狗枣猕猴桃叶黄酮提取工艺的研究

以乙醇作为提取剂,采用振荡提取法从狗枣猕猴桃叶中提取黄酮类化合物,研究了乙醇浓度、样品粒度、料液比、浸提温度、浸提时间及浸提次数对提取效果的影响。结果表明,料液比对黄酮提取效果影响最大,其次为提取时间和提取温度,而样品粒度和乙醇浓度影响较小。狗枣猕猴桃叶黄酮的最佳提取工艺条件为:乙醇浓度75%,粒度80目,料液比1∶15,浸提温度80℃,浸提时间2h,浸提次数3次,在此条件下黄酮提取率可达7.250%。     

谈粮食烘干机出机粮水分的周期性振荡

通过对不同处理量(300~500t/d)、不同烘干型式(顺流、混流、横流)、不同塔型(单塔、双塔)的粮食烘干机出机粮水分周期性振荡现象的分析,探求粮食烘干机的内在特性。     

轻轨车应急通风电源前级DC/DC变换器研制

介绍了轻轨车应急通风电源前级DC/DC变换器的结构和工作原理.针对变压器次级出现的整流桥寄生振荡问题,分析了振荡产生的原因.为了抑制该振荡,详细分析并对比了3种RCD吸收电路的工作过程及优缺点,并介绍了不同工况下吸收电路结构及参数的选取方法.最后,给出了主电路及吸收电路参数的设计公式,并搭建样机,对设计方案和吸收电路的效果进行了验证.     

水轮机调速系统转矩系数分析

水轮机调速系统包括水轮发电机组对象和调速器,其小波动暂态的阻尼特性是影响机组稳定性的主要因素,本文对调速系统附加机械阻尼以及同步力矩的形成机理和计算进行了系统的研究.以典型调速器结构为例,建立包括机组对象和控制器在内的水轮发电机组线性化模型框架,给出了水轮机及其调速系统附加机械阻尼系数和同步力矩系数的计算方法.分析机组运动特性和阻尼系数的构成,定义了稳态和动态阻尼系数两种类型,并提出以机电振荡模式特征根近似计算机组自振频率的方法.仿真表明,适当调整调速器PID参数可以提高机组动态阻尼系数,本文所提出的计算方法是有效的.     

Rickettsial Pathogen Perturbs Tick Circadian Gene to Infect the Vertebrate Host

Ixodes scapularis is a medically important tick that transmits several microbes to humans, including rickettsial pathogen Anaplasma phagocytophilum. In nature, these ticks encounter several abiotic factors including changes in temperature, humidity, and light. Many organisms use endogenously generated circadian pathways to encounter abiotic factors. In this study, we provide evidence for the first time to show that A. phagocytophilum modulates the arthropod circadian gene for its transmission to the vertebrate host. We noted a circadian oscillation in the expression of arthropod clock, bmal1, period and timeless genes when ticks or tick cells were exposed to alternate 12 h light: 12 h dark conditions. Moreover, A. phagocytophilum significantly modulates the oscillation pattern of expression of these genes. In addition, increased levels of clock and bmal1 and decreased expression of Toll and JAK/STAT pathway immune genes such as pelle and jak, respectively, were noted during A. phagocytophilum transmission from ticks to the vertebrate host. RNAi-mediated knockdown of clock gene expression in ticks resulted in the reduced expression of jak and pelle that increased bacterial transmission from ticks to the murine host. Furthermore, clock-deficient ticks fed late and had less engorgement weights. These results indicate an important role for circadian modulation of tick gene expression that is critical for arthropod blood feeding and transmission of pathogens from vector to the vertebrate host.     

构网型直驱风电机组间控制相互作用研究

构网型风电控制技术具有很好的弱电网适应性,可以有效避免风电并网次超同步振荡问题。但是虚拟同步控制引入固有的低频特征模式,接入强电网时会发生低频振荡,同时多台构网型风电机组并联运行时存在控制器相互作用。针对此问题,采用特征模式分析方法,研究了基于虚拟同步控制方法的构网型直驱风电机组并联运行时的控制相互作用及主导低频特征模式稳定性。揭示了虚拟惯量控制参数及系统运行方式对构网型风电机组并联运行低频振荡特性的影响。通过详细时域仿真验证了分析结果的正确性。     

线路阻抗对构网变流器降阶模型精度影响及次同步振荡分析

在大部分关于构网变流器(GFM)次同步振荡稳定性的研究中,GFM通常被简化为只含有功率外环的三阶模型,这种降阶方法虽然简便,但其精确度会受到线路阻抗特征的影响,因此需要对GFM降阶模型适用性问题展开讨论,并提出更加精准的降阶模型。分析电网线路阻抗特征变化对降阶模型精度的影响,结果表明线路阻感比变化或短路比变化时三阶模型不能精确反映系统特性的变化,会对系统稳定性产生错误判断,其原因在于线路阻抗参数会影响电压环与功率环的耦合特性,2个控制环路均会对GFM次同步振荡稳定性产生影响。提出一种更加准确的包含电压环的降阶模型,可以精确表征线路阻抗特征变化对系统特性的影响,更加适合复杂电网下GFM的稳定性分析。基于MATLAB/Simulink仿真验证了理论分析的正确性及所提模型的有效性。     

Approximate Model-Free Assessment of Oscillation Stability Determined by the PLLs in a Weakly Grid-Connected Wind Farm with Multiple PMSGs

Abstract

The study investigates the oscillation stability determined by phase locked loops (PLLs) in a weakly grid-connected wind farm with multiple permanent magnet synchronous generators (PMSGs). To this end, an equivalent model of the wind farm is derived. Based on the derived equivalent model, the oscillation stability of the wind farm as determined by the dynamics of the PLLs is analytically examined. This paper explains why the PLLs equipped by the PMSGs in the wind farm can lead to instability risk under the condition of weak grid connection. A simple index is proposed to approximately assess instability risk of the wind farm due to the PLLs. The parametric model of the wind farm with the PMSGs is not necessary to calculate the proposed simple index. Hence, it is model-free and applicable in practice when it is difficult to establish the parametric model. An example of a grid-connected wind farm with 12 PMSGs is presented to evaluate and demonstrate the analysis conducted and the simple index proposed in the paper.     

咪唑对磷酸中铜阳极溶解电化学振荡行为的影响研究

运用循环伏安法和恒电位法对铜在含有咪唑的磷酸溶液中电化学振荡行为进行了研究,结果发现随着咪唑浓度的升高,振荡起振电位正移,振幅、周期先减小后又增大;温度升高,振荡周期减小.恒电位下,随着电位升高电流振荡总体趋势从不规则到规则再到不规则.     

一种界面上的振荡现象--盐水振荡

将盛有盐水溶液、底部有小孔的内套管垂直放入盛有蒸馏水的外套管中,小孔处可以观察到流体上下振荡,这种现象被称为盐水振荡。本文详细地介绍盐水振荡的现象、机理和数学模型,分析化学振荡产生的必要条件,提出盐水振荡是在浓度差引起的重力作用下,灵敏初条件被破坏,产生流体振荡,流动电势引发盐水振荡的电现象。通过对三种穿过界面扩散所形成的振荡现象——液膜振荡、固体膜振荡与盐水振荡进行比较,提出将三种振荡有机结合,可改进化学振荡器的性能和应用前景。