Motivated by applications in energy-efficient scheduling in data centers,
Khuller, Li, and Saha introduced the {\em machine activation} problem as a
generalization of the classical optimization problems of set cover and load
balancing on unrelated machines. In this problem, a set of $n$ jobs have to be
distributed among a set of $m$ (unrelated) machines, given the processing time
of each job on each machine, where each machine has a startup cost. The goal is
to produce a schedule of minimum total startup cost subject to a constraint
$\bf L$ on its makespan.