Chaotic Pulse Trains. - Neil J. Balmforth; Glenn R. Ierley; Edward A. Spiegel (SIAM J. Appl. Math., 1994)

Instability of Rapidly Rotating Polytropes. - Neil J. Balmforth; L. N. Howard; Edward A. Spiegel (SIAM J. Appl. Math., 1995)