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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.
111

Formulation of an integrated approach to sustainable water management in Ho Chi Minh City, Vietnam.

Vo, Phu Le January 2008 (has links)
In 1986, Vietnam opened up the country’s economy by launching the Doi Moi (renovation) policy, which made the process of economic liberalisation possible. Accordingly, Ho Chi Minh City, the country’s biggest city, has undergone rapid growth of population, urbanisation and industrialisation. While achieving remarkable economic growth, the city faces considerable urban environmental challenges. The rapid growth of urbanisation and industry has placed increasing pressure on available freshwater resources, through excessive water use and increasing volumes of untreated wastewater. Firstly, the urban water sector has had to meet growing demand for water use for domestic purposes during the dry season. Secondly, groundwater levels have experienced a substantial drawdown in outlying urban districts as a result of over-abstraction. Thirdly, rapidly expanding industrial activities are causing severe demand on water resources. The city’s major supply sources have developed an alarming level of pollutants discharged by industry. The aim of this thesis is to formulate an integrated approach to the sustainable management of water resources in Ho Chi Minh City. In order to achieve this, the research was designed to examine institutional frameworks and arrangements and to explore the perception of water value by water users and stakeholders. The underlying reasons for ineffective management are anchored in fragmented management practices which result from inadequate institutional frameworks and arrangements, inadequate regulations and inappropriate water governance. Weak enforcement of law and insufficient cooperation between government agencies and departments in Ho Chi Minh City and their counterparts in neighbouring provinces also limit management efficacy. The research results show that stakeholders have different perceptions of water resources. Overall, water value has been considered as a social and economic good by both the urban respondents and government officials. However, most urban residents view water as a social good rather than an economic one. Public involvement in the water sector is limited. Most urban dwellers have little understanding and knowledge about the city’s water issues or the available channels to access information on water resources. Many government officials are inadequately trained, poorly qualified, inexperienced and have irrelevant or outdated background knowledge about their field of management. Government respondents did not provide consistent data and information on the water profile because there is no shared common information on water issues in place. Findings from the fieldwork show that decentralisation, privatisation and using rainwater as a potential alternative water source are preferred. Finally, the study proposes a schematic revision of existing management structures and mechanisms between local government agencies. This thesis proposes a model for a water conservation strategy for which the management and use of water resources is aligned with adequate institutional arrangements and effective regulations. Water governance and management of water resources need to work with economic and urbanisation growth. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1331639 / Thesis (Ph.D.) - University of Adelaide, School of Social Sciences, 2008
112

Formulation of an integrated approach to sustainable water management in Ho Chi Minh City, Vietnam.

Vo, Phu Le January 2008 (has links)
In 1986, Vietnam opened up the country’s economy by launching the Doi Moi (renovation) policy, which made the process of economic liberalisation possible. Accordingly, Ho Chi Minh City, the country’s biggest city, has undergone rapid growth of population, urbanisation and industrialisation. While achieving remarkable economic growth, the city faces considerable urban environmental challenges. The rapid growth of urbanisation and industry has placed increasing pressure on available freshwater resources, through excessive water use and increasing volumes of untreated wastewater. Firstly, the urban water sector has had to meet growing demand for water use for domestic purposes during the dry season. Secondly, groundwater levels have experienced a substantial drawdown in outlying urban districts as a result of over-abstraction. Thirdly, rapidly expanding industrial activities are causing severe demand on water resources. The city’s major supply sources have developed an alarming level of pollutants discharged by industry. The aim of this thesis is to formulate an integrated approach to the sustainable management of water resources in Ho Chi Minh City. In order to achieve this, the research was designed to examine institutional frameworks and arrangements and to explore the perception of water value by water users and stakeholders. The underlying reasons for ineffective management are anchored in fragmented management practices which result from inadequate institutional frameworks and arrangements, inadequate regulations and inappropriate water governance. Weak enforcement of law and insufficient cooperation between government agencies and departments in Ho Chi Minh City and their counterparts in neighbouring provinces also limit management efficacy. The research results show that stakeholders have different perceptions of water resources. Overall, water value has been considered as a social and economic good by both the urban respondents and government officials. However, most urban residents view water as a social good rather than an economic one. Public involvement in the water sector is limited. Most urban dwellers have little understanding and knowledge about the city’s water issues or the available channels to access information on water resources. Many government officials are inadequately trained, poorly qualified, inexperienced and have irrelevant or outdated background knowledge about their field of management. Government respondents did not provide consistent data and information on the water profile because there is no shared common information on water issues in place. Findings from the fieldwork show that decentralisation, privatisation and using rainwater as a potential alternative water source are preferred. Finally, the study proposes a schematic revision of existing management structures and mechanisms between local government agencies. This thesis proposes a model for a water conservation strategy for which the management and use of water resources is aligned with adequate institutional arrangements and effective regulations. Water governance and management of water resources need to work with economic and urbanisation growth. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1331639 / Thesis (Ph.D.) - University of Adelaide, School of Social Sciences, 2008
113

Formulation of an integrated approach to sustainable water management in Ho Chi Minh City, Vietnam.

