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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.
371

Engineering the performance of mixed matrix membranes for gas separations

Shu, Shu 20 September 2007 (has links)
Mixed matrix membranes that comprise domains of organic and inorganic components are investigated in this research. Such materials effectively circumvent the polymeric 'upper bound trade-off curve' and show properties highly attractive for industrial gas separations. Nevertheless, lack of intrinsic compatibility between the organic polymers and inorganic fillers poses the biggest challenge to successful fabrication of mixed matrix membranes. Consequently, control of the nanoscale interface between the sieve and polymer has been the key technical challenge to the implementation of composite membrane materials. The overarching goal of this research was to devise and explore approaches to enhance the performance of mixed matrix membranes by properly tailoring the sieve/polymer interface. In an effort to pursue the aforementioned objective, three approaches were developed and inspected: (i) use of silane coupling agents, (ii) hydrophobizing of sieve surface through alcohol etherification reactions, and (iii) a two-step modification sequence involving the use of a Grignard reagent. A comparison was drawn to evaluate these methodologies and the most effective strategy (Grignard treatment) was selected and further investigated. Successful formulation and characterization of mixed matrix membranes constituting zeolite 4A modified via the Grignard treatment are described in detail. Membranes with impressive improvements in gas separation efficiency and mechanical properties were demonstrated. The basis for the improvements in polymer/sieve compatibility enabled by this specific process were proposed and investigated. A key aspect of the present study was illuminating the detailed chemical mechanisms involved in the Grignard modification. Systematic characterization and carefully designed experiments revealed that the formation of distinctive surface structures is essentially a heterogeneous nucleation process, where Mg(OH)2 crystals grow from the nuclei previously extracted from zeolites. In addition to the main work, discovery of sonication-induced dealumination of zeolites was made during the systematic exploration of Grignard chemistry. The new procedure employing sonication can potentially be applied to prepare zeolites with a variety of Si/Al ratios under relatively mild conditions. The last part of this thesis focused on development of a technique to generalize the highly specific Grignard treatment to inorganic materials other than zeolite 4A. This work delivered composite membranes with improved interfacial adhesion. Moreover, research revealed the effect of surface nuclei density on the ultimate morphology of deposited nanostructures and how different surface morphologies influence polymer/filler interaction in composite membranes. Methods were devised to tailor the morphologies of such structures in order to optimize adhesion enhancement. The acquired results demonstrated the potential of extending this modification process to a broad domain of materials and render it a general methodology for interfacial adhesion promotion.
372

