Zhang Shuang said: "Sometimes when the weather is very bad, I have second thoughts about coming."

张爽表示：“有时天气非常糟糕，我会再三考虑会不会来。”

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Over the years, Zhang Shuang has become a close friend to many of the children.

这些年来，张爽早已成为孩子们的好伙伴。

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"By using natural crystals for the first time, rather than artificial metamaterials, we have been able to scale up the size of the cloak and can hide larger objects, thousands of times bigger than the wavelength of the light, " said Shuang Zhang, the University of Birmingham physicist who led the research.

BBC: Invisibility cloaking benefits from crystal-clear idea