126 research outputs found
A multi-cycled sequential memetic computing approach for constrained optimisation
In this paper, we propose a multi-cycled sequential memetic computing structure for constrained optimisation. The structure is composed of multiple evolutionary cycles. At each cycle, an evolutionary algorithm is considered as an operator, and connects with a local optimiser. This structure enables the learning of useful knowledge from previous cycles and the transfer of the knowledge to facilitate search in latter cycles. Specifically, we propose to apply an estimation of distribution algorithm (EDA) to explore the search space until convergence at each cycle. A local optimiser, called DONLP2, is then applied to improve the best solution found by the EDA. New cycle starts after the local improvement if the computation budget has not been exceeded. In the developed EDA, an adaptive fully-factorized multivariate probability model is proposed. A learning mechanism, implemented as the guided mutation operator, is adopted to learn useful knowledge from previous cycles.
The developed algorithm was experimentally studied on the benchmark problems in the CEC 2006 and 2010 competition. Experimental studies have shown that the developed probability model exhibits excellent exploration capability and the learning mechanism can significantly improve the search efficiency under certain conditions. The comparison against some well-known algorithms showed the superiority of the developed algorithm in terms of the consumed fitness evaluations and the solution quality
Active Encoding of Flexural Wave with Non-Diffractive Talbot Effect
This study employs the theory of conformal transformation to devise a
Mikaelian lens for flexural waves manipulation. We investigate the propagation
patterns of flexural waves in the lens under scenarios of plane wave and point
source incidence. Additionally, the study explores the Talbot effect generated
by interference patterns of multiple sources. Within the Mikaelian lens, the
Talbot effect displays non diffractive characteristics, facilitating
propagation over considerable distances. Leveraging the non-diffractive
attributes of the Talbot effect in the Mikaelian lens, the paper discusses the
feasibility of encoding flexural waves based on active interference sources.
Simulation and experimental validation attest to the lens's effective active
encoding. This research introduces novel perspectives on flexural wave
encoding, showcasing potential applications in flexural wave communication,
detection, and related fields
Piercing Through Highly Obscured and Compton-thick AGNs in the Chandra Deep Fields: I. X-ray Spectral and Long-term Variability Analyses
We present a detailed X-ray spectral analysis of 1152 AGNs selected in the
Chandra Deep Fields (CDFs), in order to identify highly obscured AGNs (). By fitting spectra with physical models, 436 (38%)
sources with are confirmed to be highly
obscured, including 102 Compton-thick (CT) candidates. We propose a new
hardness-ratio measure of the obscuration level which can be used to select
highly obscured AGN candidates. The completeness and accuracy of applying this
method to our AGNs are 88% and 80%, respectively. The observed logN-logS
relation favors cosmic X-ray background models that predict moderate (i.e.,
between optimistic and pessimistic) CT number counts. 19% (6/31) of our highly
obscured AGNs that have optical classifications are labeled as broad-line AGNs,
suggesting that, at least for part of the AGN population, the heavy X-ray
obscuration is largely a line-of-sight effect, i.e., some high-column-density
clouds on various scales (but not necessarily a dust-enshrouded torus) along
our sightline may obscure the compact X-ray emitter. After correcting for
several observational biases, we obtain the intrinsic NH distribution and its
evolution. The CT-to-highly-obscured fraction is roughly 52% and is consistent
with no evident redshift evolution. We also perform long-term (~17 years in the
observed frame) variability analyses for 31 sources with the largest number of
counts available. Among them, 17 sources show flux variabilities: 31% (5/17)
are caused by the change of NH, 53% (9/17) are caused by the intrinsic
luminosity variability, 6% (1/17) are driven by both effects, and 2 are not
classified due to large spectral fitting errors.Comment: 32 pages, 21 figures, 9 tables, accepted for publication in Ap
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