托福听力TPO7分类之生物学

2022-06-14 11:07:26

  

  TPO 7 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

  species of bat. A bat called: the laser spear nosed bat. Now, a tree should be

  huge 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.

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