Formation of bimetallic Ag-Au nanowires by metallization of artificial DNA duplexes

Uniform bimetallic nanowires, tunable in size, have been grown on artificial DNA templates via a two-step metallization process. Alkyne-modified cytosines were incorporated into 900-base-pair polymerase-chain-reaction fragments. The alkyne modifications serve as addressable metal-binding sites after conversion to a sugar triazole derivative via click chemistry. Reaction of the Tollens reagent with these sugar-coated DNA duplexes generates Ag0 metallization centers around the sugar modification sites of the DNA. After a subsequent enhancement step using gold, nanowires < or = 10 nm in diameter with a homogeneous surface profile were obtained. Furthermore, the advantage of this two-step procedure lies in the high selectivity of the process, due to the exact spatial control of modified DNA base incorporation and hence the confinement of metallization centers at addressable sites. Besides experiments on a membrane as a proof for the selectivity of the method, atomic force microscopy (AFM) studies of the wires produced on Si-SiO2 surfaces are discussed. Furthermore, we demonstrate time-dependent metallization experiments, monitored by AFM.     

白肋烟烟碱含量的机械调控技术

研究了打顶后 5d机械切根 1/ 8、1/ 4对白肋烟烟碱合成、烟叶产量和产值的影响 ,结果表明 :机械切根能明显降低烟碱含量 ,其中切根 1/ 8与对照相比 ,上部叶烟碱下降 1.9个百分点 ,降幅31.33% ;中部叶烟碱下降 2 .13个百分点 ,降幅 5 1.4 5 %。切根处理对烟叶产值、产量无明显不利影响     

白肋烟品种性状与烟碱积累的关系研究

研究结果表明,白肋烟上部叶烟碱含量与株高、茎围、节距、叶数呈现极显著负相关;与移栽-现蕾时间呈现极显著负相关;与烟叶产量呈现极显著负相关。烟碱积累与烟株打顶后时间关系可用二次方程拟合且相关极显著。烟碱积累速率同品种的成熟性密切相关,晚熟品种较早、中熟品种烟碱积累速率低且随时间变化显著降低;生产上宜选用综合性状较好的品种NC3、KY8959。      

Simulation of Explosive Welding with ANFO Mixtures

The work described here arose from a study into explosive welding. As part of that study, the impact velocity of stainless steel and titanium plates to grazing detonation of ANFO/perlite, the velocity of detonation were measured. Computer simulation required a new model which copes with an equation of state of low explosives.     

Profilometry-Based Indentation Plastometry Testing for Characterization of Case-Hardened Steels

An attraction of the profilometry-based indentation plastometry (PIP) procedure is that, while it involves interrogation of volumes sufficiently large to ensure that bulk properties are obtained, it still allows stress–strain curves to be inferred for relatively small regions, such that local properties can be mapped where they are changing over short distances. It is employed here to obtain these characteristics as a function of depth in samples that have been case hardened by the diffusional penetration of carbon, to a depth of just over a mm. This has been done for a grade of steel that is commonly treated in this way. The thickness of the layer characterized by the PIP test is around 200 μm. In addition, curvature measurements on strip samples, after incremental removal of thin layers, have been used to evaluate the (compressive) residual stresses in near-surface regions. These range up to around 200 MPa. Such stresses have only a small effect on the PIP measurements. The carburization raises the peak yield stress from the base level of around 1000 MPa to about 1400 MPa, followed by considerable work hardening. The reliability of these PIP-derived stress–strain relationships has been confirmed by comparing experimental outcomes of Vickers hardness tests with FEM predictions based on their use.     

Indentation Plastometry of Particulate Metal Matrix Composites,Highlighting Effects of Microstructural Scale

Herein, it is concerned with the use of profilometry-based indentation plastometry (PIP) to obtain mechanical property information for particulate metal matrix composites (MMCs). This type of test, together with conventional uniaxial testing, has been applied to four different MMCs (produced with various particulate contents and processing conditions). It is shown that reliable stress–strain curves can be obtained using PIP, although the possibility of premature (prenecking) fracture should be noted. Close attention is paid to scale effects. As a consequence of variations in local spatial distributions of particulate, the “representative volume” of these materials can be relatively large. This can lead to a certain amount of scatter in PIP profiles and it is advisable to carry out a number of repeat PIP tests in order to obtain macroscopic properties. Nevertheless, it is shown that PIP testing can reliably detect the relatively minor (macroscopic) anisotropy exhibited by forged materials of this type.