Now introduce diffusion only I diffuses, other components are local a/(x,) a1(, t) -kI(x, t)+k,s(x, t)+D at assume signal S varies linearly with S S(x)=S。+Sx no flux boundary conditions for a(0,)a/(,2) 0 ax in steady state this system can be solved analyticallyNow introduce diffusion: - only I diffuses, other components are local 2 2 ( , ) ( , ) ( , ) ( , ) x I x t k I x t k S x t D t I x t I I ∂ ∂ = − + + ∂ ∂ − - assume signal S varies linearly with S S x s s x o 1 ( ) = + - no flux boundary conditions for I 0 ( 0, ) ( 1, ) = ∂ ∂ = ∂ ∂ x I t x I t in steady state,this system can be solved analytically ! 10