  We review recent molecular dynamics simulations of thermally activated
undulations and defects in the lamellar $L_\alpha$ phase of a binary
amphiphile-solvent mixture, using an idealized molecular coarse-grained model:
Solvent particles are represented by beads, and amphiphiles by bead-and-spring
tetramers. We find that our results are in excellent agreement with the
predictions of simple mesoscopic theories: An effective interface model for the
undulations, and a line tension model for the (pore) defects. We calculate the
binding rigidity and the compressibility modulus of the lamellar stack as well
as the line tension of the pore rim. Finally, we discuss implications for
polymer-membrane systems.
