"Unital quantum operations on the Bloch ball and Bloch region," P.S. Bourdon and H.T. Williams, Physical Review A 69, 022314 (2004).
"Superposition solutions to the Schrdinger equation," H. Thomas Williams, American Association of Physics Teachers, DOI: 10.1119/1.1466816 (2002)
"Semantics in teaching introductory physics," H. Thomas Williams, American Association of Physics Teachers, Am. J. Phys 67 (8), Aug. 1999.