Browsing by Author "Ambika, G."

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    Non subjective approach to the GP algorithm for analysing noisy time series
    (2006-01-10) Harikrishnan, K. P.; Misra, Ranjeev; Ambika, G.; et al.
    We present an adaptation of the standard Grassberger-Proccacia (GP) algorithm for estimating the Correlation Dimension of a time series in a non subjective manner. The validity and accuracy of this approach is tested using di erent types of time series, such as, those from standard chaotic systems, pure white and colored noise and chaotic systems added with noise. The e ectiveness of the scheme in analysing noisy time series, particularly those involving colored noise, is investigated. An interesting result we have obtained is that, for the same percentage of noise addition, data with colored noise is more distinguishable from the corresponding surrogates, than data with white noise. As examples for real life applications, analysis of data from an astrophysical X-ray object and human brain EEG, are presented.
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    Non-linear behaviour of the black hole system GRS 1915+ 105
    (2006-02-05) Misra, Ranjeev; Harikrishnan, K. P.; Ambika, G.; et al.
    Using non-lin~ar ti?Ie seri.e~ analysis, along with surrogate data analysis, it is shown that the various types of lon~ t~rI? varla~lbty exhibited by the black hole system GRS 1915+105, can be explained in terms of a ~et~rmlmstlc.n?n-bnear system with some inherent stochastic noise. Evidence is provided for a non-linear limit cycle ongm of one of.the low f~eque~cy QPO detected in the source, while some other types of variability could. be due ~oan underlying low dimensional chaotic system. These results imply that the partial differential equanons which govern the magneto- ~drodynamic flow of the inner accretion disk, can be approximated by a by a small number ( ~ 3 - 5) of non-linear but ordinary differential equations. While this analysis does not reveal the exact nature of these approximate equations, they may be obtained in the future, after results of magneto-hydrodynamic simulation of realistic accretion disks become available.