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With his September 2015 speech “Breaking the tragedy of the horizon”, the President of the Central Bank of England, Mark Carney, put climate change on the agenda of financial market regulators. Until then, climate change had been framed mainly as a problem of negative externalities leading to long-term economic costs, which resulted in countries trying to keep the short-term costs of climate action to a minimum. Carney argued that climate change, as well as climate policy, can also lead to short-term financial risks, potentially causing strong adjustments in asset prices. Analysing the effect of a sustainability transition on the financial sector challenges traditional economic and financial analysis and requires a much deeper understanding of the interrelations between climate policy and financial markets.
This dissertation thus investigates the implications of climate policy for financial markets as well as the role of financial markets in a transition to a sustainable economy. The approach combines insights from macroeconomic and financial risk analysis. Following an introduction and classification in Chapter 1, Chapter 2 shows a macroeconomic analysis that combines ambitious climate targets (negative externality) with technological innovation (positive externality), adaptive expectations and an investment program, resulting in overall positive macroeconomic outcomes. The analysis also reveals the limitations of climate economic models in their representation of financial markets. Therefore, the subsequent part of this dissertation is concerned with the link between climate policies and financial markets. In Chapter 3, an empirical analysis of stock-market responses to the announcement of climate policy targets is performed to investigate impacts of climate policy on financial markets. Results show that 1) international climate negotiations have an effect on asset prices and 2) investors increasingly recognize transition risks in carbon-intensive investments. In Chapter 4, an analysis of equity markets and the interbank market shows that transition risks can potentially affect a large part of the equity market and that financial interconnections can amplify negative shocks. In Chapter 5, an analysis of mortgage loans shows how information on climate policy and the energy performance of buildings can be integrated into risk management and reflected in interest rates.
While costs of climate action have been explored at great depth, this dissertation offers two main contributions. First, it highlights the importance of a green investment program to strengthen the macroeconomic benefits of climate action. Second, it shows different approaches on how to integrate transition risks and opportunities into financial market analysis. Anticipating potential losses and gains in the value of financial assets as early as possible can make the financial system more resilient to transition risks and can stimulate investments into the decarbonization of the economy.
Gold at the nanoscale
(2020)
In this cumulative dissertation, I want to present my contributions to the field of plasmonic nanoparticle science. Plasmonic nanoparticles are characterised by resonances of the free electron gas around the spectral range of visible light. In recent years, they have evolved as promising components for light based nanocircuits, light harvesting, nanosensors, cancer therapies, and many more.
This work exhibits the articles I authored or co-authored in my time as PhD student at the University of Potsdam. The main focus lies on the coupling between localised plasmons and excitons in organic dyes. Plasmon–exciton coupling brings light–matter coupling to the nanoscale. This size reduction is accompanied by strong enhancements of the light field which can, among others, be utilised to enhance the spectroscopic footprint of molecules down to single molecule detection, improve the efficiency of solar cells, or establish lasing on the nanoscale. When the coupling exceeds all decay channels, the system enters the strong coupling regime. In this case, hybrid light–matter modes emerge utilisable as optical switches, in quantum networks, or as thresholdless lasers. The present work investigates plasmon–exciton coupling in gold–dye core–shell geometries and contains both fundamental insights and technical novelties. It presents a technique which reveals the anticrossing in coupled systems without manipulating the particles themselves. The method is used to investigate the relation between coupling strength and particle size. Additionally, the work demonstrates that pure extinction measurements can be insufficient when trying to assess the coupling regime. Moreover, the fundamental quantum electrodynamic effect of vacuum induced saturation is introduced. This effect causes the vacuum fluctuations to diminish the polarisability of molecules and has not yet been considered in the plasmonic context.
The work additionally discusses the reaction of gold nanoparticles to optical heating. Such knowledge is of great importance for all potential optical applications utilising plasmonic nanoparticles since optical excitation always generates heat. This heat can induce a change in the optical properties, but also mechanical changes up to melting can occur. Here, the change of spectra in coupled plasmon–exciton particles is discussed and explained with a precise model. Moreover, the work discusses the behaviour of gold nanotriangles exposed to optical heating. In a pump–probe measurement, X-ray probe pulses directly monitored the particles’ breathing modes. In another experiment, the triangles were exposed to cw laser radiation with varying intensities and illumination areas. X-ray diffraction directly measured the particles’ temperature. Particle melting was investigated with surface enhanced Raman spectroscopy and SEM imaging demonstrating that larger illumination areas can cause melting at lower intensities. An elaborate methodological and theoretical introduction precedes the articles. This way, also readers without specialist’s knowledge get a concise and detailed overview of the theory and methods used in the articles. I introduce localised plasmons in metal nanoparticles of different shapes. For this work, the plasmons were mostly coupled to excitons in J-aggregates. Therefore, I discuss these aggregates of organic dyes with sharp and intense resonances and establish an understanding of the coupling between the two systems. For ab initio simulations of the coupled systems, models for the systems’ permittivites are presented, too. Moreover, the route to the sample fabrication – the dye coating of gold nanoparticles, their subsequent deposition on substrates, and the covering with polyelectrolytes – is presented together with the measurement methods that were used for the articles.
Perovskite solar cells have become one of the most studied systems in the quest for new, cheap and efficient solar cell materials. Within a decade device efficiencies have risen to >25% in single-junction and >29% in tandem devices on top of silicon. This rapid improvement was in many ways fortunate, as e. g. the energy levels of commonly used halide perovskites are compatible with already existing materials from other photovoltaic technologies such as dye-sensitized or organic solar cells. Despite this rapid success, fundamental working principles must be understood to allow concerted further improvements. This thesis focuses on a comprehensive understanding of recombination processes in functioning devices.
First the impact the energy level alignment between the perovskite and the electron transport layer based on fullerenes is investigated. This controversial topic is comprehensively addressed and recombination is mitigated through reducing the energy difference between the perovskite conduction band minimum and the LUMO of the fullerene. Additionally, an insulating blocking layer is introduced, which is even more effective in reducing this recombination, without compromising carrier collection and thus efficiency. With the rapid efficiency development (certified efficiencies have broken through the 20% ceiling) and thousands of researchers working on perovskite-based optoelectronic devices, reliable protocols on how to reach these efficiencies are lacking. Having established robust methods for >20% devices, while keeping track of possible pitfalls, a detailed description of the fabrication of perovskite solar cells at the highest efficiency level (>20%) is provided. The fabrication of low-temperature p-i-n structured devices is described, commenting on important factors such as practical experience, processing atmosphere & temperature, material purity and solution age. Analogous to reliable fabrication methods, a method to identify recombination losses is needed to further improve efficiencies. Thus, absolute photoluminescence is identified as a direct way to quantify the Quasi-Fermi level splitting of the perovskite absorber (1.21eV) and interfacial recombination losses the transport layers impose, reducing the latter to ~1.1eV. Implementing very thin interlayers at both the p- and n-interface (PFN-P2 and LiF, respectively), these losses are suppressed, enabling a VOC of up to 1.17eV. Optimizing the device dimensions and the bandgap, 20% devices with 1cm2 active area are demonstrated. Another important consideration is the solar cells’ stability if subjected to field-relevant stressors during operation. In particular these are heat, light, bias or a combination thereof. Perovskite layers – especially those incorporating organic cations – have been shown to degrade if subjected to these stressors. Keeping in mind that several interlayers have been successfully used to mitigate recombination losses, a family of perfluorinated self-assembled monolayers (X-PFCn, where X denotes I/Br and n = 7-12) are introduced as interlayers at the n-interface. Indeed, they reduce interfacial recombination losses enabling device efficiencies up to 21.3%. Even more importantly they improve the stability of the devices. The solar cells with IPFC10 are stable over 3000h stored in the ambient and withstand a harsh 250h of MPP at 85◦C without appreciable efficiency losses. To advance further and improve device efficiencies, a sound understanding of the photophysics of a device is imperative. Many experimental observations in recent years have however drawn an inconclusive picture, often suffering from technical of physical impediments, disguising e. g. capacitive discharge as recombination dynamics. To circumvent these obstacles, fully operational, highly efficient perovskites solar cells are investigated by a combination of multiple optical and optoelectronic probes, allowing to draw a conclusive picture of the recombination dynamics in operation. Supported by drift-diffusion simulations, the device recombination dynamics can be fully described by a combination of first-, second- and third-order recombination and JV curves as well as luminescence efficiencies over multiple illumination intensities are well described within the model. On this basis steady state carrier densities, effective recombination constants, densities-of-states and effective masses are calculated, putting the devices at the brink of the radiative regime. Moreover, a comprehensive review of recombination in state-of-the-art devices is given, highlighting the importance of interfaces in nonradiative recombination. Different strategies to assess these are discussed, before emphasizing successful strategies to reduce interfacial recombination and pointing towards the necessary steps to further improve device efficiency and stability. Overall, the main findings represent an advancement in understanding loss mechanisms in highly efficient solar cells. Different reliable optoelectronic techniques are used and interfacial losses are found to be of grave importance for both efficiency and stability. Addressing the interfaces, several interlayers are introduced, which mitigate recombination losses and degradation.
