Influence of grain boundary on melting

The temperature behaviour of an Al bicrystal with surfaces consisting of (110) and (111) crystals is simulated using molecular dynamics. The result shows that the (110) crystal losses its crystalline order at 820K, whereas the disorder does not propagate through the (111) crystal at this temperature. Instead, some disordered atoms are recrystallized into the (111) crystal and the initial grain boundary changes into a stable order-disorder interface. Thus, it was discovered that at a temperature near its melting point, the (111) crystal grew and obstructed the propagation of disorder. Such an obstruction is helpful for understanding melting.

炸药装药的发射起爆概率与质量限定条件初探

讨论火炮发射时炮弹炸药装药的发射起爆概率、寻找制订炮弹炸药装药质量限定条件的方法。

细粒尾矿动力特性的试验研究

通过室内动三轴试验,测试了有色金属铜矿的细粒尾矿动力特性,获得了细粒尾矿在动荷载作用下的动应力与动应变、动应变与动模量及动阻尼比、动孔隙水压与动应力等相关关系,得出动孔隙水压对细粒尾矿动强度的影响有限等结论,对研究细粒尾矿的动力特性作了一些探索.

深水平台动力分析问题

<正> 世界上第一座采油平台建造于1947年,在美国的墨西哥湾,水深只有六公尺。25年来海上平台的建设得到了迅猛的发展,当前世界上已经建成了近一万座,水深也不断增加,突破了三百公尺大关。随着水深的增加,动力分析的重要性越来越突出了。平台承受的最主要的波浪载荷通常在5—15秒周期范围内为高能带,三百公尺水深的钢导管架(图1)平台的自然周期在5秒附近,正好靠近这个范围,因而造成动力放大。低于三百公尺的平台,只要它的自然周期离5秒不太远,也会有一定的动力放大,而每年数百万次的循环应力就会造成结构局部疲劳,土壤在长期循环应力作用下也有疲劳问题,会发生刚度退化导致平台的自然周期向波谱高能带漂移,使动响应进一步放大,造成恶性循环。所以平台结构动力分析的目

Micromechanics analysis of particulate-reinforced composites and their failure mechanisms

Stress fields and failure mechanisms have been investigated in composites with particles either surface treated or untreated under uniaxial tension. Previous experimental observation of failure mechanisms in a composite with untreated particles showed that tensile cracks occurred mostly at the polar region of the particle and grew into interfacial debonding. In a composite with surface-treated particles, however, shear yielding and shear cracking proceeded along the interphase-matrix interface at the polar area of the matrix and thus may improve the mechanical behaviour of the material. The finite element calculations showed that octahedral shear stress at the polar and longitudinal areas of the particle treated by coupling agents is much larger than that of materials with untreated particles, and the shear stress distribution around the interface is sensitive to the interphase property. The results suggest that a th ree-phase model can describe the composites with surface-treated fillers.

气相扩散法生长溶菌酶晶体的动态光散射研究

首次采用动态光散射研究了气相扩散法生长溶菌酶晶体 .实验中采用了两种溶解溶菌酶的方法，所得实验结果是有区别的 .这种区别表明了 NaCl对溶菌酶分子间相互作用产生十分重要的影响 .实验结果表明，晶体生长过程中，溶液中溶菌酶始终保持单分子与两分子聚集体的状态，这种状态是生长晶体的基础 .

大型光学镜子热弹性变形的有限元分析

简述了利用ANSYS软件对大型光学镜子热弹性变形进行有限元分析的一般方法，强调了在分析过程中应该注意的一些问题和实用技巧，并给出了一个分析透镜重力变形的实例。

不同退火气氛下γ-LiAlO2形貌和结构研究

研究了温度梯度法生长的γ-LiAlO2晶体在1100℃下富Li气氛和空气中退火处理后的表面形貌、表面结构以及吸收光谱。发现γ-LiAlO2晶体的抛光面在1100℃空气中退火后变为粗糙面，X射线衍射(XRD)分析表明此粗糙面为单相的LiAl5O8。而γ-LiAlO2晶体的抛光面在1100℃富Li气氛中处理后几乎没有变化。同时对不同气氛下热处理的γ-LiAlO2晶体进行了光谱分析，确认了晶片中196nm的吸收峰是由Li空位引起的。

