Yuzhong Zhang Zhigang Cao An Asymptotic PTAS for Batch Scheduling with Nonidentical Job Sizes to Minimize Makespan. 44-51 2007 conf/cocoa/2007 COCOA http://dx.doi.org/10.1007/978-3-540-73556-4_7 db/conf/cocoa/cocoa2007.html#ZhangC07