NUGU: A Group-based Intervention App for Improving Self-Regulation of Limiting Smartphone Use. - Minsam Ko; Subin Yang; Joonwon Lee; Christian Heizmann; Jinyoung Jeong; Uichin Lee; Daehee Shin; Koji Yatani; Junehwa Song; Kyong-Mee Chung (CSCW, 2015)