Sorption-enhanced steam methane reforming in fluidized bed reactors

Johnsen, Kim January 2006 (has links)
Hydrogen is considered to be an important potential energy carrier; however, its advantages are unlikely to be realized unless efficient means can be found to produce it without generation of CO2. Sorption-enhanced steam methane reforming (SE-SMR) represent a novel, energy-efficient hydrogen production route with in situ CO2 capture, shifting the reforming and water gas shift reactions beyond their conventional thermodynamic limits. The use of fluidized bed reactors for SE-SMR has been investigated. Arctic dolomite, a calcium-based natural sorbent, was chosen as the primary CO2-acceptor in this study due to high absorption capacity, relatively high reaction rate and low cost. An experimental investigation was conducted in a bubbling fluidized bed reactor of diameter 0.1 m, which was operated cyclically and batchwise, alternating between reforming/carbonation conditions and higher-temperature calcination conditions. Hydrogen concentrations of >98 mole% on a dry basis were reached at 600°C and 1 atm, for superficial gas velocities in the range of ~0.03-0.1 m/s. Multiple reforming-regeneration cycles showed that the hydrogen concentration remained at ~98 mole% after four cycles. The total production time was reduced with an increasing number of cycles due to loss of CO2 -uptake capacity of the dolomite, but the reaction rates of steam reforming and carbonation seemed to be unaffected for the conditions investigated. A modified shrinking core model was applied for deriving carbonation kinetics of Arctic dolomite, using experimental data from a novel thermo gravimetric reactor. An apparent activation energy of 32.6 kJ/mole was found from parameter fitting, which is in good agreement with previous reported results. The derived rate expression was able to predict experimental conversion up to ~30% very well, whereas the prediction of higher conversion levels was poorer. However, the residence time of sorbent in a continuous reformer-calciner system is likely to be rather low, so that only a fraction of the sorbent is utilized, highlighting the importance of the carbonation model at lower conversions. A dual fluidized bed reactor for the SE-SMR system was modeled by using a simple two-phase hydrodynamic model, the experimentally derived carbonation kinetics and literature values for the kinetics of steam reforming and water gas shift reactions. The model delineates important features of the process. Hydrogen concentrations of >98 mole% were predicted for temperatures ~600°C and a superficial gas velocity of 0.1 m/s. The reformer temperature should not be lower than 540°C or greater than 630°C for carbon capture efficiencies to exceed 90%. Operating at relatively high solid circulation rates to reduce the need for fresh sorbent, is predicted to give higher system efficiencies than for the case where fresh solid is added. This finding is attributed to the additional energy required to decompose both CaCO3 and MgCO3 in fresh dolomite. Moreover, adding fresh sorbent is likely to result in catalyst loss in the purge stream, requiring sorbents with lifetimes comparable to those of the catalyst. Thermo gravimetric analysis (TGA) was used to study the reversible CO2-uptake of sorbents. In general, the multi-cycle capacity of the dolomite was found rather poor. Therefore, synthetic sorbents that maintain their capacities upon multiple reforming-calcination cycles were investigated. A low-temperature liquid phase co-precipitation method was used for synthesis of Li2ZrO3 and Na2ZrO3. Li2ZrO3 showed a superior multi-cycle capacity compared to Arctic dolomite in TGA, but the rate of reaction in diluted CO2 atmospheres was very slow. The synthesized Na2ZrO3 proved to have both fast carbonation kinetics and stable multi-cycle performance. However, regeneration in the presence of carbon dioxide was not easily accomplished. The findings of this thesis suggest that the bubbling fluidized bed reactor is an attractive reactor configuration for SE-SMR. Low gas throughput is the major disadvantage for this configuration, and operation in the fast fluidization regime is most likely to be preferred on an industrial scale of the process. Future work should focus on developing sorbents and catalysts that are suited for high velocity operation, with respect to reactivity and mechanical strength.
373

Process of Motivational Enhancement Therapy: Relationships between Therapist and Client Behaviours, and Alcohol Use Outcome

Campbell, Samadhi Deva January 2007 (has links)
Motivational Interviewing (MI) is an evidence-based, directive, client-centered therapy designed to develop discrepancy and resolve ambivalence by eliciting and reinforcing client Change Talk. However, the exact link between the process engaged in during MI and outcome is only starting to be uncovered. The present thesis has replicated and expanded on the current knowledge of the relationship between Therapist and Client Behaviours during a MI-based intervention (Motivational Enhancement Therapy; MET) and outcome, and has provided support for the emergent theory of the inner workings of MI. This was achieved by coding 106 audiotaped MET sessions primarily by the methods outlined in the Motivational Interviewing Skill Code Version 2.0. Data was drawn from 28 participants who received 3-4 sessions of MET within the context of a randomised controlled trial for mild-moderate alcohol dependence at the Community Alcohol and Drug Service of Christchurch. Therapist and Client Behaviours were analysed within sessions (categorised into Early, Mid, or End Intervals) and across sessions, and compared with whether the client had drank within national drinking guidelines during the 6-months after MET (Controlled Drinkers). In terms of Client Behaviours during MET it was found that Uncontrolled Drinkers (compared with Controlled Drinkers) uttered a significantly higher frequency of Sustain Talk, lower Ability Language strength (over all MET and during End Intervals), and lower Commitment Language strength (during Session 2 and 4, and change over MET). Giving Information was the only Therapist Behaviour where significant differences were observed over all MET, with a higher frequency given to the Uncontrolled Drinkers. However, during End Intervals within MET Sessions, Controlled Drinkers received a significantly higher frequency of Advise without Permission and a lower frequency of Emphasise Control statements. In most instances MI-Consistent Therapist Behaviours were associated with higher strength of Ability and Commitment Language, and a lower frequency of Sustain Talk. MI-Inconsistent Therapist Behaviour, Direct, was associated with lower Client Language strength. Limitations to these results include small sample, limited ability to make inferences about causality, coder biases, and uneven reliability. However, this exploratory study was unique in investigating the relationship between Therapist Behaviours and the strength of Client Language, and in examining these factors within and across multiple sessions, and has produced a number of potentially valuable findings that warrant further investigation.
374

