  The ac conductance of a finite tubular two-dimensional electron gas is
studied in the presence of the Rashba spin-orbit interaction. When the tube is
coupled to two reservoirs, that interaction splits the steps in the dc current,
introducing energy ranges with spin-polarized currents. For this setup, we
calculate the current-current correlations (the noise spectrum) and show that
the existence of these dc spin-polarized currents can be deduced from the shot
noise. We also find that the Wigner-Smith time delay is almost unaffected by
the spin-orbit interaction. When the tube is coupled to a single reservoir, we
calculate the quantum capacitance and the charge-relaxation resistance, and
find that they exhibit singularities near the openings of new channels.
