Wiegelmann, T., & Solanki, S. K. (2004). Why are coronal holes indistinguishable from the quiet sun in transition region radiation? In R. W., Walsh, J., Ireland, D., Danesy, & B., Fleck (Eds.), Proc. SOHO 15 `Coronal Heating' (pp. 35-40). Noordwijk: ESA Publ. Div.