The Levitating Liquid Pendulum : how can rapidly shaking a liquid make unstable layers sable ⇔ rapidly shaking a pendulum make the top equil. pos. stable - Steve Mould
A Pendulum Theorem : small and fast vertical oscillations can stabilize a chain of N inverted pendulums - Acheson 1993
Inverted oscillations of a driven pendulum - Clifford, Bishop, 1997
The parametrically excited upside-down rod : an elastic jointed pendulum model