93 search hits
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Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS) in an Aquatic Ecosystem - Distribution and Fate
(2009)
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Anna Maria Becker
- Perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) belong to the family of perfluorinated surfactants (PFSs). They are widely distributed and persistent in the environment. For over 50 years, they have been used in numerous applications including paper and textile treatment, production of fluoropolymers, cosmetics and insecticides formulations, and fire fighting foams. They can enter the environment via direct and indirect emission sources such as manufacturing processes, use of commercial products containing PFSs, release of waste waters or degradation of precursor substances. Due to their physical-chemical properties, i.e. relatively good solubility, low volatility and stability under environmental conditions, water bodies are important sinks for these chemicals. The aim of this doctoral thesis was to elucidate sources, distribution and fate of PFOA and PFOS in an aquatic ecosystem that is not directly affected by fluorochemical production activity. The presented study was mainly focused on the river Roter Main, Bayreuth, Germany, and gives a good picture of the behaviour of PFOA and PFOS in such an aquatic ecosystem. In order to achieve the main goal, suitable analytical procedures for reliable quantification of trace amounts of the target analytes in different environmental matrices such as water, liquid and solid wastes, sediments, biological tissues, were developed or optimised. Each method included a solid-phase extraction step for analytes’ preconcentration and removal of interfering matrix, followed by quantitative determination via high performance liquid chromatography coupled to electrospray ionisation tandem mass spectrometery (HLPC-ESI-MS). Due to the possibility of ionisation suppression, isotope dilution or standard addition method was applied. Analysis of waste waters collected from four different waste water treatment plants (WWTPs) located in Upper Franconia, Bavaria, Germany, showed that the largest plant (Bayreuth) receiving waste waters of mostly commercial and industrial origin released the highest amount of PFOA and PFOS, whereas the smallest plant (Himmelkron) treating waste waters of only domestic source released the least. The monitoring of waste waters from the WWTP Bayreuth enabled to estimate the typical mass flows of PFOA and PFOS into river waters as about 1 and 5 g/day, respectively, showing that a plant of a medium-size, moderately industrialised city can be a major source of river pollution. Detailed investigation of PFOA and PFOS concentrations in liquid and solid wastes collected at different stages of the treatment process showed additional fluxes of these compounds inside the plant, likely due to the decomposition of their precursors. Analysis of sediments collected from the river receiving treated waste waters showed a significant increase in concentrations of both analytes downstream the outlet of the plant (up to 3- and 4-fold for PFOA and PFOS, respectively). PFOS concentrations were up to 40-fold higher in sediments than in river water, showing its higher adsorption potential in comparison to PFOA (max. sediment/water = 6). Once in the river, PFOS, and to a lower extent PFOA, can bioaccumulate in aquatic organisms. Although partially removed from water, they are still bioavailable for benthic organisms inhabiting the river thus entering the food chain. This was reflected in higher levels found in river goby - in comparison to chub - feeding on invertebrates living in the sediment. At the starting point of this doctoral thesis little information was available about environmental contamination with PFOA and PFOS in Germany, and it is the first study performed in Bavaria giving such a detailed picture of sources and fate of PFSs in a river ecosystem
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Theory and Practice of Reconciliation in Rwanda
(2009)
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Marcus Grohmann
- During recent years, scholars working on the peacebuilding process in Rwanda have often tended to single out specific aspects, for instance judicial responses to the genocide. Little research has been done, however, on the diversity of approaches that constitute the “reconciliation landscape” in Rwanda today. Basing itself on data from field research in 2006, this paper seeks to shed some light on the many programmes carried out in Rwanda related to reconciliation work. Emphasis is put on two case studies. While establishing a theoretical framework of the reconciliation process in the first part of the paper, the following chapters attempt to explain how this relates to the practice of reconciliation in the Rwandan context. The data collected suggest that in the face of political constraints, the Rwandan government must in part rely on civil society actors for the achievement of their goals of “unity and reconciliation”. The multitude of initiatives from actors with a wide range of motivations and approaches should be seen as complementary, while some may have to make up for the shortcomings and constraints of others.
