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Science China(Technological Sciences) 2011年第12期54卷 3233-3242页

作者： ji li liU Kun XIANG JunHua Institute of Aerospace and Material Engineering National Universitry of Defense Technology Changsha 410073 China

The inner-formation gravity field measurement satellite （IFS） is a novel pure gravitational orbiter. It aims to measure the Earth＇s gravity field with unprecedented accuracy and spatial resolution by means of precise orbit determination （POD） and relative state measurement. One of the key factors determining the measurement level is the outer-satellite control used for keeping the inner-satellite flying in a pure gravitational orbit stably. In this paper the integrated orbit and attitude control of IFS during steady-state phase was investigated using only thrusters. A six degree-of-freedom translational and rotational dynamics model was constructed considering nonlinearity resulted from quaternion expression and coupling induced by community thrusters. A feasible quadratic optimization model was established for the integrated orbit and attitude control using con- strained nonlinear model predictive control （CNMPC） techniques. Simulation experiment demonstrated that the presented CNMPC aigorithm can achieve rapid calculation and overcome the non-convexity of partial constraints. The thruster layout is rational with low thrust consumption, and the mission requirements of IFS are fully satisfied.

关键词： gravity field measurement satellite inner-formation integrated orbit and attitude control model predictive techniques

Complete Study on a Bi-Center Problem for the Z2-Equivariant Cubic Vector Fields

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Acta Mathematica Sinica,English Series 2011年第7期27卷 1379-1394页

作者： Yi Rong liU ji Bin li Department ofMathematics Zhejiang Normal University Jinhua 321004 P. R. China Department of Mathematics Zhejiang Normal University Jinhua 321004 P. R. China School of Science Kunming University of Science and Technology Kunming 650093 P. R. China

For the planar Z2-equivariant cubic systems having twoelementary focuses, the characterization of a bi-center problem and shortened expressions of the first six liapunov constants are completely discussed. The necessary and sufficient conditions for the existence of the bi-center are obtained. All possible first integrals are given. Under small Z2-equivariant cubic perturbations, the conclusion that there exist at most 12 small-amplitude limit cycles with the scheme （6 II 6） is proved.

关键词： Center problem liapunov constant focal value integral factor invariant integral cubic polynomial system

Z_2-Equivariant Cubic System Which Yields 13 limit Cycles

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Acta Mathematicae Applicatae Sinica 2014年第3期30卷 781-800页

作者： Yi-rong liU ji-bin li School of Mathematics Central South University Department of Mathematics Zhejiang Normal University School of Science Kunming University of Science and Technology

For the planar Z2-equivariant cubic systems having two elementary focuses, the characterization of a bi-center problem and shortened expressions of the first six Lyapunov constants are completely solved. The necessary and sufficient conditions for the existence of the bi-center are obtained. On the basis of this work, in this paper, we show that under small Z2-equivariant cubic perturbations, this cubic system has at least 13 limit cycles with the scheme 1 6 ∪ 6.

关键词： planar dynamical system limit cycles bifurcations Lyapnov constant weak focus

Energy-efficient joint relay node selection and power allocation over multihop relaying cellular networks toward LTE-Advanced

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The Journal of China Universities of Posts and Telecommunications 2011年第3期18卷 1-7页

作者： CHEN Dan ji Hong li Xi College of Information and Communication Engineering Beijing University of Posts and Telecommunications Beijing 100876 China

Cooperative relaying is emerging as an effective technology to fulfill requirements on high data rate coverage in next-generation cellular networks, like long term evolution-advanced （LTE-Advanced）. In this paper, we propose a distributed joint relay node （RN） selection and power allocation scheme over multihop relaying cellular networks toward LTE-Advanced, taking both the wireless channel state and RNs＇ residual energy into consideration. We formulate the multihop relaying cellular network as a restless bandit system. The first-order finite-state Markov chain is used to characterize the time-varying channel and residual energy state transitions. With this stochastic optimization formulation, the optimal policy has indexability property that dramatically reduces the computational complexity. Simulation results demonstrate that the proposed scheme can efficiently enhance the expected system reward, compared with other existing algorithms.