The field of gamma-ray astronomy opened a new window into the non-thermal universe that allows studying the acceleration sites of cosmic rays and the role of cosmic rays on evolutionary processes in galaxies. The detection of almost one hundred Galactic very-high-energy (VHE: 0.1−100TeV) gamma-ray sources in the Milky Way demonstrates that particle acceleration up to tens of TeV energies is a common phenomenon. Furthermore, the detection of VHE gamma rays from other galaxies has confirmed that cosmic rays are not exclusively accelerated in the Milky Way. The rapid development of gamma-ray astronomy in the past two decades has led to a transition from the detection and study of individual sources to source population studies. To answer the question, whether the VHE gamma-ray source population of the Milky Way is unique, observations of galaxies, for which individual sources can be resolved, are required. Such galaxies are the Magellanic Clouds, two satellite galaxies of the Milky Way, which have been surveyed by the H.E.S.S. experiment in the last decade. In this thesis, data from a total of 450 hours of H.E.S.S. observations towards the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are presented. During the analysis of the data sets, special emphasis is put on the evaluation of systematic uncertainties of the experiment in order to assure an unbiased flux estimation of the potential VHE gamma-ray sources of the Magellanic Clouds. A detailed analysis of the survey data revealed the detection of the gamma-ray binary LMCP3, the most powerful gamma-ray binary known so far, that is located in the LMC, and thus, increases the number of known VHE gamma-ray sources in the LMC to four. No other VHE gamma-ray source is detected in the Magellanic Clouds and integral flux upper limits are estimated. These flux upper limits are used to perform a source population study based on known VHE source classes and existing multi-wavelength catalogues. A comparison of the source populations of the Magellanic Clouds and the Milky Way revealed that no other source in the Magellanic Clouds is as bright as the most luminous VHE gamma-ray source in the LMC: the pulsar wind nebula N 157B, and that one-third of the source population of the Magellanic Clouds is less luminous than the other known VHE gamma-ray sources in the LMC. For only a couple of sources luminosity levels of Galactic VHE sources, that are more than one order of magnitude fainter than the detected sources in the LMC, are constrained. Based on the flux upper limits, differences on the TeV source populations in the Magellanic Clouds and the Milky Way as well as the importance of the source environments will be discussed.
Largescale patterns of global land use change are very frequently accompanied by natural habitat loss. To assess the consequences of habitat loss for the remaining natural and semi-natural biotopes, inclusion of cumulative effects at the landscape level is required. The interdisciplinary concept of vulnerability constitutes an appropriate assessment framework at the landscape level, though with few examples of its application for ecological assessments. A comprehensive biotope vulnerability analysis allows identification of areas most affected by landscape change and at the same time with the lowest chances of regeneration.
To this end, a series of ecological indicators were reviewed and developed. They measured spatial attributes of individual biotopes as well as some ecological and conservation characteristics of the respective resident species community. The final vulnerability index combined seven largely independent indicators, which covered exposure, sensitivity and adaptive capacity of biotopes to landscape changes. Results for biotope vulnerability were provided at the regional level. This seems to be an appropriate extent with relevance for spatial planning and designing the distribution of nature reserves.
Using the vulnerability scores calculated for the German federal state of Brandenburg, hot spots and clusters within and across the distinguished types of biotopes were analysed. Biotope types with high dependence on water availability, as well as biotopes of the open landscape containing woody plants (e.g., orchard meadows) are particularly vulnerable to landscape changes. In contrast, the majority of forest biotopes appear to be less vulnerable. Despite the appeal of such generalised statements for some biotope types, the distribution of values suggests that conservation measures for the majority of biotopes should be designed specifically for individual sites. Taken together, size, shape and spatial context of individual biotopes often had a dominant influence on the vulnerability score.
The implementation of biotope vulnerability analysis at the regional level indicated that large biotope datasets can be evaluated with high level of detail using geoinformatics. Drawing on previous work in landscape spatial analysis, the reproducible approach relies on transparent calculations of quantitative and qualitative indicators. At the same time, it provides a synoptic overview and information on the individual biotopes. It is expected to be most useful for nature conservation in combination with an understanding of population, species, and community attributes known for specific sites. The biotope vulnerability analysis facilitates a foresighted assessment of different land uses, aiding in identifying options to slow habitat loss to sustainable levels. It can also be incorporated into planning of restoration measures, guiding efforts to remedy ecological damage. Restoration of any specific site could yield synergies with the conservation objectives of other sites, through enhancing the habitat network or buffering against future landscape change.
Biotope vulnerability analysis could be developed in line with other important ecological concepts, such as resilience and adaptability, further extending the broad thematic scope of the vulnerability concept. Vulnerability can increasingly serve as a common framework for the interdisciplinary research necessary to solve major societal challenges.
Cardiac valves are essential for the continuous and unidirectional flow of blood throughout the body. During embryonic development, their formation is strictly connected to the mechanical forces exerted by blood flow. The endocardium that lines the interior of the heart is a specialized endothelial tissue and is highly sensitive to fluid shear stress. Endocardial cells harbor a signal transduction machinery required for the translation of these forces into biochemical signaling, which strongly impacts cardiac morphogenesis and physiology. To date, we lack a solid understanding on the mechanisms by which endocardial cells sense the dynamic mechanical stimuli and how they trigger different cellular responses. In the zebrafish embryo, endocardial cells at the atrioventricular canal respond to blood flow by rearranging from a monolayer to a double-layer, composed of a luminal cell population subjected to blood flow and an abluminal one that is not exposed to it. These early morphological changes lead to the formation of an immature valve leaflet. While previous studies mainly focused on genes that are positively regulated by shear stress, the mechanisms regulating cell behaviors and fates in cells that lack the stimulus of blood flow are largely unknown. One key discovery of my work is that the flow-sensitive Notch receptor and Krüppel-like factor (Klf) 2, one of the best characterized flow-regulated transcriptional factors, are activated by shear stress but that they function in two parallel signal transduction pathways. Each of these two pathways is essential for the rearrangement of atrioventricular cells into an immature double-layered valve leaflets. A second key discovery of my study is the finding that both Notch and Klf2 signaling negatively regulate the expression of the angiogenesis receptor Vegfr3/Flt4, which becomes restricted to abluminal endocardial cells of the valve leaflet. Within these cells, Flt4 downregulates the expressions of the cell adhesion proteins Alcam and VE-cadherin. A loss of Flt4 causes abluminal endocardial cells to ectopically express Notch, which is normally restricted to luminal cells, and impairs valve morphology. My study suggests that abluminal endocardial cells that do not experience mechanical stimuli loose Notch expression and this triggers expression of Flt4. In turn, Flt4 negatively regulates Notch on the abluminal side of the valve leaflet. These antagonistic signaling activities and fine-tuned gene regulatory mechanisms ultimately shape cardiac valve leaflets by inducing unique differences in the fates of endocardial cells.
The hepatokine FGF21 and the adipokine chemerin have been implicated as metabolic regulators and mediators of inter-tissue crosstalk. While FGF21 is associated with beneficial metabolic effects and is currently being tested as an emerging therapeutic for obesity and diabetes, chemerin is linked to inflammation-mediated insulin resistance. However, dietary regulation of both organokines and their role in tissue interaction needs further investigation.
The LEMBAS nutritional intervention study investigated the effects of two diets differing in their protein content in obese human subjects with non-alcoholic fatty liver disease (NAFLD). The study participants consumed hypocaloric diets containing either low (LP: 10 EN%, n = 10) or high (HP: 30 EN%, n = 9) dietary protein 3 weeks prior to bariatric surgery. Before and after the intervention the participants were anthropometrically assessed, blood samples were drawn, and hepatic fat content was determined by MRS. During bariatric surgery, paired subcutaneous and visceral adipose tissue biopsies as well as liver biopsies were collected. The aim of this thesis was to investigate circulating levels and tissue-specific regulation of (1) FGF21 and (2) chemerin in the LEMBAS cohort. The results were compared to data obtained in 92 metabolically healthy subjects with normal glucose tolerance and normal liver fat content.
(1) Serum FGF21 concentrations were elevated in the obese subjects, and strongly associated with intrahepatic lipids (IHL). In accordance, FGF21 serum concentrations increased with severity of NAFLD as determined histologically in the liver biopsies. Though both diets were successful in reducing IHL, the effect was more pronounced in the HP group. FGF21 serum concentrations and mRNA expression were bi-directionally regulated by dietary protein, independent from metabolic improvements. In accordance, in the healthy study subjects, serum FGF21 concentrations dropped by more than 60% in response to the HP diet. A short-term HP intervention confirmed the acute downregulation of FGF21 within 24 hours. Lastly, experiments in HepG2 cell cultures and primary murine hepatocytes identified nitrogen metabolites (NH4Cl and glutamine) to dose-dependently suppress FGF21 expression.
(2) Circulating chemerin concentrations were considerably elevated in the obese versus lean study participants and differently associated with markers of obesity and NAFLD in the two cohorts. The adipokine decreased in response to the hypocaloric interventions while an unhealthy high-fat diet induced a rise in chemerin serum levels. In the lean subjects, mRNA expression of RARRES2, encoding chemerin, was strongly and positively correlated with expression of several cytokines, including MCP1, TNFα, and IL6, as well as markers of macrophage infiltration in the subcutaneous fat depot. However, RARRES2 was not associated with any cytokine assessed in the obese subjects and the data indicated an involvement of chemerin not only in the onset but also resolution of inflammation. Analyses of the tissue biopsies and experiments in human primary adipocytes point towards a role of chemerin in adipogenesis while discrepancies between the in vivo and in vitro data were detected.
