Furthermore it must state that you have been officially invited as a student/researcher as well as describing possible ongoing or planned cooperation between the host institution and your home institution 为博士留学（短期客座性质）说明，host institution指的是接收你的那所外国大学，而home institution是你在国内作为博士或博士后学习或工作的大学。如何翻译得好一点。