Existence de dykes doléritiques anciens à composition de tholéiites continentales au sein de la province alcaline de la ligne du Cameroun. Implication sur le contexte géodynamique

n the Adamawa Plateau (Northern Cameroon), doleritic dykes belong to a magmatic activity which predated the Cenozoic alkaline volcanism of the Cameroon Line. They have the chemical composition of continental tholeiites with Nb-Ta- and Ti-negative anomalies. This magmatism is interpreted as being derived from a sub-continental lithospheric source, which may have been contaminated during a former subduction event, linked to the Pan-African convergence. It is related to an early stage of continental break-up, which was contemporaneous or predated the Cretaceous tholeiitic magmatism of predominantly asthenospheric origin, which indicates a lithospheric thinning

Document d'aide au déploiement d'IPv6 sur Grid5000

Ce document présente succinctement les motivations pour l'utilisation d'IPv6 dans les grilles. Une analyse des opérations nécessaires pour son déploiement dans la plateforme Grid5000 est ensuite présentée et détaillée

Neoproterozoic crustal evolution in Southern Chad: Pan-African ocean basin closing, arc accretion and late- to post-orogenic granitic intrusion.

International audienceIn the Lake Léré region, southern Chad, Neoproterozoic terrains are distributed in four lithostructural groups that reveal the geotectonic evolution of a part of the Pan-African orogenic domain. The first group includes basaltic volcanic rocks and fine-grained detrital sedimentary rocks of pre-tectonic basins that were emplaced in an extensional regime, close to a volcanic arc. The second and third groups include calc-alkaline gabbroic intrusions emplaced at an upper crustal level and a midcrustal tonalite, respectively, that are interpreted to be the roots of an active margin volcanic arc. These first three groups experienced WNW to ESE compression, and may belong to a fore-arc basic—volcanic arc—back-arc basin system that was accreted eastward to the Palaeoproterozoic Adamaoua-Yadé Block. The fourth group includes post-tectonic granite plutons invading the older groups. This paper documents the accretion processes in the southern margin of the Saharan Metacraton

Etude d'implémentations MPI dans une grille de calcul

National audienceThis paper presents an evaluation on the GRID'5000 platform of four MPI implementation: MPICH2, MPICH-Madeleine, OpenMPI et GridMPI. The comparison is based on a simple pingpong and the NAS parallel benchmarks. We show that GridMPI has the best results with regards to performances on the Grid if the implementation is well tuned. This paper details which parameters should be tuned.De nos jours, les grappes de PC ou clusters sont souvent interconnectés par des réseaux longue-distance de manière à former une grille afin d'offrir à un grand nombre d'utilisateurs un nombre plus conséquent de ressources. MPI, la bibliothèque de communication la plus utilisée pour les applications parallèles, a été efficacement implémentée dans un contexte de clusters. Deux caractéristiques des grilles, les réseaux longue-distance et l'hétérogénéité des processeurs et des réseaux, posent la question de l'efficacité de MPI sur les grilles. Cet article présente une évaluation sur la grille de recherche française GRID'5000, de 4 implémentations récentes de MPI : MPICH2, MPICH-Madeleine, OpenMPI et GridMPI. La comparaison est basée sur un pingpong, les NAS Parallel Benchmarks. Nous mettons en évidence les différences de performance obtenues avec les 4 implé- mentations. GridMPI montre les meilleures performances. L'exécution d'applications MPI sur la grille peut être bénéfique à condition de régler finement certains paramètres des implémentations. Cet article détaille les para- mètres mis en jeu et leurs réglages

Comparison and tuning of MPI implementations in a grid context

Today, clusters are often interconnected by long distance networks within grids to offer a huge number of available ressources to a range of users. MPI, the standard communication library used to write parallel applications, has been implemented for clusters. Two main features of grids: long distance networks and technological heterogeneity, raise the question of MPI efficiency in grids. This report presents an evaluation of four recent MPI implementations (MPICH2, MPICH-Madeleine, OpenMPI and GridMPI) in the french research grid: Grid'5000. The comparison is based on the execution of pingpong, NAS Parallel Benchmarks and a real application in geophysics. We show that this implementations present performance differences. Executing MPI applications on the grid can be beneficial if the parameters are well tuned. The paper details the tuning required on each implementation to get the best performances

