短脉冲激光尾流场中的前向Raman散射

用212维粒子模拟分析了前向Raman散射对激光尾流场加速电子的影响.前向Raman散射使脉冲长度在传播方向上被拉长，脉冲后沿变陡，产生的尾流场相速度明显减小，而且超热电子的最大动能明显小于理论估计值.此外激光频率整体向低频移动.     

Scanning probe microscopy characterization of gold-chemisorbed poplar plastocyanin mutants

Two poplar plastocyanin mutants adsorbed onto gold electrodes have been characterized at single molecule level by scanning probe microscopy. Immobilization of the two redox metalloprotein mutants on Au(1 1 1) surface was achieved by either a disulphide bridge (PCSS) or a single thiol (PCSH), both the anchoring groups having been introduced by site-directed mutagenesis. Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) analysis gives evidence of a stable and robust binding of both mutants to gold. The lateral dimensions, as estimated by STM, and the height above the gold substrate, as evaluated by AFM, of the two mutants well agree with crystallographic sizes. A narrower height distribution is observed for PCSS compared to PCSH, corresponding to a more homogeneous orientation of the former mutant adsorbed onto gold. Major differences between the mutants are observed by electrochemical STM. In particular, the image contrast of adsorbed PCSS is affected by tuning the external electrochemical potential to the redox levels of the mutant, consistent with some involvement of copper active site in the tunneling process. On the contrary, no contrast variation is observed in electrochemical STM of adsorbed PCSH. Moreover, scanning tunneling spectroscopy experiments reveal asymmetric I–V characteristics for single PCSS proteins, reminiscent of a rectifying-like behaviour, whereas an almost symmetric I–V relation is observed for PCSH.     

Experimental study and mathematical modelling of a new of vibro-impact moling device

In this paper experimental study and mathematical modelling of newly designed vibro-impact moling rig are presented. The design is based on electro-mechanical interactions of a conductor with an oscillating magnetic field. The rig consists of a metal bar placed within a solenoid which is connected to an RLC circuit, and an obstacle block positioned nearby. Both the solenoid and the block are attached to a base board. Externally supplied alternating voltage causes the bar to oscillate and hit the block resulting in the forward motion of the base board mimicking a mole penetration through the soil. By varying the excitation voltage and the capacitance in the circuit, a variety of system responses can be obtained.In the paper the rig design and experimental procedure are explained in detail, and the mathematical modelling of the rig is described. Then the obtained coupled electro-mechanical equations of motion are integrated numerically, and a comparison between experimental results and numerical predictions is presented.     

Thermoelastoplastic deformation of a thick-walled cylinder with a radial crack

The thermoelastoplastic fracture mechanics problem of a thick-walled cylinder subjected to internal pressure and a nonuniform temperature field is solved by the method of elastic solutions combined with the finite-element method. The correctness of the solution is provided by using the Barenblatt crack model, in which the stress and strain fields are regular. The elastoplastic problem of a cracked cylinder subjected to internal pressure and a nonuniform temperature field are solved. The calculation results are compared with available data. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 173–183, May–June, 2008.     

DUAL RECIPROCITY HYBRID BOUNDARY NODE METHOD FOR THREE-DIMENSIONAL ELASTICITY WITH BODY FORCE

Combining Dual Reciprocity Method （DRM） with Hybrid Boundary Node Method （HBNM）, the Dual Reciprocity Hybrid Boundary Node Method （DRHBNM） is developed for three-dimensional linear elasticity problems with body force. This method can be used to solve the elasticity problems with body force without domain integral, which is inevitable by HBNM. To demonstrate the versatility and the fast convergence of this method, some numerical examples of 3-D elasticity problems with body forces are examined. The computational results show that the present method is effective and can be widely applied in solving practical engineering problems.     

