Biology (Dolphins)
Narrator：
Listen to part of a lecture in a marine biology class.
Professor：
We have been talking about how sea animals find their way underwater, how they navigate, and this brings up an interesting puzzle, and one I'm sure you'll all enjoy. I mean, everybody loves dolphins, right?
And dolphins, well, they actually produce two types of sounds. Uh, one being the vocalizations you are probably all familiar with, which they emit through their blowholes. But the one we are concerned with today is the rapid clicks that they use for echolocation, so they can sense what is around them. These sounds, it has been found, are produced in the air-filled nasal sacs of the dolphin.
And the puzzle is how does the click sounds get transmitted into the water? It's not as easy as it might seem. You see, the denser the medium, the faster sound travels. So sound travels faster through water than it does through air. So what happens when a sound wave um ? OK.
You've got a sound wave traveling merrily along through one medium, when suddenly; it hits a different medium, what does gonna happen then? Well, some of the energy is going to be reflected back, and some of it is going to be transmitted into the second medium. And ? and ? and if the two media have really different densities, like air and water, then most of the energy is going to be reflected back, very little of it will keep going, uh, get transmitted into the new medium. I mean, just think how little noise from the outside world actually reaches you when your head is underwater.
So, how did the dolphin's clicks get transmitted from its air-filled nasal sacs into the ocean water? Because given the difference in density between the air in the nasal cavity and the seawater, we'd expect those sounds to just kind of go bouncing around inside the dolphin's head, which will do it no good at all. If it's going to navigate it, needs those sounds to be broadcast and bounced back from objects in its path.
Well, turns out dolphins have a structure in their foreheads, just in front of their nasal sacs, called a melon. Now, the melon is kind of a large sac-like pouch, made up of fat tissue. And this fat tissue has some rather fascinating acoustical properties. Most of the fat that you find in an animal's body is used for storing energy, but this fat, which you find in dolphins, and only in the melon and around the lower jaw. This fat is very different, very rich in oil. And it turns out it has a very different purpose as well.
Now, one way to um, modify the overcome this mismatch in the density of air and water would be ? if you travels through velocity of the sound wave, make it precisely match the speed at which water. And that's exactly what marine biologists have discovered the melon Note that the bursa, these little projections at the rear of the melon, are right up against the air-filled nasal sacs. And these bursa, it turns out, are what's responsible for transferring sound to the melon.
The sound waves are then transmitted by the bursa through the melon. First through a low velocity core, and then through a high velocity shell, where their speed is increased before they are transmitted into the surrounding seawater. So now the signals can be efficiently transferred into the water, with minimal reflection.
The only other place, this special fatty tissue, like that in the melon, the only other place is found in the dolphin, is in the lower jaw. Turns out that the lower jaw, well, it is made of a specially thin bone. And it is very sensitive to vibrations, to sound energy traveling through the seawater. It turns out that the jaw is primarily responsible for capturing and transferring returning sound waves to the dolphin’s inner ear. So these rapid clicks that are sent out bounce off objects, maybe a group of fish swimming over here, a boat coming from over there. The sounds bounce off them and the lower jaw captures the returning sounds, making it possible for the dolphin to sense what's in the surrounding water and decide where to swim.
TPO23 Lecture4
Choreography (Screen Dance)
Narrator：
Listen to part of a lecture in a choreography class.
Professor：
Now, when you think about choreography, well, uh, for your last assignment, you choreographed the dance that was performed on stage in front of live audience. Now, screen dance is very different. It is a dance routine you will be choreographing specifically to be viewed on a screen, on a computer screen, a TV screen, in a movie theater, any screen. So the question we have to ask is, what's the difference between choreography for a live performance and choreography for on-screen viewing?
OK. Think for a minute. When you see a movie, is it just a film of people acting on a stage? Of course not. Movies use a variety of camera angles and creative editing. Movies can distort time, slow movement down, or speed it up, show actors fading in and out of scenes, etc. All of these ? all of these film-making techniques, things that can't be used in a live performance, are possible in a screen dance. Now, we'll cover these concepts in greater detail later, but you should be getting the idea that I don't want you to just film dancers on stage and turn it in as your screen dance project. Uh, Yes? Debbie.
Student：
But isn't something lost here, Professor
Watson? I am a dancer, and when I perform on stage, I am so energized by the audience's reactions, the applause. I actually, and for a lot of dancers, it ? it really inspires us.
Professor：
You're right. Screen dance, which is a relatively new, isn't for everyone. Uh, some dancers may seem reluctant to participate in your project, because they do thrive on the immediacy of performing live. If this happens, you could point out that screen dance offers other ways for dancers to connect to their audience. For example, dancers can express themselves, even change the whole mood of the scene through a facial expression. And you could film close-up shots of their faces. Facial expressions aren't as important in live performances generally, because the choreographer knows that someone in the back row of a theater may not be able to see a dancer's face clearly.
Student：
But ? um, I have never used a movie camera or edited film before. How will we learn everything we need to know to ? ?
Professor：
Oh, don't worry. The cameras you will be using are pretty simple to operate. And you'll get to play with the film-editing software several times before beginning your project. You'll also have the option of working with a student in the film department, someone who's familiar with the technology. But the choreography and the end result will be your responsibility of course.
Student：
Could you talk some more about the film - making techniques, you know, the ones that work best forscreen dances?
Professor：
I'll show some of my favorite screen dances next week to give you a better idea. But, uh, OK. Here's one technique that can create the illusion of flow in a screen dance. You film the same dancer, entering and exiting the frame several times. Moving slowly at first, then faster and faster. Then in the editing room, you can digitally manipulate these images, like you might put five or ten or twenty copies of that same dancer meeting himself in the middle of the screen, to make it look like he is dancing with himself.
Obviously, this can't be done in a live performance. Another example, in one screen dance I saw, the dancers leap through sheets of fire in a big abandoned building. Of course, the building wasn't really on fire. A technique called super-imposing was used. The dancers were filmed and layered in the editing room. The fire was added to the background.
Student：
That sounds awesome. But if anyone can watch a dance on a computer screen. Why would they pay to go see a live performance? What if screen dance got so popular that it replaced live dance?
Professor：
Screen dance is an entirely different type of presentation. It could never replicate the immediacy, the kind of drama that live performance offers. There will be an audience for that. I think what screen dance will do, though, is heighten awareness of dance in general. Because it is a way ? u h, it can reach people in their homes, in their workplaces, at anytime really. And if someone discovers that they love dance by watching a screen dance, there's a good chance they will get interested enough to buy a ticket to see a live performance.
