Since the Morfey-Howell Q/S was introduced as a single-point frequency-domain nonlinearity indicator for propagation of intense broadband noise [AIAA J. 19, 986–992 (1981)], there has been debate about its validity, utility, and interpretation. In this Letter, the generalized Burgers equation is recast in terms of specific acoustic impedance along with linear absorption and dispersion coefficients, normalized quadspectral density (Q/S), and newly proposed normalized cospectral density (C/S). The formulation leads to a rather straightforward interpretation in which Q/S and C/S, respectively, represent the additional absorption and dispersion at a locale, produced by the passage of a finite-amplitude wave.

中文翻译：

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基于阻抗的频域非线性指标在有限振幅声传播中的表示

由于Morfey-霍维尔Q / S被引入作为用于激烈宽带噪声传播[AIAA J.单点频域非线性指示器19，986-992（1981）]，出现了关于它的有效性，效用辩论，和解释。在这封信中，广义Burgers方程根据比声阻抗，线性吸收和色散系数，归一化四谱密度（Q / S）和新提出的归一化共谱密度（C / S）进行了重铸。该表述导致相当简单的解释，其中Q / S和C / S分别代表通过有限振幅波通过而产生的在局部区域的附加吸收和色散。