Vo, Phu Le January 2008 (has links)
In 1986, Vietnam opened up the country’s economy by launching the Doi Moi (renovation) policy, which made the process of economic liberalisation possible. Accordingly, Ho Chi Minh City, the country’s biggest city, has undergone rapid growth of population, urbanisation and industrialisation. While achieving remarkable economic growth, the city faces considerable urban environmental challenges. The rapid growth of urbanisation and industry has placed increasing pressure on available freshwater resources, through excessive water use and increasing volumes of untreated wastewater. Firstly, the urban water sector has had to meet growing demand for water use for domestic purposes during the dry season. Secondly, groundwater levels have experienced a substantial drawdown in outlying urban districts as a result of over-abstraction. Thirdly, rapidly expanding industrial activities are causing severe demand on water resources. The city’s major supply sources have developed an alarming level of pollutants discharged by industry. The aim of this thesis is to formulate an integrated approach to the sustainable management of water resources in Ho Chi Minh City. In order to achieve this, the research was designed to examine institutional frameworks and arrangements and to explore the perception of water value by water users and stakeholders. The underlying reasons for ineffective management are anchored in fragmented management practices which result from inadequate institutional frameworks and arrangements, inadequate regulations and inappropriate water governance. Weak enforcement of law and insufficient cooperation between government agencies and departments in Ho Chi Minh City and their counterparts in neighbouring provinces also limit management efficacy. The research results show that stakeholders have different perceptions of water resources. Overall, water value has been considered as a social and economic good by both the urban respondents and government officials. However, most urban residents view water as a social good rather than an economic one. Public involvement in the water sector is limited. Most urban dwellers have little understanding and knowledge about the city’s water issues or the available channels to access information on water resources. Many government officials are inadequately trained, poorly qualified, inexperienced and have irrelevant or outdated background knowledge about their field of management. Government respondents did not provide consistent data and information on the water profile because there is no shared common information on water issues in place. Findings from the fieldwork show that decentralisation, privatisation and using rainwater as a potential alternative water source are preferred. Finally, the study proposes a schematic revision of existing management structures and mechanisms between local government agencies. This thesis proposes a model for a water conservation strategy for which the management and use of water resources is aligned with adequate institutional arrangements and effective regulations. Water governance and management of water resources need to work with economic and urbanisation growth. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1331639 / Thesis (Ph.D.) - University of Adelaide, School of Social Sciences, 2008
114

Formulation of an integrated approach to sustainable water management in Ho Chi Minh City, Vietnam.

Vo, Phu Le January 2008 (has links)
In 1986, Vietnam opened up the country’s economy by launching the Doi Moi (renovation) policy, which made the process of economic liberalisation possible. Accordingly, Ho Chi Minh City, the country’s biggest city, has undergone rapid growth of population, urbanisation and industrialisation. While achieving remarkable economic growth, the city faces considerable urban environmental challenges. The rapid growth of urbanisation and industry has placed increasing pressure on available freshwater resources, through excessive water use and increasing volumes of untreated wastewater. Firstly, the urban water sector has had to meet growing demand for water use for domestic purposes during the dry season. Secondly, groundwater levels have experienced a substantial drawdown in outlying urban districts as a result of over-abstraction. Thirdly, rapidly expanding industrial activities are causing severe demand on water resources. The city’s major supply sources have developed an alarming level of pollutants discharged by industry. The aim of this thesis is to formulate an integrated approach to the sustainable management of water resources in Ho Chi Minh City. In order to achieve this, the research was designed to examine institutional frameworks and arrangements and to explore the perception of water value by water users and stakeholders. The underlying reasons for ineffective management are anchored in fragmented management practices which result from inadequate institutional frameworks and arrangements, inadequate regulations and inappropriate water governance. Weak enforcement of law and insufficient cooperation between government agencies and departments in Ho Chi Minh City and their counterparts in neighbouring provinces also limit management efficacy. The research results show that stakeholders have different perceptions of water resources. Overall, water value has been considered as a social and economic good by both the urban respondents and government officials. However, most urban residents view water as a social good rather than an economic one. Public involvement in the water sector is limited. Most urban dwellers have little understanding and knowledge about the city’s water issues or the available channels to access information on water resources. Many government officials are inadequately trained, poorly qualified, inexperienced and have irrelevant or outdated background knowledge about their field of management. Government respondents did not provide consistent data and information on the water profile because there is no shared common information on water issues in place. Findings from the fieldwork show that decentralisation, privatisation and using rainwater as a potential alternative water source are preferred. Finally, the study proposes a schematic revision of existing management structures and mechanisms between local government agencies. This thesis proposes a model for a water conservation strategy for which the management and use of water resources is aligned with adequate institutional arrangements and effective regulations. Water governance and management of water resources need to work with economic and urbanisation growth. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1331639 / Thesis (Ph.D.) - University of Adelaide, School of Social Sciences, 2008
115

