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Unsteady simulation for a high-speed train entering a tunnel

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2011年第12期12卷 957-963页

作者： Xin-hua LI Jian DENG Da-wei CHEN fang-fang XIE Yao ZHENG School of Aeronautics and Astronautics Zhejiang University Hangzhou 310027 China National Engineering Laboratory for System Integration of High-Speed Train （South） CSR Qingdao Sifang Co. Ltd Qingdao 266111 China

In order to study the unsteady aerodynamics effects in railway tunnels,the 3D Reynolds average Navier-Stokes equations of a viscous compressible fluid are solved,and the two-equation k-ε model is used in the simulation of turbulence,while the dynamic grid technique is employed for moving *** focus on obtaining the changing tendencies of the aerodynamic force of the train and the aerodynamic pressures on the tunnel wall and train surface,and discovering the relationship between the velocity of the train and the intensity of the micro pressure wave at the tunnel *** is shown that the amplitudes of the pressure changes in the tunnel and on the train surface are both approximately proportional to the square of the train speed,so are the microwave and the drag of the train.

关键词： High-speed train Aerodynamics Railway tunnel Numerical analysis

Global Solutions of the Evolutionary Faddeev Model with Small Initial Data

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Acta Mathematica Sinica,English Series 2011年第2期27卷 309-328页

作者： Zhen LEI fang hua LIN Yi ZHOU School of Mathematical Sciences LMNS and Shanghai Key Laboratory for Contemporary Applied Mathematics Fudan University Shanghai 200433 P. R. China Courant Institute of Mathematics New York University NY 10012 USA

We consider the Cauchy problem for evolutionary Faddeev model corresponding to maps from the Minkowski space R^1＋n to the unit sphere S2, which obey a system of non-linear wave equations. The nonlinearity enjoys the null structure and contains semi-linear terms, quasi-linear terms and unknowns themselves. We prove that the Cauchy problem is globally well-posed for sufficiently small initial data in Sobolev space.

关键词： Faddeev model global existence quasi-linear wave equations semi-linear wave equations

Grassmannian precoding MU-MIMO scheme

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The Journal of China Universities of Posts and Telecommunications 2008年第3期15卷 105-109,117页

作者： fang Shu LI Li-hua ZHANG ping Key Laboratory of Universal Wireless Communications Ministry of Education Beijing University of Posts and Telecommunications Beijing 100876 China

In this article, a Grassmannian precoding multiuser multiple-input multiple-output （MU-MIMO） scheme for downlink transmission is proposed. The proposed MU-MIMO scheme will perform scheduling and precoding simultaneously at the base station, to obtain both the multiuser diversity gain and the precoding gain, to maximize the system capacity. The precoding method is related to Grassmannian precoding, which extends the point-to-point single-user Grassmannian precoding to point-to-multipoint multiuser Grassmannian precoding. It provides further significant system capacity enhancement than the single user MIMO （SU-MIMO） system and also outperforms the block dia^onalization （BD） algorithm under the same simulation environment.

关键词： multiuser MIMO cochannel interference Grassmannian precoding

Simulation of critical transitions and vulnerability assessment of Tibetan Plateau key ecosystems

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Journal of Mountain Science 2022年第3期19卷 673-688页

作者： YANG Fei MA Chao fang hua-jun State Key Laboratory of Resources and Environmental Information System Institute of Geographic Sciences and Natural Resources Research of Chinese Academy of SciencesBeijing 100101China College of Resources and Environment University of Chinese Academy of SciencesBeijing 100049China Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application Nanjing 210023China

Critical transitions in ecosystems may imply risks of unexpected collapse under climate changes,especially vegetation often responds sensitively to climate *** type of vegetation ecosystem states could present alternative stable states,and its type could signal the critical transitions at tipping points because of changed climate or other *** study analyzed the distribution of four key vegetation ecosystem types:desert,grassland,forest-steppe ecotone and forest,in Tibetan Plateau in China,using the latent class analysis method based on remote sensing data and climate *** study analyzed the impacts of three key climate factors,precipitation,temperature,and sunshine duration,on the vegetation states,and calculated the critical transition tipping point of potential changes in vegetation type in Tibetan Plateau with the logistic regression *** studied results showed that climatic factors greatly affect the vegetation states and vulnerability of the Tibetan *** comparison with temperature and sunshine duration,precipitation shows more obvious impact on differentiations of the vegetations status *** precipitation tipping point for desert and grassland transition is averagely 48.0 mm/month,70.7 mm/month for grassland and forest-steppe ecotone,and 115.0 mm/month for forest-steppe ecotone and *** temperature and sunshine duration only show different probability change between vegetation and non-vegetation type,but produce opposite *** Tibetan Plateau,the transition tipping points of vegetation and nonvegetation are about 12.1°C/month and 173.6 h/month for the temperature and sunshine duration,***,vulnerability maps calculated with the logistic regression results presented the distribution of vulnerability of Tibetan Plateau key *** vulnerability of the typical ecosystems in the Tibetan Plateau is low in the southeast and is high in the *** meteorological factors affect tree co

关键词： Vulnerability Transition Tipping point Tibetan Plateau Latent class analysis

Spectral Analysis and Atmospheric Models of Microflares

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Chinese Journal of Astronomy and Astrophysics 2006年第5期6卷 597-607页

作者： Cheng fang Yu-hua Tang Zhi Xu Department of Astronomy Nanjing University Nanjing 210093 National Astronomical Observatories / Yunnan Observatory Chinese Academy of Sciences Kunming650011

