1. Ashbaugh, M.S.: Isoperimetric and universal inequalities for eigenvalues. In: Spectral theory and geometry (Edinburgh, 1998), London Math. Soc. Lecture Note Ser., 273, Cambridge: Cambridge Univ. Press, 1999, pp. 95–139
2. Ashbaugh M.S., Benguria R.: Sharp upper bound to the first nonzero Neumann eigenvalue for bounded domains in spaces of constant curvature. J. London Math. Soc. (2) 52(2), 402–416 (1995)
3. Ashbaugh M.S., Benguria R.: On Rayleigh’s conjecture for the clamped plate and its generalization to three dimensions. Duke Math. J. 78, 1–17 (1995)
4. Ashbaugh M.S., Laugesen R.S.: Fundamental tones and buckling loads of clamped plates. Ann. Scuola Norm. Sup. Pisa Cl. Sci. (4) 23(2), 383–402 (1996)
5. Bandle C.: Isoperimetric Inequalities and Applications. Pitman Advanced Publishing Program, Boston-London-Melbourne, Pitman (1980)