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Reproductive disorders in sea urchins (Psammechinus miliaris) caused by environmental pollutants
No full textEnvironmental contaminants are suspected to impair reproductive health of exposed organisms. In the present study, the effects of environmental contaminants on gonadal biology of adult sea urchins as well as cellular events in sea urchin eggs during fertilization were investigated. Female Psammechinus. miliaris exposed to a high dose (500 µg L-1) of the polycylic aromatic hydrocarbon phenanthrene for 20 days showed severe gonadal lesions which are similar to histopathological changes in other invertebrates as well as in fish following exposure to PAHs or oil. High (150 µg L-1) and environmentally relevant (5 µg L-1) concentrations of phenanthrene on reproductive tissue induced either no or only minor histological and biochemical changes in the gonads. But, profound sex-specific differences indicate that testes are much more susceptible to oxidative stress than ovaries. Samples from a population of P. miliaris in the northern Wadden Sea showed that sex, gonadal stage and spawning affect gonadal histology and histochemistry. Phenanthrene as well as various other chemicals is known to interfere with cellular calcium signalling. One of the best studied Ca2+ signals and essential for successful reproduction is the Ca2+ wave at fertilization. For the first time, the Ca2+ signal at fertilization was recorded using the Ca2+ indicator dye Fura-2 acetoxymethylester (AM) in combination with MK571, an inhibitor of multidrug resistance associated proteins. The metal copper and the brominated compound 2,4,6-tribromophenol (TBP) significantly increased the fertilization Ca2+ signal in P. miliaris at 6.3 µM and 100 µM, respectively, which might contribute to the observed reduced fertilization rates following exposure to these compounds. The shown histopathological and cellular investigations provide a promising basis for future studies on pollutant-induced reproductive disorders not only in sea urchins but also in other invertebrates
The role of heterotrophic dinoflagellate and ciliate grazers in the food web at Helgoland Roads, North Sea
No full textThis study investigates the role of microzooplankton grazers in the food web of the North Sea at Helgoland Roads.
A 2.5 year monitoring showed that dinoflagellates and ciliates are key organisms in terms of planktonic biomass in the North Sea and constitute a highly diverse and abundant community with a clear seasonal trend.
The evaluation of methodological sources of error in standard grazing experiments resulted in a new set-up technique, which was tested and shown to represent an improvement of the state-of-the-art method, conserving fragile microzooplankton species and grazer biodiversity.
Grazing experiments during a spring bloom showed the overall important role of ciliates and dinoflagellates as phytoplankton grazers when compared to copepods. Their food selectivity shaped the bloom and led to a stabilized assemblage of the bloom forming diatoms. Copepods, in turn, selectively fed on microzooplankton and could therefore be regarded as the main top down controlling factor of this group.
Interactions between different microzooplankton predators were investigated within a model system. In spite of theoretical assumptions that predicted the extinction of the smaller dinoflagellate predator, it was promoted by prey items that were pre-conditioned by its larger predator. The advantage for the smaller predator due to this commensalistic element in the predator relationsship was of such magnitude that it potentially enables a stable coexistence of both predators.
