Nonlinear compensation research and simulation of bandlimited QPSK digital satellite channels

0　ＩＮＴＲＯＤＵＣＴＩＯＮＰｅｒｆｏｒｍａｎｃｅｐｒｅｄｉｃｔｉｏｎａｎｄａｎａｌｙｓｉｓｏｆｎｏｎｌｉｎｅａｒｄｉｇ ｉｔａｌｓａｔｅｌｌｉｔｅｃｈａｎｎｅｌｓｈａｓｍｕｃｈｔｈｅｏｒｅｔｉｃａｌａｎｄｐｒａｃｔｉｃａｌｉｎｔｅｒｅｓｔｓ .Ａｎｉｍｐｏｒｔａｎｔｅｘａｍｐｌｅｏｆａｎｏｎｌｉｎｅａｒｃｈａｎｎｅｌｉｓａｄｉｇｉｔａｌｓａｔｅｌｌｉｔｅｃｏｍｍｕｎｉｃａｔｉｏｎｌｉｎｋ ,ｗｈｉｃｈｕｓｅｓａｔｒａｖｅｌ ｌｉｎｇｗａｖｅｔｕｂｅａｍｐｌｉｆｉｅｒ(ＴＷＴＡ)ｏｐｅｒａｔｉｎｇｉｎａ…     

流动沸腾条件下窄通道内的汽泡生长和冷凝

针对过冷沸腾条件下窄通道内的汽泡生长和冷凝进行实验研究。实验中观察到了两类汽泡的生长和冷凝,分别称为第1类汽泡和第2类汽泡。其中第1类汽泡生长速度较快,且在滑移离开核化点之后迅速冷凝消失。而第2类汽泡的生长速度较慢,且滑移很长一段距离后也不会冷凝消失,具有更长的存活时间。两类汽泡的生长可采用不同的关系式进行预测,且生长冷凝特性均表现出很强的随机性,体现出汽泡周围环境的微小变化对汽泡行为的影响。     

基于压电驱动的微振动主动减振控制系统研究

本文以压电陶瓷促动器构建并联六自由度减振平台,采用NI Compact-RIO实时控制系统和Fx-LMS自适应控制算法进行振动主动控制,对次级通道辨识方法和主动控制算法进行了模拟仿真,并搭建主动减振控制系统进行实验验证。仿真与实验结果表明,设计的主动减振控制系统对于7~50 Hz范围内的低频微振动有很好的控制效果。     

三姓二期航道整治工程分流比变化分析

简述了三姓浅滩概况及二期航道整治工程的效果;报工程前后分流比的变化。     

多路穆斯堡尔谱数据获取与处理系统

本文叙述了一个以BC3-80微型计算机为基础,通过一个以Z80-CPU为中心的控制机与8个带有存贮器的数据获取通道组成的多路数据获取与处理系统。这个系统除能对8个通道的数据进行数据获取外,同时可以对其进行显示、保存和数据处理。它与穆斯堡尔谱仪部件相接,构成一个恒加速穆斯堡尔谱仪系统。 这个系统配上高计数率多丝正比室,可以使穆斯堡尔谱的探测效率大大提高。多丝室中的每根丝的信号分别通过各自的放大器、单道分析器,由相应的数据通道记录下来,然后由微机进行相加和处理。另一方面,这个系统还可以利用不同的通道同时测出样品的透射谱和散射谱,同时得到样品的内部和表面信息。     

适用于航空信道的并行STWQ信道估计算法

通过对航空信道的分析,指出其稀疏信道特征,使用普通算法对此信道进行信道估计会引入高阶自适应计算,为加快收敛速度、降低实现难度,提出了一种"并行STWQ(scrub taps waiting in a queue)信道估计算法",通过一定规律将所有抽头分组,每组单独完成STWQ算法,最终可以得到非零抽头的位置和其权值.针对具体应用给出算法的性能仿真结果,证明了算法在满足相同的性能要求时,可避免高阶自适应计算,节约了大量权值可忽略抽头所引入的资源占用和计算量,且搜索非零抽头所耗时间比STWQ算法成倍减少,可更好跟踪快变的稀疏信道.     

等通道转角挤压自增强等规聚丙烯研究

为了研究等通道转角挤压等规聚丙烯的挤压工艺条件、结构与性能之间的关系,采用90°转角模具及挤压路径A、在熔点以下的160℃制备了不同挤压次数的等规聚丙烯样品,利用广角X射线衍射(WAXD)、差示扫描量热分析(DSC)等手段对其结构进行表征.结果表明,随挤压次数增加,等规聚丙烯分子取向明显增加,材料结晶度提高,试样的力学性能提高十分显著,未挤压试样的抗拉强度为17.13 MPa,经过三次挤压后,抗拉强度提高到59.38 MPa.     

Effect of integrated extrusion–equal channel angular pressing temperature on microstructural characteristics of low carbon steel

Abstract

In the present research, a combined forward extrusion–equal channel angular pressing was developed and executed for the deformation of a plain carbon steel. In this method, two different deformation steps, including forward extrusion and equal channel angular pressing, take place successively in a single die. The deformation process was performed at different deformation start temperatures (800, 930 and 1100°C). Three-dimensional finite element simulation was used to predict the strain and temperature variations within the samples during deformation. With microstructural observations and the results of finite element simulation, the main grain refinement mechanisms were studied at different deformation temperatures. The results show that the forward extrusion–equal channel angular pressing is effective in refining the ferrite grains from an initial size of 32 μm to a final size of ～0·9 μm. The main mechanisms of grain refinement were considered to be strain assisted transformation, dynamic strain induced transformation and continuous dynamic recrystallisation, depending on the deformation temperature.     

Efficient visual communication channels

This paper compares the efficiency of uniform quantization in the spatial domain with frequency dependent quantization in the spatial frequency domain, in the context of the end-to-end performance of visual-communication channels. Results show that the minimum data density required for informationally lossless transmission depends on the design of the image-gathering device. The information in the acquired signal, not the energy, dictates the trade-off between data transmission and visual quality. Frequency dependent quantization that maintains the information capacity of the channel while reducing the entropy of the encoded signal, improves its information efficiency. Information bit-allocation is preferable for optimized visual communication for restoration, whereas energy bit-allocation can be used only for image reconstruction.This research was supported by NASA Task Assignment NAS1-18584-90 with the Department of Mathematics, Old Dominion University, Norfolk, Virginia 23529.