【推荐3】What color is a tennis ball? Ask your classmates, and they might give you some surprising answers.

US magazine The Atlantic recently asked 30,000 people this question. Among them, 52 percent said tennis balls are green, 42 percent said they are yellow, and 6 percent went with other colors. According to the International Tennis Federation, tennis balls are yellow.     1    

Scientists call this color constancy (色彩恒常性). For example, we know that China's flag is red. When we see it during sunset or under purple light, we still know that it is red, even if it looks like a different color.     2     Even if the object is seen in different kinds of light later, our brain can still tell its true color.

    3     It appears to be a combination of yellow, a ''warm'' color and green, a ''cool'' color.

According to The Atlantic, when our brains try to figure out what color the ball is, some people ignore ''cool'' colors, such as green, blue and purple. So they see the ball as being yellow.    4     They see the ball as being green.

    5     In 2015, a girl posted a picture of a dress online. Some people believed the dress was black and blue—but others thought it was gold and white. They had different opinions based on whether they ignored ''cold'' or ''warm'' colors.

【推荐1】With the weather getting hot, bites caused by mosquitoes not only annoy people, but can result in many infectious diseases. Even when people wear long clothes, mosquitoes' complex biting mechanism enables them to bite some of them through.

It would be great if clothing could be used to completely prevent people from getting bitten. Researchers tested graphene (石墨烯), a material that is incredibly thin but really strong, in order to find out if it can make clothing resistant to mosquitoes.

In the lab experiment, volunteers exposed a small patch of skin on their arm or hand to roughly 100 mosquitoes for five minutes at a time. Researchers tested three different situations: volunteers wearing no protection, wearing cheesecloth (薄纱棉布), or wearing cheesecloth plus a thin graphene layer under it.

A video camera was then used to record and quantify mosquitoes' behavior, including whether they landed on the skin, how long they stayed there, and whether they began to draw blood. The number of bites each volunteer got was also calculated based on how many swellings developed on their skin afterward. Finally, researchers dropped a little water or sweat on top of the graphene layer and studied the consequence,                                        and they also tested a slightly different graphene layer called "reduced graphene".

As a result, the number of mosquito bites on naked skin was the highest, about 16 on average; skin only protected by cheesecloth got the second, approximately 10 per five minutes' exposure. The exciting finding was that there was no swelling developing on skin covered by the thin graphene layer under cheesecloth, which means the material is effective at preventing mosquito bites. The mosquitoes landed on skin totally uncovered or covered in cheesecloth about 23 times on average, and stayed for one to two minutes. Comparatively, the mosquitoes landed on skin covered in the graphene layer fewer than 10 times, and the length of their stay was much shorter. Besides, water or sweat can ruin the graphene layer, which allows mosquitoes to bite through it. But fortunately, the number of mosquito bites in either dry or wet conditions can be lowered as long as the graphene material is improved to a certain extent.

【推荐2】A living robot has been created out of frog skin cells. Xenobots, named after the frog species Xenopus laevis that the cells come from, were first described last year. Now the team behind the robots has improved their design and demonstrated new capabilities.

To create the xenobots, Michael Levin at Tufts University in Massachusetts and his colleagues obtained tissue from 24-hour-old frog embryos after very small physical operation. Where the previous version relied on the contraction of heart muscle cells to move them forward by pushing off surfaces, these new xenobots swim around faster. They also live between three and seven days longer than their previous generation, which only lasted about seven days, and have the ability to sense their surroundings to some extent, turning red when exposed to blue light.

“The fundamental finding here is that when you free skin cells from their normal context, and you give them a chance to build other things than what they normally build,” says Levin. “To me, one of the most exciting things here is that they are plastic. This idea that even normal cells, not genetically modified, are in fact capable of building something completely different.”

Because they are created from cells, the xenobots eventually break apart and are totally biodegradable, says team member Douglas Blackiston, also at Tufts University. He therefore hopes that they can be used for biomedical and environmental applications.

Previous attempts at creating living robots, such as a wirelessly controlled cockroach, have involved dealing with live animals, raising ethical concerns. Xenobots differ from these because they are made entirely of living cells. “The approach here is maybe ethically the least problematic because everything starts with cells. They have no neurons, so it's not an animal,” says Auke ljspeert at the Swiss Federal Institute of Technology at Lausanne, who wasn't involved in the research. “It's really cells, so I find it maybe the cleanest way."

【推荐3】Next time you’re in a public place, take a look around you, and count how many people are using their phones. I can tell you now that it is probably more than half, whether you’re on public transport, in a cafe or simply walking down the street.

I’m not saying that I am not an example of this, but it always amazes me how people can spend so much time on their phones without actually talking to anyone in particular.

For example, I recently visited London and travelled on the tube while I was there. Apart from the people asleep, almost everybody else was on their phones, and because of the nature of the tube, it is difficult not to see exactly what they are all doing. Of course, being underground it is difficult for you to get any signal, which rules out texting or using the Internet, but there is still plenty you can use your phones for. People were playing games, reading articles and listening to music, and I am sure that as soon as they emerged from the train station they would start texting or calling or checking their emails.

Recently, my smartphone broke and had to be sent off to the warehouse for repair for a week or so. In the meantime I had to use a really old, basic phone just to keep me in touch with my family and friends. All I could do on this phone was send text messages, make calls and play one game. And I loved it. I loved being free from the Internet, and I really didn’t mind not having constant updates about what my friends were doing or what the latest celebrity story was. It allowed me to spend more lime taking in my surroundings.

However, I knew that as soon as I got my smartphone hack I would be one of those people once again. Perhaps I should just go back to using the basic phone and forget my smartphone.

【推荐1】Each year on February 2nd, there is special festival called Groundhog Day (土拨鼠日) forecasting event in Punxsutawney, Pennsylvania. When it comes, people from around the world, including 5,000 in the small town today, watch this tongue-twisting(发音饶舌的) small town for a sign from one groundhog that supposedly predicts when that years' spring will arrive.

If it's a cloudy day outside when the groundhog pops from its cave, then spring will arrive early that year. However, if it is sunny outside, the groundhog will supposedly be scared by its own shadow, hiding underground for six more weeks of cold weather.

Of course, Punxsutawney Phil's prediction is no more able to guarantee the extended forecast than your local weatherman. ABC News reports that an analysis by the National Climate Data Center found that Phil's predictions are more often wrong than right.

Philis is also found to have made some unpleasant predictions. Ever since 1887, he has predicted 99 extended winters and just 16 early springs .Nine of the years' predictions were unavailable, according to ABC.

The holiday began as a German tradition in 18th century and became even more of a cultural phenomenon after the 1993 film Groundhog Day starring Bill Murray.

Punxsutawney Phil has become a celebrity in his own right. Each year, the fatter animal with long teeth is watched by millions as he emerges from a cave in the town he is named after. Phil has become so beloved by the town that he actually lives in the local library with his “wife" Phyllis.

Taking inspiration from the hard state of Bill Murray’s character in the classic film, Yahoo contributor Owen Rust says Groundhog Day is a good time to reflect on one’s routines.