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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

The synthesis of nitrogen doped carbon spheres and polythiophene/carbon sphere composites

Kunjuzwa, Nikiwe 17 March 2010 (has links)
This study reports on the synthesis of N-doped carbon spheres (N-CSs) by a simple synthetic procedure. A horizontal CVD type reactor was used to synthesize N-CSs from pyridine. Depending on the dilution of the pyridine with toluene, a nitrogen content of 0.13-5 mol % was obtained. The use of a vertical CVD reactor gave N-CSs with a N-content of 0.19-3 mol % when an ammonium solution and acetylene were used as reactants. The diameters of carbon spheres were found to be in the range of 40 nm to 1000 nm for both CVD reactors. The diameter can be controlled by varying the flow rate, temperature, time, concentration and the reactor type. The samples were characterized by TEM, HRTEM, elemental analysis, Raman spectroscopy, TGA, PXRD and ESR. We have demonstrated that unsubstituted thiophene can be polymerized by Fe3+-catalyzed oxidative polymerization. The average particle size was about 50 nm, within a narrow particlesize distribution. The undoped carbon spheres (CSs) were reacted with thiophene to give polymer/carbon composites containing polythiophene and carbon nanospheres via chemical oxidative polymerization reaction. Polythiophene molecules were either chemically bonded or physically adsorbed to the surface of carbon spheres. The microstructure and properties of the two types of composites were compared. The thermogravimetric analysis data confirmed that the presence of CSs in the polymer\carbon composites is responsible for the higher thermal stability of the composite material in comparison with pristine polythiophene. The FTIR analysis showed that covalent functionalized nanocomposites exhibit a high intensity of a C-S bond This study reports on the synthesis of N-doped carbon spheres (N-CSs) by a simple synthetic procedure. A horizontal CVD type reactor was used to synthesize N-CSs from pyridine. Depending on the dilution of the pyridine with toluene, a nitrogen content of 0.13-5 mol % was obtained. The use of a vertical CVD reactor gave N-CSs with a N-content of 0.19-3 mol % when an ammonium solution and acetylene were used as reactants. The diameters of carbon spheres were found to be in the range of 40 nm to 1000 nm for both CVD reactors. The diameter can be controlled by varying the flow rate, temperature, time, concentration and the reactor type. The samples were characterized by TEM, HRTEM, elemental analysis, Raman spectroscopy, TGA, PXRD and ESR. We have demonstrated that unsubstituted thiophene can be polymerized by Fe3+-catalyzed oxidative polymerization. The average particle size was about 50 nm, within a narrow particlesize distribution. The undoped carbon spheres (CSs) were reacted with thiophene to give polymer/carbon composites containing polythiophene and carbon nanospheres via chemical oxidative polymerization reaction. Polythiophene molecules were either chemically bonded or physically adsorbed to the surface of carbon spheres. The microstructure and properties of the two types of composites were compared. The thermogravimetric analysis data confirmed that the presence of CSs in the polymer\carbon composites is responsible for the higher thermal stability of the composite material in comparison with pristine polythiophene. The FTIR analysis showed that covalent functionalized nanocomposites exhibit a high intensity of a C-S bondThis study reports on the synthesis of N-doped carbon spheres (N-CSs) by a simple synthetic procedure. A horizontal CVD type reactor was used to synthesize N-CSs from pyridine. Depending on the dilution of the pyridine with toluene, a nitrogen content of 0.13-5 mol % was obtained. The use of a vertical CVD reactor gave N-CSs with a N-content of 0.19-3 mol % when an ammonium solution and acetylene were used as reactants. The diameters of carbon spheres were found to be in the range of 40 nm to 1000 nm for both CVD reactors. The diameter can be controlled by varying the flow rate, temperature, time, concentration and the reactor type. The samples were characterized by TEM, HRTEM, elemental analysis, Raman spectroscopy, TGA, PXRD and ESR. We have demonstrated that unsubstituted thiophene can be polymerized by Fe3+-catalyzed oxidative polymerization. The average particle size was about 50 nm, within a narrow particlesize distribution. The undoped carbon spheres (CSs) were reacted with thiophene to give polymer/carbon composites containing polythiophene and carbon nanospheres via chemical oxidative polymerization reaction. Polythiophene molecules were either chemically bonded or physically adsorbed to the surface of carbon spheres. The microstructure and properties of the two types of composites were compared. The thermogravimetric analysis data confirmed that the presence of CSs in the polymer\carbon composites is responsible for the higher thermal stability of the composite material in comparison with pristine polythiophene. The FTIR analysis showed that covalent functionalized nanocomposites exhibit a high intensity of a C-S bond at 695 cm-1 , which is not observed in the noncovalent functionalized nanocomposites
112

