Mark Twain, the famous American writer and a great master of humor, liked to play jokes on others. But once a joke was played on him. One day Mark Twain was invited to give a talk in a small town. At lunch he met a young man, one of his friends.

    The young man said that he had an uncle with him. He told Mark Twain that his uncle never laughed or smiled, and that nobody and nothing was able to make his uncle smile or laugh.

    "You bring your uncle to my talk this evening," said Mark Twain. "I'm sure I can make him laugh."

    That evening the young man and his uncle sat in the front. Mark Twain began to speak. He told several funny stories and made everyone in the room laugh. But the man never even smiled. Mark Twain told more funny stories, but the old man still kept quiet. Mark Twain continued to tell his funny stories. Finally he stopped. He was tired and quite disappointed.

    Some days later, Mark Twain told another friend what had happened." Oh," said his friend, "I know that man. He's been deaf for years."

    Hummingbirds(蜂鸟) are one of nature's most energetic fliers and the only birds to hover(盘旋) in the air by relying on their strength alone.

    Now scientists have found that it is the ratio(比值) of the bird's wing length to its width that makes them so efficient. The discovery is helping experts compete with 42 million years of natural selection to build helicopters that are increasingly efficient.

    David Lentink, an assistant professor at Stanford University in California, tested wings from 12 different species of hummingbirds, which he sourced from museums. He placed them on a machine used to test the aerodynamics(气力学) of the helicopter blades(桨叶). Professor Lentink's team used the same machine to test the blades from an advanced micro-helicopter used by the UK's army. They found that the micro-helicopter's blades are as efficient at hovering as the average hummingbirds.

    But while the micro-helicopter's blades kept pace with the average hummingbird wings, they could not keep up with the most efficient hummingbird's wing. The wings of Anna's hummingbird were found to be about 27 percent more efficient than the man-made micro- helicopter's blades.

    While Professor Lentink wasn't surprised at nature's superiority, he said that helicopter blades have come a long way. “The technology is at the level of an average hummingbird,” he said. “A helicopter is really the most efficient hovering device that we can build. The best hummingbirds are still better, but I think it's amazing that we're getting closer. It's not easy to match their performance, but if we build better wings with better shapes, we might match hummingbirds.”

    Professor Lentink said that we don't know how hummingbirds maintain their flight in a strong wind, how they navigate(确定方向) through branches, or how they change direction so quickly. He thinks that great steps could be made by studying wing aspect ratios-the ratio of wing length to wing width. Understanding these abilities and characteristics could be a benefit for robotics and will be the focus of future experiments.

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    LastPass Password strength has been a topic about the Internet lately. I have seen lots of clever methods for creating and remembering strong passwords. Some are better than others, but in my opinion, none are enough. Here's the problem: It doesn't matter how strong your passwords are if you use the same one on multiple sites. All it takes is for a site to get hacked, like Gawker media, or even Sony did, and now your super-strong password has been stolen, and every site on which you used that password has been accessed.

    Enter LastPass. It's not the only password manager out there, but I like it the best. You create ONE strong password that you have to memorize and use it to access you LastPass database. The LastPass database is stored online, on LastPass's services. LastPass recognizes the site you're on and automatically logs you in (after, optionally, asking you to re-enter your master password). LastPass also has automatic form fill and automatic password generation. This means that you can have a different, unique, very strong password for every site you log into, but you only have to remember one master password. It's the best of both worlds.

    One argument against LastPass is that if their database is attacked, then all of your sites are in danger, and that's true, but if their entire line of work is keeping that information safe, I'm willing to take that chance. The alternative is rolling dice（掷骰子） or picking phrases to create passwords, writing all of them down on a piece of paper or something, and then having to manually type them in when I go to a site. A terrible mess.

    There is a free version of LastPass, with some additional features unlocked if you pay a $12 a year subscription.

    "Hey, Bruno! Great to see you again, man!" Zeca shouted. "Come over here and meet the boys." But before Bruno could move he was frisked by two guards. He cringed as the men searched his body for hidden guns, knives or other weapons.

    "He's clean, boss," one of the men shouted out.

    Zeca introduced all the members of his gang, including the man who worked inside the printer's who was going to steal the exams. He then explained all the details of the plan. It seemed foolproof and nothing could go wrong.

    They all shook hands and quickly left.

    Bruno's heart was beating fast. He was anxious to get away from the gang and phone Clara. He raced down the hill. Then he stopped at the bottom and looked behind him. It was clear, no one was following him. He took out his phone and called Clara.

    "Hey, Clara. Listen." He was out of breath, panting heavily. "Everything went according to plan. To my plan, of course, not Zeca's!" he added, laughing excitedly.

……

    "This is amazing!" the police officer said, smiling broadly, as he looked at Bruno and Clara, who were sitting in front of him at the police station. "Well done! How did you manage to come up with such a brilliant idea?"

