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Disassembly intermediates of RbsD protein remain oligomeric despite the loss of an intact secondary structure

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Science China(Life Sciences) 2009年第11期52卷 997-1002页

作者： FENG YongJun1, ZHANG Meng2. HU MingXi1, ZHENG Jie1, JIAO WangWang2.& CHANG ZengYi2.1 school of Life Science, beijing institute of technology, {2., China 2.school of Life Sciences, National Laboratory of Protein engineering and Plant Genetic engineering, Center for Protein Science, Peking University, beijing 100871, China school of Life Science Beijing Institute of Technology Beijing Chin

Many proteins exist as homo-oligomers in living organisms wherein the change of oligomeric status apparently serves as an effective means for modulating their biological activities. We have previously reported that the homo-decameric RbsD from Escherichia coli undergoes stepwise disassembly and non-stepwise reassembly. Here the structural status of the urea-induced RbsD disassembly intermediates was examined, mainly using urea-containing polyacrylamide gel electrophoresis and chemical cross-linking. Such intermediates were found to remain oligomeric while losing their intact secondary structures. Such disassembly intermediates were able to effectively refold when the concentration of the urea denaturant was reduced to a lower level, or to refold/reassemble into the native decamers when urea was completely removed, as detected by non-denaturing polyacrylamide gel electrophoresis. These novel observations strongly suggest that the assembly of oligomeric proteins may occur before the completion of subunit folding.

关键词： RbsD oligomeric protein oligomeric intermediate refolding reassembly

AFM study on the adsorption and aggregation behavior of dissolved humic substances on mica

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Science China Chemistry 2006年第3期49卷 256-266页

作者： GE Xiaopeng1, ZHOU Yanmei2. Lü Chunhua1 & TANG Hongxiao1 1. State Key Laboratory of environmental Aquatic Chemistry, Research Center for Eco-environmental Sciences, Chinese Academy of Sciences, {2. 100085, China 2. school of Civil engineering & Architecture, {2. Jiaotong University, {2. 100044, China State Key Laboratory of environmental Aquatic Chemistry Research Center for Eco-Environmental Sciences Chinese Academy of Sciences Beijing China school of Civil engineering & Architecture Beijing Jiaotong University Beijing China

Humic substances constitute the major organic fractions of soils, sediments and natural waters, and play a dominant role in the binding, mobilization, transport and ultimate fate of organic contaminants in subsurface systems. In this paper, two humic acid samples, Guanting and Tianjin, with different origin and chemical compositions have been investigated with AFM imaging for their adsorption and aggregation behaviors on mica. While the Tianjin humic sample is found to form small spheres with 2.0 to 330 nm in diameter at lower concentrations, irregular loop-chain assemblies of hundreds of nanometer in diameter with the chain width of about 40 nm are dominant for the Guanting humic sample, which may attribute to the more polar aliphatic fractions in the chemical composition in the latter. The heterogeneous and polydisperse nature of humic substances with multiple structural features, such as sponge-like structures, perforated sheets, aggregate of spheres, branches and chain-like assemblies etc., is apparent at higher concentrations for both humic samples, showing morphologically new evidence for the dominant view of the humic dual-mode sorption model. With naphthalene introduced, the assemblies of Guanting humic substances clearly become more compact with significantly narrowed branches and less porous the perforated sheet-like structures. It is indica- tive of that smaller nanometer scale rings present along the perforated assemblies could potentially represent hydrophobic domains, which may facilitate the adsorption and aggregation of naphthalene onto the natural particle surfaces and therefore lead to an important role of dissolved humic sub- stances in the sorption of {2.al pollutants.

