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In this thesis, we discuss the formulation of variational problems on supermanifolds. Supermanifolds incorporate bosonic as well as fermionic degrees of freedom. Fermionic fields take values in the odd part of an appropriate Grassmann algebra and are thus showing an anticommutative behaviour. However, a systematic treatment of these Grassmann parameters requires a description of spaces as functors, e.g. from the category of Grassmann algberas into the category of sets (or topological spaces, manifolds). After an introduction to the general ideas of this approach, we use it to give a description of the resulting supermanifolds of fields/maps. We show that each map is uniquely characterized by a family of differential operators of appropriate order. Moreover, we demonstrate that each of this maps is uniquely characterized by its component fields, i.e. by the coefficients in a Taylor expansion w.r.t. the odd coordinates. In general, the component fields are only locally defined. We present a way how to circumvent this limitation. In fact, by enlarging the supermanifold in question, we show that it is possible to work with globally defined components. We eventually use this formalism to study variational problems. More precisely, we study a super version of the geodesic and a generalization of harmonic maps to supermanifolds. Equations of motion are derived from an energy functional and we show how to decompose them into components. Finally, in special cases, we can prove the existence of critical points by reducing the problem to equations from ordinary geometric analysis. After solving these component equations, it is possible to show that their solutions give rise to critical points in the functor spaces of fields.
Within this work, three physicochemical methods for the hydrophobization of initially hydrophilic solid particles are investigated. The modified particles are then used for the stabilization of oil-in-water (o/w) emulsions. For all introduced methods electrostatic interactions between strongly or weakly charged groups in the system are es-sential. (i) Short chain alkylammonium bromides (C4 – C12) adsorb on oppositely charged solid particles. Macroscopic contact angle measurements of water droplets under air and hexane on flat silica surfaces in dependency of the surface charge density and alkylchain-length allow the calculation of the surface energy and give insights into the emulsification properties of solid particles modified with alkyltrimethylammonium bromides. The measure-ments show an increase of the contact angle with increasing surface charge density, due to the enhanced adsorp-tion of the oppositely charged alkylammonium bromides. Contact angles are higher for longer alkylchain lengths. The surface energy calculations show that in particular the surface-hexane or surface-air interfacial en-ergy is being lowered upon alkylammonium adsorption, while a significant increase of the surface-water interfa-cial energy occurs only at long alkyl chain lengths and high surface charge densities. (ii) The thickness and the charge density of an adsorbed weak polyelectrolyte layer (e.g. PMAA, PAH) influence the wettability of nanoparticles (e.g. alumina, silica, see Scheme 1(b)). Furthermore, the isoelectric point and the pH range of colloidal stability of particle-polyelectrolyte composites depend on the thickness of the weak polye-lectrolyte layer. Silica nanoparticles with adsorbed PAH and alumina nanoparticles with adsorbed PMAA be-come interfacially active and thus able to stabilize o/w emulsions when the degree of dissociation of the polye-lectrolyte layer is below 80 %. The average droplet size after emulsification of dodecane in water depends on the thickness and the degree of dissociation of the adsorbed PE-layer. The visualization of the particle-stabilized o/w emulsions by cryogenic SEM shows that for colloidally stable alumina-PMAA composites the oil-water interface is covered with a closely packed monolayer of particles, while for the colloidally unstable case closely packed aggregated particles deposit on the interface. (iii) By emulsifying a mixture of the corrosion inhibitor 8-hydroxyquinoline (8-HQ) and styrene with silica nanoparticles a highly stable o/w emulsion can be obtained in a narrow pH window. The amphoteric character of 8-HQ enables a pH dependent electrostatic interaction with silica nanoparticles, which can render them interfa-cially active. Depending on the concentration and the degree of dissociation of 8-HQ the adsorption onto silica results from electrostatic or aromatic interactions between 8-HQ and the particle-surface. At intermediate amounts of adsorbed 8-HQ the oil wettability of the particles becomes sufficient for stabilizing o/w emulsions. Cryogenic SEM visualization shows that the particles arrange then in a closely packed shell consisting of partly of aggregated domains on the droplet interface. For further increasing amounts of adsorbed 8-HQ the oil wet-tability is reduced again and the particles ability to stabilize emulsions decreases. By the addition of hexadecane to the oil phase the size of the droplets can be reduced down to 200 nm by in-creasing the silica mass fraction. Subsequent polymerization produces corrosion inhibitor filled (20 wt-%) poly-styrene-silica composite particles. The measurement of the release of 8-hydroxyquinoline shows a rapid increase of 8-hydroxyquinoline in a stirred aqueous solution indicating the release of the total content in less than 5 min-utes. The method is extended for the encapsulation of other organic corrosion inhibitors. The silica-polymer-inhibitor composite particles are then dispersed in a water based alkyd emulsion, and the dispersion is used to coat flat aluminium substrates. After drying and cross-linking the polmer-film Confocal Laser Scanning Micros-copy is employed revealing a homogeneous distribution of the particles in the film. Electrochemical Impedance Spectroscopy in aqueous electrolyte solutions shows that films with aggregated particle domains degrade with time and don’t provide long-term corrosion protection of the substrate. However, films with highly dispersed particles have high barrier properties for corrosive species. The comparison of films containing silica-polystyrene composite particles with and without 8-hydroxyquinoline shows higher electrochemical impedances when the inhibitor is present in the film. By applying the Scanning Vibrating Electrode Technique the localized corrosion rate in the fractured area of scratched polymer films containing the silica-polymer-inhibitor composite particles is studied. Electrochemical corrosion cannot be suppressed but the rate is lowered when inhibitor filled composite particles are present in the film. By depositing six polyelectrolyte layers on particle stabilized emulsion droplets their surface morphology changes significantly as shown by SEM visualization. When the oil wettability of the outer polyelectrolyte layer increases, the polyelectrolyte coated droplets can act as emulsion stabilizers themselves by attaching onto bigger oil droplets in a closely packed arrangement. In the presence of 3 mM LaCl3 8-HQ hydrophobized silica particles aggregate strongly on the oil-water inter-face. The application of an ultrasonic field can remove two dimensional shell-compartments from the droplet surface, which are then found in the aqueous bulk phase. Their size ranges up to 1/4th of the spherical particle shell.
Impact of apoplastic glycoside hydrolases on xyloglucan structure and function in arabidopsis
(2011)
Die vorliegende Arbeit beschäftigt sich mit der Synthese und Charakterisierung mesoporöser monolithischer Silica und deren Hybridmaterialien mit Ionischen Flüssigkeiten (ILs, ionic liquids). Zur Synthese der Silicaproben wurde ein Sol-Gel-Verfahren, ausgehend von einer Präkursorverbindung wie Tetramethylorthosilicat angewendet. Der Katalysator mit der geringsten Basizität führte zum Material mit der kleinsten Porengröße und der größten spezifischen Oberfläche. Eine Kombination von porösen Silica mit ILs führt zur Materialklasse der Silica-Ionogele. Diese Hybridmaterialien verbinden die Eigenschaften eines porösen Festkörpers mit denen einer IL (Leitfähigkeit, weites elektrochemisches Fenster, gute thermische Stabilität) und bieten vielfältige Einsatzmöglichkeiten z.B. in der Katalyse- Solar- und Sensortechnik. Um diese Materialien für ihren Verwendungszweck zu optimieren, bedarf es deren umfassenden Charakterisierung. Daher wurde in der vorliegenden Arbeit das thermische Verhalten von Silica-Ionogelen unter Verwendung verschiedener 1-Ethyl-3-methylimidazolium [Emim]-basierter ILs untersucht. Interessanterweise zeigen die untersuchten ILs deutliche Änderungen in ihrem thermischen Verhalten, wenn diese in porösen Materialien eingeschlossen werden (Confinement). Während sich die untersuchten reinen ILs durch klar unterscheidbare Phasenübergänge auszeichnen, konnten für die entsprechenden Hybridmaterialien deutlich schwächer ausgeprägte Übergänge beobachtet werden. Einzelne Phasenübergänge wurden unterdrückt (Glas- und Kristallisationsübergänge), während z.B. Schmelzübergänge in verbreiterten Temperaturbereichen, zum Teil als einzeln getrennte Schmelzpeaks beobachtet wurden. Diese Untersuchungen belegen deutliche Eigenschaftsänderungen der ILs in eingeschränkten Geometrien. Über Festkörper-NMR-Spektroskopie konnte außerdem gezeigt werden, daß die ILs in den mesoporösen Silicamaterialien eine unerwartet hohe Mobilität aufweisen. Die ILs können als quasi-flüssig bezeichnet werden und zeigen die nach bestem Wissen höchste Mobilität, die bisher für vergleichbare Hybridmaterialien beobachtet wurde. Durch Verwendung von funktionalisierten Präkursoren, sowie der Wahl der Reaktionsbedingungen, kann die Oberfläche der Silicamaterialien chemisch funktionalisiert werden und damit die Materialeigenschaften in der gewünschten Weise beeinflußt werden. In der vorliegenden Arbeit wurde der Einfluß der Oberflächenfunktionalität auf das thermische Verhalten hin untersucht. Dazu wurden zwei verschiedene Möglichkeiten der Funktionalisierung angewendet und miteinander verglichen. Bei der in-situ-Funktionalisierung wird die chemische Funktionalität während der Sol-Gel-Synthese über ein entsprechend funktionalisiertes Silan mit in das Silicamaterial einkondensiert. Eine postsynthetische Funktionalisierung erfolgt durch Reaktion der Endgruppen eines Silicamaterials mit geeigneten Reaktionspartnern. Um den Einfluß der physikalischen Eigenschaften der Probe auf die Reaktion zu untersuchen, wurden pulverisierte und monolithische Silicamaterialien miteinander verglichen. Im letzten Teil der Arbeit wurde die Vielfältigkeit, mit der Silicamaterialien postsynthetisch funktionalisiert werden können demonstriert. Durch die Kenntnis von Struktur-Eigenschaftsbeziehungen können die Eigenschaften von Silica-Ionogelen durch die geeignete Kombination von fester und mobiler Phase in der gewünschten Weise verändert werden. Die vorliegende Arbeit soll einen Beitrag zur Untersuchung dieser Beziehungen leisten, um das Potential dieser interessanten Materialien für Anwendungen nutzen zu können.
