Calder's three top teen acts rely heavily on Max Martin, a producer in Calder's stable.

FORBES: Jive Talking

To study them, Martin Dresler, of the Max Planck Institute of Psychiatry, in Munich, and his colleagues recruited a group of what are known as lucid dreamers.

ECONOMIST: Reading the brain

At present the K-MAX has no defensive systems, but Lockheed Martin says the helicopters could easily be fitted with armour, machine-gun pods or flares which could be fired as decoys to divert ground-launched missiles.

ECONOMIST: Autonomous helicopters