Nowhere-differentiable attractors. - Otto E. Rössler; C. Knudsen; John L. Hudson; Ichiro Tsuda (Int. J. Intell. Syst., 1995)

Catastrophe Theoretic Classification of Nonlinear oscillators. - A. Yu. Kuznetsova; Alexander P. Kuznetsov; C. Knudsen; Erik Mosekilde (Int. J. Bifurc. Chaos, 2004)