  We describe linear and nonlinear transport across a single impurity Anderson
model quantum dot with intermediate coupling to the leads, i.e., with tunnel
coupling of the order of the thermal energy k_B T. The coupling is large enough
that sequential tunneling processes alone do not suffice to properly describe
the transport characteristics. Upon applying a density matrix approach, the
current is expressed in terms of rates obtained by considering a very small
class of diagrams which dress the sequential tunneling processes by charge
fluctuations. We call this the "dressed second order" (DSO) approximation. One
major achievement of the DSO is that, still in the Coulomb blockade regime, it
can describe the crossover from thermally broadened to tunneling broadened
conductance peaks. When the temperature is decreased even further, the DSO
captures "Kondesque" behaviours of the Anderson quantum dot qualitatively: We
find a zero bias anomaly of the differential conductance versus applied bias,
an enhancement of the conductance with decreasing temperature as well as the
onset of universality of the shape of the conductance as function of the
temperature. We can address the case of a spin-degenerate level split
energetically by a magnetic field and show that, if we assume in addition
different capacitive couplings of the two spin-levels to the leads, one of the
resonance peaks is vanishing. In case spin-dependent chemical potentials are
introduced and only one of the four is varied, the DSO yields in principle only
one resonance. This seems to be in agreement with experiments with pseudo-spin.
Furthermore, we get qualitative agreement with experimental data showing a
cross-over from the Kondo to the empty orbital regime.
