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1.
Mirror extending and circular spline function for empirical mode decomposition method 总被引：4，自引：0，他引：4
The Mirror Extending (ME) approach is proposed in this paper for solving the end extending issue in the Empirical Mode Decomposition
(EMD) method. By this approach, the data extended into a closed circuit without end. The derivatives on ends are not necessary
any more for Spline fingth. The approach eliminates the possible problems in reliability and uniqueness in the original extending
approach of the EMD method. In the ME approach only one extending is necessary before the data analysis. A tipient criterion
is proposed here for checking the extending approach. ME approach has been proved to satisy the theoretical criterion automatically
and permanently. This approach makes the EMD method reliable and casy to follow.
Project supported by NSFC (49634140, 49876008). Contribution No. 2001B001 from the Key Lab of Ocean Dynamic Processes and
Satellite Oceanography, SOA. 相似文献
2.
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
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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
8.
张帆 《浙江大学学报(A卷英文版)》2004,5(5):558-566
This paper provides theoretical foundation for the problem of localization in multi-robot formations. Sufficient and necessary conditions for completely localizing a formation of mobile robots/vehicles in SE(2) based on distributed sensor networks and graph rigidity are proposed. A method for estimating the quality of localizations via a linearized weighted least-squares algorithm is presented, which considers incomplete and noisy sensory information. The approach in this paper had been implemented in a multi-robot system of five car-like robots equipped with omni-directional cameras and IEEE 802.11b wireless network. 相似文献
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INTRODUCTION In order for a team of mobile robots to navigateautonomously in some desired formations and fur-ther perform cooperative tasks, such as surveillanceand target acquisition, they must be able to localizethemselves in the formation as well as in a globalreference frame (Belta and Kumar, 2001; Das et al.,2002). Therefore, how to estimate the robots’po-sitions and orientations (poses) in a precise andefficient way is of particular interest. Our interestwas in localizing a team o… 相似文献
10.
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
11.
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
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研究了在空频块码正交频分复用(SFBC-OFDM)无线通信系统中适用于多径衰落信道下的迭代接收机的设计,导出了一种迭代的联合信道估计与符号检测的算法.在提出的算法中,信道估计器交替地工作于2种模式.在训练阶段,采用基于DFT的估计器估计出信道状态信息,并且采用所提出的算法估计出噪声方差和信道响应的互相关矩阵.在数据传输模式下,迭代地获得发送数据和信道状态信息.为了抑制由于符号检测中误判引起的错误传播,提出了一种简单的错误传播判定准则,并使用了一种自适应的训练机制来抑制误差传播.仿真结果显示,与传统的迭代算法相比,所提出的算法能够提供更好的误码性能,且节约了系统开销. 相似文献
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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
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Most of the proposed concurrency control protocols for real-time database systems are based on serializability theorem.Owing to the unique characteristics of real-time database applications and the importance of satisfying the timing constraints of transactions,serializability is too strong as a correctness criterion and not suitable for real-time databases in most cases.On the other hand,relaxed serializability including epsilon-serializability and similarity-serializability can allow more real-time transactions to satisfy their timing constraints,but database consistency may be sacrificed to some extent.We thus propose the use of weak serializability(WSR)that is more relaxed than conflicting serializability while database consistency is maintained.In this paper,we first formally define the new notion of correctness called weak serializability.After the necessary and sufficient conditions for weak serializability are shown,corresponding concurrency control protocol WDHP(weak serializable distributed high prority protocol)is outlined for distributed real time databases,where a new lock mode called mask lock mode is proposed for simplifying the condition of global consistency.Finally,through a series of simulation studies,it is shown that using the new concurrency control protocol the performance of distributed realtime databases can be greatly improved. 相似文献
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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
16.
一种利用时间序列分析的特征提取与损伤预警方法 总被引：1，自引：0，他引：1
针对结构健康监测中如何基于在线监测数据实现损伤诊断的问题,提出了一种利用时间序列分析ARMA模型的特征提取和损伤预警方法.首先对所有监测数据样本建立ARMA模型,以模型中AR部分参数的主成分矩阵构建Mahalanobis距离判别函数,提出了一种新的结构损伤敏感指标DDSF.然后,采用t-检验考察该指标在损伤前后是否存在显著性变化,从而可以有效地实现结构损伤预警.三跨连续梁数值算例表明,提出的结构损伤特征指标对结构的微小损伤具有敏感性,具备结构在线实时损伤预警的应用价值. 相似文献
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ABSTRACTPrevious research shows that many students find it difficult to learn computer programming. To learn computer programming includes both gaining theoretical understanding and learning to develop programmes in practice. To this end, teachers commonly design programming exercises for the students in the computer laboratory. To be able to improve the process of designing such exercises, there is a need of a more detailed understanding of the interaction between learning of theory and learning of practice in laboratory sessions. In this paper, an approach for investigating this interaction is proposed. Theoretically, the approach is based on phenomenography and variation theory. To illustrate the approach, it is demonstrated in detail how it was applied to a small but rich case of empirical data from a computer laboratory session. The main result presented here is the new approach for analysing data. In addition, the results of the case study shed preliminary light on the interaction between learning of practice and learning of theory when students work with programming assignments in the laboratory. 相似文献
18.
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
19.
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
20.
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