Collective and emergent problem solving based on multi-agent systems : principles and applications

A multi-agent system is composed of numerous entities, called agents, interacting in various ways between them and their common environment. This technology is applied in many domains like computer vision, robotics, system simulation or electronic commerce. We consider that problems occuring in signal processing could also be tackled by this technology. We present first the basic tools available for multi-agent systems designers : models, platforms and methodologies. Two projects illustrate our purpose : SCALA in the management of aerospace fighter patrol, and goods routing. We focus then on the adaptation ability of these systems considered as an emergent problem solving question. We detailed in this field the AMAS (Adaptive Multi-Agent System) theory allowing a MAS design where the global fonction is derived from the cooperative self-organisation of its components. An example on flood forecast gives implementation information of this theory.Un système multi-agent est constitué d’un grand nombre d’entités, appelées agents, en interaction entre elles au sein d’un même environnement. Cette technologie aborde de nombreux domaines d’applications comme la vision par ordinateur, la robotique, la simulation de systèmes, le commerce électronique. Nous considérons que les questions abordées en traitement du signal sont très pertinentes dans un cadre multi-agent. Nous présentons d’abord les principaux outils dont disposent les concepteurs de systèmes multi-agents à savoir : des modèles, des plates-formes et des méthodes de développement. Puis, le projet SCALA de simulation de résolution de problèmes par des patrouilles aériennes et un projet de simulation de système de transports illustrent la résolution de problèmes à l’aide de systèmes multi-agents. Ensuite, nous nous intéressons plus particulièrement aux capacités d’adaptation de tels systèmes que nous abordons comme une question de résolution émergente de problèmes. Dans ce cadre nous décrivons en détail la théorie AMAS (Adaptive Multi-Agent System) qui permet de concevoir des systèmes dont la fonction globale émerge à partir d’un processus d’auto-organisation coopérative de ses parties. Une application en prévision de crues donne une indication plus précise des capacités de telles approches

Electrophysiological prognostic factors of aphasia recovery

IntroductionAphasia is the main cause of communication disorders following stroke. The individual prognosis of aphasia recovery remind difficult to establish in the acute phase. The aim of this study was to investigate whether the motor evoked potentials (MEP) of the hand and the orbicularis oris in the acute phase of stroke could predict aphasia recovery.Materials and methodsThis study is ongoing at the University Hospital of Bordeaux. All consecutive patients with aphasia, first left hemispheric stroke confirmed by imaging, right-handed, non-demented, have been proposed for inclusion. MEPs were collected after stimulation of M1 the abductor pollicis and the orbicularis oris, right and left. The assessment of language performed in the acute phase was composed of: Language Screening Test (LAST) and the aphasia severity rating scale (ASRS) of the Boston Diagnostic Aphasia Examination (BDAE). Three and six months later, the language assessment was composed by: LAST, ASRS and BDAE. Good recovery from aphasia was defined as a score of ASRS 4 or 5. The association between the presence of a MEP after stimulation and good recovery was studied by Fischer exact tests.ResultsIn our interim analysis, 46 patients were followed at 3 months, and 23 at 6 months. The presence of MEP of the right hand (left cortical stimulation) was significantly associated with good recovery 3 months (P=0.003) and 6 months (P=0.003) after a stroke. The presence of MEP of the right orbicularis oris (left cortical stimulation) was significantly associated with good recovery 3 months (P=0.003) and 6 months (P=0.011).ConclusionMEP of hand and lips predict recovery from aphasia. This results suggest the importance of production systems in the recovery of language, suggesting a new approach compared semantic core highlighted in the old classic models such as Lichtheim

Remote Sensing-Driven Pacific Oyster (Crassostrea gigas) Growth Modeling to Inform Offshore Aquaculture Site Selection

