Jana Partners, the activist fund run by Barry Rosenstein, disclosed a stake in Pinnacle Foods Inc. and is urging the packaged food manufacturer to explore a sale or another transactions in the frozen food space. The New York-based hedge fund and its partners own 9.5 percent of the food manufacturing company, according to a regulatory filing Thursday. Jana said in the filing that it believes Pinnacle is in a good position to consider consolidation given its strong position in the frozen foods industry.