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[主观题]
All materials have a distinct ductile to brittle transition temperature.
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更多“All materials have a distinct …”相关的问题
In the author's opinion, Henry Moore's greatest sculpturing feat has been ______ .
A．to create three-dimensional paintings
B．to have a feeling for the materials he uses
C．to incorporate empty space into his work
D．to use marble to all its advantages
A.Cycle Counting Method
B.Live method
C.Sampling method
D.Difference Posting procedure
Bianca Sfroza was not believed to be a Leonardo for the following reasons EXCEPT
A．it is not so possible that a drawing should prove to be a Leonardo.
B．existing works of Leonardo were all drawn by other materials than vellum.
C．a real Leonardo work couldn"t have been unknown for 500 years.
D．for 75 years, no expert had ever recognized Bianca Sfroza as a Leonardo.
Recycling
One of the most important changes in how modern societies respond to the problems of waste and its disposal is the development of techniques and processes for recycling materials that have been thrown away. Of course, recycling means that the material was cycled before. What the word really means is that the material has gone from a raw material to a factory or production process to use by a consumer. Most plastics, for example, began as crude oil from oil wells. A manufacturing process changes some of the chemicals in oil to plastics. The plastics are made into thousands of products and sent on to consumers who use them. When consumers are finished with their plastic bottles or toys or packages, they throw them away.
Unfortunately, as we often see on automobile bumper stickers, "Throw it away？ There is no away." What that means, of course, is that as we produce more and more waste, safe and easy places to put it are be coming fewer and fewer. Moreover, oil for plastics, trees for paper, and coal and oil to make heat for glass and metal production are also becoming harder to find and more expensive. One solution that can help solve problems of both supply and disposal is recycling, or using the same material more than once.
As an idea, recycling has been around for a long time. In fact, we might say that it has always been around, as long as people have used something after it has been used for something else. Using a coconut shell as a container after the coconut has been eaten may have occurred long ago. Glass jars are used to store screws or nails in many homes. Many industries have reused materials. Steel mills have added old steel to their furnaces, and glass companies have done the same with old glass. Paper has also been reused. In recent years, however, recycling is being seen as a more and more important way to reduce waste and the use of raw materials.
Many cities in the United States have begun recycling programs for household waste. Household waste, or the trash and garbage that we throw away from our homes, is made up mostly of paper. Food is the second largest part, but glass and metal are the next largest. Together, paper, glass, and metal make up almost 75 percent of the trash we throw away. If we could recycle much of that, we could greatly reduce the amount of trash we have to find a place for.
Some governments are also requiring more recycling. Japan already recycles about 50 percent of its household trash. The German government now has a very strict law requiring that most plastics and metal be recycled. This law has made a big change in the way automobiles are built and sold. Under the new law, automobile manufacturers must buy a car back when it is no longer useful. The car must then be separated into materials that can be recycled—metals, plastics, glass, and so on. This law has made automobile manufacturers think more carefully about the kinds of materials that go into automobiles and how those materials are used.
Recycling does not always go smoothly. Sometimes industries are not able to use all of the old material that is available.If paper manufacturers cannot use all of the old paper that is available, there will be no one to buy it and it will still have to be thrown away. The same is true for many metals and plastics. In Germany, problems have developed with their new law, because more materials are being recovered than manufacturers of new items can use. The government has to buy these materials, and it is costing a lot of money.
Closely related to the problem of usability is the problem of cost of recovery. There are many types of plastics, and not all of them can be reused or reused together. They have to be separated, cleaned, and sorted. Automobiles are made up of many types of metals and plastics. Separating all of these materials and recovering them for re
A．Y
B．N
C．NG
Admissions Notice
John Washington,
We have (150) your completed application form. and all necessary documents and materials and other sources.
A preliminary check of the material indicates that you are academically (151) for admission. We now formally inform. you that you will be admitted (152) the Graduate School of Engineering of the Massachusetts Institute of Technology for the fall term 2009 to work towards the degree of M. S.
