@article{EXMA_2006__15_3_225221,
     author = {Antunes, Pedro and Freitas, Pedro},
     title = {New bounds for the principal {Dirichlet} eigenvalue of planar regions.},
     journal = {Experimental mathematics},
     pages = {333--342},
     publisher = {mathdoc},
     volume = {15},
     number = {3},
     year = {2006},
     zbl = {1180.35388},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EXMA_2006__15_3_225221/}
}