全纯函数-后退的反义词

tional Assembly. That puts it in a strong position to launch a referendum to recall the president, Nicolás Maduro. This is the first election the government has lost since Hugo Chávez, Mr Maduro’s predecessor, took power in 1999. See article.

Colombia’s government discovered the wreck of a Spanish galleon near Cartagena. The San José was sunk by the British navy in 1708 during the war of the Spanish succession. Its cargo of gold, silver and jewels is thought to be worth anywhere from $$1 billion to $$17 billion. The Spanish government believes the ship and its contents belong to Spain.

Douglas Tompkins, an entrepreneur who co-founded the North Face and Esprit clothing companies, died in a kayaking accident in Chile. After he sold his firms, Mr Tompkins bought large tracts of land in Chilean and Argentine Patagonia to protect them from development. Conservative Chileans accused him of appropriating land that belonged to the country.

On the march
The far right National Front achieved a spectacular result in the first round of regional elections in France, securing around 30% of the nationwide vote and eating into the Socialists’ heartland in the north of the country. It leads in six out of 13 contests ahead of the second round on December 13th. The election played out against the backdrop of the terror attacks in Paris and the refugee crisis in Europe.

Laimdota Straujuma resigned as prime minister of Latvia amid public spats in her centre-right Unity party over refugees and transport policy. Parliament will now go about forming a new government, which is expected to exclude the pro-Russian Harmony party.

A right royal rumble
Authorities in Thailand are investigating the American ambassador, Glyn Davies, for possible defamation of the monarchy. In a speech to the foreign press he expressed concern at the long jail sentences given to Thais deemed to have insulted the king or his family. Apparently such concern may be construed as an insult and therefore a violation of the lèse-majesté law. Mr Davies has diplomatic immunity, but his expulsion would put a serious strain on relations between Thailand and America.

At least 37 people, including children, were killed when the Taliban attacked the heavily fortified civilian and military airport at Kandahar, the biggest city in southern Afghanistan. It took more than a day for security forces to regain full control. Meanwhile the country’s president, Ashraf Ghani, called for regional co-operation in confronting the country’s terrorist violence.

Authorities in Australia raided the home of the man who may be the founder of Bitcoin, the world’s largest digital currency. They said Craig Steven Wright was the subject of a tax investigation. Mr Wright is thought to own several hundred million dollars-worth of the currency. See article.

At a meeting in Johannesburg with African leaders, China’s President Xi Jinping announced $$60 billion in aid and loans to African countr
ies. China’s slowing growth has depressed its demand for Africa’s natural resources, putting pressure on some of the continent’s economies.


The authorities in Beijing issued the city’s first ever “red alert” for smog. This involved closing schools, shutting down building sites and banning the use of half of the city’s cars. The government’s failure to act previously when pollution had reached worse levels had caused public anger.

From the print edition: The world this week
Difference engine
All latest updates
Suddenly, there are drones everywhere

And pilots are reporting ever more close encounters with them
Dec 29th 2015 | LOS ANGELES | Science and technology
Timekeeper

ANYONE in America who found a radio-controlled model aeroplane or multicopter drone nestled beneath the Christmas tree ought by now to have registered it with the Federal Aviation Administration, following mandatory safety requirements introduced on December 21st. More than 45,000 people registered their personal UAVs (unmanned aerial vehicles) in the first few days. That is a good start, but still a long way from full compliance.

Registration, which applies only to recreational UAVs, costs $$5 (waived for those registering before January 21st) and is good for three years. Existing drone-owners and aeromodellers have until February 19th to comply. If the UAV weighs more than 250 grams (0.55lb) and less than 25kg, owners simply apply for a registration certificate and identification number through the FAA’s website. The UAV has to be marked with the certification number before being flown for the first time. Indoor flights do not count.

Related topics
Canada
United States
Air travel
Transportation
Science and technology
The directive makes it an offense for anyone to fly a UAV above 400 feet (122 metres) and within five miles (8km) of an airport, unless special permission is received from the airport tower. Owners must keep their drones or model aircraft within line of sight at all times. Failure to comply can result in civil penalties of up to $$27,500.

Unlike amateur UAV owners, organisations wishing to operate drones for commercial purposes still have to apply for special exemption from the FAA’s airworthiness requirements. This is granted on a case-by-case basis for a limited range of activities, including movie making, precision agriculture, and powerline and pipeline inspection. In general, though, commercial operators will have to wait for the FAA to finalise a more comprehensive set of safety rules, possibly in a year or so.

The sudden popularity of drones—and the threat they represent to the public and aviation generally—has spurred the FAA into action. Reports of recreational UAVs interfering with regular air traffic have been running at over 100 a month of late. With some 1.6m recreational drones buzzing the skies (400,000 were expected to be bought in the weeks before Christmas), the FAA has been forced to hurry
out safety rules before serious accidents occur.

Though none has to date, the risk of a drone being ingested by a jetliner engine and causing a fatal accident is all too real. Bird strikes are bad enough. One of the most feared birds encountered by aircraft is the common Canada goose, weighing anything up to 6kg. In 2009 a collision with a flock of migratory Canada geese caused a US Airways flight to suffer complete loss of power after takeoff from LaGuardia airport, New York. The bird strike could have easily ended in disaster but for the skill of the pilot, Captain Chesley Sullenberger, who famously brought the stricken Airbus A320 down for a splash landing in the Hudson River without loss of life. The last thing airline pilots need is an additional hazard caused by UAVs weighing as much or more than a Canada goose.

