sources and extended sources (using the isotropic undecimated wavelet
transform as a basis function for the reconstruction step). We compare this
CS-based deconvolution method with two CLEAN-based deconvolution methods: the
H\"ogbom CLEAN and the multiscale CLEAN. This new method shows the best
performance in deconvolving extended sources for both uniform and natural
weighting of the sampled visibilities. Both visual and numerical results of the
comparison are provided.Comment: Published by A&A, Matlab code can be found:
http://code.google.com/p/csra/download
Single particle fluctuations and directional correlations in driven hard sphere glasses
Via event driven molecular dynamics simulations and experiments, we study the
packing fraction and shear-rate dependence of single particle fluctuations and
dynamic correlations in hard sphere glasses under shear. At packing fractions
above the glass transition, correlations increase as shear rate decreases: the
exponential tail in the distribution of single particle jumps broadens and
dynamic four-point correlations increase. Interestingly, however, upon
decreasing the packing fraction, a broadening of the exponential tail is also
observed, while dynamic heterogeneity is shown to decrease. An explanation for
this behavior is proposed in terms of a competition between shear and thermal
fluctuations. Building upon our previous studies [Chikkadi et al, Europhys.
Lett. (2012)], we further address the issue of anisotropy of the dynamic
correlations.Comment: 8 pages, 10 figure
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