Science fans, assemble! The world’s top superhero team is back to save the world in “Avengers: Age of Ultron.” And these superheroes use some super science to help them keep the bad guys in check. This week, Reactions looks at the chemistry of the Avengers, including Tony Stark’s suit, Captain America’s shield and Black Widow’s super-fast healing. For more on Superhero science, check out Jim Kakalios' book, The Physics of Superheros: http://amzn.to/1dobcl4.