Heat conduction in a Newtonian context is modelled by the Fourier equation, namely a parabolic partial differential equation of the kind: ∂ ∂ θ θ ∂ ∂ t = α α ∇ ∇ 2 θ θ , where θ is temperature, t is time, α = k /(ρ c) is thermal diffusivity, k is thermal conductivity, ρ is density, and c is specific heat capacity. The Laplace operator, ∇ ∇ 2 , is defined in Cartesian coordinates as ∇ ∇ 2 = ∂ ∂ 2 ∂ ∂ x 2 + ∂ ∂ 2 ∂ ∂ y 2 + ∂ ∂ 2 ∂ ∂ z 2 .