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Large-scale Modelling of Subglacial Hydrology
Get PDFSubglacial hydrology is a key component in ice sheet dynamics and controls the sliding of ice sheets. Modelling the integrated system between ice dynamics and subglacial hydrology is essential for understanding current changes in the system and projecting future evolution of ice sheets and their contribution to sea level rise. The recent acceleration of mass loss of the Greenland ice sheet can be largely attributed to dynamic thinning at the ice margin, where hydrologic processes play a significant role in the speed-up of outlet glaciers. Models of subglacial hydrology recently have progressed to incorporate multiple components of the drainage system and are able to represent observed seasonal evolution of an efficient drainage system during the melt season, but the application of models on a continental scale remains a challenge. This doctoral thesis analyzes different approaches to model the subglacial hydrology and its interaction with the ice flow in respect to their ability to be applied to large domains. Two different models are developed and analyzed. A balance flux model coupled to the ice dynamics model SICOPOLIS is used to study the effect of subglacial water on the Eurasian ice sheet, applied to the simulation of future sea level contribution of Greenland where it reveals that the effect of subglacial discharge on submarine melting is comparable to increased ocean warming. Additionally, this model is utilized in the study of subglacial lakes at Recovery Glacier, Antarctica. The second model is an equivalent aquifer model which describes the water flow in a porous layer adapted to exhibit the properties of the complex drainage system. The evolution of the system is achieved by locally adjusting the transmissivity. It is shown that this approach leads to realistic pressure and discharge distributions which compare well with more sophisticated models, while keeping computational costs low
Influence of laser generated micro textured coated tool surfaces on dry deep drawing processes
Get PDFThe idea of sustainability and resource conservation promotes the development of energy-efficient and low-emission production processes. A lubricant-free sheet metal forming process is considered as one of these environmentally friendly production technologies. Metal forming processes without conventional lubricants shorten process steps and reduce additional costs, such as removal of residual lubrication from the workpiece after forming. In order to realize such a dry forming process and effectively control the material flow, amorphous carbon coatings were applied to the tool surfaces and a brushing process was carried out as a surface finishing process for roughness adjustment. Laser generated micro features on the surface should make an effective contribution to local friction adaptation. The transferability of strip drawing test to strip bending rotation test was successfully demonstrated by dry and oiled blank reference tests. The first modification of the tool sided surface was achieved by applying ta-C and a-C:H layers. The influence of the coatings on the tribological behaviour was determined in strip drawing tests for DC04 and AA5182. Additional friction adaptation is made possible by the fine and flexible laser based micro texturing of the coated tool surface. Experiments were carried out with different coverage and depth of the laser generated features in order to analyze the tribological influence. Flat and deep features with a degree of coverage of 20 %, 35 % and 50 % are considered in order to analyze the factors influencing their tribological behavior. Compared to ta-C coated references, it can be seen that micro features on the ta-C coated tool surface causes a friction reduction for DC04, independent of the features depth. However, deep laser generated features in particular lead to an increase in friction for AA5182, so that this could potentially lead to a selective local increase in friction in the flange area. For the transferability of the tribological system from the flat application case to a curved tool surface, the basics for laser based texturing of cylinder surfaces are illustrated. The limits of the holographic beam shaping technology used for this are demonstrated
Complete Model-Based Testing Applied to the Railway Domain
Get PDFTesting is the most important verification technique to assert the correctness of an embedded system. Model-based testing (MBT) is a popular approach that generates test cases from models automatically. For the verification of safety-critical systems, complete MBT strategies are most promising. Complete testing strategies can guarantee that all errors of a certain kind are revealed by the generated test suite, given that the system-under-test fulfils several hypotheses. This work presents a complete testing strategy which is based on equivalence class abstraction. Using this approach, reactive systems, with a potentially infinite input domain but finitely many internal states, can be abstracted to finite-state machines. This allows for the generation of finite test suites providing completeness. However, for a system-under-test, it is hard to prove the validity of the hypotheses which justify the completeness of the applied testing strategy. Therefore, we experimentally evaluate the fault-detection capabilities of our equivalence class testing strategy in this work. We use a novel mutation-analysis strategy which introduces artificial errors to a SystemC model to mimic typical HW/SW integration errors. We provide experimental results that show the adequacy of our approach considering case studies from the railway domain (i.e., a speed-monitoring function and an interlocking-system controller) and from the automotive domain (i.e., an airbag controller). Furthermore, we present extensions to the equivalence class testing strategy. We show that a combination with randomisation and boundary-value selection is able to significantly increase the probability to detect HW/SW integration errors
