Inhibition of type III radio emissions due to the interaction between two electron beams: Observations and simulations

International audienceWe report the peculiar interaction of two type III bursts observed in the solar wind. As electronbeams propagating on the same magnetic field lines cross, a spectacular depletion of the type III radioemission is observed. We combine observations from the WAVES experiment on board the STEREO missiontogether with kinetic plasma simulations to study the extinction of type III radio emission resulting fromthe interaction between two electron beams. The remote observations enable to follow the electron beamsin the interplanetary medium and show that the level of radiated radio waves is recovered after the beamcrossing. The in situ observations of beam-driven Langmuir waves give evidence for Langmuir decay. Thedensity fluctuations are extracted from in situ observations. The velocity of the beams is independentlyevaluated from in situ observations of decaying Langmuir waves and remote radio observations. The kineticsimulations show that the level of beam-driven Langmuir waves is reduced as the two beams cross. Weshow that the slow beam induced a strong reduction of the quasilinear relaxation of the fast beam, limitingthe amplitude of the generated Langmuir waves. Moreover, in the case of two electron beams, the lack ofLangmuir wave coherence reduces the efficiency of the Langmuir parametric decay. We thus conclude thatthe observed depletion of the type III radio emission is independent of the radio emission mechanism, aslong as it depends on the Langmuir amplitude and coherence

Interactive visual exploration of association rules with rule-focusing methodology

International audienceOn account of the enormous amounts of rules that can be produced by data mining algorithms, knowledge post-processing is a difficult stage in an association rule discovery process. In order to find relevant knowledge for decision making, the user (a decision maker specialized in the data studied) needs to rummage through the rules. To assist him/her in this task, we here propose the rule-focusing methodology, an interactive methodology for the visual post-processing of association rules. It allows the user to explore large sets of rules freely by focusing his/her attention on limited subsets. This new approach relies on rule interestingness measures, on a visual representation, and on interactive navigation among the rules. We have implemented the rule-focusing methodology in a prototype system called ARVis. It exploits the user's focus to guide the generation of the rules by means of a specific constraint-based rule-mining algorithm

Post-Processing of Discovered Association Rules Using Ontologies

In Data Mining, the usefulness of association rules is strongly limited by the huge amount of delivered rules. In this paper we propose a new approach to prune and filter discovered rules. Using Domain Ontologies, we strengthen the integration of user knowledge in the post-processing task. Furthermore, an interactive and iterative framework is designed to assist the user along the analyzing task. On the one hand, we represent user domain knowledge using a Domain Ontology over database. On the other hand, a novel technique is suggested to prune and to filter discovered rules. The proposed framework was applied successfully over the client database provided by Nantes Habitat

Une méthodologie de recommandations produits fondée sur l'actionnabilité et l'intérêt économique des clients

National audienceDans un contexte économique difficile, la fidélisation des clients figure au premier rang des préoccupations des entreprises. En effet, selon le Gartner, fidéliser des clients existants coûterait beaucoup moins cher que prospecter de nouveaux clients. Pour y parvenir, les entreprises optimisent la marge et le cycle de vie des clients en développant une relation personnalisée aboutissant à demeilleures recommandations. Dans cet article, nous proposons une méthodologie pour les systèmes de recommandations fondée sur l'analyse des chiffres d'affaires des clients sur des familles de produits. Plus précisément, la méthodologie consiste à extraire des comportements de référence sous la forme de règles d'association et à en évaluer l'intérêt économique et l'actionnabilité. Les recommandations sont réalisées en ciblant les contre-exemples les plus actionnables sur les règles les plus rentables.Notreméthodologie est appliquée sur 12 000 clients et 100 000 produits de VMMatériaux afin d'orienter les commerciaux sur les possibilités d'accroissement de la valeur client

An Ontology-Based Autonomic System for Improving Data Warehouse Performances

International audienceWith the increase in the amount and complexity of information, data warehouse performance has become a constant issue, especially for decision support systems. As decisional experts are faced with the management of more complex data warehouses, a need for autonomic management capabilities is shown to help them in their work. Implementing autonomic managers over knowledge bases to manage them is a solution that we find more and more used in business intelligence environments. What we propose, as decisional system experts, is an autonomic system for analyzing and improving data warehouse cache memory allocations in a client environment. The system formalizes aspects of the knowledge involved in the process of decision making (from system hardware specifications to practices describing cache allocation) into the same knowledge base in the form of ontologies, analyzes the current performance level (such as query average response time values) and proposes new cache allocation values so that better performance is obtained

Les fondements de l'analyse statistique implicative et quelques prolongements pour la fouille de données

Implicative statistical analysis allows the discovery of relevant rules from a hypothesis test on various data, and offers following classical hierarchical classification, a hierarchical representation of meta-rules and an analysis of the individual and attribute contributions to the different associations. Moreover, a new measure takes into account both the notion of entropy and the intensity of implication, adequate to large data sets studied in data mining.L'analyse statistique implicative d'une part permet de déceler les règles pertinentes à partir d'un test d'hypothèse sur des données variées, d'autre part offre, selon une démarche calquée sur la classification hiérarchique classique, une représentation hiérarchique des méta-règles et une analyse des contributions des attributs et individus aux différentes associations. De plus, une nouvelle mesure permet d'intégrer à la fois la notion d'entropie et l'intensité d'implication, adaptée au traitement de données volumineuses telles qu'elles apparaissent en Extraction de Connaissances dans les Données

STEREO database of interplanetary Langmuir electric waveforms

International audienceThis paper describes a database of electric waveforms that is available at the Centre de Données de la Physique des Plasmas (CDPP, http://cdpp.eu/). This database is specifically dedicated to waveforms of Langmuir/Z-mode waves. These waves occur in numerous kinetic processes involving electrons in space plasmas. Statistical analysis from a large data set of such waves is then of interest, e.g., to study the relaxation of high-velocity electron beams generated at interplanetary shock fronts, in current sheets and magnetic reconnection region, the transfer of energy between high and low frequencies, the generation of electromagnetic waves. The Langmuir waveforms were recorded by the Time Domain Sampler (TDS) of the WAVES radio instrument on board the STEREO mission. In this paper, we detail the criteria used to identify the Langmuir/Z-mode waves among the whole set of waveforms of the STEREO spacecraft. A database covering the November 2006 to August 2014 period is provided. It includes electric waveforms expressed in the normalized frame inline image with B and Vsw the local magnetic field and solar wind velocity vectors, and the local magnetic field in the variance frame, in an interval of ±1.5 min around the time of the Langmuir event. Quicklooks are also provided that display the three components of the electric waveforms together with the spectrum of E∥, together with the magnitude and components of the magnetic field in the 3 min interval, in the variance frame. Finally, the distribution of the Langmuir/Z-mode waves peak amplitude is also analyzed