1. Biophotonics Section, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, Maryland 20892
2. National High Magnetic Field Laboratory and Department of Biological Science, The Florida State University, Tallahassee, Florida 32310
3. École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland CH-1015
4. Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892;