MINOT AIR FORCE BASE, N.D. (AP) — Defense Secretary Ash Carter, who inherited a tangled web of problems in the Air Force nuclear missile corps when he took over the Pentagon in 2015, says he sees reason to believe that a push for improvement is beginning to show results. After visiting Monday with officers and airmen who operate, maintain and secure Minuteman 3 nuclear missiles on this base in the northern reaches of North Dakota, Carter said they told him they are encouraged by changes that have been made since the problems were highlighted in a series of Associated Press stories in 2013-14. In March, the Air Force disclosed that 14 airmen responsible for securing the F.E.