Adaptive primal-dual genetic algorithms in dynamic environments

This article is placed here with permission of IEEE - Copyright @ 2010 IEEERecently, there has been an increasing interest in applying genetic algorithms (GAs) in dynamic environments. Inspired by the complementary and dominance mechanisms in nature, a primal-dual GA (PDGA) has been proposed for dynamic optimization problems (DOPs). In this paper, an important operator in PDGA, i.e., the primal-dual mapping (PDM) scheme, is further investigated to improve the robustness and adaptability of PDGA in dynamic environments. In the improved scheme, two different probability-based PDM operators, where the mapping probability of each allele in the chromosome string is calculated through the statistical information of the distribution of alleles in the corresponding gene locus over the population, are effectively combined according to an adaptive Lamarckian learning mechanism. In addition, an adaptive dominant replacement scheme, which can probabilistically accept inferior chromosomes, is also introduced into the proposed algorithm to enhance the diversity level of the population. Experimental results on a series of dynamic problems generated from several stationary benchmark problems show that the proposed algorithm is a good optimizer for DOPs.This work was supported in part by the National Nature Science Foundation of China (NSFC) under Grant 70431003 and Grant 70671020, by the National Innovation Research Community Science Foundation of China under Grant 60521003, by the National Support Plan of China under Grant 2006BAH02A09, by the Engineering and Physical Sciences Research Council (EPSRC) of U.K. under Grant EP/E060722/1, and by the Hong Kong Polytechnic University Research Grants under Grant G-YH60

Densities and abundances of hot cometary ions in the coma of P/Halley

On its flight by P/Halley, the Giotto spacecraft carried a High Energy Range Spectrometer (HERS) for measuring the properties of cometary ions picked up by the solar wind in the nearly collisionless regions of the coma. Preliminary estimates of the ion densities observed by HERS were reevaluated and extended; density profiles along the Giotto trajectory are presented for 13 values of ion mass/charge. Comparison with the physical-chemical model of the interaction of sunlight and the solar wind with the comet by other researchers reveals that, with the exception of protons and H2(+), all ion densities were at least an order of magnitude higher than predicted. The high ion densities cannot be explained on the basis of compression of the plasma, but require additional or stronger ionization mechanisms. Ratios of the densities of different ion species reveal an overabundance of carbonaceous material and an underabundance of H2(+) compared to the predictions of the Schmidt. While the densities of solar wind ions (H(+) and He(++)) changed sharply across a magnetic discontinuity located 1.35(10)(exp 5) km from the comet, this feature, which has been called both the 'cometopause' and the 'magnetic pileup boundary' was barely distinguishable in the density profiles of hot cometary ions. This result is consistent with the interpretation that the magnetic pileup boundary detected by Giotto was caused by a discontinuity in the solar wind and is not an intrinsic feature of the interaction of the solar wind with an active comet

Observations of solar wind ion charge exchange in the comet Halley coma

Giotto Ion Mass Spectrometer/High Energy Range Spectrometer (IMS/HERS) observations of solar wind ions show charge exchange effects and solar wind compositional changes in the coma of comet Halley. As the comet was approached, the He(++) to proton density ratio increased until about 1 hour before closest approach after which time it decreased. Abrupt increases in this ratio were also observed in the beginning and near the end of the so-called Mystery Region (8.6 - 5.5(10)(exp 5) km from the comet along the spacecraft trajectory). These abrupt increases in the density ratio were well correlated with enhanced fluxes of keV electrons as measured by the Giotto plasma electron spectrometer. The general increase and then decrease of the He(++) to proton density ratio is quantitatively consistent with a combination of the addition of protons of cometary origin to the plasma and loss of plasma through charge exchange of protons and He(++). In general agreement with the solar wind proton and He(++) observations, solar wind oxygen and carbon ions were observed to charge exchange from higher to lower charge states with decreasing distance to the comet. The more abrupt increases in the He(++) to proton and the He(++) to O(6+) density ratios in the mystery region require a change in the solar wind ion composition in this region while the correlation with energetic electrons indicates processes associated with the comet

Particle acceleration and the origin of gamma-ray emission from Fermi Bubbles

Fermi LAT has discovered two extended gamma-ray bubbles above and below the galactic plane. We propose that their origin is due to the energy release in the Galactic center (GC) as a result of quasi-periodic star accretion onto the central black hole. Shocks generated by these processes propagate into the Galactic halo and accelerate particles there. We show that electrons accelerated up to ~10 TeV may be responsible for the observed gamma-ray emission of the bubbles as a result of inverse Compton (IC) scattering on the relic photons. We also suggest that the Bubble could generate the flux of CR protons at energies > 10^15 eV because the shocks in the Bubble have much larger length scales and longer lifetimes in comparison with those in SNRs. This may explain the the CR spectrum above the knee.Comment: 5 pages, 4 figures. Expanded version of the contribution to the 32nd ICRC, Beijing, #0589. To appear in the proceeding

