OFL: Opportunistic Federated Learning for Resource-Heterogeneous and Privacy-Aware Devices. - Yunlong Mao; Mingyang Niu; Ziqin Dang; Chengxi Li 019; Hanning Xia; Yuejuan Zhu; Haoyu Bian; Yuan Zhang 004; Jingyu Hua; Sheng Zhong 002 (CoRR, 2025)