N. V. Sarlis

Similarity of fluctuations in correlated systems : The case of seismicity

We report a similarity of fluctuations in equilibrium critical phenomena and nonequilibrium systems, which is based on the concept of natural time. The worldwide seismicity as well as that of the San Andreas fault system and Japan are analyzed. An order parameter is chosen and its fluctuations relative to the standard deviation of the distribution are studied. We find that the scaled distributions fall on the same curve, which interestingly exhibits, over four orders of magnitude, features similar to those in several equilibrium critical phenomena (e.g., two-dimensional Ising model) as well as in nonequilibrium systems (e.g., three-dimensional turbulent flow).

Transmission of stress induced electric signals in dielectric media

The conditions under which pressure (stress) variations on solids, containing charged defects, can lead to the emission of transient electric signals, are discussed. The resulting electric field E varies as 1/d3 (where d denotes the distance from the emitting source), in the simple case when the surrounding medium is homogeneous and isotropic. We show that this behavior changes to 1/d when studying the electric field within a cylindrical channel of radius R and infinite length having conductivity appreciably larger than that of the host medium; this holds up to a certain (reduced) distance d/R, which increases versus the conductivity ratio. We also investigate the variation of the electric field, versus the distance, inside a layer of width w and infinite extent having conductivity appreciably larger than that of the host medium; we then find that the electric field decreases as 1/d2, in a wide range of distances up to a certain value of d/w, which is controlled by the conductivity ratio. In both conducti...

Investigation of seismicity after the initiation of a Seismic Electric Signal activity until the main shock

The behavior of seismicity in the area candidate to suffer a main shock is investigated after the observation of the Seismic Electric Signal activity until the impending main shock. This is based on the view that the occurrence of earthquakes is a critical phenomenon to which statistical dynamics may be applied. In the present work, analysing the time series of small earthquakes, the concept of natural time chi was used and the results revealed that the approach to criticality itself can be manifested by the probability density function (PDF) of kappa(1) calculated over an appropriate statistical ensemble. Here, kappa(1) is the variance kappa(1)(=-(2)) resulting from the power spectrum of a function defined as Phi(omega)= summation operator(k=1)(N) p(k) exp(iomegachi(k)), where p(k) is the normalized energy of the k-th small earthquake and omega the natural frequency. This PDF exhibits a maximum at kappa(1) asymptotically equal to 0.070 a few days before the main shock. Examples are presented, referring to the magnitude 6 approximately 7 class earthquakes that occurred in Greece.

Natural entropy fluctuations discriminate similar-looking electric signals emitted from systems of different dynamics.

Complexity measures are introduced that quantify the change of the natural entropy fluctuations at different length scales in time series emitted from systems operating far from equilibrium. They identify impending sudden cardiac death (SD) by analyzing 15 min electrocardiograms, and comparing to those of truly healthy humans (H). These measures seem to be complementary to the ones suggested recently [Phys. Rev. E 70, 011106 (2004)]] and altogether enable the classification of individuals into three categories: H, heart disease patients, and SD. All the SD individuals, who exhibit critical dynamics, result in a common behavior.

Numerical model of the selectivity effect and the ΔV/L criterion

Numerical solutions of Maxwell equations for a model earth with a reasonably conducting channel indicate that the electric field values are intensified within a certain region only (i.e., above the end of the channel), thus explaining the observed selectivity effect. In this region, the electric field may reach detectable values (5–10mV/km), while the magnetic field still remains low (10−2nT). The results are compatible with those obtained recently by analytical solutions (Varotsos et al. [1998]). Both the numerical and the analytical solutions lead to a natural explanation of the ΔV/L≈const criterion. This criterion, however, should not be applied over an area with strongly inhomogeneous electrical structure.

Scale-specific order parameter fluctuations of seismicity in natural time before mainshocks

We have previously shown that the probability distribution of the order parameter κ1 of seismicity in natural time turns to be bimodal when approaching a mainshock. This reflects that, for various natural time window lengths ending at a given mainshock, the fluctuations of κ1 considerably increase for smaller lengths, i.e., upon approaching a mainshock. Here, as a second step, we investigate the order parameter fluctuations, but when considering a natural time window of a fixed-length sliding through a seismic catalog. We find that when this length becomes comparable with the lead time of Seismic Electric Signals activities (i.e., of the order of a few months), the fluctuations exhibit a global minimum before the strongest mainshock. Thus, the approach of the latter is characterized by two distinct features of the order parameter fluctuations that complement each other.

Order parameter fluctuations of seismicity in natural time before and after mainshocks

It is widely accepted that the observed earthquake scaling laws indicate the proximity of the system to a critical point. Using the order parameter (OP) for seismicity suggested on the basis of natural time as well as the detrended fluctuation analysis of the magnitude time-series, we investigate the behavior of seismicity before and after significant earthquakes. The analysis reveals that the fluctuations of the OP before major earthquakes exhibit a characteristic feature which, if quantified properly, may be used as decision variable to predict the occurrence of a large earthquake in the next time step based solely on the magnitudes of previous earthquakes.

Scale-specific order parameter fluctuations of seismicity before mainshocks: Natural time and Detrended Fluctuation Analysis

The order parameter fluctuations of seismicity are investigated upon considering a natural time window of fixed length sliding through the consecutive earthquakes that occurred in California. We previously found that when this length corresponds to a time period of the order of a few months, the fluctuations exhibit a global minimum before the strongest mainshock. Here, we show that in California, during the twenty five year period 1979–2003, minima of the fluctuations are identified 1 to 5 months before four out of five mainshocks with magnitude M = 7.0 or larger as well as before the M = 6.9 Northridge earthquake. These minima are accompanied by minima of the exponent α of the Detrended Fluctuation Analysis (DFA) of the earthquake magnitude time series, which since α < 0.5 indicate anticorrelated behavior. These results of DFA alone cannot serve for prediction purposes, but do so when combined with the aforementioned minima in the fluctuations of the order parameter of seismicity identified in natural time analysis.

ORIGIN OF INFRARED BANDS IN NEUTRON-IRRADIATED SILICON

Infrared absorption measurements were made of the localized vibrational modes due to defects produced in Czochralski-grown Si material after irradiation with fast neutrons and subsequent thermal treatments. The investigation was focused, in particular, on three satellite bands in the region of the A center, located at 839, 833 and 824 cm−1 respectively, the annealing behavior of which was carefully monitored. Correlation of our results with previous infrared, electron paramagnetic resonance and positron annihilation studies favors attributing these bands to the V2O, V3O2 and V2O2 defects respectively. In addition, semiempirical calculations were carried out for the vibrational frequencies of these defects, and the predicted values are in agreement with the above assignments.

Identifying sudden cardiac death risk and specifying its occurrence time by analyzing electrocardiograms in natural time

Sudden cardiac death (SCD) is a frequent cause of death and may occur even if the electrocardiogram seems to be similar to that of a healthy individual. A method which not only identifies the risk but also provides an estimate of the time of an impending cardiac arrest is proposed. Analyzing 159 electrocardiograms in natural time, the authors find that the key quantity is the entropy change under time reversal. After it becomes maximum at the scale of 13 heartbeats, ventricular fibrillation starts within ∼3h in 16 out of 18 SCDs. The method also distinguishes congestive heart failure patients from SCD.