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On the dynamics in a transitional boundary layer

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Communications in Nonlinear Science and Numerical Simulation 2001年第3期6卷 111-171页

作者： C. B. LEE and R. LEE department of mechanics and engineering Science/State Key Laboratory for Studies of Turbulence and Complex Systems, Peking university, beijing 100871, china department of engineering mechanics, tsinghua university, beijing 100084, Chi department of mechanics and engineering Science / State Key Laboratory for Studies of Turbulence and Complex Systems Peking University Beijing 100871 China department of engineering mechanics Tsinghua University Beijing 100084 China

A model is presented to describe the dynamic physical processes that occur in a transitional boundary layer flow. The CS-solitons, the closed vortex, the secondary closed vortex and the chain of ring-like vortices are postulated to be the basic flow structures of the transitional boundary layer as well as the turbulent boundary layer. It is argued that the central features of transitional and developed turbulent boundary layer flows can be explained in terms of how the series vortices interact with each other, and with the CS-solitons. The physical process that leads to the regeneration of the new closed vortex along the border of the CS-soliton, as well as the processes of evolution of the vortices to high frequency vortices, is described. The model is supported by the important developments in a number of "kernel" experiments, which illustrate both transitional and developed turbulent boundary layer. An important aspect of the model is that it has been formulated to be consistent with accepted rational mechanics concepts that are known to provide a proper physical description of other flows.

关键词： boundary layer transition dynamic processes onset of turbulence

The application of event-tree based approach in long-term crude oil scheduling

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Science china Chemistry 2010年第6期53卷 1445-1452页

作者： ZOU LaiXi,LI ChuFu,ZHANG Ming & HE XiaoRong department of Chemical engineering,tsinghua university,beijing 100084,china department of Chemical engineering Tsinghua University Beijing China

This paper addresses the problem of optimal operation in long-term crude oil scheduling,which involves unloading crude oil from vessels,transferring it to charging tanks and feeding it to the distillation *** application of a new approach for modeling and optimization of long-term crude oil scheduling is presented and the event-tree based modeling method that is very different from mathematical programming is *** approach is developed on the basis of natural language modeling and continuous time *** triggered rules,decomposition strategy,depth-first search algorithm and pruning strategy are adopted to improve the efficiency of searching the optimum *** approach is successfully applied to an industrial-size problem over a horizon of 4 weeks,involving 7 vessels,6 storage tanks,6 charging tanks,2 crude oil distillation units,and 6 crude oil *** CPU (AMD 3000+,2.0GHz) solving time is less than 70 seconds.

关键词： crude oil scheduling modeling and optimization event-tree based depth-first search algorithm

Micro-computed tomography for small animal imaging: Technological details

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Progress in Natural Science:Materials International 2008年第5期18卷 513-521页

作者： Hao Li, Hui Zhang , Zhiwei Tang, Guangshu Hu department of Biomedical engineering, tsinghua university, beijing 100084, china department of Biomedical engineering Tsinghua University Beijing 100084 China

The high-resolution micro-computed tomography (micro-CT) system has now become an important tool for biological research. The micro-CT system enables a non-invasive inspection to screen anatomical changes in small animals. The promising advantages include high-spatial resolution, high sensitivity to bone and lung, short scan time and cost-e ectiveness. The dose received by the small animal might be a critical concern in the research. In this article, the choice of the components, fundamental physical problems, the image recon- struction algorithm and the representative applications of micro-CT are summarized. Some results from our research group are also pre- sented to show high-resolution images obtained by the micro-CT system.

关键词： Micro-computed tomography Small animal X-ray

Study on Bonding of Steel-mushy Al-7graphite

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Journal of university of Science and Technology beijing 2001年第4期8卷 283-285页

作者： Peng Zhang, Yunhui Du, Daben Zeng department of Mechanical engineering tsinghua university. beijing 100084, china department of Mechanical engineering Tsinghua University Beijing 100084 China

The bonding of steel-mushy Al-7graphite was studied. The relationship between interfacial shear strength of bonding plate and solid fraction of Al-7graphite mushy was obtained, and the interfacial structure of bonding plate was determined. The results showed that: under the condition of 500 degreesC for preheat temperature of steel plate and 10 mm/s for rolling speed, the largest interfacial shear strength of bonding plate was 70.1 MPa when solid fraction of Al-7graphite mushy was 34.6%.

关键词： interfacial shear strength solid fraction interfacial structure

On the tribological characteristics of dynamically loaded journal bearing with micropolar fluids

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Science china(Physics,mechanics & Astronomy) 2004年第Z1期47卷 45-50页

作者： WANG Xiaoli, WANG Kongying & ZHU KeqinSchool of Mechanical and Vehicular engineering, beijing Institute of Technology, beijing 100081, china department of engineering mechanics, tsinghua university, beijing 100084, china School of Mechanical and Vehicular engineering Beijing Institute of Technology Beijing China department of engineering mechanics Tsinghua University Beijing China

The addition of the additives to the lubricant oil to enhance the characteristics of the lubricant will influence the performance of the bearings. Based on the theory of micropolar fluids, the tribological characteristics of a dynamically-loaded journal bearing are numerically studied. Comparisons are made between the Newtonian fluids and the micropolar fluids. It is shown that for a dynamically-loaded journal bearing, the micropolar fluids yield an increase not only in the friction force, but also in the friction coefficient. In addition, the oil film pressure and the oil film thickness are obviously higher than that of Newtonian fluids.

