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An efficient algorithm for finding the largest chain graph according to a given chain graph

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Science china Mathematics 2005年第11期48卷 1517-1530页

作者： LIU Baijun,ZHENG Zhongguo & ZHAO Hui School of Mathematical Sciences, peking university, Beijing 100871,{2. department of Statistics, Central{2. Normal university, Wuhan 4.0079,{2. School of Mathematical Sciences Peking University Beijing China department of Statistics Central China Normal University Wuhan China

Chain graph (CG) is a general model of graphical Markov models. Some different chain graphs may describe the same conditional independence structure, then we say that these CGs are Markov equivalent. In 1990 Frydenberg showed that every class of Markov equivalent CGs has a CG which is called the largest chain graph with the greatest number of lines. This paper presents an efficient algorithm for finding the largest chain graph of the corresponding Markov equivalent class of a given CG. The computational complexity of the algorithm is O(n3). It is more efficient than the complexity O(n!) of the present algorithms. Also a more intuitive graphical characterization of the largest chain graph is provided based on the algorithm in this paper.

关键词： graphical Markov model,chain graph,largest chain graph,protected arrows,efficient algorithm

Interdecadal variations in global climate and earth rotation rate

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Chinese Science Bulletin 1997年第18期42卷 1557-1560页

作者： QIAN Weihongdepartment of Geophysics, peking university, Beijing {2., china department of Geophysics Peking University Beijing China

A science plan for future 15 a, 'A Study of Climate Variability and Predictability'(CLIVAR), was published by WMO in 1996. As the plan treated interdecadal climatic variability as a sub-plan, it showed that this problem is very important. By the implementation of 'Tropical Ocean and Global Atmosphere' (TOGA) 10-a plan during 1985—1994. the interdecadal variability that occurred in ENSO (El Nino/Southern Oscillation) ocean-atmosphere interaction has been found. This variability made the traditional ENSO prediction pattern useless

关键词： interdecadal variation climate prediction sea surface temperature earth rotation rate.

Empirical rheological law of multiphase rocks:Energy minimizing approach independent of bound theory

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Chinese Science Bulletin 2003年第22期48卷 2496-2500页

作者： ZANG Shaoxian, JIANG Yan & WEI Rongqiang department of Geophysics, peking university, Beijing {2., china department of Geophysics Peking University Beijing China

Based on energy minimizing approach of bound theory, the influence of the distribution of constituent minerals on rheological property of rocks is discussed. Energy minimizing approach independent of the bound theory is advanced after the constraint condition is improved. The strength of four multiphase rocks is calculated with the new empirical rheological law. Results indicate that the new law has a reasonable physical explanation and fits the experimental data very well.

关键词：流变学能量最小化法多相岩石地质学

Morita contexts on the Hopf algebroid

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Science china Mathematics 2005年第7期48卷 958-971页

作者： YIN Yanmin School of Mathematical Sciences, peking university, Beijing 100871,{2. department of Mathematics, Shandong Institute of Architecture and Engineering, Jinan 2.0101,{2. School of Mathematical Sciences Peking University Beijing 100871 China department of Mathematics Shandong Institute of Architecture and Engineering Jinan 250101 China

We generalize the Morita theory to the Hopf algebroid and give the characterization of the surjectivity of one of the Morita context maps.

关键词： comodule algebra, generalized smash product, Morita context.

Integrative inversion of land surface component temperature

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Science china Earth Sciences 2005年第11期48卷 2011-2019页

作者： FAN Wenjie1 & XU Xiru1,2.1. Institute of Remote Sensing and Geographical Information System, peking university, Beijing 100871,{2. 2. Center of Remote Sensing and GIS of Beijing Normal university, Beijing 100875,{2. Institute of Remote Sensing and Geographical Information System Peking University Beijing China Center of Remote Sensing and GIS of Beijing Normal university Beijing China

In this paper, the row winter wheat was selected as the example to study the com-ponent temperature inversion method of land surface target in detail. The result showed that the structural pattern of row crop can affect the inversion precision of component temperature evi-dently. Choosing appropriate structural pattern of row crop can improve the inversion precision significantly. The iterative method combining inverse matrix was a stable method that was fit for inversing component temperature of land surface target. The result of simulation and field ex-periment showed that the integrative method could remarkably improve the inversion accuracy of the lighted soil surface temperature and the top layer canopy temperature, and enhance inver-sion stability of components temperature. Just two parameters were sufficient for accurate at-mospheric correction of multi-angle and multi-spectral thermal infrared data: atmospheric trans-mittance and the atmospheric upwelling radiance. If the atmospheric parameters and component temperature can be inversed synchronously, the really and truly accurate atmospheric correction can be achieved. The validation using ATSRII data showed that the method was useful.