This study contributed new insights on: (1) the species composition and seasonality of dinoflagellates and ciliates in the North Sea, (2) methodological improvements concerning microzooplankton grazing experiments, (3) the important role of microzooplankton as grazer and also prey and (4) interactive relationships between microzooplankton predators. It furthermore revealed that investigations on the role of microzooplankton in the food web will continue to be a challenge in the future
Synthesis of Novel Picolylamine Template Catalysts and its Applications in Asymmetric Aldol Reactions
No full textA pyridine based 1,2-diamine containing only one stereogenic center has been identified for fast aldol reactions (16-48h). Using 2-5 mol% of (R)- or (S)-PicAm-2a, cyclohexanone (3.3 equiv) readily undergoes aldol reactions with o-,m- p-substituted aromatic aldehyde partners (limiting reagents), including the poor electrophile 4-methylbenzaldehyde (95-99% ee). Further more, functionalized cyclic ketone substrates have been converted into four aldol products using the lowest catalyst loading (5.0 mol%) to date with the highest yield and enatioselectivity
Explicit Second p-Descent on Elliptic Curves
No full textOne of the fundamental motivating problems in arithmetic geometry is to understand the set V (k) of rational points on an algebraic variety V defined over a number field k. When V = E is an elliptic curve, this set has a natural structure as a finitely generated abelian group (the Mordell-Weil group). The problem then becomes how to determine it in practice
Flow cytometry based screening systems for directed evolution of proteases
No full textProteases are industrially important enzymes and advances in screening technologies such as flow cytometry based in vitro compartmentalization (IVC) offer novel opportunities to tailor protease properties by directed evolution. In this project two flow cytometry based screening systems (cell-free based ProCF-FCIVC and whole-cell based Pro-FCIVC) with a high throughput (>7500 s-1) have been developed for directed evolution of proteases. Firstly, system related technologies such as generation of w/o/w double emulsions, selection of a suitable substrate and calibration of the sorting performance of flow cytometry were investigated and optimized. Then a cell-free based ProCF-FCIVC was developed using the model protease M57, a serine protease isolated from a metagenome library. Different parameters like in vitro expression of protease, enzymatic reactions in emulsions, and recovery of sorted DNA variants were investigated. Sorting and subsequent activity analysis of the M57 reference library demonstrated a proof of concept of the developed ProCF-FCIVC system. For the whole-cell based Pro-FCIVC system, an extracellular protease deficient Bacillus strain together with a Subtilisin Carlsberg (SC) secretion system were chosen due to its low background activity of other non-target proteases. Several main challenges such as background of natural occurring proteases, high diversity library generation of Bacillus, sorting strategies and growth competition effects on sorting enrichment were studied and optimized. The developed whole-cell Pro-FCIVC system was then verified by screening an epPCR library with a high mutational load (~5 mutations per 1 kb) for inhibition resistance of SC towards the antipain dihydrochloride inhibitor. One variant (SCm2) with a 1.6-fold relative to wild-type SC improved resistance was isolated from a small population of active variants (315) validating the developed protease flow cytometry screening technology for increased inhibitor resistance
Visualizing High-density Clusters in Multidimensional Data
No full textThe analysis of multidimensional multivariate data has been studied in various research areas for many years. The goal of the analysis is to gain insight into the specific properties of the data by scrutinizing the distribution of the records at large and finding clusters of records that exhibit correlations among the dimensions or variables. As large data sets become ubiquitous but the screen space for displaying is limited, the size of the data sets exceeds the number of pixels on the screen. Hence, we cannot display all data values simultaneously. Another problem occurs when the number of dimensions exceeds three dimensions. Displaying such data sets in two or three dimensions, which is the usual limitation of the displaying tools, becomes a challenge.
The main approach consists of two major steps: clustering and visualizing. In the clustering step, we propose two clustering algorithms to construct hierarchical density clusters. In the visualizing step, we propose two methods to visually analyze the hierarchical density clusters. An optimized star coordinates approach is used to project high-dimensional data into the (two- or three-dimensional) visual space, in which the leaf clusters of hierarchical density clusters (well-separated in the original data space) are projected into visual space with minimizing the overlapping. The second method, we developed to visualize the hierarchical density cluster tree, combines several information visualization techniques in linked and embedded displays: radial layout for hierarchical structures, linked parallel coordinates, and embedded circular parallel coordinates.
