"In this Oct. 25, 2012 photo, Zac Vawter kicks a soccer ball with an experimental ""bionic"" leg as biomedical student Aaron Young makes adjustments to the leg at the Rehabilitation Institute of Chicago. After losing his right leg in a motorcycle accident, the 31-year-old software engineer signed up to become a research subject, helping test a trailblazing prosthetic leg that's controlled by his thoughts. He will put this leg to the ultimate test Sunday, Nov. 4 when he attempts to climb 103 flights of stairs to the top of Chicago's Willis Tower, one of the world�s tallest skyscrapers. (AP Photo/Brian Kersey)"
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