The two rails are not only signal lines of track circuits, but also loop current line of locomotive traction current in electrified railway block.

电力牵引区段的两条钢轨，既作为轨道电路的通道来传输信号电流，又作为牵引电流的回路来传送牵引电流。

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In electric railway track circuit, the two steel tracks are both transmission line of the track signal and return line for electric locomotive tractive current back to electric substation.

在电气化铁路轨道电路中，两条钢轨即是轨道信号的传输线，又是电力机车牵引电流返回变电所的回流线。

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For the track which the robot must follow, such as line, we must divide it into many short segments, letting robot pass through two end points of the short lines in turn(track programming).

为使机器人按预定的轨迹运动，比如说按直线，必须把这一路径分成许多小段，让机器人按照分好的小段路径在两点间依次运动（轨迹规划）。

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The author cleverly lays a two-track story, one story line following the good guys, the other following the low-life evildoers.

FORBES: Fact And Comment

Under a two-year contract, for undisclosed fees, Track finds nightclubs willing to let new cardholders bring guests, jump the line and pay a reduced entrance fee or get in for free.

FORBES: Nightcrawler