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1.
MIRROR EXTENDING AND CIRCULAR SPLINE FUNCTION FOR EMPIRICAL MODE DECOMPOSITION METHOD 总被引：43，自引：0，他引：43
ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅＥｍｐｉｒｉｃａｌＭｏｄｅＤｅｃｏｍｐｏｓｉｔｉｏｎ (ＥＭＤ)ｍｅｔｈｏｄａｎｄｉｔｓＨｉｌｂｅｒｔＳｐｅｃｔｒｕｍｔｅｃｈｎｉｑｕｅｉｓａｎｅｗｌｙｄｅｖｅｌｏｐｅｄｍｅｔｈｏｄｆｏｒｔｉｍｅｓｅｒｉｅｓａｎａｌｙｓｉｓ(Ｈｕａｎｇｅｔａｌ.,1 998) .Ｔｈｉｓｍｅｔｈｏｄｉｓｓｕｉｔａｂｌｅｆｏｒａｎａｌｙｚｉｎｇｎｏｎｌｉｎｅａｒａｎｄｎｏｎ ｓｔａｔｉｏｎａｒｙｐｒｏ ｃｅｓｓｂａｓｅｄｏｎａｎｅｍｐｉｒｉｃａｌａｐｐｒｏａｃｈａｎｄｐｒｏ ｖｉｄｅｓａｐｒｅｃｉｓ… 相似文献
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经验模态分解( empirical mode decomposition,EMD)存在端点飞翼的固有问题,使信号两端出现扭曲失真。为抑制EMD端点效应,文章提出双重对称延拓法,以端部数据对称延拓作为首次延拓,以极值点对称延拓作为二次延拓,该方法可同时实现EMD分解和Hilbert变换两阶段端点效应的抑制。仿真信号和地震响应的工程算例通过IMF分量对比、瞬时频率对比,以及整体正交性、相关系数等指标的对比,验证了该方法具有良好的端点效应抑制效果,同时还能改善IMF分量之间的正交性,并节约计算时间。 相似文献
3.
A new algorithm, named segmented second empirical mode decomposition （EMD） algorithm, is proposed in this paper in order to reduce the computing time of EMD and make EMD algorithm available to online time-frequency analysis. The original data is divided into some segments with the same length. Each segment data is processed based on the principle of the first-level EMD decomposition. The algorithm is compared with the traditional EMD and results show that it is more useful and effective for analyzing nonlinear and non-stationary signals. 相似文献
4.
郑树元 《宁德师专学报(自然科学版)》2012,24(4):402-405
提出基于EMD和相对能量法相结合的消弧线圈接地系统故障选线方法．通过EMD时空滤波,在故障线路零序电流中提取暂态分量作为特征量,再求得各线路的相对能量,以能量为故障判据,从而检测出故障线路,经Matlab／simdlink仿真验证,结果表明该方法有效,且算法简便． 相似文献
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混凝土建筑物中的裂纹扩展追踪计算是确定结构安全度的重要手段。本文提出用虚拟裂纹单元及断裂力学准则(应变强度因子)追踪和模拟裂缝初始断裂、扩展并最终导致破坏的过程,给出一条逐段扩展的裂纹线,本方法计算结果与某些混凝土坝实测资料及模型试验结果吻合较好。 相似文献
7.
The fracture processes of concrete were described by a cohesive crack model based on initial toughness criterion. The corresponding analytical method to predict the instability state was proposed. In this model, the initial toughness was adopted as the crack propagation criterion and the weight function method was used to calculate the stress intensity factor and the crack opening displacement caused by the cohesive stress. The unstable toughness can be easily obtained using the proposed method without measuring parameters at the critical state that was necessary in traditional methods. The proposed method was verified by existing experimental data of wedge splitting specimens with different grades of concrete and the sensitivity of the results on the tensile softening curve was discussed. The results demonstrate that the proposed method can well predict the peak load, the critical effective crack length, and the unstable toughness of concrete specimens. Moreover, the calculated unstable toughness is not sensitive to the tensile softening curve. 相似文献
8.
无约束全局最优化中的无参数填充函数 总被引：1，自引：0，他引：1
The filled function method is an approach for finding a global minimum of multi-dimensional functions.With more and more relevant research,it becomes a promising way used in unconstrained global optimization.Some filled functions with one or two parameters have already been suggested.However,there is no certain criterion to choose a parameter appropriately.In this paper,a parameter-free filled function was proposed.The definition of the original filled function and assumptions of the objective function given by Ge were improved according to the presented parameter-free filled function.The algorithm and numerical results of test functions were reported.Conclusions were drawn in the end. 相似文献
9.