Faisabilité et potentiel de l'encapsulation de molécules d'intérêt dans des formulations filmogènes / Potential of drug encapsulation in film-forming solutions

Inkichari, Mohamed Nejmeddine 25 October 2016 (has links)
Ce travail de thèse a pour objectif une meilleure connaissance des formulations filmogènes développées par les Laboratoires URGO. Deux aspects ont été développés.Il a tout d’abord été recherché un système d’encapsulation afin de protéger des molécules d’intérêt dans des solutions filmogènes. Des polymersomes en phase aqueuses et en phase organique ont été développés à base de copolymères amphiphiles m-PEG-PCL synthétisés et caractérisés au laboratoire. Ces auto-assemblages des copolymères possèdent des tailles variables (40 nm à 800 nm) avec une membrane en bicouche. Leur caractérisation a été réalisée en phase aqueuse et organique par différentes techniques : DLS, NTA, microscopie biphotonique et AFM. Puis des techniques de caractérisation ont été mises au point pour évaluer une formulation filmogène à base de nitrocellulose contenant de l’urée libre ou encapsulée dans des polymersomes. Cette formulation a été suivie au cours d’essais de stabilité à 25°C et à 40°C pendant 6 mois. Il a été observé une chute de viscosité, surtout à 40°C, attribuée à une coupure des chaînes macromoléculaires de la nitrocellulose (par CES). Les films formés ont un module de Young stable dans le temps avec apparition d’un jaunissement (paramètre b en colorimétrie). La quantité d’urée reste stable dans le temps mais elle accélère les phénomènes de vieillissement. Le jaunissement est dû à la décomposition de l’huile de ricin. L’encapsulation de l’urée au sein des polymersomes n’a pas amélioré la stabilité de la formulation prouvant ainsi le rôle catalyseur de l’urée. / This work aims at a better understanding of film-forming formulations developed by Laboratoires Urgo. Two parts have been developed. First, an encapsulation system to protect a model drug in film forming solutions was investigated. Polymersomes in aqueous and organic media have been developed based on amphiphilic copolymers m-PEG-PCL which were synthesized and characterized in the laboratory. Auto-assemblies of copolymers display variable sizes (40 nm to 800 nm) with a bilayer membrane. Their characterization was carried out in aqueous and organic phase by various techniques: DLS, NTA, bi-photonic microscopy and AFM. In a second part, characterization techniques have been developed to assess a film forming solution based on nitrocellulose, containing free or encapsulated urea in polymersomes. This formulation was investigated during stability studies at 25°C and 40°C up to 6 months. A drop in viscosity was observed, especially at 40°C, due to cleavage of the macromolecular chains of nitrocellulose (SEC). The formed films have a stable Young's modulus over time with an appearance of yellowing (parameter b in colorimetry). The urea quantity remains stable in time, but accelerates the aging of the solution. Yellowing is caused by the decomposition of castor oil. The encapsulation of the urea within polymersomes did not improve the stability of the formulation thus proving the catalytic role of urea.
116

Local FEM Analysis of Composite Beams and Plates : free-Edge effect and Incompatible Kinematics Coupling / Analyse élément finit local des poutres et plaques composite : effet des bords libres et couplages des cinématiques incompatible

