When students returned to campus this fall, they found a series of dramatic animal heads in the Woodrow Wilson School’s Scudder Plaza. “Circle of ­Animals/Zodiac Heads,” a sculpture by the Chinese artist and social activist Ai Weiwei, was installed during the summer. The 12 bronze pieces, which depict the signs of the ­Chinese zodiac and are about 10 feet tall, will be on display for a year. Ai made headlines in 2011 when he was detained by Chinese authorities for 81 days. The University plans to host Ai Oct. 10 for a day of events focused on his art and human-rights activities.