Genetic algorithms with memory- and elitism-based immigrants in dynamic environments

Copyright @ 2008 by the Massachusetts Institute of TechnologyIn recent years the genetic algorithm community has shown a growing interest in studying dynamic optimization problems. Several approaches have been devised. The random immigrants and memory schemes are two major ones. The random immigrants scheme addresses dynamic environments by maintaining the population diversity while the memory scheme aims to adapt genetic algorithms quickly to new environments by reusing historical information. This paper investigates a hybrid memory and random immigrants scheme, called memory-based immigrants, and a hybrid elitism and random immigrants scheme, called elitism-based immigrants, for genetic algorithms in dynamic environments. In these schemes, the best individual from memory or the elite from the previous generation is retrieved as the base to create immigrants into the population by mutation. This way, not only can diversity be maintained but it is done more efficiently to adapt genetic algorithms to the current environment. Based on a series of systematically constructed dynamic problems, experiments are carried out to compare genetic algorithms with the memory-based and elitism-based immigrants schemes against genetic algorithms with traditional memory and random immigrants schemes and a hybrid memory and multi-population scheme. The sensitivity analysis regarding some key parameters is also carried out. Experimental results show that the memory-based and elitism-based immigrants schemes efficiently improve the performance of genetic algorithms in dynamic environments.This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) of the United Kingdom under Grant EP/E060722/01

Spin mapping, phase diagram, and collective modes in double layer quantum Hall systems at ν=2\nu=2

An exact spin mapping is identified to simplify the recently proposed hard-core boson description (Demler and Das Sarma, Phys. Rev. Lett., to be published) of the bilayer quantum Hall system at filling factor 2. The effective spin model describes an easy-plane ferromagnet subject to an external Zeeman field. The phase diagram of this effective model is determined exactly and found to agree with the approximate calculation of Demler and Das Sarma, while the Goldstone-mode spectrum, order parameter stiffness and Kosterlitz-Thouless temperature in the canted antiferromagnetic phase are computed approximately.Comment: 4 pages with 2 figures include

Scalar Wave Equation Modeling with Time-Space Domain Dispersion-Relation-Based Staggered-Grid Finite-Difference Schemes

The staggered-grid finite-difference (SFD) method is widely used in numerical modeling of wave equations. Conventional SFD stencils for spatial derivatives are usually designed in the space domain. However, when they are used to solve wave equations, it becomes difficult to satisfy the dispersion relations exactly. Liu and Sen (2009c) proposed a new SFD scheme for one-dimensional (1D) scalar wave equation based on the time-space domain dispersion relation and plane wave theory, which is made to satisfy the exact dispersion relation. This new SFD scheme has greater accuracy and better stability than a conventional scheme under the same discretizations. In this paper, we develop this new SFD scheme further for numerical solution of 2D and 3D scalar wave equations. We demonstrate that the modeling accuracy is second order when the conventional 2M-th-order space-domain SFD and the second order time-domain finite-difference stencils are directly used to solve the scalar wave equation. However, under the same discretization, our 1D scheme can reach 2M-th-order accuracy and is always stable; 2D and 3D schemes can reach 2M-th-order accuracy along 8 and 48 directions, respectively, and have better stability. The advantages of the new schemes are also demonstrated with dispersion analysis, stability analysis, and numerical modeling.National Natural Science Foundation of China 41074100Important National Science & Technology Specific Project of China 2008ZX05024-001Institute for Geophysic

Fiber-coupled erbium microlasers on a chip

An erbium-doped, toroid-shaped microlaser fabricated on a silicon chip is described and characterized. Erbium-doped sol-gel films are applied to the surface of a silica toroidal microresonator to create the microcavity lasers. Highly confined whispering gallery modes make possible single-mode and ultralow threshold microlasers

Studies of Higher Twist and Higher Order Effects in NLO and NNLO QCD Analysis of Lepton-Nucleon Scattering Data on F_2 and R =sigma_L/sigma_T

We report on the extraction of the higher twist contributions to F_2 and R = sigma_L/sigma_T from the global NLO and NNLO QCD fits to lepton nucleon scattering data over a wide range of Q^2. The NLO fits require both target mass and higher twist contributions at low Q^2. However, in the NNLO analysis, the data are described by the NNLO QCD predictions (with target mass corrections) without the need for any significant contributions from higher twist effects. An estimate of the difference between NLO and NNLO parton distribution functions is obtained.Comment: 5 pages, 6 figures, submitted to Eur. Phys.

Gain functionalization of silica microresonators

Erbium-doped solgel films are applied to the surface of silica microspheres to create low-threshold microcavity lasers. This gain functionalization can be applied by use of a number of different dopants, thereby extending the wavelength range of this class of device. Also, by varying the doping concentration and thickness of the applied solgel layer, one can vary the laser dynamics so that both continuous-wave and pulsating modes of operation are possible

Modeling Neutrino and Electron Scattering Cross Sections in the Few GeV Region with Effective LOPDFsLO PDFs

We use new scaling variables $x_w$ and $\xi_w$, and add low $Q^2$ modifications to GRV94 and GRV98 leading order parton distribution functions such that they can be used to model electron, muon and neutrino inelastic scattering cross sections (and also photoproduction) at both very low and high energie.Comment: 8 pages, 3 figures, Invited talk given by Arie Bodek at the X Mexican School of Particles and Fields, Playa del Carmen, Mexico, 200