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Deterministic Versus Stochastic Description of Nonlinear Dynamical Units
No full textThe dynamics in biological systems like genetic or neural networks is intrinsically stochastic. In general it is realized with a finite and fluctuating number of reactants, and reactions happen stochastically in space and time. In certain limiting cases the dynamics simplifies and allows for a deterministic description. However, when the focus is on parameter ranges for which these limits do not apply, the deterministic equations may lead to qualitatively wrong predictions of the stationary states. In the first part we consider coupled nonlinear circuits with different collective coherent behaviour. As a function of a single increasing bifurcation parameter the system shows collective fixed-point behaviour, followed by collective synchronized oscillations and again fixed-point behaviour. If we zoom into the transition region between these different stationary states, we find different patterns of how the oscillations get launched and how they later get sequentially arrested. In the second part of the thesis we consider the impact of noise, first in a refined description of the type of circuit that we considered before. There it is analysed under what conditions a coarser time resolution leads back to the original coarse-grained description and justifies the coarse-graining. We also consider another class of systems, phase oscillators, and pursue the migration of oscillator phases under the action of noise through an attractor landscape. The attractor landscape is rather rough and hierarchical, primarily due to the choice of frustrated bonds. The role of noise is also the main interest in a third class of dynamical units, which act as players in games of competition. It turns out that in these games the deterministic (mean-field) equations correctly predict the qualitative patterns of coexistence of species and coalitions between them. Patterns of coexisting spirals and domains are of special interest, because the coexistence implies to see games within games
Collective Action for the management of the fishery in the Ciénaga Grande de Santa Marta, northern Colombia
No full textThis dissertation investigates factors influencing collective action in the management of the Ciénaga Grande de Santa Marta (CGSM) fishery. The CGSM is an estuarine lagoon located in the Caribbean coast of Colombia and it is one of the most important fisheries in the country. Formally, it is part of various conservation regimes, but it is under a de facto open access regime.
The thesis presents the results of three research articles. The first article investigates why collective action for a sustainable use of the CGSM’s fishery resources has not taken place. For this purpose, Elinor Ostrom’s diagnostic Social-Ecological System framework (2009) was adapted to this coastal ecosystem. In the second article, individual and composite indicators were built to investigate the ecological impact of fishing spots and fishing gear/methods used by the CGSM’s fishermen from two different points of view, from (1) a group of experienced fishermen and (2) a group of experts with extensive knowledge on that fishery. Likewise, the influence of socioeconomic and perceptional factors on fishing behavior of the CGSM’s fishermen and how this behavior may be impacting CGSM fishery resources were analysed. The third article examines if fishermen’s contributions to a one-shot public goods experiment, together with their decisions in two time preferences experiments, can predict the level of ecological impact they exert on the CGSM’s fishery resources in real life. Therefore, it examines the external validity of these experiments.
The results show that collective action in the CGSM is contextually related to the social, economic and political settings, and a lack of problem recognition among some fishermen. Likewise, they have shown that cooperation among fishermen is possible in the experiments but outside of the experimental setting it is necessary to address the contextual factors in order to promote collective action
Quality Regulation for Monopolistic Electricity Distribution Network Companies: A Theoretical and Experimental Analysis within a Principal-Agent Framework
No full textA part of the assets built in the 60s and 70s owned by a typical monopolistic electricity distribution system operator (DSO) in Western Europe is quite old and approaching the wear-out period of their bathtub curves. The resulting increases in asset failure rates lead to higher probability of service interruptions and hence reduce the quality (reliability) level in the entire network. Assuming an ideal welfare-maximizing quality regulation (along with price-based regulation), this should incentivize the profit-maximizing DSO owner to replace these assets before the quality level begins to decline, i.e. to invest at a welfare-maximizing point in time. In such an environment, the DSO owner needs to pass these incentives on to the Chief Executive Officer (CEO) is in charge of investment decision making. This should then allow the DSO owner to undertake the profit-maximizing investments. The DSO owner believes that this transfer of his incentives can be done by a labour contract in line with the industry standard. But will the CEO behave in the interest of the DSO owner regarding profit maximization and replacement investments? This thesis shows by using a theoretical model that the own-expected-total-earnings-maximizing CEO does not behave in the interest of the profit-maximizing DSO owner because he avoids the necessary replacement investments near the end of his labour contract. Therefore, an alternative labour contract that deviates from the industry standard is proposed which encourages the CEO to act in the interest of the DSO owner and in the interest of the overall welfare maximization. Hence, the thesis uses an experiment in order to confirm the theoretical results in practice. Experimental results suggest that not every CEO with idiosyncratic risk