Taken together, the results of this thesis demonstrate that circulating FGF21 and chemerin levels are considerably elevated in obesity and responsive to dietary interventions. FGF21 was acutely and bi-directionally regulated by dietary protein in a hepatocyte-autonomous manner. Given that both, a lack in essential amino acids and excessive nitrogen intake, exert metabolic stress, FGF21 may serve as an endocrine signal for dietary protein balance. Lastly, the data revealed that chemerin is derailed in obesity and associated with obesity-related inflammation. However, future studies on chemerin should consider functional and regulatory differences between secreted and tissue-specific isoforms.
Die Praktische Fahrerlaubnisprüfung dient der Erfassung und Beurteilung der Fahrkompe-tenz von Fahrerlaubnisbewerbern. Die aus dieser Prüfung gewonnenen Rückschlüsse auf das Niveau der Fahrkompetenz sollen insbesondere auch der Weiterentwicklung des Bewerbers dienen. Bisher erhalten Bewerber nur bei nicht bestandener Praktischer Fahrerlaubnisprü-fung eine Auflistung der wichtigsten Fehler, die zum Nichtbestehen geführt haben. Für ein zielgerichtetes Weiterlernen ist es aber notwendig, dass die Ergebnisse der Leistungserfas-sung und der Leistungsbewertung gemäß prüfungsdidaktischer Grundsätze pädagogisch an-spruchsvoll an alle Fahranfänger (unabhängig vom Prüfungsergebnis) zurückgemeldet wer-den.
Das Ziel der vorliegenden Arbeit besteht darin, die Gestaltungsgrundlagen und einen Umset-zungsvorschlag für ein kompetenzbezogenes und lernförderliches Rückmeldesystem für die Praktische Fahrerlaubnisprüfung zu erarbeiten. Dieses Rückmeldesystem soll in der Praxis erprobt werden. Darüber hinaus sollen anhand einer Bewerberbefragung zur Nutzerzufrie-denheit Erkenntnisse für die Weiterentwicklung gewonnen werden. Der Entwicklungs- und Erprobungsprozess des optimierten Rückmeldesystems lässt sich in drei Projektphasen auf-teilen:
1. Im Zuge der Optimierungsarbeiten zur Praktischen Fahrerlaubnisprüfung wurde in der ersten Projektphase ein neues Rückmeldesystem erarbeitet, das aus einem kompetenz-bezogenen mündlichen Auswertungsgespräch und einer ergänzenden schriftlichen Rückmeldung einschließlich weiterführender Lernhinweise für alle Bewerber besteht. Dieses Rückmeldesystem soll einerseits die Fahranfänger dabei unterstützen, die Leis-tungsbewertung inhaltlich besser zu verstehen sowie ein zielgerichtetes Weiterlernen ermöglichen. Andererseits soll es die Bewerber dazu motivieren, die festgestellten Kompetenzdefizite weiter zu bearbeiten, und dadurch Lernzuwachs fördern.
2. Das Rückmeldesystem wurde in der zweiten Projektphase in verschiedenen Modell-
regionen Deutschlands anhand von ca. 9.000 realen Praktischen Fahrerlaubnisprüfun-gen erprobt. Die Fahrerlaubnisbewerber, die in den Modellregionen an einer optimier-ten Praktischen Fahrerlaubnisprüfung teilgenommen und somit eine schriftliche Rückmeldung gemäß der optimierten Vorgaben bzw. einen individuellen Zugangscode zum Downloadbereich erhalten haben, wurden zu einer Befragung eingeladen. Dabei wurden vor allem Aspekte der Akzeptanz und der Lernwirksamkeit aus Sicht der Be-werber erfasst. Ziel war es, die Qualität der verkehrspädagogischen Gestaltung des Rückmeldesystems und seinen Nutzen zu untersuchen, um die erprobte Rückmeldung weiterzuentwickeln. Für die Bewerberbefragung wurde eine Onlinebefragung mit ei-nem standardisierten Fragebogen durchgeführt.
3. Die Erprobungs- und Befragungsergebnisse dienten in der dritten Projektphase der Ableitung von Schlussfolgerungen für die Weiterentwicklung des Rückmeldesystems. Die vorliegenden Ergebnisse der Felderprobung deuten darauf hin, dass die Bereitstel-lung einer schriftlichen, ausführlichen Rückmeldung zu den Prüfungsleistungen der Praktischen Fahrerlaubnisprüfungen insgesamt als nützlich und gewinnbringend ange-sehen wird. Allerdings wurde auch deutlich, dass bezüglich der Umsetzung noch Op-timierungspotenzial besteht. Im Anschluss an die Erprobung wurde die schriftliche Rückmeldung daher – ausgehend von den Nutzererfahrungen während der Felderpro-bung – umfassend überarbeitet und eine revidierte Version vorgelegt.
Als Ergebnis der Arbeit liegt ein in mehreren Schritten entwickeltes, empirisch fundiertes und erprobtes Rückmeldesystem vor, das eine differenzierte Kompetenzrückmeldung er-möglicht. Die umfassende Rückmeldung bietet künftig einerseits eine verbesserte Ausgangs-lage für eine ggf. anschließende Wiederholungsprüfung und andererseits ist es dem Bewer-ber anhand der aufgezeigten Stärken und Schwächen auch nach einer bestandenen Prüfung möglich, diese Rückmeldung für das weitere Lernen zu nutzen.
Even though the majority of individuals know that exercising is healthy, a high percentage struggle to achieve the recommended amount of exercise. The (social-cognitive) theories that are commonly applied to explain exercise motivation refer to the assumption that people base their decisions mainly on rational reasoning. However, behavior is not only bound to reflection. In recent years, the role of automaticity and affect for exercise motivation has been increasingly discussed. In this dissertation, central assumptions of the affective–reflective theory of physical inactivity and exercise (ART; Brand & Ekkekakis, 2018), an exercise-specific dual-process theory that emphasizes the role of a momentary automatic affective reaction for exercise-decisions, were examined. The central aim of this dissertation was to investigate exercisers and non-exercisers automatic affective reactions to exercise-related stimuli (i.e., type-1 process). In particular, the two components of the ART’s type-1 process, that are, automatic associations with exercise and the automatic affective valuation to exercise, were under study.
In the first publication (Schinkoeth & Antoniewicz, 2017), research on automatic (evaluative) associations with exercise was summarized and evaluated in a systematic review. The results indicated that automatic associations with exercise appeared to be relevant predictors for exercise behavior and other exercise-related variables, providing evidence for a central assumption of the ART’s type-1 process. Furthermore, indirect methods seem to be suitable to assess automatic associations. The aim of the second publication (Schinkoeth, Weymar, & Brand, 2019) was to approach the somato-affective core of the automatic valuation of exercise using analysis of reactivity in vagal HRV while viewing exercise-related pictures. Results revealed that differences in exercise volume could be regressed on HRV reactivity. In light of the ART, these findings were interpreted as evidence of an inter-individual affective reaction elicited at the thought of exercise and triggered by exercise-stimuli. In the third publication (Schinkoeth & Brand, 2019, subm.), it was sought to disentangle and relate to each other the ART’s type-1 process components—automatic associations and the affective valuation of exercise. Automatic associations to exercise were assessed with a recoding-free variant of an implicit association test (IAT). Analysis of HRV reactivity was applied to approach a somatic component of the affective valuation, and facial reactions in a facial expression (FE) task served as indicators of the automatic affective reaction’s valence. Exercise behavior was assessed via self-report. The measurement of the affective valuation’s valence with the FE task did not work well in this study. HRV reactivity was predicted by the IAT score and did also statistically predict exercise behavior. These results thus confirm and expand upon the results of publication two and provide empirical evidence for the type-1 process, as defined in the ART. This dissertation advances the field of exercise psychology concerning the influence of automaticity and affect on exercise motivation. Moreover, both methodical implications and theoretical extensions for the ART can be derived from the results.
The current thesis is focused on the properties of graphene supported by metallic substrates and specifically on the behaviour of electrons in such systems. Methods of scanning tunneling microscopy, electron diffraction and photoemission spectroscopy were applied to study the structural and electronic properties of graphene. The purpose of the first part of this work is to introduce the most relevant aspects of graphene physics and the methodical background of experimental techniques used in the current thesis.
The scientific part of this work starts with the extensive study by means of scanning tunneling microscopy of the nanostructures that appear in Au intercalated graphene on Ni(111). This study was aimed to explore the possible structural explanations of the Rashba-type spin splitting of ~100 meV experimentally observed in this system — much larger than predicted by theory. It was demonstrated that gold can be intercalated under graphene not only as a dense monolayer, but also in the form of well-periodic arrays of nanoclusters, a structure previously not reported. Such nanocluster arrays are able to decouple graphene from the strongly interacting Ni substrate and render it quasi-free-standing, as demonstrated by our DFT study. At the same time calculations confirm strong enhancement of the proximity-induced SOI in graphene supported by such nanoclusters in comparison to monolayer gold. This effect, attributed to the reduced graphene-Au distance in the case of clusters, provides a large Rashba-type spin splitting of ~60 meV.
