1. The problem statement, all variables and given/known data I'm trying to figure out what exactly this equation (the one inside the red box) means for this article. The whole article is the attached PDF. 2. Relevant equations 3. The attempt at a solution I've been looking at this article for 2 days now and I'm doing OK for the most parts I think but I'm really stuck on this equation. I think that it has something to do with figures 8-10 in the article but how exactly, not so sure. Please help me.