preferences behaves according to the theoretical model. This can be explained by the fact that the experiment participants showed different behavioural types, such as indirect reciprocity, conformity, guilt aversion or forward induction, which influenced investment behaviour. In contrast, individual distribution preferences or risk attitudes showed no influence on investment behaviour. Interestingly, no participant in the experiment made the necessary replacement investments near the end of the standard labour contract. Given the stated alternative contract format, 9.5% of the respondents have made necessary investments on time. Therefore, seen from an overall welfare-maximizing perspective the results of the experiment argue to implement the alternative labour contract. A further result, which is based on the experimental data, is that the implementation of the alternative labour contract instead of the standard labour contract is more profitable for the DSO owner, regardless whether the CEO is a risk-neutral own-expected-total-earnings maximizer or a risk-neutral, non-compulsory own-expected-total-earnings maximizer. So, it is sufficient for the regulator to give the DSO owner rather a recommendation than a law or a forcing resolution to implement the alternative labour contract, because it is in the owner’s own (profit-maximizing) interest to offer the alternative rather than the standard labour contract
Geometry of Membrane Sigma Models
No full textString theory still remains one of the promising candidates for a unification of the theory of gravity and quantum field theory. One of its essential parts is relativistic description of moving multi-dimensional objects called membranes (or p-branes) in a curved spacetime. On the classical field theory level, they are described by an action functional extremalising the volume of a manifold swept by a propagating membrane. This and related field theories are collectively called membrane sigma models.
Differential geometry is an important mathematical tool in the study of string theory. It turns out that string and membrane backgrounds can be conveniently described using objects defined on a direct sum of tangent and cotangent bundles of the spacetime manifold. Mathe- matical field studying such object is called generalized geometry. Its integral part is the theory of Leibniz algebroids, vector bundles with a Leibniz algebra bracket on its module of smooth sections. Special cases of Leibniz algebroids are better known Lie and Courant algebroids.
This thesis is divided into two main parts. In the first one, we review the foundations of the theory of Leibniz algebroids, generalized geometry, extended generalized geometry, and Nambu- Poisson structures. The main aim is to provide the reader with a consistent introduction to the mathematics used in the published papers. The text is a combination both of well known results and new ones. We emphasize the notion of a generalized metric and of corresponding orthogonal transformations, which laid the groundwork of our research. The second main part consists of four attached papers using generalized geometry to treat selected topics in string and membrane theory. The articles are presented in the same form as they were published
Development of a management system for large scale algae cultures
No full textCyanobacteria and microalgae are versatile organisms for which many possible applications are proposed. Presently the economical viable applications are limited to waste water remediation and biomass production for human consumption. The widespread industrial growth of cyanobacteria and microalgae is prevented by the high costs, the low productivity and the stability of the production process. The improvement of the production process is desirable because of its independence from arable land. The work reported in this PhD thesis was aimed to develop a management system to improve long time stability of outdoor open pond algae cultures grown under extreme environmental conditions.
Therefore indigenous algae were isolated from a reed bed water treatment plant in the arid al-Wusta region of the Sultanate of Oman. They were tested for high growth rates under increasing salt stress and at high temperatures in the laboratory. The isolated species Cyanobacterium aponinum and Scenedesmus spec. were selected for growth in outdoor open pond systems. After growth was established in 600L open pond cultures it was shown that other algae would invade the cultures operated in batch mode. After harvesting the cultures every other day the pH of the cultures increased to values of up to 10.5 and the salinity did not exceed 25 mS/ cm. C. aponinum cultures reached a product ivity of 24 g/m²/ day while the contamination with other algae reached a 2 % cell/ cell threshold on day 12. Scenedesmus cultures reached a productivity of 16 g/m²/ day with contaminations breaching the 2 % cell/ cell value after 26 days the latest . This was repeated in two consecutive years.
It was shown that simple steps during the management of an algae growth process have a tremendous impact on the assertiveness of unwanted indigenous algae and the productivity of the production strain. The findings of this thesis are the first steps on other ways to manage open pond cultures. Other management modes like continuous growth and harvesting or maintaining certain nutrient levels might permit new algae to grow outdoors at economical viable production rates
Controlled Electrodeposition of Zinc Oxide : Bespoke ZnO Nanostructure Arrays and their Role in Photovoltaics
No full textNanotechnology is a key technology to provide innovation. Nano-structured materials feature unique properties that enhance technological performance. The focus of this thesis is on the analysis of the growth of electrodeposited ZnO nano-rods from aqueous zinc nitrate solution. Electrodeposition is a low-temperature method and a cost-efficient way to produce ZnO nano-structures. This deposition method offers several parameters to control the growth of ZnO and is suitable for deposition on plastic substrates.
