Sometimes, you just can't help it. Maybe you're watching a sad movie, or thinking about the friend who moved away. Next thing you know, your eyes are watering, and you havetears running down your cheeks. Why do peoplecry when they are emotional? What are tears? Scientists are working hard to find the answers to these questions.

    Ad Vingerhoets is a professor of psychology at Tilburg University, in the Netherlands. He is one ofthe few scientists in the world who have studied crying. According to Vingerhoets, there are three types of tears. Basal tearsare the first type. Theylubricate(润滑) the eyes andact as a protective barrier between the eye and the rest of the World. Next arereflex tears. They wash youreyes clean when something gets in them. Finally, there are emotional tears. “These are released in response to emotional states, ”explains Vingerhoets. “Especially when we feel helpless.”

    Scientists believe that crying has something to do with how humans developed and learned to depend on each other.“Humans are very complex social creatures,”says Lauren Bylsma, a professor at the University of Pittsburgh, in Pennsylvania.“It seems that tears serve to arouse help and support from others," She says. “Another reason we weep is that humans have the longest developmental period of almost any animal. It takes along time to grow up. ”

    Vingerhoets agrees. “I think that the reason why humans shed tears(流眼泪) has somethingto do with our childhood,”he says. “That's the time when we are stir dependent on adults for love and protection and care. The major advantage of emotional tears is that you can target them at a specific person.”Vingerhoets says this ability to target someone could have come in hand in prehistorictimes, when humans were living among dangerous animals. Crying couldattract predators(捕食者). Tears were asafer way to get attention. In this case, it is better to use a silent signal to ask for help,”he says.

    Vingerhoets and Bylsma do frequent studies to better understand why humans cry. According to Byhma, there is still much more to discover. “It's surprising,”she says,“how much we still don't know.”

    Before a new type of airplane goes into service, every part of it is tested again and again. But there are two tests that are more important than all the others.

    The first is called the "tank test". A modem airplane must fly very high in the sky. Air must be pumped into the plane so that the passengers can breathe. The metal structure (结构)of the plane has to be very strong for this reason. When the plane is filled with air, the air presses against the skin of the plane inside. The pressure (压力) on a small window is like a huge foot that is trying to get out. If a small part of the plane were to fail, the plane would explode in the sky. To test the structure of the plane, the plane is lowered into a huge tank or container of water. Then it is filled with air. Vne pressure inside the plane is greater than it ever will be when it is high up in the air. Finally, there is an explosion. This does not cause so much damage inside the water tank as it would anywhere else. Engineers can discover which part of the plane has broken. Then that part is made stronger.

    The most dangerous test happens when the new plane is going through test flights in the air. The test pilot must find out exactly what happens when the engines (发动机) are all shut off at once. The plane begins to fall like a stone. It is the pilot's job to find out how he can get control of the plane again. These two tests are examples of how planes are made safe before they ever carry passengers.

    I've worked part time since taking early retirement ten years ago. I was inspired by an older friend. We worked for the same company, and he retired two years before I was also considered “spare”, as some companies call it.

    Soon after I left work, we had lunch together. First, he assured me that there was life after work. Then he related his own experience. He didn't want to take another full-time job, so he turned his daughter's old bedroom into a home office. He arranged for some consulting work from our old company, and he picked up more projects from other contacts. Soon he was working 20 to 30 hours a week. He wasn't making as much money. His kids were grown-up, so he didn't need as much income. “As soon as I left that job,” he told me, “my back problems went away. I started to eat better and get more exercise, I make half as much money, but I feel twice as good, and I'm twice as happy.”

    I decided to follow a similar track. At the time, my younger child almost finished college, so my parental responsibilities were winding down. We sold our old house and moved into a townhouse. I went to work for myself. And the result? Today I, too, make less money. But we make ends meet. And I feel twice as good and twice as happy.

