Investigations of cooperative interactions in template induced crystallization processes and kinetic studies of nucleation and growth by small-angle neutron scattering

Zusammenfassung Um zu einem besseren Verständnis des Prozesses der Biomineralisation zu gelangen, muss das Zusammenwirken der verschiedenen Typen biologischer Makromoleküle, die am Keimbildungs- und Wachstumsprozess der Minerale beteiligt sind, berücksichtigt werden. In dieser Arbeit wird ein neues Modellsystem eingeführt, das aus einem SAM (self-assembled monolayer) mit verschiedenen Funktionalitäten und unterschiedlichen, gelösten Makromolekülen besteht. Es konnte gezeigt werden, dass die Kristallisation von Vaterit (CaCO3) sowie Strontianit (SrCO3) Nanodrähten der Präsenz von Polyacrylat in Kooperation mit einer COOH-funktionalisierten SAM-Oberfläche zugeschrieben werden kann. Die Kombination bestehend aus einer polaren SAM-Oberfläche und Polyacrylat fungiert als Grenzfläche für die Struktur dirigierende Kristallisation von Nanodraht-Kristallen. Weiter konnte gezeigt werden, dass die Phasenselektion von CaCO3 durch die kooperative Wechselwirkung zwischen einer SAM-Oberfläche und einem daran adsorbierten hb-Polyglycerol kontrolliert wird. Auch die Funktionalität einer SAM-Oberfläche in Gegenwart von Carboxymethyl-cellulose übt einen entscheidenden Einfluss auf die Phasenselektion des entstehenden Produktes aus. In der vorliegenden Arbeit wurden Untersuchungen an CaCO3 zur homogenen Keimbildung, zur Nukleation in Gegenwart eines Proteins sowie auf Kolloiden, die als Template fungieren, mittels Kleinwinkel-Neutronenstreuung durchgeführt. Die homogene Kristallisation in wässriger Lösung stellte sich als ein mehrstufiger Prozess heraus. In Gegenwart des Eiweißproteins Ovalbumin konnten drei Phasen identifiziert werden, darunter eine anfänglich vorhandene amorphe sowie zwei kristalline Phasen.

Electronic energy transfer processes and charge carrier transport in pi-conjugated polymers

Conjugated polymers have attracted tremendous academical and industrial research interest over the past decades due to the appealing advantages that organic / polymeric materials offer for electronic applications and devices such as organic light emitting diodes (OLED), organic field effect transistors (OFET), organic solar cells (OSC), photodiodes and plastic lasers. The optimization of organic materials for applications in optoelectronic devices requires detailed knowledge of their photophysical properties, for instance energy levels of excited singlet and triplet states, excited state decay mechanisms and charge carrier mobilities. In the present work a variety of different conjugated (co)polymers, mainly polyspirobifluorene- and polyfluorene-type materials, was investigated using time-resolved photoluminescence spectroscopy in the picosecond to second time domain to study their elementary photophysical properties and to get a deeper insight into structure-property relationships. The experiments cover fluorescence spectroscopy using Streak Camera techniques as well as time-delayed gated detection techniques for the investigation of delayed fluorescence and phosphorescence. All measurements were performed on the solid state, i.e. thin polymer films and on diluted solutions. Starting from the elementary photophysical properties of conjugated polymers the experiments were extended to studies of singlet and triplet energy transfer processes in polymer blends, polymer-triplet emitter blends and copolymers. The phenomenon of photonenergy upconversion was investigated in blue light-emitting polymer matrices doped with metallated porphyrin derivatives supposing an bimolecular annihilation upconversion mechanism which could be experimentally verified on a series of copolymers. This mechanism allows for more efficient photonenergy upconversion than previously reported for polyfluorene derivatives. In addition to the above described spectroscopical experiments, amplified spontaneous emission (ASE) in thin film polymer waveguides was studied employing a fully-arylated poly(indenofluorene) as the gain medium. It was found that the material exhibits a very low threshold value for amplification of blue light combined with an excellent oxidative stability, which makes it interesting as active material for organic solid state lasers. Apart from spectroscopical experiments, transient photocurrent measurements on conjugated polymers were performed as well to elucidate the charge carrier mobility in the solid state, which is an important material parameter for device applications. A modified time-of-flight (TOF) technique using a charge carrier generation layer allowed to study hole transport in a series of spirobifluorene copolymers to unravel the structure-mobility relationship by comparison with the homopolymer. Not only the charge carrier mobility could be determined for the series of polymers but also field- and temperature-dependent measurements analyzed in the framework of the Gaussian disorder model showed that results coincide very well with the predictions of the model. Thus, the validity of the disorder concept for charge carrier transport in amorphous glassy materials could be verified for the investigated series of copolymers.

