In this October 15, 2014 file photo, Katsu Nakamura, sky division manager for Yamaha USA, moves the RMax unmanned helicopter into position before a demonstration of its aerial application capabilities at the University of California, Davis' Oakville Station test vineyard in Oakville, Calif. Researchers at UC Davis have been studying the effectiveness of the drone's ability for spraying pest control and nutritional materials on the test vineyard in California's Napa Valley. (Photo by Rich Pedroncelli/AP Photo)

French twins Thomas and Vincent (L) Seris take the tram in Bordeaux, November 12, 2014. Born with Xeroderma Pigmentosum (XP), the twins cannot be exposed to the sun and its ultraviolet (UV) light, which could provoke precocious cancers due to an autosomal recessive genetic disorder of DNA repair. Colloquially referred to as Children of the Night (Les Enfants de la Lune) the Seris twins are among 70 to 80 people in France who suffer from the genetic defect. The French association “Les Enfants de la Lune” reports that there are between five and ten thousand such cases in the world. Thomas and Vincent have been testing a new protective mask for the last year which is transparent and ventilated and developed by several hospitals in France. (Photo by Regis Duvignau/Reuters)

Opposition students march against Venezuelan President Nicolas Maduro's government in Caracas February 12, 2015. Venezuelan troops blocked students during marches against Maduro on Thursday as pro-government supporters also rallied on the anniversary of 2014 protests that led to 43 deaths. In Caracas, troops cordoned off scores of students on an unauthorized march to a church where they planned a mass in honour of demonstrators who died. (Photo by Jorge Silva/Reuters)

In this photograph taken on April 1, 2015, an Indonesian resident and child walk away from an abandoned school building as Mount Sinabung erupts in Karo district on the Indonesian island of Sumatra. According to authorities about 3,500 people were displaced after the February 2014 eruption of Mount Sinabung volcano and many are still living in evacuation centers as the volcano remains active. (Photo by Sutanta Aditya/AFP Photo)

A Uyghur boy sits atop a horse as he has his picture taken outside the Id Kah Mosque before the Eid holiday on July 28, 2014 in old Kashgar, Xinjiang Province, China. Nearly 100 people have been killed in unrest in the restive Xinjiang Province in the last week in what authorities say is terrorism but advocacy groups claim is a result of a government crackdown to silence opposition to its policies. China's Muslim Uyghur ethnic group faces cultural and religious restrictions by the Chinese government. Beijing says it is investing heavily in the Xinjiang region but Uyghurs are increasingly dissatisfied with the influx of Han Chinese and uneven economic development. (Photo by Kevin Frayer/Getty Images)

A man walks down a flooded road in Islip, New York August 13, 2014. More than a foot of rain hit parts of New York's Long Island on Wednesday, enough to set a preliminary state record, triggering flash floods and swamping cars on major roads that were turned into rivers during the morning rush hour. (Photo by Lucas Jackson/Reuters)

Dynam employees say a greeting message as they receive customer-care training ahead of the grand opening of the company's pachinko parlour in Fukaya, north of Tokyo July 29, 2014. Japan's once-booming pachinko industry, grappling with a greying customer base and the threat of new competition from casinos, is adopting a softer touch and smoke-free zones to lure a new generation of players, particularly women. Pachinko, a modified version of pinball, is a fading national obsession, with about 12,000 parlours nation-wide and one in thirteen people playing the game. But that figure is declining as the population shrinks and younger people prefer games on their mobile phones. (Photo by Issei Kato/Reuters)

Abdulahi Yaroow, 13, smokes a cigarette while chewing khat at the same time in Mogadishu August 10, 2014. Grown on plantations in the highlands of Kenya and Ethiopia, tonnes of khat, or qat, dubbed “the flower of paradise” by its users, are flown daily into Mogadishu airport, to be distributed from there in convoys of lorries to markets across Somalia. Britain, whose large ethnic Somali community sustained a lucrative demand for the leaves, banned khat from July as an illegal drug. This prohibition jolted the khat market, creating a supply glut in Somalia and pushing down prices, to the delight of the many connoisseurs of its amphetamine-like high. (Photo by Thomas Mukoya/Reuters)