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Niches of abundant heterotrophic bacteria during North Sea spring algal blooms
Get PDFThe remineralization of algal biomass by heterotrophic bacteria during spring phytoplankton blooms is a globally important process in carbon cycling. Yet, the ecophysiology of environmentally relevant bacteria occurring during these events is largely unknown. In this thesis, I investigated the niches of the gammaproteobacterial genus Reinekea and the flavobacterial genera Polaribacter and Formosa, which are recurrently abundant during the 2009-2012 North Sea spring algal blooms off Helgoland. Firstly, I studied a Reinekea forsetiia , the representative of North Sea Reinekea clade, using genomic and physiological analyses. The results suggested a versatile opportunistic lifestyle comprising (i) utilization of relevant algal polysaccharides, (ii) potential toxin production, and (iii) strategies to deal with phosphorus limitation. Secondly, temporal dynamics and large niche space of diverse North Sea Polaribacter spp. was investigated using fluorescence in situ hybridization with novel oligonucleotide probes, binning of time-series metagenomes and re-analysis of in situ expression data. These analyses showed the succession of four major Polaribacter clades with varying degradation capacity for high molecular weight compounds and suggested a polysaccharide-driven niche partitioning between these closely-related bacteria. Finally, the polysaccharide niche of North Sea Formosa clade was examined using metaa omic approaches and complementary physiological and biochemical experiments. An efficient laminarin uptake and degradation mechanism, which is coupled to peptide utilization, was revealed. This thesis demonstrated how heterotrophic bacteria employ different ecological strategies to utilize diverse high molecular weight compounds released during spring algal blooms and increased our knowledge on microbially mediated carbon turnover in the surface ocean
Ecology and stable isotope geochemistry of modern planktonic foraminifera in the Northeast Atlantic
Get PDFThe understanding of the relationship between planktonic foraminifera and their surrounding environment, as well as each individual speciesa habitat and calcification behaviour are of fundamental importance to improve their use as a paleoceanographic tool. To this end, vertically stratified plankton tow hauls were used to study the vertical and horizontal distribution and stable isotope geochemistry of planktonic foraminifera in the eastern North Atlantic, a region that plays an important role in monitoring changes in the North Atlantic circulation and where the environmental conditions are particularly diverse. This work provides new insights into the vertical and horizontal distribution of individual species of planktonic foraminifera and the respective factors (temperature, chlorophyll, mixed layer depth, lunar/seasonal cycle) potentially controlling their distribution. New findings concerning the stable isotope signal recorded in the shells of four deep dwelling planktonic foraminifera species are also reported. The vertical distribution of planktonic foraminifera varied among species, allowing us to identify different groups of species, such as species living typically above 100 m, species occurring commonly between the surface (50 m) and intermediate waters (100 m) and species living mostly below 100 m. In most cases, the vertical habitat also varied within species, but the variation was found to be predictable by a combination of environmental factors and ontogenetic migration. Horizontally, species distribution is linked to the surrounding environmental conditions, resulting in specific regional and seasonal faunal associations. Unlike the composition of sedimentary assemblages, plankton assemblages are predicted by multiple environmental parameters, indicating that the strong temperature signal in fossil assemblages is the result of seasonal and interannual accumulation and averaging. The stable isotopic analysis of four deep-dwelling species confirmed that either larger size or presence of a secondary crust cause heavier isotopic signal. In three out of the four studied species, the oxygen isotopic signal could be better predicted by the Shackleton paleotemperature, whereas Globorotalia scitula signal is better described by the Kim and Oa Neil paleotemperature equation. Finally, we found inconsistencies between the living depth and the calcification depth of each species, revealing that the calcification depth does not correspond entirely to the habitat depth of a species
Artificial Cognitive Systems that can answer Human Creativity Tests : An Approach and Two Case Studies
Get PDFCreative cognitive systems are rarely assessed with the same tools as human creativity. In this paper, an approach is proposed for building cognitive systems which can solve human creativity tests. The importance of using cognitively viable processes, cognitive knowledge acquisition and organization, and cognitively comparable evaluation when implementing creative problem-solving systems is emphasized. Two case studies of artificial cognitive systems evaluated with human creativity tests are reviewed. A general approach is put forward. The applicability of this general approach to other creativity tests and artificial cognitive systems, together with ways of performing cognitive knowledge acquisition for these systems are then explored
