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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.
811

Black liquor gasification : experimental stability studies of smelt components and refractory lining

Råberg, Mathias January 2007 (has links)
Black liquors are presently combusted in recovery boilers where the inorganic cooking chemicals are recovered and the energy in the organic material is converted to steam and electricity. A new technology, developed by Chemrec AB, is black liquor gasification (BLG). BLG has more to offer compared to the recovery boiler process, in terms of on-site generation of electric power, liquid fuel and process chemicals. A prerequisite for both optimization of existing processes and the commercialization of BLG is better understanding of the physical and chemical processes involved including interactions with the refractory lining. The chemistry in the BLG process is very complex and to minimize extensive and expensive time-consuming studies otherwise required accurate and reliable model descriptions are needed for a full understanding of most chemical and physical processes as well as for up-scaling of the new BLG processes. However, by using these calculated model results in practice, the errors in the state of the art thermochemical data have to be considered. An extensive literature review was therefore performed to update the data needed for unary, binary and higher order systems. The results from the review reviled that there is a significant range of uncertainty for several condensed phases and a few gas species. This resulted in experimental re-determinations of the binary phase diagrams sodium carbonate-sodium sulfide (Na2CO3-Na2S) and sodium sulfate-sodium sulfide (Na2SO4-Na2S) using High Temperature Microscopy (HTM), High Temperature X-ray Diffraction (HT-XRD) and Differential Thermal Analysis (DTA). For the Na2CO3-Na2S system, measurements were carried out in dry inert atmosphere at temperatures from 25 to 1200 °C. To examine the influence of pure CO2 atmosphere on the melting behavior, HTM experiments in the same temperature interval were made. The results include re-determination of liquidus curves, in the Na2CO3 rich area, melting points of the pure components as well as determination of the extent of the solid solution, Na2CO3(ss), area. The thermal stability of Na2SO3 was studied and the binary phase diagram Na2SO4-Na2S was re-determined. The results indicate that Na2SO3 can exist for a short time up to 750 °C, before it melts. It was also proved that a solid/solid transformation, not reported earlier, occurs at 675 ± 10 °C. At around 700 °C, Na2SO3 gradually breaks down within a few hours, to finally form the solid phases Na2SO4 and Na2S. From HTM measurements a metastable phase diagram including Na2SO3, as well as an equilibrium phase diagram have been constructed for the binary system Na2SO4-Na2S. Improved data on Na2S was experimentally obtained by using solid-state EMF measurements. The equilibrium constant for Na2S(s) was determined to be log Kf(Na2S(s)) (± 0.05) = 216.28 – 4750(T/K)–1 – 28.28878 ln (T/K). Gibbs energy of formation for Na2S(s) was obtained as ΔfG°(Na2S(s))/(kJ mol–1) (± 1.0) = 90.9 – 4.1407(T/K) + 0.5415849(T/K) ln (T/K). The standard enthalpy of formation of Na2S(s) was evaluated to be ΔfH°(Na2S(s), 298.15 K)/(kJ mol–1) (± 1.0) = – 369.0. The standard entropy was evaluated to be S°(Na2S(s), 298.15 K)/(J mol–1 K–1) (± 2.0) = 97.0. Analyses of used refractory material from the Chemrec gasifier were also performed in order to elucidate the stability of the refractory lining. Scanning electron microscopy (SEM) analysis revealed that the chemical attack was limited to 250-300 μm, of the surface directly exposed to the gasification atmosphere and the smelt. From XRD analysis it was found that the phases in this surface layer of the refractory were dominated by sodiumaluminosilicates, mainly Na1.55Al1.55Si0.45O4.
812

Increasing Walkability Capacity Of Historic City Centers: The Case Of Mersin

Belge, Zuleyha Sara 01 October 2012 (has links) (PDF)
Sustainability, livability and quality of life have become widely and in-depth discussed issues in the literature of urban zlanning and design. This study primarily aims to investigate the concept of walkability as a part of the literature on livability. To draw a wider theoretical framework for this study, it first seeks to answer the questions of what the terms of &lsquo / livability&rsquo / and &lsquo / quality of life&rsquo / mean, and what components they constitute. Then, it focuses on the concept of &lsquo / walkability&rsquo / as one of the major components of these terms and as a measurable notion in urban design. Thus, this research seeks to define the notion of &lsquo / walkability&rsquo / and to identify a set of measures of walkability in public spaces to be used for the assessment of the &lsquo / walkability capacity&rsquo / of urban space. It should be noted that this research particularly tries to use the indicators of walkability which can directly impact on the design quality of urban space. Third, this research focuses on Mersin historic city center which has been in the process of deterioration for a while due to various current urban policies and strategies. As the case studies, it examines Uray and Atat&uuml / rk Streets which constitute the major thoroughfares of the historic city center by using the set of walkability measures. It investigates the walkability quality of four different character zones of Uray and Atat&uuml / rk Streets, and identifies their walkability capacities, problems and potentials. Finally, it suggests the policy and practical solutions on the design of these public spaces that will not only improve the walkability capacity of these streets, but also be helpful for the revitalization of the historic city center.
813

