纤维悬浮槽道湍流中纤维取向分布和流变特性

为了解悬浮槽道湍流中纤维取向分布和流变特性，对纤维悬浮湍流进行了理论分析和数值模拟.推导了纤维取向平均概率分布函数方程，得到了脉动流场速度和脉动取向概率分布函数关联项，建立了关联项与平均概率分布函数梯度以及扩散系数之间的关系，数值求解了平均概率分布函数的方程.计算结果表明，随着长径比的增大，纤维的轴向更趋向于流动方向；悬浮流的剪切应力和第一法向应力差由壁面到槽道中心逐渐接近于0；剪切应力几乎不随长径比和体积分数变化，而第一法向应力差的绝对值随体积分数的增大和长径比的减小而增大.     

CFD prediction of physical field for multi-air channel pulverized coal burner in rotary kiln

A 3-D numerical simulation with CFX software on physical field of multi-air channel coal burner in rotary kiln was carried out. The effects of various operational and structural parameters on flame feature and temperature distribution were investigated. A thermal measurement was conducted on a rotary kiln （4.5 m in diameter, 90 m in length） with four-air channel coal burner to determine the boundary conditions and to verify the simulation results. The calculation result shows that the distribution of velocity near burner exit is saddle-like; recirculation zones near nozzle and wall are useful for mixture primary air with coal and high temperature fume. A little central airflow can avoid coal backing up and cool nozzle. Adjusting the ratio of internal airflow to outer airflow is an effective and major means to regulate flame and temperature distribution in sintering region. Large whirlcone angle can intensify disturbution range at flame root to accelerate ignition and mixture. Large coal size can reduce high temperature region and result in coal combusting insufficiently. Too much combustion air will lengthen flame and increase heat loss.     

小波去噪结合信道估计在OFDM系统中的应用

在正交频分复用（OFDM：Orthogonal Frequency Division Multiplexing）系统中，我们通常从频率域的角度估计信道衰落因子，在频率域，发射的信号在经历了乘性衰落的同时还经历了加性的噪声的干扰，不论我们采用哪种方法来估计乘性的衰落因子，加性噪声的干扰始终存在，从而影响了估计的质量，将小渡去噪用于信道估计中以去除其中的加性干扰。从而在不增加复杂度的前提下，提高了信道估计的准确度，进而提高了整个系统的性能，同时证明了该方法适用于不同的信道环境（频率选择性衰落信道、平坦衰落信道、快衰落和慢衰落信道）。     

新型槽栅MOSFETs的特性

采用SIVALCO软件对槽栅与平面器件进行了仿真对比分析,结果表明槽栅器件能够有效地抑制短沟道及热载流子效应,而拐角效应是槽栅器件优于平面器件特性更加稳定的原因.对自对准工艺下成功投片所得沟道长度为140nm的槽栅器件进行测量,结果有力地证明了槽栅器件较平面器件的优越性.     

MFSK水声远程通信技术及试验研究

海洋水声信道是多途、时变和频散的信道。论文针对浅海远程80～100km,设计出基于MFSK高数据率水声远程信息传输最佳系统。本系统经湖试验证表明:该技术在远程通信恶劣条件下具有较强抗多径干扰和信道衰落能力,对同步精度要求低,可实现80～100km,40bit/s,10-4量级通信精度的信息可靠传输,性能稳健,易于工程实现。     

Performance-Based Optimization of Land and Water Resources within Irrigation Schemes. II: Application

The area and water allocation model which uses simulation–optimization technique for optimum allocation of land and water resources to different crops cultivated in different allocation units of the irrigation scheme was modified to include both productivity and equity in the process of developing the allocation plans for optimum productivity and/or maximum equity. This paper illustrates the potential of this approach with the help of a case study on Nazare medium irrigation scheme in India. The allocation plans were developed for optimization of different performance parameters (productivity and equity) for different management strategies based on irrigation amount and irrigation interval and cropping distribution strategies of free and fixed cropping. The results indicated that the two performance objectives productivity and equity conflict with each other and in this case, equitable water distribution may be preferred over free water distribution at the cost of a small loss in productivity. Though these results relate to one case study, they show the value of the approach of incorporating productivity and equity in the allocation process with the help of the simulation-optimization model described in the companion paper.     

Tuning of Robust Distant Downstream PI Controllers for an Irrigation Canal Pool. I: Theory

The paper proposes a new method to tune robust distant downstream proportional integral (PI) controllers for an irrigation canal pool. The method emphasizes the role of gain and phase margins in the controller design, by linking the selection of these robustness indicators to the time domain specifications. This leads to link the frequency domain approach used by automatic control engineers to the time domain approach used by hydraulic engineers. The maximum error corresponding to an unpredicted perturbation is shown to be directly linked to the gain margin and the settling time to the phase margin of the controlled system. The tuning method gives analytical expressions for the controller parameters as function of physical parameters of the canal pool in order to satisfy desired performance requirements. The model is first expressed in terms of dimensionless variables, in order to get generic tuning formulas. The dimensionless PI coefficients are then expressed as functions of time-domain performance requirements. The PI tuning method is evaluated by simulation on a full nonlinear model for a canal pool taken from the ASCE test cases.     

Development of GIS-Based Model to Estimate Relative Reductions in Crop Yield due to Salinity and Waterlogging

A model is introduced that utilizes geographic information systems (GIS) to predict relative reductions in crop yield due to salinity and waterlogging at a field-scale by incorporating spatially and temporally variable crop, climatic, and irrigation data to simulate crop yields. This model utilizes soil and water data commonly collected in field-scale studies. The model’s algorithms are integrated into a GIS (ARCVIEW 3.2) as an extension. The result is a model that does not require extraordinary data collection but will provide practical insight into the spatial effects of salinity and waterlogging on crop yields.     

质子交换膜燃料电池流道设计

质子交换膜燃料电池(PEMFC)以其高效率、高比能量、低污染等优点被认为是一种适合人类发展和环境要求的理想电源.双极板(流场板)是质子交换膜燃料电池的重要部件,其质量占电池堆60%以上.流场板上的流道设计对电池性能、运行效率和制造成本有很大影响.系统地综述了现有的流道设计,剖析了流道的功能及其对电池性能的影响,并在此基础上讨论了流道设计的发展趋势.     

基于特殊导频序列的多用户OFDM系统中的频偏和信道联合估计

本文提出了一种新的导频设计方法应用在多用户OFDM系统中来进行联合估计频偏和信道.根据最小化MSE准则,设计最优的导频序列以满足均方误差最小,从而得到该导频序列是等功率的且具有循环移位正交性.仿真结果表明,本文所提出的最优导频序列优于任意导频序列在对频偏和信道联合估计的运算中.同时,通过采用改进的ML(最大似然估计)算法能够大大减小运算的复杂度.这种方法在系统具有较小频率偏移的情况下非常适用.