Below is a selection from a popular science book.

    If blood is red, why are veins（静脉） blue?

    Actually, veins are not blue at all. They are more of a clear, yellowish color. Although blood looks red when it's outside the body, when it's sitting in the vein near the surface of the skin, it's more of a dark reddish purple color. At the right depth, these blood-filled veins reflect less red light than the surrounding skin, making them look blue by comparison.

    Which works harder, you heart or your brain?

    That kind of depends on whether you're busy thinking or busy exercising. Your heart works up to three times harder during exercise, and shifts enough blood over a lifetime to fill a supertanker. But in the long run, your brain probably tips it, because even when you're sitting still your brain is using twice as much energy as your heart, and it takes four to five times as much blood to feed it.

    Why do teeth fall out, and why don't they grow back in grown-ups?

    Baby (or “milk”) teeth do not last long; they fall out to make bigger room for bigger, stronger adult teeth later on. Adult teeth fall our when they become damaged, decayed and infected by bacteria. Once this second set of teeth has grown in, you're done. When they're gone, they are gone. This is because nature figures you're set for life, and what controls regrowth of your teeth switches off.

    Do old people shrink as they age?

Yes and no. Many people do get shorter as they age. But, when they do, it isn't because they're shrinking all over. They lose height as their spine（脊柱） becomes shorter and more curved due to disuse and the effect of gravity(重力). Many (but not all) men and women do lose height as they get older. Men lose and average of 3-4 cm in height as they age, while women may lose 5 cm or more. If you live to be 200 years old, would you keep shrinking till you were, like 60 cm tall, like a little boy again? No, because old people don't really shrink! It is not that they are growing backwards —- their legs, arms and backbones getting shorter. When they do get shorter, it's because the spine has shortened a little. Or, more often, become more bent and curved.

    Why does spinning make you dizzy（眩晕的）?

    Because your brain gets confused between what you're seeing and what you're feeling. The brain senses that you're spinning using special gravity-and-motion-sensing organs in your inner ear, which work together with your eyes to keep your vision balance stable. But when you suddenly stop spinning the system goes out of control, and your brain thinks you'removing while you're not.

    Where do feelings and emotions come from?

Mostly from an ancient part of the brain called the limbic system. All mammals have this brain area —- from mice to dogs, cats, and humans. So all mammals feel basic emotions like fear, pain and pleasure. But since human feelings also involve other, newer bits of the brain, we feel more complex emotions than any other animal on this planet.

    If exercise wears you out, how can it be good for you?

    Because our bodies adapt to everything we do to them. And as far as your body is concerned, it's “use it, or lose it”! It's not that exercise makes you healthy, it's more that a lack of exercise leaves your body weak and easily affected by disease

                                                                     The Diet Zone: A Dangerous Place

    Diet Coke, diet Pepsi, diet pills, no-fat diet, vegetable diet… We are surrounded by the word “diet” everywhere we look and listen. We have so easily been attracted by the promise and potential of diet products that we have stopped thinking about what diet products are doing to us. We are paying for products that harm us psychologically and physically.

    Diet products significantly weaken us psychologically. On one level, we are not allowing our brain to admit that our weight problems lie not in actually losing the weight, but in controlling the consumption of fatty, high-calorie, unhealthy foods. Diet products allow us to jump over the thinking stage and go straight for the scale(秤)instead. All we have to do is to swallow or recognize the word “diet” in food labels.

    On another level, diet products have greater psychological effects. Every time we have a zero-calorie drink, we are telling ourselves without our awareness that we don't have to work to get results. Diet products make people believe that gain comes without pain, and that life can be without resistance and struggle.

    The danger of diet products lies not only in the psychological effects they have on us, but also in the physical harm that they cause. Diet foods can indirectly harm our bodies because consuming them instead of healthy foods means we are preventing our bodies from having basic nutrients. Diet foods and diet pills contain zero calorie only because the diet industry has created chemicals to produce these wonder products. Diet products may not be nutritional, and the chemicals that go into diet products are potentially dangerous.

    Now that we are aware of the effects that diet products have on us, it is time to seriously think about buying them. Losing weight lies in the power of minds, not in the power of chemicals. Once we realize this, we will be much better able to resist diet products, and therefore prevent the psychological and physical harm that comes from using them.

    It happens from time to time: you feel terrible when you take your first bite of a certain food, but after eating more, you find yourself enjoying it. This is what is called an acquired taste. But why do our tastes change?

    The answer, according to a recent study presented at an American Chemical Society meeting in Boston, lies in proteins in our saliva (唾液).

    Most of us tend to think saliva, almost entirely made up of water, is “only a mouth lubricant (润滑剂) helping us to swallow food,” the New York Times said. However, it also contains many proteins, which can help break food down, protect our teeth and help in tasting food.

    To explain how these proteins affect taste, a team of scientists from Purdue University in the US invited 64 volunteers to drink a bitter-tasting chocolate milk three times a day for six weeks and rated their tastes at the same time.

    According to the research, the participants found a strong bitterness on the first day, but the unpleasant flavor came to decrease as time went on and finally disappeared.

