Three-dimensional reconstruction from tilted sections of fish muscle M-band

Fish muscle provides a particularly suitable specimen for studying the organization of thick filaments in vertebrate striated muscle because the filaments are arranged with a single orientation on a well ordered hexagonal lattice. The M-band consists of sets of cross-links, which join the myosin filaments in the middle of the A-band. Previous work concluded that the fish muscle M-band had the local symmetry of the dihedral point group 32. We present here a quantitative analysis of transverse sections of the M-band, using general methods developed for crystalline layers, to combine various tilted views. The three-dimensional map computed to a resolution of about 70 A confirms previous findings; it shows new features of the thick filament structure in the M-band region and provides new information on the use of three-dimensional reconstruction from sectioned biological material. The accompanying paper describes a novel technique of three-dimensional reconstruction of the fish M-band from a single view of a slightly oblique plastic section.     

基于等值面拓扑简化的三维重建算法

针对工业CT无损检测巾缺陷的窄间信息无法准确判断的问题,提出了重建缺陷的算法.该算法使用八叉树来节省内存,并同时从内部增加和外郭切除体素的方法来准确找到缺陷的边缘,利用MC提取的等值面经过拓扑简化得到最终的重建模型.实验表明,该方法可以实现对缺陷的三维空间形状观察,并提高了检测效率,得到了缺陷在空间任意方向的分布.     

Structure of the dengue virus envelope protein after membrane fusion

Dengue virus enters a host cell when the viral envelope glycoprotein, E, binds to a receptor and responds by conformational rearrangement to the reduced pH of an endosome. The conformational change induces fusion of viral and host-cell membranes. A three-dimensional structure of the soluble E ectodomain (sE) in its trimeric, postfusion state reveals striking differences from the dimeric, prefusion form. The elongated trimer bears three 'fusion loops' at one end, to insert into the host-cell membrane. Their structure allows us to model directly how these fusion loops interact with a lipid bilayer. The protein folds back on itself, directing its carboxy terminus towards the fusion loops. We propose a fusion mechanism driven by essentially irreversible conformational changes in E and facilitated by fusion-loop insertion into the outer bilayer leaflet. Specific features of the folded-back structure suggest strategies for inhibiting flavivirus entry.     

基于单幅图片的唐代服饰三维重建

针对传统建模方法的局限性和对唐代服饰进行建模自身的特点,提出了一种将数字建模和物理建模相结合的基于单幅图片的唐代服饰的三维重建的方法。由于唐代历史悠久,遗留的下来的服装文物基本为二维水彩画,陶俑等,能从中提取的信息及其有限,因此利用Open CV的自动扫描技术和根据服装横截面近似椭圆的特性计算得出服装大致的数字模型,而数字模型只有服装的大致轮廓,无法呈现逼真的三维服饰,则再将数字模型的数据数据输入三维建模软件Maya中进行细节修改,并对其添加动力学特性,纹理贴图渲染。仿真结果显示三维重建出的唐代服饰模型,不仅逼真,而且效率高。     

Three-dimensional reconstruction from a single oblique section of fish muscle M-band

A new method of three-dimensional image reconstruction from electron micrographs is presented here, which enables a three-dimensional image to be produced from a single oblique section of a two- or three-dimensional crystal. The method, which is most powerful when the section is thin and the angle of obliquity small, has several potential advantages over the conventional method of reconstruction using tilted views of the section. In particular the accumulated electron dose on the specimen is much smaller and the reconstruction is not affected by changes in the thickness of the section during exposure to the electron beam. The method involves the solution of a generally almost singular set of linear projection equations, relating through the sectioning geometry the three-dimensional crystal density to the two-dimensional projected image density. This can be achieved most conveniently by linear least squares filtering. An application of the method to determine the structure of the M-band of fish muscle is described. The resulting map agrees well with that produced by the more conventional approach involving tilted views.     

Three-dimensional reconstruction of rigor insect flight muscle from tilted thin sections

Rigor cross-bridges show two conformations paired within each 38.7-nm axial repeat. The two forms may express two stages of the cross-bridge cycle during contraction. Differing numbers of myosin heads per cross-bridge and associated helical changes in the thin filament distinguish the two forms and suggest that both myosin heads usually bind to a single thin filament.     

多孔介质模型的三维重构方法

建立准确的多孔介质模型在微观渗流机理的研究中具有重要意义.为了更加方便准确地建立多孔介质模型,总结了多孔介质模型重构的物理实验方法和数值重构方法,通过重构方法的优缺点对比及适用性分析,优选出马尔可夫链-蒙特卡洛方法(MCMC).针对3种不同性质的多孔介质,采用MCMC方法分别对其进行了重构.结果表明,MCMC方法计算速度快,适用范围广泛,重构效果好.最后将MCMC方法扩展到三维空间,重构出三维多孔介质模型,为微观渗流机理的研究提供了一个模拟平台.     

