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Self-lubricating PVD Coatings in Interaction with Textured Workpiece Surfaces for BulkMetal Forming
Full text linkBulk metal forming of steel, in particular forward extrusion, is characterized by high material utilization and resource efficiency. Currently, high quantities of mostly ecologically harmful lubricants are required, leading to the demand for lubricant-free forming. Two approaches are being pursued to achieve the objective of lubricant-free extrusion of steel. One approach focuses on the tool, the other on the workpiece.With regard to the tools, physical vapour deposition (PVD) can be used to apply self-lubricating hard coatings on forming tools. The workpiece-side approach uses texturing of the workpiece surfaces. In this work, one self-lubricating PVD hard coating as well as four different textured workpieces were investigated. The coating was produced in an industrial coating unit. Using a self-designed tool model with the same dimensions as real forming dies with two extrusion shoulders, the coating thickness distribution and the change in coating properties as a function of complex geometry of the forming dies were analysed. Using a pin-on-cylinder tribometer, which represents an open tribological system and simulates the loads of dry bulk metal forming of steel, the interactions between PVD hard coatings and textured workpiece surfaces were investigated. The combination of two approaches of tool coating and workpiece texturing leading to reduction of wear and friction
Elektronen-induzierte Reaktionen von Koordinationspolymeren zur Nanostrukturierung von Oberflächen
Full text linkElectron-induced reactions play a central role in the development of current methods for nanostructuring of surfaces. The basic principle is the decomposition of metal-containing compounds by a focused electron beam. In the present work the electron-induced reactions of three different copper-containing materials, namely, copper(II) oxalate, copper(II) squarate, and copper(II) 1,3,5-benzenetricarboxylate, were examined in detail. Reflection absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS) were used to identify chemical surface species that are formed upon electron exposure. To determine volatile decomposition products the electron-stimulated desorption (ESD) of neutral fragments was monitored with a new designed UHV setup. In addition, morphological changes of the samples were investigated by helium ion microscopy (HIM). It was shown that the molecular structure of the used anions is decisive for the efficiency and the outcome of the electron-induced decomposition. As an example, surface-bound layers of copper(II) oxalate were identified as suitable precursors for the production of metallic nanoparticles
Collaborative Localization and Mapping for Autonomous Planetary Exploration : Distributed Stereo Vision-Based 6D SLAM in GNSS-Denied Environments
Full text linkMobile robots are a crucial element of present and future scientific missions to explore the surfaces of foreign celestial bodies such as Moon and Mars. The deployment of teams of robots allows to improve efficiency and robustness in such challenging environments. As long communication round-trip times to Earth render the teleoperation of robotic systems inefficient to impossible, on-board autonomy is a key to success. The robots operate in Global Navigation Satellite System (GNSS)-denied environments and thus have to rely on space-suitable on-board sensors such as stereo camera systems. They need to be able to localize themselves online, to model their surroundings, as well as to share information about the environment and their position therein. These capabilities constitute the basis for the local autonomy of each system as well as for any coordinated joint action within the team, such as collaborative autonomous exploration. In this thesis, we present a novel approach for stereo vision-based on-board and online Simultaneous Localization and Mapping (SLAM) for multi-robot teams given the challenges imposed by planetary exploration missions. We combine distributed local and decentralized global estimation methods to get the best of both worlds: A local reference filter on each robot provides real-time local state estimates required for robot control and fast reactive behaviors. We designed a novel graph topology to incorporate these state estimates into an online incremental graph optimization to compute global pose and map estimates that serve as input to higher-level autonomy functions. In order to model the 3D geometry of the environment, we generate dense 3D point cloud and probabilistic voxel-grid maps from noisy stereo data. We distribute the computational load and reduce the required communication bandwidth between robots by locally aggregating high-bandwidth vision data into partial maps that are then exchanged between robots and composed into global models of the environment. We developed methods for intra- and inter-robot map matching to recognize previously visited locations in semi- and