Développement et implémentation parallèle de méthodes d'interaction de configurations sélectionnées

Cette thèse, ayant pour thème les algorithmes de la chimie quantique, s'inscrit dans le cade du changement de paradigme observé depuis une douzaines d'années, dans lequel les méthodes de calcul séquentielles se doivent d'être progressivement remplacées par des méthodes parallèles. En effet, l'augmentation de la fréquences des processeurs se heurtant à des barrières physiques difficilement franchissables, l'augmentation de la puissance de calcul se fait par l'augmentation du nombre d'unités de calcul. Toutefois, là où une augmentation de la fréquence conduisait mécaniquement à une exécution plus rapide d'un code, l'augmentation du nombre de cœurs peut se heurter à des barrières algorithmiques, qui peuvent nécessiter une adaptation ou un changement d'algorithme. Parmi les méthodes développées afin de contourner ce problème, on trouve en particulier celles de type Monte-Carlo (stochastiques), qui sont intrinsèquement "embarrassingly parallel", c'est à dire qu'elles sont par construction constituées d'une multitudes de tâches indépendantes, et de ce fait particulièrement adaptées aux architectures massivement parallèles. Elles ont également l'avantage, dans de nombreux cas, d'être capables de produire un résultat approché pour une fraction du coût calculatoire de l'équivalent déterministe exacte. Lors de cette thèse, des implémentations massivement parallèles de certains algorithmes déterministes de chimie quantique ont été réalisées. Il s'agit des algorithmes suivants : CIPSI, diagonalisation de Davidson, calcul de la perturbation au second ordre, shifted-Bk, et Coupled Cluster Multi Références. Pour certains, une composante stochastique a été introduite en vue d'améliorer leur efficacité. Toutes ces méthodes ont été implémentées sur un modèle de tâches distribuées en TCP, où un processus central distribue des tâches par le réseau et collecte les résultats. En d'autres termes, des nœuds esclaves peuvent être ajoutés au cours du calcul depuis n'importe quelle machine accessible depuis internet. L'efficacité parallèle des algorithmes implémentés dans cette thèse a été étudiée, et le programme a pu donner lieu à de nombreuses applications, notamment pour permettre d'obtenir des énergies de références pour des systèmes moléculaires difficiles.This thesis, whose topic is quantum chemistry algorithms, is made in the context of the change in paradigm that has been going on for the last decade, in which the usual sequential algorithms are progressively replaced by parallel equivalents. Indeed, the increase in processors' frequency is challenged by physical barriers, so increase in computational power is achieved through increasing the number of cores. However, where an increase of frequency mechanically leads to a faster execution of a code, an increase in number of cores may be challenged by algorithmic barriers, which may require adapting of even changing the algorithm. Among methods developed to circumvent this issue, we find in particular Monte-Carlo methods (stochastic methods), which are intrinsically "embarrassingly parallel", meaning they are by design composed of a large number of independent tasks, and thus, particularly well-adapted to massively parallel architectures. In addition, they often are able to yield an approximate result for just a fraction of the cost of the equivalent deterministic, exact computation. During this thesis, massively parallel implementations of some deterministic quantum chemistry algorithms were realized. Those methods are: CIPSI, Davidson diagonalization, computation of second-order perturbation, shifted-Bk, Multi-Reference Coupled-Cluster. For some of these, a stochastic aspect was introduced in order to improve their efficiency. All of them were implemented on a distributed task model, with a central process distributing tasks and collecting results. In other words, slave nodes can be added during the computation from any location reachable through Internet. The efficiency for the implemented algorithms has been studied, and the code could give way to numerous applications, in particular to obtain reference energies for difficult molecular systems

A Case Study on the Evolution of Chinese Religious Symbols from Talismanic Paraphernalia to Taoist Liturgy

This is a chronological comparative study of five visual artefacts spanning about a millennium in Chinese history and retrieved from various sources included in the mid-fifteenth century collection called in English the Taoist Canon. All five specimens are basically titled “Taiping fu” 太平符 in Chinese, literally “Great Peace Symbol”. By briefly introducing the source of each specimen, describing the specimen's morphology and contextualising its implementation and purpose, the study highlights functional changeability and raises semiological issues that invite Sinologists to revise their understanding of the category of cultural artefact to which these specimens belong

Data Quality Principles in the Semantic Web

Abstract — The increasing size and availability of web data make data quality a core challenge in many applications. Principles of data quality are recognized as essential to ensure that data fit for their intended use in operations, decision-making, and planning. However, with the rise of the Semantic Web, new data quality issues appear and require deeper consideration. In this paper, we propose to extend the data quality principles to the context of Semantic Web. Based on our extensive industrial experience in data integration, we identify five main classes suited for data quality in Semantic Web. For each class, we list the principles that are involved at all stages of the data management process. Following these principles will provide a sound basis for better decision-making within organizations and will maximize longterm data integration and interoperability

ICSE 2007

The increasing number of mobile devices and sensors equipped with wireless networking capabilities enable a new generation of pro-active applications. These applications make use of context to adapt their behaviour to better fit their current situation. To support unanticipated changes to application behaviour, mechanisms are needed to specify when and how to adapt an application during its runtime. Many dynamic platforms exist that achieve this to some extent, and that are built on general-purpose languages (GPLs). However, these approaches suffer from standard difficulties of GPLs relating to the lack of semantic expressiveness of their constructs. In this paper, we describe high-level declarative constructs that can be used to specify the adaptation of application behaviour to specific situations. The language is supported by a framework that enables the exchange and merge of behaviours on-the-fly. Our approach is evaluated against application scenarios in the domain of autonomous vehicles

Addressing dynamic contextual adaptation with a domain-specific language

The increasing number of mobile devices and sensors equipped with wireless networking capabilities enable a new generation of pro-active applications. These applications make use of context to adapt their behaviour to better fit their current situation. To support unanticipated changes to application behaviour, mechanisms are needed to specify when and how to adapt an application during its runtime. Many dynamic platforms exist that achieve this to some extent, and that are built on general-purpose languages (GPLs). However, these approaches suffer from standard difficulties of GPLs relating to the lack of semantic expressiveness of their constructs. In this paper, we describe high-level declarative constructs that can be used to specify the adaptation of application behaviour to specific situations. The language is supported by a framework that enables the exchange and merge of behaviours on-the-fly. Our approach is evaluated against application scenarios in the domain of autonomous vehicles. 1