Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, USA.|Center for Bioinformatics and Computational Biology, University of Maryland, College Park, MD, USA.|Center for Bioinformatics and Computational Biology, University of Maryland, College Park, MD, USA.|Center for Bioinformatics and Computational Biology, University of Maryland, College Park, MD, USA.|Department of Biostatistics, Product Development, Genentech Inc., South San Francisco, CA, USA.|Center for Bioinformatics and Computational Biology, University of Maryland, College Park, MD, USA.