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Simulation of nuclei morphologies for binary alloy

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Science china Mathematics 2010年第11期53卷 2927-2936页

作者： LI DaMing1, & zhang PingWen2.1{2. of Mathematics, Shanghai Jiaotong University, Shanghai 2.02.0, china 2.ey Lab of Mathematics and Applied Mathematics, Center for Applied Physics and Technology and School of mathematical sciences, Peking University, beijing 100871, china 1. department of Mathematics Shanghai Jiaotong University Shanghai 200240 China2. Key Lab of Mathematics and Applied Mathematics Center for Applied Physics and Technology and School of Mathematical Sciences Peking University Beijing 100871 China

We study the critical nuclei morphologies of a binary alloy by the string method. The dynamic equation of the string, connecting the metastable phase (liquid) and stable phase (solid), is governed by Helmholtz free energy for the binary alloy system at a given temperature. The stationary string through the critical nucleus (saddle point) is obtained if the relaxation time of the string is su?ciently large. The critical nucleus radius and energy barrier to nucleation of a pure alloy with isotropic interface energy in two and three dimensions are calculated, which are consistent with the classical nucleation theory. The critical nuclei morphologies are sensitive to the anisotropy strength of interface energy and interface thickness of alloy in two and three dimensions. The critical nucleus and energy barrier to nucleation become smaller if the anisotropy strength of the interface energy is increased, which means that it is much easier to form a stable nucleus if the anisotropy of the interface energy is considered.

关键词： nucleation crystal morphology string method

LD Pumped Q-Switching and Self-starting Mode-locked All Fiber Laser

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Chinese Journal of Lasers 1995年第3期B4卷 229-234页

作者： zhang Jian LI Jinghui JIANG Xing LIU Xiaoming PENG Jiangde(department of Electronic Engineering, {2. University, beijing 100084, china) tsinghua Univ Beijing China

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关键词： Q-switching passively mode-locking fiber laser

Learning interactions among multi-channel sequences with dynamical influence models

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Science china(Information sciences) 2010年第7期53卷 1336-1344页

作者： zhang WeiDong, CHEN Feng & XU WenLi department of Automation, National Laboratory for Information Science and Technology, {2. University, beijing 100084, china 1. department of Automation National Laboratory for Information Science and Technology Tsinghua University Beijing 100084 China

Many real applications involve simultaneous recording and analysis of multi-channel information sources. Learning and modeling the interactions among channels is the kernel step to analyze and recognize system characteristics. This paper presents a model that learns the dynamical influence among multi-channel sequences. The model, dynamical influence model, permits functional roles of individual channels to change and models the changing influence strength between channels. By querying the values of influence factors, we can recognize the functional role of each channel qualitatively and learn about to what extent the chains influence each other quantitatively at any time. The experimental results on synthetic data and application of multi-person interaction recognition show that our model is reliable and effective.

关键词： multi-channel processing dynamical interaction influence model activity recognition

Cooling effect of ripped-stone embankments on Qing-Tibet railway under climatic warming

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Science Bulletin 2003年第6期48卷 598-604页

作者： LAI Yuanming1, zhang Luxin1 , zhang Shujuan1 & MI Long{2.. State Key Lab. of Frozen Soil Engineering, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of sciences, Lanzhou 730000, china 2. department of Civil Engineering, Northern Jiaotong University, beijing 100044, china State Key Lab. of Frozen Soil Engineering Cold and Arid Regions Environmental and Engineering Research Institute Chinese Academy of Sciences Lanzhou China department of Civil Engineering Northern Jiaotong University Beijing China

The heat convection in ballast mass and ripped-stone mass in railway embankments is the problem of heat convection in porous media. In order to calculate the temperature distribution of Qing-Tibet railway embankment, from the governing equations used to study forced convec-tion for incompressible fluids porous media, the finite ele-ment formulae for heat convection in porous media are de-rived by using Galerkin抯 method. The temperature fields of the traditional ballast embankment and the ripped-stone mass embankment, constructed on July 15, have been ana-lyzed and compared under the case that the air temperature in Qinghai-Tibetan Plateau will be warmed up by 2.0℃ in the future 50 years. The calculated results indicate that, the permafrost 5 m below the traditional ballast embankment will be thawed in the regions in which the air yearly-average temperature is larger than -3.5℃ or the yearly-average temperature at the native surface is larger than -1℃. The embankment will cause large thawing settlement. The rail-way embankment will be damaged by permafrost degrada-tion. The ripped-stone mass embankment can not only resist the effect of climatic warm up on it but also provide cool energy for the permafrost under it. It can assure permafrost stability and not subjected to thawing. Therefore, it is highly recommended that the ripped-stone mass embankment be taken as the Qing-Tibet railway embankment structure in high-temperature permafrost regions so that permafrost embankment can be protected as possible as we could.

