Spherical partial differential equation with non‐constant coefficients for modeling of nonlinear unsteady heat conduction in functionally graded materials. - Delouei, Amin Amiri; Emamian, Amin; Ghorbani, Saeed; He, Fuli (ZAMM -- Journal of Applied Mathematics & Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik, 2024)