Each day, a group of men and women gathers in a waiting room at Mt. Sinai Medical Center in Manhattan. Another group heads to a hospital at Rutgers in New Brunswick. Yet another, to medical centers in Queens and Long Island. They are young and old, African-Americans, Asians, whites and others of mixed races — in short, all ages and ethnic backgrounds. But they have a singular bond. Each one is being monitored for health problems stemming from the 9/11 attacks.