The technology relies on the ink being made into a form of the so-called Janus particle. Each particle of ink is dyed so that it is dark on one side and white on the other. The two sides are given opposite electric charges, and so each pixel on the electronic paper can be made dark or white by applying the appropriate electric charge. They are named Janus particles after the Roman god of transitions, who is depicted as having two faces and is often associated with doors and gates. Because the Janus particles are physical ink and need to physically rotate when the text is changed, they cannot
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