Hetero phase polymer compositions are described. There is also provided a method of preventing inadvertent switch-off of the light source in such a video display apparatus. An electromagnetic field generator generates a transverse magnetic field, space-variant and symmetric with respect to the axis of the input particle beam, in such a way as to change the spin of the particles and attach thereto different values of orbital angular momentum in dependence on their input spin values. An output node of any of the n second circuits is electrically connected to an input node of the second circuit in a first stage through the variable resistor.