Study of the damage-induced anisotropy of quasi-brittle materials using the component assembling model

Damage-induced anisotropy of quasi-brittle materials is investigated using component assembling model in this study. Damage-induced anisotropy is one significant character of quasi-brittle materials coupled with nonlinearity and strain softening. Formulation of such complicated phenomena is a difficult problem till now. The present model is based on the component assembling concept, where constitutive equations of materials are formed by means of assembling two kinds of components' response functions. These two kinds of components, orientational and volumetric ones, are abstracted based on pair-functional potentials and the Cauchy - Born rule. Moreover, macroscopic damage of quasi-brittle materials can be reflected by stiffness changing of orientational components, which represent grouped atomic bonds along discrete directions. Simultaneously, anisotropic characters are captured by the naturally directional property of the orientational component. Initial damage surface in the axial-shear stress space is calculated and analyzed. Furthermore, the anisotropic quasi-brittle damage behaviors of concrete under uniaxial, proportional, and nonproportional combined loading are analyzed to elucidate the utility and limitations of the present damage model. The numerical results show good agreement with the experimental data and predicted results of the classical anisotropic damage models.

Occurrence of spanning of a submarine pipeline with initial embedment

For better understanding the mechanism of the occurrence of pipeline span for a pipeline with initial embedment, physical and numerical methods are adopted in this study. Experimental observations show that there often exist three characteristic phases in the process of the partially embedded pipeline being suspended: (a) local scour around pipe; (b) onset of soil erosion beneath pipe; and (c) complete suspension of pipe. The effects of local scour on the onset of soil erosion beneath the pipe are much less than those of soil seepage failure induced by the pressure drop. Based on the above observations and analyses, the mechanism of the occurrence of pipeline spanning is analyzed numerically in view of soil seepage failure. In the numerical analyses, the current-induced pressure along the soil surface in the vicinity of the pipe (i.e. the pressure drop) is firstly obtained by solving the N-S equations, thereafter the seepage flow in the soil is calculated with the obtained pressure drop as the boundary conditions along the soil surface. Numerical results indicate that the seepage failure (or piping) may occur at the exit of the seepage path when the pressure gradient gets larger than the critical value. The numerical treatment provides a practical tool for evaluating the potentials for the occurrence of pipe span due to the soil seepage failure.

A unified guide to two opposite size effects in nano elastic materials

The microstructural variation near surface of nano elastic materials is analyzed based on different potentials. The atomic/molecular mechanism underlying the variation and its effect on elastic modulus are such that the nature of long-range interactions (attractive or repulsive) in the atomic/molecular potentials essentially governs the variation near surface (looser or tighter) and results in two opposite size effects (decreasing or increasing modulus) with decreasing size.

Mechanisms underlying two kinds of surface effects on elastic constants

ABSTRACT Recently, people are confused with two opposite variations of elastic modulus with decreasing size of nano scale sample: elastic modulus either decreases or increases with decreas- ing sample size. In this paper, based on intermolecular potentials and a one dimensional model, we provide a unified understanding of the two opposite size effects. Firstly, we analyzed the mi- crostructural variation near the surface of an fcc nanofilm based on the Lennard-Jones potential. It is found that the atomic lattice near the surface becomes looser in comparison with the bulk, indicating that atoms in the bulk are located at the balance of repulsive forces, resulting in the decrease of the elastic moduli with the decreasing thickness of the film accordingly. In addition, the decrease in moduli should be attributed to both the looser surface layer and smaller coor- dination number of surface atoms. Furthermore, it is found that both looser and tighter lattice near the surface can appear for a general pair potential and the governing mechanism should be attributed to the surplus of the nearest force to all other long range interactions in the pair po- tential. Surprisingly, the surplus can be simply expressed by a sum of the long range interactions and the sum being positive or negative determines the looser or tighter lattice near surface re- spectively. To justify this concept, we examined ZnO in terms of Buckingham potential with long range Coulomb interactions. It is found that compared to its bulk lattice, the ZnO lattice near the surface becomes tighter, indicating the atoms in the bulk located at the balance of attractive forces, owing to the long range Coulomb interaction. Correspondingly, the elastic modulus of one- dimensional ZnO chain increases with decreasing size. Finally, a kind of many-body potential for Cu was examined. In this case, the surface layer becomes tighter than the bulk and the modulus increases with deceasing size, owing to the long range repulsive pair interaction, as well as the cohesive many-body interaction caused by the electron redistribution.

