where j and α α are indexes over the mechanical degrees of freedom and the leads respectively, and the subindex " e q " implies that the quantities should be evaluated at equilibrium, i.e. X ˙ ˙ = 0 and δ δ μ μ = 0 . Integrating the above equation for a system with two leads yields the well known relation between the pumped charge per cycle Q , the work done by the motor W , and the voltage bias V ,