High-resolution Studies of mRNA Expression in Brain : A Search for Genes Differently Expressed in Schizophrenia

Castensson, Anja January 2003 (has links)
Gene expression differences between patients and controls can be used to find susceptibility genes and drug targets for a disease. High-resolution strategies are required because the differences between the investigated groups may be small and numerous factors may affect the mRNA quantity. This thesis is based on the use of real-time RT-PCR combined with a new statistical approach, developed to detect small differences between patients and controls and differences due to patient subgroups. Comparisons between human brain biopsy and autopsy samples showed that post-mortem tissue can be used to make conclusions on the relative mRNA levels in the living brain. Power analysis based on human brain mRNA expression from 14 genes adjusted with two reference genes, revealed that a sample size of 50 patients and 50 controls was required to detect a 2-fold difference with a power and a confidence of 95%. A similar study in rats revealed that approximately the same sample size was required for rat brain mRNA expression studies. The mRNA levels of several genes were studied in 55 schizophrenia and 55 control prefrontal brain autopsies, using a novel and more powerful statistical analysis. The serotonin receptor 2C gene (HTR2C) showed a significant 1.5-fold decrease in the patients as compared to controls, and the monoamine oxidase B gene (MAOB) a 1.2-fold increase. The mechanism behind the decrease of HTR2C mRNA levels was investigated by studying the correlation of drug treatment and HTR2C promoter polymorphisms to the HTR2C expression levels. The observed decrease was present in untreated patients, suggesting that the HTR2C mRNA decrease is correlated with the disease and not the treatment. There was no association between promoter polymorphisms and HTR2C expression levels. Thus, the molecular mechanism for the decreased expression remains unclear. Nevertheless, the results support a role for monoaminergic synapses in schizophrenia.
814

EVOLUTION DU DOMAINE NORD-PYRENEEN AU CRETACE. AMINCISSEMENT CRUSTAL EXTREME ET THERMICITE ELEVEE: UN ANALOGUE POUR LES MARGES PASSIVES

Clerc, Camille 20 December 2012 (has links) (PDF)
Cette thèse présente une analyse structurale et thermique des marges passives crétacées inversées dans la Zone Nord Pyrénéenne (ZNP). L'application du paléothermomètre RSCM (spectrométrie Raman de la matière carbonée) sur plus de cent échantillons répartis à travers la ZNP permet de préciser l'évolution thermique de la déchirure continentale. Un métamorphisme de haute température (450 à >600°C) se développe particulièrement au droit de zones ou la croûte continentale est extrêmement amincie voire éliminée. Les sédiments pré- et syn-rift sont marqués par une intense déformation ductile. L'analyse à l'EBSD des fabriques minérales indique une déformation de Haute-température contemporaine du métamorphisme HT-BP. Les conditions de mise en place crustale des péridotites et leur exhumation localisée sont examinées dans les localités d'Urdach, Saraillé-Tos de la Coustette, Moncaup, Lherz, Caussou-Bestiac et Salvezines. Les résultats indiquent un boudinage de la croûte continentale au cours du processus de rifting. Des décollements de couverture, principalement localisés dans les évaporites triasiques conduisent à la superposition directe des sédiments pré-rift sur le manteau exhumé. La notion nouvelle de soutirage crustal est introduite pour désigner ce processus dans lequel l'écoulement gravitaire ne joue pas un rôle principal. La caractérisation sédimentologique, pétrographique et isotopique (O et C) des différentes formations de brèches et ophicalcites observées à proximité des corps de péridotites permet de reconstituer les étapes de l'exhumation du manteau en pied de marge. Enfin de nouvelles datations permettent de mieux contraindre le calendrier des évènements successifs.
815

