Molecular dynamics studies on the dislocation gliding near a tilt boundary

The gliding behavior of edge dislocation near a grain boundary(QB) in copper under pure shear stresses is simulated by using molecular dynamics(MD) method. Many-body potential incorporating the embedded atom method (EAM) is used. The critical shear stresses for a single disocation to pass across GB surface are obtained at values of sigma(c)=23MPa similar to 68 MPa and 137 MPa similar to 274 MPa for Sigma=165 small angle tilt GB at 300 K and 20 K, respectively. The first result agrees with the experimental yield stress sigma(y)(=42 MPa) quite well. It suggests that there might be one of the reasons of initial plastic yielding caused by single dislocation gliding across GB. In addition, there might be possibility to obtain yield strength from microscopic analysis. Moreover, the experimental value of sigma(y) at low temperature is generally higher than that at room temperature. So, these results are in conformity qualitatively with experimental fact. On the other hand, the Sigma=25 GB is too strong an obstacle to the dislocation. In this case, a dislocation is able to pass across GB under relatively low stress only when it is driven by other dislocations. This is taken to mean that dislocation pile-up must be built up in front of this kind of GB, if this GB may take effect on the process of plastic deformation.

激光诱发活塞的热负荷

活塞的热疲劳性能对柴油发动机的全寿命至关重要。由于能量有限和可控性差等缺点，现有实验系统均不能满意地进行活塞热负荷模拟实验。为此，提出并建立了一套激光诱发活塞热负荷的实验系统。该系统通过对激光束的空间整形，使之投射到活塞表面后诱发的温度场分布满足特定要求。基于PROFIBUS-DP现场总线技术实现了系统集成和实验过程的全反馈控制。针对活塞的典型热负荷条件，即高周热疲劳和热冲击分别进行实验，以模拟正常工作循环和“启动一停车”等热负荷或转速突变工况。通过设置加热一冷却周期或上限下限温度，可以获得相应的热负荷模拟实验效果。研究结果表明，采用经光束整形的激光进行活塞热负荷模拟实验具有周期短、可控性好等优点。 

Forced Dissociation of Selectin-ligand Complexes Using Steered Molecular Dynamics Simulation

Selectin-ligand interactions are crucial to such biological processes as inflammatory cascade or tumor metastasis. How transient formation and dissociation of selectin-ligand bonds in blood flow are coupled to molecular conformation at atomic level, however, has not been well understood. In this study, steered molecular dynamics (SMD) simulations were used to elucidate the intramolecular and intermolecular conformational evolutions involved in forced dissociation of three selectin-ligand systems: the construct consisting of P-selectin lectin (Lec) and epidermal growth factor (EGF)-like domains (P-LE) interacting with synthesized sulfoglycopeptide or SGP-3, P-LE with sialyl Lewis X (sLeX), and E-LE with sLeX. SMD simulations were based on newly built-up force field parameters including carbohydrate units and sulfated tyrosine(s) using an analogy approach. The simulations demonstrated that the complex dissociation was coupled to the molecular extension. While the intramolecular unraveling in P-LESGP-3 system mainly resulted from the destroy of the two anti-parallel sheets of EGF domain and the breakage of hydrogen-bond cluster at the Lec-EGF interface, the intermolecular dissociation was mainly determined by separation of fucose (FUC) from Ca2+ ion in all three systems. Conformational changes during forced dissociations depended on pulling velocities and forces, as well as on how the force was applied. This work provides an insight into better understanding of conformational changes and adhesive functionality of selectin-ligand interactions under external forces.

Digitized Processing Track Generation of a Computer Integrated Multi-Functional 5-Axis Laser Processing System

Based on the computer integrated and flexible laser processing system, an intelligent measuring sub-system was developed. A novel model has been built up to compensate the deviations of the main frame-structure, and a new 3-D laser tracker system is applied to adjust the accuracy of the system. To analyze the characteristic of all kind surfaces of automobile outer penal moulds and dies, classification of types of the surface、brim and ridge(or vale) area to be measured and processed has been established, resulting in one of the main processing functions of the laser processing system. According to different type of surfaces, a 2-D adaptive measuring method based on B?zier curve was developed; furthermore a 3-D adaptive measuring method based on Spline curve was also developed. According to the laser materials processing characteristics and data characteristics, necessary methods have been developed to generate processing tracks, they are explained in details. Measuring experiments and laser processing experiments were carried out to testify the above mentioned methods, which have been applied in the computer integrated and flexible laser processing system developed by the Institute of Mechanics, CAS.

