SHPB实验中试样形状和尺寸效应的数值模拟

文章采用有效的方法讨论了动态接触算法中罚函数因子K的合理数值,在此基础上,利用LS-DY-NA3D有限元动力分析软件模拟了SHPB实验过程.对于不同的试样长度、直径以及不同环厚的环形试样,分别对模拟结果进行了应力一应变曲线重构;发现当试样与压杆横截面不匹配时,SHPB实验将产生较大的误差,尤其是对于环形试样;同时发现对于小直径试样的SHPB实验存在一个极限误差;研究结论将对SHPB实验中试样尺寸的确定提供借鉴.     

Planar cell polarity signalling couples cell division and morphogenesis during neurulation

Environmental and genetic aberrations lead to neural tube closure defects (NTDs) in 1 out of every 1,000 births. Mouse and frog models for these birth defects have indicated that Van Gogh-like 2 (Vangl2, also known as Strabismus) and other components of planar cell polarity (PCP) signalling might control neurulation by promoting the convergence of neural progenitors to the midline. Here we show a novel role for PCP signalling during neurulation in zebrafish. We demonstrate that non-canonical Wnt/PCP signalling polarizes neural progenitors along the anteroposterior axis. This polarity is transiently lost during cell division in the neural keel but is re-established as daughter cells reintegrate into the neuroepithelium. Loss of zebrafish Vangl2 (in trilobite mutants) abolishes the polarization of neural keel cells, disrupts re-intercalation of daughter cells into the neuroepithelium, and results in ectopic neural progenitor accumulations and NTDs. Remarkably, blocking cell division leads to rescue of trilobite neural tube morphogenesis despite persistent defects in convergence and extension. These results reveal a function for PCP signalling in coupling cell division and morphogenesis at neurulation and indicate a previously unrecognized mechanism that might underlie NTDs.     

Social interactions among epithelial cells during tracheal branching morphogenesis

Many organs are composed of tubular networks that arise by branching morphogenesis in which cells bud from an epithelium and organize into a tube. Fibroblast growth factors (FGFs) and other signalling molecules have been shown to guide branch budding and outgrowth, but it is not known how epithelial cells coordinate their movements and morphogenesis. Here we use genetic mosaic analysis in Drosophila melanogaster to show that there are two functionally distinct classes of cells in budding tracheal branches: cells at the tip that respond directly to Branchless FGF and lead branch outgrowth, and trailing cells that receive a secondary signal to follow the lead cells and form a tube. These roles are not pre-specified; rather, there is competition between cells such that those with the highest FGF receptor activity take the lead positions, whereas those with less FGF receptor activity assume subsidiary positions and form the branch stalk. Competition appears to involve Notch-mediated lateral inhibition that prevents extra cells from assuming the lead. There may also be cooperation between budding cells, because in a mosaic epithelium, cells that cannot respond to the chemoattractant, or respond only poorly, allow other cells in the epithelium to move ahead of them.     

集料尺寸和形状及掺合料对混凝土界面的影响

研究混凝土粗集料与砂浆在宏观尺度上的界面特性,并采用砂浆中的砂粒与粗集料的平均间距(简称界面平均间距)进行表征.结合雅砻江锦屏大坝集料品种,研究了球形和片状2种粗集料形状、2组粗集料尺寸,以及粉煤灰和石灰石粉的2个掺量(10%,20%)对界面平均间距的影响.结果表明,采用界面区砂粒与粗集料的平均间距能较好地反映界面区的宏观离析和均质性,测量使用也较简便.对于球形集料,大、小集料上方与下方的界面平均间距无显著差异,表明界面较均匀,离析不明显;而对于片状集料,随着尺寸增大,上、下方的界面平均间距的差异增大,表明大的片状集料下方产生了明显的离析.研究结果还表明,采用粉煤灰或石灰石粉部分等质量取代水泥,可以改善片状集料下方浆体的离析.     

