This invention relates to sulfonated copolymers which are useful in forming polymer electrolyte membranes used in fuel cells. The device converts said provided external dimming values into internal dimming values on the basis of which the control of the connected lamps is achieved, the internal dimming values being of higher resolution than the external dimming values. The microcomputer is coupled to the camera and is configured to determine an image flow of an object of at least one pixel occurring in images captured by the camera, to determine an exposure time to achieve a predetermined image flow, and to compute an image velocity based on the exposure time of the camera. The method can be practiced with prior or subsequent static or perfusion hypothermic exposure of the organ. Finally, a second differential current amplifier is connected with its inputs to the amplifier outputs and with its output to the second amplifier output.