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A new algorithm for pole assignment of single-input linear systems using state feedback

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Science China Mathematics 2005年第3期48卷 307-321页

作者： QIAN Jiang CHENG Mingsong xu Shufang LMAM School of Mathematical Sciences Peking University Beijing 100871 China LMAM School of Mathematical Sciences Peking University Beijing 100871 China LMAM School of Mathematical Sciences Peking University Beijing 100871 China

In this paper we present a new algorithm for the single-input pole assignment problem using state feedback. This algorithm is based on the Schur decomposition of the closed-loop system matrix, and the numerically stable unitary transformations are used whenever possible, and hence it is numerically *** good numerical behavior of this algorithm is also illustrated by numerical examples.

关键词： pole assignment problem, numerical method, Schur decomposition.

FEM ANALYSIS FOR INFLUENCES OF A FAULT ON COUPLED T-H-M-M PROCESS IN DUAL-POROSITY ROCK MASS

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Acta Mechanica Solida Sinica 2012年第6期25卷 651-662页

作者： Yujun Zhang Chaoshuai Yang Gang xu State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil Mechanics The Chinese Academy of Sciences Technology Centre China Railway Tunnel Group Co. Ltd

For the case in which a large geological structure like fault existing within the surrounding rock mass in the near field of a repository for high-level radioactive nuclear waste, one kind of coupled thermo-hydro-mechanical-migratory model of dual-porosity medium for saturated- unsaturated ubiquitous-joint rock mass was established. In the present model, the seepage field and the concentration field are double, but the stress field and the temperature field are single, and the influences of sets, spaces, angles, continuity ratios, stiffness of fractures on the constitutive relationship of the medium can be considered. At the same time, a two-dimensional program of finite element method was developed. Taking a hypothetical nuclear waste repository located at a rock mass being unsaturated dual-porosity medium as a calculation example, the FEM analysis for thermo-hydro-mechanical-migratory coupling were carried out under the condition of radioac- tive nuclide leaking for the cases with and without a fault, and the temperatures, pore pressures, flow velocities, nuclide concentrations and principal stresses in the rock mass were investigated. The results show that the fracture water in the fault flows is basically along the fault direction, and its flow velocity is almost three orders of magnitude higher than that of fracture water in rock mass; the nuclide concentration in the fault is also much higher than that without fault, and the nuclides move along the fault faster; moreover, the fault has obvious influences on the pore pressures and the principal stresses in the rock mass.

关键词： fault dual-porosity medium thermo-hydro-mechanical-migratory coupling FEManalysis

A fuzzy extension for SHOIQ based on comparisons between degrees of membership

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Science China(Information Sciences) 2013年第8期56卷 166-176页

作者： KANG DaZhou xu BaoWen LI YanHui Department of Computing Science and Technology Nanjing University Jiangsu Institute of Software Quality

The current fuzzy extensions for description logics do not support representing and reasoning with complex fuzzy knowledge about comparisons between degrees of membership,which is very useful in practical *** investigate a novel approach of extending the description logic SHOIQ to SHOIQ FC by annotating concepts and roles based on comparison *** FC provides the ability to represent complex fuzzy knowledge,in addition to the expressive power of the fuzzy description logic *** main contributions are a decidability proof for the consistency problem of SHOIQ FC knowledge bases,as well as its tableau-based reasoning algorithm.

关键词： fuzzy description logic knowledge representation reasoning algorithm

On the Rigidity Theorems for Lagrangian Translating Solitons in Pseudo-Euclidean Space Ⅰ

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Acta Mathematica Sinica,English Series 2013年第7期29卷 1369-1380页

作者： Rui Wei xu Rong Li HUANG Department of Mathematics He'nan Normal University Department of Mathematics Guangxi Normal University

Let f be a smooth strictly convex solution ofdefined on a domain Ω C R^n, where ai, bi and c are constants. Then the graph Mvf of △f is a spacelike translating soliton for mean curvature flow in pseudo-Euclidean space with the translating vector（al, a2, . ., an; bz, b2, , bn）. In this paper, we will use alCfine technique to show a Berustein Theorem： if the graph Mvf is complete, then f（x） must be a quadratic polynomial and Mvf is an ailine n-plane.

关键词： Mean curvature flow translating solitons Monge-Amp^re equation Bernstein Theorem

Special issue on “Membranes and Water Treatment”

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Frontiers of Chemical Science and Engineering 2022年第5期16卷 561-563页

作者： Congjie Gao Nanping xu Weihong Xing Center for Membrane and Water Science&Technology Zhejiang University of TechnologyHangzhou 310014China State Key Laboratory of Materials-Oriented Chemical Engineering Nanjing Tech UniversityNanjing 211816China National Engineering Research Center for Special Separation Membranes Nanjing Tech UniversityNanjing 211816China

Water scarcity is becoming the greatest global crisis of our *** increasing demand for clean and safe water calls for intensive research on advanced water treatment *** decades have witnessed the rapid development of membrane technology,which are competitive for water and wastewater treatment,and encouragingly,some of them have been commercialized *** advances in material science have substantially promoted the further development of membranes technology in the aspects of membrane materials,membrane microstructure and fabrication process.