By combining cluster analysis with star coordinates or parallel coordinates, we extend these visualization techniques to cluster visualizations. We display clusters instead of data points. The advantage of this combination is scalability with both the size and dimensions of data set
Group relations at crowd events
No full textWithin recent years the elaborated social identity model of crowd behaviour, ESIM, has gained increasing support for both the explanation of conflict and the absence of violence at crowd events. Outcomes of this research have influenced practical policing, in particular with regard to the policing of football games. As existing literature focused exclusively upon the policing and psychological reactions of British fans, there was no empirical analysis of the cross cultural dimensions of the dynamics outlined within ESIM and a lack of evidence concerning the psychology, group processes and intergroup relationships with regard to groups from other nations. The present thesis was designed to fill this gap. It presents four studies of crowd behaviour and group interaction at different tournaments in Europe: The first study presents an analysis of German fan psychology at the European Championships 2004 in Portugal. The second paper examines the relations between police tactics and the psychology of different groups that attended the World Cup 2006 in Germany. The third paper focuses on group relations between German and Polish fans and between fans and the police at the game of Germany versus Poland, also during the 2006 World Cup. Finally one study examines German fan identity in relation to different contexts and follows the German fan category through three different tournaments: the Euro 2004, the World Cup 2006 and the Euro 2008 in Austria and Switzerland. Findings suggest that the social psychological processes that the ESIM proposes are also present among other cultural groups and the finding support the model as a valuable tool to explain the escalation of violence upon wider parts of the crowd. Furthermore, the studies provide support for the low-profile policing approach. Limitations of the model are discussed, in particular with regard to the initiation of violence and acts of vandalism. Suggestions are made for further research activities
Adaptation of Mathematical Documents
No full textThis work applies the topic-oriented principles of modularisation and reuse to the narrative authoring paradigm. Narrative documents are modularised into infoms, for which transitional phrases and cross-references are marked. Infoms and their semantic/narrative dependencies as well as variant relations are modelled as graphs. These graphs are processed during the content planning of narrative documents during which appropriate infoms are selected and arranged according to a user context. Since narrative transitions are visualised by words and phrases, they can reduce the adaptability of infoms. To improve the exchangeability of infoms, infoms are thus enriched with alternative narrative transitions. With this enrichment, appropriate narrative transitions can be selected according to the combination and arrangement of document parts into user-specific documents.
To illustrate the proposed adaptation services for narrative documents, mathematical documents are used. This decision required the author to take an essential aspect of mathematical text into account: The adaptation of mathematical notations. The author proposes a comprehensive framework that allows users to configure notations as well as to guide the content planning of mathematical documents regarding a semantic, narrative, and user context. To prioritise these contexts and to guide the adaptation, a combination of extensional and intensional options is provided. These give users full control over any step of the adaptation workflow: the specification of which document parts should be adapted and which should remain unchanged, the collection of adaptation objects (notation preferences, infoms, and context parameters), and the user-specific selection of the most appropriate objects to be applied in the rendering, substitution, and ordering of document parts
Macromolecular Docking. Applications to the RecA nucleofilament
No full textProtein interactions play a central role in a wide variety of biological processes where their partners can be other proteins, DNA, lipids, or small ligands. This manuscript is a summary of my work on this field, the development of a molecular docking library and its applications
Numerical modeling of an overpressured petroleum system, Kristin Field, Mid-Norwegian margin
No full textOur research work focuses on the gas-condensate Kristin Field on the mid-Norwegian margin where Middle Jurassic sandstone reservoirs are currently subjected to High Pressure and High Temperature (HPHT) conditions. A high-resolution 3D seismic dataset was interpreted to derive structural trends and horizon geometries for a full 3D basin model. The chrono-and litho-stratigraphy of the seismic sequences were tied to wells.
The calibrated heat flow simulation suggests a basal heat flow trend of 57mW/m2 during the Jurassic pre-rifting, increasing to 83mW/m2 at the end of the Jurassic rifting and decaying to a constant 53mW/m2 from the Miocene to present. The reconstructed hydrocarbon filling history shows that the Kristin traps were charged around 135Ma ago. The generated hydrocarbons could have migrated into the neighboring Smørbukk Field during the pre-Pliocene due to lateral fluid communications across the fault zones. The reconstruction of overpressure evolution and the comparison of different pressure generating processes demonstrate that only sedimentary compaction disequilibrium is not sufficient to explain the overpressure magnitudes observed in the Kristin system. Volumetric contributions from the generated gas must be taken into account. Overpressure modeling indicates that dramatic overpressure buildup in the Kristin reservoir is a recent event. It was mainly caused by secondary oil to gas cracking and closure of the fault zones both triggered by the rapid Pliocene-Pleistocene sedimentation in the area. The large volume of gas from secondary cracking may also have overprinted the geochemical signals of primary coal-gas.
This work provides significant new insights into the evolution and dynamics of the overpressured Kristin system and contributes to the understanding of petroleum compositional evolution, overpressure buildup processes, and regional hydrocarbon migration patterns on the Halten Terrace through geological time