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Structural properties and generative model of non-giant connected components in social networks

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Science China Earth Sciences 2016年第12期59卷 229-234页

作者： Jianwei niu Lei WANG State Key Laboratory of Virtual Reality Technology and Systems School of Computer Science and EngineeringBeihang University

Most previous studies have mainly focused on the analyses of one entire network(graph) or the giant connected components of networks. In this paper, we investigate the disconnected components(non-giant connected component) of some real social networks, and report some interesting discoveries about structural properties of disconnected components. We study three diverse, real networks and compute the significance profile of each component. We discover some similarities in the local structure between the giant connected component and disconnected components in diverse social networks. Then we discuss how to detect network attacks based on the local structure properties of networks. Furthermore, we propose an empirical generative model called i Friends to generate networks that follow our observed patterns.

关键词： disconnected components giant connected component structural properties significance profile generative model

ALMOST SURE AND MOMENT EXPONENTIAL STABILITY OF PREDICTOR-CORRECTOR METHODS FOR STOCHASTIC DIFFERENTIAL EQUATIONS

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Journal of Systems Science & Complexity 2012年第4期25卷 736-743页

作者： Yuanling niu Chengjian ZHANG School of Mathematics and Statistics Central South University School of Mathematics and Statistics Huazhong University of Science and Technology

This paper deals with almost sure and moment exponential stability of a class of predictor- corrector methods applied to the stochastic differential equations of Ito-type. Stability criteria for this type of methods are derived. The methods are shown to maintain almost sure and moment exponential stability for all sufficiently small timesteps under appropriate conditions. A numerical experiment further testifies these theoretical results.

关键词： Almost sure stability moment exponential stability numerical experiment stochastic differential equations.

A new micromechanical approach of micropolar continuum modeling for 2-D periodic cellular material

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Acta Mechanica Sinica 2016年第3期32卷 456-468页

作者： Bin niu Jun Yan School of Mechanical Engineering Dalian University of Technology State Key Laboratory of Structural Analysis for Industrial Equipment Department of Engineering Mechanics Dalian University of Technology

In this paper, we present a new united approach to formulate the equivalent micropolar constitutive relation of two-dimensional（2-D） periodic cellular material to capture its non-local properties and to explain the size effects in its structural analysis. The new united approach takes both the displacement compatibility and the equilibrium of forces and moments into consideration, where Taylor series expansion of the displacement and rotation fields and the extended averaging procedure with an explicit enforcement of equilibrium are adopted in the micromechanical analysis of a unit *** numerical examples, the effective micropolar constants obtained in this paper and others derived in the literature are used for the equivalent micropolar continuum simulation of cellular solids. The solutions from the equivalent analysis are compared with the discrete simulation solutions of the cellular solids. It is found that the micropolar constants developed in this paper give satisfying results of equivalent analysis for the periodic cellular material.

关键词： Cellular material Micropolar continuum Size effect Equivalent property

Generation method of GPS L1C codes based on quadratic reciprocity law

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Journal of Systems Engineering and Electronics 2013年第2期24卷 189-195页

作者： Hui Lu Ruiyao niu School of Electronic and Information Engineering Beihang University

A new code concept is used for the L1 civil（L1C） signal of the global positioning system（GPS）.The generation of L1C codes is quite different from the generation of traditional ranging ***,it is necessary to find a method for the correct generation to pave the way for future research.L1C codes are based on only one Legendre sequence which consists of Legendre *** calculate these Legendre symbols,the Euler criterion is always used to evaluate quadratic ***,due to the great length of L1C codes,this procedure causes overflow ***,the quadratic reciprocity law,some related theorems and properties are introduced to solve the ***,if the quadratic reciprocity law,some related theorems and properties are used to calculate different Legendre symbols,the combination modes may vary,which causes a complex generation *** proposed generation method deals with this complex generation process *** addition,through simulations,it is found that the autocorrelation features of obtained Legendre sequences and L1C codes are in accordance with theoretical results,which proves the correctness of the proposed method.

关键词： L1 civil (L1C) signal Legendre sequence Weil code quadratic reciprocity law.

Anomalous SmKS induced by postcritical reflection and refraction at the core-mantle boundary

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Science Bulletin 2019年第21期64卷 1601-1607页

作者： Liwei Wang Fenglin niu State Key Laboratory of Petroleum Resources and Prospecting and Unconventional Petroleum Research InstituteChina University of Petroleum BeijingBeijing 102249China Department of Earth Environmental and Planetary SciencesRice UniversityHoustonTX 77005USA

Earth’s outer core is generally thought to be a well-mixed liquid consisting mostly of iron and a small amount of lighter *** seismic studies using Sm KS waves show that the top a few hundred kilometers of the outer core possess a P-wave velocity slightly lower than the PREM model,which cannot be explained by self-compression of a chemically homogeneous outer *** investigated the Sm KS waveforms of a deep earthquake occurring beneath South America recorded by a large and dense seismic array in China,and measured the differential arrival times of the Sm KS *** found significant waveform distortion of the Sm KS caused by postcritical refraction and reflection at the core-mantle *** waveform distortion can introduce significant bias to the measured differential times,leading to incorrect estimate of P-wave velocity of the outer *** stable stratification is occurring in outer core or not requires further seismic investigations.

