HHT has not been put forward for long time, so it contains some theoretical problems, such as envelop and meancurve fit, boundary effect, modes mix and so on.
HHT刚提出不久，其理论本身还存在不少问题，如包络线和均值曲线的拟合、边界效应和模态混叠等问题。
2
There are 6 interconnected crossing Bridges (one is preserved) and among them there is one special large bridge. The circular min meancurve is 1000 meters and the Max slope is 3%.
全线设有互通立交6处(其中一处预留)，特大桥一座，最小平曲线半径1000米，最大纵坡3%。
3
You know it's automatically OK because if you have a closed curve, then the vector field is, I mean, if a vector field is defined on the curve it will also be defined inside.