University of Iowa Public Safety officials will hold a news conference this afternoon to discuss recent death threats against minorities at the Dental School. E-mails, a package and a possibly-related fire at the school promise violence unless minorities are removed from campus. U-of-I President Mary Sue Coleman says it’s important to send a message of unity.Coleman addressed a group of hundreds who marched in Iowa City yesterday to show solidarity. Dental College Dean David Johnsen says he’s proud of the way the U-of-I has pulled together.The U-of-I Office of Affirmative Action plans to hold a “Day of Dialogue” from noon until two p-m on Friday at the Iowa Memorial Union.