57 search hits
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Stability Analysis of Unconstrained Receding Horizon Control Schemes
(2011)
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Karl Worthmann
- In this thesis we are concerned with receding horizon control (RHC), also known as model predictive control. In particular, schemes which neither incorporate terminal constraints nor costs are considered. Our goal is to ensure a relaxed Lyapunov inequality which allows to conclude asymptotic stability of the RHC closed loop and, in addition, to quantify the loss of performance in comparison to infinite horizon optimal control. To this end, a (stability) condition is derived based on a controllability assumption. Then, a sensitivity analysis is carried out with respect to the most important parameters in our RHC strategy: the prediction and the control horizon. Here, the proposed stability condition is exploited in order to deduce guidelines to suitably design receding horizon stage costs. Furthermore, symmetry and monotonicity properties are rigorously shown which pave the way in order to develop algorithms such that the prediction horizon and, thus, the computational costs can be reduced while maintaining a desired performance guarantee.
Since many practically relevant discrete time systems are induced by sampled differential equations, effects linked to employing faster sampling and, thus, more accurate discretizations are analyzed. In this context a growth condition which may, e.g., reflect continuity properties, is introduced and the proposed methodology is generalized to this setting - a decisive step towards so called accumulated bounds which further improve our stability estimates and, thus, allow to derive tighter performance bounds. Moreover, the applicability and effectiveness of the presented results are demonstrated by several examples including a class of reaction diffusion equations.
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Impact of Oxygen and Pesticides on Microbial Cellulose Degradation in Aerated Agricultural Soils: A Microscaled Analysis of Processes and Prokaryotic Populations
(2011)
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Stefanie Schellenberger
- The polysaccharide cellulose is a major component of organic matter in terrestrial ecosystems and its mineralization drives carbon fluxes in soil. The degradation of plant-derived saccharides (e.g., cellulose, cellobiose, and glucose) is catalysed by a huge diversity of aerobic and anaerobic microorganisms (including Bacteria, fungi, and protists), but there is limited information about their phylogenetic identities and their in situ relevance in soil. Soil is a heterogeneous habitat in which oxic and anoxic microzones co-occur, and in which the distribution of O2 can change rapidly. Hence, the availability of O2 is an important factor that determines the activity of the saccharide-degrading community in microzones of aerated soil. Likewise, the accumulation of potential toxic pesticides in agricultural ecosystems might influence microbial activity. It is not resolved how active cellulolytic and saccharolytic taxa respond to rapid changes in the availabilities of O2. Furthermore, it is unclear if pesticides impact on the degradation of cellulose and cellulose-linked processes, and influence the activity of active saccharide-utilizing microorganisms. Hence, this study first identified cellulolytic and saccharolytic aerobic and anaerobic Prokaryotes that catalyzed the degradation of supplemented [13C]-labeled saccharides by 16S rRNA stable isotope probing. The metabolic response of major bacterial taxa to pesticides and fluctuating availabilities of O2 was further analyzed with taxon-specific qPCR assays. Eukaryotes that contributed to soil carbon flux were identified by targeting 18S rRNA genes by the collaborative group of Dr. A. Chatzinotas at the Helmholtz Centre (UFZ) in Leipzig. Cellulose, cellobiose, and glucose were mineralized to carbon dioxide under oxic conditions, whereas different fermentation products accumulated under anoxic conditions. Fermentations occurred concomitant with the apparent reduction of nitrate and ferric iron. The degradation of supplemented saccharides was stable under oxic and anoxic conditions. Archaea were no active constituents of the cellulose-degrading community in the investigated soil. [13C]-cellulose was mainly degraded by Kineosporiaceae (Actinobacteria), the cellulolytic taxon Cluster III Clostridiaceae (Firmicutes), and the new family-level taxon 'Cellu1-3' (Bacteroidetes) under anoxic conditions. Under oxic conditions, the new family-level taxa 'Sphingo1-4' (Bacteroidetes) and 'Deha1' (Chloroflexi), and Planctomycetaceae (Planctomycetes) were involved. Active community members in [13C]-cellobiose and [13C]-glucose treatments differed from those in [13C]-cellulose treatments, and were selectively activated by O2. Twenty-eight of the 48 labeled bacterial family-level taxa did not closely affiliate with cultured species. Labeled Eukaryotes belonged to the families