Aquaculture increasingly contributes to global seafood production, requiring new farm sites for continued growth. In France, oyster cultivation has conventionally taken place in the intertidal zone, where there is little or no further room for expansion. Despite interest in moving production further offshore, more information is needed regarding the biological potential for offshore oyster growth, including its spatial and temporal variability. This study shows the use of remotely-sensed chlorophyll-a and total suspended matter concentrations retrieved from the Medium Resolution Imaging Spectrometer (MERIS), and sea surface temperature from the Advanced Very High Resolution Radiometer (AVHRR), all validated using in situ matchup measurements, as input to run a Dynamic Energy Budget (DEB) Pacific oyster growth model for a study site along the French Atlantic coast (Bourgneuf Bay, France). Resulting oyster growth maps were calibrated and validated using in situ measurements of total oyster weight made throughout two growing seasons, from the intertidal zone, where cultivation currently takes place, and from experimental offshore sites, for both spat (R2 = 0.91; RMSE = 1.60 g) and adults (R2 = 0.95; RMSE = 4.34 g). Oyster growth time series are further digested into industry-relevant indicators, such as time to achieve market weight and quality index, elaborated in consultation with local producers and industry professionals, and which are also mapped. Offshore growth is found to be feasible and to be as much as two times faster than in the intertidal zone (p < 0.001). However, the potential for growth is also revealed to be highly variable across the investigated area. Mapping reveals a clear spatial gradient in production potential in the offshore environment, with the northeastern segment of the bay far better suited than the southwestern. Results also highlight the added value of spatiotemporal data, such as satellite image time series, to drive modeling in support of marine spatial planning. The current work demonstrates the feasibility and benefit of such a coupled remote sensing modeling approach within a shellfish farming context, responding to real and current interests of oyster producers

La cognition sociale au-delà du cerveau : une cognition inclusive

National audienc

Proton deflectometry of a capacitor coil target along two axes

A developing application of laser-driven currents is the generation of magnetic fields of picosecond-nanosecond duration with magnitudes exceeding. Single-loop and helical coil targets can direct laser-driven discharge currents along wires to generate spatially uniform, quasi-static magnetic fields on the millimetre scale. Here, we present proton deflectometry across two axes of a single-loop coil ranging from 1 to 2 mm in diameter. Comparison with proton tracking simulations shows that measured magnetic fields are the result of kiloampere currents in the coil and electric charges distributed around the coil target. Using this dual-axis platform for proton deflectometry, robust measurements can be made of the evolution of magnetic fields in a capacitor coil target

Wakefields in a cluster plasma

We report the first comprehensive study of large amplitude Langmuir waves in a plasma of nanometer-scale clusters. Using an oblique angle single-shot frequency domain holography diagnostic, the shape of these wakefields is captured for the first time. The wavefronts are observed to curve backwards, in contrast to the forwards curvature of wakefields in uniform plasma. Due to the expansion of the clusters, the first wakefield period is longer than those trailing it. The features of the data are well described by fully relativistic two-dimensional particle-in-cell simulations and by a quasianalytic solution for a one-dimensional, nonlinear wakefield in a cluster plasma

Measuring magnetic fields in laser-driven coils with dual-axis proton deflectometry

By driving hot electrons between two metal plates connected by a wire loop, high power lasers can generate multi-tesla, quasi-static magnetic fields in miniature coil targets. Many experiments involving laser-coil targets rely on proton deflectometry directed perpendicular to the coil axis to extract a measurement of the magnetic field. In this paper, we show that quantitative measurements using perpendicular probing are complicated by the presence of GV m-1 electric fields in the target that develop on sub-ns timescales. Probing parallel to the coil axis with fiducial grids is shown to reliably separate the electric and magnetic field measurements, giving current estimates of I ≈ 5 kA in 1 mm- and 2 mm-diameter wire loops. An analytic model of proton deflection in electric and magnetic fields is used to benchmark results from the particle-in-cell code and help deconvolve the magnetic and electric field deflections. Results are used to motivate a new experimental scheme that combines a single-plate target with axial proton probing and direct current measurements. This scheme has several important advantages over the traditional target and diagnostic set-up, enabling the robust measurement of coil magnetic fields and plasma properties, as well as making it easier to validate different theoretical models at a range of laser intensities