Navegando por Autor "Lopes, Sérgio Roberto"
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Artigo Optimizing the detection of nonstationary signals by using recurrence analysis(American Institute of Physics, 2018-08-24) Prado, Thiago de Lima; Lima, Gustavo Zampier dos Santos; Lobão-Soares, Bruno; Nascimento, George Carlos do; Corso, Gilberto; Araújo, John Fontenele; Kurths, Jürgen; Lopes, Sérgio RobertoRecurrence analysis and its quantifiers are strongly dependent on the evaluation of the vicinity threshold parameter, i.e., the threshold to regard two points close enough in phase space to be considered as just one. We develop a new way to optimize the evaluation of the vicinity threshold in order to assure a higher level of sensitivity to recurrence quantifiers to allow the detection of even small changes in the dynamics. It is used to promote recurrence analysis as a tool to detect nonstationary behavior of time signals or space profiles. We show that the ability to detect small changes provides information about the present status of the physical process responsible to generate the signal and offers mechanisms to predict future states. Here, a higher sensitive recurrence analysis is proposed as a precursor, a tool to predict near future states of a particular system, based on just (experimentally) obtained signals of some available variables of the system. Comparisons with traditional methods of recurrence analysis show that the optimization method developed here is more sensitive to small variations occurring in a signal. The method is applied to numerically generated time series as well as experimental data from physiologyArtigo Quantifying entropy using recurrence matrix microstates(American Institute of Physics, 2018-08-09) Corso, Gilberto; Prado, Thiago de Lima; Lima, Gustavo Zampier dos Santos; Kurths, Jürgen; Lopes, Sérgio RobertoWe conceive a new recurrence quantifier for time series based on the concept of information entropy, in which the probabilities are associated with the presence of microstates defined on the recurrence matrix as small binary submatrices. The new methodology to compute the entropy of a time series has advantages compared to the traditional entropies defined in the literature, namely, a good correlation with the maximum Lyapunov exponent of the system and a weak dependence on the vicinity threshold parameter. Furthermore, the new method works adequately even for small segments of data, bringing consistent results for short and long time series. In a case where long time series are available, the new methodology can be employed to obtain high precision results since it does not demand large computational times related to the analysis of the entire time series or recurrence matrices, as is the case of other traditional entropy quantifiers. The method is applied to discrete and continuous systems