Soil moisture is a key state variable that controls runoff formation, infiltration and partitioning of radiation into latent and sensible heat. However, the experimental characterisation of near surface soil moisture patterns and their controls on runoff formation remains a challenge. This subject was one aspect of the BMBF-funded OPAQUE project (operational discharge and flooding predictions in head catchments). As part of that project the focus of this dissertation is on: (1) testing the methodology and feasibility of the Spatial TDR technology in producing soil moisture profiles along TDR probes, including an inversion technique of the recorded signal in heterogeneous field soils, (2) the analysis of spatial variability and temporal dynamics of soil moisture at the field scale including field experiments and hydrological modelling, (3) the application of models of different complexity for understanding soil moisture dynamics and its importance for runoff generation as well as for improving the prediction of runoff volumes. To fulfil objective 1, several laboratory experiments were conducted to understand the influence of probe rod geometry and heterogeneities in the sampling volume under different wetness conditions. This includes a detailed analysis on how these error sources affect retrieval of soil moisture profiles in soils. Concerning objective 2 a sampling strategy of two TDR clusters installed in the head water of the Wilde Weißeritz catchment (Eastern Ore Mountains, Germany) was used to investigate how well “the catchment state” can be characterised by means of distributed soil moisture data observed at the field scale. A grassland site and a forested site both located on gentle slopes were instrumented with two Spatial TDR clusters that consist of up to 39 TDR probes. Process understanding was gained by modelling the interaction of evapotranspiration and soil moisture with the hydrological process model CATFLOW. A field scale irrigation experiment was carried out to investigate near subsurface processes at the hillslope scale. The interactions of soil moisture and runoff formation were analysed using discharge data from three nested catchments: the Becherbach with a size of 2 km², the Rehefeld catchment (17 km²) and the superordinate Ammelsdorf catchment (49 km²). Statistical analyses including observations of pre-event runoff, soil moisture and different rainfall characteristics were employed to predict stream flow volume. On the different scales a strong correlation between the average soil moisture and the runoff coefficients of rainfall-runoff events could be found, which almost explains equivalent variability as the pre-event runoff. Furthermore, there was a strong correlation between surface soil moisture and subsurface wetness with a hysteretic behaviour between runoff soil moisture. To fulfil objective 3 these findings were used in a generalised linear model (GLM) analysis which combines state variables describing the catchments antecedent wetness and variables describing the meteorological forcing in order to predict event runoff coefficients. GLM results were compared to simulations with the catchment model WaSiM ETH. Hereby were the model results of the GLMs always better than the simulations with WaSiM ETH. The GLM analysis indicated that the proposed sampling strategy of clustering TDR probes in typical functional units is a promising technique to explore soil moisture controls on runoff generation and can be an important link between the scales. Long term monitoring of such sites could yield valuable information for flood warning and forecasting by identifying critical soil moisture conditions for the former and providing a better representation of the initial moisture conditions for the latter.
Die vorliegende Arbeit basiert auf Forschungen in den Jahren 2007-2009. Sie betrachtet die saisonale Arbeitsmigration aus der polnischen Region Konin, wo die Arbeitsmigration aus ökonomischen Gründen, wie auch in ähnlich strukturierten Gebieten Polens, eine lange Tradition hat, die bis ins 19. Jahrhundert zurückgeht. Sie wird die saisonale Migration ins Ausland mit den ökonomischen, sozialen und räumlichen Auswirkungen aus der Perspektive des Einzelnen und seiner unmittelbaren Umgebung, aber auch der Gesellschaft und Herkunftsgebiet der Migranten betrachtet.
Algorithmic Trading
(2011)
Die Elektronisierung der Finanzmärkte ist in den letzten Jahren weit vorangeschritten. Praktisch jede Börse verfügt über ein elektronisches Handelssystem. In diesem Kontext beschreibt der Begriff Algorithmic Trading ein Phänomen, bei dem Computerprogramme den Menschen im Wertpapierhandel ersetzen. Sie helfen dabei Investmententscheidungen zu treffen oder Transaktionen durchzuführen. Algorithmic Trading selbst ist dabei nur eine unter vielen Innovationen, welche die Entwicklung des Börsenhandels geprägt haben. Hier sind z.B. die Erfindung der Telegraphie, des Telefons, des FAX oder der elektronische Wertpapierabwicklung zu nennen. Die Frage ist heute nicht mehr, ob Computerprogramme im Börsenhandel eingesetzt werden. Sondern die Frage ist, wo die Grenze zwischen vollautomatischem Börsenhandel (durch Computer) und manuellem Börsenhandel (von Menschen) verläuft. Bei der Erforschung von Algorithmic Trading wird die Wissenschaft mit dem Problem konfrontiert, dass keinerlei Informationen über diese Computerprogramme zugänglich sind. Die Idee dieser Dissertation bestand darin, dieses Problem zu umgehen und Informationen über Algorithmic Trading indirekt aus der Analyse von (Fonds-)Renditen zu extrahieren. Johannes Gomolka untersucht daher die Forschungsfrage, ob sich Aussagen über computergesteuerten Wertpapierhandel (kurz: Algorithmic Trading) aus der Analyse von (Fonds-)Renditen ziehen lassen. Zur Beantwortung dieser Forschungsfrage formuliert der Autor eine neue Definition von Algorithmic Trading und unterscheidet mit Buy-Side und Sell-Side Algorithmic Trading zwei grundlegende Funktionen der Computerprogramme (die Entscheidungs- und die Transaktionsunterstützung). Für seine empirische Untersuchung greift Gomolka auf das Multifaktorenmodell zur Style-Analyse von Fung und Hsieh (1997) zurück. Mit Hilfe dieses Modells ist es möglich, die Zeitreihen von Fondsrenditen in interpretierbare Grundbestandteile zu zerlegen und den einzelnen Regressionsfaktoren eine inhaltliche Bedeutung zuzuordnen. Die Ergebnisse dieser Dissertation zeigen, dass man mit Hilfe der Style-Analyse Aussagen über Algorithmic Trading aus der Analyse von (Fonds-)Renditen machen kann. Die Aussagen sind jedoch keiner technischen Natur, sondern auf die Analyse von Handelsstrategien (Investment-Styles) begrenzt.
Regulation of gene transcription plays a major role in mediating cellular responses and physiological behavior in all known organisms. The finding that similar genes are often regulated in a similar manner (co-regulated or "co-expressed") has directed several "guilt-by-association" approaches in order to reverse-engineer the cellular transcriptional networks using gene expression data as a compass. This kind of studies has been considerably assisted in the recent years by the development of high-throughput transcript measurement platforms, specifically gene microarrays and next-generation sequencing. In this thesis, I describe several approaches for improving the extraction and interpretation of the information contained in microarray based gene expression data, through four steps: (1) microarray platform design, (2) microarray data normalization, (3) gene network reverse engineering based on expression data and (4) experimental validation of expression-based guilt-by-association inferences. In the first part test case is shown aimed at the generation of a microarray for Thellungiella salsuginea, a salt and drought resistant close relative to the model plant Arabidopsis thaliana; the transcripts of this organism are generated on the combination of publicly available ESTs and newly generated ad-hoc next-generation sequencing data. Since the design of a microarray platform requires the availability of highly reliable and non-redundant transcript models, these issues are addressed consecutively, proposing several different technical solutions. In the second part I describe how inter-array correlation artifacts are generated by the common microarray normalization methods RMA and GCRMA, together with the technical and mathematical characteristics underlying the problem. A solution is proposed in the form of a novel normalization method, called tRMA. The third part of the thesis deals with the field of expression-based gene network reverse engineering. It is shown how different centrality measures in reverse engineered gene networks can be used to distinguish specific classes of genes, in particular essential genes in Arabidopsis thaliana, and how the use of conditional correlation can add a layer of understanding over the information flow processes underlying transcript regulation. Furthermore, several network reverse engineering approaches are compared, with a particular focus on the LASSO, a linear regression derivative rarely applied before in global gene network reconstruction, despite its theoretical advantages in robustness and interpretability over more standard methods. The performance of LASSO is assessed through several in silico analyses dealing with the reliability of the inferred gene networks. In the final part, LASSO and other reverse engineering methods are used to experimentally identify novel genes involved in two independent scenarios: the seed coat mucilage pathway in Arabidopsis thaliana and the hypoxic tuber development in Solanum tuberosum. In both cases an interesting method complementarity is shown, which strongly suggests a general use of hybrid approaches for transcript expression-based inferences. In conclusion, this work has helped to improve our understanding of gene transcription regulation through a better interpretation of high-throughput expression data. Part of the network reverse engineering methods described in this thesis have been included in a tool (CorTo) for gene network reverse engineering and annotated visualization from custom transcription datasets.
Resolute readings of later Wittgenstein and the challenge of avoiding hierarchies in philosophy
(2011)
This dissertation addresses the question: How did later Wittgenstein aim to achieve his goal of putting forward a way of dissolving philosophical problems which centered on asking ourselves what we mean by our words – yet which did not entail any claims about the essence of language and meaning? This question is discussed with reference to “resolute” readings of Wittgenstein. I discuss the readings of James Conant, Oskari Kuusela, and Martin Gustafsson. I follow Oskari Kuusela’s claim that in order to fully appreciate how later Wittgenstein meant to achieve his goal, we need to clearly see how he aimed to do away with hierarchies in philosophy: Not only is the dissolution of philosophical problems via the method of clarifying the grammar of expressions to be taken as independent from any theses about what meaning must be – but furthermore, it is to be taken as independent from the dissolution of any particular problem via this method. As Kuusela stresses, this also holds for the problems involving rule-following and meaning: the clarification of the grammar of “rule” and “meaning” has no foundational status – it is nothing on which the method of clarifying the grammar of expressions as such were meant to in any way rely on. The lead question of this dissertation then is: What does it mean to come to see that the method of dissolving philosophical problems by asking “How is this word actually used?” does not in any way rely on the results of our having investigated the grammar of the particular concepts “rule” and “meaning”? What is the relation of such results – results such as “To follow a rule, [...], to obey an order, [...] are customs (uses, institutions)” or “The meaning of a word is its use in the language” – to this method? From this vantage point, I concern myself with two aspects of the readings of Gustafsson and Kuusela. In Gustafsson, I concern myself with his idea that the dissolution of philosophical problems in general “relies on” the very agreement which – during the dissolution of the rule-following problem – comes out as a presupposition for our talk of “meaning” in terms of rules. In Kuusela, I concern myself with his idea that Wittgenstein, in adopting a way of philosophical clarification which investigates the actual use of expressions, is following the model of “meaning as use” – which model he had previously introduced in order to perspicuously present an aspect of the actual use of the word “meaning”. This dissertation aims to show how these two aspects of Gustafsson’s and Kuusela’s readings still fail to live up to the vision of Wittgenstein as a philosopher who aimed to do away with any hierarchies in philosophy. I base this conclusion on a detailed analysis of which of the occasions where Wittgenstein invokes the notions of “use” and “application” (as also “agreement”) have to do with the dissolution of a specific problem only, and which have to do with the dissolution of philosophical problems in general. I discuss Wittgenstein’s remarks on rule-following, showing how in the dissolution of the rule-following paradox, notions such as “use”, “application”, and “practice” figure on two distinct logical levels. I then discuss an example of what happens when this distinction is not duly heeded: Gordon Baker and Peter Hacker’s idea that the rule-following remarks have a special significance for his project of dissolving philosophical problems as such. I furnish an argument to the effect that their idea that the clarification of the rules of grammar of the particular expression “following a rule” could answer a question about rules of grammar in general rests on a conflation of the two logical levels on which “use” occurs in the rule-following remarks, and that it leads into a regress. I then show that Gustafsson’s view – despite its decisive advance over Baker and Hacker – contains a version of that same idea, and that it likewise leads into a regress. Finally, I show that Kuusela’s idea of a special significance of the model “meaning as use” for the whole of the method of stating rules for the use of words is open to a regress argument of a similar kind as that he himself advances against Baker and Hacker. I conclude that in order to avoid such a regress, we need to reject the idea that the grammatical remark “The meaning of a word is its use in the language” – because of the occurrence of “use” in it – stood in any special relation to the method of dissolving philosophical problems by describing the use of words. Rather, we need to take this method as independent from this outcome of the investigation of the use of the particular word “meaning”.
