托福听力TPO7文本(Conversation+Lecture)

　　Lecture 2

　　Biology

　　Pro: So, that is how elephant uses infrasound. Now, let’s talk about the other and the acoustic spectrums, sound that is too high for humans to hear---ultrasounds. Ultrasound is used by many animals that detected and some of them seen out very high frequency sounds. So, what is a good example? Yes, Kayo.

　　Kayo: Well, bats, since there is all blind, bets have to use sound for, you know, to keep them from flying in the things.

　　Pro: That is echolocation. Echolocation is pretty self-explanatory; using echoes reflected sound waves to located things. As Kayo said that bat used for navigation and orientation. And what is else. Make.

　　Make: Well, finding food is always important, and I guess not becoming food for other animals.

　　Pro: Right, on both accounts. Avoiding other predators, and locating prey, typically insects that fly around it at night. Before I go on, let me just respond something Kayo was saying--- this idea that is bats are blind. Actually, there are some species of bats, the one that don’t use echolocation that do rely on their vision for navigation, but its true for many bats, their vision is too weak to count on. Ok, so quick some rays if echolocation works. The bats emit the ultrasonic pulses, very high pitch sound waves that we cannot hear. And then, they analyze the echoes, how the waves bound back. Here, let me finish the style diagram I started it before the class. So the bat sends out the pulses, very focus birds of sound, and echo bounds back. You know, I don’t think I need to draw the echoes, your reading assignment for the next class; it has diagram shows this very clearly. So, anyway, as I were saying, by analyzing this echo, the bat can determine, say, if there is wall in a cave that needs to avoid, and how far away it is. Another thing uses the ultrasound to detect is the size and the shape of objects. For example, one echo they quickly identified is one way associated with moff, which is common prey for a bat, particularly a moff meeting its wings. However, moff happened to have major advantage over most other insects. They can detect ultrasound; this means that when the bat

　　approaches, the moff can detect the bat’s presence. So, it has time to escape to safety, or else they can just remain motionless. Since, when they stop meeting their wings, they will be much hard for the bat to distinguish from, oh… a leave or some other object. Now, we have tended to underestimate just how sophisticated the ability that animals that use ultrasound are. In fact, we kinds of assume that they were filtering a lot out. The ways are sophisticated radar on our system can ignore the echo from the stationary object on the ground. Radar are does this to remove ground clutter, information about the hills or buildings that they doesn’t need. But bats, we thought they were filtering out kinds of information, because they simply couldn’t analyze it. But, it looks as we are wrong. Recent there was the experiment with trees and specific piecies of bat. A bat called: the laser spear nosed bat. Now, a tree should be use and acoustic challenge for bat, right? I mean it got all kinds of surfaces with different shapes and angles. So, well, the echoes from trees are going to

　　be massive and chaotic acoustic reflection, right, not like the echo from the moff. So, we thought for a long time that the bat stop their evaluation as simply that is tree. Yet, it turns out that is or at least particular species, cannot only tell that is trees, but can also distinguish between a pine tree, deciduous tree, like a maple or oak tree, just by their leaves. And when I say, leaves, I mean pine needles too. Any idea on how we would know that?

　　Stu: Well, like with the moff, could be their shape?

　　Pro: You are on the right track---it actually the echo of all the leaves as whole the matters. Now, think, a pine trees with little densely packed needles. Those produced a large number of fain reflection in which what’s we called as: a smooth of echo. The wave forms were very even, but an oak which has fewer but bigger leaves with stronger reflections, produces a gigots wave form, or what we called: a rough echo. And these bats can distinguish between a two, and not just was trees, but with any echo come in smooth and rough shape.