(decembro 1999) “Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. I. Comparing the Photoionization and Reverberation Techniques"”, The Astrophysical Journal (en) 526 (2). doi:10.1086/308017.
Wandel, Amri (aprilo 2015). “How Many People Speak Esperanto? Esperanto on the Web”, Interdisciplinary Description of Complex Systems (en) 13. doi:10.7906/indecs.13.2.9. Alirita 12-a de aprilo 2024..