His early numerical calculations (with G. Shaviv) of a rotating gas sphere gravitational collapse (1980) were the first to show that a central object (a star) is formed surrounded by a protoplanetary disk-like nebula, provided turbulent viscosity is included. Together with J.R. Buchler he found a simplistic model of a stellar oscillator that exhibited chaotic pulsation. This oscillator was later found to be related to the Moore-Spiegel oscillator.