unstructured environments based on their estimated local geometry, which is mostly invariant to light conditions as well as different sensors and viewpoints in heterogeneous multi-robot teams. A decoupling of observable and unobservable states in the local filter allows us to introduce a novel optimization: Enforcing all submaps to be gravity-aligned, we can reduce the dimensionality of the map matching from 6D to 4D. In addition to map matches, the robots use visual fiducial markers to detect each other. In this context, we present a novel method for modeling the errors of the loop closure transformations that are estimated from these detections. We demonstrate the robustness of our methods by integrating them on a total of five different ground-based and aerial mobile robots that were deployed in a total of 31 real-world experiments for quantitative evaluations in semi- and unstructured indoor and outdoor settings. In addition, we validated our SLAM framework through several different demonstrations at four public events in Moon and Mars-like environments. These include, among others, autonomous multi-robot exploration tests at a Moon-analogue site on top of the volcano Mt. Etna, Italy, as well as the collaborative mapping of a Mars-like environment with a heterogeneous robotic team of flying and driving robots in more than 35 public demonstration runs
Study and Comparison of Elderly Care System in Germany and China
Full text linkIn the context of globalization and information revolution, the interactions in terms of knowledge exchange between developed and developing countries in the world have became more and more intensified in many aspects. This thesis focuses on the analytic study and bilateral comparison of elderly care systems in Germany and China. As one of the most important social security components, elderly care has a huge impact on the social stability and sustainability. Thus, many countries have put it on a strategic position and strive for an ideal, efficient, sustainable and adaptive solution to confront the challenges brought by population aging. Germany, as one of the most developed countries in the world, has established a solid and comprehensive elderly care system based on its social welfare foundation. China, as one of the most rapid developing and populous countries, has undergone a radical demographic change and a rapid aging process in the last several decades, which pose massive challenges for contemporary China. Therefore, a comprehensive study and comparison of the elderly care systems in both countries are of great scientific value for transferring theoretical and practical experiences. In the work, firstly a brief review and comparison of background information with respects to population development and living situation of the elderly in Germany and China are given. Then, the analysis of elderly care system is dissected in the following major dimensions: long-term care insurance (LTCI), forms of elderly care, and nursing education. Establishing a stable and sustainable long-term care insurance is imperative for elderly care system. The construction and development of LTCI in both countries are discussed and bilateral compared. The major forms of elderly care in the two countries, consisting of home care, community care, ambulant care and institutional care, are analyzed. Additionally, the insights of practical and academic nursing education systems in the two countries are depicted as well, such as the present status and future reforms. In the end, the knowledge transfer and potential collaborations are addressed
Observations of trace gases from ground-based and satellite instruments: Retrieval development and analysis of vertical and horizontal distributions
Full text linkAir pollution affects human health, ecosystems, and the climate. For a better understanding of air pollution, continuous monitoring, measurement validation, and measurement improvement is needed. Therefore, ground-based and satellite-based measurements as well as model data are analysed in this thesis with the main goal to improve the knowledge about the trace gas vertical distribution. The data are compared for three different environments: rural, biomass burning, and industrialised areas. Two different nitrogen dioxide (NO2) vertical column density retrievals for satellite measurements are compared with ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) data above Xianghe, China. The influence of satellite retrievals' a priori assumption is investigated on their agreement with MAX-DOAS data. The a priori profiles are an important difference between the retrievals' input parameters. For this purpose, the MACC2 interim reanalysis data and the MOZART-2 model are used. Generally, the retrieval version with MACC2 interim reanalysis a priori profiles agrees better with the ground-based MAX-DOAS measurements. Furthermore, the NO2 columns are often higher for cloudy scenes than for cloud-free scenes in this area in winter, which might be related to aerosols. Thus, the influence of the cloud fraction and the