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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Recursive Shortest Spanning Tree Algorithms For Image Segmentatiton

Yalcin Bayramoglu, Neslihan 01 July 2005 (has links) (PDF)
Image segmentation has an important role in image processing because it is a tool to obtain higher level object descriptions for further processing. In some applications such as large image databases or video image sequence segmentations, the speed of the segmentation algorithm may become a drawback of the application. This thesis work is a study to improve the run-time performance of a well-known segmentation algorithm, namely the Recursive Shortest Spanning Tree (RSST). Both the original and the fast RSST found in the literature are analyzed and a comparison is made between these techniques. Simple modifications and an alternative link cost structure are proposed and evaluated. Finally, a distributed implementation based on a simple image partitioning strategy is attempted. The thesis presents the results of an extensive computational study with respect to both run-time performance and image segmentation quality.
2

Décomposition de multi-flots et localisation de caches dans les réseaux / Multi flow decomposition methods and network cache location

Bauguion, Pierre-Olivier 22 September 2014 (has links)
Les nouveaux acteurs, les nouveaux services et les nouveaux contenus multimédias qui transitent sur le réseau internet génèrent un trafic et des débits de plus en plus élevés. Ceci peut occasionner une congestion, source de latence et de dépréciation de la qualité de service ressentie par les utilisateurs. Un fournisseur d'accès à internet dont l'objectif est de garantir un réseau d'excellence doit donc prendre des mesures pour améliorer sans cesse la fluidité de son réseau. Cela passe notamment par la mise en place d'un réseau de distribution de contenus (déploiement de dispositifs sur le réseau existant). Dans un premier temps cette thèse s'articule à présenter des approches de programmation dynamique de localisation de serveurs optimales dans des arborescences. Nous présentons également un approche pour résoudre le problème de déploiement de CDN et de k serveurs/caches à l'aide de l'algorithme exact et polynomial d'intersection de matroïdes. Nous explicitons ensuite ce qu'est un cache et quelles sont ses caractéristiques. Nous définissons ensuite les hypothèses effectuées et la modélisation associée pour le déploiement de caches transparents dans une arborescence, et le liens avec les algorithmes existants présentés précédemment. Nous présentons alors un modèle complet pour un programme linéaire en nombres entiers (PLNE) et un nouveau paradigme de programmation dynamique pour résoudre ce même problème. Nous montrons alors en quoi cette approche se généralise à des problèmes connexes de localisation dans les arborescences, ainsi que les performances pratiques d'une telle approche. D'un regard plus théorique, nous mesurons la capacité d'un réseau donné par le routage optimal de ses demandes, et, de ce fait, ses liens critiques. Nous manipulons alors le problème de flot concurrent maximal (FCM), un problème classique de la littérature de recherche opérationnelle. Nous exhibons alors de nouvelles formulations exactes pour résoudre ce problème, ainsi que les problèmes de multi-flots de manière plus générale. Une heuristique de construction de formulation pour le FCM est également proposée, pour tirer parti de la distribution spécifique des capacités d'une instance. Nous montrons alors la supériorité des performances de ces nouvelles formulations par le biais de comparaisons. Enfin, nous décrivons le premier algorithme exact et fortement polynomial pour résoudre le problème de flot concurrent maximal dans le cas d'une seule source; et nous montrons l'efficacité pratique d'une telle approche, comparée aux meilleures formulations explicitées précédemment / Streaming requirements on internet network are even more driven by new actors, new services and new digital contents. This leads to high probability of congestion, latency and therefore, a critical decrease of quality of service and/or experience for customers. An internet service provider (ISP) whose goal is to guarantee a first-class performance, needs to take measures to constantly enhance the fluidity of the traffic streaming on its network. One way to face the problem, is to build a Content Delivery Network (CDN). A CDN mainly consists in the deployment of different devices on an existing network. First of all, this thesis presents dynamic programming approaches to tackle server location problems in tree networks. Then, we address a variation of the matroïd intersection algorithm to solve the k-server/cache location problem. We start by giving the definition and characteristics of transparent-caching, as well as the hypothesis that we will use it to build models for transparent cache location in tree network. We tract it to a Mixed Integer Program, and formulate a new paradigm of dynamic programming. We show the relevance of such approach for our problem, and to what extent it can be tractable in other related problems. From a more theoretical point of view, we manage to measure the capacity of a network which is given by the optimal routing strategy, and hence, to identify its critical links. We deal with the Maximum Concurrent Flow (MCF), a classical combinatorial optimization problem. We propose new models and formulations to solve this problem exactly, and more general multi-flows problems as well. A heuristic is also given, to adapt the model to the specific instance values. We experiment these formulations to show the improvements they can provide. Finally, we describe the first strongly polynomial algorithm to solve the maximum concurrent flow to optimality, in the single source case. We show the efficiency of such an approach, even compared to the best models previously presented
3

Rainbow Colouring and Some Dimensional Problems in Graph Theory

Rajendraprasad, Deepak January 2013 (has links) (PDF)
This thesis touches three different topics in graph theory, namely, rainbow colouring, product dimension and boxicity. Rainbow colouring An edge colouring of a graph is called a rainbow colouring, if every pair of vertices is connected by atleast one path in which no two edges are coloured the same. The rainbow connection number of a graph is the minimum number of colours required to rainbow colour it. In this thesis we give upper bounds on rainbow connection number based on graph invariants like minimum degree, vertex connectivity, and radius. We also give some computational complexity results for special graph classes. Product dimension The product dimension or Prague dimension of a graph G is the smallest natural number k such that G is an induced subgraph of a direct product of k complete graphs. In this thesis, we give upper bounds on the product dimension for forests, bounded tree width graphs and graphs of bounded degeneracy. Boxicity and cubicity The boxicity (cubicity of a graph G is the smallest natural number k such that G can be represented as an intersection graph of axis-parallel rectangular boxes(axis-parallel unit cubes) in Rk .In this thesis, we study the boxicity and the cubicity of Cartesian, strong and direct products of graphs and give estimates on the boxicity and the cubicity of a product graph based on invariants of the component graphs. Separation dimension The separation dimension of a hypergraph H is the smallest natural number k for which the vertices of H can be embedded in Rk such that any two disjoint edges of H can be separated by a hyper plane normal to one of the axes. While studying the boxicity of line graphs, we noticed that a box representation of the line graph of a hypergraph has a nice geometric interpretation. Hence we introduced this new parameter and did an extensive study of the same.

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