Hochschulbibliographie Universität Bremen (hsb)
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Item-typ:Veröffentlichung, 71 332 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Liefergebiets - Charakterisierung proterozoischer Goldseifen in Ghana anhand von Fluideinschluß - Untersuchungen.(1995)The gold-bearing Tarkwaian conglomerates of the so-called Banket Series in the Ashanti Belt are oligomictic and consist of vein-quartz pebbles within a quartzitic matrix. The matrix consists, besides fine grained quartz, of secondary carbonates, chlorite, muscovite, tourmaline, epidote, actinolite, rutile, altered plagioclase, detrital zircon and opaque minerals. The opaque phases are mostly hematite and magnetite, which occur in about the same proportions. Free particles of gold and pyrite are rare.Fluid inclusion investigations revealed that the quartz-pebbles of the conglomerates contain predominantly CO2-rich fluids, some of which have unusually high densities (up to 1.13 g/cm3). These inclusions were probably trapped in the provenance area of the quartz pebbles. The matrix of the conglomerates is dominanted by H20-CO2-rich inclusions.The Banket Series conglomerates are underlain by the Kawere Series. The conglomerates of this series are polymictic and frequently matrix supported. Furthermore, the quartzitic matrix of the conglomerates contain small amounts of muscovite, plagioclase and epidote. These conglomerates carry no economic gold-contents, which are normally below 50 ppb. Quartzpebbles ofthese conglomerates possess H20- and H20-CO2-rich inclusions.BerichtBand:65409 198 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Functional biodiversity and seasonal transitions of pelagic protists in Disko Bay, Greenland(2022-01-24); ; ; Environments are changing more and more due to the ongoing climate change. The Arctic is warming up at approximately double the rate than other regions. To understand how the marine ecosystem will be affected by this, it is necessary to understand how it is behaving in the first place. For marine pelagic ecosystems, protists form the basis of the marine food web, encompassing most of the primary producers of biomass. The community usually follows seasonal patterns in abundance and dominance of different taxonomic groups throughout the year. Due to the relative inaccessibility, protist seasonal patterns have not been studied extensively in the Arctic environment before. This study focused on the months leading into and out of the annual spring bloom event in an Arctic environment, and how the local protist community reacted to the changing circumstances. The highly seasonal study area provided the opportunity to investigate several typical Arctic phenomena during two field trips in 2017 and 2018, including seasonal sea ice and very dark periods in winter, and the continuously shining midnight sun in summer. Embedded in contextual data, an approach with state-of-the-art metabarconding was utilized to shed light on the pelagic protist diversity. The winter community (2018) consisted of many mixotrophic, heterotrophic and parasitic organisms, which were displaced by phototrophs towards the spring bloom, especially in the microplankton size fraction. When looking at the transition from spring to summer (2017), pico- and nanoplankton had only a small percentage of phototrophs, but more heterotrophs and mixotrophs. Microplankton shifted from predominantly phototrophs during the spring bloom to mostly mixotrophs in summer. This work contributes to a better understanding of protist organisms in an Arctic context. In the future, this may help to understand the changes that are currently provoked and how they will affect these small but significant organisms.Dissertation391 163 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Policy-centred sampling in interest group research: Lessons from the INTEREURO project(2014-05-15); ; ; Proper sampling is the foundation for all scientific enquiry aimed at making generalizable claims about a wider set of cases. Indeed, inferential statistical analysis presupposes representative samples and units of analysis that can be considered as independent observations. Establishing a sample of issues on which lobbying may take place, which is at the same time representative of an overall population of issues and of the varying levels of conflict and political mobilization, however, is a major challenge for interest group research. Drawing on existing research practices, we discuss a series of different approaches that may be used to establish a sample of policy issues. The focus then is on the policy-centred stratified sampling procedure used in the INTEREURO project. While our approach has important advantages, we extensively discuss several challenges we faced as well as the procedures we developed in order to deal with these.Wissenschaftlicher ArtikelBand:3Heft:2177 298 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Advancing semantic and digital communications through machine learning(2025-10-10); ; ; Artificial Intelligence (AI) is becoming increasingly prevalent in daily life, driven by rapid