托福预测
一轮托福考试过后，很多考生会搜集下一轮考试的预测试卷，那么最新一轮的预测内容有哪些呢?这想必是不少出国人士比较关心的问题，你可以往下看文章或者点击收藏，和我爱学习网一起来看看2018年3月11日托福听力预测，欢迎阅读。
2018年3月11日托福听力预测
1. What is the lecture mainly about?
(A) Ways to generate heat for nuclear fusion
(B) Differences between nuclear fission and nuclear fusion
(C) A controversial theory regarding how to generate nuclear fusion
(D) The possibility of establishing sustained nuclear fusion
2. According to the students, what are three advantages of nuclear fusion over nuclear fission
Click on 3 answers.
(A) Nuclear fusion can use a fuel that is more easily obtained.
(B) Nuclear fusion can be achieved at lower temperatures.
(C) Nuclear fusion produces more energy.
(D) Nuclear fusion does not produce hazardous by-products.
(E) Nuclear fusion does not require as many natural resources.
3. Why does the professor mention isotopes of hydrogen?
(A) To correct a student's comment about how fusion takes place in stars
(B) To help answer a student's question about temperature requirements for fusion reactors
(C) To explain what happens to hydrogen atoms during fusion reactions
(D) To justify the need for superconducting magnets in nuclear fusion reactors
4. According to the professor, how will the ITER reactor differ from earlier experimental fusion reactors?
Click on 2 answers.
(A) It will be transportable to different locations.
(B) It will sustain nuclear reactions through heat that it generates on its own.
(C) It will heat the fuel mixture to a higher temperature.
(D) It will confine the plasma in a more energy-efficient way.
5. What does the professor say about the international effort to develop ITER?
(A) The participation of many countries may cause ITER to be delayed even more.
(B) The research orientation of ITER has encouraged international collaboration.
(C) ITER will make use of equipment made in many different countries.
(D) The lack of international cooperation on earlier fusion projects has hurt ITER.
6. What does the professor imply when he says this:
(A) He prefers to work on projects with more immediate results.
(B) He believes that research in the physical sciences requires strict time lines.
(C) He thinks it will take less time to develop ITER than most researchers expect.
(D) He is more skeptical about the future of nuclear fusion than most researchers are.
Script:
Narrator:Listen to a discussion in an environmental policy class
Professor:So, today we’re going to wind up our discussion of alternative energy sources and we’re going to talk about one that often gets overlooked. That source is nuclear fusion as opposed to nuclear fission, which is already discussed. In nuclear fission, the centers of atoms, the nuclei, are broken up. This is the reaction today that drives today’s nuclear-powered stadiums. Nuclear fusion, on the other hand, is pretty much the opposite. It occurs when two atoms collide and then nuclei combine, or fuse, to form a heavier nucleus. This is the reaction that powers the Sun, all stars. So, who can tell me what makes fusion more attractive than fission as an energy source. Julie?
Julie:Well, it releases more energy, for one thing.
Professor:Yeah, a lot more energy than fission.
Julie:Oh also, it can use hydrogen as a fuel source. And hydrogen is abundant and easily available in water. Fission uses uranium, which is way more difficult to find.
Male：Plus, fission is more dangerous. With fusion, you wouldn’t have to worry about radioactive waste, right?
Professor: Another good point.
Male：But still, I remember from my physics class, to fuse the nuclei of two hydrogen atoms require temperature found similar to the sun, like over 100 million degrees Kelvin. How can we possibly recreate those temperatures here on Earth?
Professor:Well, we can’t yet. Not sustainably. But maybe we don’t need to. See, right many countries around the globe are cooperating to realize the potential of nuclear fusion. And the project they’re putting the most resources into is called ITER. ITER stands for International Thermonuclear Experimental Reactor, a large fusion reactor that’s being built in southern France. It’s designed to create the first sustained nuclear fusion reaction, meaning the energy it will release is greater than the energy we’ll use to start it up. And I’ll get back to this point in a moment. But let’s back up.
You asked about how we generate the tremendous temperature required for fusion. Well, that’s not really the problem. There are heavier isotopes of hydrogen, deuterium and tritium that will undergo fusion at lower temperatures than regular hydrogen. And when we tend to do deuterium, tritium mixtures that much, around 40 million Kelvins, it generates what’s called a plasma, which is a cloud of ionized gas.
