Dynamic Study of Thin Wall Part Turning

The numerical simulation of machining process is a key factor in the control of parts machining process. Its development aims at improving the process reliability and reduces the time spent during the process planning stage. In this context, we use a specific time domain simulation allowing modeling the dynamics of a thin wall part turning operation. After having introduced the basics of the proposed approach we present a specific cutting test that has been designed to specifically measure and control the dynamics of the part and the cutting conditions of a finishing toolpath. The influences of the cutting speed and damping coefficient on the chatter occurrence are discussed. In order to better control the simulation uses, an analysis of the simulation parameters influences on the simulated results is proposed

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

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

Acoustic Observation of Living Organisms Reveals the Upper Limit of the Oxygen Minimum Zone

Background: Oxygen minimum zones (OMZs) are expanding in the World Ocean as a result of climate change and direct anthropogenic influence. OMZ expansion greatly affects biogeochemical processes and marine life, especially by constraining the vertical habitat of most marine organisms. Currently, monitoring the variability of the upper limit of the OMZs relies on time intensive sampling protocols, causing poor spatial resolution. Methodology/Principal Findings: Using routine underwater acoustic observations of the vertical distribution of marine organisms, we propose a new method that allows determination of the upper limit of the OMZ with a high precision. Applied in the eastern South-Pacific, this original sampling technique provides high-resolution information on the depth of the upper OMZ allowing documentation of mesoscale and submesoscale features (e.g., eddies and filaments) that structure the upper ocean and the marine ecosystems. We also use this information to estimate the habitable volume for the world’s most exploited fish, the Peruvian anchovy (Engraulis ringens). Conclusions/Significance: This opportunistic method could be implemented on any vessel geared with multi-frequency echosounders to perform comprehensive high-resolution monitoring of the upper limit of the OMZ. Our approach is a novel way of studying the impact of physical processes on marine life and extracting valid information about the pelagic habitat an

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

Nature of the Ferric Hydroperoxide Intermediate in Heme Oxygenase: A Magnetic Resonance Investigation

Chemistr

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