  Recent research on the non-stationary nature of the dynamics of complex
systems is reviewed through three specific models. The long time dynamics
consists of a slow, decelerating but spasmodic release of generalized intrinsic
strain. These events are denoted quakes. Between the quakes weak fluctuations
occur but no essential change in properties are induced. The accumulated effect
of the quakes, however, is to induce a direct change in the probability density
functions characterising the system. We discuss how the log-Poisson statistics
of record dynamics may be an effective description of the long time evolution
and describe how an analysis of the times at which the quakes occur enables one
to check the applicability of record dynamics.
