Distance runners often worry about “hitting the wall” during training or races—that terrible moment when negative thoughts become so overpowering that they make it difficult to continue.

Hitting the wall typically happens around 20 miles in a marathon, when the body's supplies become exhausted. At this point, many runners feel exhausted and discouraged, slow their pace, have trouble focusing and want to quit or walk.

“Generalized tiredness, unintentionally slowing their pace, the desire to walk, and shifting focus to just surviving the marathon appear to be particularly common characteristics of it,” said Dr. Alistair McCormick, an exercise psychologist in England who co-authored a new study. “A marathon becomes a real mental battle when runners ‘hit the wall.'”

    Psychological blocks are an extremely common experience for recreational endurance (耐力) athletes, according to the study. To learn how they affect people, sports psychologists asked 30 recreational runners and cyclers about the psychological demands of training, preparing for and participating in competitions.

     “Recreational runners and cyclists found it stressful trying to find the time to train, McCormick said. “What was also interesting was the number of potential banana skins they met with before and during competition-disasters that could cause the athletes to lose their focus and their motivation to keep persevering.”

    These roadblocks included difficult environmental conditions and equipment failure, problems with nutrition or making a mistake, the study reported. The athletes in the study said they fell these obstacles (障碍) affected their motivation and concentration, negatively affecting their overall performance.

According to the study, 43 percent of marathoners are likely to hit the wall during a race. Finding ways to move past those kinds of experiences, then, could have major benefits for an athlete's performance and well-being.

    A friend of mine named Paul received an expensive car from his brother as a Christmas present. On Christmas Eve when Paul came out of his office, a street urchin (顽童) was walking around the shining car. “Is this your car, Paul?” he asked.

    Paul answered, “Yes, my brother gave it to me for Christmas.” The boy was surprised. "You mean your brother gave it to you and it cost you nothing? Boy, I wish…"He hesitated.

    Of course Paul knew what he was going to wish for. He wished he had a brother like that. But what the boy said surprised Paul greatly.

    “I wish,” the boy went on, “that I could be a brother like that.” Paul looked at the boy in surprise, and then he said again, “Would you like to take a ride in my car?” “Oh yes, I'd love that.”

    After a short ride, the boy turned and with his eyes shining, said. “Paul, would you mind driving in front of my house?”

    Paul smiled a little. He thought he knew what the boy wanted. He wanted to show his neighbors that he could ride home in a big car. But Paul was wrong again. “Will you stop where those two steps are?” the boy asked.

    He ran up to the steps. Then in a short while Paul heard him coming back, but he was not coming fast.

    He was carrying his little. crippled (残疾) brother. He sat him down on the step and pointed to the car.

    “There he is, Buddy, just like I told you upstairs. His brother gave it to him for Christmas and it didn't cost him a cent. And some day I'm going to give you one just like it… Then you can see for yourself all the nice things in the Christmas window that I've been trying to tell you about.”

    Paul got out and lifted the boy to the front seat of his cat. The shining-eyed elder brother climbed in and three of them began an unforgettable holiday ride.

    We often ask these questions: Are African wild dogs really dogs? What's the difference between African wild dogs and the dogs we know as pets? For one thing, African wild dogs, which live in Africa, only have four toes, while domestic(驯养的）dogs and wolves have five. But you won't want to count for yourself, because they are truly wild animals.

    “Wild dogs are not somebody's domestic dogs that ran away and didn't come back, although some people used to think that,” explains Dr. MeNutt, who studies these animals at Wild Dog Research Camp in the African country of Botswana. “They are actually Africa's wolves, and just like wolves, and they do not make good pets. They need to be out in the wild doing what they are supposed to do — find the food they need to survive and feed their babies.” In fact, they travel so far that researchers have to use radio collars (颈圈) to keep track of them. The collars send out radio signals that tell people where the dogs are. No two wild dogs have the same pattern of coats, so it is easy to tell them apart.

    African wild dogs are smart and sociable, like pet dogs. Adult wild dogs, male and female, are willing to take good care of young ones.

    Millions of domestic dogs live on the planet, but there are probably fewer than 6000 African wild dogs left. Humans hunt them and farmers who don，t want them to go after cows and sheep poison them. Humans are also destroying the wild, natural habitat (栖息地) they need to survive in. Fortunately, today more farmers are finding other ways to protect their cows and sheep from African wild dogs instead of killing the animals.

    The new social robots, including Jibo, Cozmo, Kuri and Meccano M.A.X., bear some similarities to assistants like Apple's Siri, but these robots come with something more. They are designed to win us over not with their smarts but with their personality. They are sold as companions that do more than talk to us. Time magazine cheered for the robots that "could fundamentally reshape how we interact with machines." But is reshaping how we interact with machines a good thing, especially for children?