advancements in Machine Learning (ML) since 2010. These breakthroughs, enabled by innovations such as specialized hardware, Deep Neural Networks (DNNs), and advances in training techniques, have allowed AI systems to match or even exceed human performance in tasks like autonomous driving and medical diagnostics, with systems such as ChatGPT and AlphaGo standing out as key examples. These achievements have raised public awareness and acceptance of AI technologies. In the realm of wireless communication, emerging applications such as virtual reality and autonomous systems are pushing traditional digital communication systems to their limits. Conventional content-agnostic approaches struggle to meet the growing demands for bandwidth, power efficiency, and low latency. This dissertation explores mastering these challenges by integrating ML techniques into wireless communication systems. It introduces CMDNet, a novel framework for symbol detection, designed to improve communication efficiency by combining strengths of traditional model-based designs with those of advanced ML methods. Furthermore, integrating semantic content into communications is identified as crucial for further enhancing system efficiency. Semantic communication aims at transmitting the meaning conveyed by the data rather than the exact bits, which can introduce a model deficit that challenges traditional communication designs. This challenge in design of semantic communication is addressed using advanced ML techniques, as demonstrated in the SINFONY approach. Together, these contributions demonstrate how ML advances, such as DNNs, can overcome existing limitations in terms of model and algorithmic deficits and significantly enhance the efficiency and capabilities of future communication systems.Dissertation128 84 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, A multidimensional analysis of sea ice melt pond properties from aerial images(2023-04-27); ; ; ; Sea ice plays a fundamental role in Polar climate and ecosystems. Melt ponds, forming routinely on Arctic sea ice during summer, can cover and impact a considerable fraction of the ice area. However, data that allow a comprehensive understanding of pond evolution processes remain scarce. Consequently, we cannot yet predict how ponds will develop on the increasingly prevalent young ice in the future. Previous studies have drawn a very heterogeneous picture of pond coverage on young ice, which we can only improve with more detailed measurement data and analysis tools that allow the derivation of properties possibly driving pond evolution. The existence of over ten years of high-resolution aerial image data from AWI aircraft campaigns in the Arctic has motivated me to develop and refine evaluation methods for this dataset, the one-year drift campaign MOSAiC, and future measurement campaigns. I created a customized classification algorithm to classify images into sea ice surface classes with minimal manual intervention. By implementing cutting-edge photogrammetry tools and developing a spatially high-resolution albedo and pond depth retrieval method, I draw an unprecedented multidimensional picture of melt ponds. From this, I derived properties of the sea ice cover that favor and limit pond coverage. I found that within the observed areas, melt pond coverage was more constant than expected, ranging between 15% to 25%. The first-ever tracking of the evolution of the entire pond bathymetry shows that we have so far overlooked the deformability of the pond bottom ice. The multidimensional, high-resolution approach for long-range airborne measurements allowed me to make general recommendations for representative ground measurements. The tools presented, together with the refined insights into pond properties and evolution, will improve our understanding of summer sea ice and can help better assess the role and fate of ponds in the future Polar climate and ecosystems.Dissertation524 305 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The Bacterial Ectosymbionts of the Ciliate Kentrophoros(2017-10-24); ; ; Kentrophoros is a single-celled eukaryote that has a symbiosis with sulfur-oxidizing bacteria. This thesis investigates the diversity and functional significance of this symbiosis through molecular ecology and genomics. The bacteria belong to a single lineage in the Gammaproteobacteria that is specifically associated with Kentrophoros. Kentrophoros also constitutes a monophyletic group, despite their morphological diversity, which includes new species discovered during this work. Mitochondrial genes of Kentrophoros show evidence of rapid diversification during their evolutionary history. Genomes of the symbionts encode pathways for sulfur oxidation, but none of the known pathways for autotrophic carbon fixation. Instead they have the genetic potential for uptake and usage of organic carbon substrates, suggesting that this symbiosis is based on chemolithoheterotrophy, instead of chemosynthesis, as previously thought. The ecophysiological consequences of such a metabolism are discussed.Dissertation582 841 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Dei