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Now showing items 1 - 16 of 77

  • A Family of M-Ary sigma-Sequences With Good Autocorrelation

    Shi, Xiaoping   Zhu, Xiaomeng   Huang, Xinmei   Yue, Qin  

    In this letter, we propose a family of almost M-ary a' -sequences with good autocorrelation based on cyclotomic classes. The out -of -phase autocorrelation magnitude of these M-ary sequences is upper bounded by 3 or root 5.
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  • Consistent two-stage multiple change-point detection in linear models

    Jin, Baisuo   Wu, Yuehua   Shi, Xiaoping  

    A two-stage procedure for simultaneously detecting multiple change-points in linear models is developed. In the cutting stage, the change-point problem is converted into a model selection problem so that a modern model selection method can be applied. In the refining stage, the change-points obtained in the cutting stage are finalized via a refining method. Under mild conditions, consistency of the number of change-point estimates is established. The new procedure is fast and accurate, as shown in simulation studies. Its applicability in real situations is demonstrated via well-log and ozone data. (C) 2016 Statistical Society of Canada
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  • Astronomical image restoration using variational Bayesian blind deconvolution

    Shi, Xiaoping   Guo, Rui   Zhu, Yi   Wang, Zicai  

    An algorithm is presented for image prior combinations based blind deconvolution and applied to astronomical images. Using a hierarchical Bayesian framework, the unknown original image and all required algorithmic parameters are estimated simultaneously. Through utilization of variational Bayesian analysis, approximations of the posterior distributions on each unknown are obtained by minimizing the Kullback-Leibler (KL) distance, thus providing uncertainties of the estimates during the restoration process. Experimental results on both synthetic images and real astronomical images demonstrate that the proposed approaches compare favorably to other state-of-the-art reconstruction methods.
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  • Approximation to the moments of ratios of cumulative sums

    Shi, Xiaoping   Reid, Nancy   Wu, Yuehua  

    We propose an approximation to the mean of the ratio of cumulative sums of a sequence of independently distributed nonnegative random variables. Both leading term and higher-order saddlepoint approximations are presented, and the results are applied to a vector ratio approximation, change-point analysis, and kernel regression. The Canadian Journal of Statistics 42: 325-336; 2014 (c) 2014 Statistical Society of Canada Resume Les auteurs proposent une approximation pour la moyenne du ratio de la somme cumulative d'une sequence de variables aleatoires non negatives independantes. Des approximations en point de selle sont presentees pour le terme principal et les termes d'ordre superieur. Les resultats sont appliques a la distribution d'un vecteur de ratios, a une analyse du point de rupture et a la regression a noyau. La revue canadienne de statistique 42: 325-336; 2014 (c) 2014 Societe statistique du Canada
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  • Auxiliary covariate in additive hazards regression for survival data

    Shi, Xiaoping   Liu, Yanyan   Wu, Yuanshan  

    We consider the additive hazards regression analysis by utilising auxiliary covariate information to improve the efficiency of the statistical inference when the primary covariate is ascertained only for a randomly selected subsample. We construct a martingale-based estimating equation for the regression parameter and establish the asymptotic consistency and normality of the resultant estimator. Simulation study shows that our proposed method can improve the efficiency compared with the estimator which discards the auxiliary covariate information. A real example is also analysed as an illustration.
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  • Approximation to the moments of ratios of cumulative sums

    Shi, Xiaoping   Reid, Nancy   Wu, Yuehua  

    We propose an approximation to the mean of the ratio of cumulative sums of a sequence of independently distributed nonnegative random variables. Both leading term and higher-order saddlepoint approximations are presented, and the results are applied to a vector ratio approximation, change-point analysis, and kernel regression. The Canadian Journal of Statistics 42: 325-336; 2014 (c) 2014 Statistical Society of Canada Resume Les auteurs proposent une approximation pour la moyenne du ratio de la somme cumulative d'une sequence de variables aleatoires non negatives independantes. Des approximations en point de selle sont presentees pour le terme principal et les termes d'ordre superieur. Les resultats sont appliques a la distribution d'un vecteur de ratios, a une analyse du point de rupture et a la regression a noyau. La revue canadienne de statistique 42: 325-336; 2014 (c) 2014 Societe statistique du Canada
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  • Auxiliary covariate in additive hazards regression for survival data

    Shi, Xiaoping   Liu, Yanyan   Wu, Yuanshan  

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  • Consistent and powerful graph-based change-point test for high-dimensional data

    Shi, Xiaoping   Wu, Yuehua   Rao, Calyampudi Radhakrishna  

    A change-point detection is proposed by using a Bayesian-type statistic based on the shortest Hamiltonian path, and the change-point is estimated by using ratio cut. A permutation procedure is applied to approximate the significance of Bayesian-type statistics. The change-point test is proven to be consistent, and an error probability in change-point estimation is provided. The test is very powerful against alternatives with a shift in variance and is accurate in change-point estimation, as shown in simulation studies. Its applicability in tracking cell division is illustrated.
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  • Consistent and powerful graph-based change-point test for high-dimensional data

    Shi, Xiaoping   Wu, Yuehua   Rao, Calyampudi Radhakrishna  

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  • Land tenure security and land investments in Northwest China

    Ma, Xianlei   Heerink, Nico   van Ierland, Ekko   van den Berg, Marrit   Shi, Xiaoping  

