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 YBa 2 Cu 3 O 7− 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 κ 1 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 S − in natural time under time reversal, the following important difference is found: In ricepiles evolving to the critical state, S − is systematically larger than the entropy S in natural time, while in YBa 2 Cu 3 O 7− x no systematic difference between S − and S is found.