Bodonidae, Eustigmataceae, Mallomonadaceae, Opistonectidae, unclassified Chrysophyceae, and unclassified Stramenopiles. These families inhabit autotrophic algae and bacteriovorus flagellates. It is likely that these active Eukaryotes were labeled by incorporation of [13C]-carbon derived from grazing on active cellulolytic and saccharolytic soil bacteria. Fungi were not labeled in stable isotope probing experiments. The pesticides Bentazon, MCPA and Nonylphenol impaired cellulose-linked microbial processes only at pesticide concentrations far above the recommended rate. The impairment was most pronounced under anoxic conditions. Planctomycetaceae and the new family-level taxon 'Sphingo1-4' were sensitive to pesticide addition under oxic conditions, whereas Cluster I Clostridiaceae and the new family-level taxon 'Cellu1-3' were reduced under anoxic conditions. Nevertheless, the impact of pesticides on the degradation of saccharides at in situ-relevant concentrations seems to be minimal. These collective findings suggest that (i) a large uncultured diversity of Bacteria was involved in the degradation of cellulose, (ii) O2 selectively activates different cellulolytic and saccharolytic taxa, (iii) Cluster III Clostridiaceae, and the new family-level taxa 'Sphingo1-4' and 'Cellu1-3' represent the major cellulolytic constituents of the microbial community in the investigated agricultural soil, whereas Cluster I Clostridiaceae, Intrasporangiaceae and Micrococcaceae are saccharolytic satellite organisms that utilize cellulose-derived carbon, and (iv) the degradation of plant-derived saccharides is a community function that is stabilized by the rapid response of active bacterial taxa and independent of fluctuating availabilities of O2 and of pesticide application.
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The BabelNEG System - A Protocol-generic Infrastructure for Electronic SLA Negotiations in the Internet of Services
(2011)
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Sebastian Hudert
- Visions of the next-generation Internet of Services are driven by digital resources traded on a global scope. For the resulting economic setting, automated on-line techniques for handling services and resources themselves, for advertising and discovering as well as for the on-the-fly negotiation of proper terms for their use are needed. Hence, a flexible infrastructure for the respective management of services and associated service level agreements is mandatory. This thesis presents the results of my dissertation project. They comprise a service infrastructure, able to support the structured discovery and protocol-generic negotiation of electronic service level agreements (SLAs) and thus services themselves.
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The Effects of Project Management Mechanisms on Innovation Performance in Hi-Tech Firms: Mediation of Teamwork Processes and Moderating Effects of Different Team Members’ Cultural Values
(2011)
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Aim-Orn Imcharoen
- High tech firms increasingly form innovation projects composed of team members with different cultural backgrounds to respond to their customers’ needs. Prior studies have regarded these cross cultural innovation projects as an important instrument for developing innovative products, yet little effort has been investigated on the issue of the effect of project management mechanisms (autonomy and control) on these projects and the impacts of team members’ cultural backgrounds on different project management mechanisms. Moreover, prior studies have neglected to bridge the gap between the effect of these project management mechanisms on communication and coordination of teamwork processes. Therefore, this study aims to fulfill the gaps in project management and cross cultural study by exploring the effects of different project management mechanisms on several types of innovation performance. In particular, it examines the relationships of these project management mechanisms on innovation performance mediated by the teamwork processes and moderated by the different backgrounds of team members represented by their cultural values. Structural equation modelling was used to test all hypotheses from 434 new product development project team members. The results indicated that control mechanisms had stronger effects on innovation performance than providing autonomy. Additionally, the study showed that all project management mechanisms (autonomy and control mechanisms) had indirect effects on radical innovation and project efficiency through communication and coordination. However, these control mechanisms had indirect impacts on incremental innovation only through coordination but not communication. Importantly, this study revealed that control mechanisms could apply to the team members with different cultural backgrounds in encouraging higher innovation performance. In order to enhance higher innovation performance, the suggestions to apply the appropriate project management mechanisms to their team members with different cultural backgrounds are provided.
