Low density parity check decoders are described utilizing a sequential schedule called Zigzag LBP, for a layered belief propagation architecture. A conduit is associated with each of the microneedles to provide a fluid flow path for transport of fluid through a hole in the biological barrier formed by the corresponding microneedle. The first annular element may be entwined with the second annular element. The antenna may be made of a conductor wound helically about an air core with a circumference and a number of loops, and the spacing of the loops chosen based on the desired frequency of communication. The cache may also indicate which pages of memory are in use by one or more transfers, enabling the hypervisor to avoid appropriating pages of memory during a transfer.