Poröse Sol-Gel-Materialien finden in vielen Bereichen Anwendung bzw. sind Gegenstand der aktuellen Forschung. Zu diesen Bereichen zählen sowohl klassische Anwendungen, wie z. B. die Verwendung als Katalysator, Molekularsieb oder Trockenmittel, als auch nichtklassische Anwendungen, wie z. B. der Einsatz als Kontrastmittel in der Magnet-Resonanz-Tomographie oder in Form von dünnen Zeolithfilmen als Isolatoren in Mikrochips. Auch für den Einsatz in der Photonik werden poröse Materialien in Betracht gezogen, wie die Entwicklung des Zeolith-Farbstoff-Lasers zeigt. Mikroporöse Zeolithe können generell über einfache Ionenaustauschreaktionen mit Lanthanoidionen in lumineszente Materialien umgewandelt werden. Neben der Erzeugung eines lumineszenten Materials, dessen Lumineszenzeigenschaften charakterisiert werden müssen, bietet die Nutzung von Lanthanoidionen die Möglichkeit diese Ionen als Sonde zur Charakterisierung der Ion-Wirt-Wechselwirkungen zu funktionalisieren, was z. B. in Bezug auf die Anwendung als Katalysator von großer Bedeutung ist. Dabei werden die einzigartigen Lumineszenzeigenschaften der Lanthanoidionen, in diesem Fall von Europium(III) und Terbium(III), genutzt. In dieser Arbeit wurden Lanthanoid-dotierte mikroporöse Zeolithe, mikroporös-mesoporöse Hybridmaterialien und mesoporöse Silikate hinsichtlich ihrer Lumineszenzeigenschaften und ihrer Wechselwirkung des Wirtsmaterials mit den Lanthanoidionen mittels zeitaufgelöster Lumineszenzspektroskopie untersucht. Zeitaufgelöste Emissionsspektren (TRES) liefern dabei sowohl Informationen in der Wellenlängen- als auch in der Zeitdomäne. Erstmalig wurden die TRES mittels einer umfangreichen Auswertemethodik behandelt. Neben der Anpassung des Abklingverhaltens mit einer diskreten Zahl von Exponentialfunktionen, wurden unterstützend auch Abklingzeitverteilungsanalysen durchgeführt. Zeitaufgelöste flächennormierte Emissionsspektren (TRANES), eine Erweiterung der normalen TRES, konnten erstmals zur Bestimmung der Zahl der emittierenden Lanthanoidspezies in porösen Materialien genutzt werden. Durch die Berechnung der Decayassoziierten Spektren (DAS) konnten den Lanthanoidspezies die entsprechenden Lumineszenzspektren zugeordnet werden. Zusätzlich konnte, speziell im Fall der Europium-Lumineszenz, durch Kombination von zeitlicher und spektraler Information das zeitabhängige Asymmetrieverhältnis R und die spektrale Evolution des 5D0-7F0-Übergangs mit der Zeit t untersucht und somit wesentliche Informationen über die Verteilung der Europiumionen im Wirtsmaterial erhalten werden. Über die Abklingzeit und das Asymmetrieverhältnis R konnten Rückschlüsse auf die Zahl der OH-Oszillatoren in der ersten Koordinationssphäre und die Symmetrie der Koordinationsumgebung gezogen werden. Für die mikroporösen und mikroporös-mesoporösen Materialien wurden verschiedene Lanthanoidspezies, im Regelfall zwei, gefunden, welche entsprechend der beschriebenen Methoden charakterisiert wurden. Diese Lanthanoidspezies konnten Positionen in den Materialien zugeordnet werden, die sich im tief Inneren des Porensystems oder auf bzw. nahe der äußeren Oberfläche oder in den Mesoporen befinden. Erstere Spezies ist aufgrund ihrer Position im Material gut vor Feuchtigkeitseinflüssen geschützt, was sich deutlich in entsprechend langen Lumineszenzabklingzeiten äußert. Zusätzlich ist diese Europiumspezies durch unsymmetrische Koordinationsumgebung charakterisiert, was auf einen signifikanten Anteil an Koordination der Lanthanoidionen durch die Sauerstoffatome im Wirtsgitter zurückzuführen ist. Ionen, die sich nahe oder auf der äußeren Oberfläche befinden, sind dagegen für Feuchtigkeit zugänglicher, was in kürzeren Lumineszenzabklingzeiten und einer symmetrischeren Koordinationsumgebung resultiert. Der Anteil von Wassermolekülen in der ersten Koordinationssphäre ist hier deutlich größer, als bei den Ionen, die sich tiefer im Porensystem befinden und entspricht in vielen Fällen der Koordinationszahl eines vollständig hydratisierten Lanthanoidions. Auch der Einfluss von Oberflächenmodifikationen auf die Speziesverteilung und das Verhalten der Materialien gegenüber Feuchtigkeit wurde untersucht. Dabei gelang es den Einfluss der Feuchtigkeit auf die Lumineszenzeigenschaften und die Speziesverteilung durch die Oberflächenmodifikation zu verringern und die Lumineszenzeigenschaften teilweise zu konservieren. Im Fall der mesoporösen Silikamonolithe wurde auch eine heterogene Verteilung der Lanthanoidionen im Porensystem gefunden. Hier wechselwirkt ein Teil der Ionen mit der Porenwand, während sich die restlichen Ionen in der wäßrigen Phase innerhalb des Porensystems aufhalten. Das Aufbringen von Oberflächenmodifikationen führte zu einer Wechselwirkung der Ionen mit diesen Oberflächenmodifikationen, was sich in Abhängigkeit von der Oberflächenbeladung in den enstprechenden Lumineszenzeigenschaften niederschlug.
During reading oculomotor processes guide the eyes over the text. The visual information recorded is accessed, evaluated and processed. Only by retrieving the meaning of a word from the long-term memory, as well as through the connection and storage of the information about each individual word, is it possible to access the semantic meaning of a sentence. Therefore memory, and here in particular working memory, plays a pivotal role in the basic processes of reading. The following dissertation investigates to what extent different demands on memory and memory capacity have an effect on eye movement behavior while reading. The frequently used paradigm of the reading span task, in which test subjects read and evaluate individual sentences, was used for the experimental review of the research questions. The results speak for the fact that working memory processes have a direct effect on various eye movement measurements. Thus a high working memory load, for example, reduced the perceptual span while reading. The lower the individual working memory capacity of the reader was, the stronger was the influence of the working memory load on the processing of the sentence.
Answer Set Programming (ASP) is an emerging paradigm for declarative programming, in which a computational problem is specified by a logic program such that particular models, called answer sets, match solutions. ASP faces a growing range of applications, demanding for high-performance tools able to solve complex problems. ASP integrates ideas from a variety of neighboring fields. In particular, automated techniques to search for answer sets are inspired by Boolean Satisfiability (SAT) solving approaches. While the latter have firm proof-theoretic foundations, ASP lacks formal frameworks for characterizing and comparing solving methods. Furthermore, sophisticated search patterns of modern SAT solvers, successfully applied in areas like, e.g., model checking and verification, are not yet established in ASP solving. We address these deficiencies by, for one, providing proof-theoretic frameworks that allow for characterizing, comparing, and analyzing approaches to answer set computation. For another, we devise modern ASP solving algorithms that integrate and extend state-of-the-art techniques for Boolean constraint solving. We thus contribute to the understanding of existing ASP solving approaches and their interconnections as well as to their enhancement by incorporating sophisticated search patterns. The central idea of our approach is to identify atomic as well as composite constituents of a propositional logic program with Boolean variables. This enables us to describe fundamental inference steps, and to selectively combine them in proof-theoretic characterizations of various ASP solving methods. In particular, we show that different concepts of case analyses applied by existing ASP solvers implicate mutual exponential separations regarding their best-case complexities. We also develop a generic proof-theoretic framework amenable to language extensions, and we point out that exponential separations can likewise be obtained due to case analyses on them. We further exploit fundamental inference steps to derive Boolean constraints characterizing answer sets. They enable the conception of ASP solving algorithms including search patterns of modern SAT solvers, while also allowing for direct technology transfers between the areas of ASP and SAT solving. Beyond the search for one answer set of a logic program, we address the enumeration of answer sets and their projections to a subvocabulary, respectively. The algorithms we develop enable repetition-free enumeration in polynomial space without being intrusive, i.e., they do not necessitate any modifications of computations before an answer set is found. Our approach to ASP solving is implemented in clasp, a state-of-the-art Boolean constraint solver that has successfully participated in recent solver competitions. Although we do here not address the implementation techniques of clasp or all of its features, we present the principles of its success in the context of ASP solving.
