Conversion of zinc oxide nanobelts into superlattice-structured nanohelices

A previously unknown rigid helical structure of zinc oxide consisting of a superlattice-structured nanobelt was formed spontaneously in a vapor-solid growth process. Starting from a single-crystal stiff nanoribbon dominated by the c-plane polar surfaces, an abrupt structural transformation into the superlattice-structured nanobelt led to the formation of a uniform nanohelix due to a rigid lattice rotation or twisting. The nanohelix was made of two types of alternating and periodically distributed long crystal stripes, which were oriented with their c axes perpendicular to each other. The nanohelix terminated by transforming into a single-crystal nanobelt dominated by nonpolar (0110) surfaces. The nanohelix could be manipulated, and its elastic properties were measured, which suggests possible uses in electromechanically coupled sensors, transducers, and resonators.     

Tropomyosin paracrystals formed by divalent cations

Rabbit tropomyosin exhibits a polymorphism dependent on divalent cations and pH. Above a critical divalent cation concentration fibers with a period of about 400 angstroms are formed. Below this concentration, and near the isoelectric point, lattices are formed. Implications for the morphology and function of striated and smooth muscle are discussed.     

Comment on "Single-crystal X-ray structure of 1,3-dimethylcyclobutadiene by confinement in a crystalline matrix"

Legrand et al. (Reports, 16 July 2010, p. 299) reported the experimental observation of square-planar and rectangular-bent geometries of 1,3-dimethylcyclobutadiene (Me(2)CBD) confined within a crystalline matrix. However, we found no evidence for the Me(2)CBD formation. We argue that the experimental x-ray density data are better attributed to the bicyclic β-lactone intermediate where carbon dioxide is covalently bound to cyclobutadiene.     

Thunderstorm electrification of hail and graupel by polar dribble

Hail and graupel falling through rain collect water that selectively dribbles upward from the upper surface of a hailstone. When the hailstones are polarized by nearly vertical electrostatic field these vertically discharged water drops carry away free charge of the same sign as that induced on the upper surfaces. The hail thereby accumulates an equilibrium charge of opposite sign, corresponding to the charges induced on the bottom surfaces. The equilibrium charges are large enough to be important in thunderstorms.     

AcMNPV LEF-10形成难解离复合物的特性研究

【目的】将已经成功构建的AcMNPVlef-10表达载体在原核和真核表达系统中表达,研究其形成高分子复合物的特性,为揭示其高分子复合物的形成机理奠定基础。【方法】将先前成功构建的pTriEx-lef-10、pTriExlef-10-1-52、pTriEx-lef-10-27-78重组质粒分别转化至大肠杆菌BL21(DE3)和Sf 9细胞中诱导表达,产物经纯化、浓缩后,进行SDS-PAGE和Western blot检测分析;利用SDD-AGE技术估测LEF-10蛋白的分子质量;用透射电子显微镜分别观察原核和真核系统表达的LEF-10蛋白的外部形态。【结果】Western blot分析显示,LEF-10蛋白能形成高分子复合物,而C末端、N末端缺失和C末端融合GFP都可以阻断或部分阻断LEF-10高分子复合物的形成;苯酚-氯仿-异戊醇能部分打开LEF-10蛋白高分子复合体;利用SDD-AGE技术初步估测LEF-10高分子复合体分子质量集中在520~3 250ku;透射电子显微镜观察原核和真核系统表达的LEF-10,可见蛋白复合体大小不均一,呈现球形或者近球形。【结论】LEF-10蛋白在原核和真核表达系统中,都会形成高分子复合体,该复合体在强变性剂作用下,也不能完全打开,推测该复合体可能以共价键形式结合。     

Single crystals of single-walled carbon nanotubes formed by self-assembly

We report the self-assembly of single crystals of single-walled carbon nanotubes (SWCNTs) using thermolysis of nano-patterned precursors. The synthesis of these perfectly ordered, single crystals of SWCNTs results in extended structures with dimension on the micrometer scale. Each crystal is composed of an ordered array of tubes with identical diameters and chirality, although these properties vary between crystals. The results show that SWCNTs can be produced as a perfect bulk material on the micrometer scale and point toward the synthesis of bulk macroscopic crystalline material.     

用极坐标矢量法设计空间凸轮廓线

针对空间凸轮廓线设计工作量大和设计精度较低的问题，以圆柱凸轮机构为例，提出用极坐标矢量解析法设计空间凸轮廓线。利用该方法推导出了空间凸轮廓线方程，采用Matlab软件编程计算，显示了凸轮廓线形状和凸轮压力角的变化情况。研究结果表明：当从动件运动规律一定时，随着从动件升程的增大，凸轮廓线变陡，有变尖的趋势，凸轮机构压力角也增大，动力性能变差；与传统图解法相比，极坐标矢量法设计空间凸轮廓线工作量减少了约50％，并有利于凸轮廓线的精确数控加工。     

Addition radicals formed by hydroxyl radical bombardment of uracil

Direct addition of O-H radicals at room temperature to the carbon No.5 of the uracil ring has been proved by measurement of the proton hyperfine structure in the electron spin resonance of the resulting uracil + O-H radicals. Upon addition of the OH, the H originally bound to carbon No. 5 shifts to No. 6, thus forming a methylene group at carbon No. 6, with the two protons having equivalent coupling of 28 gauss. The spin density on carbon No. 5 is O.64. The radicals were produced when powdered samples of uracil were subjected to a low-velocity beam of O-H radicals coming from either hydrogen peroxide or water vapor under reduced pressure and subjected to an electric discharge.     

Superheated ice formed by the freezing of superheated water

Water, superheated with respect to the vapor phase, has been made to freeze, thus forming ice that is also superheated with respect to the vapor. This phase transformation occurred at the extension of the melting curve below the triple point pressure.     

