A Nashville hospital company and a Philadelphia hospital have been picked to develop and run a $350-million, 250-bed freestanding children's hospital that will be linked to the University of Texas Health Science Center in San Antonio. UT regents voted on Sept. 7 to choose Vanguard Health Systems Inc. of Nashville and Children's Hospital of Philadelphia for the project. Vanguard will fund the complex, and the Philadelphia hospital will help administer it. The hospital is set to open in about 30 months, but no date has been set for a construction start.