  Janus --or two-sided, charged membranes offer promise as ionic current
rectifiers. In such systems, pores consisting of two regions of opposite charge
can be used to generate a current from a gradient in salinity. The efficiency
of \textcolor{black}{nanoscale} Janus pores increases dramatically as their
diameter becomes smaller. However, little is known about the underlying
transport processes\textcolor{black}{, particularly under experimentally
accessible conditions}. In this work, we examine the molecular basis for
rectification in Janus nanopores using an applied electric field. Molecular
simulations with explicit water and ions are used to examine the structure and
dynamics of all molecular species in aqueous electrolyte solutions.
\textcolor{black}{For several macroscopic observables, the results of such
simulations are consistent with experimental observations on asymmetric
membranes. Our analysis reveals a number of previously unknown features,
including a pronounced local re-orientation of water molecules in the pores,
and a segregation of ionic species that has not been anticipated by previously
reported continuum analyses of Janus pores. Using these insights, a model is
proposed for ionic current rectification in which electric leakage at pore
entrance controls net transport.
