In 2008, the "Journal of Physics D: Applied Physics" published an article by Hans-Joachim Kunze, professor emeritus at the Institute for Experimental Physics, Ruhr University Bochum, critical of the 2003 paper authored by R. Mills and P. Ray, Extreme ultraviolet spectroscopy of helium–hydrogen. The abstract of the article is: "It is suggested that spectral lines, on which the fiction of fractional principal quantum numbers in the hydrogen atom is based, are nothing else but artefacts." Kunze stated that it was impossible to detect the novel lines below 30 nm reported by Mills and Ray because the equipment they used did not have the capability to detect them as per the manufacturer and as per "every book on vacuum-UV spectroscopy" and "therefore the observed lines must be artefacts". Kunze also stated that: "The enormous spectral widths of the novel lines point to artefacts, too."