The Eulerian cosmological fluid equations are used to study the nonlinear mode coupling of density fluctuations. We evaluate the second-order power spectrum including all four-point contributions. In the weakly nonlinear regime we find that the dominant nonlinear contribution for realistic cosmological spectra is made by the coupling of long-wave modes and is well estimated by second order pert...

A new method for pitch detection of secondary spectrum is designed in the paper, the noisy speech oval (Elliptic Filter, EF) band-pass filter is designed first in this method, and then the experience mode Decomposition(EMD)of Hilbert-Huang transform (HHT) is used to decompose the signal into a finite number of intrinsic mode functions (IMF), and IMF components of different scales are associated...