针对直流微电网中储能系统功率波动、负载侧负荷频繁投切等不确定因素引起母线电压产生波动的问题,以储能系统中三相交错并联双向DC-DC变换器为研究对象,提出一种基于级联有限时间扩张状态观测器(cascade finite-time extended state ob...针对直流微电网中储能系统功率波动、负载侧负荷频繁投切等不确定因素引起母线电压产生波动的问题,以储能系统中三相交错并联双向DC-DC变换器为研究对象,提出一种基于级联有限时间扩张状态观测器(cascade finite-time extended state observer,CFT-ESO)的微分平坦和改进型超螺旋滑模双闭环复合控制策略.首先,建立三相交错并联双向DC-DC变换器的数学模型,并根据微分平坦理论将其直流系统转化为微分平坦系统,结合两级具有快速收敛性的有限时间扩张状态观测器提高对系统集总扰动的估计精度.其次,采用内环微分平坦控制、外环改进型超螺旋滑模控制的双闭环控制系统,既能提高系统动态响应过程,又能利用高阶滑模控制算法抑制抖振,同时解决变换器升压模式中非最小相位问题.再次,通过Lyapunov理论证明控制系统的稳定性.最后,利用MATLAB/Simulink仿真软件以及搭建实验平台对控制策略进行验证,结果表明,本文所提控制策略能够很好地抵抗扰动,提高系统的暂态性能.展开更多
Effects of five incubation temperatures (25℃ ,28℃ ,31℃ ,35℃ and 37℃ for 24hours) and four incubation time periods (0.4,16 and 24 hours at 35℃) on isolated microspore culture of Chinese cabbage were studied. The ...Effects of five incubation temperatures (25℃ ,28℃ ,31℃ ,35℃ and 37℃ for 24hours) and four incubation time periods (0.4,16 and 24 hours at 35℃) on isolated microspore culture of Chinese cabbage were studied. The results showed that cultured microspores of Chinese cabbage developed into embryos at all the incubation temperatues from 28℃ to 37℃ ,but the best response to high temperature occured at 35℃. Among the four kinds of time periods, the highest yield of embryos was obtained at the 24h treatment. Therefore, the isolated microspore culture of Chinese cabbege ran be efficiently carried out at 35℃ for 24 hours.展开更多
A novel method isolated microorganisms in soil granule was built. The key steps included： repeated elutriation of soil by sterilized water, inoculation on the plates with the elutriated sediments, incubation of the p...A novel method isolated microorganisms in soil granule was built. The key steps included： repeated elutriation of soil by sterilized water, inoculation on the plates with the elutriated sediments, incubation of the plates and isolation of the actinomycetes by using selected culture medium. We formulated that most microflora included the dominant actinomycetes in the soil were carried away with the sterilized water in the elutriation procedure, some rare actinomycetes and few other microflora included bacteria were remained in the elutriated sediments, the other microflora were excluded to grew into colonies on the plates by using selective culture medium for actinomycetes in the elutriated sediments. Results showed the supposition. Non-streptomycete actinomycetes were isolated both from black soil samples from Chinese northeast area and compost samples from Chinese central area. Soil fungi in granule were isolated by using the selective conditions to favor fungi. The results showed that the method was effective展开更多
The supported isolated Pt atoms(Pt iso)and other rare metals have attracted intensive concern due to their maximized metal utilization efficiency,unique reactivity or selectivity,connection to organometallic catalysis...The supported isolated Pt atoms(Pt iso)and other rare metals have attracted intensive concern due to their maximized metal utilization efficiency,unique reactivity or selectivity,connection to organometallic catalysis and the potential for making well-defined active sites[1-3].As catalytic active sites,oxide-supported isolated Pt-group metal atoms are well known for their unique reactivity and efficient metal utilization[4-6].Even continuous efforts have been made,it is still challenging to characterize the intrinsic ca-talytic activity of these dispersed active sites on oxide supports at a level that relates local electronic and geometric structure to function,because of their atomic dispersion,heterogeneity in the local coordination,dynamic changes in local coordination under reactive environments and low loading of metal[7-9].展开更多
OBJECTIVE To evaluate the effects of flavonoids from Xindakang(Hippophae Fructus flavone)on myocardial systolic and diastolic functions of isolated frog hearts and explore the possible mechanism,and provide experiment...OBJECTIVE To evaluate the effects of flavonoids from Xindakang(Hippophae Fructus flavone)on myocardial systolic and diastolic functions of isolated frog hearts and explore the possible mechanism,and provide experimental basis for improving the effect and efficacy of Xindakang on cardiac function.METHODS The isolated frog heart perfusion specimens were prepared by Yagi′s method,and the effects of different concentrations of Xindakang on myocardial