串联补偿线路SSR分析研究

随着我国电力系统的发展,串联电容补偿在输电系统的应用越来越广泛,但其引起的次同步谐振（SSR）问题也随之而来。针对输电网中串联电容补偿引发的次同步谐振,文章采用基于时域仿真实现的复转矩系数法分析了不同发电机出力以及不同串补度对系统次同步谐振的影响。仿真验证了故障情况下,较小串补度系统对次同步谐振的稳定性。     

基于时间序列法与马尔可夫链的多沙水库动态运用研究

为了更好解决多沙河流水库蓄水和排沙间的矛盾,在传统水库运用模式的基础上,结合时间序列法和马尔可夫链原理建立多沙水库的动态运用模型。该模型首先运用时间序列法对历史水文资料进行展延,生成长系列入库水沙数据,然后根据马尔可夫链原理分析生成的水沙系列,确定不同频率洪水在不同条件下发生的概率,最后结合水库当前已发生的洪水预测即将发生的洪水的概率,对初始的水库调度参数进行调整,得到最终的水库运用参数,从而弥补水库运用参数与实时入库水沙条件不匹配的不足。将该方法应用于实际水库的控制运用,结果表明,该水库在供水量变化不大的情况下,较原有的运用方案具有更大的剩余库容。     

用小波矩阵分析法进行函数的分解与重构

就傅氏级数和小波变换之间的关系进行较全面地讨论。并采用小波矩阵分析方法,使小波变换本质跃然于纸上。同时给出小波分解和小波重构的计算公式,应用变得十分容易。     

关于降雨产流机制的几个问题的讨论

本文就当前国内外关于产流机制研究中的几个问题进行了讨论，提出了一些新的见解．这些问题是：特殊包气带的产流机制，产流机制的统一和转化，基本产流模式，地形坡度。土层各向异性及非饱和侧向流的作用等．     

Update on Glycosphingolipids Abundance in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most frequent type of primary liver cancer. Low numbers of HCC patients being suitable for liver resection or transplantation and multidrug resistance development during pharmacotherapy leads to high death rates for HCC patients. Understanding the molecular mechanisms of HCC etiology may contribute to the development of novel therapeutic strategies for prevention and treatment of HCC. UDP-glucose ceramide glycosyltransferase (UGCG), a key enzyme in glycosphingolipid metabolism, generates glucosylceramide (GlcCer), which is the precursor for all glycosphingolipids (GSLs). Since UGCG gene expression is altered in 0.8% of HCC tumors, GSLs may play a role in cellular processes in liver cancer cells. Here, we discuss the current literature about GSLs and their abundance in normal liver cells, Gaucher disease and HCC. Furthermore, we review the involvement of UGCG/GlcCer in multidrug resistance development, globosides as a potential prognostic marker for HCC, gangliosides as a potential liver cancer stem cell marker, and the role of sulfatides in tumor metastasis. Only a limited number of molecular mechanisms executed by GSLs in HCC are known, which we summarize here briefly. Overall, the role GSLs play in HCC progression and their ability to serve as biomarkers or prognostic indicators for HCC, requires further investigation.     

三维稳态晶体生长的物理本质

考虑在均匀流场的作用下,分析了金属熔液凝固过程中晶体生长的三维稳态数学模型.应用傅里叶级数展开法,在周期性条件下得到了相应的八阶常微分方程的精确解析解,并确定了解中各系数之间的关系.该解揭示了在均匀流场的作用下,晶体生长呈现了一种周期性振荡式的模式,从理论上证实了固液界面前沿浓度呈现指数振荡衰减性是晶体生长的一个本质特性.     

负荷时间序列波动性的动态时变结构研究

采用广义自回归条件异方差(GARCH)族模型分析了负荷时间序列波动性的动态时变结构,提出了模型系的概念,使用滚动数据窗技术估计了指数广义自回归条件异方差(EGARCH)和幂自回归条件异方差(PARCH)模型系;在研究动态显著性水平线(DSL)的基础上,探究了时序波动性的动态时变结构,讨论了贯穿各子样本空间的波动不对称效应。算例分析中,将所建模型应用于短期负荷预测,比较了GARCH族模型的预测能力,得到了较高的预测精度。     

激光电容半桥串联谐振充电电源研究

在重复率脉冲固体激光器中,由于储能电容需要频繁的充放电,通常采用谐振充电电路以适应其负载的大范围变化。为此研制了开关频率为20kHz,充电电流为2.1A,最高充电电压为1.86kV的半桥串联谐振充电电路。该电路工作于电流断续模式,开关管的开通和关断均为软开关。通过对周期电压、电流递推公式的分析,表明该工作模式中每个周期的平均充电电流均为恒定。应用递推公式计算稳态和暂态谐振电容电压和电流,结果显示暂态最大工作电压是稳态最大电压的2倍,暂态最大电流为稳态最大峰值电流的1.5倍,为谐振电容和开关管的选取提供了依据。     

高速动车组网侧电流谐波特性的研究

研究了高速动车组注入牵引网电流的谐波特性。分析了两电平及三电平4象限变流器的主电路拓扑及控制策略。利用双边傅立叶级数法,给出了两种4象限变流器网侧电流的谐波公式,总结了谐波分布规律。编制了CRH2和CRH5型动车组4象限变流器的仿真软件,研究了不同牵引和制动功率下,网侧电流的THD及各次谐波电流大小,验证了理论分析的正确性。     

Fast and exact synthesis of stationary multivariate Gaussian time series using circulant embedding

A fast and exact procedure for the numerical synthesis of stationary multivariate Gaussian time series with a priori prescribed and well controlled auto- and cross-covariance functions is proposed. It is based on extending the circulant embedding technique to the multivariate case and can be viewed as a modification and variation around the Chan and Wood algorithm proposed earlier to solve the same problem. The procedure is shown to yield time series possessing exactly the desired covariance structure, when sufficient conditions are satisfied. Such conditions are discussed theoretically and examined on several examples of multivariate time series models. Issues related to prescribing a priori the spectral structure rather than the covariance one are also discussed. Matlab routines implementing this procedure are publicly available at http://www.hermir.org.