NEW YORK - Although it has already taken nearly four decades to get this far in building the Internet, some university researchers with the federal government's blessing want to scrap all that and start over. The idea may seem unthinkable, even absurd, but many believe a "clean slate" approach is the only way to truly address security, mobility and other challenges that have cropped up since UCLA professor Leonard Kleinrock helped supervise the first exchange of meaningless test data between two machines on Sept. 2, 1969. The Internet "works well in many situations but was designed for completely different assumptions,"...