1,634 research outputs found
An evolutionary game based particle swarm optimization algorithm
AbstractParticle swarm optimization (PSO) is an evolutionary algorithm used extensively. This paper presented a new particle swarm optimizer based on evolutionary game (EGPSO). We map particles’ finding optimal solution in PSO algorithm to players’ pursuing maximum utility by choosing strategies in evolutionary games, using replicator dynamics to model the behavior of particles. And in order to overcome premature convergence a multi-start technique was introduced. Experimental results show that EGPSO can overcome premature convergence and has great performance of convergence property over traditional PSO
On joint analysing XMM-NuSTAR spectra of active galactic nuclei
A recently released XMM-Newton technical note has revealed a significant
calibration issue between NuSTAR and XMM-Newton EPIC, and provided an empirical
correction to EPIC effective area. To quantify the bias caused by the
calibration issue to joint analysis of XMM-NuSTAR spectra and verify the
effectiveness of the correction, in this work we perform joint-fitting of
NuSTAR and EPIC-pn spectra for a large sample of 104 observation pairs of 44
X-ray bright AGN. The spectra were extracted after requiring perfect
simultaneity between XMM-Newton and NuSTAR exposures (merging GTIs from two
missions) to avoid bias due to rapid spectral variability of AGN. Before the
correction, the EPIC-pn spectra are systematically harder than corresponding
NuSTAR spectra by , subsequently yielding significantly
underestimated cutoff energy and the strength of reflection
component R when performing joint-fitting. We confirm the correction is highly
effective and can commendably erase the discrepancy in best-fit ,
and R, and thus we urge the community to apply the correction
when joint-fitting XMM-NuSTAR spectra. Besides, we show that as merging GTIs
from two missions would cause severe loss of NuSTAR net exposure time, in many
cases joint-fitting yields no advantage compared with utilizing NuSTAR data
alone. We finally present a technical note on filtering periods of high
background flares for XMM-Newton EPIC-pn exposures in the Small Window mode.Comment: 14 pages, 8 figures, submitted. Comments are very welcome
What can be learnt from a highly informative X-ray occultation event in NGC 6814? A marvellous absorber
A unique X-ray occultation event in NGC 6814 during an XMM-Newton observation
in 2016 has been reported, providing useful information of the absorber and the
corona. We revisit the event with the aid of the hardness ratio (HR) - count
rate (CR) plot and comparison with two other absorption-free XMM exposures in
2009 and 2021. NGC 6814 exhibits a clear "softer-when-brighter" variation
pattern during the exposures, but the 2016 exposure significantly deviates from
the other two in the HR - CR plot. While spectral fitting does yield transient
Compton-thin absorption corresponding to the eclipse event in 2016, rather than
easing the tension between exposures in the HR - CR plot, correcting the
transient Compton-thin absorption results in new and severe deviation within
the 2016 exposure. We show that the eclipsing absorber shall be clumpy (instead
of a single Compton-thin cloud), with an inner denser region composed of both
Compton-thin and Compton-thick clouds responsible for the previously identified
occultation event, and an outer sparser region with Compton-thin clouds which
eclipses the whole 2016 exposure. With this model, all the tension in the HR -
CR plots could be naturally erased, with the observed spectral variability
during the 2016 exposure dominated by the variation of absorption. Furthermore,
the two warm absorbers (with different ionization and column densities but
similar outflowing velocities) detected in the 2016 exposure shall also
associate with the transient absorber, likely due to ablated or tidal
stretched/disrupted fragments. This work highlights the unique usefulness of
the HR - CR plot while analysing rare occultation events.Comment: 13 pages, 9 figures, accepted by MNRAS. For the video of the
eclipsing cloud, see
https://drive.google.com/file/d/1CEsPEWE-b5W8PfZINyI5K1sE6klHaYMa/view?usp=sharing
. Comments are welcome
Strong decays of low-lying -wave baryons with QPC model
For further decoding the inner structure of the two excited states
observed by LHCb, we perform a systematical study of the strong decays of the
low-lying -wave and excitations using the quark pair
creation model within the coupling scheme. Combining with the measured
masses and decay properties of and , the
two excited states can be explained as -mode states
and
, respectively. If
such a view were correct, and could be another
interesting channels for experimental exploring of the and
, respectively. Those calculations are good consistent with
the results within the chiral quark model. In addition, for the other missing
-wave and excitations, our predictions indicate that:(i)
the two -mode states are likely to be moderate states with a
width of MeV. The state dominantly decays into
and , while the state decays primarily
through and . (ii) The -mode
states may be moderate states with a widths of about several to dozens of MeV.
Most of the -mode states mainly decay into the -wave
bottomed baryon via the pionic decay processes. Meanwhile, several
-mode states have significant decay rates into . (iii) While, the -mode states are predicted to be very
broad states with a width of about several hundreds MeV. It will be a great
challenge to explore the -mode states in experiments for
their broad widths.Comment: 11 pages, 5 figure
Strong decays of the low-lying - and -wave baryons
In this work, we systematically study the OZI-allowed two-body strong decay
properties of - and -wave baryons within the -
coupling scheme in the framework of the quark pair creation model. For a
comparison, we also give the predictions of the chiral quark model. Some model
dependencies can be found in the predictions of two models. The calculations
indicate that: (i) The -wave -mode states most likely
to be relatively narrow states with a width of MeV. Their main
decay channels are , or , or . The
-wave -mode states most might be broad states with a width of
MeV. They dominantly decay into and
channels. Some evidences of these -wave states are most
likely to be observed in the and invariant
mass spectra around the energy range of GeV. (ii) The -wave
-mode excitations may be moderate states with a width of
about dozens of MeV. The -wave -mode states mainly decay into the
-wave charmed baryon via the pionic decay processes. Meanwhile, several
-wave -mode states have significant decay rates into or
. Hence, the and are likely to be interesting channels for
experimental exploration. (iii) Furthermore, the two -wave -mode
excitations and
are most likely to be fairly narrow state with
a width of dozens of MeV, and they mainly decay into . Some
evidences of them might be observed in the invariant mass
spectra around the energy range of GeV.Comment: 12 pages,5 figures, 4 tables. arXiv admin note: text overlap with
arXiv:2208.1011
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