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Study on Numerical Simulation of Mold Filling and Heat Transfer in Die Casting Process

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Journal of materials science & Technology 2000年第3期16卷 269-272页

作者： Liangrong JIA, Shoumei XIONG and Baicheng LIU (department of Mechanical engineering, tsinghua university, beijing 100084, china) department of Mechanical engineering Tsinghua University Beijing 100084 China

A 3-D mathematical model considering turbulence phenomena has been established based on a computational fluid dynamics technique, so called 3-D SOLA-VOF (Solution Algorithm-Volume of Fluid), to simulate the fluid flow of mold filling process of die casting. In addition, the mathematical model for simulating the heat transfer in die casting process has also been established. The computation program has been developed by the authors with the finite difference method (FDM) recently. As verification, the mold filling process of a S-shaped die casting has been simulated and the simulation results coincide with that of the benchmark test. Finally, as a practical application, the gating design of a motorcycle component was modified by the mold filling simulation and the dies design of another motorcycle component was optimized by the heat transfer simulation. All the optimized designs were verified by the production practice.

关键词： Study on Numerical Simulation of Mold Filling and Heat Transfer in Die Casting Process Mold Simulation

Semi-solid Processing of Al-7Graghite Composite

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Journal of university of science and Technology beijing 2001年第3期8卷 203-206页

作者： Peng Zhang, Yunhui Du, Daben Zeng department of Mechanical engineering, tsinghua university, beijing 100084, china Tsing Hua Univ Dept Engn Mech Beijing 100084 Peoples R China

Al-7graphite composite was processed using Al-7graphite mushy prepared by electromagnetic-mechanical stirring method, and the influence of solid fraction on the distributing of graphite particles in ingot was studied. The results shows that the relationship between solid fraction and stirring temperature of mushy is: f(s) = 591.5-0.897 t (where f(s) is the solid fraction, t is the stirring temperature). For Al-7graphite composite, with the increasing of solid fraction, the aggregation extent of graphite particles reduced gradually, and when solid fraction was larger than 30%, graphite particles could distribute evenly in ingot.

关键词： Al-7graphite composite electromagnetic-mechanical stirring method distributing of graphite particles solid fraction stirring temperature

Thermodynamic Significance of Human Basal Metabolism

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Journal of Thermal science 1993年第2期2卷 81-86页

作者： Wang Cuncheng Thermal engineering department tsinghua university, beijing 100084, P.R. china 1. Thermal engineering department tsinghua university 100084 Beijing P.R. China

The human basal state,a non-equilibrium steady state,is analysed in this paper in the light of the First and Second Laws of Thermodynamics whereby the thermodynamic significance of the basal metabolic rate and its distinction to the dissipation function and exergy loss are *** analysis demonstrates the correct expression of the effects of the blood flow on the heat balance in a human-body bio-heat model and the relationship between the basal metabolic rate and the blood perfusion.

关键词： thermodynamic laws basal metabolism blood perfusion dissipation function exergy loss

RRM:An incentive reputation model for promoting good behaviors in distributed systems

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science in china(Series F) 2008年第11期51卷 1871-1882页

作者： ZHANG Hong1,2,DUAN HaiXin1,3 & LIU Wu1,3 1 tsinghua National Laboratory for Information science and Technology,tsinghua university,beijing 100084,china 2 department of Computer science and Technology,tsinghua university,beijing 100084,china 3 Network Research Center,tsinghua university,beijing 100084,china 1. tsinghua National Laboratory for Information science and Technology Tsinghua University Beijing 100084 China 2. department of Computer science and Technology Tsinghua University Beijing 100084 China 3. Network Research Center Tsinghua University Beijing 100084 China

Reputation systems represent soft security mechanisms that complement traditional information security mechanisms. They are now widely used in online e-commerce markets and communities in order to stimulate good behaviors as well as to restrain adverse behaviors. This paper analyzes the limitations of the conversational reputation models and proposes an incentive reputation model called the resilient reputation model （RRM） for the distributed reputation systems. The objective of this reputation model is not only to encourage the users to provide good services and, therefore, to maximize the probability of good transaction outcomes, but also to punish those adverse users who are trying to manipulate the application systems. The simulation results indicate that the proposed reputation model （RRM） could effectively resist against the common adverse behaviors, while protecting the profits of sincere users from being blemished by those adversaries.

