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The mechanism of breakdown in laminar-turbulent transition of a supersonic boundary layer on a flat plate-temporal mode

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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. {2. 2. Liu-Hui Center of Applied Mathematics, Nankai University and tianjin University, tianjin 300072. {2. 1. Department of Mechanics Tianjin University 300072 Tianjin China 2. Liu-Hui Center of Applied Mathematics Nankai University and Tianjin University 300072 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.

Influence of moisture content and time on the mechanical behavior of polymer material

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Science china(Technological Sciences) 2004年第5期47卷 595-607页

作者： ZHENG Gaofei1, 2. KANG Yilan1, SHENG Jing3, QIN Qinghua1, WANG Huaiwen1 & FU Donghui1 1. Department of Mechanics, tianjin University, tianjin 300072. {2. 2. Department of Mechanics, tianjin Polytechnic University, tianjin 300160, {2. 3. Department of Material Engineering, tianjin University, tianjin 300072. {2. Correspondence should be addressed to Kang Yilan 1. Department of Mechanics Tianjin University 300072 Tianjin China 2. Department of Mechanics Tianjin Polytechnic University 300160 Tianjin China 3. Department of Material Engineering Tianjin University 300072 Tianjin China

The effects of moisture content and time on mechanical behavior of polymer materials are investigated both theoretically and experimentally in this paper. An equivalence relationship between time intervals and the moisture content for polymer nylon-6 has been established by way of experimental observation and measured results. The relationship shows that there exists equivalence between moisture and service time in affecting mechanical properties. In other words, an increase in moisture can be replaced by prolonging acting time in producing the same effect on material properties. Consequently, a moisture-time superposition principle is presented based on the experimental results and the analogy of temperature-time superposition principle. Numerical results such as stress-strain curves with different moisture contents are presented to verify the applicability and correctness. The proposed method appears very promising in study on the effect of moisture content on mechanical behavior of polymer materials.

关键词： equivalence relationship of moisture-time, moisture content, mechanical properties, shift function.

The reliability of the improved e^N method for the transition prediction of boundary layers on a flat plate

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Science china(Physics,Mechanics & Astronomy) 2012年第5期55卷 837-843页

作者： SU CaiHong1,2.1 Department of Mechanics,tianjin University,tianjin 300072.{2. 2.tianjin Key Laboratory of Modern Engineering Mechanics,tianjin 300072.{2. 1. Department of Mechanics Tianjin University Tianjin 300072 China2. Tianjin Key Laboratory of Modern Engineering Mechanics Tianjin 300072 China

The transition criterion in the improved eN method is that transition would occur whenever the velocity amplitude of disturbance reaches 1%-2. of the free stream velocity,while in the conventional eN method,the N factor is an empirical *** this paper the reliability of this key assumption in the improved eN method is checked by results of transition prediction by using the Parabolized Stability Equations(PSE).Transition locations of an incompressible boundary layer and a hypersonic boundary layer at Mach number 6 on a flat plate are predicted by both the improved eN method and the PSE *** from both methods agree fairly well with each other,implying that the transition criterion proposed in the improved eN method is reliable.

关键词： transition prediction boundary layer eN PSE

Direct numerical simulation of a supersonic turbulent boundary layer on a flat plate and its analysis

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Science china(Physics,Mechanics & Astronomy) 2005年第5期48卷 626-640页

作者： HUANG Zhangfeng1, ZHOU Heng1,2.& LUO Jisheng1,2.1. Department of Mechanics, tianjin University, tianjin 300072. {2. 2. Liu-Hui Center of Applied Mathematics, Nankai University and tianjin University, tianjin 300072. {2. 1. Department of Mechanics Tianjin University 300072 Tianjin China 2. Liu-Hui Center of Applied Mathematics Nankai University and Tianjin University 300072 Tianjin China

Temporal mode direct numerical simulation (DNS) has been done for a supersonic turbulent boundary layer on a flat plate with Mach number 4.5. It was found that the mean flow profile, the normal-wise distribution of turbulent Mach number and the root mean square (RMS) of the fluctuations of various variables, as well as the Reynolds stresses, bore similarity in nature, when the turbulence reached a fully developed state. But the compressibility effect was strong and must be considered. The strong Reynolds analogy (SRA) and the Morkovin hypothesis were no longer valid. From the end of transition to the fully developed state of turbulence, it was in the transient period, for which the similarity did not hold.

关键词： turbulence, similarity, compressibility effect, supersonic boundary layer, direct numerical simulation.

