Most people know precious gemstones (宝石) by their appearances. An emerald flashes deep green, a ruby seems to hold a red fire inside, and a diamond shines like a star. It's more difficult to tell where the gem was mined, since a diamond from Australia or Arkansas may appear the same to one from the Democratic Republic of the Congo. However, recently, a team of scientists has found a way to identify a gemstone's origin.

    Beneath the surface of a gemstone, on the tiny level of atoms and molecules（分子）, lie clues (线索) to its origin. At this year's meeting of the Geological Society of America in Minneapolis, Catherine McManus reported on a technique that uses lasers (激光) to clarify these clues and identify a stone's homeland. McManus directs scientific research at Materialytics, in Killeen, Texas. The company is developing the technique. “With enough data, we could identify which country, which mining place, even the individual mine a gemstone comes from,” McManus told Science News.

    Some gemstones, including many diamonds, come from war-torn countries. Sales of those “blood minerals” may encourage violent civil wars where innocent people are injured or killed. In an effort to reduce the trade in blood minerals, the U.S. government passed law in July 2010 that requires companies that sell gemstones to determine the origins of their stones.

    To figure out where gemstones come from, McManus and her team focus a powerful laser on a small sample of the gemstone. The technique is called laser-induced breakdown spectroscopy. Just as heat can turn ice into water or water into steam, energy from the laser changes the state of matter of the stone. The laser changes a miniscule part of the gemstone into plasma, a gas state of matter in which tiny particles（微粒）called electrons separate from atoms.

    The plasma, which is superhot, produces a light pattern. (The science of analyzing this kind of light pattern is called spectroscopy.) Different elements produce different patterns, but McManus and her team say that gemstones from the same area produce similar patterns. Materialytics has already collected patterns from thousands of gemstones, including more than 200 from diamonds. They can compare the light pattern from an unknown gemstone to patterns they do know and look for a match. The light pattern acts like a signature, telling the researchers the origin of the gemstone.

    In a small test, the laser technique correctly identified the origins of 95 out of every 100 diamonds. For gemstones like emeralds and rubies, the technique proved successful for 98 out of every 100 stones. The scientists need to collect and analyze more samples, including those from war-torn countries, before the tool is ready for commercial use.

    Scientists like Barbara Dutrow, a mineralogist from Louisiana State University in Baton Rouge, find the technique exciting. “This is a basic new tool that could provide a better fingerprint of a material from a particular locality,” she told Science News.

    Human brains begin growing and developing at a very young age. They learn from the simplest experiences, which enable your children to be aware of the world. There's no denying that outdoor play helps a lot!

Times when children have to wait for their turns on playground equipment and following the playground rules by sharing, all these form components of a healthy social-emotional development. Young children develop their social-emotional skills through practice and small steps over time.

As parents or caregivers, it is fairly simple to support your child's social-emotional skills. Acts like holding him, touching him, and speaking to him and giving him loving care and attention are all helping factors. When you allow them freedom to play, it is important to follow their interests in helping build their social-emotional skills.

Difficulties in social-emotional skills can often lead to children having trouble when playing with other children. Becoming easily angry or not empathizing (理解) with other children are all signs that may point in this direction. This can in turn lead to them not empathizing with the needs of other children.

    As for the development of cognitive (认知的) skills, these develop through practice and opportunity over time. And while some cognitive skills may be genetic, most are learned through real life situations. In other words, learning and thinking skills can be improved through experiences.

    To enable them to learn, it is important that we are mindful of what our children are interested in. And this realization is only set in place once the child is given enough room and time to grow and explore.

    Depriving children of such experiences can mean that they might struggle with higher- level thinking skills. And while it is normal to keep them safe, we forget that by rushing them and cutting down on play time, we're actually causing more harm than good.

    Staying positive through the cold season could be your best defense against getting ill,a new American study suggests.

    In an experiment that exposed healthy volunteers to a cold or flu virus,researchers found that people with a generally sunny character were less likely to fail ill.The findings,published in the journal Psychosomatic Medicine, build on evidence that a “positive emotional style” can help ward off the common cold and other illness.

    Researchers believe the reasons may be both objective―as in happiness improving immune function―and subjective―as in happy people being less troubled by a sore throat or runny nose.“People with a positive emotional style may have different immune responses to the virus,” explained lead study author Dr Sheldon Cohen of Carnegie Mellon University in Pittsburgh.“And when they do get a cold,they may interpret their illness as being less severe.”

    Cohen and his colleagues has found in a previous study that happier people seemed less likely to catch a cold, but some questions remained as to whether the emotional quality itself had the effect.

    For the new study,the researchers had 193 healthy adults complete standard measures of personality qualities, physicals health,and emotional “style”.Those who tended to be happy,energetic and easy –going were judged as having a positive emotional style,while those who were often unhappy,tense,and hostile had a negative style.

    Afterwards,the researchers gave them nose drops containing either a cold virus or a particular flu virus.Over the next six days,the volunteers reported on any aches,pains,sneezing they had,while the researchers collected objective data.Cohen and his colleagues found that happy people were less likely to develop a cold.

