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.

    Sunday is more like Monday than it used to be. Places of business that used to keep daytime“business hours” are now open late into the night. And on the Internet, the hour of the day and the day of the week have become irrelevant（不相关的）. A half century ago in the United States, most people experienced strong and precise dividing lines between days of rest and days of work, school time and summer time. Today the boundaries still exist, but they seem not clear.

    The law in almost all states used to require stores to close on Sunday; in most, it no longer does. It used to keep the schools open in all seasons except summer; in most, it still does. And whether the work week should strengthen its legal limits, or whether it should become more “flexible,” is often debated. How should we, as a society, organize our time? Should we go even further in relaxing the boundaries of time until we live in a world in which every minute is much like every other?

    These are not easy questions even to ask. Part of the difficulty is that we rarely recognize the “law of time” even when we meet it face to face. We know as children that we have to attend school a certain number of hours, a certain number of days, a certain number of years — but unless we meet the truant officer (学监), we may well think that we should go to school due to social custom and parents' demand rather than to the law. As adults we are familiar with “extra pay for overtime working,” but less familiar with the fact that what constitutes（构成）“overtime” is a matter of legal definition. When we turn the clock forward to start daylight-saving time, have we ever thought to ourselves: “Here is the law in action”? As we shall see, there is a lot of law that has great influence on how we organize and use time: compulsory education law, overtime law, and daylight-saving law — as well as law about Sunday closing, holidays, being late to work, time zones, and so on. Once we begin to look for it, we will have no trouble finding a law of time to examine and assess.

    They wear the latest fashions with the most up­to­date accessories(配饰)．Yet these are not girls in their teens or twenties but women in their sixties and seventies. A generation which would once only wear old­fashioned clothes is now favouring the same high street looks worn by those half their age.

    Professor Julia Twigg，a social policy expert，said，“Women over 75 are now shopping for clothes more often than they did when they were young in the 1960s.In the 1960s buying a coat for a woman was a serious matter. It was an expensive item that they would purchase only every three or four years—now you can pick one up at the supermarket whenever you wish to. Fashion is a lot cheaper and people get tired of things more quickly.”

    Professor Twigg analysed family expenditure(支出)data and found that while the percentage of spending on clothes and shoes by women had stayed around the same—at 5 or 6 per cent of spending—the amount of clothes bought had risen sharply.

    The professor said.“Clothes are now 70 per cent cheaper than they were in the 1960s because of the huge expansion of production in the Far East. In the 1960s Leeds was the heart of the British fashion industry and that was where most of the clothes came from，but now almost all of our clothes are sourced elsewhere. Everyone is buying more clothes but in general we are not spending more money on them.”

    Angela Barnard，who runs her own fashion business in London，said older women were much more affected by celebrity(名流)style than in previous years.

She said，“When people see stars such as Judi Dench and Helen Mirren looking attractive and fashionable in their sixties，they want to follow them. Older women are much more aware of celebrities. There's also the boom in TV programmes showing people how they can change their look，and many of my older customers do yoga to stay in shape well in their fifties. When I started my business a few years ago，my older customers tended to be very rich，but now they are what I would call ordinary women. My own mother is 61 and she wears the latest fashions in a way she would never have done ten years ago.”

    Our warming planet is expected to face serious water crisis（危机）in the coming decades — which means each nation's natural resource will be more important than ever.

    Have you ever received a gift that was so clearly not your taste that you wondered if perhaps it had been handed to you by mistake? Worse, have you ever given a present and watched your friend look as though she had opened the wrong box? Maybe she responded with a polite "Why, thank you," but you knew you had missed the mark. Why do presents sometimes go wrong? And what do your choices (good and bad） reflect about your personal qualities?

    Choosing the right gift is an art, I believe. It calls for empathy — the ability to put yourself into someone else's head and heart .We're all able to do this; in fact, we're born with a kind of natural empathy. After the earliest period of childhood, however, it needs to be reinforced (加强）—by our parents, teachers, friends. When it isn't, we're not able to understand other people's feelings as sharply. This can show in the gifts we select, and so can many other emotional (情感的） qualities.

Think back to the presents you've given over the past year, the time and effort you put into your selection, how much you spent, your thoughts while you were shopping, and your feelings when the receiver opened the package. Keep in mind that what you choose displays your inner world. Of course, you may express yourself differently with different friends, relatives, and other people you know.

    We live in a society where exchanging presents is an important part of communication. Ignoring the tradition won't make it go away. If you really dislike such a tradition, tell your friends ahead of time.

    No one is sure how the ancient Egyptians built the pyramids near Cairo. But a new study suggests they used a little rock 'n' roll. Long ago builders could have attached wooden poles to the stones and rolled them across the sand, the scientists say.

    "Technically, I think what they're proposing is possible." physicist Daniel Bonn said.

    People have long puzzled over how the Egyptians moved such huge rocks. And there's no obvious answer. On average, each of the two million big stones weighed about as much as a large pickup truck. The Egyptians somehow moved the stone blocks to the pyramid site from about one kilometer away.

    The most popular view is that Egyptian workers slid the blocks along smooth paths. Many scientists suspect workers first would have put the blocks on sleds. Then they would have dragged them along paths. To make the work easier, workers may have lubricated the paths either with wet clay or with the fat from cattle. Bonn has now tested this idea by building small sleds and dragging heavy objects over sand.

    Evidence from the sand supports this idea. Researchers found small amounts of fat, as well as a large amount of stone and the remains of paths.

    However, phyficmt Josepn West thought there might have been a simpler way, who led the new study. West said, "I was inspired while watching a television program showing how sleds might have helped with pyramid construction. I thought, "Why don't they just try rolling the things?" A square could be turned into a rough sort of wheel by attaching wooden poles to its sides, he realized. That, he noted, should make a block of stone "a lot easier to roll than a square".

    So he tried it.

    He and his students tied some poles to each of four sides of a 30-kilogram stone block. That action turned the block into somewhat a wheel. Then they placed the block on the ground.

    They wrapped one end of a rope around the block and pulled. The researchers found they could easily roll the block along different kinds of paths. They calculated that rolling the block required about as much force as moving it along a slippery path.

    West hasn't tested his idea on larger blocks, but he thinks rolling has clear advantages over sliding. At least, workers wouldn't have needed to carry cattle fat or water to smooth the paths.