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Correlation Properties (correlation + property)
Selected AbstractsSearch for direct empirical spatial correlation signatures of the critical triggering earthquake modelGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004G. Ouillon SUMMARY We propose a new test of the critical earthquake model based on the hypothesis that precursory earthquakes are ,actors' that create fluctuations in the stress field which exhibit an increasing correlation length as the critical large event becomes imminent. Our approach constitutes an attempt to build a more physically based time-dependent indicator (cumulative scalar stress function), in the spirit of, but improving on, the cumulative Benioff strain used in previous works documenting the phenomenon of accelerating seismicity. Using a simplified scalar space and time-dependent viscoelastic Green's function in a two-layer model of the Earth's lithosphere, we compute spatiotemporal pseudo-stress fluctuations induced by a series of events before four of the largest recent shocks in southern California. Through an appropriate spatial wavelet transform, we then estimate the contribution of each event in the series to the correlation properties of the simplified pseudo-stress field around the location of the mainshock at different scales. This allows us to define a cumulative scalar pseudo-stress function which reveals neither an acceleration of stress storage at the epicentre of the mainshock nor an increase of the spatial stress,stress correlation length similar to those observed previously for the cumulative Benioff strain. The earthquakes we studied are thus either simple ,witnesses' of a large-scale tectonic organization, or are simply unrelated, and/or the Green's function describing interactions between earthquakes has a significantly longer range than predicted for standard viscoelastic media used here. [source] Multifractal detrended fluctuation analysis of streamflow series of the Yangtze River basin, ChinaHYDROLOGICAL PROCESSES, Issue 26 2008Qiang Zhang Abstract Scaling and multifractal properties of the hydrological processes of the Yangtze River basin were explored by using a multifractal detrended fluctuation analysis (MF-DFA) technique. Long daily mean streamflow series from Cuntan, Yichang, Hankou and Datong stations were analyzed. Using shuffled streamflow series, the types of multifractality of streamflow series was also studied. The results indicate that the discharge series of the Yangtze River basin are non-stationary. Different correlation properties were identified within streamflow series of the upper, the middle and the lower Yangtze River basin. The discharge series of the upper Yangtze River basin are characterized by short memory or anti-persistence; while the streamflow series of the lower Yangtze River basin is characterized by long memory or persistence. h(q) vs q curves indicate multifractality of the hydrological processes of the Yangtze River basin. h(q) curves of shuffled streamflow series suggest that the multifractality of the streamflow series is mainly due to the correlation properties within the hydrological series. This study may be of practical and scientific importance in regional flood frequency analysis and water resource management in different parts of the Yangtze River basin. Copyright © 2008 John Wiley & Sons, Ltd. [source] Spatial distribution of cloud coverINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2008Pedro Garcia Abstract Satellite systems and high-altitude platform systems working in Ka and V bands require the application of adaptive techniques in order to mitigate link degradations caused by atmospheric impairments such as those due to cloud cover. Among these techniques, resource sharing system techniques and site diversity need information on the spatial distribution of impairments caused by cloud cover, including the probability of simultaneous occurrence of adverse conditions in various regions. A study has been performed in Spain, within the framework of COST Action 280, to investigate the large-scale spatial distribution of cloud cover using synoptic meteorological data. Cloud cover distribution for individual sites and the spatial correlation properties for pairs of sites have been investigated. The geographical distributions of the values obtained from the statistical analysis have been represented in maps of contour lines using standard mapping procedures. Correlation parameters are expected to decrease with distance; however, the maps derived taking a given site as reference reveal a significant influence of climatic and geographic factors such as weather fronts, orography or the proximity to the sea. The statistics and maps obtained can be useful to optimize power sharing in multi-beam satellite systems, as suggested in this paper. Copyright © 2008 John Wiley & Sons, Ltd. [source] Entanglement and parametric dynamics in quantum optics with interacting polaritonsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2008S. Portolan Abstract We report on a microscopic investigation of the polariton parametric emission in the presence of coherent and incoherent interaction processes by means of a full quantum description based on a nonequilibrium quantum Langevin approach for open systems applied to interacting-electron complexes described within the dynamics controlled truncation scheme. It provides an easy recipe to calculate multi-time correlation functions which are key-quantities in quantum optics. In particular we report on calculations of polariton intensities (i.e. single time correlators) and spectra (i.e. two times correlators). We apply our scheme to a two-pumps set-up in microcavity recently proposed showing a quantitative analysis of the quantum correlation properties of the emitted photons. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nonlinear Analysis of Heart Rate Variability: Fractal and Complexity Measures of Heart Rate BehaviorANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2 2000Juha S. Perkiömäki M.D. Many new methods of analyzing heart rate (HR) variability have been developed to describe the features in HR behavior that cannot be detected by traditional time- and frequency-domain methods. Some of the new methods, such as analysis of fractal correlation properties and complexity of HR dynamics, have provided clinically useful information in various patient populations. Importantly, some fractal analysis methods are better risk predictors of mortality than traditional HR variability measures, and analysis of complexity of HR dynamics has been shown to predict the spontaneous onset of atrial fibrillation. New analysis methods based on nonlinear dynamics are a promising tool for better understanding of normal and abnormal HR behavior. More work will be needed to establish the clinical applicability of traditional and new analysis methods of HR variability. [source] Effects of pharmacological adrenergic and vagal modulation on fractal heart rate dynamicsCLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 5 2001Mikko P. Tulppo Breakdown of short-term fractal-like behaviour of HR indicates an increased risk for adverse cardiovascular events and mortality, but the pathophysiological background for altered fractal HR dynamics is not known. Our aim was to study the effects of pharmacological modulation of autonomic function on fractal correlation properties of heart rate (HR) variability in healthy subjects. Short-term fractal scaling exponent (,1) along with spectral components of HR variability were analysed during the following pharmacological interventions in healthy subjects: (i) noradrenaline (NE) infusion (n=22), (ii) NE infusion after phentolamine (PHE) (n=8), (iii) combined NE + adrenaline (EPI) infusion (n=12), (iv) vagal blockade with high dose of atropine (n=10), (v) and vagal activation by low dose of atropine (n=10). Then ,1 decreased progressively during the incremental doses of NE (from 0·85 ± 0·250 to 0.55 ± 0·23, P<0·0001). NE also decreased the average HR (P<0·001) and increased the high frequency spectral power (P<0·001). Vagal blockade with atropine increased the ,1 value (from 0·82 ± 0·22 to 1·24 ± 0·41, P<0·05). Combined NE + EPI infusion and vagal activation with a low dose atropine did not result in any changes in ,1, and ,-adrenergic blockade by PHE did not completely reverse the effects of NE on ,1. Increased levels of circulating NE result in reduction of short-term correlation properties of HR dynamics. The results suggest that coactivation of cardiac vagal outflow at the time of high levels of a circulating sympathetic transmitter explains the breakdown of fractal-like behaviour of human HR dynamics. [source] A digital secure image communication scheme based on the chaotic Chebyshev mapINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 5 2004Xiaofeng Liao Abstract In this paper, a simple image secure communication scheme based on the chaotic Chebyshev map and chaos synchronization is proposed. The scheme relies on the excellent correlation property of chaotic sequences, which is very desirable for secure image communication. The results obtained by computer simulation indicate that the transmitted source image can be correctly and reliably recovered using the proposed scheme, even through a noisy channel. Notably, the scheme possesses relatively high security and can be easily implemented. Moreover, the quality of the recovered image is satisfactory, quantified by such common criteria as the bit-error rate performance. Copyright © 2004 John Wiley & Sons, Ltd. [source] | |||||||||||||