Mergulho de produtos de esferas e suas somas conexas em codimensão 1 / Embeddings of cartesian products of spheres and its connected sums in codimension 1

Fenille, Marcio Colombo 16 February 2007 (has links)
Estudamos inicialmente resultados de classificação de difeomorfismos de produtos de esferas de mesma dimensão. Tratado isto, estudamos os mergulhos suaves de produtos de três esferas, sendo a primeira de dimensão um e as demais de dimensão maior ou igual a um, com a dimensão da última maior ou igual a da segunda, em uma esfera em codimensão um, e buscamos a total caracterização do fecho das duas componentes conexas do complementar de tais mergulhos. Tratamos com enfoque especial os mergulhos do produto de três esferas de dimensão um na esfera de dimensão quatro, e, finalmente, estudamos problemas de classificação de mergulhos PL localmente não-enodados de somas conexas de toros em codimensão um. / We study initially results of classification of difeomorfisms of Cartesian products of spheres of same dimension. Treated this, we study the smooth embeddings of cartesian products of three spheres, being the first one of dimension one and excessively of bigger or equal dimension to one, with the dimension of the last equal greater or of second, in a sphere in codimension one, and search the total characterization of the latch of the two connected components of complementing of such embeddings. We deal with special approach the embeddings of the product to three spheres to dimension one in the sphere dimension four, and, finally, we study problems of classification of PL locally unknotted embeddings of connected sums of torus on codimension one.
113

An exploratory study of inderstanding electronic government in facilitating intergovernmental relations to encourage cooperative governance in South Africa

Mayedwa, Mziwoxolo January 2010 (has links)
<p>The study seeks to investigate the perceived lack of coordination, integration, and coherence among units of government as related to eGovernment. The nature of the study is qualitative with a focus on the use of eGovernment in the public sector and whether it can facilitate intergovernmental forums business processes in an effective and efficient manner. The scope of the study is confined to the intergovernmental fiscal system but focused on eGovernment, intergovernmental relations, and cooperative governance. The primary objective of the study is to explore the use of eGovernment whether it can facilitate, coordinate, and integrate intergovernmental relations. Some studies portray that there are challenges in the coordination of intergovernmental forums which have resulted into a disintegration of services. The study further investigates options that could mitigate these challenges through acknowledging the effective application of ICTs (eGovernment) in government services. The study has found that South Africa has a functioning system of intergovernmental which are not effectively coordinated in terms of engaging each other in matters of mutual interest. On the other hand, eGovernment promised to bring about cohesion and transparency when they are effectively employed. The study revealed that the application of eGovernment in the intergovernmental forums has the capability to improve their operations, respond to its ineffective coordination and improve delivery of services. In a nutshell, the study has found that there is a need for a radical planning outlook that recognises proper utilization of eGovernment in the intergovernmental forums to promote cooperative governance.</p>
114

Harnessing Mesoporous Spheres - transport studies and biotechnological applications

Ng, Jovice Boon Sing January 2009 (has links)
Applications in controlled release and delivery calls for a good understanding of molecular transport within the carrier material and the dominating release mechanisms. It is clear that a better understanding of hindered transport and diffusion of guest molecules is important when developing new porous materials, e.g., surfactant templated silica spheres, for biotechnological applications. Confocal laser scanning microscopy was used to quantify the bulk release and intraparticle transport of small charged fluorescent dyes, and fluorescently-tagged neutral dextran, from mesoporous silica spheres. The time dependent release and the concentration profiles within the spheres have been used to analyze the release mechanisms using appropriate models. While the small, non-adsorbing anionic dye is released following a simple diffusion driven process, the concentration of the cationic dye varies radially within the spheres after loading. The release of the cationic dye is controlled by diffusion after an initial period of rapid release, which could be due to a significant fraction of the cationic dye that remains permanently attached to the negatively charged walls of the mesoporous silica spheres. The diffusion of dextran and the resulting flat concentration profiles could be related to the complex structural feature of the cylindrical pores close to the surface, and a possible conformational change of the dextran with the concentration. The stability and leaching of a catalytic enzyme, lipase, immobilized in hydrophobilized mesoporous support has also been quantified. Colloidal monodisperse mesoporous silica spheres were synthesized and transmission electron microscopy showed that the inner pore structure display a radially extending pores. The mesoporous spheres were used as solid supports for a lipid membrane incorporated with a multi-subunit redox-driven proton pump, which was shown to remain functional. / Synthesis, functionalisation and controlled release of mesoporous materials
115

