Double layers, sheaths and potential structures: double layers; sheaths; potential structures and oscillations. Field-aligned electric fields and related particle accelerations: field-aligned potential formation; particle accelerations. Cross-field electric fields, velocity shear and vortex formation: cross-field potential structures; velocity shear; vortex formation. Solitons, shocks, waves and instabilities, and related nonlinear phenomena: solitons and shocks; waves and instabilities; nonlinear phenomena.