Experimental Study on the Ignition Process of Single Coal Particles at Microgravity

In this paper, the first Chinese microgravity (μ-g) experimental study on coal combustion was introduced. An experimental system used to study the ignition process of single coal particles was built up, complying with the requirements of the 3.5 s drop tower in the National Microgravity Laboratory of China (NMLC). High volatile bituminous and lignite coal particles with diameter of 1.5 and 2.0 mm were tested. The ignition and combustion process was recorded by a color CCD and the particle surface temperature before and at the ignition was determined by the RGB colorimetric method. Comparative experiments were conducted at normal gravity (1-g). The experiments revealed that at different gravity levels, the ignition of all tested coal particles commenced in homogeneous phase, while the shape, structure, brightness and development of the flames, as well as the volatile matter release during the ignition process are different. At μ-g, the part of volatile was released as a jet, while such a phenomenon was barely observed at 1-g. Also, after ignition, flames were more spherical, thicker, laminated and dimmer at μ-g. It was confirmed that ignition temperature decreased as the particle size or volatile content increased. However, contradicted to existing experimental results, provided other experimental conditions except gravity level were the same, ignition temperature of coal particles was about 50–80 K lower at μ-g than that at 1-g.

A molecular model of braid-like DNA structure

The three-dimensional molecular models of DNA triple helices and triple-stranded brain-like structure were built up by molecular architecture, and their structural features and energy decomposition were examined. The results showed: (i) The base triplet is the element forming braid-like and triple helix DNA; (ii) Under specified conditions, DNA could form the triplet-stranded braid-like structure; (iii) DNA stability of the braid-like structure is less than that of the triple helix structure. (C) 1995 Academic Press Limited.

Comparative studies on parallel and antiparallel duplex and triplex DNA

Parallel strand models for base sequences d(A)(10). d(T)(10), d(AT)(5) . d(TA)(5), d(G(5)C(5)). d(C(5)G(5)), d(GC)(5) . d(CG)(5) and d(CTATAGGGAT). d(GATATCCCTA), where reverse Watson-Crick A-T pairing with two H-bonds and reverse Watson-Crick G-C pairing with one H-bond or with two H-bonds were adopted, and three models of d(T)(14). d(A)(14). d(T)(14) triple helix with different strand orientations were built up by molecular architecture and energy minimization. Comparisons of parallel duplex models with their corresponding B-DNA models and comparisons among the three triple helices showed: (i) conformational energies of parallel AT duplex models were a little lower, while for GC duplex models they were about 8% higher than that of their corresponding B-DNA models; (ii) the energy differences between parallel and B-type duplex models and among the three triple helices arose mainly from base stacking energies, especially for GC base pairing; (iii) the parallel duplexes with one H-bond G-C pairs were less stable than those with two H-bonds G-C pairs. The present paper includes a brief discussion about the effect of base stacking and base sequences on DNA conformations. (C) 1997 Academic Press Limited.

Analysis of the energies of the triple base triplets

Sixty-four sets of three-dimensional models of DNA triplex base triplets (TBT) were built up based on codons by homologous modeling method and their energies were minimized. According to sequence of TBT and orientation of the third ODN strand third, the energies of monomers and water-K+-TBT ternary complexes of TBT were analyzed. The results showed: (i) The energies of the symmetric parallel monomers are generally lower than those of the symmetric anti-parallel monomers of TBT, but the energies of the symmetric parallel ternary complexes are higher than those of the symmetric anti-parallel ternary complexes of TBT. (ii) No matter TBTs are monomers or ternary complexes, the energies of asymmetric parallel TBTs are generally lower than those of the asymmetric anti-parallel ones. (iii) Although the energies of the parallel TBTs are correlated with those of the anti-parallel ones, the energy differences are significant between them. The results here suggest the sequences of TBTs and the orientations of the third ODN strands are two of the key factors that can influence the formation and stability of TBT. (C) 2002 Elsevier Science B.V. All rights reserved.