Das vorliegende Buch vergleicht Strategien biologischer Systeme mit militärischen Strategien. Die zentrale Fragestellung ist dabei darauf gerichtet, ob es neben systemischen Gemeinsamkeiten auch gemeinsame oder ähnliche Strukturmuster und ähnliche Prozessabläufe beispielsweise sowohl im biologischen Abwehrmechanismus des Immunsystems und bei Insektenstaaten als auch bei Prozessen im Militär gibt. Vor diesem Hintergrund klaffen in der Theorie der Strategie, speziell in den Militärwissenschaften Lücken, denn der Systemansatz wird nicht konsequent beachtet, wie in diesem Buch mehrfach nachgewiesen ist. Von einem allgemeinen Verständnis der Strategie als bewusstem planerischem Vorgehen ist Abstand zu nehmen. Ausgehend von der Methode der Analogie und des Vergleichs wird im theoretischen Teil dieses Buches die Allgemeine Systemtheorie erläutert. Dabei werden der Begriff der Strategie ebenso wie die Begriffe Struktur und Prozess und Ansätze aus der Kriegsphilosophie von Clausewitz untersucht. Den Ausgangspunkt und schließlich auch wieder den Endpunkt der Überlegungen bilden neben dem notwendigen weiten Verständnis von Strategie, vor allem der Begriff der Organisation, ihrer Umwelt und der in diesem Zusammenhang bestehenden Wechselwirkung. Sowohl die Wechselwirkung von Umwelt und System als auch ihre Abhängigkeit durch strukturelle Kopplung werden beschrieben. Das Zusammenspiel und die daraus entstehende Komplexität der fünf Komponenten der Wahrnehmung, der Information und der Führung im Zusammenhang der Komponenten von Raum und Zeit in einem sozialen System lassen die klassische Ziel-Mittel-Zweck-Beziehung Clausewitz´scher Strategiedefinition verkürzt erscheinen. Anhand eines kurzen Rekurses der Methoden der Sozialen Netzwerkanalyse (SNA) wird der breite und tiefgehende Analyserahmen der Messung und Transparenzerreichung in Organisationen vorgestellt. Die SNA wird als Ausprägung der Netzwerk- und Graphentheorie, in die Allgemeine Systemtheorie integriert. Sie bildet eine zukunftsweisende Methode der Untersuchung von Netzwerken wie etwa dem Internet (Facebook, Xing etc.). Der aufgezeigte Theorierahmen bildet dabei zugleich eine Methode für den Systemvergleich und kann als Vorgehensmodell künftiger Strategieentwicklung genutzt werden. Der anschließende Systemvergleich wird mit mehreren Beispielen durchgeführt. Ausgehend von der Zelle als Grundeinheit werden Strukturen und Prozesse des Immunsystems mit solchen in militärischen Strukturen, weil sie im Lauf der Evolution enorme Leistungen in Reaktion, Anpassung und Optimierung vollbracht haben. Der Vergleich geht der Frage nach, ob in diesen Bereichen der Strategie und Organisation systemische Grundregeln existieren. Das Beispiel der Wechselwirkung zwischen Parasit und Wirt zeigt, dass jeder Fortschritt und Sieg angesichts der Systemeinbettung von Strategie nur relativ wirken kann. Die Analogie zwischen Viren und Bakterien sowie die Entwicklung des Begriffs der sozialen Mimikry führen zu einem erweiterten Verständnis der Strategie von Terroristen in sozialen Systemen. Verdeutlicht wird das Grundschema des Täuschens und Eindringens in Systeme sowie die Beeinflussung und Umsteuerung von Prozessen und Strukturen in einem System durch Kommunikation und Implementation von Codes. Am Beispiel des Immunsystems und der Bildung verschiedener Kommunikations- und Steuerungsmechanismen von Zellsystemen sowie Beispielen von Schwarmbildung und der Organisation sozialer Insekten werden eine Vielzahl heuristischer Hinweise für neue Ansätze für die Organisation von Streitkräften und ihrer Steuerung gefunden. Neben der Erarbeitung eines grundlegenden Strategiebegriffs anhand von Wahrnehmung und Selektion als Grundprozess der Erzeugung von Strategie wird eine differenzierte Betrachtung von Begriffen wie Redundanz und Robustheit sowie eine relativierende Sichtweise von Risiko, Gefahr und Schaden gewonnen. Der Vergleich mit dem Immunsystems zeigt einfache Beispiele der Informationsspeicherung und -übertragung, die zudem Bypassfähigkeiten sowie dezentrale Eskalations- und Deeskalationsprinzipien veranschaulichen. Dies eröffnet in Analogie dieser Prinzipien einen weiten Raum Sicherheitsarchitekturen zu überdenken und neu zu strukturieren. Zudem kann die räumliche Ausbreitung von Information und Kräften als ein gemeinsames Grundproblem der Entwicklung und Wirksamkeit von Strategien sowohl in der Natur, als auch im Militär identifiziert werden. Die Betrachtung zeigt zudem wie Zellen mit fehlgeleiteten Prozessen und Strukturen umgehen. Die Analogie deutet auf das Erfordernis einer Veränderung im Umgang mit Fehlern und ihrer Rückführ- und Umkehrbarkeit im weitesten Sinne. Das Buch eröffnet überdies ein neues Verständnis von Staat, Gewaltenteilung und Institutionen in einem sozialen System. Die Ergebnisse sind auch auf andere Forschungsbereiche, Organisationen und unterschiedlichste soziale Systeme übertragbar. Es eröffnet sich ein breites Anwendungsspektrum für künftige strategische Untersuchungen.
Besteuerung von Unternehmensgewinnen im Licht des Konzepts der konsumorientierten Einkommensteuer
(2011)
Die Dissertation widmet sich dem Problem der fiskalischen Konsequenzen der konsumorientierten Steuern, die die unternehmerischen Gewinne unabhängig von der Rechtsform belasten. Im empirischen Teil der Arbeit wird der Untersuchungsgegenstand auf die zinsbereinigte Gewinnsteuer (allowance for corporate equity) eingegrenzt. Die Untersuchung beruht auf theoretischen Überlegungen sowie einer eigenen Simulationsanalyse. Den Schwerpunkt bilden dabei zwei Kategorien, zwischen denen ein kausaler Zusammenhang vorliegt: die Gestaltung der Bemessungsgrundlage einerseits und die Erfüllung der Fiskalfunktion andererseits. Das Hauptziel der Arbeit ist es, die fiskalischen Konsequenzen einer nach dem Konzept der Konsumorientierung modifizierten Bemessungsgrundlage der Gewinnsteuern zu überprüfen. Die Abschätzung der fiskalischen Konsequenzen wird aufgrund der vier folgenden Bereiche vorgenommen: (1) theoretische Konzepte der konsumorientierten Einkommensteuer, (2) bisherige Umsetzungen der Konzepte der konsumorientierten Gewinnsteuer, (3) bisherige Untersuchungen der konsumorientierten Gewinnsteuer, (4) eine eigene Simulation der fiskalischen Konsequenzen der konsumorientierten Gewinnsteuer. Um das Hauptziel der Arbeit zu erreichen, werden acht in Form von Teilfragen ausformulierte Untersuchungsprobleme gelöst. Sie betreffen sowohl die theoretischen Ausführungen, als auch die empirische Untersuchung. Dabei entsprechen sie den einzelnen Untersuchungsschritten, die in den aufeinander folgenden Kapiteln der Arbeit durchgeführt werden. Anhand der Analyse der bisherigen wissenschaftlichen Erkenntnisse und der praktischen Umsetzungen des Konzepts der konsumorientierten Steuern wurde die folgende Haupthypothese aufgestellt: Der Ausfall des Steueraufkommens, der ein direkter Effekt der Gestaltung der Bemessungsgrundlage nach dem Konzept der Konsumorientierung ist, schließt die Fiskalfunktion der Gewinnsteuern nicht aus. Das Verfahren, das eine Verifizierung der Haupthypothese zum Ziel hat, erfolgt durch eine Untersuchung von drei Teilhypothesen: der Hypothese über die Nullsteuer, der Hypothese über den differenzierten Aufkommensausfall und der Hypothese über die Konzentration der Steuerschuld. In der Dissertation werden empirische Daten aus drei Quellen benutzt. Sie umfassen einen Teil der in Polen in den Jahren 2004-2008 tätigen Unternehmen und ermöglichen es, eine Simulationsanalyse des Aufkommensausfalls durchzuführen. Diese bedient sich der Methodik der Mikro- und Gruppensimulation, was in den bisherigen Untersuchungen zur Unternehmensbesteuerung ein eher selten anzutreffender Ansatz ist. Die gewonnenen Ergebnisse zeigen, dass die Steuereinnahmen aus der Einkommensteuer und der Körperschaftsteuer durch die Modifizierung der Bemessungsgrundlage deutlich reduziert werden. Die relativ große fiskalische Bedeutung der beiden Steuern bleibt jedoch erhalten und der Ausfall des Steueraufkommens, der direkt nach der Einführung einer konsumorientierten Steuerreform eintreten würde, wäre der „Preis“ für eine bessere, weniger verzerrende Bemessungsgrundlage. Die Dissertation liefert Ergebnisse, die für die Gestaltung der Steuerpolitik in Polen wie auch in anderen Ländern relevant sind. Dies scheint insbesondere im Kontext des häufig diskutierten Umbaus des Systems der Einkommen- und Gewinnbesteuerung bedeutsam. Darüber hinaus bildet die Arbeit einen Ausgangspunkt für weitere, vertiefte Untersuchungen zu den möglichen Gestaltungsformen der Einkommen- und Gewinnsteuern wie auch zu deren Folgen. Die Methode der Steuersimulation kann weiterentwickelt werden und in anderen Analysen der potenziellen Konsequenzen von Steuerreformen Anwendung finden.
A key non-destructive technique for analysis, optimization and developing of new functional materials such as sensors, transducers, electro-optical and memory devices is presented. The Thermal-Pulse Tomography (TPT) provides high-resolution three-dimensional images of electric field and polarization distribution in a material. This thermal technique use a pulsed heating by means of focused laser light which is absorbed by opaque electrodes. The diffusion of the heat causes changes in the sample geometry, generating a short-circuit current or change in surface potential, which contains information about the spatial distribution of electric dipoles or space charges. Afterwards, a reconstruction of the internal electric field and polarization distribution in the material is possible via Scale Transformation or Regularization methods. In this way, the TPT was used for the first time to image the inhomogeneous ferroelectric switching in polymer ferroelectric films (candidates to memory devices). The results shows the typical pinning of electric dipoles in the ferroelectric polymer under study and support the previous hypotheses of a ferroelectric reversal at a grain level via nucleation and growth. In order to obtain more information about the impact of the lateral and depth resolution of the thermal techniques, the TPT and its counterpart called Focused Laser Intensity Modulation Method (FLIMM) were implemented in ferroelectric films with grid-shaped electrodes. The results from both techniques, after the data analysis with different regularization and scale methods, are in total agreement. It was also revealed a possible overestimated lateral resolution of the FLIMM and highlights the TPT method as the most efficient and reliable thermal technique. After an improvement in the optics, the Thermal-Pulse Tomography method was implemented in polymer-dispersed liquid crystals (PDLCs) films, which are used in electro-optical applications. The results indicated a possible electrostatic interaction between the COH group in the liquid crystals and the fluorinate atoms of the used ferroelectric matrix. The geometrical parameters of the LC droplets were partially reproduced as they were compared with Scanning Electron Microscopy (SEM) images. For further applications, it is suggested the use of a non-strong-ferroelectric polymer matrix. In an effort to develop new polymerferroelectrets and for optimizing their properties, new multilayer systems were inspected. The results of the TPT method showed the non-uniformity of the internal electric-field distribution in the shaped-macrodipoles and thus suggested the instability of the sample. Further investigation on multilayers ferroelectrets was suggested and the implementation of less conductive polymers layers too.
