This paper considers nonlinear dynamics of plasma oscillations modeled by an anharmonic oscillator. These plasma oscillations are described by a nonlinear differential equation of the form ẍ + ͑1+x 2 ͒ẋ + x + x 2 + ␦x 3 = F cos ⍀t. The amplitudes of the forced harmonic, superharmonic, and subharmonic oscillatory states are obtained using the harmonic balance technique and the multiple time scales method. Admissible values of the amplitude of the external strength are derived. Bifurcation sequences displayed by the model for each type of oscillatory states are performed numerically through the fourth-order Runge-Kutta scheme.

We investigate in this paper different states of synchronization in a ring of mutually coupled self-sustained electrical oscillators. The good coupling parameters leading to complete and partial synchronization or disordered states are calculated using the properties of the variational equations of stability. A stability map showing domains of synchronization to an external excitation locally injected in the ring is also obtained. In both cases, the numerical simulation validates and complements the results of the analytical investigation.

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We analyze the stability and optimization of the synchronization process between two coupled self-excited systems modeled by the multi-limit cycles van der Pol oscillators through the case of an enzymatic substrate reaction with ferroelectric behavior in brain waves model. The one-way and two-way couplings synchronization are considered. The stability boundaries and expressions of the synchronization time are obtained using the properties of the Hill equation. Numerical simulations validate and complement the results of analytical investigations.