  We derive the effective action for a one dimensional electron island formed
between a double barrier in a single channel quantum wire including the
electron spin. Current and energy addition terms corresponding to charge and
spin are identified. The influence of the range and the strength of the
electron interaction and other system parameters on the charge and spin
addition energies, and on the excitation spectra of the modes confined within
the island is studied. We find by comparison with experiment that spin
excitations in addition to non-zero range of the interaction and inhomogeneity
effects are important for understanding the electron transport through one
dimensional quantum islands in cleaved-edge-overgrowth systems.
