The University of Iowa dental student charged with sending threatening e-mail to fellow students is in more hot water.Twenty-three-year-old Tarsha Claiborne was charged yesterday with harassment, trespassing and making threats after admitting to sending racist e-mail threats to minority students in the University of Iowa School of Dentistry. Today, Claiborne was charged with possession of a controlled substance. Police say they found one gram of marijuana in Claiborne’s apartment during a search.