Domain Walls, Hitchin's Flow Equations and G_2-Manifolds
  We construct BPS domain wall solutions of the effective action of type-IIA string theory compactified on a half-flat six-manifold. The flow equations for the vector and hypermultiplet scalars are shown to be equivalent to Hitchin's flow equations, implying that our domain walls can be lifted to solutions of ten-dimensional type-IIA supergravity. They take the form R^{1,2} x Y_7, where Y_7 is a G_2-holonomy manifold with boundaries. 
Christoph Mayer and Thomas Mohaupt