Similarity of fluctuations in systems exhibiting Self-Organized Criticality

The time-series of avalanches in three systems exhibiting SOC are analyzed in natural time χ. In two of them, i.e., ricepiles and magnetic flux penetration in thin films of YBa2Cu3O7�x, the data come from laboratory measurements, while the third one is a deterministic model mimicking stick-slip phenomena. We show that their scaled distributions for the variance κ1 of natural time exhibit an exponential tail as previously found for the order parameter in seismicity and in other non-equilibrium or equilibrium critical systems. Upon considering the entropy Sin natural time under time reversal, the following important difference is found: In ricepiles evolving to the critical state, Sis systematically larger than the entropy S in natural time, while in YBa2Cu3O7�x no systematic difference between Sand S is found. Copyright c EPLA, 2011