aerosol content of the atmosphere on the differences between the two retrievals are discussed which provides also the opportunity to understand and reduce the differences between measurements from satellite and ground-based platforms. Not only above industrialised areas but also above rural areas validation measurements are needed. Due to the low pollutant content in these areas, the relative uncertainties of satellite measurements are high. There, satellite data regularly show enhanced levels of short-lived pollutants, which are unexpected to be present in the atmosphere at high levels so far away from any sources. Therefore, MAX-DOAS measurements were taken in the remote Atlantic Ocean to validate satellite measurements. For formaldehyde (HCHO) and glyoxal (CHOCHO), the latitudinal dependency of the MAX-DOAS measurements is similar to satellite observations and model simulations. The trace gas origin could be the African continent. Because of long transports of up to four days, the enhanced values might be related to the export of precursors from the continent which are transformed to HCHO and CHOCHO. Furthermore, the detected outflow is in elevated layers which is in agreement with FLEXPART backward simulations leading to an altitude between 1000m to 5000m. Thus, these results improve the confident in satellite measurements above remote ocean areas. The knowledge of the trace gas vertical distribution on a global scale is generally limited due to the low vertical information content of spectroscopic measurements for the absorbers. However, retrievals in different spectral ranges from satellite measurements can globally provide insight into the vertical distribution of NO2. Therefore, a new NO2 retrieval in the ultra violet spectral range was developed and compared with the standard retrieval in the blue spectral range. Due to the differences in sensitivity to the lower atmosphere, a rough estimation of the NO2 vertical distribution is possible from these two satellite retrievals. In anthropogenically polluted areas, the differences are large between the two slant column densities (approximately 60%), which indicates that the air pollution is located close to the ground. In contrast, the NO2 is uplifted into elevated layers in biomass burning areas which is reflected by reduced differences of approximately 36% between the two spectral ranges. Additionally, models can be validated by converting slant column densities into vertical column densities for both spectral ranges. In theory, if the a priori profiles are correct, the vertical column densities should be similar. Two models, TM5-MP and the MACC2 interim reanalysis data, are used for the conversion into vertical column densities. In total the TM5-MP leads to a better agreement between the ultra violet and blue spectral range. However, in this model the NO2 seems to be located too high in the atmosphere
Influence of Carbonitriding Process on Phase Transformation during Case Hardening, Retained Austenite and Residual Stresses
Full text linkThe carbonitriding process is a surface hardening technique with an ultimate goal of improving surface hardness, fatigue properties and resistance to wear of highly stressed parts. As opposed to carburizing process which enriches engineering components with carbon atoms only, carbonitriding introduces both carbon and nitrogen atoms in the surface layer. The presence of nitrogen stabilizes austenite and depending on the level of carbon and nitrogen content reached, as high as 70 mass-% of austenite can be retained. The thermal and mechanical stability of such high amount of retained austenite is vital as retained austenite should remain stable to avoid shape and dimensional changes especially in close fittings. Moreover, such high amount of retained austenite affects the nature, magnitudes and distribution of residual stresses which can influence the service properties. In the present work, the influence of carbonitriding process on the phase transformation during case hardening, retained austenite and residual stresses were investigated. In particular, the following points were taken into consideration: (1) characterization of the state after carbonitriding, (2) analysis of the state during and after tempering, (3) investigation of the state after tempering coupled with cryogenic treatment, (4) investigation of the state after thermal stabilization, and (5) investigation of the mechanical stability of carbonitrided samples. Five carbonitriding variants with different carbon and nitrogen contents were considered. The phase compositions and residual stress analysis was carried out using X-ray diffraction. For each variant, the amount of retained austenite was dependent on the level of carbon and nitrogen reached which in turn depends on the carbon and nitrogen potential in the carbonitriding atmosphere. Besides the misfit between the case and the core, the amount and distribution of retained austenite in the case affects the nature, magnitudes and distribution of residual stresses in both retained austenite and martensite