  We introduce a generalization of expander graphs, which is called a weak
expander sequence. It is proved that a uniform Roe algebra of a weak expander
sequence is not locally reflexive. It follows that uniform Roe algebras of
expander graphs are not exact. We introduce the notion of a generalized box
space to discuss box spaces and expander sequences in a unified framework. Key
tools for the proof are amenable traces and measured groupoids associated to
generalized box spaces.
