脉冲星脉冲轮廓累积的最小熵方法

获取脉冲星辐射信号累积轮廓的传统方法是先识别信号周期,再按周期对信号进行折叠累加,这种方法依赖于周期识别的准确性,对累积轮廓质量也无评价标准.本文分析了脉冲星累积轮廓和周期的强相关性,提出了周期未知时直接进行轮廓累积的最小熵方法,并对其进行证明,在此基础上,讨论了该方法在周期识别中的作用.利用仿真数据和RXTE卫星的实测数据实验验证了该方法的有效性.关键词：脉冲星最小熵累积轮廓周期识别     

非马尔科夫耗散系统长时演化下的极限环振荡现象

本文研究结构化环境中非马尔科夫耗散系统在长时演化下可能出现的极限环振荡现象. 对于欧姆型谱密度环境中的二能级系统, 由于体系只允许一个束缚态模, 给定初态系统在Bloch空间的长时演化将收敛于一个极限环. 研究揭示了极限环半径与环心位置同环境谱密度函数间的关系. 对于多带光子晶体环境中的二能级系统, 由于其可以存在多个束缚态, 研究展现了系统在长时演化下可能出现的收敛于环面或周期或准周期的振荡行为. 有关环面的特征量与环境谱密度间的量化关系同样得以刻画. 论文随后讨论了两比特系统关联量在局域非马尔科夫耗散环境中长时演化可能出现的特征行为.     

ERA-Interim中的中国地区水分循环要素的时空演变特征分析

本文利用1979–2011年欧洲中期天气预报中心 (ECMWF) 的再分析资料 (ERA-Interim), 运用经验正交函数展开 (EOF) 和相似系数等方法, 对中国地区水分循环诸要素的时空特征进行了计算与分析. 研究结果表明: 在空间分布特征上, 蒸发量、纬向水汽通量和经向水汽通量均与大气可降水量的空间分布最相似, 大气可降水量和降水量均与蒸发量的空间分布最相似, 降水量与纬向水汽通量的相似系数略大于其与经向水汽通量的相似系数; 在时间演变上: 年降水量在1979–2002年间, 呈现非常显著的上升趋势; 在2002–2011 年间, 呈现显著的下降趋势. 年蒸发量在该两个时段的变化趋势与年降水量一致, 但均比年降水量明显; 年蒸发量在1979–2011年间呈现非常显著的上升趋势, 其年际变化明显小于年降水量. 可降水量和水汽通量散度在1979–2011年间的长期变化趋势不明显, 但可降水量的年际变化呈阶段式增大, 水汽通量的年际变化一直较大. 纬向与经向水汽通量均存在2–3年为周期的年际变化; 此外, 纬向水汽通量在1979–2011年间还存在显著的下降趋势. 春、秋季的水汽通量都存在显著下降的长期变化趋势, 夏、冬季的长期变化趋势不明显. 四季都存在2–3年为周期的年际变化. 此外, 夏季还存在明显的年代际转折.关键词：水分循环时空特征EOF相似系数     

超短脉冲光束传输缓变包络近似理论的失效和空间奇异性的形成与消除

研究了单周期或更短的超短脉冲光束在真空中的传输.结果显示,在此情况下缓变包络近似理论已不再有效,其失效的原因是,该理论导致了脉冲光束解的空间奇异性,并使脉冲光束不再具有符合物理意义的光束行为,而通过复解析信号的分析方法可以消除这种空间奇异性.给出了时间波形为Gauss,Hyperbolic Secant和Lorentz的脉冲光束奇异性的计算模拟,并给出了解决这些奇异性的复解析信号解.同样,会发现在脉冲光束超过一定的长度后两种解是一致的.     

A Reduced Order Cyclic Method for Computation of Limit Cycles

A reduced order cyclic method was developed to compute limit-cycle oscillations for large, nonlinear, multidisciplinary systems of equations. Method efficacy was demonstrated for two simplified models: a typical-section airfoil with nonlinear structural coupling and a nonlinear panel in high-speed flow. The cyclic method was verified to maintain second-order temporal accuracy, yield converged limit cycles in about 10 Newton iterates, and provide precise estimates of cycle frequency. This method was projected onto a low-order space using a set of variables governing the amplitudes of empirically derived modes, which were computed with the proper orthogonal decomposition. In this reduced order form, the cyclic Jacobian was greatly compressed, allowing accurate limit cycle solutions to be very efficiently computed.The U.S. Governments right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.     

