Before revision:  The model involves two quantities , the level of social unrest, or , more general, activity u, and a field of social tension v, which play asymmetric roles : u is thought of as the actual observed or explicit quantity while v is an ambiant, sometimes implicit  field of susceptibility that modulates the growth of u.
After revision:  The model involves two quantities , the level of social unrest, or , more general, activity u, and a field of social tension v, which play asymmetric roles : u is thought of as the actual observed or explicit quantity while v is an ambiant, sometimes implicit field of susceptibility that modulates the dynamics of u.