The Size Distribution of Kuiper Belt Objects

We describe analytical and numerical collisional evolution calculations for the size distribution of icy bodies in the Kuiper Belt. For a wide range of bulk properties, initial masses, and orbital parameters, our results yield power-law cumulative size distributions, N_C propto r^{-q}, with q_L = 3.5 for large bodies with radii of 10-100 km, and q_s = 2.5-3 for small bodies with radii lesss than 0.1-1 km. The transition between the two power laws occurs at a break radius of 1-30 km. The break radius is more sensitive to the initial mass in the Kuiper Belt and the amount of stirring by Neptune than the bulk properties of individual Kuiper Belt objects (KBOs). Comparisons with observations indicate that most models can explain the observed sky surface density of KBOs for red magnitudes, R = 22-27. For R 28, the model surface density is sensitive to the amount of stirring by Neptune, suggesting that the size distribution of icy planets in the outer solar system provides independent constraints on the formation of Neptune.Comment: 24 pages of text, 12 figures; to appear in the Astronomical Journal, October 200

Observations of plasma dynamics in the coma of P/Halley by the Giotto Ion Mass Spectrometer

Observations in the coma of P/Halley by the Giotto Ion Mass Spectrometer (IMS) are reported. The High Energy Range Spectrometer (HERS) of the IMS obtained measurements of protons and alpha particles from the far upstream region to the near ionopause region and of ions from mass 12 to 32 at distances of about 250,000 to 40,000 km from the nucleus. Plasma parameters from the High Intensity Spectrometer (HIS) of the IMS obtained between 150,000 to 5000 km from the nucleus are also discussed. The distribution functions of water group ions (water group will be used to refer to ions of 16 to 18 m/q, where m is in AMU and q is in unit charges) are observed to be spherically symmetric in velocity space, indicating strong pitch angle scattering. The discontinuity known as the magnetic pile-up boundary (MPB) is apparent only in proton, alpha, and magnetometer data, indicating that it is a tangential discontinuity of solar wind origin. HERS observations show no significant change in the properties of the heavy ions across the MPB. A comparison of the observations to an MHD model is made. The plasma flow directions at all distances greater than 30,000 km from the nucleus are in agreement with MHD calculations. However, despite the agreement in flow direction, within 200,000 km of the nucleus the magnitude of the velocity is lower than predicted by the MHD model and the density is much larger (a factor of 4). Within 30,000 km of the nucleus there are large theoretical differences between the MHD model flow calculations for the plane containing the magnetic field and for the plane perpendicular to the magnetic field. The observations agreed much better with the pattern calculated for the plane perpendicular to the magnetic field. The data obtained by the High Energy Range Spectrometer (HERS) of the IMS that are published herein were provided to the International Halley Watch archive

A particle swarm optimization based memetic algorithm for dynamic optimization problems

Copyright @ Springer Science + Business Media B.V. 2010.Recently, there has been an increasing concern from the evolutionary computation community on dynamic optimization problems since many real-world optimization problems are dynamic. This paper investigates a particle swarm optimization (PSO) based memetic algorithm that hybridizes PSO with a local search technique for dynamic optimization problems. Within the framework of the proposed algorithm, a local version of PSO with a ring-shape topology structure is used as the global search operator and a fuzzy cognition local search method is proposed as the local search technique. In addition, a self-organized random immigrants scheme is extended into our proposed algorithm in order to further enhance its exploration capacity for new peaks in the search space. Experimental study over the moving peaks benchmark problem shows that the proposed PSO-based memetic algorithm is robust and adaptable in dynamic environments.This work was supported by the National Nature Science Foundation of China (NSFC) under Grant No. 70431003 and Grant No. 70671020, the National Innovation Research Community Science Foundation of China under Grant No. 60521003, the National Support Plan of China under Grant No. 2006BAH02A09 and the Ministry of Education, science, and Technology in Korea through the Second-Phase of Brain Korea 21 Project in 2009, the Engineering and Physical Sciences Research Council (EPSRC) of UK under Grant EP/E060722/01 and the Hong Kong Polytechnic University Research Grants under Grant G-YH60

An analysis of target recipient groups for monovalent 2009 pandemic influenza vaccine and trivalent seasonal influenza vaccines in 2009-10 and 2010-11

Poster Presentation: SPA5 - How to Evaluate Vaccine Effectiveness and Efficacy?: abstract no. A513PINTRODUCTION: Vaccination is generally considered to be the best primary prevention measure against influenza virus infection. Many countries encourage specific target groups of people to undertake vaccination, often with financial subsidies or a list of priority. To understand differential patterns of national target groups for influenza vaccination before, during and after the 2009 influenza pandemic, we reviewed and identified changes in national target groups for trivalent seasonal influenza and the monovalent 2009 pandemic influenza vaccines dur...postprin

Theoretical study of Ga-based nanowires and the interaction of Ga with single-wall carbon nanotubes

Gallium displays physical properties which can make it a potential element to produce metallic nanowires and high-conducting interconnects in nanoelectronics. Using first-principles pseudopotential plane method we showed that Ga can form stable metallic linear and zigzag monatomic chain structures. The interaction between individual Ga atom and single-wall carbon nanotube (SWNT) leads to a chemisorption bond involving charge transfer. Doping of SWNT with Ga atom gives rise to donor states. Owing to a significant interaction between individual Ga atom and SWNT, continuous Ga coverage of the tube can be achieved. Ga nanowires produced by the coating of carbon nanotube templates are found to be stable and high conducting.Comment: 8 pages, 8 figure