J. Scheer, K. Bruning, T. Frohlich, P. Wurz, and W. Heiland. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 157 (1-4):
208--213(August 1999)
M. Keeler. Proceedings of the 12th International Conference on Conceptual Structures (ICCS 2004), volume 3127 of Lecture Notes in Computer Science, page 242-260. Springer, (2004)