inlet diffusion in the species transport
 

Hi

I'm trying to solve the species transport equation of two species in a channel.
But, I don't know what the inlet diffusion means at the species model panel option.

1. what is the meaning of the inlet diffusion?
2. should i check this option or not?

I have also doubt with option tab in species model.
what is the use of the different diffusion? please explain that diffusion options.