Design and Synthesis of Novel Serotonin Receptor Ligands

Klenc, Jeffrey D 18 August 2010 (has links)
Novel and potent ligands to the serotonin7 (5-HT7) receptor have been synthesized. The synthesized compounds include a set of substituted pyrimidines which show high affinity to the 5-HT7 receptor, synthesized by previously described methods [1,2] in high yield. Comparing the affinities of substituted pyrimidines to previously calculated models [3,4] yielded new hypotheses about the nature of interaction between the pyrimidine ligands and the 5-HT7 binding site. Several new series of compounds were synthesized by various methods to validate these hypotheses, including a conjugate addition to vinylpyrimidines [5]. These compounds include benzofurans, oximes, hydrazones, as well as a group of substituted piperazines. All series of compounds show affinity to the 5-HT7 receptor comparable to previously synthesized 5-HT7 ligands. Several of the synthesized ligands show affinity which exceeds that of currently available ligands. The synthesized compounds were evaluated quantitatively by calculating a three-dimensional quantitative structure-affinity relationship (3D-QSAR) for the 5-HT7 receptor. Evaluation of the calculated model validated qualitative assumptions about the data set as well as described regions of interaction in greater detail than previously available. These observations give further insight on the nature of ligand-binding site interactions with highly potent ligands such as 4-(3-furyl)-2-(N-methylpiperazino)pyrimidine which will lead to more potent 5-HT7 receptor ligands. Additionally, a model was calculated for affinity to the 5-HT2a receptor. Comparing this model to that calculated for affinity to the 5-HT7 receptor identified two regions which may be exploited in future sets of ligands to increase selectivity to the 5HT7 receptor.
816

Production Of Urban Space In The Southwestern Periphery Of Ankara

Acar Ozler, Ozgul 01 October 2012 (has links) (PDF)
The aim of this thesis is to explain the production of urban space at the southwestern periphery of Ankara between 1985 and 2007. It has been argued that urban development is not a self-regulatory process / on contrary it is a process produced by urban planning practice. In this respect this thesis asks how and what extent urban planning produces particular urban pattern at the peripheral areas. The southwestern periphery is taken into account as a field of case study due to the peculiar development dynamics. Historical development in this area reveals a contrast between planned development directed by master plans and problematic development that has been produced by fragmented and incoherent planning processes. The difficulties of urban plans and urban planning are intimately related with the legal and administrative structures of the planning system. A methodology offered in this thesis is devised to analyze the incremental and piecemeal nature of planning process with reference to these structures. The results of the research has shown that when confronted with legal and administrative conflicts and struggles, fragmented planning decisions manipulating the existing master plan intensify and become the root cause of dispersed, awkward and haphazard spatial patterns of urban expansion.
817

Production Of Urban Space In The Southwestern Periphery Of Ankara

Acar Ozler, Ozgul 01 October 2012 (has links) (PDF)
The aim of this thesis is to explain the production of urban space at the southwestern periphery of Ankara between 1985 and 2007. It has been argued that urban development is not a self-regulatory process / on contrary it is a process produced by urban planning practice. In this respect this thesis asks how and what extent urban planning produces particular urban pattern at the peripheral areas. The southwestern periphery is taken into account as a field of case study due to the peculiar development dynamics. Historical development in this area reveals a contrast between planned development directed by master plans and problematic development that has been produced by fragmented and incoherent planning processes. The difficulties of urban plans and urban planning are intimately related with the legal and administrative structures of the planning system. A methodology offered in this thesis is devised to analyze the incremental and piecemeal nature of planning process with reference to these structures. The results of the research has shown that when confronted with legal and administrative conflicts and struggles, fragmented planning decisions manipulating the existing master plan intensify and become the root cause of dispersed, awkward and haphazard spatial patterns of urban expansion.
818

Microdiffraction et microtomographie in situ des transformations hétérogènes du C¦" sous haute pression et haute température