In the beginning of the chapter results and discussion, the crystal quality of electrodeposited ZnO nano-rods is analysed via SEM, TEM and Raman spectroscopy. A high crystal quality of the electrodeposited ZnO structures is found. This is followed by a systematic parametric study of the interdependence between structure growth and the main electrodeposition growth parameters: bath temperature, deposition voltage and electrolyte concentration. The results are discussed and compared to literature. In this context, the deposition time dependent current during electrodeposition has been analysed to monitor crystal growth. Characteristic features in the chronoamperograms were related to certain growth stages, e.g. the point of maximal surface area. The specific maximal surface areas at various growth conditions were compared and efficient growth conditions for maximal structure surfaces were identified.
A rather sparse formation of ZnO nanostructures on indium tin oxide (ITO) substrates was observed. It was assumed that the formation is limited by the surface pH on the working electrode. By modelling the ion diffusion during growth, the development of the OH- gradient during the reaction was described. Pulsed voltage deposition was introduced to control the OH- surface concentration (surface pH) and, thus stimulate nucleation. The model was supported by experiments, which confirmed that the sparse nucleation of ZnO nanostructures on ITO can be significantly enhanced by pulsing the deposition voltage. According to the model, the time interval between the growth periods is supposed to be at least 2.4 times longer than the growth period.
The final part of the thesis outlines the application of the investigated growth strategies in the field of photovoltaics. It is described, that absorption limited solar cell efficiencies can be enhanced by light scattering of the incident light on nanostructures. The intensity of the scattered light can be tuned by the nano-rod dimensions of the nano-structure array. In this context, ZnO arrays of different array density and rod heights were prepared on ITO via pulsed voltage deposition. Angle resolved diffusive light scatter properties were investigated in dependence on the array density and rod height. The experiments were supported by a model that predicts an ideally 50 % coverage of the substrate with nano-structures and an optimum rod height dependent on the solar cell specific material properties.
This thesis presents a highly systematic study on the fabrication of bespoke ZnO nanostructure arrays via controlled electrodeposition. It contributes to a deeper understanding of nucleation and growth of electrodeposited ZnO and provides new approaches towards nucleation and growth strategies. First ideas for potential application, e.g. in the field of photovoltaics, has been proven to be very promising. Light scattering on ZnO nano-structures can improve thin film solar cell absorption by elongating the pathway of light in the solar cell. This thesis offers a solid foundation for future work on the investigation on the application of electrodeposited ZnO nano-structure arrays in photovoltaics
Subversion in the Soviet Animation of the Brezhnev Period : An Aesopian Reading of Andrei Khrzhanovsky's Pushkiniana
No full textDespite Leonid Brezhnev's efforts to undo the consequences of his predecessor's more tolerant cultural policies, many trends in art, literature, social and political thought that had begun during Nikita Khrushchev's 'Thaw' continued into Brezhnev's 'Stagnation.' And not only did they, according to Stephen Lowell and Rosalind Marsh, continue, but they intensified, following the bifurcation of the Soviet cultural realm into official and unofficial spheres. Despite what the dichotomy of official/unofficial suggests, the two realms were not completely separate from each other. The official artists, who were both familiar with and sympathetic towards the ideas, themes and forms explored in the unofficial realm of Soviet culture, could not ignore these if they wanted their work to possess some cultural relevance. Working under the conditions of censorship, however, they could not express their creative ideas as openly as the unofficial artists; therefore, they had to develop strategies and devices that would allow them to preserve their personal integrity and artistic reputation and, at the same time, avoid confrontation with the Soviet censorship apparatus. This project is about such strategies and devices, the people who resorted to using them and, consequently, the people whose job it was to not be fooled by them. In the first three chapters I explore the historical context within which anti-censorship practices developed; the fourth chapter deals with the notion of subversion and the reasons for theorizing anti-censorship practices as subversive. In the final chapter, using a method of Aesopian analysis developed from Lev Loseff's model of Aesopian language, I analyze Andrei Khrzhanovsky's trilogy about the famous Russian poet Alexander Pushkin and argue that the films, which appear to be biographical essays, are as much about life and work of Pushkin as they are about the conflict between the creative intelligentsia and the Brezhnev's regime
Fluorescent Probes in Biomolecular Systems: Information on Peptide Dynamics and Analyte Uptake into Live Cells
No full textIn my thesis two main projects of my PhD is explained the in chapters 2 and 3 following a pertinent introduction for understanding the projects better in Chapter 1.
