A multi‐MHz single‐shot data acquisition scheme with high dynamic range: pump–probe X‐ray experiments at synchrotrons

The technical implementation of a multi‐MHz data acquisition scheme for laser–X‐ray pump–probe experiments with pulse limited temporal resolution (100 ps) is presented. Such techniques are very attractive to benefit from the high‐repetition rates of X‐ray pulses delivered from advanced synchrotron radiation sources. Exploiting a synchronized 3.9 MHz laser excitation source, experiments in 60‐bunch mode (7.8 MHz) at beamline P01 of the PETRA III storage ring are performed. Hereby molecular systems in liquid solutions are excited by the pulsed laser source and the total X‐ray fluorescence yield (TFY) from the sample is recorded using silicon avalanche photodiode detectors (APDs). The subsequent digitizer card samples the APD signal traces in 0.5 ns steps with 12‐bit resolution. These traces are then processed to deliver an integrated value for each recorded single X‐ray pulse intensity and sorted into bins according to whether the laser excited the sample or not. For each subgroup the recorded single‐shot values are averaged over ～10⁷ pulses to deliver a mean TFY value with its standard error for each data point, e.g. at a given X‐ray probe energy. The sensitivity reaches down to the shot‐noise limit, and signal‐to‐noise ratios approaching 1000 are achievable in only a few seconds collection time per data point. The dynamic range covers 100 photons pulse^?1 and is only technically limited by the utilized APD.     

基于OTSU多阈值分割算法的激光线扫点云数据表达及精简方法研究

激光线扫方式获取的点云数据量庞大,不利于点云数据的存储、处理与分析。为了对激光线扫点云数据进行有效精简,提出了一种基于OTSU多阈值分割算法的激光线扫点云数据表达及精简方法。基于点云数据坐标与图像灰度值的映射,采用OTSU多阈值分割算法进行区域分割,并将分割后的各区域进行边缘提取及细化处理。根据原映射关系将细化的二值图像重新以点云方式表示,即得到精简的点云数据。在保持原有点云数据关键信息完整度的基础上,可有效地精简点云数据。实验结果表明:基于OTSU多阈值分割算法可有效地精简点云数据,同时能够有效地去除扫描过程中的背景干扰数据,具有较大的适用性和实际应用参考价值。     

功能化碳纳米管表面高分散的钯纳米粒子在碱性溶液中的甲醇氧化行为

本工作中在水溶液体系中以芳烃重氮盐修饰的多壁碳纳米管(MWNT)为载体构筑了钯(Pd)纳米粒子碳纳米管复合结构。以MWNT的侧壁上C-C共价键接的氨基苯甲酸为沉积活化中心,制备了高分散高催化活性的钯(Pd)纳米粒子。结构成分和形貌分别用XRD和TEM表征。循环伏安(CV) 和交流阻抗的研究表明上述复合结构在碱性溶液中对甲醇的电催化氧化有很高的活性及稳定性。芳烃重氮盐修饰的MWNT是一种非常好的催化剂载体,而Pd-MWNT复合材料在燃料电池有着广泛的应用前景。     

一种以水相中微波促进下的多组分反应合成具有重要生物意义的茚并[2,1-e]吡唑并[5,4-b]吡啶的绿色方法

在无催化剂的条件下,以醛、3-甲基-1-苯基-1H-吡唑-5-胺和1,3-茚二酮为原料,通过水相中微波促进下的多组分反应,成功地实现了具有重要生物意义的茚并[2,1-e]吡唑并[5,4-b]吡啶的绿色合成。这种方法具有环境友好、反应时间短、产率高、价廉、操作简单以及广泛的适用范围等显著优点。     

A solution adaptive simulation of compressible multi‐fluid flows with general equation of state

