TOEFL Listening: ETS-TOEFL听力机经 - 82KOZ5H1I0UJCA1P

Lecture: Nanomachines & Nanoengine: Narrator: Listen to part of a lecture in a chemistry class. Professor: Today we are going to explore current developments in the world of new technology, what I'm talking about is work being done on extremely small scale machines, nanomachines, the size of bacteria or molecules that could potentially be of use in a variety of fields. For example using a machine inside the human body to assist doctors in diagnosing or treating illnesses, chemists have been able to create quite a variety of structures at the molecular scale and some of them could eventually even function as vehicles of all sorts. One group is actually working on creating a nanocar, a molecular car, and similar to an actual car it has wheels, carbon molecule four wheels. However like any car, you need a steering mechanism and an engine. And those are the two major obstacles the researchers are facing as they develop it. Chemists and physics are working to address precisely those two issues. Now when we are thinking about designing any kind of vehicle they could be used inside the human body to transport, say, a medication to the bloodstream to specific sites, or even to particular cells within an organ, well then here we face the fundamental problem which is fluid thickness. You see the smaller something is, the harder it becomes for it to move through water or through air, that kind of matter. The structures at a macro level, at the nano level, well, moving through water or air is about as difficult as it would be for you and me, if we attempt to move through an extremely thick honey or very dense syrup. So you can see why the focus in developing engines for nanovehicles, it has to be on finding a means of ensuring that the engines can provide both sufficient and reliable continuous movement given those conditions. Now researchers have learned a lot from one nanoengine prototype. We're talking about a small metal rod, but as long as a bacteria cell and half as wide. The front half of the rod is composed of platinum, while the back half is made of gold. Student: Very expensive materials, gold and platinum. Good thing is quantities is so tiny. Professor: I agree. So this rod, this is the engine. The way it works in a laboratory is the rod is immersed in a solution of water and hydrogen peroxide. The presence of the platinum causes the surrounding hydrogen peroxide to continuously break down into protons, electrons and oxygen molecules. At the same time the presence of the gold in the back half of the rod. That gold triggers a different reaction. They cause protons and electrons to be used up when they combined with a hydrogen peroxide. The end result is that there is always more protons on the platinum end of the rod and fewer protons on the gold end. As the positively charged protons then moved from the platinum and gold, they drag water molecules with them. They're attracted to their positive charge. And that water movement ends up pushing the rod forward. Student: So this is an engine that converts chemical energy into motion. Is that right? Yes, exactly that. A catalytic engine. Student: The hydrogen peroxide solution is. So it's the fuel then, isn't it? Professor: That's correct, this little engine is immersed in its own fuel. Student: I guess it doesn't even need a fuel tank then. Professor: Right, and that's in fact an advantage. In fact, it's a necessity when you're working on a nanoscale. Student: What about the steering problem you mentioned earlier? Has there been any success with that? Professor: Yes, one attempt at a steering mechanism makes use of a magnetic field in this engine we've been talking about, metal discs specifically nickel discs are embedded in the rod. The disks behave much like tiny compasses, in that they align themselves and consequently the rod to the magnetic field. Since you can change the magnetic field by turning it with external magnets, well, essentially this would allow no vehicles to be steered externally. However, for many purposes, we will definitely need nanovehicles they can still independently on their own. And there are a variety of different approaches we are working on so that these machines can basically steer themselves without external magnets. Let's take a look at some of them and what's involved.