  We present electronic structure and quantum transport calculations that
predict conducting channels induced in graphene quantum dots by lines of
adsorbed hydrogen atoms to function as highly efficient, experimentally
realizable valley filters, accumulators and switches. The underlying physics is
a novel property of graphene Dirac point resonances (DPRs) that is revealed
here, namely, that an electric current passing through a DPR-mediated
conducting channel in a given direction is carried by electrons of em only one
of the two graphene valleys. Our predictions apply to lines of hydrogen atoms
adsorbed on graphene quantum dots that are either free standing or supported on
a hexagonal boron nitride substrate.
