The fast kurtogram (FK), as a fast and effective method for fault diagnosis, is well accepted by many experts and scholars. However, the FK can only estimate the bandwidth and central frequency which come from resonance modulation of the signal. Sometimes useful information (containing faults) may be lost due to the inaccuracy of the estimated center frequency or bandwidth. In this paper, a novel method named empirical scanning spectrum kurtosis (ESSK), based on empirical wavelet transform (EWT), is proposed. Constructed by the principle of EWT, a set of filters with varying bandwidth scan and filter the whole frequency domain from low to high and a series of empirical modal components are obtained. Then, the spectral kurtosis (SK) of these components is calculated. The center frequency and bandwidth corresponding to the component which has the maximum SK are selected as the optimal center frequency and bandwidth. This method can adaptively and accurately find the frequency band containing rich fault feature information, and extract the corresponding component. Multiple simulation signals and experimental signals are used to verify the effectiveness of the proposed method. The results show that the method can maximally extract the components which contain the periodic pulse information and accurately diagnose the faults of the rolling bearing. In addition, comparisons with three popular signal processing methods, including the sparsogram, firbased FK and shorttime Fourier transform (STFT) based FK are conducted to highlight the superiority of the proposed method.

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Isosteric heat of adsorption is a key parameter to assess the thermodynamic properties in coals for gas adsorption and migration applications. To explore the relationships between isosteric heat of adsorption and gas storage and migration in intact and deformed coals, this paper carried out the isotherms experiments of CH4, low-temperature N2, and low-pressure CO2 on four coal samples with different deformation intensities. The results show that Langmuir VL in coal was dependent on temperature and coal structures. From 25 to 45 °C, Langmuir VL in coals decreased with the increased temperatures. Adsorption heat in intact coals was higher than deformed coals, illustrating that interaction actions between gas molecules and coal atoms were more intense in intact coal, which led to the hard desorption of gas molecules from intact coal surfaces. The specific area and pore volume of ultramicropore (<2 nm) and larger pores (>2 nm) positively increased with coal deformation intensities. The diffusion coefficients of four coal structures decreased as the depressurization processes, and the diffusion coefficient of tectonic coals was higher than intact coal in the whole diffusion stages. At a pressure zone of higher than 5 MPa, 1.5–5 MPa, and lower than 1.5 MPa, gas diffusion mainly occurred in macropores, mesopres, and micropores, respectively, corresponding to Fick’s, transitional, and Knudsen diffusion. Additionally, it is found that the isosteric heat of adsorption can be effectively used to predict adsorption isotherms in coals, and the high initial diffusion coefficient in deformed coals is related to the low isosteric heat of adsorption.