Quasi-local energy-momentum and energy flux at null infinity
  The null infinity limit of the gravitational energy-momentum and energy flux determined by the covariant Hamiltonian quasi-local expressions is evaluated using the NP spin coefficients. The reference contribution is considered by three different embedding approaches. All of them give the expected Bondi energy and energy flux. 
Xiaoning Wu, Chiang-Mei Chen and James M. Nester