| http://www.w3.org/ns/prov#value | - In the past, there was no great demand for such a system, so people did not have a strong motivation to look into it, points out Joannopoulos, adding, Over the past several years, portable electronic devices, such as laptops, cell phones, iPods and even household robots have become widespread, all of which require batteries that need to be recharged often.
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