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Sub-threshold J/ψ and ϒ production in γA collisions
We study sub-threshold heavy quarkonium (J/ψ and ϒ) photo-productions in γA collisions as an independent test of the universality of the nucleon-nucleon short range correlation (SRC) in nuclear scattering processes. Just below the γp threshold, the cross section is dominated by the mean field contribution of nucleons inside the nucleus. The SRC contributions start to dominate at lower photon energies, depending on the fraction of the SRC pairs in the target nucleus. We give an estimate of the cross sections in the sub-threshold region both for J/ψ and ϒ. This may be helpful for future measurements at JLab as well as at the Electron-Ion Collider in the U.S., and especially in China
The variability of the Crab Nebula in radio: No radio counterpart to gamma-ray flares
We present new Jansky Very Large Array (VLA) radio images of the Crab Nebula
at 5.5 GHz, taken at two epochs separated by 6 days about two months after a
gamma-ray flare in 2012 July. We find no significant change in the Crab's radio
emission localized to a region of <2 light-months in radius, either over the
6-day interval between our present observations or between the present
observations and ones from 2001. Any radio counterpart to the flare has a radio
luminosity of <~ times that of the nebula. Comparing our
images to one from 2001, we do however find changes in radio brightness, up to
10% in amplitude, which occur on decade timescales throughout the nebula. The
morphology of the changes is complex suggesting both filamentary and knotty
structures. The variability is stronger, and the timescales likely somewhat
shorter, nearer the centre of the nebula. We further find that even with the
excellent uv~coverage and signal-to-noise of the VLA, deconvolution errors are
much larger than the noise, being up to 1.2% of peak brightness of the nebula
in this particular case.Comment: Accepted to MNRAS; 13 pages, 6 figure
Effect of edge decoration on the energy spectrum of semi-infinite lattices
Analytical studies of the effect of edge decoration on the energy spectrum of
semi-infinite one-dimensional (1D) lattice chain with Peierls phase transition
and zigzag edged graphene (ZEG) are presented by means of transfer matrix
method, in the frame of which the sufficient and necessary conditions for the
existence of the edge states are determined. For 1D lattice chain, the
zero-energy edge state exists when Peierls phase transition happens regardless
whether the decoration exists or not, while the non-zero-energy edge states can
be induced and manipulated through adjusting the edge decoration. On the other
hand, the semi-infinite ZEG model with nearest-neighbor interaction can be
mapped into the 1D lattice chain case. The non-zero-energy edge states can be
induced by the decoration as well, and we can obtain the condition of the
decoration on the edge for the existence of the novel edge states.Comment: 6 pages,4 figure
A Novel FastICA Method for the Reference-based Contrast Functions
This paper deals with the efficient optimization problem of Cumulant-based contrast criteria in the Blind Source Separation (BSS) framework, in which sources are retrieved by maximizing the Kurtosis contrast function. Combined with the recently proposed reference-based contrast schemes, a new fast fixed-point (FastICA) algorithm is proposed for the case of linear and instantaneous mixture. Due to its quadratic dependence on the number of searched parameters, the main advantage of this new method consists in the significant decrement of computational speed, which is particularly striking with large number of samples. The method is essentially similar to the classical algorithm based on the Kurtosis contrast function, but differs in the fact that the reference-based idea is utilized. The validity of this new method was demonstrated by simulations
An Efficient Algorithm by Kurtosis Maximization in Reference-Based Framework
This paper deals with the optimization of kurtosis for complex-valued signals in the independent component analysis (ICA) framework, where source signals are linearly and instantaneously mixed. Inspired by the recently proposed reference-based contrast schemes, a similar contrast function is put forward, based on which a new fast fixed-point (FastICA) algorithm is proposed. The new optimization method is similar in spirit to the former classical kurtosis-based FastICA algorithm but differs in the fact that it is much more efficient than the latter in terms of computational speed, which is significantly striking with large number of samples. The performance of this new algorithm is confirmed through computer simulations
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