@article{10_4153_CMB_2001_027_9,
     author = {Cheung, Wai-Shun and Li, Chi-Kwong},
     title = {Linear {Operators} {Preserving} {Generalized} {Numerical} {Ranges} and {Radii} on {Certain} {Triangular} {Algebras} of {Matrices}},
     journal = {Canadian mathematical bulletin},
     pages = {270--281},
     year = {2001},
     volume = {44},
     number = {3},
     doi = {10.4153/CMB-2001-027-9},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-2001-027-9/}
}