For those interested (and with subscriptions or institutional access), here are the abstracts for the two papers, the first from the MIT group and the second from the Princeton group:
The MIT group's paper appears to be on arXiv: http://arxiv.org/abs/1502.03438 (albeit with a somewhat different abstract; perhaps a pre-acceptance version). Unfortunately the Princeton group's paper doesn't appear to be posted on arXiv.org as of right now.
The Princeton group's has a different title, and was posted March 9 (I downloaded it about a month later so pulled it off my hard drive when I saw this comment)
http://www.sciencemag.org/content/early/2015/07/15/science.a...
http://www.sciencemag.org/content/early/2015/07/15/science.a...
The MIT group's paper appears to be on arXiv: http://arxiv.org/abs/1502.03438 (albeit with a somewhat different abstract; perhaps a pre-acceptance version). Unfortunately the Princeton group's paper doesn't appear to be posted on arXiv.org as of right now.