* 2nd International Conference on Discrete Element Methods, Editors Williams, J.R. and Mustoe, G.G.W., IESL Press, 1992 ISBN 0-918062-88-8==Software==Open source and non-commercial software:*Ascalaph Molecular dynamics with fourth order symplectic integrator.
* 2nd International Conference on Discrete Element Methods, Editors Williams, J.R. and Mustoe, G.G.W., IESL Press, 1992 ISBN 0-918062-88-8* Williams, J.R. and O’Connor, R., "Discrete Element Simulation and the Contact Problem," Archives of Computational Methods in Engineering, Vol.