Density map of collision between domain wall and a bubble-droplet state. It is seen that the bubble-droplet transit to be a droplet-bubble state after colliding with the domain wall, and the domain wall keeps unchanged. This suggests that particle transition happens greatly and fast during the colliding process. The parameters are λ 1 = λ 3 = 0.4 , λ 2 = 0.6 , k 1 = k 2 = 1 , c 1 = c 2 = 3 , − α 1 = α 2 = α 3 = 3 .