sentences:  The early 1950s saw dramatic changes in the world of U.S. science fiction publishing.At the start of 1949, all but one of the major magazines in the field were in pulp format; by the end of 1955, all had either ceased publication or switched to digest format.This change was largely the work of the distributors, such as American News Company, who refused to carry the pulp magazines since they were no longer profitable; the loss of profitability was in turn associated with the rise in mass-market science fiction publishing, with paperback publishers such as Ace Books and Ballantine Books becoming established.