Accurate wave forecasting with a couple of hours of warning time offers improvements in safety for maritime operation-related activities. Autoregressive (AR) model is an efficient and highly adaptive approach for wave forecasting. However, it is based on linear and stationary theory and hence has limitations in forecasting nonlinear and non-stationary waves. Inspired by the capability of empirical mode decomposition (EMD) technique in handling nonlinear and non-stationary signals, this paper describes the development of a hybrid EMD-AR model for nonlinear and non-stationary wave forecasting. The EMDAR model was developed by coupling an AR model with the EMD technique. Nonlinearity and non-stationarity were overcome by decomposing the wave time series into several simple components for which the AR model is suitable. The EMD-AR model was implemented using measured significant wave height data from the National Data Buoy Center, USA. Prediction results from various locations consistently show that the hybrid EMD-AR model is superior to the AR model. This demonstrates that the EMD technique is effective in processing nonlinear and non-stationary waves. 相似文献
10.
Is Teaching Experience Necessary for Reliable Scoring of Extended English Questions? 总被引：1，自引：0，他引：1
Hundreds of thousands of raters are recruited internationally to score examinations, but little research has been conducted on the selection criteria for these raters. Many countries insist upon teaching experience as a selection criterion and this has frequently become embedded in the cultural expectations surrounding the tests. Shortages in raters for some of England's national examinations has led to non-teachers being hired to score a small minority of items and changes in technology have fostered this approach. For a National Curriculum test in English taken at age 14, this study investigated whether teaching experience was a necessary selection criterion for all aspects of the examination. Fifty-seven raters with different backgrounds were trained in the normal manner and scored the same 97 students' work. Accuracy was investigated using a cross-classified multilevel model of absolute score differences with accuracy measures at level 1 and raters crossed with candidates at level 2. By comparing the scoring accuracy of graduates with a degree in English, teacher trainees, experienced teachers and experienced raters, this study found that teaching experience was not a necessary selection criterion. A rudimentary model for allocation of raters to different question types is proposed and further research to investigate the limits of necessary qualifications for scoring is suggested. 相似文献
11.
In ultrasonic non-destructive tests, the echo signal at the flaw is highly complex due to the interference of multiple echoes with random amplitudes and phases, and is disturbed by all kinds of noises, such as thermal noise, digitalization noise, and structure noise. In this paper, the ultrasonic signal was decomposed by empirical mode decomposition （EMD） to obtain the intrinsic mode function （IMF） components according to ultrasonic defect echo signals occuring at the corresponding time, and the energy of the ultrasonic signal was concentrated. The IMF component selection criterion based on sub-band energy extraction was proposed to extract the ultrasonic signal component accurately and automatically from IMF components. When the selected IMF components were filtered by a band pass filter, the signal-to-noise ratio （SNR） was enhanced greatly. 相似文献
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Covariate Measurement Error Correction for Student Growth Percentiles Using the SIMEX Method 
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下载免费PDF全文 In this study, we examined the impact of covariate measurement error (ME) on the estimation of quantile regression and student growth percentiles (SGPs), and find that SGPs tend to be overestimated among students with higher prior achievement and underestimated among those with lower prior achievement, a problem we describe as ME endogeneity in this article. We proceeded to assess the effect of covariate ME correction on SGP estimation at two levels—the individual (student) and the aggregate (classroom). Our ME correction approach was limited to the simulation‐extrapolation method known as SIMEX. For both the individual and aggregate SGP, we find SIMEX effective in bias reduction. Further, because SIMEX is especially effective in reducing SGP bias for students with very high or very low prior achievement, it significantly weakens the ME endogeneity. SIMEX is also effective in reducing the MSE of aggregate SGP, provided that the students are sorted to some extent on their latent prior achievement. Our empirical study confirms the pattern of the simulation results: SIMEX mainly affects the mean SGP of classes in the highest and lowest quintiles of the prior score distribution, and significantly lowers the correlation between class SGP and prior achievement. 相似文献
13.
COQUELET Christophe RICHON Dominique 《浙江大学学报(A卷英文版)》2007,8(5):724-733
In 1987, the Montreal Protocol prohibited the worldwide use and production of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) and hydro fluorocarbons (HFCs) were proposed as alternative refrigerants. Unfortunately, HFCs have non negligible global warning potential and therefore new refrigerants must be proposed or old refrigerants must be used associated with HFC. Accurate experimental thermodynamic data and predictive techniques are required for better under-standing of the performance of the newly proposed refrigerants. In this communication, experimental techniques based on either analytic or synthetic methods are first described. Data are reported. Then two newly developed predictive models based on thermodynamic approach with the isofugacity criterion and artificial neural network method are presented. The results can provide better evaluation of refrigerants, especially with the aim of studying global warning effects. 相似文献
14.
