sandpaper-covered plates. The sinusoidal stress response signal collected
from the sample was separated into elastic and viscous stress
contributions using symmetry arguments [8]. Chebyshev polynomials
(closely related to the Fourier deconvolution) were utilized as
orthonormal basis functions to further decompose these stresses
into odd and even harmonic components having physical interpretations
[8]. Multiple steady-state wave forms were used for data
analysis (typically three cycles of data were collected, and the last
two cycles, where the data had equilibrated, were used) at each
coordinate pair (x, c0).