The obtained results not only provide a possible mechanism of SOI enhancement in this particular system, but they can be also generalized for graphene on other strongly interacting substrates intercalated by nanostructures of heavy noble d metals.
Even more intriguing is the proximity of graphene to heavy sp-metals that were predicted to induce an intrinsic SOI and realize a spin Hall effect in graphene. Bismuth is the heaviest stable sp-metal and its compounds demonstrate a plethora of exciting physical phenomena. This was the motivation behind the next part of the current thesis, where structural and electronic properties of a previously unreported phase of Bi-intercalated graphene on Ir(111) were studied by means of scanning tunneling microscopy, spin- and angle-resolved photoemission spectroscopy and electron diffraction. Photoemission experiments revealed a remarkable, nearly ideal graphene band structure with strongly suppressed signatures of interaction between graphene and the Ir(111) substrate, moreover, the characteristic moiré pattern observed in graphene on Ir(111) by electron diffraction and scanning tunneling microscopy was strongly suppressed after intercalation. The whole set of experimental data evidences that Bi forms a dense intercalated layer that efficiently decouples graphene from the substrate. The interaction manifests itself only in the n-type charge doping (~0.4 eV) and a relatively small band gap at the Dirac point (~190 meV). The origin of this minor band gap is quite intriguing and in this work it was possible to exclude a wide range of mechanisms that could be responsible for it, such as induced intrinsic spin-orbit interaction, hybridization with the substrate states and corrugation of the graphene lattice. The main origin of the band gap was attributed to the A-B symmetry breaking and this conclusion found support in the careful analysis of the interference effects in photoemission that provided the band gap estimate of ~140 meV.
While the previous chapters were focused on adjusting the properties of graphene by proximity to heavy metals, graphene on its own is a great object to study various physical effects at crystal surfaces. The final part of this work is devoted to a study of surface scattering resonances by means of photoemission spectroscopy, where this effect manifests itself as a distinct modulation of photoemission intensity. Though scattering resonances were widely studied in the past by means of electron diffraction, studies about their observation in photoemission experiments started to appear only recently and they are very scarce.
For a comprehensive study of scattering resonances graphene was selected as a versatile model system with adjustable properties. After the theoretical and historical introduction to the topic of scattering resonances follows a detailed description of the unusual features observed in the photoemission spectra obtained in this work and finally the equivalence between these features and scattering resonances is proven. The obtained photoemission results are in a good qualitative agreement with the existing theory, as verified by our calculations in the framework of the interference model. This simple model gives a suitable explanation for the general experimental observations.
The possibilities of engineering the scattering resonances were also explored. A systematic study of graphene on a wide range of substrates revealed that the energy position of the resonances is in a direct relation to the magnitude of charge transfer between graphene and the substrate. Moreover, it was demonstrated that the scattering resonances in graphene on Ir(111) can be suppressed by nanopatterning either by a superlattice of Ir nanoclusters or by atomic hydrogen. These effects were attributed to strong local variations of tork function and/or destruction of long-range order of thephene lattice. The tunability of scattering resonances can be applied for optoelectronic devices based on graphene. Moreover, the results of this study expand the general understanding of the phenomenon of scattering resonances and are applicable to many other materials besides graphene.
Cosa avviene quando coscienze linguistiche distinte, oltre ad essere separate dall’epoca, dall’area geografica di provenienza o dalla differenziazione sociale, dalle diverse dimensioni linguistiche, appartengono anche a domini semiotici diversi? È quel che accade ogni volta che comunichiamo in rete, l’interazione digitale è infatti l’ambito di comunicazione ibrido per eccellenza: in esso alla mescolanza di lingue diverse si sovrappone la mescolanza di codici diversi. Partendo dal presupposto che siano i nuovi bisogni espressivi e le nuove situazioni comunicative a spingere verso le innovazioni linguistiche, sembra dunque interessante tener conto del rilievo assunto dal repertorio visuale – e più in generale multimodale – nell’uso spontaneo dei nuovi media e constatare come le particolari strategie di costruzione del significato attualmente in atto non possano ormai più prescindere da queste seconde dimensioni. Del loro peso nell’uso digitale della lingua è bene avere consapevolezza per affrontare senza pregiudizi tutte le novità ad essa connesse. Un ruolo di centrale importanza nell’approccio al linguaggio verbale in Internet è legato alla funzione indessicale della lingua che, unito alla presenza di un archivio di riferimento di conoscenze del mondo condiviso, innesca un nuovo tipo d’inferenzialità nel ricevente. La conversazione attraverso i social network consente infatti azioni che non necessariamente sono presenti nello scambio vis-a-vis, ma che invece sono peculiari di Facebook, Twitter, G+, Instagram, Flickr e in generale dei social network: la condivisione di materiale multimediale di vario genere, l’opzione di richiamare i messaggi relativi a un tema specifico e la possibilità di glossarlo. Il materiale multimediale diventa così al tempo stesso parte integrante della comunicazione e modalità espressiva, focus del discorso e linguaggio metaforico condiviso. Questo lavoro di ricerca indaga come ambiti di ricerca diversi, e apparentemente distanti fra loro, possano interagire produttivamente con il panorama scientifico delle scienze del linguaggio, dell’immagine e della comunicazione, giungendo alla formulazione di un modello aggiornato dell'ibridazione linguistica che caratterizza la comunicazione in rete.
In recent years, a substantial number of psycholinguistic studies and of studies on acquired language impairments have investigated the case of morphologically complex words. These have provided evidence for what is known as ‘morphological decomposition’, i.e. a mechanism that decomposes complex words into their constituent morphemes during online processing. This is believed to be a fundamental, possibly universal mechanism of morphological processing, operating irrespective of a word’s specific properties.
However, current accounts of morphological decomposition are mostly based on evidence from suffixed words and compound words, while prefixed words have been comparably neglected. At the same time, it has been consistently observed that, across languages, prefixed words are less widespread than suffixed words. This cross-linguistic preference for suffixing morphology has been claimed to be grounded in language processing and language learning mechanisms. This would predict differences in how prefixed words are processed and therefore also affected in language impairments, challenging the predictions of the major accounts of morphological decomposition.
Against this background, the present thesis aims at reducing the gap between the accounts of morphological decomposition and the accounts of the suffixing preference, by providing a thorough empirical investigation of prefixed words. Prefixed words are examined in three different domains: (i) visual word processing in native speakers; (ii) visual word processing in non-native speakers; (iii) acquired morphological impairments. The processing studies employ the masked priming paradigm, tapping into early stages of visual word recognition. Instead, the studies on morphological impairments investigate the errors produced in reading aloud tasks.
As for native processing, the present work first focuses on derivation (Publication I), specifically investigating whether German prefixed derived words, both lexically restricted (e.g. inaktiv ‘inactive’) and unrestricted (e.g. unsauber ‘unclean’) can be efficiently decomposed. I then present a second study (Publication II) on a Bantu language, Setswana, which offers the unique opportunity of testing inflectional prefixes, and directly comparing priming with prefixed inflected primes (e.g. dikgeleke ‘experts’) to priming with prefixed derived primes (e.g. bokgeleke ‘talent’). With regard to non-native processing (Publication I), the priming effects obtained from the lexically restricted and unrestricted prefixed derivations in native speakers are additionally compared to the priming effects obtained in a group of non-native speakers of German. Finally, in the two studies on acquired morphological impairments, the thesis investigates whether prefixed derived words yield different error patterns than suffixed derived words (Publication III and IV).
For native speakers, the results show evidence for morphological decomposition of both types of prefixed words, i.e. lexically unrestricted and restricted derivations, as well as of prefixed inflected words. Furthermore, non-native speakers are also found to efficiently decompose prefixed derived words, with parallel results to the group of native speakers. I therefore conclude that, for the early stages of visual word recognition, the relative position of stem and affix in prefixed versus suffixed words does not affect how efficiently complex words are decomposed, either in native or in non-native processing. In the studies on acquired language impairments, instead, prefixes are consistently found to be more impaired than suffixes. This is explained in terms of a learnability disadvantage for prefixed words, which may cause weaker representations of the information encoded in affixes when these precede the stem (prefixes) as compared to when they follow it (suffixes). Based on the impairment profiles of the individual participants and on the nature of the task, this dissociation is assumed to emerge from later processing stages than those that are tapped into by masked priming. I therefore conclude that the different characteristics of prefixed and suffixed words do come into play at later processing stages, during which the lexical-semantic information contained in the different constituent morphemes is processed.
The findings presented in the four manuscripts significantly contribute to our current understanding of the mechanisms involved in processing prefixed words. Crucially, the thesis constrains the processing disadvantage for prefixed words to later processing stages, thereby suggesting that theories trying to establish links between language universals and processing mechanisms should more carefully consider the different stages involved in language processing and what factors are relevant for each specific stage.
Metal halide perovskites have merged as an attractive class of materials for photovoltaic applications due to their excellent optoelectronic properties. However, the long term stability is a roadblock for this class of material’s industrial pathway. Increasing evidence shows that intrinsic defects in perovskite promote material degradation. Consequently, understanding defect behaviours in perovskite materials is essential to further improve device stability and performance. This dissertation, hence, focuses on the topic of defect chemistry in halide perovskites.
