A rotor assembly that includes a shaft and an impeller andor a rotor core. It further relates to its use for delivery of compositions, specifically for whitening teeth. b) from about 1% to about 30% by weight, of a scavenger effective in scavenging compounds comprising an anionic unit; and c) the balance a carrier system. A camera arrangement can implement the method and system. The tank retain’s a volume such that the water remains therein for at least a period sufficient to permit a minimum 3 log reduction of pathogenic microbes. Forming only two MOS transistors other than a photodiode PD functioning as a photoelectric converter helps improve the open-area ratio.