叶面积指数(leaf area index,LAI)是反映植物冠层结构和光能利用的重要指标.随着遥感技术的不断发展,利用遥感数据获取大面积LAI已经成为监测作物生长和估产的重要手段.基于物理模型的LAI遥感反演方法经常假设作物冠层结构是均匀分布,然...叶面积指数(leaf area index,LAI)是反映植物冠层结构和光能利用的重要指标.随着遥感技术的不断发展,利用遥感数据获取大面积LAI已经成为监测作物生长和估产的重要手段.基于物理模型的LAI遥感反演方法经常假设作物冠层结构是均匀分布,然而,作为典型的垄行结构,作物冠层被公认为是介于连续植被与离散植被之间的一种过渡形式,而简单的均匀假设必然会给反演带来偏差.本文以农作物玉米为研究对象,首先重建了玉米三维冠层结构,并定量对比分析了一维辐射传输模型PROSAIL和三维辐射传输模型LESS在玉米冠层不同生长期的反射率差异,确定了玉米冠层的非均匀分布特征是引起PROSAIL模型模拟和反演误差的主要因素;然后,考虑到玉米冠层生长过程中聚集指数的变化特征,利用LESS模型定量计算了不同生育期玉米冠层结构对应的聚集指数,建立了聚集指数和有效叶面积指数(LAI_(e))之间的关系;进而,利用该关系对基于PROSAIL模型反演得到的LAI进行修正.结果表明,修正后的LAI精度有明显提高,R^(2)从0.27提高到了0.55.该方法有望提高中高分辨率遥感数据在农作物LAI反演精度.展开更多
The influence of material gate position in bur- den-flow rate has been studied by simulating exper- iments.A mathematical model describing the char- acteristics of burden-flow at the material gate of bell-less top bla...The influence of material gate position in bur- den-flow rate has been studied by simulating exper- iments.A mathematical model describing the char- acteristics of burden-flow at the material gate of bell-less top blast furnace(BF)is established in this paper,in an attempt to solve the problems in bur- den distribution,especially to eliminate the over- lapping or disconnection of the burden at the be- ginning and at the end of a ring,which plays a quite important role in the blast furnace operation.展开更多
The aim of this paper is to investigate the dynamic characteristics of a valve-less micropump. A dynamic mathe- matical model of the micropump based on a hydraulic analogue system and a simulation method using AMESim ...The aim of this paper is to investigate the dynamic characteristics of a valve-less micropump. A dynamic mathe- matical model of the micropump based on a hydraulic analogue system and a simulation method using AMESim software are developed. By using the finite-element analysis method, the static analysis of the diaphragm is carried out to ob- tain the maximum deflection and volumetric displacement. Dynamic characteristics of the valve-less micropump under different excitation voltages and frequencies are simulated and tested. Because of the discrepancy between simulation results and experimental data at frequencies other than the natural frequency, the revised model for the diaphragm maximum volumetric displacement is presented. Comparison between the simulation results based on the revised model and experimental data shows that the dynamic mathematical model based on the hydraulic analogue system is capable of predicting dynamic characteristics of the valve-less micropump at any excitation voltage and frequency.展开更多
Objective To evaluate the use of the saphenous artery as an alternative access for endovascular procedures in the porcine model. Methods Fourteen adult pigs (25-35 kg) were used in this study, 3 pigs from an acute stu...Objective To evaluate the use of the saphenous artery as an alternative access for endovascular procedures in the porcine model. Methods Fourteen adult pigs (25-35 kg) were used in this study, 3 pigs from an acute study and 11 from chronic studies. A 2-3 cm incision was made and a saphenous artery cutdown was performed in 24 sides. Micropuncture sets (Boston Scientific) or 18 G puncture needles were used to access the artery. Different sizes of introducers (4-7 F) were used to establish endovascular access. Angiographic catheters were then used to confirm if the access was usable. Four saphenous arteries were explanted in the pigs from a chronic study 4 to 28 days after surgical procedure. Results The saphenous artery was very easy to expose and 4-5 F introducer sheaths were able to be inserted to establish access for endovascular procedures in the pigs. The saphenous artery was unable to accomodate an introducer with a size larger than 6 F. Four saphenous arteries were injured when 5 and 6 F introducers were used, but angiographic procedures could still be performed. Morphologic evaluation of the explanted arteries demonstrated occlusion of the saphenous arteries without injury or disruption of the adjacent femoral arteries. Conclusion The saphenous artery can be used as an access site in pigs for angiographic and interventional procedures if the catheter size is less than 6 F. This vessel is easier to access and can preserve the femoral artery for repeat procedures in the future.展开更多