contractility(0.0125,0.025,0.05,0.1 and 0.2 g·L^(-1)),heart rate and cardiac output of isolated frog heart were studied.Acetylcholine,atropine and epinephrine were administered successively to analyze the effects of Xindakang on cardiac systolic function of isolated frogs under the action of different drugs,and compared with propranolol.The effect of extracellular calcium ion concentration on the action of Xindakang was studied by using low calcium concentration,high calcium concentration and normal Ren′s solution.To study the effect and possible mechanism of Xindakang on cardiac systolic function of frog.RESULTS The concentration of Xindakang in the range of 0.0125-0.1 g·L^(-1)could weaken the contractility of isolated frog heart and increase the concentration of Xindakang.The inhibitory effect of Xindakang on contractility of isolated frog heart was enhanced,and showed obvious dose-effect relationship.Cardiac output was significantly decreased by Xindakang(P<0.01),slow heart rate(P<0.05);M receptor blocker atropine could not antagonize the contractile effect of Xindakang,and Xindakang could not completely antagonize the contractile effect of adrenalin.Xindakang could inhibit the isolated frog heart in low calcium concentration,high calcium concentration and normal Ren′s solution,and increased with the increase of extracellular calcium concentration(P<0.01).CONCLUSION Xindakang has inhibitory effect on isolated frog heart,which may be achieved by blocking the calcium channel on myocardial cell membrane and reducing the calcium concentration in myocardial cells.展开更多
An isolated slit was placed in a single box girder to obtain passive leading-edge suction and trailing-edge jet flow to control the unsteady aerodynamic force and modify the flow structure.The Great Belt East Bridge w...An isolated slit was placed in a single box girder to obtain passive leading-edge suction and trailing-edge jet flow to control the unsteady aerodynamic force and modify the flow structure.The Great Belt East Bridge was used as a physical model at a geometric scale of 1:125.Wind tunnel experiments were conducted at an incoming airflow speed of 10 m/s,and the Reynolds number was calculated as 2.3×104 using the test model height and wind speed.The surface pressure distribution was measured,and the aerodynamic force acting on the test model with and without the isolated slit was calculated by integrating the pressure result.It was found that the control using an isolated slit can dramatically decrease the fluctuating surface pressure distribution and aerodynamic force.An analysis on the power spectral density of the lift force revealed that the isolated slit accelerated vortex shedding.Moreover,high-speed particle image velocimetry was used to investigate the wake flow structure behind the test model.A vortex separated from the upper surface was pushed to a lower location and the wake flow structure was modified by the isolated slit.A proper orthogonal decomposition(POD)of the flow field showed that the first two POD modes in the controlled case contributed less energy than those in the uncontrolled case,indicating that more energy was transferred to higher modes,and small-scale vortices had more energy.A secondary instability structure was found in the wake flow for a nondimensional jet momentum coefficient J of 0.0667.展开更多
文摘针对直流微电网中储能系统功率波动、负载侧负荷频繁投切等不确定因素引起母线电压产生波动的问题,以储能系统中三相交错并联双向DC-DC变换器为研究对象,提出一种基于级联有限时间扩张状态观测器(cascade finite-time extended state observer,CFT-ESO)的微分平坦和改进型超螺旋滑模双闭环复合控制策略.首先,建立三相交错并联双向DC-DC变换器的数学模型,并根据微分平坦理论将其直流系统转化为微分平坦系统,结合两级具有快速收敛性的有限时间扩张状态观测器提高对系统集总扰动的估计精度.其次,采用内环微分平坦控制、外环改进型超螺旋滑模控制的双闭环控制系统,既能提高系统动态响应过程,又能利用高阶滑模控制算法抑制抖振,同时解决变换器升压模式中非最小相位问题.再次,通过Lyapunov理论证明控制系统的稳定性.最后,利用MATLAB/Simulink仿真软件以及搭建实验平台对控制策略进行验证,结果表明,本文所提控制策略能够很好地抵抗扰动,提高系统的暂态性能.
文摘Effects of five incubation temperatures (25℃ ,28℃ ,31℃ ,35℃ and 37℃ for 24hours) and four incubation time periods (0.4,16 and 24 hours at 35℃) on isolated microspore culture of Chinese cabbage were studied. The results showed that cultured microspores of Chinese cabbage developed into embryos at all the incubation temperatues from 28℃ to 37℃ ,but the best response to high temperature occured at 35℃. Among the four kinds of time periods, the highest yield of embryos was obtained at the 24h treatment. Therefore, the isolated microspore culture of Chinese cabbege ran be efficiently carried out at 35℃ for 24 hours.
