spherical shell的用法和样例：
例句
- The compatible boundary conditions are evidently uniform tractions applied on the inner and outer surfaces of the shell.
可相容的边值条件显然是作用在球壳的内表面和外表面上的均匀曳力。 - Light emitted from the inner surface of a spherical shell, for instance, satisfies that requirement.
唯一的条件是，这道想像的光束一开始是会聚的，例如从球壳内层表面发出的光就满足这个条件。
