597 research outputs found

    Recurrence intervals between earthquakes strongly depend on history

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    We study the statistics of the recurrence times between earthquakes above a certain magnitude MinCalifornia.Wefindthatthedistributionoftherecurrencetimesstronglydependsonthepreviousrecurrencetime in California. We find that the distribution of the recurrence times strongly depends on the previous recurrence time \tau_0.Asaconsequence,theconditionalmeanrecurrencetime. As a consequence, the conditional mean recurrence time \hat \tau(\tau_0)betweentwoeventsincreasesmonotonicallywith between two events increases monotonically with \tau_0.For. For \tau_0wellbelowtheaveragerecurrencetime well below the average recurrence time \ov{\tau}, \hat\tau(\tau_0)issmallerthan is smaller than \ov{\tau},whilefor, while for \tau_0>\ov{\tau},, \hat\tau(\tau_0)isgreaterthan is greater than \ov{\tau}.Alsothemeanresidualtimeuntilthenextearthquakedoesnotdependonlyontheelapsedtime,butalsostronglyon. Also the mean residual time until the next earthquake does not depend only on the elapsed time, but also strongly on \tau_0.Thelarger. The larger \tau_0$ is, the larger is the mean residual time. The above features should be taken into account in any earthquake prognosis.Comment: 5 pages, 3 figures, submitted to Physica

    Power-law persistence and trends in the atmosphere: A detailed study of long temperature records

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    We use several variants of the detrended fluctuation analysis to study the appearance of long-term persistence in temperature records, obtained at 95 stations all over the globe. Our results basically confirm earlier studies. We find that the persistence, characterized by the correlation C(s) of temperature variations separated by s days, decays for large s as a power law, C(s) ~ s^(-gamma). For continental stations, including stations along the coastlines, we find that gamma is always close to 0.7. For stations on islands, we find that gamma ranges between 0.3 and 0.7, with a maximum at gamma = 0.4. This is consistent with earlier studies of the persistence in sea surface temperature records where gamma is close to 0.4. In all cases, the exponent gamma does not depend on the distance of the stations to the continental coastlines. By varying the degree of detrending in the fluctuation analysis we obtain also information about trends in the temperature records.Comment: 5 pages, 4 including eps figure

    Pore opening effects and transport diffusion in the Knudsen regime in comparison to self- (or tracer-) diffusion

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    We study molecular diffusion in linear nanopores with different types of roughness in the so-called Knudsen regime. Knudsen diffusion represents the limiting case of molecular diffusion in pores, where mutual encounters of the molecules within the free pore space may be neglected and the time of flight between subsequent collisions with the pore walls significantly exceeds the interaction time between the pore wall and the molecules. We present an extension of a commonly used procedure to calculate transport diffusion coefficients. Our results show that using this extension, the coefficients of self- and transport diffusion in the Knudsen regime are equal for all regarded systems, which improves previous literature data.Comment: 5 pages, 7 figure

    Critical dimensions for random walks on random-walk chains

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    The probability distribution of random walks on linear structures generated by random walks in dd-dimensional space, Pd(r,t)P_d(r,t), is analytically studied for the case ξr/t1/41\xi\equiv r/t^{1/4}\ll1. It is shown to obey the scaling form Pd(r,t)=ρ(r)t1/2ξ2fd(ξ)P_d(r,t)=\rho(r) t^{-1/2} \xi^{-2} f_d(\xi), where ρ(r)r2d\rho(r)\sim r^{2-d} is the density of the chain. Expanding fd(ξ)f_d(\xi) in powers of ξ\xi, we find that there exists an infinite hierarchy of critical dimensions, dc=2,6,10,d_c=2,6,10,\ldots, each one characterized by a logarithmic correction in fd(ξ)f_d(\xi). Namely, for d=2d=2, f2(ξ)a2ξ2lnξ+b2ξ2f_2(\xi)\simeq a_2\xi^2\ln\xi+b_2\xi^2; for 3d53\le d\le 5, fd(ξ)adξ2+bdξdf_d(\xi)\simeq a_d\xi^2+b_d\xi^d; for d=6d=6, f6(ξ)a6ξ2+b6ξ6lnξf_6(\xi)\simeq a_6\xi^2+b_6\xi^6\ln\xi; for 7d97\le d\le 9, fd(ξ)adξ2+bdξ6+cdξdf_d(\xi)\simeq a_d\xi^2+b_d\xi^6+c_d\xi^d; for d=10d=10, f10(ξ)a10ξ2+b10ξ6+c10ξ10lnξf_{10}(\xi)\simeq a_{10}\xi^2+b_{10}\xi^6+c_{10}\xi^{10}\ln\xi, {\it etc.\/} In particular, for d=2d=2, this implies that the temporal dependence of the probability density of being close to the origin Q2(r,t)P2(r,t)/ρ(r)t1/2lntQ_2(r,t)\equiv P_2(r,t)/\rho(r)\simeq t^{-1/2}\ln t.Comment: LATeX, 10 pages, no figures submitted for publication in PR