So what is the problem? Well, it’s twofold. First, the plasma, this cloud of plasma, is way too hot for any solid container to hold. Fortunately, high temperature plasma conducts electricity, which means we can use an electromagnetic force to hold the plasma in place to confine it. Unfortunately, that requires a lot of energy, more energy than we’d ever be able to get from the resulting fusion reaction. And this brings us back to the point I mentioned before. Creating a sustained fusion reaction, because up to now experimental fusion reactors have never been able to achieve this, this break-even point, the point where the energy output is as great as the input for more than a fraction of a second.
How will the ITER project overcome this? First, by creating a larger plasma. Twice as large as any previous generated. The advantage of this is that once the initial fusion reaction occurs, the larger plasma will generate enough energy to keep itself hot, to keep the fusion reaction going. And second, ITER will use super-conducting magnets to form the magnetic field, magnets that consume less electrical power than those used in previous attempts. So, less energy goes in. More energy comes out. Theoretically, it should do the trick.
Now, keep in mind, the ITER reactor has been in the works for about twenty years and it will probably take another decade to build. And even then, of course it will be used for research purposes. Commercial fusion won’t be feasible for at least another twenty years after ITER is built. So that’s a long timeline, right? Not something I’d be comfortable in my own work. I need shorter term goals to motivate me. But for those who can handle it, well, it means this project is not about short term economic competition or gains. So in a way, it’s easier to get countries to work together on it. If we cooperate, we’ll get there sooner because we know how much difficult it is to do it alone.
今天我们将讨论替代能源的话题我们将讨论一个经常被忽视的问题。这个来源是核聚变，而不是核裂变，这已经被讨论过了。在核裂变中，原子中心，原子核，被分解。这就是今天驱动核动力体育场的反应。而核聚变则恰恰相反。它发生在两个原子碰撞，然后原子核结合，或融合，形成一个较重的原子核。这是太阳，所有恒星的能量反应。所以，谁能告诉我什么使核聚变比裂变更有吸引力，而不是能源。朱莉?
朱莉:嗯，一方面，它释放出更多的能量。
教授:是的，比裂变更多的能量。
朱莉:哦，它还可以用氢作为燃料。而且氢很丰富，在水中很容易获得。裂变使用铀，这是很难找到的。
男:另外,裂变更危险。有了核聚变，你就不用担心放射性废料了，对吧?
教授:另一个很好的观点。
男:但是,我记得从我的物理课,融合两个氢原子的原子核要求温度发现了类似的太阳,就像在1亿开尔文。我们怎么可能重现地球上的温度呢?
教授:好,我们不能。不是可持续的。但也许我们不需要。看，世界上许多国家正在合作实现核聚变的潜力。他们投入最多资源的项目叫做ITER。ITER是国际热核实验反应堆，一个在法国南部建造的大型核聚变反应堆。它的设计是为了制造第一个持续的核聚变反应，这意味着它释放的能量大于我们用来启动它的能量。一会儿我会回到这一点。但是让我们后退。
你问我们如何产生聚变所需的巨大温度。这不是问题所在。有较重的氢、氘和氚同位素，在较低的温度下会比普通的氢进行聚变。当我们倾向于氘，氚混合物的时候，大约有4000万，它产生了所谓的等离子体，这是一团电离气体。
那么问题是什么呢?这是双重的。首先，等离子体，这团等离子体，对于任何固体容器来说都太热了。幸运的是，高温等离子体导电，这意味着我们可以使用电磁力来控制等离子体，以限制它。不幸的是，这需要大量的能量，比我们能从核聚变反应中得到的能量还要多。这让我们回到我之前提到的观点。创造一个持续的聚变反应，因为到目前为止，实验聚变反应堆从来没有能够实现这个，这个收支平衡点，能量输出和输入一样大的点，超过了一秒钟的时间。
ITER项目将如何克服这个问题?首先，创造一个更大的等离子体。是之前的两倍大。这样做的好处是，一旦最初的聚变反应发生，较大的等离子体就会产生足够的能量来保持热，以保持聚变反应的继续。第二，ITER将使用超导磁体形成磁场，磁体消耗的电能比之前尝试的要少。所以能量减少了。更多的能量。从理论上讲，它应该奏效。
现在，请记住，ITER反应堆已经运行了大约20年，可能还要再花10年才能建成。即使这样，它当然也会被用于研究目的。在ITER建成后，至少再过20年，商业融合是不可能实现的。这是一个很长的时间轴，对吧?在我自己的工作中，我不会感到自在。我需要更短期的目标来激励我。但是对于那些能够应付的人来说，这意味着这个项目不是短期的经济竞争或收益。所以在某种程度上，让各国一起合作更容易。如果我们合作，我们很快就会到达那里，因为我们知道单靠它是多么困难。
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