关键词： components temperature, inverse pattern, atmospheric correction

New direction of computational fluid dynamics and its applications in industry

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Science china(Technological Sciences) 2007年第5期50卷 521-533页

作者： CHEN YaoSong1, SHAN XiaoWen2.& CHEN HuDong2.1 department of Mechanics, peking university, Beijing {2., china 2.Exa Corporation, Burlington, MA 01803 USA department of Mechanics Peking University Beijing China Exa Corporation Burlington USA

For the past ten years there has been much progress in computational fluid dy- namics (CFD), among which the formation and development of the lattice Boltz- mann method (LBM) are an important new direction. We give a review on the main aspect and the latest development of this method in this article, and at the same time we also discuss the related development of scientific software and its impact on the real-world applications in industry.

关键词： lattice method, Boltzmann equation, CFD

Random Weighting T-Statistics in Linear Regression Models

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Acta Mathematica Sinica,English Series 1995年第2期11卷 188-199页

作者： Shi Jian Zheng Zhongguo department of Probability and Statistics peking university Beijing, {2. china department of Probability and Statistics Peking University Beijing People's Republic of China

In this paper, we have constructed a random weighting statistic to approximate the distribution of studentized least square estimator in a linear regression model with ideal accuracy o(n-1/2.. Thus, we have provided a... 详细信息

关键词： Random Weighting T-Statistics in Linear Regression Models

Utilization of a spiropyran derivative in a polymeric film optode for selective fluorescent sensing of zinc ion

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Science china Chemistry 2006年第3期49卷 246-255页

作者： ZHANG Ying1, SHAO Na1, YANG Ronghua1, LI Ke’an1, LIU Feng1, CHAN Winghong2.& MO Tian2.1. College of Chemistry and Molecular Engineering, peking university, Beijing 100871,{2. 2. department of Chemistry, Hong Kong Baptist {4., Hong Kong,{2. College of Chemistry and Molecular Engineering Peking University Beijing China department of Chemistry Hong Kong Baptist University Hong Kong China

A new spiropyran derivative was synthesized and first utilized in a polymericfilm-based optical sensor for zinc ion. Spiropyrans, combining the characteristics of metal bindingand signal transduction, show potential function in the design of optical chemical sensors(optodes) toward metal ions. When embedded in a plasticized poly (vinyl chloride) (PVC) membrane,the newly synthesized spiropyran derivative 1 exhibits obvious fluorescence enhancement at 630 nm inthe presence of zinc ion in aqueous solution. With the optimum condition described, the optodemembrane responds to zinc ion over a dynamic range of 4.94.10^(-7) to 4.15x10^(-4.mol·L^(-1), witha detection limit of 1.51x10^(-7) mol·L^(-1). The membrane not only displays excellentphotostability, reproducibility and reversibility, but also exhibits high selectivity toward zincion over transition metal ions including Hg^(2.), Cd^(2.), Pb^(2.), Cu^(2.), Fe^(3+) and commoncationic ions presented in the physiological fluids.

关键词： spiropyran, sensor, PVC membrane, zinc ion, fluorescent spectroscopy.

On the Markov equivalence of maximal ancestral graphs

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Science china Mathematics 2005年第4期48卷 548-562页

作者： ZHAO Hui, ZHENG Zhongguo & LIU Baijun School of Mathematical Sciences, peking university, Beijing 100871,{2. department of Statistics, Central{2. Normal university, Wuhan 4.0079,{2. School of Mathematical Sciences Peking University Beijing China

Necessary and sufficient conditions for a maximal ancestral graph (MAnG)to be Markov equivalent to another MAnG and to a DAG are provided respectively. Also a polynomial-time algorithm for converting a MAnG into its e... 详细信息

关键词： maximal ancestral graph, Markov equivalence, minimal collider path, m-separation.