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Major element diffusion in garnet and the exsolution of majoritic garnet from aluminous enstatite in Earth's Upper Mantle
(2011)
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Willem L. van Mierlo
- Majorite is a high pressure polymorph of enstatite with the garnet structure. The amount of enstatite that can be dissolved in garnet as a majorite component increases significantly with pressure, and therefore, majoritic garnet is thought to be a major constituent of the Earth's transition zone. The transport properties of majoritic garnet are, however, not well constrained at the moment. The magnitude of the diffusivity of the majorite component in garnet influences our understanding of the homogenization time scale of Earth's mantle. This is important in subduction zone settings, where the subducting oceanic crust will form a majorite inhomogeneity in the transition zone because of its higher aluminium content. Reaction kinetics in the dry transition zone are diffusion controlled and therefore an improved dataset on the diffusivity of the majorite component in garnet will enable us to better understand the of role of disequilibrium in subduction zones. This dissertation therefore reports the results of diffusion experiments on garnet. Diffusion experiments have been conducted with diffusion couples of majoritic garnet – Dora Maira pyrope, Dora Maira pyrope and Ötztal almandine and Ötztal almandine and majoritic garnet in a multi-anvil press between 1400 – 1900 °C and 12 – 20 GPa. The diffusion experiments with the majoritic garnet – Dora Maira pyrope garnet couples show that the diffusion of the majorite component in garnet is very slow, comparable to the diffusivity of silicon in wadsleyite and ringwoodite. The activation energy, activation volume and the pre-exponential for diffusion of the majorite component in garnet were determined to be 241 ± 54 kJ mol-1, 3.3 ± 0.1 cm3 mol-1 and 2.3 x 10-7 cm2 s-1, respectively. The diffusivity of the majorite component in garnet was determined to be 2-3 orders of magnitude slower than the self-diffusivity of Mg, Fe and Ca in garnet at the same conditions. Also Fe – Mg interdiffusion appeared to be significantly faster in majoritic garnet than in almandine garnet. Comparison with diffusion data on wadsleyite and ringwoodite shows that the diffusivity of the majorite component in garnet is very similar to that of the silicon self-diffusivity in the high-pressure polymorphs of olivine. The diffusion data obtained in this PhD has been used to determine whether solid state diffusion can homogenize the mantle after subduction. The diffusion distance of majoritic garnet has been calculated assuming grain boundary diffusion is the main mechanism, and it can be concluded that solid state diffusion is not able to homogenize the mantle. Next to this, a numerical model has been developed that determines whether diffusion of the majorite component is fast enough such that enstatite can dissolve into garnet during subduction. The results show that there will be a significant delay in case of the lower lithospheric mantle of the subducted slab. Due to its lower tempeture, the oceanic crust can, however, only dissolve a fraction of its pyroxene content and metastable pyroxene is thus expected to be present during subduction into the transition zone. The metastable presence of pyroxene leads to the question to what will happen to its aluminium contents as it is expected to get exsolved as garnet. Experiments were performed on aluminous enstatite at 1700 °C and 15 GPa. It is shown that majoritic garnet exsolves with the dominant topotactic relation being [001]clinoenstatite parallel to <111>garnet. Also a high density of stacking faults were observed with a displacement vector of R = ½[1 1 1] which can be explained by the transformation of HP high-clinoenstaite to low-clinoenstatite. Using the aluminium concentration profiles in clinoenstatite directly adjacent to the garnet precipitates the aluminium diffusivity in HP high-clinoenstatite was determined to be at least 6 x 10-11 cm2 s-1 at 1700 °C and 15 GPa. Comparison with data in diopside shows there is a discrepancy between diffusion data at high pressure and at low pressure, which might indicate a strong dependence of Al diffusivity in clinopyroxene on Ca contents or a change in diffusion mechanism. The results of the experiments conducted in this PhD study show that the low diffusivity of components in the Earth may severely hamper reaction kinetics in the Earth in the case where mass transport is required.