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Synthesis of New Alkyn-1-ylsilanes. 1,1-Organoboration, 1,2-Hydroboration
(2009)
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Ezzat Khan
- New alkyn-1-ylsilanes were prepared, characterized and their use in 1,2-hydroboration, 1,1-organoboration reactions or combination of these two was demonstrated. Although the silanes were in general obtained as mixtures, they could be purified by fractional distillation or crystallization. Many of these silanes were fully characterized for the first time by modern NMR spectroscopic techniques and in some cases by X-ray structural analysis. The monoalkyn-1-yl(chloro)silanes were treated with BEt3 at 373-393 K for prolonged periods of time (up to 30 d), and the reactivity of the products was explored. For the first time the 1,2-hydroborating behavior of BEt3 was discovered in a series of reactions. Silanes containing two or more than two (up to four) alkyn-1-yl groups were used for the synthesis of different heterocyclic systems e.g., 1-silacyclobutenes, 1-silacyclopent-2-enes, siloles, borolenes, etc. Intermediates of sufficient stability and final products were studied by multinuclear NMR spectroscopy (1H, 11B, 13C, 29Si and 119Sn NMR). Numerous molecular structures were determined by X-ray structural analysis. Alkenes bearing Si-Cl function(s) are useful precursors for further transformations. They were converted into 1-silacyclobutene derivatives. Various intermediates on the way to 1-silacyclobutenes were discovered aiding in the understanding of the reaction mechanism. The aforementioned heterocycles were also prepared by reacting dialkyn-1-ylsilanes with 9-BBN at 353-373 K. In a first step, alkenyl(alkyn-1-yl)silanes are formed as a result of intermolecular 1,2-hydroboration followed by intramolecular 1,1-vinylboration at the same temperature to afford 1-silacyclobutene derivatives. The first molecular structure of one example was determined by X-ray structural analysis. Corresponding tetraalkyn-1-ylsilanes afforded 4-silaspiro[3,3]hepta-1,5-diene derivatives. The hydroborating reagent 9-BBN, on reaction with alkyn-1-yl(vinyl)silanes, leads to the 1-silacyclopent-2-ene derivatives at ambient temperature. Dialkyn-1-yl(divinyl)silanes gave 5-silaspiro[4,4]nona-1,6-diene derivatives. X-ray structures for representative examples 1-silacyclopent-2-ene as well as for spirosilanes were determined for the first time. Many dialkynylsilanes react with BEt3 and 9-Et-9-BBN under harsh reaction conditions (at 373-393 K for several days) to afford siloles as the result of a slow intermolecular 1,1-alkylboration followed by a fast intramolecular 1,1-vinylboration. This method is very simple and useful and fairly pure siloles were isolated. Protodeborylation using acetic acid as protic reagent was successful for a large number of novel heterocycles. New protodeborylated compounds were prepared and studied. The boron was found as part of a boron-oxygen bicyclic compound which was for the first time isolated and characterized by single crystal X-ray structural analysis.