    "Thanks. I guess it was kind of clever." Bruno answered, acknowledging the compliment with a polite smile. He felt slightly embarrassed. "Believe it or not, the idea just popped into my head while I was taking a shower. I remembered I saw an advert once on the Internet for special spy-camera sunglasses. They have a tiny, hidden, built-in video recorder. Here they're only used by detectives and law enforcement agencies, but anybody can buy them on the Internet."

    When Bruno talked to Clara before his meeting with Zeca's gang, they both agreed it would be wrong to steal the exams, and help Zeca sell them to other people. But Bruno had worked out an ingenious plan to dounle-cross Zeca and stay out of trouble himself.

    First of all, he had wisely agreed to go along with Zeca's plan, and go to the meeting with the gang of thieves. When he arrived at the hideout, they frisked him for hidden weapons, but no one ever imagined that Bruno was wearing sunglasses with a tiny built-in camera. Bruno had secretly videoed the entire meeting, making sure he had taken close-up shots of all the gang members. Their conversations with all the details of their plan had also been recorded.

    Then, as soon as he was sure that he wasn't being followed, he phoned Clara and together they went to the police with the camera and told them the whole story.

    "Thanks to this evidence we can finally catch Zeca and his entire gang red-handed," the police officer continued. "But we need you and Clara to help us. It's very important that you both continue to act as if nothing has happened. You must play along with whatever Zeca wants. We'll be following your every move from now on. Just do everything Zeca tells you to, OK?"

    The police then went to the printer's and spoke to the owner. He agreed to co-operate and they installed some hidden cameras there, too. The day of the theft they saw the thief copy the exam papers on Closed Circuit Television(闭路电视), but they did not arrest him yet.

    Then they waited until Zeca made the next move.

    Eight Days Best of China Tour

    This tour covers two ancient capital cities of China — Beijing & Xi'an, as well as the most developed city — Shanghai. It's not overstated to call it the most classic China tour, for China's past, present and future are epitomized（成为…的缩影）in the golden triangle cities for your exploration.

    Highlights of this tour:

    Be thrilled by the grand of Great Wall, as well as the delicacy and majesty of Forbidden City and Summer Palace in Beijing.

    Experience the World Heritage Site of Terracotta Warriors in Xi'an, the ancient capital city of China.

    Feel the charm and vitality of Shanghai, the most prosperous and modernized city in China.

    Our tour — at a glance

    Day 1-4 Arrival & Beijing Tour

Two full days and a half day sightseeing covering the grand Tiananmen Square, historical Forbidden City, spectacular Temple of Heaven, manmade wonder Great Wall of China, royal park Summer Palace and traditional Hutong.

    Day 5-6 Xi'an Tour & Flight to Shanghai

    One full day to visit the incredible Terracotta Warriors, leisurely walk on the Ancient City Wall and Muslim Quarter. Before leaving for Shanghai, explore the Big Wild Goose Pagoda and Shan'xi History Museum.

    Day 7-8 Shanghai Tour & Departure

    Experience the great contrast of Shanghai by visiting the traditional Yu Garden and Jade Buddha Temple, modern and prosperous Shanghai World Financial Center, Nanjing Road and the Bund, etc.

    Start planning your tailor-made holiday by contacting one of our specialists. Once enquired, you'll get a response within 0.5-23.5 hours.

    Rich countries are racing to dematerialise payments. They need to do more to prepare for the side-effects.

    For the past 3,000 years, when people thought of money they thought of cash. Over the past decade, however, digital payments have taken off— tapping your plastic on a terminal or swiping a smartphone has become normal. Now this revolution is about to turn cash into an endangered species in some rich economies. That will make the economy more efficient—but it also causes new problems that could hold back the transition(转型).

    Countries are removing cash at varying speeds. In Sweden the number of retail cash transaction per person has fallen by 80% in the past ten years. America is perhaps a decade behind. Outside the rich world, cash is still king. But even there its leading role is being challenged. In China digital payments rose from 4% of all payments in 2012 to 34% in 2017.

    Cash is dying out because of two forces. One is demand— younger consumers want payment systems that plug easily into their digital lives. But equally important is that suppliers such as banks and tech firms (in developed markets) and telecoms companies (in emerging ones) are developing fast, easy-to-use payment technologies from which they can pull data and pocket fees. There is a high cost to running the infrastructure behind the cash economy—ATMs, vans carrying notes, tellers who accept coins. Most financial firms are keen to abandon it, or discourage old-fashioned customers with heavy fees.

    In the main, the prospect of a cashless economy is excellent news. Cash is inefficient. When payments dematerialise, people and shops are less open to theft. It also creates a credit history, helping consumers borrow.

    Yet set against these benefits are a couple of worries. Electronic payment systems may risk technical failures, power failure and cyber-attacks. In a cashless economy the poor, the elderly and country folk may be left behind. And a digital system could let governments watch over people's shopping habits and private multinationals exploit their personal data.