Sobotka, M., Brandt, P. N., Simon, G. W. Lifetimes and motions of penumbral grains - preliminary results. In: RIMMELE, T.R., BALASUBRAMANIAM, K.S., RADICK, R.R., eds. High resolution solar physics: theory, observations, and techniques. San Francisco: Astronomical Society of the Pacific, 1999, s. 116-123. ASP Conference series., 183.