  When neutral nano-particles are heated or cooled in a polar liquid, they will
interact with each other as if they carry an electrostatic charge that is
proportional to the temperature difference between the particle and the
surrounding fluid. The same should hold for paramagnetic liquids, in which case
the nano-particles should behave as magnetic monopoles. However, the analogy
with electrostatics/magnetostatics is not complete: heated/cooled
nano-particles do not move under the influence of an applied field. They
should, however, interact as monopoles.