针对分数阶模型参考自适应系统(Fractional Order Model Reference Adaptive System,FOMRAS)在永磁直线同步电机(Permanent Magnet Linear Synchronous Motor,PMLSM)直接推力控制(Direct Force Control,DFC)下转速估计误差大、响应速度...针对分数阶模型参考自适应系统(Fractional Order Model Reference Adaptive System,FOMRAS)在永磁直线同步电机(Permanent Magnet Linear Synchronous Motor,PMLSM)直接推力控制(Direct Force Control,DFC)下转速估计误差大、响应速度慢、抗干扰能力差等现象,提出一种改进FOMRAS算法,即速度辨识中使用改进的分数阶自适应律,对转速进行跟踪,减小推力响应的抖动,确保估计值快速逼近真实值。运用于DFC中,实现无速度传感器控制。仿真结果表明:采取改进FOMRAS的无速度传感器PMLSM-DFC,抗扰动能力明显加强,具有良好的动静态能力,确保了系统稳定性。展开更多
文摘叶面积指数(leaf area index,LAI)是反映植物冠层结构和光能利用的重要指标.随着遥感技术的不断发展,利用遥感数据获取大面积LAI已经成为监测作物生长和估产的重要手段.基于物理模型的LAI遥感反演方法经常假设作物冠层结构是均匀分布,然而,作为典型的垄行结构,作物冠层被公认为是介于连续植被与离散植被之间的一种过渡形式,而简单的均匀假设必然会给反演带来偏差.本文以农作物玉米为研究对象,首先重建了玉米三维冠层结构,并定量对比分析了一维辐射传输模型PROSAIL和三维辐射传输模型LESS在玉米冠层不同生长期的反射率差异,确定了玉米冠层的非均匀分布特征是引起PROSAIL模型模拟和反演误差的主要因素;然后,考虑到玉米冠层生长过程中聚集指数的变化特征,利用LESS模型定量计算了不同生育期玉米冠层结构对应的聚集指数,建立了聚集指数和有效叶面积指数(LAI_(e))之间的关系;进而,利用该关系对基于PROSAIL模型反演得到的LAI进行修正.结果表明,修正后的LAI精度有明显提高,R^(2)从0.27提高到了0.55.该方法有望提高中高分辨率遥感数据在农作物LAI反演精度.
文摘The influence of material gate position in bur- den-flow rate has been studied by simulating exper- iments.A mathematical model describing the char- acteristics of burden-flow at the material gate of bell-less top blast furnace(BF)is established in this paper,in an attempt to solve the problems in bur- den distribution,especially to eliminate the over- lapping or disconnection of the burden at the be- ginning and at the end of a ring,which plays a quite important role in the blast furnace operation.
基金Project supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, Ministry of Education of China (Grant No. 24403604)the Fundamental Research Funds for the Central Universities, China (Grant No. ZYGX2011J083)
文摘The aim of this paper is to investigate the dynamic characteristics of a valve-less micropump. A dynamic mathe- matical model of the micropump based on a hydraulic analogue system and a simulation method using AMESim software are developed. By using the finite-element analysis method, the static analysis of the diaphragm is carried out to ob- tain the maximum deflection and volumetric displacement. Dynamic characteristics of the valve-less micropump under different excitation voltages and frequencies are simulated and tested. Because of the discrepancy between simulation results and experimental data at frequencies other than the natural frequency, the revised model for the diaphragm maximum volumetric displacement is presented. Comparison between the simulation results based on the revised model and experimental data shows that the dynamic mathematical model based on the hydraulic analogue system is capable of predicting dynamic characteristics of the valve-less micropump at any excitation voltage and frequency.
文摘Objective To evaluate the use of the saphenous artery as an alternative access for endovascular procedures in the porcine model. Methods Fourteen adult pigs (25-35 kg) were used in this study, 3 pigs from an acute study and 11 from chronic studies. A 2-3 cm incision was made and a saphenous artery cutdown was performed in 24 sides. Micropuncture sets (Boston Scientific) or 18 G puncture needles were used to access the artery. Different sizes of introducers (4-7 F) were used to establish endovascular access. Angiographic catheters were then used to confirm if the access was usable. Four saphenous arteries were explanted in the pigs from a chronic study 4 to 28 days after surgical procedure. Results The saphenous artery was very easy to expose and 4-5 F introducer sheaths were able to be inserted to establish access for endovascular procedures in the pigs. The saphenous artery was unable to accomodate an introducer with a size larger than 6 F. Four saphenous arteries were injured when 5 and 6 F introducers were used, but angiographic procedures could still be performed. Morphologic evaluation of the explanted arteries demonstrated occlusion of the saphenous arteries without injury or disruption of the adjacent femoral arteries. Conclusion The saphenous artery can be used as an access site in pigs for angiographic and interventional procedures if the catheter size is less than 6 F. This vessel is easier to access and can preserve the femoral artery for repeat procedures in the future.
文摘针对分数阶模型参考自适应系统(Fractional Order Model Reference Adaptive System,FOMRAS)在永磁直线同步电机(Permanent Magnet Linear Synchronous Motor,PMLSM)直接推力控制(Direct Force Control,DFC)下转速估计误差大、响应速度慢、抗干扰能力差等现象,提出一种改进FOMRAS算法,即速度辨识中使用改进的分数阶自适应律,对转速进行跟踪,减小推力响应的抖动,确保估计值快速逼近真实值。运用于DFC中,实现无速度传感器控制。仿真结果表明:采取改进FOMRAS的无速度传感器PMLSM-DFC,抗扰动能力明显加强,具有良好的动静态能力,确保了系统稳定性。
