From an experimental point of view, it is certainly never observed.

从实验的角度来看，这种情况从未被观测到。

youdao

Two volunteers cut off from the rest world for eight months stepped out on a mock-up of Mars on Monday, reaching the dramatic half-way point of their experimental "voyage" to the Red Planet.

周一，两名同外部世界隔离了8个月之久的志愿者在模拟火星上迈出了第一步，进而让这个关于火星旅行的实验到达了关键性的中间点。

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But to Mr Gove's team, experimental risk is not the downside of setting schools free (more than 1, 000 have gained academy status since 2010) : it is the point.

但对于戈夫先生的团队来说，实验的风险不是学校自由度的缩小(2010年以来，1000多所学校获得专科资格)：这才是问题的关键所在。

youdao

You can see some people in the back with cameras as part of an experimental pilot program funded by the Hewlett Foundation and at some point they will decide what they will do with these lectures.

你们能看到后面的摄像人员,这是个由休利特基金会赞助的实验性试播项目,在某种程度上来说,是由他们决定,如何使用这些课堂录像

耶鲁公开课 - 基础物理课程节选

Meanwhile, research into fusion power (in which energy is generated by fusing hydrogen atoms together at very high temperatures) has left behind a different kind of debris: a trail of experimental reactors, none of which has yet reached the break-even point where the amount of energy that comes out exceeds the amount put in.

ECONOMIST: Nuclear waste

In nineteen eighty-one, Iraq was on the point of acquiring nuclear power. 10.17.01 Narrator The Osirak reactor was an experimental plutonium plant.

BBC