However, vacuum column operations present an arduous environment for efficient fractionation, which makes upgrading product from bottoms to distillate more difficult.

然而，有效馏分的提取会使减压操作处境变得困难，也使塔底物料中蒸馏出更多的产品变得更加困难。

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So far we've considered only basic model operations, like displaying or editing simple column values.

到现在为止，我们只考虑了基本的模型操作，例如显示或编辑简单的列值。

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Note that if several counting functions or tests operate on the same column, then the sort and count operations only need to be done once.

注意，如果多个计数函数或测试在同一列上运行，那么排序与计数操作仅需做一次。

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For example, in the Operations column, the action steps focus on safety and on-time performance.

FORBES: Communications: Develop Your Flight Plan