Filters








36 Hits in 0.73 sec

VHF-electromagnetic evidence of the underlying pre-seismic critical stage

Panayiotis Kapiris, John Polygiannakis, Athanassios Peratzakis, Konstantinos Nomicos, Konstantinos Eftaxias
2002 Earth, Planets and Space  
focal area (Eftaxias et al., 2000) .  ...  et al., 2000 (Eftaxias et al., , 2001 .  ... 
doi:10.1186/bf03352452 fatcat:v6pqfzobjrbzhfyp4bm7wmzmme

Are There Pre-Seismic Electromagnetic Precursors? A Multidisciplinary Approach [chapter]

Konstantinos Eftaxias
2012 Earthquake Research and Analysis - Statistical Studies, Observations and Planning  
How to reference In order to correctly reference this scholarly work, feel free to copy and paste the following: Konstantinos Eftaxias (2012) . Are There Pre-Seismic Electromagnetic Precursors?  ... 
doi:10.5772/28069 fatcat:ypy256icibe67kggxuehnu7r64

Constrained LMS for dynamic flow networks

Konstantinos Eftaxias, Clive Cheong Took, Bruno Venturini, David Arscott
2017 2017 International Joint Conference on Neural Networks (IJCNN)  
In this era of climate change, there is a growing need to offer adaptive learning algorithms in the optimisation of natural resources. These resources are typically optimised by evolutionary algorithms. However, evolutionary algorithms (EAs) are no longer adequate due to the 'drift' component introduced by environmental factors such as flash flooding. We therefore propose a novel constrained Least Mean Squares (LMS) algorithm for the optimisation of flow networks. For rigor, we provide a
more » ... ty analysis of our adaptive algorithm, which enables us to interpret the physical meaning of the network at equilibrium. We evaluate our proposed method against genetic algorithm (GA), the most common evolutionary algorithm. The results are promising: not only the proposed constrained LMS has a performance advantage over GA, but its computational cost is significantly lower making it more suitable for real-time applications.
doi:10.1109/ijcnn.2017.7966263 dblp:conf/ijcnn/EftaxiasTVA17 fatcat:bwzu4qgjzbbtla2hkmkmu7jrhe

Dynamical complexity inDsttime series using non-extensive Tsallis entropy

Georgios Balasis, Ioannis A. Daglis, Constantinos Papadimitriou, Maria Kalimeri, Anastasios Anastasiadis, Konstantinos Eftaxias
2008 Geophysical Research Letters  
1] Nonlinearly evolving dynamical systems, such as space plasmas, generate complex fluctuations in their output signals that reflect the underlying dynamics. The non-extensive Tsallis entropy has been proposed as a measure to investigate the complexity of system dynamics. We employ this method for analyzing D st time series. The results show that Tsallis entropy can effectively detect the dissimilarity of complexity between the pre-storm activity and intense magnetic storms (D st < À150 nT),
more » ... ch is convenient for space weather applications. Citation: Balasis,
doi:10.1029/2008gl034743 fatcat:56jat7feijdarfdenniydhbnsy

An Adaptive Filtering Approach Using Supervised SSA for Identification of Sleep Stages From EEG

Samaneh Kouchaki Kouchaki, Konstantinos Eftaxias, Saeid Sanei
2014 Frontiers in biomedical technologies  
Purpose: Sleep is a complex physiological state and an indicator of the changes in the brain function similar to those occurring in many psychiatric and neurological conditions. Since visual sleep scoring consuming process, automatic sleep staging methods, also called scoring, hold promise in diagnosing alterations in the sleep process and the sleep EEG more effectively. Method: In this paper, a supervised approach for sleep scoring from single channel EEG signals is proposed. First, a
more » ... d singular spectrum analysis (SSA) which is a subspace based method is used to extract the desired signal for each stage of sleep. Then, two recursive least squares (RLS) adaptive filters are trained and used to identify first and deep sleep stages. Result: The proposed system which can be considered as a filter bank for separating multiple signal subbands is tested using real EEG where the results verify the accuracy of the proposed method. Conclusion: The overall result show the effectiveness of algorithm for detection of sleep stages from EEG signals often characterised by a sharp increase in delta and a rapid decrease in alpha as sleep deepens.
doaj:8bfc3355f5c64d019beaefcd6e48ebb8 fatcat:fqm2ij64djdchfrqc7x4vz76jy

Distinguished seismological and electromagnetic features of the impending global failure: Did the 7/9/1999 M5.9 Athens earthquake come with a warning?

