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

You can blame Republicans who won't pass a budget, or Democrats who spend every single cent of tax money that comes in during the booms, borrow some more and then act all surprised when revenues, in a totally unprecedented, inexplicable and unforeseeable chain of events, fall during a recession.

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One of these tricks is the ability to swivel its instrument in quick time to acquire a strip, or mosaic, of images around its target in a single pass overhead.

BBC: Sharp-eyed Pleiades returns first pictures