The market for net interest margin securities showed signs of a slowdown during the first half of 2005, a new analysis reveals. [One data table included] According to data compiled by affiliated newsletter Inside MBS & ABS, $6.57 billion in NIMs, or securities backed by leftover cash flows from MBS deals, were issued during the first six months of the year. That marked an 8.1 percent decrease from the same period last year. …