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Anomalous magnetotransport in LaMn_(1-x)Te_xO_3

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Science china(Physics,Mechanics & Astronomy) 2009年第7期52卷 987-992页

作者： TAN GuoTai1,2, CHEN ZhengHao3.& ZHANG XiaoZhong4,5 1 key Laboratory of Beam Technology & Materials Modification of the Ministry of Education, Institute of Low Energy Nuclear Physics, beijing Normal university, beijing 100875, china 2 beijing Radiation Center, beijing 100875, china 3.Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, beijing 100080, china 4 key Laboratory of Advanced Materials of the Ministry of Education, Department of Materials Science and engineering, tsinghua university, {13., china 5 beijing National Center for Electron Microscopy, tsinghua university, {13., china 1. key Laboratory of Beam Technology & Materials Modification of the Ministry of Education Institute of Low Energy Nuclear Physics Beijing Normal University Beijing 100875 China 2. beijing Radiation Center Beijing 100875 China 3. Laboratory of Optical Physics Institute of Physics Chinese Academy of Sciences Beijing 100080 China 4. key Laboratory of Advanced Materials of the Ministry of Education Department of Materials Science and Engineering Tsinghua University Beijing 100084 China 5. beijing National Center for Electron Microscopy Tsinghua University Beijing 100084 China

The LaMn1-xTexO3.δ (x=0.1, 0.2, 0.3. were synthesized using solid-state reaction method for the first time. X-ray photoemission spectrum (XPS) shows that in the samples the Te ions have a valence of Te4+, and Mn3. ions are partly converted into Mn2+ and Mn4+ due to the excess oxygen and Te doping. The magnetotransport associated with Mn2+, Mn3. and Mn4+ was investigated. The experimental results show that the samples are insulator at 0 T when the amount of Mn3. is much larger or less than the sum of Mn2+ and Mn4+; by contrast, the samples display metal to insulator transition with increasing temperature when the amount of Mn3. is close to the sum of Mn2+ and Mn4+. These anomalous magnetotransport behaviors were analyzed in the frame of the double-exchange (DE) mechanism.

关键词： colossal magnetoresistance La-Te-Mn-O magnetotransport

Influence of magnetic current on the ground state entanglement in an isotropic transverse XY chain

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Progress in Natural Science:Materials International 2007年第10期17卷 1147-1151页

作者： Liu Dan1,2 , Zhang Yong3.and Long Guilu1,2(1. key Laboratory for Atomic and Molecular NanoSciences, and Department of Physics, tsinghua university, beijing 100084, {3. 2. Center of Quantum Information Science and Technology, tsinghua National Laboratory for information Science and Technology, beijing 100084, {3. 3. Institute of Physics, School of Sciences, beijing university of Posts and Telecommunications, beijing 100876, {3.) key Laboratory for Atomic and Molecular NanoSciences and Department of Physics Tsinghua University Beijing 100084 China Center of Quantum Information Science and Technology Tsinghua National Laboratory for information Science and Technology Beijing 100084 China Institute of Physics School of Sciences Beijing University of Posts and Telecommunications Beijing 100876 China

We study the ground state entanglement in a three-qubit XY chain under the influence of a magnetization current. It is found that the ground state changes from a W state to a disentangled state as the magnetic field varies. When the Lagrange multiplier λ>3. namely under a strong magnetic current, the ground state holds onto a W state for a large range of the magnetic field strength. A phase transition to the magnetization-current phase occurs under a certain condition.

关键词： Heisenberg-XY chain magnetic-current phase transition.

A STUDY OF DRAG COEFFICIENT RELATED WITH VEGETATION BASED ON THE FLUME EXPERIMENT

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Journal of Hydrodynamics 2010年第3期22卷 329-337页

作者： HUI Er-qing HU Xing-e JIANG Chun-bo MA Fang-kai ZHU Zhen-duo china Three Gorges Corporation Yichang 443002 China state key Laboratory of hydroscience and {3. Tsinghua University Beijing 100084 China state key Laboratory of hydroscience and {3. Tsinghua University Beijing 100084 China

This study is focused on the effects of ecological factors （diameter and flexibility） and vegetation community composition on the drag coefficient related with vegetation. The single leafy shrub and three mixed communities （including shrub-grass, shrub-reed and reed-grass community） were studied. The flow velocity and water level were measured and used to calculate the drag coefficient based on the Bernoulli＇s equation, Darcy drag formula and the expression for the drag coefficient related with Darcy drag factor. The trend of the drag coefficient in the vertical direction was analyzed against flow depth, diameter, diameter P（eynolds number, flow depth Reynolds number and relative roughness height in different discharges. The results show that beside the dense leafy shrubs community, the vertical trend of the drag coefficient among other cases against flow depth, diameter, diameter Reynolds number, flow depth Reynolds number and relative roughness height can be approximately expressed by power law functions under different flow discharges. Moreover, in a mixed community with two plants with distinctly different ecological factors, the one with the most distinct variations of ecological factors determines the vertical trend of the drag coefficient; the other one only affects the magnitude of the drag coefficient. Furthermore, if the ecological factors of the vegetation in the vertical direction are kept almost not changed, the drag coefficient can be approximately regarded as a constant.

