Bosnian men urge their horses to pull logs up a hill during a competition in the Bosnian town of Sokolac 50 kms west of Sarajevo, Bosnia,on Monday, April, 13, 2015. The annual festival celebrates the centuries old tradition of pulling logs honoring the owners of the strongest horses. Owners of the horses gather from all over Bosnia and beyond, and compete in a show of horse strength. (Photo by Amel Emric/AP Photo)

A solar-powered plane takes off from Jiangbei International Airport in southwest China's Chongqing Municipality, Tuesday, April 21, 2015. The Solar Impulse 2 departed Chongqing on Tuesday for a 1190-kilometer (642-mile) flight to the city of Nanjing in eastern China, the sixth leg of its around-the-world flight. (Photo by Chinatopix via AP Photo)

“Mountain Goats, Colorado”. A herd of mountain goats huddle together on top of Mount Evans, Colorado during a lightning storm. This photo was selected out of more than 5,000 entries to go on display in “Wilderness Forever: 50 Years of Protecting America’s Wild Places”, a new photo exhibition at the Smithsonian’s National Museum of Natural History, which will run through summer 2015. (Photo by Verdon Tomajko/Smithsonian Wilderness Forever Photo Contest)

Matthias Broda, inventor and designer of the wooden e-bike, cycles a prototype along a street in Berlin, November 20, 2014. The wooden e-bike produced by German company Aceteam from ash wood, will be launched on the market by spring 2015 and will cost around 3,950 euro (4,950 dollars). The e-bike will be equipped with an 250W e-bike motor for a range of up to 100 kilometer (62 miles) with a rechargeable battery. (Photo by Fabrizio Bensch/Reuters)

A woman sings as Tibetans celebrate the 80th birthday of their spiritual leader, the Dalai Lama, in Kathmandu, Nepal, Monday, July 6, 2015. Around 1,000 monks and other Tibetans gathered at the school compound to celebrate their spiritual leader's birthday. Exiled Tibetans allowed celebrating the Dalai Lama's birthday only inside school compound and refugee camps as long as the facilities do not contain slogans or banners protesting against China. Nepalese government has banned all kinds of Tibetan activities against Chinese rule in Tibet. (Photo by Niranjan Shrestha/AP Photo)

A young fan cheers while waiting for the ticker tape parade to celebrate the U.S. women's soccer team World Cup victory, Friday, July 10, 2015, in New York. The World Cup winning U.S. women's football team rolled up New York City's “Canyon of Heroes” on Friday, with a blizzard of confetti swirling overhead in the first ticker-tape parade honouring a women's sports team. (Photo by Adam Hunger/AP Photo)

A motorcycle modified to run on rails is seen inside a tunnel connected to the Altiplano Federal Penitentiary and used by drug lord Joaquin “El Chapo” Guzman to escape, in Almoloya de Juarez, on the outskirts of Mexico City, July 15, 2015. U.S. law enforcement officials met with agents of the Mexican attorney general's office this week to share information related to the escape from prison of Guzman and coordinate efforts to apprehend him, a Mexican government official said on Wednesday. (Photo by Edgard Garrido/Reuters)

A Hindu woman gives money to an elephant outside the Lord Jagannath temple ahead of the annual Rath Yatra, or chariot procession, in Ahmedabad, India, July 16, 2015. The annual religious procession commemorates a journey by Hindu god Jagannath, his brother Balabhadra and sister Subhadra, in specially made chariots. The annual Rath Yatra is celebrated on July 18. (Photo by Amit Dave/Reuters)