Influence of p-layer on the performance of n-i-p μc-Si:H thin film solar cells

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Science china(Physics,Mechanics & Astronomy) 2010年第11期53卷 2042-2046页

作者： YUAN YuJie 1,2.ZHANG KaiLiang 1,2.WEI Zhen 1,2.& GENG XinHua 3 1 College of Electronics Information Engineering,tianjin University of Technology,tianjin 300384,{2. 2.tianjin Key Laboratory of Film Electronic and Communication Devices,tianjin University of Technology,tianjin 300384,{2. 3 Institute of Photo-Electronics Thin Film Devices and Technique,Nankai University,tianjin 300071,{2. 1. College of Electronics Information Engineering Tianjin University of Technology Tianjin 300384 China2. Tianjin Key Laboratory of Film Electronic and Communication Devices Tianjin University of Technology Tianjin 300384 China3. Institute of Photo-Electronics Thin Film Devices and Technique Nankai University Tianjin 300071 China

The high pressure radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) process was adopted to prepare the n-i-p microcrystalline silicon solar cells,the influence of p-type layers on the performance of the solar cells was investigated,and the optimum p layer suited to the n-i-p microcrystalline silicon solar cells was *** experimental results demonstrate that the performance of the solar cells can be highly affected by the structural and optical properties of the p-layers,and the performance of solar cells can be greatly improved by optimizing p *** have achieved an initial active-area efficiency of 8.17% (V oc =0.49 V,J sc =2..9 mA/cm 2.,FF=67%) for the μc-Si:H single-junction n-i-p solar cells and an initial active-area efficiency of 10.93% (V oc =1.31 V,J sc =13.09 mA/cm 2.,FF=64%) for the a-Si:H/μc-Si:H tandem n-i-p solar cells.

关键词： microcrystalline silicon solar cells quantum confinement effect p-type layers

Search for B_c (ns) via the B_c (ns) → B_c (ms) π^+ π^- transition at LHCb and Z^0 factory

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Science china(Physics,Mechanics & Astronomy) 2010年第11期53卷 2019-2024页

作者： KE HongWei 1 & LI XueQian 2.1 School of Science,tianjin University,tianjin 300072.{2. 2.School of Physics,Nankai University,tianjin 300071,{2. 1. School of Science Tianjin University Tianjin 300072 China2. School of Physics Nankai University Tianjin 300071 China

It is interesting to study the characteristics of the whole family of B c which contains two different heavy *** and the proposed Z 0 factory provide an opportunity because a large database of the B c family will be achieved.B c and its excited states can be identified via their decay *** suggested by experimentalists,B-c (ns) → B c +γ is not easy to be clearly measured,instead,the trajectories of π + and π- occurring in the decay of B c (ns) → B c (ms) + π + π( n > m ) can be unambiguously identified,thus the measurement seems easier and more reliable;therefore this mode is more favorable at the early running stage of LHCb and the proposed Z 0 *** this work,we calculate the rate of B c (ns) → B c (ms) + π + π-in terms of the QCD multipole-expansion and the numerical results indicate that the experimental measurements with the luminosity of LHC and Z 0 factory are feasible.

关键词： meson hadronic decay QCD multipole-expansion

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

A combined numerical model of three-dimensional tidal motion and sediment transport in tidal current and its application

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Acta Oceanologica Sinica 2000年第1期19卷 145-154页

作者： Dong Wenjun Bai Yuchuan Li Shisen (1. Department of Mathematics, tianjin University, tianjin 300072. {2. 2. Department of Hydraulics, tianjin University, tianjin 300072. {2.) Department of Mathematics Tianjin University Tianjin 300072 China Department of Hydraulics Tianjin University Tianjin 300072 China

A calculation scheme, which combines a horizontal upwind finite element method with vertical implicit differences, is used to establish a three-dimensional mathematical model of tidal motion and sediment transport in tidal current. Compared with those of the relative theoretical formula, the results are satisfactory. The model mentioned above has been applied to the water area of the Lianzhou Bay, Guangxi Province. On the basis of the analysis and comparison with the field data, it shows clearly that the model calculation results are reasonable.

关键词： Tidal current sediment transport in tidal current upwind finite element three- dimensional numerical simulation

Gymnosperms on the eve of the terminal Permian mass extinction in North china and their survival strategies

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Chinese Science Bulletin 1998年第11期43卷 889-897页

作者： WANG Ziqiang+1 and ZHANG Zhiping+2. 1. tianjin Institute of Geology and Mineral Resources, Chinese Academy of Geological Sciences, tianjin 300170, {2. 2. tianjin Centre of Physical and Chemical Techniques, tianjin 300050, {2. tianjin Institute of Geology and Mineral Resources Chinese Academy of Geological Sciences Tianjin China tianjin Centre of Phyhical and Chemical Techniques Tianjin China

Main characteristics of the Permian redbed gymnosperms in North china have been summarized: dominant peltasperms and conifers, numerous enigmatics such as Gigantonoclea and Psygmophyllum, and abundant precursors of Mesozoic gymnosperms. Furthermore, stresses affecting these plants survival are suggested to be paleoatmospheric CO-2.concentration, water stress, wind and fire activities, and fungal infection. Consequently, a preliminary analysis accounts for the ecological strategies of these gymnosperms to the P-Tr event.

关键词： North china Permian gymnosperms mass extinction.