The needs for sustainable energy generation, but also a sustainable chemistry display the basic motivation of the current thesis. By different single investigated cases, which are all related to the element carbon, the work can be devided into two major topics. At first, the sustainable synthesis of “useful” carbon materials employing the process of hydrothermal carbonisation (HC) is described. In the second part, the synthesis of heteroatom - containing carbon materials for electrochemical and fuel cell applications employing ionic liquid precursors is presented. On base of a thorough review of the literature on hydrothermolysis and hydrothermal carbonisation of sugars in addition to the chemistry of hydroxymethylfurfural, mechanistic considerations of the formation of hydrothermal carbon are proposed. On the base of these reaction schemes, the mineral borax, is introduced as an additive for the hydrothermal carbonisation of glucose. It was found to be a highly active catalyst, resulting in decreased reaction times and increased carbon yields. The chemical impact of borax, in the following is exploited for the modification of the micro- and nanostructure of hydrothermal carbon. From the borax - mediated aggregation of those primary species, widely applicable, low density, pure hydrothermal carbon aerogels with high porosities and specific surface areas are produced. To conclude the first section of the thesis, a short series of experiments is carried out, for the purpose of demonstrating the applicability of the HC model to “real” biowaste i.e. watermelon waste as feedstock for the production of useful materials. In part two cyano - containing ionic liquids are employed as precursors for the synthesis of high - performance, heteroatom - containing carbon materials. By varying the ionic liquid precursor and the carbonisation conditions, it was possible to design highly active non - metal electrocatalyst for the reduction of oxygen. In the direct reduction of oxygen to water (like used in polymer electrolyte fuel cells), compared to commercial platinum catalysts, astonishing activities are observed. In another example the selective and very cost efficient electrochemical synthesis of hydrogen peroxide is presented. In a last example the synthesis of graphitic boron carbon nitrides from the ionic liquid 1 - Ethyl - 3 - methylimidazolium - tetracyanoborate is investigated in detail. Due to the employment of unreactive salts as a new tool to generate high surface area these materials were first time shown to be another class of non - precious metal oxygen reduction electrocatalyst.
Im Rahmen einer prospektiven Längsschnittuntersuchung wurde der Berufseinstieg von ÄrztInnen (N = 185) als normatives kritisches Lebensereignis untersucht. Dazu wurden sie insgesamt drei Mal im Abstand von jeweils sechs Monaten im ersten Jahr nach ihrem Studiumsabschluss befragt (T1: in den ersten zwei Wochen nach dem Staatsexamen, T2: kurzzeitig nach dem Berufseinstieg, T3: im Schnitt 9.5 Monate nach dem Berufseinstieg). Die Ergebnisse zeigten zunächst, dass unlängst examinierte Jung-ÄrztInnen, die sich vergleichsweise schlechter auf den Beruf durch das Studium vorbereitet fühlten, ihren bevorstehenden Berufseinstieg negativer bewerteten und schon vor diesem beanspruchter waren. Die Bewertung des Berufseinstiegs vermittelte dabei den Zusammenhang zwischen einer schlechten Vorbereitung und der Beanspruchung. Arbeitsspezifische Copingfunktionalität wiederum pufferte den Zusammenhang zwischen einer schlechten Vorbereitung und der Bewertung des Berufseinstiegs. Das Problem einer als schlecht empfundenen Vorbereitung verdeutlichte sich in der Längsschnittanalyse – sie sagte eine höhere Beanspruchung zum zweiten Messzeitpunkt, d.h. nach dem Berufseinstieg, vorher. In der Untersuchung der Beanspruchungsentwicklung über die drei Messzeitpunkte hinweg fanden sich nur wenige Veränderungen. Es ließ sich zwar eine deutliche Zunahme der mittleren Depressivitäts-Ausprägungen über den Berufseinstieg hinweg herausstellen (T1-T2); auf anderen Beanspruchungsindikatoren zeigte sich jedoch kein direkter Effekt des Arbeitsbeginns bzw. fand sich auch keine Adaptation der Jung-ÄrztInnen an ihre neue Situation im Sinne einer sich verringernden Beanspruchung im weiteren Verlauf (T2-T3). In der Erklärung interindividueller Unterschiede in der Beanspruchung im Untersuchungszeitraum zeigte sich, dass die sich mit dem Berufseinstieg einstellende Arbeitsbelastung zum zweiten und dritten Messzeitpunkt erwartungsgemäß positiv mit Beanspruchung assoziiert war. Die Arbeitsbelastungs-Beanspruchungs-Beziehung bestand jedoch nur im Querschnitt; in der Längsschnittanalyse fand sich kein Effekt der T2-Arbeitsbelastung auf die T3-Beanspruchung. Ausgangsunterschiede in psychischen Ressourcen wirkten einerseits direkt auf die Beanspruchung zu T2, zum Teil moderierten sie aber auch den Zusammenhang zwischen der Arbeitsbelastung und Beanspruchung: Eine höhere Resilienz und die Wahrnehmung sozialer Unterstützung sagten eine geringere Beanspruchung nach dem Berufseinstieg vorher. Jung-ÄrztInnen, die sich durch eine stärkere Arbeitsbelastung auszeichneten, aber über ein funktionaleres Bewältigungsverhalten im Arbeitskontext verfügten, waren kurzzeitig nach dem Berufseinstieg weniger beansprucht als stark arbeitsbelastete Jung-ÄrztInnen mit weniger funktionalem Coping. Verringerungen in den psychischen Ressourcen über den Berufseinstieg hinweg wirkten sich direkt, d.h. per se ungünstig auf die Beanspruchung zum dritten Messzeitpunkt aus. Zudem interagierten sie mit der zu diesem Zeitpunkt bestehenden Arbeitsbelastung in Vorhersage der Beanspruchung. Stärker arbeitsbelastete Jung-ÄrztInnen, deren Copingfunktionalität und Wahrnehmung sozialer Unterstützung vom ersten zum dritten Messzeitpunkt abgenommen hatte, waren am Ende des Untersuchungszeitraums am stärksten beansprucht. Hinsichtlich der Auswirkungen des Berufseinstiegs auf die Persönlichkeit der Jung-ÄrztInnen fanden sich ungünstige Veränderungen: Sowohl die Ausprägungen psychischer Ressourcen (Widerstandsfähigkeit, Wahrnehmung sozialer Unterstützung hinsichtlich der Arbeitstätigkeit) als auch die der Big Five-Faktoren nahmen im Mittel ab. Interindividuelle Unterschiede in den Veränderungen ließen sich auf die Beanspruchung kurzzeitig nach dem Berufseinstieg (T2) bzw. auf deren Entwicklung in den Folgemonaten (T2-T3) zurückführen: Jene Jung-ÄrztInnen, die vergleichsweise stark beansprucht auf den Berufseinstieg reagiert hatten bzw. deren Beanspruchung im weiteren Verlauf zunahm, zeigten entsprechend ungünstige Veränderungen. Die Ergebnisse zusammengefasst verdeutlicht sich folgende Problematik: Jung-ÄrztInnen, die weniger gut, d.h. persönlichkeitsbasiert geschützt den Berufseinstieg absolvieren, reagieren stärker beansprucht und sind dann auch diejenigen, deren Persönlichkeit sich in den ersten Arbeitsmonaten ungünstig verändert. Jung-ÄrztInnen mit geringen psychischen Ressourcen sind folglich nicht nur besonders vulnerabel für die Entwicklung von Beanspruchung angesichts belastender Arbeitsbedingungen, sondern ihre vergleichsweise hohe Beanspruchung bedingt eine weitere Verringerung des Schutz- und Pufferpotenzials ihrer Persönlichkeit. Es kommt zu einer ungünstigen Akzentuierung der ohnehin schon vergleichsweise ressourcenschwachen Persönlichkeit, welche die Vulnerabilität für zukünftige Beanspruchung erhöht. Aus den Ergebnissen lässt sich ein Unterstützungsbedarf junger ÄrztInnen in der sensiblen und wegweisenden Berufseinstiegsphase ableiten. Neben einer Verbesserung ihrer Arbeitsbedingungen stellen eine rechtzeitige Sensibilisierung junger ÄrztInnen für den Arbeitsbelastungs-Beanspruchungs-Zusammenhang, ihre regelmäßige Supervision sowie vor allem aber auch kompetenzorientiertes und ressourcenstärkendes Feedback von den Mentoren und Vorgesetzten die Grundlage dafür dar, dass die Jung-MedizinerInnen selbst gesund bleiben und sie die ärztliche Tätigkeit trotz ihres wohl stets hohen Belastungspotenzials als erfüllend und zufriedenstellend erleben.
In this work, the development of a new molecular building block, based on synthetic peptides derived from decorin, is presented. These peptides represent a promising basis for the design of polymer-based biomaterials that mimic the ECM on a molecular level and exploit specific biological recognition for technical applications. Multiple sequence alignments of the internal repeats of decorin that formed the inner and outer surface of the arch-shaped protein were used to develop consensus sequences. These sequences contained conserved sequence motifs that are likely to be related to structural and functional features of the protein. Peptides representative for the consensus sequences were synthesized by microwave-assisted solid phase peptide synthesis and purified by RP-HPLC, with purities higher than 95 mol%. After confirming the desired masses by MALDI-TOF-MS, the primary structure of each peptide was investigated by 1H and 2D NMR, from which a full assignment of the chemical shifts was obtained. The characterization of the peptides conformation in solution was performed by CD spectroscopy, which demonstrated that using TFE, the peptides from the outer surface of decorin show a high propensity to fold into helical structures as observed in the original protein. To the contrary, the peptides from the inner surface did not show propensity to form stable secondary structure. The investigation of the binding capability of the peptides to Collagen I was performed by surface plasmon resonance analyses, from which all but one of the peptides representing the inner surface of decorin showed binding affinity to collagen with values of dissociation constant between 2•10-7 M and 2.3•10-4 M. On the other hand, the peptides representative for the outer surface of decorin did not show any significant interaction to collagen. This information was then used to develop experimental demonstration for the binding capabilities of the peptides from the inner surface of decorin to collagen even when used in more complicated situations close to possible appications. With this purpose, the peptide (LRELHLNNN) which showed the highest binding affinity to collagen (2•10-7 M) was functionalized with an N-terminal triple bond in order to obtain a peptide dimer via copper(I)-catalyzed cycloaddition reaction with 4,4'-diazidostilbene-2,2'-disulfonic acid. Rheological measurements showed that the presence of the peptide dimer was able to enhance the elastic modulus (G') of a collagen gel from ~ 600 Pa (collagen alone) to ~ 2700 Pa (collagen and peptide dimer). Moreover, it was shown that the mechanical properties of a collagen gel can be tailored by using different molar ratios of peptide dimer respect to collagen. The same peptide, functionalized with the triple bond, was used to obtain a peptide-dye conjugate by coupling it with N-(5'-azidopentanoyl)-5-aminofluorescein. An aqueous solution (5 vol% methanol) of the peptide dye conjugate was injected into a collagen and a hyaluronic acid (HA) gel and images of fluorescence detection showed that the diffusion of the peptide was slower in the collagen gel compared to the HA gel. The third experimental demonstration was gained using the peptide (LSELRLHNN) which showed the lower binding affinity (2.3•10-4 M) to collagen. This peptide was grafted to hyaluronic acid via EDC-chemistry, with a degree of functionalization of 7 ± 2 mol% as calculated by 1H-NMR. The grafting was further confirmed by FTIR and TGA measurements, which showed that the onset of decomposition for the HA-g-peptide decreased by 10 °C compared to the native HA. Rheological measurements showed that the elastic modulus of a system based on collagen and HA-g-peptide increased by almost two order of magnitude (G' = 200 Pa) compared to a system based on collagen and HA (G' = 0.9 Pa). Overall, this study showed that the synthetic peptides, which were identified from decorin, can be applied as potential building blocks for biomimetic materials that function via biological recognition.