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Les acteurs locaux du tourisme de désert au Maroc : Cas de lerg Chebbi et de Zagora-Mhamid
(2009)
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Asmae Bouaouinate
- Cette étude porte sur les acteurs locaux du tourisme de désert au Maroc, aussi bien à l erg Chebbi qu à Zagora-M hamid, dans un contexte où l Etat (le ministère du tourisme) est absent et où les initiatives locales, bonnes et moins bonnes foisonnent. Nous entendons par acteur l ensemble des prestataires de services au désert, tels : le chamelier, le (faux)guide, le chauffeur de Land-rover, le cuisinier, le propriétaire des unités d hébergement, le bivouaqueur, le caravanier, le bazariste, le « faux »-guide. L erg Chebbi est considéré comme une destination classique du tourisme de désert, car il s y est développé depuis les années 1970. Tandis que Zagora-M hamid s est développé une décennie plus tard à cause de la conjoncture politique défavorable de l époque qui ne favorisait pas l émergence d un tourisme de désert dans tout ce rayon géographique. La particularité de cette forme de tourisme qu´est le tourisme de désert réside dans son développement à partir d initiatives privées, locales, dans un milieu aride, refoulé au début dans l imaginaire marocain et considéré comme un espace marginalisé et enclavé mais qui s´est vu réapproprié la perception des touristes, notamment européens, et s est imposé comme espace mythique et comme produit touristique défini. Le désert marocain, proche du vieux continent et offrant la sécurité, s impose comme une destination du tourisme saharien quoique le Maroc ne dispose pas, en comparaison avec d autres pays sahariens, de très grands ergs, tels que l imaginaire du touriste européen se le représente. Et pourtant, en feuilletant les guides et les livres touristiques ainsi que les brochures des tour-opérateurs, il apparaît clair que cette partie du sud-est marocain est bien positionnée dans l échiquier touristique saharien. Le tourisme de désert au Maroc ou précisément à l erg Chebbi et à Zagora-M hamid est d une part considéré par l Etat, par le ministère du tourisme, comme une offre touristique qui étofferait les formules de voyages proposées dans le pays et par le ministère de l Intérieur, comme un moyen de fixer les populations locales dans leurs régions natales. Et d autre part il est considéré par les acteurs locaux essentiellement comme un moyen de gain économique et secondairement comme un moyen d´échange culturel et de valorisation de l identité locale mais dont ils deviennent, au fil des ans, fort dépendants. Tandis que pour les touristes, le tourisme de désert est cette forme de voyage sélective dont ils optent pour réaliser leur mythe : découvrir le Sahara. C est dans ce contexte qu on s est intéressé à approcher les efforts des acteurs locaux pour avoir de la clientèle, leurs réseaux et stratégies, leurs interactions avec les touristes et si derrière cette quête de gain la durabilité n est-elle pas mise en cause ?
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Dynamics and underlying processes of N2O and NO soil-atmosphere exchange under extreme meteorological boundary conditions
(2009)
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Stefanie Goldberg
- Climate models predict an increasing frequency and intensity of summer drought periods with subsequent heavy rainfall or soil frost and thaw events in mountain regions of Central Europe. These indirect effects of global warming may considerably influence soil microbial processes and in consequence emissions of climate-relevant trace gases. Regarding the nitrogen cycle, N2O and NO emissions are of concern, since they are involved in climate warming and soils represent a main source for these two gases. In spite of a growing number of studies on this subject, knowledge on effects of climate change on soil N2O and NO emissions is still scarce. This is mainly due to a hitherto poor mechanistic understanding of underlying processes within soil. In this thesis, the impact of extreme meteorological boundary conditions on N2O and NO fluxes in a Norway spruce forest and an acidic fen in the Fichtelgebirge area was investigated. The summer drought period and precipitation were experimentally increased in the forest and the fen over a 2-year span. Soil frost was induced in the forest by removal of the natural snow cover. The experiments were run in three replicates each and non-manipulated plots served as controls. Throughout the experiments, N2O and NO fluxes were recorded in weekly to monthly intervals. In addition, N2O concentrations and isotope signatures in soil air were measured along soil profiles to identify and localise the underlying biogenic production and consumption processes. Prolonged drought continuously reduced the N2O emission from the forest soil and even turned the soil temporarily into a sink for atmospheric N2O. Soil freezing and thawing caused a burst of N2O release contributing 84 % of the annual emission. Soil air N2O concentration and stable isotope profiles provide a new mechanistic explanation tool for all of these findings. N2O concentration in the soil air decreased in most cases exponentially from the subsoil to the soil surface. This observation identifies microbial activity in the subsoil (at >= 70 cm soil depth) as an additional source for N2O and diffusion to the soil surface along a concentration gradient. Furthermore, isotope abundance analysis identified simultaneous microbial N2O consumption (reduction to N2). Drought reduced the source strength of the organic layers for N2O while simultaneously the sink function of the mineral soil for N2O remained active. This resulted in a net N2O sink function of the forest soil under severe drought. Frost in the topsoil was the only exception for these trends in N2O concentration and isotope