A chromatography column and method of maintenance is described which does not require the use of a hoist or crane for disassembly. The movable subsystem includes an electrical component providing electrical signal including information. When HCCI+RVT mode is selected, intake valves operate with regular valve timing, and the engine is fueled to cause homogeneous-charge compression-ignition combustion. The computer or computers responsible for controlling access to a resource may, for example, download one or more interrogator agents onto the remote computer to determine its operating environment. More generally, certain pre-executable counterparts of likely-to-stall operations that form dependency chains may be scheduled above operations that are themselves likely-to-stall.