Comparison and tuning of MPI implementation in a grid context

International audienceToday, clusters are often interconnected by long distance networks to compose grids and to provide users with a huge number of available ressources. To write parallel applica- tions, developers are generally using the standard communication library MPI, which has been optimized for clusters. However, two main features of grids - long distance networks and technological heterogeneity - raise the question of MPI efficiency in grids. This paper presents an evaluation and tuning of four recent MPI implementations (MPICH2, MPICH-Madeleine, OpenMPI and YAMPII) in a research grid: Grid'5000. The comparison is based on the execution of pingpong and NAS Parallel Bench- marks. We show that these implementations present several performance differences. We show that YAMPII performs better results than the others. But we argue that executing MPI appli- cations on a grid can be beneficial if some specific parameters are well tuned. The paper details, for each implementation, the tuning leading the best performances

Interaction between MPI and TCP in grids.

As MPI applications are more and more resource consuming, they need to be executed on grids. The communications on the WAN interconnecting clusters mostly use TCP which suffers from WAN features: high latency, sharing between users, bandwidth smaller than the aggregate bandwidth of the nodes. In this report, we first study the interaction between MPI and TCP on grids. We show why the nature of MPI traffic raises problems while using TCP on WAN links. TCP's loss detection and congestion control mechanism can both slow down the application. Then, we propose MPI5000, a transparent applicative layer between MPI and TCP, using proxies to improve the execution of MPI applications on a grid. Proxies aim at splitting TCP connections in order to detect losses faster and avoid to return in a slowstart phase after an idle time. Finally, we test our layer on Grid'5000, the French research grid, using MPICH2. The results on the NPB (NAS Parallel Benchmarks) validate our architecture that reduces the number of idle timeout and the number of long-distance retransmissions for certain benchmarks, namely BT, SP and LU benchmarks. Using MPI5000, these applications can decrease their execution time by 35%, 28%, and, 15% respectively

Évolution volcanologique du mont Manengouba (Ligne du Cameroun) ; nouvelles données pétrographiques, géochimiques et géochronologiques<br /> Volcanological evolution of the mount Manengouba (Cameroon line), new petrographical, geochemical, and geochronological data

Le mont Manengouba est un complexe volcanique polygénique de la Ligne du Cameroun édifié au Quaternaire, entre 1,55 et 0 Ma, en trois phases principales. La première phase, de 1,55 à 0,7 Ma, correspond à la construction du volcan Elengoum. La deuxième, entre 0,7 et 0,56 Ma, est marquée par l'effondrement de la partie sommitale de l'Elengoum. La troisième, de 0,56 à 0 Ma, voit l'édification du volcan Eboga, puis la formation de la caldeira, et comporte une activité fissurale adventive à partir de 0,48 Ma. Les produits émis définissent une série alcaline sodique, allant des basaltes à néphéline à des trachytes. Toutes ces laves ont évolué par cristallisation fractionnée dans une chambre magmatique périodiquement réalimentée. The mount Manengouba is a polygenic volcanic complex of the Cameroon line, which was built in the Quaternary, between 1.55 and 0 Ma, during three stages. The first stage, from 1.55 to 0.7 Ma, corresponds to the building of the Elengoum volcano. The second, between 0.7 and 0.56 Ma, points to the collapse of the Elengoum summit. The third, from 0.56 to 0 Ma, fits with the erection of the Eboga volcano and its caldera sinking, and, from 0.48 Ma, with the adventive fissural activity. The products define an alkaline sodic series, from nepheline-bearing basalts to trachytes. All the lavas evolved by fractional crystallization in a periodically replenished magmatic chamber

Comparison and tuning of MPI implementation in a grid context

International audienceToday, clusters are often interconnected by long distance networks to compose grids and to provide users with a huge number of available ressources. To write parallel applica- tions, developers are generally using the standard communication library MPI, which has been optimized for clusters. However, two main features of grids - long distance networks and technological heterogeneity - raise the question of MPI efficiency in grids. This paper presents an evaluation and tuning of four recent MPI implementations (MPICH2, MPICH-Madeleine, OpenMPI and YAMPII) in a research grid: Grid'5000. The comparison is based on the execution of pingpong and NAS Parallel Bench- marks. We show that these implementations present several performance differences. We show that YAMPII performs better results than the others. But we argue that executing MPI appli- cations on a grid can be beneficial if some specific parameters are well tuned. The paper details, for each implementation, the tuning leading the best performances