sentences:  The dynamics of one-component systems is subject to certain restrictions as the evolution equation can also be written in the variational form
  
  and therefore describes a permanent decrease of the "free energy" formula_4 given by the functional
  
  with a potential such that 
  In systems with more than one stationary homogeneous solution, a typical solution is given by travelling fronts connecting the homogeneous states.These solutions move with constant speed without changing their shape and are of the form with , where is the speed of the travelling wave.Note that while travelling waves are generically stable structures, all non-monotonous stationary solutions (e.g.