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Konzept zur Bearbeitung und tribologischen Prüfung von Fließpressmatrizen für das Trockenumformen von Aluminium
Get PDFBei der Erprobung neuer Oberflächenmodifikationen für den Einsatz in umformtechnischen Prozessen werden in der Regel mehrstufige Prüfserien durchgeführt. Vor allem zur Ermittlung des tribologischen Verhaltens werden zunächst experimentelle Untersuchungen mittels Tribometern und einfach bearbeitbarer Probenkörper genutzt. Das genutzte Tribometer wird auf Basis des im Realprozess auftretenden Lastkollektivs gewählt. Positiv bewertete Oberflächenmodi-fikationen werden in einer nächsten Prüfstufe in Laborversuchen mit prozessähnlichen Werkzeuggeometrien getestet, bevor schließlich Feldversuche im Realprozess folgen. In diesem Beitrag wird ein prozessnaher Laborversuch mit ge-schlitzten Fließpressmatrizen für das Trockenumformen von Aluminium vorgestellt. Dabei wurde vor allem auf die Anforderungen hinsichtlich eines variablen Lastkollektivs, der Möglichkeiten zur Oberflächenbearbeitung (Laserpolie-ren und Funktionalisieren) und zur Verschleißanalyse, als auch auf die Reduktion von Werkzeugkosten durch mehrfa-che Verwendung einzelner Komponenten geachtet. Insgesamt wurde sowohl das entwickelte Werkzeugkonzept für ausgewählte Werkzeuggeometrien erfolgreich getestet, als auch die Möglichkeiten einer Oberflächenmodifikation der Matrizenfunktionsflächen mittels Laserpolitur und Abscheidung von SAM (selbstanordnende Monolage) demonstriert
Games of Social Control : A Sociological Study of 'Addiction' to Massively Multi-Player Online Role-Playing Games
Get PDFResearch report on games and social contro
Dynamik und Stabilität der Dampfkapillare beim Laserstrahltiefschweißen
Get PDFThe keyhole which is typical for laser deep penetration welding is responsible for the highly dynamic process behavior, which results in unwanted pore and spatter formation. This work aims to better understand the dynamic keyhole properties and occurrence of process defects. Therefore, a semi-analytical model is developed and validated by optical emission analysis. Spatter characteristics are evaluated in high speed videos and porosity in x-ray analysis. Correlations between keyhole behavior and spatter and pore characteristics could show that pores can form due to a keyhole collapse and spatter detachment requires more than the momentum from keyhole wall fluctuations. Dynamic behavior and process defects are influenced by the spatial laser intensity distribution
R/V SONNE Cruise Report SO256, TACTEAC, Temperature And Circulation History of The East Australian Current, Auckland (New Zealand) - Darwin (Australia), 17 April - 09 May 2017.
Get PDFProcess Studies on the Generation of Near-Inertial Internal Gravity Waves by Wind
Get PDFThe generation of internal gravity waves in the ocean associated to wind stress forcing is studied with the aid of two numerical models. In a non-linear, axisymmetric and Boussinesq model the response to an idealized stationary wind stress pulse is investigated. The major generation mechanisms for internal gravity waves, inertial pumping, excites radially outward propagating low mode wave packets. The energy radiated relative to the wind work is found to be only about 0.02%, which is 2-3 orders of magnitude lower than generally observed. In addition to the detailed axisymmetric simulation, a simplified hybrid slab model based on the classical slab model of (Pollard and Millard, 1970) is considered. In particular, the inertial pumping resulting from the divergent, horizontal, near-inertial response of the surface slab is regarded the boundary condition to the internal gravity wave field below the mixed layer. In a set of idealized experiments, laterally moving wind stress fronts are the most efficient driver for vertical motion depending on their translation speed. The application of the hybrid slab model to the North Atlantic for the years 1989 and 1996 as examples of opposite phases of the North Atlantic Oscillation shows latitude bands with characteristic ratio of energy radiated as internal gravity waves to the wind work. These are partly associated to the wind field structure in these meridional regimes. The ratio of total energies transferred equals to 9% for both years. In an application of the hybrid slab model to the axisymmetric setup it is found that the structure of the inertial oscillations of the axisymmetric simulation are well reproduced. However, the near-inertial response of the hybrid slab model has an 8 times larger amplitude and does not include non-linear effects. The ratio of radiated energy to the wind work for the stationary storm estimated with the hybrid slab model is about 1%. This ratio is increased by a factor 30 when the same wind stress structure is moving across the domain with 21 km/h
Analyse und Vergleich experimenteller Untersuchungen zur Flammenausbreitung längs zylindrischer und ebener PMMA-Proben unter Normal- und Mikrogravitation
Get PDFIn der vorliegenden Arbeit wird der Einfluss einer strukturierten Oberfläche auf die Flammenausbreitungsgeschwindigkeit bei Proben aus Polymethylmethacrylat (PMMA) thematisiert. Zu diesem Zweck wird eine Oberfläche mit einer einzelnen Stufe unter terrestrischen Bedingungen untersucht, wobei die Stufenhöhe von drei bis hin zu 20 Millimetern variiert wird. Die Messergebnisse werden mit den bisherigen Arbeiten zu der Thematik des Struktureinflusses verglichen und darüber hinaus genutzt, um ein bereits entwickeltes empirisches Modell zu erweitert. Dieses ermöglicht durch die Berechnung eines Strukturfaktors Propagationsraten für implementierte Geometrien in Relation zu einer Referenzprobe vorherzuberechnen. Des Weiteren wird ein Verbrennungsexperiment unter reduzierter Schwerkraft durchgeführt, bei dem zylindrische PMMA-Proben mit und ohne Oberflächenstrukturierung verbrannt werden. Die Daten des Experimentes werden anschließend terrestrischen Referenzversuchen gegenübergestellt. Alle Untersuchungen werden mit Hilfe eines Infrarotkamerasystems aufgezeichnet und softwaregestützt ausgewertet. Im Zuge der Diskussion wird der Einfluss der gestuften Geometrie auf die Verbrennung aufgearbeitet, bevor die Arbeit mit einem Ausblick auf in der Zukunft sinnvoll zu untersuchende Oberflächenstrukturen schließt
