A method of and apparatus for controlling heat transfer in a fluidized bed reactor having a heat transfer chamber with a bed of solid particles therein, means for introducing fluidizing gas into the heat transfer chamber for fluidizing the bed of solid particles therein and heat transfer surfaces in contact with the bed of solid particles in the heat transfer chamber. The electronic alert apparatus also includes a processor operatively connected to the radio frequency receiver and configured to decode the encoded emergency message. When locked, the locking device acts on the locking member by being arranged to prevent the movement of the locking member away from the first contact surface. The up-converter resonant cavity light emitting diode device has applications in head mounted projection display optical system using spectrally selective beam splitters to eliminate spectral overlap between colors and to combine the red, green and blue beams.