NEW YORK, N.Y. (AP).- Architect Michael Arad first imagined the twin reflecting pools with cascading waterfalls — he calls them voids — as two empty spaces in the Hudson River, west of the smoldering World Trade Center. When Arad entered a competition for a trade center memorial in 2003, the voids were in the footprints of the towers themselves, and manmade waterfalls replaced the churning river. A jury including Vietnam Veterans Memorial designer Maya Lin chose Arad’s twin waterfalls out of 5,201 entries, saying it embodied the grief and the desire for healing that the Sept. 11 terrorist attacks inspired. The 42-year-old Arad’s 9/11 moment is arriving on the 10th anniversary of the attacks, culminating a journey for