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From microstructures to macroscale carbon export : influences of marine snow composition on settling velocity and microbial colonization
Full text linkSinking marine aggregates are an integral component of the marine biological carbon pump. The specific focus of this thesis was on techniques to study the composition and sinking behavior of single aggregates collected in situ. Thin-sectioning of aggregates in soft and hard embedding media was used to examine the structure and colonization patterns of aggregates at high spatial resolution. This enabled detailed characterization of the aggregate matrix and localization of selected bacterial colonizers. To study the effect of aggregate composition on sinking velocity, I used Particle Image Velocimetry to analyze the fluid flow around settling aggregates in a flow chamber. Aggregate flow fields strongly resembled those of impermeable, porous spheres which suggested that Stokes law is applicable to settling marine aggregates. The influence of aggregate composition on export flux was studied in a laboratory experiment through incorporation of plastic microfibers into settling aggregates. Microfiber addition decreased potential export flux by 30-60% and, if confirmed in situ, may substantially reduce the efficiency of the biological carbon pump
Funktionstests der Nutzlast für die MICROSCOPE-Mission : Freifalltests am Fallturm Bremen
Full text linkThe payload of the french space mission MICROSCOPE containing two differential accelerometers had to be tested in zero-g conditions before launch. By using special drop capsules at the drop tower Bremen at ZARM (University of Bremen) it was possible to test the payload successfully and to demonstrate the correct function of the system. The MICROSCOPE mission aims at testing the Weak Equivalence Principle (WEP) with a new level of accuracy. The correct function of the payload was an important requirement to achieve the mission goal. Another part of the thesis is the development of a new technique for measuring the accelerometer bias by using the catapult mode of the drop tower
Kingdom Come: Deliverance. A Bohemian Forest Simulator
No full textReview of the video game Kingdom Come: Deliveranc
Mapping Solidarity in Europe: Discourse Networks in the Euro Crisis and Europe's Migration Crisis
Full text linkThe dissertation analyses solidarity in Europe in times of crisis. It focuses on the Euro crisis and Europea s migration crisis discourse in the European Union (EU) member states Germany and Ireland from 2010 to 2015. I theorise solidarity from a discursive perspective and develop the discursive construction of solidarity approach to examine actorsa public statements on solidarity. The dissertation is situated in a discursive institutionalist framework and deploys a discourse network methodology in order to examine the changing meanings and varying actor constellations that shape the discourses on solidarity. The cumulative dissertation contains five different chapters that highlight different theoretical and empirical aspects in the study of solidarity discourses in times of crisis. By doing so, the dissertation points out new directions and signals new paths for future studies on solidarity
Überwachung von Faserverbundwerkstoffen mit miniaturisierten flexiblen Interdigital Sensoren
Full text linkThe focus of this work is the monitoring of fibre composites and adhesives with a miniaturized flexible Sensor. Monitoring of the curing process is one of the relevant parameters to optimize the production process and ensure the quality of the composite. The presented sensor measures the curing process locally in the material based on impedance spectroscopy. This enables the monitoring of specific critical points in a part. With this method it is also possible to distinguish between the curing process of different adhesives and resins of fibre composites. Using different mechanical test it can be shown that the sensor does not influence the mechanical properties of the material significantly. An inlay of polyimide with 5 I m thickness and holes in the substrate has the smallest influence on the mechanical properties. It has a net-shaped structure with all the dimensions in the range of the fibres diameter. The sensors are fabricated on this substrate and can therefore stay in the fibre composite without downgrading the mechanical stability. Hence the sensors can also be used for lifetime monitoring of the fibre composite. Here it is shown that measuring the moisture diffusion inside the composite is possible with the interdigital sensor. The changes of the impedance can be correlated to the mass change which is created by moisture uptake. Using multiple sensors the distribution of the moisture in the composite can be determined due to the local measurement of the sensors. In addition it is shown that the presented sensors can be used to analyse the internal configurations of shape memory polymers. These materials are a combination of thermoset and thermoplastic which should be covalent bonded to have a shape memory behaviour. Measuring the impedance with the interdigital sensor covalent bonded mixtures can be distinguished from those which are not covalent bonded. An external stimuli, here temperature, is used to be able to deform the material. This change in internal structure can also be measured with the sensor. Furthermore the curing process of adhesives can be monitored with interdigital structures. In many cases an adhesive is used to bond to parts together. Therefore one of these parts can be used to screenprint the interdigital structure on top, which is quite fast and cost effective. This is the reason why also printed sensors are investigated. With the printed sensors it is possible to monitor influence of the environmental conditions on the curing process of adhesives