Alvarez murga, Michelle jenice 06 November 2012 (has links)
Le diagramme des phases du C60 continue d'être un sujet de discussion et de controverse, malgré la grande quantité de travaux expérimentaux et théoriques fait au fil des ans. Ceci est principalement dû au manque d'études in situ, a l'existence d'états désordonnés présentant des pics de diffraction très mal résolus et à la coexistence de plusieurs polytypes de faible densité. Ce manuscrit présente une étude systématique in situ des transformations hétérogènes du C60 sous haute pression et haute température dans la gamme 1-10 GPa et 300-1200 K. Afin de discriminer les poly(a)morphes de densité similaire dans des échantillons hétérogènes, nous avons utilisé une combinaison de micro-diffraction et micro-tomographie. Les échantillons ont été synthétisés dans une cellule Paris-Edimbourg et caractérisés à l'aide de diffraction des rayons X in situ en dispersion angulaire. Des images tridimensionnels à haute résolution ont été obtenus sur des échantillons trempés par la méthode de micro-tomographie de diffraction/diffusion. Cette méthode permet l'analyse 3D de l'intensité de diffusion reconstruite à partir de séries de projections 2D. Une telle analyse est non destructive et offre une grande sensibilité (0,1% en volume), une haute résolution spatiale (μm3) et peut être multimodale, fournissant des données quantitatives sur la morphologie, la densité, la composition élémentaire ou la structure des matériaux. En outre, nous décrivons le développement d'un système de micro-tomographie in situ sous haute pression et haute température en utilisant une nouvelle cellule rotative Paris-Edimbourg (RoToPEC), combinée avec le rayonnement synchrotron. La capacité à tourner complètement la chambre de l'échantillon sous charge, surmonte la contrainte d'ouverture angulaire limitée des cellules ordinaires et permet l'acquisition de projections tomographiques pour l'imagerie de plein champ ainsi que pour l'imagerie par micro-diffraction. Cette méthode innovante permet l'étude des matériaux sous conditions extrêmes de pression, température ou stress, et pourra être appliquée dans des domaines variés tels que la physique, la chimie, la science des matériaux ou la géologie. Le potentiel de cette nouvelle technique expérimentale est démontré par l'étude de la polymérisation de C60 sous haute-pression et haute température. Mots-clés: C60, diagramme de phase, diffraction, micro-tomographie, haute pression et haute température
819

Magma-Crust Interaction at Subduction Zone Volcanoes

Jolis, Ester M. January 2013 (has links)
The focus of this work is magma-crust interaction processes and associated crustal volatile release in subduction zone volcanoes, drawing on rock, mineral, and gas geochemistry as well as experimental petrology. Understanding the multitude of differentiation processes that modify an original magma during ascent to the surface is vital to unravel the contributions of the various sources that contribute to the final magmas erupted at volcanoes. In particular, magma-crust interaction (MCI) processes have been investigated at a variety of scales, from a local scale in the Vesuvius, Merapi, and Kelut studies, to a regional scale, in the Java to Bali segment of the Sunda Arc.  The role of crustal influences is still not well constrained in subduction systems, particulary in terms of the compositional impact of direct magma crust interplay. To address this shortcoming, we studied marble and calc-silicate (skarn) xenoliths, and used high resolution short timescale experimental petrology at Vesuvius volcano. The marbles and calc-silicates help to identify different mechanisms of magma-carbonate and magma-xenolith interaction, and the subsequent effects of volatile release on potential eruptive behaviour, while sequential short-duration experiments simulate the actual processes of carbonate assimilation employing natural materials and controlled magmatic conditions. The experiments highlight the efficiency of carbonate assimilation and associated carbonate-derived CO2 liberated over short timescales. The findings at Merapi and Kelut demonstrate a complex magmatic plumbing system underneath these volcanoes with magma residing at different depths, spanning from the mantle-crust boundary to the upper crust. The erupted products and volcanic gas emissions enable us to shed light on MCI-processes and associated volatile release in these systems. The knowledge gained from studying individual volcanoes (e.g., Merapi and Kelut) is then tested on a regional scale and applied to the entire Java and Bali arc segment. An attempt is presented to distinguish the extent of source versus crustal influences and establish a quantitative model of late stage crustal influence in this arc segment. This thesis therefore hopes to contribute to our knowledge of magma genesis and magma-crust interaction (MCI) processes that likely operate in subduction zone systems worldwide.
820

Urban Transformation Process: Ulus Historcial City Center Planning Project

Osmancavusoglu, Atanur 01 August 2006 (has links) (PDF)
This thesis, firstly, examines the main characteristics of comprehensive and strategic spatial planning and by comparing both planning understandings indicates that strategic spatial planning is thought as more suitable to the demands of both developing and developed countries in the contemporary era. Then, the main argument of the thesis is presented as Ulus Historical Center Conservation and Improvement Plan is an example of a strategic plan prepared for the purposes of conservation (development). In conformity with the general conviction that strategic plan is more flexible, adaptable to changing circumstances, action oriented, open to negotiation by various actors involved in the planning process and allowing participation by beneficiaries of the planning process, this study aims to find out the strategic plan characteristics of Ulus Historical Center Conservation and Improvement Plan by looking at its development stage, main characteristics and the implementation process. As a conclusion, displaying an alternative view and as a planning process Ulus Planning Project is different than the traditional comprehensive conservation (development) plans more displaying the characteristics of strategic spatial planning.

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