关键词： cooling effect ripped-stone embankment climatic warming.

Theoretical study on the reaction mechanism of(CH_3)_3CO+CO

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Science china Chemistry 2005年第1期48卷 18-24页

作者： ZHAO Hongmei1,2.3, SUN Chengke1,4, zhang Rongchang3, XI Hongmin3 & LI Zonghe1 1. department of Chemistry, {2. Normal University, {2. 100875, china 2. The Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of sciences, {2. 100080, china 3. department of Chemistry, Beihua University, Jilin 132.13, china 4. department of Chemistry, Qujing Normal University, Yunnan 655000, china 1. department of Chemistry Beijing Normal University 100875 Beijing China 2. The Laboratory of Molecular Reaction Dynamics Institute of Chemistry Chinese Academy of Sciences 100080 Beijing China 3. department of Chemistry Beihua University 132013 Jilin China 4. department of Chemistry Qujing Normal University 655000 Yunnan China

The reaction mechanism of (CH3)3CO with CO has been theoretically investigated using density-functional theory (DFT) calculations at B3LYP/6-31G* level. In order to get more reliable energy values the single-point energy is evaluated at CCSD (T)/6-31++G** level. The results show that the reaction is multi-channel and the reaction of (CH3)3CO radical with CO mostly produces (CH3)3C + CO2. The reaction could play a role in eliminating air pollution.

关键词： DFT, B3LYP, (CH3)3CO, radical.

Effects of abnormally high heat stress on petroleum in reservoir——An example from the Tazhong 18 Well in the Tarim Basin

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Science china Earth sciences 2008年第4期51卷 515-527页

作者： ZHU DongYa1, JIN ZhiJun1, HU WenXuan2.& zhang XueFeng3 1 Petroleum Exploration and Production Institute, china Petroleum & Chemical Corporation, {2. 100083, china 2.department of Earth sciences, Nanjing University, Nanjing 2.0093, china 3 School of Resource and Information, china University of Petroleum, {2. 102.49, china Petroleum Exploration and Production Institute China Petroleum & Chemical Corporation Beijing China department of Earth sciences Nanjing University Nanjing China School of Resource and Information China University of Petroleum Beijing China

An igneous intrusion of 94m thick was discovered intruding into the Silurian sandstone from Tazhong 18 Well. The petroleum previously preserved in the Silurian sandstone reservoir was altered into black carbonaceous bitumen by abnormally high heat stress induced by the igneous intrusion. The reflec-tance of the carbonaceous bitumen reaches as high as 3.54%, indicating that the bitumen had evolved into a high thermal evolution level. Similar to the Silurian samples from the neighboring Tazhong 11, Tazhong 12. Tazhong 45 and Tazhong 47 wells, the distribution of C2., C2. and C2. steranes of the car-bonaceous bitumen is still "V" -shaped and can still be employed as an efficient parameter in oil source correlation. The "V" -shaped distribution indicates that the hydrocarbons from the Tazhong 18 and the neighboring wells were all generated from the Middle-Upper Ordovician hydrocarbon source rocks. However, the oil source correlation parameters associated with and terpanes had been changed greatly by the high heat stress and can no longer be used in oil source correlation. The δ 13C values of the pe-troleum from the neighboring wells are between -32.53‰ and -33.37‰, coincident with those of the Paleozoic marine petroleum in the Tarim Basin. However, the δ 13C values of the carbonaceous bitumen from the Tazhong 18 Well are between -2..18‰ and -2..2.‰, isotopically much heavier than the pe-troleum from the neighboring wells. The content of light hydrocarbons (nC14-nC2.) of the saturated hydrocarbon fraction in the carbonaceous bitumen is extremely higher than the content of heavy hy-drocarbons. The light/heavy hydrocarbon ratios (ΣnC2.-/ΣnC2.+) are between 4.56 and 39.17. In the saturated fraction, the even numbered hydrocarbons are predominant to the odd numbered, and the OEP (Odd to Even Predominance) values are between 0.2. and 0.49. However, the content of light hy-drocarbons in the petroleum from the neighboring wells is relatively low and the content of the even numb