Die internationale Staatengemeinschaft steht Sezessionsbestrebungen zur Aufspaltung bestehender Staaten gewöhnlich ablehnend gegenüber. Gleichzeitig wendet sie in vielen Ländern Instrumente der Entwicklungspolitik an und greift so auch in den dortigen politischen Prozess ein. Untersucht wird, inwiefern Entwicklungspolitik so gestaltet werden kann, dass sie nicht, quasi als Nebenwirkung, einer Sezessionsbewegung zum Durchbruch verhilft. Betrachtet wird dabei neben der gezielten Förderung wirtschaftlichen Wachstums auch das Instrument der Dezentralisierung, das oft als Mittel zur „Beruhigung“ separatistischer Bestrebungen vorgeschlagen wird. Zuvor jedoch wird aufgewiesen, dass eine Politik, die Sezessionen verhindern will, zumindest in vielen Fällen auch moralphilosophisch schlüssig begründet werden kann. Den Abschluss der Arbeit bilden drei Fallstudien zu Sezessionen auf dem Gebiet der ehemaligen Sowjetunion.
Ein neuentwickeltes azobenzenhaltiges Material, das auf einem supramolekularen Konzept basiert, wird bezüglich seiner Strukturbildung während einer holografischen Belichtung bei 488 nm untersucht. Im Mittelpunkt stehen dabei eindimensionale, sinusförmige Reliefs mit Periodizitäten kleiner 500 nm. Es wird gezeigt, wie der Grad der Vernetzung der photosensitiven Schicht die Strukturbildung in diesem Größenbereich beeinflusst. Zur Maximierung der Strukturtiefe werden gezielt Prozessparameter der Belichtung sowie Materialparameter variiert. Unter Standardbedingungen und moderaten Belichtungsintensitäten von ca. 200 mW/cm² bilden sich innerhalb weniger Minuten bei einer Periode von 400 nm Strukturtiefen von bis zu 80nm aus. Durch die Beeinflussung von Materialparametern, wie Oberflächenspannung und Viskosität, wird die maximale Strukturtiefe auf 160nm verdoppelt. Durch Mehrfachbelichtungen wird auch die Bildung von zweidimensionalen Gittern untersucht. Die Originalstrukturen werden in einem Abformverfahren kopiert und in Schichten von unter UV-Licht aushärtenden Polymeren übertragen. Durch das Abformen kommt es zu einer geringfügigen Verschlechterung der Oberflächenqualität sowie Abnahme der Strukturtiefe. Dieser Verlust wird durch eine Verringerung der Prozesstemperatur verringert. Mithilfe kopierter Oberflächengitter werden organische Distributed Feedback-(DFB)-Laser zweiter Ordnung hergestellt, um den Einfluss von Gitterparametern auf die Emissionseigenschaften dieser Laser zu untersuchen. Dazu erfolgt zunächst die Charakterisierung der optischen Verstärkungseigenschaften ausgewählter organischer Emittermaterialien mittels der Variablen Strichlängenmethode. Das mit dem Laserfarbstoff Pyrromthen567 (PM567) dotierte Polystyrol (PS) zeigt dabei trotz konzentrationsbedingter geringer Absorption eine vergleichsweise geringe Gewinnschwelle von 50µJ/cm² bei ca. 575 nm. Das aktive Gast-Wirt-System der konjugierten Polymere MEH-PPV und F8BT* weist eine hohe Absorption und eine kleine Gewinnschwelle von 2,5 µJ/cm² bei 630 nm auf. Dieses Verhalten spiegelt sich auch in den Emissionseigenschaften der damit hergestellten DFB-Laser wieder. Die Dicke der aktiven Schichten liegen im Bereich hunderter Nanometer und wird so eingestellt, dass sich nur die transversalen Grundmoden im Wellenleiter ausbreiten können. Die Gitterperiode sind so gewählt, dass ein Lichtmode im Verstärkungsbereich des Emittermaterials liegt. Die Emissionslinien der Laser sind mit FWHM-Werten von bis zu 0,3 nm spektral sehr schmalbandig und weisen auf eine sehr gute Gitterqualität hin. Die Untersuchungen liefern minimale Laserschwellen und maximale differentielle Effizienzen von 4,0µJ/cm² und 8,4% für MEH-PPV in F8BT* (bei ca. 640nm) sowie 80 µJ/cm² und 0,9% für PM567 in PS (bei ca. 575 nm). Die Vergrößerung der Strukturtiefe von 40nm auf 80nm in mit MEH-PPV dotierten F8BT*-Lasern zu einem deutlichen Anstieg der ausgekoppelten Energie sowie der differentiellen Effizienz und einem geringen Absinken der Laserschwelle. Dies ist ein Resultat der erhöhten Kopplung von Lasermode und Gitter. Die Emission von DFB-Lasern mit zweidimensionalen Oberflächengittern zeigen eine Verringerung der Divergenz aber kein Einfluss auf die Laserschwelle. Abschließend erfolgt eine Vermessung der Photostabilität von DFB-Lasern unter verschiedenen Bedingungen. Das Einbringen eines konjugierten Polymers in eine aktive Matrix sowie der Betrieb in einer Stickstoffatmosphäre führen dabei zu einer Erhöhung der Lebensdauer auf über eine Million Pulse. Durch die Kombination von Oberflächengittern in PDMS-Filmen mit elektroaktiven Substraten wird eine elektrisch steuerbare Deformation des Beugungsgitters erreicht und auf einen DFB-Laser übertragen. Die spannungsinduzierte Verformung wird zunächst in Beugungsexperimenten charakterisiert und ein optimaler Arbeitspunkt bestimmt. Mit den beiden Elastomeren SEBS12 und VHB4910 werden in den Gittern maximale Periodenänderungen von 1,3% bzw. 3,4% bei einer Steuerspannung von 2 kV erreicht. Der Unterschied resultiert aus den verschiedenen Elastizitätsmoduln der Materialien. Übertragen auf DFB-Laser resultiert eine Variation der Gitterperiode senkrecht zu den Gitterlinien in einer kontinuierlichen Verschiebung der Emissionswellenlänge. Mit einem Spannungssignal von 3,25 kV wird die schmalbandige Emission eines elastischen DFB-Lasers kontinuierlich um fast 50nm von 604 nm zu 557 nm hin verschoben. Aus dem Deformationsverhalten sowohl der reinen Beugungsgitter als auch der Laser werden Rückschlüsse auf die Elastizität der verwendeten Materialien gezogen und erlauben Verbesserungen der Bauteile.
AM symbiosis has a positive influence on plant P-nutrition and growth, but little is known about the molecular mechanism of the symbiosis adaptation to different phosphate conditions. The recently described induction of several pri-miR399 transcripts in mycorrhizal shoots and subsequent accumulation of mature miR399 in mycorrhizal roots indicates that local PHO2 expression must be controlled during symbiosis, presumably in order to sustain AM symbiosis development, in spite of locally increased Pi-concentration. A reverse genetic approach used in this study demonstrated that PHO2 and thus the PHR1-miR399-PHO2 signaling pathway, is involved in certain stages of progressive root colonization. In addition, a transcriptomic approach using a split-root system provided a comprehensive insight into the systemic transcriptional changes in mycorrhizal roots and shoots of M. truncatula in response to high phosphate conditions. With regard to the transcriptional responses of the root system, the results indicate that, although the colonization is drastically reduced, AM symbiosis is still functional at high Pi concentrations and might still be beneficial to the plant. Additionally, the data suggest that a specific root-borne mycorrhizal signal systemically induces protein synthesis, amino acid metabolism and photosynthesis at low Pi conditions, which is abolished at high Pi conditions. MiRNAs, such as miR399, are involved in long-distance signaling and are therefore potential systemic signals involved in AM symbiosis. A deep-sequencing approach identified 243 novel miRNAs in the root tissue of M. truncatula. Read-count analysis, qRT-PCR measurements and in situ hybridizations clearly indicated a regulation of miR5229a/b, miR5204, miR160f*, miR160c, miR169 and miR169d*/l*/m*/e.2* during arbuscular mycorrhizal symbiosis. Moreover, miR5204* represses a GRAS TF, which is specifically transcribed in mycorrhizal roots. Since miR5204* is induced by high Pi it might represent a further Pi status-mediating signal beside miR399. This study provides additional evidence that MtNsp2, a key regulator of symbiosis-signaling, is regulated and presumably spatially restricted by miR171h cleavage. In summary, a repression of mycorrhizal root colonization at high phosphate status is most likely due to a repression of the phosphate starvation responses and the loss of beneficial responses in mycorrhizal shoots. These findings provide a new basis for investigating the regulatory network leading to cellular reprogramming during interaction between plants, arbuscular mycorrhizal fungi and different phosphate conditions.