汽车制动阀安装板坯料形状与尺寸的确定

非规则成形件的毛坯形状与尺寸的确定,一般都是通过成形模并采取试错的方法来完成的。然而,试错要考虑多种因素,又由于落料模必须要在由试错来确定最后的形状与尺寸后才能设计制造,如此就要影响板料零件的生产周期和成本。汽车制动阀安装板是一个比较典型的非规则成形件,在要求极短的周期内同时完成其落料模与成形模的设计制造,用初始网格法来确定汽车制动阀安装板的毛坯形状与尺寸,可在较短时间内完成模具生产工作。     

Selective assembly on a surface of supramolecular aggregates with controlled size and shape.

The realization of molecule-based miniature devices with advanced functions requires the development of new and efficient approaches for combining molecular building blocks into desired functional structures, ideally with these structures supported on suitable substrates 1-4.Supramolecular aggregation occurs spontaneously and can lead to controlled structures if selective and directional non-covalent interactions are exploited. But such selective supramolecular assembly has yielded almost exclusively crystals or dissolved structures 5; the self-assembly of absorbed molecules into larger structures 6-8, in contrast, has not yet been directed by controlling selective intermolecular interactions. Here we report the formation of surface-supported supramolecular structures whose size and aggregation pattern are rationally controlled by tuning the non-covalent interactions between individual absorbed molecules.Using low-temperature scanning tunnelling microscopy, we show that substituted porphyrin molecules adsorbed on a gold surface form monomers, trimers, tetramers or extended wire-like structures. We find that each structure corresponds in a predictable fashion to the geometric and chemical nature of the porphyrin substituents that mediate the interactions between individual adsorbed molecules.Our findings suggest that careful placement of functional groups that are able to participate in directed non-covalent interactions will allow the rational design and construction of a wide range of supramolecular architectures absorbed to surfaces.     

激光散射研究絮凝剂的分子结构与性能

目的通过对絮凝剂分子性能及机理的研究,为确切探知提高絮凝效果提供实验依据和理论依据. 方法利用激光散射技术进行测量絮凝剂聚合氯化铝(PAC)、聚合氯化铝和矾(PAC-V)在水中自然状态下的分子结构. 结果重均相对分子质量Mw(PAC)=1.23×105,Mw(PAAC-V)=2.63×105; 颗粒的流体力学半径Rh(PAC)=23.15 nm,Rh(PAC-V)=82.22 nm; 回转半径Rg(PAC)=25.5,Rg(PAC-V)=44.8; 溶液第二维里系数A2(PAC)=2.94×10-5,A2(PAC-V)=3.58×10-6. 结论(1)两种絮凝剂在水中的粒度分布呈近乎单弥散分布;(2)絮凝剂的重均相对分子质量、颗粒大小及形状不随浓度的改变而变化;(3)与实际去除效果相比,絮凝剂的重均相对分子质量、粒径大小与分布、形态结构对絮凝性能有重要影响并可作为评判其性能的重要指标.     

二氧化铈前驱体煅烧过程中的遗传性研究

用尿素均匀沉淀法制备了不同形状的二氧化铈前驱体，研究了前驱体形貌、大小、结晶度以及煅烧温度对CeO2颗粒形貌、大小、结晶度的影响．煅烧过程中球形和棒状前驱体煅烧前后颗粒的形状和大小基本不变，颗粒在形貌和尺寸上具有遗传性，片状前驱体在形状上有遗传性．随着煅烧温度的升高，球形颗粒热分解和原子重排速度增大，CeO2颗粒结晶度增大，但是颗粒形状和大小变化都不大．前驱体颗粒的形貌和结晶度影响CeO2颗粒的结晶度，粒径较小、结晶度较低的粉体热分解和原子结构重排都相对容易，煅烧后CeO2颗粒结晶度较高．     

