The properties of Bell number in proper order are studied with the use of elementary method, some identities involving the sum of product of Bell number in proper order are obtained.
利用初等方法研究了有序贝尔数的性质，给出了关于有序贝尔数的一组恒等式。
2
The thickness of the famous ancient "Great bell" in Beijing was for the first time measured with ultrasonic method.
利用超声测厚的方法第一次测定了北京永乐古钟的壁厚。
3
A contact analytical modal of hanging rod linking big bell in blast furnace was built in finite element method (FEM) according to fatigue reasons of hanging rod linking big bell.