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Biphasic, Homogeneous, and Heterogeneous Hydrocarbon Conversion Reactions with Novel Aluminum Chloride Based Catalyst Systems
(2011)
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Matthias Dötterl
- The aim of this thesis was the development of novel cocatalysts for nickel catalyzed olefin dimerization and oligomerization reactions. For this purpose, cheap and air stable Lewis acidic chloroaluminate ionic liquids were the starting point for our investigations. Chloroaluminate melts are immiscible with hydrocarbon phases, and thus, biphasic oligomerization reactions allow a simple product separation by decantation. Unmodified chloroaluminate melts containing excess aluminum chloride predominantly catalyze non selective, cationic olefin oligomerization reactions. We found that the addition of triphenylamine, triphenylphosphine, or triphenylbismuth donors efficiently suppressed these side reactions to yield an ideal cheap and air stable ionic liquid cocatalyst for common nickel complexes used for olefin dimerization reactions. Especially triphenylbismuth was able to buffer slightly acidic chloroaluminate melts as well as highly acidic compositions. For nickel catalyzed dimerization reactions, we found that high buffering levels led to very high selectivities to give dimers, while systems with lower buffer contents were less selective but extremely active. Further, the melting points of acidic chloroaluminate melts were reduced upon addition of BiPh3. Thus, room temperature ionic liquid compositions derived from 100 different organic halide salts were screened towards their performances in nickel catalyzed selective propene dimerization reactions. Amines and BiPh3 used for such systems can be easily recovered by acid base extraction. Subsequently, an optimized composition was successfully employed to dimerize ethene, propene, 1-butene, and 1-hexene with high activities and selectivities. In order to minimize leaching effects and to investigate the interactions of a donor additive with the ionic liquid, a cationic para-trimethylammonium substituted triphenylphosphine derivative was synthesized and its interaction with the ionic liquid was monitored by means of 31P NMR spectroscopy. The concept of buffering highly Lewis acidic aluminum chloride centers was also transferred to binary homogeneous systems. In combination with stoichiometric amounts of BiPh3 or N-methylpyrrole buffer, aluminum chloride readily dissolved in toluene and methylene chloride to form a highly efficient, cheap and air stable cocatalyst for nickel catalyst precursors. Furthermore, the Lewis acidities of these binary homogeneous cocatalyst solutions could be tuned precisely by the choice of the solvent and the type and amount of buffer. Also, buffer addition efficiently suppressed isomerization reactions of the 1-olefinic products. The interaction of BiPh3 and N-methylpyrrole with AlCl3 was monitored by 27Al NMR spectroscopy. Further, the concept of buffering highly Lewis acidic aluminum species was extended to heterogeneous systems. The Lewis acidities of EtAlCl2 or Et2AlCl modified silicas were reduced by the addition of BiPh3 or N-methylpyrrole buffers. Buffered surface modified silica cocatalysts were successfully employed to activate nickel complexes for highly selective olefin dimerization reactions. Also, surface modified silica proved to be an ideal substrate for the formation of supported ionic liquid phase (SILP) cocatalyst systems used in nickel catalyzed olefin dimerization reactions. Buffered aluminum based cocatalysts were also able to activate a nickel diimine complex for biphasic, homogeneous, and heterogeneous ethene polymerization reactions. The polymer yields, molecular weights and polydispersities of the polyethylenes could be influenced by varying the solvent or the type and amount of buffer. We developed the first air stable cocatalyst systems solely based on aluminum chloride. With the right combination of solvent, type and amount of buffer, and process parameters, tailor-made homogeneous, heterogeneous and biphasic cocatalysts for numerous catalyst precursors can be designed. The systems proved to be highly active, long term stable and very selective for olefin dimerization or polymerization reactions. Due to the cheap components and the possibility to recycle buffers or halide salts, these new systems provide promising alternatives to established alkylaluminum based cocatalyst systems.
