The most difficult tech­nolo­gies riddles

On Dec. 6, 1923, the first presidential address was broadcast on the radio. President Calvin Coolidge delivered what is now known as the State of the Union address to a joint session of Congress. Mr. Coolidge was known as a quiet man, but he was the first president to use the medium of radio to his advantage.

Jan Koum is a Ukrainian American computer programmer. In January 2009, Koum bought an iPhone and realized that the then seven-month-old App Store was about to spawn a whole new industry of apps. He visited his friend Alex Fishman and the two talked for hours about Koum's idea for an app. Koum almost immediately chose the name WhatsApp because it sounded like "what's up", and a week later on his birthday, February 24, 2009, he incorporated WhatsApp Inc. in California.

Participants in the Global Game Jam are of all skill levels and in various fields. Everyone from professional game developers to educators to artists and designers is welcome to participate. Once the jam begins, participants come up with game ideas, before pitching those ideas to each other and forming teams to work together on a project.

A run-flat tire is a pneumatic vehicle tire that is designed to resist the effects of deflation when punctured, and to enable the vehicle to continue to be driven at reduced speeds. These tires contain an extra lining within the tire that self-seals in the event of a small hole due to a nail or screw. In this way, the loss of air is prevented from the outset such that the tire is either permanently self-repairing or at least loses air very slowly.