Retraction Note.
[This retracts the article e20302 in vol. 17.][This retracts the article e19403 in vol. 17.][This retracts the article e12596 in vol. 17.][This retracts the article e29706 in vol. 17.][This retracts the article e28974 in vol. 17.][This retracts the article e21341 in vol. 17.][This retracts the article e19406 in vol. 17.][This retracts the article e22053 in vol. 17.][This retracts the article e18631 in vol. 18.][This retracts the article e26095 in vol. 17.][This retracts the article e17211 in vol. 17.][This retracts the article e12257 in vol. 18.]
Central Office, Heerlen, The Netherlands.