There is not direct mathematical relations among virtual front time, virtual tail time and theoretical front time, theoretical tail time of lightning impulse.

雷电波的视在波头时间和视在波尾时间与理论波头时间和理论波尾时间没有直接的数学关系。

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On the PC front, we've seen concept laptops with two displays for some time now, usually with the idea that the bottom screen can be used as a virtual keyboard when needed.

在个人电脑领域，如今可见装有两个显示器的手提电脑，通常其底部屏幕在必要的时候可以作为虚拟键盘使用。

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Like Dr Ehrsson's experiment, volunteers were fitted with stereoscopic headsets and were shown images of virtual figures -- this time the figures appeared in front of them.

CNN: Scientists recreate out-of-body experience