Acquisition and Processing Techniques for Image-Based Prospective Motion Correction in Magnetic Resonance Imaging
Get PDFThe sensitivity to subject motion is one of the major reasons of image quality degradation in magnetic resonance imaging (MRI). Subjects need to be very calm to maintain the relationship between spatial image information and subject anatomy throughout the scan. In case of moving subjects, prospective motion correction can regain this relationship by constantly adapting the image slice positioning to follow the subject in real time. This requires continuous estimates of the current motion state, which is complicated for a variety of MRI applications. In this dissertation, image-based prospective motion correction techniques are developed to increase the image quality as well as quantitative imaging parameters in diffusion-weighted imaging, high-resolution 2D imaging and functional MRI
Logistik, eine technologisch-ökonomische Revolution? - Eine historisch-konzeptionelle Studie aus innovationswissenschaftlicher Perspektive
Get PDFMathematical aspects of catalyst positioning in Lithium/Air Batteries
Get PDFLithium/air batteries has been taken interest by many scientists over the last years. The catalyst positioning problem describing the porous cathode during the discharge process is concerned in the research of optimizing the capacity of Lithium/air batteries. During discharge process, there is a critical issue: the discharge oxygen reduction products is insoluble in the organic electrolytes. This clogs the oxygen entrance to the pore to be reacted with Lithium ions and limits the capacity of the batteries by narrowing the active surface inside the pore. The dynamics of the discharge process is described by the initial mixed boundary value problem for two one-dimensional partial differentiable equations. The two variables of the system are the pore radius inside the cathode and the Oxygen concentration at certain coordinate and time. The subject of the thesis is to investigate some catalyst positioning models and to maximize the free volume of the pore after pore clogging by the deposited discharged products. We aim at the following fields: First, we research analytically the forward model describing continuous catalyst positioning in Li/air batteries: well-posedness of the problems, the Fr echet differentiability of the pore radius and the oxygen concentration with respect to catalytic function in some spaces. Second, we present optimization problems and analyze the sensitivity and adjoint method to solve them. Finally, some numerical methods are carried out to solve the forward problems and some numerical approach for solving optimization problem are also examined to illustrate the theoretical results
Effects of hypoxia and hypercapnia on thermal tolerance: an integrative assessment on the green abalone (Haliotis fulgens).
Get PDFWith the rise in atmospheric concentration of greenhouse gases, most marine ecosystems are facing increasing seawater temperatures, ocean acidification and a higher frequency or intensity of extreme warming events. Moreover, rising seawater temperature is expected to interact more frequently with falling oxygen levels (hypoxia) and increased CO2 concentration (hypercapnia). Both drivers may impose constraints on physiological mechanisms that define thermal Limits thereby increasing the vulnerability towards warming in marine ectotherms. The green abalone Haliotis fulgens is an economically important marine gastropod at the Pacific Coast of Mexico. In recent years, an increased frequency and intensity of environmental extremes, such as El Nino events and upwelling of highly hypoxic or hypercapnic water, has been associated with mass mortality events, threatening natural populations. Within this framework, the present study aimed at investigating the thermal tolerance and the underlying metabolic and molecular response in multiple tissues of H. fulgens under conditions of hypoxia and hypercapnia. Juvenile abalone (25.05 A /- 2.57 mm shell length) were exposed to a temperature ramp (from 18 degree Celsius to 32 degree Celsiu 3 degree Celsius day-1) under hypoxia (50% air saturation) and hypercapnia (a 1000 I atm PCO2), both individually and in combination; the conditions are based on natural oxygen declines occurring along the Baja California Peninsula and PCO2 values predicted by the end of the century, respectively. Hypoxia constrained the whole-organism oxygen consumption at moderate temperature (27 degree Celsius) paralleled by the accumulation of anaerobic metabolites (succinate, lactate, and alanine) in