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Our theoretical work is organized in two independent parts: Part I belongs to the field of condensed matter theory and deals with the spectral signatures of collective states in one dimensional (1D) metals: Electrons in 1D metals are expected to fractionalize into collective spin and charge degrees of freedom. A recent candidate material for the realization of a 1D metal are mirror-twin boundaries in monolayer MoS2. Scanning tunneling spectroscopy was used to record the local density of states along these 1D line defects. In our purely theoretical work, we calculate the local density of states as predicted by Tomonaga-Luttinger-liquid theory in order to reveal the nature of the 1D states spectroscopically. The comparison of measured and theoretical spectra allows us to identify the observed doubling of the energy levels as signature of emergent spin and charge excitations. Part II belongs to the field of non-equilibrium physics and deals with the macroscopic description of equilibration: Equilibration of closed systems is hampered by the diffusive transport of locally conserved quantities as described by fluctuating hydrodynamics. After a sudden perturbation, the buildup of equilibrium fluctuations occurs only algebraically slowly, giving rise to hydrodynamic long-time tails. However, the standard tool in transport theory, the Boltzmann equation, fails to describe equilibration. Adding a noise term restores the missing correlations, resulting in a stochastic Langevin-Boltzmann equation. In our work, we derive a simplified version: a fluctuating relaxation-time approximation. We also set up a stable integration scheme for this type of equation and demonstrate that the numerical solution is in agreement with the predictions of fluctuating hydrodynamics. As an addition, we discuss slow changes of state. We show that the entropy production vanishes algebraically slowly in the adiabatic limit due to the presence of hydrodynamic slow modes.

Future autonomous vehicles will no longer have a driver as a fallback solution in case of critical failure scenarios. However, it is costly to add hardware redundancy to achieve a fail-operational behaviour. Here, graceful degradation can be used by repurposing the allocated resources of non-critical applications for safety-critical applications. The degradation problem can be solved as a part of an application mapping problem. As future automotive software will be highly customizable to meet customers' demands, the mapping problem has to be solved for each individual configuration and the architecture has to be adaptable to frequent software changes. Thus, the mapping problem has to be solved at run-time as part of the software platform. In this paper we present an adaptable demonstrator platform consisting of a distributed simulation environment to evaluate such approaches. The platform can be easily configured to evaluate different hardware architectures. We discuss the advantages and limitations of this platform and present an exemplary demonstrator configuration running an agent-based graceful degradation approach.

Two- or three-dimensional metals are usually well described by weakly interacting, fermionic quasiparticles. This concept breaks down in one dimension due to strong Coulomb interactions. There, low-energy electronic excitations are expected to be bosonic collective modes, which fractionalize into independent spin- and charge-density waves. Experimental research on one-dimensional metals is still hampered by their difficult realization, their limited accessibility to measurements, and by competing or obscuring effects such as Peierls distortions or zero bias anomalies. Here we overcome these difficulties by constructing a well-isolated, one-dimensional metal of finite length present in MoS2 mirror-twin boundaries. Using scanning tunneling spectroscopy we measure the single-particle density of the interacting electron system as a function of energy and position in the 1D box. Comparison to theoretical modeling provides unambiguous evidence that we are observing spin-charge separation in real space.

