CO_2微通道气体冷却器压降与传热特性研究

在微通道平行流式气冷器内进行了CO2的压降和换热特性实验研究,探讨了跨临界CO2循环换热过程中制冷剂质量流量、系统压力对气冷器换热性能、进出口压降的影响.实验结果表明:在接近临界温度时,CO2物理性能受压力和温度的影响较大,换热系数是远离临界区的7～9倍;随着CO2质量流量的提高,微通道管内流体Re相应提高,而较高的Re又使得湍流扩散率、管内温度梯度增大,同时在制冷剂入口附近的微通道换热器高温区域面积增大,表明当系统压力相同时,制冷剂入口温度随CO2质量流量的增加而增大.在一定的质量流量或压力下,存在着一个最佳的压力或质量流量,使得气冷器进出口压降达到最小.随着Re增加,气冷器的CO2压降关联式的预测精度均有所提高,为此提出了新的换热关联式和压降关联式.     

套管式地埋管换热器设计计算方法

 以线热源理论为基础建立套管式地埋管换热器换热的简化模型,给出基于热响应试验的套管式换热器设计计算方法。以湖南省韶山市一实际工程为实例对钻孔现场进行测试,采用该方法可计算出其综合导热系数和钻孔内总热阻。同时对该工程的另一钻孔进行双U测试及计算,以此作对比分析。考察两组测试在综合导热系数、钻孔内总热阻、换热温差和换热量上的内在联系。计算结果和测试结果表明,该计算方法在套管式换热器设计上具有适用性,避开了钻孔内层层热阻的复杂计算,简化了计算过程,可为实际工程提供计算参考。     

地球同步轨道SAR两维奇异值分解成像方法

针对地球同步轨道合成孔径雷达(geosynchronous synthetic aperture radar, GEO-SAR)长合成时间和大观测场景严重的二维空变将影响二维聚焦深度的问题,该文提出了一种GEO-SAR两维奇异值分解成像方法。该方法首先对距离空变信号进行奇异值分解得到距离多普勒的耦合特性,通过距离频率插值和重采样完成距离空变校正;接着,对方位空变信号进行奇异值分解将方位空变与多普勒分离,通过级联的两步奇异值分解和方位非线性变标操作完成方位空变校正,实现整个场景的聚焦。最后,仿真结果验证了该方法的有效性。     

Ranking approach of cross-efficiency based on improved TOPSIS technique

The cross-efficiency evaluation method is reviewed which is developed as a date envelopment analysis (DEA) extensive tool.The cross-efficiency evaluation method is utilized to identify the decision making unit (DMU) with the best practice and to rank the DMUs by their respective cross-efficiency scores.The main drawbacks of the cross-efficiency evaluation method when the ultimate average cross-efficiency scores are used to evaluate and rank the DMUs are also pointed out.With the research gap,an improved technique for order preference by similarity to ideal solution (TOPSIS) is introduced to rank the cross-efficiency by eliminating the average assumption.Finally,an empirical example is illustrated to examine the validity of the proposed method.     

IUKF neural network modeling for FOG temperature drift

A novel neural network based on iterated unscented Kalman filter （IUKF） algorithm is established to model and com- pensate for the fiber optic gyro （FOG） bias drift caused by temperature. In the network, FOG temperature and its gradient are set as input and the FOG bias drift is set as the expected output. A 2-5-1 network trained with IUKF algorithm is established. The IUKF algorithm is developed on the basis of the unscented Kalman filter （UKF）. The weight and bias vectors of the hidden layer are set as the state of the UKF and its process and measurement equations are deduced according to the network architecture. To solve the unavoidable estimation deviation of the mean and covariance of the states in the UKF algorithm, iterative computation is introduced into the UKF after the measurement update. While the measure- ment noise R is extended into the state vectors before iteration in order to meet the statistic orthogonality of estimate and mea- surement noise. The IUKF algorithm can provide the optimized estimation for the neural network because of its state expansion and iteration. Temperature rise （-20-20℃） and drop （70-20℃） tests for FOG are carried out in an attemperator. The temperature drift model is built with neural network, and it is trained respectively with BP, UKF and IUKF algorithms. The results prove that the proposed model has higher precision compared with the back- propagation （BP） and UKF network models.     

