北极涛动对华北沙尘暴频次的影响

This study has investigated the influence of Arctic Oscillation (AO) on dust storm frequency in North China in spring seasons during 1961-2007. There is a significant linkagebetween dust storm frequency and AO; a negative (positive) AO phase is related to an in-creased (decreased) dust storm frequency in North China. This relationship is closely related to changes in the cold air activity in Mongolia. The cold air activity exerts large impacts on the dust storm frequency; the frequency of cold air activity over Mongolia not only positively cor-relates with the dust storm frequency in North China, but also shows a long-term decreasing trend that is an important reason for the long-term decreasing of dust storm frequency in North China. The AO has large influence on the frequency of cold air activity over Mongolia; a negative (positive) AO phase is highly related to an increased (decreased) frequency of cold air activity over Mongolia, which results in an increased (decreased) dust storm frequency in North China.     

自适应变结构控制在弹道导弹中段控制的应用

随着弹道导弹技术的发展,中段机动变轨需要进行高精度的姿态指向、快速的大角度机动以及有效地节省能量等复杂的姿态控制。该文将自适应变结构控制应用于弹道导弹中段姿态控制中,推导了滑模到达条件,设计了相应形式的切换函数,给出了一种参数选择方案井设计了一种控制器以抑制抖振,给出了详尽的实现方法。仿真结果表明,该方法可以很好地实现中段姿态控制。具有良好的应用意义。     

基于Prony方法的电力系统振荡模式分析及PSS参数设计

Prony分析是获取系统振荡模式的一种非常有效的分析方法,它可以通过给定输入信号下的响应直接估计系统的振荡频率、阻尼、幅值和相对相位。文章介绍了基于Prony分析的电力系统等值线性模型的辨识方法,对传统的Prony方法进一步扩充,考虑了输入信号对输出信号的影响,得到了系统的传递函数,并根据其相应留数,采用留数方法对电力系统稳定器(PSS)进行了参数的协调配置。两个算例的仿真结果证明了该方法在系统振荡模式分析和PSS参数设计中的有效性。     

"摇摆"的教堂——象山丹城基督教堂设计札记

教堂作为特定文化内涵下的西方传统建筑类型,在国内的建设必然面对文化、传统、地域、情感等诸多问题.该文结合丹城基督教堂的设计实践,从传统与现代、神性与人性、独立与交融、形制与创作这四个方面来探讨其创作思路和设计方法.     

Large-Eddy/Reynolds-averaged Navier–Stokes simulation of combustion oscillations in a cavity-based supersonic combustor

Combustion oscillations in a supersonic combustor with hydrogen injection upstream of a cavity flameholder are investigated numerically using a hybrid RANS/LES (Reynolds-Averaged Navier–Stokes/Large-Eddy Simulation) method acting as a wall-modeled LES. A turbulent boundary layer with thickness of δ_inf = 2.5 mm is considered and a recycling/rescaling method is adopted to treat the unsteady inflow. The results show that combustion oscillations can mainly be attributed to two mechanisms. One is the unsteady flame spreading from the cavity shear layer to the main stream, which is greatly influenced by the interaction of the jet-with-cavity shear layer. This mechanism leads to relatively low-frequency oscillations that correspond to the cavity-shear layer oscillations. The other is the auto-ignition of the combustible fluid packets formed around the fuel jet accompanied by the generation of the hairpin-like vortices, which leads to relatively high-frequency oscillations that correspond to the jet instabilities.     

非线性二阶微分方程的振动定理

本文考虑二阶非线性方程 (r(t)Y′(t))′ P(t)Y′(t) q(t)f(Y(t))=0 (1) 其中P,q,r:[t_0,∞)→R,f:R→R是连续函数。f(t)>0,t≥t_0。且Yf(Y)>0,y≠0。利用加权积分平均的技,讨论方程(1)的振动性质。所得结果推广并改进了一些已知的振动准则。     

二阶非线性强迫振动

本文研究二阶非线性方程[q(t)x’]’ a(t)f(x)=g(t)的解的振动性。如果或者,那么在一定条件下,方程是振动的。本文推广了文[1]的结论。     

静止式气波机振荡器振荡机理分析及振荡特性的研究

静止式气波机振荡特性取决于振荡源的形式。以共鸣器为振荡源，从管路阻抗的角度和射流噪声的角度对其振荡机理进行了分析。对机器振荡特性进行了实验研究，结果表明，从射流噪声角度解释共鸣器振荡机理更为合理，同时发现机器运行过程中出现了“压力变频”现象，在稳定的高频振荡区和低频振荡区所形成的激波强度相差很大。从而为静止式气波机的效率的提高及结构的改进提供了有益的结果。     

Test suite oscillations

This paper proposes a set of new software test-diversity measures based on control oscillations of test suites. Oscillation Diversity uses conversion, inversion, and phase transformation to vary test suite amplitudes, frequencies, and phases. Resistance and inductance are defined as measures of diversification difficulty. The experimental results show correlation between some Oscillation Diversity measures and fault-detection effectiveness.     

一类化学反应的振荡性

本文讨论化学反应A+B→2B,B→C中有逆反应时,其对应的数学模型,给出了存在唯一极限环的条件,并考虑了其何时产生强迫振荡。