Direkte und inverse elektromagnetische Streuprobleme für lokal gestörte periodische Medien
Full text linkWe consider the direct and inverse scattering problem of electromagnetic and acoustic wave phenomena for an unbounded, inhomogeneous and bi-periodic media, which includes a local defect. At first, we show the unique solvability of the vector valued scattering problem formulated in terms of the Maxwell's equations, as well as the scalar valued scattering problem modeled by the Helmholtz equation, by assuming some reasonable presumptions on the regularity of the parameter. Moreover, we show some regularity results for the Bloch-Floquet transformed solution w.r.t. the quasiperiodicy and derive a numerical method for the approximation of the solution based on the finite-elements method. We continue with the inverse problem of reconstructing the perturbation. For that, we consider different measurement operators, prove the injectivity and apply a Newton method. Furthermore, we introduce the Factorization method as a fast imaging method to localize the support of the perturbation
Social Representations Approach to a Peace Process : The Case of Turkey
Full text linkAbstract This doctoral dissertation describes a longitudinal research project seeking to contribute to our understanding the role of meaning-making processes in creating or obstructing societal and political transformations towards peace. The focus of the project is on the plurality and dynamicity of social knowledge in peace processes, thus I draw on the social representations theory, a constructivist approach to social knowledge. I investigated the case of the peace/resolution process regarding the Kurdish question in Turkey through three empirical studies using media data. First, various constructions of the concept of peace, their discursive function, and change in the constructions as the peace/resolution process continued are investigated by using corpus linguistic methods in the corpora of five newspapers for two-years period. Later, various representations of the peace/resolution process, their underlying cultural and ideological resources as well as their action orientations are scrutinized by performing critical discourse analysis. Lastly, various understandings of the peace process and communication strategies in dealing with other understandings are investigated by conducting qualitative content analysis and discourse analysis on readersa comments to an online newspaper. Through these studies, I investigate the historical, cultural, and political factors that influence constructions of different understandings of peace. I look at how these various subjective understandings exist together, how they deal with each other and how they orient people to treat othersa understandings. I also identify how the various understandings change as a result of interactions with each other and adapt to changing physical realities. Lastly, I interpret how these various understandings constitute social context that promote or impede social change towards peace. By doing so, I address the reciprocal and simultaneous influence between society members and social and political context through plurality and dynamics of social knowledge. I argue that focus on these relations provide a conceptual framework to address the complexity of move towards peace
Heterogeneous Catalysis with supported Nanoparticles : Particle Size Effects and Metal-Support Interactions
Full text linkIn this work supported surfactant-free Pt NPs were used as heterogeneous catalysts for CO oxidation. First, a synthesis strategy was developed to tune the particle size of these surfactant-free Pt NP between 1- 4 nm. Following these NPs were supported onto inert (Al2O3) and active (Fe3O4) support materials. In kinetic investigations reaction mechanism and catalytic performances were analysed and it was found that the particle size, the support material, and the use of bimetallic NPs influences the activity and the reaction mechanism of CO oxidation under CO rich conditions and a reaction temperature of 200AdegreeC
On the excess velocity of Taylor-droplets in square microchannels
Full text linkThis thesis deals with the movement of Taylor-droplets in microscopic multiphase flows and reports a phenomenological model to improve the description of the instantaneous droplet velocity. The chosen approach can be seen as a holistic-hybrid between measurement methodology, high-speed image averaging and semi-analytic greybox modeling. For the first time, the influential parameters on the excess velocity are described for squared microchannels. Different valuable benefits arose on this journey beside the final model: A novel noninvasive and cost-efficient measurement device based on near-infrared photometry is developed and successfully tested, the flow-induced Taylor-droplet cap deformation is correlated to the Ca-number and genetic algorithms are successfully adapted for model adjustment. Model validation drives the development of a novel refractive index matching (RIM) approach. The phenomenology of the model is subsequently validated using carefully performed microPIV measurements
