  We analyze the electron transmission through a ballistic quantum dot which is
connected to two quantum point contacts. We demonstrate that the transmission
and reflection of this structure is determined by the transfer time of the
quantum-dot region which, in turn, is dependent on the applied electric field.
The electric-field dependence of the transmission coefficient exhibits clearly
pronounced peaks, and regions with negative differential transmission, and we
discuss the conditions that should be satisfied in order to observe these
effects in experiment.