关键词： atomic force microscopy (AFM) dissolved humic substances morphology aggregation adsorption

Preparation and High Temperature Oxidation Properties of Micro-crystalline MGH754 ODS Alloy Coatings

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Journal of University of Science and technology beijing 2001年第1期8卷 28-34页

作者： Huibub Qi Hongmei Pang Yedong He Deren Wang Wei Gao Material Seience and engineering school, University of Science and {2. beijing, beijing 100083, China Department of chemical and Material Engineeing, the University of Auckland, New Zealand Material Science/engineering school Univ. of Science/Technology Beijing Beijing 100083 China

A special coating technique, electro-spark deposition (ESD), was developed to produce micro-crystalline ODS MGH754 alloy coatings on a commercial 1Cr18Ni9Ti stainless steel and a cast Ni2.Cr alloy substrates. The coatings have a very fine grain structure and metallurgical bonding with the substrates. The isothermal oxidation tests at 1000 degreesC in air showed that the micro-crystalline ODS alloy coatings had a much reduced oxidation rate and improved scale spallation resistance compared with the uncoated alloys. The selective oxidation of Cr was greatly promoted to form protective and continuous Cr2.3 scales on the alloy surface. Micro-crystallization and oxide dispersions have synergistic effects on the improvement of oxidation resistance. The beneficial effects were discussed based on the experimental results.

关键词： electro-spark deposition (ESD) ODS coating oxidation

ANALYSIS OF THE DEFLECTION OF REEDS IN AUTOMOTIVE HYDRAULIC SHOCK ABSORBERS

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Chinese Journal of Mechanical engineering 2000年第3期13卷 241-244页

作者： Chen Yong,Sun Fengchun (school of Vehicular engineering, {2.) Wang Ying, Zhang Jianrong (Taiyuan Heavy Machinery institute Liaoning institute of technology) 北京理工大学北京太原重型机械学院山西辽宁工学院辽宁锦州

The deformation of reeds in automotive hydraulic shock absorbers is analyzed with the finite element method. Combination of different thick reeds mounted on different supports is studied. The computational results show that deformation of the overlapped reeds is not always equal to the sum of deflection of single reed under any conditions. Experimental results prove computational results to be correct and computational method effective. The method of analysis and view of point can provide reference to the design and manufacture of hydraulic shock absorbers using reeds.

关键词： Hydraulic shock absorber Reed Finite element method

Effect of welding speed on the material flow patterns in friction stir welding of AZ31 magnesium alloy

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Rare Metals 2007年第2期26卷 158-162页

作者： ZHANG Hua Wu Huiqiang Huang Jihua LIN Sanbao WU Lin Materials Science and engineering school University of Science and Technology Beijing Beijing 100083 China beijing institute of Astronautical Systems {2. Beijing 100076 China State Key Lab of Advanced Welding Production technology Harbin Institute of Technology Harbin 150001 China

The clear zigzag-line pattern on transverse cross sections can be used to explain the formation mechanism of the weld nugget when friction stir welded AZ31 magnesium alloy without any other insert material is used as mark. It provides a simple and useful method to research the joining mechanism of friction stir welding. The rotation speed is kept at 1000 r/min and the welding speed changes from 12. mm/min to 600 mm/min. The macrostructure on the transverse cross section was divided into several parts by faying surface. The results show that the shape and formation procedure of the weld nugget change with the welding speed. There are two main material flows in the weld nugget： one is from the advancing side and the other is from the retreating side. A simple model on the weld nugget formation of FSW is presented in this article.

关键词： AZ31 magnesium alloy friction stir welding faying surface materials flow formation model

Modified HDDR Process for Producing Anisotropic NdFeB Powders

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Journal of University of Science and technology beijing 2001年第2期8卷 111-114页

作者： Xubo Liu, Yue Ming, Yaofu Xiao, Qi Zeng, Zhengyi Zhang, Run Wang (Material Science and engineering school, University of Science and {2. beijing, beijing 100083, China) (beijing institute of Aeronautical Materials, beijing 100095, China) Material Sci. and engineering school University of Science and Technology Beijing 100083 China

The effect of HDDR (hydrogenation-decomposition-desorption-recombination process) treating conditions on magnetic anisotropy of Nd13FebalCo17B7Ga1Zr0.1 powders has been studied. It is found that increasing recombination temperature is effective for magnetic anisotropy formation, but at the cost of reducing the coercive force. The microstructure analysis (TEM) indicates that the NdFeB recombination nucleation takes place markedly during the transition range from decomposition stage to recombination stage, in which both temperature and H-2.pressure change sharply. In order to create a more stable treatment condition for recombination nucleation, a modified HDDR process is established in which the conventional continuous transition range is divided into several stages. The experimental results have proved that such a process can effectively enhance the remanence of the magnet powders with high certainty, while only cause a little reduction in coercivity.

