Colloidal nanocrystal quantum dots comprising an inner core having an average diameter of at least 1. Each of the frequency sub-bands includes a left sub-band signal and a right sub-band signal. The control unit controls the two electric motors and the engagement of the gears of the gearbox to provide at least a first operating mode in which the first gear and the second gear are engaged at the same time and a second operating mode in which the second gear and the third gear are engaged at the same time. In examples, the samples form a sample sketch which is used to find the top k most frequently occurring items without the need to examine every item in the data center. A filler rod can be used to fill an unused port in the seal block assembly.