Stoichiometry determination of chalcogenide superlattices by means of X-ray diffraction and its limits

In this paper we explore the potential of stoichiometry determination for chalcogenide superlattices, promising candidates for next-generation phase-change memory, via X-ray diffraction. To this end, a set of epitaxial GeTe/Sb2Te3 superlattice samples with varying layer thicknesses is sputter-deposited. Kinematical scattering theory is employed to link the average composition with the diffraction features. The observed lattice constants of the superlattice reference unit cell follow Vegard's law, enabling a straight-forward and non-destructive stoichiometry determination.Comment: physica status solidi (RRL) - Rapid Research Letters (2019

Spatiotemporal analysis of sheet and cloud cavitation and its damage potential

The cavitation regime has a substantial influence on the damage potential, thus it has to be considered in any specific investigation. For this purpose, we set up a test rig at the Technische Universität Darmstadt using a Circular Leading Edge hydrofoil (CLE) to analyse the damage potential of sheet and cloud cavitation. Exceeding a critical Reynolds number Re c, the cavitation regime transitions from harmless sheet cavitation to aggressive cloud cavitation. High-speed recordings of the cavitation regime are correlated with high frequency pressure data from a wall-mounted piezoelectric pressure transducer. Spatial and temporal content of the cavitating flow are captured applying proper orthogonal decomposition (POD) to the high-speed recordings. In order to determine the damage potential of the cavitation regime we apply a copper foil on the hydrofoil surface, on which plastic, crater-shaped deformations due to bubble collapses occur. Images of the surface are recorded before and after each run via two-dimensional Pit-Count microscopy. We correlate spatial modes from the cavitating flow field with the eroded surface rate from pitting tests leading to the result that cloud cavitation associated with increasing cloud size is more aggressive. A power law is identified where pitting rate increases with fourteenth power of the Reynolds number

Rheological modelling of viscoelastic fluid in a generic gap of screw pump

In this study, the leakage of a non-Newtonian fluid, i.e. silicone oil, in a generic gap was numerically investigated. A CFD tool is used to determine the relationship between leakage flow, gap length and pressure difference. The investigated fluid is viscoelastic and its properties are modelled by a Maxwell equation. The Maxwell model can be used to precisely define the phenomenon of stress relaxation. Moreover, a comparison of the viscosity of measured data with simplified models shows that the Maxwell model is best suited for viscosity prediction. Furthermore, simulation results showed that at low pressures, leakage is reduced by decreasing the gap angle. However, this effect changes with increasing viscosity and relaxation time of the molecule. To determine the pressure drop, the Bagley plot is used. The results confirmed that as the shear rate increases, the elastic pressure drop values increase. In addition, the leakage flow increases with an increasing slenderness ratio

The classically perfect fixed point action for SU(3) gauge theory

In this paper (the first of a series) we describe the construction of fixed point actions for lattice $SU(3)$ pure gauge theory. Fixed point actions have scale invariant instanton solutions and the spectrum of their quadratic part is exact (they are classical perfect actions). We argue that the fixed point action is even 1--loop quantum perfect, i.e. in its physical predictions there are no $g^2 a^n$ cut--off effects for any $n$. We discuss the construction of fixed point operators and present examples. The lowest order $q {\bar q}$ potential $V(\vec{r})$ obtained from the fixed point Polyakov loop correlator is free of any cut--off effects which go to zero as an inverse power of the distance $r$.Comment: 34 pages (latex) + 7 figures (Postscript), uuencode

Digitalisierung in der Erwachsenenbildung

Aus dem Inhalt: Digitalisierung in der Erwachsenenbildung - zur Einleitung in den Themenschwerpunkt; Erwachsenenbildung in der digitalen Welt: Handlungsebenen der digitalen Transformation; Digitalisierung und Mediatisierung in der Erwachsenenbildung/Weiterbildung; Digitale Lernumwelten in produzierenden Betrieben; Zur Modellierung einer Kultur der Digitalität; Bildungsberatung in Beschäftigung und Weiterbildung im Kontext der Digitalisierung; Best-practice-Beispiele für digitale Weiterbildungsangebote

Roles for the Conserved Spc105p/Kre28p Complex in Kinetochore-Microtubule Binding and the Spindle Assembly Checkpoint

