A diesel engine emission control system uses an upstream oxidation catalyst and a downstream SCR catalyst to reduce NOx in a lean exhaust gas environment. Nominal pressure corresponding to the parameters is determined by an electronic evaluation unit and generated by the pump. The piezoelectric ultracapacitor of the present invention may be used in various contexts, including power generation, switching and control and memory. The upper support surface is generally planar. A connecting link, which may be a direct connection between the user support and exercise arm, translates movement of the exercise arm assembly to movement of the user support assembly so that pivotal movement in the exercise arm assembly results in a self-aligning, pivoting movement of the user support assembly.