gta5低端显卡设置:为什么鲨鱼能游这么快

为什么鲨鱼会游这么快？

By ScienceNow  November 30, 2011  |  10:15 am  |  Categories: Animals, Physics 

ScienceNow，2011年11月30日|10:15|类别：动物，物理

By Elizabeth Pennisi, ScienceNOW

     伊利莎白·彭尼斯(Elizabeth Pennisi) ScineceNOW

Researchers have discovered what makes the shark almost impossible to outswim. By using an engineering imaging technique, researchers have discovered that as a shark’s tail swings from side to side, it creates twice as many jets of water as other fishes’ tails, smoothing out the thrust and likely making swimming more efficient. Sharks do this by stiffening the tail midswing, a strategy that might one day be applied to underwater vehicles to improve their performance.

      研究人员已发现鲨鱼游动速度几乎无法超越的原因。通过使用工程成像技术，研究人员发现鲨鱼每摆动一次尾鳍，激起的水量是其他鱼的两倍，这会缓和推力并有助于游动。鲨鱼是通过在摆动中让尾巴变硬达到这一效果的。这种策略有可能用于改善水下交通工具的性能。

“The authors have made a persuasive argument that muscles in the fin are modifying the shape and possibly the texture of the fin to modify the [water] flow” throughout the stroke cycle, says Frank Fish, a biomechanist at West Chester University in Pennsylvania.

   “作者的论据非常有说服力。在一次行程中鱼鳍上的肌肉可以修改鱼鳍的形状甚至纹理来调节水流的大小。”来自宾夕法尼亚州的西彻斯特大学的生物医学专家弗朗克·菲什(Frank Fish)说到。

For fish to move forward, they have to push water backward. And sharks have an added burden: they sink when they stop swimming, so they must be in constant motion. To help generate lift to keep midwater, the top of the tail extends farther back than the bottom, creating a slant along the back edge. Most other fish have tails that are essentially symmetrical from top to bottom.

    鱼要想往前游，它们必须往后推水。对鲨鱼来说，还有别的负担：它们停止游动时就会下沉，所以它们必须不停地游动。为了保持在水中不至于沉底，尾部的顶端比底端向后延伸，沿着后端形成一个斜面，产生提力。其他鱼的尾巴基本上都是从上到下对称的。

Curious about how the shark tail works, Harvard University biomechanist Brooke Flammang has been examining its structure and function. In 2005, she discovered a tail muscle that seemed to activate at peculiar times during the tail’s swing back and forth. To understand the muscle’s role, she decided to track in fine detail how the shark pushes water backward.

    为了弄清鲨鱼尾巴的工作原理，哈佛大学的生物医学专家布鲁克?弗拉芒一直在研究它的结构和功能。2005年她发现尾巴上的一块肌肉好像能在尾巴前后摆动时在特殊的时候激活。为了了解肌肉的作用，她决定探究鲨鱼向后推水的细节。

To do this, researchers typically put a lot of small particles in the water. As the tail swings, the water moves and drags the particles along. The particles reflect light from flashing lasers, so they can be tracked using high-speed cameras. A computer program uses the images to generate pictures of water flow. The jets of water are hard to see, but these jets create rings or vortices of water that resemble smoke rings and can be readily detected.

    为此，研究人员在水里放了很多细小的颗粒。当尾巴摆动时，水会移动并拖动颗粒。颗粒会反射闪射的激光，这样高速的摄像机就可以跟踪拍摄。计算机程序可使用图像产生水流的图画。水流的喷射很难观察到，但这些喷射可以产生和烟圈相似的水圈或漩涡，很容易被侦测到。

Typically, this imaging technique employs two cameras to track the particles in the horizontal and vertical directions, and based on that data, researchers estimate how the particles move along the third dimension, depth. But Flammang wanted to see directly how particles moved in three dimensions. So she adapted a more advanced imaging system, one that use three cameras, that until now had only been used to study water flow coming off cylinders with pistons generating the force. “Engineers have employed this technique for years, but its application is new to biology,” Fish notes.

