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• Position control of d. c. motors has been done by means of pulse width modulation .
  直流电机位置用脉冲宽度调制法控制。
• The rate at which work is being done by some force is often of interest .
  力在单位时间内所做的功是我们经常感兴趣的问题。
• This is done by a great number of ring shaped air jets on the bottom of the craft .
  这是靠船底上的许多环形喷气口来做到的。
• This is done by a great number of ring-shaped air-jets on the bottom of the craft .
  船底装上大量环状喷气嘴就可以做到这一点。
• In motion with a fixed frictionless constraint, no work is done by the constraint .
  在固定的无摩擦约束运动中，约束力不作功。
• We had to make the best of it, and that is never worth doing by halves .
  我们必须竭力把事情做好，有头无尾的事是不值得一试的。
• Something always has to be done by someone else before the saudis can act .
  沙特阿拉伯人总是让别人先干起来，然后他们才采取行动。
• This work, of sending out the drawings for tender is done by the buying department .
  这种将发出投标图纸的工作，是由采购部门进行的。
• The minus sign indicates that the work done by the force decreased the kinetic energy of the neutron .
  负号表明这个力所作的功降低了中子的动能。
• I have never known much good done by those who affected to trade for the public good .
  我从来没有听说过，那些假装为公众幸福而经营贸易的人做了多少好事。