Dynamisches Prozessverhalten bei der laserinduzierten thermochemischen Mikrostrukturierung von Metallen
Get PDFThis work deals with the process behavior of laser-induced thermochemical material removal of self-passivation metallic materials in order to enable a stable and process reliable micro structuring. The main focus hereby is on the identification of the causes and their influencing factors for the origin of discontinuities in process quality. The results show that laser-induced gas bubble formation, both by boiling of the electrolyte and by reaction-induced release of hydrogen, is a major contributor of the disruption of material removal. With the achieved knowledge and the model-based description of the removal process, suitable machining parameters for a high-quality and disturbance-free processing can be identified
Urban Gardening im internationalen Städtevergleich : eine Analyse der Auswirkungen des neuen Gärtnerns auf die Lebensqualität im Hinblick auf ökologische, ökonomische und soziale Faktoren am Beispiel der Städte Berlin und Detroit
Get PDFIn der vorliegenden Bachelorarbeit soll untersucht werden, welche sozialen, ökonomischen und ökologischen Effekte urbane Gärten auf die Lebensqualität von Menschen in größeren Städten haben. Dabei stehen sich exemplarisch die wachsende deutsche Hauptstadt Berlin und die shrinking city Detroit, ehemals blühende Metropole des Bundesstaates Michigan, in den USA gegenüber. Um die Auswirkungen des neuen Gärtnerns im internationalen Städtevergleich zu ermitteln, wird der Ist-Zustand der Gartenprojekte anhand einer explorativen Literaturrecherche aufgezeigt und anschließend die Ergebnisse der leitfadengestützten Experteninterviews dargestellt, um Erkenntnisse über die Bedeutung von Gemeinschaftsgärten zu gewinnen. Die Forschungsergebnisse der Arbeit zeigen, dass urbane Gärten entscheidend auf die Lebensqualität von Stadtbewohnern einwirken.Sie fördern einen nachhaltigen Lebensstil, stärken soziale, wie kulturelle Verknüpfungen und können sogar ökonomisch neue Perspektiven liefern. In ihnen werden alternative Lebensentwürfe generiert und es entsteht ein Umdenken bezüglich der Begriffe Wohlstand, Besitz und Umwelt
Anthropogenic input of heavy metals to near-coastal sediment depocenters in the eastern North Sea and the Hauraki Gulf in historical times
Get PDFSince the beginning of the industrial revolution, and even earlier, near-coastal marine ecosystems are affected by various anthropogenic influences such as the enhanced input of heavy metals. In this thesis, the anthropogenically induced historical heavy metal input to near-coastal sediment depocenters in the eastern North Sea, the Helgoland mud area and the Skagerrak, and the Hauraki Gulf, NZ, is analysed and discussed. Enhanced heavy metal inputs to the Helgoland mud area and the Skagerrak commenced in medieval times and are attributed to early mining and smelting activities in medieval mining centres in Germany and Sweden. Due to the low present-day sediment input and the strong reworking of the sediments, the sediments of the Hauraki Gulf do not reveal any signal of heavy metal inputs, but provide new insights in the deposition and reworking of surficial sediments as a consequence of the interactions of wind-generated waves and the modern hydrodynamic regime
Einfluss des Handpolierens von Probenkörpern auf Gestaltabweichungen erster Ordnung und das Verschleißverhalten in Tribometerversuchen
Get PDFTribometerversuche werden zur Untersuchung von tribologischen Eigenschaften verschiedener neuartiger Oberflächen eingesetzt. Häufig werden handpolierte Referenzflächen getestet, da diese eine geringe Welligkeit (Gestaltabweichung 2. Ordnung) und Rauheit (Gestaltabweichungen 3. und 4. Ordnung) aufweisen. Bei der Bearbeitung kleiner Probenkörper besteht allerdings die Gefahr, durch Handpolieren auch Formabweichungen (Gestaltabweichung 1. Ordnung), zum Beispiel eine schiefe Kontaktebene, zu erzeugen. Inwieweit eine Vergleichbarkeit mit weiteren tribologischen Untersuchungen dadurch noch geben ist, ist unklar. In diesem Manuskript werden daher Stahlprobenkörper für ein DruckTorsions-Tribometer handpoliert, die Oberflächengestalt vermessen und anschließend Triboversuche gegen Reinaluminium durchgeführt. Im Folgenden wird gezeigt, dass eine Verkippung der Kontaktfläche auch die tribologischen Messgrößen, wie die Anhaftungen am Probenkörper und den Verlauf des übertragenen Drehmoments, beeinflussen kann. Hingegen ist der Einfluss einer Abrundung des Probenkörpers durch Handpolieren auf die genannten Größen gering
Characterization of the tribological behaviour of tool surfaces depending on higher contact pressures
