@article{CRMATH_2007__344_3_169_0,
     author = {Hamel, Fran\c{c}ois and Nadirashvili, Nikolai and Russ, Emmanuel},
     title = {Some isoperimetric problems for the principal eigenvalues of second-order elliptic operators in divergence form},
     journal = {Comptes Rendus. Math\'ematique},
     pages = {169--174},
     publisher = {Elsevier},
     volume = {344},
     number = {3},
     year = {2007},
     doi = {10.1016/j.crma.2006.11.025},
     language = {en},
     url = {http://www.numdam.org/articles/10.1016/j.crma.2006.11.025/}
}