The elasto-damage theory of the components assembling model

The potential energy in materials is well approximated by pair functional which is composed of pair potentials and embedding energy. During calculating material potential energy, the orientational component and the volumetric component are derived respectively from pair potentials and embedding energy. The sum of energy of all these two kinds of components is the material potential. No matter how microstructures change, damage or fracture, at the most level, they are all the changing and breaking atomic bonds. As an abstract of atomic bonds, these components change their stiffness during damaging. Material constitutive equations have been formulated by means of assembling all components' response functions. This material model is called the component assembling model. Theoretical analysis and numerical computing indicate that the proposed model has the capacity of reproducing some results satisfactorily, with the advantages of great conceptual simplicity, physical explicitness, and intrinsic induced anisotropy, etc.

适用于中等耦合等离子体的碰撞算子

完全电离等离子体中，当试探粒子分布函数fα是关于试探粒子速度vα的偶函数时，导出了一个新的动力学方程的碰撞算子．该碰撞算子同时包括了大角散射（库仑近碰撞）和小角散射（库仑远碰撞）的二体碰撞的贡献，因此，该碰撞算子同时适用于弱耦合（库仑对数ln∧≥10）和中等耦合（库仑对数2≤ln∧≤10）等离子体．而且经过修改的碰撞算子和Rosenbluth势有直接的联系，当试探粒子和场粒子满足条件mα＜mβ（如电子-离子碰撞或Lorentz气体模型）和｜vα｜〉｜vβ｜时，经约化的电子-离子碰撞算子同最初的Fokker

TWO-DIMENSIONAL ARRAY OF ION TRAPS ON A PLANAR CHIP

We investigate a planar ion chip design with a two-dimensional array of linear ion traps for the scalable quantum information processor. The segmented electrodes reside in a single plane on a substrate and a grounded metal plate, a combination of appropriate rf and DC potentials are applied to them for stable ion confinement, and the trap axes are located above the surface at a distance controlled by the electrodes' lateral extent and the substrate's height as discussed. The potential distributions are calculated using static electric field qualitatively. This architecture is conceptually simple and many current microfabrication techniques are feasible for the basic structure. It may provide a promising route for scalable quantum computers.

三峡库区岸边植物水分利用研究

随着三峡大坝建设，在2003年6月三峡库区蓄水到135 m水位，之后人为调节使其在137-139 m范围内波动变化。从2003年7月开始，我们对库区植物的水分关系及其对三峡水位上升的可能反应进行了系统研究。 在库区中残存的次生松栎混交林，我们从江边沿海拔梯度设置了3块样地：Riparian，Mid-hill和Top-hill样地，垂直高度相差约20 m。从2003年7月到2004年7月，我们比较了岸边样地内与高处两样地内植物的木质部水分稳定同位素D和18O值，植物清晨和中午水势，叶片碳稳定同位素值13C，以及2004年7月测定的气体交换。岸边 植物木质部水分同位素值显著高于江水的同位素值，而与高处两样地内植物木质部水分同位素相近。岸边植物与高 处植物具有相近的清晨水势和中午水势，也表明对岸边植物来说，江水并不是它们重要的水分来源。同样，岸边植 物叶片 13C值与高处同种植物的值也不存在显著差异。我们研究的3种植物清晨水势都与土壤含水量正相关，尤 其浅层土壤更为显著。研究结果表明岸边植物几乎没有利用江水，而同高处两样地内植物一样，都是以利用渗入到土壤中的降雨为主。 松栎混交林中，马尾松与槲栎相比，净光合速率和气孔导度，叶片含N量，以及清晨水势低于槲栎，而中午水势，叶片13C值高于槲栎。两种树木叶片13C值与含N量都成正相关关系。槲栎叶片13C值与清晨水势成负相关，而马尾松针叶13C值与清晨水势相关性并不显著。 在岸边的松栎混交幼林与成年林相比，幼树的清晨水势略高于对应的成年树，叶片13C值低于成年树;幼树的光合速率和气孔导度略高于成年树，而瞬时水分利用效率低于成年树，但差异均不显著。马尾松幼苗为实生苗，与成年树相比，更偏向于利用浅层土壤水;而槲栎幼树多为从原来被砍伐的树上萌生的，木质部水分同位素与成年树相近。 从2004年5月到10月，我们又对大坝下游江段岸边植物（马尾松，枫杨和柑桔）的水分关系进行了研究。木质部水分同位素比率表明，岸边植物木质部水分同位素比率与高处植物具相近的值，且显著高于江水同位素值。研究表明岸岸边和高处植物以降雨或靠降雨补充的浅层地下水为主要水分来源，即便岸边植物也几乎不利用江水。岸边植物与高处植物具有相近的清晨水势和中午水势，光合速率和气孔导度，以及叶片C值等，也进一步说明岸边植物与高处植物具有相近的水分生理特征。 叶片13C可以指示植物的一些生理过程，我们对松栎混交林中不同生活型植物的13C值进行了分析，乔木层叶片 13C值比较高，其中常绿针叶的值又高于落叶阔叶树木的值;林下灌木，非禾本科草本，及藤本植物的13C值都明显低于乔木层。 三峡大坝改变河水对植物生理生态过程的影响是一个长期的过程，库区水位上涨是否影响到岸边植物的生理过程及生长等，需要进一步作长期、定位和连续的观测研究。