Functional nanostructured hydrothermal carbons for sustainable technologies : heteroatom doping and superheated vapor

Wohlgemuth, Stephanie-Angelika January 2012 (has links)
The underlying motivation for the work carried out for this thesis was the growing need for more sustainable technologies. The aim was to synthesize a “palette” of functional nanomaterials using the established technique of hydrothermal carbonization (HTC). The incredible diversity of HTC was demonstrated together with small but steady advances in how HTC can be manipulated to tailor material properties for specific applications. Two main strategies were used to modify the materials obtained by HTC of glucose, a model precursor representing biomass. The first approach was the introduction of heteroatoms, or “doping” of the carbon framework. Sulfur was for the first time introduced as a dopant in hydrothermal carbon. The synthesis of sulfur and sulfur/nitrogen doped microspheres was presented whereby it was shown that the binding state of sulfur could be influenced by varying the type of sulfur source. Pyrolysis may additionally be used to tune the heteroatom binding states which move to more stable motifs with increasing pyrolysis temperature. Importantly, the presence of aromatic binding states in the as synthesized hydrothermal carbon allows for higher heteroatom retention levels after pyrolysis and hence more efficient use of dopant sources. In this regard, HTC may be considered as an “intermediate” step in the formation of conductive heteroatom doped carbon. To assess the novel hydrothermal carbons in terms of their potential for electrochemical applications, materials with defined nano-architectures and high surface areas were synthesized via templated, as well as template-free routes. Sulfur and/or nitrogen doped carbon hollow spheres (CHS) were synthesized using a polystyrene hard templating approach and doped carbon aerogels (CA) were synthesized using either the albumin directed or borax-mediated hydrothermal carbonization of glucose. Electrochemical testing showed that S/N dual doped CHS and aerogels derived via the albumin approach exhibited superior catalytic performance compared to solely nitrogen or sulfur doped counterparts in the oxygen reduction reaction (ORR) relevant to fuel cells. Using the borax mediated aerogel formation, nitrogen content and surface area could be tuned and a carbon aerogel was engineered to maximize electrochemical performance. The obtained sample exhibited drastically improved current densities compared to a platinum catalyst (but lower onset potential), as well as excellent long term stability. In the second approach HTC was carried out at elevated temperatures (550 °C) and pressure (50 bar), corresponding to the superheated vapor regime (htHTC). It was demonstrated that the carbon materials obtained via htHTC are distinct from those obtained via ltHTC and subsequent pyrolysis at 550 °C. No difference in htHTC-derived material properties could be observed between pentoses and hexoses. The material obtained from a polysaccharide exhibited a slightly lower degree of carbonization but was otherwise similar to the monosaccharide derived samples. It was shown that in addition to thermally induced carbonization at 550 °C, the SHV environment exhibits a catalytic effect on the carbonization process. The resulting materials are chemically inert (i.e. they contain a negligible amount of reactive functional groups) and possess low surface area and electronic conductivity which distinguishes them from carbon obtained from pyrolysis. Compared to the materials presented in the previous chapters on chemical modifications of hydrothermal carbon, this makes them ill-suited candidates for electronic applications like lithium ion batteries or electrocatalysts. However, htHTC derived materials could be interesting for applications that require