IMA Materialforschung und Anwendungstechnik

An essential ingredient for the production of Majorana fermions for use in quantum computing is topological superconductivity1,2. As bulk topological superconductors remain elusive, the most promising approaches exploit proximity-induced superconductivity3, making systems fragile and difficult to realize4–7. Due to their intrinsic topology8, Weyl semimetals are also potential candidates1,2, but have always been connected with bulk superconductivity, leaving the possibility of intrinsic superconductivity of their topological surface states, the Fermi arcs, practically without attention, even from the theory side. Here, by means of angle-resolved photoemission spectroscopy and ab initio calculations, we identify topological Fermi arcs on two opposing surfaces of the non-centrosymmetric Weyl material trigonal PtBi2 (ref. 9). We show these states become superconducting at temperatures around 10 K. Remarkably, the corresponding coherence peaks appear as the strongest and sharpest excitations ever detected by photoemission from solids. Our findings indicate that superconductivity in PtBi2 can occur exclusively at the surface, rendering it a possible platform to host Majorana modes in intrinsically topological superconductor–normal metal–superconductor Josephson junctions.

Abstract Die 2019 erschienene FKM‐Richtlinie nichtlinear enthält aktuell noch keine Definition für einen zyklischen Auslastungsgrad in Lastrichtung. Grund hierfür ist unter anderem das nichtlineare Materialverhalten, das die Berechnung eines Auslastungsgrades in Lastrichtung erschwert. Um die Definition eines zyklischen Auslastungsgrades zu ermöglichen, wird zunächst der zyklische Auslastungsgrad nach der FKM‐Richtlinie Rechnerischer Festigkeitsnachweis genauer untersucht und ein Vorschlag für ein effizientes Iterationsverfahren für die Berechnung des Auslastungsgrades basierend auf der konsequenten Miner‐Regel gemacht. Dabei kann gezeigt werden, dass dieses Iterationsverfahren eine vergleichbare Treffsicherheit wie das Newton‐Verfahren aufweist. Anders als der Rechnerische Festigkeitsnachweis berücksichtigt die FKM‐Richtlinie nichtlinear bei der Berechnung der Bauteillebensdauer elastisch‐plastisches Materialverhalten. Dadurch entsteht eine Nichtlinearität in der Berechnung, die eine Definition einer Zielfunktion für das Newton‐Verfahren schwierig macht. Dem Anwender bleibt hier aktuell nur der Weg einer Intervallschachtelung, die jedoch mit erheblichem Rechenaufwand verbunden ist. Das neu eingeführte effiziente Iterationsverfahren benötigt hingegen nicht die Definition einer Zielfunktion und deren Ableitung, um den nächsten Iterationswert zu berechnen. Die Einführung des effizienten Iterationsverfahrens ermöglicht so erstmalig die schnelle Berechnung eines zyklischen Auslastungsgrades nach der FKM‐Richtlinie nichtlinear, der innerhalb dieses Beitrages definiert und für den ein Abbruchkriterium empfohlen wird.

Abstract This paper compares two methods for transforming a stress or load spectrum into a damage-equivalent constant amplitude loading, i.e., the required fatigue strength (RFS) and the consistent equivalent strength (CES) concepts. Because of their shared fundamentals, i.e., the modified Palmgren-Miner hypothesis for a given allowable damage sum, the resulting RFS- and CES-amplitudes are comparable to each other, but not equal, when the slopes after the knee-points of the Woehler-lines differ. The RFS-method delivers a damage-equivalent stress as the knee-point of a fictitious bi-linear or linear Woehler-line by positioning of the Woehler-line for a given allowable damage sum. In contrast to this, the CES-method also results in a damage-equivalent stress as the knee-point, which depends on the consistent fatigue strength reduction by increasing cumulating damage until the allowable damage sum is reached. Thus, the main difference to the RFS-method is that the CES-method retains the constant amplitude loading slope after the knee-point. Both methods indicate a lowest necessary strength quality, but, like the calculated fatigue lives, they differ according to the calculation methods, and depend on the slopes of the Woehler-lines after the knee-points.

Abstract An implementation of a Non-Axiomatic Reasoning System-inspired system is presented in this paper. This implementation features a goal system which features deep derivation depths, which allows the system to solve moderately complicated problems. The reasoner is utilizing Non-Axiomatic Logic for procedural and non-procedural reasoning. Most of the internal tasks are done under the Assumption of Insufficient Knowledge and Resources fulfilling various timing and resource constraints.

A quarter of the world's nation states and territories are ruled by dictators. Moreover, there are many regimes in which democratic and autocratic elements of rule are mixed in various ways. It thus behoves political scientists to study the trajectories, manifestations and perspectives of non-democratic rule in general and autocratic rule in particular. After a period of stagnation, research on autocracies has in recent years become revitalized. Much of this research has a comparative orientation and a range of global datasets that have become available, which enable the systematic testing of hypotheses. Yet, current research on autocracies goes beyond large-N studies. It is a pluralistic enterprise, characterized by the use of a multitude of theoretical, analytical and methodological approaches, lenses and tools. This special issue attempts to fill some gaps in the newer literature by addressing questions of legitimation and repression (as well as co-optation) in autocracies, by probing into the origins of a number of competitive authoritarian regimes and into pre-electoral dynamics in non-democracies, and by finally asking what happens to dictators once autocratic regimes fall.

For the characterisation and accreditation of materials the aeronautical industry accesses the expertise and the support of independent test laboratories.

This paper focuses on mechanical tests of materials and structures. Those tests are essential to assess structural integrity of aircrafts.