Crystal structure of spinach major light-harvesting complex at 2.72 A resolution

The major light-harvesting complex of photosystem II (LHC-II) serves as the principal solar energy collector in the photosynthesis of green plants and presumably also functions in photoprotection under high-light conditions. Here we report the first X-ray structure of LHC-II in icosahedral proteoliposome assembly at atomic detail. One asymmetric unit of a large R32 unit cell contains ten LHC-II monomers. The 14 chlorophylls (Chl) in each monomer can be unambiguously distinguished as eight Chla and six Chlb molecules. Assignment of the orientation of the transition dipole moment of each chlorophyll has been achieved. All Chlb are located around the interface between adjacent monomers, and together with Chla they are the basis for efficient light harvesting. Four carotenoid-binding sites per monomer have been observed. The xanthophyll-cycle carotenoid at the monomer-monomer interface may be involved in the non-radiative dissipation of excessive energy, one of the photoprotective strategies that have evolved in plants.     

Vesicular restriction of synaptobrevin suggests a role for calcium in membrane fusion

Release of neurotransmitter occurs when synaptic vesicles fuse with the plasma membrane. This neuronal exocytosis is triggered by calcium and requires three SNARE (soluble-N-ethylmaleimide-sensitive factor attachment protein receptors) proteins: synaptobrevin (also known as VAMP) on the synaptic vesicle, and syntaxin and SNAP-25 on the plasma membrane. Neuronal SNARE proteins form a parallel four-helix bundle that is thought to drive the fusion of opposing membranes. As formation of this SNARE complex in solution does not require calcium, it is not clear what function calcium has in triggering SNARE-mediated membrane fusion. We now demonstrate that whereas syntaxin and SNAP-25 in target membranes are freely available for SNARE complex formation, availability of synaptobrevin on synaptic vesicles is very limited. Calcium at micromolar concentrations triggers SNARE complex formation and fusion between synaptic vesicles and reconstituted target membranes. Although calcium does promote interaction of SNARE proteins between opposing membranes, it does not act by releasing synaptobrevin from synaptic vesicle restriction. Rather, our data suggest a mechanism in which calcium-triggered membrane apposition enables syntaxin and SNAP-25 to engage synaptobrevin, leading to membrane fusion.     

浅谈普通话习得过程中的中介语

在普通话的学习中,由于学习动机、环境、方言等因素的影响,学生的普通话大多时候是处在中介语阶段。作为中间状态的中介语对普通话的习得具有非常重要的意义。     

Coal mine blasting caps refused to burst cause analysis and prevention

在煤矿井下爆破过程中,受井下客观环境条件影响,经常出现雷管拒爆导致的个别丢炮或成组丢炮现象.为了有效地遏制丢炮现象,文章探讨了煤矿井下爆破中丢炮的主要影响因素,并给出相应的预防措施,对有效杜绝拒爆、漏炮有一定的借鉴意义.     

外伤性瞳孔散大法医学鉴定的探讨

通过对１０例外伤性忆散大法医学鉴定的分析，为准确评定损伤程度提供参考。     

基于Gauss滤波的多媒体图像的可视化检索

基于图像的可视化特征的图像检索和查询，是当前多媒体系统的重要研究方向。对于基于图像局部匹配的检索，传统的模板匹配和区域分割方法只能在目标图像中检索非常相似的对象，对尺度或形状有较大变化的目标则难以得到满意的结果。提出了一种不依赖于模板匹配的方法——图像的多尺度高斯滤波表示，用于图像的特征提取和局部匹配，并在分布并行索引结构下实现了该方法的快速索引和搜索算法。实验表明，该方法能够在较大尺度和视角变化范围内，更有效地进行图像的特征提取和检索，对基于图像局部区域相似性的匹配能达到较好的效果。     

壳梭孢素与某些植物激素在黄化绿豆下胚轴切段伸长中的相互作用

以黄化绿豆幼苗下胚轴切段为材料,观察IAA、GA、ABA和FC单独或混合对切段伸长的效应,同时也观察前三种植物激素与FC处理先后不同对切段生长的影响.试验得知,FC显著促进切段伸长,IAA也有促进效果,GA促进效应不明显,ABA抑制伸长生长.IAA和ABA分别与FC混合则呈抑制效应,GA和FC混合具相加效应.在作用顺序性方面,无论对IAA、GA或ABA来说,都是FC预处理对切段伸长的效果最好.     

Cu-La-O体系热力学研究

为开拓稀土元素在铜及其合金中的有效利用,本文在1390—1475 K温度下,用固相-液相平衡法研究了Cu-La-O体系的热力学,用固体电解质氧浓差电池法测定了铜液中氧的活度,得到镧的脱氧常数,及脱氧常数与温度的关系式。由测得的数据还求得镧在熔铜中的溶解自由能、活度系数与温度的关系和铜液中镧自身的相互作用系数。     

大各向异性改性PbTiO3压电陶瓷材料设计与研究

自行设计一种以 (Mn1/ 3 Sb2 / 3 ) 4+ B位取代Ti4 + 为特征的新型改性PT压电陶瓷材料 ,典型配方主要性能参数为 :TC=2 52℃、εT3 3 /ε0 =1 60、tgδ =1 % ;d3 3 =70× 1 0 -12 C/N、kt=0 .60、kp≈ 0、kt/kp→∞ ;Qm=4 3、Nt=2 0 0 4Hz·m .该材料具有良好的烧结特性及高厚度机电耦合系数、大压电各向异性、低机械品质因素、小介电常数等优异特性 ,在超声换能器尤其是NDT探头、水听器及宽带高频滤波器的研制上显示出好的应用前景 .     

金属醇盐的合成

本文介绍了金属醇盐作为原料用于制备无机材料的独特优点,并系统地综述了金属醇盐的合成方法.