   f^{\mu} = - 8\pi  { G \over { 3 c^4   }   } \left (  {A \over 2} T_{\alpha \beta}  + {B \over 2} T \eta_{\alpha \beta} \right ) \left ( \delta^{\mu}_{\nu} + u^{\mu} u_{\nu} \right )  u^{\alpha} x^{\nu} u^{\beta} 