Constructions of E_n Operads
  This paper discusses the question of how to recognize whether an operad is E_n (ie. equivalent to the little n-cubes operad). A construction is given which produces many new examples of E_n operads. This construction is developed in the context of an infinite family of right adjoint constructions for operads. Some other related constructions of E_n operads, so-called generalized tensor products, are also described. 
Z. Fiedorowicz