 You're listening to Unexpected Elements from the BBC World Service. So far, we've been talking about presidential jet lag, bizarre migrations and taking the long way around. So I think we've established that travelling takes its toll. And I wanted to talk to someone who knows a thing or two about it. Rosemary Brown is an associate professor at Northwestern University who's looked into how we might be able to prevent jet lag. And she joins me now. Hello, Rosemary.