Get PDFDuring deep drawing, different contact pressures between the sheet and the tool surface occur. Under the blankholder the contact pressure is relatively low, can be analytically calculated and adjusted. Generally, the highest contact pressures result at the drawing radius, which can be calculated using finite element methods. Besides of the material combination of the tool and the sheet, the surface structures, the intermediate medium and the relative speed, the contact pressures have a significant influence on the tribological system. Strip drawing tests offer the possibility to characterize tribological systems for sheet metal forming under variation of the contact pressure. In this work, the tribological behaviour of three different tool surfaces was investigated: hot-working steel, aluminium bronze and metal matrix composite (MMC). The MMC-surface had a supporting plateau out of hard particles with a depression of 3 micrometre. The tests were carried out with and without lubrication by applying different contact pressures up to 20 MPa. Using hot-working steel in dry-sliding resulted in friction coefficients at times higher than 1 even at low surface pressures of 4 MPa. It was shown that the friction force was successively increased each time of strip drawing. This was an indication for significant progressive wear in dry sliding, whereby the first strip draw led to a smooth forcepath curve comparable to lubricated sliding and the subsequent experiments showed pronounced peaks in the force-path curves. By contrast to the tribological behavior of the hot-working steel, the friction coefficients in dry sliding using aluminium bronze and the MMC surface were significantly lower. By increasing the surface pressure by a factor of five the friction coefficients in lubricated strip drawing were decreased by up to 8% and in dry sliding the friction coefficients were increased by up to 63%
Measurements of horizontal trace gas distributions using airborne imaging differential optical absorption spectroscopy
Get PDFNitrogen oxides (NOx = NO NO2) are a key species in the atmosphere, impacting on human health, tropospheric ozone formation, acid rain and climate. The major source of NOx are combustion processes. The lifetime of NOx in the atmosphere is short. Hence, it is found close to its sources and can serve as a proxy to identify anthropogenic pollution. The distinct spectral features of NO2 enable to retrieve its abundance by remote sensing, using differential optical absorption spectroscopy (DOAS). Spaceborne measurements of trace gases using the DOAS method have been performed for more than two decades and provided new insights on the atmospheric composition on a global and regional scale. Within this work, the DOAS technique is applied to airborne imaging DOAS measurements of the AirMAP instrument, developed at the University of Bremen. As the instrument is operated on an aircraft, the measurements have a much higher spatial resolution than the ones from satellite, due to the lower flight altitude. The aircraft platform provides a tool to gaplessly map the horizontal NO2 distribution at the scale of a large city, such as Berlin, in a time window of about two hours. The derived high resolution trace gas maps reveal spatial patterns in the NO2 distribution that cannot be resolved by the satellite measurements. This thesis presents trace gas maps from research flights covering different target areas, including shipping lanes, power plants and cities at a resolution better than 100 meter. Special efforts were made to increase the accuracy of the measurements by accounting for parameters that affect the atmospheric radiative transfer, such as scattering in the atmosphere and reflection at the surface. The air mass factors, which are needed to convert the measured differential slant column densities (dSCDs) to vertical column densities (VCDs), have a strong dependence on the surface reflectance, which has to be accounted for in the retrieval. This is especially important for measurements above urban areas, where surface properties vary strongly. As the instrument is not radiometrically calibrated, a method was developed to derive the surface reflectance from relative intensities measured by AirMAP. This method is based on radiative transfer calculations with SCIATRAN and a reference area for which the surface reflectance is known. Furthermore, the influence of aerosols on the retrieval was investigated for a variety of aerosol profiles that were measured in the context of the AROMAT campaigns in which AirMAP participated. Validation with independent measurements shows in general good agreement. The measurement datasets created, as well as the methods developed within this work, provide the basis to validate other high resolution datasets, such as regional chemistry models or satellite measurements at high resolution, such as the ones performed by the Sentinel-5p, launched in October 2017
Draußen tanzen : eine Ethnographie der Bremer Free Open Air Szene
Get PDFZiel der Arbeit ist es eine Übersicht über die Free Open Air und Outdoor Szene der Stadt Bremen zu schaffen. Der Fokus richtet sich dabei darauf, was die entsprechenden Partys ausmachen und welchen Stellenwert sie im Leben der Akteure besitzen. Zur Auswertung der durch teilnehmende Beobachtung, Interviews und Recherche gewonnen Daten wurde zum einen die ethnographische Medienanalyse nach Drackle, als auch die pragmatische Festtheorie nach Deile genutzt. Im Ergebnis lässt sich festhalten, dass es sich bei den untersuchten Veranstaltungen um Feste handelt, bei denen die Bedeutungsebene hinter der Gemeinschafts- und Formebene zurücktritt