The first part of the dissertation gives a brief overview of the defect properties in halide perovskite. Subsequently, the second part shows that doping methylammonium lead iodide with a small amount of alkaline earth metals (Sr and Mg) creates a higher quality, less defective material resulted in high open circuit voltages in both n-i-p and p-i-n architecture. It has been found that the mechanism of doping has two distinct regimes in which a low doping concentration enables the inclusion of the dopants into the lattice whereas higher doping concentrations lead to phase segregation. The material can be more n-doped in the low doping regime while being less n-doped in the high doping regime. The threshold of these two regimes is based on the atomic size of the dopants.
The next part of the dissertation examines the photo-induced degradation in methylammonium lead iodide. This degradation mechanism links closely to the formation and migration of ionic defects. After they are formed, these ionic defects can migrate, however, not freely depending on the defect concentration and their distribution. In fact, a highly concentrated defect region such as the grain boundaries can inhibit the migration of ionic defects. This has implications for material design as perovskite solar cells normally employ a polycrystalline thin-film which has a high density of grain boundary.
The final study presented in this PhD dissertation focuses on the stability of the state-of-the-art triple cation perovskite-based solar devices under external bias. Prolonged bias (more than three hours) is found to promote amorphization in halide perovskite. The amorphous phase is suspected to accumulate at the interfaces especially between the hole selective layer and perovskite. This amorphous phase inhibits the charge collection and severely affects the device performance. Nonetheless, the devices can recover after resting without bias in the dark. This amorphization is attributed to ionic defect migration most likely halides. This provides a new understanding of the potential degradation mechanisms in perovskite solar cells under operational conditions.
After endosymbiosis, chloroplasts lost most of their genome. Many former endosymbiotic genes are now nucleus-encoded and the products are re-imported post-translationally. Consequently, photosynthetic complexes are built of nucleus- and plastid-encoded subunits in a well-defined stoichiometry. In Chlamydomonas, the translation of chloroplast-encoded photosynthetic core subunits is feedback-regulated by the assembly state of the complexes they reside in. This process is called Control by Epistasy of Synthesis (CES) and enables the efficient production of photosynthetic core subunits in stoichiometric amounts. In chloroplasts of embryophytes, only Rubisco subunits have been shown to be feedback-regulated. That opens the question if there is additional CES regulation in embryophytes. I analyzed chloroplast gene expression in tobacco and Arabidopsis mutants with assembly defects for each photosynthetic complex to broadly answer this question. My results (i) confirmed CES within Rubisco and hint to potential translational feedback regulation in the synthesis of (ii) cytochrome b6f (Cyt b6f) and (iii) photosystem II (PSII) subunits. This work suggests a CES network in PSII that links psbD, psbA, psbB, psbE, and potentially psbH expression by a feedback mechanism that at least partially differs from that described in Chlamydomonas. Intriguingly, in the Cyt b6f complex, a positive feedback regulation that coordinates the synthesis of PetA and PetB was observed, which was not previously reported in Chlamydomonas. No evidence for CES interactions was found in the expression of NDH and ATP synthase subunits of embryophytes. Altogether, this work provides solid evidence for novel assembly-dependent feedback regulation mechanisms controlling the expression of photosynthetic genes in chloroplasts of embryophytes.
In order to obtain a comprehensive inventory of the rbcL and psbA RNA-binding proteomes (including factors that regulate their expression, especially factors involved in CES), an aptamer based affinity purification method was adapted and refined for the specific purification these transcripts from tobacco chloroplasts. To this end, three different aptamers (MS2, Sephadex ,and streptavidin binding) were stably introduced into the 3’ UTRs of psbA and rbcL by chloroplast transformation. RNA aptamer based purification and subsequent chip analysis (RAP Chip) demonstrated a strong enrichment of psbA and rbcL transcripts and currently, ongoing mass spectrometry analyses shall reveal potential regulatory factors. Furthermore, the suborganellar localization of MS2 tagged psbA and rbcL transcripts was analyzed by a combined affinity, immunology, and electron microscopy approach and demonstrated the potential of aptamer tags for the examination of the spatial distribution of chloroplast transcripts.
Depending on the biochemical and biotechnical approach, the aim of this work was to understand the mechanism of protein-glucan interactions in regulation and control of starch degradation. Although starch degradation starts with the phosphorylation process, the mechanisms by which this process is controlling and adjusting starch degradation are not yet fully understood. Phosphorylation is a major process performed by the two dikinases enzymes α-glucan, water dikinase (GWD) and phosphoglucan water dikinase (PWD). GWD and PWD enzymes phosphorylate the starch granule surface; thereby stimulate starch degradation by hydrolytic enzymes. Despite these important roles for GWD and PWD, so far the biochemical processes by which these enzymes are able to regulate and adjust the rate of phosphate incorporation into starch during the degradation process haven‘t been understood. Recently, some proteins were found associated with the starch granule. Two of these proteins are named Early Starvation Protein 1 (ESV1) and its homologue Like-Early Starvation Protein 1 (LESV). It was supposed that both are involved in the control of starch degradation, but their function has not been clearly known until now. To understand how ESV1 and LESV-glucan interactions are regulated and affect the starch breakdown, it was analyzed the influence of ESV1 and LESV proteins on the phosphorylating enzyme GWD and PWD and hydrolysing enzymes ISA, BAM, and AMY. However, the analysis determined the location of LESV and ESV1 in the chloroplast stroma of Arabidopsis. Mass spectrometry data predicted ESV1and LESV proteins as a product of the At1g42430 and At3g55760 genes with a predicted mass of ~50 kDa and ~66 kDa, respectively. The ChloroP program predicted that ESV1 lacks the chloroplast transit peptide, but it predicted the first 56 amino acids N-terminal region as a chloroplast transit peptide for LESV. Usually, the transit peptide is processed during transport of the proteins into plastids. Given that this processing is critical, two forms of each ESV1 and LESV were generated and purified, a full-length form and a truncated form that lacks the transit peptide, namely, (ESV1and tESV1) and (LESV and tLESV), respectively. Both protein forms were included in the analysis assays, but only slight differences in glucan binding and protein action between ESV1 and tESV1 were observed, while no differences in the glucan binding and effect on the GWD and PWD action were observed between LESV and tLESV. The results revealed that the presence of the N-terminal is not massively altering the action of ESV1 or LESV. Therefore, it was only used the ESV1 and tLESV forms data to explain the function of both proteins.
However, the analysis of the results revealed that LESV and ESV1 proteins bind strongly at the starch granule surface. Furthermore, not all of both proteins were released after their incubation with starches after washing the granules with 2% [w/v] SDS indicates to their binding to the deeper layers of the granule surface. Supporting of this finding comes after the binding of both proteins to starches after removing the free glucans chains from the surface by the action of ISA and BAM. Although both proteins are capable of binding to the starch structure, only LESV showed binding to amylose, while in ESV1, binding was not observed. The alteration of glucan structures at the starch granule surface is essential for the incorporation of phosphate into starch granule while the phosphorylation of starch by GWD and PWD increased after removing the free glucan chains by ISA. Furthermore, PWD showed the possibility of starch phosphorylation without prephosphorylation by GWD.
Biochemical studies on protein-glucan interactions between LESV or ESV1 with different types of starch showed a potentially important mechanism of regulating and adjusting the phosphorylation process while the binding of LESV and ESV1 leads to altering the glucan structures of starches, hence, render the effect of the action of dikinases enzymes (GWD and PWD) more able to control the rate of starch degradation. Despite the presence of ESV1 which revealed an antagonistic effect on the PWD action as the PWD action was decreased without prephosphorylation by GWD and increased after prephosphorylation by GWD (Chapter 4), PWD showed a significant reduction in its action with or without prephosphorylation by GWD in the presence of ESV1 whether separately or together with LESV (Chapter 5). However, the presence of LESV and ESV1 together revealed the same effect compared to the effect of each one alone on the phosphorylation process, therefore it is difficult to distinguish the specific function between them. However, non-interactions were detected between LESV and ESV1 or between each of them with GWD and PWD or between GWD and PWD indicating the independent work for these proteins. It was also observed that the alteration of the starch structure by LESV and ESV1 plays a role in adjusting starch degradation rates not only by affecting the dikinases but also by affecting some of the hydrolysing enzymes since it was found that the presence of LESV and ESV1leads to the reduction of the action of BAM, but does not abolish it.
Im Jahre 1960 behauptete Yamabe folgende Aussage bewiesen zu haben: Auf jeder kompakten Riemannschen Mannigfaltigkeit (M,g) der Dimension n ≥ 3 existiert eine zu g konform äquivalente Metrik mit konstanter Skalarkrümmung. Diese Aussage ist äquivalent zur Existenz einer Lösung einer bestimmten semilinearen elliptischen Differentialgleichung, der Yamabe-Gleichung. 1968 fand Trudinger einen Fehler in seinem Beweis und infolgedessen beschäftigten sich viele Mathematiker mit diesem nach Yamabe benannten Yamabe-Problem. In den 80er Jahren konnte durch die Arbeiten von Trudinger, Aubin und Schoen gezeigt werden, dass diese Aussage tatsächlich zutrifft. Dadurch ergeben sich viele Vorteile, z.B. kann beim Analysieren von konform invarianten partiellen Differentialgleichungen auf kompakten Riemannschen Mannigfaltigkeiten die Skalarkrümmung als konstant vorausgesetzt werden.