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The role of life history traits for coexistence and forest recovery after disturbance – a modelling perspective. Towards a better understanding of species-rich forests
(2011)
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Claudia Dislich
- Tropical forests are well known for their exceptional species richness – high diversity of plant species constitutes the basis for an equivalently rich fauna. An astonishing variety of plant life strategies has evolved, manifesting itself also in different compositions of life history traits in trees. This thesis investigates the role of tree life history traits (growth, mortality and recruitment) on different processes structuring species-rich forests. Our study system is a montane rainforest located in the Tropical Andes hotspot of biodiversity in southern Ecuador. Here, we find a mosaic of steep ridges and deeply incised valleys, covered with predominantly broadleaf forest. Forest structure and species composition differ considerably depending on altitude and topographic position. The forest cover is frequently interrupted by scars of landslides, which constitute an important type of natural disturbance in this ecosystem. We utilize ecological models as tools to gain deeper insights into key processes driving the maintenance of tree species richness and affecting forest recovery after landslides. The first part of this thesis concerns the question of species coexistence. We develop a theoretical model to analyze how different trade-offs between life history traits (tree growth, seed dispersal, tree mortality) affect tree species coexistence. We find that the considered trade-offs alone are not sufficient to explain long-term species coexistence. Additional 'stabilizing' mechanisms seem to be indispensable to facilitate coexistence in species-rich forests. Such mechanisms could result from biotic interactions that alter the relation between inter- and intra-specific competition depending on (local) species abundances (e.g. density-dependent mortality). Other possible coexistence mechanisms likely to be relevant to our particular study system are driven by external, abiotic factors like a complex topography resulting in locally differing habitat types (each supporting a different set of species), or the character of a prevailing disturbance regime (e.g. shallow landslides). In the second part of the thesis, we investigate the growth dynamics of the ridge forest in our study system. To this end, we utilize the process-based forest growth model FORMIND. We show that after calibration, the model successfully reproduces forest dynamics on different levels of complexity (e.g. basal area and stem size distribution). We then use this forest model to investigate the influence of landslide disturbances on forest dynamics both on the local scale of a single landslide and on the landscape scale. On landslide sites, changes in environmental conditions might lead to changes in different tree life history traits. We analyze scenarios with changes in different traits (tree recruitment, tree growth, tree mortality) and find that while tree biomass can recover within the first hundred years after a landslide, the time until forest structure and species composition is restored is considerably longer (approximately 200 years). Changes in different traits result in differing spatial distributions of tree biomass: reduced tree growth leads to a more homogeneous distribution of biomass, whereas reduced recruitment and increased mortality yield a more heterogeneous biomass distribution ('patchy' vegetation). On the landscape level, overall forest biomass is substantially reduced by landslides (8-14%), compared to only 2-3% of the area marked by visible traces of landslides. Thus this particular type of disturbance considerably influences the total forest carbon balance. In a complementary investigation we study abiotic and biotic factors that potentially trigger landslide occurrence in our study system. For this, we develop an extension of a standard physically-based model of slope stability. We find that due to the predominantly shallow tree roots, some of the observed landslides might be triggered by the vegetation itself. This thesis demonstrates that ecological models are useful tools to gain deeper insights into important processes shaping forest communities. They can be applied for theoretical questions such as the question of species coexistence, as well as for more applied, management related questions like predicting forest recovery after disturbances.