    Volcanic forcing improves Atmosphere-Ocean Coupled General Circulation Model scaling performance

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    Recent Atmosphere-Ocean Coupled General Circulation Model (AOGCM) simulations of the twentieth century climate, which account for anthropogenic and natural forcings, make it possible to study the origin of long-term temperature correlations found in the observed records. We study ensemble experiments performed with the NCAR PCM for 10 different historical scenarios, including no forcings, greenhouse gas, sulfate aerosol, ozone, solar, volcanic forcing and various combinations, such as it natural, anthropogenic and all forcings. We compare the scaling exponents characterizing the long-term correlations of the observed and simulated model data for 16 representative land stations and 16 sites in the Atlantic Ocean for these scenarios. We find that inclusion of volcanic forcing in the AOGCM considerably improves the PCM scaling behavior. The scenarios containing volcanic forcing are able to reproduce quite well the observed scaling exponents for the land with exponents around 0.65 independent of the station distance from the ocean. For the Atlantic Ocean, scenarios with the volcanic forcing slightly underestimate the observed persistence exhibiting an average exponent 0.74 instead of 0.85 for reconstructed data.Comment: 4 figure

    Long term persistence in the sea surface temperature fluctuations

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    We study the temporal correlations in the sea surface temperature (SST) fluctuations around the seasonal mean values in the Atlantic and Pacific oceans. We apply a method that systematically overcome possible trends in the data. We find that the SST persistence, characterized by the correlation C(s)C(s) of temperature fluctuations separated by a time period ss, displays two different regimes. In the short-time regime which extends up to roughly 10 months, the temperature fluctuations display a nonstationary behavior for both oceans, while in the asymptotic regime it becomes stationary. The long term correlations decay as C(s)sγC(s) \sim s^{-\gamma} with γ0.4\gamma \sim 0.4 for both oceans which is different from γ0.7\gamma \sim 0.7 found for atmospheric land temperature.Comment: 14 pages, 5 fiure

    Supremacy distribution in evolving networks

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    We study a supremacy distribution in evolving Barabasi-Albert networks. The supremacy sis_i of a node ii is defined as a total number of all nodes that are younger than ii and can be connected to it by a directed path. For a network with a characteristic parameter m=1,2,3,...m=1,2,3,... the supremacy of an individual node increases with the network age as t(1+m)/2t^{(1+m)/2} in an appropriate scaling region. It follows that there is a relation s(k)km+1s(k) \sim k^{m+1} between a node degree kk and its supremacy ss and the supremacy distribution P(s)P(s) scales as s12/(1+m)s^{-1-2/(1+m)}. Analytic calculations basing on a continuum theory of supremacy evolution and on a corresponding rate equation have been confirmed by numerical simulations.Comment: 4 pages, 4 figure

    Percolation of randomly distributed growing clusters: Finite Size Scaling and Critical Exponents

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    We study the percolation properties of the growing clusters model. In this model, a number of seeds placed on random locations on a lattice are allowed to grow with a constant velocity to form clusters. When two or more clusters eventually touch each other they immediately stop their growth. The model exhibits a discontinuous transition for very low values of the seed concentration pp and a second, non-trivial continuous phase transition for intermediate pp values. Here we study in detail this continuous transition that separates a phase of finite clusters from a phase characterized by the presence of a giant component. Using finite size scaling and large scale Monte Carlo simulations we determine the value of the percolation threshold where the giant component first appears, and the critical exponents that characterize the transition. We find that the transition belongs to a different universality class from the standard percolation transition.Comment: 5 two-column pages, 6 figure

    Nonlinear Volatility of River Flux Fluctuations

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    We study the spectral properties of the magnitudes of river flux increments, the volatility. The volatility series exhibits (i) strong seasonal periodicity and (ii) strongly power-law correlations for time scales less than one year. We test the nonlinear properties of the river flux increment series by randomizing its Fourier phases and find that the surrogate volatility series (i) has almost no seasonal periodicity and (ii) is weakly correlated for time scales less than one year. We quantify the degree of nonlinearity by measuring (i) the amplitude of the power spectrum at the seasonal peak and (ii) the correlation power-law exponent of the volatility series.Comment: 5 revtex pages, 6 page
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