That's when the MIT duo decided to miniaturize a solid-oxide fuel cell instead.

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The North is not believed to have mastered the technology needed to miniaturize nuclear bombs enough to mount them on long-range missiles.

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This suggests a technology using highly-enriched uranium, which is easier to miniaturize than the plutonium bombs North Korea previously tested in 2006 and 2009.

FORBES: Move up http://i.forbesimg.com t Move down

Second, North Korea would have to miniaturize its warhead.

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The U.S. has said North Korea does not possess a nuclear warhead or the required technology to miniaturize one to fit on its rockets, but it could put a "dirty bomb" or conventional weapon on one.

CNN: Analysis: Amid pending launch, N. Korea only shows half its hand

"As we approach the ultimate limits of Moore's Law, however, silicon will have to be replaced in order to miniaturize further, " said Jeffrey Bokor, deputy director for science at the Molecular Foundry at the Lawrence Berkeley National Laboratory and Professor at UC-Berkeley.

ENGADGET: Stanford engineers find work around for barriers to carbon nanotube computers