  We calculate the linear and nonlinear conductance of spinless fermions in
clean, long quantum wires where short-ranged interactions lead locally to
equilibration. Close to the quantum phase transition where the conductance
jumps from zero to one conductance quantum, the conductance obtains an
universal form governed by the ratios of temperature, bias voltage and gate
voltage. Asymptotic analytic results are compared to solutions of a Boltzmann
equation which includes the effects of three-particle scattering. Surprisingly,
we find that for long wires the voltage predominantly drops close to one end of
the quantum wire due to a thermoelectric effect.
