When I saw the pink energy shields in the power core of Theed, I understood them to be doors that close and open at set intervals. Apparently from what other people are saying, these doors are being seen as something else. Mr. Lucas has become aware of this and, perhaps jokedly or not, he promises to make the doors clearer in a future special edition of "The Phantom Menace".
It could be taken that Qui-Gon was using the Force to deactive them after Maul used the Force to activate them. I thought this when Qui-Gon kneeled and shut his eyes. But the way Maul is pacing it is clear that no battle of the Force is taking place and the shields are timed. Maul is simply waiting and Qui-Gon is probably ridding his fear and focusing his concentration.
Well, I'm not real sure what they were at all, either, but the impression I got the first time I saw them was that Qui-Gon felt himself losing his concentration and control, so activated them to give himself a chance to calm down--hence the meditation he went into. Perhaps also he hoped to give Obi Wan a chance to relax as well. *shrugs* I'm reading the novel now. Maybe it will say.
------------------ Clones are People Two
"The Force is like duct tape: it has a dark side and a light side, and it holds the universe together" ([[[[[[*]}»»»»»»»»»»»»»»»»»»»»»»»»»