Exercise may help to safeguard the mind against depression(沮丧) through previously unknown effects on working muscles, according to a new study involving mice.

    Mental health experts have long been aware that even mild, repeated stress can contribute to the development of depression and other mood disorders in animals and people. Scientists have also known that exercise seems to cushion against depression. But precisely how exercise, a physical activity can reduce someone's risk for depression, a mood state, has been mysterious. So for the new study, researchers at the Karolinska Institute in Stockholm studied the brains and behavior of mice in a complicated and novel fashion.

    We can't ask mice if they are feeling cheerful or in low spirits. Instead, researchers have pictured certain behaviors that indicate depression in mice. If animals lose weight, stop seeking out a sugar solution when it's available — because, probably, they no longer experience normal pleasures — or give up trying to escape from the cold-water zone just freeze in place, they are categorized as depressed. And in the new experiment, after five weeks of frequent but low-level stress, such as being lightly shocked, mice displayed exactly those behaviors. They became depressed.

    The scientists could then have tested whether exercise blunts (延缓) the risk of developing depression after stress by having mice run first. But, frankly, from earlier research, they wanted to know how, so they bred pre-exercised mice. A wealth of earlier research by these scientists and others had shown that aerobic exercise, in both mice and people, increases the production within muscles of an enzyme (酶) called PGC-1alpha. The Karolinska scientists suspected（怀疑） that this enzyme somehow creates conditions within the body that protect the brain against depression. Then, the scientists exposed the animals, which without exercising, were in high levels of PGC-1alpha to five weeks of mild stress. The mice responded with slight symptoms of worry. But they did not develop depression. They continued to seek out sugar and fought to get out of the cold-water zone. Their high levels of PGC-1alpha appeared to make them depression-resistant（抵抗的）. Finally, to ensure that these findings are relevant to people, the researchers had a group of adult volunteers complete three weeks of frequent endurance training, consisting of 40 to 50 minutes of moderate cycling or jogging. The scientists conducted muscle biopsies (活体检查) before and after the program and found that by the end of the three weeks, the volunteers' muscle cells contained substantially more PGC-1alpha than at the study's start.

    The finding of these results, in the simplest terms, is that “you reduce the risk of getting depression when you exercise,” said Maria Lindskog, a researcher at the Karolinska Institute.

    He wishes the holiday season would end already. His back aches, his red suit feels like a spacesuit, his cheeks have gone tight from smiling for 12 hours—and still the kids keep coming and coming, like ants at a picnic. As Christmas becomes more commercialized (商业化) across the U. S. and Canada, so must Santa Claus. As the holiday begins earlier each year, so must its spokesmen.

    The questions from children these days are harder than ever. Now, with thousands of children expecting a father or mother serving in Iraq or Afghanistan, the questions are as heart­breaking as they are unanswerable. For example, “Can you please bring Daddy home from the war in time for Christmas morning？”

    Santa Claus; also have a pretty good chance of getting sued (指控). A professional Santa Claus in Canada told a story: A Santa had a girl on his knee, and he commented, “You have nice eyes and nice hair.” The girl later said it was sexual harassment (骚扰). When a Santa feels anxious, he often shows it in the same ways ordinary people do. The Santa Claus were always seen to hang around at the dinner table when the show ended. Many of them just sleep in bed for several days and don't see other children again.

    （I）It was a surprising announcement: SpaceX, a private company（私人公司）, said it would fly two people to the moon next year (2019). This has not been attempted since NASA's Apollo moon landings about 45 years ago. In the news conference, Elon Musk. SpaceX founder said two people have already paid SpaceX a “wonderful” amount of money to send them on a weeklong flight just beyond the moon.

    （II）Exercise reduces the risks of dying from all causes, including cancer and heart disease. But many people who work all week have little time for exercise. They try to take exercise or do chores to increase their heart rates over the weekend. A new study suggests that it is healthy to do that, which can reduce their risk of cancer and cardiovascular（心血管疾病）disease.

    （III）Scientists in London have found a possible way to solve the problem of plastic bottle waste. They have made a water bottle you can eat. The product is called Ooho, made of seaweed, a plant that grows in the ocean. Oohos are tasteless and look like bubbles or balls. They can hold water or any other liquid（液体）inside. When people drink Oohos, the outside bursts in the mouth and can be eaten. Even if you throw it away, it will degrade in about four weeks. It is good for the environment.

