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Eingeladener Vortrag
- nein (16)
Ceramic parts possessing an ordered porosity were produced for the first time by powder-based three-dimensional printing of a preceramic polymer followed by pyrolysis in an inert atmosphere. The main parameters involved in the process were investigated, and the precision of the printed and ceramized parts was assessed by means of scanning electron microscopy and micro computed tomography. The influence of two different printing solvents was investigated and the use of a mixture of 1-hexanol and hexylacetate in particular allowed the production of parts with a relative density of 80% both in the polymeric and in the ceramic state. The mixing of a cross-linking catalyst directly with the printing liquid greatly simplified the process, minimizing the necessity of preprocessing the starting powder. Three-dimensional printing of a preceramic polymer not containing any inert or active fillers was proved to be a feasible, convenient and precise process for the production of porous ceramic possessing a complex, ordered structure, such as stretch-dominated lattices.
Die Produktion von elektronischen, optischen und elektro-mechanischen Mikro- und Nanosystemen stellt hohe Anforderungen an die Messtechnik, um die Fertigungsprozesse zu optimieren und die Qualität zu prüfen. Existierende Messverfahren unterliegen Beschränkungen hinsichtlich des Auflösungsvermögens, der Messfeldgröße und des Ergebnisses der Messung. Der kombinierte Einsatz von Sensoren mit unterschiedlichen Fähigkeiten in den Auflösungsstufen mittels einer intelligenten Messstrategie ermöglicht eine effiziente Prüfung.
Neben den geeigneten Prüfstrategien werden auch Methoden zur Fusion und Auswertung der Daten von Sensoren mit unterschiedlichen Auflösungsfähigkeiten benötigt. Datenfusion bezeichnet dabei das Zusammenfügen verschiedener Messungen, um entweder unterschiedliche Eigenschaften eines Messobjekts in einem gemeinsamen Koordinatensystem angeben zu können oder um aus verschiedenen Messungen derselben Eigenschaft des Messobjekts einen Datensatz von höherer Qualität gegenüber den einzelnen Datensätzen zu erhalten. Voraussetzung für die Datenfusion ist Registrierung, die eine Überführung von Messdaten unterschiedlicher Messfelder oder Messmittel in ein gemeinsames Koordinatensystem darstellt und Thema dieses Beitrages ist.
The Final Gravettian level (level 2) of the abri Pataud (Dordogne, France) yielded a large assemblage of body ornaments that consists essentially of 85 quite standardized rectangular beads. Some uncertainty remained about the raw material in which these small beads were made: mammoth ivory, reindeer antler or bone? Non-invasive methods were employed in order to determine the raw material. First chemical analyses using microbeam Proton Induced X-ray Emission analysis (microPIXE) did not enable us to conclude definitively. Therefore, synchrotron and laboratory X-ray microtomography (microCT) were applied on eight beads and allowed us to identify ivory for all of them except for one, which shows slightly different morphological features.
Most knowledge about the structure, function, and evolution of early compound eyes is based on investigations in trilobites. However, these studies dealt mainly with the cuticular lenses and little was known about internal anatomy. Only recently some data on crystalline cones and retinula cells were reported for a Cambrian trilobite species. Here, we describe internal eye structures of two other trilobite genera. The Ordovician Asaphus sp. reveals preserved crystalline cones situated underneath the cuticular lenses. The same is true for the Devonian species Archegonus (Waribole) warsteinensis, which in addition shows the fine structure of the rhabdom in the retinula cells. These results suggest that an apposition eye with a crystalline cone is ancestral for Trilobita. The overall similarity of trilobite eyes to those of myriapods, crustaceans, and hexapods corroborates views of a phylogenetic position of trilobites in the stem lineage of Mandibulata.
Ein dreidimensionaler Prüfkörper für die Lunkererkennung in Gussteilen mittels Computertomographie
(2010)
The effects of refraction (phase-contrast) are normally considered as disturbances in high-resolution μCT-measurements. We show that in the case of small objects with low absorption a single-distance phase-retrieval algorithm not only reduces the edge enhancement, but also raises the signal-to-noise ratio sufficiently to allow dimensional measurements. This is exemplified at an optical element for optical fibre connectors.