Genetic variation is crucial for the long-term survival of the species as it provides the potential for adaptive responses to environmental changes such as emerging diseases. The Major Histocompatibility Complex (MHC) is a gene family that plays a central role in the vertebrate’s immune system by triggering the adaptive immune response after exposure to pathogens. MHC genes have become highly suitable molecular markers of adaptive significance. They synthesize two primary cell surface molecules namely MHC class I and class II that recognize short fragments of proteins derived respectively from intracellular (e.g. viruses) and extracellular (e.g. bacteria, protozoa, arthropods) origins and present them to immune cells. High levels of MHC polymorphism frequently observed in natural populations are interpreted as an adaptation to detect and present a wide array of rapidly evolving pathogens. This variation appears to be largely maintained by positive selection driven mainly by pathogenic selective pressures. For my doctoral research I focused on MHC I and II variation in free-ranging cheetahs (Acinonyx jubatus) and leopards (Panthera pardus) on Namibian farmlands. Both felid species are sympatric thus subject to similar pathogenic pressures but differ in their evolutionary and demographic histories. The main aims were to investigate 1) the extent and patterns of MHC variation at the population level in both felids, 2) the association between levels of MHC variation and disease resistance in free-ranging cheetahs, and 3) the role of selection at different time scales in shaping MHC variation in both felids. Cheetahs and leopards represent the largest free-ranging carnivores in Namibia. They concentrate in unprotected areas on privately owned farmlands where domestic and other wild animals also occur and the risk of pathogen transmission is increased. Thus, knowledge on adaptive genetic variation involved in disease resistance may be pertinent to both felid species’ conservation. The cheetah has been used as a classic example in conservation genetics textbooks due to overall low levels of genetic variation. Reduced variation at MHC genes has been associated with high susceptibility to infectious diseases in cheetahs. However, increased disease susceptibility has only been observed in captive cheetahs whereas recent studies in free-ranging Namibian cheetahs revealed a good health status. This raised the question whether the diversity at MHC I and II genes in free-ranging cheetahs is higher than previously reported. In this study, a total of 10 MHC I alleles and four MHC II alleles were observed in 149 individuals throughout Namibia. All alleles but one likely belong to functional MHC genes as their expression was confirmed. The observed alleles belong to four MHC I and three MHC II genes in the species as revealed by phylogenetic analyses. Signatures of historical positive selection acting on specific sites that interact directly with pathogen-derived proteins were detected in both MHC classes. Furthermore, a high genetic differentiation at MHC I was observed between Namibian cheetahs from east-central and north-central regions known to differ substantially in exposure to feline-specific viral pathogens. This suggests that the patterns of MHC I variation in the current population mirrors different pathogenic selective pressure imposed by viruses. Cheetahs showed low levels of MHC diversity compared with other mammalian species including felids, but this does not seem to influence the current immunocompetence of free-ranging cheetahs in Namibia and contradicts the previous conclusion that the cheetah is a paradigm species of disease susceptibility. However, it cannot be ruled out that the low MHC variation might limit a prosperous immunocompetence in the case of an emerging disease scenario because none of the remaining alleles might be able to recognize a novel pathogen. In contrast to cheetahs, leopards occur in most parts of Africa being perhaps the most abundant big cat in the continent. Leopards seem to have escaped from large-scale declines due to epizootics in the past in contrast to some free-ranging large carnivore populations in Africa that have been afflicted by epizootics. Currently, no information about the MHC sequence variation and constitution in African leopards exists. In this study, I characterized genetic variation at MHC I and MHC II genes in free-ranging leopards from Namibia. A total of six MHC I and six MHC II sequences were detected in 25 individuals from the east-central region. The maximum number of sequences observed per individual suggests that they likely correspond to at least three MHC I and three MHC II genes. Hallmarks of MHC evolution were confirmed such as historical positive selection, recombination and trans-species polymorphism. The low MHC variation detected in Namibian leopards is not conclusive and further research is required to assess the extent of MHC variation in different areas of its geographic range. Results from this thesis will contribute to better understanding the evolutionary significance of MHC and conservation implications in free-ranging felids. Translocation of wildlife is an increasingly used management tool for conservation purposes that should be conducted carefully as it may affect the ability of the translocated animals to cope with different pathogenic selective pressures.
Top-Manager stehen seit einigen Jahren verstärkt im Visier der Medien. Durch die mediale Aufmerksamkeit erlangen sie einen Prominentenstatus, der in der angloamerikanischen Managementforschung zu schillernden Bezeichnungen wie Celebrity CEO oder Superstar CEO führt. Nadine Bültel widmet sich in ihrer Arbeit diesem neuartigen Star- Phänomen von Top-Managern und untersucht die Ursachen und Auswirkungen ihrer medialen Prominenz. Sie analysiert, wie Manager eine Starreputation aufbauen und welche Rolle die Medien hierbei spielen. Im Mittelpunkt steht dabei auch die Frage, ob und warum Starmanager eine höhere Vergütung erhalten als ihre weniger prominenten Kollegen.
Public debate about energy relations between the EU and Russia is distorted. These distortions present considerable obstacles to the development of true partnership. At the core of the conflict is a struggle for resource rents between energy producing, energy consuming and transit countries. Supposed secondary aspects, however, are also of great importance. They comprise of geopolitics, market access, economic development and state sovereignty. The European Union, having engaged in energy market liberalisation, faces a widening gap between declining domestic resources and continuously growing energy demand. Diverse interests inside the EU prevent the definition of a coherent and respected energy policy. Russia, for its part, is no longer willing to subsidise its neighbouring economies by cheap energy exports. The Russian government engages in assertive policies pursuing Russian interests. In so far, it opts for a different globalisation approach, refusing the role of mere energy exporter. In view of the intensifying struggle for global resources, Russia, with its large energy potential, appears to be a very favourable option for European energy supplies, if not the best one. However, several outcomes of the strategic game between the two partners can be imagined. Engaging in non-cooperative strategies will in the end leave all stakeholders worse-off. The European Union should therefore concentrate on securing its partnership with Russia instead of damaging it. Stable cooperation would need the acceptance that the partner may pursue his own goals, which might be different from one’s own interests. The question is, how can a sustainable compromise be found? This thesis finds that a mix of continued dialogue, a tit for tat approach bolstered by an international institutional framework and increased integration efforts appears as a preferable solution.
The present thesis was born and evolved within the RAdial Velocity Experiment (RAVE) with the goal of measuring chemical abundances from the RAVE spectra and exploit them to investigate the chemical gradients along the plane of the Galaxy to provide constraints on possible Galactic formation scenarios. RAVE is a large spectroscopic survey which aims to observe spectroscopically ~10^6 stars by the end of 2012 and measures their radial velocities, atmospheric parameters and chemical abundances. The project makes use of the UK Schmidt telescope at Australian Astronomical Observatory (AAO) in Siding Spring, Australia, equipped with the multiobject spectrograph 6dF. To date, RAVE collected and measured more than 450,000 spectra. The precision of the chemical abundance estimations depends on the reliability of the atomic and atmosphere parameters adopted (in particular the oscillator strengths of the absorption lines and the effective temperature, gravity, and metallicity of the stars measured). Therefore we first identified 604 absorption lines in the RAVE wavelength range and refined their oscillator strengths with an inverse spectral analysis. Then, we improved the RAVE stellar parameters by modifying the RAVE pipeline and the spectral library the pipeline rely on. The modifications removed some systematic errors in stellar parameters discovered during this work. To obtain chemical abundances, we developed two different processing pipelines. Both of them perform chemical abundances measurements by assuming stellar atmospheres in Local Thermodynamic Equilibrium (LTE). The first one determines elements abundances from equivalent widths of absorption lines. Since this pipeline showed poor sensibility on abundances relative to iron, it has been superseded. The second one exploits the chi^2 minimization technique between observed and model spectra. Thanks to its precision, it has been adopted for the creation of the RAVE chemical catalogue. This pipeline provides abundances with uncertains of about ~0.2dex for spectra with signal-to-noise ratio S/N>40 and ~0.3dex for spectra with 20>S/N>40. For this work, the pipeline measured chemical abundances up to 7 elements for 217,358 RAVE stars. With these data we investigated the chemical gradients along the Galactic radius of the Milky Way. We found that stars with low vertical velocities |W| (which stay close to the Galactic plane) show an iron abundance gradient in agreement with previous works (~-0.07$ dex kpc^-1) whereas stars with larger |W| which are able to reach larger heights above the Galactic plane, show progressively flatter gradients. The gradients of the other elements follow the same trend. This suggests that an efficient radial mixing acts in the Galaxy or that the thick disk formed from homogeneous interstellar matter. In particular, we found hundreds of stars which can be kinetically classified as thick disk stars exhibiting a chemical composition typical of the thin disk. A few stars of this kind have already been detected by other authors, and their origin is still not clear. One possibility is that they are thin disk stars kinematically heated, and then underwent an efficient radial mixing process which blurred (and so flattened) the gradient. Alternatively they may be a transition population" which represents an evolutionary bridge between thin and thick disk. Our analysis shows that the two explanations are not mutually exclusive. Future follow-up high resolution spectroscopic observations will clarify their role in the Galactic disk evolution.
In the living cell, the organization of the complex internal structure relies to a large extent on molecular motors. Molecular motors are proteins that are able to convert chemical energy from the hydrolysis of adenosine triphosphate (ATP) into mechanical work. Being about 10 to 100 nanometers in size, the molecules act on a length scale, for which thermal collisions have a considerable impact onto their motion. In this way, they constitute paradigmatic examples of thermodynamic machines out of equilibrium. This study develops a theoretical description for the energy conversion by the molecular motor myosin V, using many different aspects of theoretical physics. Myosin V has been studied extensively in both bulk and single molecule experiments. Its stepping velocity has been characterized as a function of external control parameters such as nucleotide concentration and applied forces. In addition, numerous kinetic rates involved in the enzymatic reaction of the molecule have been determined. For forces that exceed the stall force of the motor, myosin V exhibits a 'ratcheting' behaviour: For loads in the direction of forward stepping, the velocity depends on the concentration of ATP, while for backward loads there is no such influence. Based on the chemical states of the motor, we construct a general network theory that incorporates experimental observations about the stepping behaviour of myosin V. The motor's motion is captured through the network description supplemented by a Markov process to describe the motor dynamics. This approach has the advantage of directly addressing the chemical kinetics of the molecule, and treating the mechanical and chemical processes on equal grounds. We utilize constraints arising from nonequilibrium thermodynamics to determine motor parameters and demonstrate that the motor behaviour is governed by several chemomechanical motor cycles. In addition, we investigate the functional dependence of stepping rates on force by deducing the motor's response to external loads via an appropriate Fokker-Planck equation. For substall forces, the dominant pathway of the motor network is profoundly different from the one for superstall forces, which leads to a stepping behaviour that is in agreement with the experimental observations. The extension of our analysis to Markov processes with absorbing boundaries allows for the calculation of the motor's dwell time distributions. These reveal aspects of the coordination of the motor's heads and contain direct information about the backsteps of the motor. Our theory provides a unified description for the myosin V motor as studied in single motor experiments.
In the present work synchronization phenomena in complex dynamical systems exhibiting multiple time scales have been analyzed. Multiple time scales can be active in different manners. Three different systems have been analyzed with different methods from data analysis. The first system studied is a large heterogenous network of bursting neurons, that is a system with two predominant time scales, the fast firing of action potentials (spikes) and the burst of repetitive spikes followed by a quiescent phase. This system has been integrated numerically and analyzed with methods based on recurrence in phase space. An interesting result are the different transitions to synchrony found in the two distinct time scales. Moreover, an anomalous synchronization effect can be observed in the fast time scale, i.e. there is range of the coupling strength where desynchronization occurs. The second system analyzed, numerically as well as experimentally, is a pair of coupled CO₂ lasers in a chaotic bursting regime. This system is interesting due to its similarity with epidemic models. We explain the bursts by different time scales generated from unstable periodic orbits embedded in the chaotic attractor and perform a synchronization analysis of these different orbits utilizing the continuous wavelet transform. We find a diverse route to synchrony of these different observed time scales. The last system studied is a small network motif of limit cycle oscillators. Precisely, we have studied a hub motif, which serves as elementary building block for scale-free networks, a type of network found in many real world applications. These hubs are of special importance for communication and information transfer in complex networks. Here, a detailed study on the mechanism of synchronization in oscillatory networks with a broad frequency distribution has been carried out. In particular, we find a remote synchronization of nodes in the network which are not directly coupled. We also explain the responsible mechanism and its limitations and constraints. Further we derive an analytic expression for it and show that information transmission in pure phase oscillators, such as the Kuramoto type, is limited. In addition to the numerical and analytic analysis an experiment consisting of electrical circuits has been designed. The obtained results confirm the former findings.
