Thi V. Duong Dinh Q. Phung Hung Hai Bui Svetha Venkatesh Efficient duration and hierarchical modeling for human activity recognition. 830-856 2009 173 Artif. Intell. 7-8 http://dx.doi.org/10.1016/j.artint.2008.12.005 db/journals/ai/ai173.html#DuongPBV09