Adaptive stabilization of second-order systems with bounded time-varying coefficients

Concerns the problem of adaptive stabilization for a class of second-order time-varying systems under full-state feedback. Interpreting the system states as position and velocity, the system is assumed to have unknown, time-varying damping and stiffness coefficients, which are assumed only to be piecewise continuous and bounded. Furthermore, these bounds need not be known. The novel aspect of the controller is the fact that global convergence is guaranteed under nonparametric assumptions about the time-variation