Methods of controlling three-dimensional glasses, a display apparatus, and a control terminal for controlling brightness of a 3D image, and the 3D glasses, the display apparatus, the control terminal, and a 3D display system related to the same are provided. A time segment of an audio signal is obtained, and an estimate of the spectral density or \u201cspectrum\u201d of the time segment is derived. The change in polarization state of the light reflected from the sample is arranged to evaluate characteristics of a sample. In embodiments, another of the advantages of the present invention is that the processing aid according to the invention can be used in very low levels relative to the other processing aids and oils. A method for producing biodiesel also is disclosed.