phase. The thermal stability of retained austenite and residual stress relaxation during the process of tempering was captured in situ, using a diffractometer equipped with a position sensitive detector with high resolution and a heating system. This study establishes the range of thermal stability of retained austenite and its kinetics of decomposition during continuous heating and isothermal holding. Further, it helped to quantify the magnitudes and kinetics of residual stress relaxation. Analysis of state after cryogenic treatment revealed that indeed tempering prior cryogenic treatment does stabilize retained austenite which then becomes difficult to transform to martensite during cryogenic treatment. The new martensite formed during the cryogenic treatment enhances significantly the compressive residual stresses in the martensite phase. Via shot-peening treatment it could be revealed that retained austenite was mechanically unstable and readily transforms; consequently high compressive residual stresses in both retained austenite and martensite phase are resulting
Ocean State Estimation for the Last Glacial Maximum : Combining Models and Proxy Data via Data Assimilation
No full textInvestigating past climate states is essential to understand the global climate system and to validate climate models. Data assimilation can be used to obtain estimates of past climate and ocean states that are consistent with model physics as well as with proxy data. The Last Glacial Maximum (LGM, 19-23 ka) was a time interval when the climate was substantially different from today. Even though primary boundary conditions are comparatively well known, the large-scale patterns of the global ocean circulation, especially the strength of the Atlantic Meridional Overturning Circulation (AMOC), remain uncertain. Most studies indicate the presence of a shallower North Atlantic Deep Water (NADW) and a more extensive Antarctic Bottom Water (AABW) during the LGM. However, previous studies using proxy data, models, or a combination of models and proxy data via data assimilation show dissimilar results regarding the AMOC strength. As of yet, only a few state estimates of the LGM ocean obtained from combining models and proxy data exist. To date, no state estimate exists that is based on global surface data as well as on global data from the deep ocean and it is unclear how robust previous results of ocean state estimation are and which influence the assimilation of additional data would have. Furthermore, the adjoint method, which has been used to obtain previous ocean state estimates, requires the adjoint of the model code, which is not easily obtained for most models. In this thesis a new technique for ocean state estimation is developed that combines a Kalman smoother method with a state reduction approach. The new technique and the adjoint method are used to obtain estimates of the ocean state during the LGM constrained by global annual and seasonal sea surface temperature reconstructions and by data on the oxygen isotopic composition of calcite from benthic and planktic foraminifera. The estimates are, therefore, constrained by global surface as well as deep-ocean data. The new technique does not require an adjoint and is very computationally efficient if the control space is small. It is tested through pseudo-proxy data experiments and, additionally, it is used to investigate the influence of data from within and outside of the Atlantic Ocean on state estimates. The results of the state estimation for the LGM indicate that SST and oxygen isotope data alone do not necessarily support a shallower NADW and a more extensive AABW during the LGM. The results from ocean state estimation depend strongly on the assimilated proxy data and the experimental design. More proxy data would be required to obtain reliable ocean state estimates. However, the pseudo-proxy data experiments indicate that proxy data at LGM coverage are sufficient to reconstruct the global ocean circulation if no or only a small model error is present. Additional adjoint sensitivity experiments show that especially data from the deep North Atlantic and the global deep Southern Ocean would be important to constrain the AMOC strength. This thesis provides a step forward in using data assimilation for paleo-state estimation with different climate models and highlights the need for more proxy data to obtain realiable reconstructions of the LGM ocean state
Biogeochemistry of marine dissolved organic Sulfur : quantification, distribution, molecular composition, and reactivity
