Distributed computing is very popular in the field of computer science and is widely used in web applications. In such systems, tasks and resources are partitioned among several computers so that the workload can be shared among the different computers in the network, in contrast to systems using a single server computer. Distributed system designs are used for many practical reasons and are often found to be more scalable, robust and suitable for many applications. The aim of this thesis is to study the properties of a distributed tree data-structure that allow searches, insertions and deletions of data elements. In particular, the b- tree structure [13] is considered, which is a generalization of a binary search tree. The study consists of analyzing the effect of distributing such a tree among several computers and investigates the behavior of such structure over a long period of time by growing the network of computers supporting the tree, while the state of the structure is instantly updated as insertions and deletions operations are performed. It also attempts to validate the necessary and sufficient invariants of the b-tree-structure that guarantee the correctness of the search operations. A simulation study is also conducted to verify the validity of such distributed data-structure and the performance of the algorithm that implements it. Finally, a discussion is provided in the end of the thesis to compare the performance of the system design with other distributed tree structure designs.

Distributed computing is very popular in the field of computer science and is widely used in web applications. In such systems, tasks and resources are partitioned among several computers so that the workload can be shared among the different computers in the network, in contrast to systems using a single server computer. Distributed system designs are used for many practical reasons and are often found to be more scalable, robust and suitable for many applications. The aim of this thesis is to study the properties of a distributed tree data-structure that allow searches, insertions and deletions of data elements. In particular, the b- tree structure [13] is considered, which is a generalization of a binary search tree. The study consists of analyzing the effect of distributing such a tree among several computers and investigates the behavior of such structure over a long period of time by growing the network of computers supporting the tree, while the state of the structure is instantly updated as insertions and deletions operations are performed. It also attempts to validate the necessary and sufficient invariants of the b-tree-structure that guarantee the correctness of the search operations. A simulation study is also conducted to verify the validity of such distributed data-structure and the performance of the algorithm that implements it. Finally, a discussion is provided in the end of the thesis to compare the performance of the system design with other distributed tree structure designs.

In this thesis, we implement a rule-based machine ranslation (MT) system for Personal Digital Assistants (PDAs). Rule-based MT system has three modules in general: analysis, transfer and generation. Grammars used in our system are lexicalized tree automata-based grammar (LTA) and synchronous lexicalized tree adjoining grammar (SLTAG). LTA is used for analysis, and SLTAG is used for transfer and generation. We adjust developed parser to PDAs as a parser in the analysis module. The SLTAG parser in the transfer module would search possible source side of SLTAG in source parse tree. Then, growing target parse tree and scoring each hypothesis is based on language model and rule probability. To avoid too much estimation, generation step would prune some hypotheses under threshold. Compared with other rule-based MT systems, we can build rules automatically and design a flexible rule type. SLTAG parser is coded specially for the rule type. In experiments, Chinese-English BTEC is our training and test data. We can get 17% BLEU score for the test data.

Je présente dans ce mémoire mes travaux sur les limites d'échelle de grandes structures aléatoires. Il s'agit de décrire les structures combinatoires dans la limite des grandes tailles en prenant un point de vue objectif dans le sens où on cherche des limites des objets, et non pas seulement de paramètres caractéristiques (même si ce n'est pas toujours le cas dans les résultats que je présente). Le cadre général est celui des structures critiques pour lesquelles on a typiquement des distances caractéristiques polynomiales en la taille, et non concentrées. Sauf exception, ces structures ne sont en général pas adaptées aux applications informatiques. Elles sont cependant essentielles de part l'universalité de leurs propriétés asymptotiques, prouvées ou attendues. Je parle en particulier d'arbres uniformément choisis, de graphes aléatoires, d'arbres couvrant minimaux et de partitions récursives de domaines du plan:<br/> <strong>Arbres aléatoires uniformes.</strong> Il s'agit ici de mieux comprendre un objet limite essentiel, l'arbre continu brownien (CRT). Je présente quelques résultats de convergence pour des modèles combinatoires ''non-branchants'' tels que des arbres sujets aux symétries et les arbres à distribution de degrés fixée. Je décris enfin une nouvelle décomposition du CRT basée sur une destruction partielle.<br/> <strong>Graphes aléatoires.</strong> J'y décris la construction algorithmique de la limite d'échel-le des graphes aléatoires du modèle d'Erdös--Rényi dans la zone critique, et je fais le lien avec le CRT et donne des constructions de l'espace métrique limite. <strong>Arbres couvrant minimaux.</strong> J'y montre qu'une connection avec les graphes aléatoires permet de quantifier les distances dans un arbre convrant aléatoire. On obtient non seulement l'ordre de grandeur de l'espérance du diamètre, mais aussi la limite d'échelle en tant qu'espace métrique mesuré. Partitions récursives. Sur deux exemples, les arbres cadrant et les laminations du disque, je montre que des idées basées sur des théorèmes de point fixe conduisent à des convergences de processus, où les limites sont inhabituelles, et caractérisées par des décompositions récursives.

