The "hat" distinguishes symmetry operations from symmetryelements.
“帽号”用来将对称操作与对称元素区别开。
2
The geometric structure of carbon nanotubes (CNTs) is introduced, the symmetry of zigzag and armchair CNTs is analyzed and these symmetryelements are abstracted and summarized.
Note that even though these two design elements (and a few more throughout the site) add visual interest, they still balance each other out to maintain symmetry in the design.