signature along soil profiles. Under conditions of soil frost the topsoil served no longer as a sink for N2O, thus leading to the observed burst in N2O emission. NO emissions from the forest soil exceeded the N2O emissions by up to two orders of magnitude. Prolonged drought in- or decreased NO emissions depending on the soil moisture content of the organic layers. Wetting after long-lasting drought periods – which turned out to be of less importance regarding N2O fluxes – strongly increased biogenic NO emissions and contributed 44 % to the annual loss. In contrast to the forest soil, NO fluxes from the fen were always one to two orders of magnitude lower than the N2O fluxes. These results support earlier findings that this highly reactive gas is either only marginally produced in the fen soil or undergoes chemical conversion before escaping from the soil surface. Nevertheless, water table reduction resulted in significantly increased net NO emission. Regarding N2O, this thesis suggests that summer drought periods may drastically increase emissions from minerotrophic fens depending on the reduction of water table height. Furthermore, heavy rainfall following drought periods caused short lived, but strong N2O peaks having significant impact on the annual N2O loss, that have not been reported so far. N-15 and O-18 isotope data provide evidence that these N2O peaks are due to newly produced N2O in the upper soil. This thesis documents the huge impact of extreme weather events on soil N2O and NO emissions and provides so far scarcely considered mechanistic explanations for these observations. A major outcome of this work is the finding of a hitherto unconsidered sink function of forest soils for atmospheric N2O, when soil net N2O production is compensated for by net consumption during long-lasting droughts. This work underlines the importance of investigating the fate of N2O within soil profiles next to flux measurements to improve the current knowledge on the complex interactions between meteorological boundary conditions and soil biogenic processes and thus help further upgrading global N2O balances.
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New Approaches to the Synthesis of Porous and/or High Surface Area Transition Metal Oxides
(2009)
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Ram Sai Yelamanchili
- We have explored the applicability of hypothesized approaches to the synthesis of porous and/or high surface area transition metal oxides. In addition, applicability and advantage of charged templates where strong Coulomb interactions favour the supramolecular arrangements/assembly were studied. The problems related with the dynamics of polymeric nanostructures for the synthesis of predesigned mesostructures could be avoided by crosslinking micelles, strictly speaking non-continuous phase in the bulk structure. Thereby, we presented a new approach for the grafting of Keggin POMs around the core-crosslinked PB-P2VP worm-like polymer templates (A 1 and 2). The produced POM-1 exhibits high dispersion, improved surface area and is thus expected to be useful in catalytic, electrochemical and biotechnology related applications. The general applicability of the method to other Keggin POMs and spherical polymer nanostructures were studied. Developed Keggin POMs-1 to 6 showed high dispersion of Keggin POM and surface areas. To the best of our knowledge, our approaches lead to Keggin POM nanocomposites with the highest surface areas reported todate. As-synthesized Keggin POM nanocomposites are amorphous. We have studied the removal of polymer template and crystallization of hybrid to corresponding metal oxides through step-wise calcinations under argon followed by air. We have presented another approach to the synthesis of high surface area and mesoporous keggin POM framework materials using amphiphilic PI-PDMAEMA block copolymers (A 3). The calcined mesoporous materials exhibit Keggin POM hexagonal pore structure with high keggin POM dispersion, improved surface area. These developed materials are expected to be useful in catalytic applications. A fundamental principle involved in this method is that an attractive interaction between the organic block copolymer and the keggin POM precursors is obtained via Coulombic interactions through in situ quaternization (protonation) of PDMAEMA part, which also ensure the formation of a homogeneous hybrid material without any macrophase separation. Further, step-wise calcinations under argon and air lead to evolution of mesoporous keggin POM material. To the best of our knowledge, this is the first hexagonally ordered mesoporous Keggin POM framework material. We have presented a low-temperature, non-hydrothermal synthesis route to rutile nanocrystals. Both rutile and anatase nanocrystals exhibit positive surface charges. In contrary to the above approaches where polymer templates are cationic and inorganic precursors are anionic, in this case, inorganic nanocrystals are cationic and polymer templates are anionic. In this approach, we have demonstrated that crystalline TiO2 nanocomposites with well-defined crystalline form could be directly synthesized at temperatures as low as 40 oC by mesostructuring the positively charged crystalline titania colloids over anionic spherical polyelectrolyte brush particles under aqueous conditions. Stepwise calcinations first under argon followed with a second calcination in air lead to the complete removal of polymer template without collapse and hollow porous spheres with crystalline framework are obtained. Porosity and surface areas increased dramatically after stepwise calcinations. Moreover, the porous rutile nanomaterials are photocatalytically active. We proved that our hypothesis to the synthesis of crystalline TiO2 nanocomposites with well-defined crystalline form and morphologie is feasible.