Diode-pumped Yb : YAG ceramic laser

Transparent polycrystalline Yb:YAG ceramics were fabricated by solid-state reactive sintering a mixture of commercial Al2O3, Y2O3, and Yb2O3 powders. The powders were mixed in ethanol and doped with 0.5 wt% tetraethoxysilane, dried, and pressed. Pressed samples were sintered at 1730 degrees C in vacuum. Transparent fully dense samples with grain sizes of several micrometers were obtained. The phase from 1500 degrees to 1700 degrees C was important for the grain growth, in which the grains grew quickly and a mass of pores were eliminated from the body of the sample. Annealing was an important step to remove the vacancies of oxygen and transform Yb2+ to Yb3+. The 1 at.% Yb:YAG ceramic sample was pumped by a diode laser to study the laser properties. The maximum output power of 1.02 W was obtained with a slope efficiency of 25% at 1030 nm. The size of the lasering sample was 4 mm x 4 mm x 3 mm.

杉科植物的系统发育、 分类和地理分布

本文对杉科植物的分类系统作了回顾。以形态学为依据，参考其他学科的研究成果，用分支分析和表征分析两种方法探讨了杉科植物的系统演化关系．提出了新的分类系统。对杉科植物的系统分类作了修订．通过对各属现代分布和地史分布的研究，结合古地理和古气候资料，讨论了杉科植物的分布中心、起源时间、起源地、散布途径及现代分布格局的成因．主要结论如下： 1．属间关系：柳杉属是现存杉科植物中最原始的类群．水松属和落羽杉属关系密切，二者与柳杉属近缘．巨杉属和北美红杉属关系密切，是中级进化水平的类群．水杉属的系统位置比较孤立，与巨杉属和北美红杉属的关缘关系相对较近．杉木属、密叶杉属和台湾杉属关系密切，是杉科植物中的高级进化类群，其中台湾杉属最为进化． 2．系统排列：支持金松科的成立．将杉科分成5族，即柳杉族（仅含柳杉属）、落羽杉族（含水松属、落羽杉属）、北美红杉族（含巨杉属、北美红杉属）、水杉族（仅含水杉属）和杉木族（含杉木属、密叶杉属及台湾杉属）． 3．分类：经修订，杉科植物共9属12种4变种．将德昌杉木、米德杉木和厚皮杉木归并，作为杉木的变种，支持柳杉作为日本柳杉的变种、台湾杉木作为杉木的变种、秃杉和台湾杉归并的观点。 4．地理分布：我国长江、秦岭以南至华南一带是杉科的现代分布中心，我国华北北部及东北、朝鲜、日本和前苏联西伯利亚东南部等地可能为起源中心和早期分化中心，起源时间可追溯至早侏罗纪或晚三叠纪．杉科的现存各属均为古老的孑遗类群．

New symbiotic hypothesis on the origin of eukaryotic flagella

The origin of eukaryotic flagella has long been a mystery. Here we review the possibility that flagella sprouted evolutionarily from the eukaryotic cell proper seems very unlikely because it is hard to imagine what function and benefit in natural selection the flagella would have provided to the cells when they first emerged as simple buds. Lynn Margulis' 1970 spirochete hypothesis, though popular still, has never been confirmed. Moreover, the absence of tubulin and axonemal dynein in the spirochetes and the incapability of the bacterial and eukaryotic membranes' making a continuum now suggest that the hypothesis is outdated. Tubulin genes were recently identified in a new bacteria division, verrucomicrobia, and microtubules have also been found in one of these species, epixenosomes, the defensive ectosymbionts. On the basis of these data, we propose a new symbiotic hypothesis: that the mid-ancestor of eukaryotic cells obtained epixenosomelike verrucomicrobia as defensive ectosymbionts and the ectosymbionts later became endosymbiotic. They still, however, protruded from the surface of their host to play their role. Later, many genes were lost or incorporated into the host genome. Finally, the genome, the bacterial membrane, and the endosymbiotic vesicle membrane were totally lost, and fingerlike protrusions with microtubules formed. As the cells grew larger, the defensive function of the protrusions eventually weakened and then vanished. Some of the protrusions took on a new role in cell movement, which led them to evolve into flagella. The key step in this process was that the dynein obtained from the host evolved into axonemal dyneins, attaching onto the microtubules and forming motile axonemes. Our hypothesis is unproven, but it offers a possible explanation that is consistent with current scientific thought. We hope that our ideas will stimulate additional studies on the origin of eukaryotic flagella and on investigations of verrucomicrobia. Whether such studies confirm, refine, or replace our hypothesis, they should nevertheless further our understanding of the origin of eukaryotic cells.