Solid state NMR characterization of formation of poly(ϵ‐caprolactone)/maghnite nanocomposites by in situ polymerization

Results of multinuclear MAS NMR spectroscopy are reported for poly (ε‐caprolactone)/maghnite nanocomposite formation, with ε‐caprolactone in situ polymerized in the presence of maghnite, a proton exchanged montmorillonite clay. Exfoliated and intercalated materials with different maghnite loading in the range 3–15 wt % were investigated. ¹H NMR evidences Brønsted acid hydroxyl groups in the silicate layers and shows that their broad signal at 7.6 ppm present in the parent clay disappears in the nanocomposite material. ²⁷Al MAS NMR results show that beside the hexacoordinated aluminum signal, two additional peaks corresponding to two different tetrahedral Al sites are present in the clay framework. The NMR signal intensity of only one of them was found to be affected in the nanocomposites compared with the parent maghnite, suggesting that these specific aluminum sites are the reactive ones at the initial stages of the polymerization. However almost no changes occurred in the ²⁹Si NMR spectra, confirming that the polymer grafting, as indicated earlier by atomic force microscopy, took place on the aluminum tetracoordinated sites rather than on the silicon sites. A mechanism of maghnite surface catalyzed polymerization of ε‐caprolactone was proposed, involving Brønsted and Lewis acid sites. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3060–3068, 2007     

扫描力显微术在高聚物薄膜玻璃化转变研究中的应用

简述了高聚物薄膜玻璃化转变的复杂性，并结合文章作者的的一些研究结果介绍了扫描力显微术(SFM)在研究高聚物玻璃化转变中的一些方法，包括观察高聚物薄膜形貌的变化，测量其摩擦力、粘附力和弹性模量等物理量的变化，最后指出SFM是研究高聚物薄膜玻璃化转变的有力工具。     

Surface roughness investigation of semi-conductor wafers

Conventionally, surface roughness is predominantly determined through the use of stylus instruments. However, there are certain limitations involved in the method, particularly when a test specimen, such as a silicon wafer, has a smooth mirror-like surface. Hence, it is necessary to explore alternative non-contact techniques. Light scattering has recently been gaining popularity as an optical technique to provide prompt and precise inspection of surface roughness. In this paper, the total integrated scattering (TIS) model is modified to retrieve parameters on surface micro-topography through light scattering. The applicability of the proposed modified TIS model is studied and compared with an atomic force microscope. Experimental results obtained show that the proposed technique is highly accurate for measuring surface roughness in the nanometer range.     

提高YBCO块材在外磁场中悬浮力

本给出了三种提高YBCO块材在外磁场中悬浮力的方法．第一种方法是增强外磁场，对于此方法，本研究了一块直径为30mm的圆柱状YBCO块材分别在圆柱状NdFeB永磁体和NdFeB永磁导轨上的悬浮力．测量结果表明在77K温度下YBCO块在圆柱状NdFeB永磁体上的最大悬浮力为50N，在NdFeB永磁导轨上的最大悬浮力为103．ON．第二种方法是提高YBCO块材自身的性能，包括临界电流密度、俘获磁通和块材尺寸，对于此方法，本仅研究了块材尺寸对悬浮力的影响．三块直径分别为30mm、35mm、40mm的圆柱状YBC0块材在NdFeB永磁导轨上的悬浮力被测量，77K温度下5mm悬浮间距时的悬浮力分别为103．ON、134．5N、175．ON．第三方法是将YBCO块材变成准永久磁体，此种情况下，直径为40mm的圆柱状YBCO块材在77K温度下5mm悬浮间距时的悬浮力高达218．3N．     

非保守力和非完整约束对Hamilton系统Lie对称性的影响

研究非保守力和非完整约束对Hamilton系统的Lie对称性和守恒量的影响.分别研究了Hamilt on系统受到非保守力和非完整约束作用时，系统的Lie对称性保持不变的条件，同时给出了 系统的结构方程和守恒量保持不变的条件.以著名的Emden方程和Appell-Hamel模型为例进行 了分析讨论. 关键词： 分析力学 Hamilton系统 非保守力 非完整约束 对称性 守恒量