Crosstalk analysis of a fiber laser sensor array system based on digital phase-generated carrier scheme

A detailed study on analyzing the crosstalk in a wavelength division multiplexed fiber laser sensor array system based on a digital phase generated carrier interferometric interrogation scheme is reported. The crosstalk effects induced by the limited optical channel isolation of a dense wavelength division demultiplexer (DWDM) are presented, and the necessary channel isolation to keep the crosstalk negligible to the output signal was calculated via Bessel function expansion and demonstrated by a two serial fiber laser sensors system. Finally, a three-element fiber laser sensor array system with a 50-dB channel-isolation DWDM was built up. Experimental results demonstrated that there was no measurable crosstalk between the output channels.

沈阳城市森林结构与净化生态效益研究

城市森林的结构和功能一直是城市森林生态学研究的一个重要内容。但至今仍缺乏一种有效的结构分析及效益量化手段，尤其是生态效益价值的量化比较困难，缺乏具体的数量指标。本研究以沈阳建成区为研究对象，第一次将目前国际上通用的CITYgreen模型应用到中国城市的森林结构及效益评价研究中，是一种方法上的突破。以CITYgreen3.0版本为基本运行界面，采用林业调查与GIS技术相结合的方法，对沈阳市建成区（二环以内）城市森林结构及净化生态效益进行了量化分析，得到如下主要结论：（1）城市森林组成成分单一，单一成分优势过于明显（2）城市森林结构在树木个体数量上以低矮、小胸径树木为骨架，整体健康水平低（3）城市森林分布不均、布局不合理（4）绿化状况较从前有显著提高，现有城市森林将在10年后开始逐渐发展为相对合理的结构布局（5）对不同污染物的净化效应有明显的区别，SO2的吸收量严重不足（6）CITYgreen模型是一种有效的效益量化工具，经过修改的模型适合于中国城市森林。

