528 research outputs found
Multi-level agent-based modeling with the Influence Reaction principle
This paper deals with the specification and the implementation of multi-level
agent-based models, using a formal model, IRM4MLS (an Influence Reaction Model
for Multi-Level Simulation), based on the Influence Reaction principle.
Proposed examples illustrate forms of top-down control in (multi-level)
multi-agent based-simulations
One-dimensional parametric determining form for the two-dimensional Navier-Stokes equations
The evolution of a determining form for the 2D Navier-Stokes equations (NSE),
which is an ODE on a space of trajectories is completely described. It is
proved that at every stage of its evolution, the solution is a convex
combination of the initial trajectory and the fixed steady state, with a
dynamical convexity parameter , which will be called the characteristic
determining parameter. That is, we show a remarkable separation of variables
formula for the solution of the determining form. Moreover, for a given initial
trajectory, the dynamics of the infinite-dimensional determining form are
equivalent to those of the characteristic determining parameter which
is governed by a one-dimensional ODE. %for the parameter specifying the
position on the line segment. This one-dimensional ODE is used to show that if
the solution to the determining form converges to the fixed state it does so no
faster than , otherwise it converges to a projection
of some other trajectory in the global attractor of the NSE, but no faster than
, as , where is the
evolutionary variable in determining form. The one-dimensional ODE also
exploited in computations which suggest that the one-sided convergence rate
estimates are in fact achieved. The ODE is then modified to accelerate the
convergence to an exponential rate. Remarkably, it is shown that the zeros of
the scalar function that governs the dynamics of , which are called
characteristic determining values, identify in a unique fashion the
trajectories in the global attractor of the 2D NSE. Furthermore, the
one-dimensional characteristic determining form enables us to find
unanticipated geometric features of the global attractor, a subject of future
research
Trade-off between somatic and germline repair in a vertebrate supports the "expensive germ line" hypothesis
The disposable soma theory is a central tenet of the biology of aging where germline immortality comes at the cost of an aging soma [T. B. L. Kirkwood, Nature 270, 301â304 (1977); T. B. L. Kirkwood, Proc. R. Soc. Lond. B Biol. Sci. 205, 531â546 (1979); T. B. L. Kirkwood, S. N. Austad, Nature 408, 233â238 (2000)]. Limited resources and a possible trade-off between the repair and maintenance of the germ cells and growth and maintenance of the soma may explain the deterioration of the soma over time. Here we show that germline removal allows accelerated somatic healing under stress. We tested âthe expensive germ lineâ hypothesis by generating germline-free zebrafish Danio rerio and testing the effect of the presence and absence of the germ line on somatic repair under benign and stressful conditions. We exposed male fish to sublethal low-dose ionizing radiation, a genotoxic stress affecting the soma and the germ line, and tested how fast the soma recovered following partial fin ablation. We found that somatic recovery from ablation occurred substantially faster in irradiated germline-free fish than in the control germline-carrying fish where somatic recovery was stunned. The germ line did show signs of postirradiation recovery in germline-carrying fish in several traits related to offspring number and fitness. These results support the theoretical conjecture that germline maintenance is costly and directly trades off with somatic maintenance
ModĂ©lisation de la tempĂ©rature dâun corps par automates cellulaires
