Today, there are three main types of space sail: solar ( the one NASA plans to test), electric (being developed in Finland) and magnetic (a concept popular in the 1980s that never quite took off).

现今已有3种主要的太阳帆：太阳驱动（NASA计划测试的类型），电驱动（正在芬兰开发）和磁驱动（1980年代很时髦如今也不算太过时）。

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Although the ecosystem concept was very popular in the 1950s and 1960s, it is no longer the dominant paradigm.

虽然生态系统概念在20世纪50年代和60年代非常流行，但它已不再是主导的概念。

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Everyone remembers when the concept of "grid computing" first became popular.

每个人都还记得“网格计算”概念首次流行起来时的情景。

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For a concept as popular as destroying chemical weapons, Umatilla's experience suggests a surprising array of obstacles.

ECONOMIST: Chemical weapons

The concept has been popular for kids with www.virtualpets.com, www.adoptme.com, and www.neopets.com.

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But the concept really became popular during World War II and the Cold War.

CNN: Guest worker issue may kill immigration reform