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One-dimensional hybrid nanomaterials based on cylindrical polymer brushes
(2009)
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Jiayin Yuan
- Cylindrical polymer brushes (CPBs) have been synthesized via the combination of anionic polymerization (for the backbone) and atom transfer radical polymerization (for the side chains) via the "grafting from" technique to achieve a narrow molecular weight distribution in both the backbone and the side chains. They were employed as template for the preparation of various types of one-dimensional (1D) polymer-inorganic hybrid nanomaterials. In the case of well-defined core-shell superstructured CPBs, depending on the aimed func-tional 1D hybrid nanostructures, different combinations of core and shell have been chosen. CPBs with a poly(3-acryloylpropyl trimethoxysilane) core and a poly(oligo(ethylene glycol) methacrylate) (POEGMA) shell were hydrolyzed by aqueous ammonia to produce water-soluble organo-silica hybrid nanowires. Since the trimethoxysilyl group was directly incorporated into the structure of the CPB, the addition of an external inorganic precursor in this case is avoided. These hybrid nanowires can form a lyotropic phase and serve as in-situ template for the pyrolytic formation of inorganic silica nanowires. Amphiphilic CPBs with a hydrophilic poly(acrylic acid) (PAA) core and a hydrophobic poly(n-butyl acrylate) (PnBA) shell were used as cylindrical templates and nanoreactors for the fabrication of CdSe semiconductor nanowires, due to the coordination ability of PAA with Cd2+ ions. Since the chemical structure of the PAA core was resumed, a double-loading process was carried out to load more CdSe nanoparticles into the CPB. AFM, TEM and UV-Vis characteriza-tions have proven the increasing amount of CdSe in the hybrids. Bishydrophilic CPBs with a poly(2-hydroxyethyl methacrylate) (PHEMA) core and a POEGMA shell were employed for the fabrication of a wormlike assembly of TiO2 semiconductor nanoparticles, forming a kind of titania-CPB hybrid nanowires. The titanium alkoxide precursor was introduced into the CPB via a transalcoholysis reaction between Ti(OC4H9)4 and the PHEMA block. The titania-CPB hybrid nanowires were used to generate anatase titania nanowires via pyrolysis at 550 °C. In general, all these inorganic nanowires templated by the core-shell CPB showed very uni-form size in length as well as diameter, due to the low molecular weight distribution of the CPB backbone and the side chains. The shell of the CPBs protects the fabricated inorganic nanowires from agglomeration, and in addition, renders the hybrid nanomaterials soluble in various sol-vents, including water. Poly(tert-methyl methacrylate) (PtBMA) homopolymer CPBs were used to support the forma-tion of uniform single-crystalline tellurium nanorods (length up to 822 nm, D ~ 36.1 + - 7.9 nm, aspect ratio from 2.7 to 22) at room temperature in THF. These rods with polymer attached on their surface are very stable in THF, and able to assemble tellurium or magnetite (Fe3O4) nanoparticles on the Te nanorods. The strategy to synthesize the Te nanorods was further ex-tended to linear PtBMA polymers with high molecular weight. The assembly of Fe3O4 nanoparti-cles on these Te nanorods was controlled by the stoichiometric ratio of the nanoparticles and nanorods. The Fe3O4-decorated Te nanorods are superparamagnetic. They were aligned in the presence of an external magnetic field when deposited from THF solution on a solid substrate. These novel one-dimensional hybrid nanomaterials based on CPBs can have many potential applications due to their electronic, optical, catalytic, semiconducting, and magnetic properties.