关键词： cooperative relaying LTE-Advanced relay selection power allocation residual energy restless bandit

The relations between the metallicity and orbital parameters of Galactic disk stars

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Science China(Physics,Mechanics & Astronomy) 2010年第7期53卷 1348-1356页

作者： li ji SUN jianAn FU RuiJuan College of Physics Science&Information Engineering Hebei Normal UniversityShijiazhuang 050016China

The iron abundance gradient in the Galactic disk provides fundamental constraints on the chemical evolution of this important component of the ***,there are still some arguments about the shape of the iron abundance gradient across the Galactic stellar *** provide quantitative constraints on these trends,we constructed an unbiased stellar sample from the common objects of two large *** sample consists of 4004 disk stars in the solar neighborhood with the range of metallicity [Fe/H] from ^-1.0 to ~0.5,including 3855 thin disk stars and 146 thick disk *** range of their mean Galactocentric distances R m is from ~4 to ~11 kpc,and the range of their maximum vertical distance from the Galactic Plane Z max is from 0 to ~3.5 *** relations of the stellar metallicity [Fe/H] with the orbital eccentricity e,and [Fe/H] with R m,as well as [Fe/H] with Z max are investigated in *** results showed that:(1) The orbital eccentricity of disk stars decreases with increasing metallicity,while this trend becomes flat for stars with [Fe/H]>-0.2.(2) For thin disk,there is a clear radial iron gradient of-0.051±0.005 dex/***,this metallicity gradient is discontinuous once we split the sample into the inner(Rm<8kpc) and outer disk(Rm≥8 kpc):a slope of about 0 dex/kpc is present in the inner disk and a slope of-0.12 dex/kpc is in the outer *** the thick disk,there is no trend of [Fe/H] with R m.(3) The vertical gradient of iron abundance is-0.146 dex/kpc and-0.251 dex/kpc for the thick and thin disks,***,the vertical abundance gradient shows a steeper trend with the evolution of the *** results confirm the collapse mechanism associated with the formation and evolution of the Galactic disk.

关键词： Galaxy Galactic disk star orbital eccentricity abundance gradient

Cauchy Problems for KdV-type Equations and Higher-Order Conditional Symmetries

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Communications in Theoretical Physics 2008年第3期49卷 545-548页

作者： li ji-Na ZHANG Shun-li ZUO Su-li Center for Nonlinear Studies Department of Mathematics Northwest University Xi＇an 710069 China Center of Nonlinear Science Ningbo University Ningbo 315211 China

We develop the generalized conditional symmetry （GCS） approach to solve the problem of dimensional reduction of Cauchy problems for the KdV-type equations. We characterize these equations that admit certain higherorder GCSs and show the main reduction procedure by some examples. The obtained reductions cannot be derived within the framework of the standard lie approach.

关键词： KdV-type equations generalized conditional symmetry Cauchy problem

ROBUST INEXACT ALTERNATING OPTIMIZATION FOR MATRIX COMPLETION WITH OUTliERS

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Journal of Computational Mathematics 2020年第2期38卷 337-354页

作者： ji li jian-Feng Cai Hongkai Zhao Beijing Computational Science Research Center Beijing 100193China Department of Mathematics Hong Kong University of Science and TechnologyClear Water BayKowloonHong Kong Department of Mathematics University of CaliforniaIrvineCAUSA

We investigate the problem of robust matrix completion with a fraction of observation corrupted by sparsity outlier *** propose an algorithmic framework based on the ADMM algorithm for a non-convex optimization,whose objective function consists of an l1 norm data fidelity and a rank *** reduce the computational cost per iteration,two inexact schemes are developed to replace the most time-consuming step in the generic ADMM *** resulting algorithms remarkably outperform the existing solvers for robust matrix completion with outlier *** the noise is severe and the underlying matrix is ill-conditioned,the proposed algorithms are faster and give more accurate solutions than state-of-the-art robust matrix completion approaches.

