An ink jet head has a substrate, partition walls disposed on a main surface of the substrate and spaced apart at a preselected interval to form channels for receiving ink. In one embodiment, methods, systems and computer software are provided for comparative gene expression analysis using intensity dependent normalization factors. The input block comprises:\u2014a first resistive network operatively connected to both the input terminal and the output terminal ;\u2014a second resistive network connected between the output terminal and a reference potential. These agents are generally selected from the group consisting of 3TC, AZT, -FTC, ddI, ddC, abacavir, tenofovir, D-D4FC, D4T, Racivir, L-D4FC, NVP, DLV, EFV, SQVM, RTV, IDV, SQV, NFV, APV, LPV, fuseon and mixtures thereof.