Capturing the experimental behaviour of a point-absorber WEC by simplified numerical models

The paper presents a wave basin experiment of a direct-driven point-absorber wave energy converter moving in six degrees of freedom. The goal of the work is to study the dynamics and energy absorption of the wave energy converter, and to verify under which conditions numerical models restricted to heave can capture the behaviour of a point-absorber moving in six degrees of freedom. Several regular and irregular long-crested waves and different damping values of the power take-off system have been tested. We collected data in terms of power output, device motion in six degrees of freedom and wave elevation at different points of the wave basin. A single-body numerical model in the frequency domain and a two-body model in the time domain are used in the study. Motion instabilities due to parametric resonance observed during the experiments are discussed and analysis of the buoy motion in terms of the Mathieu instability is also presented. Our results show that the simplified models can reproduce the body dynamics of the studied converter as long as the transverse non-linear instabilities are not excited, which typically is the case in irregular waves. The performance of the more complex time domain model is able to reproduce both the buoy and PTO dynamics, while the simpler frequency domain model can only reproduce the PTO dynamics for specific cases. Finally, we show that the two-body dynamics of the studied wave energy converter affects the power absorption significantly, and that common assumptions in the numerical models, such as stiff mooring line or that the float moves only in heave, may lead to incorrect predictions for certain sea states.     

Fused vs. spiro: Kinetic,not thermodynamic preference may direct the reaction of α-carbonyl oxonium ylides

Rh(II)-catalyzed decomposition of certain cyclic α-diazocarbonyl compounds in the presence of cyclic ethers has been shown to give bicyclic ring expansion products. These are thought to arise from a [1,4]-alkyl shift toward the carbonyl oxygen atom and are in contrast with the recently observed spirocyclic products of a Stevens-type [1,2]-alkyl shift within the postulated oxonium ylide intermediate. Quantum chemical calculations performed at the B3LYP/6-31G* level of theory showed that the former reaction pathway (toward fused bicycles) is kinetically preferred.     

超声光栅实验及其多普勒频移的一种简单研究方法

采用光子学方法,对超声光栅衍射实验和实验中出现的多普勒频移现象进行了研究,所得结论与采用光的波动性观点的惠更斯-菲涅耳原理及傅里叶变换等常规方法相同.该方法进一步加深了对衍射的本质和光的粒子性的理解并对光子的信息传递能力有初步的认识.     

天文斑点成像技术中的噪声影响分析

为进一步说明天文像复原新方法-迭代位移叠加法的性质，对探测器的附加噪声在斑点干涉术、斑点掩模法和迭代位移叠加法中的影响分别进行了分析。结果表明：在斑点掩模法中，复杂的噪声高阶矩统计被引入了重谱的噪声偏差，因此对噪声极为敏感，使数据处理更加复杂化；与斑点掩模法相比，迭代位移叠加法仅涉及对噪声的一阶矩统计平均，所以此新方法的特点是对噪声不敏感，具有图像复原处理过程简单快捷的优越性。     

飞秒孤子传输演化的数值研究

利用分步傅里叶法数值模拟了飞秒孤子在光纤中的传输演化过程。对光纤中单个孤子的传输及二阶孤子的自陡峭效应和自频移效应进行了分析,指出在一定的参数取值范围内,自频移效应对二阶fs孤子传输的影响要比自陡峭效应大,占主导地位,且对自陡峭效应有一定的抑制作用。     

The Markov power moment problem in problems of controllability and frequency extinguishing for the wave equation on a half-axis

In this paper necessary and sufficient conditions of null-controllability and approximate null-controllability are obtained for the wave equation on a half-axis. Controls solving these problems are found explicitly. Moreover, bang-bang controls solving the approximate null-controllability problem are constructed with the aid of solutions of a frequency extinguishing problem in the restricted band (−a,a) for this equation and the Markov power moment problem.     

光纤光栅激光器激射波长的研究

一般认为，用光纤光栅作选频元件的光纤激光器，激射波长与光纤光栅中心反射波长一致，本文报道了不同的实验研究结果。通过细致的实验研究，发现光纤光栅激光器激射波长相对于光纤光栅中心反射波长有一定的偏移。激射波长可以出现在光栅中心反射波长的长波端，也可以出现在其短波端。对不同腔结构的掺镱、掺铒光纤光栅激光器的深入研究证明，谐振腔的各向异性对激光器的激射波长偏移起到决定性的作用，波长最大偏移量主要受限于光纤光栅的反射带宽。通过激光腔内的偏振控制器改变谐振腔的各向异性，可以在光纤光栅的反射带宽内控制激射波长的位置。