  Using non-equilibrium renormalized perturbation theory, we calculate the
retarded and lesser self energies, the spectral density rho(omega) near the
Fermi energy, and the conductance G through a quantum dot as a function of a
small bias voltage V, in the general case of electron-hole asymmetry and
intermediate valence. The linear terms in omega and V are given exactly in
terms of thermodynamic quantities. When the energy necessary to add the first
electron (Ed) and the second one (Ed+U) in the quantum dot are not
symmetrically placed around the Fermi level, G has a linear term in V if in
addition either the voltage drop or the coupling to the leads is not symmetric.
The effects of temperature are discussed. The results simplify for a symmetric
voltage drop, a situation usual in experiment.