Full text linkDissolved organic matter (DOM) is ubiquitous in natural waters and plays a central role in the biogeochemistry of riverine, estuarine and marine environments. The heteroatomic fraction of DOM consists mainly of nitrogen, phosphorous, and sulfur. While the biogeochemical cycling of C, N, and P has been intensely studied, dissolved organic sulfur (DOS) has been only marginally addressed. Nevertheless, it is an essential element for marine primary production and organic sulfur compounds play a critical role in biogeochemistry, ecology, and climate processes. The analysis of DOS quantity and distribution in marine environments as well as its chemical characterization is of urgent need to further understand the underlying processes of DOS biogeochemistry. This study is based on more than 600 samples from different marine environments, from the surface to the deep ocean, and thus, represents the so far most comprehensive dataset of DOS in the ocean. Within this thesis, a basin-scale distribution of extractable DOS in the East Atlantic Ocean, the Atlantic sector of the Southern Ocean, and the Weddell Sea is presented. A first conservative global inventory of the marine non-volatile DOS stock was calculated using a combination of state-of-the-art approaches. The results suggest that the marine DOS inventory is by far the largest oceanic reservoir of organic sulfur (OS), exceeding the atmospheric stock and the volatile marine DOS by several orders of magnitude. Decades of research on the marine DOS cycle have focused on only 2 % of the total OS inventory (DMSP cycle). The marine DOS distribution and stoichiometry was compared to radiocarbon age of dissolved organic carbon (DOC), suggesting a primarily autochthonous biogenic origin and an active involvement of this DOS in the microbial loop - similar to organic nitrogen. The contribution of the sulfur-containing amino acid methionine to extractable DOS was found to be only 2 %. Additionally, ultrahigh-resolution mass spectrometry identified a diverse suite of sulfur containing molecular formulas and their relative contribution suggested shorter residence times relative to DOC supporting the active involvement of DOS in biogeochemical cycles, ecological processes and ecosystem functions. Rivers are also important sources of (sulfur containing) organic matter to marine environments. Here I quantified DOS and trace metals along a salinity gradient and explored the complexation of trace metals with organic matter, in particular with sulfur-containing compounds. Despite decreasing DOM concentrations along the salinity gradient due to estuarine mixing, we showed that DOS is degrading faster than DOC, underpinning the active involvement of DOS in biogeochemical cycles and ecological processes. We found indication for complexation of trace metals with (sulfur containing) organic ligands and confirmed that the stability of metal-organic complexes followed the Irving-Williams order. The results of this thesis challenge current views of DOS dynamics and suggest that there remain major gaps in our understanding of the marine sulfur cycle, which will be of interest to ocean (biogeo-) chemists, atmospheric scientists, microbial ecologists, and ocean-/climate modelers
Ecophysiological performance and life cycle strategies of North Sea shrimps
Full text linkThe high level of digestive enzyme polymorphism in C. crangon specimens seems to be an important feature for their biological success in the North Sea. This pronounced polymorphism has different impacts on the metabolism of North Sea shrimps. On the one hand, it affects the sequence of proteins necessary for the accumulation of lipids. This change in the sequence of specific proteins is a challenge to the metabolism of C. crangon, because it results in a limited lipid storage capacity. Lipid storage is important to overcome periods of food paucity and to fuel reproduction. However, in C. crangon the midgut gland does not function as principal energy depot. Instead, the midgut gland serves as a dynamic metabolic center that directly provides dietary energy necessary for diverse biological processes including reproduction. This metabolic center seems to be supported by the expression of digestive enzyme isoforms
Adhesive Wear Initiation during Blanking of Austenitic Stainless Steel, with regard to Thermoelectricity
Full text linkBlanking and cold metal forming are two important large-scale manufacturing processes, and therefore have to be costefficient whilst allowing for the production of parts subject to the highest of quality requirements. These conditions require long tool service life, which necessitates a reduction of adhesive wear, especially when processing materials with a high tendency to bond adhesively, like aluminum or stainless steel. To meet this objective, all wear-causing interactions have to be understood. One key aspect in this context is thermoelectricity, a phenomenon that occurs when two connected electric conductors are subject to a temperature gradient. This constellation causes a thermoelectric current to flow, which influences adhesive bonding and entails processes like local melting of the sheet metal. This paper deals with the comparison of two continuous stroke blanking processes with regard to adhesive wear development. One process represents an ordinary blanking tool configuration, and one is performed with externally influenced thermoelectric currents. The results show a significant impact between the initial development of adhesive wear and tool configuration, with regard to thermoelectricity