- Correspondence to Chenkai Wu, School of Biological and Population Health Sciences, College of Public Health and Human Sciences, Oregon State University, 206 Bates Hall, Corvallis, OR 97331, USA;
- Received 15 December 2015
- Revised 23 February 2016
- Accepted 4 March 2016
- Published in print 1 September 2016.
- Published online 11 August 2016.
- Published first 21 March 2016.
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