Multi-agent collaborative search : an agent-based memetic multi-objective optimization algorithm applied to space trajectory design

This article presents an algorithm for multi-objective optimization that blends together a number of heuristics. A population of agents combines heuristics that aim at exploring the search space both globally and in a neighbourhood of each agent. These heuristics are complemented with a combination of a local and global archive. The novel agent-based algorithm is tested at first on a set of standard problems and then on three specific problems in space trajectory design. Its performance is compared against a number of state-of-the-art multi-objective optimization algorithms that use the Pareto dominance as selection criterion: non-dominated sorting genetic algorithm (NSGA-II), Pareto archived evolution strategy (PAES), multiple objective particle swarm optimization (MOPSO), and multiple trajectory search (MTS). The results demonstrate that the agent-based search can identify parts of the Pareto set that the other algorithms were not able to capture. Furthermore, convergence is statistically better although the variance of the results is in some cases higher

Harvest and Nitrogen Management of Three Perennial Grasses as Biomass Feedstock in Subarctic Alaska

High energy costs in high-latitude regions have generated interest in the feasibility of bioenergy cropping. The goal of this study was to determine the N response and best harvest regime for biomass production of three perennial, cool-season grass species—tufted hairgrass (Deschampsia caespitosa (L.) P. Beauv.), slender wheatgrass (Elymus trachy­caulus (Link) Gould ex Shinners), and smooth bromegrass (Bromus inermis Leyss)—at two locations in central Alaska. Maximum dry matter yields were 11.3 Mg ha-1 for smooth bromegrass, 8.1 Mg ha-1 for tufted hairgrass, and 8.0 Mg ha-1 for slender wheatgrass, but yields varied greatly among years. We found a linear N response in most cases, with highest yields at the 100 kg N ha-1 application rate. Yields for the double-harvest regime usually did not vary significantly from those of the fall harvest, but spring harvest sometimes reduced yields dramatically. Biomass in the spring harvest was usually dry enough not to require additional drying for storage. Results of this study indicate it may be possible to produce grass biomass yields high enough for use as bioenergy feedstocks in central Alaska, but questions remain about the best management practices and the economics of growing bioenergy crops in Alaska.Les coûts élevés de l’énergie en haute latitude incitent les gens à se pencher sur la faisabilité d’entreprendre des cultures bioénergétiques. L’objectif de cette étude consistait à déterminer la réponse à l’azote et le meilleur régime d’exploitation pour la bioproduction de trois espèces de graminées vivaces en saison fraîche, soit la deschampsie cespiteuse (Deschampsia caespitosa (L.) P. Beauv.), l’élyme à chaumes rudes (Elymus trachycaulus (Link) Gould ex Shinners) et le brome inerme (Bromus inermis Leyss), à deux endroits du centre de l’Alaska. Le rendement maximum de matière sèche était de 11,3 tm ha-1 dans le cas du brome inerme, de 8,1 tm ha-1 dans le cas de la deschampsie cespiteuse et de 8,0 tm ha-1 dans le cas de l’élyme à chaumes rudes, bien que les rendements aient connu d’importantes variations d’une année à l’autre. Nous avons trouvé une réponse linéaire à l’azote dans la plupart des cas, les rendements les plus élevés étant ceux de la dose d’application de 100 kg N ha-1. Le rendement du régime à double récolte ne variait généralement pas beaucoup du régime à récolte d’automne, bien que les récoltes du printemps donnaient parfois un rendement considérablement réduit. De manière générale, la biomasse de la récolte du printemps était suffisamment sèche pour ne pas avoir besoin d’être asséchée davantage avant d’être stockée. Les résultats de cette étude indiquent qu’il peut être possible de produire des rendements en biomasse suffisamment élevés à partir de graminées pour être utilisés comme charge bioénergétique dans le centre de l’Alaska, mais cela dit, il y a toujours lieu de répondre aux questions portant sur les pratiques de gestion exemplaires et le caractère économique des productions bioéner­gétiques en Alaska

