The Coast Guard called off its search Thursday for an acclaimed computer scientist whose sailboat has disappeared off Northern California, ending a four-day hunt. Despite unusually calm weather, searchers have exhausted any area Jim Gray could have drifted or sailed after leaving for a solo sailing trip Sunday to scatter his mother's ashes at sea, a Coast Guard spokesman said. A cargo plane, a helicopter and six patrol boats dispatched by the Coast Guard had scoured more than 132,000 square miles of the Pacific since Monday in the search for Gray, whose database innovations led to some of the most widespread technological innovations of the past 30 years.