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Analysis of the "nurse-tree effect" of exotic shelter trees on the growth of the indigenous Podocarpus falcatus in an Ethiopian montane forest
(2011)
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Simone Strobl
- Ethiopian forests disappear with a rate of 1.1% per year due to the high demand of firewood and timber. To protect the remaining parts of the forests, exotic tree plantations were established 60 years ago. But there are considerable concerns regarding exotic plantations: they have the reputation to cause damage to the ecosystems due to high demand of water and nutrients. Considering the environmental deterioration caused by monotonous plantations of exotic tree species, the chance for indigenous woody plants to rejuvenate naturally in those plantations appears to be very small. But there are observations of indigenous tree species regenerating under the shelter of exotic tree plantations. This enhanced growth of indigenous saplings under the canopy of exotics has been termed “nurse-tree effect”. In the Munessa-Shashamene Forest, a tropical montane forest in Ethiopia consisting of plantations of exotic tree species and remnants of natural forest, regeneration and an enhanced growth of native Podocarpus falcatus saplings under the shelter of exotic tree plantations (Pinus and Eucalyptus) was observed. The focus of this work was to examine the different growth patterns of the saplings in the sites, the effects of the on the photosynthetic performance, and to compare the water relations of the Podocarpus saplings and those of the shelter-trees. The results of the study are summarized as follows: 1. Observations over two years showed that the relative growth rates of the saplings were more than three times higher in the Pinus plantation compared to the natural forest and the Eucalyptus plantation. Relative growth rates during the dry and the rainy season were more or less identical. 2. Investigation of the sub-canopy microclimate proved PAR and VPD as major components with impact on the photosynthetic performance of the saplings. 71% of the variations in photosynthetic carbon uptake could be explained by PAR and 4% by VPD. The Pinus plantation was slightly warmer and drier compared to the other two sites. Also highest PAR values of all sites were recorded in the Pinus plantation. In the Eucalyptus plantation, PAR values were the lowest of the three sites, caused by the two-tired canopy of coppiced and uncoppiced Eucalyptus trees. 3. For an assessment of the photosynthetic efficiency of the light climate, the efficacy of the shares of the irradiation from diffuse light and light flecks were determined from light curves. The time spans and distribution of these shares of the daily accumulated radiation were recorded from the daily courses. In the Pinus plantation, the efficiency of the radiation was relatively low (70%), because of the high intensity of the sunflecks, especially during the dry season. On cloudy days the efficiency was nearly 100% and resulted in an optimum photosynthetic performance of the saplings in the Pinus plantation. In the Eucalyptus plantation, the two-tired canopy resulted in a higher proportion of diffuse radiation and less daily accumulated PAR from sunflecks (46%). Also the efficiency of the actual radiation was the lowest of all sites on cloudy (72%) and sunny (53%) days. Daily accumulated PAR under the canopy of the natural forest was in between the other forest types. Such mid-position was also true for the share of the sunflecks and the CO2 uptake. Efficacy of the radiation was 80% on sunny and 86% on cloudy days. 4. Water relations can substantially affect the photosynthetic performance of plants. Especially in the afternoons of the dry season a decrease of photosynthetic CO2 uptake by the Podocarpus saplings became apparent. Whole-tree water consumption was determined by measuring sap flow with the Granier system. In principle sap flow (and transpiration) followed VPD. Comparison of the daily courses of transpiration and stomatal conductance and sap flow showed an earlier decrease of transpiration by the leaves of the saplings than by the shelter-trees, suggesting slight water shortage especially during the dry season. This interpretation is corroborated by the higher 13C values in the leaf tissue of the saplings from the Pinus plantation. Nevertheless severe drought stress did not occur during the two years of investigation. 5. The literature on the „nurse-tree effect“ mentions in particular Eucalyptus as shelter-tree, a finding which is not in agreement with the data of this study: Neither photosynthesis nor growth was enhanced compared with the control saplings in the natural forest. The discrepancy between this work and the literature can be solved when the management of the Eucalyptus plantation is considered. As long as the Podocarpus saplings grow under the two-tired canopy of the coppiced trees, growth is as slow as in the natural forest. However, after coppicing the light climate for the saplings ameliorates considerably and growth rates increase. Thus, a shelter-tree effect could also be observed under Eucalyptus, but its dynamics is stepwise rather than continuous.
