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• n  where the air is unconfined

• outdoors
• out-of-doors
• open

News & Articles

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• Atomic Clocks Are Getting Even More Accurate
  The ultimate accessory in exact timekeeping — the atomic clock — is set to become even more precise, after ultrashort laser pulses were successfully transmitted across open air to help synchronize the "ticking" of new optical atomic clocks.
  June 17, 2013 - Business Insider