Room temperature-operating spin-valve transistors formed by vacuum bonding

Functional integration between semiconductors and ferromagnets was demonstrated with the spin-valve transistor. A ferromagnetic multilayer was sandwiched between two device-quality silicon substrates by means of vacuum bonding. The emitter Schottky barrier injected hot electrons into the spin-valve base. The collector Schottky barrier accepts only ballistic electrons, which makes the collector current very sensitive to magnetic fields. Room temperature operation was accomplished by preparing Si-Pt-Co-Cu-Co-Si devices. The vacuum bonding technique allows the realization of many ideas for vertical transport devices and forms a permanent link that is useful in demanding adhesion applications.     

Calcium carbonate concretions formed by the decomposition of organic matter

Bacterial decomposition of butterfish and smelts in small sealed jars containing seawater and other solutions, for periods ranging from 65 to 205 days, results in a large increase in concentrations of dissolved bicarbonate, carbonate, and ammonia (plus volatile amines). Accompanying this is a rise in pH and the precipitation of Ca(++) ion from solution. The Ca(++) is not precipitated as CaCO(3) but instead as a mixture of calcium fatty acid salts or soaps with from 14 to 18 carbon atoms. This can be explained by the thermodynamic instability of CaCO(3) relative to Ca soaps in the presence of excess free fatty acid. It is suggested that some ancient CaCO(3) concretions, especially those enclosing fossils of soft-bodied organisms, may have formed rapidly after death in the form of natural Ca soap (adipocere) which was later converted to CaCO(3).     

稻瘟病菌链状分生孢子形成突变体的研究

通过三种途径得到了稻瘟病菌产生链状着生分生孢子的突变体菌株，并对这些突变菌株的DNA指纹图谱、致病性及孢子形成等特性与原菌株分别作了比较研究。用复合位点探针MAGGY和MGR586进行的DNA指纹图谱分析结果表明，这些突变体确系野生型稻瘟病菌的突变体。虽然这些突变菌株都能产生病斑，但其致病性较野生型菌株有明显下降。叶鞘接种结果表明，所用突变菌株均能形成附着孢并能穿透寄主细胞壁。突变菌株能形成链状着生的分生孢子，多数有两个分隔，呈弯膝形或长镰刀状，透明或灰橄榄色。突变菌株在病斑上和燕麦片培养基上都能产生链状着生的分生孢子，也能产生正常的分生孢子。通过单孢分离后，在燕麦片培养基上形成的两种孢子的比例基本稳定，表明突变菌株的孢子形成是一种受遗传控制的稳定性状。     

Single-crystal elastic properties of the modified spinel (Beta) phase of magnesium orthosilicate

The single-crystal elastic moduli of the modified spinel structure (beta phase) of magnesium orthosilicate (Mg(2)SiO(4)) have been measured by Brillouin spectroscopy under ambient conditions. Single crystals with dimensions up to 500 micrometers were grown at 22 gigapascals and 2000 degrees C over a period of 1 hour. Growth of crystals larger than 100 micrometers was achieved only when the pressure was within 5 percent of the pressure of the phase boundary separating the beta- and gamma-phase stability fields. A comparison of the elastic properties of the modified spinel phase with those of the olivine phase suggests that the 400-kilometer seismic discontinuity in the earth's mantle can be described by a mantle with 40 percent olivine. These results confirm that the 400-kilometer discontinuity can be due to the transition from olivine to modified spinel. The amount of olivine that must be present is less than that in a pyrolite model, although the results do not exclude pyrolite as a possible mantle model.     

Calcareous septa formed in snail shells by larvae of snail-killing flies

Larvae of 13 species of Pherbellia and Colobaea that feed in exposed aquatic snails uitilize a product of the Malpighian tubules before they pupate to form a plate-like structure within the shell or to reinforce the anterior end of the puparium. The substance is partly calcium carbonate, and carbonic anhydrase may be involved in its production.     

链板式对虾开背装置的试验研究

针对国内对虾开背设备短缺状况,研制了一种链板式对虾开背装置。以环渤海的南美白对虾为研究对象,在该装置上分别以2种不同输送姿态、2种开背刀具类型、3种输送速度进行开背效果的比较试验。试验结果表明:对虾以背部朝下头朝前的姿态、刀片类型为有齿圆盘刀、输送转速为150mm/s时开背质量到达最佳。该研究可以为对虾机械开背设备的研制提供参考。     

Observation of antiferromagnetic domains in epitaxial thin films

Antiferromagnetic domains in an epitaxial thin film, LaFeO(3) on SrTiO(3)(100), were observed using a high-spatial-resolution photoelectron emission microscope with contrast generated by the large x-ray magnetic linear dichroism effect at the multiplet-split L edge of Fe. The antiferromagnetic domains are linked to 90 degrees twinned crystallographic regions in the film. The Neel temperature of the thin film is reduced by 70 kelvin relative to the bulk material, and this reduction is attributed to epitaxial strain. These studies open the door for a microscopic understanding of the magnetic coupling across antiferromagnetic-ferromagnetic interfaces.     

Dynamics of Saturn's south polar vortex

The camera onboard the Cassini spacecraft has allowed us to observe many of Saturn's cloud features. We present observations of Saturn's south polar vortex (SPV) showing that it shares some properties with terrestrial hurricanes: cyclonic circulation, warm central region (the eye) surrounded by a ring of high clouds (the eye wall), and convective clouds outside the eye. The polar location and the absence of an ocean are major differences. It also shares properties with the polar vortices on Venus, such as polar location, cyclonic circulation, warm center, and long lifetime, but the Venus vortices have cold collars and are not associated with convective clouds. The SPV's combination of properties is unique among vortices in the solar system.