George Washington wrote:
Thank you for Mr. Heller's outstanding article, Taking a Closer Look: Hard Science and the Collapse of the World Trade Center.

I have been researching and writing on 9-11 for years (see for example this summary) and this is the single best article I've read on the physics behind controlled demo of the world trade center. It makes the anomolies apparent even for someone with no physics training, and puts it together in a more intuitive way than even Jim Hoffman has done.