Paquet R pour l'estimation d'un mélange de lois de Student multivariées à échelles multiples

National audienceL'utilisation d'un modèle de mélange de lois est une approche statistique classique en classification non-supervisée. Un mélange fréquemment utilisé pour sa simplicité est le mélange gaussien. Cependant, un tel modèle est sensible aux données atypiques. Pour remédier à cela, nous présentons ici le mélange de lois de Student multivariées à échelles multiples, que nous sommes en train d'incorporer au sein d'un paquet R. Ces lois peuvent gérer des queues de lourdeurs différentes selon les directions alors que les lois gaussiennes et les lois de Student multivariées standards sont contraintes à être symétriques

Comparing Regulations to Protect the Commons: An Experimental Investigation

We test in a laboratory experiment three regulations imposed on a common-pool resource game: an access fee and subsidy scheme, transferable quotas and non-transferable quotas. Theory predicts that they all reduce resource use from free access to the same target level without hurting users. We find that all regulations perform equally in reducing resources, although with more variance under the fee scheme. All fail to make all the users better off. The fee scheme performs better than transferable quotas in sorting out the most efficient users but at the cost of hurting them more often

Des données géographiques à la simulation à base d'agents : application de la plate-forme GAMA

International audienceCes dernières années, la simulation à base d’agents a révélé certains intérêts en géographie. Néanmoins, s’il existe aujourd’hui de nombreuses plates-formes permettant de faciliter le développement de modèle, celles-ci sont souvent trop complexes pour être utilisées par des non-informaticiens (par exemple Repast Symphony) ou trop limitées pour développer des modèles riches intégrant de nombreux agents et données (par exemple Netlogo). La plate-forme GAMA a pour objectif d’offrir aux modélisateurs une plate-forme à la fois puissante et simple d’accès grâce à langage de modélisation dédié. Dans cet article, nous présentons les capacités particulièrement avancées de la nouvelle version de la plate-forme GAMA pour la gestion de l’espace. Cette plate-forme permet en particulier de gérer simultanément plusieurs environnements basés sur trois types de topologie (continue, grille, graphe), d’intégrer très simplement des données géographiques (vectorielles et rasters) et de représenter des géométries dans un environnement 3D. Les capacités détaillées dans cet article sont illustrées par un modèle sur les problématiques de ségrégation urbaine

Morphologie urbaine et mobilité : outils et méthodes d’analyse conjointe des bases de données morphologiques et de mobilité

International audienceOur proposal is on the first hand to present the Remus model and its abilities to analyse urban morphological patterns; and on the second hand to present the first results obtained by characterizing the relations between morphology and mobility, using multiple regression models and landscape metrics.Ce projet de communication propose une méthode de caractérisation de la morphologie des tissus urbains, du point de vue des proximités, de l‘accessibilité et du fonctionnement des mobilités, par des indicateurs de graphes et des indicateurs morphologiques. Ces indicateurs sont ensuite réutilisés pour être confrontés à des indicateurs de mobilité, afin d’étudier les liens entre les morphologies territoriales et urbaines et les mobilités

Spatial modeling of the potential of agricultural or forestry production for sustainable land use planning

In Central Africa, oil palm is a major food-crop used in everyday cooking. All the countries of the region are importing palm oil, often from south-east Asia, to cover their domestic demand. Palm oil production is dominated by small scale agriculture, with a diversity going from the small backyard garden to the monospecific plantation of several hundred hectares. Most of the industrial plantations date from colonial periods. New industrial plantations have been expanding in the last decade, with successes and failures, with the help of southeast Asian and European multinationals and domestic investors. The States want to increase their national palm oil production and industrial investments. They hope for socioeconomic benefits and food security. Such plans for agricultural development also present threats such as deforestation, loss of biodiversity and land use conflicts, and caution and planning are needed to avoid negative social and environmental impacts. In order to provide decision-makers with accurate information and useful decision-making tools to plan the development of the palm oil sector at national and subregional scales, the WWF asked CIRAD to map lands potentially favourable to the production of sustainable (P&C RSPO) palm oil in 5 countries of the Congo basin: Cameroon, Gabon, Republic of Congo, Democratic Republic of Congo and Republic of Central Africa. We use a step by step method to 1/ measure and locate territories which are suitable for oil palm culture, 2/ prevent threats over biodiversity and land use by respecting the social and environmental constraints edited by the principles and criteria of the Roundtable on Sustainable Palm Oil (P&C RSPO), 3/ plan development strategies for palm oil production which are coherent with the national context and specificities (through an evaluation of the adequacy of various production models). The maps resulting from this study are useful decision-making tools that allow analysing trade-offs between opportunities of production and prevention of threats on biodiversity and land use issues. These maps can be useful in the design of national programs of agricultural development that avoid deforestation and preserve biodiversity corridors. Our results in Gabon are consistent with the maps of biodiversity and conservation importance produced by the National Agency of National Parks. In Republic of Congo, they are used in the discussions on the agricultural component of the REDD+ program. (Texte intégral

Social identity-based motivation modulates attention bias toward negative information: an event-related brain potential study: Social identity, motivation and attention

International audienceResearch has demonstrated that people readily pay more attention to negative than to positive and/or neutral stimuli. However, evidence from recent studies indicated that such an attention bias to negative information is not obligatory but sensitive to various factors. Two experiments using intergroup evaluative tasks (Study 1: a gender-related groups evaluative task and Study 2: a minimal-related groups evaluative task) was conducted to determine whether motivation to strive for a positive social identity - a part of one's self-concept - drives attention toward affective stimuli. Using the P1 component of event-related brain potentials (ERPs) as a neural index of attention, we confirmed that attention bias toward negative stimuli is not mandatory but it can depend on a motivational focus on affective outcomes. Results showed that social identity-based motivation is likely to bias attention toward affectively incongruent information. Thereby, early onset processes - reflected by the P1 component - appeared susceptible to top-down attentional influences induced by the individual's motivation to strive for a positive social identity

Modélisation des assemblages de ballons pressurisés stratosphériques

Long duration super-pressure balloon design and manufacturing is a great challenge for the CNES in scientific ballooning. They are made of 50 µm thick polymer films (PET/PA/PET) which are joined with 23 µm thick adhesive PET bands. To date, during flight missions, a real problem appears: some balloons explode prematurely. This is why this study deals with the mechanical behaviour of the stratospheric pressurized balloons and particularly with the assembly of the constitutive materials. Firstly, a nanoindentation test campaign makes it possible to identify the elastic properties of the materials directly in the assembly at two different temperatures. Then, we simulate a nominal assembly in two approaches: 2D and 3D. More particularly, we present an example concerning a defect of the junction in 3D approach using the submodeling technique. Finally, we use the factorial design method at two levels and finite-element models to study the influence of the various conception parameters on the mechanical behaviour of the assembly

Simulating Urban Growth with Raster and Vector models: A case study for the city of Can Tho, Vietnam

Urban growth has been widely studied and many models (in particular Cellular Automata and Agent-Based Models) have been developed. Most of these models rely on two representations of the geographic space: raster and vector. Both representations have their own strengths and drawbacks. The raster models are simpler to implement and require less data, which explains their success and why most of urban growth models are based on this representation. However, they are not adapted to microscopic dynamics such as, for example, the construction of buildings. To reach such goal, a vector-based representation of space is mandatory. However, very few vector models exist, and none of them is easily adaptable to different case studies. In this paper, we propose to use a simple raster model and to adapt it to a vector representation of the geographic space and processes allowing studying urban growth at fine scale. Both models have been validated by a case study concerning the city of Can Tho, Vietnam