Equation Icon  ΔX (x, t) ---------= sX(¯ϕ)[¯ϕ(t) − ϕ0] + {sX (¯ϕ) + s′X(¯ϕ )[¯ϕ(t) − ϕ0]}δϕ(x,t) X0 ≡ sX(¯ϕ)Δ ¯ϕ + 𝒮X (¯ϕ)δϕ (x, t). (223 )