Turning wind into power : effects of stakeholder networks on renewalbe energy governanace in India
(2011)
Actin-based directional motility is important for embryonic development, wound healing, immune responses, and development of tissues. Actin and myosin are essential players in this process that can be subdivided into protrusion, adhesion, and traction. Protrusion is the forward movement of the membrane at the leading edge of the cell. Adhesion is required to enable movement along a substrate, and traction finally leads to the forward movement of the entire cell body, including its organelles. While actin polymerization is the main driving force in cell protrusions, myosin motors lead to the contraction of the cell body. The goal of this work was to study the regulatory mechanisms of the motile machinery by selecting a representative key player for each stage of the signaling process: the regulation of Arp2/3 activity by WASP (actin system), the role of cGMP in myosin II assembly (myosin system), and the influence of phosphoinositide signaling (upstream receptor pathway). The model organism chosen for this work was the social ameba Dictyostelium discoideum, due to the well-established knowledge of its cytoskeletal machinery, the easy handling, and the high motility of its vegetative and starvation developed cells. First, I focused on the dynamics of the actin cytoskeleton by modulating the activity of one of its key players, the Arp2/3 complex. This was achieved using the carbazole derivative Wiskostatin, an inhibitor of the Arp2/3 activator WASP. Cells treated with Wiskostatin adopted a round shape, with no of few pseudopodia. With the help of a microfluidic cell squeezer device, I could show that Wiskostatin treated cells display a reduced mechanical stability, comparable to cells treated with the actin disrupting agent Latrunculin A. Furthermore, the WASP inhibited cells adhere stronger to a surface and show a reduced motility and chemotactic performance. However, the overall F-actin content in the cells was not changed. Confocal microscopy and TIRF microscopy imaging showed that the cells maintained an intact actin cortex. Localized dynamic patches of increased actin polymerization were observed that, however, did not lead to membrane deformation. This indicated that the mechanisms of actin-driven force generation were impaired in Wiskostatin treated cells. It is concluded that in these cells, an altered architecture of the cortical network leads to a reduced overall stiffness of the cell, which is insufficient to support the force generation required for membrane deformation and pseudopod formation. Second, the role of cGMP in myosin II dynamics was investigated. Cyclic GMP is known to regulate the association of myosin II with the cytoskeleton. In Dictyostelium, intracellular cGMP levels increase when cells are exposed to chemoattractants, but also in response to osmotic stress. To study the influence of cyclic GMP on actin and myosin II dynamics, I used the laser-induced photoactivation of a DMACM-caged-Br-cGMP to locally release cGMP inside the cell. My results show that cGMP directly activates the myosin II machinery, but is also able to induce an actin response independently of cAMP receptor activation and signaling. The actin response was observed in both vegetative and developed cells. Possible explanations include cGMP-induced actin polymerization through VASP (vasodilator-stimulated phosphoprotein) or through binding of cGMP to cyclic nucleotide-dependent kinases. Finally, I investigated the role of phosphoinositide signaling using the Polyphosphoinositide-Binding Peptide (PBP10) that binds preferentially to PIP2. Phosphoinositides can recruit actin-binding proteins to defined subcellular sites and alter their activity. Neutrophils, as well as developed Dictyostelium cells produce PIP3 in the plasma membrane at their leading edge in response to an external chemotactic gradient. Although not essential for chemotaxis, phosphoinositides are proposed to act as an internal compass in the cell. When treated with the peptide PBP10, cells became round, with fewer or no pseudopods. PH-CRAC translocation to the membrane still occurs, even at low cAMP stimuli, but cell motility (random and directional) was reduced. My data revealed that the decrease in the pool of available PIP2 in the cell is sufficient to impair cell motility, but enough PIP2 remains so that PIP3 is formed in response to chemoattractant stimuli. My data thus highlights how sensitive cell motility and morphology are to changes in the phosphoinositide signaling. In summary, I have analyzed representative regulatory mechanisms that govern key parts of the motile machinery and characterized their impact on cellular properties including mechanical stability, adhesion and chemotaxis.
Corvino, Corvino and Schoen, Chruściel and Delay have shown the existence of a large class of asymptotically flat vacuum initial data for Einstein's field equations which are static or stationary in a neighborhood of space-like infinity, yet quite general in the interior. The proof relies on some abstract, non-constructive arguments which makes it difficult to calculate such data numerically by using similar arguments. A quasilinear elliptic system of equations is presented of which we expect that it can be used to construct vacuum initial data which are asymptotically flat, time-reflection symmetric, and asymptotic to static data up to a prescribed order at space-like infinity. A perturbation argument is used to show the existence of solutions. It is valid when the order at which the solutions approach staticity is restricted to a certain range. Difficulties appear when trying to improve this result to show the existence of solutions that are asymptotically static at higher order. The problems arise from the lack of surjectivity of a certain operator. Some tensor decompositions in asymptotically flat manifolds exhibit some of the difficulties encountered above. The Helmholtz decomposition, which plays a role in the preparation of initial data for the Maxwell equations, is discussed as a model problem. A method to circumvent the difficulties that arise when fast decay rates are required is discussed. This is done in a way that opens the possibility to perform numerical computations. The insights from the analysis of the Helmholtz decomposition are applied to the York decomposition, which is related to that part of the quasilinear system which gives rise to the difficulties. For this decomposition analogous results are obtained. It turns out, however, that in this case the presence of symmetries of the underlying metric leads to certain complications. The question, whether the results obtained so far can be used again to show by a perturbation argument the existence of vacuum initial data which approach static solutions at infinity at any given order, thus remains open. The answer requires further analysis and perhaps new methods.
Fundraising interdisziplinär : ein Beitrag zur Erneuerung der Kultur gemeinwohlbezogenen Gebens
(2011)
Non-mycorrhizal fungal endophytes are able to colonize internally roots without causing visible disease symptoms establishing neutral or mutualistic associations with plants. These fungi known as non-clavicipitaceous endophytes have a broad host range of monocot and eudicot plants and are highly diverse. Some of them promote plant growth and confer increased abiotic-stress tolerance and disease resistance. According to such possible effects on host plants, it was aimed to isolate and to characterize native fungal root endophytes from tomato (Lycopersicon esculentum Mill.) and to analyze their effects on plant development, plant resistance and fruit yield and quality together with the model endophyte Piriformospora indica. Fifty one new fungal strains were isolated from desinfected tomato roots of four different crop sites in Colombia. These isolates were roughly characterized and fourteen potential endophytes were further analyzed concerning their taxonomy, their root colonization capacity and their impact on plant growth. Sequencing of the ITS region from the ribosomal RNA gene cluster and in-depth morphological characterisation revealed that they correspond to different phylogenetic groups among the phylum Ascomycota. Nine different morphotypes were described including six dark septate endophytes (DSE) that did not correspond to the Phialocephala group. Detailed confocal microscopy analysis showed various colonization patterns of the endophytes inside the roots ranging from epidermal penetration to hyphal growth through the cortex. Tomato pot experiments under glass house conditions showed that they differentially affect plant growth depending on colonization time and inoculum concentration. Three new isolates (two unknown fungal endophyte DSE48, DSE49 and one identified as Leptodontidium orchidicola) with neutral or positiv effects were selected and tested in several experiments for their influence on vegetative growth, fruit yield and quality and their ability to diminish the impact of the pathogen Verticillium dahliae on tomato plants. Although plant growth promotion by all three fungi was observed in young plants, vegetative growth parameters were not affected after 22 weeks of cultivation except a reproducible increase of root diameter by the endophyte DSE49. Additionally, L. orchidicola increased biomass and glucose content of tomato fruits, but only at an early date of harvest and at a certain level of root colonization. Concerning bioprotective effects, the endophytes DSE49 and L. orchidicola decreased significantly disease symptoms caused by the pathogen V. dahliae, but only at a low dosis of the pathogen. In order to analyze, if the model root endophytic fungus Piriformospora indica could be suitable for application in production systems, its impact on tomato was evaluated. Similarly to the new fungal isolates, significant differences for vegetative growth parameters were only observable in young plants and, but protection against V. dahliae could be seen in one experiment also at high dosage of the pathogen. As the DSE L. orchidicola, P. indica increased the number and biomass of marketable tomatoes only at the beginning of fruit setting, but this did not lead to a significant higher total yield. If the effects on growth are due to a better nutrition of the plant with mineral element was analyzed in barley in comparison to the arbuscular mycorrhizal fungus Glomus mosseae. While the mycorrhizal fungus increased nitrogen and phosphate uptake of the plant, no such effect was observed for P. indica. In summary this work shows that many different fungal endophytes can be also isolated from roots of crops and, that these isolates can have positive effects on early plant development. This does, however, not lead to an increase in total yield or in improvement of fruit quality of tomatoes under greenhouse conditions.
A systems biological approach towards the molecular basis of heterosis in Arabidopsis thaliana
(2011)
Heterosis is defined as the superiority in performance of heterozygous genotypes compared to their corresponding genetically different homozygous parents. This phenomenon is already known since the beginning of the last century and it has been widely used in plant breeding, but the underlying genetic and molecular mechanisms are not well understood. In this work, a systems biological approach based on molecular network structures is proposed to contribute to the understanding of heterosis. Hybrids are likely to contain additional regulatory possibilities compared to their homozygous parents and, therefore, they may be able to correctly respond to a higher number of environmental challenges, which leads to a higher adaptability and, thus, the heterosis phenomenon. In the network hypothesis for heterosis, presented in this work, more regulatory interactions are expected in the molecular networks of the hybrids compared to the homozygous parents. Partial correlations were used to assess this difference in the global interaction structure of regulatory networks between the hybrids and the homozygous genotypes. This network hypothesis for heterosis was tested on metabolite profiles as well as gene expression data of the two parental Arabidopsis thaliana accessions C24 and Col-0 and their reciprocal crosses. These plants are known to show a heterosis effect in their biomass phenotype. The hypothesis was confirmed for mid-parent and best-parent heterosis for either hybrid of our experimental metabolite as well as gene expression data. It was shown that this result is influenced by the used cutoffs during the analyses. Too strict filtering resulted in sets of metabolites and genes for which the network hypothesis for heterosis does not hold true for either hybrid regarding mid-parent as well as best-parent heterosis. In an over-representation analysis, the genes that show the largest heterosis effects according to our network hypothesis were compared to genes of heterotic quantitative trait loci (QTL) regions. Separately for either hybrid regarding mid-parent as well as best-parent heterosis, a significantly larger overlap between the resulting gene lists of the two different approaches towards biomass heterosis was detected than expected by chance. This suggests that each heterotic QTL region contains many genes influencing biomass heterosis in the early development of Arabidopsis thaliana. Furthermore, this integrative analysis led to a confinement and an increased confidence in the group of candidate genes for biomass heterosis in Arabidopsis thaliana identified by both approaches.