TY - JOUR A1 - Zaourar, Naima A1 - Hamoudi, Mohamed A1 - Holschneider, Matthias A1 - Mandea, Mioara T1 - Fractal dynamics of geomagnetic storms JF - Arabian journal of geosciences N2 - We explore fluctuations of the horizontal component of the Earth's magnetic field to identify scaling behaviour of the temporal variability in geomagnetic data recorded by the Intermagnet observatories during the solar cycle 23 (years 1996 to 2005). In this work, we use the remarkable ability of scaling wavelet exponents to highlight the singularities associated with discontinuities present in the magnetograms obtained at two magnetic observatories for six intense magnetic storms, including the sudden storm commencements of 14 July 2000, 29-31 October and 20-21 November 2003. In the active intervals that occurred during geomagnetic storms, we observe a rapid and unidirectional change in the spectral scaling exponent at the time of storm onset. The corresponding fractal features suggest that the dynamics of the whole time series is similar to that of a fractional Brownian motion. Our findings point to an evident relatively sudden change related to the emergence of persistency of the fractal power exponent fluctuations precedes an intense magnetic storm. These first results could be useful in the framework of extreme events prediction studies. KW - Geomagnetic field KW - Magnetosphere KW - Geomagnetic storm KW - Multiscale analysis KW - Spectral exponent Y1 - 2013 U6 - https://doi.org/10.1007/s12517-011-0487-0 SN - 1866-7511 VL - 6 IS - 6 SP - 1693 EP - 1702 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Cotronei, Mariantonia A1 - Holschneider, Matthias T1 - Partial parameterization of orthogonal wavelet matrix filters JF - Journal of computational and applied mathematics N2 - In this paper we propose a procedure which allows the construction of a large family of FIR d x d matrix wavelet filters by exploiting the one-to-one correspondence between QMF systems and orthogonal operators which commute with the shifts by two. A characterization of the class of filters of full rank type that can be obtained with such procedure is given. In particular, we restrict our attention to a special construction based on the representation of SO(2d) in terms of the elements of its Lie algebra. Explicit expressions for the filters in the case d = 2 are given, as a result of a local analysis of the parameterization obtained from perturbing the Haar system. KW - Full rank matrix filters KW - Multichannel wavelets KW - Quadrature mirror filters KW - Vector subdivision schemes Y1 - 2013 U6 - https://doi.org/10.1016/j.cam.2012.11.016 SN - 0377-0427 VL - 243 IS - 4 SP - 113 EP - 125 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Schröter, M-A A1 - Sturm, H. A1 - Holschneider, Matthias T1 - Phase and amplitude patterns in DySEM mappings of vibrating microstructures JF - Nanotechnology N2 - We use a dynamic scanning electron microscope (DySEM) to analyze the movement of oscillating micromechanical structures. A dynamic secondary electron (SE) signal is recorded and correlated to the oscillatory excitation of scanning force microscope (SFM) cantilever by means of lock-in amplifiers. We show, how the relative phase of the oscillations modulate the resulting real part and phase pictures of the DySEM mapping. This can be used to obtain information about the underlying oscillatory dynamics. We apply the theory to the case of a cantilever in oscillation, driven at different flexural and torsional resonance modes. This is an extension of a recent work (Schroter et al 2012 Nanotechnology 23 435501), where we reported on a general methodology to distinguish nonlinear features caused by the imaging process from those caused by cantilever motion. Y1 - 2013 U6 - https://doi.org/10.1088/0957-4484/24/21/215701 SN - 0957-4484 VL - 24 IS - 21 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Zöller, Gert A1 - Holschneider, Matthias A1 - Hainzl, Sebastian T1 - The Maximum Earthquake Magnitude in a Time Horizon: Theory and Case Studies JF - Bulletin of the Seismological Society of America N2 - We show how the maximum magnitude within a predefined future time horizon may be estimated from an earthquake catalog within the context of Gutenberg-Richter statistics. The aim is to carry out a rigorous uncertainty assessment, and calculate precise confidence intervals based on an imposed level of confidence a. In detail, we present a model for the estimation of the maximum magnitude to occur in a time interval T-f in the future, given a complete earthquake catalog for a time period T in the past and, if available, paleoseismic events. For this goal, we solely assume that earthquakes follow a stationary Poisson process in time with unknown productivity Lambda and obey the Gutenberg-Richter law in magnitude domain with unknown b-value. The random variables. and b are estimated by means of Bayes theorem with noninformative prior distributions. Results based on synthetic catalogs and on retrospective calculations of historic catalogs from the highly active area of Japan and the low-seismicity, but high-risk region lower Rhine embayment (LRE) in Germany indicate that the estimated magnitudes are close to the true values. Finally, we discuss whether the techniques can be extended to meet the safety requirements for critical facilities such as nuclear power plants. For this aim, the maximum magnitude for all times has to be considered. In agreement with earlier work, we find that this parameter is not a useful quantity from the viewpoint of statistical inference. Y1 - 2013 U6 - https://doi.org/10.1785/0120120013 SN - 0037-1106 VL - 103 IS - 2A SP - 860 EP - 875 PB - Seismological Society of America CY - Albany ER - TY - JOUR A1 - Zaourar, N. A1 - Hamoudi, M. A1 - Mandea, M. A1 - Balasis, G. A1 - Holschneider, Matthias T1 - Wavelet-based multiscale analysis of geomagnetic disturbance JF - EARTH PLANETS AND SPACE N2 - The dynamics of external contributions to the geomagnetic field is investigated by applying time-frequency methods to magnetic observatory data. Fractal models and multiscale analysis enable obtaining maximum quantitative information related to the short-term dynamics of the geomagnetic field activity. The stochastic properties of the horizontal component of the transient external field are determined by searching for scaling laws in the power spectra. The spectrum fits a power law with a scaling exponent beta, a typical characteristic of self-affine time-series. Local variations in the power-law exponent are investigated by applying wavelet analysis to the same time-series. These analyses highlight the self-affine properties of geomagnetic perturbations and their persistence. Moreover, they show that the main phases of sudden storm disturbances are uniquely characterized by a scaling exponent varying between 1 and 3, possibly related to the energy contained in the external field. These new findings suggest the existence of a long-range dependence, the scaling exponent being an efficient indicator of geomagnetic activity and singularity detection. These results show that by using magnetogram regularity to reflect the magnetosphere activity, a theoretical analysis of the external geomagnetic field based on local power-law exponents is possible. KW - Geomagnetic field KW - magnetosphere KW - geomagnetic storm KW - multiscale analysis KW - spectral exponent Y1 - 2013 U6 - https://doi.org/10.5047/eps.2013.05.001 SN - 1343-8832 SN - 1880-5981 VL - 65 IS - 12 SP - 1525 EP - 1540 PB - TERRA SCIENTIFIC PUBL CO CY - TOKYO ER -