Mortgage-conduit activity continued to gain speed rapidly during the second quarter of this year, as industry-wide production of new securities backed by a variety of nonconforming home-loan products jumped to $48.25 billion. The second-quarter volume of new issuance by mortgage conduits represented a 21.4 percent gain over the already strong level of $39.76 billion recorded in the first quarter. On a year-to-date basis, the $88.01 billion in deals issued in the first half of 2001