I understand the impulse to separate the two, but I think in reality it gives you much more dimension and humanity if you enact multiple identities simultaneously on Twitter. Would you not talk about your family with your students? Share a joke? Give an opinion? If you would do these things in real life, it's perfectly acceptable on Twitter. That said, I have two accounts, because one of them is an institutional account: @PalmerMuseum. My Palmer tweets are exclusively about the museum—they represent the museum and not me. So if you are going to disseminate info, announce events/deadlines, etc., then you might consider a separate account. I'll follow you either way. : )