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A web-based learning tool improves student performance in statistics: A randomized masked trial

COMPUTERS & EDUCATION 2010年第2期55卷 704-713页

作者： Gonzalez, Jose A. Jover, Lluis Cobo, Erik Munoz, Pilar UPC Dept Stat & Operat Res Barcelona 08034 Spain Univ Barcelona Dept Publ Hlth Barcelona Spain

Background: e-status is a web-based tool able to generate different statistical exercises and to provide immediate feedback to students' answers. Although the use of Information and Communication Technologies (ICTs) is becoming widespread in undergraduate education, there are few experimental studies evaluating its effects on learning. Method: All of the students (121) from an introductory course for statistics in dentistry were randomly assigned to use the tool with one of two 6-problem sets, known as types A and B. The primary endpoint was the grade difference obtained in the final exam, composed of two blocks of questions related to types A and B. The exam evaluator was masked to the intervention group. Results: We found that the effect of e-status on the student grade was an improvement of 0.48 points (95% Cl: 0.10-0.86) on a ten-point scale. Among the 94 students who actually employed e-status, the effect size was 0.63 (95% Cl: 0.17-1.10). Conclusions: It is feasible to formally assess the learning effect of an innovative tool. Providing e-status exercises to students has a direct effect on learning numerical operations related to statistics. Further effects on higher cognitive levels still have to be explored. (C) 2010 Elsevier Ltd. All rights reserved.

关键词： Applications in subject areas Evaluation methodologies Interactive learning environments probability and statistics

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Scale-dependent bounds on effective elastoplastic response of random composites

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2001年第3期49卷 655-673页

作者： Jiang, M Ostoja-Starzewski, M Jasiuk, I Inst Paper Sci & Technol Atlanta GA 30318 USA Georgia Inst Technol Atlanta GA 30318 USA Eaton Corp Rochester Hills MI 48308 USA Georgia Inst Technol George W Woodruff Sch Mech Engn Atlanta GA 30332 USA

We consider the mechanical response of random, heterogeneous materials, where each phase is elastic-plastic with an associated flow rule, and the microstructure's statistics is homogeneous and ergodic. Under proportional monotonic loading, the effective tin the macroscopic sense, or overall) elastoplastic response is shown to be bounded from above and below by those obtained, respectively, from displacement and traction boundary conditions applied to finite size domains (square shaped windows). A scale dependent hierarchy of these bounds is obtained by extending the methods used earlier for the elastic moduli estimation: the larger the scale relative to the heterogeneity, the closer are the bounds. A fiber reinforced metal matrix composite is employed to illustrate the theoretical results. Its constitutive response and plastic strain field are investigated by computational micromechanics for different window sizes under both types of boundary conditions;it is found here that the displacement conditions result in denser and more uniformly distributed slip band patterns, while the traction conditions lead to more localized fields. We also investigate a mixed boundary condition, under which the mechanical response of composite is found to fall between those under displacement and traction controlled boundary conditions. (C) 2001 Elsevier Science Ltd. All rights reserved.

关键词： scale and boundary conditions effects fiber-reinforced composite material energy methods finite elements probability and statistics

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Probabilistic modeling of microstructure evolution using finite element representation of statistical correlation functions

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INTERNATIONAL JOURNAL OF PLASTICITY 2012年 30-31卷 62-80页

作者： Sundararaghavan, V. Kumar, A. Univ Michigan Ann Arbor MI 48109 USA

A probabilistic finite element scheme is presented for simulating evolution of polycrystalline microstructures during deformation. The microstructure is described using conditional orientation correlation function (COCF), defined as the probability density of occurrence of a crystal orientation g' at a distance r from a given orientation g. The COCF is represented using three interconnected layers of finite element meshes in the g' r and g spaces. As the microstructure evolves, the reoriented neighborhood and strain fields close to an orientation (g) are captured by updating probability fields in these finite element meshes. For this purpose, a novel total Lagrangian approach has been developed that allows evolution of probability densities while satisfying normalization constraints, probability interdependencies and symmetries. The improvement in prediction of texture and strains achieved by the COCF approach over ODF-based methods is quantified through deformation analysis of a planar polycrystalline microstructure. (C) 2011 Elsevier Ltd. All rights reserved.