中国红树林生态系统外来种的潜在入侵性研究

外来生物入侵已严重影响生态系统的结构和功能，威胁生物多样性，受到国内外学者的高度重视。我国50%的外来有害植物是人为引种的结果。因此，在引种造林之前对引入种的入侵潜力的研究和评估极为重要。过去几十年，中国南方地区外来的红树植物物种经常被用于人工造林，但这些外来植物的入侵性却缺乏系统的研究。本研究将个体、种群、群落和生态系统四个尺度的研究有机结合，对海南和广东两地的原产于孟加拉国的红树植物无瓣海桑(Sonneratia apetala) (1985年由申达本引入海南东寨港，1993年引种到深圳)和原产我国海南的海桑(S.caseolaris) (1993年引种到深圳)的生物学特性如种子和幼苗的扩散特性、光合生理特性、抵抗潮汐淹水特性以及本地种、外来种林下和光滩大型底栖动物的营养关系进行了综合研究，结论如下： 1． 果期长和果实种子数量大是海桑属植物的共有特点，但海南的本地种海桑不管在海南还是在引种地深圳都具有比引入种无瓣海桑更优势的萌发和漂浮能力。在没有天然海桑属植物分布的天然红树林区开展海桑属植物造林，应高度重视海桑属红树植物果实和种子的漂浮以及萌发早期的幼苗漂浮可能造成的扩散。 2． 通过对深圳福田红树林保护区实验区引种海桑和无瓣海桑幼苗的自然更新和种苗扩散的调查结果表明：海桑和无瓣海桑在深圳湾经过十几年的引种驯化之后，幼苗的更新和扩散能力逐年增高。虽然林下当年生幼苗受光强和温度等环境因子的影响在定居后大量死亡，林缘、林内空地和光滩上良好的光照条件很适合这些红树幼苗的生长。这是近年来深圳福田国家级自然保护区周边出现海桑和无瓣海桑幼苗扩散现象的主要原因。幼苗成功定居相关的机制有待进一步的研究。 3． 在海南，引种的无瓣海桑的光合速率(A)和光合N利用率(PNUE)都低于本地种海桑和白骨壤，而在深圳引种的海桑和无瓣海桑其光合速率和营养循环速度与本地种相当或低于本地种。因此，海南的外来种与本地种红树植物竞争生境的可能性不大，而深圳的外来种海桑具有较高的光合速率(A)和光合N利用率(PNUE)，和本地红树植物竞争生境的可能性依然存在。因此，海南以外的天然红树林区，引种的海桑与本地的红树植物竞争生境的可能性依然存在。 4． 无瓣海桑对潮汐淹水时间的敏感性低于海南本地种海桑，在淹水时间最长的10-12 h的淹水处理下，无瓣海桑还能通过增加茎长度、扩大叶面积来缓解厌氧胁迫和增加光合速率。因此，无瓣海桑比海桑具有更强的抗淹水能力。从叶片气体交换和养分利用的特征上来看，由于同属的海桑和无瓣海桑在天然状态下存在生态位重叠，因此，从本研究的结果看，它们对于中低潮带的生态位竞争是可能存在的。在低潮带无瓣海桑的生长较海桑有优势，因此低潮带区域很可能成为无瓣海桑与海桑竞争空间和资源的主要区域。 5． 人工海桑林的动物营养结构相对于光滩和天然白骨壤林都发生了一定的变化。人工海桑林的动物之间对于食物的竞争大于天然白骨壤林。因而，造林后的海桑人工林的营养结构的稳定性可能低于天然白骨壤林。但是，对于各种底栖动物的可能食物来源和营养关系的证明还需要进一步研究。 基于以上研究结果，本研究结论如下： 两种海桑属植物的果实、种子的数量和种苗的漂浮扩散特性都可能导致外来种幼苗在原生红树林周边的光滩和林缘空地成功定居，这一特点需要长期的监测。但是从植株的光合特性、潮汐淹水的适应性等生理生态学的证据表明：现阶段两个研究样地上的两种外来种红树植物发生生物入侵的可能性不大。但是，引种后在中、低潮位滩涂上存在外来种无瓣海桑与海南本地种海桑竞争生态位的可能性依然存在。对引种后人工生态系统的底栖动物多样性还需要进一步研究。