Es stellt sich nun die Frage, ob die entsprechende Aussage auch auf Lorentz-Mannigfaltigkeiten gilt. Das Lorentz'sche Yamabe Problem lautet somit: Existiert zu einer gegebenen räumlich kompakten global-hyperbolischen Lorentz-Mannigfaltigkeit (M,g) eine zu g konform äquivalente Metrik mit konstanter Skalarkrümmung? Das Ziel dieser Arbeit ist es, dieses Problem zu untersuchen.
Bei der sich aus dieser Fragestellung ergebenden Yamabe-Gleichung handelt es sich um eine semilineare Wellengleichung, deren Lösung eine positive glatte Funktion ist und aus der sich der konforme Faktor ergibt. Um die für die Behandlung des Yamabe-Problems benötigten Grundlagen so allgemein wie möglich zu halten, wird im ersten Teil dieser Arbeit die lokale Existenztheorie für beliebige semilineare Wellengleichungen für Schnitte auf Vektorbündeln im Rahmen eines Cauchy-Problems entwickelt. Hierzu wird der Umkehrsatz für Banachräume angewendet, um mithilfe von bereits existierenden Existenzergebnissen zu linearen Wellengleichungen, Existenzaussagen zu semilinearen Wellengleichungen machen zu können. Es wird bewiesen, dass, falls die Nichtlinearität bestimmte Bedingungen erfüllt, eine fast zeitglobale Lösung des Cauchy-Problems für kleine Anfangsdaten sowie eine zeitlokale Lösung für beliebige Anfangsdaten existiert.
Der zweite Teil der Arbeit befasst sich mit der Yamabe-Gleichung auf global-hyperbolischen Lorentz-Mannigfaltigkeiten. Zuerst wird gezeigt, dass die Nichtlinearität der Yamabe-Gleichung die geforderten Bedingungen aus dem ersten Teil erfüllt, so dass, falls die Skalarkrümmung der gegebenen Metrik nahe an einer Konstanten liegt, kleine Anfangsdaten existieren, so dass die Yamabe-Gleichung eine fast zeitglobale Lösung besitzt. Mithilfe von Energieabschätzungen wird anschließend für 4-dimensionale global-hyperbolische Lorentz-Mannigfaltigkeiten gezeigt, dass unter der Annahme, dass die konstante Skalarkrümmung der konform äquivalenten Metrik nichtpositiv ist, eine zeitglobale Lösung der Yamabe-Gleichung existiert, die allerdings nicht notwendigerweise positiv ist. Außerdem wird gezeigt, dass, falls die H2-Norm der Skalarkrümmung bezüglich der gegebenen Metrik auf einem kompakten Zeitintervall auf eine bestimmte Weise beschränkt ist, die Lösung positiv auf diesem Zeitintervall ist. Hierbei wird ebenfalls angenommen, dass die konstante Skalarkrümmung der konform äquivalenten Metrik nichtpositiv ist. Falls zusätzlich hierzu gilt, dass die Skalarkrümmung bezüglich der gegebenen Metrik negativ ist und die Metrik gewisse Bedingungen erfüllt, dann ist die Lösung für alle Zeiten in einem kompakten Zeitintervall positiv, auf dem der Gradient der Skalarkrümmung auf eine bestimmte Weise beschränkt ist. In beiden Fällen folgt unter den angeführten Bedingungen die Existenz einer zeitglobalen positiven Lösung, falls M = I x Σ für ein beschränktes offenes Intervall I ist. Zum Schluss wird für M = R x Σ ein Beispiel für die Nichtexistenz einer globalen positiven Lösung angeführt.
Ferruginous conditions were a prominent feature of the oceans throughout the Precambrian Eons and thus throughout much of Earth’s history. Organic matter mineralization and diagenesis within the ferruginous sediments that deposited from Earth’s early oceans likely played a key role in global biogeochemical cycling. Knowledge of organic matter mineralization in ferruginous sediments, however, remains almost entirely conceptual, as modern analogue environments are extremely rare and largely unstudied, to date. Lake Towuti on the island of Sulawesi, Indonesia is such an analogue environment and the purpose of this PhD project was to investigate the rates and pathways of organic matter mineralization in its ferruginous sediments.
Lake Towuti is the largest tectonic lake in Southeast Asia and is hosted in the mafic and ultramafic rocks of the East Sulawesi Ophiolite. It has a maximum water depth of 203 m and is weakly thermally stratified. A well-oygenated surface layer extends to 70 m depth, while waters below 130 m are persistently anoxic. Intensive weathering of the ultramafic catchment feeds the lake with large amounts of iron(oxy)hydroxides while the runoff contains only little sulfate, leading to sulfate-poor (< 20 µM) lake water and anoxic ferruginous conditions below 130 m. Such conditions are analogous to the ferruginous water columns that persisted throughout much of the Archean and Proterozoic eons. Short (< 35 cm) sediment cores were collected from different water depths corresponding to different bottom water redox conditions. Also, a drilling campaign of the International Continental Scientific Drilling Program (ICDP) retrieved a 114 m long sediment core dedicated for geomicrobiological investigations from a water depth of 153 m, well below the depth of oxygen penetration at the time of sampling. Samples collected from these sediment cores form the fundament of this thesis and were used to perform a suite of biogeochemical and microbiological analyses.
Geomirobiological investigations depend on uncontaminated samples. However, exploration of subsurface environments relies on drilling, which requires the use of a drilling fluid. Drilling fluid infiltration during drilling can not be avoided. Thus, in order to trace contamination of the sediment core and to identify uncontaminated samples for further analyses a simple and inexpensive technique for assessing contamination during drilling operations was developed and applied during the ICDP drilling campaign. This approach uses an aqeous fluorescent pigment dispersion commonly used in the paint industry as a particulate tracer. It has the same physical properties as conventionally used particulate tracers. However, the price is nearly four orders of magnitude lower solving the main problem of particulate tracer approaches. The approach requires only a minimum of equipment and allows for a rapid contamination assessment potentially even directly on site, while the senstitivity is in the range of already established approaches. Contaminated samples in the drill core were identified and not included for further geomicrobiological investigations.
Biogeochemical analyses of short sediment cores showed that Lake Towutis sediments are strongly depleted in electron acceptors commonly used in microbial organic matter mineralization (i.e. oxygen, nitrate, sulfate). Still, the sediments harbor high microbial cell densities, which are a function of redox conditions of Lake Towuti’s bottom water. In shallow water depths bottom water oxygenation leads to a higher input of labile organic matter and electron acceptors like sulfate and iron, which promotes a higher microbial abundance. Microbial analyses showed that a versatile microbial community with a potential to perform metabolisms related to iron and sulfate reduction, fermentation as well as methanogenesis inhabits Lake Towuti’s surface sediments.
Biogeochemical investigations of the upper 12 m of the 114 m sediment core showed that Lake Towuti’s sediment is extremely rich in iron with total concentrations up to 2500 µmol cm-3 (20 wt. %), which makes it the natural sedimentary environment with the highest total iron concentrations studied to date. In the complete or near absence of oxygen, nitrate and sulfate, organic matter mineralization in ferruginous sediments would be expected to proceed anaerobically via the energetically most favorable terminal electron acceptors available - in this case ferric iron. Astonishingly, however, methanogenesis is the dominant (>85 %) organic matter mineralization process in Lake Towuti’s sediment. Reactive ferric iron known to be available for microbial iron reduction is highly abundant throughout the upper 12 m and thus remained stable for at least 60.000 years. The produced methane is not oxidized anaerobically and diffuses out of the sediment into the water column. The proclivity towards methanogenesis, in these very iron-rich modern sediments, implies that methanogenesis may have played a more important role in organic matter mineralization thoughout the Precambrian than previously thought and thus could have been a key contributor to Earth’s early climate dynamics.
Over the whole sequence of the 114 m long sediment core siderites were identified and characterized using high-resolution microscopic and spectroscopic imaging together with microchemical and geochemical analyses. The data show early diagenetic growth of siderite crystals as a response to sedimentary organic matter mineralization. Microchemical zoning was identified in all siderite crystals. Siderite thus likely forms during diagenesis through growth on primary existing phases and the mineralogical and chemical features of these siderites are a function of changes in redox conditions of the pore water and sediment over time. Identification of microchemical zoning in ancient siderites deposited in the Precambrian may thus also be used to infer siderite growth histories in ancient sedimentary rocks including sedimentary iron formations.
Die Gesundheitswirtschaft in Deutschland steht vor zahlreichen Veränderungen in ihrem Umfeld. Dabei mangelt es der Krankenhauslandschaft an ärztlichem Personal. Es fehlt insbesondere an Arztstunden bei zugleich steigendem Bedarf an medizinischen Leistungen. Der demografische Wandel, Abwanderung ins Ausland (z. B. in die Schweiz) und Extrapolationen wie Feminisierung des Arztberufs und der Wertewandel respektive Generationenforschung begünstigen diese
Entwicklung. Zudem wird der Arbeitsplatz Krankenhaus zunehmend als unattraktiv von zukünftigen Arbeitnehmerkohorten angesehen. Nachwuchsärzte entscheiden sich bereits im Studium vermehrt gegen die kurative Medizin beziehungsweise gegen eine medizinisch-klinische Tätigkeit. Ein virulentes Beschaffungsproblem zeichnet sich ab, das es zu lösen gilt.
