149 research outputs found
Urinary calcium excretion in children with spina bifida: correlation to level of lesion, mobility and frequency of fractures?
Evidence for topological band inversion of the phase change material Ge2Sb2Te5
We present an angle-resolved photoemission study of a ternary phase change
material, namely Ge2Sb2Te5, epitaxially grown on Si(111) in the metastable
cubic phase. The observed upper bulk valence band shows a minimum at Gamma-bar
being 0.3 eV below the Fermi level E_F and a circular Fermi contour around
Gamma-bar with a dispersing diameter of 0.27-0.36 Anstroms^-1. This is in
agreement with density functional theory calculations of the Petrov stacking
sequence in the cubic phase which exhibits a topological surface state. The
topologically trivial cubic KH stacking shows a valence band maximum at Gamma
in line with all previous calculations of the hexagonal stable phase exhibiting
the valence band maximum at Gamma for a trivial Z_2 topological invariant nu_0
and away from Gamma for non-trivial nu_0. Scanning tunneling spectroscopy
exhibits a band gap of 0.4 eV around E_F
Effects of Ultrashort Pulsed Direct Laser Writing on Ni/Al Reactive Multilayer Foils
Reactive multilayer foils (RMFs) for joining processes have attracted a great deal of attention
over the last few years. They are capable of exothermic self-propagating reactions and can serve
as localized heat sources for joining applications when ignited by suitable means. Using short and
ultrashort pulsed lasers with carefully selected parameters, cutting and shaping of RMFs makes it
possible to tailor heat release characteristics without triggering the reaction. The present study is an
investigation of microstructural changes induced by femtosecond laser machining of a commercially
available Ni/Al-based RMF. The effects of the specific laser parameters pulse duration and repetition rate on the heat-affected zone (HAZ) are investigated by scanning and transmission electron
microscopy. Debris consisting of oxide deposits can be found at a distance of several tens of microns
from the cut edge. A negligible HAZ extending to less than 100 nm was observed for all parameters
tested and no signs of ignition of a self-propagating reaction were observed. These results underline
the suitability of femtosecond lasers for metal machining with minimal heat input
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Strong and Weak 3D Topological Insulators Probed by Surface Science Methods
The contributions of surface science methods to discover and improve 3D topological insulator materials are reviewed herein, illustrated with examples from the authorsâ own work. In particular, it is demonstrated that spin-polarized angular-resolved photoelectron spectroscopy is instrumental to evidence the spin-helical surface Dirac cone, to tune its Dirac point energy toward the Fermi level, and to discover novel types of topological insulators such as dual ones or switchable ones in phase change materials. Moreover, procedures are introduced to spatially map potential fluctuations by scanning tunneling spectroscopy and to identify topological edge states in weak topological insulators. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Sub-nm wide electron channels protected by topology
Helical locking of spin and momentum and prohibited backscattering are the
key properties of topologically protected states. They are expected to enable
novel types of information processing such as spintronics by providing pure
spin currents, or fault tolerant quantum computation by using the Majorana
fermions at interfaces of topological states with superconductors. So far, the
required helical conduction channels used to realize Majorana fermions are
generated through application of an axial magnetic field to conventional
semiconductor nanowires. Avoiding the magnetic field enhances the possibilities
for circuit design significantly. Here, we show that sub-nanometer wide
electron channels with natural helicity are present at surface step-edges of
the recently discovered topological insulator Bi14Rh3I9. Scanning tunneling
spectroscopy reveals the electron channels to be continuous in both energy and
space within a large band gap of 200 meV, thereby, evidencing its non-trivial
topology. The absence of these channels in the closely related, but
topologically trivial insulator Bi13Pt3I7 corroborates the channels'
topological nature. The backscatter-free electron channels are a direct
consequence of Bi14Rh3I9's structure, a stack of 2D topologically insulating,
graphene-like planes separated by trivial insulators. We demonstrate that the
surface of Bi14Rh3I9 can be engraved using an atomic force microscope, allowing
networks of protected channels to be patterned with nm precision.Comment: 17 pages, 4 figures, and supplementary material, Nature Physics in
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Age-related macular degeneration associated polymorphism rs10490924 in ARMS2 results in deficiency of a complement activator
Acknowledgements: The authors thank all German AMD patients for their participation. We also thank Maria Pötsch (Leibniz Institute for Natural Product Reseach and Infection Biology, Jena) for MS analyses. Funding: This research was supported by the German Council âDeutsche Forschungs-Gemeinschaftâ SK46, Zi432, LA1206, the âPro Retinaâ foundation and the Thuringian Ministry of Science and Education, Germany. HN is a member of the DFG-funded excellence cluster ImmunoSensation (EXC 1023). YL is a doctoral researcher at the International Leibniz Research School (ILRS), part of the Jena school of Microbial Communication (JSMC). Availability of data and materials: Materials are available at [email protected] reviewedPublisher PD
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