International audienceDans cet article, nous traitons d'une alternative aux mĂ©thodes analytiques classiques dans le cadre de la modĂ©lisation de systĂšmes complexes. Devant le caractĂšre imprĂ©visible de ces systĂšmes (oĂč le nombre de composants et l'intensitĂ© des interactions sont importants), les mĂ©thodes analytiques semblent mal adaptĂ©es et des modĂšles dynamiques discrets, comme les automates cellulaires, peuvent permettre de faireĂ©merger des comportements globaux complexes en dĂ©terminant simplement le comportement local et les interactions d'entitĂ©s primitives. Nous illustrons notre propos en nous intĂ©ressantĂ un problĂšme issu de la mĂ©decine lĂ©gale : la modĂ©lisation du comportement thermique d'un cadavre. Aucun des modĂšles de tempĂ©rature actuels, empiriques ou basĂ©s sur les lois physiques de transfert de chaleur, ne prend en compte des simulations sous tempĂ©ratures variables. Nous proposons une solution qui remĂ©dieĂ ce problĂšme. Nous en dĂ©taillons les spĂ©cifications, implĂ©mentations et rĂ©sultats. Nous terminons sur l'utilisation de nos travaux, intĂ©grĂ©s au sein d'un systĂšme multi-agents, et les perspectives de travail
Stratégies d'observation dans les simulations orientées agent
Extended version of Stratégies d'observation de simulations orientées agent, Actes des 17Úmes Journées Francophones sur les SystÚmes Multi-Agents (JFSMA'09), pp. 233-236National audienceL'observation de simulations orientées agent composées de nombreux agents est une tùche coûteuse en temps de calcul. Dans cet article, nous proposons deux méthodes, trÚs simples à mettre en oeuvre, basées sur la théorie des sondages et la notion d'auto-observation, permettant d'optimiser le calcul d'observables. Ces méthodes sont évaluées et comparées empiriquement sur un problÚme jouet
Thermoregulation in P. Terraenovae aggregations, an agent-based approach
International audienceThis paper deals with an important issue of forensic entomology: the estimation of the temperature in a "maggot mass". An agent-based model of the thermoregulation behaviour of fly (Protophormia terraenovae) larvae is described. Simulation results show that the model reproduces an important observed pattern and thus, might be used in entomological expertises
Super-twisting sliding mode controller for freeway ramp metering
Colloque avec actes et comitĂ© de lecture. internationale.International audienceIn this paper we propose a new feedback controller for freeway ramp metering. It is based on a second order sliding mode technique called super twisting sliding mode controller (STSMC). It is a simple and robust controller. It is less sensitive to parameter values and the model uncertainty with less problem of chattering phenomenon compared to the ïŹrst order sliding mode controller. And then, this new controller is compared with a well known feedback controller for freeway ramp metering called ALINEA. The simulations show a good result of the new controller for freeway ramp metering. Moreover, compared to ALINEA, the STSMC can cope better the system in term of robustness and uncertainty
GESTION TEMPS REEL DâUN RESEAU DâASSAINISSEMENT BASEE SUR LA SIMULATION D'UN MODELE CONTINU
Colloque avec actes et comitĂ© de lecture. internationale.International audience"Les outils actuels de gestion en temps rĂ©el des rĂ©seaux sâappuient sur deux outils logiciels : les logiciels de prĂ©vision mĂ©tĂ©orologique et les logiciels de simulation hydraulique. Lâusage des premiers est une cause importante dâimprĂ©cision et dâincertitude, lâusage des seconds oblige Ă des pas temporels de dĂ©cision importants du fait de leur besoin en temps de calcul. Cette façon de procĂ©der fait que les rĂ©sultats obtenus sont gĂ©nĂ©ralement Ă©loignĂ©s de ceux attendus.LâidĂ©e force du projet CARDIO est de changer de paradigme de base en abordant la problĂ©matique par la face « automatique » plutĂŽt que par celle « hydrologie ». Lâobjectif est de rendre possible la rĂ©alisation dâun grand nombre de simulations en des temps trĂšs courts (quelques secondes) permettant de se passer des prĂ©visions mĂ©tĂ©orologiques en utilisant directement les donnĂ©es pluviomĂ©triques recueillies en temps rĂ©el. Lâobjectif est de parvenir Ă un systĂšme oĂč la prise de dĂ©cision est rĂ©alisĂ©e Ă partir de donnĂ©es fiables et oĂč la correction de lâerreur est permanente.Les premiers rĂ©sultats obtenus Ă partir d'une simulation d'un exemple test montrent l'efficacitĂ© de lâapproche dĂ©veloppĂ©e.
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