chemical inertness but do not require specific electronic properties. The final section of this thesis therefore revisited the latex hard templating approach to synthesize carbon hollow spheres using htHTC. However, by using htHTC it was possible to carry out template removal in situ because the second heating step at 550 °C was above the polystyrene latex decomposition temperature. Preliminary tests showed that the CHS could be dispersed in an aqueous polystyrene latex without monomer penetrating into the hollow sphere voids. This leaves the stagnant air inside the CHS intact which in turn is promising for their application in heat and sound insulating coatings. Overall the work carried out in this thesis represents a noteworthy development in demonstrating the great potential of sustainable carbon materials. / Das Ziel der vorgelegten Arbeit war es, mit Hilfe der Hydrothermalen Carbonisierung (HTC) eine Palette an verschiedenen Materialien herzustellen, deren physikalische und chemische Eigenschaften auf spezifische Anwendungen zugeschnitten werden können. Die Motivation hierfür stellt die Notwendigkeit, Alternativen zu Materialien zu finden, die auf fossilen Brennstoffen basieren. Dabei stellen vor allem nachhaltige Energien eine der größten Herausforderungen der Zukunft dar. HTC ist ein mildes, nachhaltiges Syntheseverfahren welches prinzipiell die Nutzung von biologischen Rohstoffen (z. B. landwirtschaftlichen Abfallprodukten) für die Herstellung von wertvollen, Kohlenstoff-basierten Materialien erlaubt. Es wurden zwei verschiedene Ansätze verwendet, um hydrothermalen Kohlenstoff zu modifizieren. Zum einen wurde HTC unter „normalen“ Bedingungen ausgeführt, d. h. bei 180 °C und einem Druck von etwa 10 bar. Der Zucker Glukose diente in allen Fällen als Kohlenstoff Vorläufer. Durch Zugabe von stickstoff und /oder schwefelhaltigen Additiven konnte dotierte Hydrothermalkohle hergestellt werden. Dotierte Kohlenstoffe sind bereits für ihre positiven Eigenschaften, wie verbesserte Leitfähigkeit oder erhöhte Stabilität, bekannt. Zusätzlich zu Stickstoff dotierter Hydrothermalkohle, die bereits von anderen Gruppen hergestellt werden konnte, wurde in dieser Arbeit zum ersten Mal Schwefel in Hydrothermalkohle eingebaut. Außerdem wurden verschiedene Ansätze verwendet, um Oberfläche und definierte Morphologie der dotierten Materialien zu erzeugen, welche wichtig für elektrochemische Anwendungen sind. Schwefel- und/oder stickstoffdotierte Kohlenstoff Nanohohlkugeln sowie Kohlenstoff Aerogele konnten hergestellt werden. Mit Hilfe von einem zusätzlichen Pyrolyseschritt (d. h. Erhitzen unter Schutzgas) konnte die Leitfähigkeit der Materialien hergestellt werden, die daraufhin als Nichtmetall-Katalysatoren für Wasserstoff-Brennstoffzellen getestet wurden. Im zweiten Ansatz wurde HTC unter extremen Bedingungen ausgeführt, d. h. bei 550 °C und einem Druck von ca. 50 bar, welches im Wasser Phasendiagram dem Bereich des Heißdampfes entspricht. Es konnte gezeigt werden, dass die so erhaltene Hydrothermalkohle ungewöhnliche Eigenschaften besitzt. So hat die Hochtemperatur-Hydrothermalkohle zwar einen hohen Kohlenstoffgehalt (mehr als 90 Massenprozent), enthält aber auch viele Wasserstoffatome und ist dadurch schlecht leitfähig. Da damit elektrochemische Anwendungen so gut wie ausgeschlossen sind, wurde die Hochtemperatur-Hydrothermalkohle für Anwendungen vorgesehen, welche chemische Stabilität aber keine Leitfähigkeit voraussetzen. So wurden beispielsweise Hochtemperatur-Kohlenstoff-Nanohohlkugeln synthetisiert, die großes Potential als schall- und wärmeisolierende Additive für Beschichtungen darstellen. Insgesamt konnten erfolgreich verschiedenste Materialien mit Hilfe von HTC hergestellt werden. Es ist zu erwarten, dass sie in Zukunft zu nachhaltigen Technologien und damit zu einem weiteren Schritt weg von fossilen Brennstoffen beitragen werden.
116