Wenzel, Christian 07 October 2014 (has links)
Cette thèse traite des problèmes des concentrations de contraintes locales, en particularité des effets des bords libres dans des structures stratifiés. À l'interface entre deux couches avec des propriétés élastiques différentes, les contraintes ont un comportement singulier dans le voisinage du bord libre en supposant un comportement de matériau élastique linéaire. Par conséquent, ils sont essentiels pour promouvoir le délaminage. Via Formulation unifiée de la Carrera (CUF) différents modèles cinématiques sont testés dans le but de capter les concentrations de contraintes. Dans la première partie de ce travail, les approches de modélisation dimensionnelle réduits sont comparées. Deux classe principale sont présentés: la couche équivalent (ESL) et l'approche par couche, LW. Par la suite leurs capacités à capter les singularités sont comparées. En utilisant une fonction a priori singulière, via une expression exponentielle, une mesure des contraintes singulières est introduite. Seulement deux paramètres décrivent pleinement les composantes des contraintes singulières au voisinage du bord libre. Sur la base des paramètres obtenus les modèles sont comparés et aussi les effets sous des charges d'extension et de flexion et pour différents stratifiés. Les résultats montrent une nécessité des modèles complexes dans le voisinage du bord libre. Cependant loin des bords libres, dans le centre de plaques composite, aucune différence significative ne peut être noté pour les modèles plutôt simples. La deuxième partie de ce travail est donc dédiée au couplage de modèles cinématique incompatibles. Modèles complexes et coûteux sont utilisés seulement dans des domaines locaux d'intérêt, tandis que les modèles économiques simples seront modéliser le domaine global. La eXtended Variational Formulation (XVF) est utilisé pour coupler les modèles de dimensionnalité homogènes mais de cinématique hétérogènes. Ici pas de recouvrement de domaine est présent. En outre, le XVF offre la possibilité d'adapter les conditions imposées à l'interface en utilisant un paramètre scalaire unique. On montre que, pour le problème de dimensionnalité homogène, que deux conditions différentes peuvent être imposées par ce paramètre. Un correspondant à des conditions fortes des Multi Point Constraints (MPC) et un second fournir des conditions faibles. La dernière offre la possibilité de réduire extrêmement le domaine qui utilise le modèle cinématique complexe, sans perte de précision locale. Comme il s'agit de la première application de la XVF vers les structures composites, le besoin d'un nouvel opérateur de couplage a été identifié. Un nouveau formulaire est proposé, testé et sa robustesse sera évaluée. / This work considers local stress concentrations, especially the free-Edge effects of multilayered structures. At the interface of two adjacent layers with different elastic properties, the stresses can become singular in the intermediate vicinity of the free edge. This is valid while assuming a linear elastic material behaviour. As a consequence this zones are an essential delamination trigger. Via the Carrera Unified Formulation (CUF), different kinematical models are testes in order to obtain the correct local stress concentration. In the first part of this work, the reduced dimensional modelling approaches are compared. Two main class are presented: Equivalent Single Layer (ESL) models treating the layered structure like one homogenous plate of equal mechanical proper- ties, and the Layer Wise approach, treating each layer independently. Subsequently their capabilities to capture the appearing singularities are compared. In order to have a comparable measurement of those singularities, the obtained stress distributions will be expressed via a power law function, which has a priori a singular behaviour. Only two parameters fully describe therefore the singular stress components in the vicinity of the free edge. With the help of these two parameters not only the different models capabilities will be compared, but also the free edge effect itself will be measured and compared for different symmetrical laminates and the case of extensional and uniform bending load. The results for all laminates under both load cases confirm the before stated need for rather complex models in the vicinity of the free edge. However far from the free edges, in the composite plates centre, no significant difference can be noted for rather simple models. The second part of this work is therefore dedicated to the coupling of kinematically incompatible models. The use of costly expensive complex models is restricted to local domains of interest, while economic simple models will model the global do- main. The Extended Variational Formulation (XVF) is identified as the most suitable way to couple the kinematically heterogenous but dimensional homogenous models. As it uses a configuration with one common interface without domain overlap, the additional efforts for establishing the coupling are limited. Further the XVF offers the possibility to adapt the conditions imposed at the interface using a single scalar parameter. It will be shown that for the homogenous dimensional problem under consideration only two different conditions can be imposed by this parameter. One matching the strong conditions imposed by the classical Multi Point Constrains (MPC) and a second one providing a weak condition. The last one is shown to provide the possibility to reduce further the domain using the complex kinematical model, without the loss of local precision. As this is the first application of the XVF towards composite structures, the need for a new coupling operator was identified. A new form is proposed, tested and its robustness will be evaluated.
117