关键词： Tarim Basin igneous intrusive abnormally high heat stress bitumen carbon isotope PAH

Effect of Post-spinning Modification on the PAN Precursors and Resulting Carbon Fibers

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Journal of Wuhan University of Technology(Materials Science) 2006年第3期21卷 44-48页

作者：张旺玺 department of Mechanics Engineering Zhongyuan Institute of TechnologyZhengzhou 450070China

The impregnation of a special grade PAN precursor,fibers wus carried out in a 8 wt% KMnO4 aqueous solution to obtain modified PAN precursor fibers. The effects of modification on the chemical stncture and the mechanical properties of precursor fibers thermally stabilized and their resulting carbon fibers u＇ere characterized by the combiination use of densities, wide-angle X-ray diffraction （WAXD）, X-ray photoelectron speetroscopy （XPS）, elemental analysis （ EA ）, Fourier traasform infrared spectroscopy （FT-IR） and scanning electron microscope （SEM）, ***4 as a strong oxidizer can swell, oxidize and corrode the skin of a ***, and transform C≡N groups to C≡N ones, meamchile , it can decreuse the crystal .size increuse the orientation index and the costallinity index, furthermore it can increuse the densities of modified PAN precursors and resuhing thermally stabilized fibers. As a result, the carbon fibers developed from modified PAN fibers show an improvement in tensile strength of 31.2. % and an improvement in elongation of 77.78 % , but a decrease of 16. 52. in Young＇s modulus.

关键词： carbon fibers carbon precursor chemical treatment mechanical properties

Orthogonal linear polarized lasers (Ⅲ)——Applications in self-sensing

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Progress in Natural Science:Materials International 2005年第11期15卷 961-971页

作者： zhang Shulian, DU Wenhua and LIU Gang (The State Key Laboratory of Precision Measurement Technology and Instruments, department of Precision Instruments, {2. University, beijing 100084, china) The State Key Laboratory of Precision Measurement Technology and Instruments Department of Precision Instruments Tsinghua University Beijing 100084 China

In this paper, the applications of orthogonal linear polarized lasers in self-sensing are reviewed. The properties for such a laser include the production of a new frequency in one longitudinal mode spacing, the tuning of frequency difference, the change of polarization states as cavity tuning, the control of mode competition intensity, the optical feedback, and so on. The orthogonal polarized lasers have been used as a laser nanometer ruler based on competition between two polarized lights in a HeNe laser and as a displacement measurement tool based on the optical feedback in the orthogonal polarized lasers. They are also used in the phase retardation measurement of a waveplate, the angle measurement, the vibration measurement, the pressure/force measurement, the weak magnetic field measurement, and so on. The structures of these new devices are simple and compact with the great advantages of high resolution and high accuracy. Some of these devices can trace to the source of the laser wavelength. The nanometer laser ruler is an example whose measurement range is 12.mm, resolution is 79 nm and linearity is less than 5×10-5. The repeatability of the phase retardation measuring system of waveplate can reach 3’.

关键词： orthogonal polarized laser frequency splitting optical feedback vibration measurement displacement measurement waveplate measurement angle measurement.

CONCENTRATION DISTRIBUTION OF SEDIMENT IN BED LOAD LAYER

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Journal of Hydrodynamics 2004年第1期16卷 28-33页

作者： ZHONGDe-yu zhangHong-wu departmentofHydraulicEngineering TsinghuaUniversityBeijing100084China

In this paper the concentration profile in bed load layer is derived based onkinetic theory. According to observations, particles moving in near wall region behave differentlyduring ejection and sweeping of turbulence burst, as indicates that they are subject to differentinfluences from turbulence, and therefore, the forces acting on particles are not the ***, particles moving in bed load layer are classified into two groups, one lifted upwardby ejections, the other carried back to bed by sweepings, and the forces corresponding to upward anddownward motions are proposed. By solving the basic transport equation of kinetic theory, thevelocity distribution functions, upward and downward fluxes of particles in bed load layer arederived. Upon assumption of e-quilibrium sediment transport, concentration profile in bed load layeris obtained. Verification is also presented in this paper, which shows that the concentrationprofile produced by the relation proposed in this paper agrees with observations well.

关键词： bed load concentration distribution turbulence burst