70,602 research outputs found
Genetic algorithms with immigrants and memory schemes for dynamic shortest path routing problems in mobile ad hoc networks
This article is posted here with permission of IEEE - Copyright @ 2010 IEEEIn recent years, the static shortest path (SP) problem has been well addressed using intelligent optimization techniques, e.g., artificial neural networks, genetic algorithms (GAs), particle swarm optimization, etc. However, with the advancement in wireless communications, more and more mobile wireless networks appear, e.g., mobile networks [mobile ad hoc networks (MANETs)], wireless sensor networks, etc. One of the most important characteristics in mobile wireless networks is the topology dynamics, i.e., the network topology changes over time due to energy conservation or node mobility. Therefore, the SP routing problem in MANETs turns out to be a dynamic optimization problem. In this paper, we propose to use GAs with immigrants and memory schemes to solve the dynamic SP routing problem in MANETs. We consider MANETs as target systems because they represent new-generation wireless networks. The experimental results show that these immigrants and memory-based GAs can quickly adapt to environmental changes (i.e., the network topology changes) and produce high-quality solutions after each change.This work was supported by the Engineering
and Physical Sciences Research Council of U.K. underGrant EP/E060722/
Statistics Of The Burst Model At Super-critical Phase
We investigate the statistics of a model of type-I X-ray burst [Phys. Rev. E,
{\bf 51}, 3045 (1995)] in its super-critical phase. The time evolution of the
burnable clusters, places where fire can pass through, is studied using simple
statistical arguments. We offer a simple picture for the time evolution of the
percentage of space covered by burnable clusters. A relation between the
time-average and the peak percentage of space covered by burnable clusters is
also derived.Comment: 11 Pages in Revtex 3.0. Two figures available by sending request to
[email protected]
An unexpectedly low-redshift excess of Swift gamma-ray burst rate
Gamma-ray bursts (GRBs) are the most violent explosions in the Universe and
can be used to explore the properties of high-redshift universe. It is believed
that the long GRBs are associated with the deaths of massive stars. So it is
possible to use GRBs to investigate the star formation rate (SFR). In this
paper, we use Lynden-Bell's method to study the luminosity function and
rate of \emph{Swift} long GRBs without any assumptions. We find that the
luminosity of GRBs evolves with redshift as with
. After correcting the redshift evolution through
, the luminosity function can be expressed as
for dim GRBs and for bright GRBs, with the break point
. We also find that the formation
rate of GRBs is almost constant at for the first time, which is
remarkably different from the SFR. At , the formation rate of GRB is
consistent with the SFR. Our results are dramatically different from previous
studies. Some possible reasons for this low-redshift excess are discussed. We
also test the robustness of our results with Monte Carlo simulations. The
distributions of mock data (i.e., luminosity-redshift distribution, luminosity
function, cumulative distribution and distribution) are in good
agreement with the observations. Besides, we also find that there are
remarkable difference between the mock data and the observations if long GRB
are unbiased tracers of SFR at .Comment: 33 pages, 10 figures, 1 table, accepted by ApJ
Comment on Decay
We calculate the rate for decay using Chiral
Perturbation Theory. This isospin violating process results from -
mixing, and its amplitude is proportional to . Experimental information on the branching
ratio for can provide insight into the pattern of
violation in radiative decays.Comment: 7 pages with 2 figures not included but available upon request,
CALT-68-191
Comment on Path Integral Derivation of Schr\"odinger Equation in Spaces with Curvature and Torsion
We present a derivation of the Schr\"odinger equation for a path integral of
a point particle in a space with curvature and torsion which is considerably
shorter and more elegant than what is commonly found in the literature.Comment: LaTeX file in sr
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