An invisible force field that punches sharks in the face

This summer, 61-year-old distance swimmer Diana Nyad will be attempting a 103-mile swim through the shark-populated waters separating Cuba and Florida — and she'll be doing it without a shark cage. Instead, the marathon swimmer will be accompanied by an electronic shark-deterrent device called Shark Shield, which… » 8/05/11 5:02pm 8/05/11 5:02pm