关键词： HDDR anisotropy NdFeB

The influence of defects on the effective Young's modulus of a defective solid

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Chinese Physics B 2013年第4期22卷 307-311页

作者：沈伟范群波王富耻马壮 Central Iron and Steel Research institute school of Materials Science and engineering Beijing Institute of Technology

It is difficult to establish structure-property relationships in a defective solid because of its inhomogeneous-geometry microstructure caused by defects. In the present research, the effects of pores and cracks on the Young’s modulus of a defective solid are studied. Based on the law of the conservation of energy, mathematical formulations are proposed to indicate how the shape, size, and distribution of defects affect the effective Young’s modulus. In this approach, detailed equations are illustrated to represent the shape and size of defects on the effective Young’s modulus. Different from the results obtained from the traditional empirical analyses, mixture law or statistical method, for the first time, our results from the finite element method （FEM） and strict analytical calculation show that the influence of pore radius and crack length on the effective Young’s modulus can be quantified. It is found that the longest crack in a typical microstructure of ceramic coating dominates the contribution of the effective Young’s modulus in the vertical direction of the crack.

关键词： defects effective Young’s modulus conservation of energy pore radius and crack length

Debating about the climate warming

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Progress in Natural Science:Materials International 2006年第1期16卷 1-6页

作者： WANG Shaowu1, LUO Yong2. ZHAO Zongci2. DONG Wenje2.and YANG Bao3 (1.Department of Atmospheric Sciences, school of Physics, Peking University, beijing 100871, China 2. Laboratory for Climate Studies, China Meteorological Administration, {2., China 3. institute of Cold and Arid Regions environmental and engineering, Chinese Academy of Sciences, Lanzhou 730000, China) Department of Atmospheric Sciences School of Physics Peking University Beijing 100871 China

Debating about the climate warming is reviewed. Discussions have focused on the validity of the temperature reconstruction for the last millennium made by Mann et al. Arguments against and for the reconstruction are introduced. Temperature reconstructions by other authors are examined, including the one carried out by Wang et al. in 1996. It is concluded that: (1) Ability of reproducing temperature variability of time scale less than 10 a is limited, so no sufficient evidence proves that the 1990s was the warmest decade, and 1998 was the warmest year over the last millennium. (2. All of the temperature reconstructions by different authors demonstrate the occurrence of the MWP (Medieval Warm Period) and LIA (Little Ice Age) in low frequency band of temperature variations, though the peak in the MWP and trough in LIA varies from one reconstruction to the others. Therefore, terms of MWP and LIA can be used in studies of climate change. (3) The warming from 1975 to 2.00 was significant, but we do not know if it was the strongest for the last millennium, which needs to be proved by more evidence.

关键词： climate warming MWP LIA the 2.th century.

A New Method for Fractal Dimension Determination by STM at Nanometer Scale

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International Journal of Minerals,Metallurgy and Materials 1999年第1期13卷 64-68页

作者： Qikai Li Yue Zhang Wuyang Chu Chen Wang Chunli Bai (Applied Science school. University of Science and technology {2., {2. 100083. China)(chemical institute, Chinese Academy of Science, {2. 100080. China) Applied Science school University of Science and Technology Beijing Beijing 100083 China chemical institute Chinese Academy of Science Beijing 100080 China

A new method for determining the fractal dimension by STM at nanomeler scale has been ***- Mandelbrot fractal curves were used to verify the accuracy and reliability. The Computer simulation showed that fractal dimen- sion obtained with this method generally outran the traditional yard method. The new method has been applied to the fractal dimension determination of the fractures of Ti3Al and Ti-2.Al-11Nb alloys. The results show that the fractal dimension of Ti-2.Al-11Nb alloy is higher than that of Ti3Al, and it varies with the crark extending orientation.

关键词： fractal dimension STM nanometer scale Ti-Al alloy