The present invention is directed to a compound represented by the following structural formulaor a pharmaceutically acceptable salt thereof. The first rotary screw compressor has a first displacement and is driven by a first power source. Specifically, the invention relates to reverse transcriptase enzymes which have been mutated or modified to increase thermostability, decrease terminal deoxynucleotidyl transferase activity, andor increase fidelity, and to methods of producing, amplifying or sequencing nucleic acid molecules using these reverse transcriptase enzymes or compositions. The VCO is modified to have an additional control port to adjust the duty cycle. The engagement mechanism is biased against the bin wall to prevent undesired movement of the moveable bin divider.