Panayiotis Kapiris, Konstantinos Nomicos, George Antonopoulos, John Polygiannakis, Konstantinos Karamanos, John Kopanas, Athanassios Zissos, Athanassios Peratzakis, Konstantinos Eftaxias
2005 Earth, Planets and Space  
Eftaxias would like to thank N. Gershenzon, and G. Bambakidis for several helpful conversations. This research was supported in part by NATO Grant JSTC.  ...  ., at 3 kHz and 10 kHz, before the Athens EQ (Eftaxias et al., 2000 (Eftaxias et al., , 2001a .  ...  Eftaxias et al. (2000 Eftaxias et al. ( , 2001b have attempted to explain this effect based on a model for the micro-fracture of granular media which consists of rigid grains separated by interstices  ... 
doi:10.1186/bf03351818 fatcat:zeuan3zs6jd6ngk5mekpg224vi

Magnetovariational and Magnetotelluric study of Ioannina region sensitive to Seismic Electric Signals (SES). II

Georgios Balasis, Nikolaos Bogris, Konstantinos Eftaxias
2002 Journal of Atmospheric Electricity  
The Ioannina electromagnetic response dataset was firstly presented in Eftaxias et al. (2002) (hereafter called Part 1).  ... 
doi:10.1541/jae.22.139 fatcat:7abrqk7hw5giloohckc72lxj4e

Statistical Mechanics and Information-Theoretic Perspectives on Complexity in the Earth System

Georgios Balasis, Reik Donner, Stelios Potirakis, Jakob Runge, Constantinos Papadimitriou, Ioannis Daglis, Konstantinos Eftaxias, Jürgen Kurths
2013 Entropy  
This review provides a summary of methods originated in (non-equilibrium) statistical mechanics and information theory, which have recently found successful applications to quantitatively studying complexity in various components of the complex Entropy 2013, 15 4845 system Earth. Specifically, we discuss two classes of methods: (i) entropies of different kinds (e.g., on the one hand classical Shannon and Rényi entropies, as well as non-extensive Tsallis entropy based on symbolic dynamics
more » ... ues and, on the other hand, approximate entropy, sample entropy and fuzzy entropy); and (ii) measures of statistical interdependence and causality (e.g., mutual information and generalizations thereof, transfer entropy, momentary information transfer). We review a number of applications and case studies utilizing the above-mentioned methodological approaches for studying contemporary problems in some exemplary fields of the Earth sciences, highlighting the potentials of different techniques.
doi:10.3390/e15114844 fatcat:v243ceatvjcrzdsafzj74bfd3a

Quantifying Dynamical Complexity of Magnetic Storms and Solar Flares via Nonextensive Tsallis Entropy

Georgios Balasis, Ioannis A. Daglis, Constantinos Papadimitriou, Anastasios Anastasiadis, Ingmar Sandberg, Konstantinos Eftaxias
2011 Entropy  
doi:10.3390/e13101865 fatcat:s2bqu65pmfcn5epykq56uoh3ae

Detection of Dynamical Complexity Changes in Dst Time Series Using Entropy Concepts and Rescaled Range Analysis [chapter]

Georgios Balasis, Ioannis A. Daglis, Anastasios Anastasiadis, Konstantinos Eftaxias
2011 The Dynamic Magnetosphere  
Using an array of diagnostic tools including entropy concepts and rescaled range analysis, we establish that the Dst index time series exhibits long-range correlations, and that the underlying stochastic process can be modeled as fractional Brownian motion. We show the emergence of two distinct patterns in the geomagnetic variability of the terrestrial magnetosphere: (1) a pattern associated with intense magnetic storms, which is characterized by a higher degree of organization (i.e., lower
more » ... lexity or higher predictability for the system) and persistent behavior, and (2) a pattern associated with normal periods, which is characterized by a lower degree of organization (i.e., higher complexity or lower predictability for the system) and anti-persistent behavior.
doi:10.1007/978-94-007-0501-2_12 fatcat:nizmeq7ilrek5nly7mszhvx3em

Investigating dynamical complexity in the magnetosphere using various entropy measures

Georgios Balasis, Ioannis A. Daglis, Constantinos Papadimitriou, Maria Kalimeri, Anastasios Anastasiadis, Konstantinos Eftaxias
2009 Journal of Geophysical Research  
The complex system of the Earth's magnetosphere corresponds to an open spatially extended non-equilibrium (input -output) dynamical system. The non-extensive Tsallis entropy has been recently introduced [Balasis et al. (2008) , Geophys. Res. Lett., 35, L14102, doi:10.1029/2008GL034743] as an appropriate information measure to investigate dynamical complexity in the magnetosphere. The method has been employed for analyzing D st time series and gave promising results, detecting the complexity
more » ... imilarity among different physiological and pathological magnetospheric states (i.e., pre-storm activity and intense magnetic storms, respectively). This paper explores the applicability and effectiveness of a variety of computable entropy measures (e.g. Block entropy, Kolmogorov entropy, T -complexity and Approximate entropy) to the investigation of dynamical complexity in the magnetosphere. We show that as the magnetic storm approaches there is clear evidence of significant lower complexity in the magnetosphere. Overall, Approximate entropy and Tsallis entropy yield superior results for detecting dynamical complexity in the magnetosphere in comparison to the other entropy measures presented herein. Ultimately, the analysis tools developed in the course of this study for the treatment of D st index can provide convenience for space weather applications.
doi:10.1029/2008ja014035 fatcat:qkcr53ddxzd7xmpzsoxh4v7wx4

An Exploratory Study of Geospace Perturbations Using Financial Analysis Tools in the Context of Complex Systems