    What's more,when happy folks did develop a cold,their symptoms were less severe than expected based on objective measures.

    On the contrary,people with negative characters were not at increased risk of developing a cold based on objective measures,though they did tend to get down about their symptoms.

    “We find that it's really positive emotions that have the big effect,” Cohen said,“not the negative ones.”

    So can a bad-tempered person fight a cold by deciding to be happy?

    Zoe Chambers was a successful PR (Public Relations) consultant (顾问) and life was going well—she had a great job, a beautiful flat and a busy social life in London. Then one evening in June last year, she received a text message telling her she was out of work. The first two weeks were the most difficult to live through.” she said. “After everything I'd done for the company, they dismissed me by text!I was So angry and I just didn't feel like looking for another job. I hated everything about the city and my life.”

    Then, Zoe received an invitation from an old school friend, Kathy, to come and stay. Kathy and her husband, Huw, had just bought a farm in north-west Wales. Zoe jumped at the chance to spend a weekend away from London, and now, ten months later, she is still on the farm.

    “The moment I arrived at Kathy's farm, I loved it and I knew I wanted to stay.” said Zoe.“ Everything about

my past life suddenly seemed meaningless.”

    Zoe has been working on the farm since October of last year and says she has no regrets. “It's a hard life, physically very tiring. ”she says. “In London I was stressed and often mentally exhausted. But this is a good, healthy tiredness. Here, all I need to put me in a good mood is a hot bath and one of Kathy's wonderful dinners. ”

    Zoe says she has never felt bored on the farm. Every day brings a new experience. Kathy has been teaching her how to ride a horse and she has learnt to drive a tractor. Since Christmas, she has been helping with the lambing-—watching a lamb being born is unbelievable, she says, “It's one of the most moving experiences I've ever had. I could never go back to city life now. ”

The young boy saw me, or rather, he saw the car and quickly ran up to me, eager to sell his bunches of bananas and bags of peanuts. Though he appeared to be about twelve, he seemed to have already known the bitterness of life. "Bananas 300 naira. Peanuts 200 naira." He said in a low voice. I bargained him down to 200 for the fruit and nuts. When he agreed, I handed him a 500 naira bill. He didn't have change. So I told him not to worry. He said thanks and smiled a row of perfect teeth.

    When, two weeks later, I saw the boy again, I was more aware of my position in a society where it's not that uncommon to see a little boy who should be in school standing on the corner selling fruit in the burning sun. My parents had raised me to be aware of the advantage we had been afforded and the responsibility it brought to us.

I pulled over and rolled down my window. He had a bunch of bananas and a bag of peanuts ready. I waved them away. "What's up?" asked him. "I…I don't have money to buy books for school." I reached into my pocket and handed him two fresh 500 naira bills. "Will this help?" I asked. He looked around nervously before taking the money. One thousand naira was a lot of money to someone whose family probably made about 5,000 naira or less each year. "Thank you, sir." he said. "Thank you very much!"

    When driving home, I wondered if my little friend actually used the money for schoolbooks. What if he's a cheat? And then I wondered why I did it. Did I do it to make myself feel better? Was I using him? I didn't know his name or the least bit about him, nor did I think to ask.

    Over the next six months, I was busy working in a news agency in northern Nigeria. Sometime after I returned, I went out for a drive. When I was about to pull over, the boy suddenly appeared by my window with a big smile ready on his face.

"Oh, gosh! Long time."

"Are you in school now?" I asked.

    He nodded.

"That's good," I said. A silence fell as we looked at each other, and then I realized what he wanted. "Here," I held out a 500 naira bill. "Take this." He shook his head and stepped back as if hurt. "What's wrong?" I asked. "It's a gift."

He shook his head again and brought his hand from behind his back. His face shone with sweat. He dropped a bunch of bananas and a bag of peanuts in the front seat before he said, "I've been waiting to give these to you."

    Grown-ups are often surprised by how well they remember something they learned as children but have never practiced ever since. A man who has not had a chance to go swimming for years can still swim as well as ever when he gets back in the water. He can get on a bicycle after many years and still ride away. He can play, catch and hit a ball as well as his son. A mother who has not thought about the words for years can teach her daughter the poem that begins "Twinkle, twinkle, little star" or remember the story of Cinderella or Goldilocks and the Three Bears.

    One explanation is the law of overlearning, which can be stated as follows: Once we have learned something, extra learning trials (尝试) increase the length of time we will remember it.

    In childhood we usually continue to practice such skills as swimming, bicycle riding, and playing baseball long after we have learned them. We continue to listen to and remind ourselves of words such as "Twinkle, twinkle, little star" and childhood tales such as Cinderella and Goldilocks. We not only learn but overlearn.

    The multiplication tables (乘法口诀表) are an exception (例外) to the general rule that we forget rather quickly the things that we learn in school, because they are another of the things we overlearn in childhood.

The law of overlearning explains why cramming (突击学习) for an examination, though it may result in a passing grade, is not a satisfactory way to learn a college course. By cramming, a student may learn the subject well enough to get by on the examination, but he is likely soon to forget almost everything he learned. A little overlearning, on the other hand, is really necessary for one's future development.