Crystal orientations in glass-ceramics determined using electron backscatter diffraction (EBSD)

Die vorliegende kumulativen Dissertation besteht aus sieben Publikationen, die in den Zeitschriften Crystal Growth & Design und CrystEngComm erschienen sind. Der Fokus dieser Arbeiten ist die Untersuchung von Kristallorientierungen in Glaskermiken mittels Electron Backscatter Diffraction (EBSD). Diese Methode ermöglicht die lokale Auflösung von Kristallorientierungen im Raster Elektronen Mikroskop (REM) und wird im Rahmen der Einleitung genauer beschrieben. Die Untersuchung von Oberflächenkristallisation zeigte, dass bisherige Modelle über die Bildung orientierter Schichten auf diesem Weg falsch bzw. unvollständig waren und ermöglichte eine korrektere Beschreibung der auftretenden orientierten Schichten und deren Entstehung. Auch die Untersuchung von Glaskeramiken die mittels elektrochemisch induzierter Keimbildung hergestellt wurden führte zu neuen Erkenntnissen wie z.B. der Detektion von abweichend orientierten Kristallen in den sonst extrem homogen orientierten Dendtiten. Weiterhin wurde festgestellt, dass die Orientierung innerhalb gewachsener Mullitnadeln keineswegs homogen ist sondern vielmehr lokal variiert. Die bisher angenommen Orientierung der Mullitkristallen konnte auf den experimentellen Aufbau anstatt der Methode der Kristallisation zurückgeführt werden. Letztlich konnten auch offenstehende Fragen über die Entstehung von Kristallen, die sowohl Hämatit als auch Magnetit enthalten, d.h. aus zwei Phasen bestehen, anhand der mit EBSD ermittelten Kristallorientierungen der beiden Phasen beantwortet werden

Pre--Main-Sequence stellar populations across Shapley Constellation III. I. Photometric Analysis and Identification

We present our investigation of pre--main-sequence (PMS) stellar populations in the Large Magellanic Cloud (LMC) from imaging with Hubble Space Telescope WFPC2 camera. Our targets of interest are four star-forming regions located at the periphery of the super-giant shell LMC 4 (Shapley Constellation III). The PMS stellar content of the regions is revealed through the differential Hess diagrams and the observed color-magnitude diagrams (CMDs). Further statistical analysis of stellar distributions along cross-sections of the faint part of the CMDs allowed the quantitative assessment of the PMS stars census, and the isolation of faint PMS stars as the true low-mass stellar members of the regions. These distributions are found to be well represented by a double Gaussian function, the first component of which represents the main-sequence field stars and the second the native PMS stars of each region. Based on this result, a cluster membership probability was assigned to each PMS star according to its CMD position. The higher extinction in the region LH 88 did not allow the unambiguous identification of its native stellar population. The CMD distributions of the PMS stars with the highest membership probability in the regions LH 60, LH 63 and LH 72 exhibit an extraordinary similarity among the regions, suggesting that these stars share common characteristics, as well as common recent star formation history. Considering that the regions are located at different areas of the edge of LMC 4, this finding suggests that star formation along the super-giant shell may have occurred almost simultaneously.Comment: Accepted for publication in the Astrophysical Journal. 19 pages, 19 figures (three omitted due to size limitations, without affecting the comprehension of the manuscript

Lignite planning, structural change and coal phase-out in Germany

Lignite planning in the Rhineland, central German and Lusatian coalfields is a core spatial development planning task at the federal state and regional levels. The Lignite Planning Information Group and Initiative (Informations- und Initiativkreis Braunkohlenplanung) was founded in 1994 at the ARL - Academy for Territorial Development in the Leibniz Association to provide a platform for expert discussion. Starting from experiences with the Rhineland and the structural upheavals in the new federal states in the early 1990s, it has since continuously addressed new technical and legal requirements involving resettlement, water balance issues, environmental assessments, the energy transition and the common good. Against the backdrop of rapid change and geopolitical events, the combination of structural change and the politically initiated phase-out of lignite-based power generation in a time frame between 'ideally 2030' and no later than the end of 2038 constitutes a challenge that will have to be met by the active players from the perspective of both federal state and regional planning and of regional development. This position paper takes stock of the situation across federal states and across coalfields and describes the required actions for lignite planning as a basis for reaching conclusions about a process with far-reaching national consequences. The various aspects of this process are subject to constant change and call for proactive strategies to exploit opportunities, tap potential, and effectively identify and avoid negative developments

Polarimetric Imaging of Large Cavity Structures in the Pre-transitional Protoplanetary Disk around PDS 70: Observations of the disk

We present high resolution H-band polarized intensity (PI; FWHM = 0."1: 14 AU) and L'-band imaging data (FWHM = 0."11: 15 AU) of the circumstellar disk around the weak-lined T Tauri star PDS 70 in Centaurus at a radial distance of 28 AU (0."2) up to 210 AU (1."5). In both images, a giant inner gap is clearly resolved for the first time, and the radius of the gap is ~70 AU. Our data show that the geometric center of the disk shifts by ~6 AU toward the minor axis. We confirm that the brown dwarf companion candidate to the north of PDS 70 is a background star based on its proper motion. As a result of SED fitting by Monte Carlo radiative transfer modeling, we infer the existence of an optically thick inner disk at a few AU. Combining our observations and modeling, we classify the disk of PDS 70 as a pre-transitional disk. Furthermore, based on the analysis of L'-band imaging data, we put an upper limit mass of companions at ~30 to ~50MJ within the gap. Taking account of the presence of the large and sharp gap, we suggest that the gap could be formed by dynamical interactions of sub-stellar companions or multiple unseen giant planets in the gap.Comment: accepted by APJ

Near-Infrared Imaging Polarimetry of Inner Region of GG Tau A Disk

By performing non-masked polarization imaging with Subaru/HiCIAO, polarized scattered light from the inner region of the disk around the GG Tau A system was successfully detected in the $H$ band with a spatial resolution of approximately 0.07\arcsec, revealing the complicated inner disk structures around this young binary. This paper reports the observation of an arc-like structure to the north of GG Tau Ab and part of a circumstellar structure that is noticeable around GG Tau Aa extending to a distance of approximately 28 AU from the primary star. The speckle noise around GG Tau Ab constrains its disk radius to <13 AU. Based on the size of the circumbinary ring and the circumstellar disk around GG Tau Aa, the semi-major axis of the binary's orbit is likely to be 62 AU. A comparison of the present observations with previous ALMA and near-infrared (NIR) H$_2$ emission observations suggests that the north arc could be part of a large streamer flowing from the circumbinary ring to sustain the circumstellar disks. According to the previous studies, the circumstellar disk around GG Tau Aa has enough mass and can sustain itself for a duration sufficient for planet formation; thus, our study indicates that planets can form within close (separation $\lesssim$ 100 AU) young binary systems.Comment: Accepted for publication in AJ, 12 pages, 5 figure