Flash floods and their effects on the development in El-Qaá plain area in South Sinai, Egypt

The arid regions are dominated to a much larger degree than humid regions by major catastrophic events. Although most of Egypt lies within the great hot desert belt; it experiences especially in the north some torrential rainfall, which causes flash floods all over Sinai Peninsula. Flash floods in hot deserts are characterized by high velocity and low duration with a sharp discharge peak. Large sediment loads may be carried by floods threatening fields and settlements in the wadis and even people who are living there. The extreme spottiness of rare heavy rainfall, well known to desert people everywhere, precludes any efficient forecasting. Thus, although the limitation of data still reflects pre-satellite methods, chances of developing a warning system for floods in the desert seem remote. The relatively short flood-to-peak interval, a characteristic of desert floods, presents an additional impediment to the efficient use of warning systems. The present thesis contains introduction and five chapters, chapter one points out the physical settings of the study area. There are the geological settings such as outcrop lithology of the study area and the deposits. The alluvial deposits of Wadi Moreikh had been analyzed using OSL dating to know deposits and palaeoclimatic conditions. The chapter points out as well the stratigraphy and the structure geology containing main faults and folds. In addition, it manifests the pesent climate conditions such as temperature, humidity, wind and evaporation. Besides, it presents type of soils and natural vegetation cover of the study area using unsupervised classification for ETM+ images. Chapter two points out the morphometric analysis of the main basins and their drainage network in the study area. It is divided into three parts: The first part manifests the morphometric analysis of the drainage networks which had been extracted from two main sources, topographic maps and DEM images. Basins and drainage networks are considered as major influencing factors on the flash floods; Most of elements were studied which affect the network such as stream order, bifurcation ratio, stream lengths, stream frequency, drainage density, and drainage patterns. The second part of this chapter shows the morphometric analysis of basins such as area, dimensions, shape and surface. Whereas, the third part points the morphometric analysis of alluvial fans which form most of El-Qaá plain. Chapter three manifests the surface runoff through rainfall and losses analysis. The main subject in this chapter is rainfall which has been studied in detail; it is the main reason for runoff. Therefore, all rainfall characteristics are regarded here such as rainfall types, distribution, rainfall intensity, duration, frequency, and the relationship between rainfall and runoff. While the second part of this chapter concerns with water losses estimation by evaporation and infiltration which are together the main losses with direct effect on the high of runoff. Finally, chapter three points out the factors influencing desert runoff and runoff generation mechanism. Chapter four is concerned with assessment of flood hazard, it is important to estimate runoff and tocreate a map of affected areas. Therefore, the chapter consists of four main parts; first part manifests the runoff estimation, the different methods to estimate runoff and its variables such as runoff coefficient lag time, time of concentration, runoff volume, and frequency analysis of flash flood. While the second part points out the extreme event analysis. The third part shows the map of affected areas for every basin and the flash floods degrees. In this point, it has been depending on the DEM to extract the drainage networks and to determine the main streams which are normally more dangerous than others. Finally, part four presets the risk zone map of total study area which is of high inerest for planning activities. Chapter five as the last chapter concerns with flash flood Hazard mitigation. It consists of three main parts. First flood prediction and the method which can be used to predict and forecast the flood. The second part aims to determine the best methods which can be helpful to mitigate flood hazard in the arid zone and especially the study area. Whereas, the third part points out the development perspective for the study area indicating the suitable places in El-Qaá plain for using in economic activities.

