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Nonpartonic components in the nucleon structure functions at small Q^2 in a broad range of x

We construct a simple two-phase model of the nucleon structure functions valid for both small and large Q^2 and in the broad range of Bjorken x. The model incorporates hadron dominance at small x and Q^2 and parton model at large Q^2. The VDM contribution is modified for small fluctuation times of the hadronic state of the photon. With two free parameters we describe SLAC, CERN NMC, Fermilab E665 and CERN BCDMS data for both proton and deuteron structure functions. Our model explains some phenomenological higher-twist effects extracted from earlier analyses. A good description of the NMC F_2^p(x) - F_2^n(x) data is obtained in contrast to other models in the literature. We predict faster vanishing of the partonic component at low Q^2 than previously expected and strong Q^2 dependence of the Gottfried Sum Rule below Q^2 ~ 4 GeV^2.