Browsing by Author "Hernandez, Esteban"

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    A partially averaged system to model neuron responses to interferential current stimulation
    (SPRINGER HEIDELBERG, 2023) Cerpa Jeria, Eduardo Esteban; Courdurier Bettancourt, Matías Alejandro; Hernandez, Esteban; Medina, Leonel E.; Paduro Williamson, Esteban Andrés
    The interferential current (IFC) therapy is a noninvasive electrical neurostimulation technique intended to activate deep neurons using surface electrodes. In IFC, two independent kilohertz-frequency currents purportedly intersect where an interference field is generated. However, the effects of IFC on neurons within and outside the interference field are not completely understood, and it is unclear whether this technique can reliable activate deep target neurons without side effects. In recent years, realistic computational models of IFC have been introduced to quantify the effects of IFC on brain cells, but they are often complex and computationally costly. Here, we introduce a simplified model of IFC based on the FitzHugh-Nagumo (FHN) model of a neuron. By considering a modified averaging method, we obtain a non-autonomous approximated system, with explicit representation of relevant IFC parameters. For this approximated system we determine conditions under which it reliably approximates the complete FHN system under IFC stimulation, and we mathematically prove its ability to predict nonspiking states. In addition, we perform numerical simulations that show that the interference effect is observed only for a narrow set of IFC parameters and, in particular, for a beat frequency no higher than about 100 [Hz]. Our novel model tailored to the IFC technique contributes to the understanding of neurostimulation modalities using this type of signals, and can have implications in the design of noninvasive electrical stimulation therapies.
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    A TRACKING PROBLEM FOR THE STATE OF CHARGE IN A ELECTROCHEMICAL LI-ION BATTERY MODEL
    (2022) Hernandez, Esteban; Prieur, Christophe; Cerpa, Eduardo
    In this paper the Single Particle Model is used to describe the behavior of a Li-ion battery. The main goal is to design a feedback input current in order to regulate the State of Charge (SOC) to a prescribed reference trajectory. In order to do that, we use the boundary ion concentration as output. First, we measure it directly and then we assume the existence of an appropriate estimator, which has been established in the literature using voltage measurements. By applying backstepping and Lyapunov tools, we are able to build observers and to design output feedback controllers giving a positive answer to the SOC tracking problem. We provide convergence proofs and perform some numerical simulations to illustrate our theoretical results.
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    Approximation and stability results for the parabolic FitzHugh-Nagumo system with combined rapidly oscillating sources
    (2025) Cerpa Jeria, Eduardo Esteban; Courdurier, Matías; Hernandez, Esteban; Medina, Leonel E.; Paduro Williamson, Esteban Andres
    The use of high-frequency currents in neurostimulation has received increased attention in recent years due to its varied effects on tissues and cells. Neurons are commonly modeled as nonlinear systems, and questions such as stability can thus be addressed with well-known averaging methods. A recent strategy called interferential currents uses electrodes delivering sinusoidal signals of slightly different frequencies, and thus classical averaging (well-adapted to deal with a single frequency) cannot be directly applied. In this paper, we consider the one-dimensional FitzHugh-Nagumo system under the effects of a source composed of two terms that are sinusoidal in time and quadratically decaying in space. To study this setting we develop a new averaging strategy to prove that, when the frequencies involved are sufficiently high, the full system can be approximated by an explicit highly-oscillatory term plus the solution of a simpler -- albeit non-autonomous -- system. This decomposition can be seen as a stability result around a varying trajectory. One of the main novelties of the proofs presented here is an extension of the contracting rectangles method to the case of parabolic equations with space and time-depending coefficients.