One way to visualize this issue is to compare U.S. unemployment with job openings since 2001. The result can be seen on the attached chart: a scorpion-shaped curve that tracks the swelling ranks of the long-term jobless. The chart’s creators were Rand Ghayad, a Ph.D. candidate in economics at Northeastern University, and his adviser, labor economist William Dickens. Their work was part of a report they wrote that was published last year by the Federal Reserve Bank of Boston. It was so striking that the Boston Fed named Ghayad a visiting fellow.