Fatigue strength of metallic and composite materials under repeated high-cycle bending

The problem of fatigue strength analysis of metallic and composite materials subjected to combined static and cyclic bending is resolved. The analysis is based on limit-state models, which allow describing limiting-stress curves of all known shapes, including convex, rectilinear, S-shaped, and concave. The fatigue strength of the following materials is evaluated: carbon and alloyed steels, aluminum alloys, unidirectional organic plastics, laminated plastics, and glassfiber-reinforced plastics. The calculated and experimental data are in satisfactory agreement __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 5, pp. 26–36, May 2006.     

A multiscale approach of fatigue and shakedown for notched structures

The aim of this paper is to analyse the fatigue phenomena in the presence of stress gradients. It is well-known that most fatigue criteria fail to predict the lifetime of components in the presence of high stress concentrations or stress gradients, as it is the case in the neighbourhood of cracks, holes notches and encountered for example in riveted or threaded structures. Proposed is a numerical approach in the framework of the high cycle fatigue domain in order to give a qualitative answer. The work starts from the numerical computation of macroscopic loading corresponding to some fatigue experiments on specimens with an inclusion of metallic grains embedded in a macroscopic matrix. The computed fields are then analysed in terms of the HCF (high cycle fatigue) criterion [1], which is based on the estimation of the shakedown limit at the grain scale. The infinite lifetime prediction is based on the assumption that fatigue occurs if at least one grain fails, i.e. reaches plastic shakedown. The predictions at mesoscopic and macroscopic scales are close if the macroscopic stress distribution is homogeneous. However in the case of the stress gradient, lifetime predicted at the macroscopic scale is underestimated when compared to the predictions made at the mesoscopic scale. Another result is that the gap between microscopic and macroscopic predictions obtained from these numerical computations can roughly be estimated by a diminution of stress of the same order of magnitude as found in the experiments and phenomenological observations.     

A Directed Percolation Model for Clogging in a Porous Medium with Small Inhomogeneities

We propose a microscopic model based on directed percolation for the process of mechanical clogging of a porous medium by particles suspended in a fluid flow. Under appropriate conditions the deposited particles may form fractal clusters. A criterion for the occurrence of fractal clogging is presented. It links together the particle size and the pore size distribution. The effect of microscopic inhomogeneities is studied inside and outside the critical region using Monte Carlo calculations in two dimensions. The critical exponents remain unchanged because the perturbation induced by these inhomogeneities is irrelevant. The percolation threshold is found to shift to higher values almost linearly with increasing size of obstacles. For size distributed obstacles the arithmetic mean of the distribution is the only significant parameter which determines the shift. Type and broadness of the distribution have no influence. Also the percolation probability depends only on the mean even outside the critical region for all values of the occupation probability. Occupying the same fraction of the porous matrix, large obstacles cause more particles to deposit than small ones.     

GPS载波相位差分技术实时测姿的研究与应用

从运动载体姿态测量实时性的要求出发，介绍了应用GPS相位差分技术，进行实时姿态测量系统的研究和开发，介绍了系统的设计思路和信息处理的基本过程，实现了载体姿态的实时测量，达到了要求的技术指标。该系统适用于静态姿态测量与定位和中、低动态载体的姿态测量与定位。     

Systemic view of learning scientific concepts: A description in terms of directed graph model

This study suggests a systemic view on concept learning, in which concepts are seen as complex, dynamically evolving structures with robust and persistent patterns emerging from loosely connected elemental pieces. The model is represented in the form of a directed graph, and it explains many empirically identified features of learning paths, including: (1) the stability of learned concepts, (2) changes in concept attributions (ontological shift) as guided by theoretical knowledge, and (3) the evolution of concepts as driven by model competition with the accumulation of evidence. The results thus show applicability of the systemic view and the directed graph model. © 2013 Wiley Periodicals, Inc. Complexity 19: 27–37, 2014