Analysis of Unified Power Flow Controller in Damping Low Frequency Oscillation of Power System

With the development and complication of power system, the problem of low frequency oscillation in electric network becomes obvious. Unified Power Flow Controller is one of the most powerful facilities in Flexible AC Transmission Systems, which can improve the transient stability and damp the low oscillation in power system with suitable control. Considering the characteristics of inverter's output voltage magnitude, adjustment of phase and process of charge and discharge of dc capacitance, the dynamic model of UPFC is proposed by a series of nonlinear differential coefficient equations. Based on UPFC's dynamic model, the linear optimal controller of UPFC with state feedback is proposed. In this way, the low frequency oscillation is damped effectively. A simulation is processed basing the theory.     

The Biological Effects of Low Frequency Electromagnetic Fields on Cells

The biological effects of ELFMES including proliferation and apoptosis of cells as well as the damage of DNA are initially evaluated with the treatment of plant cells and human pulmonary fibroblasts in low frequency magnetic fields with certain intensity and different time intervals in vitro. Cell culture, counting in vitro, fluorescent dyeing analysis and single cell gel electrophoresis are adopted. The results demonstrate that the electromagnetic field with the intensity of 3mT can affect the proliferation and apoptosis of cells significantly.     

Effects of Wave Speed on Frequencies of the Self excited Oscillation Pulsed Abrasive Water Jets

The effects of cavitation and abrasive acceleration in the self excited oscillation pulsed abrasive water jets are directly determined by its oscillating frequencies, so the wave speed in the jets and its effects on pulsed frequencies are discussed. The numerical results show that the oscillating frequencies of the jets increase obviously with decreasing wave speed, and the abrasive parameters have almost no effects on the wave speed, whereas the exit of air in fluid has significant consequences on the wave speed.It was found that these conclusions were applicable for design the nozzle of the jets.     

Modeling and Simulation for 440 t/h CFB Boiler Steam/Water System

Dynamic mathematical model,which is based on the character of power-plant boiler system,is established by the means of modularization. On the basis of dynamic mathematical models,simulation model of the object is created with the advanced continuous simulation language(ACSL).The validity of this model has been verified by the simulation experiments and analysis.The simulation model helps to evaluate the influences that the dynamic process in steam/water's side brings to the boiler's operation and have some directive significance to design method of boiler and optimize run.     

Research on Influence of Frequency Flood on Water Environment Quality

Based on the two-dimensional hydrodynamic model,the two-dimensional water quality model is presented in this paper.According to the numerical simulation and analysis of water environment quality at different frequency floodwater,it concludes that the flood runoff is the first factor for the water environment quality,and points out that the water environment quality is better in low frequency flood than that in high frequency in respect of organic contamination,in addition,the concentration of heavy metal in high frequency flood tends to be increased greatly.     

低温弱光对西葫芦叶片光合特性及显微结构的影响

在不同温度和光照条件下研究了低温弱光对西葫芦幼苗叶片解剖结构的影响。结果表明:低温弱光处理使得西葫芦叶片上下表皮细胞密度、细胞直径、气孔大小以及气孔密度均变小,栅栏组织厚度及叶片厚度均减小,海绵组织也变得更为疏松,栅栏组织/海绵组织的比值减小,细胞间隙变大。低温弱光处理后西葫芦幼苗叶片光合速率及叶绿素含量下降较明显。     

低温对燕山板栗枝条生理的影响研究

为了探讨低温处理对燕山板栗枝条生理的影响,以燕山板栗‘燕龙’品种一年生健壮枝条为材料,采取不同低温处理,测定其电导率、丙二醛(MDA)含量、多酚氧化酶(PPO)活性生理指标以及嫁接成活率。板栗枝条电解质渗出率、伤害率均随处理温度的降低而增加;在-20℃之前,MDA含量随温度的降低而增加,在-20℃,MDA含量达到最高,而在-25℃时MDA含量又降低到极低水平;PPO活性在0~20℃之间随温度的降低而逐渐降低,在-20℃之后PPO活性又升高;成活率随处理温度降低而降低,在0℃下的枝条嫁接成活率最高(60%)在-20℃以下处理的嫁接成活率为0%。-20℃是‘燕龙’板栗枝条所受到低温极限;MDA含量、PPO活性在其承受的低温极限处出现拐点。初步认定在不同低温处理下,可以用MDA含量和PPO活性出现拐点的温度预示测定植物或材料可以承受的极限低温。     

Analysis on the Control of Variable Speed Wind Turbine Using Neural Network Controller

It is very difficult to build the accurate mathematical model of the wind turbine generator system because of the uncertainty of air kinetics and the complexity of power electronics, especially when the wind speed changes abruptly or there is a disturbance. But the classical control needs the model. Using neural network controller to the wind turbine generator system can overcome these difficulties. The wind speed can be followed and the maximum power can be obtained under low wind speed by using the power coefficient curve BP neural network and the optimum pitch angle BP neural network. The maximum power can be kept and under the allowed range in the condition of high wind speed. The simulation model and result are given under the environment of MATLAB. The fluctuation of wind speed can be controlled and the disturbance can be cancelled by BP neural network controller.     

