Greff-Lefftz, M., Legros, H., & Dehant, V. (2000). Influence of the inner core viscosity on the rotational eigenmodes of the Earth. Physics of the Earth and Planetary Interiors, 122(3-4), 187-204. https://doi.org/10.1016/S0031-9201(00)00179-5 (Original work published 2000)