关键词： Matrix completion ADMM Outlier noise Inexact projection

Rotational motion of polyanion versus volume effect associated with ionic conductivity of several solid electrolytes

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Rare Metals 2018年第6期37卷 497-503页

作者： Qian Zhao li Pan Yuan-ji li li-Quan Chen Si-Qi Shi Materials Genome Institute Shanghai University School of Materials Science and Engineering Shanghai University Qianweichang College Shanghai University Institute of Physics Chinese Academy of Sciences

Volume effect has been extensively investigated in several families of solid electrolytes, i.e., expanding the skeleton lattice by bigger-size substitution favors the ionic conduction. However, this effect is not applicable in α-li2SO4 and α-Na3PO4 based inorganic ionic plastic crystal electrolytes, a unique family of solid electrolytes. Here, it is proposed that the underlying rotational motion effect of polyanion, which is actually inhibited by the substitution of bigger-size polyanion in single-phase solid solution region and causes the unexpected lowering of the ionic conductivity instead, should need the more consideration. Furthermore, through utilizing the rotational motion effect of polyanion, it is given that a new explanation of the ionic conductivities of li10MP2S12 （M = Si, Ge, Se） electrolytes deviating from the volume effect. These results inspire new vision of rationalization of the high-performance solid electrolytes by tuning the rotational motion effect of polyanion.

关键词： Volume effect Rotational motion ofpolyanion Ionic conductivity Inorganic plastic crystalelectrolyte

A novel satellite-equipped receiver for autonomous monitoring of GNSS navigation signal quality

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Science China(Technological Sciences) 2016年第7期59卷 1137-1146页

作者： YANG jian YANG YiKang li ji Sheng li HengNian YANG TianShe School of Electronic and Information Engineering Xi'an Jiaotong University Xi'an 710049 China State Key Laboratory of Astronautic Dynamics (ADL) Xi'an Satellite Control Center Xi'an 710043 China

Global navigation satellite system(GNSS) comes with potential unavoidable application risks such as the sudden distortion or failure of navigation signals because its satellites are generally operated until failure. In order to solve the problems associated with these risks, receiver autonomous integrity monitoring(RAIM) and ground-based signal quality monitoring stations are widely used. Although these technologies can protect the user from the risks, they are expensive and have limited region coverage. Autonomous monitoring of satellite signal quality is an effective method to eliminate these shortcomings of the RAIM and ground-based signal quality monitoring stations; thus, a new navigation signal quality monitoring receiver which can be equipped on the satellite platform of GNSS is proposed in this paper. Because this satellite-equipped receiver is tightly coupled with navigation payload, the system architecture and its preliminary design procedure are first introduced. In theory, code-tracking loop is able to provide accurate time delay estimation of received signals. However, because of the nonlinear characteristics of the navigation payload, the traditional code-tracking loop introduces errors. To eliminate these errors, the dummy massive parallel correlators(DMPC) technique is proposed. This technique can reconstruct the cross correlation function of a navigation signal with a high code phase resolution. Combining the DMPC and direct radio frequency(RF) sampling technology, the satellite-equipped receiver can calibrate the differential code bias(DCB) accurately. In the meantime, the abnormities and failures of navigation signal can also be monitored. Finally, the accuracy of DCB calibration and the performance of fault monitoring have been verified by practical test data and numerical simulation data, respectively. The results show that the accuracy of DCB calibration is less than 0.1 ns and the novel satellite-equipped receiver can monitor the signal qualit

关键词： satellite-equipped receiver dummy massive parallel correlators(DMPC) differential code bias(DCB) signal quality monitoring

Thermal Modeling and Cooling Analysis of High-power lithium Ion Cells

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Journal of Thermal Science 2011年第6期20卷 570-575页

作者： Zhuqian Zhang li ji a Nan Zhao lixin Yang School of Mechanical Electronic and Control Engineering Beijing Jiaotong UniversityNo.3 Shangyuancun Beijing 100044 China

The heat generation model and three-dimensional computational fluid dynamics model for lithium ion cells were established with boundary conditions *** order to provide a better insight about the behaviors of high-power lithium ion cells under realistic discharge conditions,the temperature difference of the cells and an active thermal management system with a pure air-cooling mode were analyzed and predicted with the factors affecting the unevenness of temperature field *** results show a significant effect of the cooling flow rate on the temperature rise of the cells for all discharge *** surface temperatures are relatively uniform at lower discharge rate that makes it easier to control the temperature of the *** temperatures are expected to rise significantly toward the end of discharge and they show non-uniformity at higher discharge *** air flow rate of active cooling is required at high discharge rate and high ambient temperature for practical pack thermal management system.

关键词： lithium ion battery thermal management system air-cooling temperature rise