Oscillation Theorems of Systems of High Order Nonlinear Delay Partial Differential Equations

Partial functional differential equations come from many mathematical models in physics,biology,engineering and other fields,which have strongly practical background.The oscillation theory is the one of the important branches of qualitative theory of partial functional differential equations. Therefore,it is of great theoretical and practical value to research the oscillation of partial functional differential equations.The anthors study the oscillation of the systems of a class of high order nonlinear delay partial functional differential equations.By using Green's theorem and Riccati transformation,they obtain some sufficient criteria for oscillation of all solutions of the systems under two kinds of different boundary value conditions,which are illustrated by some examples.These results offer the foundation of mathematical theory for solving the practical problems of the above fields.     

跌落振荡对鲜核桃冻藏品质的影响

以“清香”核桃为试材,研究跌落处理对鲜核桃在-7~-5 ℃冻藏条件下感官品质、营养品质及油脂品质的影响,评价跌落振荡（人工或机械振落采摘）生产操作在鲜核桃冷冻-解冻复鲜保鲜中应用的可行性,为建立鲜核桃冷冻-解冻复鲜保鲜技术体系提供理论依据。结果表明,与手工无伤采摘相比,离地3 m处跌落振荡处理对-7~-5 ℃下冻藏10个月的鲜核桃感官品质、核仁营养品质及油脂品质无显著不良影响,冻藏10个月时,核仁含水率大于22%,总脂肪含量大于50%,不饱和脂肪酸总含量大于92%,酸价小于0.61 mg/g,过氧化值小于1.93 mmol/kg。综合分析,打采振落采摘方式可用于鲜核桃冻藏保鲜的前处理工序。     

Rise Time Measurement System of Steep Pulse Based on Frequency Difference Multiply Technology

To accurately measure the ascendant time of a high-voltage steep pulse, the pace and precision of counter is highly challenged. The authors put forward the design of high-speed count system based on CPLD and DSP. In this system, the outer crystal oscillator of CPLD act as low-frequency clock whose frequency division and phase invertion are done by D-trigger group designed with CPLD, and finally,they get the counter with 200 MHz i. e. 5ns per period by the method of frequency difference multiply. The counting pace and precision are promoted, and meet the demand to measure the ascendant time of high-voltage steep pulse. It can be extended to measure the descendant time of pulse, pulse width and periods.     

振荡方式对土壤磷素分级的影响

探究不同振荡方式对磷形态的影响有助于理解磷分级的测定条件,本研究利用Tiessen磷素分级方法,通过分析2种振荡方式对土壤磷形态的影响揭示外界条件对土壤磷形态测定的影响。结果表明：2种振荡方式对水溶性磷和残留态磷含量有显著影响,振荡过程中横置离心管提取的水溶性磷浓度是竖置的1.8倍;横置离心管振荡提取的残留态的磷浓度较竖置降低了19 mg/kg;而对总磷、总有机磷、总无机磷及其他各形态的有机磷和无机磷则均无影响。从组成比例上,横置离心管提取测定磷形态导致水溶性磷的分布比例较竖置离心管提取测定提高6%。采用横置离心管振荡的方式提取的土壤水溶性磷和残留态磷浓度高于竖置方式。     

稀酸催化蒸汽爆破预处理提高竹子糖化效果的研究

采用稀酸浸泡结合蒸汽爆破预处理方式,对竹子的糖化效果进行了条件筛选。对浸泡酸浓度、浸泡时间、蒸汽爆破压强及、爆破压力维持时间4个因素进行探索,以酶解得到的还原糖含量高低作为衡量指标。结果表明：在单因素实验中,最优条件与其对应的还原糖浓度分别为：浸泡酸浓度2.5%时,还原糖浓度39.4301 g/L;浸泡时间10 h时,还原糖浓度35.2116 g/L;蒸汽爆破压强2 MPa时,还原糖浓度31.7554 g/L;蒸汽爆破压力维持时间150 s时,还原糖浓度30.3634 g/L。通过正交试验优化并验证后,得到最优的预处理条件：常温条件下,将竹子浸泡在2.5%的硫酸中8 h,于压强2 MPa的蒸汽爆破装置中维持180 s后爆破,可以得到最高的还原糖产量42.3707 g/L,且上述单因素影响主次顺序为：浸泡酸浓度＞浸泡时间＞压力维持时间＞爆破压强。     