    More than a hundred years ago, two boys were fishing in a small river. They sat in a heavy-bottomed boat, each holding a long, bent pole in his hands and eagerly waiting for "a bite". When they wanted to move the boat from one place to another they had to push against a long pole into the bottom of the stream.

    "This is slow work, Robert," said the older of the boys. "Yes, Christopher, and it's hard work, too." answered Robert. "I think there's some better way of moving a boat."

    Christopher advised rowing it and Robert promised to make some paddles (桨). The next day Robert's aunt heard a great noise in her house. The two boys were there, busily working. "What are you making, Robert?" she asked. He told his plan. His aunt laughed and said, "Well done! I hope you'll succeed."

    After much work, they succeeded in making two paddle wheels. They were very rough, but strong and usable. They fixed each of these wheels to the end of an iron rod (长杆) which they passed through the boat from side to side. The rod was bent in the middle. When the work was finished, the old fishing boat looked rather strange, with a paddle wheel on each side. The boys lost no time in trying it. One of the boys could guide the boat while the other turned the paddle wheels.

    That night when Christopher went home, he told his father a wonderful story. "Robert Fulton planned the whole thing," he said, "and I helped him make the paddles and put them on the boat." When Robert Fulton became a man, he didn't forget his experiment with the old fishing boat. He kept on thinking and working, until at last he succeeded in making a boat with paddle wheels that could be run by steam. He's now honored as the inventor of the steamboat.

    Outside, it's a cold winter's day. Inside a large shopping center, people are hanging around. But then, without warning, a pop song starts to play loudly. A teenager boy walks lazily to the center of the open space, and dances crazily to the music. He's joined by two of his friends, then some of the old people. Within the space of a few seconds, more than sixty people are dancing to the music - all in time and all in step. At first, onlookers are baffled, then they start smiling and clapping. They now know what they're seeing: a flash mob （快闪）.

    According to Wikipedia, the term "flash mob" was created by Bill Wasik, an editor at Harper's Magazine, in 2003. Within a year, the phrase had entered the Concise Oxford English Dictionary. Since then, hundreds - possibly thousands - of flash mobs have been carried out around the world, in almost every kind of public space imaginable!

    Each flash mob has its own style, but most flash mobs follow a similar formula （方案）. Often, the organizers search for willing participants using social media. Instructions and dance moves are given through email or video download. There are usually several rehearsals （排练） before the big day.

    While it's happening, a few lucky passers-by watch it live. Most people who watch it, however, will see it later online. Some of the most popular flash mobs on YouTube have been watched more than 10million times. A famous example is MP3Experiment Eight, a flash mob that took place in New York City in July 2011 with over 3,500 participants. This event differed from normal flash mobs in that much of it was completely silent - and there were no rehearsals.

    Flash mobs provide the participants, onlookers and online viewers with a lot of enjoyment and pleasure. For this reason alone, they're a modern, popular art form that should be celebrated.

     At one time, computers were expected largely to remove the need for paper copies of documents because they could be stored electronically. But for all the texts that are written, stored and sent electronically, a lot of them are still ending up on paper.

     It is difficult to measure the quantity of paper used as a result of the use of Internet-connected computers, although just about anyone who works in an office can tell you that when email is introduced, the printers start working overtime. "I feel in my bones this revolution is causing more trees to be cut down," says Ted Smith of the Earth Village Organization.  

     Perhaps the best sign of how computer and Internet use pushes up demand for paper comes from the high-tech industry itself, which sees printing as one of its most promising new markets. Several Internet companies have been set up to help small businesses print quality documents from a computer. Earlier this week Hewlett-Packard Co. announced a plan to develop new technologies that will enable people to print even more so they can get a hard copy of a business document, a medical record or just an online email, even if they are nowhere near a computer. As the company sees it, the more use of the Internet the greater demand for printers.

     Does all this mean environmental concerns have been forgotten? Some activists suggest people have been led to believe that a lot of dangers to the environment have gone away. "I guess people believe that the problem is taken care of, because of recycling," said Kelly Quirke, director of the Rainforest Action Network in San Francisco. Yet Quirke is hopeful that high-tech may also prove helpful. He says printers that print on both sides are growing in popularity.

     The action group has also found acceptable paper made from materials other than wood, such as agricultural waste.