Alternative reproductive tactics, sexual selection and the effects of inbreeding in the ant Hypoponera opacior

Inbreeding can lead to a fitness reduction due to the unmasking of deleterious recessive alleles and the loss of heterosis. Therefore, most sexually reproducing organisms avoid inbreeding, often by disperal. Besides the avoidance of inbreeding, dispersal lowers intraspecific competition on a local scale and leads to a spreading of genotypes into new habitats. In social insects, winged reproductives disperse and mate during nuptial flights. Therafter, queens independently found a new colony. However, some species also produce wingless sexuals as an alternative reproductive tactic. Wingless sexuals mate within or close to their colony and queens either stay in the nest or they found a new colony by budding. During this dependent colony foundation, wingless queens are accompanied by a fraction of nestmate workers. The production of wingless reproductives therefore circumvents the risks associated with dispersal and independent colony foundation. However, the absence of dispersal can lead to inbreeding and local competition.rnIn my PhD-project, I investigated the mating biology of Hypoponera opacior, an ant that produces winged and wingless reproductives in a population in Arizona. Besides the investigation of the annual reproductive cycle, I particularly focused on the consequences of wingless reproduction. An analysis of sex ratios in wingless sexuals should reveal the relative importance of local resource competition among queens (that mainly compete for the help of workers) and local mate competition among males. Further, sexual selection was expected to act on wingless males that were previously found to mate with and mate-guard pupal queens in response to local mate competition. We studied whether males are able to adapt their mating behaviour to the current competitive situation in the nest and which traits are under selection in this mating situation. Last, we investigated the extent and effects of inbreeding. As the species appeared to produce non-dispersive males and queens quite frequently, we assumed to find no or only weak negative effects of inbreeding and potentially mechanisms that moderate inbreeding levels despite frequent nest-matings.rnWe found that winged and wingless males and queens are produced during two separate seasons of the year. Winged sexuals emerge in early summer and conduct nuptial flights in July, when climate conditions due to frequent rainfalls lower the risks of dispersal and independent colony foundation. In fall, wingless sexuals are produced that reproduce within the colonies leading to an expansion on the local scale. The absence of dispersal during this second reproductive season resulted in a local genetic population viscosity and high levels of inbreeding within the colonies. Male-biased sex ratios in fall indicated a greater importance of local resource competition among queens than local mate competition among males. Males were observed to adjust mate-guarding durations to the competitive situation (i.e. the number of competing males and pupae) in the nest, an adaptation that helps maximising their reproductive success. Further, sexual selection was found to act on the timing of emergence as well as on body size in these males, i.e. earlier emerging and larger males show a higher mating success. Genetic analyses revealed that wingless males do not actively avoid inbreeding by choosing less related queens as mating partners. Further, we detected diploid males, a male type that is produced instead of diploid females if close relatives mate. In contrast to many other Hymenopteran species, diploid males were here viable and able to sire sterile triploid offspring. They did not differ in lifespan, body size and mating success from “normal” haploid males. Hence, diploid male production in H. opacior is less costly than in other social Hymenopteran species. No evidence of inbreeding depression was found on the colony level but more inbred colonies invested more resources into the production of sexuals. This effect was more pronounced in the dispersive summer generation. The increased investment in outbreeding sexuals can be regarded as an active strategy to moderate the extent and effects of inbreeding. rnIn summary, my thesis describes an ant species that has evolved alternative reproductive tactics as an adaptation to seasonal environmental variations. Hereby, the species is able to maintain its adaptive mating system without suffering from negative effects due to the absence of dispersal flights in fall.rn

Atmospheric and climate effects of biomass burning using different injection heights

Inspired by the need for a representation of the biomass burning emissions injection height in the ECHAM/MESSy Atmospheric Chemistry model (EMAC)