On a new compactification of moduli of vector bundles on a surface, IV:   Nonreduced moduli
  The construction for nonreduced projective moduli scheme of semistable admissible pairs is performed. We establish the relation of this moduli scheme with reduced moduli scheme built up in the previous article and prove that nonreduced moduli scheme contains an open subscheme which is isomorphic to moduli scheme of semistable vector bundles. 
Nadezda V. Timofeeva
math.AG math-ph math.MP