Kinetochores attach sister chromatids to microtubules of the mitotic spindle and orchestrate chromosome disjunction at anaphase. Although S. cerevisiae has the simplest known kinetochores, they nonetheless contain approximately 70 subunits that assemble on centromeric DNA in a hierarchical manner. Developing an accurate picture of the DNA-binding, linker and microtubule-binding layers of kinetochores, including the functions of individual proteins in these layers, is a key challenge in the field of yeast chromosome segregation. Moreover, comparison of orthologous proteins in yeast and humans promises to extend insight obtained from the study of simple fungal kinetochores to complex animal cell kinetochores.We show that S. cerevisiae Spc105p forms a heterotrimeric complex with Kre28p, the likely orthologue of the metazoan kinetochore protein Zwint-1. Through systematic analysis of interdependencies among kinetochore complexes, focused on Spc105p/Kre28p, we develop a comprehensive picture of the assembly hierarchy of budding yeast kinetochores. We find Spc105p/Kre28p to comprise the third linker complex that, along with the Ndc80 and MIND linker complexes, is responsible for bridging between centromeric heterochromatin and kinetochore MAPs and motors. Like the Ndc80 complex, Spc105p/Kre28p is also essential for kinetochore binding by components of the spindle assembly checkpoint. Moreover, these functions are conserved in human cells.Spc105p/Kre28p is the last of the core linker complexes to be analyzed in yeast and we show it to be required for kinetochore binding by a discrete subset of kMAPs (Bim1p, Bik1p, Slk19p) and motors (Cin8p, Kar3p), all of which are nonessential. Strikingly, dissociation of these proteins from kinetochores prevents bipolar attachment, even though the Ndc80 and DASH complexes, the two best-studied kMAPs, are still present. The failure of Spc105 deficient kinetochores to bind correctly to spindle microtubules and to recruit checkpoint proteins in yeast and human cells explains the observed severity of missegregation phenotypes

Learning How to Use a Digital Workbench: Guided or Explorative?

In dieser Studie lernten Berufsschullehrer und wissenschaftliche Mitarbeiter, wie sie eine neue digitale Werkbank durch einen geführten oder ungeleiteten Unterrichtsansatz nutzen können. Wir untersuchten den Einfluss der beiden Unterrichtsansätze auf unterschiedliche Lernziele. Die Ergebnisse zeigen, dass der geführte Unterricht zu einer signifikant besseren Leistung bei einem strukturierten Lernziel (Quantität der erfüllten Aufgaben), einer besseren Leistung bei einem zweiten strukturierten Lernziel (Qualität der erfüllten Aufgaben) und ähnlichen Ergebnissen wie bei einem eher unstrukturierten Lernziel (Untersuchung der Funktionalitäten der Werkbank) führte. Darüber hinaus fanden wir heraus, dass die Teilnehmer des geführten Zustands weniger zeitlichen Stress und ein höheres Selbstvertrauen berichteten, um bei den gegebenen Aufgaben gut abzuschneiden. Hinsichtlich der Einstellungen zur Nutzung der Werkbank zeigten die Teilnehmer der ungeführten Gruppe etwas positivere Werte, obwohl die Unterschiede statistisch nicht signifikant waren. Abschließend fanden wir Vorteile für den geführten Unterrichtsansatz mit ausgearbeiteten Beispielen, wenn die Teilnehmer lernen müssen, eine völlig neue digitale Werkbank zu bedienen

Cross-linked proton-exchange membranes with strongly reduced fuel crossover and increased chemical stability for direct-isopropanol fuel cells

Isopropanol fuel cells offer an attractive way to provide electric energy from a liquid, easily transportable fuel without producing significant amounts of CO2. The oxidation product acetone can be easily hydrogenated back to isopropanol to close the storage cycle, thereby avoiding the sophisticated handling of fugitive molecular hydrogen. Until now, Direct-Isopropanol Fuel Cells (DIFC) usually rely on various perfluorosulfonic acid ionomers, like Nafion, which are costly and have an unfavorable high fluorine content. Additionally, the dissolution of Nafion in isopropanol/acetone/water solutions within respective applications has prevented the long time operation of DIFCs so far. The swelling of those ionomers during operation promotes fuel crossover and reduces the system's overall energy efficiency. This study uses ionic cross-linking of polymer blends to manufacture chemically stable membranes and introduces a new click-like covalent cross-linking strategy for ion exchange polymers. Compared to Nafion XL, the manufactured membranes increase the maximum power density by up to 10 %, resist a dissolution stress test up to 84 w-% and reduce the detected isopropanol/acetone crossover up to 75/100 % during fuel cell operation. Consequently, the material can be considered a major step toward the technical implementation of isopropanol fuel cell technologies