@PhdthesisMisc{G09_846, author = {Gisela Widmer}, title = {Sparse finite elements for radiative transfer}, note = {Dis_no 18420, Prof. Dr. Ralf Hiptmair}, school = {ETH Z{\"u}rich}, doi = {http://dx.doi.org/10.3929/ethz-a-005916456}, year = {2009} }