By use of the high-resolution spectral data obtained with THEMIS on 2002 September 5, the spectra and characteristics of five well-observed microflares have been analyzed. Our results indicate that some of them are located near the longitudinal magnetic polarity inversion lines. All the microflares are accompanied by mass motions. The most obvious characteristic of the Hα microflare spectra is the emission at the center of both Hα and CaⅡ 8542A lines. For the first time both thermal and non-thermal semi-empirical atmospheric models for the conspicuous and faint microflares are computed. In computing the non-thermal models, we assume that the electron beam resulting from magnetic reconnection is produced in the chromosphere, because it requires lower energies for the injected particles. It is found there is obvious heating in the low chromosphere. The temperature enhancement is about 1000-2200 K in the thermal models. If the non-thermal effects are included, then the required temperature increase can be reduced by 100-150 K. These imply that the Hα microflares can probably be produced by magnetic reconnection in the solar lower atmosphere. The radiative and kinetic energies of the Hα microflares are estimated and the total energy is found to be 10^27 - 4× 10^28 erg.

关键词： Sun Microflares - Sun spectrum - Sun semi-empirical modelling

Effectiveness of Soil Conservation Methods in Preventing Red Soil Erosion in Southern China

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Journal of Mountain Science 2015年第5期12卷 1281-1291页

作者： ZHANG Guo-hua XIE Chong-Bao pi Xiao-Yu ZUO Chang-Qing China Irrigation and Drainage Development Center The Water Service Bureau of Chaoyang of Beijing City China Institute of Water Resources and Hydropower Research

Rainfall, runoff(surface runoff and interflow) and soil loss were recorded from 2002 to2005 in an experiment with four treatments on sloping red soil land in southern China. Treatments consisted of bare sloping ground(control check, CK),interplanting with soybean in spring or radish in autumn(I), level terrace(i.e., grass planted on the riser and bunds built at the edge of a bench terrace)(II), and level terraces of orchards with Bahia grass planted on the riser(III). The surface runoff and erosion in treatment II and III during the four years were low despite the occurrence of potentially erosive rains. By contrast, the CK plot had both the highest surface runoff coefficient and the highest sediment yield among all the plots. The surface runoff and soil erosion of the CK plot significantly differed from that of the treatment plots(p I > III > II, whereas their order in terms of interflow was II > III > I > CK. The effects of treatment II were excellent, indicating that level terrace(i.e., grass planted on the riser and bunds built at the edge of a bench terrace) can be an excellent practice for soil and water conservation on sloping red soil land. Soil loss in southern China can be reduced through the widespread use of this approach.

关键词： Red soil Runoff Soil erosion Interflow

Continuity of functors with respect to generalized inductive limits

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Frontiers of Mathematics in China 2019年第3期14卷 551-566页

作者： Jiajie hua Xiaochun fang Xiao-Ming XU School of Mathematics Physics and Information Engineering Jiaxing University Jiaxing 314001 China Department of Mathematics Tongji University Shanghai 200092 China School of Science Shanghai Institute of Technology Shanghai 201418 China

Let(Ai,φi,i+1) be a generalized indue Live system of a sequeiiee (Ai) of unital separable C^*-algebras,with A =limi→∞(Ai,φi,i+1). Set φj,i=φi-1,i^0…0φj+1,j+2^0 φj,j+1 for all i>j. We prove that if φj,i are order zero completely positive contractions for all j and i>j, And L:=inf{λ|λ∈σ(φj,i(1Aj)) for all j uud i>j}>0, where σ(φj,i(1Aj)) is the speetrum of φj,i(1Aj),than limi→∞(Cu(Ai),Cu((φi,i+1))=Cu(A), where Cu(A) is a stable version of the Cuntz semigroup of C^*-algebra A. Let (An,φm,n) be a generalized inductive syfitem of C^*-algahrafl, with the ipmkn order zero completely positive contractions. We also prove that if the decomposition rank (nuclear dimension) of ,4n is no more t han some integer k for each n, then the decompostition rank (nuclear dimension) of A is also no more than k.

关键词： Completely positive map order zero generalized inductive limits classification of C^*-algebra

Extension of Radiative Viscosity to Superfluid Matter

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Chinese Physics Letters 2011年第10期28卷 299-301页

作者： pi Chun-Mei YANG Shu-hua ZHENG Xiao-ping Department of Physics and Electronics Hubei University of EducationWuhan 430205 Institute of Astrophysics Huazhong Normal UniversityWuhan 430079

The radiative viscosity of superfluid npe matter is studied and it is found that to the lowest order ofδμ/T,the ratio of radiative viscosity to bulk viscosity is the same as that of its normal matter.

关键词： viscosity radiative lowest

Peakon and Foldon Excitations in a （2＋1）—Dimensional Breaking Soliton System

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Chinese Physics Letters 2003年第6期20卷 783-786页

作者： ZHENGChun-Long ZHANGJie-fang huaNGWen-hua CHENLi-Qun ShanghaiInstituteofMathematicsandMechanics ShanghaiUniversityShanghai200072 InstituteofNonlinearPhysics ZhejiangNormalUniversityJinhua321004

Starting from the standard truncated Painlevé expansion and a variable separation approach, a general variable separation solution of the breaking soliton system is derived. In addition to the usual localized coherent soliton excitations like dromions, lumps, rings, breathers, instantons, oscillating soliton excitations, and previously revealed chaotic and fractal localized solutions, some new types of excitations, peakons and foldons, are obtained by introducing appropriate lower-dimensional piecewise smooth functions and multiple valued functions.

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