gill and hepatopancreas, suggesting a limitation in the aerobic capacity and reduced thermal tolerance. On the contrary, warming under hypercapnic exposure did not constrain Oxygen consumption, but the higher Q10 in metabolic rate and the increased levels of anaerobic metabolites at the warmest temperature (32 degree Celsius) indicate some stimulatory effect on metabolism. Finally, warming under combined hypoxia and hypercapnia resulted in negative synergistic impacts with an accumulation of anaerobic metabolites at a lower temperature (24 degree Celsius), followed by a depletion of metabolites, declining whole animal oxygen consumption indicating some hypometabolic state, and finally, the onset of muscular failure and death at the warmest temperature. The integrative approach from the molecular to the systemic levels and the use of different tissues in the present thesis allowed to identify promising indicators of physiological and metabolic traits responding sensitively to environmental challenges. Therefore, the identified traits and the approaches presented here represent a powerful tool in the assessment of the sensitivity of natural populations of green abalone to climate change
Ecological observations of pelagic bacterial and archaeal communities in the Atlantic-Arctic boundary zone
Get PDFThe global climate change has an unprecedented impact on the Arctic Ocean, resulting in warming of the Arctic surface air at much faster rates than the global average. The warming temperatures lead to constantly declining Arctic sea ice cover, which reached in September 2018 the sixth lowest summertime minimum extent in the satellite record (since the late 1970s). Shrinking sea ice has a strong impact on the entire Arctic marine ecosystem, through alterations of the primary production, grazers communities, and subsequently the biological carbon pump. Current predictions of entirely sea-ice free summers in the Arctic Ocean already in the second half of this century urges the need to understand the ongoing oceanographic and biological processes in order to predict how the Arctic ecosystem will respond to further environmental changes. The differentiation between natural temporal ecosystem variability and anthropogenically-induced impact of the climate change requires long-term observations. The Ocean Observing System FRAM (FRontiers in Arctic marine Monitoring), which was established in 2014, is an Arctic long-term observatory for investigating the impact of changing ocean properties and sea ice conditions of the Arctic Ocean on its marine ecosystem. The starting point for the FRAM project was the already existing long-term observatory HAUSGARTEN, situated in the main gateway between the Arctic and the Atlantic Oceans - the Fram Strait. To date, despite their importance for the biogeochemical cycling, very little is known regarding the diversity and function of microbial communities in the Arctic Ocean in general, and specifically in the Fram Strait. In the framework of FRAM, a Molecular Observatory was established, for conducting standardized molecular-based high-resolution observations of the Arctic microbial communities. This thesis was conducted as part of the FRAM Molecular Observatory, and as part of the establishment process of the observatory it contributes to the methodological and procedural standardization required for long-term microbial observations. This thesis provides a first comprehensive overview of currently existing long-term microbial observatories around the world, it provides guidelines for initial steps towards establishing a community network between them, and stresses the urgent need in community efforts towards methods standardization. Furthermore, as part of the methods standardization for long-term microbial observations, this thesis includes a performance comparison between two, broadly used in microbial oceanography, 16S rRNA gene primer sets. The main focus of the thesis is on the ecology of pelagic bacterial and archaeal communities in the Fram Strait. Its overall objective was to investigate the distribution of these communities in the Fram Strait, and to identify environmental drivers of their diversity. The observations of this thesis reveal that sea ice has a strong impact on the development of the seasonal phytoplankton bloom during the summer. As a result, sea ice conditions are affecting the bacterial diversity in surface water, and are leading to a distinct community in sea-ice free and sea-ice covered regions of the Fram Strait. However, the impact of the sea ice is not limited to the surface ocean, as it also heavily affects the vertical export of aggregated organic matter to the deep ocean. The results of this thesis also show that aggregates formed under the sea ice sink faster, and by that provide a stronger vector for transport of bacterial and archaeal taxa to the deep ocean, compared to ice-free waters. Altogether, this thesis contributes to the baseline knowledge needed for further long-term observations of pelagic microbial communities in the Arctic marine ecosystem. Furthermore, it provides an important insight into the strong impact of the sea ice on bacterial and archaeal communities throughout the entire water column, underlining the potential impact of further environmental changes on the Arctic Ocean in the light of prevalent global warming and climate change
