PLEASANTON -- Four defendants have been charged in federal court with visa fraud for their alleged roles in the case of a fake university in Pleasanton being used as a front for foreign students seeking to establish U.S. immigration status, according to court documents unsealed Tuesday. Vishal Dasa, 25, Anji Reddy Dirisinala, Ramakrishna Reddy Karra and Tushar Tambe each pleaded not guilty Tuesday in U.S. District Court in Oakland to conspiracy to commit visa fraud. Last year, an undercover agent with the U.S. Immigration and Customs Enforcement went to Tri-Valley University in Pleasanton and posed as a prospective foreign student...