Equilibria in transition

We investigate the motion of a single particle in transition from one equilibrium state to another via time-frequency analysis. Between quasi-stationary regimes a sudden change of state occurs, and we show that the Cohen-Lee local variance tracks well this highly nonstationary, sudden transient motion. In the quasi-stationary regime, instantaneous equilibria yield simple harmonic motion when the amplitude of oscillation is sufficiently small. Nonlinear effects induce harmonic generation for larger amplitude oscillations.