  Recent studies of the Q^2 dependence of ep scattering in the large x region
and in the Q^2 range: 1 < Q^2 <leq 30 Gev^2, confirm the validity of the
phenomenon of quark-hadron duality - the similarity of the deep inelastic
(parton) and resonance (hadron) spectra - for values of the invariant mass, W^2
> 2.4 GeV^2 At lower values of W^2, duality is found to be significantly
violated by an amount that cannot be parametrized in terms of the first few
terms of a series of power corrections. We present a dynamical model that
explains the Q^2 dependence of the data: at low W^2, non-partonic components
given by color neutral clusters dominate the cross section and the Q^2
dependence is governed by their mass spectrum, predicted within the
preconfiment property of Q CD; at large W^2 the structure function is
determined by a convolution of the cluster mass spectrum with the parton
distributions.