Optimisation du comportement mécanique de composites structuraux PEKK/Fibres de carbone par ensimage oligomères de PEKK / Optimization of mechanical behavior of PEKK/carbon fibers structural composites by PEKK oligomers sizing

Alexandre, Mike Abidine 14 November 2017 (has links)
L'objectif de cette recherche est la conception et l'analyse d'un ensimage pour composites structuraux PEKK/Fibres de carbone (FC) continues. Les oligomères de PEKK (oPEKK) ont été synthétisés en laboratoire pour définir les caractéristiques physico-chimiques permettant leur utilisation comme agent d'ensimage. A partir de ce cahier des charges, un oligomère " pilote " a pu être synthétisé afin de mener des études sur la formulation de l'ensimage. A partir d'une étude quantitative de relation structure-propriété (QSPR) et des réseaux de neurone artificiels (ANN), le développement et l'optimisation d'une formulation d'ensimage " solvantfree " ont été réalisés Le dépôt de cet ensimage a été effectué selon deux protocoles : nous avons ainsi réalisé un " ensimage laboratoire " et " ensimage sur pilote ". Les performances mécaniques des composites PEKK/FC ensimés oPEKK ont été étudiées par analyse mécanique dynamique (AMD) ; quel que soit le protocole, l'ensimage optimise les performances mécaniques de manière significative. Il est intéressant de souligner que l'" ensimage sur pilote " est plus efficace que l'" ensimage laboratoire ". Outre, l'intérêt de l'ensimage au niveau de la mise en œuvre des composites, le transfert de contraintes fibre/ matrice est optimisé ce qui se traduit par une augmentation des modules mécaniques conservatif et dissipatif. / The objective of this research is to design and analyze a sizing for PEKK / continuous carbon fiber (CF) structural composites. PEKK oligomers (oPEKK) were synthesized in the laboratory to define the physicochemical characteristics allowing their use as a sizing agent. From these specifications, a "pilot" oligomer was synthesized in order to carry out studies on the sizing formulation. From a study of quantitative structure-property relationship (QSPR) and artificial neural networks (ANN), the development and optimization of a "solvent-free" sizing formulation was performed. The deposit of this sizing was achieved according to two protocols: we thus produced a "laboratory sizing" and "pilot sizing". Mechanical performances of PEKK / CF without and with oPEKK sizing composites were studied by dynamic mechanical analysis (DMA). Whatever the protocol is, the sizing optimizes the mechanical performances significantly. It is interesting to note that "pilot sizing" is more efficient than "laboratory sizing". Besides the advantage of sizing for fiber placement in composite processing, the fiber / matrix stress transfer is optimized. Then, it results in an increase of both storage and loss modulus.
118

Farmaceutické aplikace polyesterů jako nanonosičů léčiv / Pharmaceutical applications of polyesters as drug nanocarriers

Staňková, Petra January 2018 (has links)
Charles University Faculty of Pharmacy in Hradci Králové Department of Pharmaceutical Technology Consultant: PharmDr. Ondřej Holas, PhD. Student: Petra Staňková Title of Thesis: Pharmaceutical applications of polyesters as drug nanocarriers Nanoparticles are nowadays intensively studied and perspective type of a drug carrier. Its potential is based on a possibility of targeted drug delivery and controlled drug release. The theoretical part is about nanoparticles types, polymers derived from α-hydroxyacids (PLA, PGA, PLGA). Focus is given on methods of nanoparticles preparation: dispersion of preformed polymers or the polymerization of monomers. The modification of particles surface and practical use of nanomedicine in healthcare are described in other chapters. The research in experimental part is focused on the influence of different types of PLGA and their weighing on the size, polydispersity, nanoparticles zeta potential and encapsulation efficiency of rhodamine B. Nanoparticles were prepared by nanoprecipitation method or by solvent evaporation method. The Zetasiser ZS 90 device was used to measure the size of the nanoparticles and to measure zeta potential. The result of the research shows the most suitable weighing for creation of nanoparticles is 25 mg. The samples of this weighing show a...
119

Problem Map: a Framework for Investigating the Role of Problem Formulation in Creative Design