Electrochemical and morphological characterization of the Interface at negative electrodes in aqueous metal-ion batteries Gas Evolution & electrodepostion Efficiency
Get PDFProviding a sufficient amount of energy is a primary problem for current and future societies. To achieve this goal, it is essential to expand the use of renewable energy sources such as the sun and wind, as soon as possible. These energy sources are inherently intermittent. Thus, appropriate grid-scale energy storage systems are required to store high amount of energy in a very short period of time. One possible choice for stationary applications in which volumetric and gravimetric energy densities are not primary factors is aqueous metal-ion batteries. Recently, aqueous zinc-ion batteries based on copper hexacyanoferrate with an average potential of 1.73 V have been developed. The main limiting factors for this new family of batteries include a low electrodeposition efficiency and hydrogen evolution on the negative electrode. These problems are related to the use of zinc as the negative electrode, in which the electrochemical reduction potential is sufficiently low that, at least thermodynamically, hydrogen evolution becomes favorable. Hydrogen evolution negatively influences the electrodeposition efficiency of the electrode and performance of the battery, hindering the power density, and lowering the overall energy efficiency. Therefore, decreasing the level of hydrogen evolution and increasing the electrodeposition efficiency are of primary importance in this type of battery. In the first part of this dissertation, a new electrochemical cell was designed for in-operando characterization of gas evolution in batteries via differential electrochemical mass spectrometry (DEMS). Different parameters such as the position, size, and shape of the electrodes, flow of the carrier gas, contact between the current connectors and electrodes, sealing of the cell, and setup to run the DEMS measurements were all discussed. The performance of the cell for DEMS measurements was validated by investigating the gas evolution at the graphite electrode in an organic electrolyte. To do so, cyclic voltammetry (CV) was combined with the DEMS method. Moreover, the ability of the cell to perform electrochemical impedance spectroscopy (EIS) measurements was confirmed. Subsequently, the cell was used to study hydrogen evolution on negative electrodes in an aqueous zinc-ion battery based on Prussian blue derivatives. To accomplish this goal, galvanostatic cycling with potential limitation (GCPL) was combined with the DEMS method. The results showed that increasing the concentration of the electrolyte could suppress the level of hydrogen evolution. The second part of this dissertation studied the morphology of zinc electrodeposition on the negative electrode at different current densities. Several constant current densities were applied and the surface morphology investigated via SEM and color 3D laser microscopy. The results showed that below the limiting current density, no preferential growth was observed on iv the surface of the electrode. However, above the limiting current density, large hexagonal crystals were formed all over the surface. Thereafter, the effect of Branched Polyethyleneimine (BPEI) as an electrolyte additive on the zinc electrodeposition mechanism was studied. It was determined that the presence of BPEI in the range of 30 ppm inside the electrolyte could suppress the growth of hexagonal crystals and stabilize the electrodeposition efficiency of zinc. The third part of this dissertation focused the application of layered double hydroxide (LDH) as a substrate for zinc electrodeposition. To do so, GCPL was used and the electrodeposition efficiency of zinc on different substrates serving as the negative electrode was examined. The results showed that the appropriate ratio of zinc to LDH as a substrate considerably enhanced the efficiency of zinc electrodeposition in 500 mM of zinc sulfate, from 88% to 98%. Moreover, LDH suppressed the intense potential drop at the beginning of the reduction reaction that could be attributed to the elimination of hydrogen evolution. LDH, in an appropriate combination with zinc, was determined to be a very good alternative for use as a negative electrode in aqueous zinc-ion batteries
Entwicklung einer hocheffektiven Magnetfeldabschirmung für die Forschungsraketenmission MAIUS-1
Get PDFThe goal of the MAIUS-1 sounding rocket mission is the realization of the first Bose-Einstein-Condensate and following atom interferometry measurements in space. The hardware of this experiment is specifically designed to match the requirements of a sounding rocket mission. Since the different techniques to create a Bose-Einstein-Condensate like magneto-optical traps and the following atom interferometry methods are very sensitive to external magnetic fields, a effective magnetic shielding is necessary. In this work the design and also the magnetic properties and flight-readiness test procedures are described in great detail. The three-layer magnetic shielding provides a high shielding effectiveness factor of S 1000 for an undisturbed operation of the experiment. With this magnetic shielding it was possible to create the first Bose-Einstein-Condensate in space during the flight of the MAIUS-1 sounding rocket