Recycled waste tires when mixed with soil can play an important role as lightweight materials in retaining walls and embankments, machine foundations and railroad track beds in seismic zones. Having high damping chara...Recycled waste tires when mixed with soil can play an important role as lightweight materials in retaining walls and embankments, machine foundations and railroad track beds in seismic zones. Having high damping characteristic, rubbers can be used as either soil alternative or mixed with soil to reduce vibration when seismic loads are of great concern. Therefore, the objective of this work was to evaluate the dynamic properties of such mixtures prior to practical applications. To this reason, torsional resonant column and dynamic triaxial experiments were carried out and the effect of the important parameters like rubber content and ratio of mean grain size of rubber solids versus soil solids(D50,r/D50,s) on dynamic response of mixtures in a range of low to high shearing strain amplitude from about 4×10-4% to 2.7% were investigated. Considering engineering applications, specimens were prepared almost at the maximum dry density and optimum moisture content to model a mixture layer above the ground water table and in low precipitation region. The results show that tire inclusion significantly reduces the shear modulus and increases the damping ratio of the mixtures. Also decrease in D50,r/D50,s causes the mixture to exhibit more rubber-like behavior. Finally, normalized shear modulus versus shearing strain amplitude curve was proposed for engineering practice.展开更多
建立了分析测定水环境中十氯酮的液相色谱-串联质谱法。水样经液液萃取、净化后，采用 Eclipse plus C18柱（100 mm×2.1 mm，3.5μm）分离，乙腈和水为流动相进行梯度洗脱，在电喷雾负离子多反应监测模式下进行检测，同位素内标法...建立了分析测定水环境中十氯酮的液相色谱-串联质谱法。水样经液液萃取、净化后，采用 Eclipse plus C18柱（100 mm×2.1 mm，3.5μm）分离，乙腈和水为流动相进行梯度洗脱，在电喷雾负离子多反应监测模式下进行检测，同位素内标法定量。结果表明：采用液相色谱-质谱联用技术，证实了十氯酮在甲醇中以半缩醛的形式存在，而在丙酮/乙腈中以偕二醇的形式存在。由于十氯酮极性较强，在净化时难以洗脱，并且不耐酸，所以不能与其他有机氯农药一起分析。十氯酮在5～100μg / L 范围有良好的线性关系，相关系数 r2=0.999，检出限及定量限分别为0.70 ng / L 和2.8 ng / L；在5、40和100 ng / L 3个浓度添加水平的平均回收率为95.1％～98.9％，相对标准偏差为3.85％～4.72％。本方法具有良好的灵敏度、回收率和重现性，适用于水环境中十氯酮的测定。展开更多
现有全脉冲结构波形与处理方法,如相位编码波形匹配处理存在多普勒容忍度差的固有缺陷,线性调频(linear frequency modulation,LFM)波形加窗处理降低了距离分辨率和信噪比(signal-to-noise ratio,SNR)增益,难以适应高速多目标探测的任...现有全脉冲结构波形与处理方法,如相位编码波形匹配处理存在多普勒容忍度差的固有缺陷,线性调频(linear frequency modulation,LFM)波形加窗处理降低了距离分辨率和信噪比(signal-to-noise ratio,SNR)增益,难以适应高速多目标探测的任务需求。为此,本文提出了一种面向高速目标探测的多子脉冲结构波形设计与处理方法。首先,构建具有多子脉冲结构波形的回波模型,利用分段子脉冲压缩处理和子脉冲间相参处理方法,导出多子脉冲结构波形的距离-多普勒响应函数;然后,根据感兴趣的目标距离速度区间,建立恒模约束下以最小化加权积分距离-多普勒旁瓣电平为目标函数的多子脉冲结构波形优化设计问题;最后,引入坐标下降(coordinate descent,CD)优化框架,将高维非凸约束优化问题的求解转变为多个一维优化问题的迭代求解,且推导出这些低维问题的闭式解。仿真表明,所设计的多子脉冲结构波形具有较好的多普勒容忍度和较低的局部距离-多普勒旁瓣电平,且在高速多目标认知探测场景下,相比于LFM波形、模糊函数优化波形和LFM-noise波形具有更好的高速目标探测能力。展开更多
文摘Recycled waste tires when mixed with soil can play an important role as lightweight materials in retaining walls and embankments, machine foundations and railroad track beds in seismic zones. Having high damping characteristic, rubbers can be used as either soil alternative or mixed with soil to reduce vibration when seismic loads are of great concern. Therefore, the objective of this work was to evaluate the dynamic properties of such mixtures prior to practical applications. To this reason, torsional resonant column and dynamic triaxial experiments were carried out and the effect of the important parameters like rubber content and ratio of mean grain size of rubber solids versus soil solids(D50,r/D50,s) on dynamic response of mixtures in a range of low to high shearing strain amplitude from about 4×10-4% to 2.7% were investigated. Considering engineering applications, specimens were prepared almost at the maximum dry density and optimum moisture content to model a mixture layer above the ground water table and in low precipitation region. The results show that tire inclusion significantly reduces the shear modulus and increases the damping ratio of the mixtures. Also decrease in D50,r/D50,s causes the mixture to exhibit more rubber-like behavior. Finally, normalized shear modulus versus shearing strain amplitude curve was proposed for engineering practice.
文摘建立了分析测定水环境中十氯酮的液相色谱-串联质谱法。水样经液液萃取、净化后，采用 Eclipse plus C18柱（100 mm×2.1 mm，3.5μm）分离，乙腈和水为流动相进行梯度洗脱，在电喷雾负离子多反应监测模式下进行检测，同位素内标法定量。结果表明：采用液相色谱-质谱联用技术，证实了十氯酮在甲醇中以半缩醛的形式存在，而在丙酮/乙腈中以偕二醇的形式存在。由于十氯酮极性较强，在净化时难以洗脱，并且不耐酸，所以不能与其他有机氯农药一起分析。十氯酮在5～100μg / L 范围有良好的线性关系，相关系数 r2=0.999，检出限及定量限分别为0.70 ng / L 和2.8 ng / L；在5、40和100 ng / L 3个浓度添加水平的平均回收率为95.1％～98.9％，相对标准偏差为3.85％～4.72％。本方法具有良好的灵敏度、回收率和重现性，适用于水环境中十氯酮的测定。
文摘现有全脉冲结构波形与处理方法,如相位编码波形匹配处理存在多普勒容忍度差的固有缺陷,线性调频(linear frequency modulation,LFM)波形加窗处理降低了距离分辨率和信噪比(signal-to-noise ratio,SNR)增益,难以适应高速多目标探测的任务需求。为此,本文提出了一种面向高速目标探测的多子脉冲结构波形设计与处理方法。首先,构建具有多子脉冲结构波形的回波模型,利用分段子脉冲压缩处理和子脉冲间相参处理方法,导出多子脉冲结构波形的距离-多普勒响应函数;然后,根据感兴趣的目标距离速度区间,建立恒模约束下以最小化加权积分距离-多普勒旁瓣电平为目标函数的多子脉冲结构波形优化设计问题;最后,引入坐标下降(coordinate descent,CD)优化框架,将高维非凸约束优化问题的求解转变为多个一维优化问题的迭代求解,且推导出这些低维问题的闭式解。仿真表明,所设计的多子脉冲结构波形具有较好的多普勒容忍度和较低的局部距离-多普勒旁瓣电平,且在高速多目标认知探测场景下,相比于LFM波形、模糊函数优化波形和LFM-noise波形具有更好的高速目标探测能力。