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Composites of Spherical Polyelectrolyte Brushes and Nanoparticles – Synthesis, Characterization and Their Use in Catalysis
(2011)
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Frank Polzer
- The main objective of this thesis was the synthesis of colloidal stable managanese oxide nanoparticles (MnOxNP) for applications as a catalyst in aqueous solution. Spherical polyelectrolyte brushes (SPBs) with poly(2-trimethyl ammonium ethyl methacrylate chloride) (pTMAEMC) chains were used as support particles to stabilize the MnOxNP by immobilization. In a first step we established and investigated the method of the in situ generation of the MnOxNP within SPBs. It was found that no reducing agent is needed for the reduction of the permanganate precursors and that they do not react with the cationic polymer chains of the SPBs. By a combination of powder X-ray diffraction (PXRD), transmission electron microscopy (TEM) and cryogenic TEM (cryoTEM) it was found that the platelet-like MnOxNP are of layered topology built up from MnO6 octahedra denoted as birnessite. The PXRD patterns revealed a disorder along the stacking direction of the single layers of hexagonal sheets. Furthermore, the structure of the composite material observed by TEM strongly differs compared to that in cryoTEM micrographs. The composite material was furthermore analyzed by high resolution TEM (HRTEM) and X-ray absorption fine structure (XAFS) analysis. The qualitative X-ray absorption near-edge structure (XANES) analysis using reference compounds confirmed the crystallographic similarity of the MnOxNP to a c-disordered birnessite. The local structure of the MnOxNP was investigated by a quantitative extended X-ray absorption fine structure (EXAFS) analysis that revealed that no significant difference between the MnOxNP@SPB in aqueous solution and in the dried state. In general, the hexagonal sheets of edge-share MnO6 octahedra are compressed along the c-direction, that is, along the stacking direction. Additionally, a new kind of composite material composed of star-shaped pTMAEMC homopolymer and MnOxNP was synthesized and characterized To test the MnOxNP@SPB composite material for its catalytic activity, the oxidation of morin by hydrogen peroxide was established as a model reaction. It could be shown by UV/vis measurements that the rate of the decomposition is highly depending on the ratio between morin and the oxidant H2O2. This finding was modeled by a Langmuir-Hinshelwood reaction mechanism. The study proved the potential application of the composite material as a catalyst especially for water-based catalysis. Furthermore, a detailed kinetic analysis of the reduction of 4-nitrophenol by sodium borohydride using gold and platinum nanoparticles immobilized on SPBs has been conducted. In analogy to the work on the oxidative decomposition of morin, a Langmuir-Hinshelwood model was used for the description of the reaction mechanism. Using this model, the adsorption constants for both reactants as well as the rate constant of the surface reaction could be determined for both noble metal nanoparticles. This showed that the higher catalytic activity of Pt is mainly due to the higher rate constant of the surface reaction. Additionally, the induction period of the reduction of 4-nitrophenol could be assigned to a surface reconstructuring of the nanoparticles due to the adsorption of 4-nitrophenol. Finally, the synthesis of a novel zwitterionic SPB could be realized using aqueous atom transfer radical polymerization. These particles show a surprisingly high colloidal stability in aqueous medium though the poly(2-(methacryloyloxy)ethyl dimethyl-(3-sulfopropyl)ammonium hydroxide) (pMEDSAH) chains are not soluble in pure water. The solution behavior in water was furthermore studied by dynamic light scattering, TEM and cryoTEM proving the collapsed state of the brush layer. The zwitterionic shell undergoes an internal phase separation leading to a surface-near layer whereas only a minor part of the chains reaches further out into the solution. The collapse was explained by the formation of aggregates of monomer units by zwitterionic or hydrophobic interactions. It was shown that the zwitterionic shell swells upon the addition of high amounts of salts and/or upon increasing the temperature due to the presence of an upper critical solution temperature. In conclusion, this thesis presented a new method for the generation and stabilization of MnOxNP of layered topology using cationic SPBs. The mechanism of the in situ generation could be elucidated as well as the microscopic structure of the composite material in the aqueous dispersed state. Using state of the art characterization methods like XAFS, the local environment of the MnOxNP around the Mn absorber could be determined. The catalytic activity of the MnOxNP was studied in detail applying a Langmuir-Hinshelwood model to the catalytic degradation of morin. A similar study gave new insights into the reduction of 4-nitrophenol using noble metal nanoparticles applying a similar model. The synthesis and analysis of zwitterionic SPBs gave important information about their solution behavior.