January 2015 (has links)
abstract: Design problem formulation is believed to influence creativity, yet it has received only modest attention in the research community. Past studies of problem formulation are scarce and often have small sample sizes. The main objective of this research is to understand how problem formulation affects creative outcome. Three research areas are investigated: development of a model which facilitates capturing the differences among designers' problem formulation; representation and implication of those differences; the relation between problem formulation and creativity. This dissertation proposes the Problem Map (P-maps) ontological framework. P-maps represent designers' problem formulation in terms of six groups of entities (requirement, use scenario, function, artifact, behavior, and issue). Entities have hierarchies within each group and links among groups. Variables extracted from P-maps characterize problem formulation. Three experiments were conducted. The first experiment was to study the similarities and differences between novice and expert designers. Results show that experts use more abstraction than novices do and novices are more likely to add entities in a specific order. Experts also discover more issues. The second experiment was to see how problem formulation relates to creativity. Ideation metrics were used to characterize creative outcome. Results include but are not limited to a positive correlation between adding more issues in an unorganized way with quantity and variety, more use scenarios and functions with novelty, more behaviors and conflicts identified with quality, and depth-first exploration with all ideation metrics. Fewer hierarchies in use scenarios lower novelty and fewer links to requirements and issues lower quality of ideas. The third experiment was to see if problem formulation can predict creative outcome. Models based on one problem were used to predict the creativity of another. Predicted scores were compared to assessments of independent judges. Quality and novelty are predicted more accurately than variety, and quantity. Backward elimination improves model fit, though reduces prediction accuracy. P-maps provide a theoretical framework for formalizing, tracing, and quantifying conceptual design strategies. Other potential applications are developing a test of problem formulation skill, tracking students' learning of formulation skills in a course, and reproducing other researchers’ observations about designer thinking. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2015
120

Term selection in information retrieval

Maxwell, Kylie Tamsin January 2016 (has links)
Systems trained on linguistically annotated data achieve strong performance for many language processing tasks. This encourages the idea that annotations can improve any language processing task if applied in the right way. However, despite widespread acceptance and availability of highly accurate parsing software, it is not clear that ad hoc information retrieval (IR) techniques using annotated documents and requests consistently improve search performance compared to techniques that use no linguistic knowledge. In many cases, retrieval gains made using language processing components, such as part-of-speech tagging and head-dependent relations, are offset by significant negative effects. This results in a minimal positive, or even negative, overall impact for linguistically motivated approaches compared to approaches that do not use any syntactic or domain knowledge. In some cases, it may be that syntax does not reveal anything of practical importance about document relevance. Yet without a convincing explanation for why linguistic annotations fail in IR, the intuitive appeal of search systems that ‘understand’ text can result in the repeated application, and mis-application, of language processing to enhance search performance. This dissertation investigates whether linguistics can improve the selection of query terms by better modelling the alignment process between natural language requests and search queries. It is the most comprehensive work on the utility of linguistic methods in IR to date. Term selection in this work focuses on identification of informative query terms of 1-3 words that both represent the semantics of a request and discriminate between relevant and non-relevant documents. Approaches to word association are discussed with respect to linguistic principles, and evaluated with respect to semantic characterization and discriminative ability. Analysis is organised around three theories of language that emphasize different structures for the identification of terms: phrase structure theory, dependency theory and lexicalism. The structures identified by these theories play distinctive roles in the organisation of language. Evidence is presented regarding the value of different methods of word association based on these structures, and the effect of method and term combinations. Two highly effective, novel methods for the selection of terms from verbose queries are also proposed and evaluated. The first method focuses on the semantic phenomenon of ellipsis with a discriminative filter that leverages diverse text features. The second method exploits a term ranking algorithm, PhRank, that uses no linguistic information and relies on a network model of query context. The latter focuses queries so that 1-5 terms in an unweighted model achieve better retrieval effectiveness than weighted IR models that use up to 30 terms. In addition, unlike models that use a weighted distribution of terms or subqueries, the concise terms identified by PhRank are interpretable by users. Evaluation with newswire and web collections demonstrates that PhRank-based query reformulation significantly improves performance of verbose queries up to 14% compared to highly competitive IR models, and is at least as good for short, keyword queries with the same models. Results illustrate that linguistic processing may help with the selection of word associations but does not necessarily translate into improved IR performance. Statistical methods are necessary to overcome the limits of syntactic parsing and word adjacency measures for ad hoc IR. As a result, probabilistic frameworks that discover, and make use of, many forms of linguistic evidence may deliver small improvements in IR effectiveness, but methods that use simple features can be substantially more efficient and equally, or more, effective. Various explanations for this finding are suggested, including the probabilistic nature of grammatical categories, a lack of homomorphism between syntax and semantics, the impact of lexical relations, variability in collection data, and systemic effects in language systems.

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