Viewers of Ken Burns recent PBS series “The Vietnam War” learned about the major themes and events of the conflict. Journalist Mark Bowden further explores one of the pivotal battles of the Tet Offensive – the 24-day fight for the city of Hue. His new book is called “Hue 1968: A Turning Point of the American War in Vietnam” (Atlantic Monthly Press). He signs books tonight at Barnes and Noble in Plano and Wednesday night at Interbang Books in Dallas.