The following is a brief guide to the use of volunteers and interns under federal law.

FORBES: Using Volunteers and Interns: Is It Legal?

In 1998, Hawking published "A Brief History of Time, " a layman's guide to the origins of the universe.

CNN: Ask Stephen Hawking a space question

" The American Medical Association's guide for physicians says studies show "a clear link between brief exposure to violence on TV or movies and increases in aggressive and even physically violent behavior in young persons.

WSJ: Campbell Brown: The President Gives Hollywood a Pass on Violence