  We investigate the {\em power-down mechanism} which decides when a machine
transitions between states such that the total energy consumption,
characterized by execution cost, idle cost and switching cost, is minimized. In
contrast to most of the previous studies on the offline model, we focus on the
online model in which a sequence of jobs with their release time, execution
time and deadline, arrive in an online fashion. More precisely, we exploit a
different switching on and off strategy and present an upper bound of 3, and
further show a lower bound of 2.1, in a dual-machine model, introduced by Chen
et al. in 2014 [STACS 2014: 226-238], both of which beat the currently best
result.
