Further evidence of the absence of Replica Symmetry Breaking in Random Bond Potts Models

In this short note, we present supporting evidence for the replica symmetric approach to the random bond q-state Potts models. The evidence is statistically strong enough to reject the applicability of the Parisi replica symmetry breaking scheme to this class of models. The test we use is a generalization of one formerly proposed by Dotsenko et al. and consists in measuring scaling laws of disordered-averaged moments of the spin-spin correlation functions. Numerical results, obtained via Monte Carlo simulations for several values of q, are shown to be in fair agreement with the replica symmetric values computed by using perturbative CFT for the second and third moments of the q=3 model. RSB effects, which should increase in strength with moment, are unobserved.Comment: 7 pages, some minor modifications (mainly misprints). To Appear in Europhysics Letter

Population extremal optimisation for discrete multi-objective optimisation problems

The power to solve intractable optimisation problems is often found through population based evolutionary methods. These include, but are not limited to, genetic algorithms, particle swarm optimisation, differential evolution and ant colony optimisation. While showing much promise as an effective optimiser, extremal optimisation uses only a single solution in its canonical form – and there are no standard population mechanics. In this paper, two population models for extremal optimisation are proposed and applied to a multi-objective version of the generalised assignment problem. These models use novel intervention/interaction strategies as well as collective memory in order to allow individual population members to work together. Additionally, a general non-dominated local search algorithm is developed and tested. Overall, the results show that improved attainment surfaces can be produced using population based interactions over not using them. The new EO approach is also shown to be highly competitive with an implementation of NSGA-II.No Full Tex

A parallel implementation of ant colony optimization

Ant Colony Optimization is a relatively new class of meta-heuristic search techniques for optimization problems. As it is a population-based technique that examines numerous solution options at each step of the algorithm, there are a variety of parallelization opportunities. In this paper, several parallel decomposition strategies are examined. These techniques are applied to a specific problem, namely the travelling salesman problem, with encouraging speedup and efficiency results.Full Tex

RIOJA (Repository Interface to Overlaid Journal Archives) project: final report

RIOJA (Repository Interface to Overlaid Journal Archives) was a 18-month partnership between UCL (University College London), Imperial College London, and the Universities Glasgow, Cambridge and Cornell. The project was funded by the JISC (Joint Information Systems Committee, UK). The project team worked with the Astrophysics community investigate aspects of overlay journals. For the purposes of the project, an overlay was defined as a quality-assured journal whose content is deposited to and resides more open access repositories. The project had both technical aims and supporting, non-technical aims. The primary technical deliverable from the project was a toolkit for the creation and maintenance overlay journals. The toolkit supports the exchange of data between a repository and piece of journal software. It supports functions such as author validation, metadata extraction from the source repository, and submission tracking. The toolkit is platform-neutral and could, in theory, be employed by any journal using content from any number repositories, in any discipline. The project also implemented a demonstrator overlay applying the RIOJA toolkit to the arXiv subject repository, and a demonstrator implementation of the RIOJA tool for GNU EPrints. Aside from creating the demonstrator and its underlying tools, the project aimed to acceptibility and feasibility of the overlay model. First, a large-scale survey of the Astrophysics community was undertaken. The survey collected data about research publishing practices within this community, and probed its reaction to the principle publishing. Second, the views of editors and publishers in this discipline were sought through interviews. These views were added to findings from the literature and summarised in a more general report on issues around the sustainability of an overlay journal

Spreading Speed, Traveling Waves, and Minimal Domain Size in\ud Impulsive Reaction-diffusion Models

How growth, mortality, and dispersal in a species affect the species’ spread and persistence constitutes a central problem in spatial ecology. We propose impulsive reaction-diffusion equation models for species with distinct reproductive and dispersal stages. These models can describe a seasonal birth pulse plus nonlinear mortality and dispersal throughout the year. Alternatively they can describe seasonal harvesting, plus nonlinear birth and mortality as well as dispersal throughout the year. The population dynamics in the seasonal pulse is described by a discrete map that gives the density of the populationat the end stage as a possibly nonmonotone function of the density of the population at the beginning of the stage. The dynamics in the dispersal stage is governed by a nonlinear reaction-diffusion equation in a bounded or unbounded domain. We develop a spatially explicit theoretical framework that links species vital rates (mortality or fecundity) and dispersal characteristics with species’ spreading speeds, traveling wave speeds, as well as and minimal domain size for species persistence. We provide an explicit formula for the spreading speed in terms of model parameters, and show that the spreading speed can be characterized as the slowest speed of a class of traveling wave solutions. We also determine an explicit formula for the minimal domain size using model parameters. Our results show how the diffusion coefficient, and the combination of discrete- and continuous-time growth and mortality determine the spread and persistence dynamics of the population in a wide variety of ecological scenarios. Numerical simulations are presented to demonstrate the theoretical results

Parasite spill-back from domestic hosts may induce an Allee effect in wildlife hosts

The exchange of native pathogens between wild and domesticated animals can lead to novel disease dynamics. A simple model reveals that the spill-back of native parasites\ud from domestic to wild hosts may cause a demographic Allee effect. Because parasite spill-over and spill-back decouples the abundance of parasite infectious stages from the abundance of the wild host population, parasitism and mortality of the wild host population increases non-linearly as host abundance decreases. Analogous to the effects of satiation of generalist predators, parasite spill-back can produce an unstable equilibrium in the abundance of the host population above which the host population persists and below which it is at risk of extirpation. These effects are likely to be most pronounced in systems where the parasite has a high efficiency of transmission from domestic to wild host populations due to prolonged sympatry, disease vectors, or proximity of domesticated populations to wildlife migratory corridors

Workload modeling using time windows and utilization in an air traffic control task

In this paper, we show how to assess human workload for continuous tasks and describe how operator performance is affected by variations in break-work intervals and by different utilizations. A study was conducted examining the effects of different break-work intervals and utilization as a factor in a mental workload model. We investigated the impact of operator performance on operational error while performing continuous event-driven air traffic control tasks with multiple aircraft. To this end we have developed a simple air traffic control (ATC) model aimed at distributing breaks to form different configurations with the same utilization. The presented approach extends prior concepts of workload and utilization, which are based on a simple average utilization, and considers the specific patterns of break-work intervals. Copyright 2011 by Human Factors and Ergonomics Society, Inc. All rights reserved

Notes on Mayfly Nymphs from Northeastern Minnesota Which Key to \u3ci\u3eStenonema Vicarium\u3c/i\u3e (Ephemeroptera: Heptageniidae)

(excerpt) A review of the literature indicates that Stenonema vicarium (Walker) adults have not been collected from northeastern Minnesota. However, mayfly nymphs which key to that species, based on the descriptions in Lewis (1974), have been collected from many streams in the area which are also inhabited by nymphs of the closely related species, Stenonema fuscum (Clemens)