A visitor experiences the Sorakara Point, that uses LED lights and glass walls, to create a space in which the visitors feels they are floating, at the top of Tokyo Sky Tree, the world's tallest self-standing structure, in downtown Tokyo, Japan, 17 April 2012. Tokyo Sky Tree is a telecommunications tower of 634-meters in height that consists of two observatories and commercial facilities. (EPA)

A woman gets off a bus with images on top depicting South American leaders before a demonstration in support of a bill proposed by Argentina's President Cristina Fernandez outside the government house in Buenos Aires, Argentina, April 16, 2012. Fernandez proposed a bill to expropriate 51% of the shares of YPF oil company that is controlled by Spain's Repsol, despite fierce opposition from Madrid. (Natacha Pisarenko/AP Photo )

Marathon runner Connie Robinson reacts as Eytan Nicholson sprays her with mist as she reaches the top of Heartbreak Hill, in Newton, Mass., during the Boston Marathon, April 16, 2012. It was the second-slowest Boston race since 1985, as temperatures rising into the 80s slowed the leaders and may have convinced as many as 4,300 entrants to sit this one out. (Steven Senne/AP Photo)

The Tokyo Sky Tree soars in Tokyo, April 17, 2012. The world's tallest freestanding broadcast structure that stands 2,080 ft. will open to the public in May. (Itsuo Inouye/AP Photo)

Guild riders circle around the "Boeoegg" on the Sechselaeuten meadow in Zurich, Switzerland, April 16, 2012. The ringing of the six o'clock bells is a traditional end of winter festival which includes the burning of the Boeoegg, a symbolic snowman, at 6 pm. According to traditional superstition the faster the Boeoegg burns, the hotter the summer will be. (Steffen Schmidt/AP Photo)

Virginia Tech students pass the flame of a memorial candle, on the Virginia Tech campus in Blacksburg, Va, April 16, 2012. The vigil was one of several events held in observance of the fifth anniversary of the April 16, 2007, shootings on the campus. (Daniel Lin/The Roanoke Times/AP Photo)

Myanmar opposition leader Aung San Suu Kyi greets supporters as she leaves after a visit to her constituency on the occasion of festivities surrounding the country's new year in Kawhmu outside Yangon, April 17, 2012. Suu Kyi was elected in the recent April 1 parliamentary by-elections in a Kawhmu constituency. (Soe Than Win/AFP/Getty Images)

Chinese young athletes practice Taekwondo techniques before the rehearsal of ceremony to mark 100-day countdown to London 2012 Olympic Games outside the Bird's Nest, April 17, 2012 in Beijing, China. The 100-day countdown to London 2012 Olympic Games falls on April 18, 2012.(Feng Li/Getty Images)

A view of a smoke cloud from the Popocatepetl volcano as seen from the San Andres Cholula town, Puebla state, Mexico, April 16, 2012. The volcano has been emitting a constant emission of gas and water vapor between 500 and 1000 meters in height according to a report from the National Center for Disaster Prevention. (EPA)