Fully Threaded Transport Engine: New Method for Multi-Scale Radiative   Transfer
  A new, very fast method for 3D radiative transfer on fully threaded grids with arbitrarily high angular resolution is presented. The method uses completely cell-based discretization, and is ideally suited for problems with diffuse background radiation, often encountered in cosmological and star formation models. We find that for accurate statistical study of intergalactic Ly-alpha absorption lines one needs of order of few hundred angular discretization elements even for models without radiative feedback from star forming galaxies. 
A. O. Razoumov, C. Y. Cardall