因为级别的数量仍然保持一致而不用管地图的现实范围，地图瓦片可以被浏览器在多级别的情况下进行缓存。

Since the number of levels remains the same regardless of the map extent, map tiles can be cached by the browser in multiple levels.

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行波管多级降压收集极是将废电子注按照速度分类收集的装置。

Multistage depressed collector of Traveling wave tube is the device used for collecting spent beam according to their speed.

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采用多级降压收集极（MDC）是提高行波管效率的重要方法。

The multistage depressed collector (MDC) is an important method of improving the TWT efficiency.

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