TY  - GEN
A1  - Spiekermann, Georg
A1  - Harder, M.
A1  - Gilmore, Keith
A1  - Zalden, Peter
A1  - Sahle, Christoph J.
A1  - Petitgirard, Sylvain
A1  - Wilke, Max
A1  - Biedermann, Nicole
A1  - Weis, Thomas
A1  - Morgenroth, Wolfgang
A1  - Tse, John S.
A1  - Kulik, E.
A1  - Nishiyama, Norimasa
A1  - Yavaş, Hasan
A1  - Sternemann, Christian
T1  - Persistent Octahedral Coordination in Amorphous GeO₂ Up to 100 GPa
by Kβ'' X-Ray Emission Spectroscopy
T2  - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe
N2  - We measure valence-to-core x-ray emission spectra of compressed crystalline GeO₂ up to 56 GPa and of amorphous GeO₂ up to 100 GPa. In a novel approach, we extract the Ge coordination number and mean Ge-O distances from the emission energy and the intensity of the Kβ'' emission line. The spectra of high-pressure polymorphs are calculated using the Bethe-Salpeter equation. Trends observed in the experimental and calculated spectra are found to match only when utilizing an octahedral model. The results reveal persistent octahedral Ge coordination with increasing distortion, similar to the compaction mechanism in the sequence of octahedrally coordinated crystalline GeO₂ high-pressure polymorphs.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 699 
KW  - rutile-type
KW  - glass
KW  - crystalline
KW  - pressures
KW  - complexes
KW  - silicon
KW  - oxygen
KW  - SIO₂
KW  - MO
KW  - CU
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-427755
SN  - 1866-8372
IS  - 699
ER  - 
TY  - GEN
A1  - Pick, Leonie
A1  - Effenberger, Frederic
A1  - Zhelavskaya, Irina
A1  - Korte, Monika
T1  - A Statistical Classifier for Historical Geomagnetic Storm Drivers Derived Solely From Ground-Based Magnetic Field Measurements
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Solar wind observations show that geomagnetic storms are mainly driven by interplanetary coronal mass ejections (ICMEs) and corotating or stream interaction regions (C/SIRs). We present a binary classifier that assigns one of these drivers to 7,546 storms between 1930 and 2015 using ground‐based geomagnetic field observations only. The input data consists of the long‐term stable Hourly Magnetospheric Currents index alongside the corresponding midlatitude geomagnetic observatory time series. This data set provides comprehensive information on the global storm time magnetic disturbance field, particularly its spatial variability, over eight solar cycles. For the first time, we use this information statistically with regard to an automated storm driver identification. Our supervised classification model significantly outperforms unskilled baseline models (78% accuracy with 26[19]% misidentified interplanetary coronal mass ejections [corotating or stream interaction regions]) and delivers plausible driver occurrences with regard to storm intensity and solar cycle phase. Our results can readily be used to advance related studies fundamental to space weather research, for example, studies connecting galactic cosmic ray modulation and geomagnetic disturbances. They are fully reproducible by means of the underlying open‐source software (Pick, 2019, http://doi.org/10.5880/GFZ.2.3.2019.003)
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 982 
KW  - geomagnetic observatory data
KW  - geomagnetic storm drivers
KW  - historical geomagnetic storms
KW  - supervised machine learning
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-474996
SN  - 1866-8372
IS  - 982
SP  - 2000
EP  - 2015
ER  -