The KdV equation is an asymptotic model of the propagation of nonlinear dispersive waves. X-ray spectra can be measured either by energy dispersive or wavelength dispersive spectrometers. EDS is often contrasted with its spectroscopic counterpart, WDS (wavelength dispersive X-ray spectroscopy). Solitons are caused by a cancellation of nonlinear and dispersive effects in the medium. For a given distance between the dispersive elements, prisms generate much less dispersion than gratings. There are three principal advantages for an FT spectrometer compared to a scanning (dispersive) spectrometer. An alternate method for acquiring spectra is the "dispersive" or "scanning monochromator" method. Apochromatic designs require optical glasses with special dispersive properties to achieve three color crossings. For an achromatic dispersive lens the converse must be adopted. PST is a spin-off from research on the time stretch dispersive Fourier transform. When lasers are used, a single detector without any dispersive elements might be sufficient. This is because shallow water waves are not dispersive. The collared dove is not migratory, but is strongly dispersive. Can be found only in dispersive media. Dispersive and distributive mixing as well as heat are important factors.