  In this paper we establish Koszul duality between dg categories and a class
of curved coalgebras, generalizing the corresponding result for dg algebras and
conilpotent curved coalgebras. We show that the normalized chain complex
functor transforms the Quillen equivalence between quasicategories and
simplicial categories into this Koszul duality. This allows us to give a
conceptual interpretation of the dg nerve of a dg category and its adjoint. As
an application, we prove that the category of representations of a
quasicategory is equivalent to the coderived category of comodules over its
chain coalgebra. A corollary of this is a characterization of the category of
constructible dg sheaves on a stratified space as the coderived category of a
certain dg coalgebra.