统筹城乡发展 缩小城乡差距——以嘉兴地区为例

统筹城乡发展，缩小城乡差距是构建社会主义和谐社会题中之义。本文根据嘉兴地区城乡发展的实际，提出了缩小城乡差距的对策思考。     

山西岩溶地貌形态特征与形成过程

山西是北方岩溶发育大省。文章介绍了其特有的一些形态特征和地貌组合,并探讨了影响其发育的因素及形成的2个主要时期。     

The morphogenesis of feathers

Feathers are highly ordered, hierarchical branched structures that confer birds with the ability of flight. Discoveries of fossilized dinosaurs in China bearing 'feather-like' structures have prompted interest in the origin and evolution of feathers. However, there is uncertainty about whether the irregularly branched integumentary fibres on dinosaurs such as Sinornithosaurus are truly feathers, and whether an integumentary appendage with a major central shaft and notched edges is a non-avian feather or a proto-feather. Here, we use a developmental approach to analyse molecular mechanisms in feather-branching morphogenesis. We have used the replication-competent avian sarcoma retrovirus to deliver exogenous genes to regenerating flight feather follicles of chickens. We show that the antagonistic balance between noggin and bone morphogenetic protein 4 (BMP4) has a critical role in feather branching, with BMP4 promoting rachis formation and barb fusion, and noggin enhancing rachis and barb branching. Furthermore, we show that sonic hedgehog (Shh) is essential for inducing apoptosis of the marginal plate epithelia, which results in spaces between barbs. Our analyses identify the molecular pathways underlying the topological transformation of feathers from cylindrical epithelia to the hierarchical branched structures, and provide insights on the possible developmental mechanisms in the evolution of feather forms.     

热处理对铜基形状记忆合金晶粒大小和相变点的影响

为了探讨不同热处理工艺对材料晶粒大小和Ms点的影响规律,对成分一定的铜基形状记忆合金(Cu-Mn-Al-Zn-Zr)制成的试样进行不同的热处理,分别采用金相法及电阻法对晶粒平均直径d和相变点Ms进行测定。结果表明,热处理对合金的晶粒大小和相变点影响较大,Ms与d-1/2之间存在线性关系。     

堆浸过程中矿岩散体粒间孔隙尺寸的演化规律

根据X射线CT技术无损伤地探测细菌浸出前、后矿岩散体介质孔隙结构特征,利用MATLAB环境编写程序对矿岩散体介质颗粒间横向及纵向孔隙尺寸分布进行统计,研究细菌浸出过程中矿岩散体粒间孔隙尺寸演化规律及其对溶浸液渗流特性的影响.研究结果表明:矿岩散体介质孔隙尺寸分布不均匀,分布范围广,基本呈正态规律分布;浸出后顶部区域中等孔隙和大孔隙数量增加,小孔隙数量减少,底部区域中等孔隙也有所增加,但小孔隙数量减少,横向大孔隙数量减少,纵向大孔隙数量变化不明显;浸出后平均孔隙尺寸比浸出前有所增大,大孔隙含量增加,加强了浸堆的渗流各向异性;微细颗粒的运移和沉积对孔隙尺寸演化影响程度最大.     

2-D shape completion with shape priors

We propose new techniques for 2-D shape/contour completion, which is one of the important research topics related to shape analysis and computer vision, e.g. the detection of incomplete objects due to occlusion and noises. The purpose of shape completion is to find the optimal curve segments that fill the missing contour parts, so as to acquire the best estimation of the original complete object shapes. Unlike the previous work using local smoothness or minimum curvature priors, we solve the problem under a Bayesian formulation taking advantage of global shape prior knowledge. With the priors, our methods are expert in recovering significant shape structures and dealing with large occlusion cases. There are two different priors adopted in this paper: (i) A generic prior model that prefers minimal global shape transformation (including non-rigid deformation and affine transformation with respect to a reference object shape) of the recovered complete shape; and (ii) a class-specific shape prior model learned from training examples of an object category, which prefers the reconstructed shape to follow the learned shape variation models of the category. Efficient contour completion algorithms are suggested corresponding to the two types of priors. Our experimental results demonstrate the advantage of the proposed shape completion approaches compared to the existing techniques, especially for objects with complex structure under severe occlusion.     