In chapter 2, the effect of charge repulsion on homo repeat hexapeptides will be explained. The peptides investigated are homo repeats of either acidic (Glu,Asp) or a basic (Arg, His and Lys) amino acid and labeled at two ends for measuring their end-to-end distance and flexibility by methods explained in great detail in chapters 1 and 2. As a function of pH, negative or positive charges appear on the peptide side chains. The repulsion occurs mainly between the N-terminus and the side chains in basic peptides. Astonishingly, no effective negative charge repulsion among the acidic side chains or the C-terminus with the side chains was observed. This can be explained by the difference in binding affinities of water towards carboxylates versus positively charged groups, which results in screening of the negative charges. Charge repulsion between negative charges was recovered when I changed the solvent from water to a 92.5% methanol/water.
In the second project –that was explained in Chapter 3− an in vivo host‒dye displacement was carried out: In this project V79 and CHO cells were loaded with a host−dye complex called p-sulfonatocalix[4]arene (CX4) / lucigenin (LCG). The fluorescence of LCG is quenched inside the CX4. The cationic analytes acetylcholine, choline and protamine were sent into the cells. The dye displaced with analyte and made a fluorescence turn-on signal. The invented method can be used for assaying the analyte in the cells. My results also show that CX4 facilitate the membrane passage of LCG. Therefore, CX4 can be considered as a carrier
Femtosecond Time-resolved Exciton Dynamics and Non-linear Imaging with Sub-wavelength Resolution in Organic Semiconductors
No full textIn the last 25 years, nano science has developed rapidly because of increased scientific demand and technological interest not only in material science, but also in e.g. life sciences and other related fields. The properties of bulk and nano-structured materials differ considerably; therefore the interest to investigate the fundamental properties of materials on a nanometer scale continues to grow.
In our research, we focus on the investigation of elementary processes, including energy transfer, charge transport, and exciton diffusion in nano-systems, which also involve the vibrational properties of these systems and their environments. These processes occur on ultrashort time scales, and therefore require femtosecond temporal resolution as well as high spatial resolution for their investigation.
However, the standard far-field diffraction-limited microscopic techniques cannot access the detailed local properties of nanostructure-based organic electronic devices made of thin films, whereas certain local details can severely hamper the performance of organic semiconductors. In order to obtain relevant information, the best if not the only solution is to apply a technique able to access high spatially localized and temporal information, and to this end, the combination of scanning near-field microscopy (SNOM) with time-resolved spectroscopy offers a superior tool, which can be used.
In this thesis, we demonstrate that the combination of nanometer spatial resolution and femtosecond time resolution is feasible for model samples of novel organic semiconductors. We introduce different nonlinear spectroscopic techniques such as pump-probe transient absorption measurements as well as coherent anti-Stokes Raman scattering (CARS), combined with scanning near field optical microscopy and apply them to different organic semiconductor systems, focusing mainly on 3, 4, 9, 10-perylene tetra carboxylic dianhydride (PTCDA) and poly 3-hexylthiophene (P3HT)
A Bacteria-Plant Model System to Study Nitrogen Fixation in Mangrove Ecosystems
No full textMangrove ecosystems are highly productive and rich in organic matter. However, they are considered low-nutrient environments, being nitrogen one of the main nutrients limiting mangrove growth. Nitrogen-fixing bacteria are one of the main inputs of nitrogen to these forests. High nitrogen fixation rates have been detected in mangrove sediments and roots. Moreover, studies indicated that the relationship between diazotrophs and mangroves might be mutualistic. Several diazotrophs from mangrove roots and the associated rhizosphere have been isolated or identify by phylogenetic studies of the nitrogenase-coding nifH gene. However, our knowledge about the molecular signals and cellular mechanisms that govern diazotroph-mangrove interactions is scarce. Thus, in this thesis a diazotroph-mangrove model system was established to better understand the importance of this interaction for the ecosystem and how environmental changes could impact this organismal interplay. For this, nitrogen-fixing bacteria were isolated from mangrove roots. Moreover, root colonization pattern of the selected nitrogen fixer and the impact of some of the environmental factors that could affect its nitrogen fixation were investigated. The first result showed that the diazotroph M. mangrovicola Gal22 was a prominent candidate for the establishment of the model system. This bacterium was shown to possess all features and requirements needed for being a representative model organism. Thus a detail phenotypic and genotypic characterization of strain Gal22 was conducted. A strong mangrove root colonization was observed by M. mangrovicola in the absence of carbon and nitrogen sources, suggesting that root exudates were instrumental in establishing the interaction. Nitrogen fixation by this diazotroph was increased in the presence of the roots, supporting the above results. Finally, changes in environmental factors such as temperature and salinity had a rather minor impact on nitrogen fixation by M. mangro