| 摘 要： | An investigation is described for instability problem of flow through a pipe of circularcross section.As a disturbance motion,we consider an axisymmetric nonlinear mode.Anassociated amplitude or modulation equation has been derived for this perturbation.Thisequation belongs to the diffusion type.The coefficient of it can be negative with Reynoldsnumber increasing,because of the complex interaction between molecular diffusion andconvection.The negative diffusion,when it occurs,causes a concentration and focusing ofenergy within the decaying slug,acting as a role of reversing natural decays.
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