  On directed lattices, with half as many neighbours as in the usual undirected
lattices, the Ising model does not seem to show a spontaneous magnetisation, at
least for lower dimensions. Instead, the decay time for flipping of the
magnetisation follows an Arrhenius law on the square and simple cubic lattice.
On directed Barabasi-Albert networks with two and seven neighbours selected by
each added site, Metropolis and Glauber algorithms give similar results, while
for Wolff cluster flipping the magnetisation decays exponentially with time.
