Their numbers are controlled by the concentrations of impurity elements, i.e. doping concentration. Prior approaches involved doping graphene with other substances. U.S. federal prosecutors pursued allegations of doping by Armstrong from 2010 to 2012. Tour de France was marred by doping scandals. Such electrodes also employ electrochemical doping or dedoping of the polymers with anions and cations. The following year Blonska was banned for life for her second career doping offence. He admitted to blood doping in 2013. Oxide may also be grown with impurities (alloying or "doping"). In 2010, he admitted to having been involved in doping. The event was affected by a series of scandals and speculations related to doping. She remains the only Hawaii Ironman winner to be disqualified for doping offences. Social pressure is one of the factors that leads to doping in sport. For years, he denied involvement in doping. In December 2016 UFC was notified of a potential USADA doping violation by Cyborg. The 2012 Olympic results are still undecided as a result of multiple doping cases.