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Sep 23, 2013
09/13

by
M. Reza Rahimi Tabar; Muhammad Sahimi; K. Kaviani; M. Allamehzadeh; J. Peinke; M. Mokhtari; M. Vesaghi; M. D. Niry; F. Ghasemi; A. Bahraminasab; S. Tabatabai; F. Fayazbakhsh

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We propose a novel method for analyzing precursory seismic data before an earthquake that treats them as a Markov process and distinguishes the background noise from real fluctuations due to an earthquake. A short time (on the order of several hours) before an earthquake the Markov time scale $t_M$ increases sharply, hence providing an alarm for an impending earthquake. To distinguish a false alarm from a reliable one, we compute a second quantity, $T_1$, based on the concept of extended...

Source: http://arxiv.org/abs/physics/0510043v1

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42

Sep 22, 2013
09/13

by
F. Ghasemi; Muhammad Sahimi; J. Peinke; M. Reza Rahimi Tabar

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We describe a method for analyzing the stochasticity in the non-stationary data for the beat-to-beat fluctuations in the heart rates of healthy subjects, as well as those with congestive heart failure. The method analyzes the returns time series of the data as a Markov process, and computes the Markov time scale, i.e., the time scale over which the data are a Markov process. We also construct an effective stochastic continuum equation for the return series. We show that the drift and diffusion...

Source: http://arxiv.org/abs/physics/0603130v1

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51

Sep 22, 2013
09/13

by
T. Laubrich; F. Ghasemi; J. Peinke; H. Kantz

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We study the statistics of the horizontal component of atmospheric boundary layer wind speed. Motivated by its non-stationarity, we investigate which parameters remain constant or can be regarded as being piece-wise constant and explain how to estimate them. We will verify the picture of natural atmospheric boundary layer turbulence to be composed of successively occurring close to ideal turbulence with different parameters. The first focus is put on the fluctuation of wind speed around its...

Source: http://arxiv.org/abs/0811.3337v1

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40

Sep 23, 2013
09/13

by
G. R. Jafari; S. M. Fazeli; F. Ghasemi; S. M. Vaez Allaei; M. Reza Rahimi Tabar; A. Iraji zad; G. Kavei

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We investigate Markov property of rough surfaces. Using stochastic analysis we characterize the complexity of the surface roughness by means of a Fokker-Planck or Langevin equation. The obtained Langevin equation enables us to regenerate surfaces with similar statistical properties compared with the observed morphology by atomic force microscopy.

Source: http://arxiv.org/abs/cond-mat/0312455v1

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82

Sep 21, 2013
09/13

by
M. Sadegh Movahed; G. R. Jafari; F. Ghasemi; Sohrab Rahvar; M. Reza Rahimi Tabar

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We use multifractal detrended fluctuation analysis (MF-DFA), to See query 1 study sunspot number fluctuations. The result of the MF-DFA shows that there are three crossover timescales in the fluctuation function. We discuss how the existence of the crossover timescales is related to a sinusoidal trend. Using Fourier detrended fluctuation analysis, the sinusoidal trend is eliminated. The Hurst exponent of the time series without the sinusoidal trend is $0.12\pm 0.01$. Also we find that these...

Source: http://arxiv.org/abs/physics/0508149v2

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34

Sep 21, 2013
09/13

by
M. Sadegh Movahed; F. Ghasemi; Sohrab Rahvar; M. Reza Rahimi Tabar

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We investigate the statistical anisotropy and Gaussianity of temperature fluctuations of Cosmic Microwave Background radiation (CMB) data from {\it Wilkinson Microwave Anisotropy Probe} survey, using the multifractal detrended fluctuation analysis, rescaled range and scaled windowed variance methods. The multifractal detrended fluctuation analysis shows that CMB fluctuations has a long range correlation function with a multifractal behavior. By comparing the shuffled and surrogate series of CMB...

Source: http://arxiv.org/abs/astro-ph/0602461v2

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31

Oct 24, 2014
10/14

by
Taheri, N; Semnani, S; Roshandel, G; Namjoo, M; Keshavarzian, H; Chogan, AG; Kebria, F Ghasemi; Joshaghani, H

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This article is from Iranian Journal of Public Health , volume 41 . Abstract Background:: Due to the high toxicity of aflatoxin and its effects on public health, determination of aflatoxin level in Wheat flour samples in the Golestan province, north of Iran was investigated. To examine the effect of seasonal changes, summer and winter sampling was performed with standard sampling methods. Methods:: A total of 200 flour samples were collected from 25 factories. HPLC method with immunoaffinity...

Source: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3494214

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38

Sep 23, 2013
09/13

by
F. Ghasemi; A. Bahraminasab; M. Sadegh Movahed; Sohrab Rahvar; K. R. Sreenivasan; M. Reza Rahimi Tabar

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We investigate the stochasticity in temperature fluctuations in the cosmic microwave background (CMB) radiation data from {\it Wilkinson Microwave Anisotropy Probe}. We show that the angular fluctuations of the temperature is a Markov process with a {\it Markov angular scale}, $\Theta_{\rm Markov}=1.01^{+0.09}_{-0.07}$. We characterize the complexity of the CMB fluctuations by means of a Fokker-Planck or Langevin equation and measure the associated Kramers-Moyal coefficients for the fluctuating...

Source: http://arxiv.org/abs/astro-ph/0312227v2

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46

Sep 21, 2013
09/13

by
G. R. Jafari; M. Sadegh Movahed; P. Noroozzadeh; A. Bahraminasab; Muhammad Sahimi; F. Ghasemi; M. Reza Rahimi Tabar

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We report on a study of the Tehran Price Index (TEPIX) from 2001 to 2006 as an emerging market that has been affected by several political crises during the recent years, and analyze the non-Gaussian probability density function (PDF) of the log returns of the stocks' prices. We show that while the average of the index did not fall very much over the time period of the study, its day-to-day fluctuations strongly increased due to the crises. Using an approach based on multiplicative processes...

Source: http://arxiv.org/abs/0706.1460v1

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50

Sep 23, 2013
09/13

by
J. Peinke; M. Reza Rahimi Tabar; Muhammad Sahimi; F. Ghasemi

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We propose a novel inverse method that utilizes a set of data to construct a simple equation that governs the stochastic process for which the data have been measured, hence enabling us to reconstruct the stochastic process. As an example, we analyze the stochasticity in the beat-to-beat fluctuations in the heart rates of healthy subjects as well as those with congestive heart failure. The inverse method provides a novel technique for distinguishing the two classes of subjects in terms of a...

Source: http://arxiv.org/abs/cond-mat/0411529v2