We heartily welcome you to join us on our campus.
Yours Truly
Andrew Boswell
Admissions Officer
(50)
A．receives
B．receiving
C．receive
D．received
根据以下材料，回答题
New Understanding of Natural Silk"s Mysteries
Natural silk， as we all know， has a strength that manmade materials have long struggled to match. In a discovery that sounds more like an ancient Chinese proverb than a materials science breakthrough， MIT researchers have discovered that silk gets its strength from its weakness. Or，more specifically， its many weaknesses. Silk gets its extraordinary durability and ductility from an unusual arrangement of hydrogen bonds that are inherently very weak but that work together to create a strong， flexible structure.
Most materials- especially the ones we engineer for strength- get their toughness from brittleness. As such， natural silks like those produced by spiders have long fascinated both biologists and engineers because of their light weight， ductility and high strength （pound for pound， silk is stronger than steel and far less brittle）. But on its face， it doesn"t seem that silks should be as strong as they are; molecularly， they are held together by hydrogen bonds， which are far weaker than the covalent bonds found in other molecules.
To get a better understanding of how silk manages to produce such strength through such weak bonds， the MIT team created a set of computer models that allowed them to observe the way silk behaves at the atomic level. They found that the arrangement of the tiny silk nanocrystals is such that the hydrogen bonds are able to work cooperatively， reinforcing one another against extemal forces and failing slowly when they do fail， so as not so allow a sudden fracture to spread across a silk structure.
The result is natural silks that can stretch and bend while retaining a high degree of strength.
But while that"s all well and good for spiders， bees and the like， this understandingof silk geometry could lead to new materials that are stronger and more ductile than those we can currently manufacture. Our best and strongest materials are generally expensive and difficult to produce （requiring high temperature treatments or energy-intensive processes）.
By looking to silk as a model， researchers could potentially devise new manufacturing methods that rely on inexpensive materials and weak bonds to create less rigid， more forgiving materials that are nonetheless stronger than anything currently on offer. And if you thought you were going to get out of this materials science story without hearing about carbon nanotubes， think again. The MIT team is already in the lab looking into ways of synthesizing silk-like structures out of materials that are stronger than natural silk—— like carbon nanotubes. Super-silks are on the horizon.
MIT researchers carry out the study to illustrate an ancient Chinese proverb. 查看材料
A.Right
B.Wrong
C.Not mentioned
What is the point the speaker is trying to make about technology development？
A．A mature technology requires less innovation.
B．Technical evolution is close to maturation in certain fields.
C．New types of energy are expected to mature in the near future.
D．Nanomaterials or photonics and carbon nanotubes are environmentally friendly.
M: Of course, Madame. Here is the minutes of the meeting. The meeting was delayed by thirty minutes and started at 2 : 30 p. m. and it last for two and a half hours.
W: Did you tell the chairman that I was very ill and couldn't attend？
M: Yes, I did. Also, here are all the reports and materials handed out in the meeting. I think you will have to do some replies.
What does the man do？
A．He is a manager.
B．He is a clerk.
C．He is a secretary.
D．He is a chairman.
Today things have changed a lot. T-shirts have become colourful and fashionable. It can be seen almost everywhere and on everyone. Women and children wear T-shirts as well as teenagers, university students and men from all walks of life. T-shirts are worn on the playground, on the beach or in town. They can also be worn for work. Yet, T-shirts remain relatively inexpensive and long wearing, as well as easy to care for. Smart but comfortable and convenient to wear, they have become one of the newest ideas in fashion over the world.
Although T-shirts are now available in a wide variety of bright materials and styles, the most popular kind is the traditional cotton T-shirts with a slogan or a picture printed on the front. A T-shirt may bear a single word, a popular phrase, pictures of sportsmen, or an advertisement. As T-shirts are becoming more and more popular, new designs are coming up all the time.
When do people most probably wear T-shirts, according to the speaker？
A．Taking part in sports.
B．Listening to music.
C．Watching TV.
D．Enjoying a film.
