Concentrations of positively charged particles develop at the top and bottom of the cloud, but the middle region becomes negatively charged.

带正电荷的粒子集中在云团的顶部和底部，但中间区域形成的是带负电荷的粒子。

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The wing of Xenicibis (top) compared with that of a typical ibis Eudocimus (middle) and the extinct, flightless ibis Apteribis (bottom).

始祖鸟的翅膀(顶部)与典型鹮类(中部)和已灭绝不飞行的鹮类(底部)样本对比。

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The planet's real fault line is between elites and the middle class in some countries, and the bottom of the pyramid, everywhere.

全球范围内真正的断层线存在于一些国家的社会精英、中产阶级和金字塔底层人们之间，而且这种分化无处不在。

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Nelson's injuries destroyed all three main skin layers - the epidermis, dermis and hypodermis (the top, middle and bottom), in some places right down to the periosteum, the membrane overlying the bone.

BBC: US Army seeks new ways to treat facial skin injuries

Whether it's the gap between the top tenth and the bottom tenth, or between the middle and the bottom - they all got smaller in 2010-11.

BBC: Britain's recession: Harsh but fair?

The trend for huge celebrations has "extended socially from middle and top down to bottom" and "now we all expect these events to be big and lavish".

BBC: Why has everything become a costly milestone event?