Officials have urged opposition leaders to move Monday's rally to a field outside of Islamabad's center to improve security.

VOA: standard.2009.03.14

If we put a dipole that has the freedom to move, we put that dipole in an electric field, it will align itself with the field lines.

若我们将偶极释放到自由空间中，比如说放到电场里，他们会自动排序按同一方向。

麻省理工公开课 - 固态化学导论课程节选