Chang, Yao-Chang, and Leszek Demkowicz. “Vibrations of a Spherical Shell. Comparison of 3-D Elasticity and Kirchhoff Shell Theory Results”. Computer Assisted Methods in Engineering and Science, vol. 2, no. 3, July 2023, pp. 187-06, https://cames3.ippt.pan.pl/index.php/cames/article/view/1472.