It follows from the expression of the first moment that β β ( ⟨ ⟨ E ⟩ ⟩ ) = m / ⟨ ⟨ E ⟩ ⟩ , while from the second central moment, ⟨ ⟨ ( Δ Δ E ) 2 ⟩ ⟩ = ⟨ ⟨ E ⟩ ⟩ 2 / m . Introducing these two expressions into the expression of the structure function evaluated at the mean value of the energy leads to