铜基形状记忆合金异常相变内耗的研究

文章研究了Cu-Al-Ni-Mn-Ti多晶形状记忆合金的异常相变内耗。实验结果和理论分析表明,合金的高温相变内耗峰在测量频率较低、马氏体片较多及升温速度较大的情况下,分解为一个正峰和一个倒峰,这种现象是由于2种正、负耗散弹性模量的马氏体变体间相互作用引起的;具有负弹性模量的形状记忆合金能够稳定存在的条件,是需要从环境吸收热量引起熵的增加。     

Fibronectin requirement in branching morphogenesis

Many organs, including salivary glands, lung and kidney, are formed during embryonic development by epithelial branching. In branching morphogenesis, repetitive epithelial cleft and bud formation create the complex three-dimensional branching structures characteristic of many organs. Although the mechanisms are poorly understood, one might involve the site-specific accumulation of some regulatory protein. Here we show that the extracellular matrix protein fibronectin is essential for cleft formation during the initiation of epithelial branching. Fibronectin messenger RNA and fibrils appeared transiently and focally in forming cleft regions of submandibular salivary-gland epithelia, accompanied by an adjacent loss of cadherin localization. Decreasing the fibronectin concentration by using small interfering RNA and inhibition by anti-fibronectin or anti-integrin antibodies blocked cleft formation and branching. Exogenous fibronectin accelerated cleft formation and branching. Similar effects of fibronectin suppression and augmentation were observed in developing lung and kidney. Mechanistic studies revealed that fibrillar fibronectin can induce cell-matrix adhesions on cultured human salivary epithelial cells with a local loss of cadherins at cell-cell junctions. Thus, fibronectin expression is required for cleft formation in branching morphogenesis associated with the conversion of cell-cell adhesions to cell-matrix adhesions.     

Role of Bax and Bak in mitochondrial morphogenesis

Bcl-2 family proteins are potent regulators of programmed cell death. Although their intracellular localization to mitochondria and the endoplasmic reticulum has focused research on these organelles, how they function remains unknown. Two members of the Bcl-2 family, Bax and Bak, change intracellular location early in the promotion of apoptosis to concentrate in focal clusters at sites of mitochondrial division. Here we report that in healthy cells Bax or Bak is required for normal fusion of mitochondria into elongated tubules. Bax seems to induce mitochondrial fusion by activating assembly of the large GTPase Mfn2 and changing its submitochondrial distribution and membrane mobility-properties that correlate with different GTP-bound states of Mfn2. Our results show that Bax and Bak regulate mitochondrial dynamics in healthy cells and indicate that Bcl-2 family members may also regulate apoptosis through organelle morphogenesis machineries.     

外源多胺对宁夏枸杞离体形态发生过程中可溶性蛋白组分和过氧化物酶同工酶酶谱的影响

利用已建立的宁夏枸杞(Lycium barbarum L.)器官发生和体细胞胚发生体系,对多胺在高等植物离体形态发生中的作用以及部分生化特征进行了研究。将不同多胺预处理过的愈伤组织诱导器官发生的实验中,Spd能显著提高不定芽的再生频率,而CHA的预处理对不定芽形成产生的阻碍最为严重。在体细胞胚发生体系中,Spd,Put的处理能促进体细胞胚成苗,而MGBG,CHA的处理明显降低了成苗率。不同的多胺及其生物合成抑制剂均能影响两种再生体系的可溶性蛋白组分和过氧化物酶(POD)同工酶谱的表达;但对器官发生和体细胞胚发生途径特异多肋(46．3,36．2kD)的合成没有明显影响;而对存在于器官发生全过程、仅出现于体细胞胚发生后期阶段的44kD多肽,MGBG在两种途径中都能阻碍它的表达,Put仅在体细胞胚发生中有抑制作用。这些结果显示多胺可能在高等植物离体形态发生中起“第二信使”作用。