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英['lɪs(ə)n] 美['lɪsn]
vi. 听,倾听;听从,听信
n. 听,倾听

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草莓小菇凉:说的非常好,十分有道理,棒棒棒!

06-08 15:44:55

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OG真题练习-Swimming Machines

Swimming Machines

Tunas, mackerels, and billfishes (marlins, sailfishes, and swordfish) swim continuously. Feeding, courtship, reproduction, and even "rest" are carried out while in constant motion. As a result, practically every aspect of the body form and function of these swimming "machines" is adapted to enhance their ability to swim.

Many of the adaptations of these fishes serve to reduce water resistance (drag). Interestingly enough, several of these hydrodynamic adaptations resemble features designed to improve the aerodynamics of high-speed aircraft. Though human engineers are new to the game, tunas and their relatives evolved their "high-tech" designs long ago.

Tunas, mackerels, and billfishes have made streamlining into an art form. Their bodies are sleek and compact. The body shapes of tunas, in fact, are nearly ideal from an engineering point of view. Most species lack scales over most of the body, making it smooth and slippery. The eyes lie flush with the body and do not protrude at all. They are also covered with a slick, transparent lid that reduces drag. The fins are stiff, smooth, and narrow, qualities that also help cut drag. When not in use, the fins are tucked into special grooves or depressions so that they lie flush with the body and do not break up its smooth contours. Airplanes retract their landing gear while in flight for the same reason.

Tunas, mackerels, and billfishes have even more sophisticated adaptations than these to improve their hydrodynamics. The long bill of marlins, sailfishes, and swordfish probably helps them slip through the water. Many supersonic aircraft have a similar needle at the nose.

Most tunas and billfishes have a series of keels and finlets near the tail. Although most of their scales have been lost, tunas and mackerels retain a patch of coarse scales near the head called the corselet. The keels, finlets, and corselet help direct the flow of water over the body surface in such as way as to reduce resistance (see the figure). Again, supersonic jets have similar features.

Because they are always swimming, tunas simply have to open their mouths and water is forced in and over their gills. Accordingly, they have lost most of the muscles that other fishes use to suck in water and push it past the gills. In fact, tunas must swim to breathe. They must also keep swimming to keep from sinking, since most have largely or completely lost the swim bladder, the gas-filled sac that helps most other fish remain buoyant.

One potential problem is that opening the mouth to breathe detracts from the streamlining of these fishes and tends to slow them down. Some species of tuna have specialized grooves in their tongue. It is thought that these grooves help to channel water through the mouth and out the gill slits, thereby reducing water resistance.

There are adaptations that increase the amount of forward thrust as well as those that reduce drag. Again, these fishes are the envy of engineers. Their high, narrow tails with swept-back tips are almost perfectly adapted to provide propulsion with the least possible effort. Perhaps most important of all to these and other fast swimmers is their ability to sense and make use of swirls and eddies (circular currents) in the water. They can glide past eddies that would slow them down and then gain extra thrust by "pushing off" the eddies. Scientists and engineers are beginning to study this ability of fishes in the hope of designing more efficient propulsion systems for ships.

The muscles of these fishes and the mechanism that maintains a warm body temperature are also highly efficient. A bluefin tuna in water of 7°C (45°F) can maintain a core temperature of over 25°C (77°F). This warm body temperature may help not only the muscles to work better, but also the brain and the eyes. The billfishes have gone one step further. They have evolved special "heaters" of modified muscle tissue that warm the eyes and brain, maintaining peak performance of these critical organs.

金枪鱼,鲭鱼,和长嘴鱼(或者说成是枪鱼、旗鱼和箭鱼)的游动从不停止。它们的进食,求偶,繁殖,甚至“休息”都在不断的运动中进行。事实上,这些游泳“机器”身体结构的每个部位及其功能都有利于它们更好地游行。 

为了减少在水中前行的阻力,这类鱼身上产生了很多适应性变化。非常有趣的是,人类为了降低空气阻力加快高速飞机运行速度所进行的设计和这些鱼的适应性变化非常相似。这种设计只是人类工程师的初步尝试,但金枪鱼和他们的同类们已经拥有这种“高科技”设计很久很久。

金枪鱼、鲭鱼和长嘴鱼的流线体型简直就是一件工艺品。他们的身体光滑而坚实。从工程师的角度来看,金枪鱼的体型近乎完美。很多鱼类的绝大多数皮肤上是没有鱼鳞的,特别光滑。它们的眼睛和身体处于同一平面,根本不会凸显出来。身体表面还覆盖着一层光滑透明的外衣,鱼鳍部分坚硬、平稳而狭窄,这些特征都有助于降低前行中的阻力。当鱼儿们不使用鱼鳍时,会将它们折回到特殊的沟槽或者凹陷的地方,与身体保持同一平面,以维持它们平滑的外形。飞机收回起落装置,和这是同样的道理。

和上述特征相比,金枪鱼、鲭鱼和长嘴鱼们拥有更加精明的手段来增加它们在水中的适应性,比如他们的大长嘴。很多超音速飞机的头部就有类似的针状设计。

大多数金枪鱼和长嘴鱼的尾巴附近会长有一串脊骨和小鳍。虽然它们身上大部分地方是无鳞的,但在头部附近还保留着一块较粗的鳞片,叫做(鱼的)胸甲。脊骨、小鳍和胸甲有助于水直接流经鱼体表面,降低阻力(见附图)。同样,超音速飞机的喷头也有类似的特征。

因为金枪鱼的游动从不停止,它们必须张着嘴使水流经它们的腮。而其他鱼类的嘴里都会有一块肌肉,用于吸水和从腮里排水,金枪鱼的这块肌肉已经退化。实际上,它们必须通过游泳来呼吸。大部分金枪鱼很大程度上已经丧失了其他鱼类用于保持漂浮状态的鱼鳔,或者说已经完全丧失,因此,它们必须保持持续游泳的状态。

一个可能存在的问题在于,金枪鱼张嘴呼吸破坏了它们的流线型体型,有可能会降低它们的游泳速度。为此有的金枪鱼会在舌头上长有特殊的凹槽,以便引导水流通过嘴巴从腮缝流出,从而减少了阻力。

和降低阻力一样,金枪鱼们在游泳动力的加强上也有产生适应性变化。人类工程师在他们面前不得不自叹不如。向后倾斜并且长而狭窄的尾部非常有利于它们用最省力的方式前行。对这些鱼儿以及其他的鱼类游泳健将们来说,要保持在水里快速前行,最重要的可能就是对漩涡和逆流感知及利用的能力。漩涡会降低它们的速度,但它们在流经漩涡时不仅可以轻而易举地滑过而且会通过“推动”漩涡获得额外的动力。科学家和工程师们正在研究鱼的这种能力,以期设计出更高效的轮船推进系统。 

这些鱼类的肌肉组织和保温机制也非常高效。一只蓝鳍金枪鱼在7°C (45°F)的温度下可以保持25°C (77°F)以上的体温。温暖的体温可以使得肌肉、大脑和眼睛更好地运转。长嘴鱼更厉害。它们有专门改善肌肉组织的加热器,可以使眼睛和大脑保持一定温度,从而保证自己的重要的器官保持在最好的运行状态中。

中文翻译

The word “sophisticated” in the passage is closest in meaning to

  • Tunas, mackerels, and billfishes have even more sophisticated adaptations than these to improve their hydrodynamics.  A.complex B.amazing C.creative D.practical sophisticated
正确答案: A

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