PhD theses

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    Models and Tools for Usage-based e-Learning Documents Reengineering
    (2019-04-25) Sadallah, Madjid
    Providing high-quality content is of utmost importance to drive successful reading. Besides, designing documents that are received the way the author wishes has always been difficult, and the digital world increases this difficulty by multiplying the possibilities related to mixed medias and interactivity. This compels authors to continuously review the delivered content to meet readers' needs. Yet it remains challenging for them to detect the comprehension barriers that may exist within their documents, and to identify how these latter can be improved accordingly. This compels authors to continuously review the delivered content to meet readers' needs. Yet it remains challenging for them to detect the comprehension barriers that may exist within their documents, and to identify how these latter can be improved accordingly. In this thesis, we focus on an educational context, where reading is a fundamental activity and the basis of many other learning activities. We propose a learning analytics approach for assisting course authors to maintain their courses to sustain learning. The proposals are based on theoretical background originated from research on learning analytics, reading comprehension and content revision. We advocate \usage-based document reengineering", a process defined as a kind of reengineering that changes document content and structures based on the analysis of readers' usages as recorded in their reading traces. We model reading activity using the concept of reading-session and propose a new session identification method. Using learners' reading sessions, a set of indicators related to different aspects of the reading process are computed and used to detect comprehension issues and to suggest corrective content revisions. The results of the analytics process are presented to authors through a dashboard empowered with assistive features. We instantiate our proposals using the logs of a major e-learning platform, and validate it through a series of studies. The results show the effectiveness of the approach and dashboards in providing authors with guidance in improving their courses accordingly.
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    Scalable and Fault Tolerant Hierarchical B&B Algorithm for Computational Grids
    (2012-06-07) Bendjoudi, Ahcène
    Solving to optimality large instances of combinatorial optimization problems using Branch and Bound (B&B) algorithms requires a huge amount of computing resources. Nowadays, such power is provided by large scale environments such as computational grids. However, grids induce new challenges: scalability, heterogeneity, and fault tolerance. Most of existing grid-based B&Bs are developed using the Master-Worker paradigm, their scalability is therefore limited. Moreover fault tolerance is rarely addressed in these works. In this thesis, we propose three main contributions to deal with these issues: P2P-B&B, H-B&B, and FTH-B&B. P2P-B&B is a MW-based B&B framework which deals with scalability by reducing the task request frequency and enabling direct communication between workers. H-B&B also deals with scala- bility. Unlike the state-of-the-art approaches, H-B&B is fully dynamic and adaptive, meaning it takes into account the dynamic acquisition of new computing resources. FTH-B&B is based on new fault tolerant mechanisms enabling efficient building of the hierarchy and maintainingits balancing, and minimizing of work redundancy when storing and recovering tasks. The proposed approaches have been implemented using ProActive grid-middleware and applied to the Flow-Shop scheduling Problem (FSP). The large scale experiments performed on Grid’5000 proved the efficiency of the proposed approaches.
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    Security in Mobile Ad hoc Networks: Detection and Isolation of Selfish Nodes
    (2007-04) Djenouri, Djamel; Badache, Nadjib
    Ad hoc networking is a research field that attracts more and more attention amongst researchers. It includes a variety of topics involving many challenges. In this thesis, we deal with security problems, and focus on one related to the energy constraint of the nodes forming the ad hoc network, namely node selfish misbehavior or node non-cooperation. This problem threatens the service availability, one of the security requirement. It consists of a misbehavior in which the node, anxious about its battery shortage, drops packets originated from other nodes it is assumed to route, while using them as routers to transmit its own packets toward remote nodes. We first provide a general review of some security problems, along with the current solutions, then we survey the selfish misbehavior in a separate chapter. Before attempting to mitigate the selfishness problem we first treat its cause, by tackling the power management, and proposing a power aware-routing protocol. However, although the power-aware routing protocols, such as the one we propose, help improving the battery life time, they are far from eliminating this challenging problem. Therefore, a solution that detects and isolates selfish nodes is mandatory for self-organized ad hoc networks. We then propose a new solution to monitor, detect, and isolate such nodes.
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    Stratégies d'ordonnancement conditionnelles utilisant des automates temporisés
    (Université Joseph Fourier -Grenoble 1, 2006-10-02) Kerbaa, Abdelkarim Aziz; Maler, Oded
    Cette thèse développe une méthodologie pour résoudre les problèmes d'ordonnancement de programmes conditionnels où savoir si une tâche doit être exécutée n'est pas connue à l'avance mais dynamiquement. Le modèle utilisé est à base d'automates temporisés représentant l'espace d'états à explorer. Le problème est donc formulé comme le calcul d'une stratégie gagnante (pire cas optimale) dans un jeu contre l'environnement. Dans un premier temps nous étudions le problème d'ordonnancement sur graphes de tâches déterministe puis nous étendons l'étude au problème d'ordonnancement avec incertitude conditionnelle. Pour les deux problèmes nous étudions différentes classes d'ordonnancements et de stratégies pour réduire l'espace d'états, des décompositions en chaînes pour réduire sa taille, puis nous investiguons plusieurs classes d'algorithmes exactes pour en évaluer l'efficacité et à partir desquels nous dérivons de bonnes heuristiques. Des résultats expérimentaux sur plusieurs exemples de benchmarks sont présentés afin de montrer l'efficacité de chaque algorithme et la précision des heuristiques proposées, puis des bornes théoriques sont déduites pour prouver la garantie de performance pire cas de chaque heuristique
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    Scalable and fault tolerant hierarchical B&B algorithms for computational grids
    (Université Abderrahmane Mira de Béjaia : Faculté des Sciences Exactes, 2012-06-07) Bendjoudi, Ahcène; Talbi, El-Ghazali
    La résolution exacte de problèmes d’optimisation combinatoire avec les algorithmes Branch and Bound (B&B) nécessite un nombre exorbitant de ressources de calcul. Actuellement, cette puissance est offerte par les environnements large échelle comme les grilles de calcul. Cependant, les grilles présentent de nouveaux challenges : le passage à l’échelle, l’hétérogénéité et la tolérance aux pannes. La majorité des algorithmes B&B revisités pour les grilles de calcul sont basés sur le paradigme Master-Worker, ce qui limite leur passage à l’échelle. De plus, la tolérance aux pannes est rarement adressée dans ces travaux. Dans cette thèse, nous proposons trois principales contributions : P2P-B&B, H-B&B et FTH-B&B. P2PB& B est un famework basé sur le paradigme Master-Worker traite le passage à l’échelle par la réduction de la fréquence de requêtes de tâches et en permettant les communications directes entre les workers. H-B&B traite aussi le passage à l’échelle. Contrairement aux approches proposées dans la littérature, H-B&B est complètement dynamique et adaptatif i.e. prenant en compte l’acquisition dynamique des ressources de calcul. FTH-B&B est basé sur de nouveaux mécanismes de tolérance aux pannes permettant de construire et maintenir la hiérarchie équilibrée, et de minimiser la redondance de travail quand les tâches sont sauvegardées et restaurées. Les approches proposées ont été implémentées avec la plateforme pour grille ProActive et ont été appliquées au problème d’ordonnancement de type Flow-Shop. Les expérimentations large échelle effectuées sur la grille Grid’5000 ont prouvé l’efficacité des approches proposées