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    Why is pink or purple a color for girls and blue or brown for boys?

    The answer depends largely on cultural values as well as personal experiences.To the Egyptians,green was a color that represented the hope and joy of spring,while for Muslims,it means heaven.Red is a symbol of good luck in many cultures.In China,children are given money in a red envelope to bring good fortune in the New Year.For many nations,blue is a symbol of protection and religious beliefs.Greek people often wear a blue necklace hoping to protect themselves against evils.

    People's choice of colors is also influenced by their bodies' reactions toward them.Green is said to be the most restful color.It has the ability to reduce pain and relax people both mentally and physically.People who work in green environment have been found to have fewer stomach aches.

    Red can cause a person's blood pressure to rise and increase people's appetites.Many decorators will include different shades of red in the restaurant.Similarly,many commercial websites will have a red "Buy Now" button because red is a color that easily catches a person's eye.

    Blue is another calming color.Unlike red,blue can cause people to lose appetite.So if you want to eat less,some suggest that eating from blue plates can help.

    The next time you are deciding on what to wear or what color to decorate your room,think about the color carefully.

    Along the river banks of the Amazon and the Orinoco there lives a bird that swims before it can fly, flies like a fat chicken, eats green leaves, has the stomach of a cow and has claws(爪) on its wings when young. They build their homes about 4.6m above the river, an important feature(特征) for the safety of the young. It is called the hoatzin(麝雉).

    In appearance, the birds of both sexes look very much alike with brown on the back and cream and red on the underside. The head is small, with a large set of feathers on the top, bright red eyes, and blue skin. Its nearest relatives are the common birds, cuckoos. Its most striking feature, though, is only found in the young.

    Baby hoatzins have a claw on the leading edge of each wing and another at the end of each wing tip. Using these four claws, together with the beak(喙), they can climb about in the bushes, looking very much like primitive birds. When the young hoatzins have learned to fly, they lose their claws.

    During the drier months between December and March hoatzins fly about the forest in groups of 20 to 30 birds, but in April, when the rainy season begins, they collect together in smaller living units of two to seven birds for producing purposes.

    Cao Yuan, a PhD student from China, had two papers published on strange behaviour in atom-thick layers of carbon that have opened up a new field of physics.

    Pablo Jarillo-Herrero's group at MIT was already layering and rotating (旋转) sheets of carbon at different angles when Cao joined the lab in 2014. Cao's job was to find out what happened when one graphene (石墨烯) sheet was twisted only slightly wiht respect to the other, which one theory predicted would thoroughly change the material's behaviour.

    Many physicists doubted the idea. But when Cao set out to create the subtly twisted stacks, he spotted something strange. Exposed to a small electric field and cooled to 1.7 degrees above absolute zero, the graphene—which ordinarily conducts electricity—became an insulator. That by itself was surprising. But the best was yet to come: with a slight change to the field, the twisted sheets became a superconductor, in which electricity flowed without resistance.

    The ability to get atom-thick carbon into a complex electronic state through a simple rotation now has physics demanding to engineer exciting behavior in other twisted 2D materials. Some even hope that graphene could shed light on how more-complex materials superconduct at much higher temperatures. "There are so many things we can do," says Cory Dean, a physicist at Columbia University. "The opportunities at hand now are almost irresistible."

    Hitting graphene's “magic angle”—a rotation between parallel sheets of around 1.1°—involved some trial and error, but Cao was soon able to do it reliably. His experimental skill was extremely important, says his supervisor Jarillo-Herrero. Cao pioneered a method of tearing a single sheet of graphene so that he could create a stack of two layers, from which he could then fine-tune alignment (微调校准).

    Cao loves to take things apart and rebuild them. A heart, he is “a tinkerer”, his supervisor says. On his own time, this means photographing the night sky using homemade cameras and telescopes—pieces of which usually lie across Cao's office. "Every ime I go in, it's a huge mess, with computers taken apart and pieces of telescope all over his desk," says Jarillo-Herrero.