et Apostolicae Sedis Gratia: Über die Entstehung von Personenherrschaft in den Bistümern Bremen und Verden im frühen Mittelalter und die Rezeption dieser Zeit in liturgischen Schriften des Erzbischofs Christoph von Braunschweig-Lüneburg.This works focuses on the political history of the bishopries of Bremen and Verden (North-Western Germany) during their first 300 years, beginning as unimportant mission-territories until their establishment as confident territories of the Holy German Empire in the 12th century. The second part is emphasizing on the reflection this time has found in liturgical prints during the reign of Archbishop Christoph of Brunswick, whose reign can be seen as a borderline between catholic middle ages and the beginning reformation.Dissertation5400 726 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Glacial and Interglacial Changes in Southwest Pacific Water Mass Ventilation and Circulation(2014-12-22); ; ; On glacial/interglacial timescales, Southern Ocean air-sea gas exchange is considered to be an important factor, driving the variability of atmospheric CO2 concentrations. To understand the role of oceanic variability in the global carbon cycle, it is necessary to reconstruct changes in deep- and intermediate-water circulation and chemistry of Southern Ocean water masses. In this context,we used a transect of sediment cores to reconstruct ventilation and circulation changes of the South Pacific. The data show the presence of very old and CO2 enriched waters between 2000 and 4300 m water depth. Because the deep-water rejuvenation is parallel to the trend in atmospheric CO2, we propose that the deep Pacific Ocean significantly contributet to the deglacial rise in atmospheric CO2. Furthermore, we were able to show that the intermediate-water off New Zealand was significantly shallower during glacial stages, furthermore expanding the volume of the glacial carbon pool.Dissertation339 153 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The analysis of coral reef resilience - a generic modelling tool(2012-11-02); ; ; Coral reefs, rainforests of the sea, are of greatest ecological and economical importance. Although they cover just a small fraction of sea floor, they provide indispensable functions for the associated flora and fauna, and invaluable services for livelihoods of large human populations in tropical coastal regions. Within the last few decades coral reefs have been increasingly endangered for various reasons, which can be directly or indirectly ascribed to anthropogenic influence. Chronic stresses can undermine the resilience of coral reefs, which then become more susceptible to the effects of pulse stresses, like hurricanes or thermally induced bleaching. Such an event may then diminish relevant ecosystem properties beyond a threshold, and thus trigger a sudden shift to an alternative state, which may not be in favour of corals but an alternative live form that then achieves dominance. In my thesis I developed a spatially explicit individual-based model to simulate a benthic reef community, typical for a reef in the Western Indian Ocean region. The application was then used to explore key variables and -processes for resilience and to identify potential triggers for phase shifts. Several coral species with contrasting life histories and algae compete for space under different environmental influences. Evoked by direct neighbourhood-interactions and individual responses to environmental conditions, the system performs dynamic self-organisation, and properties of superordinate hierarchical levels (population, community) emerge as a consequence. In multiple scenarios I tested the influences of (i) two different perturbation types (bleaching and mechanical disturbances), -intensities and frequencies, as well as (ii) various levels of grazing and recruitment on the dynamics of coral reef communities. As the results show, perturbations can generate heterogeneous outcomes. While extreme temperature events render a disadvantage for more susceptible branching coral species, these species can dominate under high frequencies of mechanical disturbance events, because they recolonize empty space faster, due to their faster growth rates. Low disturbance levels always benefit the dominance of massive growth forms and a combination of both perturbations at intermediate levels leads to high evenness in the community composition. The results additionally confirm, that herbivory and recruitment are crucial processes for the resilience and persistence of coral reefs. This study also highlights the importance of a diversified analysis of coral reef dynamics to understand the full magnitude of consequences, caused by environmental change. The presented application renders an excellent tool (a) to integrate current knowledge, which can be kept up to date with little effort and (b) can be coupled with other modelling systems that operate on different spatial and temporal scales. Complexity and non-linear dynamics of coral reef functioning can thus be simulated and analysed with a high level of detail and informative value.Dissertation365 193