Other papers
Du Xinxing, 1997
Madhava Rao and Kaila, 1986
Liritzis and Tsapanos, 1992
Periodicities
7; 14; 22 and 42 years.
3 to 12 years.
3; 4.5; 6.5; 8; 9; 14 - 20
and 31 - 34 years.