低温胁迫对甜菜抗氧化系统的影响

旨在研究低温胁迫对甜菜细胞膜过氧化及抗氧化系统的影响,并为研究其他植物的抗寒性生理机制提供参考依据。以甜菜品种‘KWS9147'为实验材料,采用水培方式栽培,设置了4℃的低温处理(L)和25℃的室温对照(CK),测定低温处理前后甜菜叶片中丙二醛(MDA)含量和抗氧化系统酶活性的变化。结果表明,低温胁迫会对细胞膜造成损害并促使抗氧化系统产生防御作用,甜菜低温胁迫处理1天后与对照组对比,丙二醛(MDA)含量和抗氧化系统酶活性发生了显著的变化,丙二醛(MDA)的含量增加了31.32%,总抗氧化能力(T-AOC)、超氧化物歧化酶(SOD)、过氧化物酶(POD)、抗坏血酸过氧化物酶(APX)及过氧化氢酶(CAT)活性显著上升,分别上升了10.74%、4倍、2.22倍、32.85%、和2.56倍。综上,甜菜在低温胁迫下抗氧化能力提高,从而清除活性氧自由基(ROS)的积累,减缓细胞膜脂过氧化对细胞造成的伤害。     

临界低温弱光对黄瓜光合特性及其酶变化的影响

在连续4d单一临界低温15℃／8℃(昼／夜)和临界低温弱光下对黄瓜的光合性状及其酶变化进行了测定。结果表明：在单一临界低温下黄瓜各品种叶绿素含量、叶绿素荧光量子产额(yield)、光合速率显著降低，而在临界低温弱光下，叶绿素荧光量子产额上升后又下降，叶绿素含量降低速度变慢，反映碳同化酶活性的M峰值减弱，RuBp羧化酶活性显著降低后又有回升，处理过程中电解质渗漏率降低。处理4d时黄瓜光饱和点显著降低。温度-光合速率曲线变化表明，黄瓜的光合适温发生偏移，表现出低温适应性，品种间以新泰密刺表现出较强的耐低温性。     

西瓜高频再生系统的研究

以西瓜栽培种中育1号为材料对影响西瓜组织培养的多个因素进行了研究,建立了西瓜茎尖、子叶块的高频再生系统。结果表明无菌苗子叶呈淡绿色时不定芽诱导率最高,茎尖和子叶块适于直接诱导不定芽,其中茎尖的诱导率稍高于子叶块,MS+6-BA1.0+IBA0.5可较好的诱导子叶块分化不定芽,MS+6-BA1.0+IBA0.1对茎尖较为合适,低浓度的IAA有利生根,低温、高湿可提高移栽的成活率。     

不同预处理对低温贮藏香椿嫩芽风味及色泽的影响

为探究不同预处理方式对低温贮藏条件下香椿嫩芽挥发性成分及色泽的影响,新鲜香椿分别经烫漂和液氮速冻预处理,然后于-20℃条件下低温贮藏270 d,以直接低温贮藏为对照。采用顶空固相微萃取法与气相色谱-质谱联用技术分析香椿嫩芽贮藏30 d、90 d和270 d时的挥发性成分,对贮藏270 d解冻后香椿嫩芽进行感官评价,并对L、a、b值和叶绿素含量进行测定。结果表明:与直接冷冻和烫漂加热处理方式相比,液氮速冻技术在香椿嫩叶色泽上占明显优势,经过长期低温冻藏其叶绿素含量和L、a、b值显著高于其他两组(P0.05)。在挥发性成分保留方面,烫漂加热香椿的挥发性成分种类在低温贮藏期间均高于其他两组处理,但在贮藏270 d后种类骤然降低,与其他两组无明显差异。低温贮藏期间含硫类化合物相对含量均随着贮藏时间的延长逐渐升高,使香椿呈现刺激性臭味,影响香椿品质。     

Analysis of Low frequency Noise of Bridge Considering the Vibration of Bridge Deck

Under the dynamic load of vehicle, the bridge will vibrate and radiate low frequency noise which is harmful to human health. A method for predicting the low frequency noise is proposed based on the analysis of vibration of bridge deck. The prediction includes the analysis of vehicle bridge coupling vibration considering the bridge deck and the analysis of sound radiation and propagation in the air. By taking a bridge with low frequency noise as example, the vibration and sound radiation of the bridge are analyzed respectively by the current method and the previous method based on the grillage model. The results show that the prediction based on the vibration of bridge deck is more accurate. Furthermore, the measures to reduce the noise of bridge are explored, and the results indicate that a smoother road surface leads to lower noise. But when the condition of road surface is up to the extremely good standard defined by ISO, the effect of reducing the roughness of surface is not significant. Also, strengthening the crossbeam in the bridgehead is a simple and effective way to reduce the low frequency noise of bridge.