coupling mechanism between upper level and low level jet
fiscal system at county level and township level
interaction between upper level and lower level
municipal level and county level
Talbot s law
塔波特定律：当两点完全融合而感觉一致时
视神经盘所接受的光量必定均匀一致
故两点的光强度应相同
Talbot s root canal reamer