About the Authors
Department of Mathematics, University of California Irvine, Irvine, California, United States of America
The authors have declared that no competing interests exist.
Conceived and designed the experiments: NLK. Performed the experiments: NLK CJT. Analyzed the data: NLK CJT. Contributed reagents/materials/analysis tools: NLK CJT. Wrote the paper: NLK.