    That is not all that was changing. A noticeable increase in the levels of proline-rich (富含脯氨酸的) proteins was found in the saliva samples of the test subjects in the research period. These proteins serve to reduce the bitterness we taste and improve our adaptation to this flavor.

    “We think the body adapts to reduce the negative feeling of these bitter compounds,” said Cordelia Running, a food scientist at Purdue University. “Saliva changes flavor, which in turn changes eating choices.”

    This change in taste not only makes the food tastier, but also helps people keep an appetite for healthy food whose flavor might otherwise keep them away.

    One day, these proteins may even be extracted (提炼) and used as a separate food additive that could help people stick to healthy food whose flavor they continue to dislike, researchers told Science Alert. And according to Running, even it doesn't happen, the idea that “maybe some little piece of your body is actually trying to help you” could really benefit some people. Let's wait and see.

    Asking for help is a sign of strength rather than weakness. In American culture, the independent individual is seen as their ideal. As the University of Missouri at St. Louis states on its website under the heading Key American Values, “Americans have been trained since very early in their lives to consider themselves as separate individuals who are responsible for their own situations in life and their own destinies.” The value also makes them think they can do everything themselves, and makes them feel badly about asking for help when they need it.

    And when it comes to work situations, when they think about asking for help there, sometimes they fear that a request for help would make them look inept. While this has always been true for men, many women in the workplace have felt the need to try twice as hard as their male colleagues and do twice as much to get just as far and to prove their worth. Sometimes when we think about asking for help, our inner voices tell us, "See, if you admit you can't do this on your own, they'll see you for the imposter(骗子) you really are."

    But the fact is, even though individualism is on the rise, we can't do everything by ourselves and we shouldn't try.

    Apple founder Steve Jobs once told the Santa Clara Valley Historical Association about the power of asking for help, and how he "never found anybody who didn't want to help me when I asked them for help". He said, at the age of 12, he called Bill Hewlett, co-founder of Hewlett-Packard, on the phone after getting his number from the phone book and asking him for spare parts so he could build a frequency counter(计频器). And Hewlett agreed and offered young Jobs a summer job assembling frequency counters.

    "If you're afraid of failing, you won't get very far," Jobs said.

    A new study from brain researchers helps explain how the human brain evolved or changed over time, to permit people to speak and write.

    Michael Ullman, the lead researcher, a professor at Georgetown University Medical School in Washington, D.C, has been studying language learning for more than 20 years.

    Ullman says his research shows that the human brain does not have a special area or system for making language. Over time we have simply reused or co-opted (指派) parts of our brain for language. And those parts, he says, are ancient-older even than humans themselves.

    "This study examines the theoretical framework (准则) that language is learned, stored and' processed in two ancient learning and memory systems in the brain."

    Ullman, Hamrick and the rest of the team looked at data from 16 other studies on language. They found that people learn language using two memory systems: declarative and procedural. Memorizing vocabulary, for example, is a declarative memory process. But learning grammar is, mostly, a procedural memory process.

    "Declarative memory, in humans at least, is what we think of as learning memory', such as, 'Oh, remember what you said last night' or things like that. And procedural motor memory is what we often call motor memory' such as how you learn to ride a bicycle." Or, Ullman adds, "These procedural memory skills become so deeply leaned that we are no longer aware that we are doing them."

    However, Ullman explains that the two long-term memory systems can share tasks. And, he adds, the adult brain uses the systems to learn language a bit differently than a child's brain.

    "Adult language learners of a second language may use their declarative memory for using grammar patterns. They think about it purposefully. For a child, the grammar may come more naturally. They don't have to think about the grammar rules before speaking."

    In addition to language learners, Ullman's study could help people who have a brain injury that affects speaking and writing. This knowledge can also help those who have learning disabilities such as dyslexia (阅读障碍). People with dyslexia have difficulty recognizing words and symbols accurately.

A rainy day can be a chance to recharge. While you relax on the sofa with a movie, the raindrops falling on your windows might one day provide the power for your TV. This is the idea behind an invention that harvests energy from water. 

The technology is based on the triboelectric (摩擦电的) effect. An engineer at the University of Hawaii, David Ma knew that it was possible to generate electricity by rubbing two things together. So, he thought, "Why don't we use water?"

A drop of water sliding across a surface coated with two different materials would generate enough friction(摩擦) to create an electrical charge. By placing metal wires that the drop of water touched as it moved, it should be possible to harvest electricity, he reasoned. 

It worked. In fact, the researchers lit up 15 LED bulbs with a single moving water drop. 

This is not the first time that scientists have got electricity from water-generated friction. Earlier experiments, though, harvested the charge produced in a surface by a sliding drop of water. There, the surface had acted as an electrode(电极). This is different. The energy of friction is being harvested from the water itself. 

"The technology could someday power phones, sensors or other small electronics," says Christopher Oshman, an engineer at the Colorado School of Mines. "This work is a step towards harvesting the energy of moving objects all around us, including ourselves, to power the electronic devices we use every day," he says. 

"Ma has shown that the technology can work in a lab," Oshman says. Next, the Colorado researcher would like to see it tried on a larger scale, such as on an umbrella.