1 National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA. galperin@ncbi.nlm.nih.gov dshalaeva@uos.de.
2 School of Bioengineering and Bioinformatics, Moscow State University, Moscow 119992, Russia. galperin@ncbi.nlm.nih.gov dshalaeva@uos.de.
3 School of Physics, University of Osnabrück, Osnabrück D-49069, Germany.