基于ITS 序列和matK 基因序列的中国药用石斛及其混伪品的分子鉴定

为了从分子水平对中国药用石斛及其混伪品进行鉴定，本文选取了核rDNA ITS 序列和叶绿体DNA 的matK 基因序列进行研究。采用改良的CTAB 法提取石斛的基因组DNA，PCR 产物直接测序法对17 种（共32 份）药用石斛的核糖体内转录间隔区ITS 全序列进行测定，克隆测序法对12 种（共22 份）药用石斛的叶绿体的matK 基因序列进行测定，运用BioEd it，MEGA4.0 等生物软件分析了石斛属植物的rDNA ITS 序列及叶绿体的matK 基因序列的特征，比较了石斛属间、种间、种内不同居群（品种）间的序列碱基差异及遗传距离，应用邻接法构建分子系统树。主要研究结果如下： （1）建立了17 种（共32 份）药用石斛rDNA ITS 区碱基全序列数据库，其中，ITS1 的长度为228~234 bp，GC 含量为45.7%~53.0%，变异位点167 个，占总位点67.34%，信息位点106 个，占总位点42.74%，ITS2 长度为241~247 bp，GC含量为44.8%~55.7%，变异位点165 个，占总位点66.27%，信息位点115 个，占总位点46.18%。 （2）建立了12 种（共22 份）药用石斛的叶绿体matK 基因全序列数据库，叶绿体matK 基因长1410 bp，变异位点51 个，信息位点11 个。除了存在碱基替换的遗传变异外，还存在碱基的插入和缺失。 （3）通过ITS 序列比较分析了各材料间的遗传距离和碱基差异，属间的遗传距离为0.295，石斛种间的平均遗传距离为0.142，碱基相差2~156 个，种内各居群间的平均遗传距离为0.002，碱基相差1~2 个。属间的遗传距离大于种间的遗传距离，种间的遗传距离大于种内不同居群（品种）间的遗传距离。 （4）根据分析石斛叶绿体的matK 基因序列得到，外类群（密花石豆兰）与石斛属间最小遗传距离为0.027，石斛种间的平均遗传距离为0.008，种间最大的遗传距离0.014， 最小的遗传距离为0.003，碱基相差8~20 个。种内不同居群（品种）遗传距离为0.001，相差1~5 个碱基。 （5）利用17 种石斛的全序列数据库及遗传分析软件，通过对待检种rDNA I TS区进行序列测定，成功地对10 个待检种进行了鉴定，并且在原植物开花后得到了验证。 （6）运用12 种石斛的matK 基因全序列数据库及遗传分析软件，成功地对4个待检种进行了鉴定，同样在原植物开花后得到了验证。 （7）本文利用石斛的核糖体内转录间隔区ITS 序列和叶绿体的matK 基因序列数据库分别构建了NJ 树，外类群与石斛属间石斛种间以及种内不同居群（品种）间均能在NJ 树中明显分化开来，二者构建的分子系统树一致，为石斛的分子鉴定提供了依据。 In order to identify Chinese Herba Dendrobii and its adulterant species on molecular level, we studied the sequences of rDNA ITS and chloroplast matK gene. Genomic DNA of Dendrobium was extracted using the modified cetyltrimethyl ammonium bromide (CTAB) method. The PCR products of the rDNA ITS sequences of Dendrobium (32 materia ls) were purified and then sequenced. The PCR products of chloroplast matK gene of Dendrobium (22 materia ls) were purified, cloned and then sequenced. The characteristic of the sequences and the genetic dista nce were compared between Bulbophyllum odoratissimum and Dendrobium, Dendrobium interspecies, and different populations. Phylogenetic trees were constructed using the NJ method by the biology softwares including BioEd it, MEGA4.0 etc. The ma in results as follows: (1) It was built up that the database of rDNA ITS sequences of 17 species of Herba Dendrobii (32 materia ls). The ITS1 was 228~234 bp, the GC content accounting for 45.7%~53.0%. Its variable sites were 167, accounting for 67.34%. The Parsim-Informative positions were 106, accounting for 42.74%. The ITS2 was 241~247 bp, the GC accounting for 44.8%~55.7%. The variable sites were 165, accounting for 66.27%. The Parsim-Informative positions were 115, accounting for 46.18%. (2) The database of the chloroplast matK gene sequences was built up, which contained 12 species of Herba Dendrobii (22 materia ls). The matK gene sequences were about 1410bp in length. There were 51 variable sites and 11 Parsim-Informative sites. And there were nucleotides insertions and deletions in some species , in addition to the nucleotides substitutions. (3) The rDNA ITS sequences were compared and analyzed by the biology softwares. The genetic dista nce between Bulbophyllum odoratissimum and Dendrobium was 0.295. The avera ge genetic dista nce was 0.142 between Dendrobium species, and there were 2~156 variable nucleotides. The avera ge genetic dista nce between different populations was 0.002, and there were 2~156 variable nucleotides. The genetic dista nce between Bulbophyllum odoratissimum and Dendrobium was greater tha n that of Denrobium interspecies. Meanwhile, the genetic dista nce between Denrobium species was also greater tha n that of different populations (variaties). (4) The characteristics of the chloroplast matK gene sequences were obtained after analyzing by the biology softwares. The minima l genetic dista nce was 0.027 between Bulbophyllum odoratissimum and Dendrobium . The ma xima l genetic dista nce was 0.014 between Dendrobium species, and there were 20 variable nucleotides. The minima l genetic dista nce between populations was 0.003, and there were 8 variable nucleotides.The genetic dista nce between populations was 0.001, and there were 1~5 variable nucleotides. (5) The molecular Phylogeny tree was constructed on the database of rDNA ITS the sequences of 17 species of Herba Dendrobii using the biology softwares. Then we authenticated 10 materia ls on molecular level. What’s more, they had been proved when these pla nts flowered. (6) The molecular Phylogeny tree was built up on the database of chloroplast matK gene sequences of 12 species of Herba Dendrobii with the biology softwares.Then 4 materia ls were authenticated on molecular level. Moreover, they had also been proved when these pla nts were in flower. (7) The Phylogenetic trees were separately constructed on the sequences of rDNA ITS and chloroplast matK gene B. odoratissimum and Dendrobium all could be distinguished on the Phylogenetic trees. Meanwhile, the Phylogenetic trees based on two groups of sequences were coincident. rDNA ITS and matK gene sequence could be used as molecular markers for authentication of Herba Dendrobii.