飞秒脉冲在透明介质中的三维光存储及读出对比度研究

将波长为800nm，脉冲宽度为150fs的近红外激光脉冲，聚焦到聚甲基丙烯酸甲酯(Ploymethyl Metacrtlate，简记PMMA)和熔融石英中，实现了三维逐位式光数据存储．分别记录了5，10，15和20层数据位点，并利用相位对比光学显微原理，对各层数据并行读出，从而分析了各层数据位点读出对比度的变化．结果表明，各层数据位点的折射率对比度由内至外依次增加．记录层数越多，内部层的对比度下降越明显．由于飞秒激光脉冲与透明介质相互作用中熔融石英比PMMA内部产生的残余应力大，因此，在数据位点参数相同的情况下，利用聚甲基丙烯甲酯(PMMA)材料记录的层数更多．     

Three-dimensional structure of a complex of antibody with influenza virus neuraminidase

The structure of a complex between influenza virus neuraminidase and an antibody displays features inconsistent with the inflexible 'lock and key' model of antigen-antibody binding. The structure of the antigen changes on binding, and that of the antibody may also change; the interaction therefore has some of the character of a handshake.     

Three-dimensional structure of an antigenic mutant of the influenza virus haemagglutinin

Antigenic variation in the haemagglutinin (HA) glycoprotein of influenza virus is associated with recurrent epidemics of respiratory disease in man (for review see ref. 1). We have examined the size of structural changes necessary to alter the antigenicity of HA by determining the three-dimensional structure of the HA from an antigenic mutant containing a single amino acid substitution which was selected by growth of virus in the presence of monoclonal antibodies. Here we present evidence that the simple addition of an amino acid side chain which results in only minor local distortions of the structure of the HA is sufficient structural alteration for a virus to escape neutralization by a monoclonal antibody. Our results also demonstrate that single amino acid substitutions can cause only local changes in the HA structure, verifying the assumption made in several studies to locate antigenic sites on the HA and other molecules, and indicate that proposals of large conformational changes to account for variations in HA antigenicity are unnecessary in this case. The structure of the variant antigen has independently been successfully predicted (M. Karplus, personal communication).     

Three-dimensional structure of aspartyl protease from human immunodeficiency virus HIV-1

The crystal structure of the protease of the human immunodeficiency virus type (HIV-1), which releases structural proteins and enzymes from viral polyprotein products, has been determined to 3 A resolution. Large regions of the protease dimer, including the active site, have structural homology to the family of microbial aspartyl proteases. The structure suggests a mechanism for the autoproteolytic release of protease and a role in the control of virus maturation.     

Generation of tetraploid complementation mice from embryonic stem cells cultured with chemical defined medium

Mouse embryonic stem cells(mESCs)derived from inner cell mass(ICM)of pre-implantation embryos,can maintain undifferentiated state when cultured in N2B27 medium supplemented with GSK3inhibitor CHIR99021 and MEK inhibitor PD0325901(‘‘2i’’)and leukemia inhibitor factor(LIF).Compare to conventional culture medium,all components of this medium are defined.With the N2B27 medium,‘‘2i’’and LIF,mESCs can contribute to the germline of the chimeric embryos,however,whether the‘‘all-ES cells’’mice can been generated by tetraploid complementation is unclear yet,while the tetraploid complementation serve as a golden standard to assess the pluripotency of ES cells.Here,our study showed that mESCs derived and cultured with the N2B27 complete medium could generate fertile mice by tetraploid complementation.In addition,the survival rate of tetraploid complementation mice produced by inbred mES cell lines is higher than the conventional culture condition,and increased the percentage of Oct4 positive cells contrast to conventional medium either.Therefore,the N2B27 medium supplemented with‘‘2i’’and LIF is an alternative choice forthe derivation and long-term culture of mouse embryonic stem cells.     

Identification of antiviral- relevant genes in the cultured fish cells induced by UV-inactivated virus

~~Identification of antiviral- relevant genes in the cultured fish cells induced by UV-inactivated virus~~     

一维平行平板系统介质辐射参数和高浓度区域高度的同时重建

不同浓度区域介质辐射参数对炉膛辐射传热计算有着十分重要的作用.基于牛顿法和最小二乘法对一维平行平板系统辐射参数和高浓度区域高度的同时重建进行模拟研究.结果表明,在有限的迭代次数内,重建参数能收敛在真值附近,并且介质辐射参数在真值附近振荡,而其振荡范围基本不变;随着测量误差的增大,重建误差也逐渐增大.