Examinando por Autor "Rajasekar, S."

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Delay-induced resonance suppresses damping-induced unpredictability
(The Royal Society, 2020) Cantisan, Julia; Coccolo, Mattia; Seoane, Jesús M.; F. Sanjuan, Miguel A.; Rajasekar, S.
Combined effects of the damping and forcing in the underdamped time-delayed Duffing oscillator are considered in this paper. We analyse the generation of a certain damping-induced unpredictability due to the gradual suppression of interwell oscillations. We find the minimal amount of the forcing amplitude and the right forcing frequency to revert the effect of the dissipation, so that the interwell oscillations can be restored, for different time delay values. This is achieved by using the delay-induced resonance, in which the time delay replaces one of the two periodic forcings present in the vibrational resonance. A discussion in terms of the time delay of the critical values of the forcing for which the delay-induced resonance can tame the dissipation effect is finally carried out.
Vibrational resonance in biological nonlinear maps
(Springer, 2012-08) Rajasekar, S.; Used, Javier; Wagemakers, Alexandre; Sanjuán, Miguel A.F.
We investigate vibrational resonance in two different nonlinear maps driven by a biharmonic force: the Bellows and the Rulkov map. These two maps possess dynamical features of particular interest for the study of these phenomena. In both maps, the resonance occurs at the low-frequency of the biharmonic signal as the amplitude of the high-frequency signal is varied. We also consider an array of unidirectionally coupled maps with the forcing signal applied to the first unit. In this case, a signal propagation with several interesting features above a critical value of the coupling strength is found, while the response amplitude of the ith unit is greater than the first one. This response evolves in a sigmoidal fashion with the system number i, meaning that at some point the amplitudes saturate. The unidirectional coupling acts as a low-pass filter for distant units. Moreover, the analysis of the mean residence time of the trajectory in a given region of the phase space unveils a multiresonance mechanism in the coupled map system. These results point at the relevance of the discrete-time models for the study of resonance phenomena, since analyses and simulations are much easier than for continuous-time models
Vibrational resonance in the FitzHugh-Nagumo neuron model under state-dependent time delay
(American Institute of Physics, 2025-02-03) Siewe Siewe, Martin; Rajasekar, S.; Coccolo, Mattia; Sanjuán, Miguel A.F.
Proponemos un modelo neuronal no lineal de FitzHugh–Nagumo con un potencial asimétrico, impulsado por una señal de alta frecuencia y otra de baja frecuencia. Nuestro análisis numérico se centra en la influencia de un retraso temporal dependiente del estado en los fenómenos de resonancia vibracional y resonancia inducida por el retraso. Para caracterizar estas resonancias, se explora la amplitud de respuesta a la señal de baja frecuencia. Nuestros resultados muestran que, para valores pequeños de la amplitud del componente de velocidad del retraso temporal dependiente del estado, en el modelo neuronal ocurren resonancia vibracional y multi-resonancia. Para valores grandes de la amplitud de excitación de alta frecuencia, la resonancia vibracional aparece con un solo pico. Además, observamos un cambio en la respuesta cuando aumenta la amplitud del componente de velocidad del retraso temporal dependiente del estado. También analizamos cómo los componentes de posición y velocidad de este retraso pueden dar lugar a la resonancia inducida por el retraso, tanto por separado como en conjunto. Los hallazgos clave de este trabajo demuestran que el componente de velocidad del retraso temporal dependiente del estado desempeña un papel crucial en ambos fenómenos. En particular, el parámetro de retraso actúa como un factor de control crítico, capaz de desencadenar el inicio de ambas resonancias
Vibrational resonance: A review
(Elsevier, 2024-05) Yang, Jianhua; Rajasekar, S.; Sanjuán, Miguel A.F.
Over the past two decades, vibrational resonance has garnered significant interest and evolved into a prominent research field. Classical vibrational resonance examines the response of a nonlinear system excited by two signals: a weak, slowly varying characteristic signal, and a fast-varying auxiliary signal. The characteristic signal operates on a much longer time scale than the auxiliary signal. Through the cooperation of the nonlinear system and these two excitations, the faint input can be substantially amplified, showcasing the constructive role of the fast-varying signal. Since its inception, vibrational resonance has been extensively studied across various disciplines, including physics, mathematics, biology, neuroscience, laser science, chemistry, and engineering. Here, we delve into a detailed discussion of vibrational resonance and the most recent advances, beginning with an introduction to characteristic signals commonly used in its study. Furthermore, we compile numerous nonlinear models where vibrational resonance has been observed to enhance readers’ understanding and provide a basis for comparison. Subsequently, we present the metrics used to quantify vibrational resonance, as well as offer a theoretical formulation. This encompasses the method of direct separation of motions, linear and nonlinear vibrational resonance, re-scaled vibrational resonance, ultrasensitive vibrational resonance, and the role of noise in vibrational resonance. Later, we showcase two practical applications of vibrational resonance: one in image processing and the other in fault diagnosis. This presentation offers a comprehensive and versatile overview of vibrational resonance, exploring various facets and highlighting promising avenues for future research in both theory and engineering applications