关键词： reputation model distributed system trust soft security

Preparation of NiFe binary alloy nanocrystals for nonvolatile memory applications

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science china(Technological sciences) 2010年第9期53卷 2320-2322页

作者： WANG Li,SUN HongFang,ZHOU HuiHua & ZHU Jing beijing National Center for Electron Microscopy Laboratory,department of materials science and engineering,tsinghua university,beijing 100084,china 1. beijing National Center for Electron Microscopy Laboratory Department of Materials Science and Engineering Tsinghua University Beijing 100084 China

In this work,an idea which applies binary alloy nanocrystal floating gate to nonvolatile memory application was *** relationship between binary alloy’s work function and its composition was discussed theoretically.A nanocrystal floating gate structure with NiFe nanocrystals embedded in SiO2 dielectric layers was fabricated by magnetron *** micro-structure and composition deviation of the prepared NiFe nanocrystals were also investigated by TEM and EDS.

关键词： nanocrystal nonvolatile memory work function magnetron sputtering

NUMERICAL DISSIPATION FOR THREE-POINT DIFFERENCE SCHEMES TO HYPERBOLIC EQUATIONS WITH UNEVEN MESHES

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Journal of Computational Mathematics 2003年第4期21卷 519-534页

作者： Zi-niu Wu(department of engineering Mechanics, tsinghua university, beijing 100084, china) department of engineering Mechanics Tsinghua University Beijing 100084 China

The widely used locally adaptive Cartesian grid methods involve a series of abruptly refined interfaces. The numerical dissipation due to these interfaces is studied here for three-point difference approximations of a hyperbolic equation. It will be shown that if the wave moves in the fine-to-coarse direction then the dissipation is positive (stabilizing), and if the wave moves in the coarse-to-fine direction then the dissipation is negative (destabilizing).

关键词： Refined interfaces Numerical dissipation Three-point difference approxima-tion Hyperbolic equation.

A SINGLE-PERIOD INVENTORY SYSTEM WITH A GENERAL S-SHAPED UTILITY AND EXPONENTIAL DEMAND

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Journal of Systems science and Systems engineering 2010年第2期19卷 227-236页

作者： Wei GENG1 Xiaobo ZHAO2 Deng GAO3 department of Industrial engineering,tsinghua university,beijing 100084,china department of Industrial engineering Tsinghua University Beijing China

We discuss a single-period inventory system with a general S-shaped utility function and exponential demand. It is shown that there exists a state-dependent order-up-to policy to be optimal. Behaviors of optimal polic... 详细信息

关键词： Inventory S-shaped utility function order-up-to policy

CORROSION BEHAVIOR OF Cu-Nb AND Ni-Nb AMORPHOUS FILMS PREPARED BY ION BEAM ASSISTED DEPOSITION

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Acta Metallurgica Sinica(English Letters) 2003年第4期16卷 266-270页

作者： B. Zhao, F. Zeng, DM. Li and F. PanLaboratory of Advanced materials, department of materials science and engineering, tsinghua university, beijing 100084, china Laboratory of Advanced materials Department of Materials Science and Engineering Tsinghua Univexsity

The Cu25 Nb75 and Ni45Nb55 amorphous films with about 500nm thickness were prepared by ion beam assisted deposition (IBAD). Potentiodynamic polarization measurement was adopted to investigate the corrosion resistance of samples and the tests were carried out respectively in 1mol/L H2SO4 and NaOH aquatic solution. The corrosion performance of the amorphous films was compared with that of multilayered and pure Nb films. Experimental results indicated that the corrosion resistance of amorphous films was better than that of the corresponding multilayers and pure Nb films for both Ni-Nb system with negative heat of formation and Cu-Nb system with positive heat of formation.

关键词： amorphous film ion beam assisted deposition corrosion resis- tance polarization measurement

Multiple time step molecular dynamics simulation for interaction between dislocations and grain boundaries

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Acta Mechanica Sinica 2005年第4期21卷 371-379页

作者： X.Y.Li W.Yang department of engineering Mechanics,tsinghua university,beijing 100084.china department of engineering Mechanics Tsinghua University Beijing 100084 China

A multiple time step algorithm, called reversible reference system propagator algorithm, is introduced for the long time molecular dynamics simulation. In contrast to the conventional algorithms, the multiple time method has better convergence, stability and efficiency. The method is validated by simulating free relaxation and the hypervelocity impact of nano-clusters. The time efficiency of the multiple time step method enables us to investigate the long time interaction between lattice dislocations and low-angle grain boundaries.

关键词： Multiple time step Molecular dynamics ,Dislocation Grain boundary