关键词： Microstructural descriptors Numerical algorithms Crystal plasticity Microstructures probability and statistics

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Day-ahead and intra-day wind power forecasting based on feedback error correction

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IET RENEWABLE POWER GENERATION 2021年第13期15卷 2840-2848页

作者： Gupta, Akshita Kumar, Arun Boopathi, Kadhirvel Indian Inst Technol Roorkee Hydro & Renewable Energy Dept Roorkee 247667 Uttarakhand India Indian Inst Technol Roorkee Hydro & Renewable Energy Dept Roorkee Uttarakhand India Natl Inst Wind Energy NIWE Res & Dev Resource Data Analyt & Forecasting & Solar Radiat Chennai Tamil Nadu India

The major hindrance in the development of large-scale grid integration of wind energy into the power system is the production of intermittent and variable power. A largescale integration requires a forecasting mechanism to support the power system operators while operating the grids. This study forecasts the day-ahead and intra-day wind power using the wavelet decomposition, followed by the autoregressive integrated moving average. The forecasting has been attempted on two datasets, actual and error wind power. The forecasting using the wavelet decomposition employs the discrete wavelets consisting of 16 wavelets, grouped into 5 families. The optimum length of the past data used for the model formulation has also been examined for the various scenarios. The forecasting results have been compared based on various performance metrics. The results of the forecasted values have been compared with the reference ARIMA model to see the effectiveness of the proposed wavelet-ARIMA model. The results indicate that the feedback mechanism used in the error dataset have improved the forecasting efficiency over the use of actual data in both the day-ahead and intra-day forecasting. Also, it has been observed that some of the wavelet families outperformed the other families in terms of accuracy and speed.

关键词： Wind power plants probability and statistics Power system planning and layout

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Parametric bispectral estimation of EEG signals in different functional states of the brain

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IEE PROCEEDINGS-SCIENCE MEASUREMENT AND TECHNOLOGY 2000年第6期147卷 374-377页

作者： Shen, M Chan, FHY Sun, L Beadle, PJ Shantou Univ Sci Res Dept Guangzhou 515063 Peoples R China Univ Hong Kong Dept Elect & Elect Engn Hong Kong Hong Kong Peoples R China Univ Portsmouth Sch Syst Engn Portsmouth PO1 3DJ Hants England

Higher-order statistics is applied to the analysis of electroencephalograms (EEG) in order to investigate the non-Gaussianity and nonlinearity of EEG signals. The parametric bispectral estimate is proposed for the purpose of extracting more information beyond second order statistics. The actual EEGs, with normal subjects in several different functional states of the brain, are analysed in terms of the parametric bispectral estimate. The experimental results show that all kinds of spontaneous EEG exhibit obvious quadratic nonlinear interactions of EEG signals, but the bispectral pattern of normal EEG changes with different functional states of the brain. It is suggested that the bispectrum could be regarded as the main feature in the study of EEG signals, and an effective quantitative measure for analysing and processing electroencephalography in different physiological states of the brain is provided.

关键词： Bioelectric signals Digital signal processing statistical analysis Biology and medical computing parameter estimation Signal processing and detection Electrical activity in neurophysiological processes Electrodiagnostics and other electrical measurement techniques quadratic nonlinear interactions General, theoretical, and mathematical biophysics effective quantitative measure EEG signals electrodiagnostics medical signal processing spectral analysis EEG processing parametric bispectral estimation probability and statistics EEG analysis spontaneous EEG brain functional states probability theory, stochastic processes, and statistics electroencephalography

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Neighbourhood structure estimation of images using hierarchical testing

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ELECTRONICS LETTERS 1999年第25期35卷 2188-2189页

作者： Zimeras, S Aykroyd, RG INRIA IRISA F-35042 Rennes France Univ Leeds Dept Stat Leeds LS2 9JT W Yorkshire England

Methods for estimating model parameters using likelihood techniques are examined and a model selection procedure is proposed for classifying the neighbourhood structure of the image. The techniques are investigated us... 详细信息

