9.26
So that’s how elephants use infrasound. Now let’s talk about the other end of the acoustic spectrum, sound that is too high for humans to hear ultra sound. Ultrasound is used by many animals that detect, and some of them send out very high frequency sounds. So, what’s a good example? Yes, Carol?
Well, bats, since they are all blind, bats have to use sound for, you know to keep from flying into things.
That’s echolocation.
Echolocation is pretty self-explanatory: using echoes
reflected sound waves to located things.
As Carol said, that’s used for navigation or intention, What else, Mike?
Well, finding food is always important and I guess not becoming food for other animals.
Right, on both counts, avoiding other predators and locating prey, typically in sense of flying around it at night. Now before I go on, let me just respond something Carol was saying, this idea that bats are blind. Actually, there some spices of bats, the ones that don’t use echolocation
that do rely on their vision for navigation, but it’s true that for many bats, their vision is too weak to count on. Ok, so quick summary of how echolocation works. The bat emits the ultrasonic pulses, very high pitch sound waves that we can’t hear. And then, they analyze the echoes, how the waves bounce back. Here, let me finish the style diagram I started before the class. So the bat sends out the pulses, very focused verses of sound and echo bounce back. You know, I don’t think I need to draw the echoes, your reading assignment for the next class, it has a diagram shows this very clearly. Anyway, as I was saying, by analyzing these echoes, the bat can determine, say, if there is a wall in a cave that needs to avoid, and how far away it is. Another thing it 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 moth, which is common prey for a bat, particularly a moth beating its wings. However, moth happened to have a major advantage over most other insects. They can detect ultrasound; this means that when the bat approaches, the moth 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 beating their wings, they will be much harder for the bat to distinguish from, oh…a leave or some other objects. Now, we have tended to underestimate just how sophisticated the ability of animals that use ultrasound are. In fact, we kind of assume that they were filtering a lot out. The ways are sophisticated radar on our system can ignore the echo on the stationary object on the ground. Radar does this to remove ground clutter, information about hills and buildings that it doesn’t need. But bats, we thought they were filtering out this kind of
information, because they simply couldn’t analyze it, but it looks as we were wrong. Recently, there was the experiment with trees and a specific spices of bats. A bat called the lesser spear-nosed bat. Now, a tree should be a huge and acoustic challenge for bats, right? I mean It’s got all kinds of surfaces with different shapes and angles. So, well, the echoes from a tree are going to be massive and chaotic acoustic reflections, right? Not like the echo from a moth. So, we thought for a long time that the bats stop their valuation as simply that’s a tree. Yet, it turns out that the bats or at least this particular spices, can not only tell that it’s a tree, but can also distinguish between say, a pine tree and a deciduous tree, like a maple or an oak tree, just by their leaves. And when I say, leaves, I mean pine-needles too. Any ideas on how we would know that?
Well, like with the moth, could it be their shape.
You are on the right track-- it’s actually the echo of all the leaves as a whole that matters. Now, think, a pine trees with all those little densely packed needles.
Those produced a large number of fain reflection in which what’s called as: a smooth echo. The wave forms were even, an oak which has fewer but bigger leaves with stronger reflections, produce a jagged wave form, or what we called: a rough echo. And these bats can distinguish between the two, and not just was trees, with any echo comes in smooth or rough shape.
Infrasound 次声
10.3
Listen to part of a lecture in a health class and answer the question.
Let’s look at this interesting piece of news. Oh, first, do any of you have a tattoo? I’ve got an eagle on my back.
Anybody else? No, ok! Did you know that 16% of adult Americans have tattoos? Cristina, Aguilera and Beyonce have tattoos! Do you think they are safe? Did you know that absolutely no national regulations exist? When you get a tattoo, you put yourself at risk-allergies to the dyes, keloid scarring, and infections including hepatitis, tetanus and even HIV. Now, isn’t that scary.
If you still want one and you have thought about what it look like in 30 years, there are some tips you should follow. Everything should be clean and sanitary, even the appearance of the person doing the tattooing. Take a good look at the sterilizing equipment. Does it have a recent testing certificate?
If you can, try to watch someone else getting tattooed. The needles, in sterilized packages of course should be opened in front of the customer. There should be a biohazard container for ones that have been used. Watch the artists to see if he or she changes gloves after touching things other than needles. There are no regulations governing tattooing, but there are state licensing regulations. Look for the certificate on the wall. If the artist belong to Alliance of professional Tattooists, that’s a sign of a good reputation. Be patient, your tattoo will take seven to ten days heal.
Tattoo 纹身
keloid scarring 蟹足肿
hepatitis 肝炎