2-Medians in trees with pos/neg weights. - Rainer E. Burkard; Eranda Çela; Helidon Dollani (Discret. Appl. Math., 2000)

Linear Approximations in a Dynamic Programming Approach for the Uncapacitated Single-Source Minimum Concave Cost Network Flow Problem in Acyclic Networks. - Rainer E. Burkard; Helidon Dollani; Phan Thien Thach (J. Glob. Optim., 2001)

Robust location problems with pos/neg weights on a tree. - Rainer E. Burkard; Helidon Dollani (Networks, 2001)

The Obnoxious Center Problem on a Tree. - Rainer E. Burkard; Helidon Dollani; Yixun Lin; Günter Rote (SIAM J. Discret. Math., 2001)

A Note on the Robust 1-Center Problem on Trees. - Rainer E. Burkard; Helidon Dollani (Ann. Oper. Res., 2002)

Center problems with pos/neg weights on trees. - Rainer E. Burkard; Helidon Dollani (Eur. J. Oper. Res., 2003)