    Some researchers in favor of the robots don't see a problem with this. People have relationships with many kinds of things. Some say robots are just another thing with which we can have relationships. To support their argument, roboticists sometimes point to how children deal with toy dolls. Children animate (赋予…生命) dolls and turn them into imaginary friends. Jibo, in a sense, will be one more imaginary friend, and arguably a more intelligent and fun one.

    Getting attached to dolls and sociable machines is different, though. Today's robots tell children that they have emotions, friendships, even dreams to share. In reality, the whole goal of the robots is emotional trickery. For instance, Cozmo the robot needs to be fed, repaired and played with. Boris Sofman, the chief executive of Anki, the company behind Cozmo, says that the idea is to create "a deeper and deeper emotional connection ... And if you neglect him, you feel the pain of that." What is the point of this, exactly? What does it mean to feel the pain of neglecting something that feels no pain at being neglected, or to feel anger at being neglected by something that doesn't even know it is neglecting you?

    This should not be our only concern. It is troubling that these robots try to understand how children feel. Robots, however, have no emotions to share, and they cannot put themselves in our place. No matter what robotic creatures "say", they don't understand our emotional lives. They present themselves as empathy machines, but they are missing the essential equipment. They have not been born, they don't know pain, or death, or fear. Robot thinking may be thinking, but robot feeling is never feeling, and robot love is never love.

    What is also troubling is that children take robots' behavior to indicate feelings. When the robots interact with them, children take this as evidence that the robots like them, and when robots don't work when needed, children also take it personally. Their relationships with the robots affect their self-esteem (自尊). In one study, an 8-year-old boy concluded that the robot stopped talking to him because the robot liked his brothers better.

    For so long, we dreamed of artificial intelligence offering us not only simple help but conversation and care. Now that our dream is becoming real, it is time to deal with the emotional downside of living with robots that "feel".

    A society that lives by the plastic fork may very well die from it. That's how things are looking. Anyway, for a world so used to disposable(一次性的) habits, any hope for a solution(解决方案) also increasingly seems to be buried.

    Sure, there have been some hopeful ideas. Boyan Slat, the Dutch inventor developed a plan for Covering the Great Pacific Garbage Patch. Not long after it started, Slat's system experienced "material fatigue(疲劳)"-likely the result of being strained(使受到压力) by all that trash-and the task was delayed.

    All the while, the plastic increases. Its growth is very fast, according to Linda Wang, a professor of chemical engineering at Purdue University. She says, "We'll have more plastic than fish by 2050." Yet Wang, along with other researchers at Purdue, may have a solution not only to this plastic problem, but also to the growing need for clean energy.  Her team has developed a system that turns waste, a durable, lightweight material that accounts for about a quarter of all plastic waste, into a highly pure form of gasoline.

    Publishing their findings in the journal Sustainable Chemistry and Engineering, the scientists' state that instead of making plastic go away, they can break it down and reuse it, using chemistry to destroy what chemistry brought to the world when plastic was developed back in 1907.

    The process uses "supercritical" water-heated to around 450 degrees Celsius (842 degrees Fahrenheit),beyond the key point at which distinct liquid and vapor phases(气液态) exist-to boil plastic waste into an oil, the researchers explain. It takes a couple of hours for the supercritical water to complete the transformation, but the result is a kind of oil that can be used as gasoline or fuel. It can also be turned into other products.

    The researchers have only made the transformation in a laboratory setting so far, but they suggest turning the process to a commercial scale(规模) may not be far off. And considering the 300 million tons of plastic into the environment every year, that day can't come soon enough. But it will come in time.

    Not many years ago, a wealthy and rather strange old man named Johnson lived alone in a village in the south of England. He had made a lot of money in trading with foreign countries. When he was seventy – five, he gave $ 60,000 to the village school to buy land and equipment for a children's ground.

    As a result of his kindness, he became famous. Many people came to visit him. Among them was a newspaperman. During their talk, Johnson remarked that he was seventy-five and expected to live to be hundred. The newspaperman asked him how he managed to be healthy at seventy-five. Johnson had a sense of humor. He liked whisky and drank some each day. "I have an injection (注射) in my neck each evening," he told the newspaperman, thinking of his evening glass of whisky.

    The newspaperman did not understand what Johnson meant. In his newspaper he reported that Johnson was seventy-five and had daily injection in his neck. Within a week Johnson received thousands of letters from all over Britain, asking him for the secret of his daily injection.