基金Supported by the Youth Foundation of College of Resources and Environment of Northeast Agricultural University
文摘A novel method isolated microorganisms in soil granule was built. The key steps included： repeated elutriation of soil by sterilized water, inoculation on the plates with the elutriated sediments, incubation of the plates and isolation of the actinomycetes by using selected culture medium. We formulated that most microflora included the dominant actinomycetes in the soil were carried away with the sterilized water in the elutriation procedure, some rare actinomycetes and few other microflora included bacteria were remained in the elutriated sediments, the other microflora were excluded to grew into colonies on the plates by using selective culture medium for actinomycetes in the elutriated sediments. Results showed the supposition. Non-streptomycete actinomycetes were isolated both from black soil samples from Chinese northeast area and compost samples from Chinese central area. Soil fungi in granule were isolated by using the selective conditions to favor fungi. The results showed that the method was effective
文摘The supported isolated Pt atoms(Pt iso)and other rare metals have attracted intensive concern due to their maximized metal utilization efficiency,unique reactivity or selectivity,connection to organometallic catalysis and the potential for making well-defined active sites[1-3].As catalytic active sites,oxide-supported isolated Pt-group metal atoms are well known for their unique reactivity and efficient metal utilization[4-6].Even continuous efforts have been made,it is still challenging to characterize the intrinsic ca-talytic activity of these dispersed active sites on oxide supports at a level that relates local electronic and geometric structure to function,because of their atomic dispersion,heterogeneity in the local coordination,dynamic changes in local coordination under reactive environments and low loading of metal[7-9].
基金Natural Science Foundation of Tibet Autonomous Region(2015ZR-13-16)。
文摘OBJECTIVE To evaluate the effects of flavonoids from Xindakang(Hippophae Fructus flavone)on myocardial systolic and diastolic functions of isolated frog hearts and explore the possible mechanism,and provide experimental basis for improving the effect and efficacy of Xindakang on cardiac function.METHODS The isolated frog heart perfusion specimens were prepared by Yagi′s method,and the effects of different concentrations of Xindakang on myocardial contractility(0.0125,0.025,0.05,0.1 and 0.2 g·L^(-1)),heart rate and cardiac output of isolated frog heart were studied.Acetylcholine,atropine and epinephrine were administered successively to analyze the effects of Xindakang on cardiac systolic function of isolated frogs under the action of different drugs,and compared with propranolol.The effect of extracellular calcium ion concentration on the action of Xindakang was studied by using low calcium concentration,high calcium concentration and normal Ren′s solution.To study the effect and possible mechanism of Xindakang on cardiac systolic function of frog.RESULTS The concentration of Xindakang in the range of 0.0125-0.1 g·L^(-1)could weaken the contractility of isolated frog heart and increase the concentration of Xindakang.The inhibitory effect of Xindakang on contractility of isolated frog heart was enhanced,and showed obvious dose-effect relationship.Cardiac output was significantly decreased by Xindakang(P<0.01),slow heart rate(P<0.05);M receptor blocker atropine could not antagonize the contractile effect of Xindakang,and Xindakang could not completely antagonize the contractile effect of adrenalin.Xindakang could inhibit the isolated frog heart in low calcium concentration,high calcium concentration and normal Ren′s solution,and increased with the increase of extracellular calcium concentration(P<0.01).CONCLUSION Xindakang has inhibitory effect on isolated frog heart,which may be achieved by blocking the calcium channel on myocardial cell membrane and reducing the calcium concentration in myocardial cells.
基金Projects(51978222,51722805,U2106222) supported by the National Natural Science Foundation of ChinaProject(HIT.BRETIV 201803) supported by the Fundamental Research Funds for the Central Universities,China。
文摘An isolated slit was placed in a single box girder to obtain passive leading-edge suction and trailing-edge jet flow to control the unsteady aerodynamic force and modify the flow structure.The Great Belt East Bridge was used as a physical model at a geometric scale of 1:125.Wind tunnel experiments were conducted at an incoming airflow speed of 10 m/s,and the Reynolds number was calculated as 2.3×104 using the test model height and wind speed.The surface pressure distribution was measured,and the aerodynamic force acting on the test model with and without the isolated slit was calculated by integrating the pressure result.It was found that the control using an isolated slit can dramatically decrease the fluctuating surface pressure distribution and aerodynamic force.An analysis on the power spectral density of the lift force revealed that the isolated slit accelerated vortex shedding.Moreover,high-speed particle image velocimetry was used to investigate the wake flow structure behind the test model.A vortex separated from the upper surface was pushed to a lower location and the wake flow structure was modified by the isolated slit.A proper orthogonal decomposition(POD)of the flow field showed that the first two POD modes in the controlled case contributed less energy than those in the uncontrolled case,indicating that more energy was transferred to higher modes,and small-scale vortices had more energy.A secondary instability structure was found in the wake flow for a nondimensional jet momentum coefficient J of 0.0667.
