Time delays play an important role in many fields such as engineering, physics or biology. Delays occur due to finite velocities of signal propagation or processing delays leading to memory effects and, in general, infinite dimensional systems. Time delay systems can be described by delay differential equations and often include non-negligible nonlinear effects. This theme issue covers new fundamental results in this interdisciplinary field as well as recent developments in applications. Fundamentally new results were obtained especially for systems with time-varying delay and state-dependent delay and for delay system with noise, which do often appear in real systems in engineering and nature. The applications range from climate modelling over network dynamics and laser systems with feedback to human balancing and machine tool chatter.
This issue is available to buy in print. Visit our information for readers page for more purchasing options.
https://doi.org/10.1098/rsta.2019.0220

Cover image
The Lyapunov exponent over a two-dimensional parameter plane of a time-varying delay, which determines the character of chaotic signals in nonlinear delay systems: turbulent (bottom) in yellow and laminar (top) in blue regions. Copyright: David Müller-Bender, Andreas Otto and Günter Radons.