题型:阅读理解 题类:常考题 难易度:普通
江苏省海安高级中学2019届高三上学期英语12月月考试卷
Anyone watching the autumn sky knows that migrating birds fly in a V formation, but scientists have long debated why. A new study finds that these big-winged birds carefully position their wingtips and flap(拍动) at the same rate, probably to catch the upward movement of air and save energy during flight.
There are two reasons birds might fly in a V formation: It may make flight easier, or they're simply following the leader. Squadrons(中 队) of planes can save fuel by flying in a V formation, and many scientists suspect that migrating birds do the same. Models that treated flapping birds like fixed-wing airplanes show that they probably save energy by drafting off each other, but currents created by airplanes are far more stable than those coming off of birds.
Just as aerodynamic(气动力) calculations would predict, the birds positioned themselves to fly just behind and to the side of the bird in front, timing their wing flaps to catch the uplifting eddies(涡流). When a bird flew directly behind another, the timing of the flapping reversed(相反) so that it could minimize the effects of the downdraft coming off the back of the bird's body. “We didn't think this was possible,” Usherwood says, considering that the difficult achievement requires careful flight and incredible awareness of one's neighbors. “Perhaps these big V formation birds can be thought of quite like an airplane with wings that go up and down.”
The findings likely apply to other long-winged birds, such as pelicans and geese, Usherwood says. Smaller birds create more complex wakes(尾波) that would make drafting too difficult. The researchers did not attempt to calculate the birds' energy savings because the necessary physiological measurements would be too invasive for an endangered species. Previous studies show that birds can use 20% to 30% less energy while flying in a V.
Scientists do not know how the birds find that aerodynamic sweet spot, but they suspect that the animals line themselves up either by sight or by sensing air currents through their feathers. In future studies, the researchers will switch to more common birds, such as pigeons or geese. They plan to investigate how the animals decide who sets the course and the pace, and whether a mistake made by the leader can ripple through the rest of the flock to cause traffic jams.
For: Boys & Girls aged 7-10 Dates: 3 Sundays ● Sunday, April3 ● Sunday, April24 ● Sunday, May15 Time: Sundays: 10 am--3:15 pm Cost: $80 per day, per kid Instructors: Jonathan Gonzalez, Stephanie Giesel, Paul Tobin, teen instructors and other visiting elders. Location: Stony Kill Road in Accord, NY Additional Questions and Information: Please contact Simon Abram-son with questions about the content of this program. Simon is reachable at(845) 256-9830 or simon@wilderth.org. | Spring Discovery This spring, we will gather in the forest to play games, tell stories around the fire, explore the nature and so much more! Join us for any of the Kestrel Sundays! Together, we will safely explore the nature and build lasting friendships with each other and stay in the village where the children have enriched each summer at camp. Children walk away from Kestrel feeling at home in nature and at home in themselves. Each day begins with a morning circle where thanksgiving, songs and games bring us further into our bodies. The days are filled with nature-based games that expand our awareness, storytelling from skilled instructors and visiting elders, songs inspired by nature's beauty, exploring the forest and looking for mysteries, sculpting clay, and wandering the caves. At the end of the day, with leaf and flower on our heads,our faces painted and smiles on our faces, we'll return! Kestrel is where your child will: Play and explore the beautiful outdoors. Experience and practice a variety of wilderness skills and native technology. Practice awareness, quiet-mind, animal forms, curiosity, exploration, telling the story of the day, and gratitude. Face personal and group challenges tailored to build awareness, self-confidence and group unity. Our Kestrel instructors are experts in guiding children to safety and freely move in the direction of their own curiosity. |
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