Temporal distribution of cold-water corals in the northwest Atlantic through the Late Quaternary : footprint of intermediate water mass circulation
Get PDFOver the last two decades, extensive geological investigations on cold-water coral (CWC) areas of the northeastern Atlantic revealed that the temporal occurrence of framework-forming CWC presents a climate-dependent pattern. The pattern follows the glacial-interglacial changes of the surface ocean conditions and intermediate-depth water masses. Over geological time scales, CWC can form substantial seabed features, called CWC mounds that may serve as archives for assessing their long-term development. Several CWC mound areas have been described in the northwestern Atlantic, where the presence of living reef-like structures advocates for favorable conditions for CWC at present. A limited number of ages of fossil CWC collected from various sites in the northwestern Atlantic further suggests that conditions were also favorable during the last glacial. However, the less of a handful of available ages emphasizes the need for a thorough investigation of the temporal pattern of CWC occurrence in this area. This study was designed (1) to identify the periods of sustained CWC growth in two coral mound areas of the northwestern Atlantic (the Campeche CWC Province, southern Gulf of Mexico, and the Cape Lookout CWC area, off North Carolina) and (2) to detect the environmental factors influencing their long-term development. The temporal occurrence of CWC was established by using U-series dating, while a multi-proxy approach was followed to reconstruct the present and past environmental conditions (incl. water column analyses; ROV video observation and sampling; foraminifera-based stable isotope analyses, Mg/Ca-thermometry and assemblage analyses; grain size and carbonate content analyses of sediments). The results suggest that for the last 260,000 years, pronounced coral growth at these two coral mound areas was restricted to interglacial periods, which confirms a climate influence on the CWC temporal occurrence also in these northwestern Atlantic areas. The pattern coincides with the glacial-interglacial changes of the intermediate-depth water masses, where periods favorable for CWC growth are marked by enhanced hydrodynamics that increase the food supply to the CWC. At the Campeche CWC area, such conditions result from the density gradient between the Antarctic Intermediate Water and the overlying Tropical Atlantic Central Water, whereas at the Cape Lookout CWC area, coral growth is steered by the Gulf Stream presence. Although similar occurrence patterns were found in the two studied areas, they differ from the few ages previously reported for the NE Gulf of Mexico and the East Florida Strait CWC mound areas, where CWC occur today but obviously also occurred under glacial conditions. Therefore, it is necessary to conduct further research in order to better constrain the general pattern of CWC occurrence in coral mound areas of the northwestern Atlantic and its possible connection to the intermediate-depth circulation
Transportmodi für die letzte Meile : Konzeptueller Vergleich und Zukunftsszenarien in chinesischen Megastädten
Get PDFUsing Multimodal MRI Techniques to Derive a Biomarker for Tracking the Pathological Changes Occurring at Different Stages of Cognitive Decline in Parkinson's Disease in a Cross-Sectional Study Design
Get PDFCognitive impairment is common in Parkinson's disease (PD) and can range from mild cognitive impairment (PD-MCI) to dementia (PDD). The aim of this study was to derive a multi-modal MRI-based biomarker for the reliable discrimination of PD patients at different stages of cognitive decline and to identify pathologic patterns related with dementia risk. The resting-state functional MRI (rs-fMRI), diffusion tensor imaging (DTI), Arterial Spin Labeling and MR spectroscopic imaging data of 60 PD patients (PD-N, PD-MCI, PDD) were collected. The rs-fMRI data revealed a combination of resting-state networks with significant discriminative power based on the expression scores of the resting-state networks. In combination with the DTI data we obtained a successful model for the discrimination of PDD patients and were able to identify progressive pathological changes that can be used as biomarker for PDD and could be established as clinical diagnostic tool for PD patients with high dementia risk
History of ice sheets surrounding Baffin Bay and its link with oceanic conditions since MIS3
Get PDFBaffin Bay provides the ideal setting for studying the past interaction between the marine realm and the cryosphere. It was an important, but often overlooked, conduit for meltwater into the Labrador Sea and North Atlantic: a key site for deep-water formation and thus climate modulation. Marine sediment archives capture evidence of both ice sheet behaviour and oceanic conditions. Using two sediment cores collected from central Baffin Bay, with good preservation of biogenic carbonate, allowed for the construction of a robust, radiocarbon-dated chronology, as well as multi-proxy paleoceanographic reconstructions. Results indicate several periods of ice-sheet instability (termed Baffin Bay Detrital Carbonate Events, BBDCs) that have no clear phase-relationship with abrupt climatic changes seen over the last ca. 50 kyr BP. During the last deglacial period, these events do not appear to have been directly triggered by changing oceanic conditions. Results highlight the need for understanding the region response of ice-sheets to abrupt climatic changes and complex phase-relationships between the ocean and the cryosphere