Das Forschungsziel ist die Entwicklung eines ganzheitlichen strategischen Lösungsansatzes mit marktorientierter Akzentuierung für den Arbeitgeber Krankenhaus. Dabei wird das Krankenhaus als wissens- und kompetenzintensive Dienstleistungsorganisation definiert. Employer Branding stellt den Bezugsrahmen eines marktorientierten Personalmanagements dar. Ein forschungstheoretischer Unterbau wird durch strategische Managementansätze integriert. Employer Branding schlägt die Brücke vom Market-based View zum Competence-based View und ist Markenmanagement im Kontext des strategischen Personalmanagements. In der vorliegenden Arbeit wird ein holistischer Bezugsrahmen vorgestellt, der die Wirkungszusammenhänge respektive Employer Branding darstellt. Das Herzstück ist die Employer Value Proposition, die auf der Markenidentität der Organisation basiert. Ziel des Employer Branding Ansatzes ist es, unter anderem eine präferenzerzeugende Wirkung im Prozess der Arbeitsplatzwahl sicherzustellen.
Die Zielrichtung und die Erkenntnis-Interessen erfordern einen breit angelegten Forschungsansatz, der qualitative und quantitative Methoden kombiniert. Ziel der leitfadengesteuerten Tiefeninterviews (exploratives Studiendesign) ist es, bestehende und noch zu entwickelnde Kompetenzstärken der Krankenhausorganisationen zu identifizieren. Bei der Stichprobe handelt es sich um ein „Typical Case Sampling“ (N=12). Defizitäre Befunde, welche Werte und Attraktivitätsfaktoren bei angehenden Ärzten ausgeprägt sind, werden bestätigt. In der Krankenhauslandschaft wird eine fragmentarische und reaktive Herangehensweise identifiziert, die die erfolgreiche Rekrutierung von qualifiziertem Krankenhauspersonal erschwert.
Durch die qualitative Marktforschung werden Anforderungen des Marktes – also zukünftiges, ärztliches Krankenhauspersonal – auf faktorenanalytischer Basis analysiert. Die Stichprobe (N=475) ist isomorph. Dabei wird der Prozess der Einstellungsbildung in das neobehavioristische Erklärungsmodell des Käuferverhaltens eingeordnet. Die Vereinbarkeit von Beruf, Karriere und Familie sowie die betriebliche Kinderbetreuung werden als Schlüsselkomponenten erkannt.
Wichtigste Arbeitswerte in Bezug auf einen attraktiven Arbeitgeber sind Verlässlichkeit, Verantwortung und Respekt. Diese Komponenten haben kommunikativen Nutzen und Differenzierungskraft. Schließlich bewerten Bewerber ein Krankenhaus positiver im Prozess der Arbeitsplatzwahl, je mehr die Werte des potentiellen Arbeitnehmers mit dem Werteprofil der Person übereinstimmen (Person-Organisation Fit).
Krankenhausorganisationen, die den Employer Branding Ansatz implementieren und als Chance zur Definition ihrer Stärken, ihrer Vorzüge und ihres Leistungsangebots als Arbeitgeber annehmen, rüsten sich für das verstärkte Werben um Jungmediziner. Schließlich setzt Employer Branding als marktorientierter Strategieansatz intern und extern Kräfte frei, die Differenzierungsvorteile gegenüber anderen Arbeitgebern bringen. Dabei hat Employer Branding positive Auswirkungen auf den Human Ressource-Bereich entlang der Wertschöpfungskette und mindert das gesamtwirtschaftliche Problem.
In nature, bacteria are found to reside in multicellular communities encased in self-produced extracellular matrices. Indeed, biofilms are the default lifestyle of the bacteria which cause persistent infections in humans. The biofilm assembly protects bacterial cells from desiccation and limits the effectiveness of antimicrobial treatments. A myriad of biomolecules in the extracellular matrix, including proteins, exopolysaccharides, lipids, extracellular DNA and other, form a dense and viscoelastic three dimensional network. Many studies emphasized that a destabilization of the mechanical integrity of biofilm architectures potentially eliminates the protective shield and renders bacteria more susceptible to the immune system and antibiotics. Pantoea stewartii is a plant pathogen which infects monocotyledons such as maize and sweet corn. These bacteria produce dense biofilms in the xylem of infected plants which cause wilting of plants and crops. Stewartan is an exopolysaccharide which is produced by Pantoea stewartii and secreted as the major component to the extracellular matrix. It consists of heptasaccharide repeating units with a high degree of polymerization (2-4 MDa). In this work, the physicochemical properties of stewartan were investigated to understand the contributions of this exopolysaccharide to the mechanical integrity and cohesiveness of Pantoea stewartii biofilms. Therefore, a coarse-grained model of stewartan was developed with computational techniques to obtain a model for its three dimensional structural features. Here, coarse-grained molecular dynamic simulations revealed that the exopolysaccharide forms a hydrogel in which the exopolysaccharide chains arrange into a three dimensional mesh-like network. Simulations at different concentrations were used to investigate the influence of the water content on the network formation. Stewartan was further purified from 72 h grown Pantoea stewartii biofilms and the diffusion of bacteriophage and differently-sized nanoparticles (which ranged from 1.1 to 193 nm diameter) was analyzed in reconstituted stewartan solutions. Fluorescence correlation spectroscopy and single-particle tracking revealed that the stewartan network impeded the mobility of a set of differently-sized fluorescent particles in a size-dependent manner. Diffusion of these particles became more anomalous, as characterized by fitting the diffusion data to an anomalous diffusion model, with increasing stewartan concentrations. Further bulk and microrheological experiments were used to analyze the transitions in stewartan fluid behavior and stewartan chain entanglements were described. Moreover, it was noticed, that a small fraction of bacteriophage particles was trapped in small-sized pores deviating from classical random walks which highlighted the structural heterogeneity of the stewartan network. Additionally, the mobility of fluorescent particles
also depended on the charge of the stewartan exopolysaccharide and a model of a molecular sieve for the stewartan network was proposed. The here reported structural features of the stewartan polymers were used to provide a detailed description of the mechanical properties of typically glycan-based biofilms such as the one from Pantoea stewartii.
In addition, the mechanical properties of the biofilm architecture are permanently sensed by the embedded bacteria and enzymatic modifications of the extracellular matrix take place to address environmental cues. Hence, in this work the influence of enzymatic degradation of the stewartan exopolysaccharides on the overall exopolysaccharide network structure was analyzed to describe relevant physiological processes in Pantoea stewartii biofilms. Here, the stewartan hydrolysis kinetics of the tailspike protein from the ΦEa1h bacteriophage, which is naturally found to infect Pantoea stewartii cells, was compared to WceF. The latter protein is expressed from the Pantoea stewartii stewartan biosynthesis gene cluster wce I-III. The degradation of stewartan by the ΦEa1h tailspike protein was shown to be much faster than the hydrolysis kinetics of WceF, although both enzymes cleaved the β D GalIII(1→3)-α-D-GalI glycosidic linkage from the stewartan backbone. Oligosaccharide fragments which were produced during the stewartan cleavage, were analyzed in size-exclusion chromatography and capillary electrophoresis. Bioinformatic studies and the analysis of a WceF crystal structure revealed a remarkably high structural similarity of both proteins thus unveiling WceF as a bacterial tailspike-like protein. As a consequence, WceF might play a role in stewartan chain length control in Pantoea stewartii biofilms.
Sekundäre Pflanzenstoffe und ihre gesundheitsfördernden Eigenschaften sind in den letzten zwei Jahrzehnten vielfach ernährungsphysiologisch untersucht und spezifische positive Effekte im humanen Organismus zum Teil sehr genau beschrieben worden. Zu den Carotinoiden zählend ist der sekundäre Pflanzenstoff Lutein insbesondere in der Prävention von ophthalmologischen Erkrankungen in den Mittelpunkt der Forschung gerückt. Das ausschließlich von Pflanzen und einigen Algen synthetisierte Xanthophyll wird über die pflanzliche Nahrung insbesondere grünes Blattgemüse in den humanen Organismus aufgenommen. Dort akkumuliert es bevorzugt im Makulapigment der Retina des menschlichen Auges und ist bedeutend im Prozess der Aufrechterhaltung der Funktionsfähigkeit der Photorezeptorzellen. Im Laufe des Alterns kann die Abnahme der Dichte des Makulapigments und der Abbau von Lutein beobachtet werden. Die dadurch eintretende Destabilisierung der Photorezeptorzellen im Zusammenhang mit einer veränderten Stoffwechsellage im alternden Organismus kann zur Ausprägung der altersbedingten Makuladegeneration (AMD) führen. Die pathologische Symptomatik der Augenerkrankung reicht vom Verlust der Sehschärfe bis hin zum irreversiblen Erblinden. Da therapeutische Mittel ausschließlich ein Fortschreiten verhindern, bestehen hier Forschungsansätze präventive Maßnahmen zu finden. Die Supplementierung von luteinhaltigen Präparaten bietet dabei einen Ansatzpunkt. Auf dem Markt finden sich bereits Nahrungsergänzungsmittel (NEM) mit Lutein in verschiedenen Applikationen. Limitierend ist dabei die Stabilität und Bioverfügbarkeit von Lutein, welches teilweise kostenintensiv und mit unbekannter Reinheit zu erwerben ist. Aus diesem Grund wäre die Verwendung von Luteinestern als die pflanzliche Speicherform des Luteins im Rahmen eines NEMs vorteilhaft. Neben ihrer natürlichen, höheren Stabilität sind Luteinester nachhaltig und kostengünstig einsetzbar.
