1. van den Berg, M.: Estimates for the torsion function and Sobolev constants. Potential Anal. 36, 607–616 (2012)
2. van den Berg, M., Buttazzo, G., Pratelli, A.: On the relations between principal eigenvalue and torsional rigidity, preprint (2019), available at arXiv:1910.14593
3. van den Berg, M., Ferone, V., Nitsch, C., Trombetti, C.: On a Pólya functional for rhombi, isosceles triangles, and thinning convex sets, preprint (2018), available at arXiv:1811.04503
4. van den Berg, M., Ferone, V., Nitsch, C., Trombetti, C.: On Pólya’s inequality for torsional rigidity and first Dirichlet eigenvalue. Integral Equ. Oper. Theory 86, 579–600 (2016)
5. Brasco, L.: On principal frequencies and isoperimetric ratios in convex sets, to appear on Ann. Fac. Sci. Toulouse Math., available at http://cvgmt.sns.it/paper/3891/