关键词： vegetated channel drag coefficient flume experiment

Effect of Carbon on Dynamic Recrystallization Behavior of Vanadium Microalloy Steels

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Journal of Iron and Steel Research International 2011年第S1期18卷 129-134页

作者： LIU Guo-quan 1,2,ZHAO Hai-tao 1,WU Jin-bin 1,WANG Cheng-yang 1,XU Lei 1,3.(1.School of Materials Science and engineering,university of Science and Technology beijing,beijing 100083.china 2.state key Laboratory for Advanced Metals and Materials,university of Science and Technology beijing,beijing 100083.china 3.Department of Materials Science and engineering,tsinghua university,{13.,china) Univ Sci & Technol beijing Sch Mat Sci & Engn Beijing 100083 Peoples R China Univ Sci & Technol beijing State Key Lab Adv Met & Mat Beijing 100083 Peoples R China tsinghua Univ Dept Mat Sci & Engn Beijing 100084 Peoples R China

The hot working behavior especially dynamic recrystallization of low-carbon and medium-carbon vanadium microalloy steels has been studied by performing isothermally compression tests and Avrami *** Avrami plots of the two experiment steels have been constructed based on flow stress curves following a new approach (Jonas,et *** Mater.,2009,57(2):2748-2756;Wu et al,Acta ***.,2010,46(7):83.-843..It is experimentally found that the carbon effect on dynamic recrystallization is opposite to each other in lower and higher strain ranges:Carbon causes a softening effect at low strain rates (0.01,0.1,and 1.0 s-1),and a hardening effect at high strain rates (10.0 and 3..0 s-1).Correspondingly,carbon promotes the dynamic recrystallization at low strain rates and retards the dynamic recrystallization at high strain rates in the experimental *** phenomenon is then tentatively explained based on the possible mechanisms of dynamic process at different strain rates.

关键词： vanadium microalloy steels hot working dynamic recrystallization carbon strain rate Avrami modeling

Numerical simulation of air-water two-phase flow over stepped spillways

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Science china(Technological Sciences) 2006年第6期49卷 674-684页

作者： CHENG Xiangju1, CHEN Yongcan1 & LUO Lin2 1. Department of Hydraulic engineering, tsinghua university, beijing 100084, {3. 2. state key Laboratory of Hydraulics and Mountain River engineering, Sichuan university, Chengdu 610065, {3. Department of Hydraulic engineering Tsinghua University Beijing 100084 China state key Laboratory of Hydraulics Mountain River engineering Sichuan University Chengdu 610065 China

Stepped spillways for significant energy dissipation along the chute have gained interest; popularity among researchers; dam engineers. Due to the complexity of air-water two-phase flow over stepped spillways, the finite volume computational fluid dynamics module of the FLUENT software was used to simulate the main characteristics of the flow. Adopting the RNG k- turbulence model, the mixture flow model for air-water two-phase flow was used to simulate the flow field over stepped spillway with the PISO arithmetic technique. The numerical result successfully reproduced the complex flow over a stepped spillway of an experiment case, including the interaction between entrained air bubbles; cavity recirculation in the skimming flow regime, velocity distribution; the pressure profiles on the step surface as well. The result is helpful for understanding the detailed information about energy dissipation over stepped spillways.

关键词： stepped spillway, mixture model, RNG k-εmodel, air-water two-phase flow.

A SEMI-IMPLICIT 3.D NUMERICAL MODEL USING SIGAM-COORDINATE FOR NON-HYDROSTATIC PRESSURE FREE-SURFACE FLOWS

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Journal of Hydrodynamics 2011年第2期23卷 212-223页

作者： HU De-chao FAN Bei-lin WANG Guang-qian ZHANG Hong-wu state key Laboratory of hydroscience and {3. Tsinghua University Beijing 100084 China Yangtze River Scientific Research Institute Wuhan 430010 China