Mohammad Mahdavi Mazdeh Seyed-Mostafa Razavi Roozbeh Hesamamiri Mohammad-Reza Zahedi Behin Elahi 《Higher Education》2013,65(2):207-226
The purpose of this study is to propose a framework to evaluate the entrepreneurship intensity (EI) of Iranian state universities. In order to determine EI, a hybrid multi-method framework consisting of Delphi, Analytic Network Process (ANP), and VIKOR is proposed. The Delphi method is used to localize and reduce the number of criteria extracted from a deep literature review, according to the social and economic conditions of Iranian state universities by using an expert panel, including sixty-eight country-wide academicians and practitioners. After that, a group approach to ANP was utilized as an evaluation method to derive the weights of each criterion. Next, the evaluation data were gathered through a questionnaire, and, finally, the compromise ranking of universities was calculated using the VIKOR method. Moreover, this study applies weight-variance analysis (WVA) to suggest improvement actions. The paper proposes an evaluation framework for determining the performance of entrepreneurship development initiatives in universities. By using this framework, twenty-two Iranian state universities are evaluated in terms of their EI, and the results are discussed. 相似文献
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针对齿轮常见故障及信号在传统EMD算法分解中产生的端点效应,提出一种基于改进经验模态分解（EMD）与快速独立分量分析（FastICA）—样本熵的齿轮故障特征提取方法。首先对信号进行EMD分解,得到一系列IMF分量和残余量,在此过程中通过匹配差别最小的极值包络线段确定端点处极值,然后从每个信号中分别选取周期性明显的分量与原始信号组成混合信号作为FastICA的输入,获得ICA计算后的分量,最后分别计算EMD分量与各独立分量的样本熵。实验结果表明,改进后的EMD算法可以有效改善端点效应问题,并通过与EMD—样本熵的对比,表明FastICA—样本熵能更明显、稳定地反映齿轮故障,因此可作为一种有效的故障特征。 相似文献
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A latent variable modeling method is outlined, which accomplishes estimation of criterion validity and reliability for a multicomponent measuring instrument with hierarchical structure. The approach provides point and interval estimates for the scale criterion validity and reliability coefficients, and can also be used for testing composite or simple hypotheses about these coefficients. The proposed method is illustrated with a numerical example. 相似文献
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针对谱系聚类的有效性,提出了一个新的聚类准则用于汶川地震灾害评估,并选用经典的Iris花蕾数据和Wine葡萄酒数据与流行的模糊C均值聚类准则比较,结果表明新准则计算简单且更符合实际情况. 相似文献
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The permutation flowshop scheduling problem (PFSP) is one of the most well-known and well-studied production scheduling problems with strong industrial background. This paper presents a new hybrid optimization algorithm which combines the strong global search ability of artificial immune system (AIS) with a strong local search ability of extremal optimization (EO) algorithm. The proposed algorithm is applied to a set of benchmark problems with a makespan criterion. Performance of the algorithm is evaluated. Comparison results indicate that this new method is an effective and competitive approach to the PFSP. 相似文献
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Longitudinal studies offer unique opportunities to identify the specificity variance in the components of a psychometric scale that is administered repeatedly. This article discusses a procedure for evaluation of the relationship between true scale scores and criterion variables uncorrelated with measurement errors in longitudinally presented measures comprising unidimensional multicomponent instruments. The approach provides point and interval estimates of the true scale criterion validity with respect to a criterion that is assessed once or repeatedly, as well as a means for testing temporal stability in this validity. The outlined method is based on an application of the latent variable modeling methodology, is readily applicable with popular software, and is illustrated using empirical data. 相似文献
20.
Short-term load forecasting (STLF) plays a very important role in improving the economy and security of electricity system operations. In this paper, a hybrid STLF method is proposed based on the improved ensemble empirical mode decomposition (IEEMD) and back propagation neural network (BPNN). To alleviate the mode mixing and end-effect problems in traditional empirical mode decomposition (EMD), an IEEMD is presented based on the degree of wave similarity. By applying the IEEMD method, the nonlinear and nonstationary original load series is decomposed into a finite number of stationary intrinsic mode functions (IMFs) and a residual. Among these components, the high frequency (namely IMF1) is always so small that it has little contribution to model fitting, while it sometimes has a great disturbance for the STLF. Therefore, the IMF1 is removed in the proposed hybrid method for denoising. The remaining IMFs and residual are forecast by BPNN, and then the forecasting results of each component are combined with BPNN to obtain the final predicted load series. Three groups of studies were done to evaluate the effectiveness of the proposed hybrid method. The results show that the proposed hybrid method outperforms other methods both mentioned in this paper and previous studies in terms of all the three standard statistical indicators considered in this study. 相似文献