    这种成像技术通常会使用两架摄像机分别从水平和垂直方向来跟踪拍摄颗粒。根据拍摄的数据，研究人员可以估计颗粒沿第三维度-深度移动的情况。但弗拉芒想直接观察颗粒在三个维度移动的情况。因而她采用了一种更先进的成像系统，使用三架摄像机。直到现在，该系统只用于研究活塞发力时水从气缸中流出的情况。“工程师使用这项技术已经多年了，但它从未用于生物学。”费什（Fish）解释到。

Flammang and her colleagues tested two spiny dogfish and two chain dogfish by putting them in a water tank with a constant water flow so the sharks swam in place. She also looked at the water flow coming off a shark “robot” that had a flexible plastic tail. (For more, see these videos of a spiny dogfish swimming and a robotic fin.) Most fish create a ring of water at the end of each tail flick. The tail pushes the water as it moves to the side, then sends the water twirling away as it stops to change direction. Sharks were thought to produce two rings at that point, one small and one large one because of the shape of the tail, and that’s what happens with the robotic tail.

    弗拉芒（Flammang）和她的同事把两只白斑角鲨和两只网纹猫鲨放到水箱里，让水箱里的水一直流动，让鲨鱼在里游动。水箱里还放了一只机器鲨鱼，有一条灵活的塑料尾巴。（如需更多信息，可观看白斑角鲨游动和机器鱼鳍的视频。）大部分的鲨鱼在甩尾后都会产生水圈。当它游到侧面时尾巴就会推水，当它停止改变方向时就会让水旋转。鲨鱼在一点上可以产生两个水圈，一大一小。这是尾巴的形状引起的，机器鱼鳍也是如此。

But in reality, a shark’s tail spins off the second ring right as it reaches the midline of the animal, Flammang and her colleagues report in the 22 December issue of the Proceedings of the Royal Society B. That ring is larger and connects to the ring generated at the end of the tail flick. “That provides a big advantage,” Flammang says. Instead of just getting a push as the tail reaches the extent of its bend, the shark has added thrust midswing. “It may be allowing the animal to produce almost continuous thrust.” Flammang thinks the shark uses the muscle she characterized to stiffen the tail midswing, changing its shape slightly, to throw off the extra vortex.

    但在现实中，鲨鱼的尾巴会脱离第二个水圈直达动物的中线。弗拉芒和她的同事在《英国皇家学会学报B辑》的12月22日的那一期上对此进行了报道。那个水圈比较大并能连到甩尾时产生的水圈上。 “这有很大优势。”弗拉芒说。鲨鱼不仅通过弯曲尾部获得推力，它还在摆动中获得推力。“这可让动物持续地产生推力。”弗拉芒认为鲨鱼使用她之前描述的那块肌肉让尾巴在摆动中变硬，并轻微地改变形状来摆脱额外的漩涡。

“The shark has one more degree of sophistication” in generating thrust, says Michael Triantafyllou, an ocean engineer at the Massachusetts Institute of Technology in Cambridge. “Such observations can lead to better designs” for underwater vehicles, he notes, though he cautions that designing shape-shifting components “seems to complicate things.” However, Flammang is undaunted: “I would like to build a fully functioning shark tail model that can [change] the stiffness.”

   在产生推力时，“鲨鱼还有一点比较复杂。”迈克（Michael Triantafyllou) 说。他是剑桥MIT的海洋工程师。“这些观察可以引发更好的设计” ，为水下交通工具的设计，他解释道，虽然他提醒设计变换形状的部件“看起来会让东西变得更加复杂。”然而，弗拉芒(Flammang)并不泄气：“我想建造一个可以改变硬度的全功能的鲨鱼尾巴模型。”

This story provided by ScienceNOW, the daily online news service of the journal Science.

    这篇文章是由ScienceNow提供的。ScienceNow是《Science》期刊的每日在线新闻服务。

Image: As it moves, a shark’s tail (shown) creates two connected rings of moving water (blue and red represent opposing flows) that help make this fish such a powerful swimmer. (Brooke E. Flammang)

图：当鲨鱼移动时，尾巴会产生两个连接在一起的流动的水圈（蓝色和红色代表相反的水流），这使得鲨鱼有着强大的游动能力。