Is it appropriate to apply for the same job twice if it's re-advertised?
Give them a call. Only they know if/why they rejected you the first time or simply didn't get to your application.
It might be good to consider the channels through which you've seen the application both times. If the first time was through the institute's official website, and the second time through a third party source, it may be that the third party didn't know the job ad was filled.