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Climate change impacts on habitats and biodiversity :
From environmental envelope modelling to nature conservation strategies
(2011)
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Torsten Bittner
- Climate change will pose entirely new challenges for nature conservation. A literature study of 852 publications (between 2003 and 2010) illuminates this topic, examines driving research forces as well as focal points and shows recent research gaps. Here could be shown that changes in species distribution, diverse consequences for habitats, changing communities as well as biotic interactions and general aspects of diversity are the major challenges. The potential climatic modifications can alter deeply the distribution of animals and plants. Range changes due to recent climate change already exist and are traceable. In order to quantify such changes, environmental envelope modelling can be used. In addition to individual species, changes in distribution of more complex units are also conceivable. The present work mainly focuses on habitat types listed in the Annex I of the European Habitats Directive. To reveal the potential range changes of habitat types, two principally different modelling approaches have been developed. An indirect approach modelling the distribution of a habitat type using the distribution of its characteristic plant species and a direct approach, using the distribution of the habitat type itself. These two approaches were tested by modelling five grassland habitat types. Looking at the modelled results all habitats are projected to lose between 22% and 93% of their range in the ‘no dispersal’ scenario. Both approaches produce reasonable results. However, modelling an extensive set of habitat types using the indirect approach is currently not possible, because of the required but actually lacking amount of plant distribution data. Therefore, the direct approach is an appropriate instrument for modelling habitat types. Here, all 127 widespread terrestrial habitat types defined in the Annex I of the Habitats Directive were modelled and, resulting from this, a map of terrestrial habitat type diversity was calculated. Several habitat types are projected to lose many of their actually suitable areas, in particular bogs, rocky habitats, grassland and in part forests. Due to their developmental time or rather due to their special abiotic requirements, bogs and rocky habitats even lose under the assumption of a full dispersal scenario. However, most heath and grassland habitats are also projected to lose in the full dispersal scenario. Pooling all modelled results together, terrestrial habitat type diversity is shifting partly to mountain regions and the atlantic biogeographical region is projected to decrease in habitat type diversity. According to the Habitats Directive habitat types listed in Annex I are protected in ‘sites of community interest’ aiming to maintain or restore them at a favourable conservation status. Due to the projected changes a static nature conservation concept could face problems which particularly concern the coherence of the protected area network. This could lead to a loss of protective goods in spite of protected areas. To illustrate the potential problems and difficulties emerging with respect to spatial coherence of habitat types between protected areas, an analysis of spatial coherence under future conditions for a variety of habitat types in Germany was conducted. Here, a combination of environmental envelope modelling and graph theory is presented to assess the coherence of nature conservation networks. The possible incapacity of species to reach all climatically suitable areas is currently debated. Therefore, spatial scales are not only crucial for the coherence of protected areas but also for the question if future projected suitable areas could be colonized. Dispersal movements of species are only infrequently possible in our highly fragmented landscape. To answer this raising question, Odonata listed in the Habitats Directive with known dispersal distances were contemplated. The species Coenagrion ornatum, C. mercuriale and Ophiogomphus cecilia are projected to lose range when incorporating specific dispersal distances, while they are projected to extend their range in the unrestricted dispersal scenario. Furthermore, suitable climatic conditions tend to decline for Leucorrhinia albifrons and L. caudalis, whereas L. pectoralis is projected to gain distribution area assuming either species-specific or unrestricted dispersal. The nature conservation measure of translocation is an at least 100 years old methodology with pros and cons. In this thesis, the emerging problems and opportunities of this species preservation strategy are presented. Further, a new question about the ‘focal unit’ is pointed out as well as the problem of genetic variability and the aspect of pre-adopted subspecies. Moreover, a selective assisted colonisation not by moving species but ecotypes is referred.