HYDRA: Distributed Multi-Objective Optimization for Designers

Architectural design problems can be quite involved, as there is a plethora of – usually conflicting – criteria that one has to address in order to find an optimal, performative solution. Multi-Objective Optimization (MOO) techniques can thus prove very useful, as they provide solution spaces which can traverse the different trade-offs of convoluted design options. Nevertheless, they are not widely used as (a) they are computationally expensive and (b) the resulting solution space can be proven difficult to visualize and navigate, particularly when dealing with higher dimensional spaces. This paper will present a system, which merges bespoke multi-objective optimization with a parametric CAD system, enhanced by supercomputing, into a single, coherent workflow, in order to address the above issues. The system architecture ensures optimal use of existing compute resources and enables massive performance speed-up, allowing for fast review and delivery cycles. The application aims to provide architects, designers and engineers with a better understanding of the design space, aiding the decision-making process by procuring tangible data from different objectives and finally providing fit (and sometimes unforeseen) solutions to a design problem. This is primarily achieved by a graphical interface of easy to navigate solution spaces of design options, derived from their respective Pareto fronts, in the form of a web-based interactive dashboard. Since understanding high-dimensionality data is a difficult task, multivariate analysis techniques were implemented to post-process the data before displaying it to end users. Visual Data Mining (VDM) and Machine Learning (ML) techniques were incorporated to facilitate knowledge discovery and exploration of large sets of design options at an early design stage. The system is demonstrated and assessed on an applied design case study of a master-planning project, where the benefits of the process are more evident, especially due to its complexity and size

Sex pheromone signal and stability covary with fitness

If sexual signals are costly, covariance between signal expression and fitness is expected. Signal–fitness covariance is important, because it can contribute to the maintenance of genetic variation in signals that are under natural or sexual selection. Chemical signals, such as female sex pheromones in moths, have traditionally been assumed to be species-recognition signals, but their relationship with fitness is unclear. Here, we test whether chemical, conspecific mate finding signals covary with fitness in the moth Heliothis subflexa. Additionally, as moth signals are synthesized de novo every night, the maintenance of the signal can be costly. Therefore, we also hypothesized that fitness covaries with signal stability (i.e. lack of temporal intra-individual variation). We measured among- and within-individual variation in pheromone characteristics as well as fecundity, fertility and lifespan in two independent groups that differed in the time in between two pheromone samples. In both groups, we found fitness to be correlated with pheromone amount, composition and stability, supporting both our hypotheses. This study is, to our knowledge, the first to report a correlation between fitness and sex pheromone composition in moths, supporting evidence of condition-dependence and highlighting how signal–fitness covariance may contribute to heritable variation in chemical signals both among and within individuals

Power laws and self-similar behavior in negative ionization fronts

We study anode-directed ionization fronts in curved geometries. When the magnetic effects can be neglected, an electric shielding factor determines the behavior of the electric field and the charged particle densities. From a minimal streamer model, a Burgers type equation which governs the dynamics of the electric shielding factor is obtained. A Lagrangian formulation is then derived to analyze the ionization fronts. Power laws for the velocity and the amplitude of streamer fronts are observed numerically and calculated analytically by using the shielding factor formulation. The phenomenon of geometrical diffusion is explained and clarified, and a universal self-similar asymptotic behavior is derived.Comment: 25 pages, 9 figure

Full Elite Sets for Multi-Objective Optimisation

Copyright © 2002 Springer. The final publication is available at link.springer.com5th International Conference on Adaptive Computing in Design and Manufacture (ACDM 2002), Exeter, UK, 16-18 April, 2002Multi-objective evolutionary algorithms frequently use an archive of non-dominated solutions to approximate the Pareto front. We show that the truncation of this archive to a limited number of solutions can lead to oscillating and shrinking estimates of the Pareto front. New data structures to permit efficient query and update of the full archive are proposed, and the superior quality of frontal estimates found using the full archive is illustrated on test problems

Sprite discharges on Venus, Jupiter and Saturn: a laboratory investigation in planetary gas mixtures

Lightning was detected on several planets in the solar system, where it could also produce sprites in the upper layers of these atmospheres. Large sprite discharges at mesospheric altitudes on Earth have been found to be physically similar to streamer discharges in air at sea level density. Based on this understanding, we investigate possible sprite discharges on the Gas Giant planets and on Venus through laboratory experiments on streamers in H2-He and CO2-N2 mixtures. Streamer diameters, velocities, radiance and overall morphology are investigated for sprites on Jupiter, Saturn and Venus, by means of a fast ICCD camera. The spectra of the streamer discharges are measured; they are dominated by the minority species N2 on Venus, and by radiative dissociative continuum radiation of H2 in the Gas Giants. The spectrum of a fully developed spark on Venus and Saturn is also measured