  To investigate an effect of social interaction on the bystanders'
intervention in emergency situations a rescue model was introduced which
includes the effects of the victim's acquaintance with bystanders and those
among bystanders from a network perspective. This model reproduces the
experimental result that the helping rate (success rate in our model) tends to
decrease although the number of bystanders $k$ increases. And the interaction
among homogeneous bystanders results in the emergence of hubs in a helping
network. For more realistic consideration it is assumed that the agents are
located on a one-dimensional lattice (ring), then the randomness $p \in [0,1]$
is introduced: the $kp$ random bystanders are randomly chosen from a whole
population and the $k-kp$ near bystanders are chosen in the nearest order to
the victim. We find that there appears another peak of the network density in
the vicinity of $k=9$ and $p=0.3$ due to the cooperative and competitive
interaction between the near and random bystanders.
