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21.
本文利用经验正交分解法(Empirical Orthogonal Function,EOF)对不同月平均和10天平均的西北太平洋海洋表面温度距平数据进行分解,得到月平均和10天平均的西北太平洋海洋表面温度距平分布模态,并对分布模态进行比较。发现尽管数据源相同,但是不同时间分辨率的EOF结果出现正好相反的情况,文章最后从数学的角度解释了月平均和10天平均的海洋表面温度距平模态及其时间系数发生反向的原因。 相似文献
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本文运用声波导的理论讨论钻井声场的共振模式问题,特别注意稳态现象和暂态现象的区别与联系.本文考察了共振模式的存在性及其在声波测井信号中的反映. 相似文献
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资源安全供应是保障国民经济持续健康发展的必要条件。阐述了发达国家资源安全供应的3个模式:比较优势模式、贸易一投资模式和系统论模式。通过实例,就模式的作用机理进行了简要分析。结合我国的实际情况,借鉴发达国家资源安全供应的经验,就我国资源的安全供应提出了4个方面的建议。 相似文献
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David Al-Attar 《Geophysical Journal International》2007,171(2):755-760
A formal solution to the elastodynamic equation in an anelastic earth model is presented. The derivation also incorporates the effects of aspherical structure, rotation, self-gravitation, and pre-stress. It is found that the solution can be expressed as a sum of the normal modes of the earth model along with additional terms accounting for anelastic relaxation processes. However, the derivation does not assume that such an eigenfunction expansion is possible, and so avoids difficulties previously encountered due to the non self-adjointness of the problem. 相似文献
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In this paper, the adaptive chirplet decomposition combined with the Wigner-Ville transform and the empirical mode decomposition combined with the Hilbert transform are employed to process various non-stationary signals (strong ground motions and structural responses). The efficacy of these two adaptive techniques for capturing the temporal evolution of the frequency content of specific seismic signals is assessed. In this respect, two near-field and two far-field seismic accelerograms are analyzed. Further, a similar analysis is performed for records pertaining to the response of a 20-story steel frame benchmark building excited by one of the four accelerograms scaled by appropriate factors to simulate undamaged and severely damaged conditions for the structure. It is shown that the derived joint time–frequency representations of the response time histories capture quite effectively the influence of non-linearity on the variation of the effective natural frequencies of a structural system during the evolution of a seismic event; in this context, tracing the mean instantaneous frequency of records of critical structural responses is adopted.The study suggests, overall, that the aforementioned techniques are quite viable tools for detecting and monitoring damage to constructed facilities exposed to seismic excitations. 相似文献
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Least-squares self-coherency analysis of superconducting gravimeter records in search for the Slichter triplet 总被引:3,自引:0,他引:3
We develop a new approach for the spectral analysis of the superconducting gravimeter data to search for the spheroidal oscillation 1S1 of the Earth solid inner core. The new method, which we call least-squares (LS) self-coherency analysis, is based on the product of the least-squares spectra of segments of the time series under consideration. The statistical foundation of this method is presented in the new least-squares product spectrum theorem that establishes rigorously confidence levels for detecting significant peaks. We apply this approach along with a number of other innovative ideas to a 6-year long gravity series collected at the Canadian Superconducting Gravimeter Installation (CSGI) in Cantley, Canada, by splitting it into 72 statistically independent monthly records. Each monthly record is analysed spectrally and all monthly LS spectra are multiplied to construct the self-coherency spectrum of the 6-year gravity series. The self-coherency spectrum is then used to detect significant peaks in the band 3-7 h at various significant levels with the aim to identify a triplet of periods associated with the rotational/ellipsoidal splitting of 1S1 (Slichter triplet). From all the Slichter periods predicted by various researchers so far, Smylie's triplet appears to be the most supported one, albeit very weakly, both, before and after the atmospheric pressure effect is removed from the series. Using the viscous splitting law [Smylie, D.E., 1992. The inner core translational triplet and the density near Earth's center. Science 255, 1678-1682] as guide, we can also see one interesting and statistically significant triplet with periods A = {4.261 h, 4.516 h, 4.872 h}, which changes slightly to A′ = {4.269 h, 4.516 h, 4.889 h} after the atmospheric pressure correction is applied to the gravity series. 相似文献
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