Visual linearization of image data for the display of digital intraoral radiographs /

Li, Gang, January 2004 (has links)
Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 6 uppsatser.
375

Magnetic resonance imaging of the hepatobiliary system using hepatocyte-specific contrast media /

Dahlström, Nils, January 2009 (has links)
Licentiatavhandling (sammanfattning) Linköping : Linköpings universitet, 2009. / Härtill 2 uppsatser.
376

Distortion correction for diffusion weighted magnetic resonance images

Stinson, Eric Gregory, January 1900 (has links)
Thesis (M.Sc.). / Written for the Medical Physics Unit. Title from title page of PDF (viewed 2009/09/07). Includes bibliographical references.
377

An in-vitro comparison of working length determination between a digital system and conventional film when source-film/sensor distance and exposure time are modified

Ley, Paul J. January 2009 (has links)
Thesis (M.S.D.)--Indiana University School of Dentistry, 2009. / Title from PDF t.p. (viewed Aug. 11, 2009) Advisors: Mychel Vail, Chair of the Research Committee, Susan Zunt, Ted Parks, Kenneth Sponik, Joseph Legan. Curriculum vitae. Includes abstract. Includes bibliographical references (leaves 103-119).
378

The Conservation Reserve Enhancement Program agricultural-environmental policy and its impact on land use and county discretion in northwest Ohio /

Luginbuhl, April M. January 2002 (has links)
Thesis (M.A.)--Ohio University, June, 2002. / Title from PDF t.p. Includes bibliographical references (leaves 76-79)
379

A UNIVERSIDADE FEDERAL DE SANTA MARIA E SUA RELAÇÃO COM A VALORIZAÇÃO DO PATRIMÔNIO CULTURAL: um olhar para o curso de Arquitetura e Urbanismo. / FEDERAL UNIVERSITY OF SANTA MARIA AND ITS RELATION TO THE RECOVERY OF THE CULTURAL HERITAGE: A LOOK TO THE COURSE OF ARCHITECTURE AND URBAN PLANNING.

Baptaglin, Leila Adriana 12 March 2010 (has links)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The present thesis aims to investigate how the Undergraduate Courses in the Federal University of Santa Maria, especially the Course of Architecture and Urban Design has been working the issue of cultural heritage. This verification was made through an analysis of recent curricular changes in the various courses of the Federal University of Santa Maria (UFSM). Subsequently I performed an investigation in the curricular organization of the last two decades (1990 and 2000) the courses involved with the Graduation Program of Cultural Heritage. Finally, we performed further analysis of the Architecture and Urbanism, through semi-structured interviews with four (4) teachers of this course, directly involved with the courses and also through an analysis of the final-year undergraduate students from 2004 to 2009. Thus, based on the data of this research it was possible to establish a comprehensive systematization points referring to the presence of the theme of Cultural Heritage in graduate courses at the Federal University of Santa Maria (UFSM), but also produce a more detailed analysis on how the course of Architecture and Urban Design has been building his actions and organizations in the midst of curricular context. Thus, what I realized is that the studies and researches at the University must be more present in the society of Santa Maria. Situation, that which comes to be conceived and crafted in 2010 in the Council for the Coordination of Historical and Artistic Heritage (COMPHIC), where actions and proposals for heritage education began to be thought about and worked in order to implement this effective participation, knowledge and interest of the community in the assets of the town of Santa Maria. / O presente trabalho busca investigar como os Cursos de Graduação da Universidade Federal de Santa Maria, em especial o Curso de Arquitetura e Urbanismo vem trabalhando a questão do Patrimônio Cultural. Esta verificação se deu através de uma análise nas últimas reformulações curriculares dos diferentes cursos da Universidade Federal de Santa Maria (UFSM). Posteriormente realizei uma investigação na organização curricular das duas últimas décadas (1990 e 2000) dos cursos envolvidos com o programa de Pós-Graduação em Patrimônio Cultural. Finalmente, foi realizada uma análise mais aprofundada frente ao curso de Arquitetura e Urbanismo, através de entrevistas semi-estruturadas com quatro (4) professores deste curso, envolvidos diretamente com disciplinas que abordam o tema. E também, através de uma análise dos Trabalhos Finais de Graduação dos anos de 2004 a 2009. Desta forma, a partir dos dados desta pesquisa foi possível estabelecer a sistematização pontos abrangentes que referenciam a presença da temática do Patrimônio Cultural nos cursos de graduação da Universidade Federal de Santa Maria (UFSM), mas também, apresentar uma análise mais aprofundada que acerca de como o curso de Arquitetura e Urbanismo vem estruturando suas ações e organizações curriculares em meio ao contexto patrimonial santamariense. Desta forma, o que percebi é que os estudos e as pesquisas realizadas na Universidade têm de estarem mais presentes na sociedade. Situação, esta, que passa a ser pensada e trabalhada no ano de 2010 na coordenação do Conselho do Patrimônio Histórico e Artístico (COMPHIC), onde ações e propostas de Educação Patrimonial começam a ser pensadas e trabalhadas no intuito de realizar esta efetiva participação, conhecimento e interesse da comunidade para com os bens patrimoniais da localidade de Santa Maria.
380

