Chang's said roughly 1 million people clicked, recirculated or otherwise interacted with the Twitter ad.

WSJ: Twitter's Mobile Ads Begin to Click

The recirculated air usually passes through high-efficiency particulate (HEPA) filters before delivery into the cabin.

CNN: Commentary: Flu and your health on a plane

To minimize the risk of disease spread by aircraft, regulations requiring HEPA filters for any aircraft that uses recirculated air should be seriously considered.

CNN: Commentary: Flu and your health on a plane

But he said there was no evidence air conditioning systems in buildings, or the recirculated air on planes, was involved in the spread of the disease.

BBC: Scientists home in on mystery bug

The EPA pulled off the feat by sharply increasing the amount of oxygen-poor exhaust that is recirculated into the combustion chamber and increasing the pressure of the fuel being forced into the cylinder.

FORBES: EPA, Inc.

Ventilation can involve either 100 percent fresh air in which outside air enters and leaves the cabin in a single pass or a system in which various fractions of air are recirculated from the aircraft cabin and mixed with fresh air.

CNN: Commentary: Flu and your health on a plane

In the wake of Lin's historic New York explosion, Weiland's eerily prescient post has quickly recirculated around the Internet, as a rare example of someone who saw potential in a player who wasn't drafted and was abandoned by two teams before getting a chance with the Knicks.

WSJ: Jeremy Lin and the Guy Who Saw Linsanity Coming