Typically, the number of active service class periods in a system should not exceed 30.

通常，系统中的活动服务分类周期的数量不应该超过30。

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However, for a limited number of people living in known high background radiation areas of the world, doses can exceed 20 mSv per year.

然而对于数量不多的生活在全球已知高辐射环境地区的人们来说，每年的剂量可超过20 mSv。

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When maxperm is a strict-limit, the kernel does not allow the number of non-computational pages to exceed maxperm, even if there is free memory available.

当maxperm是严格限制的时候，即使有可供使用的空闲内存，内核也不允许非计算性分页的数目超出maxperm的限制。

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They maintain that the key feature of Bitcoin is that the supply can never exceed a certain number - 21 million - and that it has recovered from previous crashes when its demise was predicted.

BBC: The Bitcoin bubble

Changes in the number of houses for sale are widely seen as a good 'leading indicator' of price-changes: in a boom-period there are more buyers than sellers, so the number of properties for sale diminishes, and in a 'bust' period sellers exceed the number of those willing to buy at current prices, so prices tend to fall, as seems already to be happening in many areas.

BBC: NEWS | Business | UK house prices go into reverse

As for the number of MEPs in the European Parliament, this is limited to a number that "shall not exceed 700".

BBC: Europe: The issues