a strange problem on DPM model
 

I happen to a strange problem on DPM model.

This problem is that.

DEFINE_DPM_EROSION(dpm_accr, p, t, f, normal, alpha, Vmag, Mdot)

I want to know the meaning of Mdot
For example，the total flow rate = 6e-6 kg/s，step time=0.1 The particles are uniform distributing；the number of net at in inlet of the particles are 10.
when step time=0.1，Mdot=6e-8；
when step time=0.01，Mdot=6e-9；
what is meaning about the Mdot? is there some relationships among total flow rate,step time and Mdot？
Thanks for your help！

I also wanna know the differences between P_FLOW_RATE(p) and Mdot？