Dissertation, Rheinisch‐Westfälische Technische Hochschule Aachen, 2019; Aachen : Gießerei-Institut der RWTH Aachen, Ergebnisse aus Forschung und Entwicklung 25, 1 Online-Ressource (VI, 148 Seiten) : Illustrationen, Diagramme (2019). doi:10.18154/RWTH-2019-05056 = Dissertation, Rheinisch‐Westfälische Technische Hochschule Aachen, 2019, 0.1 Introduction and motivation: High-silicon nodular graphite cast iron offers numerous advantages over conventional ferritic-perlitic grades. The solid solution strengthened ferritic matrix offers an increased ratio of elongation and strength and provides a more cost-effective mechanical machinability. However, the tensile strength is limited to a maximum of 600 MPa at 4.3% wt-% silicon. Higher silicon contents cause a strong decrease in elongation at fracture as well as a decrease in tensile strength and yield strength. The risk of exceeding a critical silicon content means a reduced process reliability against variations in silicon content during charging and melt treatment. Another disadvantage is the low impact energy of solid solution solidified grades, which is used as a measure of toughness in many guidelines for the design of castings. The aim of this work is to generate well-founded knowledge on materials, on the basis of which new alloy designs can be proposed and tested with which the property range of high silicon-containing ferritic ductile iron can be specifically extended to higher strengths, the process reliability of existing grades can be increased and the toughness can be increased. 0.2 Experimental: To achieve this objective, the cause of the embrittlement phenomenon caused by silicon, i.e. the cause of the decrease in the mechanical properties at more than 4.3 wt-% silicon, is first examined. Subsequently, the suitability of the alloying elements cobalt, nickel, copper and aluminium used individually and in combination for targeted solid solution strengthening with high silicon contents is investigated systematically. With the knowledge about the effect of further alloying elements, the possibility of substituting parts of silicon, which reduces impact energy, is evaluated by the use of selected solid solution strengthening elements. Depending on the varied parameters, matrix and graphite formation, tensile strength, 0.2 % yield strength and elongation at fracture are analysed, interpreted and discussed as experimental target variables, and in selected test series the segregation profiles and the impact energy. 0.3 Results and discussion: In systematic investigations of the mechanical and microstructural properties of alloys with silicon content varying between 3.95 and 5.63 wt-%, the properties of the graphite phase such as nodule size and nodule count as well as the formation of irregular graphite are not coherent with the embrittlement phenomenon and therefore cannot be identified as the main cause of it. In transmission electron microscopic investigations, the existence of ordered areas in high silicon-containing ductile iron is determined. With 3.95 wt-% silicon, a small proportion of B2-ordered areas is detected. A higher proportion of B2-ordered regions together with a comparatively lower proportion of DO3-ordered regions is observed for the brittle failing alloy with 5.36 wt-% silicon. Derived from findings in the field of high silicon steels, the formation of small DO3-ordered domains within larger B2 domains can be identified as the main cause for the complete embrittlement of high silicon-containing GJS with silicon contents above 4.85 wt-%.The suitability for the targeted solid solution strengthening of high-silicon ductile iron was investigated in the present work in extensive alloying experiments. To this end, the solid solution strengthening effect of selected alloying elements and the technologically feasible alloy contents were quantified. The use of copper at 3.8 wt-% silicon is limited to about 0.25 wt-% due to its pearlite forming effect. Copper contents below do not have a solid solution strengthening effect. The use of cobalt leads to combinations of properties that exceed those of the grades that can be achieved with silicon. However, the optimizations achieved are low in relation to the very high price of cobalt and the high alloy contents required. The addition of aluminium leads to a strong strengthening of the ferrite matrix, but with a considerable reduction in elongation, which is due to the interfering effect of aluminium on graphite formation. The full-ferritic alloy produced with 3.8% wt. silicon and 1.5 % wt. nickel provides a tensile strength of 647.3 ± 4.6 MPa with an elongation at fracture of 14.9 ± 0.98 %. The proposed alloy concept thus offers a better performance spectrum than an EN-GJS-600-10 which has been achieved under identical test conditions over 4.3 wt-% silicon, both in strength and elongation at fracture. If the advantages of a single-phase matrix are to be retained, the use of nickel is reduced to 1.5 wt-% due to the perlite promoting effect. By adding 0.7 wt-% aluminium, the formation of pearlite can be shifted to a nickel content of 2.0 wt-%. The combination of 3.8 wt-% silicon, 2.0 wt-% nickel and 0.7 wt-% aluminium with a tensile strength of 712.0 ± 5.9 MPa and an elongation at fracture of 6.7 ± 1.0 % represents the highest strength all-ferritic alloy configuration. These properties correspond approximately to those that can be achieved with an EN-GJS-700-2 strengthened by pearlite, whereby the yield strength exceeds the requirement of the standard by 150 MPa. The best ratio of strength to elongation at fracture is achieved at 3.8 wt-% silicon, 1.5 wt-% nickel and 0.2 wt-% aluminium with a tensile strength of 652.5 ± 9.3 MPa, a yield strength of 524.0 ± 4.3 MPa and an elongation at fracture of 16.0 ± 0.8 %.The findings on the effect of other alloying elements are used to increase the toughness of high-silicon ductile iron materials. The high silicon content is considered to be the reason for the low impact energy. This can be reduced by using alternative solid solution strengtheners while maintaining constant mechanical properties. This concept is investigated by the use of various alloying elements to replace silicon. Toughness can be increased considerably, especially through the use of nickel. After removal of the pearlite resulting from the lowered ratio of ferritizing to pearlite stabilizing elements by a ferritizing heat treatment, the substitution of 0.67 wt-% silicon by 1.47 wt-% nickel causes a reduction of the transition temperature by 50 °C measured in the impact test.0.4 Conclusion and outlook: The understanding of the cause of embrittlement, which occurs at silicon contents above 4.4 wt-%, forms the basis for alloy optimization with the aim of improving the mechanical properties. Knowledge of the cause of embrittlement, the order of iron and silicon atoms, paves the way for the use of further alloying elements for solid solution solidification. Of the alloying elements examined, cobalt, nickel and aluminium are suitable for increasing the strength of ferrite. From a technical point of view, the use of cobalt and nickel is preferable to the use of aluminium. The elongation at fracture during strengthening with nickel and cobalt decreases less than with silicon, in comparison to the use of aluminium, due to the tendency towards improved graphite formation. The use of nickel is economically advantageous due to its significantly lower price compared to cobalt. Compared to ductile iron solidified exclusively with silicon, alloy concepts with an increased performance density are thus available. The lightweight construction potential of high silicon GJS is thus increased. In addition, alloying with nickel and aluminium can significantly improve process reliability and reduce the associated effort involved in process control measures and scrap rates. An improvement of the material behaviour is to be expected in application-related toughness testing methods. The basis for this is the increase in toughness indicated by the shift in the transition temperature. The possibility of increasing toughness by substituting silicon with alternative solid solution solidifying elements can therefore be used to develop new applications in which, due to the toughness requirements, only low-strength ductile iron materials can be used., Published by Gießerei-Institut der RWTH Aachen, Aachen