A paper shredder with a thermo-regulated motor, a universal motor, and a method for cooling a motor. The V-belt continuously variable transmission and the gear-type transmission are placed in this order from upstream in a power transmission path from the engine to wheels. The presence of labeled target nucleic acids on the array surface is then detected and used to determine the presence of the one or more nucleic acid analytes in the sample. The E-E transformer has a first E core and an identical second E core ; each E core has two outer legs and an inner leg ; the E cores together form a double closed magnetic circuit and two outer links as well as an inner link.