in agreement with earlier definition κ κ ( θ θ → → ) = Σ Σ Σ Σ c r as the ratio of projected density with the critical density. Here we used ∇ ∇ 2 1 / r = − − 4 π π δ δ ( r ) and ∇ ∇ θ θ → → = D d ∇ ∇ .