The fluctuations, under time reversal, of the natural time and the entropy distinguish similar looking electric signals of different dynamics

We show that the scale dependence of the fluctuations of the natural time itself under time reversal provides a useful tool for the discrimination of seismic electric signals (critical dynamics) from noises emitted from man made sources as well as for the determination of the scaling exponent. We present recent data of electric signals detected at the Earth's surface, which confirm that the value of the entropy in natural time as well as its value under time reversal are smaller than that of the entropy of a "uniform" distribution.Comment: 29 pages including 24 figure and 1 Tabl

Comment on "Effects of Thickness on the Spin Susceptibility of the Two Dimensional Electron Gas"

A comment on a recent paper (PRL {\bf 94}, 226405 (2005)) by S. De Palo, M. Botti, S. Moroni, and Gaetano Senatore

Effect of significant data loss on identifying electric signals that precede rupture by detrended fluctuation analysis in natural time

Electric field variations that appear before rupture have been recently studied by employing the detrended fluctuation analysis (DFA) as a scaling method to quantify long-range temporal correlations. These studies revealed that seismic electric signals (SES) activities exhibit a scale invariant feature with an exponent $\alpha_{DFA} \approx 1$ over all scales investigated (around five orders of magnitude). Here, we study what happens upon significant data loss, which is a question of primary practical importance, and show that the DFA applied to the natural time representation of the remaining data still reveals for SES activities an exponent close to 1.0, which markedly exceeds the exponent found in artificial (man-made) noises. This, in combination with natural time analysis, enables the identification of a SES activity with probability 75% even after a significant (70%) data loss. The probability increases to 90% or larger for 50% data loss.Comment: 12 Pages, 11 Figure

Theoretical investigation of nitrogen-vacancy defects in silicon

Nitrogen-vacancy defects are important for the material properties of silicon and for the performance of silicon-based devices. Here, we employ spin polarized density functional theory to calculate the minimum energy structures of the vacancy-nitrogen substitutional, vacancy-dinitrogen substitutionals, and divacancy-dinitrogen substitutionals. The present simulation technique enabled us to gain insight into the defect structures and charge distribution around the doped N atom and the nearest neighboring Si atoms. Using the dipole–dipole interaction method, we predict the local vibration mode frequencies of the defects and discuss the results with the available experimental data

Identifying the occurrence time of an impending mainshock: A very recent case

The procedure by means of which the occurrence time of an impending mainshock can be identified by analyzing in natural time the seismicity in the candidate area subsequent to the recording of a precursory Seismic Electric Signals (SES) activity is reviewed. Here, we report the application of this procedure to an Mw5.4 mainshock that occurred in Greece on 17 November 2014 and was strongly felt in Athens. This mainshock (which is pretty rare since it is the strongest in that area for more than half a century) was preceded by an SES activity recorded on 27 July 2014 and the results of the natural time analysis reveal that the system approached the critical point (mainshock occurrence) early in the morning on 15 November 2014. Similar SES activities that have been recently recorded are also presented. Furthermore, in a Note we discuss the case of the Mw5.3 earthquake that was also strongly felt in Athens on 19 July 2019.Comment: An early version of this paper appeared in Earthq. Sci. 28 (2015) 215-222 [doi:10.1007/s11589-015-0122-3], whereas in the present version new data collected during 2019 and 2020 have been added. 8 pages, 11 figure