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(причастием, герундием, отглагольным существительным):
1. It is no use going there now. 2. Coming out of the wood, the travellers saw a ruined castle in the distance. 3. My greatest pleasure is travelling. 4. Growing tomatoes need a lot of sunshine. 5. Growing corn on his desert island, Robinson Crusoe hoped to eat bread one day.
16. Употребите сказуемое в следующих предложениях в Present Perfect Continuous (Progressive). Переведите предложения на русский язык:
Образец: Не has worked at the plant for many years.
He has been working at the plant for many years.
Он работает на этом заводе в течение многих лет.
1. He has done very little work recently.
2. They have argued about that or more than two hours.
3. They have lived in Moscow since 1953.
17. Переведите следующие предложения на русский язык, обращая внимание на времена группы Perfect Continuous (Progressive):
1. For how long have you already been doing your morning exercises?
2. He had been speaking for an hour and a half when he decided to have an interval.
18. Замените в следующих предложениях действительный залог страдательным, обращая внимание на времена группы Indefinite (Simple):
Образец: They build many new houses every year.
Many new houses are built every year.
1. They did not adopt the resolution yesterday.
2. The teacher will examine the students next week.
19. Замените в следующих предложениях действительный залог страдательным, обращая внимание на времена группы Continuous (Progressive):
Образец: They are building a new house in our street.
A new house is being built in our street.
1. She was reading a letter when I entered the room.
2. They will be working with this text when you return.
20. Замените в следующих предложениях действительный залог страдательным, обращая внимание на времена группы Perfect:
Образец: They have built a new house in our street.
A new house has been built in our street.
1. By Saturday he had found all the necessary material.
2. She had finished her work by this time yesterday.
21. Переведите следующие предложения на русский язык, обращая внимание на употребление глагола should:
1. You should ask permission before doing it.
2. He should take more physical exercises.
3. He should not waste so much time on unimportant details.
22. Переведите текст, составьте 5 вопросов, раскрывающих основное содержание текста:
Plastic Parts That Remember
Thermoplastics can be bent, pulled, or squeezed into various useful shapes. But eventually—especially if you add heat — they return to their original form. This is known as plastic memory. Plastic memory offers some interesting design possibilities.
When most materials are bent, stretched, or compressed, they somehow alter their molecular structure or grain orientation to accommodate the deformation — permanently. Not so with polymers. Polymers temporarily assume the deformed shape but always maintain internal stresses that want to force the material back to its original shape. Usually, this desire to change shape is called plastic memory.
This so-called memory is often undesirable. Sometimes people prefer that thermoplastic parts forget their original shape and stay put — especially when the parts must be formed, machined, or rapidly cooled. However, this memory, or instability, can be used advantageously.
The time/temperature-dependent change in mechanical properties results from stress relaxation and other viscoelastic phenomena typical of polymers. When the change is an unwanted limitation, it is called creep. When the change is skilfully adapted to the overall design, it is called plastic memory.
Most plastic parts can be produced with a built-in memory. That is, the tendency to move into a new shape is included as an integral part of the design. So then, after the parts are assembled in place, a small amount of heat can make them change shape. Seals, gaskets and seamless covers for tubing and wiring are typical examples.
In other applications, plastic parts can be deformed during assembly, then allowed to return to their original shape. In this case, parts can be stretched around obstacles without permanent damage. Potential memory exists in all thermoplastics. Polyolefins, neoprene, silicone, and some other polymers can be given a memory either by radiation or by a chemical change.
Memory can be exploited in four ways:
1) The component is deformed at room temperature. Upon heating, the component recovers its original dimensions.
2) The component is deformed at an elevated temperature and — while held in the strained condition — it is cooled to room temperature so that the deformation is "frozen in". Upon reheating, the component returns to its original dimensions.
3) The component is used in a confined situation under constant stress. The deformed sections try to return to their original dimensions or form. Since the part is restrained from doing this, a stress — in addition to the normal elasticity— is produced which is most often used for sealing.
4) The component is deformed for a short interval, then the stress is removed. After a time, at room temperature, most of the deformation is recovered.
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