Electromagnetic behavior of two-dimensional quasi-crystal left-handed materials with dendritic unit

We demonstrated a two-dimensional quasi-crystal dendritic structure model with negative permeability. The microwave transmission and reflection properties of periodic and quasi-crystal dendritic structure mediums with varied angle incidence were measured. The results showed that the resonant peaks of quasi-crystal negative permeability samples and left-handed samples had tiny shift with the altering of incident angle. Because of the influence of coupling between quasi-crystal dendritic cells, the resonance of the entire material was enhanced or weakened. The quasi-crystal dendritic structure model will provide an easy method to design isotropic left-handed materials （LHMs）.     

ZnO/WO_3纳米片薄膜的光电催化性能研究

采用水热法在不锈钢基底上制备WO3纳米片阵列,然后将其浸渍于不同浓度Zn(NO_3)_2溶液中以负载ZnO纳米颗粒,从而制备出ZnO/WO_3纳米片薄膜。采用场发射扫描电镜(FESEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、紫外-可见吸收光谱(UV-Vis)和电化学阻抗图谱(EIS)等方法对ZnO/WO_3复合薄膜的形貌、结构、物相组成和光电性能等进行分析,重点考察了薄膜电极对亚甲基蓝(MB)的光电催化降解性能。结果表明,WO_3纳米片均匀垂直于基底生长,Zn元素以ZnO颗粒的形式分布在WO_3表面;ZnO的引入促进了WO_3中产生的光生电子-空穴对的分离,从而使ZnO/WO_3复合薄膜表现出比纯WO_3薄膜更优异的光电性能和光电催化活性;在Zn(NO_3)_2浸渍液浓度为20mmol/L时,所制ZnO/WO_3复合薄膜具有最佳的光电催化性能,在MB溶液初始浓度为10mg/L、外加偏压为0.8V、光照1h的条件下,采用该样品对MB的降解率达96.5%,并且复合薄膜具有良好的循环稳定性,在重复使用5次后,对MB的光电催化降解效率没有明显降低,有望在实际污水处理中得到应用。     

玉米生育期和籽粒淀粉含量的海拔效应研究

为使高海拔地区玉米生产布局和品种类型利用更加合理,采用作物生态学田间试验为主要研究方法,开展了玉米生育期和籽粒淀粉含量的海拔效应研究.用3个统一参试品种,于2006-2007年在甘肃省38°56'N,100°26'E范围内,布设了5个试点,分别是海拔1 280.0、1 506.5、1 706.5、2 000.0和2 231.5 m,进行了垂直生态试验.结果表明,在播期大体相同的条件下,玉米成熟期随海拔高度的升高而相应延迟.反映生育期长短的播种-成熟天数与海拔高度之间呈0.01水平的正相关.海拔高度每升降100 m,参试玉米品种生育期延长、缩短4～5 d.直链淀粉/粗淀粉与海拔之间呈负相关性.     

玉米生育期和品质性状的纬度效应研究

为探讨玉米生育期和一些品质性状的纬度效应及玉米优质栽培的布局问题,用不同玉米品种在南北纬度不同的南京、北京、沈阳、辽中和法库5个试点,进行了生态试验.结果表明,在海拔高度相近的同期播种条件下,在低纬度试点,玉米品种的生育进程加快,生育期长短与纬度呈正向对应关系;在海拔基本一致的前提下,玉米品种的籽粒脂肪含量与纬度有正相关趋势,r=0.8586*;而籽粒粗蛋白含量与纬度有负相关趋势.r=-0.7862.因此,纬度是影响玉米生育期和品质性状的重要地理因素.     

河南省粮食产量周期波动分析

利用1951--2005年河南省粮食产量统计数据,应用波动理论和周期理论分析河南省粮食产量波动规律,考察河南省粮食产量波动的历史过程和数量特征．结果表明,河南省粮食产量波动具有短周期的显著特征,平均波动周期3.3年左右,波幅较小,扩张期略长于收缩期．