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 pole s to the stones and rolled then 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(滑板). 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, physicist Joseph West thinks 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 notes , 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(滑的)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.

Dear SJ,

    Losing a best friend is never easy.

    Your problem, is not just that you miss your best friend, it is that you feel empty and lost without her friendship.

    It takes time to get over a lost, and during that time, your mind is getting used to a new way of being. This is usually a good thing, even if it feels like a bad thing.

    Now that you are on your own, you are being forced to learn to be by yourself and to rely upon your own inner voice for guidance. I am sure that this feels strange for you, but if you can hang on for a bit longer, it may work to your advantage.

    Best friends are cool, but it is important to know the difference between missing someone and being too independent upon them.

    At your age, girls do tend to stick together and having a good boyfriend may not yet be the better choice. Your friend is leaving you, her best friend, for a boyfriend. Boyfriends are completely different from best friends. The distinction is that boyfriends come and go, while girl friends often stay in your life throughout high school, and even afterwards. It is a completely different sort of bond.

    I suggest that you take advantage of this period in your life to expand your horizons. Enjoy the freedom of having no best friend for a while, and hang with the group. By the time your former best friend breaks up with her boyfriend, you will be in a completely different place, a far better place.

    And, by the way, next time you feel empty and lost, try to write about it in a diary. In several months, you will look back and read it with curiosity about yourself. “Who was I then, and what could I have been thinking?”

    A student is learning to speak British English. He wonders: Can I communicate with Americans? Can they understand me? Learners of English often ask: What are the differences between British and American English? How important are these differences?

    Certainly there are some differences between British and American English. There are a few differences in grammar. For example, speakers of British English say “in hospital” and “Have you a pen?” Americans say “in the hospital!” and “Do you have a pen?” Pronunciation is sometimes different. Americans usually sound theirs in words like “bird” and “hurt”. Speakers of British English do not sound theirs in these words. There are differences between British and American English in spelling and vocabulary. For example, “colour” and “honour” are British, “color” and honor” are American.

    These differences in grammar, pronunciation, spelling and vocabulary are not important. However, for the most part, British and American English are the same language.

    The term “formal learning” refers to all learning which takes place in the classroom regardless of whether such learning is informed by conservative or progressive ideologies(思想意识). “Informal learning”, on the other hand, is used to refer to learning which takes place outside the classroom.

    These definitions(定义) provide the basic difference between the two models of learning. Formal learning is separated from daily life and may actually promote ways of learning and thinking which often run counter to those obtained form practical daily life. A characteristic feature of formal learning is the centrality of activities which can prepare for the changes of adult life outside the classroom, but it cannot, by its nature, consist of these challenges.

    In doing this, language plays an important role as a major channel for information exchange.  The language of the classroom is more similar to the language used by middle-class families than that used by working-class families. Middle class children thus find it easier to gain the language of the classroom than their working-class classmates.

Informal learning, in contrast, occurs in the setting to which it relates, making learning immediately relevant (相关的). In this context, language does not occupy such an important role: the child's experience of learning is more direct, involving sight, touch, taste, and smell senses that are not used in the classroom. Whereas formal learning is transmitted by teachers selected to perform this role, informal learning is gained as a natural part of child's socialization. Adults or older children who are proficient (熟练的) in skill or activity provide—sometimes unintentionally (无意义地)—target models of behavior in the course of everyday activity.

    Informal learning, therefore, can take place at any time and place. The motivation of learner provides another important difference between the two models of learning. The formal learner is generally motivated by some kind of external goal such as parental approval, social status, and possible financial reward. The informal learner, however, tends to be motivated by successful completion of the task itself and the partial knowledge of adult status.

    Given that learning systems develop as a response to the social and economic contexts in which they are firmly, it is understandable that modern, high urbanized (城市化) societies have concentrated almost specially on the establishment of formal education systems. What these societies have failed to recognize are the ways in which formal learning inhibits the child's multi-sensory acquisition of practical skills. The failure to provide a child with a direct education may in part account for many of the social problems which trouble our societies.

    Chocolate is good for your heart, skin and brain. Usually, people think that chocolate is bad for their health. They describe chocolate as “something to die for” or say “death by chocolate”. Now they should bite their tongues! Evidence is showing that some kinds of chocolate are actually good for you in the following ways:

    A happier heart

    Scientists at Harvard University recently examined 136 studies on cocoa—the main ingredient in chocolate and found that it does seem to strengthen the heart．Studies have shown heart benefits from increased blood flow. These benefits are the result of coca's chemicals, which seem to prevent both cell damage and inflammation (炎症)．

    Better blood pressure

    If yours is high, chocolate may help. Jeffrey Blumberg from Tufts University recently found that people with high blood pressure who ate 3.5 ounces of dark chocolate per day for two weeks saw their blood pressure drop quickly.

    Muscle magic

    Chocolate milk may help you recover after a hard workout (锻炼). In a small study at Indiana University, people who drank chocolate milk between workouts did better on a tiredness test than those who had some sports drinks.

    Better for your skin

    German researchers gave 24 women a half-cup of special cocoa every day. After three months, the women's skin was moister (滑润的) and smoother. The research shows that chocolate helps protect and increase blood flow to the skin, improving its appearance．

Brain gains

    It sounds almost too good to be true, but research suggests that chocolate may improve your memory, attention span, reaction time, and problem-solving by increasing blood flow to the brain．