Aspects can be for ray tracing of 3-D scenes, and include dynamically controlling a population of rays being stored in a memory, to keep the population within a target, a memory footprint or other resource usage specification. A flange extends from the tubular member. Another exemplary property may be magnetic permeability. The capacitance of the capacitor changes in accordance with a displacement of the movable electrode so that an outer circuit detects the acceleration as a capacitance change. In a further embodiment, a request to the storage system to reduce a retention period includes authentication information that the storage system may use to verify the request.