@article{EMJ_2013_4_3_a6,
     author = {P. D. Lamberti and L. Provenzano},
     title = {A maximum principle in spectral optimization problems for elliptic operators subject to mass density perturbations},
     journal = {Eurasian mathematical journal},
     pages = {70--83},
     publisher = {mathdoc},
     volume = {4},
     number = {3},
     year = {2013},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EMJ_2013_4_3_a6/}
}