Pavlos I. Zitis, Stelios M. Potirakis, Georgios Balasis, Konstantinos Eftaxias
2021 Geosciences  
In the frame of complex systems research, methods used to quantitatively analyze specific dynamic phenomena are often used to analyze phenomena from other disciplines on the grounds that are governed by similar dynamics. Technical analysis is considered the oldest, currently omnipresent, method for financial markets analysis, which uses past prices aiming at the possible short-term forecast of future prices. This work is the first attempt to explore the applicability of technical analysis tools
more » ... on disturbance storm time (Dst) index time series, aiming at the identification of similar features between the Dst time series during magnetic storms (MSs) and asset price time series. We employ the following financial analysis tools: simple moving average (SMA), Bollinger bands, and relative strength index (RSI), formulating an analysis approach based on various features, appearing in financial time series during high volatility periods, that could be found during the different phases of the evolution of an MS (onset, main development, and recovery phase), focusing on the temporal sequence they occur. The applicability of the proposed analysis approach is examined on several MS events and the results reveal similar behavior with the financial time series in high volatility periods. We postulate that these specialized data analysis methods could be combined in the future with other statistical and complex systems time series analysis methods in order to form a useful toolbox for the study of geospace perturbations related to natural hazards.
doi:10.3390/geosciences11060239 fatcat:rwmi7etdjne4xbcfsjmx5i3tae

Magnetovariational and Magnetotelluric study of loannina region sensitive to Seismic Electric Signals (SES). I

Konstantinos Eftaxias, Igor I. Rokityansky, Nikolaos Bogris, Georgios Balasis, Panayiotis Varotsos
2002 Journal of Atmospheric Electricity  
A detailed magnetovariational (MVP) and magnetotelluric (MT) study was conducted at 42 sites around Ioannina SES sensitive station. The following tentative model is suggested, as being compatible with the MVP and MT data: a regional 2D structure ofN40°W strike, which contains a crustal layer (CL) with a gap 26±5 km wide. Near the center of this gap, crustal conductor(s) does exist which creates an MVP anomaly with a maximum anomalous field at periods around 300s and spatial dimension of a few
more » ... ns of km. Furthermore, a set of narrow (no more than 1 km wide) and shallow (1-3 km deep) conductors of limited length is manifested by the MTS E-polarization data; these conductors can be limited in the vertical dimension or can be continued in the deeper interior. It seems quite plausible that one (or two) of these shallow conductors is connected to the regional crustal conductor of quasi-2D behavior which can have continuation long outside the area studied and also can be continued in the deeper interior.
doi:10.1541/jae.22.113 fatcat:boknbflxyfhuhkxgcuta6pggce

On the use of financial analysis tools for the study of Dst time series in the frame of complex systems [article]

Stelios M. Potirakis, Pavlos I. Zitis, Georgios Balasis and Konstantinos Eftaxias
2016 arXiv   pre-print
Technical analysis is considered the oldest, currently omnipresent, method for financial markets analysis, which uses past prices aiming at the possible short-term forecast of future prices. In the frame of complex systems, methods used to quantitatively analyze specific dynamic phenomena are often used to analyze phenomena from other disciplines on the grounds that are governed by similar dynamics. An interesting task is the forecast of a magnetic storm. The hourly Dst is used as a global
more » ... for the monitoring of Earth's magnetosphere, which could be either in quiet (normal) or in magnetic storm (pathological) state. This work is the first attempt to apply technical analysis tools on Dst time series, aiming at the identification of indications which could be used for the study of the temporal evolution of Earth's magnetosphere state. We focus on the analysis of Dst time series around the occurrence of magnetic storms, discussing the possible use of the resulting information in the frame of multidisciplinary efforts towards extreme events forecasting. We employ the following financial analysis tools: simple moving average (SMA), Bollinger bands, and relative strength index (RSI). Using these tools, we formulate a methodology based on all indications that could be revealed in order to infer the onset, duration and recovery phase of a magnetic storm, focusing on the temporal sequence they occur. The applicability of the proposed methodology is examined on characteristic cases of magnetic storms with encouraging results for space weather forecasting.
arXiv:1601.07334v1 fatcat:ove2yo5l3rflnabr3nwhzmfz2i

Universality in solar flare, magnetic storm and earthquake dynamics using Tsallis statistical mechanics

Georgios Balasis, Ioannis A. Daglis, Anastasios Anastasiadis, Constantinos Papadimitriou, Mioara Mandea, Konstantinos Eftaxias
2011 Physica A: Statistical Mechanics and its Applications  
The universal character of the dynamics of various extreme phenomena is an outstanding scientific challenge. We show that X-ray flux and D st time series during powerful solar flares and intense magnetic storms, respectively, obey a nonextensive energy distribution function for earthquake dynamics with similar values for the Tsallis entropic index q. Thus, evidence for universality in solar flares, magnetic storms and earthquakes arise naturally in the framework of Tsallis statistical
more » ... The observed similarity suggests a common approach to the interpretation of these diverse phenomena in terms of driving physical mechanisms that have the same character.
doi:10.1016/j.physa.2010.09.029 fatcat:omw2dvqyt5bhre4uvaq4edi2hi
« Previous Showing results 1 — 15 out of 36 results