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Nonequilibrium conductance of a nanodevice for small bias voltage

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.