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Science china(Physics,Mechanics & Astronomy) 2005年第5期48卷 614-625页

作者： HUANG Zhangfeng 1, CAO Wei 1,2 & ZHOU Heng 1,2 1. Department of Mechanics, tianjin University, tianjin 300072, china 2. Liu-Hui Center of Applied Mathematics, Nankai University and tianjin University, tianjin 300072, china Department of Mechanics Tianjin University Tianjin China Liu-Hui Center of Applied Mathematics Nankai University and Tianjin University Tianjin China

Temporal mode direction numerical simulation has been done for the transition of a supersonic boundary layer on a flat plate with Mach number 4.5. Analysis of the result showed that during the breakdown process in laminar-turbulent transition, the mechanism causing the mean flow profile to evolve swiftly from laminar to turbulent was that the modification of mean flow profile by the disturbances,when they became larger,led to a remarkable change of its stability characteristics. Though the most unstable T-S wave was of second mode for laminar flow, the first mode waves played the key role in the breakdown process in laminar-turbulent transition.

关键词： supersonic boundary layer, transition, breakdown.

Effects of GH Admixture on the Early Strength of Fly Ash Concrete and Mortar

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Journal of Wuhan University of Technology(Materials Science) 2008年第5期23卷 755-760页

作者：亢景付 School of Civil Engineering Tianjin University

The enhancement effects of GH admixture on the early strengths of fly ash concrete and mortar were studied, and the mechanism was analyzed by X-ray diffraction （XRD） and scanning electro microscope （SEM）. Experimental results show that, by the incorporation of GH admixture, both of cement hydration and pozzolanic reaction of fly ash are accelerated, the strengths of fly ash concrete and mortar are enhanced noticeably, especially the early strength. With a mixture design of 200 kg/m^3 OPC （Ordinary Portland Cement ）, 200 kg/m^3 fly ash and 50 kg/m^3 GH admixture, the strength of concrete at 1 d, 3 d and 28 d reaches 25 MPa, 50 MPa and 70 MPa respectively.

关键词： building materials fly ash concrete GH admixture strength microstructure

Stochastic DEA model with undesirable outputs: An application to the prediction of anti-HIV therapy efficiency

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Progress in Natural Science:Materials International 2006年第7期16卷 753-759页

作者： BIAN Fuping and TANG Xiaoqin ( Department of Mathematics, School of Science, tianjin University, tianjin 300072, china Liuhui Institute of Applied Mathematics, Nankai University and tianjin University, tianjin 300072, china) tianjin Univ Sch Sci Dept Math Tianjin 300072 Peoples R China Nankai Univ Liuhui Inst Appl Math Tianjin 300072 Peoples R China

This paper proposes a stochastic prediction DEA model with undesirable outputs and simplifies the process using chance-constrained techniques in order to obtain an equivalent linear programming formulation. The existence and stability of the optimal solutions have been proved. And the model is used to describe and predict the efficiency of anti-HIV therapy in AIDS patients.

关键词： data envelopment analysis (DEA) decision making units (DMU) undesirable outputs stochastic DEA model anti-HIV therapy.

Comparative analysis of CO_2-based transcritical Rankine cycle and HFC245fa-based subcritical organic Rankine cycle using low-temperature geothermal source

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Science china(Technological Sciences) 2010年第6期53卷 1638-1646页

作者： GUO Tao,WANG HuaiXin & ZHANG ShengJun Department of Thermal Energy and Refrigeration Engineering,tianjin University,tianjin 300072,china Department of Thermal Energy and Refrigeration Engineering Tianjin University

A detailed thermodynamic and techno-economic comparison is presented for a CO2-based transcritical Rankine cycle and a subcritical organic Rankine cycle (ORC) using HFC245fa (1,1,1,3,3-pentafluoro-propane) as the working fluid driven by the low-temperature geothermal source,in order to determine the configuration that presents the maximum net power output with a minimum *** evaluations of both Rankine cycles have been performed based on equal thermodynamic mean heat rejection temperature by varying certain system operating parameters to achieve each Rankine cycle's optimum design at various geothermal source temperature levels ranging from 80oC to *** results obtained show that the optimum ther-modynamic mean heat injection temperatures of both Rankine cycles are distributed in the scope of 55% to 65% of a given geothermal source temperature level,and that the CO2-based transcritical Rankine cycle presents 3% to 7% higher net power output,84% reduction of turbine inlet volume flow rate,47% reduction of expansion ratio and 1.68 times higher total heat transfer capacity compared with the HFC245fa-based subcritical *** is also indicated that using the CO2-based transcritical system can reduce the dimension of turbine ***,it requires larger heat transfer areas with higher strength heat exchanger materials because of the higher system pressure.