Séparation de sources en ligne dans des environnements réverbérants en exploitant la localisation des sources / Online source separation in reverberant environments exploiting known speaker locations

Harris, Jack 12 October 2015 (has links)
Cette thèse porte sur les techniques de séparation de sources en aveugle en utilisant des statistiques de second ordre et statistiques d'ordresupérieur pour les environnements de réverbération. Un objectif de la thèse est la simplicité algorithmique en vue de l'implantation en lignedes algorithmes. Le principal défi des applications de séparation de sources aveugles est de s'occuper des environnements acoustiques de réverbération; une complication supplémentaire concerne les changements dans l'environnement acoustique lorsque les sources humaines se déplacent physiquement.Une nouvelle méthode dans le domaine temporel qui utilise une paire de filtres à réponse impulsionnelle finie est proposée. Cette méthode, dite les angles principaux, sur un décomposition en valeurs singulières. Une paire de filtres, jouant le rôle de formation de voie, est estimée de façon à annuler une des sources. Une étape de filtrage adaptatif estensuite utilisée pour récupérer la source restante, en exploitant la sortie de l'étage de beamforming en tant que une référence de bruit. Une approche commune de la séparation de sources aveugle est d'utiliser des méthodes fondée sur les statistiques d'ordre supérieur comme l'analyse en composantes indépendantes. Cependant, pour des mélanges convolutifs audio et vocales réalistes, la transformation dansle domaine fréquentiel pour chaque fréquence de calcul est nécessaire. Ceci introduit le problème de permutations, inhérentes à l'analyse en composantes indépendantes, pour tout les fréquences. L'analyse en vecteur indépendant résout directement cette question par la modélisation des dépendances entre les fréquences de calcul, à partir d'a priori sur les sources. Un algorithme de gradient naturel en temps réel est également proposé proposé avec un autre a priori sur les sources. Cette méthode exploite la fonction de densité de probabilité de Student, est connu pour être bien adapté pour les sources de parole, en raison de queues de distribution plus lourdes. L'algorithme final est implanté en temps réel sur un processeur numérique de signal à virgule flottante de Texas Instruments.Les sources mobiles, avec des environnements réverbérant, causent des problèmes significatifs dans les systèmes de séparation desources réalistes car les filtres de mélange deviennent variants dans le temps. Dans ce cadre, une méthode qui utilise conjointement leprincipe de la paire de filtres d'annulation et le principe de l'analyse en vecteurs indépendant. Cette approche permet de limiter les baisses de performance lorsque les sources sont mobiles. Les résultats montrent également que les temps moyen de convergence des divers paramètres sont diminués.Les méthodes en ligne qui sont introduites dans la thèse, sont testées en utilisant des réponses impulsionnelles mesurées dans des environnements de réverbération. Les résultats montrent leur robustesse et d'excellentes performances par rapport à d'autres méthodes classique, dans plusieurs situations expérimentales. / Methods for improving the real-time performance and speed of various source enhancement and separation are considered. Two themes of research are considered so far: a method which relies only on second order statistics to enhance a target source exploiting video cues. Secondly, a higher-order statistics method, independent vector analysis is implemented in real-time on a digital signal processor, where an alternative source prior has been used performance is shown to have improved.

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