Distributed computing is very popular in the field of computer science and is widely used in web applications. In such systems, tasks and resources are partitioned among several computers so that the workload can be shared among the different computers in the network, in contrast to systems using a single server computer. Distributed system designs are used for many practical reasons and are often found to be more scalable, robust and suitable for many applications. The aim of this thesis is to study the properties of a distributed tree data-structure that allow searches, insertions and deletions of data elements. In particular, the b- tree structure [13] is considered, which is a generalization of a binary search tree. The study consists of analyzing the effect of distributing such a tree among several computers and investigates the behavior of such structure over a long period of time by growing the network of computers supporting the tree, while the state of the structure is instantly updated as insertions and deletions operations are performed. It also attempts to validate the necessary and sufficient invariants of the b-tree-structure that guarantee the correctness of the search operations. A simulation study is also conducted to verify the validity of such distributed data-structure and the performance of the algorithm that implements it. Finally, a discussion is provided in the end of the thesis to compare the performance of the system design with other distributed tree structure designs.

Please read the abstract in the dissertation / Dissertation (MSc (Agric))--University of Pretoria, 2001. / Plant Production and Soil Science / unrestricted

Distributed computing is very popular in the field of computer science and is widely used in web applications. In such systems, tasks and resources are partitioned among several computers so that the workload can be shared among the different computers in the network, in contrast to systems using a single server computer. Distributed system designs are used for many practical reasons and are often found to be more scalable, robust and suitable for many applications. The aim of this thesis is to study the properties of a distributed tree data-structure that allow searches, insertions and deletions of data elements. In particular, the b- tree structure [13] is considered, which is a generalization of a binary search tree. The study consists of analyzing the effect of distributing such a tree among several computers and investigates the behavior of such structure over a long period of time by growing the network of computers supporting the tree, while the state of the structure is instantly updated as insertions and deletions operations are performed. It also attempts to validate the necessary and sufficient invariants of the b-tree-structure that guarantee the correctness of the search operations. A simulation study is also conducted to verify the validity of such distributed data-structure and the performance of the algorithm that implements it. Finally, a discussion is provided in the end of the thesis to compare the performance of the system design with other distributed tree structure designs.

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Networks of tree-ring data are commonly applied in statistical reconstruction of spatial fields of climate variables. The importance of elevation to the climatic interpretation of tree-ring networks is addressed using 281 station precipitation records, and a network of 79 tree-ring chronologies from different species and a range of elevations in the eastern Mediterranean. Cluster analysis of chronologies identifies 6 tree-ring groups, delineated principally by site elevation. Correlation analysis suggests several of the clusters are linked to homogenous elevational moisture regimes. Results imply that climate stations close to the elevations of the tree-ring sites are essential for assessing the seasonal climatic signal in tree-ring chronologies from this region. A broader implication is that the elevations of stations contributing to gridded climate networks should be considered in the design and interpretation of field reconstructions of climate from tree rings. Finally, results suggest elevation-stratified tree-ring networks as a strategy for seasonal climate reconstruction.

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