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Mechanism of carbon monoxide oxidation at the active site [Ni-4Fe-5S] cluster of carbon monoxide dehydrogenase from Carboxydothermus hydrogenoformans
(2009)
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Seung-Wook Ha
- The carbon monoxide (CO) metabolism relies on CO-dehydrogenase (CODH) that oxidizes CO with H2O to CO2. The crystal structures of the native Ni-Fe CODHIICh from the CO-grown thermophilic hydrogenogenic anaerobic bacterium Carboxydothermus hydrogenoformans reveal the active site as a [Ni-4Fe-5S] cluster C, carrying a bimetallic Ni-(mu2S)-Fe1 subsite with a bridging mu2S. This is the assumed site, where the oxidation of CO occurs. However, cluster C in other catalytically active Ni-Fe CODHs, from Rhodospirillum rubrum, Moorella thermoacetica, and recombinant CODHIICh expressed in Escherichia coli, for example, lack the ¥ì2S bridging Ni and Fe and contain a [Ni-4Fe-4S] form of a cluster C. The CO oxidation mechanism proposed based on crystallographical and biochemical studies involved the apical binding of CO at the nickel ion and the activation of water at the Fe1 ion of the cluster. In order to understand how CO interacts with the active site of native CODHIICh and what function does the bridging mu2S ligand fulfill in the enzyme, this research work focuses (i) on the interaction of cluster C with CO analogue potassium cyanide and analysis of the resulting type of nickel coordination and (ii) on the effect of sodium sulfide on the enzymatic activities of the native CODHIICh. Under catalytic conditions, cyanide acts as a competitive inhibitor of CODHIICh with respect to CO. Under N2 gas phase without electron acceptor (non-catalytic conditions), cyanide inhibits CODHIICh at highly reduced state (low redox-potentials - 500 mV), not at oxidized and slightly reduced (- 320 mV) states. Cyanide is not able to inhibit CODHIICh at reduced conditions (- 500 mV) when CO is present in the atmosphere. Therefore, the interaction of cyanide with reduced active site is expected to mimic the substrate. The binding of cyanide to the nickel ion has been discovered by x-ray absorption spectroscopy and confirmed by x-ray crystallography at the atomic resolution. This structure comprises an intermediate state of cluster C with CO in NiFe-CODHIICh. In this reaction, cyanide displaces the mu2S ligand giving rise to square-planar Ni with three S and one CN ligands. Cluster C and its protein environment undergo significant conformational changes induced by the binding of cyanide. Remarkably, Fe1 is displaced by 1,1 A, which reduces the Fe1 to Ni distance by 0,1 A. Electron densities of the CN ligand estimate an occupancy of 80 % and N atom of cyanide is in hydrogen bonding distance to His93 and Lys563, which are involved in proton transfer network. The binding of cyanide eliminates the bridging ¥ì2S from the cluster C yielding H2S, whereas the Ni-(mu2S)-Fe1 bridge is reformed after the catalytic cycle. It is likely that the high rate of CO oxidation (Kcat/Km of 1.7 x 109 M-1 s-1 at 70 ¡ÆC) and subsequent rebinding of mu2S would prevent the release of this ion from the protein by diffusion-controlled process (108 to 109 M-1 s-1). Cyanide-inhibited reduced CODHIICh is fully reactivated after the release of cyanide upon incubation at 70 ¡ÆC in the presence of low-potential reductants. The square-planar NiS4-coordinated cluster C is recovered by reactivation with sulfide, resulting in fully active enzyme, which includes the reformation of the Ni-(mu2S)-Fe1 bridge. Reactivation in the absence of sulfide generates the NiS3-coordination, lacking the mu2S ligand, and results in partially active enzyme. NiS3-coordinated cluster C is readily converted to NiS4-conformation by incorporation of sulfide. This conversion results in an increase of CO oxidation activity and a stabilization of cluster C at growth temperatures of the bacterium. In addition, the NiS4-conformation displays better catalytic efficiency (Kcat/Km) than NiS3 under low concentrations of CO. Inhibition of CO2 reduction activity by sulfide and higher CO2 reduction activity of NiS3-conformation suggest that the mu2S ligand retards the binding of CO2 to Ni. The crystal structure of CO2 loaded NiS3-cluster further convinces this assumption. The mu2S ligand accelerates the physiologically relevant CO oxidation, prevents inhibition by the product CO2, and inhibits a non-physiological CO2 reduction. These functions of the bridging mu2S are of physiologically importance for the metabolism of C. hydrogenoformans in highly reducing, CO-limited, and CO2-rich volcanic environments. Thus, it is concluded that the [Ni-4Fe-5S]-form of cluster C is the biologically relevant species in CODHIICh. A CO oxidation mechanism developed in this thesis is based on the structures of cyanide-bound intermediated state and CO2-bound state, as well as on the kinetic data on the reactivity of the enzyme with CO, potassium cyanide and sodium sulfide.
