Hummingbirds(蜂鸟) are one of nature's most energetic fliers and the only birds to hover(盘旋) in the air by relying on their strength alone.

    Now scientists have found that it is the ratio(比值) of the bird's wing length to its width that makes them so efficient. The discovery is helping experts compete with 42 million years of natural selection to build helicopters that are increasingly efficient.

    David Lentink, an assistant professor at Stanford University in California, tested wings from 12 different species of hummingbirds, which he sourced from museums. He placed them on a machine used to test the aerodynamics(气力学) of the helicopter blades(桨叶). Professor Lentink's team used the same machine to test the blades from an advanced micro-helicopter used by the UK's army. They found that the micro-helicopter's blades are as efficient at hovering as the average hummingbirds.

    But while the micro-helicopter's blades kept pace with the average hummingbird wings, they could not keep up with the most efficient hummingbird's wing. The wings of Anna's hummingbird were found to be about 27 percent more efficient than the man-made micro- helicopter's blades.

    While Professor Lentink wasn't surprised at nature's superiority, he said that helicopter blades have come a long way. “The technology is at the level of an average hummingbird,” he said. “A helicopter is really the most efficient hovering device that we can build. The best hummingbirds are still better, but I think it's amazing that we're getting closer. It's not easy to match their performance, but if we build better wings with better shapes, we might match hummingbirds.”

    Professor Lentink said that we don't know how hummingbirds maintain their flight in a strong wind, how they navigate(确定方向) through branches, or how they change direction so quickly. He thinks that great steps could be made by studying wing aspect ratios-the ratio of wing length to wing width. Understanding these abilities and characteristics could be a benefit for robotics and will be the focus of future experiments.

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    Recent summer temperatures in parts of Australia were high enough to melt asphalt. As global warming speeds up the heat and climatic events increase, many plants may be unable to cope. But at least one species of eucalyptus tree can resist extreme heat by continuing to “sweat” when other essential processes stop, a new study finds.

    As plants change sunlight into food, or photosynthesize (光合作用), they absorb carbon dioxide through pores on their leaves. These pores also release water via transpiration(蒸腾), which circulates nutrients through the plant and helps cool it by evaporation(蒸发). But exceptionally high temperatures are known to greatly reduce photosynthesis—and most existing plant models suggest this should also decrease transpiration, leaving trees in danger of fatally overheating. Because it is difficult for scientists to control and vary trees' conditions in their natural environment, little is known about how individual species handle this situation.

    Ecologist John Drake of the S.U.N.Y. College of Environmental Science and Forestry and his colleagues grew a dozen Parramatta red gum (Eucalyptus parramattensis) trees in large, climate-controlled plastic pods that separated the trees from the surrounding forest for a year in Richmond, Australia. Six of the trees were grown at surrounding air temperatures and six at temperatures three degrees Celsius higher. The researchers withheld (扣留) water from the surface soil of all 12 trees for a month to imitate a mild dry spell, then induced a four-day “extreme” heat wave: They raised the maximum temperatures in half of the pods（three with surrounding temperatures and three of the warmer ones）— to 44 degrees ℃.

    Photosynthesis ground to a near halt in the trees facing the artificial heat wave. But to the researchers' surprise, these trees continued to transpire at close-to-normal levels, effectively cooling themselves and their surroundings. The trees grown in warmer conditions coped just as well as the others, and photosynthesis rates bounced back to normal after the heat wave passed, Drake and his colleagues reported online in Global Change Biology.

    The researchers think the Parramatta red gums were able to effectively sweat — even without photosynthesis — because they are particularly good at tapping into water deep in the soil. But if a heat wave and a severe drought (干旱) were to hit at the same time and the groundwater was exhausted, the trees may not be so lucky, Drake says.

    Other scientists call the finding encouraging. “It's definitely good news,” says Trevor Keenan, an ecologist at Lawrence Berkeley National Laboratory, who was not part of the study. “It would be very interesting to know how this translates to other species,” he adds. Drake hopes to conduct similar experiments with trees common in North America.

    Oh, the places you'll go!

    When it comes to habitat, human beings are creatures of habit. It has been known for a long time that, whether his habitat is a village, a city or, for real globe-trotters (周游世界者), the planet itself, an individual person generally visits the same places regularly. The details, though, have been surprisingly obscure. Now, thanks to an analysis of data collected from 40,000 smartphone users around the world, a new property of humanity's locomotive (移动的) habits has been revealed.

    It turns out that someone's "location capacity", the number of places which he or she visits regularly, remains constant over periods of months and years. What constitutes a "place" depends on what distance between two places makes them separate. But analyzing movement patterns helps illuminate the distinction and the researchers found that the average location capacity was 25. If a new location does make its way into the set of places an individual tends to visit, an old one drops out in response. People do not, in other words, gather places like collector cards. Rather, they cycle through them. Their geographical behavior is limited and predictable, not fancy-free.