The unstructured quadrilateral mesh‐based solution adaptive method is proposed in this article for simulation of compressible multi‐fluid flows with a general form of equation of state (EOS). The five equation model (J. Comput. Phys. 2002; 118 :577–616) is employed to describe the compressible multi‐fluid flows. To preserve the oscillation‐free property of velocity and pressure across the interface, the non‐conservative transport equation is discretized in a compatible way of the HLLC scheme for the conservative Euler equations on the unstructured quadrilateral cell‐based adaptive mesh. Five numerical examples, including an interface translation problem, a shock tube problem with two fluids, a solid impact problem, a two‐dimensional Riemann problem and a bubble explosion under free surface, are used to examine its performance in solving the various compressible multi‐fluid flow problems with either the same types of EOS or different types of EOS. The results are compared with those calculated by the following methods: the method with ROE scheme (J. Comput. Phys. 2002; 118 :577–616), the seven equation model (J. Comput. Phys. 1999; 150 :425–467), Shyue's fluid‐mixture model (J. Comput. Phys. 2001; 171 :678–707) or the method in Liu et al. (Comp. Fluids 2001; 30 :315–337). The comparisons for the test problems show that the proposed method seems to be more accurate than the method in Allaire et al. (J. Comput. Phys. 2002; 118 :577–616) or the seven‐equation model (J. Comput. Phys. 1999; 150 :425–467). They also show that it can adaptively and accurately solve these compressible multi‐fluid problems and preserve the oscillation‐free property of pressure and velocity across the material interface. Copyright © 2010 John Wiley & Sons, Ltd.     

Positive solutions for singular systems of multi‐point boundary value problems

We study the existence of positive solutions for systems of singular nonlinear second‐order ordinary differential equations subject to multi‐point boundary conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

A simple SPH algorithm for multi‐fluid flow with high density ratios

In this paper, we describe an SPH algorithm for multi‐fluid flow, which is efficient, simple and robust. We derive the inviscid equations of motion from a Lagrangian together with the constraint provided by the continuity equation. The viscous flow equations then follow by adding a viscous term. Rigid boundaries are simulated using boundary force particles in a manner similar to the immersed boundary method. Each fluid is approximated as weakly compressible with a speed of sound sufficiently large to guarantee that the relative density variations are typically 1%. When the SPH force interaction is between two particles of different fluids, we increase the pressure terms. This simple procedure stabilizes the interface between the fluids. The equations of motion are integrated using a time stepping rule based on a second‐order symplectic integrator. When linear and angular momentum should be conserved exactly, they are conserved to within round‐off errors. We test the algorithm by simulating a variety of problems involving fluids with a density ratio in the range 1–1000. The first of these is a free surface problem with no rigid boundaries. It involves the flow of an elliptical distribution with one fluid inside the other. We show that the simulations converge as the particle spacing decreases, and the results are in good agreement with the exact inviscid, incompressible theory. The second test is similar to the first but involves the nonlinear oscillation of the fluids. As in the first test, the agreement with theory is very good, and the method converges. The third test is the simulation of waves at the interface between two fluids. The method is shown to converge, and the agreement with theory is satisfactory. The fourth test is the Rayleigh–Taylor instability for a configuration considered by other authors. Key parameters are shown to converge, and the agreement with other authors is good. The fifth and final test is how well the SPH method simulates gravity currents with density ratios in the range 2–30. The results of these simulations are in very good agreement with those of other authors and in satisfactory agreement with experimental results.Copyright © 2012 John Wiley & Sons, Ltd.     

Modeling of large scale solar cell handling robot with belt-driven flexible arms

To increase the competition of the solar energy collection system, the size of the solar panel module during the manufacturing process is being increased continuously. As the size of the solar panel increases, the size of the robot to handle the panel increased also. The change in scale of the robot inevitably results in the amplification of the adverse effect of the flexure. The main source of the flexure in the large scale solar cell panel handling system is the long and thin fork fingers of the hand and the solar cell panel. In addition, the belt-driven actuator system used by most of the large scale panel handling robot is another significant source of the vibration. In this paper, the flexible multi body dynamic model of a large scale solar cell panel handling robot, which is being designed and constructed with the help of Kyung Hee University, is developed. The belt-driven system in the robot is also modeled as flexible system and included in the robot to represent the actual vibration characteristics of the actuator system.     

A new enrichment space for the treatment of discontinuous pressures in multi‐fluid flows

In this work, a new enrichment space to accommodate jumps in the pressure field at immersed interfaces in finite element formulations, is proposed. The new enrichment adds two degrees of freedom per element that can be eliminated by means of static condensation. The new space is tested and compared with the classical P₁ space and to the space proposed by Ausas et al (Comp. Meth. Appl. Mech. Eng., Vol. 199, 1019–1031, 2010) in several problems involving jumps in the viscosity and/or the presence of singular forces at interfaces not conforming with the element edges. The combination of this enrichment space with another enrichment that accommodates discontinuities in the pressure gradient has also been explored, exhibiting excellent results in problems involving jumps in the density or the volume forces. Copyright © 2011 John Wiley & Sons, Ltd.