树突状细胞与 HIV-1 辅助蛋白相互作用的体外研究——细胞系模型研究价值的验证和新的研究方向的确立

树突状细胞（Dendritic cells，DCs）作为人类免疫缺陷病毒（Human Immunodeficiency Virus，HIV）感染的第一靶细胞和第一道防线， 在HIV-1感染 和传播过程当中发挥重要的功能。DC的免疫功能主要包括抗原的捕获、加工、 递呈并激活T细胞对HIV-1作出免疫反应，这些功能的发挥依赖于其自身接受刺 激有效地分化和成熟。 与其它慢病毒（lentivirus）相同，HIV-1所具有的6种辅助蛋白（Nef，Rev， Tat，Vif，Vpr和Vpu），决定着病毒自身的复制增殖和对机体的感染和致病力。 目前，HIV-1辅助蛋白对CD4+ T细胞影响的研究较为深入，是否影响和调节DC 的分化和成熟尚不够清楚，现有的文献报道很少，且相互不一致甚至矛盾。因此， 建立合适的体外研究体系和细胞模型，有针对性地进行研究DC与HIV-1之间的相 互作用，将有助于加深对HIV/AIDS致病和发病机理的理解，具有重要的生物医 学意义。 本实验选择了可被HIV-1感染的白血病细胞系THP-1为实验模型，首先评价 了THP-1作为DC前体在研究DC分化、成熟中的可用性，特别是判定DC分化成熟 和功能状态的主要细胞表面标记的动态变化和规律。进而在相同条件下分析了6 个辅助蛋白基因对THP-1的凋亡诱导作用，证实了Nef和Tat确可诱导转染细胞自 身凋亡，而Rev和Vpr可在THP-1细胞中持续表达，形成了稳定的细胞系，为进一 步研究和比较Rev、Vpr对DC的分化、成熟的影响奠定了实验基础。更重要的是， 我们发现，Vif和Vpu不能在THP-1中有效表达，其原因可能直接与限制性因子 APOBEC3G的存在有关，提示Vpu与APOBEC3G可能存在着新的相互作用——这 一线索已作为实验室新的研究方向，进一步深入的研究可能为HIV/AIDS致病、 发病机理和机体的抗病机制提供新的科学依据。

The influence of Mozart's sonata K.448 on visual attention: An ERPs study

In the present study, the effects of Mozart's sonata K.448 on voluntary and involuntary attention were investigated by recording and analyzing behavioral and event-related potentials (ERPs) data in a three-stimulus visual oddball task. P3a (related to inv

Different masking effects on "hole" and "no-hole" figures

Global information is considered the primitive of visual perception in Gestalt psychology. Further, L. Chen ( 2005) proposed a new theory of topological visual perception. According to this theory, the perception of topological difference is faster than o

Characterization of acid-sensing ion channels in dorsal horn neurons of rat spinal cord

Acid-sensing ion channels (ASICs) are ligand-gated cation channels activated by extracellular protons. In periphery, they contribute to sensory transmission, including that of nociception and pain. Here we characterized ASIC-like currents in dorsal horn neurons of the rat spinal cord and their functional modulation in pathological conditions. Reverse transcriptase-nested PCR and Western blotting showed that three ASIC isoforms, ASIC1a, ASIC2a, and ASIC2b, are expressed at a high level in dorsal horn neurons. Electrophysiological and pharmacological properties of the proton-gated currents suggest that homomeric ASIC1a and/or heteromeric ASIC1a + 2b channels are responsible for the proton-induced currents in the majority of dorsal horn neurons. Acidification-induced action potentials in these neurons were compatible in a pH-dependent manner with the pH dependence of ASIC-like current. Furthermore, peripheral complete Freund's adjuvant-induced inflammation resulted in increased expression of both ASIC1a and ASIC2a in dorsal horn. These results support the idea that the ASICs of dorsal horn neurons participate in central sensory transmission/modulation under physiological conditions and may play important roles in inflammation-related persistent pain.

Phosphorus in interstitial water induced by redox potential in sediment of Dianchi Lake, China

The sediment redox potential was raised in the laboratory to estimate reduction of internal available phosphorus loads, such as soluble reactive phosphorus (SRP) and total phosphorus (TP), as well as the main elements of sediment extracts in Dianchi Lake. Several strongly reducing substances in sediments, which mainly originated from anaerobic decomposition of primary producer residues, were responsible for the lower redox potential. In a range of -400 to 200 mV raising the redox potential of sediments decreased TP and SRP in interstitial water. Redox potentials exceeding 320 mV caused increases in TP, whereas SRP maintained a relatively constant minimum level. The concentrations of Al, Fe, Ca2+, Mg2+, K+, Na+ and S in interstitial water were also related to the redox potential of sediments, suggesting that the mechanism for redox potential to regulate the concentration of phosphorus in interstitial water was complex.