Methods and compositions for identification of candidate antigen-specific variable regions as well as generation of antibodies or antigen-binding fragments that could have desired antigen specificity are provided. A backside excess-suction-pressure region is provided such that pressure higher than suction pressure by a constant value is applied to a backside of scroll members to produce an attractive force to attract both scroll members. So that the coupling element can meet the requirements made on its employment in the field connected with health, the receiving element is covered by a cup-shaped cover which has a central through-opening for passing the support arm through and which has an edge area circumferentially supported on the receiving element. In a particular embodiment, a run length detector monitors the output of the differential amplifier and provides a run length feedback signal or an average bit density feedback signal to the set the selected voltage between periods of data reception.