Wenjun Sun, Song Jiang and Kun Xu. (2017). An Implicit Unified Gas Kinetic Scheme for Radiative Transfer with Equilibrium and Non-Equilibrium Diffusive Limits.
            <i>Communications in Computational Physics</i>. <i>22</i> (4).
            889-912.
         doi:10.4208/cicp.OA-2016-0261