1. D. A. Hutchins, in Physical Acoustics edited by W. P. Mason and R. N. Thurston (Academic Press, New York, 1988), Vol. XVIII, p. 21.
2. J. W. Wagner, in Physical Acoustics edited by W. P. Mason and R. N. Thurston (Academic Press, New York, 1990), Vol. XIX, p. 201.
3. B. R. Tittmann, R. S. Linebarger and R. C. Addison, Jr., in Review of Progress in Quantitative Nondestructive Evaluation, edited by D. O. Thompson and D. E. Chimenti (Plenum Press, New York, 1990), Vol. 9A, p. 479.
4. A. D. W. McKie and R. C. Addison, Jr., in Nondestructive Characterization for Advanced Technologies - Paper Summaries, (The American Society for Nondestructive Testing, Ohio, 1991), p. 39.