关键词： SmKS Hilbert transform Postcritical phase shift Outer-core P-wave velocity Outer core stratification Ultra-low-velocity-zone

Fractional-order generalized thermoelastic diffusion theory

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Applied Mathematics and Mechanics(English Edition) 2017年第8期38卷 1091-1108页

作者： Chunbao XIONG Yanbo niu School of Civil Engineering Tianjin UniversityTianjin 300072China

The present work aims to establish a fractional-order generalized themoelastic diffusion theory for anisotropic and linearly thermoelastic diffusive media. To numerically handle the multi-physics problems expressed by a sequence of incomplete differential equations, particularly by a fractional equation, a generalized variational principle is obtained for the unified theory using a semi-inverse method. In numerical implementation, the dynamic response of a semi-infinite medium with one end subjected to a thermal shock and a chemical potential shock is investigated using the Laplace transform. Numerical results, i.e., non-dimensional temperature, chemical potential, and displacement, are presented graphically. The influence of the fractional order parameter on them is evaluated and discussed.

关键词： fractional Laplace anisotropic infinite variational handle unified inverse Liouville calculus

Constraining the non-Einsteinian polarizations of gravitational waves by pulsar timing array

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Science China(Physics,Mechanics & Astronomy) 2019年第7期62卷 63-75页

作者： Rui niu Wen Zhao CAS Key Laboratory for Researches in Galaxies and Cosmology Department of Astronomy University of Science and Technology of China School of Astronomy and Space Science University of Science and Technology of China

Pulsar timing array(PTA) provides an excellent opportunity to detect the gravitational waves(GWs) in nanoHertz frequency *** particular, due to the larger number of "arms" in PTA, it can be used to test gravity by probing the non-Einsteinian polarization modes of GWs, including two spin-1 shear modes labeled by "sn" and "se", the spin-0 transverse mode labeled by "b" and the longitudinal mode labeled by "l". In this paper, we investigate the capabilities of the current and potential future PTAs, which are quantified by the constraints on the amplitudes parameters(c_b, c_(sn), c_(se), c_l), by observing an individual supermassive black hole binary in Virgo cluster. We find that for binary with total mass M_c= 8.77 × 10~8 M_⊙ and GW frequency f = 10^(-9) Hz, the PTA at current level can detect these GW modes if c_b> 0.00106, c_l> 0.00217, c_(se)> 0.00271, c_(sn)> 0.00141, which will be improved by about two orders if considering the potential PTA in SKA era. Interesting enough, due to effects of the geometrical factors, we find that in SKA era, the constraints on the l, sn, se modes of GWs are purely dominated by several pulsars, instead of the full pulsars in PTA.

关键词： gravitational waves pulsar timing array

Iterative Learning Control Algorithm with a Fixed Step

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Chinese Journal of Mechanical Engineering 2011年第4期24卷 669-675页

作者： WANG Yan niu Jianjun School of Transportation Science and Engineering Beihang University Beijing 100191 China International Petroleum Exploration and Production Corporation China Petroleum ＆ Chemical Corporation Beijing 100083 China

Iterative Learning Control （ILC） captures interests of many scholars because of its capability of high precision control implement without identifying plant mathematical models, and it is widely applied in control engineering. Presently, most ILC algorithms still follow the original ideas of ARIMOTO, in which the iterative-learning-rate is composed by the control error with its derivative and integral values. This kind of algorithms will result in inevitable problems such as huge computation, big storage capacity for algorithm data, and also weak robust. In order to resolve these problems, an improved iterative learning control algorithm with fixed step is proposed here which breaks the primary thought of ARIMOTO. In this algorithm, the control step is set only according to the value of the control error, which could enormously reduce the computation and storage size demanded, also improve the robust of the algorithm by not using the differential coefficient of the iterative learning error. In this paper, the convergence conditions of this proposed fixed step iterative learning algorithm is theoretically analyzed and testified. Then the algorithm is tested through simulation researches on a time-variant object with randomly set disturbance through calculation of step threshold value, algorithm robustness testing,and evaluation of the relation between convergence speed and step size. Finally the algorithm is validated on a valve-serving-cylinder system of a joint robot with time-variant parameters. Experiment results demonstrate the stability of the algorithm and also the relationship between step value and convergence rate. Both simulation and experiment testify the feasibility and validity of the new algorithm proposed here. And it is worth to noticing that this algorithm is simple but with strong robust after improvements, which provides new ideas to the research of iterative learning control algorithms.

关键词： iterative learning control fixed step time variant system simulating study robot control

CLT OF WAVELET ESTIMATOR IN SEMIPARAMETRIC MODEL WITH CORRELATED ERRORS

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Journal of Systems Science & Complexity 2012年第3期25卷 567-581页

作者： Sili niu Yamei LIU Department of Mathematics Tongji University Department of Mathematics and Physics Henan University of Urban Construction

This paper considers the semiparametric regression model Yi = xiβ＋g（ti）＋ Vi （1 ≤ i≤ n）, where （xi, ti） are known design points, fl is an unknown slope parameter, g（.） is an unknown function, the correlated errors Vi = ∑^∞j=-∞cjei-j with ∑^∞j=-∞｜cj｜〈 ∞, and ei are negatively associated random variables. Under appropriate conditions, the authors study the asymptotic normality for wavelet estimators ofβ and g（·）. A simulation study is undertaken to investigate finite sample behavior of the estimators.

关键词： Asymptotic normality correlated error negatively associated semiparametric model wavelet estimator.