    The study demonstrating this, just published in Nature Human Behavior, does not offer any explanation for the limited location capacity it measures. But a statistical analysis carried out by the authors shows that it cannot be explained solely by constraints on time. Some other factor is at work. One of the researchers draws an analogy. He suggests that people's cognitive capacity limits the number of places they can visit routinely, just as it limits the number of other people an individual can routinely socialize with. That socialization figure, about 150 for most people, is known as the Dunbar number, after its discoverer, Robin Dunbar.

    Lehmann says his group is now in search of similar data from other primates (灵长目动物), in an attempt to work out where human patterns of mobility have their roots. For those, though, they will have to rely on old-fashioned methods of zoological observation unless they can work out a way to get chimpanzees to carry smartphones.

    Generally speaking, waiting rooms are always filled with a lot of impatient people. However, a project carried out by The Observer suggests that people regard these spaces as a place of refuge (避难), a window in their tightly scheduled lives.

    Ella Doroudy, Margate Station

    We were at the beach for the day, and now are on our way home. We don't have to wait very long, because we checked the timetable so we got here in time for the train. I just chat with my mates, really, and listen to music until the train comes. Waiting with other people is easier because you can kill time when you're talking about stuff.

    Caroline Lacey, Streatham Dental Center

    I don't really get nervous about seeing the dentist, but since these two fillings (补牙的材料) came out I've been in sharp pain. It's very bright and airy here, so it's quite calming. Usually I kill time by reading magazines. I've been coming to the dentist as and when I need to, but now it's got to be regular.

    Katie Hawkins, Model Casting

    I was a bit late today, which I'm quite pleased about because some of these girls have been waiting ages. I can't help but look at everyone else a bit — I look at the other girls and think: "I wonder if they'll like her better than they like me." While I'm waiting, I'm thinking: "Oh come on. I do have a life!"

    Paul Thomas, Royal London Hospital

    I feel pretty indifferent (满不在乎的)  while I'm waiting here, to be honest. It's something I've got very used to since my motorbike accident seven years ago. I've had about 32 operations so far. It's no good rushing in thinking you're going to escape in five minutes, so I just sit back and people-watch, really.

    Since 50 years ago, scientists have been searching for ways to link the brain with computers. Brain Computer Interface (BCI) technology could help people with disabilities send commands to machines.

    Recently, two researchers, Jose Millan and Michelle Tavella from the Federal Polytechnic School in Lausanne, Switzerland, demonstrated (展示) a small robotic wheelchair directed by a person's thoughts.

    In the laboratory, Tavella operated the wheelchair just by thinking about moving his left or right hand. He could even talk as he watched the vehicle and guided it with his thoughts.

    "Our brain has billions of nerve cells. These send signals through the spinal cord (脊髓) to the muscles to give us the ability to move. But spinal cord injuries or other conditions can prevent these weak electrical signals from reaching the muscles," Tavella says, "Our system allows disabled people to communicate with external world and also to control devices."

    The researchers designed a special cap for the user. This head cover picks up the signals from the scalp (头皮) and sends them to a computer. The computer interprets the signals and commands the motorized wheelchair. The wheelchair also has two cameras that identify objects in its path. They help the computer react to commands from the brain.

    Prof. Millan, the team leader, says scientists keep improving the computer software that interprets brain signals and turns them into simple commands. "The practical possibilities that BCI technology offers to disabled people can be grouped in two categories: communication, and controlling devices. One example is this wheelchair." He says his team has set two goals. One is testing with real patients, so as to prove that this is a technology they can benefit from. And the other is to guarantee that they can use the technology over long periods of time.

When I was about twelve, I headed to a restaurant for dinner with my family. It was winter, and on that night the wind was really blowing hard. 

As my mum and I headed to the restaurant from our car, a girl about my age and her mother came up to us. They asked if we had any spare change(零钱). My mum right away asked where they lived. They pointed to an old car in a parking lot across the street. The girl said there were six of them living in that car. 

My mum said she had something to do after handing the people a few dollars. She sent me inside the restaurant with my dad and my three siblings(兄弟姐妹). But she didn't come. Later, I found out she had gone home and put all the food in our cupboards into a few bags. Then, she brought that food over to the car and handed the bags to the family. I wasn't there when that happened, but I can only imagine the joy it brought to those people. A few days later, when I actually found out about what she had done, I asked her why she helped those people. She told me that they were not lucky. I remembered the face of that girl who had asked us for change. She was the same age as me, yet we looked so different. 

Here I stood, dressed in almost new clothes, headed to eat in a restaurant and then went back home to the bedroom I shared with my younger sister. I remembered thinking the other girl didn't have any food to eat and that she was heading back to a cold car shared with five other people. 

After painting this picture in my mind, I understood why my mum had done what she did. I will never forget what she did that night, and how she taught me one of the best lessons I have ever learned.