Wenxing Zhu A provable better Branch and Bound method for a nonconvex integer quadratic programming problem. 107-117 2005 70 J. Comput. Syst. Sci. 1 http://dx.doi.org/10.1016/j.jcss.2004.07.002 db/journals/jcss/jcss70.html#Zhu05