关键词： micropolar fluids, dynamic loads journal bearing tribological characteristics.

A measurement error model for microarray data analysis

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Progress in Natural Science:Materials International 2005年第7期15卷 614-620页

作者： zhou Yiming and CHENG Jing ( department of Biological Sciences and Biotechnology, tsinghua university, beijing 100084, china State Key Laboratory of Biomembrane and Membrane Biotechnology, tsinghua university, beijing 100084, china National engineering Research Center for beijing Biochip Technology, 18 Life Science Parkway, beijing 102206, china) department of Biological Sciences and Biotechnology Tsinghua University Beijing 100084 China State Key Laboratory of Biomembrane and Membrane Biotechnology Tsinghua University Beijing 100084 China National engineering Research Center for beijing Biochip Technology 18 Life Science Parkway Beijing 102206 China

Microarray technology has been widely used to analyze the gene expression levels by detecting fluorescence intensity in a high throughput fashion. However, since the measurement error produced from various sources in microarray experiments is heterogeneous and too large to be ignored, we propose here a measurement error model for microarray data processing, by which the standard deviation of the measurement error is demonstrated to be linearly increased with fluorescence intensity. A robust algorithm, which estimates the parameters of the measurement error model from a single microarray without replicated spots, is provided. The model and algorithm for estimating of the parameters from a given data set are tested on both the real data set and the simulated data set, and the result has been proven satisfactory. And, combining the measurement error model with traditional Z-test method, a full statistical model has been developed It can significantly improve the statistical inference for identifying differentially expressed genes.

关键词： microarray measurement error model parameter estimation differentially expressed genes.

Bauschinger and size effects in thin-film plasticity due to defect-energy of geometrical necessary dislocations

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Acta Mechanica Sinica 2011年第2期27卷 266-276页

作者： Zhan-Li Liu · Zhuo Zhuang · Xiao-Ming Liu · Xue-Chuan Zhao · Yuan Gao department of engineering mechanics, School of Aerospace, tsinghua university, 100084 beijing, china department of engineering mechanics School of Aerospace Tsinghua University Beijing China

The Bauschinger and size effects in the thinfilm plasticity theory arising from the defect-energy of geometrically necessary dislocations （GNDs） are analytically investigated in this paper. Firstly, this defect-energy is deduced based on the elastic interactions of coupling dislocations （or pile-ups） moving on the closed neighboring slip plane. This energy is a quadratic function of the GNDs density, and includes an elastic interaction coefficient and an energetic length scale L. By incorporating it into the work- conjugate strain gradient plasticity theory of Gurtin, an energetic stress associated with this defect energy is obtained, which just plays the role of back stress in the kinematic hardening model. Then this back-stress hardening model is used to investigate the Bauschinger and size effects in the tension problem of single crystal Al films with passivation layers. The tension stress in the film shows a reverse dependence on the film thickness h. By comparing it with discrete-dislocation simulation results, the length scale L is determined, which is just several slip plane spacing, and accords well with our physical interpretation for the defect- energy. The Bauschinger effect after unloading is analyzed by combining this back-stress hardening model with a friction model. The effects of film thickness and pre-strain on the reversed plastic strain after unloading are quantified and qualitatively compared with experiment results.

关键词： Thin film · Crystal plasticity · Defect energy · Back stress · Size effect

Mapping and overlapping based carrier frequency searching technique for rapid GNSS long PN-code acquisition

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Science china(Information Sciences) 2010年第12期53卷 2642-2652页

作者： LI Hong ,LU MingQuan & FENG ZhenMing department of Electronic engineering,tsinghua university,beijing 100084,china department of Electronic engineering Tsinghua University Beijing China

In global navigation satellite systems(GNSS),because of the long period and high chip rate of long pseudo-noise(PN) code,the rapid acquisition is hard to *** speed up search process,in the paper,a mapping and overlapping based carrier frequency searching technique is *** mapping incoming signals of the same interval to different carrier frequency cells and overlapping together the mapped incoming signals that correspond to the same code phase,the technique reduces the number of the cells to be *** effect of the technique on detection and mean acquisition time performance is *** is shown that the technique reduces the cells to be searched and shortens mean acquisition time at the expense of degrading detection *** technique is fit to the previously published acquisition methods and is capable of improving their mean acquisition time *** and simulation results validate the analysis.

关键词： carrier frequency cells mapping overlapping acquisition performance

INTERFACIAL REACTIONS OF METAL FILMS WITH AlN SUBSTRATE

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中国有色金属学会会刊：英文版 1996年第2期6卷 81-85页

作者： He Xiangjun Tao Kun Fan Yudian (department of Materials Science and engineering, tsinghua university, beijing 100084) department of Materials Science and engineering Tsinghua University Beijing 100084 China

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关键词： thin films interfacial reactions AlN substrate