Fourier filtering of luciferase-reported molecular rhythm. (a) Fluctuating antennal luminescence (from a tim-luc sped men pair), from which the linear trend was removed (cf. Figure 4); these data are plotted in the time domain. (b) Result of transforming the data in (a), such that they are now plotted in the frequency domain (abscissa: period, i.e., 1/frequency, for convenience). In (b) the most appreciable feature of the frequency domain occurs within the shaded region, wherein periods between 48 and out to 136 are represented. (c) Dismissal of Fourier coefficients corresponding to periods > 48 hours, to emphasize periodicity in the circadian range. (d) Transformation of the values represented in (c) back to the time domain, with such reconstructed data appearing to have lost the nonlinear trend.