抛光机磨头结构改进及其对振动的影响实验研究

为了降低摆动式抛光机磨头振动,对现有磨头的结构进行了改进。建立了改进后磨头的激振力方程,分析了改进后磨头的减振机理。由一系列的改进前与改进后磨头振动加速度的对比实验表明,改进后磨头振动性能优于改进前的磨头,有显著的减振作用。     

Influences of heat treatment and DeNOx performance of cordierite honeycombs washcoated with spinel catalysts

Spinel powders MAl₂O₄ (M = Ga and Zn) have been prepared by the co-precipitation of aqueous solutions containing corresponding metal, aluminum nitrate and ammonium carbonate. The NO reduction activities of composite spinel type powders in the Ga₂O₃–Al₂O₃–ZnO (GAZ) system were studied, in regard to their high-temperature application as an automotive lean-burn exhaust catalyst. A correlation between the NH₃-TPD results and the activity of GAZ reveals that a high population of surface acid sites is important to achieve high activity. The cordierite honeycombs with cell sizes 100, 200, 400 and 900 cpsi (cells per square inch) were washcoated with the GAZ slurries and their NO reduction activity was evaluated. The durability of GAZ/cordierites was studied in the presence of H₂O vapor, SO₂ and O₂.     

工程结构极限承载力上限分析的弹性模量缩减法

基于弹性模量缩减法和基准体法,建立了工程结构极限承载力上限分析的方法。该法结合弹性有限元法进行迭代分析,以广义屈服函数表达的单元承载比作为弹性模量调整的控制参数,根据单元承载比均匀度确定模量调整的阀值——基准承载比,利用单元应变能转化中的能量守恒原理建立单元弹性模量调整策略,通过缩减高应力单元的弹性模量模拟结构弹塑性损...     

地震动加加速度反应谱的概念及特性研究

加加速度是加速度关于时间的变化率,反映了结构受力变化情况。地震动加加速度及其反应谱的研究可以加强人们对地震动非平稳性的认识。阐述了加加速度的力学意义及研究价值,探讨了计算DriDri速度的动力学方法并对其优缺点进行了比较。建立了地震动下弹性及弹塑性加加速度反应谱的求解方法。根据场地类型、放大系数、延性系数及折减系数等影...     

爆聚法合成P(AA-ODA-NVP)聚合物及其溶液性质

在超临界二氧化碳介质中,通过自由基爆聚反应制备了一系列不同投料比的丙烯酸、丙烯酸十八酯与乙烯基吡咯烷酮共聚物.通过扫描电镜、红外光谱、乌氏黏度计、旋转黏度计研究了聚合物结构与性质;并研究了不同的投料比和反应压力对共聚反应的影响.实验结果表明,在一定的压力及投料比下,共聚反应发生爆聚,利用超临界二氧化碳压力可调的特点,通...     

聚丙烯腈/二甲基亚砜纺丝原液流变性及流变方程拟合

以高黏均分子量(-Mη)聚丙烯腈(PAN)为研究对象,系统研究了黏均分子量(-Mη,以下简称分子量)、温度(T)、固含量(wt)和剪切速率(γ)对聚丙烯腈(PAN)/二甲基亚砜(DMSO)纺丝原液流变性能的影响。结果表明,纺丝原液分子量和剪切速率皆存在一个临界值。在临界值之前,表观黏度随分子量增加迅速增大,随剪切速率的增加迅速降低,在临界值之后,变化趋势均趋于平缓;且临界值不随温度变化而改变;依据试验结果进行表观黏度与四因素线性相关方程拟合,经对比,计算值与实验值相差不大,可以为纺丝原液表观黏度的预测和后续纺丝工艺的改进提供理论参考。     

Performance evaluation of OFDM and single‐carrier systems using frequency domain equalization and phase modulation

In this paper, we study the performance of the continuous phase modulation (CPM)‐based orthogonal frequency division multiplexing (CPM‐OFDM) system. Also, we propose a CPM‐based single‐carrier frequency domain equalization (CPM‐SC‐FDE) structure for broadband wireless communication systems. The proposed structure combines the advantages of the low complexity of SC‐FDE, in addition to exploiting the channel frequency diversity and the power efficiency of CPM. Both the CPM‐OFDM system and the proposed system are implemented with FDE to avoid the complexity of the equalization. Two types of frequency domain equalizers are considered and compared for performance evaluation of both systems; the zero forcing (ZF) equalizer and the minimum mean square error (MMSE) equalizer. Simulation experiments are performed for a variety of multipath fading channels. Simulation results show that the performance of the CPM‐based systems with multipath fading is better than their performance with single path fading. The performance over a multipath channel is at least 5 and 12 dB better than the performance over a single path channel, for the CPM‐OFDM system and the proposed CPM‐SC‐FDE system, respectively. The results also show that, when CPM is utilized in SC‐FDE systems, they can outperform CPM‐OFDM systems by about 5 dB. Copyright © 2010 John Wiley & Sons, Ltd.     

基于监督局部线性嵌入的飞机目标识别方法

维数约简是目标识别的一个重要预处理步骤.由于飞机目标图像对各种空间变换(包括平移、尺度、旋转等变换)和观察角度、位置以及光照等因素都比较敏感,使得很多线性维数约简算法不能有效地用于飞机目标识别.局部线性嵌入(LLE)是一种有效的非线性维数约简方法,提出了一种基于LLE的监督LLE算法,并应用于多种条件下的飞机目标识别中...     

一种改进的多视极化白化滤波算法

针对极化合成孔径雷达(PolSAR)图像的相干斑抑制问题,提出一种快速有效的多视极化白化滤波改进算法。该算法在分块加权法的块处理基础上,采用边缘检测模板对非同质类子块进行二次分类,从而提高了多视极化白化滤波(MPWF)算法的参数估计精度。利用美国宇航局喷气推进实验室(NASA/JPL)的AIRSAR系统实测数据进行了实验,实验结果表明文中方法不仅在斑点抑制效果和运算量上优于MPWF,而且有效地克服了分块处理带来的边缘模糊问题。