The present invention provides spheroidal particles of coal slag, and methods of making the spheroidal particles. The recessed light fixture rotation ring has a mechanical brake for locking the ring in place after positioning of the lamp. The housing has transfer port defining an opening in fluid communication with the second flow path and a volume outside of the housing. In exemplary embodiments, the sensor is implemented as a current source responsive to temperature fluctuations, and the frequency controller is implemented as a plurality of controlled reactance modules which are selectively couplable to the resonator or to one or more control voltages. The received RR frame is sent from a non-PC station in the BSS when at least one centralized contention opportunity is available during the CCI after the CC frame. The core material is surrounded by a shell that includes an amorphous matrix.