In dieser Arbeit wurden physikochemische und ernährungsphysiologisch relevante Aspekte in dem Produktentwicklungsprozess eines NEMs mit Luteinestern in einer kolloidalen Formulierung untersucht. Die bisher einzigartige Anwendung von Luteinestern in einem Mundspray sollte die Aufnahme des Wirkstoffes insbesondere für ältere Menschen erleichtern und verbessern. Unter Beachtung der Ergebnisse und der ernährungsphysiologischen Bewertung sollten u.a. Empfehlungen für die Rezepturzusammensetzungen einer Miniemulsion (Emulsion mit Partikelgrößen <1,0 µm) gegeben werden. Eine Einschätzung der Bioverfügbarkeit der Luteinester aus den entwickelten, kolloidalen Formulierungen konnte anhand von Studien zur Resorption- und Absorptionsverfügbarkeit in vitro ermöglicht werden.
In physikalischen Untersuchungen wurden zunächst Basisbestandteile für die Formulierungen präzisiert. In ersten wirkstofffreien Musteremulsionen konnten ausgewählte Öle als Trägerphase sowie Emulgatoren und Löslichkeitsvermittler (Peptisatoren) hinsichtlich ihrer Eignung zur Bereitstellung einer Miniemulsion physikalisch geprüft werden. Die beste Stabilität und optimale Eigenschaften einer Miniemulsion zeigten sich bei der Verwendung von MCT-Öl (engl. medium chain triglyceride) bzw. Rapsöl in der Trägerphase sowie des Emulgators Tween® 80 (Tween 80) allein oder in Kombination mit dem Molkenproteinhydrolysat Biozate® 1 (Biozate 1).
Aus den physikalischen Untersuchungen der Musteremulsionen gingen die Präemulsionen als Prototypen hervor. Diese enthielten den Wirkstoff Lutein in verschiedenen Formen. So wurden Präemulsionen mit Lutein, mit Luteinestern sowie mit Lutein und Luteinestern konzipiert, welche den Emulgator Tween 80 oder die Kombination mit Biozate 1 enthielten. Bei der Herstellung der Präemulsionen führte die Anwendung der Emulgiertechniken Ultraschall mit anschließender Hochdruckhomogenisation zu den gewünschten Miniemulsionen. Beide eingesetzten Emulgatoren boten optimale Stabilisierungseffekte. Anschließend erfolgte die physikochemische Charakterisierung der Wirkstoffe. Insbesondere Luteinester aus Oleoresin erwiesen sich hier als stabil gegenüber verschiedenen Lagerungsbedingungen. Ebenso konnte bei einer kurzzeitigen Behandlung der Wirkstoffe unter spezifischen mechanischen, thermischen, sauren und basischen Bedingungen eine Stabilität von Lutein und Luteinestern gezeigt werden. Die Zugabe von Biozate 1 bot dabei nur für Lutein einen zusätzlichen Schutz. Bei längerer physikochemischer Behandlung unterlagen die in den Miniemulsionen eingebrachten Wirkstoffe moderaten Abbauvorgängen. Markant war deren Sensitivität gegenüber dem basischen Milieu. Im Rahmen der Rezepturentwicklung des NEMs war hier die Empfehlung, eine Miniemulsion mit einem leicht saurem pH-Milieu zum Schutz des Wirkstoffes durch kontrollierte Zugabe weiterer Inhaltstoffe zu gestalten.
Im weiteren Entwicklungsprozess des NEMs wurden Fertigrezepturen mit dem Wirkstoff Luteinester aufgestellt. Die alleinige Anwendung des Emulgators Biozate 1 zeigte sich dabei als ungeeignet. Die weiterhin zur Verfügung stehenden Fertigrezepturen enthielten in der Öl-phase neben dem Wirkstoff das MCT-ÖL oder Rapsöl sowie a-Tocopherol zur Stabilisierung. Die Wasserphase bestand aus dem Emulgator Tween 80 oder einer Kombination aus Tween 80 und Biozate 1. Zusatzstoffe waren zudem als mikrobiologischer Schutz Ascorbinsäure und Kaliumsorbat sowie für sensorische Effekte Xylitol und Orangenaroma. Die Anordnung der Basisrezeptur und das angewendete Emulgierverfahren lieferten stabile Miniemulsionen. Weiterhin zeigten langfristige Lagerungsversuche mit den Fertigrezepturen bei 4°C, dass eine Aufrechterhaltung der geforderten Luteinestermenge im Produkt gewährleistet war. Analoge Untersuchungen an einem luteinhaltigen, marktgängigen Präparat bestätigten dagegen eine bereits bei kurzfristiger Lagerung auftretende Instabilität von Lutein.
Abschließend wurde durch Resorptions- und Absorptionsstudien in vitro mit den Präemulsionen und Fertigrezepturen die Bioverfügbarkeit von Luteinestern geprüft. Nach Behandlung in einem etablierten in vitro Verdaumodell konnte eine geringfügige Resorptionsverfügbarkeit der Luteinester definiert werden. Limitiert war eine Micellarisierung des Wirkstoffes aus den konzipierten Formulierungen zu beobachten. Eine enzymatische Spaltung der Luteinester zu freiem Lutein wurde nur begrenzt festgestellt. Spezifität und Aktivität von entsprechenden hydrolytischen Lipasen sind als äußerst gering gegenüber Luteinestern zu bewerten. In sich anschließenden Zellkulturversuchen mit der Zelllinie Caco-2 wurden keine zytotoxischen Effekte durch die relevanten Inhaltsstoffe in den Präemulsionen gezeigt. Dagegen konnten eine Sensibilität gegenüber den Fertigrezepturen beobachtet werden. Diese sollte im Zusammenhang mit Irritationen der Schleimhäute des Magen-Darm-Traktes bedacht werden. Eine weniger komplexe Rezeptur könnte die beobachteten Einschränkungen möglicherweise minimieren. Abschließende Absorptionsstudien zeigten, dass grundsätzlich eine geringfügige Aufnahme von vorrangig Lutein, aber auch Luteinmonoestern in den Enterocyten aus Miniemulsionen erfolgen kann. Dabei hatte weder Tween 80 noch Biozate 1 einen förderlichen Einfluss auf die Absorptionsrate von Lutein oder Luteinestern. Die Metabolisierung der Wirkstoffe durch vorherigen in vitro-Verdau steigerte die zelluläre Aufnahme von Wirkstoffen aus Formulierungen mit Lutein und Luteinestern gleichermaßen. Die beobachtete Aufnahme von Lutein und Luteinmonoestern in den Enterocyten scheint über passive Diffusion zu erfolgen, wobei auch der aktive Transport nicht ausgeschlossen werden kann. Dagegen können Luteindiester aufgrund ihrer Molekülgröße nicht über den Weg der Micellarisierung und einfachen Diffusion in die Enterocyten gelangen. Ihre Aufnahme in die Dünndarmepithelzellen bedarf einer vorherigen hydrolytischen Spaltung durch spezifische Lipasen. Dieser Schritt limitiert wiederum die effektive Aufnahme der Luteinester in die Zellen bzw. stellt eine Einschränkung in ihrer Bioverfügbarkeit im Vergleich zu freiem Lutein dar.
Zusammenfassend konnte für die physikochemisch stabilen Luteinester eine geringe Bioverfügbarkeit aus kolloidalen Formulierungen gezeigt werden. Dennoch ist die Verwendung als Wirkstoffquelle für den sekundären Pflanzenstoff Lutein in einem NEM zu empfehlen. Im Zusammenhang mit der Aufnahme von luteinreichen, pflanzlichen Lebensmitteln kann trotz der zu erwartenden geringen Bioverfügbarkeit der Luteinester aus dem NEM ein Beitrag zur Verbesserung des Luteinstatus erreicht werden. Entsprechende Publikationen zeigten eindeutige Korrelationen zwischen der Aufnahme von luteinesterhaltigen Präparaten und einem Anstieg der Luteinkonzentration im Serum bzw. der Makulapigmentdichte in vivo. Die geringfügig bessere Bioverfügbarkeit von freiem Lutein steht im kritischen Zusammenhang mit seiner Instabilität und Kostenintensität. Bilanzierend wurde im Rahmen dieser Arbeit das marktgängige Produkt Vita Culus® konzipiert. Im Ausblick sollten humane Interventionsstudien mit dem NEM die abschließende Bewertung der Bioverfügbarkeit von Luteinestern aus dem Präparat möglich machen.