On September 21-26th, ACM UbiComp 2021 annual conference was held online. The papers of REN Yan and SU Jinhua, master students of RUC School of Statistics, were accepted by UbiComp 2021. ACM UbiComp is a world-class conference in the field of pervasive computing, listed as an A-class conference by China Computer Society. UbiComp 2021 attracted nearly 800 scholars from 44 countries and regions to participate in online communication. UbiComp 2021: Multiple Tree Model Integration for Transportation Mode Recognition Author: REN Yan UbiComp 2021: Triple-O for SHL Recognition Challenge: An Ensemble Framework for Multi-class Imbalance and Training-testing Distribution Inconsistency by OvO Binarization with Confidence Weight of One-class Classification Authors: SU Jinhua, ZHANG Yuanyuan