关键词： Image and video coding simulated data model parameters probability theory, stochastic processes, and statistics image coding Computational complexity image neighbourhood structure neighbourhood structure estimation likelihood techniques computational complexity probability and statistics hierarchical testing Image processing and restoration model selection procedure Computer vision and image processing techniques statistical analysis

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Harmonic Summation and Assessment Based on probability Distribution

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IEEE TRANSACTIONS ON POWER DELIVERY 2012年第2期27卷 1030-1032页

作者： Xiao, Yao Yang, Xavier Extra High Voltage Power Transmiss Co Maintenance & Test Ctr China So Power Grid Guangzhou 510663 Guangdong Peoples R China Henderson Ctr Elect France China Div R&D Dept Beijing 100005 Peoples R China

At the point of common coupling, there are many cases where the phase-angle difference between harmonic vectors is unknown. In practice, for example, in calculating the steady-state rating of the ac passive harmonic filter, the arithmetic summation method is often used in determining the maximal harmonic level. This summation law is very conservative as it may result in high cost of equipment ratings. Actually, a compromise should be made in taking into account the equipment safety and the risk of overrating as well as excessive costs. Based on uniform distribution of the difference in phase angles, this letter provides an algorithm to calculate the probability upon which the magnitude of summation vector of two harmonics may exceed a given value. This may also result in a recommendation of another harmonic summation method for the standard IEC/TR 61000-3-6.

关键词： Harmonic filter harmonic summation power harmonics harmonics probability and statistics

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OPTICAL ASK HETERODYNE RECEIVER - COMPARISON OF A THEORETICAL-MODEL WITH EXPERIMENT

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ELECTRONICS LETTERS 1986年第3期22卷 170-171页

作者： JACOBSEN, G GARRETT, I BRITISH TELECOM RES LABS IPSWICH IP5 7RESUFFOLKENGLAND

A recently reported ASK heterodyne system experiment has been analysed using a comprehensive theoretical model including the effects of laser phase noise, receiver noise, IF bandwidth, postdetection filtering and noise statistics following nonlinear demodulation and linear filtering. The excellent agreement between the theory and the quite independent experiment results lends strong support to our models for the effects of laser phase noise and filtering of non-Gaussian processes.

关键词： IF bandwidth receivers amplitude modulation interference (signal) nonlinear demodulation Optical communication Modulation and coding methods laser phase noise receiver noise filtering and prediction theory linear filtering optical ASK heterodyne receiver postdetection filtering optical communication equipment random processes probability and statistics Signal processing and detection noise statistics nonGaussian processes

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Maximum likelihood sequence detector for dicode pulse position modulation

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IET OPTOELECTRONICS 2011年第6期5卷 261-264页

作者： Charitopoulos, R. A. Sibley, M. J. N. Mather, P. J. Univ Huddersfield Sch Comp & Engn Dept Engn & Technol Huddersfield HD1 3DH W Yorkshire England

It is shown that the dicode pulse position modulation (DiPPM) scheme, presented in this study, demonstrates several key advantages in comparison with other existing PPM schemes, because of the compact structure and efficient recovery process of the clock signal. An error corrector for the DiPPM scheme is presented, where experimental results prove the theoretical expectations of a previous publication. Thus, it is demonstrated that DiPPM with the use of a maximum likelihood sequence detector (MLSD) error corrector, significantly reduces or eliminates errors incurred during the transmission. Comparison of and discussion on the outcomes of a DiPPM system with and without the error corrector are included.

关键词： error correction MLSD ) error corrector pulse code modulation Codes pulse position modulation probability and statistics maximum likelihood sequence detector dicode pulse position modulation Optical communication DiPPM optical fibre communication maximum likelihood sequence estimation

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SUMMATION OF HARMONICS WITH RANDOM PHASE ANGLES

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PROCEEDINGS OF THE INSTITUTION OF ELECTRICAL ENGINEERS-LONDON 1973年第3期120卷 362-363页

作者： KENDALL, PG ELECT RES ASSOC POWER ENGN DIVLEATHERHEADSURREYENGLAND

Comments are presented on a recent paper by W. G. Sherman (see Eng Index, Feb 1973 Monthly, p 170, Abst No. 008250), and the latter's reply is included.

关键词： summation current probability and statistics harmonics random processes

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