Prediction of extreme events in the OFC model on a small world network

We investigate the predictability of extreme events in a dissipative Olami-Feder-Christensen model on a small world topology. Due to the mechanism of self-organized criticality, it is impossible to predict the magnitude of the next event knowing previous ones, if the system has an infinite size. However, by exploiting the finite size effects, we show that probabilistic predictions of the occurrence of extreme events in the next time step are possible in a finite system. In particular, the finiteness of the system unavoidably leads to repulsive temporal correlations of extreme events. The predictability of those is higher for larger magnitudes and for larger complex network sizes. Finally, we show that our prediction analysis is also robust by remarkably reducing the accessible number of events used to construct the optimal predictor.Comment: 5 pages, 4 figure

The formation volume of Frenkel defect in silver halides

The formation volume νf of a (cation) Frenkel Defect is calculated in AgCl and AgBr. The proposed formula for νf has no adjustable parameters and contains the formation enthalpy (of a Frenkel defect), the compressibility of the solid at absolute zero and the pressure derivative of the compressibility. The calculated values are in good agreement with the experimental results. © 1978

An estimate of the pressure dependence of the dielectric constant in alkali halides

The determination of the pressure dependence of the static dielectric constant, ϵS, from the Szigeti relations, demands the knowledge of the volume dependence of the Szigeti charge e*, which unfortunately is unknown. By using the classical Lorentz‐Lorenz relation and connecting the ionic polarizability to the bulk modulus a simple relation for dϵS/dP is derived; although it gives the correct order of magnitude, the calculated values exceed the experimental ones by a factor 1.2 to 2. This difference is possibly due to the increase of e* with pressure. A simple relation for the Gruneisen constant of the transverse optical mode is also given. Copyright © 1978 WILEY‐VCH Verlag GmbH & Co. KGa

The formation volume of Frenkel defect in silver halides

The formation volume νf of a (cation) Frenkel Defect is calculated in AgCl and AgBr. The proposed formula for νf has no adjustable parameters and contains the formation enthalpy (of a Frenkel defect), the compressibility of the solid at absolute zero and the pressure derivative of the compressibility. The calculated values are in good agreement with the experimental results. © 1978

The temperature dependence of the static dielectric constant

It is shown that in alkali halides the increase of the static dielectric constant ε with temperature is exclusively due to anharmonic effects. A simple formula is given which permits the calculation of ε at any temperature if we know : (i) the dielectric constant at room temperature and (ii) the thermal variation of bulk modulus and of the lattice parameter. Furthermore Flynn's explanation for the high formation entropy per Schottky defect is discussed.On montre que l'accroissement de la constante diélectrique statique ε des halogénures alcalins avec la température est exclusivement dû à des effets d'anharmonicité. On donne une formule simple qui permet le calcul de s à toute température si l'on connait : (i) ε à la température ambiante et (ii) les variations thermiques du module de compression et du paramètre de réseau. On discute en outre l'explication avancée par Flynn de la grande entropie de formation des défauts de Schottky

Recent Seismic Electric Signals (SES) activities in Greece

Quite recently two intense Seismic Electric Signals activities were recorded at Pirgos station in western Greece. They have been followed by two strong earth-quakes with magnitudes 6.1 and 6.9 that occurred in western Greece and southern Greece; the latter is the strongest earthquake that occurred in Greece during the last two decades. The compatibility of these results with some relationship between selectivity and earthquake focal mechanism suggested by Uyeda et al. (1999) is discussed. © Institute of Geophysics, Polish Academy of Sciences 2006

What happened before the last five strong earthquakes in Greece: Facts and open questions

During the period October 2005 - January 2006, five strong earthquakes occurred in Greece as follows: three magnitude 6.0 consecutive earthquakes with almost the same epicenter in the Aegean Sea close to the western coast of Turkey, one magnitude 6.1 in western Greece and one magnitude 6.9 in southern Greece. In March 2005 and September 2005, intense anomalous geoelectric changes were observed at two different stations respectively: one in the Aegean Sea and the other in western Greece. These changes were immediately reported to international journals well in advance of earthquake occurrences. Natural time analysis of seismicity subsequent to the September changes around the epicenter of the last 6.9 earthquake is made. The results indicate that the occurrence time of the 6.9 earthquake can be specified with a narrow range around two days

Influence of anharmonicity on some transport properties of AgBr

Recent measurements show that the migration entropy for Na+ diffusion in AgBr is 5.1 kB. This value is appreciably higher than that found in alkali halides for cation vacancy motion. A plausible explanation of this fact is proposed. Furthermore, a calculation is made of the migration volumes for the vacancy and interstitial motion of Ag + in AgBr which leads to values comparable with experiment.Des mesures récentes montrent que l'entropie de migration pour la diffusion de Na+ dans AgBr est de 5,1 kB. Cette valeur est notablement supérieure à celle trouvée dans les halogénures alcalins pour le mouvement des lacunes cationiques. Une explication plausible est, de ce fait, proposée. De plus, on a fait un calcul des volumes de migration pour le mouvement des lacunes et interstitiels de Ag+ dans AgBr qui mène à des valeurs comparables aux expériences

An estimate of the pressure dependence of the dielectric constant in alkali halides

The determination of the pressure dependence of the static dielectric constant, ϵS, from the Szigeti relations, demands the knowledge of the volume dependence of the Szigeti charge e*, which unfortunately is unknown. By using the classical Lorentz‐Lorenz relation and connecting the ionic polarizability to the bulk modulus a simple relation for dϵS/dP is derived; although it gives the correct order of magnitude, the calculated values exceed the experimental ones by a factor 1.2 to 2. This difference is possibly due to the increase of e* with pressure. A simple relation for the Gruneisen constant of the transverse optical mode is also given. Copyright © 1978 WILEY‐VCH Verlag GmbH & Co. KGa