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.     

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.     

Molecular dynamics of cyclically contracting insect flight muscle in vivo

Flight in insects--which constitute the largest group of species in the animal kingdom--is powered by specialized muscles located within the thorax. In most insects each contraction is triggered not by a motor neuron spike but by mechanical stretch imposed by antagonistic muscles. Whereas 'stretch activation' and its reciprocal phenomenon 'shortening deactivation' are observed to varying extents in all striated muscles, both are particularly prominent in the indirect flight muscles of insects. Here we show changes in thick-filament structure and actin-myosin interactions in living, flying Drosophila with the use of synchrotron small-angle X-ray diffraction. To elicit stable flight behaviour and permit the capture of images at specific phases within the 5-ms wingbeat cycle, we tethered flies within a visual flight simulator. We recorded images of 340 micros duration every 625 micros to create an eight-frame diffraction movie, with each frame reflecting the instantaneous structure of the contractile apparatus. These time-resolved measurements of molecular-level structure provide new insight into the unique ability of insect flight muscle to generate elevated power at high frequency.     

Cross-bridge interaction with oppositely polarized actin filaments in double-overlap zones of insect flight muscle

An unresolved problem in understanding muscular contraction is why the internal resistance to sarcomere shortening increases progressively during contraction. We have addressed this problem here by investigating the movement of detached acting filaments in the sarcomeres of insect flight muscle. The final position of the detached actin filaments shows that they were able to slide freely into regions where they have the wrong polarity to interact actively with myosin (double-overlap zones) but where they prevent the exertion of force by cross-bridges between myosin and the correctly polarized acting filaments. These observations indicate that the isometric tension at all sarcomere lengths is directly proportional to the number of cross-bridges in the region of single-overlap of correctly polarized actin and myosin filaments. The decrease in tension as sarcomeres shorten is thus the result of the decrease in the number of effective cross-bridges as actin filaments slide into regions where they are of the wrong polarity to form cross-bridges, and where they inhibit the existing cross-bridges.     

昆翅在飞行中的动态形变

通过理论模化途径研究昆翅在飞行中的动态形变机制.设计翅气动力试验平台,验证翅准静态形变影响气动力的"柔性楔形效应"理论解释.探讨昆翅的变刚度特性表明,弦向刚度分布规律符合二项式函数时具有优越性和现实性,进而指出昆姻结构的变刚度特性是产生高升力的基本条件.建立了柔性翅的简化力学模型,通过坐标变换法求解在气动力和惯性力共同...     

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.     

基于投影的断层间多连通物体轮廓表面重建

提出一种基于轮廓投影关系判断的断层间多连通轮廓的表面重建方法,在分析轮廓投影关系特性的基础上,建立了“连接表面投影区”;在连接表面投影区域内,利用距离函数生成过渡区域的体数据,进行表面重建的计算;并可根据需要进行插值计算,生成分辨率较高的体数据;最后对MT算法进行改进,抽取等值面,完成物体的表面重建,该方法缩短了体数据的构造时间,加快了整个表面的重建速度,保证了重建表面的正确性。     

Three-dimensional reconstruction of mature dengue virus cultured in neutral medium

Dengue virus (DEN), a single positively stranded RNA virus, is a family member of Flaviviridae; it uses the mosquito Aeodes aegypti as its principle vector to cause what is known as Dengue fever. Its genome is -10.8-kb in size and has one open reading frame encoding three structural proteins: capsid (C), precursor of the membrane (prM) and envelope (E), as well as seven non-structural proteins from a single polypeptide. The immature DEN particles are assembled on the inner surface of the endoplasmic reticulum(ER) and budded into the lumen of the ER.     

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。     

不同断面形式在万安坝灌区渠道防渗改造中的应用

渠道防渗衬砌技术是渠道提高输水能力和农业灌溉的重要途径.文章对灌区渠道的不同断面形式及其水力计算进行了介绍分析,结合休宁县万安坝灌区的实际情况,对灌区干渠采用圆底三角形断面形式,对灌区支、斗渠采用U型断面.     

The continuity of thick filaments between sarcomeres in honey bee flight muscle

One of the most frequently discussed problems of insect flight muscle morphology is the structure of the thick filaments, especially at the Z line. Many attempts have been to solve these problems but no unequivocal answers have been given so far. It is well known that physiological specialisation is accompanied by certain anatomical features in the myofibrillar level; the myofibrils have very short I bands in the resting state and the muscle acts under nearly isometric conditions. In this paper, a fresh approach is used to demonstrate the fine structure at the Z line in honey bee flight muscle.     

Three-dimensional structure of the lipovitellin-phosvitin complex from amphibian oocytes

Microcrystals of the lipoprotein-phosphoprotein complex which are found in the oocytes of Xenopus laevis were examined using electron microscopy. Analysis of Fourier transforms of the images of the (010) and (001) projections showed the space group to be P2(1)22(1). Ten projections were combined to produce a map of the complex having about 20 A resolution. The lipoprotein complex consists of two subunits related by a local twofold symmetry axis. The density was averaged around the local symmetry and reasonably well defined structural domains can be seen in the resulting model.