A single-particle breakage model is constructed with material mechanics.Fragmentation of two-dimensional grains under applied pressures is simulated with molecular dynamics.It demonstrates that ultimate grain size distributions follow a power-law distribution with a fractal dimension of about 1.1,which indicates that fragmentation processe of two-dimensional grains is a fractal process.

Effect of limited velocity on traffic flow is studied with cellular automaton.The simulation indicates that a saturated traffic flow determined by limited speed exists.The limited velocity results in various phase separations.In a fixed model,as the car density is low,two free-flow phases occur.As the density is high,a separation of maximum traffic flow phase from a free flow phase is observed.In an random model,as the density is high,a maximum flow-jamming-free flow appears.The traffic flow and critical density are given.