    Purpose - The purpose of this paper is to examine the effect of perceived land tenure security in China on farmers' decisions to invest in relatively long-term land quality improvement measures, taking into account the potential endogeneity of tenure security. Design/methodology/approach - Data from a survey held in 2008 and 2010 among 259 households in Minle County, Gansu province, covering the years 2007 and 2009, are used to estimate the factors affecting land levelling investments, irrigation canal investments and perceived land tenure security. The authors use the 2SCMIL technique and the IVLS method to estimate a selection model and a non-limited regression model, respectively, and use WP methods to examine the robustness of the results. Findings - The authors' results indicate that perceived land tenure security significantly affects self-governed investments but does not affect individual investments in land quality improvements. In particular, the authors find that households that consider land certificates as important for protecting land rights invest significantly more in irrigation canals construction and maintenance. The authors' results further provide evidence that individual investments in land quality improvement contribute to higher perceived land tenure security. Originality/value - The paper contributes to the available literature on the relationship between land tenure security and land investments by examining the role of perceived (instead of formal) land tenure security and by making a distinction between individual household investments and self-governed land investments. The authors' results provide an explanation for the phenomenon that land readjustments still take place in some parts of China, but not in others.
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  • Reconstruction and transmission of astronomical image based on compressed sensing

    Shi, Xiaoping   Zhang, Jie  

    In the process of image transmission, the famous JPEG and JPEG-2000 compression methods need more transmission time as it is difficult for them to compress the image with a low compression rate. Recently the compressed sensing (CS) theory was proposed, which has earned great concern as it can compress an image with a low compression rate, meanwhile the original image can be perfectly reconstructed from only a few compressed data. The CS theory is used to transmit the high resolution astronomical image and build the simulation environment where there is communication between the satellite and the Earth. Number experimental results show that the CS theory can effectively reduce the image transmission and reconstruction time. Even with a very low compression rate, it still can recover a higher quality astronomical image than JPEG and JPEG-2000 compression methods.
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  • Reconstruction and transmission of astronomical image based on compressed sensing

    Shi, Xiaoping   Zhang, Jie  

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  • Links between the spatial structure of weather generator and hydrological modeling

    Li, Zhi   Lu, Zhemin   Li, Jingjing   Shi, Xiaoping  

    Impacts of the spatial structure of weather generators on hydrological modeling have been largely qualitatively discussed; however, their links have been rarely quantified. The precipitation occurrence and amount were respectively generated with Markov chain and the mixed exponential distribution for single sites, and then the procedures were extended to multi-site simulation according to Wilks (1998). In the multi-site model, precipitation amounts were respectively generated with untapered or tapered mixed exponential scale parameters. The generated precipitation series were used as inputs of Soil and Water Assessment Tool (SWAT) to interpret the links between the spatial structure of weather generators and hydrological modeling. The single-site and multi-site model using untapered scale parameters gave similar averages for monthly and annual streamflow; however, the untapered multi-site model was superior to simulating hydrological variability. The single-site model underestimated the maxima and variances while overestimated the minima of streamflow; therefore, the use of single-site models for hydrological variability simulation should be cautious. The multi-site model using tapered scale parameters greatly overestimated the averages, extremes, and variances of streamflow. The Wilks model for multi-site precipitation simulation using tapered scale parameters is not appropriate for hydrological modeling, and the untapered version is thus recommended. Overall, the spatial structure of weather generators has significant impacts on hydrological modeling, especially for hydrological variability simulation; therefore, the links between them should be paid great attentions.
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  • High noise astronomical image denoising via 2G-bandelet denoising compressed sensing

    Zhang, Jie   Zhang, Huanlong   Shi, Xiaoping   Geng, Shengtao  

    In deep space exploration, high resolution astronomical image captured is often contaminated by various cosmic noise signals during its shooting and long distance transmission, which has brought inconvenience to astronomical image analysis. The famous compressed sensing (CS) proposed by Candes et al. can successfully solve the problem of high resolution astronomical image compression and low noise reconstruction. In this paper, we further concern how to reconstruct a high quality image from a high resolution and high noise astronomical image. A 2G-bandelet denoising compressed sensing (BDCS) is first proposed based on the advantage of CS in image denoising and the superior ability of 2G-bandelet in sparse representation of astronomical images, then iterative bandelet thresholding (IBT-BTCS) algorithm based on BDCS is proposed for high resolution and high noise astronomical image reconstruction. Firstly, an iterative bandelet thresholding method is designed to obtain optimal approximation of original image; Secondly, to further improve the reconstructed image quality, group sparse total variation with stepsize constraints (GSTV-SC) method is proposed to adjust the reconstructed astronomical image in each iteration. The simulation results show that the proposed algorithm can quickly reconstruct a high quality astronomical image only using a few observations, preserve more astronomical image details and effectively solve high noise astronomical image denoising problem.
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  • Continuous auxiliary covariate in additive hazards regression for survival data

    Shi, Xiaoping   Liu, Yanyan   Wu, Yuanshan  

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  • Income implications of political capital and agricultural land use in western China

    Komarek, Adam M.   Spoor, Max   Feng, Shuyi   Shi, Xiaoping  

    Purpose - The purpose of this paper is to explore the expansion of agricultural production into marginal lands, also known as "wasteland," and examine the association between political capital, household income, and using additional marginal lands for agriculture in the Xinjiang Uyghur Autonomous Region of western China. Design/methodology/approach - The paper uses exploratory data analyses methods, including descriptive statistics, graphical analysis, econometrics and propensity score matching, and data from a 2008 survey of 342 households in Awat County of Aksu Prefecture to explore the role of political capital in an agricultural household setting. Findings - Preliminary results suggest that wasteland usage has a positive association with income, and that household political capital, in the form of Communist Party membership or being a village cadre, correlates with wasteland usage because it improves access to irrigation water. Originality/value - A constant topic of debate in China is the role of political capital in influencing livelihoods. The authors aim to add modest insights into this debate and provide a starting point to foster additional debates regarding the role of political capital, rural livelihoods, and natural resource usage.
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