    Our experience isn't for everybody. But a lot of people have retired early and lived to tell the tale, which proves it possible. Jack, another friend, was a salesman for a communication firm. He had a long distance to work and did a lot of traveling. He decided to leave the corporate world, in part because he had health problems and he wanted to spend more time with his family. Later, he quit his job with flexible hours and was restored to his health. And now he has found a part-time job, and he, together with his family, is leading a more relaxing life.

    As for old people, some of the applications are hard to use because they didn't grow up with them. They don't have simple models of how they should work, what to do when something doesn't work or where to go for help. We make it as easy as possible to be used for people who are not familiar with the technology.

    I think there is huge potential (潜力) and we are designing it. The ability to connect to friends, who remember the same movies and news and music, is really important, especially as people get old. They end up in retirement homes and they aren't always close to their friends. Allowing the network to help them connect with friends and family is a really powerful thing.

    My mother is an enthusiastic user of the Internet, although it took me years to get her to use e-mail. She was born with normal hearing, but lost it when she was 3. She was totally deaf for many years, until age 53, when she got ear aids. They work really well. That is a big change for her. But before then, her friends couldn't call her on the phone, so they insisted she use e-mail to communicate with them.

    Young people don't even think of the Internet as technology. It's just there, and they use it. There's been a very interesting change in communications styles between old people and young people. There are some kids who are now in their teens and aren't willing to make phone calls. And they think of e-mail as old-fashioned and slow.

    The reason why teens don't make phone calls seems to be that they don't know what to say. When they call they often stop for a while and there's this silence. On the other hand, texting is considered proper, and it's okay if you don't answer. You might have been distracted. It's not considered rude. But it is considered strange if you're in this kind of voice conversation and simply stop talking.

    Steven Spielberg's 2002 science-fiction thriller Minority Report produced a world where computers could read minds and predict the future. It seemed fanciful at the time, but fantasy is edging closer to fact.

    On Jan 31, a team of scientists at UC Berkeley, led by Robert Knight programmed computers to decode (破译) brain waves and replay them as words. Five months earlier, another group of Berkeley scientists showed their colleagues short movies and used computers to play back in color what people saw.

    These experiments are a big advance from 2006, when a French scientist first replayed images from a human mind, a black-and-white checkerboard pattern. The possibilities are great: a disabled person could" speak"; doctors could access the mind of a patient who fainted; you could rewatch your dreams on an iPad. There are, of course, equally dark side, such as the involuntary take out of information from the brain.

    In spite of these breakthroughs, Jack Gallant, the neuroscientist who led the first Berkeley team, says current technology for decoding brain activity is still "relatively primitive". The field is held back by its poor machinery, in particular the FMRI.

    "Eventually," says Gallant, "someone will invent a decoding machine you can wear as a hat." Such an advance into the human mind, he says, might take 30 years.

    Still, the recent advances at Berkeley offer small answers, which scientists can use to begin unlocking the secrets of memory and consciousness.

Africa's Most Amazing Places to Visit

    Pyramids of Giza, Egypt

    The most famous of the structures at Giza, near Cairo, the Pyramid of King Khufu was built around 2650 BC from 2.5 million blocks of stone. Its sides face north, south, east and west.

    Sahara Dunes, Morocco

    The most user-friendly part of the Sahara is accessible from the northern edge of Morocco. You can camp out in Tazzarine, where runners from all over the world complete the weeklong Marathon every spring. The foot of the Merzouga Dunes is the best location for gazing at stars, totally free of light pollution.

    Lake Retba (Lac Rose), Senegal

    There are few pink lakes in the world and one of them, Lake Retba, also called Lac Rose by locals is in the Cap-Vert peninsula in Senegal. The best times to see the lake at its pinkest is during Senegal's dry season, between November and June.

    Nyika Plateau National Park, Malawi

    With a plateau cut by numerous rivers that reach Lake Malawi by way of waterfalls off the eastern edge of the mountains, Nyika, the largest national park in Malawi, is one of the most beautiful in Africa. The eastern border of the plateau forms the wall of the Great Rift Valley. The great domes of hills have gentle slopes, making Nyika perfect for both hiking and mountain biking as well as Jeep exploration.