University of Stuttgart

About: University of Stuttgart is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Laser & Finite element method. The organization has 27715 authors who have published 56370 publications receiving 1363382 citations. The organization is also known as: Universität Stuttgart.

Observation of kinks and antikinks in colloidal monolayers driven across ordered surfaces

Abstract: The frictional properties of a two-dimensional colloidal crystal reveal that excitations known as kinks and antikinks form when the crystal is dragged along a solid surface. This phenomenon, which was predicted previously but never observed, demonstrates the potential of using colloidal crystals to study frictional properties that are otherwise difficult to characterize. Friction between solids is responsible for many phenomena such as earthquakes, wear or crack propagation1,2,3,4. Unlike macroscopic objects, which only touch locally owing to their surface roughness, spatially extended contacts form between atomically flat surfaces. They are described by the Frenkel–Kontorova model, which considers a monolayer of interacting particles on a periodic substrate potential5,6,7,8. In addition to the well-known stick–slip motion, such models also predict the formation of kinks and antikinks9,10,11,12, which greatly reduce the friction between the monolayer and the substrate. Here, we report the direct observation of kinks and antikinks in a two-dimensional colloidal crystal that is driven across different types of ordered substrate. We show that the frictional properties only depend on the number and density of such excitations, which propagate through the monolayer along the direction of the applied force. In addition, we also observe kinks on quasicrystalline surfaces, which demonstrates that they are not limited to periodic substrates but occur under more general conditions.

Effects of Delay in Multi-Agent Consensus and Oscillator Synchronization

Abstract: The coordinated motion of multi-agent systems and oscillator synchronization are two important examples of networked control systems. In this technical note, we consider what effect multiple, non-commensurate (heterogeneous) communication delays can have on the consensus properties of large-scale multi-agent systems endowed with nonlinear dynamics. We show that the structure of the delayed dynamics allows functionality to be retained for arbitrary communication delays, even for switching topologies under certain connectivity conditions. The results are extended to the related problem of oscillator synchronization.