Identity Across Borders : A Study in the "IKEA-World"

Salzer, Miriam January 1994 (has links)
How do people construct shared views of what the organization is all about in the international, complex; company? Within a cultural perspective, organizational identity can be tmderstood as organizational members' shared views and definitions of the organization. As people make sense of actions, events, decisions, etc., shared meanings develop which provide organizational members with a sense of organization. Through an ethnographic study in the corporate setting of lKEA I have tried to create an understanding of the processes tluough which organizational identities become constructed across borders. In the study it is shown how organizational members through the processes of sense-making construct collective self-views. By drawing borders against the outside world, mirroring themselves and talking to the self, organizational members come to create definitions of what the organization is all about. In the international, complex organization, these processes take place in different national contexts and in various local spheres of meaning. In order to offset divergent views and differentiation of meanings, managers try to create a global supra-identity through the fabrication of culture. At the same time, however, there is a heterogenization of meanings as predefined meanings from the top are constantly interpreted, rejected, recreated or adopted in the local spheres. Thus, in the complex organization, there are many collective selfviews and multiple identities. The organization, then, is to be Wlderstood as an arbitrary boundary around a set of spheres of meaning that overlap and interact.Index
117

Constructing Professionalism: Reifying the Historical Inevitability of Commercialization in Mass Media Communication

Keith, RuAnn Rae 14 July 2009 (has links)
American political culture has virtually precluded public discussion about the fundamental weaknesses of capitalism, forcing media reformers to argue defensively that commercial broadcasting is a special case of market failure. This investigation questions the historical inevitability of commercialized mass media structure by examining how the ideology of media professionalism is deployed in public debate over noncommercial uses of mass media resources. The work of John Dewey and Walter Lippmann frame a theoretical understanding of how professional autonomy works in opposition to community, and thus how professionalization works in opposition to a shared democratic sphere. Relying on the fundamental concepts of discursive formations studied in depth by Michel Foucault, three case studies analyze historic moments (the invention of listener support by Lewis Hill, the rise of news reporting by community television volunteers, and the introduction of media literacy in K-12 public education) that offer evidence of discursive breaks within the constructions of professionalism that support commercialization, and what those breaks suggest about the re-instantiation of the historical inevitability of the commercial regime. The conclusion discusses how conditions have led us to a point of deprofessionalization, a state in which media consumers disarm the notion of professionalism before it can be deployed as a governing relation, and how deproduction of authoritative texts effectively contains the power of professionalized norms. INDEX WORDS: Professionalism, Professionalization, Media reform, Commercialization, Noncommercial media, Dewey-Lippmann debate, Lewis Hill, Community television, Media literacy, Deproduction, Deprofessionalization
118

Gentlewomen: The Westernizing of Chinese American Prostitutes in San Francisco, 1870-1940 A History on Chinese American Prostitution, Missionaries and the Law

Dykman, Jennifer Becker 02 April 2010 (has links)
By considering San Francisco’s legal, social, and cultural history during the late 19th and early 20th centuries in relation to American law, missionary women, and Chinese American prostitutes, this thesis argues that by aggressively trying to control Chinese sexuality through laws, “yellow slave” narratives, Christianizing, and the immigration process, the American government and missionaries created an atmosphere ripe for Chinese prostitutes in America with varying degrees of sexual freedoms.
119

An exploratory study of inderstanding electronic government in facilitating intergovernmental relations to encourage cooperative governance in South Africa

Mayedwa, Mziwoxolo January 2010 (has links)
<p>The study seeks to investigate the perceived lack of coordination, integration, and coherence among units of government as related to eGovernment. The nature of the study is qualitative with a focus on the use of eGovernment in the public sector and whether it can facilitate intergovernmental forums business processes in an effective and efficient manner. The scope of the study is confined to the intergovernmental fiscal system but focused on eGovernment, intergovernmental relations, and cooperative governance. The primary objective of the study is to explore the use of eGovernment whether it can facilitate, coordinate, and integrate intergovernmental relations. Some studies portray that there are challenges in the coordination of intergovernmental forums which have resulted into a disintegration of services. The study further investigates options that could mitigate these challenges through acknowledging the effective application of ICTs (eGovernment) in government services. The study has found that South Africa has a functioning system of intergovernmental which are not effectively coordinated in terms of engaging each other in matters of mutual interest. On the other hand, eGovernment promised to bring about cohesion and transparency when they are effectively employed. The study revealed that the application of eGovernment in the intergovernmental forums has the capability to improve their operations, respond to its ineffective coordination and improve delivery of services. In a nutshell, the study has found that there is a need for a radical planning outlook that recognises proper utilization of eGovernment in the intergovernmental forums to promote cooperative governance.</p>
120

Akroasis der akustische Sinnesbereich in der griechischen Literatur bis zum Ende der klassischen Zeit /

Wille, Günther. January 1900 (has links)
Habilitation Thesis--Universität Tübingen, 1958. / Includes bibliographical references (p. 1115-1120) and index.

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