用MXAN拟合钩端螺旋体去甲酰化酶XANES谱

钩端螺旋体去甲酰化酶(Leptospira interrogans PDF)是一种重要的含锌金属蛋白酶, 对钩端螺旋体这一广泛存在的致病菌的蛋白合成起着关键的催化作用, 是一个很好的药物设计靶蛋白. 本文测试了LiPDF在pH3.0的溶液状态下的X射线吸收近边结构(XANES: X-Ray Absorption Near-Edge Structure)谱, 利用以从头计算(ab. initio)的多重散射(Multiple Scattering)为基础的MXAN方法确定金属蛋白活性中心的精细结构. 研究发现结合合适的初始结构模型, 可以更好地重现LiPDF蛋白的XANES曲线, 从而能够得到更加准确的结构参数. 活性中心的精细结构为理解LiPDF的pH依赖的催化活性提供了结构基础.     

同步辐射X射线成像光束线劳厄双晶单色器设计

上海光源X射线成像光束线采用多极扭摆器(wiggler)作为辐射光源, 提出一种劳厄双弯晶单色器的设计方案. 计算结果显示, 可获得固定出口的平行单色光束, 能量调谐范围覆盖19—120keV, 在33keV时, 输出光子通量及通量密度分别为1.9×10¹³phs/s和3.8×10¹⁰phs/s/mm². 分析了劳厄晶体的聚焦及单色化性能, 计算了输出光子通量及单色器的热负载情况. 与传统的双平晶方案相比, 本设计在获得高通量和解决热负载等方面有明显的优越性, 并能有效控制热形变.     

天鹅绒阴极产生的双脉冲强流相对论电子束特性实验研究

在时间分辨的模式下, 实验研究了天鹅绒阴极产生的双脉冲相对论强流电子束的束心运动、束包络和束的发射度. 在实验中, 电子束流强度和电子束心运动用电阻环进行测试, 而电子束和石英玻璃的相互作用产生的契仑科夫辐射用来给出电子束包络和发射度信息. 电子束和石英玻璃作用产生的契仑科夫辐射用1台8幅分幅相机记录. 实验结果表明, 天鹅绒阴极产生的相对论强流双脉冲电子束在束流大小、束心运动轨迹、束包络及束发射度等方面具有较好的一致性.     

Investigation of Ti/TiN multilayered films in a reactive mid-frequency dual-magnetron sputtering

Influence of the process parameters like (i) sputtering gas pressure, (ii) target current, (iii) substrate bias voltage and (iv) substrate temperature of a reactive mid-frequency dual-magnetron sputtering on (a) surface defects and (b) mechanical properties of Ti/TiN multilayered films was investigated. The forming mechanisms of the observed droplets and craters were analyzed. Results showed when: (1) pressure of Ar/N₂ gases PAr/N₂ was at 0.31 Pa and substrate temperature was in certain range, the size and the density of the surface defects on the TiN films tended to decrease with increasing the target current and the pulsed bias voltage; (2) the optimal deposition parameters for accomplishing fewer surface defects were used, increasing the thickness of the Ti buffer layer decreased the microhardness in certain level, and the adhesion was firstly increased and then decreased as thickness reaching and/or beyond a critical value. Results also showed that selection of optimized process parameters evidently minimized the surface defects and improved the mechanical properties of the film.     

Neural network applied to reconstruction of complex objects based on fringe projection

The neural network has been introduced into the reconstruction of the complex object based on fringe projection. In this method, the neural network with powerful property of approximation is used to get the continuous approximate function of a discrete fringe pattern captured by an image frame grabber. The depth-related phase of the measured object modulated into the fringe pattern can be demodulated by dealing with the approximate function. Compared with the Fourier transform profilometry (FTP), in the network method, one deformed fringe pattern is needed to reconstruct the tested object, and a high spatial resolution is maintained for no filtering process. Therefore, this method performs better than FTP in the measurement of the complex object. Moreover, the network method is capable of demodulating more depth-related phase even in the case that the local shadow exists in the fringe pattern. Computer simulations and experiments validate the feasibility of this method.     

High-Sensitivity Sensor Based on Surface Plasmon Resonance Enhanced Lateral Optical Beam Displacements

We present a new optical sensor based on surface plasmon resonance （SPIt） enhanced lateral optical beam displacements. Compared with the traditional SPIt methods, the new method provides higher sensitivity to the sensor system. Theoretical simulations show that the refractive index （RI） detection sensitivity of the SPR sensor based on the displacement measurement has a strong dependence on the thickness of the metal film. When the optimal thickness of the metal film is selected, the RI resolutlon of the SPIt sensor is predicted to be 2.2 × 10^-7 refractive index units （RIU）. Furthermore, it is found that the incidence angle can be used as a parameter to adjust the operating range of the sensor to different refractive index ranges.     

Stability of Motion of a Nonholonomic System

Perturbation differential equations of motion of a general nonholonomic system subjected to the ideal nonholonomic constraints of Chetaev＇s type are established, and the equation of variation of energy is deduced by using the perturbation equations of the system. A criterion of the stability is obtained and an example is given to illustrate the application of the result.     

Oscillatory Activities in Regulatory Biological Networks and Hopf Bifurcation

Exploiting the nonlinear dynamics in the negative feedback loop, we propose a statistical signal-response model to describe the different oscillatory behaviour in a biological network motif. By choosing the delay as a bifurcation parameter, we discuss the existence of Hopf bifurcation and the stability of the periodic solutions of model equations with the centre manifold theorem and the normal form theory. It is shown that a periodic solution is born in a Hopf bifurcation beyond a critical time delay, and thus the bifurcation phenomenon may be important to elucidate the mechanism of oscillatory activities in regulatory biological networks.     

Development of the Technique for Fabricating Submicron Moire Gratings on Metal Materials Using Focused Ion Beam Milling

A focused gallium ion （Ga＋） beam is used to fabricate micro/submicron spacing gratings on the surface of porous NiTi shape memory alloy （SMA ）. The crossing type of gratings with double-frequency （25001/mm and 50001/mm） using the focused ion beam （FIB） milling are successfully produced in a combination mode or superposition mode. Based on the double-frequency gratings, high-quality scanning electron microscopy （SEM） Moird patterns are obtained to study the micro-scale deformation of porous NiTi SMA. The grating fabrication technique is discussed in detail. The experimental results verify the feasibility of fabricating high frequency grating on metal surface using FIB milling.     

Electrochemical Deposition and Properties of ZnTe Nanowire Array

Pulsed electrodeposited technique is applied to fabricate ZnTe nanowire arrays with different diameters into the anodic alumina membrane in citric acid solution. The x-ray powder diffraction, scanning electron microscopy and transmission electron microscopy indicate that the high ordered, uniform and single-crystalline nanowires have been fabricated. The optical absorption spectra of the nanowire array show that the optical absorption band edge of the ZnTe nanowire array exhibit a blue shift compared with that of bulk ZnTe, and the nonlinear current-voltage characteristic is observed.