沈阳市建成区行道树的结构与功能研究

In the case of Shenyang, the structure and function of street trees in built-up area was studied. With the typical method of community sampling survey, the relative quantitative index, vertical distribution,and horizontal distribution were analysed. With CITY GREEN software, we analyzed the benefits of pollutants removal, and achieved some quantitative result. The results showed that the structure and function of street trees in Shenyang is becoming simple gradually. The regional difference is obvious and the benefits are not in balance, caused by unreasonable structure.

Spatial patterns and driving forces of land use change in China during the early 21st century

Land use and land cover change as the core of coupled human-environment systems has become a potential field of land change science (LCS) in the study of global environmental change. Based on remotely sensed data of land use change with a spatial resolution of 1 km x 1 km on national scale among every 5 years, this paper designed a new dynamic regionalization according to the comprehensive characteristics of land use change including regional differentiation, physical, economic, and macro-policy factors as well. Spatial pattern of land use change and its driving forces were investigated in China in the early 21st century. To sum up, land use change pattern of this period was characterized by rapid changes in the whole country. Over the agricultural zones, e.g., Huang-Huai-Hai Plain, the southeast coastal areas and Sichuan Basin, a great proportion of fine arable land were engrossed owing to considerable expansion of the built-up and residential areas, resulting in decrease of paddy land area in southern China. The development of oasis agriculture in Northwest China and the reclamation in Northeast China led to a slight increase in arable land area in northern China. Due to the "Grain for Green" policy, forest area was significantly increased in the middle and western developing regions, where the vegetation coverage was substantially enlarged, likewise. This paper argued the main driving forces as the implementation of the strategy on land use and regional development, such as policies of "Western Development", "Revitalization of Northeast", coupled with rapidly economic development during this period.

Impacts of LUCC processes on potential land productivity in China in the 1990s

Using meteorological data and RS dynamic land-use observation data set, the potential land productivity that is limited by solar radiation and temperature is estimated and the impacts of recent LUCC processes on it are analyzed in this paper. The results show that the influence of LUCC processes on potential land productivity change has extensive and unbalanced characteristics. It generally reduces the productivity in South China and increases it in North China, and the overall effect is increasing the total productivity by 26.22 million tons. The farmland reclamation and original farmlands losses are the primary causes that led potential land productivity to change. The reclamation mostly distributed in arable-pasture and arable-forest transitional zones and oasises in northwestern China has made total productivity increase by 83.35 million tons, accounting for 3.50% of the overall output. The losses of original farmlands driven by built-up areas invading and occupying arable land are mostly distributed in the regions which have rapid economic development, e.g. Huang-Huai-Hai plain, Yangtze River delta, Zhujiang delta, central part of Gansu, southeast coastal region, southeast of Sichuan Basin and Urumqi-Shihezi. It has led the total productivity to decrease 57.13 million tons, which is 2.40% of the overall output.

Study on spatial pattern of land-use change in China during 1995-2000

It is more and more acknowledged that land-use/cover dynamic change has become a key subject urgently to be dealt with in the study of global environmental change. Supported by the Landsat TM digital images, spatial patterns and temporal variation of land-use change during 1995 -2000 are studied in the paper. According to the land-use dynamic degree model, supported by the 1km GRID data of land-use change and the comprehensive characters of physical, economic and social features, a dynamic regionalization of land-use change is designed to disclose the spatial pattern of land-use change processes. Generally speaking, in the traditional agricultural zones, e.g., Huang-Huai-Hai Plains, Yangtze River Delta and Sichuan Basin, the built-up and residential areas occupy a great proportion of arable land, and in the interlock area of farming and pasturing of northern China and the oases agricultural zones, the reclamation I of arable land is conspicuously driven by changes of production conditions, economic benefits and climatic conditions. The implementation of "returning arable land into woodland or grassland" policies has won initial success in some areas, but it is too early to say that the trend of deforestation has been effectively reversed across China. In this paper, the division of dynamic regionalization of land-use change is designed, for the sake of revealing the temporal and spatial features of land-use change and laying the foundation for the study of regional scale land-use changes. Moreover, an integrated study, including studies of spatial pattern and temporal process of land-use change, is carried out in this paper, which is an interesting try on the comparative studies of spatial pattern on change process and the change process of spatial pattern of land-use change.