  The transport properties of serially coupled quantum dots (SCQDs) embedded in
a matrix connected to metallic electrodes are theoretically studied in the
linear and nonlinear regimes. The current rectification and negative
differential conductance of SCQDs under the Pauli spin blockade condition are
attributed to the combination of bias-direction dependent probability weight
and off-resonant energy levels yielded by the applied bias across the
junctions. We observe the spin-polarization current rectification under the
Zeeman effect. The maximum spin-polarization current occurs in the forward bias
regime. Such behavior is different from the charge current rectification.
Finally, the Seebeck coefficient ($S$)of SCQDs is calculated and analyzed in
the cases without and with electron phonon interactions. The application of
SCQDs as a temperature detector is discussed on the basis of the nonlinear
behavior of $S$ with respect to temperature difference across the junction.