关键词： transcritical Rankine cycle organic Rankine cycle (ORC) low-temperature geothermal CO2 HFC245fa

Deposition of Bioactive Layer on NiTi Alloy by Chemical Treatment

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Journal of Materials Science & Technology 2002年第6期18卷 534-537页

作者： Ya LIU, Xianjin YANG, Minfang CHEN, Shengli ZHU and Zhenduo GUISchool of Materials Science and Engineering, tianjin University, tianjin 300072, china Sch. of Mat. Sci. and Eng. Tianjin Univ. Tianjin 300072 China

A simple chemical method was developed for inducing bioactivity on NiTi alloys (50 at. pct by Ni/Ti). A layer of calcium phosphate was deposited on the surface to improve biocompatibility of the alloy. NiTi alloys were first etched in HNO3 aqueous solution, and then treated with boiling diluted NaOH solution. A rough surface was created and a thin TiO2 layer was formed on the surface. Pre-calcification was then introduced by immersing the treated NiTi alloys in supersaturated Na2HPO4 solution and supersaturated Ca(OH)2 solution in turn before calcification in simulated body fluid (SBF). A dense and uniform bonelike calcium phosphate (Ca-P) bioactive layer was formed on the surfaces of the specimen, which would improve their biocompatibility. Morphology and element analysis on NiTi surfaces during the treatments were investigated in detail by means of environment scanning electron microscopy (ESEM), energy dispersion X-ray spectroscopy (EDXS), and X-ray diffraction (XRD).

关键词： NiTi alloy Chemical method Bioactive layer Biocompatibility

Precipitation of α″-Fe_(16)N_2 Phase

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Journal of Materials Science & Technology 1998年第5期14卷 473-474页

作者： Haimei ZHENG Chunyang LI Jian WANG and Baoyn LI (Dept. of Material Science and Engineering, tianjin University, tianjin 300072, china) Dept. of Material Science and Engineering Tianjin University Tianjin 300072 China

Characteristics of the precipitate α″-Fe16N2 phase have been investigated by X-ray diffraction and TEM analysis. VSM measurements give the saturation magnetization of the α″ phase.

关键词： Fe Precipitation of N2 Phase

Research and application of CO_2 refrigeration and heat pump cycle

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Science china(Technological Sciences) 2009年第6期52卷 1563-1575页

作者： TIAN Hua,YANG Zhao,LI MinXia & MA YiTai Thermal Energy Research Institute,tianjin University,tianjin 300072,china Thermal Energy Research Institute Tianjin University

The environmental problem caused by refrigerant has become the focus all over the *** the most typical natural refrigerant,CO2,of course,becomes the research *** paper introduces the development and application status of CO2 refrigeration and heat pump *** researches on CO2 refrigeration and heat pump,carried out by Thermal Energy Research Institute,tianjin University,also are presented in this paper.

关键词： environmental problem natural refrigerant CO2 refrigeration heat pump

Study on the Basic Mechanical Behaviors of High Density Polyethylene Electrofusion Welded Joints at Different Temperature

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Journal of Materials Science & Technology 2003年第6期19卷 603-606页

作者： Lixing HUO, Fangjuan QI, Yufeng ZHANG, Hongyang JING and Xinqi YANGSchool of Materials Science and Engineering, tianjin University, tianjin 300072, china Sch. of Mat. Sci. and Eng. Tianjin Univ. Tianjin 300072 China

The basic mechanical behaviors of high density polyethylene electrofusion welded joint at different temperatures were studied by using differently designed specimens in this paper. The results show that the strength of weld bonding plane is higher than that of the pipe and socket materials at room temperature. In order to get the shear strength of electrofusion welded joint, the effective bond lengths were reduced by cutting artificial groove through the socket. The effective bonding length of welded joint to get the shear strength is decreased with decreasing testing temperature. The shear strength and the sensibility to sharp notch of HDPE material increased with decreasing temperature.

关键词： Basic mechanical behaviors High density polyethylene Electrofusion welded joint

New Developed Welding Electrode for Improving the Fatigue Strength of Welded Joints

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Journal of Materials Science & Technology 2002年第6期18卷 527-531页

作者： Wenxian WANG, Lixing HUO, Yufeng ZHANG, Dongpo WANG and Hongyang JINGCollege of Material Science and Engineering, tianjin University, tianjin 300072, china Coll. of Mat. Sci. and Eng. Tianjin Univ. Tianjin 300072 China

A new welding electrode, low transformation temperature electrode (LTTE), was introduced in this paper. It was described in design principle, mechanics, chemical compositions of their deposited metal and manufacturing methods. It was proved that the best transformation starting temperature from austenite to martensite of the deposited metal of LTTE was at about 191℃ and it was obtained by adding alloying elements such as Cr, Ni, Mn and Mo. The microstructure of the weld metal of the LTTE was low carbon martensite and residual austenite. The compressive residual stress was induced around the weld of the LTTE and the -145 MPa in compression could be obtained in middle of weld metal. The fatigue tests showed that the fatigue strength of the longitudinal welded joints welded with the LTTE at 2×106 cycles was improved by 59% compared with that of the same type of welded joints welded with conventional E5015 and the fatigue life was increased by 47 times at 162 MPa. It is a very valuable method to improve the fatigue performance of welded joints.

关键词： Low transformation temperature electrode Compressive residual stress Fatigue strength Welded joints

Converse Result on Szász-Type Operators

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Transactions of tianjin University 2010年第2期16卷 135-137页

作者：宋占杰 School of Sciences Tianjin University Institute of TV and Image Information Tianjin University

Szasz-type operators can be constructed by a Poisson process. The purpose of this paper is to derive the converse result in connection with Szasz-type operators by Steckin-Marchaud-type inequalities and new Ditzian mo... 详细信息

关键词： Sz^isz-type operators Poisson process Steckin-Marchaud-type inequalities continuity approximation