A 3.D numerical formulation is proposed on the horizontal Cartesian, vertical sigma-coordinate grid for modeling non-hydrostatic pressure flee-surface flows. The pressure decomposition technique and 0 semi-implicit method are used, with the solution procedure being split into two steps. First, with the implicit parts of non-hydrostatic pressures excluded, the provisional velocity field and free surface are obtained by solving a 2-D Poisson equation. Second, the theory of the differential operator is employed to derive the 3.D Poisson equation for non-hydrostatic pressures, which is solved to obtain the non-hydrostatic pressures and to update the provisional velocity field. When the non-orthogonal sigma-coordinate transformation is introduced, additional terms come into being, resulting in a 15-diagonal, diagonally dominant but unsymmetric linear system in the 3.D Poisson equation for non-hydrostatic pressures. The Biconjugate Gradient Stabilized （BiCGstab） method is used to solve the resulting 3.D unsymmetric linear system instead of the conjugate gradient method, which can only be used for symmetric, positive-definite linear systems. Three test cases are used for validations. The successful simulations of the small-amplitude wave, a supercritical flow over a ramp and a turbulent flow in the open channel indicate that the new model can simulate well non-hydrostatic flows, supercritical flows and turbulent flows.

关键词： 3.D numerical model non-hydrostatic sigma-coordinate semi-implicit pressure-splitting

Lightning electromagnetic field generated by grounding electrode considering soil ionization

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Progress in Natural Science:Materials International 2006年第9期16卷 1002-1006页

作者： ZENG Rong , HE Jinliang, ZHANG Bo and GAO Yanqing (state key Laboratory of Power Systems, Department of Electrical engineering, {3., beijing 100084, china) state key Laboratory of Power Systems Department of Electrical Engineering Tsinghua University Beijing 100084 China

A circuit model with lumped time-variable parameter is proposed to calculate the transient characteristic of grounding electrode under lightning current, which takes into consideration the dynamic and nonlinear effect of soil ionization around the grounding electrode. The ionization phenomena in the soil are simulated by means of time-variable parameters under appropriate conditions. The generated electromagnetic field in the air is analyzed by using electrical dipole theory and image theory when the lightning current flows into the grounding electrode. The influence of soil ionization on the electromagnetic field is investigated.

关键词： electromagnetic field grounding electrode soil ionization transient characteristic.

Preparation of MWNTs/Al_2O_3.composites and their mechanical and electrical properties

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Science china(Technological Sciences) 2005年第6期48卷 622-631页

作者： FAN Jinpeng1,2, ZHAO Daqing1,2, XU Zening1,2 & WU Minsheng1,2 1. Department of Mechanical engineering, tsinghua university, beijing 100084, {3. 2. key Laboratory for Advanced Manufacturing by Materials Processing Technology, tsinghua university, beijing 100084, {3. 1. Department of Mechanical engineering Tsinghua University 100084 Beijing China 2. key Laboratory for Advanced Manufacturing by Materials Processing Technology Tsinghua University 100084 Beijing China

The mechanical and electrical properties of MWNTs/Al2O3.composite prepared fabricated by hot pressing are investigated. The relation between properties and microstructure of composites is also discussed. With 4wt% MWNTs as reinforcement, the fracture toughness of composite obtained reaches 5.55 MPa·m1/2, which is 80% higher than that of pure Al2O3.obtained in the same conditions. The main toughening mechanism is CNTs’ pinning alumina grain boundaries, and the pullout of CNTs takes effect also. Through adding 2wt% MWNTs and altering the mix method, the fracture toughness of the composite obtained is 3.97 MPa·m1/2. Furthermore, the electrical resistivity is as low as 8.4×10?3.?·m, decreasing by 14 orders of magnitude compared with pure alumina ceramics. The function of CNTs in composite is related to the distribution state of CNTs in composite, and the distribution state of CNTs in matrix is dependent on preparation procedures.

关键词： MWNTs, alumina, composite, fracture toughness, electrical properties.

Fuzzy tracking control design for hypersonic vehicles via T-S model

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Science china(Information Sciences) 2011年第3期54卷 521-528页

作者： GAO DaoXiang 1 & SUN ZengQi 2 1 School of Technology, beijing Forestry university, beijing 100083. {3. 2.state key Laboratory of Intelligent Technology and System, Department of Computer Science and Technology, tsinghua university, beijing 100084, {3. 1. School of Technology Beijing Forestry University Beijing 100083 China2. State Key Laboratory of Intelligent Technology and System Department of Computer Science and Technology Tsinghua University Beijing 100084 China

The main focus of this paper is on designing a T-S fuzzy controller for the hypersonic vehicle. The longitudinal dynamics of the vehicle are studied using time-scale decomposition to reduce the complexity of T-S modeling. The dynamic inversion with PI control technique is applied for the slow dynamics to derive the flight path angle command and throttle setting by taking the pilot altitude and velocity command as its inputs. The T-S fuzzy controller is designed for the fast dynamics to derive the elevator deflection to track the flight path angle command. The discrepancy between the T-S model and real vehicle model is considered by using sliding mode control for the system stability. Simulation results are included to show the effectiveness of the controller.

关键词： fuzzy control T-S model sliding mode control hypersonic vehicle