It was pointed at the lock and a separate piece of x-ray sensitive film was used to read the scatter.

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These contain a silicon chip so sensitive it captures images up to 30 times faster than conventional film.

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"There's no question that China is very sensitive to its image, " said Stanley Rosen, an expert on the Chinese film industry, and director of the East Asian Studies Center at the University of Southern California in Los Angeles.

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Sensitive and self-doubting, he includes interviews with Minter, her response to public screenings of the short film, and footage that she shot to deliver her own perspective on the relationship.

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Sir Adam Roberts, president of the British Academy, and Sir Paul Nurse, president of the Royal Society said the film raised "serious issues" about the credibility and security of UK academics working overseas in highly-sensitive circumstances.

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