defense following the north claim of testing an h-bomb. south korea renewing the propaganda broadcasts on loud speakers across the demilitarized zone. this is something the north considers an act of war. let's go to cnn's will ripley in pyongyang. you got back from a tour of the north korean science center. what did you learn there? >> reporter: it is interesting, alison, because this science center just opened up a few days ago. of course, this week, we have the announcement that north korea's fourth nuclear test in the last 15 years. i was talking to people, students mostly doing research at the science center. i asked what they thought about the nuclear test. everybody was enthusiastic. saying they were overjoyed by the accomplishment of their country. when you walk through the science center, which has the centerpiece of the whole thing is a missile in the center of it. the missile that was launched in