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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    Experience the newly opened Grand Canyon West Skywalk in Colorado.Departing from Grand Canyon's South Rim by Airplane to Grand Canyon's West Rim,you will land and take a ground tour to the Skywalk! Walk on air for 70 feet over the edge of Grand Canyon West.

    This Skywalk has been open since March 28,2007.Daily visitor-ship to the Skywalk has been over 4000 people. Please be patient to enjoy your moment on the Skywalk.

    After you have experienced the one and only Grand Canyon Skywalk Glass Bridge from where you can enjoy the scenery better,you will return to the Grand Canyon West airport and take your Airplane for a flight back to the South Rim of the Canyon.This is a tour never to be forgotten as you will have walked on air over the Grand Canyon.

Tour Itinerary

    Sumeja Tulic had moved from London to New York nine months ago to attend journalism school. Yet her time in New York met with a season of never-ending ugliness in politics and acts of terrorism(恐怖主义) around the world. “One day you laugh, and then you're angry,” said Tulic. As she walked toward the subway station, she thought, “I want to see something nice. Enough of this craziness.”

    At the City Hall station, she saw a man resting against a pillar(柱子), the way anyone might, waiting for the train. The stillness was interrupted(打断) by an announcement that the next train was two stations away. Then Tulic saw the man at the pillar falling forward onto the tracks.

    The man who had fallen was not moving. In what seemed like an instant, three men jumped down to help.

    I don't know where these men got the intelligence and the quickness," Tulic said. "The man who fell was about six feet tall and quite heavy. He was kind of stuck in the tracks. It was terrifying to know that the train was coming. Will it stop? Will they succeed in pulling him out?"

    On the tracks, the unconscious(失去知觉的) man was put into a sitting position by the three men, who then lifted him from below to others who lifted from above and rolled him onto the platform. Then the rescuers were themselves rescued, pulled back to safety by helping hands. As soon as they were all clear, the train pulled in. People getting off the train walked around this unconscious man.

    Two of the men who had jumped onto the platform were holding his hands. “They were saying, ‘You're going to be fine,'” Tulic said. “This was an additional layer of goodness.”

    Doctors arrived, and the man was taken to a local hospital with serious but non-life-threatening injuries.

    “That is the greatest thing,” Tulic said. “The infrastructure(基础) in this city of millions is the people themselves providing, being there for others, without even knowing the person, who he is. It was beautiful to see.”

    Last year, when our three-year-old great-granddaughter Kylie was taken to see Santa Claus, she made sure to give him her wish list of toys. A week later, she ran into a different Santa in a mall. He stopped to ask what she wanted for Christmas. Kylie was surprised and let him know: “If you can't remember what I told you last week, how are you going to remember on Christmas Eve?”

    Mary Paul, Milwaukee, Wisconsin

    As my son Mike and I drove to the mall, we passed a Salvation Army Santa ringing his bell. “Mike,” I said, “there's Santa!” He shook his head. “That's just some guy in a Santa suit,” he said. It saddened me to think that maybe my son no longer believed in Santa, and we drove the rest of the way in silence. At the mall, we spotted another Santa greeting young believers. Suddenly, Mike took off toward him. Turning back to me, he shouted. “Now, there's the real Santa!”

    Michael E. Fahey, Huntley, Illinois

    We immigrated to America from China when I was six. Because I was shy and didn't speak English, I had few friends. My days were spent at home with my brother. Sometimes we'd help our neighbor Mr. Mueller pull weeds. One Christmas Day, there was a knock at the door. Grandma opened it, and there stood a big fellow in red with a snow-white beard, laughing, “Ho, ho, ho!” He handed out presents and made us laugh. I had so much fun. It was years later when I learned that our special Santa was our neighbor Mr. Mueller.

    Joanne Tang, Litchfield Park, Arizona

    A build-it-yourself solar still（蒸馏器） is one of the best ways to obtain drinking water in areas where the liquid is not readily available. Developed by two doctors in the U. S. Department of Agriculture, it's an excellent water collector. Unfortunately, you must carry the necessary equipment with you, since it's all but impossible to find natural substitutes. The only components required, though, are a 5＇  5＇ sheet of clear or slightly milky plastic, six feet of plastic tube, and a container — perhaps just a drinking cup — to catch the water. These pieces can be folded into a neat little pack and fastened on your belt.

    To construct a working still, use a sharp stick or rock to dig a hole four feet across and three feet deep. Try to make the hole in a damp area to increase the water catcher's productivity. Place your cup in the deepest part of the hole. Then lay the tube in place so that one end rests all the way in the cup and the rest of the line runs up — and out — the side of the hole.

    Next, cover the hole with the plastic sheet, securing the edges of the plastic with dirt and weighting the sheet's center down with a rock. The plastic should now form a cone(圆锥体) with 45-degree-angled sides. The low point of the sheet must be centered directly over, and no more than three inches above, the cup.

    The solar still works by creating a greenhouse under the plastic. Ground water evaporates (蒸发) and collects on the sheet until small drops of water form, run down the material and fall off into the cup. When the container is full, you can suck the refreshment out through the tube, and won't have to break down the still every time you need a drink.

    We're often reminded of the importance of preserving the planet as we see it for future generations—and children at St Oswald's Primary School in Chester certainly agree.

    Nine-year-old Isobel Kelleher from the school's Hummingbirds class thinks adults need to take note. “Sometimes they can be busy and I don't think they think they can make a difference，but if everyone does a little bit it all adds up，” she tells HuffPost UK.“ We started looking at plastic pollution in our oceans and the things like plastic bags and broken down pieces of plastic that are polluting them.” she says.“ Fish can eat the plastic and they can die，or we might even eat the fish ourselves.”

    Mr Timms，Isobel's teacher，has been spearheading a new project at the school which lets children loose creatively to raise awareness of the need to be more environmentally friendly. The entire Hummingbirds class，which is made up of 9 and 10-year-old pupils，has been busy writing poems and creating online video adverts to warn adults about the serious situation of our oceans and wildlife.

    Mr Timms thinks children have an important role to play in teaching us how to take care of the things around us. We sometimes overlook how much we can really learn from children.” he says.“ It has been really hard to believe having parents come in saying that their children have been asking them to stop using plastic，and to recycle more，and even stopping them using plastic straws.”

    Mr Timms is proud of his Hummingbirds class.“ The message that they would like to send to the world is simple stopping this isn't someone else's job，and it won't be OK if we just leave it.”