title: Some properties of the entropy in the natural time.
abstract: We show that the entropy S , defined as S identical with chi ln chi - chi ln chi [Phys. Rev. E 68, 031106 (2003)] where chi stands for the natural time [Phys. Rev. E 66, 011902 (2002)], exhibits positivity and concavity as well as stability or experimental robustness. Furthermore, the distinction between the seismic electric signal activities and "artificial" noises, based on the classification of their S values, is lost when studying the time-reversed signals. This reveals the profound importance of considering the (true) time arrow.
authors.affiliation: Solid State Section, Physics Department, University of Athens, Zografos, Greece. pvaro@otenet.gr
authors.forename: P A
authors.initials: PA
authors.lastname: Varotsos
authors.forename: N V
authors.initials: NV
authors.lastname: Sarlis
authors.forename: H K
authors.initials: HK
authors.lastname: Tanaka
authors.forename: E S
authors.initials: ES
authors.lastname: Skordas