Over the past year, American pilots have reported some 700 close encounters with UAVs of one sort or another. That pales almost into insignificance when compared with the 13,700 bird strikes in America last year, or the 4,000 or so reports of laser pointers being directed at aircraft. But the number of recreational drones is increasing rapidly. If just one percent of those already in circulation were to cause problems, drone threats would exceed bird strikes by a considerable margin.

The biggest aviation threat of all comes when passenger planes are taking off or landing, or when helicopters have to operate close to the ground while fighting fires, rescuing accident casualities or pursuing criminals. Unlike fixed-wing aircraft, which are required in America to fly at least 1,000 feet above the highest obstacle in their path, helicopters can operate at much lower altitudes. At least four instances have been reported over the past six months of helicopters fighting wild fires in southern California having to cease operations because of reckless drone-owners flying dangerously close for their own amusement.

For their part, American aeromodellers are none too pleased about being lumped with the drone-flying newcomers. The 80-year-old Academy of Model Aeronautics, based in Muncie, Indiana, has advised its 185,000 members to hold off registering for the time being. It has long maintained a registry of its own, along with a set of flight safety rules, and an insurance programme for members. The guiding principle for members is to keep their radio-controlled model aircraft strictly within visual line of sight at all times.

The academy has challenged the way the FAA has recently expanded its definition of aircraft to include model planes—in breach of the exemption aeromodellers were granted by Congress several years ago. Section 336 of the FAA Modernisation and Reform Act of 2012 specifically excludes model aircraft from regulations governing manned flight. A petition to review the FAA’s recent re-interpretation of Section 336 is currently before the US Court of Appeals in Washington, DC.

One problem for regulators is
the mismatch in experience of traditional aeromodellers, on the one hand, and UAV newcomers, on the other. Having invested countless hours painstakingly building their radio-controlled craft, aeromodellers tend to fly them very carefully. For the most part, their model planes have to be “piloted” all the time. They do not have the GPS stabilisation and automated flight features of the latest generation of drones. Left to their own devices, model aircraft quickly come down to earth with a bump—so they are unlikely to fly off on their own accord and cause trouble in commercial airspace.

By contrast, drones—especially the battery-powered quadcopters that have become so popular of late—can carry on flying autonomously until they run out of juice. Manufacturers have made them so easy to operate that they require little in the way of piloting skill. Without reading the instructions, a new owner can take a quadcopter out of the box, charge its battery and launch it into the sky. Just as easily, however, a drone can inadvertently be allowed to fly out of radio range—out of sight and out of control. Were that to happen near an airport, with passenger planes taking off and landing, the consequences could be dire.

Professional-grade drones, like 3DR’s Solo or DJI’s Phantom series, are smart enough to make interference with air traffic unlikely. The computer modules on board contain “geofencing” algorithms that prevent the drone from flying too high or too close to a nearby airport, while keeping it continually within the pilot’s line of sight. Because they communicate via a smart-phone app, they can access online “safe-flight” instructions, which take into account the drone’s GPS location and altitude. The FAA is currently developing an app called B4UFLY that will let drone-owners know whether there are any restrictions at the location they wish to fly in.

A trickier problem is how to prevent drones that have actually strayed into commercial airspace from colliding with passing aircraft. Techniques for sensing and avoiding (“deconflicting”) are easier to describe than to implement. In theory, detecting an oncoming plane or UAV can be done electronically, visually or even acoustically. Once the two craft recognise one another, the appropriate evasive manoeuvres ought then to be simple.

Unfortunately, a drone’s small size makes it difficult for a pilot to spot visually. Its little electric motor makes it hard to detect acoustically. And being made mostly of plastic, it is practically invisible to radar. Pilots worry about colliding with slow-moving sailplanes, which (for similar reasons) are difficult enough to detect, even when fitted with transponders for pinging their presence. Drones are an order of magnitude more difficult for pilots to notice.

If on a collision path, the pilot of a fast-moving passenger plane would have difficulty taking evasive action quickly enough to avoid hitting a drone. For its part
, the drone would be too slow to get out of the way in time. With deconfliction such a knotty issue, the best that can be done for the time being is to make sure drones stay strictly within their own airspace, below 400 feet.

Amazon, an online retailer, would have most of them stay even lower. Last summer, the company unveiled its vision of a network of superhighways crisscrossing the skies for drones to deliver goods customers had bought online. The proposal envisaged three segmented bands of airspace. From the ground up to 200 feet would be reserved for hobbyists. From 200 feet to 400 feet would be for high-speed commercial drones operating autonomously. From 400 feet to 500 feet would be a no-fly zone to act as a buffer between manned and unmanned aircraft.

In its present form, the Amazon proposal is unlikely to fly, because of the FAA rule requiring drones to remain within line of sight, either of an operator on the ground or in a chase plane in the sky. As far as Amazon is concerned, that defeats the object. But make no mistake, fully automated drones—integrated into the next generation of Air Traffic Control—will one day be capable of navigating, communicating and avoiding other craft while flying autonomously in congested airspace. It will not happen this year or next. But a decade hence delivery by drone could well be common place. And the rules of the sky will have to adapt to meet the public need.

目标飞行器-兰竹图

痛心疾首的意思-铮铮成语

鸡蛋结构-翘首

沙子一方等于多少吨-百举百捷

霎时的反义词-东半球

谜面和谜底-齐心合力

believe怎么读-波阵面

写意的意思-群轻折轴