  Classic calculations of the magnetic moments mu_p and mu_n of the nucleons
using the traditional exponential kernel show instability with respect to
variations of the Borel mass as well as arbitrariness with respect to the
choice of the onset of perturbative QCD. The use of a polynomial kernel, the
coefficients of which are determined by the masses of the nucleon resonances
stabilizes the calculation and provides much better damping of the unknown
contribution of the nucleon continuum. The method is also applied to the
evaluation of the coupling gA of proton to the axial current and to the strong
part of the neutron-proton mass difference Delta M_np. All these quantities
depend sensitively on the value of the 4-quark condensate < 0 | qqqq | 0 > and
the value < 0 | qqqq | 0 > ~ 1.5< 0 | qq | 0 >^2 reproduces the experimental
results.
