Michele Slack, who had been director of digital media for Hearst Newspapers, was named yesterday as the head of SFGate.com, the Chron’s online arm, replacing Peter Negulescu, a former AOL executive who had been the Chron’s vp for digital media since mid-2004. No reason was given for the change in a brief item published this morning. The article said the change was effective immediately. Slack has been at Hearst since 2005, arriving there from the digital side of The New York Times.