关键词： wastewater treatment becoming

CSMA/CN+: Improving the Performance of Collision Notification for Wireless LANs

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China Communications 2017年第7期14卷 34-43页

作者： Qinglin Zhao Fangxin xu Shangguang Wang The Faculty of Information Technology Macao University of Science and Technology State Key Laboratory of Networking and Switching Technology Beijing University of Posts and Telecommunications

In CSMA/CN, whenever inferring that a receiving frame gets corrupted, the receiver sends back its signature as a collision notification(CN) to the sender. Upon detecting an arrival of the CN, the sender will abort the ongoing transmission immediately. However, in low signal-to-interference-plus-noise ratio(SINR), the false alarm of the CN occurs frequently, which might force a sender not to transmit any frame at all. To overcome this drawback, this paper proposes CSMA/CN+ to enhance the performance of CSMA/CN. In CSMA/CN+, we introduce an additional signature. The receiver, adapting to channel conditions and self-signal suppression capability, prudently determines whether to send back zero, one, or two signatures to the sender. In this way, we can reduce or exclude false alarms and therefore improve the system performance. In this paper, we first present the design of CSMA/CN+. We then apply the design in a wireless LAN, and theoretically analyze the detection performance of the notification and the system throughput. Extensive simulations verify that CSMA/CN+ can remarkably improve the system throughput of CSMA/CN and our analysis is very accurate.

关键词： PHY/MAC CSMA/CN collision detection correlation

Effective Maxwell Equations from Time-dependent Density Functional Theory

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Acta Mathematica Sinica,English Series 2011年第2期27卷 339-368页

作者： Weinan E Jianfeng LU xu YANG Department of Mathematics and Program in Applied and Computational Mathematics Princeton University Princeton NJ 08544 USA Beijing International Center for Mathematical Research and School of Mathematical Sciences Peking University Beijing 100871 P. R. China Department of Mathematics Courant Institute of Mathematical Sciences New York University New York NY 10012 USA

The behavior of interacting electrons in a perfect crystal under macroscopic external electric and magnetic fields is studied. Effective Maxwell equations for the macroscopic electric and magnetic fields are derived starting from time-dependent density functional theory. Effective permittivity and permeability coefficients are obtained.

关键词： Time-dependent density functional theory Maxwell equations effective permittivity electromagnetic fields

Three Solutions of p-Laplacian Equations Via a Critical Point Theorem of Ricceri

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Acta Mathematicae Applicatae Sinica 2014年第1期30卷 171-178页

作者： Chun-yan xuE He-yu xu School of Science Beijing Information Science and Technology University School of Mathematics Beijing Institute of Technology

In this paper,we consider the following quasilinear diferential equation（p（u′））′＋λf（t,u）=0subject to one of the two boundary conditions：u（0）=u′（1）=0,u′（0）=u（1）=*** transforming them into a problem of symmetrical solutions,the existence of three solutions of the problem is obtained by using a recent critical point theorem of *** example is given to demonstrate our main result.

关键词： boundary value problem critical point theorem three solutions symmetrical solution

Crop area and leaf area index simultaneous retrieval based on spatial scaling transformation

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Science China Earth Sciences 2010年第11期53卷 1709-1716页

作者： Fan WenJie Yan BinYan xu XiRu Peking Univ Inst RS & GIS Beijing 100871 Peoples R China

Accurate estimation of crop yields is crucial for ensuring food security. However, crops are distributed so fragmentally in China that mixed pixels account for a large proportion in moderate and coarse resolution remote sensing images. As a result, unmixing of mixed pixel becomes a major problem to estimate crop yield by means of remote sensing method. Aimed at mixed pixels, we developed a new method to introduce additional information contained in the spatial scaling transformation equation to the canopy reflectance model. The crop area and LAI can be retrieved simultaneously. On the basis of a precise and simple canopy reflectance model, directional second derivative method was chosen to retrieve LAI from optimal bands of hyper-spectral data; this method can reduce the impact of the canopy non-isotropic features and soil background. To evaluate the performance of the method, Yingke Oasis, Zhangye City, Gansu Province, was chosen as the validation area. This area was covered mainly by maize and wheat. A Hyperion/EO-1 image with the 30 m spatial resolution was acquired on July 15, 2008. Images of 180 m and 1080 m resolutions were generated by linearly interpolating the original Hyperion image to coarser resolutions. Then a multi-scale image serial was obtained. Using the proposed method, we calculated crop area and the average LAI of every 1080 m pixel. A SPOT-5 classification figure serves as the validation data of crop area proportion. Results show that the pattern of crop distribution accords with the classification figure. The errors are restrained mainly to -0.1-0.1, and approximate a Normal Distribution. Meanwhile, 85 LAI values obtained using LAI-2000 Plant Canopy Analyzer, equipped with GPS, were taken as the ground reference. Results show that the standard deviation of the errors is 0.340. The method proposed in the paper is reliable.

关键词： scale transformation remote sensing crop yield estimation simultaneous retrieval crop area leaf area index