Tidal Fields and Structure Formation
  The role of tidal shear in the formation of structure in the Universe is explored. To illustrate the possible and sometimes dramatic impact of tidal fields we focus on the evolution of voids. We firstly analyze the role of tidal fields both in the highly symmetric situation of an initially homogeneous ellipsoidal underdensity embedded in an artificially imposed tidal field. In addition, we present selfconsistent case studies consisting of N-body simulations that start from constrained Gaussian initial conditions in which the matter distribution is appropriately sculpted to yield an a priori specified tidal field. We conclude that voids may indeed be induced to collapse. Also, we present evidence for the strong relation between tidal fields and filaments in the mass distribution. 
Rien van de Weygaert (Kapteyn Astronomical Institute, University of   Groningen, the Netherlands)