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Solution Properties of Polymer Nanostructures Studied by Scattering Techniques
(2009)
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Sreenath Bolisetty
- The main aim of this thesis is to understand the solution properties of flexible cylindrical polymer brushes, dendronized polymers and the thermosensitive microgel systems. The work comprises of different polymer nanostructured systems mainly studied by using the scattering techniques at the solution state . The importance of the studying the solution properties of the polymer systems can be related to the solution related applications. In this context the solution properties of the flexible cylindrical brushes and spherical microgels are studied at dilute and semi dilute concentration regime by using scattering techniques. The structure of the cylindrical polymer brushes and understanding the conformational changes of the flexible cylinders with the concentration was especially studied by using the small angle neutron scattering (SANS) and small angle light scattering (SLS). The change in dynamics of the cylindrical polymer brushes at the dilute and semi-dilute concentration regimes was studied by using the dynamic light scattering. The thermodynamic transition and kinetics of the cylindrical thermosensitive dendronized polymers to fully reversible mesoglobule structure formation at high temperature conditions (above than lower critical solution temperature) was studied by using the dynamic light scattering. The kinetics of the mesoglobule formation is carefully examined by using the time resolved dynamic light scattering measurements. The aim of this thesis is not only the study of the cylindrical brushes but also to understand the dynamics of the spherical microgel system. The last part of the thesis is focused on the solution dynamics (translational and the rotational dynamics) of the thermosensitive core shell microgel characterized by using the polarized and depolarized dynamic light scattering. In order to understand the shape fluctuations, the coupling phenomenon of the microgel and the influence in the rotational dynamics by embedding the nanoparticles within the thermosensitive shell is studied by the light scattering technique.
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Effiziente taskbasierte Programmausführung irregulärer Applikationen mit adaptiver Lastbalancierung
(2009)
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Ralf Hoffmann
- Zur parallelen Ausführung irregulärer Applikationen auf Parallelrechnern mit gemeinsamem Speicher eignet sich ein taskbasierter Ansatz, da durch eine dynamische Lastverteilung einzelner Tasks geeignet auf die irreguläre Abarbeitungsstruktur der Applikation reagiert werden kann. In dieser Arbeit wird das KOALA-Framework zur Abarbeitung feingranularer Tasks paralleler Programme vorgestellt. Es wird ein adaptiver Taskpool beschrieben, der effizient auf wechselnde Lastzustände innerhalb einer Applikation reagieren kann. Durch adaptiv angepasste Taskblöcke kann der adaptive Taskpool auch bei einer sehr großen Anzahl von ausführungsbereiten Tasks mit nur wenigen Operationen Taskumverteilungen durchführen, um die Berechnungen möglichst gleichmäßig auf die Prozessoren zu verteilen. Verschiedene irreguläre Applikationen werden getestet, um die unterschiedlichen Taskpool-Implementierungen zu vergleichen. Dabei erzielen die adaptiven Taskpools im Gegensatz zu konventionellen Taskpools bei allen untersuchten Applikationen gute Ergebnisse. Die einzelnen funktionalen Bestandteile des KOALA-Frameworks können ohne Änderungen in der Applikation ausgetauscht werden. Eine spezielle Implementierung der Lock-Komponente erlaubt so die Nutzung von Hardware-Operationen zur effizienten Synchronisation der beteiligten Threads. Weiterhin wird eine Profiling-Komponente vorgestellt, mit der die Taskstruktur einer Applikation analysiert werden kann. An einem Fallbeispiel werden Engstellen in einer Applikation identifiziert, durch deren Behebung eine erhebliche Verbesserung der Laufzeit erreicht werden konnte.
