5,261 research outputs found
Parameter selection and performance comparison of particle swarm optimization in sensor networks localization
Localization is a key technology in wireless sensor networks. Faced with the challenges of the sensors\u27 memory, computational constraints, and limited energy, particle swarm optimization has been widely applied in the localization of wireless sensor networks, demonstrating better performance than other optimization methods. In particle swarm optimization-based localization algorithms, the variants and parameters should be chosen elaborately to achieve the best performance. However, there is a lack of guidance on how to choose these variants and parameters. Further, there is no comprehensive performance comparison among particle swarm optimization algorithms. The main contribution of this paper is three-fold. First, it surveys the popular particle swarm optimization variants and particle swarm optimization-based localization algorithms for wireless sensor networks. Secondly, it presents parameter selection of nine particle swarm optimization variants and six types of swarm topologies by extensive simulations. Thirdly, it comprehensively compares the performance of these algorithms. The results show that the particle swarm optimization with constriction coefficient using ring topology outperforms other variants and swarm topologies, and it performs better than the second-order cone programming algorithm
Integral and Rxte/Asm Observations on Igr J17098-3628
To probe further the possible nature of the unidentified source IGR
J17098-3628, we have carried out a detailed analysis of its long-term time
variability as monitored by RXTE/ASM, and of its hard X-ray properties as
observed by INTEGRAL. INTEGRAL has monitored this sky region over years and
significantly detected IGR J17098-3628 only when the source was in this dubbed
active state. In particular, at 20 keV, IBIS/ISGRI caught an outburst in
March 2005, lasting for 5 days with detection significance of 73
(20-40 keV) and with the emission at 200 keV. The ASM observations reveal
that the soft X-ray lightcurve shows a similar outburst to that detected by
INTEGRAL, however the peak of the soft X-ray lightcurve either lags, or is
preceded by, the hard X-ray (20 keV) outburst by 2 days. This
resembles the behavior of X-ray novae like XN 1124-683, hence it further
suggests a LMXB nature for IGR J17098-3628. While the quality of the ASM data
prevents us from drawing any definite conclusions, these discoveries are
important clues that, coupled with future observations, will help to resolve
the as yet unknown nature of IGR J17098-3628.Comment: 15 pages, 7 figure, accepted in PAS
Possible hard X-ray shortages in bursts from KS 1731-260 and 4U 1705-44
Aims: A hard X-ray shortage, implying the cooling of the corona, was observed
during bursts of IGR J17473-272, 4U 1636-536, Aql X-1, and GS 1826-238. Apart
from these four sources, we investigate here an atoll sample, in which the
number of bursts for each source is larger than 5, to explore the possible
additional hard X-ray shortage during {\it Rossi X-ray timing explorer (RXTE)}
era. Methods: According to the source catalog that shows type-I bursts, we
analyzed all the available pointing observations of these sources carried out
by the {\it RXTE} proportional counter array (PCA). We grouped and combined the
bursts according to their outburst states and searched for the possible hard
X-ray shortage while bursting. Results: We found that the island states of KS
1731-260 and 4U 1705-44 show a hard X-ray shortage at significant levels of 4.5
and 4.7 and a systematic time lag of s and
s with respect to the soft X-rays, respectively. While in their banana branches
and other sources, we did not find any consistent shortage.Comment: 5 pages, 4 figures, accepted by A&A as a research not
Quantum properties of fermionic fields in multi-event horizon spacetime
We investigate the properties of quantum entanglement and mutual information
in the multi-event horizon Schwarzschild-de Sitter (SdS) spacetime for massless
Dirac fields. We obtain the expression for the evolutions of the quantum state
near the black hole event horizon (BEH) and cosmological event horizon (CEH) in
the SdS spacetime. Under the Nariai limit, the physically accessible
entanglement and mutual information are maximized, and the physically
inaccessible correlations are zero. With the increase in temperature of either
horizon, the physically accessible correlations experience degradation.
Notably, the initial state remains entangled and can be utilized in
entanglement-based quantum information processing tasks, which differs form the
scalar field case. Furthermore, the degradation of physically accessible
correlations is more pronounced for small-mass black holes. In contrast, the
physically inaccessible correlations separated by the CEH monotonically
increase with the radiation temperature, and such correlations are not
decisively influenced by the effect of particle creation at the BEH. Moreover,
a similar phenomenon is observed for the inaccessible correlations separated by
the BEH. This result differs from the single event spacetime, in which the
physically inaccessible entanglement is a monotonic function of the Hawking
temperature.Comment: 14 pages, 7 figure
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